International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
INSTITUTO NACIONAL DEL CARBÓN INCAR
Programme for the International Conference on Coal Science and Technology 2011, Oviedo 9-13 October Sunday 9th October 2011 017:00-19:30 Registration and documents 19:30-21:00
Ice-break party
Monday, 10th October, 2011 08:30-09:00
Registration and documents Multiusos Room
09:00-10:00 10:00-11:00 11:00-11:30
Plenary Lecture: R. Kandiyoti
11:30-13:20
Coal combustion
13:20-15:00 15:00-16:30
Coal combustion
Room 10
Room 11 Opening Ceremony
Coffee break Coal characterization and coal Coal pyrolysis and liquefaction: structure thermoplasticity of coal Lunch Coal characterization and coal Coal pyrolysis and liquefaction: structure liquids from coal Coffee break
16:30-17:00 17:00-18:00
CO2 Storage
Coal characterization and coal structure Welcome cocktail
19:30-21:30 Tuesday, 11th October, 2011 Multiusos Room Plenary Lecture: D. Harris 09:00-10:00 10:00-11:00
CO2 Transport and storage
11:00-11:30 11:30-13:20 13:20-15:00
Coal pyrolysis and liquefaction: general
CO2 Capture and storage: oxyfuel
Room 11
Room 12
Coal mineralogy and coal ash: coal Coal pyrolysis and liquefaction: ash liquefaction Coffee break Coal gasification and clean fuels Lunch
Coal pyrolysis and liquefaction: fundamentals
Room 12
Carbons from coal
Coal and the environment
15:00-16:30 16:30-17:00 17:00-18:00
Clean coal technology: Mercury emissions
Coal petrology
Coal pyrolysis and liquefaction: direct liquefaction
Coffee break & Poster Viewing Poster session: coal chemistry, coal petrology, coal mineralogy, coal upgrading, coal pyrolysis, carbons from coal Typical Asturian dinner
19:30-23:00
Wednesday, 12th October, 2011 Multiusos Room Room 11 Room 12 Plenary Lecture: R. Malhotra 09:00-10:00 Clean coal technology: Mercury Coal gasification and clean fuels: 10:00-11:00 Coal pyrolysis emissions mineral matter Coffee break 11:00-11:30 CO2 Capture and storage: Mineral matter and coal ash: Coal pyrolysis and liquefaction: 11:30-13:20 mineral matter coke microstructure chemical looping Lunch 13:20-15:00 CO2 Capture and storage: 15:00-16:30 Coal gasification and clean fuels Coal upgrading gasification Coffee break & Poster Viewing 16:30-17:00 Poster Session: Coal combustion, clean coal technologies, coal gasification, CO2 Capture and storage, 17:00-18:00 coal and the environment Conference dinner
20:00-23:00
Thursday, 13th October, 2011 Multiusos Room Room 11 Plenary Lecture: J. C. Abanades 09:00-10:00 CO2 Capture and storage 10:00-11:00 Coal gasification and clean fuels
12:50-13:30 13:30-15:00
Coal upgrading
Coffee break
11:00-11:30 11:30-12:50
Room 12
CO2 Capture and Storage
Coal gasification and clean fuels Closing ceremony Lunch
Coal pyrolysis and liquefaction: biomass
Monday, 10th October, 2011
08:30-09:00
Registration and documents Opening ceremony
09:00-10:00 10:00-11:00
Plenary Lecture: (Chair: R. Moliner ) A00 Thermal breakdown in middle rank coals R. Kandiyoti Coffee break
11:00-11:30 Session A
Session B
Session C
Session D
Coal combustion Chairs: F. Montagnaro & B. Arias
Coal characterization and coal structure Chairs: E. Suuberg & M. Sciazko
Coal pyrolysis and liquefaction: thermoplasticity of coal Chairs: S. Krzack & C. Barriocanal
Carbons from coal Chairs: G. Gryglewicz & M. Granda
11:30-12:00
B01 Visualizing the macromolecular network structure of a large-scale A01 Ash deposition (50,000 atom) Illinois No. 6 characteristics determined in pilot bituminous coal molecular plant tests burning bituminous representation in 3D and 2D lattice and sub- bituminous coals. views. M. Shimogori , N. Ooyatsu, N. Y. E. Alvarez, J. C. Katson, J.O Takarayama, T. Mine Pou, F. Castro-Marcano, J. P. Mathews
12:00-12:20
B02 Brown coal solubilisation with A02 Investigation of contributions novel ionic liquids. to unburned carbon in a 200MWe A. L Chaffee , C. Patzschke, D. power utility boiler. Russell, D. Kelley, Y. Qi, V. H. Gao , A. Majeski, A. Verheyen, M. Marshall, V. Runstedtler, M. Sybring Ranganathan, D. MacFarlane
C01 1H-NMR Study on the thermoplasticity of coking coaleffects of coal blending and additives. H. Kumagai , N. Okuyama, T. Shishido, K. Sakai, M. Hamaguchi, N. Komatsu
D01 A relationship between the structures of graphitized anthracites and isotropic graphite. M.S. Nyathi, C.E. Burgess Clifford, H.H. Schobert
C02 A systematic study of the effects of pyrolysis conditions on coal devolatilisation. M.A. Kochanek, D.G. Roberts, B. Garten, S. Russig, D.J. Harris
D02 Benzene and toluene adsorption on high surface area activated carbons obtained from an anthracene oil derivative. N.G. Asenjo , P. Álvarez, C. Blanco, R. Santamaría, M. Granda, R. Menéndez
Session A
Session B
Session C
Session D
12:20-12:40
A03 Impact of biomass on char burn-out under air and oxy-fuel conditions. T. S. Farrow, D. Zhao, C. Sun, C.E. Snape
B03 Comparison of structure and reactivity of an Australian algal coal and a Jordanian oil shale. W. R. Jackson , M. W. Amer, Y. Fei, M. Marshall, A.L. Chaffee
C03 The role of sulfur in coals plastic layer formation. L. Butuzova , R. Makovskyi, T. Budinova, S. P. Marinov
D03 High performance electric double-layer capacitor using cctivated carbon from hyper-coal. K. Sato, K. Magarisawa, T. Takarada
12:40-13:00
A04 Numerical study on the reburning of ash with high unburned carbon in pc boiler. M.-y. Hwang , G.-B. Kim, J.-h. Song, S.-Mo Kim, C.-H. Jeon
B04 Ethanol effect on the average structural parameters of IDF soot soluble organic fraction. M. Salamanca , M. Velásquez, F. Mondragon, A. Santamaria
C04 Understanding the effects of biomass addition to coking coals during carbonisation. M. Castro-Díaz , A. Dufour, N. Brosse, R. Olcese, C. Snape
D04 Degradation characteristics of SOFC by trace elements in coal gasified gas. Y. Ueki , T. Kobayashi, R. Yoshiie, I. Naruse
A05 Characteristics of hydrogen sulfide formation in pulverized coal combustion. H. Shirai , M. Ikeda, H. Aramaki
B05 An analysis of the research performed with the Argonne Premium Coals and its contribution to coal science. J. P. Mathews , Y.E. Alvarez, R.E. Winans
C05 Influence of alkali additives on the swelling behavior of a high swelling bituminous coal. C.A.Strydom, J.R. Bunt, Y. van Staden, J. Collins
D05 Coupling gasification and solid oxide fuel cells: effect of tar on anode materials. M. Millan , E. Lorente, J. Mermelstein, C. Berrueco, N.P. Brandon
13:00-13:20
Lunch
13:20-15:00 Coal combustion Chairs: E. Lester & C.-H. Jeon
15:00-15:30
A06 Numerical study of the influence of heterogeneous kinetics on the carbon consumption by oxidation of a single coal particle. P.A. Nikrityuk, M. Gräbner , M. Kestel, B. Meyer
Coal characterization and coal Coal pyrolysis and liquefaction: structure coke microstructure Chairs: A.L. Chaffee & L. Butuzova Chairs: S. Niksa & M.A. Diez B06 Porosity and gas absorption of coals studied by X-ray scattering and modeling. R.E. Winans, S. Seifert, D. Locke, P. Chupas, K. Chapman, M. R. Nariewicz, J. P. Mathews , J. M. Calo
C06 Estimation of coking pressure in coke ovens by Koppers-Incar test. R. Alvarez , C.Barriocanal, M.A. Díez
Coal and the environment Chairs: M.J. Lázaro & L. Santos
D06 Explosions in Coal Mines due to Emission of Molecular Hydrogen via Atmospheric Weathering Processes. H. Cohen
Session A
Session B
Session C
B07 Organic sulphur form alterations in consecutively chemically- and bio-treated lignites. L.Gonsalvesh , S.P.Marinov, M.Stefanova, R.Carleer, J.Yperman
C07 The potential to upgrade petroleum cokes using high temperature processing. M. Ismail , J. W Patrick, E. Lester
D07 A thermo-petrographic method to identify coals prone to self-oxidation. C. Avila, E. Lester
C08 A study of the feasibility of an anthracene oil-based pitch for isotropic carbon fibres preparation N. Díez , P. Álvarez, R. Santamaría, C. Blanco, R. Menéndez M. Granda
D08 Monitoring hot spots in bituminous coal piles stored at atmospheric conditions. H. Cohen , U. Green, F. Gildemeister, L. Metzger, M. Pesimberg, S. Wasserman
15:30-15:50
A07 Pyrolisis and combustion kinectics using the distributed activation energy model. F. Saloojee, S. Kauchali, N. Wagner
15:50-16:10
A08 Plasma supported coal ignition and combustion. V.E. Messerle, E.I. Karpenko, A.B. Ustimenko
B08 Rank dependant formation enthalpy of coal. M. Sciazko
16:10-16:30
A09 A graphite furnace atomic absorption spectrometer as an experimental platform for studying matrix effects in trace element vaporization during coal combustion. E. I. Kozliak , O. V. Klykov, A. A. Raeva, D. T. Pierce, W. S. Seam
C09 Advanced characterisation of liquid hydrocarbons from South B09 Ion beam tomography for coal African high volatile bituminous characterization. coal. A. Bhargava , P.J. Masset, N. M.H. Makgato , H.W.J.P Gordillo, C. Habchi, P. Moretto Neomagus, R.C Everson, J.H.L. Jordaan, H.H. Schobert
16:30-17:00
Coffee break
D09 Reducing the environmental impact of sponteaneous coal combustion in coal waste gobs by applying soil covers. X. Querol , X. Zhuang, J. Li, O. Font, M. Izquierdo, A. Alastuey, B.L. van Drooge, T. Moreno, J. O. Grimalt, F. Plana
Session A
Session B
Session C
CO2 Storage Chairs: M. Lupión & D. Casal
Coal characterization and coal structure Chairs : R. Menéndez & Y. Fernández
Coal pyrolysis and liquefaction: general Chairs: J.-i Hayashi & P. Álvarez
17:00-17:20
A10 Diffuse soil CO2 flux to assess the reliability of CO2 storage in the MazarrónGañuelas Tertiary Basin (Spain). J. Rodrigo-Naharro, O. Vaselli, B. Nisi, M. Lelli, R. Saldaña, C. Clemente-Jul , L. Pérez del Villar
B10 The current state of affairs of coal research in U.S. Universities J. P. Mathews , B. G. Miller, C. S. Song, H. H. Schobert, F. Botha, R.B. Finkleman
C10 Decoupling in Thermochemical Conversion: Approach and Technologies. G. Xu, J. Zhang , Y. Wang, S. Gao
17:20-17:40
A11 Carbon and storage by pH swing aqueous mineralisation using a mixture of ammonium salts. A. Sanna , M. Dri, X. Wang, M. R Hall, M. Maroto-Valer
B11 The Current state of coal research in the United Kingdom, Germany, Australia and South Africa J. P. Mathews , B.G. Miller, C. S. Song, H.H. Schobert, F.Botha, R.B. Finkleman, A. Chaffee
C11 Integrated process of coal pyrolysis with CH4/CO2 activation by dielectric barrier discharge plasma. X. He, H. Hu , L. Jin, Y. Zhao
17:40-18:00
A12 New equipment for characterization of rocks for geological CO2 storage in coal seams. P. Cienfuegos, J.Loredo
B12 Adsorption behavior and biogasification of Soma lignite. M. Baysal, S. İnan, F. Duygun , Y. Yürüm
C12 Effect of steam treatment of a sub-bituminous coal on its caking and coking properties. H. Shui , C. Shan, H. Chang, Z.Wang, Z. Lei, S. Ren, S. Kang
Tuesday, 11th October, 2011 09:00-10:00
Plenary Lecture: (Chair: C.E.Snape) A20 The role of coal science in development and deployment of high efficiency energy technologies. D.J. Harris Session A Session B Session C CO2 transport and storage. Chairs: N.R. Marcilio & M.V. Gil
Coal mineralogy and coal ash: coal ash Chairs: X. Querol & E. Kozliak
Coal pyrolysis and liquefaction: liquefaction Chairs: O. Yamada & R. García
10:00-10:20
A21 Gas adsorption capacity of coaly shales from Japan and B21 Viscosity behaviour of slags USA -Implications for CO2 from coal-petroleum coke blends. storage in coal-bearing formationA. Ilyushechkin , M. Duchesne S. Shimada , Y. Nishiiri, N. Sakimoto, K. Ohga, Y-S. Jun
C21 Interpreting coal conversion under elevated H2 pressures with FLASHCHAIN and CBK. S. Niksa
10:20-10:40
A22 Relationships between the sorption capacity of methane, carbon dioxide, nitrogen and ethane on bituminous coals. R. Sakurovs , S. Day, S. Weir
C22 Development of a ZeroEmission Coal-to-Liquids Plant. W. Atcheson, K. Myers, L. O’Sullivan, H.H. Schobert
10:40-11:00
A23 CIUDEN CO2 Transport Test Rig: Technical Description and Experimental Plan. B. Navarrete ; P. Otero; I. Llavona; M.A. Delgado
11:00-11:30
B22 Study on clinker generation control in coal combustion boiler; clinker controlling effect of Febased coal additive. N. Wakabayashi , H. Shirai B23 Properties, microstructure and leaching of coal slag with additives during high temperature gasification. Y. Ninomiya , Y. Wei, K. Honma, T. Tanosaki, H. Li, M. Kawaguchi, N. Tatarazako Coffee break
Session A
Session B
Session C
CO2 capture and storage: oxyCoal pyrolysis and liquefaction: Coal gasification and clean fuels fundamentals fuel Chairs: J. P. Mathews & E. Jorjani Chairs: R. Malhotra & J.J. Chairs: R. Davidson & A. Fernández Ustimenko
11:30-12:00
A24 Doosan Power Systems B24 What is Reactive Surface Area OxyCoal™ Technology. in Coal Chars? M.D. Maloney , B. Dhungel, D.W. E. M. Suuberg , I. Aarna, I. Külaots Sturgeon, P. Holland-Lloyd
C24 Direct CTL: innovative analyses for high quality distillates. A. Quignard , N. Caillol, N. Charon, M. Courtiade, D. Dendroulakis
12:00-12:20
A25 CIUDEN CO2 Technology Development Centre on Oxycombustion. M Lupion , V J Cortes, M Gomez, A Fernandez
B25 The properties of chars derived from inertinite-rich, high ash coals and CO2 gasification: major properties affecting reactivity. G. N. Okolo, R.C. Everson , H.W.J.P. Neomagus
C25 Direct coal-liquid hydrogenation over NiMoNX / Al2O3 catalysts. C. Qi , G. Lin, F. Jie , L. Wenying , X. Kechang
12:20-12:40
A26 Oxy-fuel coal gasification in fluidised beds. N. Spiegl, E. Lorente, N. Paterson, C. Berrueco, M. Millan
B26 Characterization and carbon dioxide gasification kinetics of high ash inertinite-rich South African coals. R. Kaitano , R. C Everson, H.W J P Neomagus
C26 Preparation of activated carbons from direct coal liquefaction residue. J. Zhang, L. Jin, B. Qiu, H. Hu
12:40-13:00
A27 Experimental and numerical investigations of oxy-coal combustion in an entrained flow reactor. L. Álvarez , M. Gharebaghi, A. Williams, M. Pourkashanian, J. Riaza, C. Pevida, J.J. Pis, F. Rubiera
B27Gasification kinetics of coal char using direct measurement of particle temperature. R. Kim, H. Lim, C. Kim, J. Song, C.H. Jeon
Session A
13:00-13:20
Session B
Session C
B28 Performance simulations for coA28 Char characterisation from gasification of coal and methane. oxyfuel combustion. S. Niksa , J.-P. Lim, D. del Rio Diaz A. Nuamah , E. Lester, T. Drage, Jara, D. Steele, D. Eckstrom, R. G. Riley Malhotra, R. B. Wilson Lunch
13:20-15:00 Clean coal technology: Mercury emissions Chairs: D.A. Spears & M. DíazSomoano
Coal petrology Chairs: I.Suárez-Ruiz & D. van Niekerk
Coal pyrolysis and liquefaction: fundamentals Chairs: W.R. Jackson & H. Hu
15:00-15:30
A29 Avoiding mercury emissions from coal combustion:postcombustion research strategies. M. R. Martínez-Tarazona , M. A. López-Antón, R. OchoaGonzález, A. Fuente-Cuesta, P. Abad- Valle, J. RodríguezPérez, F. Inguanzo-Fernández, M. Díaz-Somoano and R. García
B29 Biomarker and Petrographic Evidence for the Origin and Maturity of Oil-Prone Arctic Coal and Associated Bitumen. C. Marshall, D.J. Large, C.E. Snape , W. Meredith, B. Spiro, I Mokogwu
C29 Attempted Production of Blast Furnace Coke from Victorian Brown Coal. A.L. Chaffee , M. M. Mollah, R. S. Higgins, M. Marshall,W. R. Jackson
15:30-15:50
A30 Interpreting the re-emission of elemental mercury during wet FGD scrubbing. B. Krishnakumar, S. Niksa , N.Fujiwara
B30 Coal quality from a mega coal basin from Xianjiang, Northwest China. J. Li , X. Zhuang, X. Querol, O. Font, P.Córdoba
C30 Chlorine retention during the pyrolysis of a Western Australian lignite in a fluidised-bed reactor. J. Zhang, C. Kelly, A. Rossiter, S. Wang, C.-Z. Li
Session A
15:50-16:10
16:10-16:30
16:30-17:00
17:00-18:00
Session B B31 The effect of particle size and petrographic composition on A31 The fate of Hg at two coal combustion behaviour of selected power plants equipped with FGD. Russian coals. P Córdoba , O Font, M. V. Hudspith, A. Nuamah , A.C. Izquierdo, X. Querol Scott, T. Drage, J. Powis. G. Riley, M.E. Collinson, E.Lester A32 Aqueous chemistry of mercury in flue gas desulphurization conditions. R. Ochoa-González , M. DíazSomoano, M. R. MartínezTarazona
B32 The effect on coal flotation of segregating group macerals based on particle size. E. Jorjani , S. Esmaeili, M.T. Khorami
Session C C31 Dimethyl ether production from Victorian brown coal biomass: a comparative process modelling study. K. B. Kabir, G. Grills, J. Walter, S. Bhattacharya C32 Synchronous fluorimetric characterization of preasphaltene and asphaltene from direct liquefaction of coal. Z. Wang, C. Wei, H. Shui , Z. Wang, C. Pan, S. Ren, Z. Lei
Coffee break Poster Session: Coal Chemistry, Coal Petrology, Coal Mineralogy, Coal Upgrading, Coal Pyrolysis, Carbons from Coal P1.01 Jurassic perhydrous coals of the Lusitanian Basin, Portugal. Petrography, geochemical and textural characteristics A. Costa , C. Tomás, I. Suárez-Ruiz, P.P. Cunha, D. Flores, B. Ruiz P1.02 Rank distribution of the Cretaceous coals in the region of San Juan de Sabinas, Coahuila de Zaragoza, Mexico N. Piedad-Sánchez , I. Suárez-Ruiz, F. R. Carrillo-Pedroza, J. A. Moreno-Hirashi, G. de la RosaRodríguez, K. Flores-Castro, R. Corona-Esquivel, J. L. Cadena-Zamudio, J. O. Navarro-Lozano, B. Santiago-Carrasco, F. González-Carrillo P1.04 Correlation between fluidity and structure transformation of three coal ashes. X. Lin , J. Miyawaki, S.-H. Yoon, I. Mochida P1.05 Nanominerals and ultra-fine particles within coal ashes. L.F.O. Silva; F. Waanders; M.L. S. Oliveira ; K. da Boit P1.06 Properties of fly ash from biomass combustion. R. P. Girón , I. Suárez-Ruiz, B. Ruiz, E. Fuente, R. R. Gil P1.08 Characteristics of crush strength in coal briquette molded with polymer as a binder. S.-H. Moon , S.-J. Lee, I.-S. Ryu, Y.-W. Kim, T.-I. Ohm
P1.09 Characteristics of dried low-rank coal by hot oil immersion drying method for the upgrading T.-I. Ohm , J.-S. Chae, S.-H. Moon P1.10 Energy and exergy analysis of continuous microwave dryer. M. B. Alvarado , E. J. Muñoz, S.C. Navarro, F. Chejne, H. Velazquez P1.11 Moisture re-adsorption characteristics of coal samples of dried by a pneumatic dryer. S. Kim , Y. Rhim, S. Lee P1.12 Moisture readsorption characteristics of upgraded low rank coal. H. Choi , S. Kim, J. Yoo, D. Chun, J. Lim, Y. Lim, S. Lee P1.13 Solar drying technology of coal in the open in the Iron and Steel Research Center. A. Leyva. Mormul , A. D. Castillo, O. S. Leyva González , J.A. Trotman Gavilán, O. Figueredo Stable P1.14 A New Supercritical Solid Acid for Breaking Car-Calk Bond in Di(1-naphthyl)methane. X.-M. Yue , X.-Y. Wei, B. Sun, Y.-H. Wang, Z.-M. Zong, Z.-W. Liu 17:00-18:00
P1.15 Briquetting of carbon-containing wastes from steelmaking for metallurgical coke production. M.A. Diez , R. Alvarez, J.L.G. Cimadevilla P1.16 Co-carbonization behaviour of coal and biomass-derived products and its effect on coke structure and properties. M.A. Diez , R. Alvarez, M. Fernández P1.17 Evolution of volatile products of coal and plastic wastes during co-pyrolysis. S. Melendi, M.A. Diez , R. Alvarez P1.18 Role of selected coal- and petroleum-based additives in low- and high-temperature co-pyrolysis with coal blends. E. Rodríguez , S. Melendi, R. García, R. Alvarez, M.A. Diez P1.19 Effect of volatile matter evolution on optical properties of macerals from different rank coals A. Guerrero , M.A. Diez, A.G. Borrego P1.20 Semi-pilot scale carbonization to assess blast furnace coke quality. E. Díaz-Faes, R. Alvarez , C. Barriocanal, M.A. Díez
P1.21 Fundamental investigation of pyrolysis behavior of low rank coals. T. Harada , S. Matsuda, N. Wada, Y. Matsushita, I. Mochida P1.22 High pressure pyrolysis of different coal types – Influence of pressure on devolatilisation characteristics using TGA/MS. M. Klinger , B. Meyer P1.23 Brown coal and rape cake co-pyrolysis products in the range 5 to 40 per cent. J. Vales , J. Kusy, L. Andel, M. Safarova P1.24 Integrated coal pyrolysis with methane aromatization over Mo/HZSM-5 catalyst for improving tar yield. X. Zhou, H. Hu , L.Jin P1.25 Integrated process of coal pyrolysis and CO2 reforming of methane over Ni/Al2O3-MgO catalyst. J. Liu, H. Hu , L. Jin, S. Zhu P1.26 Kinetics of co-pyrolysis of high- and low-sulfur coal blends with additives. L. Butuzova , R. Makovskyi, V. Bondaletova, D. Dedovets, G. Butuzov 17:00-18:00
P1.27 Effect of elemental composition of various additives on the modification of coal thermoplastic properties. M.G. Montiano , C. Barriocanal, R. Alvarez P1.28 Influence of residual volatile matter in semicokes on coking pressure. E. Díaz-Faes, C. Barriocanal , R. Alvarez P1.29 Pyrolysis of wastes from tyre grinding. B. Acevedo, C. Barriocanal, R. Alvarez P1.30 Secondary reactions of HCl during coal pyrolysis: studies on reactions of HCl with model carbons. N. Tsubouchi , N. Ohtaka, A. Kawashima, Y. Ohtsuka P1.31 Solvent modulation in getting high purity of anthracene and carbazole from crude anthracene. M. Fan, C. Ye , H. Zheng, T. Wu, J. Feng , W. Li P.1.32 Study of coal, char and coke fines structures and their proportions in the off-gas blast furnace samples by X-Ray diffraction. A.S. Machado, A.S. Mexias, A.C.F. Vilela, E. Osório P1.34 Yields of the pyrolysis tests of brown coals mined in the Czech Republic. J. Kusý, L. Anděl , M. Šafářová, J. Valeš
P1.37 Wet oxidation of anthracene oil-based pitch - a way to porous carbons. H. Machnikowska, K. Torchała, G. Gryglewicz , J. Machnikowski
17:00-18:00
P1.38 Adsorption of phenol on nitrogen enriched activated carbons prepared from coal-tar pitch and polymers. E. Lorenc-Grabowska, G. Gryglewicz , M.A. Diez, C. Barriocanal P1.39 Mineral matter and heat treatment temperature effects on the development of graphitic structure in two South African anthracites as studied by Raman Spectroscopy and XRD M. Vanegas-Chamorro , K. Tamargo-Martínez, J. Xiberta, A. Martínez-Alonso, J. M. D. Tascón P1.40 Structural evolution upon thermal treatment of two South African anthracites as studied by XRD. M. Vanegas-Chamorro , K. Tamargo-Martínez, J. Xiberta, A. Martínez-Alonso, J. M. D. Tascón
Wednesday, 12th October, 2011 09:00-10:00
Plenary Lecture: (Chair: H.H. Schobert) A40 A cubic mile of oil: realities and options for averting the looming global energy crisis. R. Malhotra Session A
Session B
Clean coal technology: Coal gasification and clean fuels: Mercury emissions mineral matter Chairs:H. Cohen & N. Tsubouchi Chairs: A. Sharma & Q. Campbell
10:00-10:20
A41 Gold-impregnated carbon materials as regenerable sorbents for mercury retention. J. Rodríguez-Pérez , F. InguanzoFernández, E. Rodríguez, M. A. López-Antón, R. García, M. DíazSomoano, M. R. MartínezTarazona
B41: Entrained-flow gasification of coal under slagging conditions: properties of solid wastes and relevance of char-wall interaction phenomena. F. Montagnaro , P. Brachi, P. Salatino
Session C Coal Pyrolysis Chairs: R. Kandiyoti & N. Okuyama
C41 Characterization of the hydrocarbon components from sequential flash pyrolysis for a vitrinite-rich and inertinite-rich coal. D. van Niekerk , C. du Sautoy, J. van Heerden
Session A
Session B
10:20-10:40
A42 Speciation and fate of mercury in oxy coal combustion. O. Font , P. Córdoba P, C. Leiva, L.M. Romeo, I. Bolea, I. Guedea, N. Moreno, X. Querol, C. Fernandez-Pereira, L.I. Díez
B42 Mineral-char interaction during the gasification of high ash coals in a fluidised bed gasifier: Redistribution of mineral phases within the char matrix. B.O. Oboirien, A.D. Engelbrecht, B.C. North, R. Falcon
C42 Characterisation of coal and biomass based on kinetic parameter distributions for pyrolysis. N. Sonoyama , J.-i. Hayashi
10:40-11:00
A43 Experimental study on the SO2 emission and Calcium-based desulfurization in the coal Oxygen-enriched combustion. L. Tian , H. Chen, H. Yang, X. Wang, S. Zhang, C. Zeng
B43 Introduction of a ternary diagram for comprehensive evaluation of gasification processes for high ash coals. M. Gräbner , B. Meyer
C43 Effect of the pyrolysis conditions on the microstructure of anthracene oil-based cokes. P. Alvarez, N. Díez, R. Santamaría, C. Blanco, R. Menéndez , M. Granda
Coffee break
11:00-11:30
11:30-12:00
12:00-12:20
Session C
CO2 capture and storage: Chemical looping Chairs T. Drage & S. Bhattacharya A44 Current status of the chemical looping combustion technology. F. García-Labiano , L. F. de Diego, P. Gayán, A. Abad, J. Adánez A45 Oxygen transfer from metal oxides during chemical looping combustion of Victorian brown coal – An experimental and modelling study. C. Saha, T. X. Seng, A. Auxilio , S. Bhattacharya
Mineral matter and coal ash: Mineral matter Chairs: R.C. Everson & M.R. Martínez-Tarazona
Coal pyrolysis and liquefaction: coke microstructure Chairs: R. Sakurovs & S. Melendi
B44 The determination of trace element distributions in coal. A "new" approach. D.A. Spears
C44 Optical and scanning electron microscopy of coke: microstructure & minerals. S. Gupta, E Lester , M Ismail, G O'Brien
B45 Solid-state NMR study on mineral structure and transformation behaviors of coal ash. X. Lin, K. Ideta, J.Miyawaki, S.-H. Yoon , I.Mochida
C45 Small scale determination of metallurgical coke CSR. T. MacPhee , L. Giroux, K.W. Ng, T. Todoschuk, M. Conejeros, C. Kolijn
Session A
Session B
12:20-12:40
A46 Chemical looping combustion of coal using a residue from alumina production. T. Mendiara , G. Ferrer, P. Gayán, A. Abad, F. GarcíaLabiano, L. F. de Diego, J. Adánez
B46 The effect of minerals on the moisture adsorption and desorption properties of South African fine coal. S.M. du Preez , Q.P. Campbell
C46 3-D Structural analysis for metallurgical coke microstructure using micro X-ray CT. Y. Yamazaki , K. Hiraki, T. Kanai, X. Zhang, A. Uchida, M. Shoji, Y. Matsushita, H. Aoki, T. Miura, S. Nomura, H. Hayashizaki
12:40-13:00
A47 Chemical looping combustion of char with a Cubased carrier. A. Coppola, O. Senneca, R. Solimene, R. Chirone, L. Cortese, P. Salatino
B47 Structural changes and possible modes of interaction in bituminous coal fly ash due to treatments with neutral and acidic aqueous solutions. R.N. Lieberman , R.Nitzsche, H. Cohen
C47 Preparation of high-strength coke from hot-briquetted brown coal. A. Mori, Y. Huang, K. Norinaga, S. Kudo, T. Kanai, H. Aoki, J.-i. Hayashi
13:00-13:20
A48 Theoretical approach on the CLC performance with solid fuels: optimizing the solids inventory. A. Cuadrat, A. Abad, P. Gayán, L. F. de Diego, F. García-Labiano, J. Adánez
B48 Prediction of selective trace element emissions during oxy-CFB combustion of Victorian brown coals. B. Roy, W. L. Choo, S. Bhattacharya
C48 A mechanism of improvement in coke strength by adding a solvent-extracted coal N. Okuyama , T. Shishido, K. Sakai, M. Hamaguchi, N. Komatsu
Lunch
13:20-15:00 CO2 capture and storage: Chairs: M. Millan & M. Alonso
15:00-15:30
Session C
A49 Puertollano IGCC: Towards zero emissions power plants. F. García Peña , P. Coca Llano
Coal gasification and clean fuels Chairs: D. Harris & F. Mondragon B49 Evolution of Victorian brown coal char structure during the gasification in CO2 and steam. H.-L. Tay, S. Kajitani, C.-Z. Li
Coal Upgrading Chairs: K. Miura & T. MacPhee C49 Coal drying and dewatering for power generation – current status, research and development needs. D. Stokie, J. Yu, A. Auxilio , S. Bhattacharya
Session A
Session B
Session C
15:30-15:50
A50 Pre-combustion CO2 capture: laboratory- and benchscale studies of a sweet watergas-shift catalyst for H2 and CO2 production. J.M. Sánchez , M. Maroño, D. Cillero, L. Montenegro, E. Ruiz
15:50-16:10
A51 Regeneration of used alkali carbonates for removal of gaseous sulfur compounds in gasification process. S. Raharjo , Y.Ueki, R. Yoshiie, I. Naruse
B51 A CeO2-La2O3-based Cu catalyst for application in hightemperature water-gas shift reaction. L D. Morpeth , Y. Sun, S.S. Hla, G.J. Duffy, J.H. Edwards, D.J. Harris, D.G. Roberts
C51 Upgrading and dewatering of low rank coals realizing the suppression of self-ignition tendency through solvent treatment at around 350°C. H. Fujitsuka , R. Ashida, K Miura
16:10-16:30
A52 Step Change Adsorbents and Processes for CO2 capture “STEPCAP”. T.C. Drage , A.I Cooper, R Dawson, J Jones, C Cazorla Silva, C.E. Snape, L. Stevens, X. Guo, J. Wood, J. Wang
B52 Coal plasma gasification for clean synthesis gas production. V.E. Messerle, A.B. Ustimenko , N. Slavinskaya, O.A. Lavrichshev, E.F. Ossadchaya
C52 Upgrading of low-quality coals by thermal extraction. T. Takanohashi , N. Sakimoto, K. Koyano, Y. Harada, H. Fujimoto
16:30-17:00
17:00-18:00
B50 Development of a new synthesis gas production process from coal by catalytic gasification of HyperCoal using steam-CO2 as gasifying agent. A.Sharma , T. Takanohashi
C50 Coprocessing of low-rank coal and biomass utilizing mild solvent treatment at around 350°C. X. Li, J. Wannapeera, N. Worasuwannarak, R. Ashida , K. Miura
Coffee break Poster Session: Coal Combustion, Clean Coal Technologies, Coal Gasification, CO2 Capture and Storage, Coal and The Environment P2.01 Arsenic leachability and speciation in fly ashes from coal fired power plants. S. Kambara, M. Endo , S. Takata, K. Kumabe, H. Moritom i P2.02 Low temperature SNCR by photochemical activation of ammonia. S. Kambara , M. Kondo, N. Hishinuma, M. Masui, K. Kumabe, H. Moritomi P2.03 Optimum temperature for sulphur retention in fluidised beds working under oxy-fuel combustion conditions. A. Rufas , M. de las Obras-Loscertales, L.F. de Diego, F. García-Labiano, A. Abad, P. Gayán, J. Adáne z P2.04 Carbon based catalytic briquettes for NOx removal in flue gases. M.J. Lázaro , M.E. Gálvez, S. Ascaso, I. Suelves, R. Moliner
P2.05 Identification of operational regions in the chemical- looping with oxygen uncoupling (CLOU) process with a Cu-based oxygen- carrier. I. Adánez-Rubio , A. Abad, P. Gayán, L. F. de Diego, F. García-Labiano, J. Adánez P2.06 Influence of hydrogenation on the mercury capture by active carbons. J. Rodríguez-Pérez , M. A. López-Antón, R. García, M. Díaz-Somoano, M. R. Martínez-Tarazona P2.07 Sub-products of gasification as sorbents for mercury retention. A. Fuente-Cuesta , M. Diaz-Somoano, M.A. Lopez-Anton, M.R. Martinez-Tarazona P2.08 Biomimetic sequestration of CO2 and conversion to CaCO3 using enzyme extracted oyster. S.K. Jeong, Y.I. Yoon, S.C. Nam P2.09 Carbon dioxide sequestration by aqueous mineral carbonation of serpentine and explanation of experimental results. K. Alizadehhesari , K. Steel P2.10 Characterization of a novel flat-panel airlift photobioreactor with the internal heat exchanger L. H. Kochem, N. C. da Fré, C. Redaeli, N. R. Marcílio , R. Rech
17:00-18:00
P2.11 Clean coal technologies scenario and evaluation of present CO2 dwindling initiatives to approach zero emission power stations by coal combustion. Deployment situation and evaluation study. F. Guerrero, C. Clemente-Jul P2.12 Co-combustion of coal and biomass blends in an entrained flow reactor under oxy-fuel atmospheres. J. Riaza, L. Álvarez , M.V. Gil, C. Pevida, F. Rubiera, J.J. Pis P2.13 Effect of the activation temperature and the burn - off degree on the CO2 capture capacity of microporous activated carbons. M.V. Gil , M. Martínez, S. García, J.J. Pis, F. Rubiera, C. Pevida P2.14 Influence of light over CO2 biofixation by the microalgae Chlorella minutissima. C. Redaelli, R. Rech, N. R. Marcilio P2.15 Influence of temperature and salinity over CO2 biofixation by the microalgae Dunaliella tertiolecta. N. C. da Fré, R. Rech, N. R. Marcílio P2.16 Carbon oxides emission via the atmospheric oxidation of coals: effect of coal rank. U. Green, Z. Aizenstat, H. Cohen P2.18 Environmental pollution by migration of gas produced in the Underground Coal Gasification process. M. Ludwik-Pardał a, K. Stańczyk
P2.19 Fly ash as a potential scrubber for low activity radioactive waste. R.N. Liberman , G. Segev, E. Elish, E. J. C. Borojovich, H. Cohen P2.20 Mobility of major and minor species in fly ash-brine co-disposal systems: up-flow percolation test. O.O. Fatoba , W.M. Gitari, L.F. Petrik, E.I. Iwuoha P2.21 Removal of arsenate from water by adsorption onto lignite. Y. Yürüm , Z. Özlem Kocabas P2.22 Biomass and mineral coal in South Brazil: potential use for energy generation in bubbling fluidized bed. G.M.F.Gomes, L.Dalla Zen , A.C.F. Vilela, E. Osório P2.23 Effect of particle size in the devolatilization behaviour of coal chars of different rank. K.S. Milenkova and A.G. Borrego P2.24 The element distribution during the co-combustion of coal with wood and wood wastes. Z. Klika , L. Bartoňová P2.25 The influence of particle size and density on the combustion of Highveld coal. G.W. van der Merwe, R.C. Everson , H.W.J.P. Neomagus, J.R. Bunt 17:00-18:00
P2.26 Effect of blending waste materials with coal on minerals and reactivity of char and coke. A.M. Fernández, C. Barriocanal, S. Gupta, D. French P2.27 An investigation into the catalytic potential of coal ash constituents on the CO2 gasification rate of high ash, South African coal. B.B. Hattingh, R.C. Everson, H.W.J.P. Neomagus, J.R. Bunt P2.28 Catalyst recovery using by support in steam gasification of lignite at low temperature. Y.-K. Kim , J.-I. Park, J. Miyawaki, I. Mochida, S.-H. Yoon P2.29 Evaluation of coal gasification reaction from composition of gases produced (2). M. Kaiho, O. Yamada , H. Yasuda, S. Shimada, M. Fujioka P2.30 Effect of calcium on the interaction of CO2 with carbonaceous materials during coal gasification. J. D. González , F. Mondragón, J. F. Espinal P2.31 Interaction of calcium with carbonaceous materials: A DFT Study. J.D. González , F. Mondragón, J. F. Espinal P2.32 Use of a waste generated in the cement industry as an additive in the process of coal gasification in fluidized bed. E. Rodríguez Acevedo, F. Chejne , W. Jurado
17:00-18:00
P2.33 Modelling and simulation of a coal gasification process in the pressurized fluidized bed. F. Chejne , E. Lopera, C. A. Londoño, C. A. Gómez P2.34 Preliminary studies on ash-free coal gasification at mild condition. J. Yoo , S. Jin, H. Choi, Y. Rhim, J. Lim, D. Chun, S. Kim, S. Lee P2.37 Kinetic study on the lignite- CO2 gasification in the presence of K2CO3. V.C. Bungay , B.H. Song, S.D. Kim, J.M. Sohn, H.M. Shim, Y.J. Kim, G.T. Kim, S.R. Park, Y.I. Lim P2.38 Prediction of steam reforming of the simulated coke oven gas with a detailed chemical kinetic model. K. Norinaga , R. Sato, J.-i. Hayashi P2.39 Invention of quantitative method of char and soot to clarify soot production and reaction behavior in coal gasification. S. Umemoto , S. Kajitani, S. Hara
Thursday, 13th October, 2011 09:00-10:00
Plenary Lecture: (Chair:J. van Heerden) A60 Calcium looping technologies for CO2 capture C. Abanades Session A Session B CO2 capture and storage Chairs: F. García-Labiano & J. Chamberlain
10:00-10:20
A61 N2O and CO emissions increase during oxy-char combustion in fluidized bed. A.Sánchez, Y. Betancur, E. Eddings, F. Mondragón
Session C
Coal gasification and clean fuels Chairs: C.-Z. Li & J.M. Sánchez
Coal Upgrading C. Clemente-Jul & M.A. López Antón
B61 Chemical Looping Combustion of Coal-derived Synthesis Gas containing H2S over Supported Fe2O3 - MnO2 Oxygen Carrier. E. Ksepko , R.V. Siriwardane, H. Tian, T. Simonyi, M. Sciazko
C61 Drying behavior of brown coal under the various temperature conditions with halogen heat source and its formulation. Y. Matsushita, N. Mitsuhara, T. Harada
Session A
Session B
Session C
10:20-10:40
A62 New candle prototype for hot gas filtration industrial applications. M. Rodríguez-Galán, M. Lupión , B. Alonso-Fariñas, J. MartínezFernández
B62 Measurement of gasification rate of coal char under high pressure and high temperature using a mini directly-heated reactor. K. Miura , M. Makino, E. Sasaoka, S. Imai, R. Ashida
C62 Mobility of hazardous elements of Coal Cleaning Residues. L.F.O. Silva; F. Waanders ; M.L.S. Oliveira; K. da Boit
10:40-11:00
A63 Fluid dynamic simulation of dry filter for removal of particulates from coal and biomass gasification. C. B. da Porciúncula, N. R. Marcilio , M. Godinho, A.R.Secchi
B63 Implementation of coal gasification in a fluidized bed firing system for brick tunnel kiln. F. Chejne , C. londono, C. Gómez, J. Espinosa, F. Mondragon, J.J Fernandez, E. Arenas, L. C Cuartas Coffee break
11:00-11:30 CO2 capture and storage Chairs: C. Abanades & M.D. Maloney
11:30-11:50
A64 Capture of CO2 during low temperature biomass combustion in a fluidized bed using CaO. A new larger scale experimental facility. J.R. Chamberlain , C. Perez Ros
Coal gasification and clean fuels Chairs: F. Chejne & M. Gräbner
B64 Catalytic steam gasification of large coal particles. S. Nel , H.W.J.P Neomagus, J.R. Bunt, R.C. Everson
C63 Modelling of coal slag viscosity: Focus on the volume fraction of solid particles. A. Bronsch , P. J. Masset
Biomass Processing Chairs: Z. Klika & E. Osorio
C64 Effect of ash components on devolatilisation behaviour of coal and biomass – product yields, properties and heat requirement. D. Reichel , M. Klinger, S. Krzack, B. Meyer
Session A
11:50-12:10
A65 La Pereda CO2. A 1.7 MWt pilot to test postcombustion CO2 capture with CaO. A. Sánchez-Biezma, J Paniagua, L. Diaz, E. de Zarraga, J. López, J Alvarez, B. Arias , M. Alonso, J.C. Abanades
12:10-12:30
A66 Fluidized bed desulfurization using lime obtained after slow calcination of limestone particles. F. Scala , R. Chirone, P. Meloni, G. Carcangiu, M. Manca, G. Mulas, A. Mulas
12:30-12:50
A67 Synthetic gas bench study of CO2 capture from PCC power plants. E. Ruiz , J. M. Sánchez, M. Maroño, J. Otero
12:50-13:30 13:30-15:00
Session B
Session C
B65 The influence of particle size on the steam gasification of coal. G. H. Coetzee , H.W.J.P Neomagus, R.C. Everson
C65 How closely do low volatile bituminous coals prepared by hydrous pyrolysis of woody biomass and low-rank coals correspond to prime coking coals?. S. Kokonya, M. C. Diaz, C. Uguna, C. Snape , A.D. Carr
B66 Effect of iron and calcium catalysts on pyrolysis and steam gasification of wood. K. Murakami, M. Sato, T. Kato, K. Sugawara
C66 Biomass characterisation and link with char morphology and ashing behaviour. C. H. Pang , T. Wu, E. Lester
B67 Thermodynamic efficiency analysis of gasification of high ash coal and biomass. R. Rodrigues, N.R. Marcilio , J.O. Trierweiler, M. Godinho Closing ceremony Lunch
Authors A Aarna, I.
B24
Álvarez, P.
C08, C43, D02
Abad, A.
A44, A46, A48, P2.03, P2.05
Álvarez, R.
C06, P1.15, P1.16, P1.17, P1.18, P1.20, P1.27, P1.28, P1.29
Abad-Valle, P.
A29
Álvarez, Y.E.
B01, B05
Abanades, J.C.
A60, A65
Amer, M.W.
B03
Acevedo, B.
P1.29
Anděl, L.
P1.23, P1.34
Adánez, J.
A44, A46, A48, P2.03, P2.05
Aoki, H.
C46, C47
Adánez-Rubio, I.
P2.05
Aramaki, H.
A05
Aizenstat, Z.
P2.16
Arenas, E.
B63
Alastuey, A.
D09
Arias, B.
A65
Alizadehhesari, K.
P2.09
Ascaso, S.
P2.04
Alonso, M.
A65
Asenjo, N.G.
D02
Alonso-Fariñas, B.
A62
Ashida, R.
B62, C50, C51
Alvarado, M.B.
P1.10
Atcheson, W.
C22
Álvarez, J.
A65
Auxilio, A.
A45, C49
Álvarez, L.
A27, P2.12
Avila, C.
D07
Barriocanal, C.
C06, P1.20, P1.27, P1.28, P1.29, P1.38, P2.26
Botha, F.
B10, B11
Bartoňová, L.
P2.24
Brachi, P.
B41
Baysal, M.
B12
Brandon, N.P.
D05
Berrueco, C.
A26, D05
Bronsch, A.
C63
B
Betancur, Y.
A61
Brosse, N.
C04
Bhargava, A.
B09
Budinova, T.
C03
Bhattacharya, S.
A45, B48, C31, C49
Bungay, V.C.
P2.37
Blanco, C.
C08, C43, D02
Bunt, J.R.
B64, C05, P2.25, P2.27
Bolea, I.
A42
Burgess Clifford, C.E.
D01
Bondaletova, V.
P1.26
Butuzov, G.
P1.26
Borojovich, E.J.C.
P2.19
Butuzova, L.
C03, P1.26
Borrego, A.G.
P1.19, P2.23
C Cadena-Zamudio, J.L.
P1.02
Chun, D.
P1.12, P2.34
Caillol, N.
C24
Chupas, P.
B06
Calo, J.M.
B06
Cienfuegos, P.
A12
Campbell, Q.P.
B46
Cillero, D.
A50
Carcangiu, G.
A66
Cimadevilla, J.L.G.
P1.15
Carleer, R.
B07
Clemente-Jul, C.
A10, P2.11
Carr, A.D.
C65
Coca Llano, P.
A49
Carrillo-Pedroza, F.R.
P1.02
Coetzee, G.H.
B65
Castillo, A.D.
P1.13
Cohen, H.
B47, D06, D08, P2.16, P2.19
Castro-Díaz, M.
C04
Collins, J.
C05
Castro-Marcano, F.
B01
Collinson, M.E.
B31
Cazorla Silva, C.
A52
Conejeros, M.
C45
Chae, J.S.
P1.09
Cooper, A.I.
A52
Chaffee, A.L.
B02, B03, B11, C29
Coppola, A.
A47
Chamberlain, J.R.
A64
Córdoba, P.
A31, A42, B30
Chang, H.
C12
Corona-Esquivel, R.
P1.02
Chapman, K.
B06
Cortés, V,J.
A25
Charon, N.
C24
Cortese, L.
A47
Chejne, F.
B63, P1.10, P2.32, P2.33
Costa, A.
P1.01
Chen, H.
A43
Courtiade, M.
C24
Chirone, R.
A47, A66
Cuadrat, A.
A48
Choi, H.
P1.12, P2.34
Cuartas, L.C.
B63
Choo, W.L.
B48
Cunha, P.P.
P1.01
da Boit, K.
C62, P1.05
Diaz, L.
A65
da Fré, N.C.
P2.10, P2.15
Díaz, M.C.
C65
da Porciúncula, C.B.
A63
Díaz-Faes, E.
P1.20, P1.28
Dalla Zen , L.
P2.22
Díaz-Somoano, M.
A29, A32, A41, P2.06, P2.07
Dawson, R.
A52
Díez, L.I.
A42
Day, S.
A22
Díez, M.A.
C06, P1.15, P1.16, P1.17, P1.18, P1.19, P1.20, P1.38
de Diego, L.F.
A44, A46, A48, P2.03, P2.05
Díez, N.
C08, C43
de la Rosa-Rodríguez, G.
P1.02
Drage, T.C.
A28, A52, B31
de las Obras-Loscertales, M.
P2.03
Dri, M.
A11
de Zarraga, E.
A65
du Preez, S.M.
B46
Dedovets, D.
P1.26
du Sautoy, C.
C41
del Río Díaz Jara, D.
B28
Duchesne, M.
B21
Delgado, M.A.
A23
Duffy, G.J.
B51
Dendroulakis, D.
C24
Dufour, A.
C04
D
Dhungel, B.
A24
Duygun, F.
B12
Eckstrom, D.
B28
Engelbrecht, A.D.
B42
Eddings, E.
A61
Esmaeili, S.
B32
Edwards, L.H.
B51
Espinal, J.F.
P2.30, P2.31
Elish, E.
P2.19
Espinosa, J.
B63
Endo, M.
P2.01
Everson, R.C.
B25, B26, B64, B65, C09, P2.25, P2.27
Falcon, R.
B42
Figueredo Stable, O.
P1.13
Fan, M.
P1.31
Finkleman, R.B.
B10, B11
Farrow, T.S.
A03
Flores, D.
P1.01
Fatoba, O.O.
P2.20
Flores-Castro, K.
P1.02
Fei, Y.
B03
Font, O.
A31, A42, B30, D09
Feng, J.
P1.31
French, D.
P2.26
Fernández, A.
A25
Fuente, E.
P1.06
Fernández, A.M.
P2.26
Fuente-Cuesta, A.
A29, P2.07
Fernández, J.J.
B63
Fujimoto, H.
C52
Fernández, M.
P1.16
Fujioka, M.
P2.29
Fernandez-Pereira, C.
A42
Fujitsuka, H.
C51
Ferrer, G.
A46
Fujiwara, N.
A30
P2.04
Gómez, C.
B63
E
F
G Gálvez, M.E.
Gao, H.
A02
Gómez, C.A.
P2.33
Gao, S.
C10
Gómez, M.
A25
García Peña, F.
A49
Gonsalvesh, L.
B07
García, R.
A29, A41, P1.18, P2.06
González, J.D.
P2.30, P2.31
García, S.
P2.13
González-Carrillo, F.
P1.02
García-Labiano, F.
A44, A46, A48, P2.03, P2.05
Gordillo, N.
B09
Garten, B.
C02
Gräbner, M.
A06, B43
Gayán, P.
A44, A46, A48, P2.03, P2.05
Granda, M.
C08, C43, D02
Gharebaghi, M.
A27
Green, U.
D08, P2.16
Gil, M.V.
P2.12, P2.13
Grills, G.
C31
Gil, R.R.
P1.06
Grimalt, J.O.
D09
Gildemeister, F.
D08
Gryglewicz, G.
P1.37, P1.38
Girón, R.P.
P1.06
Guedea, I.
A42
Giroux, L.
C45
Guerrero, A.
P1.19
Gitari, W.M.
P2.20
Guerrero, F.
P2.11
Godinho, M.
A63, B67
Guo, X.
A52
Gomes, G.M.F.
P2.22
Gupta, S.
C44, P2.26
Habchi, C.
B09
Higgins, R.S.
C29
Hall, M.R.
A11
Hiraki, K.
C46
Hamaguchi, M.
C01, C48
Hishinuma, N.
P2.02
Hara, S.
P2.39
Hla, S.S.
B51
Harada, T.
C61, P1.21
Holland-Lloyd, P.
A24
Harada, Y.
C52
Honma, K.
B23
H
Harris, D.J.
A20, B51, C02
Hu, H.
C11, C26, P1.24, P1.25
Hattingh, B.B.
P2.27
Huang, Y.
C47
Hayashi, J.-i.
C42, C47, P2.38
Hudspith, V.
B31
Hayashizaki, H.
C46
Hwang, M.Y.
A04
He, X.
C11
I Ideta, K.
B45
Inguanzo-Fernández, F.
A29, A41
Ikeda, M.
A05
Iondono, C.
B63
Ilyushechkin, A.
B21
Ismail, M.
C07, C44
Imai, S.
B62
Iwuoha, E.I.
P2.20
Ínan, S.
B12
Izquierdo, M.
A31, D09
Jackson, W.R.
B03, C29
Jones, J.
A52
Jeon, C.H.
A04, B27
Jordaan, J.H.L.
C09
Jeong, S.K.
P2.08
Jorjani, E.
B32
Jie, F.
C25
Jun, Y.S.
A21
Jin, L.
C11, C26, P1.24, P1.25, P2.34
Jurado, W.
P2.32
Kabir, K.B.
C31
Kim, S.M.
A04
Kaiho, M.
P2.29
Kim, Y.J.
P2.37
Kaitano, R.
B26
Kim, Y.K.
P2.28
Kajitani, S.
B49, P2.39
Kim, Y.W.
P1.08
Kambara, S.
P2.01, P2.02
Klika, Z.
P2.24
J
K
Kanai, T.
C46, C47
Klinger, M.
C64, P1.22
Kandiyoti, R.
A00
Klykov, O.V.
A09
Kang, S.
C12
Kobayashi, T.
D04
Karpenko, E.I.
A08
Kochanek, M.A.
C02
Kato, T.
B66
Kochem, L.H.
P2.10
Kauchali, S.
A07
Kokonya, S.
C65
Kawaguchi, M.
B23
Kolijn, C.
C45
Kawashima, A.
P1.30
Komatsu, N.
C01, C48
Kechang, X.
C25
Kondo, M.
P2.02
Kelley, D.
B02
Koyano, K.
C52
Kelly, C.
C30
Kozliak, E.I.
A09
Kestel, M.
A06
Krishnakumar, B.
A30
Khorami, M.T.
B32
Krzack, S.
C64
Kim, C.
B27
Ksepko, E.
B61
Kim, G.B.
A04
Kudo, S.
C47
Kim, G.T.
P2.37
Külaots, I.
B24
Kim, R.
B27
Kumabe, K.
P2.01, P2.02
Kim, S.
P1.11, P1.12, P2.34
Kumagai, H.
C01
Kim, S.D.
P2.37
Kusý, J.
P1.23, P1.34
Large, D.J.
B29
Lim, J.P.
B28
Lavrichshev, O.A.
B52
Lim, Y.
P1.12
Lázaro, M.J.
P2.04
Lim, Y.I.
P2.37
Lee, S.
P1.11, P1.12, P2.34
Lin, G.
C25
L
Lee, S.J.
P1.08
Lin, X.
B45, P1.04
Lei, Z.
C12, C32
Liu, J.
P1.25
Leiva, C.
A42
Liu, Z.W.
P1.14
Lelli, M.
A10
Llavona, I.
A23
Lester, E.
A28, B31, C07, C44, C66, D07
Locke, D.
B06
Leyva González , O.S.
P1.13
Londoño, C.A.
P2.33
Leyva Mormul, A.
P1.13
Lopera, E.
P2.33
Li, C.Z.
B49, C30
López, J.
A65
Li, H.
B23
López-Antón, M.A.
A29, A41, P2.06, P2.07
Li, J.
B30, D09
Loredo, J.
A12
Li, W.
P1.31
Lorenc-Grabowska, E.
P1.38
Li, X.
C50
Lorente, E.
A26, D05
Lieberman, R.N.
B47, P2.19
Ludwik-Pardała, M.
P2.18
Lim, H.
B27
Lupion, M.
A25, A62
Lim, J.
P1.12, P2.34
M MacFarlane, D.
B02
Meredith, W.
B29
Machado, A.S.
P1.32
Mermelstein, J.
D05
Machnikowska, H.
P1.37
Messerle, V.E.
A08, B52
Machnikowski, J.
P1.37
Metzger, L.
D08
MacPhee, T.
C45
Mexias, A.S.
P1.32
Magarisawa, K.
D03
Meyer, B.
A06, B43, C64, P1.22
Majeski, A.
A02
Milenkova, K.S.
P2.23
Makgato, M.H.
C09
Millán, M.
A26, D05
Makino, M.
B62
Miller, B.G.
B10, B11
Makovskyi, R.
C03, P1.26
Mine, T.
A01
Malhotra, R.
A40, B28
Mitsuhara, N.
C61
Maloney, M.D.
A24
Miura, K.
B62, C50, C51
Manca, M.
A66
Miura, T.
C46
Marcilio, N.R.
A63, B67, P2.10, P2.14, P2.15
Miyawaki, J.
B45, P1.04, P2.28
Mari, A.
C47
Mochida, I.
B45, P1.04, P1.21, P2.28
Marinov, S.P.
B07, C03
Mokogwu, I.
B29
Maroño, M.
A50, A67
Moliner, R.
P2.04
Maroto-Valer, M.
A11
Mollah, M.M.
C29
Marshall, C.
B29
Mondragón, F.
A61, B04, B63, P2.30, P2.31
Marshall, M.
B02, B03, C29
Montagnaro, F.
B41
Martínez, M.
P2.13
Montiano, M.G.
P1.27
Martínez-Alonso, A.
P1.39, P1.40
Moon, S.H.
P1.08, P1.09
Martínez-Fernández, J.
A62
Moreno, N.
A42
Martínez-Tarazona, M.R.
A29, A32, A41, P2.06, P2.07
Moreno, T.
D09
Masset, P.J.
B09, C63
Moreno-Hirashi, J.A.
P1.02
Masui, M.
P2.02
Moretto, P.
B09
Mathews, J.P.
B01, B05, B06, B10, B11
Moritomi, H.
P2.01, P2.02
Matsuda, S.
P1.21
Morpeth, L.D.
B51
Matsushita, Y.
C46, C61, P1.21
Mulas, A.
A66
Melendi, S.
P1.17, P1.18
Mulas, G.
A66
Meloni, P.
A66
Muñoz, E.J.
P1.10
Mendiara, T.
A46
Murakami, K.
B66
Menéndez, R.
C08, C43, D02
Myers, K.
C22
N Nam, S.C.
P2.08
Niksa, S.
A30, B28, C21
Nariewicz, M.R.
B06
Ninomiya, Y.
B23
Naruse, I.
A51, D04
Nishiiri, Y.
A21
Navarrete, B.
A23
Nisi, B.
A10
Navarro, S.C.
P1.10
Nitzsche, R.
B47
Navarro-Lozano, J.O.
P1.02
Nomura, S.
C46
Nel, S.
B64
Norinaga, K.
C47, P2.38
Neomagus, H.W.J.P.
B25, B26, B64, B65, C09, P2.25, P2.27
North, B.C.
B42
Ng, K.W.
C45
Nuamah, A.
A28, B31
Nikrityuk, P.A.
A06
Nyathi, M.S.
D01
Oboirien, B.O.
B42
Olcese, R.
C04
O'Brien, G.
C44
Oliveira, M.L.S.
C62, P1.05
Ochoa-González, R.
A29, A32
Ooyatsu, N.
A01
Ohga, K.
A21
Osório, E.
P1.32, P2.22
Ohm, T.I.
P1.08, P1.09
Ossadchaya, E.F.
B52
Ohtaka, N.
P1.30
O'Sullivan, L.
C22
Ohtsuka, Y.
P1.30
Otero, J.
A67
Okolo, G.N.
B25
Otero, P.
A23
Okuyama, N.
C01, C48
Özlem Kocabas, Z.
P2.21
O
P Pan, C.
C32
Pesimberg, M.
D08
Pang, C.H.
C66
Petrik, L.F.
P2.20
Paniagua, J.
A65
Pevida, C.
A27, P2.12, P2.13
Park, J.I.
P2.28
Piedad-Sánchez,N.
P1.02
Park, S.R.
P2.37
Pierce, D.T.
A09
Paterson, N.
A26
Pis, J.J.
A27, P2.12, P2.13
Patrick, J.W.
C07
Plana, F.
D09
Patzschke, C.
B02
Pou, J.O.
B01
Pérez del Villar, L.
A10
Pourkashanian, M.
A27
Pérez-Ros, C.
A64
Powis, J.
B31
Qi, C.
C25
Querol, X.
A31, A42, B30, D09,
Qi, Y.
B02
Quignard, A.
C24
Qiu, B.
C26
Q
R Raeva, A.A.
A09
Rodríguez, E.
A41, P1.18
Raharjo, S.
A51
Rodríguez-Galán, M.
A62
Ranganathan, V.
B02
Rodríguez-Pérez, J.
A29, A41, P2.06
Rech, R.
P2.10, P2.14, P2.15
Romeo, L.M.
A42
Redaelli, C.
P2.10, P2.14
Rossiter, A.
C30
Reichel, D.
C64
Roy, B.
B48
Ren, S.
C12, C32
Rubiera, F.
A27, P2.12, P2.13
Rhim, Y.
P1.11, P2.34
Rufas, A.
P2.03
Riaza, J.
A27, P2.12
Ruiz, B.
P1.01, P1.06
Riley, G.
A28, B31
Ruiz, E.
A50, A67
Roberts, D.G.
B51, C02
Runstedtler, A.
A02
Rodrigo-Naharro, J.
A10
Russell, D.
B02
Rodrigues, R.
B67
Russig, S.
C02
Rodríguez Acevedo, E.
P2.32
Ryu, I.S.
P1.08
Šafářová, M.
P1.23, P1.34
Shishido, T.
C01, C48
Saha, C.
A45
Shoji, M.
C46
Sakai, K.
C01, C48
Shui, H.
C32
Sakimoto, N.
A21, C52
Shui, H.
C12
Sakurovs, R.
A22
Silva, L.F.O.
C62, P1.05
Salamanca, M.
B04
Simonyi, T.
B61
Salatino, P.
A47, B41
Siriwardane, R.V.
B61
Saldaña, R.
A10
Slavinskaya, N.
B52
Saloojee, F.
A07
Snape, C.E.
A03, A52, B29, C04, C65
Sánchez, A.
A61
Sohn, J.M.
P2.37
Sánchez, J.M.
A50, A67
Solimene, R.
A47
Sánchez-Biezma, A.
A65
Song, B.H.
P2.37
Sanna, A.
A11
Song, C.S.
B10, B11
Santamaría, A.
B04
Song, J.
B27
Santamaría, R.
C08, C43, D02
Song, J.H.
A04
Santiago-Carrasco, B.
P1.02
Sonoyama, N.
C42
S
Sasaoka, E.
B62
Spears, D.A.
B44
Sato, K.
D03
Spiegl, N.
A26
Sato, M.
B66
Spiro, B.
B29
Sato, R.
P2.38
Stańczyk, K.
P2.18
Scala, F.
A66
Steel, K.
P2.09
Schobert, H.H.
B10, B11, C09, C22, D01
Steele, D.
B28
Sciazko, M.
B08, B61
Stefanova, M.
B07
Scott, A.C.
B31
Stevens, L.
A52
Seam, W.S.
A09
Stokie, D.
C49
Secchi, A.R.
A63
Strydom, C.A.
C05
Segev, G.
P2.19
Sturgeon, D.W.
A24
Seifert, S.
B06
Suárez-Ruiz, I.
P1.01, P1.02, P1.06
Seng, T.X.
A45
Suelves, I.
P2.04
Senneca, O.
A47
Sugawara, K.
B66
Shan, C
C12
Sun, B.
P1.14
Sharma, A.
B50
Sun, C.
A03
Shim, H.M.
P2.37
Sun, Y.
B51
Shimada, S.
A21, P2.29
Suuberg, E.M.
B24
Shimogori, M.
A01
Sybring, M.
A02
Shirai, H.
A05, B22
T Takanohashi, T.
B50, C52
Tian, H.
B61
Takarada, T.
D03
Tian, L.
A43
Takarayama, N.
A01
Todoschuk, T.
C45
Takata, S.
P2.01
Tomás, C.
P1.01
Tamargo-Martínez, K.
P1.39, P1.40
Torchała, K.
P1.37
Tanosaki, T.
B23
Trierweiler, J.O.
B67
Tascón, J.M.D.
P1.39, P1.40
Trotman Gavilán, J.A.
P1.13
Tatarazako, N.
B23
Tsubouchi, N.
P1.30
Tay, H.L.
B49
U Uchida, A.
C46
Umemoto, S.
P2.39
Ueki, Y.
A51, D04
Ustimenko, A.B.
A08, B52
Uguna, C.
C65
V Valeš, J.
P1.23, P1.34
Vanegas-Chamorro, M.
P1.39, P1.40
van der Merwe, G.W.
P2.25
Vaselli, O.
A10
van Drooge, B.L.
D09
Velásquez, M.
B04
van Heerden, J.
C41
Velázquez, H.
P1.10
van Niekerk, D.
C41
Verheyen, V.
B02
van Staden, Y.
C05
Vilela, A.C.F.
P1.32, P2.22
Waanders, F.
C62, P1.05
Watson, J.C.
B01
Wada, N.
P1.21
Wei, C.
C32
Wagner, N.
A07
Wei, X.Y.
P1.14
Wakabayashi, N.
B22
Wei, Y.
B23
W
Walter, J.
C31
Weir, S.
A22
Wang, J.
A52
Wenying, L.
C25
Wang, S.
C30
Williams, A.
A27
Wang, X.
A11, A43
Wilson, R.B.
B28
Wang, Y.
C10
Winans, R.E.
B05, B06
Wang, Y.H.
P1.14
Wood, J.
A52
Wang, Z.
C12, C32
Worasuwannarak, N.
C50
Wannapeera, J.
C50
Wu, T.
C66, P1.31
Wasserman, S.
D08
P1.39, P1.40
Xu, G.
C10
Yamada, O.
P2.29
Yoon, Y.I.
P2.08
Yamazaki, Y.
C46
Yoshiie, R.
A51, D04
Yang, H.
A43
Yperman, J.
B07
Yasuda, H.
P2.29
Yu, J.
C49
Ye, C.
P1.31
Yue, X.M.
P1.14
Yoo, J.
P1.12, P2.34
Yürüm, Y.
B12, P2.21
Yoon, S.H.
B45, P1.04, P2.28
X Xiberta, J. Y
Z Zeng, C.
A43
Zheng, H.
P1.31
Zhang, J.
C10, C26, C30
Zhou, X.
P1.24
Zhang, S.
A43
Zhu, S.
P1.25
Zhang, X.
C46
Zhuang, X.
B30, D09
Zhao, D.
A03
Zong, Z.M.
P1.14
Zhao, Y.
C11
International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
ORGANISING COMMITTEE Chair: Prof. Juan M. D. Tascón Technical Programme: Dr. Angeles G. Borrego Members Dr. Nicolás de Abajo Martínez Dr. Juan Otero Prof. Antonio Valero Prof. Vicente Cortés Mr. Francisco García-Peña Dr. Juan Carlos Ballesteros Prof. Jorge Loredo Prof. Carmen Clemente-Jul Mr. Fermín Corte Mr. Francisco Javier Alonso Ms. Yolanda Fernández Mr. Juan Ramón G. Secades Prof. Juan Adánez Dr. Rosa de Vidania Muñoz Mr. Alfonso Martínez Mr. Isaac Pola Prof. Ángel Linares-Solano
Co-chair: Dr. María A. Díez
ARCELORMITTAL CIEMAT CIRCE CIUDEN ELCOGAS ENDESA ETSIMO ETSIMinas-UPM FAEN Gas Natural Fenosa HC Energía HUNOSA ICB-CSIC IGME Industrial Química del Nalón SL Mining and Energy Office. Government of the Principality of Asturias University of Alicante
International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
LOCAL ORGANISING COMMITTEE Dr. Mónica Alonso Carreño
Dr. Patricia Álvarez Rodríguez
Dr. Borja Arias Rozada
Dr. Carmen Barriocanal Rueda
Dr. Dolores Casal Banciella
Dr. Mercedes Díaz Somoano
Dr. Roberto García Fernández
Dr. Susana García López
Dr. Mª Victoria Gil Matellanes
Dr. Mª Antonia López Antón
Ms. Concha Prieto Alas
Ms. Juliana Sánchez Villar
International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
INTERNATIONAL ORGANISING COMMITTEE Prof. Chun-Zhu Li
Australia
Dr. Fari Goodarzi
Canada
Dr. Tony Macphee
Canada
Prof. Wolfgang Klose
Germany
Dr. Robert Davidson
IEA CCC UK
Prof. Isao Mochida
Japan
Dr. Osamu Yamada
Japan
Prof. Jieshan Jason Qiu
P. R. China
Dr Johannes van Heerden
South Africa
Prof. Quentin Campbell
South Africa
Prof. Rosa Menéndez
Spain
Prof. Colin Snape
UK
Dr. Edward Lester
UK
Dr. Mildred Perry
USA
Dr. Jonathan Mathews
USA
International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
TECHNICAL PROGRAMME Chairperson: Dr. Angeles G. Borrego COAL CHEMISTRY AND STRUCTURE Prof. Amelia Martínez-Alonso (INCAR-CSIC) COAL UPGRADING Prof. Carmen Clemente-Jul (ETSIMinas-UPM) COAL GEOLOGY AND ORGANIC PETROLOGY Dr. Isabel Suárez-Ruiz (INCAR-CSIC) Dr. Carlos I. Salvador (University of Oviedo) COAL COMBUSTION Dr. Luis Romeo (University of Zaragoza) Dr. Luis de Diego (ICB-CSIC) COAL GASIFICATION AND CLEAN FUELS Prof. José L.G. Fierro (ICP-CSIC) Prof. José L. Valverde (University of Castilla La Mancha) CLEAN COAL TECHNOLOGIES Dr. Francisco García-Labiano (ICB-CSIC) CO2 CAPTURE AND STORAGE Dr. Roberto Martínez (IGME) Dr. Carlos Abanades (INCAR-CSIC) COAL PYROLYSIS AND LIQUEFACTION Dr. María Antonia Diez (INCAR-CSIC) Dr. Vicente Cebolla (ICB-CSIC) COAL MINERALOGY AND COAL ASH Dr. Rosa Martínez-Tarazona (INCAR-CSIC) Dr. Diego Álvarez (INCAR-CSIC)
COAL AND THE ENVIRONMENT Dr. María Jesús Lázaro (ICB-CSIC) Prof. Xavier Querol (ICTJA-CSIC) CARBONS FROM COAL Dr. Marcos Granda (INCAR-CSIC) Prof. Rosa Menéndez (INCAR-CSIC)
International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
INTERNATIONAL ADVISORY GROUP Dr. David Harris Dr. Richard Sakurovs Prof. Terry F. Wall Prof. Colin Ward Prof. Kechang Xie Prof. Fanor Mondragón Prof. Klaus Hein Prof. Kim Dam-Johansen Prof. Mikko Hupa Prof. Piero Salatino Prof. Kouichi Miura Prof. Takayuki Takarada Prof. Jacek Machnikowski Dr. Ibrahim Gulyurtlu Dr. Nicola Wagner Prof. Ana María Mastral Prof. Rafael Moliner Dr. Petra David Prof. Yuda Yürüm Prof. Rafael Kandiyoti Prof. John Patrick Prof. Alan Williams Prof. Ripudaman Malhotra Prof. Harold Schobert
Australia Australia Australia Australia China Colombia Germany Denmark Finnland Italy Japan Japan Poland Portugal South Africa Spain Spain The Netherlands Turkey UK UK UK USA USA
International Conference on Coal Science and Technology, Oviedo-Spain 2011 (ICCS&T 2011)
SPONSORED BY Science and Innovation Ministry
Grupo Hunosa
Science, Technology and Innovation Research Programme Asturias-Spain
HC Energía
Oviedo Council
Industrial Química del Nalón S.A. NalonChem
Ciudad de la Energía, Ciuden
International Energy Agency
Spanish National Research Council
LECO
Gas Natural Fenosa
KEYNOTE PAPER THERMAL BREAKDOWN IN MIDDLE RANK COALS* Rafael Kandiyoti Department of Chemical Engineering, Imperial College London, Prince Consort Road, London SW7 2AZ, UK
1. Introduction The past decade has seen a sharp turn away from research on coal utilization, in favour of work on the mitigation of its environmental consequences. Coal utilization has potential to pollute and activities aiming to clean up past pollution, as well as mitigating the environmental consequences of future utilization are necessary. In my opinion, however, the emphasis given to CO2 capture and sequestration needs to be critically re-evaluated. Statistics show that worldwide coal production and utilization is vast and expanding. The need to support a component of research aiming to make utilization more efficient and less polluting is self evident. And as ever, we need to know more about the structure of coals and to further develop methods for their utilization. In this report, I aim to bring together experimental information in a manner that might help improve our understanding of thermal breakdown in middle rank coals. My purpose is to sift through and collate information, rather than to innovate. The first line of approach will be to compare thermal breakdown phenomena observed during pyrolysis and liquefaction. The initial questions that need answers are: (1) When does thermal breakdown actually begin? (2) Are there similarities between reaction pathways in pyrolysis and liquefaction? (3) When and how do these reaction pathways begin to diverge? As allied questions we will explore (4) Why and when pyrolysis product distributions are affected by heating rates, and, (5) How retrogressive re-combination reactions work. These are questions relevant to improve our understanding of the fundamentals of most coal utilization activities: combustion, gasification, liquefaction and coking. 2. Electron spin resonance spectrometry of thermal breakdown Middle rank coals normally contain of the order of ~1019 free radicals per gram. The relative reactivities of free radicals depend on whether and how the host structure allows delocalization of unpaired electrons. The ESR spectrum of a coal reflects the stable free radical population embedded in the coal matrix. During and after thermal treatment, we observe additional unpaired electrons left over from completed processes. With appropriate corrections, the change in spin population as a function of the temperature may be calculated. However, observing reactive free radicals in coals by ESR is difficult, due to their short lifetimes and their low concentrations relative to much higher stable free radical concentrations [1]. As with ordinary pyrolysis experiments, acquired ESR spectra of pyrolysing samples reflect, to some degree, the configuration of the sample and the experimental design [2]. Figure 1 presents a schematic diagram of typical spin population vs. temperature curves, observed when coal samples are heated in a quartz fixed-bed reactor fitted with a gas sweep facility and placed inside the cavity of an ESR spectrometer. Spin populations (S) have been defined as free radicals per gram of initial sample. Three distinct types of thermally induced processes have been identified. *
This review was developed using material first presented at the BCURA “Coal Science Lecture” of 2006. The experimental results discussed may be found in Ref [9(a)].
Region I (T < T1): S increases to a relatively shallow maximum (near 200°C), due to the recovery of signal through desorption of gases adsorbed on sample surfaces. These gases, primarily moisture and oxygen, would have been adsorbed by previous exposure to air. Region II (T2 > T > T1): S decreases to a minimum (near 300°C). This decline is thought to be associated with recombination reactions, resulting from the thermally induced mobility of occluded material with sufficient reactivity. Region III (T > T2): Above T2, S increases monotonically with rising temperature, signalling an increase in the free-radical population, as the coal pyrolyzes within the ESR cavity. T2 is thought to mark the onset of covalent bond cleavage reactions. For the range of coals tested, T2 increased from 310ºC for a lignite, to about 340ºC for higher rank coals (Table 1; also cf. [3]).
Figure 1. Schematic diagram showing main characteristics of spin population vs. temperature diagrams [3]. (Reproduced with permission: Carbon 1989, 27, 197; Copyright 1989 Elsevier) 19
Table 1 ESR parameters of coals given as “spin populations x 10 ” in the flow cell [3].
In coal liquefaction, extract yields increase and molecular mass distributions get broader as the temperature reaches 375-400°C [4, 5]. This range is well above the 310 – 340 °C interval signalled for the onset of covalent bond cleavage, suggesting that several bonds must rupture before large molecular fragments are released from the solid matrix. Figure 2 shows that the rate of dissolution accelerates with increasing temperature from about 375 °C onwards. Point of Ayr (UK) coal shows this more graphically than many other coals.
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Figure 2 Sample weight loss from Point of Ayr and Pittsburgh No. 8 coals as a function of temperature in the flowing -1 solvent reactor. Samples were heated at 5°C s to 450°C with 400 s hold. Tetralin flow rate: 0.9 ml/s at 70 bar [6]. (Reproduced with permission: Energy & Fuels 1996, 10, 1115; Copyright 1996 Am.Chem.Soc.)
Liquefaction thus allows recovering large amounts of coal as extract at temperatures near 400 °C, provided a “good” solvent for coal derived materials is used. In pyrolysis, covalent bond cleavage patterns appear to follow similar paths; however, much of the “extractable” material that detaches from the solid matrix remains within the coal particles and, at 400 °C, sample weight loss remains low (about 5 % in Figure 3).
Figure 4 The atmospheric pressure wire-mesh reactor with the early (a) and present (b) tar trap designs. Legend: [1] Copper Current Carrier; [2] Live Electrode; [3] Brass Clamping Bar; [4] Sample Holder Support Plate; [5] Mica Strip; [6] Wire-mesh Sample Holder; [7] Electrode; [8] Stainless Steel Tubes; [9] Mica Layer; [10] Brass Pillars; [11] Sintered Pyrex Glass Disk; [12] Base Plate; [13] Pyrex Bell; [14] O-ring Seal; [15] Off-take Column; [16] O-ring; [17] Carrier Gas Entry Port; [18] Connection for Vacuum Pump. (Reproduced with permission: Fuel 68, (1989), 895; Copyright 1989 Elsevier).
Figure 3 Effect of peak temperature on pyrolysis tar and total -1 volatile yields. Heating rate: 1,000°C s . Linby coal. 30 s holding at peak temperature; sweep gas, helium at 1.2 bar -1 flowing at 0.1–0.2 m s . Particle size range: 106–152 μm [7]. (Reproduced with permission: Fuel 1989, 68, 895; Copyright 1989 Elsevier).
Initial conclusions: Up to about 375 – 400 °C, no significant divergences were observed between reaction pathways during pyrolysis and liquefaction. This is understood in terms bond rupture being primarily a
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function of the temperature. Pathways diverged during and after “solvent extractable” tar precursors broke off from the coal matrix and gradually accumulated within the coal particles. In liquefaction, increasing amounts of material, soluble in the solvent used, could be removed from the coal particles. In pyrolysis, however, little of the material released into the particles could exit into the gaseous environment surrounding the particle. The “extractables” (tar precursors) mostly remained within the coal particles. The next task was to trace the fate of “extractable” material residing within pyrolysing coal particles, as the temperature was raised. It was also relevant to explore why product distributions change when the heating rate is increased. 3. The fate of “extractables” accumulated in coal particles: pre-pyrolysis temperatures Figure 4 presents a schematic diagram of the wire-mesh reactor used in experiments described below. The apparatus is best known through seminal work by Howard and co-workers at MIT [8]. The reactor has a useful configuration for approximating single particle behaviour. Stages in the evolution of its design in various laboratories have been described elsewhere [9(b)]. The atmospheric pressure version shown in Figure 4 is capable of variable heating rates between 1°C s-1 and 10,000°C s-1 and temperatures up to 2,000°C. In early work, the reactor enabled observing changes in product distributions with increasing heating rate (Figure 5; [7]). In Figure 5, the lines tracing tar and total volatile yields very nearly rise in parallel with increasing heating rate. The weakly-coking Linby coal showed plastic behaviour only when heated rapidly; progressively more extensive plasticity was observed as the heating rate was increased [7, 10]. We will see below that tar yields and plasticity are related to the amount of extractable material (tar precursors) that accumulates within coal particles during heat-up.
Figure 5 Effect of heating rate on tar and total volatile yields. Peak temperature of 700°C. Linby coal. 30 s holding at peak -1 temperature; sweep gas, helium at 1.2 bar flowing at 0.1–0.2 m s . Particle size range: 106–152 μm [7]. (Reproduced with permission: Fuel 1989, 68, 895; Copyright 1989 Elsevier).
In the iron making industry, these and similar observations have led to an interesting pilot application. At Nippon Steel Corporation, crushed coal was rapidly pre-heated in a riser to about 400ºC. The sticky mass of particles was then slowly heated in a retort to 800-900ºC. The effect was to form a stronger coke than would have otherwise been possible, using the same coal (or blend) heated slowly from ambient temperature [11].
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The procedure was found to be effective for improving the coking properties of weakly-coking coals. For prime coking coals, the initial rapid heating step provided no significant improvement in the amount or strength of product coke. Table 2 Characteristics of three Australian coal blends used in the study.
Coal A
Coal B
Coal C
Volatile Matter, % Fixed Carbon, % Ash, % Crucible Swelling No.
35.2 52.4 9.0 3.5
24.1 65.1 9.3 6.5
17.9 72.3 8.9 8.0
C (%,db) H (%,db) S (%,db) N (%,db) O (%,db)
83.6 5.6 0.55 1.8 8.3
87.7 5.0 0.57 1.7 4.8
90.7 4.6 0.15 0.8 3.3
4. Examining pre-pyrolysis phenomena in coals The accumulation of extractable material within coal particles prior to full blown pyrolysis was used as a diagnostic tool, in order to explore how the plastic properties of weakly coking coals may be improved by faster heating [12]. Part of the answer was known from previous work. In the 1960ies, Brown and Waters had shown that coking properties correlated well with amounts of chloroform extractable material found in coals heated (slowly) to between 300 and 400ºC [13]. The experiments we conducted aimed to explore relationships between (i) “extractable” contents of heated particles, (ii) the temperature of exposure and (iii) the heating rate. Three coal blends from the pilot study by Nippon Steel were used. Weakly coking Newcastle Blend Coal was labelled as “Coal A”, strongly coking Goonyella as “Coal B” and the “very” strongly coking K-9 Blend as “Coal C”. Table 2 presents some of the properties of the three samples. The initial set of experiments followed one of two sequences: Sequence I: (1) Fast heating (1,000ºC s-1) to 400ºC, (2) 30 seconds holding at 400ºC, (3) Slow (1ºC s-1) heating to an intended temperature, between 400 and 500ºC, (4) 30 seconds holding at the intended temperature, followed by cooling and extraction with NMP (1-methyl-2-pyrrolydinone) [12]. Sequence II: Differed from Sequence I by heating “slowly” to 400ºC (at 1ºC s-1) during Step 1. Figure 6 shows the differences in the amounts of extractable material recovered from Coal A particles heated to 400ºC rapidly (1,000ºC s-1; ~66% extract), compared to slow heating (1ºC s-1; about 33 % extract) in Step 1. The extract yield from untreated Coal A was about 35 %. As the temperature was then raised at 1ºC s-1 from 400ºC, the amount of extractables within the initially fast heated particles increased slowly to about 80 % near 475ºC before declining rapidly. These results give rise to two follow-up questions. First, is there a characteristic temperature which must be reached, before differences between fast and slow heating become apparent? Second, how fast does “fast heating” have to be for differences between extractable yields begin to emerge?
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Extract Yield (mass%,daf)
90 80 70 60 50 40 30 20
rapid400+slow slow
10 0 400
450 Temperature (° C )
500
Figure 6. Comparison of NMP-extractables recovered from Coal A particles treated by one of two heating sequences: Fast (1,000ºC s-1) or slow (1ºC s-1) heating to 400ºC in Step 1 [12]. (Reproduced with permission from Energy & Fuels 2004, 18, 1140; Copyright Amer. Chem. Soc 2004).
To answer the first question, Coal A particles were heated at 1,000ºC s-1 to temperatures between 350 and 400ºC, followed by cooling and extraction with NMP. Figure 7 shows a sharp transition to greater “extractable” accumulation after 370ºC. Near 400ºC, the extractable yields rose towards the same point (~65 %) reported in Figure 6, showing satisfactory internal consistency. The faster rise in extractables above 370ºC was consistent with the temperature for the onset of massive breakdown inferred from ESR data and liquefaction experiments in Figure 2. Recalling that results from ESR spectroscopy indicated the onset of individual bond rupture in the 310-340ºC range, data in Figure 7 appear consistent with the proposition that several bonds need to break before larger molecular mass material might detach from the solid matrix.
Extract Yield (mass%,daf)
80 70 60 50 40 30 20 10 0 350
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370 380 Temperature (° C)
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400
Figure 7 Extractables accumulating in particles of Coal A during “fast” heating to between 350 and 400ºC. (Reproduced with permission from Energy & Fuels 2004, 18, 1140; Copyright Amer. Chem. Soc 2004)
The next point is perhaps more difficult to explain. The sharper increase in extract accumulation above 370ºC is not observed when slow heating (1ºC s-1) is applied. In general, bond cleavage is known to be mainly a
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function of the temperature. The lower proportion of extractables recovered after the slow heating experiment suggests that more retrogressive recombination reactions occurred during slow heating. Furthermore, data in Figure 8 show that internally released extractables, which had survived during heat-up to 400°C at either heating rate, were stable at 400°C for as long as 120 s. Thus, in contrast to the extractable loss during heat-up at slow heating rates, the retrogressive repolymerization reactions between extractables that survive to 400°C proceed through far slower recombination reactions, if at all. Figure 6 shows that the temperature needs to rise to above 450°C for recombination reactions within the residual “extractable” mass to lead to significant char formation. No clear char formation trend was observed within the particles heated initially at 1ºC s-1, which seem surprisingly inert between 400 and 500ºC.
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Figure 8. Effect of holding time at 400°C on NMP-extract yields for Coal A samples heated at 1 and 1,000°C s . (Reproduced with permission from Energy & Fuels 2004, 18, 1140;Copyright Amer. Chem. Soc 2004)
These data provide evidence that the more reactive free radicals within the “extractables” recombine during slow heat-up between 370 – 400°C and that during rapid heating, these recombination reactions are blocked. Below, we will suggest that when fast heating is applied, internally released hydrogen, native to the coal, may be entering the reaction mixture to quench the more reactive free radicals, blocking at least a part of the potential retrogressive recombination reactions. The larger pool of extractables (tar precursors) contained in rapidly heated particles goes some way towards explaining the higher tar yields from some middle-rank coals during rapid heating. However, tests on many coals show that the maximum difference in tar yields measured (between slow and fast heating) is in the range of 4 – 8 %, compared to a 30 % difference in extractable (tar precursor) accumulation. It appears therefore that char formation rather than tar ejection remains the dominant reaction route when temperatures are raised above 600ºC. The stability of extractable materials in coal particles for up to 2 minutes (and probably beyond, had the experiment been continued; see Figure 8) is consistent with data from Fong et al. [14]. These authors reported a depletion rate for pyridine extractables for the higher temperature interval of 600 – 800°C, characterized by the reaction rate constant k = 1.9 x 1010 exp (-21,200/T) (s-1). The depletion rate at 400°C of “extractable” materials calculated using this equation is almost negligible. It also appears that depletion by volatilization of the extractables is not a significant factor at 400°C. The possibly relatively small weight loss through devolatilization during the first few seconds after reaching 400°C appears to be made up by new release of “extractable” material.
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These data lead indicate that rapid recombination reactions during heat-up take place between more reactive free radicals, unless they are somehow blocked. Meanwhile, less reactive free radicals in the extractable mass surviving to 400°C (Figure 6), produce char at far slower rates at temperatures above 400°C (Figure 6).
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Figure 9. Relationship between heating rate and NMP-extract yield; heating rate: 1,000°C s . (Reproduced with permission from Energy & Fuels 2004, 18, 1140; Copyright Amer. Chem. Soc 2004)
5. The heating rate and extractables accumulation in weakly/strongly coking coal particles Experiments were carried out by heating sample particles to 400°C at increasing rates, followed by extraction with NMP. Figure 9 shows how the amounts of extractable material accumulated in heated particles increased as a function of the heating rate. The transition above 500C s-1 was sharp and repeatable. In response to the two questions raised at the bottom of page 5, we found that the sample must be heated to ≥ 375ºC before large amounts of extractable may be released and the effective “fast” heating rates lie above 500 – 1,000ºC s-1 for this coal. The enhanced formation of NMP-extractables is thus observed to be a direct function of the heating rate. Whilst we should be hard put to explain why the particular heating rate threshold value of 500 – 1,000ºC s-1 turns out to be the critical one, it seems sufficient for present purposes to note that a “high” heating rate is required for recovering larger amounts of extractables from Coal A particles. We have meanwhile arrived at a working explanation for observations at Nippon Steel. We know from previous work that coal plasticity and extractable content are linked. Work at MIT has also shown (for temperatures above 600ºC) that minimum viscosity and maximum pyridine-extractable contents correlate [14]. Prior characterization work had already shown that the temperature of maximum extractables of Coal A was near its temperature of maximum thermo-plasticity, between 400 and 430ºC [11]. Finally, the stability of extractables during at least two minutes (Figure 8) appears to allow sufficient time for the particles in plastic state to form coherent lumps within the retort. Rapid heating thus leads to improved coke strength via the related increase in thermo-plasticity of Coal A. However, we still need to explain why greater amounts of extractable material are recovered from heated particles after “fast” heating. To explore this further, let us recall that “Coal A” was a weakly coking coal. How do “good” coking coals behave in analogous experiments?
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rapid400+slow
100
slow
90
rapid350
80
untreated coal
Extract Yield (mass%, daf)
Extract Yield (mass%, daf)
100
70 60 50 40 30 20 10 0
1000°C/s 1°C/s
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70 60 50 40 30 20 10 0
0
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200 300 400 500 Temperature (°C)
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(a) (b) Figure 10. Relationship between NMP-extract yield and temperature for samples of Goonyella (Coal B) and K-9 (Coal C), -1 both coking coals, heated at 1 and 1,000°C s to 400°C, followed by heating at 1°C to a variable peak temperatures up to 600°C (30 s holding at peak temperature). Carbon contents and crucible swelling numbers are given in Table 2. (Reproduced with permission from Energy & Fuels 2004, 18, 1140; Copyright Amer. Chem. Soc 2004)
Figure 10 shows that prime coking coals, Coal B and Coal C, show marginal heating rate sensitivities with regard to the accumulation of extractables. When heated, samples from the two coals gave high extract yields and became fluid, irrespective of the heating rate. High heating rates thus appear to improve the plastic behaviour of only weakly coking coals. Higher tar yields during fast heating was previously explained by the explosive ejection of tar precursors (i.e. “extractables”). In this sense, rapid heating is seen as reducing the probability of repolymerization reactions of tar-precursors through their rapid removal [15]. What we observed in our work was that during fast heating, a larger pool of tar precursors develops within the particles of coals that have marginal coking ability. The two elements are internally consistent and provide a possible contributing factor to increased tar yields observed at higher heating rates (Figure 5). The question that remains to be answered is how the larger pool of “extractable” material came about when particles of Coal A, the marginally coking coal, were heated rapidly. 6. Effect of rapid heating: Possible mechanistic explanations It is widely known that when middle rank coals are heated, small amounts of hydrogen are released from about ~ 285 - 300ºC [e.g. cf. 16]. There is also a “consensus” view from previous work [13, 17], that before tar evaporation, pyrolysis works as an internal liquefaction process, where free radicals are quenched and stabilised by internally released hydrogen. Fast heating telescopes the sequence of events into a narrower time frame and shifts upwards the temperature scale of successive pyrolytic events. Thus, any internally released hydrogen is more likely to remain in contact with the pyrolysing mass up to higher temperatures during “fast” heating (say 1,000ºC s-1 or faster) compared with “slow” heating. The internally released hydrogen is thus more likely to react with some of the free radicals and block (quench) some recombination reactions. We have no direct proof for this; however, this hypothesis would explain data showing Coal A retain more extractable material during heat-up at 1,000ºC s-1 compared to 1ºC s-1. This explanation also lends us a language by which we can begin to explain the behaviour of coals like Goonyella (above) or indeed the behaviour of H2-rich species such as liptinites, which show little sensitivity to heating rate [11(b), 18, 19]. The latter samples present relatively high elemental H2 and relatively low
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elemental O2-contents, evidently providing a combination capable of swamping the “internal liquefaction process” with sufficient hydrogen to block some of the rapid recombination reactions, irrespective of the heating rate. By comparison, marginally hydrogen deficient vitrinites show more pronounced heating rate sensitivity during pyrolysis, with respect to both plastic behaviour and tar yields [11(b), 18, 19]. 6.1 Tar yields and (alkyl+hydroaromatic) structures in coals: Figure 11 presents data for a rank ordered (and otherwise randomly selected) set of Northern Hemisphere coals, showing reasonably smooth trends of increasing tar yields with increasing “alkyl” content. Both sets of data lump together signal from alkyl and hydroaromatic (alicyclic) structures.
Figure 11. (a) Pyrolysis tar and total volatile yields as function of FT-ir-derived aliphatic:aromatic hydrogen ratios. Rank-1 ordered series of Northern Hemisphere coals: + tar, Δ total volatile. Pyrolysis in atm. pressure helium at 1,000 ºC s to 700°C with 30 s holding time. Non-melting coals: Taff Merthyr, Emil Mayrisch, Tilmanstone; melting coals: Heinrich Robert, Santa Barbara,Longannet, Candin, Bentinck, Thoresby, Gelding, Linby, Illinois No.6. (b) Pyrolysis tar yields as a function 13 of C-nmr-derived 15–37 nm aliphatic band intensity for a rank-ordered series of Northern Hemisphere coals. Coals and pyrolysis conditions as in (a). (Reproduced with permission: Fuel 1994, 73, 851; Copyright 1994 Elsevier).
It is widely thought that H-donor ability during the “internal liquefaction process” resides in the hydroaromatic component of coals [13, 17]. However, we do not have a reliable, rapid method for determining hydroaromatic contents in coals. It thus seems reasonable to conclude, but difficult to prove, that increased tar and total volatile yields in Figure 11 are due to progressively improving internal hydrogen transfer from the gradually increasing hydroaromatic component, with increasing coal rank. What we can show, on the other hand, is that the straight chain alkane molecule, hexadecane, contributes little to the coal liquefaction process, either in terms of solvent power or of H-donor activity. 6.2 Differentiating between the effects of alkyl and hydroaromatic structures: Figure 12 presents a schematic diagram of a “flowing solvent” coal liquefaction reactor, which allows products released from the fixed bed of coal to be swept away by solvent pumped through the system [6]. This reactor configuration limits the residence times of coal derived products in the reaction zone. Table 3 presents data from experiments performed with samples of Point of Ayr coal (UK), liquefied in (1) hydrogen donor solvent tetralin, (2) a mixture of non-H-donor compounds quinoline and phenanthrene, which are known as strong solvents for coal derived materials, and (3) hexadecane, a straight chain alkane, which is neither a good solvent for coal derived materials, nor an H-donor solvent. Results were compared with pyrolysis experiments under comparable conditions.
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PRESSURE REGULATOR PURGE SOLVENT RESERVOIR
PRESSURE RELIEF VALVE (AUTO) (MANUAL)
N2 STEPPER MOTOR C/W OUT
COAL/SAND BED FLOW METER
C/W IN SURGE CHECK VALVE
COOLING WATER HEAT EXCHANGER
DRAIN VALVE
FILTER DRAIN VALVE
REACTOR PRESSURE GAUGE
SOLVENT RESERVOIR
Figure 12. Schematic diagram of the flowing solvent reactor system. Solvent is forced through the fixed bed of coal and sweeps dissolved product away from the reaction zone and into the heat exchanger. The letdown valve is attached to a computer controlled stepper motor and serves to control the flow rate [6]. (Reproduced with permission: Energy & Fuels 1996, 10, 1115; Copyright 1996 Am.Chem.Soc.). -1
Table 3 Comparing conversions in different solvents [20]: Liquefaction experiments with solvent flow rate of 0.9 mL s at 70 bar (g). All data are given on % w/w dry ash free basis. (Reproduced with permission: Copyright 2006 Elsevier).
The positive contribution made by tetralin in the dissolution of the samples showed what we already knew, that the hydroaromatic component performs an H-donor function during coal thermal breakdown. Furthermore, when using n-C16H34 (hexadecane) as the liquefaction medium, the absence of both H-donor activity and solvent power was evident. The data show that coal conversion in hexadecane was comparable to the conversion observed in helium. 7. More/less reactive free radicals: fast/slow recombination reactions Table 3 shows that up to 350 °C, more coal derived material could be removed by quinoline or the mixture of quinoline and phenanthrene, compared to tetralin. Coal sample weight loss at up to 350°C is likely to represent (mostly) the extraction of already soluble material native to the original coal, rather than material made soluble through thermal breakdown. These data confirm that quinoline and phenanthrene are stronger solvents for coal derived materials compared to tetralin.
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7.1 Rapid retrogressive reactions in liquefaction: Table 3 also shows that, when the temperature was raised from 350 to 450°C, the proportion of coal sample dissolved and removed from the reaction zone increased significantly in the presence of both tetralin and the non-donor solvents. In closed (batch) reactors, conversions in non-H-donor materials decline at longer residence times. In this instance, the high conversions in the non-donor solvents can be explained in terms of the short residence times of dissolved products in the reaction zone (less than 10 s), followed by rapid cooling of products and the high product dilution ratio: about 150 mg coal-derived material in more than a litre of solvent. However, the systematically higher conversion to soluble material at 450 °C in the presence of tetralin, compared to the non-donor “strong” solvents requires explanation. The reversal of the trend, compared with results at 350°C, is consistent with the H-donor ability of tetralin being better able to block rapid retrogressive reactions during heat-up, compared to the non-donor solvents that are unable to provide this function. In other words, data in Table 3 suggest that, in the absence of H-donor ability, rapid retrogressive reactions occur with greater frequency during heat-up. The analogy with the “internal liquefaction process” posited for coal pyrolysis is clear. 7.2 Slow retrogressive reactions in liquefaction: Figure 13 compares conversions of Point of Ayr (UK) coal in two different reactor configurations: the “flowing-solvent” reactor and a small “mini-bomb” batch reactor. During initial experiments, using a tetralin-to-coal ratio of about 4:1 in the batch reactor, only minor differences were observed with conversions observed in the “flowing-solvent” reactor [21]. However, it took longer, about 1-hour, in the batch reactor to reach the level of conversion, which the “flowing-solvent” reactor achieved in several minutes. The difference appears due to slower diffusion of extracts out of coal particles in the batch reactor, caused by the gradually increasing extract concentration in the fluid surrounding the particles.
Figure 13 Flowing Solvent Reactor & Mini-Bomb reactor comparison using 1-methylnaphthalene as the liquefaction medium. Solvent/coal ratio in mini-bomb reactor: 4/1 by weight. Flowing-Solvent Reactor: Heating at 5°C s-1; solvent flow -1 rate: 0.9 mL s at 70 bars [21]. (Reproduced with permission: Fuel 1991, 70, 380; Copyright 1991 Elsevier).
In subsequent experiments, a non-donor solvent, 1-methylnaphthalene, was used as the liquid medium. Comparing conversions from the two reactors at 400 and 450°C showed that, in the “flowing-solvent” reactor, conversions increased with contact time at both 400 and 450°C. The differences between the two conversion lines for 400 ºC reflect conversion loss due to rapid recombination reactions in the batch reactor, where products cannot be moved away from the reaction zone before the termination of the experiment [cf. Ref 21].
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However, at 450°C, Figure 13 shows clear evidence for retrogressive char forming reactions in the mini-bomb reactor. At contact times longer than 100 s, conversions diminished and residual solids increased. In fact, there is nothing unusual about liquefaction with non-donor solvents in batch reactors giving yields that trace a maximum and eventually decline. This aspect of the data is consistent with trends observed during earlier work [e.g. cf. 22]. The relevance of these results in the present context is the demonstration of slow, indeed very slow, char forming reactions. Figure 13 showed a loss of 12 – 13% soluble material in about 25 minutes (1500 s). These slow char forming reactions contrast sharply with inferred rapid rates of retrogressive reactions during heat-up in non-donor solvents. The latter are only apparent when conversions are compared (i) with liquefaction in a donor solvent and (ii) when compared with short contact time yields in the flowing solvent reactor. 8. Conclusions: Overview of coal thermal breakdown Initial stages: Similar effects are observed during the initial stages of coal pyrolysis and liquefaction. This may be understood in terms of bond rupture being a function of the temperature alone. The onset of covalent bond cleavage, observed by ESR, was near 310 °C for a lignite and rose to 340 °C with increasing coal rank. Massive thermal breakdown in middle rank coals was observed near 375 ºC. This temperature is consistent with several bonds rupturing before larger molecular mass materials detach from the solid matrix and are released within the coal particles. Reaction pathways in pyrolysis and liquefaction begin to diverge during and after solvent extractable materials accumulate within coal particles at 375 - 400 ºC. In liquefaction, “extractables” may be removed from coal particles using a solvent. During the early stages of pyrolysis, on the other hand, accumulated “extractables” mostly remain inside the coal particles, as the temperature rises. Larger contents of extractable materials tend to improve the plasticity of coal particles. Greater tar yields correlate well with larger pre-pyrolysis extractable (tar precursor) contents and the greater plasticity of coal particles. Likely mechanisms: As coal particles are heated, internally released hydrogen is thought to quench reactive free radicals and effectively block some of the rapid recombination reactions. Fast heating tends to telescope the sequence of events into a narrower time frame and to shift the temperature scale of pyrolytic events to higher temperatures. Hydrogen released from pyrolysing solids from about ~ 285 - 300ºC is thought to remain in contact within the pyrolysing mass, as higher temperatures are reached more rapidly. Donatable hydrogen in coals is thought to reside in the hydroaromatic component. Internally released donatable hydrogen appears to play an analogous role during pyrolysis to donor solvents (e.g. tetralin) during liquefaction. In both cases, the availability of donatable hydrogen appears to block potentially rapid free radical recombination reactions. Weakly coking coals are thought to be marginally deficient in hydrogen. More “extractables” accumulate and greater plasticity is observed during the fast heating of these coals. The effect is observed at heating rates greater than 500ºC s-1. Meanwhile, “good” coking coals have sufficiently high donatable hydrogen (and correspondingly low hydrogen-scavenging oxygen) contents to show plastic behaviour irrespective of the heating rate.
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Fast and slow recombination reactions: The evidence presented suggests that, as thermally induced bondcleavage accelerates between 375 and 400⁰C, the more reactive of the free radicals show a tendency to recombine. The outcomes of these reactions are determined by the relative abundance of locally available “internally released” hydrogen. During slow heating (~1⁰C s-1), internally released hydrogen may escape before effective reaction temperatures are reached. Thus rapid recombination reactions taking place during slow heating produce more char and less “extractable” material compared to rapid heating; the effect is particularly observable in coals that are marginally deficient in hydrogen. Similarly, during liquefaction in the flowing solvent reactor, the use of a “strong” but non-H-donor solvent allows more repolymerization reactions to take place during heat-up, reducing the extract yield by about 5 – 8 %, compared to liquefaction in tetralin. In pyrolysis, the extractable mass that survives the heat-up stage to 400ºC and accumulates within coal particles was observed to be relatively stable and to convert to char only slowly above 450⁰C. Similarly, during liquefaction in non-H-donor solvents in batch reactors, already dissolved extracts were observed to form solids at 450⁰C, at a very slow rate (12–13% in 25 minutes.). These reactions appear distinct from, and slower than, rapid recombination reactions observed during heat-up. These observations provide evidence for wide ranges of free radical reactivities and wide ranges of rates for radical recombination reactions. Acknowledgements The work reported in this paper was supported by UK SRC (and its successor organizations SERC, EPSRC), British Coal, the European Coal and Steel Community, the European Union and the Nippon Steel Corporation. Of the many colleagues who contributed to this study, I am only able to thank a few by name in the space available: Tim Fowler, Keith Bartle, Jon Gibbins, Li Chunzhu, Alec Gaines, Alan Herod, Geoff Kimber, Şebnem Madralı, Xu Bin and Koichi Fukuda. Many others contributed with discussions and criticism. Trevor Morgan read a late draft, but I take responsability for my errors. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
Fowler, T.G., Bartle, K.D. & Kandiyoti, R., Energy and Fuels 1989;3; 515-522. Fowler, T.G., Bartle, K.D. and Kandiyoti, R., Carbon 1987; 25; 709-715. Fowler, T.G., Kandiyoti, R., Bartle, K.D. and Snape, C.E., Carbon 1989;27;197-208. Xu, B., Madrali, E.S., Wu, F., Li, C-Z., Herod, A.A. and Kandiyoti, R., Energy & Fuels 1994; 8; 1360-1369. Li, C-Z., Wu, F., Xu, B. and Kandiyoti, R., Fuel 1995; 74; 37-45. Xu, B. and Kandiyoti, R., Energy and Fuels 1996;10;1115-1127. Gibbins, J.R. and Kandiyoti, R., Fuel 1989;68;895-903. Howard, J. B. (1981) Chemistry of Coal Utilization Second Supplementary Volume (ed. Elliott, M. M.), Wiley, NY, Chapter 12 Kandiyoti, R., Herod, A.A. and Bartle, K.D., “Solid Fuels and Heavy Hydrocarbon Liquids: Thermal Characterization and Analysis” Elsevier Science Pub. (2006), Amsterdam Oxford London New York. (a) p.199; (b) p. 43. Gibbins-Matham, J.R. and Kandiyoti, R., Energy & Fuels 1988;2;505-511 Aramaki, T.; Arima, T.; Yamashita, Y.; Inaba, A.; Tetsu to Hagane 1996; 82; 5-34 Fukuda, K., Dugwell, D.R., Herod, A.A. and Kandiyoti, R., Energy & Fuels;2004;18;1140-1148. Brown & Waters: Fuel 1966; 45; 17; Brown, H. R., Waters, P. L. Fuel 1966; 45; 41 Fong, W. S., Khalil Y. F., Peters W. A., Howard J. B. Fuel 1986; 65;195 Gray V.R., Fuel 1988; 67;1298 Neuburg, H.J., Kandiyoti, R., O'Brien, R.J., Fowler, T.G. and Bartle, K.D., Fuel 1987;66;486-492. Neavel, R. C. Coal Science, Academic Press, 1981, 1-19 Li, C-Z., Madrali, E.S., Wu, F., Xu, B., Cai, H-Y., Güell, A.J. and Kandiyoti, R., Fuel 1994;73;851-865. Li, C-Z., Bartle, K.D. and Kandiyoti, R., Fuel 1993; 72;3-11. Xu, B., Madrali, E.S., Wu, F., Li, C-Z., Herod, A.A. and Kandiyoti, R, Energy & Fuels 1994;8; 1360-1369. Gibbins, J.R., Kimber, G., Gaines, A.F., and Kandiyoti, R., Fuel 1991;70;380-385. Clarke, J.W., Kimber, G.M., Rantell, T.D. and Shipley, D.E. (1980) ACS Symp. Ser. No. 139, D.D. Whitehurst, Editor, 111
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Oviedo ICCS&T 2011. Extended Abstract
Ash deposition characteristics determined in pilot plant tests burning bituminous and sub-bituminous coals
Miki Shimogori, Noriyuki Ooyatsu, Noboru Takarayama, Toshihiko Mine Kure Research Laboratory, Babcock-Hitachi K.K., 5-3 Takaramachi, Kure-shi, Hiroshima-ken 737-0029, Japan e-mail:
[email protected] The original paper regarding the contents presented here was submitted to "FUEL" in April 2011 and the paper is currently under review.
Abstract The purpose of this study was to obtain practical knowledge in selecting suitable coals for boiler operations without ash related problems. For this purpose, the effects of fine ash particles and alkali metals on heat transfer characteristics at the early stages of ash deposition have been evaluated in 1.5 MWth pilot plant tests. Ash deposition characteristics of four bituminous and three sub-bituminous coals were studied using a slagging probe set in the high temperature zone simulating the water wall in actual boilers. To determine ash deposition characteristics quantitatively, heat flux through the slagging probe was calculated and the decreasing rate of heat flux per unit weight of ash(dq/dt･ash) was compared for each coal as slagging potential. Deposits analysis results showed that particle fraction with a diameter less than 10 µm (R10under) of bituminous coals varied from 5 to 45 wt %, while it was almost the same, around 20 30 wt %, for sub-bituminous coals. In terms of alkali components, deposits of bituminous coals enriched Fe and Ca. On the other hand, mainly Na and K were condensed in deposits of sub-bituminous coals. To evaluate the influence of these factors on slagging potential (dq/dt･ash) quantitatively, a multiple regression analysis of heat flux data was performed using the following parameters: R10under in deposit
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Oviedo ICCS&T 2011. Extended Abstract
samples and sum of Na2O and K2O values in each parent coal. Calculation using the regression equation agreed well with experimental data. 1. Introduction Ash deposition on heat transfer surfaces during coal combustion is a common concern of all coal firing boilers. In tackling ash-related problems, a number of studies have been made on characteristics of coal-ash deposition. These studies [1-5] show that the initial stage of coal ash deposition has a significant effect on heat transfer characteristics during the whole ash deposition process. According to such studies, the inner layer formed at the initial stage of ash deposition consists of fine particles smaller than 10 µm and condensed alkali vapor. However, these effects have not been evaluated quantitatively, specifically the impact of these parameters on decreasing heat flux at the initial stage of deposition growth. The difficulty in selecting suitable coals for boilers without ash related problems stems from this lack of quantitative knowledge. In this study, to obtain practical knowledge in selecting coals, the effects of fine ash particles and alkali metals on heat transfer characteristics were evaluated quantitatively by conducting slagging tests at a pilot scale test plant. 2. Experimental Slagging characteristics of seven types of bituminous and sub-bituminous coals have been studied in a 1.5 MWth pilot plant with a slagging probe simulating the water wall of actual boilers (Fig.1). The furnace is a cylindrical down flow furnace, 6 m in height with a diameter of 1.35 m. The burner is at the top and three After Air Ports (AAP) are located 2, 3 and 4m down from the burner exit for staged combustion. During tests, exhaust gas passing through the furnace is cooled by an air heater then introduced to the flue-gas treatment system. Table 1 lists coal identification and operation times of tested coals. Fuel ratio of tested coals varies from 1.1 to 1.5 and ash content changes from 1.9 to 11.9 wt %. The pilot plant was operated at a minimum of 4hours and at a maximum of 100 hours. A decrease in heat flux due to growing ash deposits on the test probe is evaluated in each test run. After each run, ash deposits on the probe surface are sampled and analyzed for particle sizes and their chemical components.
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Oviedo ICCS&T 2011. Extended Abstract Flue-gas treatment system
Burner
Combustion Air
Air heater Vertical probe （Water-cooled）
Furnace Horizontal probe （Water-cooled）
AAP （After Air Port）
Probe temperature control（873K ） Horizontal probe （Air-cooled） Water seal
Fig.1 Schematic diagram of 1.5 MWth pilot plant.
Table 1 Coal identification and operation times of tested coals. Coal classification Coal ID Fuel ratio (-) Ash (wt%,db) Operation time (h)
Bituminous coals MP 1.2 5.2 4
AN SW 1.5 1.1 9.2 11.1 4 100
VC 1.5 11.9 69
Sub-bituminous coals DA PS RB 1.1 1.3 1.1 1.9 4.9 4.5 75 10 8
3. Results and Discussion For all test cases, heat flux through the test probe decreased dramatically at the beginning of the test. We analyzed the initial decrease of heat flux by a linear regression method and compared the decreasing rate of heat flux per unit weight of ash (dq/dt･ash) to discuss slagging potential of each coal. Slagging potential (dq/dt･ash) of tested coals was greatest for MP, followed by PS, AN, DA, RB, VC and SW. All deposits sampled from the test probe after each test were classified into three types: deposits with molten particles, powdered and agglomerated deposits. Deposits consisted of multiple layers, and in every case, the innermost layer was formed by numerous fine particles. Deposits analysis results showed that particle fraction with a diameter less than 10 µm (R10under) varied from 5 to 45 wt % for bituminous coals, while it was almost the same for subbituminous coals: around 20 - 30 wt %,. In terms of enriched components, deposits of bituminous coals enriched Fe and Ca, whereas those of sub-bituminous coals contained
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Oviedo ICCS&T 2011. Extended Abstract
higher ratio of Na, K and Si. From the correlation of analysis results and slagging potential (dq/dt･ash) of each coal, it was found that slagging potential of bituminous coals was high when R10under in the deposit was high and that the potential of subbituminous coals was high when the coal enriched Na2O and K2O. Given these results, a multiple regression analysis of slagging potential was performed using the following parameters: R10under in sampled deposits, and the sum of Na2O and K2O values in each parent coal. Calculation using a regression equation agreed well with experimental data. 4. Conclusions To obtain practical knowledge in selecting coals for boiler operations without ash related problems, slagging potential (dq/dt ･ ash) of seven types of coals including bituminous and sub-bituminous coals have been studied in slagging tests at a 1.5 MWth pilot plant. The effects of fine particles and alkalis on slagging potential were evaluated quantitatively. Calculation using regression equation having parameters of R10under, Na2O and K2O agreed well with experimental data and will provide useful knowledge for selecting suitable coals for actual boilers. References [1] Raask E. Mineral impurities in coal combustion, behavior, problems, and remedial measures. USA: Hemisphere Publication Corporation; 1985. [2] Benson SA and Sondreal, Impact of Mineral Impurities in Solid Fuel Combustion 1999; 121. [3] Laursen K, Frandsen FJ and Larsen OH, Impact of Mineral Impurities in Solid Fuel Combustion, 1999; 357-366. [4] Bryers RW, Fireside slagging fouling , and high-temperature corrosion of heat-transfer surcface due to impurities in steam-raising fuels. Prog Energy Combust. Sci 1996; 22(1):29120. [5] Courch G., Understanding slagging fouling in PF combustion. Research, I.C. Editor. London, UK; 1994: 118.
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Investigation of Contributions to Unburned Carbon in a 200 MWe Utility Boiler H. Gao, A. Majeski, A. Runstedtler, M. Sybring CanmetENERGY, Natural Resources Canada, 1 Haanel Drive, Ottawa, Ontario, Canada K1A 1M1 Tel No: 001 613 9965194, Fax: 001 613 9929335, E-mail:
[email protected] Keywords: Utility boiler, CIA, Residence time, CFD Abstract This study presents a novel examination of coal behavior in the computational fluid dynamics (CFD) model results for a 200 MWe tangentially-fired utility boiler. Data for thousands of particles were extracted and summarized for characteristics such as injection location, size, residence time, and unburned carbon content in fly ash (carbon-in-ash, or CIA). The analysis revealed that residence times for coal particles vary widely, the availability of oxygen along the trajectories of the coal particles at top levels plays an important role in the burnout process. Contributions to unburned carbon from different particle size classes, burner and burner levels were also investigated. Additionally, it was found that a noticeable amount of burning may still be occurring in the platen super heater region beyond the furnace outlet. The findings from this study can provide useful information for boiler design and retrofit, particularly in clean coal technology areas. Suggestions for possible design and operating improvements are put forward. 1. Introduction Unburned carbon content in fly ash (CIA) reduces both power utility boiler efficiency (since it is unburned fuel) and fly ash salability (since it reduces concrete strength). Minimizing unburned carbon in fly ash is therefore in the interests of power utility companies. Moreover, the wide application of low NOx technologies in utility boilers has caused an increase in CIA in many boilers. Currently, the only measureable data for unburned carbon in utility boilers is from fly ash sample analysis. The fly ash used for these analyses typically contains a mixture of coal particles from all burners in the unit and all of the different particle size classes. This obscures contributions to CIA from individual burners and particle size classes. Particle residence time is an important criteria for boiler design, and it is usually taken to be the travel time for the particles from burner outlet to the furnace outlet (shown in Figure 1). It is typically assumed that the majority of the coal particles complete combustion within that time. However, residence time in a utility boiler is traditionally estimated using a plug flow assumption, which may not be totally accurate given that a utility boiler usually has multiple coal burners
arranged at different locations. Moreover, the trajectories of coal particles from even a single burner are varied and complicated. With their rapid development in recent decades, computational fluid dynamics (CFD) modeling technologies can now provide a reasonable prediction of coal combustion in utility boilers. As a result, the application of CFD to utility boilers [1, 2, 3, 4, 5] is growing rapidly. CFD modeling technology solves the aerodynamics equations in a boiler simulation, as well as the heat transfer and combustion related equations, to predict boiler performance. In the mean time, thousands of coal particles with different properties, representing different size classes, from different coal burners are tracked in their travels throughout the boiler while undergoing both devolatilisation and char oxidation processes [6]. Particle properties including diameter, char and volatile fractions, particle travel time and coordinates are all recorded in a data file for further processing. These data are used to investigate the coal particle burnout behaviour in the boiler and it is the focus of this work to process and present this data in a novel way, in order to gain a level of understanding beyond the usual analysis of CFD results. 2. The Boiler Figure 1A shows the 200 MWe tangentially-fired utility boiler and its two groups of platen super heaters in the upper furnace. The coal burners (labeled by levels A, B, C and D), the air nozzles
Figure 1: The 200MWe boiler, its air nozzles, coal burners and injection angles. (labeled by levels AA, AB, BC, CD and DD) and oil guns (OA, OB), identical for each corner, are shown in Figure 1B. The injection directions of the air nozzles, coal burners and oil guns are the
same in each corner and are shown in Figure 1C. These injections angles are designed to generate a rotating flow in the boiler. The boiler is firing a bituminous coal; the coal size distribution listed in Table 1 is calculated according to the sieve data sampled at the power plant. Table 1 Coal particle size distributionc Particle diameter, micron Mass fraction, %
Class 1 29 43.8
Class 2 67 21.7
Class 3 105 13.6
Class 4 143 8.3
Class 5 181 12.6
3. Results and discussion A CFD simulation was performed for this boiler at full load operating conditions. The air nozzles, coal burners and the two platen super heater groups in Figure 1A are all included in the simulation domain. The predicted temperature distributions appear reasonable compared with field observations and the predicted CIA (3.27%) is close to the field measurement (3.0% to 6.2%). 3.1 Unburned Carbon in Fly Ash CIA measured at power plants results from the mixture of coal particles from all burners and all size classes. The contribution of each burner or size class to the total unburned carbon can not be identified. In a CFD simulation however, the individual particle information for thousands of coal particles along their trajectories, including the char and volatile fractions, travelling times, diameters can all be recorded. To process the data file, a script was written to extract the recorded particle information as particles crossed a designated plane. By analyzing this data, we could determine the CIA of the coal particles at this designed plane. Further, it was possible to identify the CIA for a particular burner by sorting the data by burner. Table 2 summaries the results at the furnace plane I (refer to Figure 1). CIA varies widely among burners in this table: it is higher than 8% for some burners and lower than 1% for other burners. Even on the same level, the CIA is quiet different among burners. From bottom level (Level A) to top level (Level D), CIA increases from less than 1% to 4.26%. The predicted CIA of all tracked coal particles taken together is 3.27%, which is close to the fly ash sample analysis results in the field as mentioned earlier. Table 2 CIA (%) at the furnace plane I Level D Level C Level B Level A Average
Corner 1 8.02 3.73 1.95 1.05
Corner 2 7.52 6.64 2.90 1.47
Corner 3 0.22 1.33 4.37 0.52 3.27
Corner 4 0.71 5.15 1.59 0.75
Average 4.26 4.25 2.77 0.91
Further processing of the data enables the contribution of each burner on total unburned carbon to
be calculated, Table 3 shows these results. More than 73% of the unburned carbon in fly ash is from Level D and Level C. Six burners (Corner 1 and Corner 2 of level D, Corner 1, Corner 2 and Corner 4 of Level C, Corner 3 of Level B) contribute about 80% of the unburned carbon among the 24 coal burners. This type of information can guide boiler operation, because fewer than half of burners need to be targeted to reduce CIA rather than all of them. Table 3 Contribution (%) of burners on total unburned carbon in ash Level D Level C Level B Level A
Corner 1 17.99 7.98 3.51 1.73
Corner 2 16.74 14.65 5.78 1.49
Corner 3 0.46 2.77 9.40 0.75
Corner 4 1.47 11.17 2.99 1.11
Total 36.67 36.57 21.68 5.08
The relationship between particle sizes and unburned carbon in fly ash is presented in Table 4. Despite of the fact that the mass fraction of the largest coal particles (Class 5, 181 micron) entering the boiler is only 12.6% (Table 1), almost 50% of the unburned carbon in fly ash is found in this class. The smallest particles (Class 1 and 2) contribute only 11% of the unburned carbon in ash despite their accounting for over 65% (Table 1) of the coal entering the boiler. This data provides guidance for operators to adjust fineness for pulverisers at different levels. Coal particles at the top levels need to be finer, while the coarser coal particles at bottom may not necessarily increase CIA. Moreover, the finding suggests using different pulverizers or classifiers for different levels right in the boiler design stage. Table 4 Contribution (%) of particle size classes on unburned carbon in ash Class 1 Class 2 Class 3 Class 4 Class 5
Level A 0.23 0.64 1.08 1.12 1.90
Level B 0.29 1.35 4.06 5.11 10.43
Level C 0.39 2.88 6.59 7.88 18.11
Level D 0.84 4.39 7.46 7.90 17.33
Total 1.75 9.26 19.20 22.01 47.77
3.2 Residence time Table 5 summaries the residence times extracted from particle data.
As elevation increases from
level A to level D, particle residence time reduces from 5.96s to 1.60s. On any given level, the averages among the corners tend fall within 2s. For these particles with a relative short residence time (level D and C), a relative longer residence time doesn’t necessary create a better burnout, this conclusion can be clearly seen on Figure 2 which plotted the CIA versus the residence time for the particles from each coal burner. To find the reason behind this, the average oxygen volume fraction along particle trajectories of level D was calculated. The average oxygen volume fraction for particles of Corner 1 and Corner 2 is 3.2% to 4.6%, while it is 5.4% to 6.5% for Corner 3 and
Corner 4. The CIA of them (Corner 1, 2 and Corner 3, 4) are quiet different as indicated in Table 2 although their residence time are similar. Maybe the oxygen availability along the particle trajectories is more important for burnout for this level. Table 4 Residence time ( s ) of each coal burner Corner 1 1.80 1.97 4.23 5.31
Level D Level C Level B Level A
Corner 2 1.39 1.88 3.37 7.78
Corner 3 1.51 1.77 2.44 5.59
Corner 4 1.68 2.05 3.72 5.16
Average 1.60 1.92 3.44 5.96
c
9
8
7
C I A, %
6
5
4
3
2
1
0 1
2
3
4
5
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7
8
Residence time,s
Figure 2:
Particle residence time versus CIA of each burner
Furnace plane I
Furnace outlet plane
12
10
C I A, %
8
6
4
2
Level D
Level C
Level B
Corner 4
Corner 3
Corner 2
Corner 1
Corner 4
Corner 3
Corner 2
Corner 1
Corner 4
Corner 3
Corner 2
Corner 1
Corner 4
Corner 3
Corner 2
Corner 1
0
Level A
Figure 3: CIA at furnace outlet plane and furnace plane I
The particles of level A and B have longer residence times as well as a good chance to pass through an oxygen rich region because most of the air nozzles are above (downstream of) the burners. This
result reveals the importance of creating a uniform oxygen distribution beyond the burner region to unsure all particles encounter with oxygen-rich regions. 3.3 Combustion beyond the furnace outlet plane The furnace outlet plane is defined in Figure 1A. Although field observations have suggested that coal particles may still be burning beyond the furnace outlet plane, there have been no measurements to prove it. Traditionally it is believed that most combustion of coal particles stops beyond this plane because of the quenching effect of the platen super heater groups. To examine if combustion is still occurring beyond the furnace outlet plane, Figure 3 compares the CIA at the furnace outlet plane and at furnace plane I (labeled in Figure 1) for all coal burners. This figure indicates that there is a noticeable reduction in CIA beyond the furnace outlet plan for all burners, average CIA reduces to 3.27% at furnace plane I from 4.1% at furnace outlet plane. This figure supports the supposition that coal particles are still burning beyond the furnace outlet, led to a reduction in CIA in the upper furnace. Continued burning in the upper furnace may create some potential to further reduce NOx emissions. Some separated over fire air (SOFA) nozzles may be arranged in this region to achieve a deeper air staging. Also a small fraction of air injection in this region may help reduce CIA. 4. Conclusions CFD modeling, combined with novel data analysis, has provided an unprecedented capacity to characterize coal particle burnout history in a utility boiler and can answer questions that have long existed in utility power industry. Predicted residence times for coal particles could vary widely among burners in a utility boiler, and it ranges from 1.6s to 6s in this boiler. The CIA of each coal burner could be quiet different and the unburned carbon in fly ash could be mainly from some larger coal particles of a few coal burners as predicted for this 200MWe utility boiler. This study also supports the notion that coal combustion may continue to occur in the upper furnace region, leading to a reduction in CIA in the upper furnace. Oxygen availability along particle trajectories appears important for burnout for the coal burners at top levels. This approach to investigating the coal particle burnout characteristics in a boiler can provide new ideas to design and operate a utility boiler as noted in the discussion. Acknowledgements This study was supported by the Federal Program on Energy Research and Development (PERD) of the Canadian Federal Government.
References
[1] Yin CG, Caillat S., Harion JL, Baudoin B., Perez E. Investigation of the flow, combustion, heat-transfer and emissions from a 609MW utility tangentially fired pulverized-coal boiler. Fuel 2002; 997:1006-81. [2] Philip j. Stopford, Recent application of CFD modeling in the power generation and combustion industries, Applied Mathematical Modelling 2002; 26:351-374 [3] Eddy H. Chui, Haining Gao, Estimation of NOx emissions from coal-fired utility boilers. Fuel 2010; 89:2977-2984. [4] Haining Gao, Eddy H. Chui, Numerical Investigation of the Impact of Air Distribution on the Performance of a 360 MW W-Fired Boiler. International Pittsburgh Coal Conference, Osaka, Japan, 2004 [5] Chui E.H., Haining Gao, Reduction of emissions from coal-based power generation, International conference on climate change 2007. Hong Kong; 2007. [6] AEA Technology Engineering Software Limited, CFX-TASCflow Theory Documentation Version 2.12, Sept. 20 2002
Oviedo ICCS&T 2011. Extended Abstract
Visualizing The Macromolecular Network Structure Of A Large-Scale (50,000 atoms) Illinois No. 6 Coal Molecular Representation In 3D And 2D Lattice Views 1
Alvarez, Y. E.; 2 Watson, J. C. K.; 3 Pou, J. O.; 1Castro-Marcano, F.; 1Mathews, J. P.
1
John and Willie Leone Family Department of Energy & Mineral Engineering and the EMS Energy Institute, 110 Hosler Building, 2The Applied Research Laboratory, The Pennsylvania State University, University Park 16802, USA
[email protected] 3 Departament d’Enginyeria Química, Escola Tècnica Superior IQS, Via Augusta 390, 08017 Barcelona, Spain Abstract The utility of large-scale structural models of coal is currently limited by their scale (>20,000 atoms) and complexity. A novel computational approach that performs systematic simplifications of complex 3D structural models into corresponding 2D lattice representations was used to generate equivalent reduced models for an Illinois no. 6 bituminous coal molecular representation of >50,000 atoms. The visualization of molecular entities (clusters, cross-links and molecules) from the original representation is enhanced by the 2D lattice model which is able to capture the network and portray the properties of the original representation under various color schemes. 1. Introduction Capturing the continuum of coal structure requires large-scale coal models that enable inclusion of molecular weight distribution and structural diversity. However, construction of large-scale representations is time-consuming, challenging, and requires considerable expertise. Recent work [1, 2] has attempted to capture aromatic alignment and stacking and the distribution of structural features for carbonaceous materials such as coals, chars and soots from HRTEM lattice fringe images directly via Fringe3D. With this approach, a large-scale model for Illinois no. 6 Argonne Premium coal was constructed based on available experimental data [3] in an effort to move towards capturing the continuum structure [4]. The model contains 50789 atoms in 728 crosslinked aromatic clusters with a continuous molecular weight distribution ranging from 100 to 2850 Da and it is the largest, most complex coal representation currently available.
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Oviedo ICCS&T 2011. Extended Abstract
The utility of large-scale structural models of coal has been challenged by their scale (>20,000 atoms) and complexity. The very feature that allows them to successfully represent coal behavior by the incorporation of a molecular weight distribution and structural diversity hinders their use in bond-altering simulations due to the associated computational cost. Hence, in view of the visualization and utility challenges involving complex structural models, an enabling computational tool for the simplification of large-scale molecular representations [5, 6] of coal was developed, consisting of two main scripts, Col2D and Molecwalk, capable of generating equivalent 3D coarse-grained and 2D lattice molecular models from the complex original molecular representation. This is accomplished by pattern recognition of hydroaromatic/aromatic clusters and cross-links, which are correspondingly reduced into lattice nodes and linkage lines. The approach enables a reduction of scale down to 3% of the original number of atoms, and while the view is simplistic, the coarse-graining process is able to retain all of the structural and chemical information of the reduced units (clusters and cross-links), facilitating the manipulation for visualization and simulation of the lattice and coarse-grained models. The various stages of simplification process by Col2D and Molecwalk are shown in Figure 1 for a 3D Wiser bituminous coal model [7]. Initially rings (stage 1) and clusters (stage 2) are identified and adjacent/connected elements (such as functional groups and sidechains) are collapsed into nodes (stage 3). Cross-links that may consist of multiple atoms are further collapsed into linkages (stage 4), thus Col2D creates a 3D coarsegrained view. The functional group information is retained along with the node and cross-links’ composition, for further consideration in reactivity calculations. A 2D lattice is generated from the simplified 3D structure (stage 5) through the Molecwalk script which performs ‘random walks’ of the skeletal molecules in a lattice space, obtaining a unique 2D lattice model of the original coal representation.
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Figure 1. Simplification process by Col2D and Molecwalk for the Wiser bituminous coal model [7]. In stage 5 white nodes are empty lattice slots. Generic non-structure specific lattices have been used in the past to represent the macromolecular structure of coal and to describe thermal network decomposition through inexpensive statistical approaches [8-11]. Linking complex models to structurederived lattices could continue to provide paths for exploring the reactive behavior of coal and similar carbonaceous systems. It is expected that the lattice model will be a means of simulating, through network statistics, thermal breakdown processes related to pyrolysis and/or liquefaction; thus, this approach adds a visual feature and the incorporation of a coal-specific network model that is lacking in previous network decomposition modeling approaches [8-11]. In the current study, the Col2D and Molecwalk approach was utilized to generate corresponding 3D coarse-grained and 2D lattice representations of the Illinois no. 6 coal model to demonstrate the utility of structure-specific 2D lattice molecular models. 2. Methodology Here, the 3D coarse-grained and 2D lattice models are referred to as reduced models. During the execution of Col2D, an extra set of molecular files are generated which enable a connection between the coarse-graining results and the original atomic file. This extra set of InsightII files are known as the ‘Link’ files. These files treat the reducible molecular parts of the original atomic model (i.e. hydroaromatic clusters and cross-links) as independent entities (molecules), thus allowing the later extraction of
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Oviedo ICCS&T 2011. Extended Abstract
their chemical information based on individual atomic composition. However, a feature not yet included is that the functional groups are not transferred into the reduced molecules, and thus their presence is not accounted for select property calculations. The naming scheme assigned to the molecular parts in the reduced models (nodes and linkages) is consistent with the atomic reducible groups in the Link files (hydroaromatic clusters and cross-links), keeping reduced models and original atomic model relatable. This is illustrated in Figure 2.
Figure 2. Demonstration of molecular variations from original atomic file to 'Link' file and naming scheme A series of scripts (in Perl and Visual Basic) were developed to extract the chemical information from each molecular part of the Link files. By submitting the “Link” files to these model-analysis scripts, it is possible to index each node and linkage line to a series of composition-based chemical properties. This enables the formation of a summary table termed ‘reduced unit property table’ that contains properties such as elemental composition, molecular weight, chemical groups in cross-link, cross-link classification, naming scheme, etc. of each reduced unit (RU). A sample of this table showing a few properties for various reduced units in the Illinois no. 6 coal model is shown in Table 1. Table 1. Reduced unit property table for 3 molecules from Illinois no. 6 coal model Molecule_RU Name
C
H
O
N
S
MW
RU Type
Cross-link groups
Sketch520_C0
6
6
0
0
Sketch520_C1
10
8
0
0
0
78
cluster
n/a
0
128
cluster
n/a
Sketch520_C2
10
12
0
0
0
132
cluster
n/a
Sketch520_B0
2
6
Sketch520_B1
4
1
0
0
46
cross-link
-O-
0
0
0
58
cross-link
- CH2 CH2-
Sketch528_C0
10
8
0
0
0
128
cluster
Sketch536_C0
17
19
0
1
0
237
cluster
n/a
Sketch536_C1
10
12
0
0
0
132
cluster
n/a
Sketch536_B0
4
10
1
0
0
74
cross-link
- CH2 CH2O -
Table lines separate reduced units of individual molecules
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Oviedo ICCS&T 2011. Extended Abstract
Other properties this table may include are: NMR aromaticity parameter (fa), solubility parameter (calculated directly from the model with scripts written from previous work [12]), and atomic composition by force field type, which is basically the list of atoms in the original component under their force field type. Reduced unit property tables organize the chemical data of the model’s components making it accessible for manipulation of the lattice view based on any of the table properties. Once the desired properties are tabulated, a different series of Perl scripts executed in a modeling platform (Materials Studio 5.0) can be executed to change the visualization of the lattice, by coloring it under selected color-schemes for each property. A modelsensitive legend is also generated so that the range of property values within the molecular weight distribution is well represented. 3. Results and Discussion The large-scale Illinois no. 6 bituminous coal representation was processed by the simplification approach [5, 6], hence obtaining reduced models as illustrated in Figure 3. Given the density and scale of the original model, it is still very difficult to visually distinguish the reduced molecules in the 3D coarse-grained (Figure 3b); hence it was more desirable to portray the all molecular entities through a 2D lattice model [5, 6] (Figure 3c), which distributed the 728 molecules in an 80x80 grid space.
Figure 3. Atomic large-scale representation of Illinois no. 6 bituminous coal model transformed to 3D coarse-grained and 2D lattice equivalents by Col2D and Molecwalk approach. The reduction of scale was from 50879 atoms to 2459 pseudo atoms, comprised of 1592 nodes and 867 linkage lines. The lattice may aid visualization, to portray the properties Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
of molecules, clusters or cross-links. For example, the script “Colorby_MW.pl” analyzes the range of the molecular weight of the clusters in the model (not including attachments), and assigns each node to a color representative of molecular weight. The molecular weight of the Illinois no. 6 clusters is shown in Figure 4.
Figure 4. Color-coding by molecular weight of lattice clusters from Illinois no. 6 bituminous coal model. Linkage lines are colored grey to aid visualization.
Figure 5 shows the lattice after being colored by cross-link types. Cross-links were classified according to their chemical composition and based on a predominant functionality (methylene, carbonyl, ether oxygen, etc.); some cross-links may be composed of a mix of functionalities, hence their type is termed “plus” to indicate the possible presence of other groups; in most cases, this “mix” is composed of the namedgroup plus methylene groups, for example -CH2-S-CH2- for “sulfur-plus” cross-links. Analyzing the chemical composition of the cross-links also enables the assignment of cleavage or reaction probabilities that would aid in a statistically-based reaction model.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 5. Illinois no. 6 bituminous coal lattice with linkage lines color-coded by crosslink type. Nodes are gray.
The model and hence network is mainly cross-linked with oxygen and methylene bridges [-(CH2)n-(O)m-(CH2)p-; n,p=0=3, m=0-1]. There is also a significant incidence of ‘sulfur plus’ bridges, which are any bridges that contain sulfur mixed with other groups (thioethers). This is characteristic of the high organic sulfur content in Illinois no. 6 coal [3]. Other colored-coding examples at the molecular level are included in Figure 6. These result from running scripts on the original atomic model, and not the Link files, thus extracting the full chemical properties of the original molecules. The Painter solubility parameter [13] (cal. cm-3)0.5 was calculated for each molecule and these were classified and colored under the 12 color-ranges that are a function of the minimum and maximum solubility parameters in the model, providing a visual sense of the model’s theoretical extractability by a specific solvent (Figure 6a). Similarly, distances (Å) of the molecular-centroid to the center of the model in 3D space are individually calculated and classified by a 12 division of the model’s total distance range. The 3D distance
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Oviedo ICCS&T 2011. Extended Abstract
lattice color scheme may be useful for mass transfer and extractability studies where knowledge of the molecule’s position to the surface of the model is relevant (Figure 6b).
Figure 6. Illinois no. 6 lattice colored by a) Painter solubility parameter (cal. cm-3)0.5 b) Proximity of molecular centroid to the center of the model in 3D space (Å)
It is expected as future work that the lattice may serve as the visual interface for the structural changes generated from reactive simulations performed directly on the coarsegrained 3D model. 4. Conclusions Visualization has increasingly become a valuable research tool exploited by scientists to obtain insights of phenomena and to make scientific knowledge more accessible. Currently, the visualization capabilities are significantly enhanced by the generation of 3D and 2D lattice molecular representations of specific complex large-scale representations, thus reproducing a representation that captures the network and its molecular properties analyzed under various color schemes through the lattice view; however, it is expected that this will move forward to include the visualization of the lattice post-simulation, displaying transitions in the properties of the model components and in the network structure as a whole. Acknowledgements. This project was funded by the Illinois Clean Coal Institute with funds made available through the Office of Coal Development of the Illinois Department of Commerce and Economic Opportunity. We thank Alan Chaffee for the 3D Wiser model.
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Oviedo ICCS&T 2011. Extended Abstract
References [1] V. Fernandez-Alos, J.K. Watson, R.v. Wal, J.P. Mathews, Soot and char molecular representations generated directly from HRTEM lattice fringe images using Fringe3D, Combustion and Flame, available in ASAP articles DOI: doi:10.1016. (2011). [2] V. Fernandez-Alos, Improved molecular model generation for soot, chars, and coals: high resolution transmission electron microscopy lattice fringes reproduction with Fringe3D, in: Master Thesis, Energy and Geo-Environmental Engineering,, Pennsylvania State University, University Park, PA, 2010. [3] F. Castro-Marcano, J.P. Mathews, Constitution of Illinois no. 6 Argonne Premium coal: a review, Energy Fuels, 25 (2011) 845–853. [4] F. Castro-Marcano, V. Lobodinb, R. Rodgers, A. McKenna, A. Marshall, J. Mathews, A molecular model for Illinois no. 6 Argonne Premium coal: moving toward capturing the continuum structure, Fuel, Subtmitted (2011). [5] Y.E. Alvarez, Development of a reactive coarse-graining approach for the utility enhancement of complex large-scale molecular models of coal, in: Masters Thesis, Energy and Mineral Engineering, The Pennsylvania State University, University Park, PA, 2011. [6] Y.E. Alvarez, J.K. Watson, J.P. Mathews, Improving the utility of large-scale coal molecular models by simplifying the view: 3D models to reactive lattice grids, Prepr. Pap. -Am. Chem. Soc., Div. Fuel Chem., 55 (2010). [7] W.H. Wiser, Conversion of bituminous coals to liquids and gases, NATO ASI Series C, 124 (1983). [8] D.M. Grant, R.J. Pugmire, T.H. Fletcher, A.R. Kerstein, Chemical-model of coal devolatilization using percolation lattice statistics, Energy & Fuels, 3 (1989) 175-186. [9] S. Niksa, A.R. Kerstein, On the role of macromolecular configuration in rapid coal devolatilization, Fuel, 66 (1987) 1389-1399. [10] P.R. Solomon, D.G. Hamblen, R.M. Carangelo, M.A. Serio, G.V. Deshpande, General-model of coal devolatilization, Energy & Fuels, 2 (1988) 405-422. [11] P.R. Solomon, D.G. Hamblen, Z.-Z. Yu, M.A. Serio, Network models of coal thermal decomposition, Fuel, 69 (1990) 754-763. [12] D. Van Niekerk, Structural elucidation, molecular representation and solvent interactions of vitrinite-rich and inertinite-rich South African coals, in: Energy and Geo-Environmental Engineering, Pennsylvania State University, University Park, PA, 2008. [13] P.C. Painter, J. Graf, M.M. Coleman, Coal solubility and swelling. 1. Solubility parameters for coal and the Flory x parameter, Energy & Fuels, 4 (1990) 379-384.
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Oviedo ICCS&T 2011. Extended Abstract
Brown Coal Solubilisation with Novel Ionic Liquids
Alan L Chaffee1, Christin Patzschke1, Douglas Russell1, Daniel Kelley1, Ying Qi1, Vincent Verheyen2, Marc Marshall1, Vijay Ranganathan1 and Douglas MacFarlane1 1
School of Chemistry,Monash University, Clayton, Victoria 3800, Australia School of Applied Science and Engineering,, Gippsland Campus, Monash University, Churchill, Victoria 3842, Australia
2
Corresponding Author: Alan L. Chaffee Email:
[email protected] Abstract Ionic liquids (ILs) are now recognised as an important medium for solubilisation and reaction in a variety of chemical applications. For example, cellulose, lignin and other biopolymers can be selectively solubilized and separated from complex biomass mixtures. A recent study has shown that significant extraction yields can also be obtained from some bituminous coals with the use of specific ILs or IL/solvent mixtures. However, there are unresolved issues with the separation of the IL from the extract and also with the recovery / recycling the IL. We have commenced a study into the solubility of Victorian brown coal in novel ILs that are based on the association of CO2 with low molecular weight amines. Victorian brown coal is observed to disperse very well in these ILs and significant solvent-free extract yields (~20%) can be obtained. The structures of the products (extracts and residues) have been evaluated by a variety of analytical techniques, including FTIR, 13CNMR and pyrolysis-GC-MS. Structural differences are illustrated and the character of the separations with different ILs described.
1. Introduction Ionic liquids (ILs) consisting of large organic cations associated with inorganic anions have attracted considerable attention as potential alternatives to conventional organic solvents in a variety of synthetic, catalytic and electrochemical applications. Research in recent years has found ILs to be able to dissolve plant materials such as cellulose and lignin [1-3]. Painter et al [4-5] used specific ILs with or without catalyst to extract bituminous coals and achieved significantly extraction yields. Victorian brown coal has provided an abundant and cheap energy resource for the State of Victoria, Australia, for decades. However, with the increasing price of petroleum
1
Oviedo ICCS&T 2011. Extended Abstract
products, there may be an opportunity to diversify its end-use into new fields of application. The objective of this study is to investigate the solubility of Victorian brown coal in novel ILs that are based on the association of CO2 (a weak acid) with low molecular weight amines and characterize the chemical structures of the products (extracts and residues). The advantage of such ILs is that they dissociate into their precursor components at relatively low temperatures and can be readily removed from the products by this means. 2. Experimental section ILs used in the study were N,N-dimethylammonium N’,N’-dimethylcarbamate (DIMCARB) synthesized in the laboratory and 1-ethyl-3-methylimidazolium chloride ([emim]Cl) obtained from Sigma-Aldrich. Whilst [emim]Cl has very low volatility, DIMCARB dissociates into dimethylamine and carbon dioxide at ~ 60°C. The coal used was run-of-mine Loy Yang coal from the Latrobe Valley, Australia, milled to less than 1 mm, and with a determined moisture content of 50 %. Raw coal with 50% moisture was mixed with the selected IL at a mass ratio of 1:10 in a beaker or a centrifuge tube using a magnetic stirrer (20-24 hr) or an ultrasonic bath (3 min). All sonicated mixtures were left over night for further solubilisation and to ensure comparable conditions. Due to the solid state of [emim]Cl at room temperature, the experiments were carried out by heating the mixture to the corresponding melting points. The solid residue was then separated by vacuum filtration or centrifugation. The residual and extracted products of DIMCARB were dried in an oven at 105 °C to remove any residual of IL and water. After separating the extract and residue of the [emim]Cl extraction, the IL was removed by washing with water. The products were then dried in an oven at 105 °C. The dried materials were weighed after being cooled to room temperature in a desiccator. The dried samples of coal and extraction products (residues and extracts) were analysed for FTIR (Fourier Transform Inferred Spectroscopy), Pyrolysis-GC-MS and Solid state 13C-NMR (Nuclear Magnetic Resonance Spectroscopy). 3. Results and Discussion 3.1. Extraction yield The yields of extracted material were mostly between 10 % and 20 % depending on the IL used and the method for solubilisation (Table 1). Mixing the IL and coal by stirring gave higher extraction yields than those observed using an ultrasonic bath. Separation of the coal residue and the extract by centrifuging or filtration seemed to have little effect on the achievable yield. Using the stirring method, DIMCARB demonstrated better extraction capabilities than [emim]Cl.
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Oviedo ICCS&T 2011. Extended Abstract
Table 1 Extraction Yield using ILs. IL (g) Coal (g, db) DIMCARB
[emim]Cl
5.16 5.21 4.19 20.98 22.18 4.14 5.45
0.28 0.28 0.22 1.11 1.10 0.11 0.17
Solubilisation/ Separation method Stirring/filtration Stirring/centrifuging Sonication/filtration Stirring/filtration Stirring/filtration Sonication/filtration Sonication/centrifuging
Extraction yield (%) 22.2 21.7 13.4 20.5 15.5 17.7 12.5
3.2. FTIR analysis FTIR spectra of the extraction products show the similarities of the major absorption bands to that of the original coal (Figure 1). However, the band in the 3200-3400 cm-1 range for the extracts and residues of both [emim]Cl (not shown) and DIMCARB is stronger and sharper than for the coal. This may be due to the N-H bond from the residues of the ionic liquids in the extraction products. The C-O stretching in the range of 1250-1300 cm-1 in the spectra of the extraction products is also weaker and very broad compared to that of the coal. The relative intensity of the band of C=O stretching (an indication of carboxyl group) at 1700 cm-1 compared to that of the C=C stretching at 1600 cm-1 is more prominent in the extract than in the residue and all weaker than in the coal. coal
CO2 artifact CH2 O-H
C=O
CH3
C-O-H C=C
C-O
DIMCARB extract
DIMCARB residue
3600
3100
2600
cm ‐1
2100
1600
1100
600
Figure 1 FTIR spectra of original Loy Yang coal, DIMCARB extract and DIMCARB residue. 3
Oviedo ICCS&T 2011. Extended Abstract
3.3. Solid state 13C-NMR Figure 2 compares the spectra of Solid state 13C-NMR of coal and DIMCARB residue and extract. It shows that the extract and residue are clearly different from each other and from the coal. The extract contains significantly higher portion of carboxyl carbons (160-180 ppm) than the residue. Higher proportions of aromatic carbons (100-150 ppm) are present in the residue than in the extract and there is an interesting difference in the distribution of aliphatic carbons between the two products. There is some evidence of entrainment of the DIMCARB in the extract (peak at ~40 ppm may be due to aminated carbon) in spite of the fact that the sample was treated at 105°C prior to analysis.
Coal
DIMCARB residue
DIMCARB extract
260
240
220
200
180
160
140
120
100
80
60
40
20
0
ppm
Figure 2 Solid state 13C-NMR Spectra of original Loy Yang coal, DIMCARB extract and DIMCARB residue. 3.4. Pyrolysis-GC-MS analysis The volatile components of each sample were thermally desorbed at 340°C and analysed by GC-MS. Following this analysis, the residue from thermal desorption was pyrolysed at 720°C and analysed by GC-MS in a similar fashion. Figure 3 compares the thermal desorption chromatograms (only) for the original Loy Yang coal and the extracts. Figure 4 compares the chromatograms of the 720°C pyrolysis products (only) for the coal and residues. Mass spectrometric characterisation of some lower molecular components in the chromatograms, such as the labelled peaks in Figures 3 and 4, indicates the presence of nitrogen containing compounds, which almost certainly point to the entrainment of some ionic liquid within the products. It can be seen that entrained DIMCARB is removed by thermal desorption at 340°C. However, entrained [emim]Cl is principally evident from the higher temperature (720°C) pyrolysis run.
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Oviedo ICCS&T 2011. Extended Abstract
Coal 340°C
[emim]Cl extract 340°C
IL residue
DIMCARB extract 340°C IL residue
Figure 3 Comparison of GC-MS chromatograms of thermal desorption products of coal and solvent extracts at 340°C. Coal 720°C
[emim]Cl residue 720°C
IL residue
DIMCARB residue 720°C
Figure 4 Comparison of pyrolysis-GC-MS chromatograms of pyrolysis products of coal and residues at 720°C. At the lower (thermal desorption) temperature, it can be seen that the extracts provide a different product distribution than the whole coal itself. At the higher temperature (not
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Oviedo ICCS&T 2011. Extended Abstract
shown), the DIMCARB extract produces more low molecular weight compounds than the [emim]Cl extract. This is in agreement with the extraction yields, suggesting DIMCARB as a better solvent than [emim]Cl. Pyrolysis of the residues shows that the composition resembles that of the original coal with the presence of hydrocarbon homologues (Figure 4). A more detailed evaluation of the mass spectroscopy results is underway. 4. Conclusions The extraction yields of raw coal without any pre-treatment by [emim]Cl and DIMCARB range between 10 and 20 % depending on the solubilisation and separation methods used. FTIR data indicate differences in the C=O and C-O regions of the spectra products between the extracts and the residues and compared to the original coal. Solid state 13C-NMR measurement indicates that the DIMCARB extract contains higher proportions of carboxyl carbons whereas the residue contains higher proportions of aromatic carbon. Pyrolysis-GC-MS indicates the entrainment of some ionic liquid within the products. It is also showed that the composition of thermal desorption products from the extracts differs considerably from the whole coal. The DIMCARB extract provides a lower molecular weight distribution of products than the [emim]Cl extract. Acknolwedgement This work has been supported via a BCIA (Brown Coal Innovation Australia) Research Leadership Fellowship. References [1]
[2]
[3]
[4]
[5]
Binder Joseph, B, Raines Ronald, T. Simple chemical transformation of lignocellulosic biomass into furans for fuels and chemicals. J Am Chem Soc 2009;131:1979-85. Fort, DA, Remsing, RC, Swatloski, RP, Moyna, P, Moyna, G, Rogers, RD. Can ionic liquids dissolve wood? Processing and analysis of lignocellulosic materials with 1-n-butyl-3-methylimidazolium chloride. Green Chem. 2007;9:63-9. Fu, D, Mazza, G, Tamaki, Y. Lignin Extraction from Straw by Ionic Liquids and Enzymatic Hydrolysis of the Cellulosic Residues. J Agri Food Chem 2010;58:2915-22. Painter, P, Cetiner, R, Pulati, N, Sobkowiak, M, Mathews, J. Dispersion of Liquefaction Catalysts in Coal Using Ionic Liquids. Energy Fuels 2010;24:308692. Painter, P, Pulati, N, Cetiner, R, Sobkowiak, M, Mitchell, G, Mathews, J. Dissolution and Dispersion of Coal in Ionic Liquids. Energy Fuels 2010;24:1848-53.
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Oviedo ICCS&T 2011. Extended Abstract 1
H-NMR Study on the Thermoplasticity of Coking Coal - Effects of coal blending and additives H. Kumagai1, N. Okuyama2, T. Shishido2, K. Sakai2, M. Hamaguchi2, N. Komatsu2 1
Graduate School of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo 060-8628, Japan. E-Mail:
[email protected] 2 Coal & Energy Technology Dept., KOBE STEEL, Ltd., 2-3-1, Shinhama, Arai-cho, Takasago 676-8670, Japan Abstract This study aim to investigate the effects of HPC addition on the thermoplasticity of coal blends. The thermolasticity of coal blends with HPC were monitored with in-situ high temperature 1H-NMR relaxation measurement. The solid echo pulse sequence was employed to generate 1H-NMR transverse relaxation signals. The echo signals obtained during heat treatment under a flow of nitrogen at a heating rate of 3K/min were deconvoluted into a set of one Gaussian and two Exponential decay components which represent the immobile, intermediate and mobile component, respectively. The changes in the fractional intensity of mobile component, fHm, calculated from the signals well corresponded to the softening and resolidification phenomena of coal blends. The fHm and molecular mobility of mobile component represented by Spin-Spin relaxation time, T2Hm, increased with HPC addition at lower temperature range. At higher temperature range, that is thermoplastic temperature range, fHm and T2Hm shows almost the same value as those for original coal blends. These results indicate that the HPC can be added as a substitution for coking coals. 1. Introduction Because of the importance of thermoplastic properties, which have definitive effects on the properties of the resultant coke, a wide range of experimental techniques have been applied to study the thermal transformation of materials. Most established dynamic measurement techniques specifically devised for the characterization of thermoplastic behavior of coking coal are concerned with rheological or dilatometric properties1). The dynamic measurement techniques, such as the Gieseler plastometer, and other conventional testing techniques, such as crucible swelling and reflectance measurement, are useful to characterize the properties of coking coal and enable the empirical evaluation of the quality of the resultant coke. However, relationships between the
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Oviedo ICCS&T 2011. Extended Abstract
changes in the parameters obtained from the conventional techniques and actual changes in the reactivity and structure of the coal during heating are not clear yet. Of the in-situ measurement techniques available, high temperature in-situ
1
H-NMR relaxation
measurement allows the progress of thermal transformation to be monitored by quantitatively recording the hydrogen content of residual specimens and as a result the sensitivity of the relaxation signal to the molecular properties of specimens2). In principle, 1H-NMR relaxation measurement is applicable to materials which have nuclear spins regardless of the state of the materials, that is, solid, liquid, gaseous or a mixture of these states. Furthermore, relaxation characteristics of nuclear spins are closely related to the mobility and motion of molecules. Thus, the phase transformation of materials can be detected as a variation in relaxation behavior of nuclear spins. The coal extracts named High Performance Caking additive, HPC, was produced by thermal extraction of coal using 2-ring aromatic solvent. HPC appeals an excellent thermal plasticity although the parent coal appeals no thermal plasticity. HPC softens at low temperature, keeps a highly fluidity in a wide temperature range and re-solidifies at high temperature. These thermoplastic properties exhibit that HPC can be available as a caking additive to make strong coke for the blast furnace. Presented in this study is a quantitative and qualitative evaluation of the thermoplasticity of coal blend with HPC, which was attempted using in-situ 1H-NMR relaxation measurement. 2. Experimental section 2. 1. Samples In this study, three Australian strongly caking coals (A, B, C) and one slightly caking coal (D) was used as sample. Table 1 shows the results of proximate analysis and Gieseler plastometry of the coal samples, and Table 2 shows the blending ratio of each coal sample. Base-1 consists of 75wt% of strongly caking coals, coal-A : B: C : D = 15: 26: 34: 25, and Base-2 consists of 50wt% of strongly caking coals, coal-A : B: C : D = 15: 30 : 5: 50. Coal-C was replaced with HPC for Base-1, and coal-B was replaced for Base-2. HPC was extracted from Australian steaming coal (MO) at 400ºC for 1 hour, and insoluble matter was separated using the settling and filtration system. The properties of MO coal are shown in Table 1. 2. 2. NMR measurements Spin-spin relaxation time, T2, measurements were conducted using a Techmag Apollo Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
Pulse NMR spectrometer equipped with a CSIRO Australia produced high temperature 1
H-NMR probe.
The solid echo pulse sequence3), 90x-τ-90y, was employed to
generate 1H-NMR transverse relaxation signals. The advantage of the solid echo pulse sequence is that loss of information from the rapidly decaying free induction decay, FID, signals, which is encountered due to dead time, can be avoided. Thus, it becomes possible to observe the entire transverse relaxation signal. Theoretically, for sufficiently small τ compared with the transverse relaxation time T2, the peak amplitude of the solid echo is proportional to the total hydrogen content of the specimen and the subsequent signal decay is a full representation of the transverse relaxation4).
3. Results and Discussion 3. 1. Data analysis Change in the signal intensity, It, with decay time, t, is defined by Equation 1. It = I0 exp[-(t/T2)mi] mi=1 for exponential, mi=2 for Gaussian
1)
where I0 is the intensity of the signal at decay time t=0 corresponding to the number of protons in the specimen, and T2 is the spin-spin relaxation time reflecting the mobility of molecules in which the protons are embedded. When the specimen consists of several components, the obtained signal can be deconvoluted on the basis of the relaxation
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Oviedo ICCS&T 2011. Extended Abstract
characteristics and the signal can be described as a sum of each of the components. ItTotal = ∑Iti 2) where Iti is signal intensity for component i described in Equation 1 and ItTotal is the sum of the components corresponding to the observed signal. The spin-spin relaxation time, T2, and the fractional intensity, fH, of
250000 Observed Hm component Hint component Him component Fitting curve
each component was calculated according to measurements,
each
1
H-NMR relaxation component
was
deconvoluted on the basis of relaxation characteristics of protons which are closely related to the molecular mobility, so
200000
Intensity, a.u.
Equation 1. In the
150000 100000 50000
therefore the term “component” here does
0 0
not refer directly to particular molecules or groups of molecules. Figure 1 depicts a typical
solid
echo
signal
and
curve
Coal-C at 420℃
200
400
600
800
1000
Decay Time, µs Figure 1 Typical solid echo signal and curve deconvolution result of coal.
deconvolution result of coal. 3. 2. Effects of coal blending The echo signals of coal blends obtained during heat treatment were deconvoluted into three components: the rapidly decaying component, Him, described with a Gaussian function arising from the proton attached to immobile components in the coal; an intermediate component, Hint; and the most slowly decaying tail of the signal, Hm, described with an Exponential function arising from the proton attached to mobile components. It has already been ascertained that the deconvolution of the signal into three components is appropriate for evaluating the thermoplastic phenomenon of coal upon heating, and also that the thermoplastic phenomenon is closely related to the change of the Hm component, which has the highest molecular mobility5). Change in the fractional intensity of the Hm components, fHm, calculated from the signals during heat treatment are presented in Figure 2. For both of Base-1 and Base-2, the fluidity determined by the Gieseler plastometer varies in agreement with the variation in the fractional intensity of Hm, and the temperature of the maximum in the fluidity curve corresponds to the temperature at which fHm shows its maximum value. The fHm for Base-1 which consists of 75wt% of strongly caking coals shows higher value than for Base-2. The temperature at which fHm for Base-1 shows its maximum value is about Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
20˚C lower than that for Base-2. The temperature dependence of Spin-Sipn relaxation time for the Hm, T2Hm, is shown in Figure 3. In the thermoplastic temperature range, the T2Hm for Base-1 maintains larger value than for Base-2. These results indicate that the necessity of an ample amount of strongly coking coal for sufficient termoplasticity of coal blend, furthermore, the thermoplasticity of coal is affected by the quantity and the quality of Hm component.
fHm, -
Base-1 Base-2
0.3
4.0 3.0
0.2
2.0
0.1
1.0
0 100
200
300
400
500
Base-1 Base-2
Log(Fluidity/ddpm)
0.4
80
5.0 Base-1 Base-2
60
T2Hm, µs
0.5
20
0 100
0.0 600
200
300
400
500
600
Temperature, ℃
Temperature, ℃ Figure 2 Correspondence between fHm and Gieseler fluidity as a function of temperature.
40
Figure 3 Temperature dependence of T2Hm for coal blends.
3.3. Effects of HPC addition As described above, compared with Base-1 which consist of 75wt% of strongly coking coal, the thermoplasticity of Base-2 is insufficient. In order to improve the thermoplastic properties of Base-2, coal-B was replaced with HPC. Temperature dependence of the fHm for Base-2 and Base-2 with HPC is plotted in Figure 4. The fHm for Base-2 increase with increase in the amount of HPC addition. The maximum temperature of fHm shifts to lower temperature with HPC addition. The fHm for B1+HPC10% shows almost the same maximum value as the fHm for Base-1 which is shown in Figure 2. Figure 5 depicts the variation of T2Hm for Base-2 and HPC added Base-2. In addition to the T2Hm peak at around 440˚C, new peak at below 400˚C appear with HPC addition. This peak might be result from thermal plasticity of HPC. The T2Hm value increases with increase in the amount of HPC addition. Thus, the thermoplastic properties of Base-2 have been improved not only quantitatively but also qualitatively with HPC addition. The strength of coke can be evaluated with drum index, DI, number. The DI15015 means the percentage of remaining +15mm square hole after the impact of 150 revolutions. The DI15015 for Base-2 is improved from 77.4 to 85.4 with 10wt% of HPC addition, Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
B2+HPC10%. The DI15015 for B2+HPC10% is comparable to that for Base-1 of 84.0. The improvement of the coking phenomenon of Base-2 with HPC addition can be attributed to the quantitative and qualitative change of Hm component.
fHm, -
0.4 0.3
80
Base-2 B2+HPC5% B2+HPC10% B2+HPC15% B2+HPC20%
60
T2Hm, µs
0.5
0.2
20
0.1 0.0 100
40
200
300
400
500
0 100
600
Temperature, ℃ Figure 4 Temperature dependence of fHm for Base-2 and Base-2 with HPC.
Base-2 B2+HPC5% B2+HPC10% B2+HPC15% B2+HPC20% 200
300
400
500
600
Temperature, ℃ Figure 5 Variation of T2Hm for Base-2 and HPC added Base-2.
4. Summry The information obtained by means of 1H-NMR relaxation measurements of coal blend with HPC are listed as follows. 1. The thermoplastisity of coal can be evaluated both quantitatively and qualitatively with high temperature in-situ 1H-NMR relaxation measurement. 2. There is a needs for an ample amount of strongly coking coal for sufficient termoplasticity of coal blend, furthermore, the thermoplasticity of coal is affected by the quantity and the quality of Hm component. 3. The thermoplastic properties of coal blend are able to improve not only quantitatively but also qualitatively with HPC addition. 4. The improvement of the coking phenomenon of coal blend with HPC is attributed to the quantitative and qualitative change of Hm component. Acknowledgement This study was carried out as a part of Japanese national project called COURSE50 (CO2 Ultimate Reduction in Steelmaking process by innovative technology for cool Earth 50). We thank NEDO for the support of this study.
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Oviedo ICCS&T 2011. Extended Abstract
References 1. van D.W.Krevelen: Coal, 3rd revised ed., Elsevier, Amsterdam, (1993), Chapters 23, 24 2. L.J.Lynch, D.S.Webster, N.A.Bacon and W.A.Barton: Magnetic Resonance; Introduction, Advanced Topics and Applications to Fossil Energy, NATO Adv. Study Inst. Ser., ed. By L.Petrakis, J.P.Fraissard, Reidel Publ., Dordrecht, Netherlands, (1984), 617 3. J.G.Powles and P.Mansfield: Phys. Lett., 2(1962), 58 4. J.G.Powles and J.H.Strahge: Proc. Phys. Soc. London, 6(1963), 82 5. H. Kumagai, K. Tanabe, and K.Saito: 1H-NMR study of Relaxation Mechanisms of Coal Aggregate in Structure and Thermoplasticity of Coal, Nova Science, (2005), 35
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Oviedo ICCS&T 2011. Extended Abstract
A Systematic Study of the effects of Pyrolysis Conditions on Coal Devolatilisation M A Kochanek1, D G Roberts*1, B Garten2, S Russig2, and D J Harris1 1 2
CSIRO Energy Technology, Brisbane QLD, AUSTRALIA
Department of Energy Process Engineering and Chemical Engineering, TU Bergakademie Freiberg, GERMANY
ABSTRACT The effects of pressure and temperature on specific aspects of the devolatilisation process are generally understood; however, there remains considerable uncertainty associated with any predictions of coal pyrolysis behaviour under intense, entrained flow gasification conditions. The net effects of temperature, pressure, and heating rate on volatile yields and char structure are difficult to predict with any certainty, and how such behaviour is affected by coal properties is also unclear. This paper, as part of a wider study into high pressure, high temperature coal devolatilisation and char formation, presents some results of a systematic study into the effects of temperature and pressure on volatile yields and char properties. New data on volatile yields as a function of temperature and pressure are presented, and chars formed are studied for their physical characteristics and reactivity to CO2 and H2O. Whilst the separate effects of temperature and pressure on volatile yields are, in general, consistent with previous work, it is shown that the effects of increasing pressure and temperature are strongly influenced by coal type, and that there is some interaction between the two (such that effects of pressure are different at different temperatures). More work is required to clarify the impacts of these two important parameters on coal pyrolysis behaviour and char formation.
1
INTRODUCTION
The competing effects of pressure, temperature, and heating rate on coal devolatilisation make understanding coal-specific pyrolysis behaviour under gasification conditions difficult. It is generally understood that increasing pressure decreases volatile yields, and that increasing temperature increases volatile yields. The coal-specific nature of these effects, however, means that predicting the net outcome of these (and other) phenomena for a specific coal (under specific gasification conditions) is a difficult task.
*
Corresponding author:
[email protected] Oviedo ICCS&T 2011. Extended Abstract This issue is particularly important when models of the gasification system require such information so they can be used with some confidence for fuel assessment or process optimisation studies. Volatile matter data from proximate assays are often used as part of an assessment of a coal for use in entrained flow gasification; however, the significant differences in the conditions of the standard to those found in practical gasifiers makes this an unreliable indicator. It has also been shown that the reactivity of the chars produced can be as significant to overall gasification behaviour as the volatile yield, therefore understanding the impact of pyrolysis conditions on char properties is also important. This paper presents some new experimental measurements made as part of a wider study whereby the effects of temperature, heating rate, and pressure on volatile yields and char properties are investigated using a suite of coals ranging in rank from lignite to semi-anthracite.
2 2.1
EXPERIMENTAL Coal selection
Two separate studies were performed. In the first study, the volatile yields of six coals with ranks ranging from lignite to semi-anthracite were measured as a function of pyrolysis temperature and pressure. In the second study, the reactivity and surface area of selected chars formed from two (lignite and sub-bituminous) of the coals investigated in the first study were measured. The coals used in these studies were crushed and sieved to the particle size range -260+105 μm. The results of proximate analysis of the coals used in the volatile yield study are shown in Table 1. Rank
Lignite
Coal
TUF102 40.6 5.1 30.8 23.5 8.6 51.9 39.6
Moisture % (ar) Ash % (ar) VM % (ar) FC % (ar) Ash % (db) VM % (db) FC % (db)
Sub‐Bituminous
CRC252 8.7 10.1 40.1 41.1 11.1 43.9 45.0
CRC704 7.0 9.7 42.4 40.9 10.4 45.6 44.0
CRC701 25.0 5.3 28.3 41.4 7.1 37.7 55.2
Bituminous
Semi‐ Anthracite
CRC272 4.0 9.6 34.8 51.6 10.0 36.3 53.8
CRC703 6.6 9.5 7.4 76.5 10.2 7.9 81.9
Table 1: Proximate analysis of coals used in this study.
2.2
High Pressure Pyrolysis: Wire Mesh Reactor
In the first study the volatile yields of the six pulverised and sieved coals were performed in a Wire Mesh Reactor (WMR) using a procedure similar to that outlined previously [1, 2]. The following conditions were used to produce six volatile yield measurements for each coal: • • •
Pressure: 1bar, 10bar and 20bar Heating rate: 1000°C/s Hold time: 10s
Oviedo ICCS&T 2011. Extended Abstract • • •
Hold temperature: 900°C, 1100°C Initial dry sample mass: 20 to 30mg Sweep gas: High purity helium flow rate of 6 L/min at standard conditions to prevent secondary reactions
In the second study, chars produced in the pyrolysis experiments from coals TUF102 and CRC704 were characterised further. For each sample, the surface area and low-temperature reactivity were investigated using established techniques [2, 3]. 2.3
Char Characterisation
2.3.1
Surface Area
The CO2 adsorption isotherm for each pyrolysis char was measured non-destructively using a Tristar II 3020 surface area analyser. Adsorption isotherm analysis using the DubininRadushkevich (DR) equation was used to determine each char’s surface area. Char sample masses of 200±100mg were required for the surface area analysis. To produce the required quantity of char, the chars from multiple identical WMR experiments were combined to form a single sample. 2.3.2
Gasification Reactivity
Char reaction rates were measured at low temperatures, under experimental conditions designed to allow determination of ‘intrinsic’ reaction rates; that is, those obtained under conditions where diffusion through char porosity does not limit the reaction rate. A thermogravimetric analyser (TGA) was used to measure these rates using techniques previously described [2, 3]. The following conditions were used to measure the gasification reactivity of the chars: • • • •
Pressure: 5bar and 15bar Reactant gas: CO2 or H2O at a flow rate of 3 L/min at standard conditions with 100% concentration Temperature: 900°C for CO2 and 800°C for H2O reactant gas Initial dry sample mass: 40±20mg
The specific reaction rate is calculated as a function of conversion using the equation:
rate = −
1 dw ⋅ w dt
g g-1 s-1
where w is the instantaneous mass of reacting sample. The reaction rates used for analysis are initial reaction rates, determined on a specific (as measured) and intrinsic (normalised to surface area) basis.
Oviedo ICCS&T 2011. Extended Abstract 3 3.1
RESULTS AND DISCUSSION Volatile Yields
Figure 1 shows the effects of pyrolysis pressure and temperature on the volatile yields of the six coals used in this study. The results are presented as a ‘volatile enhancement’, which is a representation of the difference between the yield measured under the experimental conditions (volatile yield) and that determined in a proximate analysis (volatile matter). Here, volatile enhancement is calculated by:
⎛ %VY − %VM ⎞ VE = ⎜ ⎟ × 100 %VM ⎝ ⎠ Where %VY is volatile yield as determined under experimental conditions, and %VM volatile matter as determined by proximate analysis performed to Australian Standard AS1038A.
Figure 1: Volatile yield enhancement for a range of coals as a function of pressure at 900°C and 1100°C and with a heating rate of 1000°C/s.
For the lignite, the volatile enhancement is positive (i.e. more volatiles are released under these conditions than suggested by the proximate analysis) and most significant of all the samples. However this does not seem to be an effect of temperature or pressure, suggesting that perhaps heating rate is important for this coal. The absolute vales of volatile enhancement for the subbituminous and bituminous coals were less than that for the lignite; however the effects of temperature and pressure were clearer. This is also true for the semi-anthracite. At 900°C, the samples are readily differentiated in terms of the volatile enhancement, with lower rank coals having a greater VE than the higher ranked coals. These coal-specific effects are significantly reduced at 1100°C, however, with all coals (except for the lignite) having similar VE data as a function of pressure. These results suggest that significant differences between samples in terms of proximate volatile matter need not necessarily translate to real differences in volatile release under process conditions. For lignite samples, fast heating rate pyrolysis is likely to lead to a significantly
Oviedo ICCS&T 2011. Extended Abstract greater release of volatiles. For bituminous and sub-bituminous samples the effect is less certain, with interactions apparent between the effects of temperature and pressure; however the differences between different coal types appears to be significantly reduced at the higher temperature. 3.2
Surface Areas
Figure 2 shows measurements of char surface area, determined using CO2 adsorption at 0°C, for chars made from CRC704 and TUF102. Both coals produce chars with high surface areas, consistent with gasification chars studied in previous work [4-6]. For chars from TUF102, there is a clear effect of increasing temperature, with chars made at 1100°C having significantly less surface area than chars made at 900°C. For CRC704, this effect is less apparent. There is no strong effect of devolatilisation pressure on char surface area. Previous work [6] has suggested that for specific coals, increasing devolatilisation pressure can increase the surface area of the char produced from pyrolysis (the previous work was undertaken using flow reactors, suggesting that there may be a role of secondary reactions and/or partial reaction in the trends observed). A slight increase in surface area with increasing pyrolysis pressure is notable for the chars made from TUF102 at 900°C; the remaining sets of data suggest little effect, with some evidence to suggest a decrease in surface area with increasing pyrolysis pressure for CRC704 chars made at 1100°C. Ongoing work using the more extensive set of samples discussed above may lead to more clarity around this issue.
Figure 2: Char surface area (CO2) as a function of pyrolysis pressure at 900°C and 1100°C.
3.3
Char Reactivity
Figure 3-Figure 6 present specific and intrinsic reaction rate measurements of chars made from TUF102 and CRC704, to CO2 (at 900°C) and H2O (at 800°C). The surface areas discussed in the previous section were used to calculate initial intrinsic rate data from the measured specific reaction rates. Chars from TUF102 are consistently more reactive than those from CRC704; this is consistent with the expectation that lignite chars are, in general, more reactive than chars from sub-
Oviedo ICCS&T 2011. Extended Abstract bituminous coals. Figure 3 and Figure 4 show that in general, increasing devolatilisation pressure decreases the measured reaction rate to both CO2 and H2O for chars made from both coals. This effect is quite clear for the CO2 data (Figure 3), and the data for H2O suggest that this effect is less significant for the chars made at higher temperatures (Figure 4). The effect of pyrolysis temperature is clear: consistent with the significant amount of work reported in the literature, chars made at high temperatures have lower reaction rates to CO2 and H2O than chars made at lower temperatures. Surface areas can account for some of this difference; however as will be shown in the next section, temperature is also likely to significantly affect the crystalline nature of the carbon matrix, and consequently the intrinsic reactivity of the chars.
Figure 3: Specific reaction rates of chars made from CRC704 and TUF 102 at 900°C and 1100°C, to 5 and 15 bar CO2 at 900°C.
Figure 4: Specific reaction rates of chars made from CRC704 and TUF 102 at 900°C and 1100°C, to 5 and 15 bar H2O at 800°C.
Oviedo ICCS&T 2011. Extended Abstract Intrinsic reaction rates are shown in Figure 5 and Figure 6. As with the specific rate data discussed above, the lignite chars are also more reactive than the coal chars in both reactants on an intrinsic basis, reinforcing the notion that factors other than surface area alone (such as catalysts, carbon crystallinity, etc) are significant in determining the reactivity of lignite chars. For chars reacting with CO2, increasing pyrolysis pressure at 900°C leads to a decrease in intrinsic reactivity, consistent with those observed above for specific reaction rate data. This observation is far less clear for the chars produced at 1100°C, suggesting some interaction between the effects of temperature and pressure on the pyrolysis process, in particular the char formation aspects. This will be explored in more detail in ongoing work.
Figure 5: Intrinsic reaction rates of chars made from CRC704 and TUF 102 at 900°C and 1100°C, to 5 and 15 bar CO2 at 900°C.
Figure 6: Intrinsic reaction rates of chars made from CRC704 and TUF 102 at 900°C and 1100°C, to 5 and 15 bar H2O at 800°C.
Oviedo ICCS&T 2011. Extended Abstract 4
CONCLUSIONS
This work has presented some results from a wider study investigating the pyrolysis behaviour of coals under entrained flow gasification conditions. This work focussed on the volatile yields (and how they are affected by temperature and pressure) and the reactivity of the chars produced. Consistent with previous investigations, increasing pyrolysis temperature increased the volatile yields. Whilst increasing the pyrolysis pressure generally decreases the volatile yields, the effect of pressure is strongly dependent on coal type and pyrolysis temperature. There is some evidence of interactions between these variables; for example, increasing temperature from 900 to 1100°C removes a lot of the influence of coal type on volatile yields, in particular for the sub-bituminous and bituminous coals used in this study. For the lignite sample, the volatile yields were significantly greater than those expected based on proximate analysis, although the data presented here showed very little impact of temperature or pressure. This suggests that heating rate is a particularly significant variable determining the volatile yields from lignite pyrolysis. Heating rate is not a variable that was explicitly studied here; however, it is a parameter that will be studied in more detail in ongoing work. Chars made at higher temperatures were less reactive to CO2 and H2O than those made at lower temperatures, consistent with literature studies. Increasing devolatilisation pressure generally led to less reactive chars (to both CO2 and H2O) on both a specific (as-measured) and intrinsic (normalised to surface area) basis. This was more apparent for chars made at 900°C than those made at 1100°C, and suggests a pressure effect on the carbon structure (or chemical composition) of the chars.
5
REFERENCES
1.
C J Mill, D J Harris and J F Stubington. Pyrolysis of Fine Coal Particles at High Heating Rates and High Pressure, 8th Australian Coal Science Conference, Sydney (1998).
2.
M D Kelly, D J Harris, D G Roberts and C J Mill. Volatile Yield and Char Gasification Reactivity of Australian Coals at Elevated Pressures, 18th Annual International Pittsburgh Coal Conference, Newcastle, Australia (2001).
3.
D G Roberts and D J Harris. The Role of Bench-Scale Reactivity Data in the Assessment of Coals for use in Gasification, 12th International Conference on Coal Science, Cairns, Queensland, Australia (2003).
4.
L M Lu, C H Kong, V Sahajwalla and D Harris. Char structural ordering during pyrolysis and combustion and its influence on char reactivity, Fuel 81 1215- 1225 (2002).
5.
D G Roberts and D J Harris. Char Gasification in Mixtures of CO2 and H2O: Competition and Inhibition, Fuel 86(17-18) 2672-2678 (2007).
6.
D G Roberts, D J Harris and T F Wall. On the Effects of High Pressure and Heating Rate during Coal Pyrolysis on Char Gasification Reactivity, Energy and Fuels 17(4) 887-895 (2003).
Oviedo ICCS&T 2011. Extended Abstract
A Relationship Between the Structures of Graphitized Anthracites and Isotropic Graphite M.S. Nyathi, C.E. Burgess Clifford, and H.H. Schobert Department of Energy and Mineral Engineering and The EMS Energy Institute, The Pennsylvania State University, University Park, PA, USA.
[email protected] Abstract Two anthracites from Pennsylvania (USA) were evaluated as possible filler materials for the production of isotropic or near-isotropic graphites. Native and demineralised samples were graphitized at 3000°. Products were characterized by an array of analytical techniques, including X-ray diffraction, Raman spectroscopy, and temperatureprogrammed oxidation. The anthracite of higher rank produced, upon graphitization, materials with better-developed crystalline structure. Demineralization of either anthracite prior to graphitization yielded products having better degree of graphitization, density, and oxidation resistance (in temperature-programmed oxidation). The enhancement of la in graphitization of native anthracites was facilitated by formation and subsequent decomposition of silicon carbide. Graphitizing the lower-rank sample gave a product of lower anisotropy, closer to an isotropic material that would be more desirable as starting material for a nuclear graphite. Chances of obtaining a near-isotropic material are also enhanced by demineralizing the samples before graphitization.
1. Introduction We and our colleagues have been investigating the non-fuel uses of anthracitic coals for some time, with a focus on the anthracites of Pennsylvania in the United States [1-6]. Much of our previous work has been directed to graphitization of molded or extruded formulations of anthracite and coal tar pitch, for use in electrode or specialty applications. Currently we are investigating the potential of producing isotropic, or nearisotropic graphites from anthracites for, e.g., applications as nuclear graphite. A general approach to the production of finished synthetic graphite artifacts involves use of a graphtizable carbonaceous solid, such as petroleum coke, as filler, and mixing the coke with a binder of coal tar pitch [7]. This mixture is formed into the desired shape, e.g. by extrusion or molding. The shaped item is baked. If needed, the baked item is impregnated with petroleum pitch and re-baked. Several impregnation and Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
re-baking cycles may be required. When the density of the baked item is adequate, it is graphitized, and finally, machined to the desired size. The purpose of the work reported here was to investigate the factors affecting the graphitization behavior of two anthracites to assess their potential for use as fillers in the production of nuclear graphite. We did not investigate the blending of the anthracites with coal tar pitch, nor measure some of the physical properties important for showing that a particular graphite is fit for use in nuclear applications. Thus the focus of this work is on evaluation of prospective new filler materials, and not on actually producing nuclear graphite.
2. Experimental Section Extensive details on the selection, characterization, graphitization, and analysis of the samples are available elsewhere [8]. Here we present a brief overview of the principal aspects of the experimental work. Samples. Two anthracites were used in this work. Their characteristics are given in Table 1. The samples PSOC-1515 and DECS-21 were obtained from the Penn State Coal Sample Bank. Demineralization of PSOC and DECS samples was performed following the earlier work of Pappano [6]. Table 1. Characteristics of the anthracites used in this study. Proximate analysis, dry basis, % Fixed carbon Volatile matter Ash Ultimate analysis, daf basis, % Carbon Hydrogen Nitrogen Sulfur Oxygen
DECS-21
PSOC-1515
84.34 4.51 11.15
62.39 8.44 29.17
90.3 4.0 0.8 0.6 4.3
88.1 3.9 1.1 0.8 6.1
Graphitization. Graphitization of the PSOC and DECS samples was performed at GrafTech, Parma, Ohio, USA, at was 3000°C. Analyses and characterization. X-ray diffraction analysis was performed using a PANalytical X’Pert Pro powder diffractometer and Cu-Kα radiation. Raman spectroscopic measurements were obtained using a WITec CRM200 argon-laser spectrometer. Temperature-programmed oxidation experiments were run in a LECO
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Oviedo ICCS&T 2011. Extended Abstract
RC612 multiphase carbon analyzer, with 750 mL/min oxygen flow, heat-up rate of 30°/min to a maximum temperature of 900°, and hold at 900° for 6 min. BET surface area was measured with a Micromeritics ASAP20 instrument, using nitrogen as the adsorbate at 78 K and densities with a Qunatichrome Multipycnometer MVP-1 in helium.
3. Results and Discussion X-ray diffraction. The X-ray diffraction results of graphitized native and demineralized PSOC and DECS anthracites show the characteristic diffraction patterns of graphite, Figure 1. DECS21‐DM DECS21 PSOC1515
Intensity, a.u.
PSOC1515‐DM
10
20
30
40
50
60
70
80
90
2 theta, degrees
Figure 1. X-ray diffractograms of graphitized native and demineralized PSOC-1515 and DECS-21 anthracites. All diffractograms show a sharp, intense, narrow (002) peak at 2Θ = 26.4°. Also important is the (112) peak at 2Θ ≈ 83°, since peaks for which all of the Miller indices are non-zero signal three-dimensionality in the structure. The structural parameters are summarized in Table 2.
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Oviedo ICCS&T 2011. Extended Abstract
Table 2. X-ray diffraction parameters for anthracites graphitized at 3000°. Samples identified with –DM suffix were demineralized prior to graphitization. Data on native anthracites are provided for comparison. Sample
Status
PSOC1515 PSOC1515-DM DECS21 DECS21-DM PSOC1515 PSOC1515-DM DECS21 DECS21-DM
Native Native Native Native Graphitized Graphitized Graphitized Graphitized
d002, nm 0.3522 0.3521 0.3521 0.3498 0.3371 0.3365 0.3369 0.3361
lc, nm
la, nm
DOG
p
N
lc /la
1.4 2.8 1.7 3.1 46.0 48.0 53.6 58.0
60.9 59.1 62.4 61.2
0.7930 0.8162 0.8244 0.8267
0.2069 0.1837 0.1755 0.1732
136 142 159 172
0.76 0.80 0.85 0.94
Heat treatment at 3000° provides marked improvement in d002 and lc. DECS-21 shows slightly better structural development, as indicated by, e.g., d-spacing, degree of graphitization (DOG), and probability of random orientation between layer planes (p). TEM observation of the native anthracites showed that DECS-21 had a better developed microstructure and more flattened pores than PSOC-1515. This is consistent with reports of a relationship between graphitizability and preferred planar orientation [9,10], and consistent with reports of relationships with porosity or pore shape [10-13]. For these two anthracites, slightly better structural development is obtained using the demineralized samples; i.e., there is no evidence for in situ catalytic graphitization by aluminum compounds, or aluminum-rich minerals. Although it is well established that some minerals catalyze graphitization of anthracites, in this case X-ray analysis showed that the minerals in these anthracites were dominated by kaolinite. It has been established that kaolinite does not catalyze graphitization [6], likely because it transforms to a highly stable mullite structure during calcination or heat treatment [13].. Formation of mullite was confirmed by X-ray analysis of the calcined anthracites. Nonetheless, a silicon carbide phase that formed during graphitization of the native anthracites, appeared to enhance la, consistent with earlier work [6] on catalytic graphitization of Pennsylvania anthracites. The measured densities of the graphitized samples agree well with the degree of graphitization (DOG) as measured by X-ray diffraction, as shown in Table 3.
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Oviedo ICCS&T 2011. Extended Abstract
Table 3. Relationship of densities and degrees of graphitization of graphitized anthracite samples. Sample Density, g/cm3 DOG PSOC-1515 1.78 0.7930 PSOC-1515-DM 1.85 0.8162 DECS-21 1.89 0.8244 DECS-21-DM 2.01 0.8267 Raman spectroscopy confirms the results obtained by X-ray diffraction. Table 4 provides a comparison of spectroscopic results for native and graphitized anthracites. Table 4. Raman spectroscopy parameters for native and graphitized anthracites Sample
Status
PSOC1515 PSOC1515-DM DECS21 DECS21-DM PSOC1515 PSOC1515-DM DECS21 DECS21-DM
Native Native Native Native Graphitized Graphitized Graphitized Graphitized
FWHM (cm-1) D-band G-band 387.93 74.43 386.76 73.86 386.11 73.44 385.07 72.69 50.86 25.04 53.25 27.86 51.68 23.86 50.12 24.42
ID / (ID+IG) (%) 42.03 41.78 41.52 40.44 9.69 13.22 5.54 9.15
Products from DECS-21 have lower disorder parameters than those produced from PSOC-1515. In addition, demineralization leads to an increase in the demineralization parameter. The disorder parameters measured by Raman spectroscopy relate to changes in the value of la, as shown in Figure 2.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 2. Relationship of la measured by X-ray diffraction to Raman disorder factors. Temperature-programmed oxidation results are shown in Figure 3.
PSOC1515 DECS21
Intensity, a.u.
PSOC1515‐DM
100
DECS21‐DM
200
300
400
500 600 Temperature, oC
700
800
900
Figure 3. Temperature-programmed oxidation of graphitized samples of native and demineralized PSOC-1515 and DECS-21. Products from DECS-21 are less reactive (as indicated by a shift of peak position to Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
higher temperatures) than products from PSOC-1515. Further, products of graphitization of demineralized anthracites are less reactive than those from native anthracites. These oxidation results can be related to the degree of structural ordering, and in particular, the value of N, the number of carbon layer planes in a stacked crystallite. This relationship is illustrated in Figure 4.
Figure 4. Relationship between the oxidation reactivity, as measured by peak position in temperature programmed oxidation, and the number of stacked layer planes.
4. Summary and Conclusions The DECS-21 sample, which is of higher rank than PSOC-1515, has a more developed lamellar structure. This is particularly noticeable in transmission electron microscopy, results of which are presented elsewhere [8]. Upon graphitization, the anthracite with the more developed structure, i.e., DECS-21, produces materials with better-developed crystalline structure. Demineralization of either anthracite prior to graphitization yields products having better degree of graphitization, density, and oxidation resistance (in temperature-programmed oxidation). However, the enhancement of la in graphitization of native anthracites appears to be facilitated by formation and subsequent decomposition of silicon carbide, consistent with earlier work from our group [6]. Graphitizing the lower-rank sample, i.e., PSOC-1515, this gives a product of Submit before May 15th to
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lower anisotropy, closer to an isotropic material that would be more desirable as starting material for a nuclear graphite. Chances of obtaining a near-isotropic material are also enhanced by demineralizing the samples before graphitization.
Acknowledgements Various aspects of this work were supported by the U.S. Air Force Office of Scientific Research, and the U.S. Department of Energy Consortium for Premium Carbon Products from Coal, and we gratefully acknowledge this support.
References [1] Gergova K, Eser S, Schobert HH. Preparation and characterization of activated carbon from anthracite. Energy Fuels 1993;7:661-8. [2] Gergova K, Eser S, Schobert HH, Klimkiewicz M, Brown PW. Environmental scanning electron microscopy of activated carbon produced from anthracite by one-step pyrolysis activation. Fuel 1995;74:1042-8. [3] Atria JV, Rusinko F, Schobert HH. Structural ordering of Pennsylvania anthracite on heat treatment to 2000-2900°C. Energy Fuels 2002;16:1343-7. [4] Andrésen JM, Burgess CE, Pappano PJ, Schobert HH. New directions for non-fuel uses of anthracite. Fuel Proc. Technol.2004;85:1373-92. [5] Pappano PJ, Rusinko F, Schobert HH, Struble DP. Dependence of physical properties of isostatically molded graphites on crystallite height. Carbon 2004;42:30079. [6] Pappano PJ, Schobert HH. Effect of natural mineral inclusions on the graphitizability of a Pennsylvania anthracite. Energy Fuels 2009;23:422-8. [7] Pierson, HO. Handbook of carbon, graphite, diamond and fullerenes. Park Ridge, NJ: Noyes; 1993. [8] Nyathi, MS. Evaluation of coal-petroleum blend coke and anthracites as precursors to isotropic or near-isotropic graphite. PhD Dissertation, University Park: The Pennsylvania State University; 2011. [9] Oberlin A, Terriere G. Graphitization studies of anthracites by high resolution electron microscopy. Carbon 1975; 13: 367-76. [10] Blanche C, Rouzaud JN, Dumas D. Proceedings of the 22nd biennial conference on carbon. American Carbon Society 1995;695. [11] Atria JV. Novel approach to the production of graphite from anthracite. MS Thesis, Submit before May 15th to
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University Park: The Pennsylvania State University; 1995. [12] Pusz S, Kwiecinska BK, Duber S. Textural transformation of thermally treated anthracites. Int. J. Coal Geol. 2003;54:115-23. [13] Gonzalez D, Montes-Moran MA, Suarez-Ruiz I; Garcia AB. Structural characterization of graphite materials prepared from anthracites of different characteristics: a comparative analysis. Energy Fuels 2004;18:365-70.
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Benzene and toluene adsorption on high surface area activated carbons obtained from an anthrecene oil derivative N.G. Asenjo1, P. Álvarez, C. Blanco, R. Santamaría, M. Granda, R. Menéndez Instituto Nacional del Carbón (CSIC), c/ Francisco Pintado Fe, 26 – 33011 Oviedo (Spain) – Tel. +34 985119090; Fax. +34 985297662 1
[email protected] Abstract A carbon obtained from a coal-derived pitch was chemically activated to produce a high surface area (∼3,200 m2/g) carbon with a porosity made up of both micropores and mesopores. Its adsorption capacities under the conditions tested in this work were found to be among the highest ever reported in literature, reaching values of 860 mg/g and 1,200 mg/g for the adsorption of benzene and toluene, respectively, and 1,200 mg/g for the combined adsorption of benzene and toluene from an industrial wastewater. Such high values are only possible if the entire pore system, including the mesopore fraction, is involved in the adsorption process. The filling of almost the entire pore system is thought to be due to the high relative concentrations of the tested solutions, resulting from the low saturation concentration values for benzene and toluene, which were obtained by fitting the adsorption data to the BET equation in liquid phase. The kinetics of adsorption in the batch experiments which were conducted in a syringe-like adsorption chamber was observed to proceed in accordance with the pseudo-second order kinetic model. The combined presence of micropores and mesopores in the material is thought to be the key to the high kinetic performance, which was outstanding in a comparison with other porous materials reported in the literature.
1. Introduction The main objective of this work is to analyze the performance of an anthracene oil-based activated carbon in the liquid phase adsorption of benzene and/or toluene from synthetic solutions and an industrial wastewater. The total adsorption capacities will be analyzed and compared with those reported in the literature for other systems tested under gas and liquid phase conditions. Special emphasis will be placed on a kinetic analysis of the adsorption process, which will serve as a basis for comparison with other adsorbent materials described in the literature. A combination of equilibrium and kinetic analyses
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allows us to conclude that, under the conditions of this study, the coal-derived activated carbon offers the best results ever reported in terms of adsorption capacity and kinetic rate
2. Experimental Section To produce the activated carbon an anthracene oil-based coke was subjected to chemical activation with anhydrous KOH at a weight ratio of 1:5, carbonized at 700 ºC in N2, and thoroughly washed with HCl and water. The textural characteristics of the samples were characterized by means of N2 adsorption at 77 K and CO2 adsorption at 273 K. For the kinetic experiments a set up comprising a purpose-designed syringe-like adsorption chamber was employed. Four different aqueous solutions were analyzed: synthetic aqueous solutions of (i) benzene (190-210 ppm), (ii) toluene (175 225 ppm), (iii) a mixture of both (175-225 ppm each) and (iv) an industrial wastewater from a local chemical company containing a mixture of benzene (~120 ppm) and toluene (~120 ppm), together with trace amounts of chloroform. The collected liquid samples were analyzed by means of High Performance Liquid Chromatography (HPLC) (Agilent 1100 series apparatus) and UV spectrometer (Shimadzu UV 1800). The amount of benzene and toluene adsorbed on the activated carbon at equilibrium, be, and the concentration of adsorbate in solution at equilibrium, Ce, were obtained from the kinetic data experiments at the longest time (always over 10 min).
3. Results and discussion The activated carbon has a very high volume of micropores, slightly over 1 cm3/g and a high mesopore volume (~0.6 cm3/g) which is a specific characteristic of the material developed here. At the other end of the pore distribution, the narrow microporosity (below 0.7 nm) displays a total volume of ~0.6 cm3/g. Figure 1 shows the benzene and toluene adsorption isotherms for the aqueous solutions. The results for the industrial wastewater (Figure 1, solid squares) indicate that benzene was adsorbed up to ~400-500 mg/g, whereas toluene was simultaneously adsorbed up to ~700 mg/g. Therefore, the maximum combined adsorption of both aromatic species was around 1,200 mg/g. Similar values were obtained for the synthetic mixed solution (Figure 1, empty squares), indicating that the presence of other substances in the industrial wastewater did not seem to significantly affect the performance of the adsorbent.
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Single component Synthetic water (210 ppm toluene)
1000
Industrial wastewater (115 ppm toluene)
800 be (mg/g)
C s=1,800 ppm (solubility)
600
Cs=223 ppm
400 200 Benzene adsorption isotherms 0 0
20
40
60
80
100
120
140
Ce (ppm) Single component Synthetic mixture (200 ppm benzene) Industrial wastewater (120 ppm benzene)
1400 1200
Cs=470 ppm (solubility)
be (mg/g)
1000
C s=69 ppm
800 600 400 200
Toluene adsorption isotherms 0 0
10
20
30
40
50
60
Ce (ppm)
Figure 1. Benzene and toluene adsorption isotherms for the activated carbon analyzed in different adsorption media. Lines through the single component points represent fittings to BET equation for Cs values equal to the solubility values of the single components in water at RT (dashed lines) and for Cs values that maximize the R2 coefficient (continuous lines)
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For the single component solutions (Figure 1, solid circles), the maximum amounts of adsorbed benzene and toluene (non competitive adsorption) reached ~870 and ~1,200 mg/g, respectively. These results evidence the high adsorption performance of this activated carbon and its ability to remove both molecules from polluted water streams with equal efficiency. Furthermore, these high capacities prove that adsorption is not restricted to the narrow microporosity of the activated carbon but involves the entire pore system. The use of the entire porosity of the adsorbent used in this study might imply high values of the relative concentrations (Ce/Cs) of benzene and toluene in the solutions employed in this work. Figure 1 shows the fitting of BET equation to the adsorption curves for the single components in two different cases; (a) where Cs=S and (b) where Cs is a variable that is modified to maximize the value of R2. Only when Cs is adjusted to maximize R2, the fittings are acceptable. By applying the Cs values obtained in this case (Figure 1), the relative concentrations for the highest values of adsorption capacity become 0.53 and 0.63 for benzene and toluene, respectively. Thus, in terms of the adsorption isotherm, the liquid phase equilibria take place at relatively high values of relative concentration, making the adsorption of aromatics in liquid phase more similar to that in saturated gas streams than to that in diluted gas streams. Consequently almost total occupation of the activated carbon pores can be expected, as our results indeed confirm. The results from all the batch kinetic experiments were found to follow a pseudo-second order kinetic model with the kinetic values obtained from the pseudo-second order kinetic model, it is possible to compare the kinetic performance of the anthracene oilbased activated carbon with that of other materials reported in the literature [1-6]. For the purpose of this comparison the best data representation is that offered by Figure 2, which shows the variation of kSE with be for toluene adsorption. Points on the right of a given isokinetic line (diagonal lines) are thought to represent faster adsorption systems than points on the left of the same isokinetic line. The effect of the presence of benzene in solution does not affect the toluene adsorption rates of our activated carbon; in fact the kinetic performance of the activated carbon is almost independent of the type of solution analyzed. In this figure, the kinetic points obtained for the different materials are grouped according to their main textural properties. From the pseudo-isokinetic lines, it can be seen that the adsorption rates of the microporous materials are lower than
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Figure 2. Variation of the pseudo-second order kinetic rate constant (kSE) with the value of be calculated by means of the PSOKM for the toluene adsorption experiments carried out in this work in different adsorption media (legend), together with the kinetic data obtained from the literature values. that of the mesoporous material, and that this is in turn lower than the adsorption rates achieved by the coal derived activated carbon used in this study, whose porosity is made up of both micropores and mesopores. The results of our work suggest that mesopores act both as a transport and as a concentrating medium and thus enhance the adsorption rate in the micropore system. This could be the explanation for the outstanding performance of the coal-derived activated carbon in the adsorption of benzene and toluene from aqueous solutions.
4. Conclusions The benzene and toluene adsorption capacity of the anthracene oil-based activated carbon is among the highest ever reported in the literature (860 mg/g for benzene, 1,200 mg/g for toluene and 1,200 mg/g for a mixture of both molecules in solution). The extensive pore filling is thought to be due to the high relative concentrations of the tested solutions, resulting from the low saturation concentration values for benzene and
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toluene. The adsorption capacities of the activated carbon were similar both for the synthetic mixtures and for the industrial wastewater. The kinetics of adsorption in the batch experiments was observed to follow the pseudo-second order kinetic model. The combined presence of micropores and mesopores in the activated carbon is thought to be the key to its high kinetic performance, which can be described as outstanding when compared with other porous materials reported in the literature.
Acknowledgments The authors thank the Spanish Science and Innovation Ministry (CONSOLIDER INGENIO 2010, Ref. CSD2009-00050) for financial support and Dr. Patricia Álvarez for her Ramón y Cajal contract.
References [1] Lesage G, Sperandio M, Tiruta-Barna L. Analysis and modelling of non-equilibrium sorption of aromatic micro-pollutants on GAC with a multi-compartment dynamic model. Chem Eng J 2010:160(2):457-65. [2] Choi JW, Yang KS, Kim DJ, Lee CE. Adsorption of zinc and toluene by alginate complex impregnated with zeolite and activated carbon. Current Applied Physics 2009;9(3):694-7. [3] Lee SJ, Chung SG, Kim DJ, Lee CE, Choi JW. New method for determination of equilibrium/kinetic sorption parameters. Current Applied Physics 2009;9(6):1323-5. [4] Arora M, Snape I, Stevens GW. The effect of temperature on toluene sorption by granular activated carbon and its use in permeable reactive barriers in cold regions. Cold Regions Science and Technology 2011;66(1):12-6. [5] Su F, Lu C, Hu S. Adsorption of benzene, toluene, ethylbenzene and p-xylene by NaOCl-oxidized carbon nanotubes. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2010;353(1):83-91. [6] Wang D, McLaughlin E, Pfeffer R, Lin YS. Aqueous phase adsorption of toluene in a packed and fluidized bed of hydrophobic aerogels. Chem Eng J 2011;doi: 10.1016/j.cej.2011.02.014.
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Impact of biomass on char burn-out under air and oxy-fuel conditions
Timipere S. Farrow, Donglin Zhao, Chenggong Sun and Colin E. Snape
Department of Chemical & Environmental Engineering, Faculty of Engineering, University Park, Nottingham NG7 2RD, UK
[email protected] Abstract Although biomass co-firing is now well established in pulverised fuel (PF) combustion, there is little information available on how biomass affects coals during oxy-fuel firing. Therefore, this study involving thermo gravimetric analysis (TGA) and a drop tube furnace (DTF) examines the impact of co-firing biomass and coal under oxy-fuel and air fired conditions with particular emphasis on the catalytic effect of biomass-contained alkali and alkaline metals on coal char burnout. Sawdust and a South African coal, Kleinkopje have been used.
For the burn-out studies, the sawdust and coal chars
prepared in the DTF and under slow-heating conditions at different temperature were blended using a 50:50 mass ratio. The addition of the sawdust chars to the coal chars improved burnout and the effect was slightly more pronounced under oxy-fuel conditions. To confirm that the improved burnout rates arise from the catalytic effects of inorganic alkali and alkaline metals, the sawdust was extracted with 5M hydrochloric acid. The burn-out rates for the blends were reduced considerably and these were close to the predicted values.
1. Introduction For effective utilisation of the biomass and coal as pulverised fuel (PF), compatibility of the fuels during combustion is desirable and chemical interactions between the two fuels during co-firing could increase the carbon burnout of coal char, allowing the fly ash to meet up specification for other uses. Interactions between biomass and coal have been investigated during co-pyrolysis. For example, Haykiri-Acma and Yaman [1, 2] reported that synergetic interaction occurred during combustion of biomass and coal in air using TGA from ambient to 900oC. This effect has resulted in higher volatile yields [3, 4] . Presumably, the improved product yields may be dependent upon the contact time of the fuel particles, and the relative rates of pyrolysis of the different fuels, though blending
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ratios, temperature and hydrogen content in biomass could also influence interaction between the two fuels [5, 6]. While the synergetic interaction between biomass and coal in co-pyrolysis has been extensively studied, the limited literature exists on the impact of biomass char on coal char burnout during co-combustion or gasification. However, Kastanaki et al [7] assessed the combustion of biomass-coal char blend using non isothermal TGA with two coal types and different biomass fuels over a temperature range of 20-850 oC and at slow heating rate with biomass/coal chars blend ratios of 5:95; 10:90; 20:80 wt%. The results showed that the burnout times of the coal char was slightly reduced and the burnout (final) temperatures were lowered by 22-45 oC for 20 wt% biomass blends. Similar reports on biomass/coal char combustion and gasification have revealed some interaction depending on biomass type [8, 9]. However, these studies have not considered the effect of DTF biomass chars which simulates pulverised fuel combustion better than TGA with high temperatures, high heating rates and short residence times for coal char burnout being achieved. Additionally, the improved char reactivity which is likely to be the potential catalytic effect of biomass contained alkali and alkaline metals have not been fully investigated. Therefore, this paper examines how coal char burnout will be affected by the addition of biomass char prepared at high temperature and high heating rate during co-firing and the catalytic effect of biomass-contained alkali and alkaline metals. TGA reactivity assessment of the blend chars will be investigated in terms of burnout times and reaction rate constants for low and high heating rate chars. To prove the catalytic influence of mineral matter in biomass on coal char combustion, demineralised sawdust/coal char were investigated. Synergetic effects will be examined by comparing the predicted behaviour of the mixture with the experimental data available for the single fuels.
2. Experimental section 2.1 Sample Preparation Sawdust and pine wood chars were produced in a laboratory horizontal tube furnace (HTF) by imitating TGA devolatilisation conditions in Nitrogen and Carbon dioxide atmospheres respectively, while coals chars were produced in the HTF at 900 – 1100oC DTF coal char was produced from South African coal, Kleinkopje (KK) 53-75 µm particle size at 1100 - 1300oC 200 and 600 ms in a nitrogen atmosphere with 1 % oxygen to prevent tar acumulation. Detailed description of the HTF and DTF char preparation methods can be found elsewhere[10]. Properties of the samples used are presented in Submit before May 15th to
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Table 1. 2.2 Char blending methods Sawdust char produced from 125-250 µm was used to blend with coal char. The two chars were measured and manually mixed together in a sample bottle. The ratio of blending of biomass/coal was 10:90 wt%, 25:75 wt% and 50:50 wt%. 2.3 TGA analysis About 2-5 mg of char is heated at the rate of 50oC min-1 to burnout temperature under nitrogen to remove possible moisture and volatiles and then the furnace is switched to air at 500 oC for 80 minutes for combustion. From the TGA burnout profiles the reaction rate constants were calculated between 5-95 % conversion levels and burnout times up to 90 % carbon conversion were taken. 2.4 Demineralisation of sawdust. Removal of inorganic minerals in the sample was carried out by adding 1g of the sample in 50 ml of 5 M hydrochloric acid solution. The mixture was stirred at 60 oC for 12hrs and then allowed to cool. It was then filtered and the sample was washed with deionised water until the acid is neutralised. Char was produced from the demineralised sample for co-blending and TGA analysis as stated above. Also ash samples were produced in a furnace at 350 oC in air for ICP elemental analysis.
Table 1. TGA proximate analysis of the samples used Sample
Moisture
Volatiles
Fixed carbon Ash
(wt %)
(wt % daf)
(wt % daf)
(wt %)
Raw sawdust
6.4
83.9
16.1
0.9
5M HCl washed sawdust
8.6
87.3
12.7
0.04
Kleinkopje (KK)
3.1
36.6
63.4
15.5
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Figure 1: Schematic diagram of the experimental approach
3. Results and Discussion
3.1 Combustion reactivity of low heating rate sawdust and coal char blend
Figures 2 and 3 show carbon burnout profiles of sawdust and coal chars produced at low heating rate and their 50:50 wt% blends under air and oxy-fuel fired conditions respectively. The plots demonstrate how the burnout of coal char is greatly improved by the addition of sawdust chars under both conditions but slightly more pronounced under oxy-fuel firing. This is further illustrated in Table 2 with the reaction rate constants and the 90% carbon burnout times. The difference between the experimental burnout profile of the blend and the predicted burnout is an indication of a synergetic effect during cofiring.
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100
KK char N₂ 1000⁰C
Carbon burnout (wt%)
Predicted 50:50 blend 80
50: 50 wt% blend sawdust N₂ char 700⁰C
60
40
20
0 0
20
40
60
80
Time (min)
Figure 2. TGA burnout profiles of sawdust and coal chars produced at low heating rate and their blend under air fired conditions 100
Carbon burnout (w%)
KK HTF CO₂ char 1000⁰C Predicted 50:50 wt% Blend
80
Expt 50-50 wt% blend sawdust HTF CO₂ char 700⁰C
60
40
20
0 0
20
40
60
80
Time (min)
Figure 3. TGA burnout profiles of sawdust and coal chars produced at low heating rate and their blend under oxy-fuel fired conditions
Table 2. Comparison of combustion reactivity of low heating rate sawdust, coal char and their blend Samples
N2 chars and air firing
CO2 chars and oxy-fuel firing
Rate constants 90 % burnout Rate constants 90 % burnout (min-)
time (min)
(min-)
time (min)
50:50wt% blend
0.1002
22.15
0.1089
20.65
Predicted blend
0.0829
25.60
0.0720
31.60
Co-firing pine wood char with coal char also exhibited similar improved burnout
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behaviour of coal char as presented in Figures 3 and 4. Here two particle size fractions were used to investigate the effect of particle during co-firing. The burnout profiles indicated that particle size had no significant effect for the particle sizes considered in this study. A possible explanation for the improved coal char burnout propensity lies in the alkali and alkaline metals contained in biomass fuel which catalysed the reactions. It therefore means that all biomass fuels containing alkali and alkaline metal will potentially give similar effect during co-firing. 100 Coal char 106-150 @1100⁰C Predicted 50:50 wt% Blend
Carbon burnout (wt%)
80
50:50 wt% Blend Pinewood 90-106 @700⁰C
60
40
20
0 0
20
40
60
80
Burnout Time (min)
Figure 4. TGA carbon burnout profiles of pine (90-106 µm) and coal chars and their blends 100
Carbon burnout (wt%)
Coal char 106-150 @1100⁰C Predicted 50:50 wt% Blend
80
50:50 wt% Blend Pinewood 125-250 @700⁰C
60
40
20
0 0
20
40
60
80
Burnout Time (min)
Figure 5. TGA carbon burnout profiles of pine (125-250µm) and coal chars and their blends
3.2 Combustion reactivity of High heating rate sawdust and coal chars In order to produce chars which correlate directly to chars produced in a pulverised
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furnace, both sawdust and coal chars were produced in the DTF with high heating rate, high temperatures and at different residence times under air fired and oxy-fuel conditions (Figures 6 and 7, respectively). The burnout profiles of the blend demonstrate that sawdust char improved the burnout of coal char even at chars produced closer to pf furnace. However, the burnout of coal in oxy-fuel condition was about 2 times faster. This is because CO2 promotes both combustion and gasification reaction. Additionally, the CO2-char gasification reaction activates the char surface areas for easy accessibility of oxygen into the char active sites for combustion. 100 KK DTF N₂ char 1300⁰C 200ms
carbon burnout (wt%)
Predicted 50:50 wt% blend
80
50:50 wt% blend saw DTF N₂ char 1300⁰C 200ms
60
40
20
0 0
20
40
60
80
Time (min)
Figure 6. TGA burnout profiles of DTF devolatilised chars and blends in air condition 100
Carbon burnout (wt%)
KK DTF CO₂ char 1300⁰C 200 ms predicted 50:50 wt% blend
80
50:50 wt% blend saw DTF CO₂ char 1300⁰C 200 ms
60
40
20
0 0
20
40
60
80
Time (min)
Figure 7. TGA burnout profiles of DTF devolatilised chars and blends in air condition 3.3 Effect of biomass blending ratio on coal char reactivity In order to maximise the catalytic impact of biomass inherent minerals on coal char burnout, 50:50 wt% blend have been used in this work. However, 25:75 and 10:90 wt% biomass/coal char blends were investigated to examine the effect of smaller biomass
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blend ratios on coal char reactivity. As demonstrated in the burnout profiles in Figures 8 and 9, coal char burnout efficiency was increased with increase in biomass ratio in the blend. Also, interaction of the two fuels is minimal in the 10:90 wt% blend compared to the 25:75 wt% blends. Assessment of the reactivity parameters in Table 3 reaffirms the impact of blending ratio. 100
Carbon burnout (wt%)
KK DTF char 1100C 600ms Predicted 25:75 wt% blend
80
25:75 wt% blend sawdust DTF 1100C 600ms
60
40
20
0 0
20
40
60
80
Time (min)
Figure 8. TGA Carbon burnout profile of DTF chars for 25:75 wt% under air fired condition
Carbon burnout (wt %)
100
KK DTF char 1100⁰C 600ms Predicted 10:90 wt% blend
80
10:90 wt% blend sawdust DTF char 1100⁰C 600ms
60
40
20
0 0
20
40
60
80
Time (min)
Figure 9. TGA Carbon burnout profile of DTF chars for 10:90 wt% under oxy-fuel condition Table 3. Effect of biomass/ coal char blending ratio on co-combustion reactivity Sample
1st order rate constants -
(min ¹)
90% burnout time (min)
25:75 wt % N₂ char blend
0.0725
34.00
10:90 wt % N₂ char blend
0.0601
43.00
3.3. Effect of sawdust demineralisation on coal char burnout
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The char produced from the acid washed sawdust sample was blended with the coal char in 50:50 wt% ratios. It was observed that the removal of alkali/alkaline metals reduced the burnout efficiency of coal char under both conditions compared to the burnout observed earlier in Figures 2 and 3. This confirmed the fact the improved coal char burnout was as a result of the catalytic influence of the alkali/alkaline metals inherence in biomass. The reduction in the concentration of metals due to acid wash is presented in Table 4. However, improved coal char burnout is still observed in oxy-fuel condition due to CO2-char gasification. 100 kk HTF N₂ char 1000⁰C
Carbon burnout (wt%)
50:50 wt% blend 80
Predicted 50:50 wt% Acid washed sawdust HTF char 700⁰C
60
40
20
0 0
20
40
Time (min)
60
80
Figure 10. TGA burnout profiles of sawdust/coal char blend highlighting the impact of mineral catalysis during co-combustion under air fired condition. 100
Carbon burnout (wt%)
kk HTF CO₂ char 1000⁰C Predicted 50:50 wt% blend
80
50:50 wt% blend Acid washed sawdust HTF CO₂ char 700⁰C
60
40
20
0 0
20
40
60
80
Time (min)
Figure 11. TGA burnout profiles of sawdust/coal char blend highlighting the impact of mineral catalysis during co-combustion under oxy-fuel condition. Table 4. Concentration of alkali and alkaline metals in raw and acid washed sawdust
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Sample
Na (wt %)
Mg (wt %) K (wt %)
Ca (wt %)
Raw sawdust
0.12
0.09
0.21
0.75
5M HCl washed sawdust
0.02
0.02
0.008
0.006
4. Conclusions 1. The addition of sawdust char into coal char improved the burnout efficiency of coal char under air fired and oxy-fuel conditions for both low and high heating rate chars. 2. The improved burnout rates were as a result of the catalytic inorganic alkali and alkaline metals present in biomass. 3. Improved coal char burnout in oxy-fuel condition after demineralisation is due to CO2char gasification. Acknowledgement. The authors wish to the authors wish to acknowledge the financial support from the Petroleum Trust Development Funds (Nigeria) for this research. References [1] H. Haykiri-Acma, S. Yaman, Synergy in devolatilization characteristics of lignite and hazelnut shell during co-pyrolysis, Fuel, 86 (2007) 373-380. [2] H. Haykiri-Acma, S. Yaman, Effect of co-combustion on the burnout of lignite/biomass blends: A Turkish case study, Waste Management, 28 (2008a) 20772084. [3] D.K. Park, S.D. Kim, S.H. Lee, J.G. Lee, Co-pyrolysis characteristics of sawdust and coal blend in TGA and a fixed bed reactor, Bioresource Technology, 101 (2010) 61516156. [4] K. Sjöström, G. Chen, Q. Yu, C. Brage, C. Rosén, Promoted reactivity of char in cogasification of biomass and coal: synergies in the thermochemical process, Fuel, 78 (1999) 1189-1194. [5] H. Haykiri-Acma, S. Yaman, Interaction between biomass and different rank coals during co-pyrolysis, Renewable Energy, 35 (2010) 288-292. [6] L. Zhang, S. Xu, W. Zhao, S. Liu, Co-pyrolysis of biomass and coal in a free fall reactor, Fuel, 86 (2007) 353-359. [7] E. Kastanaki, D. Vamvuka, A comparative reactivity and kinetic study on the combustion of coal - biomass char blends, Fuel, 85 (2006) 1186-1193. [8] J. Fermoso, M.V. Gil, C. Pevida, J.J. Pis, F. Rubiera, Kinetic models comparison for non-isothermal steam gasification of coal-biomass blend chars, Chemical Engineering Journal, 161 (2010) 276-284. [9] S.G. Sahu, P. Sarkar, N. Chakraborty, A.K. Adak, Thermogravimetric assessment of combustion characteristics of blends of a coal with different biomass chars, Fuel Processing Technology, 91 (2010) 369-378. [10] K. Le Manquais, C. Snape, I. McRobbie, J. Barker, V. Pellegrini, Comparison of the Combustion Reactivity of TGA and Drop Tube Furnace Chars from a Bituminous Coal, Energy & Fuels, 23 (2009) 4269-4277.
Submit before May 15th to
[email protected] 10
Oviedo ICCS&T 2011. Extended Abstract
Numerical simulation on the re-burning of ash with high unburned carbon in pc boiler Min-young Hwang1, Gyu-Bo Kim2, Ju-hun Song3, Seung-Mo Kim4 and Chung-Hwan Jeon*
1. School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-3035, Fax: 82-51-582-9818, Email:
[email protected] 2. School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-3035, Fax: 82-51-512-5236, Email:
[email protected] 3. School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-7330, Fax: 82-51-512-5236, Email:
[email protected] 4. School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-3035, Fax: 82-51-512-5236, Email:
[email protected] * Corresponding author, Associate Professor, School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51510-7324, Fax: 82-51-582-9818, Email:
[email protected] Abstract In thermal power generation companies, refined ash (LOI6%) along with pulverized coal in PC boiler was considered in this study. In a real scale application, direct re-burning method seems to be a worthwhile subject to investigate. It allows economics, safety and stability without many change of the PCboiler. Hence, it is necessary to focus on obtain appropriate operating condition to acquire the refine ash by re-burning. Ash sample with 8% LOI was selected by the proximate analysis. Also, combustion kinetic parameters which were used to numerical
Submit before 31 May 2011
[email protected] 1
Oviedo ICCS&T 2011. Extended Abstract
study of the ash and a coal were obtained through the results in a drop tube furnace. For numerical studies of ash re-burning, a 500MW PC-boiler geometry was mashed with 2000000 cell. As a reaction model, 2-step devolatilization model and kinetic-diffusion limited char model were adopted. A number of simulations have been performed as a function of fuel ratio and supply position. Through the results, the supplying position and the feeding ratio of the ash were decided at conditions with appropriate boiler temperature and emission
1. Introduction Loss on ignition (LOI) is defined by unburned carbon fraction in ash after combustion. Constantly increasing coal cost and decreasing overall amount of high lank coal cause using of low rank coal. Using a low rank coal on the conventional tangential firing boiler brought out high LOI contents because of the boiler was optimally designed for standard coal condition. In thermal power generation companies, refined ash (LOI 0
L1 L2 L3 Number of Nodes 75D 75D 75D 23205 40D 30D 100D 59668
Table 1: Size of the domain and grid resolution
In this work we utilize the pseudo-steady-state approach (PSS), see [7], due to the fact that the conversion time of the mm-size particle is always long compared to the convective and diffusion time scales for the gas phase (see [4]), which is typical for fluidized bed systems. The Navier-Stokes equations coupled with the energy and species conservation equations are used to solve the problem in pseudo-steady state approach. At the surface of the particle, the balance of mass, energy and species concentration is applied including the effect of the Stefan flow and the heat loss by radiation at the surface of the particle. The complete formulation of governing equations, interfacial boundary conditions and model validation against analytic two-film model can be found in [14, 15, 16]. The transport properties of the gas are calculated using kinetic theory and polynomials [17]. The gas flow was treated as incompressible ideal gas following model described in [18].
4
Figure 2: Comparison of the reaction rate kr for several carbon types reacting with O2 , H2 O and CO2 . The sources of the data are presented in tables 3 to 6
3. Selection of heterogeneous and homogeneous reactions The chemistry is modeled using semi-global homogeneous and heterogeneous reactions written as follows [4]: 1 CO + O2 + H2 O → CO2 + H2 O 2 CO + H2 O → CO2 + H2 CO2 + H2 → CO + H2 O 1 C + O2 → CO 2 C + CO2 → 2CO C + H2 O → CO + H2
(exothermic)
(1)
(exothermic) (endothermic)
(2) (3)
(exothermic)
(4)
(endothermic) (endothermic)
(5) (6)
The semi-global reaction rates of homogeneous chemical reactions are given f b in Tab. 2. The rate constants kCO , kshif t and kshif t are computed using the 5
Arrhenius expression:
Er
kr = Ar T nr exp− R T
(7)
where Ar is the pre-exponential factor, nr is the temperature exponent (in this work nr = 0 for all homogeneous reactions), Er is the activation energy and R is the universal gas constant. The rate expression for the reaction describing CO oxidation, eq. 1, was proposed by [19]. Notice that the reaction order is not related to the stoichiometry of the reaction due to the global character of this reaction, see Tab. 2. Basically, semi-global homogeneous chemical reactions are widely used by the modeling of industrial combustors or gasifiers using computational fluid dynamics software, e.g. see [20]. However it should be noted that global reactions rates are only valid in a narrow range of conditions and should be used very cautiously. In this work we employ four sets of semiglobal heterogeneous surface rate data, which have been adopted from [4], [13], [12] and [21], see tables 3, 4, 5 and 6, respectively. The data is provided in terms of extended Arrhenius expression according to eq. 7. The analysis of the tables shows that most of the data is gathered in 1970 and 1980s. We note here that in order to find origin source of kinetic data published in the literature we had to follow long chains of links. Finally we found out that lots of authors refer back to only a few works. In some publications the original data were even changed due to recalculating in new dimensions. For example Turns in his book [4] utilizes the heterogeneous kinetic data from Mon and Amundson [6], who recalculated data from Howard [22] and Dutta [23] and fitted it in order to eliminate the linear temperature dependency of the Arrhenius expression. Libby and Blake [12] refer to Field [24] and Dobner [25] corresponding to not archival literature in the form of internal reports. However good news is that most cited data comes from archival literature and was established by Mayers [26] and Field [27]. For detailed analysis of the kinetic data published in the literature we refer to [28]. As illustration of the influence of coal type on the reaction rate constants kr , the selected kinetic data sets are exhibited in Figure 2. Distinguished by the gaseous reactant, it is obvious that the C + O2 is fastest whereas the Boudouard reaction C + CO2 is the slowest. Also the comparison indicates the temperature range of the experimental investigation. A distinct difference between the several types of carbon is not observed due to many overlaps. Hence, the numerical study is essential to assess the effect of the combined 6
reactions. Reac.
i,r [kmol/m3 · s] R
Ar
1 2 3
kCO [CO] [H2O]0.5 [O2 ]0.25 f kshif t [CO] [H2 O] b kshif t [CO2 ] [H2 ]
2.24 · 1012 2.74 · 109 1.00 · 108
Er [J/kmol] nr
source
1.6736 · 108 8.368 · 107 6.28 · 107
[4], p. 211 [29] [29]
0 0 0
Table 2: Reaction rates for homogeneous reactions
4. Results and Discussions The results of simulations of a single coal particle behavior in a hot quiescent air (corresponding to YO∞2 = 0.233, YH∞2 O = 0.001) and reduced-air (YO∞2 = 0.11, YH∞2 O = 0.074) atmospheres are presented in Figs. 3 and 4. In particular, Figs. 3a and 3b show the carbon net mass flux m ˙ C as a function of the ambient temperature Tin calculated under the condition of quiescent air and reduced-air environments using four sets of heterogeneous kinetic data denoted by Turns, Smoot & Smith, Libby & Blake and Hla et al., see tables 3, 4, 5 and 6), respectively. The comparison of both figures reveals two significant effects. First, it can be seen that the use of Turns and Hla et al. data sets produces similar qualitative behavior of m ˙ C in dependence on the ambient temperature Tin for Tin > 1500 K. However for low ambi ˙C ent temperatures Tin < 1300 K a descrepancy can be observed between m predicted using both data sets, see Fig. 3. In particular, the use of Turns kinetic data produces earlier ignition in comparison to results obtained by use of Hla et al. kinetics. The comparison of the carbon net mass fluxes Reac. C + O2 C + CO2 C + H2 O
Ar [m/s] 3.007 · 105 4.02 · 108 1.21 · 109
Er [J/mol] 1.49 · 105 2.48 · 105 2.48 · 105
nr 0 0 0
source [24], [5], [4] [23], [6], [4] [6], [4]
Table 3: Rate coefficients for heterogeneous reaction mechanism called as Turns. Carbon type is bituminous coal char. The order of all reactions is unity.
7
Reac. C + O2 C + CO2 C + H2 O
Ar [m/(s K)] 1.692 25.9 1.33
Er [J/mol] 0.852 · 105 2.25 · 105 1.47 · 105
nr 1 1 1
source [30] [30] [26]
Table 4: Rate coefficients for heterogeneous reaction mechanism called as Smoot & Smith. Carbon type is an American standard bituminous coal (Pittsburgh #8). The order of all reactions is unity.
Reac. C + O2 C + CO2 C + H2 O
Ar [m/(s K nr )] 3.007 · 105 4.605 11.25
Er [J/mol] 1.4937 · 105 1.751 · 105 1.751 · 105
nr 0 1 1
source [24], [5], [4] [25] [25]
Table 5: Rate coefficients for heterogeneous reaction mechanism called as Libby & Blake. Carbon type is the average for coal char. The order of all reactions is unity.
Reac. C + O2 C + CO2 C + H2 O
Ar [m/(s K nr )] Er [J/mol] 20.2 1.57 · 105 6 1.59 · 10 2.91 · 105 75900 2.68 · 105
nr 0.8 0.3 0.4
source [21] [21] [21]
Table 6: Rate coefficients for heterogeneous reaction mechanism called as Hla et al. gained at pressurized atmospheres. Carbon type is an Australian high-volatile bituminous coal (CRC299). The reaction order of each reaction corresponds to nr .
8
predicted using Smoot & Smith and Libby & Blake data sets for ’air’ and ’gasification’ conditions show relative close behavior of m ˙ C in dependence on Tin . At the same time we found out that at high ambient temperatures Tin > 3000 K all four data sets produce comparable carbon net mass fluxes. This fact is explained by approaching the diffusionally controlled combustion. Second, it can be observed that at reduced atmosphere conditions the transition between kinetically and diffusionally controlled regimes occurs at higher ambient temperatures in comparison to the air atmosphere. For the definition of the diffusionally and kinetically controlled regimes we refer to the book [4]. In order to demonstrate the influence of different kinetic data on local characteristics near the particle surface we plot in Fig. 4 the spatial distribution of the temperature calculated using Turns’s and Libby & Blake’s data sets. The simulations performed using Turns’s kinetic data reveal the flame sheet at Tin = 2000 K. Whereas the use of Libby & Blake’s set predicts no flame sheet around the particle. The comparison of Figs. 4a and 4c shows that the flame sheet thickness increases with decrease of O2 . The effect of the motion of a reacting coal particle relative to the surrounding gas is demonstrated in Figs. 5 and 6. In particular, Fig. 5 illus trates the comparison of the surface net mass flux of carbon m ˙ C in dependence on Tin calculated using four data sets for the case of a movable particle (Re = 10). It can be seen that qualitative behavior of m ˙ C is similar to the case Re = 0. Thus, the calculations made using Turns and Hla et al. kinetic data sets produced close results. However, the oxidation rate of the particle increases with the velocity of the particle due to the flow-enhanced transfer of O2 between the gas and the surface. The same is true for the carbon net mass flux calculated using Smoot & Smith and Libby & Blake kinetic data. Additionally, the comparison of Figs. 3 and 5 demonstrates that increase of the Reynolds number leads to the prolongation of kinetically controlled regime to higher temperatures. Fig. 6 plots spatial distribution of the temperature near the particle predicted using Turns’s and Libby & Blake’s data sets for the air and reduced air atmospheres. It can be seen that the utilization of Turns’s kinetic constants for the case Re = 10 and Tin = 2000 K results in combustion regime in the form of classical flame sheet around the particle. At the same time the adaptation of Libby & Blake’s data for the same case leads to the gasification regime, where no flame exists. To sum up the obtained results converge to the conclusion that Turns (bituminous coal char) and Hla et al. (Australian high-volatile bituminous coal) data sets correspond to coal with high reactivity whereas Smoot & 9
.
.
0.015 0.01
0.015 0.01 0.005
0.005 0 1000
0.02
Hla et al. Turns Smoot and Smith Libby and Blake
2
0.02
0.025
2
m ’ [kg/m s]
0.025
0.03
Hla et al. Turns Smoot and Smith Libby and Blake m ’ [kg/m s]
0.03
1500
2000 Tin [K]
2500
0 1000
3000
a
1500
2000 Tin [K]
2500
3000
b
Figure 3: Predicted carbon net mass flux m ˙ C as a function of the ambient temperature Tin by quiescent environment corresponding to a) - air: YO∞2 = 0.233, YH∞2 O = 0.001 and b) - rediced O2 atmosphere: YO∞2 = 0.11, YH∞2 O = 0.074.
Smith (Pittsburgh #8) and Libby & Blake (average for coal char) data set characterize the coal with lower reactivity. This is to a certain extent in contrast the impression one can get while only interpreting the reaction rate constants as illustrated in Figure 2. 5. Summary In this work we performed the numerical study of the influence of heterogeneous kinetics on the oxidation rates of a single carbon particle in quiescent and non-quiescent environments. Three heterogeneous reactions (C + O2 , C + CO2 and C + H2 O) and two homogeneous semi-global reactions, namely carbon monoxide oxidation and water-gas shift reaction, were employed. Several semi-global reaction rate expressions taken from the literature were utilized. Based on the results of the numerical simulations carried out for a coal particle with a diameter of 1 mm we found out that using Turns and Hla et al. data sets for heterogeneous kinetics produces identical carbon net mass flux and others qualitative features of the carbon particle oxidation. The same is true for Libby & Blake and Smoot & Smith. For all kinetic adat sets used in this work we found out that the end of kinetically controlled regime is shifted to the higher temperatures with the decrease of O2 concentration in the ambient atmosphere and the increase of Re. The flame thickness increases with decrease of YO∞2 . 10
a b
c d Figure 4: Contour plots of the temperature calculated for the air (a,b) and reduced O2 atmosphere (c,d) using different data sets for heterogeneous kinetics: a) and c) - Turns, b and d - Libby & Blake. Here the ambient temeparture is Tin = 2000 K. Reynolds number is Re = 0.
Acknowledgment The authors appreciate the financial support of the Government of Saxony and the Federal Ministry of Education and Science of the Federal Republic of Germany as a part of the Centre of Innovation Competence VIRTUHCON. References [1] M. Gr¨abner, O. von Morstein, D. Rappold, W. G¨ unster, G. Beysel, B. Meyer, Constructability study on a German reference IGCC power plant with and without CO2-capture for hard coal and lignite, Energy Conversion and Management 51 (2010) 2179–2187. [2] W. Nusselt, Der Verbrennungsvorgang in der Kohlenstaubfeuerung., Zeitschrift des Vereins Deutsche Ingenieure 68 (1924) 124–128.
11
0.03
0.03
0.025
0.025 2
m ’ [kg/m s]
0.035
0.02 0.015
Hla et al. Turns Smoot and Smith Libby and Blake
0.02 0.015
.
.
2
m ’ [kg/m s]
0.035
0.01
Hla et al. Turns Smoot and Smith Libby and Blake
0.005 0 1000
1500
2000 Tin [K]
2500
0.01 0.005 0 1000
3000
a
1500
2000 Tin [K]
2500
3000
b
Figure 5: Predicted carbon net mass flux m ˙ C as a function of the ambient temperature Tin by non-quiescent environment (Re = 10) corresponding to a) - air: YO∞2 = 0.233, YH∞2 O = 0.001 and b) - reduced O2 atmosphere: YO∞2 = 0.11, YH∞2 O = 0.074.
a
b
c
d
Figure 6: Contour plots of the temperature calculated for the air (a,b) and reduced O2 atmosphere (c,d) using different data sets for heterogeneous kinetics: a) and c) - Turns, b and d - Libby & Blake. Here the ambient temeparture is Tin = 2000 K. Reynolds number is Re = 10.
[3] S. Burke, T. Schuman, in: Proceedings of the 3rd Int. Conf. Bituminous Coal, pp. 485–489.
12
[4] S. Turns, An Introduction to Combustion, McGraw-Hill, Boston, 2nd edition, 2000. [5] H. Caram, N. Amundson, Diffusion and Reaction in a Stagnant Boundary Layer about a Carbon Particle, Industrial & Engineering Chemistry Fundamentals 16 (1977) 171–181. [6] E. Mon, N. Amundson, Diffusion and Reaction in a Stagnant Boundary Layer about a Carbon Particle. 2. An Extension, Industrial & Engineering Chemistry Fundamentals 17 (1978) 313–321. [7] S. Sundaresan, N. Amundson, Diffusion and Reaction in a Stagnant Boundary Layer about a Carbon Particle. 6. Effect of Water Vapor on the Pseudo-Steady-State Structure, Industrial & Engineering Chemistry Fundamentals 19 (1980) 351–357. [8] F. Higuera, Combustion of a coal particle in a stream of dry gas, Combustion and Flame 152 (2008) 230–244. [9] H. Chelliah, The influence of heterogeneous kinetics and thermal radiation on the oxidation of graphite particles, Combust. Flame 104 (1996) 81–94. [10] D. Bradley, D. G., S. El-DinHabik, E. Mushi, The oxidation of graphite powder in flame reaction zones, Proc. Combust. Inst. 20 (1984) 931–940. [11] R. Stauch, U. Maas, Transient detailed numerical simulation of the combustion of carbon particles, International Journal of Heat and Mass Transfer 52 (2009) 4584–4591. [12] P. Libby, T. Blake, Burning carbon particles in the presence of water vapor., Combust. Flame 41 (1981) 123–147. [13] L. Smoot, P. Smith, Coal Combustion and Gasification (The Plenum Chemical Engineering Series), Springer, 1st edition, 1985. [14] M. Kestel, P. Nikrityuk, B. Meyer, Numerical study of partial oxidation of a single coal particle in a stream of air, in: 14th Int. Heat Transfer Conf., Washington D.C., USA, pp. CD: ISBN 978–0–7918–3879–2, 2010 by ASME.
13
[15] M. Kestel, P. Nikkrityuk, O. Henning, C. Hasse, Numerical study of the partial oxidation of a coal particle in steam and dry air atmosphere, IMA Journal of Applied Mathematics (under review 2010). [16] S. Schulze, P. Nikkrityuk, B. Meyer, Microscale modeling of co2 utilisation by carbon gasification, Energy & Environmental Science submitted (2011). [17] B. Bride, S. Gordon, M. Reno, Coefficients for Calculating Thermodynamic and Transport Properties of Individual Species, Technical Report, NASA., 1993. [18] A. Tomboulides, J. Lee, S. Orszag, Numerical simulation of low Mach number reactive flows, J. Scietific Computing 12 (1997) 139–167. [19] F. L. Dryer, I. Glassman, High temperature oxidation of CO and CH4 ., Proc. Combust. Inst. 14 (1973) 987–1003. [20] Y. Wu, P. J. Smith, J. Zhang, J. N. Thornock, G. Yue, Effects of turbulent mixing and controlling mechanisms in an entrained flow coal gasifier, Energy Fuels 24 (2010) 1170–1175. [21] S. S. Hla, D. J. Harris, D. G. Roberts, A coal conversion model for interpretation and application of gasification reactivity data, in: International Conference on Coal Sci. and Tech., Okinawa, Japan, p. 2005. [22] R. H. Essenhigh, R. Froberg, J. B. Howard, Combustion behavior of small particles, Industrial & Eng. Chem. 57 (1965) 32–43. [23] C. Dutta, C. Wen, R. Belt, Reactivity of coal and char. 1. In carbon dioxide atmosphere, Industrial & Eng. Chem. Proc. Design and Develop. 16 (1977) 20–30. [24] M. Field, R. Roberts, Measurement of the ratio of reaction of carbon particles with oxygen in the pulverized coal size range for gas temperature between 1400 K and 1800 K., Technical Report 325, BCURA Memb. Circ., England, 1967. [25] S. Dobner, Modelling of Entrained Bed Gasification: the Issues, EPRI, Palo Alto, CA, 1976.
14
[26] M. Mayers, The rate of reduction of carbon dioxide by graphite, J. American Chem. Society 56 (1934) 70–76. [27] F. M.A., Rate of combustion of size-graded fractions of char from a low-rank coal between 1200 K and 2000 K, Comb. Flame 13 (1969) 237–252. [28] M. Gr¨abner, Modeling-based Evaluation of Gasification Processes for low-grade Coals, Ph.D. thesis, Technische Universit¨at Bergakademie Freiberg, Germany, 2011. [29] W. Jones, R. Lindstedt, Global reaction schemes for hydrocarbon combustion, Combustion and Flame 73 (1988) 233–249. [30] G. Goetz, K. Nsakala, K. Patel, T. Lao, Combustion and gasification kinetics of chars from four commercially significant coals of varying rank, in: Proceedings of the 2nd Annual Conf. on Coal Gasification, EPRI Palo, Alto, CA, p. 1982.
15
Oviedo ICCS&T 2011. Extended Abstract
Comparison of structure and reactivity of an Australian algal coal and a Jordanian oil shale W. Roy. Jackson1,2* , Mohammad W. Amer1,2, Yi Fei1,2, Marc Marshall1,2, and Alan L. Chaffee1,2 1
School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
2
Centre for Green Chemistry, Monash University, Victoria 3800, Australia
Corresponding author name: W. Roy. Jackson Email:
[email protected] Abstract An Australian algal coal (torbanite) and a Jordanian oil shale (from El-Lajjun) are compared. Literature data indicate that both materials are highly aliphatic in nature. Their reactivity towards pyrolysis and hydropyrolysis, both in the presence and absence of tin catalysts, is compared and a detailed analysis of the products of these reactions is presented. Experiments in our laboratory confirm that the depolymerization of the torbanite and the oil shale occurs in a narrow temperature range. Establishment of a clearer understanding of this depolymerization process could lead to the discovery of more efficient methods for the extraction of oil from the kerogen in the Jordanian oil shale. 1.
Introduction
This paper describes experiments designed to provide information on the structural features of the organic component of a Jordanian oil shale from the El Lajjun deposit, by comparison of its reactivity with that of an algal coal, torbanite, from Muswellbrook, NSW, whose organic structure is reasonably well characterized [1, 2]. The organic matter in the oil shale is derived from marine algae [3], whereas the organic matter in torbanite is from fresh water algae [1]. The deposition conditions for the Jordanian oil shale are responsible for its significantly higher sulfur content [4]. In addition the oil shale is much younger, originating no earlier than the Maastrichtian age (Cretaceous period) [3, 4], whereas the torbanite comes from the much older Permian period, leading to its low oxygen content [1]. The influence of these differences on reactivity will be discussed. Pyrolysis reactions under N2 and hydropyrolysis both with and without added Sn catalysts have been carried out, and the yields and product compositions determined. 2.
Experimental
2.1
Oil shale and coal preparation and characterization
Oil shale from the El Lajjun deposit in Jordan was received as -2mm particles and was ground to -180 µm. The torbanite sample was obtained as a solid block which was ground to -180 µm. Ash 1
Oviedo ICCS&T 2011. Extended Abstract
yields were determined by heating at 490oC in air to constant weight. The water content of the samples was taken as the loss of weight observed when they were heated under a flow of N2 for 3h at 105oC, and samples were all dried by this procedure before reaction. The sample of shale for elemental analysis was washed with 0.5M HCl following the procedure of Redlich at al [5] to remove the carbonate minerals. Elemental analyses were carried out by HRL Technology Ltd for C, H, N, S, Cl and Fe for raw and acid-washed oil shale and for C, H, N and S for raw torbanite by the Campbell Microanalytical Laboratory, University of Otago. The values of organic C, H, N and O contents and the concentrations of the different forms of S were calculated from the elemental analyses, the ash yields and the loss of weight on acid washing. The solid state 13C NMR spectra for acid-washed oil shale and untreated torbanite were determined using a Bruker 400 (1H)/100(13C) MHz spectrometer with cross polarization-magic angle spinning (CP/MAS).To introduce the tin catalyst, the samples was mixed with an aqueous slurry of SnO2 (0.5 mol/kg db for the Jordanian oil shale, 1 mol/kg db for the torbanite) stirred for a few minutes under vacuum in order to promote good mixing, and then overnight in a nitrogen atmosphere. The liquid water was removed by blowing nitrogen through the mixture with continued stirring. 2.2
Reactions and workup
Reactions were carried out in 27 ml stainless steel autoclaves fitted with a stainless steel liner and charged with 2.1g of 105oC-dried oil shale or torbanite (unless otherwise stated) and 3MPa (cold) of the appropriate gas (10 MPa H2 for the Sn-treated torbanite reaction). The autoclave was evacuated and weighed before and after the gas was charged, so that the free space in the autoclave could be calculated. In the case of H2 reactions, the autoclave was evacuated and weighed before and after charging a known pressure of N2 to determine the free space in the autoclave, and then the autoclave was vented and evacuated before again weighing, charging with H2 and weighing. The autoclave was lowered into a preheated sand bath and came to the required temperature in 2-4 minutes. It was continuously shaken while in the sand bath. The autoclave was held at temperature for 1 hour, removed, allowed to cool and weighed. The gas was vented through an Agilent 3000 Micro Gas Chromatograph, equipped with four columns: MS 5A PLOT, 10m×0.32mm (110oC column temperature) for N2 and CH4, PLOT U, 8m×0.32mm (100oC column temperature) for CO, CO2, C2 hydrocarbons, H2S and COS. Alumina PLOT, 10m×0.32mm (140oC column temperature) for C3-C5 hydrocarbons and OV-1, 10m×0.15mm×2.0μm (90oC column temperature) for isobutane and n-hexane. The inlet and injector temperatures were 100oC. After the analysis the autoclave was vented and the total weight of the gas in the autoclave was calculated. On the assumption that the gases detected (and hydrogen or nitrogen by difference) were the only gases present, the yields of all the gases detected and the hydrogen consumption (in runs with hydrogen) could be calculated. The solid and liquid products were washed and scraped out of the autoclave with dichloromethane into a flask, and subjected to Lundin distillation to remove water. The waterfree material was ultrasonicated for 10 minutes, filtered, more dichloromethane added to the filter cake and the process repeated. The dichloromethane insolubles were dried at 105oC in flowing N2 for at least 2 hours, cooled and weighed. Most of the dichloromethane was removed from the dichloromethane-soluble material by rotary evaporation and n-hexane (20:1 by weight) added. The mixture was ultrasonicated for 3 minutes and filtered to give insoluble material, asphaltene, which was dried in a vacuum oven (0.1KPa) at 55oC and weighed. Most of the n-hexane was removed from the filtrate by rotary evaporation and the residual hexane solubles (oil) were stored at 4oC for later analysis. The oil yield was determined by difference. 2
Oviedo ICCS&T 2011. Extended Abstract
Based on weighing uncertainties and the spread of results for replicated runs, the uncertainty in CH2Cl2 solubles and gas was about ±1.5 wt% db, and in oil+water and asphaltene yields about ±2 wt% db. The uncertainty in the yields of individual gases taking into account weighing and calibration uncertainties was about 15% of the result, but the spread of results for replicated runs indicated higher uncertainties. 2.3
Product analysis
Some oil samples were analysed by gas-chromatography-mass spectrometry (GC-MS) on a HP6890 instrument in split mode. For GC, a HP 19091S-433 capillary column (HP-5MS 5% phenylmethyl siloxane), 30m long, 0.25mm diameter, 0.25μm nominal film thickness, was used. The inlet temperature was 230oC. The oven temperature was initially held at 50oC for 2 min then raised to 200oC at a rate of 4oC/min, held at 200oC for 2 min, then raised to 300oC at 8oC/min and held at 300oC for 3 min. For MS, the ionizing potential was 70 eV, the accelerating voltage 1.9 kV, the mass range scanned 45-600 m/z and the ion source temperature 200-250oC. For 1H NMR, the oils were dissolved in CDCl3 and spectra were obtained using a 400MHz instrument, with a 90o pulse flip angle (9.5μs). 3.
Results and Discussion
3.1
Characterisation of the oil shale
The Jordanian oil shale was obtained from the El Lajjun deposit in the Karak region. The moisture content was 1.3 wt%. The organic content as determined from the ash yield at 490oC was 24.2±0.5 wt% db. The acid-soluble fraction of the oil shale was 51.9±0.5 wt% db, indicating a high carbonate concentration. The total S and Fe were 3.6 and 1.9 wt% db respectively and the organic material in the shale had C, 71.9; H, 8.7; N, 1.7; S, 9.9 and O (by difference) 7.8 wt% dmmf of the total oil shale. These values are typical of those reported previously [6]. A solid state 13 C NMR CP/MAS spectrum of the acid-washed shale showed a Car to Caliph of 0.21: 0.79 indicating a high aliphatic content, as implied by the H/C atomic ratio for the total organic material of 1.44. 3.2
Characterization of torbanite
The torbanite came from the Greta coal measures at Muswellbrook (Bayswater Colliery) in the Sydney coal basin, NSW. The moisture content was 0.7 wt%. The ash yield at 490 oC was 4.3± 0.5 wt% db. The ultimate analysis gave C, 82.62; H, 10.64; N, 0.79; S, 0.10; O (by difference), 5.85 wt% dmmf of the torbanite. The solid state 13C NMR CP/MAS spectrum showed, as for the oil shale, a strongly aliphatic character with a Car to Caliph of 0.12 : 0.88. The atomic H/C ratio of 1.64 was even higher than that of oil shale. 3.3
Extraction yields
Table 1 compares the yields of product fractions from reactions at 355 oC, 390 oC and 425 oC. The Jordanian oil shale (JOS) and torbanite (TOR) samples showed very different reactivity patterns. The JOS broke down to give significant yields of asphaltene and oil even at 355 oC in either H2 or N2, whereas the TOR showed hardly any conversion. Reactions of brown coals with much higher organic O content than JOS also show very low conversions to liquid products in this temperature range [7].
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Oviedo ICCS&T 2011. Extended Abstract
Table 1: The extraction yields (wt % dmmf) of product fractions for JOS and TOR at different temperatures. T (oC) Reactant Gas
JOS
Asphaltene
N2
70.7±6.6
4.9±1.8
62.8±6.5
3.0±3.6
1.5±1.6
H2
89.6±1.1
6.1±0.1
72.2±5.0
11.3±6.0
1.5±0.2
H2
82.6
6.2
64.0
12.4
0.9
N2
86.1±2.6
12.6±0.4
72.4±2.2
1.2±0.04
0.8±0.03
H2
86.9±2.6
13.8±0.4
70.3±2.2
2.8±0.1
1.7±0.1
c H2
71.9
13.4
55.5
3.0
1.8
N2
78.5±5.4
18.4±0.3
57.9±4.8
2.1±0.9
1.2±0.1
H2
84.1±2.5
9.2±1.6
74.7±3.9
0.3±0.2
0.2±0.2
N2
14.8±0.5
1.1±0.04
13.5±0.4
0.1±0.00
0.4±0.01
H2
14.0±0.4
1.3±0.04
12.7±0.4
0.04±0.00
0.1±0.00
N2
64.3
26.8
33.8
3.6
3.3
H2
69.7
30.0
38.3
1.5
0.7
N2
6.4
0.4
5.9
0.1
0.6
H2
3.5
0.3
3.2
0.0
0.1
c
425 TOR
JOS 390 TOR
JOS 355 TOR
b
CH2Cl2-CO2
Oil+H 2O HC+Sulfide gas
CO2
a - extraction for 1 hour, errors are standard deviations calculated from the results for duplicate reactions. b - oil + asphaltene + hydrocarbon and sulfide gas c - tin treated The H/C ratios for JOS and TOR samples are similar and the dmmf O content is only slightly higher in the JOS. The main difference in the elemental composition is the presence of a 10% organic S content on a dmmf basis in JOS. The dissociation enthalpy of C-S bonds in aliphatic systems is less than that of C-O or C-C bonds (CH3-S-CH3, 301 kJ/mol, CH3-O-CH3, 352 kJ/mol and CH3-CH3, 352 kJ/mol) [8] and this could explain the greater reactivity at lower temperatures of JOS. Increasing the reaction temperature to 390 oC resulted in only a small change in the reactivity of TOR but for JOS there was not only an increase in the total conversion, but also a major shift in product distribution from asphaltene to oil. This shift preference for oil was particularly noticeable for reactions in H2, which may be associated with the significant Fe content of the shale (1.9 wt% db) having a catalytic effect. Reactions of JOS at 425 oC showed no significant increase in the oil yield over reactions at 390 oC and the increase in the total conversion was mainly associated with increase in gases. In contrast, reactions of TOR at 425 oC in both N2 and H2 showed high conversion to oil with small amounts of asphaltene and gas. A structural formula proposed for torbanite has alkene bonds, remote from the termini of the long aliphatic chains [9]. Preferential thermal cleavage of C-C bonds near to the alkenes in this homogeneous polymeric structure could be responsible for the facile conversion to oil products. The use of Sn catalysts was examined for reactions of both JOS and TOR with H2 at 425oC. Addition of tin compounds to hydrogen reactions has been shown to have beneficial effects on oil yield from plant derived coals of all ranks [10]. However, addition of Sn to reactions of both JOS and TOR surprisingly reduced the overall conversion by reduction of the oil yield. Asphaltene and gas yields were unchanged.
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Oviedo ICCS&T 2011. Extended Abstract
3.4
Product Characterization
The oils were examined by 1H NMR and GC-MS. 3.4.1.
1
H NMR
The oils obtained from reactions of both JOS and TOR at 425oC are listed in Table 2. The hydrogen types are classified following Bartle and Jones [11]. Table 2: 1H NMR data for JOS and TOR at 425oC 1
Reactant
H NMR
gas Har
Hα
Hβ
Hγ
JOS
N2
0.04
0.10
0.56
0.30
JOS
H2
0.07
0.17
0.59
0.17
TOR
N2
0.05
0.10
0.67
0.18
TOR
H2
0.08
0.15
0.59
0.17
Under these conditions, where high oil yields were obtained (Table 1), low Har and high Hβ values were found in all cases. The oils from reactions of JOS with H2 and TOR with both H2 and N2 showed very similar spectra. The oil from reaction of JOS with N2 was obtained in lower yield (Table 1) and had a higher Hγ value, suggesting that more extensive fragmentation of the aliphatic chains had occurred. 3.4.2. GC-MS data GC-MS data for the oils from reactions of JOS and TOR at 425 oC in both N2 and H2 are shown in Figure 1.
a
b
c
d
Figure 1. Total ion chromatogram of GC-MS (a) JOS oil at 425oC under N2 (b) JOS oil at 425oC under H2 (c) TOR oil at 425oC under N2 (d) TOR oil at 425oC under H2 The chromatograms in general are consistent with 1H NMR data in that the trace for the oil from reaction of JOS with H2 is very similar to those of TOR with both H2 and N2, whereas the oil from JOS with N2 shows a lower proportion of long chain hydrocarbons.
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Oviedo ICCS&T 2011. Extended Abstract
4.
Conclusion
Although the reactivity of JOS and TOR are significantly different, the structure of the major product, the oils, from reactions with H2 at 425oC are remarkably similar. The oil from reaction of JOS at 425oC with N2 was obtained in lower yields and 1H NMR and GC-MS data showed evidence for more fragmentation of the long chain hydrocarbons. The comparison of reactions suggests that catalysis of scission of C-S bonds in Jordanian oil shale may open the path to obtaining good oil yields under even milder conditions. Addition of Sn compounds to reactions of both JOS and TOR showed no evidence of catalytic effects, in contrast to what is observed for similar reactions of plant-derived coals. Acknowledgments We thank the Sentient Group and Jordan Energy for financial support and provision of the oil shale sample. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Cane RF, Albion PR. Organic geochemistry of torbanite precursors. Geochimica et Cosmochimica Acta 1973;37:1543-1549. Zilm KW, Pugmire RJ, Larter SR, Allan J, Grant DM. Carbon-13 CP/MAS spectroscopy of coal macerals. Fuel 1981;60:717-722. Hamarneh Y, Al-Ali, J., Sawaqed, S., Oil Shale Resources Development in Jordan. Amman, Jordan. Natural Resources Authority; 2006 Abed AM, Arouri KR, Boreham CJ. Source rock potential of the phosphorite-bituminous chalk-marl sequence in Jordan. Marine and Petroleum Geology 2005;22:413-425. Redlich P, Jackson WR, Larkins FP. Hydrogenation of brown coal. 9. Physical characterization and liquefaction potential of Australian coals. Fuel 1985;64:1383-1390. Haddadin RA, Mizyed FA. Thermogravimetric analysis kinetics of Jordan oil shale. Industrial & Engineering Chemistry Process Design and Development 1974;13:332-336. Hulston CKJ, Redlich PJ, Jackson WR, Larkins FP, Marshall M, Sakurovs RJ. Reactivity and structure of two coals containing significant methoxy group concentrations. Fuel 1995;74:1865-1869. Lide DR. CRC Handbook Of Chemistry And Physics Version 2005. Boca Raton, Florida, U.S.A. CRC Press; 2004 Knights BA, Brown AC, Conway E, Middleditch BS. Hydrocarbons from the green form of the freshwater alga Botryococcus braunii. Phytochemistry (Elsevier) 1970;9:13171324. Redlich PJ, Jackson WR, Larkins FP. Studies related to the structure and reactivity of coals. 15. Conversion characteristics of a suite of Australian coals. Fuel 1989;68:231-237. Bartle KD, Jones DW. Nuclear magnetic resonance spectroscopy. Anal. Methods Coal Coal Prod. 1978;2:103-160.
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Oviedo ICCS&T 2011. Extended Abstract
Ethanol effect on the average structural parameters of IDF soot soluble organic fraction Maurin Salamanca, Mauricio Velásquez, Fanor Mondragon, Alexander Santamaria* Universidad de Antioquia, Medellín, Colombia *Corresponding author:
[email protected] Abstract In this study, conventional analytical methods such as infrared spectroscopy, 1H-NMR, elemental analysis and vapor pressure osmometry (VPO) were combined to characterize the soot precursor material present in the soluble organic fraction (SOF) of young soot of aliphatic and aromatic inverse diffusion flames doped with ethanol. The results of this study indicated that the aliphatic fraction of SOF decreases as the height above the burner increases due to thermal effects, and although this behavior was also observed for the ethanol-doped flames, the aliphatic character and the evidence of oxygenated species of SOF will depend on the fuel chemical nature. It could be observed that the aromatic-ethanol flames produce SOF with higher aliphatic and oxygenated species compared to the undoped flame, whereas the aliphatic-ethanol flames showed the opposite. The increase in the oxygenated functional groups on samples indicates that part of the oxygen coming from ethanol was incorporated into the SOF.
1. Introduction In the lasts decades the use of biofuels has more acceptance because it reduces fuel petroleum dependence as well as the greenhouse gases emissions from fossil fuels. The development of low-priced processes for obtaining biofuels and the increment on petroleum prices made biofuels an interesting choice [1-2]. In the last decades a variety of oxygenated compounds such as alcohols, ethers and acetals have been studied because of their capacity to change the combustion dynamics of the fuels, especially because they can introduce different kinds of radicals that could increase particulate matter precursors or change the species involved in oxidation processes [3-5]. Ethanol is one of the most studied oxygenated additives because it can be obtained from biomass at reasonable cost and reduces the petroleum dependence on fuels [6-7]. Ethanol as an additive has been studied in several combustion systems, on engines applications and different flames configurations [5]. These works have established a
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Oviedo ICCS&T 2011. Extended Abstract
reduction on soot, low molecular weight PAHs and acetylene emissions [8-10]. However, it has been found that the amount of oxygenated species, specially acetaldehyde and formaldehyde, increased when ethanol was used [11-12]. Some studies have found that the differences in particle nanostructure as well as soot oxidation rate are due to differences on chemical nature of initial fuel [13-14]. However, few studies have been focused on the influences of additives in the chemical composition of soluble organic fraction of soot, also referred as SOF. Santamaria et al, using combined information obtained by nuclear magnetic resonance (NMR), infrared spectroscopy (IR), vapor pressure osmometry (VPO) and elemental analysis, described the SOF coming from benzene and ethylene flames in terms of average structural parameters [15]. Therefore, the purpose of this study was to evaluate the chemical effect of ethanol addition on SOF coming from hexane and benzene flames in terms of average structural parameters, such as chain length and number of fused aromatic rings.
2. Experimental section 2.1. Burner and sampling In this study, benzene, hexane and blends with 20% of ethanol were used as fuels to generate an inverse diffusion flame. The burner is composed of three concentric stainless steel tubes; the central tube was used to supply the air, the annular tube to supply the fuel and the outer tube to generate a nitrogen shield to avoid the interaction of the flame with the surrounding air. The liquid fuel (benzene and hexane with and without ethanol) was delivered using an HPLC pump to a vaporizer at 150°C. A flow rate of 0.75 cm3.min-1 and 1.25 cm3.min-1 for benzene and hexane, respectively was used in the experiments. Then the fuel vapors were mixed and carried towards the burner mouth with nitrogen as carrier. Under these conditions, a flame height of 60 mm was obtained in all cases. Soot sampling was made using a filter system at the inception point and 60 mm height above the burner mouth at the lateral axis of the flame, (Figure 1).
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Oviedo ICCS&T 2011. Extended Abstract
Filter Filtro Llama Flame Venteo Vent
Bomba de Vacum vacio Pump
Trampa Tramp
N2
N2
Air Aire Fuel Combustible
Fuel Combustible
Figure 1. Experimental set up for sampling from flame 2.2. Chemical characterization of SOF Chemical analysis of the soot fraction soluble in chloroform was done. The infrared analysis was made using the KBr pellet method in a Nicolet Magna IR 560 spectrometer with a MCT/A detector operated at 77K on the wavelength range from 600 to 4000 cm1
. Each sample was taken at least three times to estimate reproducibility. For the 1H-
NMR analysis, the extracts were dried and re-dissolved in CDCl3 containing trace amounts of tetramethylsilane (TMS), which was used as an internal chemical shift reference. All spectra were taken in a Bruker AMX 300 spectrometer. Then, each spectra were baseline corrected and integrated manually at least four times and the results were averaged to reduce the uncertainty (less than 5%) generated by the manual adjustment. Elemental analysis was carried out in a CHNSO Leco Instruments. Average molecular weight data of the extractable material of soot generated in the flame was determined by vapor pressure osmometry (VPO) in a Knauer K7000 osmometer using chloroform as solvent and benzyl as calibration standard. All measurements were carried out using sample and standard solutions of 1g/kg and 0,0160 mol/kg respectively.
2.3. Structural Parameters The spectrum of each sample was separated into characteristic regions according to the Santamaria’s work [16]. Then this information was correlated with molecular weight and elemental analysis data to obtain structural parameters, such as those reported in Table 1.
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Oviedo ICCS&T 2011. Extended Abstract
Table 1. Structural parameters definition fa
Aromatic atomic carbon fraction 0.33
fal
0.4
%
2
0.5
1
2
1600
Chain length number of carbon atoms per average structural unit #
#
Ra
0.5
Average number of oxygen on carbonyl groups #
L
1
Aliphatic atomic carbon fraction 0.33
#O
0.4
#
Number of fused aromatic rings per average structural unit 1
#
#
2
Where: C* Molar fraction of carbons obtained by elemental analysis. H* Molar fraction of hydrogen obtained by elemental analysis. O* Molar fraction of oxygen obtained by elemental analysis. MW Average molecular weight of the samples Hγ (Aliphatic hydrogen in methyl group on γ position or further to an aromatic ring), Hβ1 (Alycyclic hydrogen in β position to two aromatic rings), Hβ2 (Aliphatic hydrogen in methyl or methylene groups in β position to an aromatic ring), Hα (Hydrogen of CH, CH2, CH3 on α position to aromatic rings), Hf (Hydrogen fluorene type), Ho (Oleofinic hydrogen) and Ha (Hydrogen on aromatic rings).
3. Results discussion 3.1. Soluble Organic Fraction The Figure 3 shows the mass percentage of soluble organic fraction as function of the flame height and ethanol addition. The amount of SOF decreases as a function of flame height for both reference and ethanol-doped flames. This reduction is mainly caused by competition between thermal and oxidative processes of soot particles upstream of the flame. However, upon comparing the amount of SOF coming from the ethanol-doped benzene flame with the reference benzene flame at a particular position, a 10% increase was observed. This behavior is opposite to that observed in hexane flames, which indicates that oxidation and pyrolysis processes will depend on the chemical nature of starting fuel. For instance, the increment in the amount of SOF observed for ethanol-doped benzene flame is due to an increment in the pyrolysis process through the ethyl radical coming from ethanol decomposition, leading to the production of acetylene and low molecular weight PAHs, whereas, the opposite behavior observed in hexane flame can be explained by an increase in the oxidation process caused by the OH radical, which in turn reduces the soot precursors material. Although the oxidation can also take place in ethanol benzene flames, the degree of pyrolysis overcome the oxidation.
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Oviedo ICCS&T 2011. Extended Abstract 90 75 60 45 30
B
75
SOF (%)
SOF (%)
90
A
15
60 45 30 15
0
0 Benzene
Ben:20%EtOH
Hexane
HAB (mm)
Hex:20%EtOH
HAB (mm) Incepction
60 mm
Figure 3. SOF on chloroform for the soot samples (A) Benzene (B) Hexane
3.2. Infrared spectroscopy The Figure 4 shows the infrared spectra of the SOF coming from hexane and benzene flames with and without ethanol. For hexane flames, it is observed that the C-H stretch signal of aliphatic groups decreases as a function of height from soot inception point up to 60 mm, however the intensity of C-H aromatic signal depends on ethanol addition, for instance, the relative intensities of the CHar/CHal observed for samples taken at 60 mm height of hexane flames, decreased when the ethanol was added. This behavior can be interpreted by two competitive processes, soot precursors oxidation and polycyclic aromatic condensation, which agrees with the information obtained by solubility. On the other hand, when ethanol was added to the benzene flame, a significant increase of the aliphatic and oxygenated functional groups were observed, which is opposite to result obtained for hexane flame. As stated early, the effect of ethanol addition depends on the chemical nature of the starting fuel. Therefore, the increase in the aliphatic character of benzene SOF can be attributed to an increase in the pyrolysis process over the oxidation, leading to the formation of low molecular weight PAHs and aliphatic compounds. Additionally, the presence of oxygenated groups on samples coming from ethanol-doped flames indicates that some additional oxidation steps are taking place in the flame compared to those normally occurring with just the molecular oxygen coming from air.
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Oviedo ICCS&T 2011. Extended Abstract Benzene Benzene:20EtOH
c
d
3500
3000
C=O
b
C-Hal
a
C-Har
Absorbance (a.u)
Hexane Hexane:20EtOH
1600
1200
800
3500
3000 -1
1600
1200
800
Wavelenght (cm )
Figure 4. Infrared spectra for SOF obtained from hexane, benzene, hexane 20%EtOH and benzene 20%EtOH. a, b sample taken at the inception point and c,d sample taken at 60 mm. 3.3. 1H-Nuclear Magnetic Resonance Figure 5 shows the 1H-NMR spectra of SOF of hexane and hexane-20% ethanol flames at the inception point. Ethanol addition did not affect the aromatic hydrogen fraction, which remains constant at this point, but caused a relative increases in the aliphatic hydrogen content, result that corroborates what has been published in the literature (15). At low flame positions, the temperature is high enough to cause ethanol fragmentation into aliphatic and oxygenated radicals. Although, it is though that the aliphatic fragment can be bonded to the aromatic species, this fact has not been corroborated yet. Figure 6 summarizes the hydrogen distribution of SOF coming from hexane flames. Ethanol addition caused an increase in the aromatic character (aromatic hydrogen, Ha) as a function of flame height, followed by a reduction in the aliphatic content (aliphatic hydrogen: Hα, Hβ, Hγ), except for sample taken at the inception point as was described early. On the other hand, the SOF of soot from benzene flames had opposite behavior compared to hexane flame samples (data not shown).
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Oviedo ICCS&T 2011. Extended Abstract Hexane
Hexane:20EtOH Hβ
Signal (a.u)
Ha
Hγ
10
9
8
7
2.5
2.0
1.5
1.0
0.5
0.0
Frequency (ppm)
Figure 5. 1H-NMR spectra of the SOF obtained from hexane and hexane 20%EtOH sample taken at the inception point.
Hexane
0,80 0,70
13
0,60
30
40
0,70 0,60
0,50
0,50
0,40
0,40
0,30
0,30
0,20
0,20
0,10
0,10
0,00
Hexane:20%EtOH
0,80
60.00
Ha Ho
Hf
Hα Hß2 Hß1
H γ
0,00
Ha
Ho
13
30
Hf
Hα
40
60
Hß2 Hß1 H γ
Figure 6. Hydrogen distribution of SOF coming from hexane soot as a function of flame height.
3.4. Elemental analysis and vapor pressure osmometry Table 2 shows the average molecular weight obtained by VPO. The average molecular weight increases with the flame height; this is an expected tendency for precursors and soot growing processes. For benzene flames, the average molecular weight of SOF was ~25% higher compared to samples from hexane flames. This fact is attributable to the chemical nature of starting fuel and its aromatic polymerization rate, being faster for benzene than for hexane, since the last one required much more time to generate the basic aromatic moieties. On the other hand, the ethanol addition caused about 6% reduction on the average molecular weight for both fuels. This reduction can be explained by both a promotion of the oxidation process and/or an increase in the rate of formation low molecular weight PAHs, as apparently occurs in the benzene flame.
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Oviedo ICCS&T 2011. Extended Abstract
Table 2 also shows the C/H ratio obtained by elemental analysis, although there is not an apparent effect of ethanol on this parameter, the results indicate that the aromatic condensation degree is consistent with flame height. Table 2. Average molecular weight and C/H of elemental analysis for SOF Hexane Hexane:20% EtOH Benzene Benzene:20%EtOH HAB MW* C/H MW* C/H MW* C/H MW* C/H Inception 326 1.34 296 1.33 471 2.04 446 1.97 point 60 mm 393 1.41 363 1.41 528 2.22 503 2.11 * MW Molecular weight (g/mol)
3.5. Structural parameters The main structural parameters calculated for samples are shown on Table 3. In general, all samples showed a tendency to increase the aromatic fraction, (fa), followed by a subsequent reduction on the aliphatic fraction, (fal), as flame height increases. However, upon comparing hexane and benzene results, it is clear that benzene flames generate soot precursors with a higher degree of aromatic condensation, (Ra), since the polymerization mechanism through aromatic moieties is faster. On the other hand, whereas the number of fused aromatic rings is higher for samples coming from benzene flame, the average chain length (L) is higher for samples coming from hexane, especially when ethanol is added to the flame, indicating that the pyrolysis process of the aliphatic fragment of ethanol plays an important role in the soot precursor’s formation. It is also observed, that the oxygen content found in SOF samples, related to #O, has a slight increase when ethanol is added to the benzene flame; however this tendency was not observed for hexane, which indicates that the degree of oxidation also depends on the chemical nature of fuel.
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Oviedo ICCS&T 2011. Extended Abstract
Table 3. Structural parameter calculated for SOF.
fa
Hexane Hexane:20% EtOH Benzene Benzene:20%EtOH In. 60 In. 60 In. point 60 mm In. point 60 mm point mm point mm 0.78 0.76 0.78 0.82 0.90 0.93 0.85 0.88
fal
0.18
0.17
0.17
0.11
0.07
0.05
0.09
0.07
#O
0.86
2.09
0.98
1.82
0.80
0.13
1.02
0.24
L
4.44
4.76
3.74
3.00
1.01
0.40
2.71
2.45
Ra
5.32
6.03
4.74
4.96
12.8
15.1
11.4
13.5
Structural Parameter
4. Conclusions The effect of ethanol added to the fuels evaluated in this study depended on the chemical nature of the initial fuel. For hexane flames, it was observed that the addition of ethanol increased the aromatic character of SOF, although the average number of fused aromatic rings remains constant (Ra∼5) compared to that obtained from pure hexane. In contrast, the ethanol addition to benzene flame caused an increase in the aliphatic character of SOF samples, which corresponds to an increase of 2 aliphatic carbons by structural unit. The reason for this behavior is due to the dual effect of ethanol, which will depend on the chemical nature of fuel. One effect is the effect of the aliphatic fragment of ethanol in the formation of soot precursors in aromatic flames. The other effect is due to the OH radical which will play an important role in the oxidation process of the aliphatic flames. These results demonstrate that ethanol addition can change the chemical nature of soot and its precursors obtained in IDFs. A final question is ¿can ethanol produce the same effect on soot chemistry, when is it used as additive on traditional combustion devices?
Acknowledgements The authors are grateful to COLCIENCIAS and University of Antioquia for the financial
support
given
through
the
Project
1115-405-20283.
M.S.
thanks
COLCIENCIAS and the University of Antioquia for her PhD scholarship. M.V also thanks COLCIENCIAS for the economical support granted during his undergraduate studies.
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Oviedo ICCS&T 2011. Extended Abstract
References [1] Gaffney JS, Marley NA. The impacts of combustion emissions on air quality and climate – From coal to biofuels and beyond. Atmospheric Environment. 2009;43:23-39. [2] Cardona CA, Sánchez OJ. Fuel ethanol production: Process design trends and integration opportunities. Bioresource Technology 2007;98:2415-57. [3] Kohse-Höinghaus K, Oßwald P, Cool TA, et al. Biofuel Combustion Chemistry: From Ethanol to Biodiesel. Angewandte Chemie International Edition. 2010;49:3572-97. [4] Inal F, Senkan SM. Effects of oxygenate additives on polycyclic aromatic hydrocarbons(pahs) and soot formation. 2002;174(9):1-19. [5] Litzinger T, Colket M, Kahandawala M, et al. Fuel Additive Effects on Soot across a Suite of Laboratory Devices, Part 1: Ethanol Combustion Science and Technology. 2009;181(2):31028. [6] Lin Y, Tanaka S. Ethanol fermentation from biomass resources: current state and prospects. Applied microbiology and biotechnology. 2006;69(6): 627-42. [7] Galbe M, Zacchi G. A review of the production of ethanol from softwood. Applied microbiology and biotechnology. 2002;59(6): 628-38. [8] Wu J, Song KH, Litzinger T, et al. Reduction of PAH and soot in premixed ethylene–air flames by addition of ethanol. Combustion and Flame. 2006;144: 675-87. [9] Lapuerta M, Armas O, Herreros JM. Emissions from a diesel–bioethanol blend in an automotive diesel engine. Fuel. 2008;87: 31-7. [10] Therrien RJ, Ergut A, Levendis YA, Richter H, Howard JB, Carlson JB. Investigation of critical equivalence ratio and chemical speciation in flames of ethylbenzene–ethanol blends. Combustion and Flame. 2010; 157: 296-312. [11] McEnally CS, Pfefferle LD. The effects of dimethyl ether and ethanol on benzene and soot formation in ethylene nonpremixed flames. Proceedings of the Combustion Institute. 2007;31: 603-10. [12] Yao C, Yang X, Raine RR, Cheng C, Tian Z, Li Y. The Effects of MTBE/Ethanol Additives on Toxic Species Concentration in Gasoline Flame. Energy & Fuels. 2009;23: 354348. [13] Alfè M, Apicella B, Barbella R, Rouzaud J-N, Tregrossi A, Ciajolo A. Structure–property relationship in nanostructures of young and mature soot in premixed flames. Proceedings of the Combustion Institute. 2009;32: 697-704. [14] Wal RLV, Tomasek AJ. Soot oxidation: dependence upon initial nanostructure. Combustion and Flame 2003;134: 1–9. [15] Santamaría A, Eddings EG, Mondragón F. Effect of ethanol on the chemical structure of the soot extractable material of an ethylene inverse diffusion flame. Combustion and Flame. 2007;151: 235-44. [16] Santamaría A, Mondragón F, Molina A, Marsh ND, Eddings EG, Sarofim AF. FT-IR and 1H NMR characterization of the products of an ethylene inverse diffusion flame. Combustion and Flame. 2006;146:52-62. Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
An Analysis Of The Research Performed With The Argonne Premium Coals And Its Contribution To Coal Science Jonathan P. Mathews1, Yesica E. Alvarez1, Randall E. Winans2 1
John and Willie Leone Family Department of Energy & Mineral and EMS Energy Institute, 110 Hosler Building.# The Applied Research Laboratory, The Pennsylvania State University, University Park 16802, USA 2 X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.
[email protected] Abstract The Argonne Premium Coal program collected eight USA coals of industrial relevance and provides well-mixed, -characterized, -preserved coal samples in borosilicate glass vials to the coal science community. Since being available in 1985, 33,235 ampules have been shipped. These ampules were sent around the globe and have been utilized in a wide variety of coal characterizations and studies. They are thus the most well evaluated coals in existence. The peer-reviewed web of science journal literature was examined for the terms ‘Argonne Premium Coal’, the individual coal names, and papers citing the seminal 1990 Vorres Argonne Premium Coal paper. The resulting 600+ Argonne Premium Coal journal articles were examined to determine which coals in the suite had been evaluated and to generally classify the research topic. Wordle and other analyses were used to determine the interest in various coals, topics, and author contributions.
The Illinois no. 6 bituminous coal was found to be the most well-studied coal appearing in >180 journal articles. Many of the other coals are well-studied with >130 papers. The “least well-studied” coals were the Lewiston-Stockton and the Blind Canyon bituminous coals with around 90 and 110 articles respectively. This is consistent with the vial shipment data evaluated by Vorres et al. in 1994.
A Wordle analysis of the article titles, an analysis of the general subject, and an analysis of the journal showed: 1) frequent use of the terms: analysis, structure, carbon, solvent, swelling, NMR, spectroscopy, and sorption. 2) The leading authors (determined by this approach) were Takanohashi, Kelemen, Suuberg, Kwiatek, Iino, Kandiyoti, Larsen, Wertz, Gorbaty, Saito, Schroeder among 140 authors. 3) When classed by subject,
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structure, NMR, swelling, extraction, sorption, pyrolysis and liquefaction were frequent subject areas in a widely diverse field. The missing piece of this body of work is the databases, created here, to ease the discovery of the state-of-knowledge.
The creation of this sample suite has resulted in ad-hoc international-peer-reviewed literature collaboration. The success of the program has been immense and the field of coal science owes Argonne and the Office of Basic Energy Sciences (Chemical Sciences Division) a thank you for this exceptional gift of still expanding knowledge.
1. Introduction Coal is complex and highly variable in behavior and composition, within multiple aspects, making its systematic study extremely challenging. It is thus highly desirable to have coal standards that are available to the community, such that a body of knowledge can be produced and the field can more forward with scientific exploration building on the existing data suite. There have been several coal sample banks but in the U.S. the two most utilized sample banks are the Argonne Premium Coal suite [1] and the Pennsylvania State University Coal Sample Bank [2, 3]. They serve different purposes; the Argonne Premium Coal suite is 8 coals shipped in borosilicate glass vials (5g of 100 mesh or 10g of -20 mesh) while the Penn State Coal Sample Bank contains data for >1450 coals with many historic samples (>1100 available) and a suite of 38 wellpreserved Department of Energy Coal Samples (DECS) samples typically available in 300 g, 2.5 kg, or 12 kg foil multilaminate bags [4]. Thus the Argonne Premium Samples are well suited for advanced characterization and small-scale behavioral investigations.
For coal selection a cluster analysis of 200 samples in the Penn State Coal Sample Bank was used to determine desirable range of parameters for compositional selections of C, H, N, O, and S for coal mined in the United States. Five of the coals were selected based on C content across the rank range: lignite to low-volatile bituminous coal (anthracite although historically important and actively mined in small quantities was not included). Variation in S content and desire to include a coking coal (Pittsburgh) further expanded the selection. The inclusion of Blind Canyon was for its high liptinite content, similarly Lewiston Stockton for high sporinite and inertinite contents [1]. Table 1 shows the coal sample, rank and state. There are currently two extensive structural reviews available: Pocahontas No. 3 [5] and Illinois No. 6 [6]. Submit before May 15th to
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Table 1. Argonne Premium Coal Samples, State and Rank Number
Seam
State
Rank
1
Upper Freeport
PA
mvb
2
Wyodak-Anderson
WY
subbit.
3
Illinois No. 6
IL
high-vol bit.
4
Pittsburgh (No. 8)
PA
high-vol bit.
5
Pocahontas No. 3
VA
low-vol bit.
6
Blind Canyon
UT
high-vol bit.
7
Lewiston-Stockton
WV
high-vol bit.
8
Beulah-Zap
ND
lig.
Previously the status of the Argonne Premium Coal Sample Program was evaluated in 1987 [7], 1988 [8] and 1994 [9]. The goal here is to update that information and to create a database that will better serve the coal community by determining which coals have been studied throughout the broad literature. Furthermore, the paper evaluates the impact of this program on coal science.
2. Methodology An ISI Web of Knowledge (using the web of science database) evaluation of journal articles with “Argonne Premium Coal” in the title, as well as searching for individual coal names, was used to identify appropriate journal articles. A search was also performed to determine additional papers based on a citation evaluation of the 1990 Vorres paper “The Argonne Premium Coal Sample Program” [1]. The data was transferred into an Endnote library and supplemented by the lead authors Endnote library that had utilized Argonne Premium as keywords (to better enable coal data collection). The papers were examined to determine which of the suite had been utilized and non-Argonne suite coals were rejected and duplicate citations removed. Keywords were also added to the Endnote references to classify the general research area: combustion, pyrolysis, liquefaction, extraction, gasification, swelling, drying, characterization, adsorption, structure, among many others, as well as the individual coals studied. Search capabilities of Endnote allowed the determination of the number of journal articles that had evaluated which coal. The analysis was performed in December 2010 and so would miss more recent contributions. The ISI Web of Submit before May 15th to
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Knowledge and supplemented journal articles are certainly an underestimation of the work. The inclusion of the lead authors’ database may also bias the selection. However, it is an excellent starting point and considerations are underway for the sharing of the database and the inclusion of omissions.
Endnote was also used to generate an authors list and the journal titles listing for evaluation with Wordle [10]. Wordle creates a visual representation of text frequency. The terms “Argonne Premium Coal” and “Coal/Coals” were removed from the journal titles with Words’ find and replace function to allow a visual representation of the word frequency in the titles. Wordle removes authors’ initials thus the evaluation is at risk of over promoting authors with common surnames. Wordle distinguishes between the English spelling variations and also between singular and plural and so in titles solvents and solvent will appear as separate entitles. Subject classifications were also evaluated using Wordle.
3. Results and Discussion For the breakdown of the frequency of the coals evaluation in journal articles Illinois no. 6 bituminous coal was found to be the most well studied coal appearing in >180 journal articles. Many of the other coals are well studied with >130 papers. The “least well-studied” coals were the Lewiston-Stockton and the Blind Canyon bituminous coals with around 90 and 110 articles respectively. This is consistent with the vial shipment data evaluated by Vorres et al. in 1994 [9]. The Lewiston-Stockton coal is the liptiniterich coal sample while Blind Canyon is the high sporinite and inertinite content sample, which probably explains the reduced frequency. Much of the work has evaluated the rank range suite of which the 2 previous non-vitrinite maceral-rich coals are considered “spoilers”.
Figure 1 shows a Wordle view of the titles of journal articles that evaluated the Argonne Premium Coal suite. The color is an aid for viewing; it is the size of the word that provides an indication of the frequency of its occurrence. The frequent words were analysis, structure, carbon, solvent, swelling, NMR, spectroscopy, and sorption, etc. The figure is also word-rich indicating a wide variety of research topics.
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Figure 1. A Wordle view of the frequency of terms in the titles of Argonne Premium Coal articles. Figure 2 shows a Wordle view of the authors. Among the 140 authors the prominent authors were: Takanohashi, Kelemen, Suuberg, Kwiatek, Iino, Kandiyoti, Larsen, Wertz, Gorbaty, Saito, Schroeder among others. This represents a range of international authors from academia, industry, and government entities.
Figure 2. A Wordle view of the frequency of authors in the titles of Argonne Premium Coal articles.
Figure 3 shows the Wordle view of the frequency of classification terms for Illinois no. 6, the most well-studied of the coals. As expected many of the papers deal with characterization as well as behavior with swelling, extraction, and with liquefaction.
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Figure 3. A Wordle view of the frequency of classification terms for Illinois no. 6 coal articles.
It is difficult to place a research value to the body of work that the Argonne Premium suite has enabled but it is likely in excess of $20 million (assuming conservatively that $100,000 could produce 3 journal articles). We have, at our fingertips a body of knowledge that spans chemical, physical and behavioral aspects. These contributions to our understanding of coal structure and reactivity are highly significant and could not be covered in a short discussion. However, select examples will be. Characterization of sulfur types has always been difficult until the X-ray spectroscopy technique (SXANES) was developed by Kelemen and Gorbaty [11]. They were able to determine the sulfur types in these coals and have expanded it to other coals and kerogens [12, 13]. However, they continually used the Argonne coals as a test when trying new approaches with this technique. Solids NMR has been an excellent tool to look directly at the coal structure but there was always uncertainties about the quantitation. A large number of groups around the world evaluated these coals and compared their results in a bookproducing ACS symposium [14]. More recently when carbon sequestration in coal seams became important, the Argonne coals where used to evaluate CO2 uptake in coals by a number of labs [15, 16]. The coal suite, and more importantly the data generated has enabled coal science to advance more rapidly, strategically, and with more meaningful results than would have otherwise been possible due to the ad-hoc collaboration of numerous universities, government agencies, and industry worldwide.
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Oviedo ICCS&T 2011. Extended Abstract
Conclusions The Argonne Premium Coal program was established to provide research samples of a small number of representative US coals. The samples are homogeneous and protected from oxidation allowing meaningful research from different labs and different times can be compared without worrying about the history of the sample. Since being available in 1985, 33,235 ampules have been shipped with their resultant data being produced in the peer-review literature. A ISI Web of Knowledge (using the web of science database) evaluation of journal articles with “Argonne Premium Coal” in the title, as well as searching for individual coal names, was used to identify appropriate journal articles in an Endnote database that were used to evaluate the coals studied, subject areas, and authors contributions. From the suite, Illinois no. 6 bituminous coal was found to be the most commonly shipped and most well studied coal appearing in >180 journal articles. Many of the other coals are well studied with >130 papers. Wordle was used to evaluate word frequencies from titles and authors contributions. The frequent words within the journal article titles were: analysis, structure, carbon, solvent, swelling, NMR, spectroscopy, and sorption, etc. Among the 140 authors the prominent authors were: Takanohashi, Kelemen, Suuberg, Kwiatek, Iino, Kandiyoti, Larsen, Wertz, Gorbaty, Saito, Schroeder among others. This represents a range of international authors from academia, industry, and government entities. The coal suite, and more importantly the data generated has enabled coal science to advance more rapidly, strategically, and with more meaningful results than would have otherwise been possible due to the ad-hoc collaboration of numerous universities, government agencies, and industry worldwide. Work is continuing and efforts are underway to further capture the body of knowledge and to share this database resource with coal scientists worldwide.
Acknowledgements. Many have contributed to the success of the Argonne Premium Coal Program. The original planners were: Randall Winans, Phil Horwitz, John Unik, Gary Dyrkacz and John Young (facility designer); Karl Vorres built the processing facility, acquired the samples and managed the facility; the staff of the U. S. Geological Survey who supervised the sample collection: C. Blaine Cecil, Ron Stanton and Peter Warwick. Over the last few decades the program manager has been: Karl Vorres, Ken Anderson, Jerry Hunt, Randall Winans with Deborah Vervack the facility administrator. Program Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
funding by the Office of Basic Energy Sciences (Chemical Sciences Division) was responsible for allowing this coal suite collection and operation. In addition many coal scientists have contributed to the success of the program and their individual efforts are also recognized.
References [1] Vorres KS, The Argonne Premium coal sample program. Energy Fuels 1990, 4, 4206. [2] Glick DC, Davis A, Operation and composition of the Penn State Coal Sample Bank and Data-Base. Organic Geochemistry 1991, 17, (4), 421-30. [3] The Pennsylvania State University Penn State Coal Sample Bank and Data Base. http://www.energy.psu.edu/copl/index.html [4] Glick DC, Mitchell GD, Davis A, Coal sample preservation in foil multilaminate bags. Int. J. Coal Geol. 2005, 63, 178-89. [5] Stock LM, Muntean JV, Chemical constitution of Pocahontas No. 3 coal. Energy Fuels 1993, 7, 704-9. [6] Castro-Marcano F, Mathews JP, Constitution of Illinois No. 6 Argonne Premium coal: a review. Energy Fuels 2011, 25, (3), 845-53. [7] Vorres KS, Preparation and distribution of Argonne Premium coal samples, Prepr. Pap.-Am. Chem. Soc, Div. Fuel Chem., 1987, New Orleans, LA, 32, 221-6 [8] Vorres KS, Sample preparation for, and current status of the Argonne Premium Coal sample program, 1988, Los Angeles, CA, 33, 1-6 [9] Vorres KS, Kruse CW, Glick DC, Davis A, Nater KA, A perspective on the status of coal research from shipments of samples, Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem., 1994, San Diago, CA, 39, 1-6 [10] Feinberg J Wordle. http://www.wordle.net/ [11] George GN, Gorbaty ML, Kelemen SR, Sansone M, Direct determination and quantification of sulfur forms in coals from the Argonne Premium Sample Program. Energy Fuels 1991, 5, (1), 93. [12] Gorbaty ML, Kelemen SR, Characterization and reactivity of organically bound sulfur and nitrogen fossil fuels. Fuel Process. Technol. 2001, 71, (1-3), 71-8. [13] Kelemen SR, Afeworki M, Gorbaty ML, Kwiatek PJ, Sansone M, Walters CC, et al., Thermal transformations of nitrogen and sulfur forms in peat related to coalification. Energy Fuels 2006, 20, (2), 635. [14] Botto RE, Sanada Y, Magnetic Resonance of Carbonaceous Solids. American Chemical Society: 1992; Vol. 229. [15] Goodman AL, Busch A, Bustin RM, Chikatamarla L, Day S, Duffy GJ, et al., Inter-laboratory comparison II: CO2 Isotherms measured on moisture-equilibrated Argonne Premium coals at 55 degrees C and up to 15 MPa. Int. J. Coal Geol. 2007, 72, (3-4), 153-64. [16] Goodman AL, Busch A, Duffy GJ, Fitzgerald JE, Gasem KAM, Gensterblum Y, et al., An inter-laboratory comparison of CO2 isotherms measured on Argonne Premium coal samples. Energy Fuels 2004, 18, (4), 1175-82.
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Porosity and Gas Absorption of Coals Studied by X-ray Scattering and Modeling Randall E. Winans1, Soenke Seifert1, Darren Locke1, Peter Chupas1, Karena Chapman1, Marielle R. Nariewicz2, Jonathan P. Mathews2, Joseph M. Calo3 1
X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA 2 Department of Energy & Mineral Engineering and EMS Energy Institute, 126 Hosler Building. The Pennsylvania State University, University Park, PA 16802, USA 3 Brown University, Division of Engineering, Box D, 182 Hope St., Providence, RI 02912, USA
[email protected] Abstract Small angle x-ray scattering (SAXS) and high energy wide angle scattering with pair distribution function (PDF) analysis has been used to study coal structure and to elucidate changes with exposure to high pressure CO2 at ambient temperatures. SAXS provides pore size, size distribution, shape and surface morphology over broad length scales, while PDF provides atom-atom correlations out to several nm. The studies were done on a series of coal pieces in a high pressure cell which was transparent to X-rays. This method allowed the real-time determination of porosity changes due to CO2 uptake or loss resulting in coal swelling and deswelling. The data suggested it may be possible to determine adsorption and pore filling quantitatively. Both SAXS and PDF calculated scattering data from large-scale molecular models of these coals and models with CO2 qualitatively described experimental observations. The series of Argonne Premium Coals where studied and a dramatic rank effect was evident.
1. Introduction Small angle X-ray scattering (SAXS) and high energy wide angle scattering with pair distribution function (PDF) analysis are used to follow changes in coal and oil shale structure as the solids are being exposed to reactive gases or solvents and high pressures.
For example, this approach is being used to better understand the
fundamental changes in coal structure when exposed to pressurized CO2, to model carbon sequestration[1]. SAXS provides pore size, size distribution, shape and surface morphology over broad length scales. PDF provides atom-atom correlations out to at least 2 nm. Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
In early work, SAXS was used to investigate the porosity of coals[2] and determine fractal properties of small pores[3]. More recently SAXS and SANS has been used to better understand the pore structure of coals.[4] It has been demonstrated that CO2 pore-fills and dissolves in coals and causing swelling. In addition the dissolved CO2 appears to plasticize the coal [5, 6]. This swelling however causes errors in quantifying CO2 capacity with common techniques coal swelling[7].
2. Experimental
For coal SAXS and PDF experiments one mm thick samples of the Argonne Premium Coal Samples and a New Zealand subbituminous coal, Ohai, shown in Table 1 were used. Table 1. Coal properties.
Coal
Rank
%C
%H
%N
%S
%O
%
(daf)
(daf)
(daf)
(daf)
(daf)
ash
%H2O
Ohai
Subbituminous
75.3
4.36
1.31
0.42
18.6
4.16
23.1
Illinois 6
hvC bituminous
77.7
5.00
1.12
2.38
13.5
15.5
7.97
Upper
mv Bituminous
85.5
4.70
1.55
0.74
7.51
13.8
1.13
Freeport
The coals were sealed in cells constructed of two conflat flanges with a 1 mm spacing between the kapton windows which were glued over holes drilled in the flanges to allow penetration by the X-ray beam. The cells where pressurized with an Isco syringe pump from 50 - 75 bar gas pressue. The SAXS data were obtained at the 12-ID beamline at the Advanced Photon Source [8]. The scattered X-rays (12 keV) are detected by a CCD detector (Mar 156 or mosaic APS). Data were obtained every two seconds as the samples were pressurized. The scattered intensities have been corrected for absorption, the empty cell scattering, and instrument background. The differential scattering cross section is expressed as a function of the scattering sector Q, which is defined as: Q =
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Oviedo ICCS&T 2011. Extended Abstract
(4π/λ)SinΘ, where λ is the wavelength of the X-rays and Θ is the half angle of the scattering. For the PDF experiments the same cell was used. The cell was mounted on the instrument at beamline 11-ID-B at the Advanced Photon Source, Argonne National Laboratory with the incident (and scattered) beam directed through the hole in the cell. High-energy X-rays (90.48 keV, λ = 0.1370 Å) were used in combination with a MAR345 image plate detector to record diffraction images[9] to high values of momentum transfer (Q ~ 20 Å−1). Corrections for multiple scattering, X-ray polarization, sample absorption, and Compton scattering were then applied to obtain the structure function S(Q). Direct Fourier transform of the reduced structure function F(Q) = Q[S(Q) − 1] up to Qmax ~ 20 Å−1 gave G(r), the pair distribution function. The PDF, G(r), gives the probability of finding an atom at a given distance r from another atom and for shorter distances can be considered as a bond length distribution. It is obtained from the powder diffraction (X-ray or neutron) via a Fourier transform of the normalized scattering intensity, S(Q):
where ρ(r) is the microscopic pair density, ρ0 is the average number density, and Q is the magnitude of the scattering vector (Q = (4πsin θ)/λ). Experimentally it is not possible to measure data up to infinite Q, and the cutoff at finite values of Qmax decreases the real space resolution of the PDF. This causes some aberrations in the form of “termination ripples” which propagate through G(r) as high frequency noise. For both X-ray scattering experiments, high energies (> 60keV) are required to access high values of Qmax to obtain the most accurate Fourier transform of the reduced structure function F(Q). For the large-scale coal model (50,000 atoms) the construction was based on: (1) HRTEM image analysis, (2) construction of the aromatic clusters, (3) inclusion of heteroatoms and functional groups via scripting, (4) addition of aliphatic side chains and generation of a cross-linked network structure, and (5) arrangement of cross-linked clusters into a simulation cell. This procedure enabled simplifying the model construction process, eliminating researcher structural bias and generating large-scale continuum molecular representations with improved accuracy. Molecular dynamics
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Oviedo ICCS&T 2011. Extended Abstract
(MD) simulations and energy minimizations were performed with Materials Studio 5.0 software from Accelrys Inc. [36]. Energetic interactions were modeled by the consistent-valence force field (CVFF) [37-39], which is intended for application to a wide range of organic systems. The non-bonded interactions were modeled with a Lennard-Jones (LJ) 12-6 potential for van der Waals interactions and a Coulomb potential for long-range electrostatic interactions. The LJ parameters for the cross interactions were determined by the standard Lorentz-Berthelot mixing rules. The velocity Verlet algorithm was used to integrate Newton's equations of motion, and the classical conjugate gradient and steepest descents algorithms were utilized for energy minimizations. The time step used in the MD simulations was taken as 1.0 fs.
3. Results and Discussion Preliminary experiments on a suite of North American and New Zealand coals established that SAXS could be used to observe directly the changes in coal structure caused by CO2 uptake. Subsequent experiments have shown that, at least for high rank coals, the process can be interpreted in terms of a simplified two-phase model beginning with shorter term void/pore filling and gas adsorption onto the solid matrix followed by longer term coal swelling.
1.2e-4 Uppper Freeport (APCS 1) Ohai Illinois No. 6 (APCS 3)
Invariant
1.1e-4
1.0e-4
9.0e-5
8.0e-5 0
100
200
300
400
Time (min)
Figure 1. Changes with time of the invariant at 900 psi of CO2.
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Oviedo ICCS&T 2011. Extended Abstract
Decrease in the invariant is the result of a decrease in difference in electron density, which occurs as the CO2 is filling the pores. ∞
Q = ∫0 q2dq·I(q)
These processes are consistent with an overall decrease in scattering intensity with increasing degree of coal swelling due to the disappearance of the smallest scatterers (voids/pores) accompanied by a shift of the normalized void/pore distribution to larger scatterers (Figure 1). The decrease is consistent with swelling of the solid matrix primarily via a Class II type diffusion process typically associated with a glassy polymer or gel structure.
The data suggested it may be possible to determine adsorption and pore filling in the coal samples quantitatively. Both SAXS and PDF calculated scattering data from large molecular models of these coals[10] and models with CO2[11] qualitatively described what is observed in the experiments. A model of a high rank Pocahontas coal filled with CO2 is shown in the top of Figure 3.
1e+9 3
A
1e+8
1e+7
rco2_150707_0111_s5_00432__bsub rco2_150707_0111_s5_00438__bsub rco2_150707_0111_s5_00444__bsub rco2_150707_0111_s5_00450__bsub rco2_150707_0111_s5_00456__bsub rco2_150707_0111_s5_00468__bsub rco2_150707_0111_s5_00480__bsub rco2_150707_0111_s5_00498__bsub rco2_150707_0111_s5_00534__bsub rco2_150707_0111_s5_00570__bsub rco2_150707_0111_s5_00624__bsub rco2_150707_0111_s5_00690__bsub rco2_150707_0111_s5_00780__bsub
0.01 9 8
6 5
-1
I(Q) (cm )
Intensity
7
1e+6
1e+5
1e+4
B
UpperFreeport APCS 1 Blank air subtracted
2
4
3
Coal Coal + CO2
2
0.001 9 8
1e+3
7 6 5
1e+2 0.01
4
0.1
1
Q(A-1)-1
Q(A )
3
4
5
6
7
8
9
2
3
4
5
6
7
0.1 -1
Q (Å )
-1
Q(A )
Figure 2. Modelling of a high rank bituminous coal. A - Calculated SAXS data for model with and without CO2; B – SAXS scattering for Upper Freeport coal (APCS 1) under 900 psi of CO2.
From this model and the model without CO2 the SAXS were calculated using CRYSOL[12]. Since his model has a finite and small size compared to coal samples the scatting does not change a lower Q which is normally observed at lower Q ( < 0.07). However, a decrease in scattering is clearly observed in the model at an intermediate Q
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Oviedo ICCS&T 2011. Extended Abstract
range with the addition of CO2, Figure 2A.
While in the coal the same effect is
observed as the coal swells with the diffusion of CO2 into the coal structure, Figure 2B. This gives one confidence with the validity of the model. The PDF was calculated from the model using the DISCUS method[13]. In Figure 3 the results of the calculated data from the model in compared to a high-rank coal measured PDF. The data is dominated by distances between carbons with the largest peak being the C-C aromatic bond. The second largest peak represents the first and third carbon in C-C-C. The fit is actually very good considered the complexity of the structure being studied. The calculated PDF fit for the CO2 expanded model has been difficult to obtain and is being further investigated.
Figure 3. Comparison of PDF from the high rank model (without CO2) with the PDF of the Pocahontas lv bituminous coal (APCS 5).
. With de-swelling, the scattering intensities increase with time as the CO2 progressively empties from the voids/pores, increasing the electron density contrast and then more slowly evaporates from the swollen solid matrix, re-opening voids/pores that were shrunken. However, the scattering curves of the de-swollen coal did not return to their initial early “unswollen” values. This suggests that, at least on the timescale of hours, there is a significant “memory effect” of the swelling process on the solid coal matrix.
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Oviedo ICCS&T 2011. Extended Abstract
4. Conclusions The SAXS technique is able to directly observe changes in coal structure that accompany injection of CO2 at room temperature and 5,500 kPa (800 psi) and to provide new understanding of the process. For hig rank coals, the uptake of CO2 may be regarded as a combination of processes beginning with shorter term void/pore filling and gas adsorption onto the solid matrix, followed by longer-term coal swelling. Consideration of the Porod invariant data derived from the initial scattering plots suggests that the solid matrix swells primarily via a Class II type diffusion process typically associated with a glassy polymer or gel structure. Also, the swelling process shows some degree of hysteresis. Comparison of large-scale coal models with experimental scattering data shows reasonable agreement. The effect of CO2 promoted swelling can be observed with SAX Sand used to verify coal representations utility.
Acknowledgement. The authors would like to acknowledge the contributions of the late Tony Clemens, CRL who was a key contributor to the initiation and execution of this project. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357.
References [1] R.E. Winans, T. Clemens, S. Seifert, In situ SAXS studies on the effects of reactive solvents and gases on coal structure, Preprints of Symposia - American Chemical Society, Division of Fuel Chemistry, 51 (2006) 165. [2] M. Kalliat, C.Y. Kwak, P.W. Schmidt, Small-angle x-ray investigation of the porosity in coals, ACS Symp. Ser., 169 (1981) 3-22. [3] H.D. Bale, P.W. Schmidt, Small-angle x-ray-scattering investigation of submicroscopic porosity with fractal properties, Phys. Rev. Lett., 53 (1984) 596-599. [4] A.P. Radlinski, M. Mastalerz, A.L. Hinde, M. Hainbuchner, H. Rauch, M. Baron, J.S. Lin, L. Fan, P. Thiyagarajan, Application of SAXS and SANS in evaluation of porosity, pore size distribution and surface area of coal, International Journal of Coal Geology, 59 (2004) 245-271.
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Oviedo ICCS&T 2011. Extended Abstract
[5] J.W. Larsen, The effects of dissolved CO2 on coal structure and properties, International Journal of Coal Geology, 57 (2004) 63-70. [6] A.L. Goodman, R.N. Favors, J.W. Larsen, Argonne Coal Structure Rearrangement Caused by Sorption of CO2, Energy & Fuels, 20 (2006) 2537-2543. [7] V.N. Romanov, A.L. Goodman, J.W. Larsen, Errors in CO2 Adsorption Measurements Caused by Coal Swelling, Energy & Fuels, 20 (2006) 415-416. [8] S. Seifert, R.E. Winans, D.M. Tiede, P. Thiyagarajan, Design and performance of a ASAXS (Anomalous Small Angle X-ray Scattering) instrument at the Advanced Photon Source, Journal of Applied Crystallography, 33 (2000) 782-784. [9] P.J. Chupas, X. Qiu, J.C. Hanson, P.L. Lee, C.P. Grey, S.J.L. Billinge, Rapidacquisition pair distribution function (RA-PDF) analysis, Journal of Applied Crystallography, 36 (2003) 1342-1347. [10] M.R. Narkiewicz, J.P. Mathews, Improved Low-Volatile Bituminous Coal Representation: Incorporating the Molecular-Weight Distribution, Energy & Fuels, 22 (2008) 3104-3111. [11] M.R. Narkiewicz, J.P. Mathews, Visual Representation of Carbon Dioxide Adsorption in a Low-Volatile Bituminous Coal Molecular Model, Energy & Fuels, 23 (2009) 5236-5246. [12] D. Svergun, C. Barberato, M.H.J. Koch, CRYSOL - a program to evaluate x-ray solution scattering of biological macromolecules from atomic coordinates, Journal of Applied Crystallography, 28 (1995) 768-773. [13] T. Proffen, R.B. Neder, DISCUS: a program for diffuse scattering and defectstructure simulation, Journal of Applied Crystallography, 30 (1997) 171-175.
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The role of sulfur in coals plastic layer formation L. Butuzova1, R. Makovskyi1, T. Budinova2 , Stefan Marinov2 1
Donetsk National Technical University, 58 Artema str., Donetsk 83000, Ukraine,
tel fax: +38(0622) 55-85-24,
[email protected] [email protected] 2
Bulgarian Academy of Sciences, Institute of Organic Chemistry, 9 Acad. G.Bonchev str., Sofia 1113, Bulgaria,
[email protected] Abstract Coals blends with all possible combinations of high- and low-sulfur coals of the same rank and petrographic composition were pyrolysed in centrifugal field, allowing to separate solid, fluid and gaseous products. It has been shown that replacement of the low-sulfur by the high-sulfur coking coal of the same rank (≈83–88 % Cdaf) in blends leads to substantial increasing of fluid products yield which can be of great practical value. Using the EPR and DRIFT-spectroscopy methods the structural peculiarities of the obtained products have been studied. An apparent correspondence between the content of sulfur in coal, content of paramagnetic centers in plastic layer and coal coking ability has been discovered. Keywords: coal, blend, sulfur, plastic layer 1. Introduction The differences in coal thermoplastic properties have been attributed to higher hydrogen transfer reactions and to differences in the amount of tar produced during the plastic range [1]. The existing schemes of formation of coal plastic matter ignore a vital role of heteroatoms in coal organic matter (COM) and thus allow no definite prediction of the yield, composition and properties of pyrolysis products. Thermal transformations of COM heterorganic compounds, as well as the processes of donor hydrogen transfer and redistribution, are determined by the molecular structure of coal. Accordingly, studies of the chemical structure of coals with different sulphur and oxygen contents and their behavior during heating should play a crucial role in understanding of cokemaking as a process. A particular characteristic of seams from Donets coal basin is the occurrence of high- and lowsulfur coals, of the same rank differing by some physicochemical properties [1]. These differences are due to specified genetic types formed in alluvial or marine depositional environments during diagenesis processes [2]. The aim of this research is to study the effect of sulphur content in individual components of coal blends on the yield and characteristics of the plastic layer responsible for coking. 2. Experimental Two pairs of the isometamorphic Donets coals homogeneous by their petrographic composition, but formed under reductive (RC) or less reductive conditions (LRC) and different by their sulphur
content (Sdt=1,09-1,22 for LRC; Sdt=2,49-2,81 for RC) were used as objects of research. It was coals of J-Grade (Cdaf = 85,4 - 86,1; Vdaf = 30,5 - 32,7; Sdt = 1,1 - 4,1) and G-Grade (Cdaf =83,8 85,1; Vdaf=36,0 - 38,7; Sdt =1,22 - 2,49 according to Ukrainian classification. On the basis of these coals, blends (J:G=70:30) with all possible combinations of LRC and RC type coals were prepared. These coals and their blends were thermally treated up to 600°C at the rate of 1500 rev/min using the method of centrifugal thermal filtration (Ukrainian National Standard 17621-89). This method enables one to separate primary products that form the plastic mass, immediately, thus preventing their secondary transformations. The yields of the following products were found: the solid oversieve residue (OR), fluid non-volatile products (FNP) and vapour-gas compounds (VG). The amount and composition of FNP largely determine the processes of caking and coking. The theoretical plastic mass yield was calculated for the above blends using the rule of additivity. The EPR-spectra of the coals were recorded on a Bruker ER 200D SRC radiospectrometer at ambient temperature. Active coal with the content of paramagnetic centres (PMC) N=6.25 х 1016 was used as a standard. The IR-spectra were recorded on a Bruker FTS-7 spectrometer using the DRIFT technique. Semiquantitative processing of the IR-spectra was performed with the help of the software package Origin 6.1 using the basic-line technique. 3. Results and discussion Figure1 demonstrates a great difference in FNP yields and, therefore, in the caking capacity of coals of the same brand, but different coal-facies. This indicator is essentially higher (2.5 times) for LRC coals of G-Grade and RC coals of J-Grade as compared with their pairs of the same rank. theoretical
experimental
The
most
(maximum
35
advantageous FNP
yields)
composition is
a
blend
30
containing the reduced J-Grade (JRC) and the
25
low-reduced of G-Grade (GRC) coals. The
20
greatest deviation of the experimental values
15
from the calculated by the rule of additivity
10
is observed for the JRC + GRC blend, which
5
permits an assumption about the strongest
0 Jrc+Grc
Jrc+Glrc
Jlrc+Glrc
Jlrc+Grc
J : G = 70 : 30
Figure1. A comparative characteristics of the calculated and experimental values for plastic mass yields from samples under investigation
interaction between the components [3]. To understand the nature of this interaction it is useful to compare the parameters of the EPR-signals for the original coals, blends and their thermal filtration products.
As is seen from Table1, PMC concentration (N) in the samples under discussion essentially depends on the components genetic type by reductivity. When the GRC coal is transformed into a plastic
state, the basic amount of PMCs remains in the solid product, i.e. the over-sieve residue, whereas in FNP the concentration of PMCs is ≈ 35 times lower. Table 1. The results of EPR and IR-spectroscopy of coals and the products of thermal destruction Coals, Paramagnetic The results of IR-spectroscopy fluid mobile characteristics products, over-sieve N, ΔН, g-factor Relative intensity residues of coals and spin E Ix/I2920 Ix/I1440 Ix/I1600 blends -1 1190 1260 3040 1260 1600 1260 g x -17 10 G LRC 2,24 6,43 2,0039 0,37 0,34 0,30 0,45 1,89 0,24 origin G RC 64,25 6,79 2,0040 0,33 0,32 0,26 0,41 1,80 0,23 coals J LRC 64,28 7,02 2,0039 0,37 0,31 0,23 0,36 1,64 0,22 J RC 43,16 5,21 2,0040 0,31 0,25 0,19 0,31 1,32 0,24 G LRC 38,50 6,06 2,0040 0,28 0,24 0,36 0,45 1,46 0,31 G RC 1,78 6,01 2,0040 0,20 0,18 0,34 0,38 0,93 0,41 J LRC 114,9 6,25 2,0040 0,45 0,39 0,27 0,52 2,07 0,25 fluid J RC 159,9 6,26 2,0040 0,40 0,32 0,23 0,36 1,67 0,21 mobile products GRC+ JRC 110,5 7,07 2,0040 0,42 0,34 0,25 0,41 1,59 0,26 GLRC+JRC 111,4 6,92 2,0040 0,04 0,03 0,03 0,04 0,18 0,19 GLRC+JLRC 43,14 5,79 2,0040 0,55 0,48 0,48 0,70 2,42 0,29 GRC+JLRC 45,38 5,68 2,0040 0,65 0,55 0,42 0,65 2,25 0,29 G LRC 2,0040 2,78 13,5 0,21 G RC 61,14 6,64 2,0040 2,84 1,05 3,22 0,48 5,00 0,10 J LRC 6,5 6,92 2,0040 J RC 4,0 6,60 2,0040 oversieve GRC + JRC 2,0039 1,88 7,64 0,25 residues G +J 0,11 4,00 2,0040 6,03 20,3 0,30 LRC RC GLRC+JLRC 0,03 4,04 2,0040 4,18 2,17 1,93 4,42 GRC+JLRC 0,19 5,23 2,0040 17,2 0,26 The JRC coal is forming FNP with the PMC concentration ≈ 4 times higher than that in the original coal. At the same time, an increase in the yield of liquid thermodestruction products is observed, which is 2.5 times higher for the reduced coals as compared to the low-reduced ones (Fig.1). These results indicate that reactions resulting in the formation of the plastic layer occur with the participation of free radicals. The JRC coals characterized by narrower EPR signals (ΔН ~ 5.21 E), contain the most stable PMCs. The maximum rigidity of the polyconjugated areas is observed for solid residues of thermal filtration of the blends (ΔН ~ 4.00 - 4.04 E). The width and form of broad resonance lines in the EPR-spectra of coals are basically determined by hyperfine interaction with magnetic nuclei [4,5]. Thus, the observed differences in the paramagnetic properties of RC and LRC coals indicate greater
molecular rigidity of polyconjugated areas in the structure of reduced coals, primarily the JRC coal. When coal of JRC is added to coals of brand G (GLRC and GRC), the concentration of PMCs in FNP drastically goes up (by 2.5 times). In the FNP based on JLRC coal the concentration of PMCs is 2.6 times lower. These data obtained permit to attribute the optimal properties of the GLRC + JRC blend to the highest PMC concentration in FNP. The RC samples yield the plastic layer characterized by high content of aliphatic groups (2920сm-1 and 1440сm-1). When JLRC coal replacement by JRC in the blends the relative concentration of CHal groups in the FNP increases. The GLRC + JRC blend is characterized by a minimal relational proportion of -О-(-S-)/CHal groups (I1190,1260/ I2920) and proportion of СНаr/CHal (I3040/I2920 and I1600/I1440) groups. So, FNP of the blend with JRC coal is rapidly saturated with hydrogen and the solid residue - with aromatic and bridge segments, which conduces to the formation of the plastic layer and subsequently to caking coke. A comparison of the IR-spectra of GLRC and GRC coals and their over-sieve residues demonstrates that low-reduced coal and its OR are also distinguished by a much higher Har/Hal and –S– (–O–)/Hal ratio as compared to GRC. 4. Conclusions Generally, a replacement of one of the blend components by coal of the same rank but different sulfur content (different genetic type by reductivity) changes the PMC concentration, structuregroup composition and yield of thermal filtration products. The heteroatoms content in coals determines the quality and quantity of the plastic layer and the character of interaction between the blends components. The data obtained unambiguously indicate that it is necessary to consider the coal-facies when making coking blends. References [1] Nomura M., Kidena K., Hiro M., Murata S. Mechanistic study on the plastic phenomena of coal. Energ. Fuel 2000;14:904-9. [2] Bechtel, A., Butuzova, L., Turchanina, O., Gratzer, R. Thermochemical and geochemical characteristics of sulphur coals. Fuel Processing Technology 2002;77–78:45–52. [3] Zubkova, V.V. Investigation of influence of interaction between coals in binary blends on displacement of non-volatile mass of coal charge during carbonization. Fuel Processing Technology. 2002;76:105–119. [4] Butuzova, L., Krzton, A. and Kozlova, I. The paramagnetic characteristics of pyrolysis products for coals treated by alkali and acid, Proceedings 9th International Conference on Coal Science. Essen (Germany). 1997;1:91–4. [5] Butuzova, L., Rozhkov, S., Makovskyi, R., Rozhkova, N., Butuzov, G. The contribution of radical reactions during thermal processing of low-quality coals. GeoLines. 2009;22, № 5: 9–14.
Oviedo ICCS&T 2011. Extended Abstract
Understanding the effects of biomass addition to coking coals during carbonisation
M. Castro-Díaz1, A. Dufour2, N. Brosse3, R. Olcese2, C. Snape1 1
2
Department of Chemical & Environmental Engineering, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, UK E-mail:
[email protected] CNRS, Nancy Université, Reactions and Processes Engineering Laboratory (LRGP), ENSIC, 1 rue Grandville, B.P. 20451, 54000, Nancy Cedex, France. 3
Nancy Université, Faculté des Sciences et Techniques, LERMAB, B.P. 239, 54506 Vandoeuvre les Nancy Cedex, France
Abstract The addition of biomass to coking blends has the potential benefits of reducing the amount of expensive coking coals and reducing carbon emissions. Therefore, an easily available biomass (miscanthus) has been chosen to study the effect of this additive on the fluidity properties of the coal. High-temperature 1H NMR and high-temperature rheometry were used to determine the fluidity of the miscanthus and some of its constituents (i.e. lignin, cellulose and xylan). The miscanthus was also pyrolysed at 250°C for 1 hour to produce torrefied miscanthus. The biomass samples were blended with high volatile (> 30 wt% daf) caking coals in the range of 5-15 wt%. It was found that the miscanthus constituent that develops more fluidity is lignin. Indeed, lignin developed 100% fluid material, followed by xylan (60%) and cellulose (< 40%). However, the miscanthus and the lignin produce chars at > 420°C that interact and destroy the fluid components in the coal. On the other hand, the torrefied miscanthus reduced the fluidity in the blend to a lesser extent than the pristine miscanthus. The addition of 5 wt% torrefied miscanthus did not cause a significant detrimental effect on the fluidity of the coal and hence this additive could be potentially be used in coking blends.
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Oviedo ICCS&T 2011. Extended Abstract
1. Introduction The reduced availability of prime coking coal has led to the blending of poor coking coals with carbonaceous materials to produce good coking coals. In this manner, the use of additives to partially substitute coal in coke-making and to improve the properties of the coal blends has been widely investigated by various authors [1-5]. However, there is little research related to the application of biomass as an additive in coking blends. High-temperature rheometry and 1H NMR are two powerful techniques that can monitor fluidity development in biomass and coal during pyrolysis. These techniques have been used in the past to elucidate the effect of different additives in coking blends [5]. The aims of this work are to identify the constituents in biomass that control fluidity development and elucidate the effect of biomass on the fluidity of coking blends.
2. Experimental section The miscanthus was used as a powder of 80-200 μm and the particle sizes for the two coals used was 53-212 μm. Coal A has a volatile matter content of 31.9 wt% daf, ash content of 9.8 wt% db and Gieseler maximum fluidity of 534 ddpm. Coal B has a volatile matter content of 35.7 wt% daf, ash content of 7.2 wt% db and Gieseler maximum fluidity of 8018 ddpm. The lignin of the miscanthus was separated using the Organosolv process. A description of this process can be found elsewhere [6]. A Doty 200 MHz 1H NMR probe was used in conjunction with a Bruker MSL300 instrument to determine fluidity development in the biomass samples. A flow of 25 dm3/min dry nitrogen was used to transfer heat to the samples and to remove the volatiles that escaped from the container. Below the sample region, a flow of 60 dm3/min of dry air prevented the temperature rising above 50°C to protect the electrical components. In addition, air was blown at 20 dm3/min into the region between the top bell Dewar enclosing the sample region and the outer side of the probe to prevent the temperature from exceeding 110°C. The sample temperature was monitored using a thermocouple in direct contact with the sample container.
The solid echo pulse
sequence (90o-τ-90o) was used to acquire the data. A pulse length of 3.50 μs was maintained throughout the test. Approximately 50 mg of sample was packed lightly into a boron nitride container, and 100 scans were accumulated using a recycle delay of 0.3 seconds. The samples were heated from room temperature to the final temperature at approximately 3°C/min. Duplicate analyses were carried out to ensure reproducibility in
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Oviedo ICCS&T 2011. Extended Abstract
the results. The spectra obtained were deconvoluted into Gaussian and Lorentzian distribution functions, which enabled the calculation of the fraction of total hydrogen that is mobile and its mobility (T2L). The higher the concentration and mobility of the fluid phase the higher the fluidity, and thus, fluidity depends on both concentration and mobility of the fluid or mobile phase. Rheological measurements were performed in a Rheometrics RDA-III high-torque controlled-strain rheometer. Coal, biomass and coal/biomass mixtures (1.5 g) were compacted under 5 tonnes of pressure in a 25 mm die to form disks with thickness of approximately 2.6 mm. The tests involved placing the sample disk between two 25 mm parallel plates which had serrated surfaces to reduce slippage. The coal and coal blends were heated quickly to 330°C and heated to 520°C at a rate of 3°C/min. The furnace surrounding the sample was purged with a constant flow of nitrogen to transfer heat to the sample and remove volatiles.
The sample temperature was monitored using a
thermocouple inside the furnace.
A continuous sinusoidally varying strain with
amplitude of 0.1 % and frequency of 1 Hz (6.28 rad/s) was applied to the sample from the bottom plate throughout the heating period. The stress response on the top plate was measured to obtain the complex viscosity (η*) as a function of temperature.
3. Results and Discussion Figure 1 shows the high-temperature 1H NMR results for the miscanthus and its constituents. Lignin develops 100% fluid material at 200°C and fluidity remains high up to 350°C. Xylan develops up to 60% fluid material at 275°C. The fluidity decreases for miscanthus (< 45% fluid material) and cellulose develops fluidity below 40% at high temperatures (325°C). The mobility of the fluid material in the samples, as indicated by T2L, show different trends. Xylan possesses the highest mobility although its maximum occurs at low temperatures (175°C) and this could be an artefact of the low NMR signal. The mobility of the fluid phase in lignin remains fairly constant between 225°C and 350°C, similarly to the trend for the concentration of fluid phase. The trends for miscanthus and cellulose show similar mobility values with temperature. These results suggest that lignin could be responsible for most of the fluid material developing in miscanthus. However, lignin is much less thermally stable than the other constituents and its mobility development originates from bond cleavages after glass transition.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 1. Percentage of fluid phase (a) and mobility of the fluid phase (b) as a function of temperature for the miscanthus and its constituents.
High-temperature rheometry results for the miscanthus and the lignin are presented in Figure 2. These results are in agreement with the 1H NMR results, showing that the low the lignin is highly fluid above 150°C whereas the miscanthus has a minimum viscosity (or maximum fluidity) at 350°C.
The minimum in viscosity at 100°C could be
attributable to the presence of moisture in the sample. Figure 3 shows that lignin destroys the fluidity of coal when it is a added in concentrations of 5 wt%. This result suggests that the fluid material evolving from the lignin does not contribute to the fluid properties of the blend within experimental error, and that the char originating from the lignin above 420°C interacts with the coal and completely destroys its fluid phase. Similar results were found with other additives that were chars at the thermoplastic temperature of the coal [5]. The effect of miscanthus on coal fluidity (not shown) was also detrimental but to a lesser extent than that of lignin.
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Oviedo ICCS&T 2011. Extended Abstract
6
10
5
10
η* ( ) [Pa-s]
Miscanthus Lignin 4
10
103
2
10
0.0
100.0
200.0
300.0
400.0
500.0
Temp [°C]
Figure 2. Complex viscosity as a function of temperature for the miscanthus and its lignin constituent.
7
10
Coal Coal + lignin (5 %) 6
η* ( ) [Pa-s]
10
5
10
104
3
10 300.0
350.0
400.0
450.0
500.0
550.0
Temp [°C]
Figure 3. Complex viscosity as a function of temperature for coal A and the mixture of coal A and lignin (5 wt%).
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Oviedo ICCS&T 2011. Extended Abstract
The miscanthus was also torrefied at 250°C under nitrogen for 1 hour. The torrefied miscanthus was analysed in the rheometer and the results show that there is a small reduction in fluidity in the pre-treated sample as indicated by the smaller peak (Figure 4).
6
η* ( ) [Pa-s]
10
5
10
Miscanthus Torrefied miscanthus
4
10
0.0
100.0
200.0
300.0
400.0
500.0
Temp [°C]
Figure 4. Complex viscosity as a function of temperature for miscanthus and torrefied miscanthus.
The torrefied miscanthus was blended with coal B in the range of 5-15 wt% to elucidate the effect in the fluidity of the coal. The results are presented in Figure 5 and show a gradual reduction in fluidity as the concentration of biomass in the blend increases. This reduction seems to be directly related to the low fluidity of the torrefied miscanthus, especially after char formation, rather than any interaction with the coal. Moreover, the addition of 5 wt% torrefied miscanthus does not seem to cause a significant deleterious effect on the fluid properties of the coal and this additive may potentially be used in coking blends without affecting coke quality.
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Oviedo ICCS&T 2011. Extended Abstract
6
10
5
η* ( ) [Pa-s]
10
4
10
103
2
10 375.0
Coal Coal + torrefied miscanthus (5 %) Coal + torrefied miscanthus (10 %) Coal + torrefied miscanthus (15 %) 400.0
425.0
450.0
475.0
500.0
Temp [°C]
Figure 5. Complex viscosity as a function of temperature for coal B and mixtures of coal B and torrefied miscanthus (5-15 wt%).
4. Conclusions This work has shown that lignin develops high concentration of fluid material during pyrolysis. However, the fluid material in lignin and miscanthus evolves at temperatures lower than the thermoplastic temperature of coal, and the char forming in the biomass above 420°C interacts with the coal constituents causing a deleterious effect on fluidity development. The torrefaction of miscanthus removes the moisture and also reduces some fluid material, but the torrefied biomass does not interact to a great extent with the coal in blends containing 5 wt% biomass. Therefore, there is scope to use this pretreated material as additive in coking blends without altering the properties of the coking blend.
Acknowledgement The authors would like to thank Dr Paul Pernot from Centre de Pyrolyse de Marienau (CPM) in France and Drazen Gajic from DMT GmbH in Germany for supplying the coals.
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Oviedo ICCS&T 2011. Extended Abstract
References [1] Sakurovs R. Some factors controlling the thermoplastic behaviour of coals. Fuel 2000;79:379–389. [2] Nomura S, Kato K, Nakagawa T, Komaki I. The effect of plastic addition on coal caking properties during carbonization. Fuel 2003;82:1775–1782. [3] Sakurovs R. Interactions between coking coals and plastics during co-pyrolysis. Fuel 2003;82:1911–1916. [4] Uzumkesici ES, Casal-Barciella MD, McRae C, Snape CE, Taylor D. Co-processing of single plastic wastestreams in low temperature carbonisation. Fuel 1999;78:1697–1702. [5] Castro Diaz M, Steel KM, Drage TC, Patrick JW, Snape CE. Determination of the effect of different additives in coking blends using a combination of in situ high-temperature 1H NMR and rheometry. Energy & Fuels 2005;19:2423–2431. [6] Brosse N, Sannigrahi P, Ragauskas A. Pretreatment of Miscanthus x giganteus Using the Ethanol Organosolv Process for Ethanol Production. Ind Eng Chem Res 2009;48:8328–8334.
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Oviedo ICCS&T 2011. Extended Abstract
Influence of alkali additives on the swelling behavior of a high swelling bituminous coal 1
C.A.Strydom1, J.R. Bunt1,2 , Y. van Staden1 and J Collins1 Chemical Resource Beneficiation, North - West University, Potchefstroom Campus, South Africa 2 Sasol Technology (PTY) Ltd, Box 1, Sasolburg, 1947, South Africa Corresponding author:
[email protected] Abstract The effect of the addition of some alkali compounds to a South African coal with a high swelling propensity was investigated. A vitrinite-rich bituminous coal from the Tshikondeni coal mine in the Limpopo province of South Africa was used in this study. CaCO3, NaCO3, K2CO3 and KHCO3 were added to the coal in mass percentages of 5%, 10%, 15%, 20%, 30% and 40%. The free swelling index (FSI), FTIR, Gieseler fluidity and dilatometry of the samples were measured. The FSI results showed that all additives significantly reduced the swelling properties and the order of effectiveness of the additives was found to be: KHCO3 >K2CO3>Na2CO3>CaCO3. A 40% addition of KHCO3 reduced the swelling index by a factor of three. The Gieseler fluidity results showed a narrowing in the plastic range with the addition of KHCO3. The dilatometry results
showed that the dilation reduced with addition of KHCO3 and the plastic
properties of the coal samples were changed from euplastic to subplastic.. It is concluded that the addition of alkali carbonates and bicarbonates to coal reduce the free swelling of coal, with alkali bicarbonates having the most impact on reduction of swelling.
1. Introduction Oxidation of coals exhibiting high swelling properties has been reported to influence the physical and chemical properties to various extends [1,2]. The deterioration of caking and coking abilities of coal after oxidation is well documented and ascribed to a loss of plastic properties of the coal [1-5]. Volatile bituminous coals have been known to undergo swelling and have been used as coking coals throughout the world [6]. The formation of cross-links within the macromolecular chemical structure of the coal at temperatures below that required for pyrolysis may reduce or eliminate swelling [7].
Oviedo ICCS&T 2011. Extended Abstract
Bexley and co-workers [8] claimed that alkali carbonates and bicarbonates decrease or completely destroy the dilatation of the coal, possibly through reaction with the phenolate and carboxylate groups of the studied Illinois No. 6 coal. The alkali compounds seem to act as catalysts, catalyzing the formation of ether cross-links at temperatures of approximately 573 K [8].
The Grootegeluk mine in the Waterberg area in South Africa produces 17 million tonnes per year of a high swelling coal. The mine has a resource of 75-billion tonnes of coal [9] and is the largest coal reserve in South Africa. Tshikondeni colliery is situated in the Limpopo province and has coal reserves of six-million tonnes and a resource of 32million tonnes of coal. 400 000 tonnes per year of premium hard coking coal is produced at this mine [10]. The paper described the study of the influence of CaCO3, Na2CO3, K2CO3 and KHCO3 additions on the swelling properties of the Tshikondeni coal during thermal treatment in air.
2. Experimental section A coal sample from the Tshikondeni colliery in South Africa was crushed and ground to sizes of K2CO3>Na2CO3>CaCO3. Bexley et al. [8] found CaCO3 to have only a small effect on the swelling properties of the Illinois no. 6 bituminous coal they studied, with the effect of Na2CO3, K2CO3 and KHCO3 additions much larger. Their results thus followed the same overall trend as observed in this study. Further analyses were performed on the coal samples with KHCO3 additions of 10% and 40%. 9
CaCO3 8
Na2CO3 7
K2CO3
6
KHCO3
FSI
5
4
3
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1
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5
10
15
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25
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35
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45
Additive Concentration [mass (%)]
Figure 1: FSI values of coal with additions of CaCO3, Na2CO3, K2CO3 and KHCO3.
Oviedo ICCS&T 2011. Extended Abstract
The Gieseler fluidity results for the coal samples with 10% and 40% additions of KHCO3 are given in figure 2.
4000
Raw Coal 3500
10% KHCO3 3000
Fluidity (dd/min)
40% KHCO3 2500
2000
1500
1000
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0 399
409
419
429
439
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Temperature ( C)
Figure 2: Gieseler fluidity results of the raw coal, and coal with 10% and 40% KHCO3. Gieseler fluidity results showed that the softening temperature of the coal sample and coal with 10% KHCO3 was 402°C and for the 40% KHCO3 coal sample 420°C. The resolidification temperatures of the raw coal, 10% and 40% KHCO3 additive was 503°C, 500°C and 491°C respectively. The increase in softening temperature and the decrease in re-solidification temperatures, results in a narrowing of the plastic range upon addition of KHCO3. Figure 3 represents the dilatation versus temperature results of the coal and coal with 10% and 40% KHCO3 additions. The coal behaves as a euplastic compound, but addition of KHCO3 changes the samples to behave as subplastic compounds, thus showing a decrease in volume.
Oviedo ICCS&T 2011. Extended Abstract
200
Raw Coal 10% KHCO3
Dilatation (%)
150
40% KHCO3
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50
0
-50 330
350
370
390
410
430
450
470
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Figure 3: Dilatometry graphs of coal sample and coal with 10% and 40% additions of KHCO3. FTIR spectra for the coal and coal with 10% and 40% additions of KHCO3 are given in figure 4. The carboxylic C=O peak at 1605 cm-1 decreased substantially with the addition of KHCO3. Bexley et al. [8] suggested that a chemical reaction occurs between the additive and the carboxylate and phenolate groups of the coal. The intensity of the phenolic O-H stretching vibration at 3434 cm-1 decreased upon addition of KHCO3. This suggests that the additive may have reacted with the phenolic groups of the coal. The strong band at 1033 cm-1 is possibly a C-O phenol stretching vibration which decreased with addition of KHCO3. The carboxylic C=O peak at 1605 cm-1 also decreased with the addition of KHCO3. The peaks at 2924 and 1445 cm-1 (possibly aliphatic C-H groups) decreased with 10% KHCO3 addition and almost disappeared with 40% KHCO3 addition. This may be due to a reaction taking place between the additives and the coal, thus changing the structure of the coal. The same can be said for aromatic C-H bands at 3045, 880, 804 and 750 cm-1, which also showed a large decrease in peak intensity.
Oviedo ICCS&T 2011. Extended Abstract
1.6
Raw coal 1.4
10% KHCO3 40% KHCO3
Absorbance
1.2
1
0.8
0.6
0.4
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500
1000
1500
2000
2500
3000
3500
4000
4500
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Figure 4: FTIR spectra of raw coal and coal with 10% and 40% additions of KHCO3.
4. Conclusions
The order of largest decreasing effect on the swelling index of the additives was found to be: KHCO3>K2CO3>Na2CO3>CaCO3. The addition of KHCO3 changes the plastic properties of the sample from a euplastic to a subplastic coal, thus changing the coal sample into a coal for which no swelling occurs upon heating in air. The plastic range of the coal with KHCO3 additions was also decreased. According to literature alkali carbonates and bicarbonates may react with phenolate and carboxylate surface functional groups of coal, which then affects the swelling of coal through cross linking leading to the stabilization of the structure. A decrease in the number of these functional groups were observed on the FTIR spectra.
Acknowledgement. The authors would like to thank North-West University and SASOL Technology, Research and Development for financial support for the investigation.
Oviedo ICCS&T 2011. Extended Abstract
References [1] Iglesias MJ, De la Puente G, Fuente E and Pis JJ. Compositional and structural changes during aerial oxidation of coal and their relations with technological properties. Vib. Spectr. 1998:17:41-52. [2] Song Ch, Saini AK and Schobert HH. Effects of Drying and Oxidation of Wyodak Subbituminous Coal on Its Thermal and Catalytic Liquefaction.Spectroscopic Characterization and Products Distribution. Energy Fuels. 1994:8:301-312. [3] Larsen JW, Lee D, Schmidt T and Grint A. Multiple mechanisms for the loss of coking properties caused by mild air oxidation. Fuel. 1986:65:595-596. [4] Pis JJ, Cagigas A, Simon P, Lorenzana JJ. Effect of aerial oxidation of coking coals on the technological properties of the resulting cokes. Proc. Technol. 1988:20:307-316. [5] Khan MR and Jenkins RG, Influence of K and Ca additives in combination on swelling, plastic and devolatilization properties of coal at elevated pressure. Fuel. 1989:68:1336-1339. [6] Yu D, Xu M, Yu Y and Lui X. Swelling behaviour of a Chinese bituminous coal at different pyrolysis temperatures. Energy Fuels. 2005:19:2488-2494. [7] McCormick RL and Jha MC. Effect of catalyst impregnation conditions and coal cleaning on caking and gasification of Illinois No. 6 coal. Energy Fuels. 1995:9:10431050. [8] Bexley K, Green PD and Thomas KM. Interaction of mineral and inorganic compounds with coal. Fuel. 1986:65:47-53. [9] Njobeni, S. 2010. Looking for power that won't run out. Times Live, 21 Feb. http://www.timeslive.co.za/business/article317763.ece. [10] Creamer, M. 2009. Water, rail plans in place in Waterberg. Mining Weekly, 11 Dec. http://www.miningweekly.com/print-version/water-and-rail-plans-in-place-forgrowing-waterberg. [11] Speight JG. Handbook of Coal Analysis. Hoboken, New Jersey: John Wiley & Sons. 2005: p. 142-145. [12] Schobert HH. The Chemistry of Hydrocarbon Fuels. Londen: Butterworth Publishers. 1990.
Oviedo ICCS&T 2011. Extended Abstract
Estimation of the coking pressure in coke ovens by Koppers-INCAR test
R. Alvarez, C.Barriocanal, M.A. Díez Instituto Nacional del Carbón, CSIC, Apartado 73, 33080 Oviedo. Spain email:
[email protected] Abstract A laboratory test : Koppers-INCAR, designed and patented by INCAR has been used to control the coking pressure developed by coking coals during carbonization. Laboratory results were backed by tests carried out to semi-industrial and industrial scale. These results have been compared with semi-pilot and pilot scale tests. 1. Introduction There are several causes of “stickers” and “heavy pushes” at the end of the coking process [1]. The consequence of these problems can be costly, including reduced coke production, damage to machinery and oven walls and extra man power. However, coal or blend characteristics are the most important parameters determining coal expansion and coke contraction behaviour during carbonisation and this is the major source of coke pushing difficulties. It is well known that some coals are liable to damage the coke oven walls because of excessive pressure developed during carbonisation (coking pressure) or insufficient coke contraction at the end of the process. It has been suggested [2] that the existence of little or no contraction is a sign of high pressure during carbonisation and it seems probably that coals giving cokes with not enough contraction will develop dangerous pressures of sufficient magnitude to damage coke oven walls during carbonisation. The problem of coking pressure generation has been widely studied [3-5] and although it is not fully understood is generally accepted its relation with the development of internal gas pressure [3,6-8]. Many test methods have been used for the evaluation of coals with regard to their expansion and contraction behaviour in the coking process [9]. The use of the movable wall oven has been the most widely accepted and has also been fundamental to try to explain the mechanism of coking pressure generation [10]. The Spanish National Coal Institute (INCAR) has been largely involved in the study of the mechanism of coking pressure generation and the development and utilization of
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Oviedo ICCS&T 2011. Extended Abstract
tests to measure expansion and contraction during carbonisation. INCAR has developed and patented [11] the Koppers INCAR test, based on the early Koppers laboratory test and taking into account the Mott and Spooner modifications [12]. This Koppers test has been substantially modified by INCAR [13], contraction being the dominant parameter in determining the degree of danger associated with a coal. Laboratory results have been backed by tests carried out to a semi-industrial scale [14]. 2. Experimental Two movable wall ovens are available at INCAR at this moment : MWO 250( Figure 1) and MWO 15; the first one has a capacity of 250-300 kg of coal and the second one 15 kg. The MWO250 is a electrically heated gravity-charged oven with a length of 915 mm length, 840 mm height and 455 mm width. The oven works with a coking time of 18 h. the initial temperature is 880 °C and the final 1132 °C with a heating rate of 14 °C/h. During the test, wall pressure, temperature in the centre of the charge and in the wall, together with vertical contraction can be measured. The data are continuously recorded and displayed in a computer. The MWO15 is a gravity charging, electrically heated oven with a length of 250mm, a height of 800 mm and a width of 150 mm. The oven has a coking time of 2h45min, the temperature of the wall is maintained at 1010 °C and the final coke temperature is 950 °C. During the test, wall pressure, temperature in the centre of the charge and in the wall together with vertical contraction can be measured. The data are continuously recorded and displayed in a computer. Figure 2 shows a diagram of the equipment used to carry out the Sole heated oven (ASTM D 2014-85). A coal mass between 4,25 and 5,30 kg, crushed to no less than 70% and no more than 85% below 3,35 mm, with 1% moisture was enclosed in the carbonisation chamber at a bulk density of 881 kg/m3. A constant force of 15,2 kPa was applied on the top of the charge. Carbonisation temperature rose from 550ºC on the sole to 950ºC. The test was considered finished when the temperature of the top of the charge reached 500ºC. Figure 3 shows the Koppers-INCAR apparatus. Although the geometry of the most important parts of the early Koppers test was maintained, the heating system and some of the test constants (pressure on the charge, rate and duration of heating) were modified taking into account Mott and Spooner modifications and INCAR research. 3. Results and Discussion 3.1. Koppers-INCAR results Figure 4 shows typical curves obtained in this test for three different coals. The Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
interpretation of the graph obtained may be summarised as: “coals giving a contraction greater than 10 mm are not dangerous during carbonisation”. Coals giving curves of type I are classified as dangerous and coals giving curves of type III as safes. Coals giving curves of type II represent the limit between dangerous and not dangerous coals. To establish this classification, laboratory results were backed by tests carried out to a semi-industrial scale [15] and to industrial scale [16]. 3.2. Semi-industrial scale tests This laboratory test was used to resolve the problem of coking a dangerous Spanish coal: Sabero (20.5%VM). The indications of this test were used to determine the minimum amounts of three different high volatile coals: Eskar, Carrocera and Hullasa (35.5, 37.3 and 41.1 VM respectively) that it was necessary to add, to reduce the risk of coking this dangerous coal. Laboratory results were backed by tests carried out on a semi-industrial scale, without losing sight of certain safety limits [14]. Using the laboratory data from the Koppers-INCAR tests (Figure 5) it was established that Sabero coal could be coked without risk by adding the following minimum amounts of the corrective coals : 10% Hullasa or 20% Carrocera or 30% Eskar. 3.3. Industrial scale tests During 1990 the Spanish Steel Industry, Ensidesa, was using blends and the KoppersINCAR curves from June to December are shown in Figure 6. At the beginning of 1991 due to problems with the coal received, a dangerous coal blend was coked. Stickers and heavy pushes were produced in the Veriña battery but not in the Avilés battery. This can be explained because the bulk density is 780 to 790 kg/m3 in Veriña (6.5 m high ovens) and 710 m to 720 m in Avilés battery (4.5 high ovens). The Koppers-INCAR curves of January 2 and January 3 of Figure 6 show the reliability of the Koppers-INCAR test. The Koppers- INCAR test has been used in several INCAR research works [13-22] and ECSC Projects [23-29] and also it has started in 2010 year a new one. The relationship among the Koppers-INCAR test and the other tests to measure the coking pressure available at INCAR are shown in Figures 7 (MWO 250-300 kg) [24], 8 (ASTM SHO) [24] and 9 (MWO 15-17 kg) [28]. 4. Conclusions The Koppers-INCAR test is a reliable method to predict the expansion and contraction behaviour of coals and blends during carbonization (coking pressure) and is also a rapid a cheap method compared with the used more frequently for coking pressure control at the coke oven plants. Since 2009 is being used for the control in advance of the blends Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
prepared by the Spanish Steel Industry. References [1]
Kevin F. De Vanney. Coke plant pushing problems-Causes and troubleshooting guidelines. 2002 Ironmaking Conference Proceedings, 339-346
[2]
B.C.R.A. Technical Paper. December 1948
[3]
Loison R, Foch P, Boyer A. Coke Quality and Production. Butterworth, London, 1989 (p. 353-412).
[4]
Tucker J, Everitt G. 2nd International Cokemaking Congress, London, 1992 p. 40-49
[5]
Coke oven wall pressures. Measurement, Cause and Effect. Publication of the Iron and Steel Society,1990,ISBN 0-932897-525
[6]
Jordan P, Patrick JW, Walker A. A laboratory study of internal gas pressure generated during the coking of coals. Cokemaking Int.1992;4:12-15.
[7]
Te Lindert M, Van der Velden B. Research into internal gas pressure and shrinkage. Ironmaking Conference Proceedings,1994; 53:12-15.
[8]
Barriocanal C, Patrick JW, Walker A. The laboratory identification of dangerous coking coals. Fuel 1998; 77:881-884.
[9]
Meltzhein C, Buisine M. Etude de la poussée sur les parois des fours a coke. Rev.Gen.Therm. 1968;47: 147-165.
[10] Loison R, Foch P, Boyer A. Coke Quality and Production. Butterworth, London, 1989 p..336 [11] Procedimiento y sistema para evaluar el empuje de los carbones o mezclas coquizables. Patente de invención nº 524,258,1983 [12] Mott RC, Spooner C. The assessment of coals liable to damage oven walls Fuel 1939; 18:322-344. [13] Alvarez R, Pis JJ, Barriocanal C, Lázaro M. et al. Characterization of dangerous coals during carbonization. Effects of air oxidation and ash content of coals. Cokemaking Int.1991; 3:37-42. [14] Alvarez R, Miyar EA, Escudero JB. Application of a laboratory test to resolve the problem of coking a dangerous coal. Fuel 1990; 69:1151-1156. [15] J.B.Escudero, R.Alvarez. Influence of air oxidation on the pressure exerted by coking coals during carbonization. Fuel 1981; 60:251-253. [16] Alvarez R, Pis JJ, Barriocanal C, Sirgado M. Practical application of a laboratory test to measure expansion and contraction during carbonization. Cokemaking Int. 1992; 4:16-18. [17] Alvarez R,. Pis JJ, Lorenzana JJ. Characterization of dangerous coals during carbonization. Fuel Processing Technology 1990; 24:91-97. [18] Alvarez R, Pis JJ, Díez MA, Marzec A, Czajkowska S Studies on generation of Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract excessive coking pressure.1.Semicoke contraction versus thermoplastic properties. Energy and Fuels 1997; 11:978-991. [19] Marzec A, Czajkowska S, Alvarez R, Pis JJ, Díez MA, Schulten H. Studies on generation of excessive coking pressure.2.Field Ionization Mass Spectrometry of coals showing different contraction during Carbonization. Energy and Fuels 1997; 11:982-986. [20] Casal MD, Canga CS, Díez MA, Alvarez R, Barriocanal C. Low temperature pyrolisis of coals with different coking pressure characteristics. J Anal.Applied Pyrolisis 2005; 74:96-103. [21] Casal MD, Diaz-Faes E, Díez MA, Alvarez R, Barriocanal C.. Influence of porosity and fissuring on coking pressure generation Fuel 2008;87:2437-2443. [22] Barriocanal C, Díez MA, Alvarez R, Casal MD. Relationship between coking pressure generated by coal blends and the composition of their primary tars.J.of Anal.Applied Pyrolisis 2009; 85:14-520. [23] R.Alvarez. Coal Weathering. ECSC 7220-EB/755, 1994. [24] R.Alvarez.Caracterización de carbones con empuje peligroso. ECSC 72220-EB/756 1995. [25] R.Alvarez. Low cost of coke by increasing low volatile coals in blends ECSC 7220EB/344, 1997. [26] R.Alvarez. Coking pressure studies. 7220-EB/345, 2000. [27] R.Alvarez, C.Barriocanal. Study of parameters involved in coking pressure generation. ECSC 7220-PR/069, 2002. [28] R.Alvarez, C.Barriocanal. Laboratory and pilot scale tests to assess coke quality and coking pressure. ECSC 7220-PR/119, 2004. [29] R.Alvarez, C.Barriocanal. Coking pressure generation and moderation ECSC 7220PR/140, 2005. [30] C.Barriocanal. Generation of Swelling Pressure in a Coke Oven, Transmission on oven walls and consequences on wall degradation (SPRITCO) 2010.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 1. MWO 250.
Figure 2. Sole Heated Oven (SHO).
Figure 3. Koppers-INCAR test.
Figure 4. Typical curves obtained in the Koppers-INCAR test. Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
Figure 5. Koppers-INCAR curves of coal blends: a, Sabero-Eskar; b, Sabero-Carrocera; c, Sabero-Hullasa.
Figure 6. Koppers-INCAR curves of ENSIDESA blends. Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
Figure 7. Relationship between KI and coking Figure 8. Relationship between KI and pressure in the MWO250.
S.H.O. contraction.
2
Wall pressure MWO15(kN/m )
90 80 70 60 50 40 30 20 10 0 -30
-20 -10 0 Contraction/expansion Koppers-INCAR (mm)
10
Figure 9. Relationship between KI and coking pressure in the MWO15.
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Oviedo ICCS&T 2011. Extended Abstract
High Performance Electric Double-Layer Capacitor using Activated Carbon from HyperCoal
K. Sato, K. Magarisawa, T. Takarada Department of Chemical & Environmental Engineering, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma, 376-8515 Japan Contact address:
[email protected] A high performance electric double-layer capacitor (EDLC) was fabricated using activated carbon derived from ash-less HyperCoal. The activation was carried out at 500 - 800 ºC for 0.5- 4 h under flowing argon atmosphere using HyperCoal derived char. NaOH and KOH were used as activation agent. Specific surface area (SSA) of activated carbon and specific capacity of resultant EDLC are strongly depend on the activation conditions including variety and amount of activation agent, activation temperature and holding time. The largest SSA of 2560 and 3110 m2·g-1 was achieved for activated carbon when it was activated at 700 ºC for 3 h using KOH and NaOH, respectively. The resultant specific capacitance of EDLC fabricated from these activated carbons was 43.9 and 44.1 F·g-1 which are comparable or higher than EDLC fabricated from conventional phenol resin derived activated carbon.
1. Introduction Electric double layer capacitor (EDLC) is a promising energy storage device in the future because of their safety, environmentally benign and fast charge-discharge properties compared to those of other devices such as secondary ion batteries. [1, 2] Higher energy density and lower cost must be achieved for wide spreading of EDLCs in a number of applications. The capacity of EDLC can be described as; C=∫(ε/L)dS
(1)
where ε is the specific capacitance of the electrolyte within the electric double layer, L the thickness of the electric double layer, and dS the surface area of the electrodes available for the charge- discharge process, respectively. Activated carbons (ACs) are widely used for EDLC electrodes since it has very high specific surface area (SSA) and relatively high electrical conductivity.
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Oviedo ICCS&T 2011. Extended Abstract
The fabrication of ACs from the abundant natural resources such as coals and biomass has the advantage in material cost. However ash component involved in these resources may reduce the performance of EDLC, and inhibit the reuse of activation agents resulting in higher cost. A solvent extraction and condensation process can significantly reduce the ash content in coals. [3] The materials fabricated through the process is called as HyperCoal. The material cost of HyperCoal is expected to be still one order of magnitude lower than the synthetic phenol resin which is widely used to fabricate the ACs for EDLCs. In addition, much of the activation agents could be reused, providing lower total costs.[4] Here we try to fabricates ACs from HyperCoal, and investigate the its applicability for EDLC electrodes.
2．Experimental section A Gregory coal derived HyperCoal supplied from Kobe Steel Ltd. was used as starting material. Proximate and ultimate analysis results is shown in Table 1. The ash content was reduced to be 0.06 wt % in dry-bases through the HyperCoal fabrication. The HyperCoal was carbonized at 600 ºC for 7 min under flowing Ar of 3 L·min-1. The char yield was 69.2 %. The fabricated char was sieved to be < 105 μm and 1 g of the sieved char was spreaded onto alumina boat and then the activation reagent (KOH or NaOH) was put onto the char. The activation was carried out between 500 and 800 ºC for 0.5- 4 h under flowing Ar of 400 ml·min-1. The activated sample was washed by 2 M of hydrochloric acid aqueous solution and then filtered to remove alkaline species. The sample was rinsed by de-ionized water several times. Finally ACs were obtained by drying the washed and rinsed samples in the vacuumed oven at 200 ºC for 2 h. The SSA and pore size distribution are measured using N2 gas adsorption instrument. Table 1 Proximate and ultimate analysis results of the Gregory coal derived HyperCoal
Proxim ate analysis [w t%] (d.b.) M oist. V.M . Ash 0.38 39.45 0.06 U ltim ate analysis [w t%] (d.a.f.) C H N 82.14 6.39 1.59
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O diff. 9.27
2
Oviedo ICCS&T 2011. Extended Abstract
A couple of EDLC electrodes was fabricated using the ACs. The ACs of 30 mg was mixed with 3.45 mg of acetylene black and 1.03 mg of Polytetrafluoroethylene using pestle and mortar, and then uni-axially pressed at 40 MPa for 20 min in a metal die. The diameter of the electrode pellets was 13 mm. An aluminum mesh was used as current correctors and attached to the electrodes by dry-pressing. A tetra-ethyl ammonium fluoroborate and propylene carbonate mixture was used as electrolyte. Infiltration of the electrolyte into the porosity of the electrodes was performed under vacuumed condition followed by set-up in a airtight grove box. The two electrode set-up was used for the performance evaluation of the cell. The cell was charged under the constant current density of 40 mA/g-ACs to be 2.5 V of cell voltage, and then discharged under the constant current density of 10 mA/g-ACs to be 0 V. The specific capacitance was determined using the following equation, Cg=I(dT/dV)
(2)
where Cg is specific capacitance, I the current density, dT/dV was gradient of timevoltage diagram between 2 and 1 V in discharge process.
3. Results and discussion Figure 1 shows the effect of holding time for activation at 800 ºC on the SSA of ACs and the Cg of EDLCs. The yield of ACs decreased with increasing holding time and was in the range of 61.0- 50.0 % relative to the char. The SSA increased during the first 1 h and then become constant up to 4 h. The Cg increased up to 3 h and then decreased. The highest Cg was 42.7 F·g-1 when holding time was 3 h. Figure 2 shows the effect of activation agent and temperature on the SSA of ACs and the Cg of EDLCs. The holding time was fixed to be 2 h. The yield of ACs decreased with increasing the temperature, and was in the range of 55.9-84.0 % and 39.1-76.7 % relative to the char for the case of KOH and NaOH as activation agent, respectively. The largest SSA of 2560 and 3110 m2·g-1 was achieved for activated carbon when it was activated at 700 ºC for 3 h using KOH and NaOH, respectively. The reduction of the SSA at 800 º C would be attributed to the pore coalescence by excessively proceeded activation. The Cg well followed the SSA change up to 700 ºC for both NaOH and KOH systems. The highest Cg was observed at 700 ºC and was 43.9 and
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Oviedo ICCS&T 2011. Extended Abstract
43.1 F·g-1 for NaOH and KOH, respectively. These performances were comparable or higher than that fabricated from conventional phenol resin (40.0 F·g-1). This means that HyperCoal is a promising source of ACs for high performance EDLC electrodes. Although the SSA was significantly decreased at 800 ºC, the Cg was not so much decreased. Figure 3 shows pore size distributions of ACs activated using NaOH and KOH at various temperatures. Average pore diameter increased with increasing activation temperature and reached to be about 1 nm at 800 ºC. Thus the only slight change of Cg between 700 and 800 ºC even though the significant SSA reduction can be attributed to the improved pore structure. These results indicated that both the SSA and the pore structure must be controlled for further enhanced performance.
2000 35
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3000
4000 KOH/C =4 in mass
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KOH/C =4 in mass
Specific capacity / F·g-1
Specific surface area / m2·g -1
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Figure 1 Effect of holding time on the
Figure 2 Effect of activation agent and
SSA of ACs and the Cg of EDLCs.
temperature on the SSA of ACs and the
The activation was carried out at 800 º
Cg of EDLCs. Holding time for the
C using KOH as the activation agent.
activation was 2 h.
Figure 3 Pore size distributions of ACs fabricated using (a) NaOH and (b) KOH at various temperatures. The holding time for activation was 2 h.
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Oviedo ICCS&T 2011. Extended Abstract
4. Conclusion It is demonstrated that the ash-less HyperCoal is a candidate starting materials of ACs for cost effective high performance EDLC electrodes. Both the increase of SSA and the pore structure must be controlled for higher performance EDLCs.
References [1] Sharma P, Bhatti TS, Energ Convers Manage 2010; 51: 2901-12. [2] Zhao XY, Cao JP, Morishita K, Ozaki J, Takarada T, Energy Fuel, 2010; 24: 188993. [3] Okuyama N, Komatsu N, Shigehisa T, Kaneko T, Tsuruya S. Fuel Process Technol 2004;85:947–67. [4] Sharma A, Takanohashi T, Morishita K, Takarada T, Saito I, Fuel, 2008; 87: 491-97
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Oviedo ICCS&T 2011. Extended Abstract
Degradation Characteristics of SOFC by Trace Elements in Coal Gasified Gas Y. Ueki1, T. Kobayashi2, R. Yoshiie2, and I. Naruse2 1
Energy Science Division, EcoTopia Science Institute, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, JAPAN 2 Department of Mechanical Science and Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, JAPAN
[email protected] Abstract Integrated coal Gasification Combined Cycle (IGCC) and Integrated coal Gasification Fuel Cell combined cycle (IGFC) are recognized as one of highly effective power generation systems for clean coal technologies. However, adverse effects of corrosion in a gas turbine and chemical and/or physical degradation of the fuel cell affect those performances since some trace elements exist in the coal gasified gas. In the present work, influences of trace elements of As and Se in the coal gasified gas on Solid Oxide Fuel Cell (SOFC) installing in the IGFC system were theoretically and experimentally elucidated. First, thermodynamic equilibrium calculations were carried out to estimate chemical compositions of the trace elements on anode of the SOFC. Second, actual reaction behaviors of the trace elements on the anode were tested, using a simulated coal gasified gas, which was supplied into a button-type SOFC. From the thermodynamic equilibrium calculations, The As converted to a solid phase NiAs, and 100 % of Se existed as H2Se gas at low temperature. As the experimental results, Se doping into the simulated gasified gas showed bad effect on power generation slightly, but the power generation performance came back to the initial performance after cutting the Se doping. For As doping, on the other hand, As reacted with Ni in the anode, so that the SOFC performance gradually decreased, and did not recovered after cutting the dope. Key words: Solid oxide fuel cell, Trace element, Coal gasified gas
1. Introduction Integrated coal Gasification Combined Cycle (IGCC) and Integrated coal Gasification Fuel Cell combined cycle (IGFC) have been recognized as one of the highly effective power generation systems for clean coal technologies. The IGFC is
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mainly composed of a gas turbine, a fuel cell and a steam turbine. However, adverse effects of corrosion in a gas turbine and chemical and/or physical degradation of the fuel cell affect those performances since some trace elements exist in the coal gasified gas. Therefore, many researchers have studied the effect of trace elements on Solid Oxide Fuel Cell (SOFC). Currently, the effect of trace elements on the SOFC power generation has been studied, using hydrogen or methane as a fuel. However, the effect of trace elements in the coal gasified gas on the SOFC power generation has not been elucidated yet. In the present work, influences of the trace elements of As and Se in the coal gasified gas on the SOFC power generation were theoretically and experimentally studied. First, actual reaction behaviors of the trace elements on the anode were tested, using a simulated gasified gas, which was supplied into a button-type SOFC. Moreover, the anode surface before and after the experiments was observed by using a SEM/EDX. Second, thermodynamic equilibrium calculations were carried out to estimate chemical compositions of trace elements on the anode of SOFC.
2. Experimental 2.1 Sample of the button-type SOFC A photograph and a schematic diagram of the button type cell employed in this power generation experiment are shown in Figs. 1 and 2, respectively. A Ni-YSZ cermet (Ni-Yttrium Stabilized Zirconia composite materials) is used for an anode (Fuel side), and a YSZ (Yttrium Stabilized Zirconia) is used for an electrolyte. The anode diameter is 10mm, and the diameter of the electrolyte is 20mm, and the thickness of the anode and the electrolyte is about 1 mm. To collect the electricity generated, a Pt mesh is installed in both the anode and the cathode. Moreover, the electricity collected there connects with an electrochemistry measurement device through a lead wire and is measured continuously. On the other hand, the lead wire, that is called a reference electrode, is applied to the circumference of the button type cell to put an external load (constant voltage), and this is connected with the electrochemistry measurement device.
2.2 Experimental apparatus Figure 3 shows a schematic diagram of an experimental apparatus used for power generation experiments by the button type cell. The supply lines of gases in this experimental apparatus divides into a fuel gas (simulated coal gasified gas) and a Submit before 31 May 2011 to
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Pt mesh as current collector (Anode)
Fuel gas Lead wire
Anode (Ni-YSZ cermet)
Solid electrolyte (YSZ) Reference electrode (Lead wire)
Pt mesh as current collector (Cathode)
Lead wire
O2 in air
Fig. 1 Photograph of the button type
Fig. 2 Schematic diagram of the button type
cell
cell
gaseous trace element. The anode gas (fuel gas) and the cathode gas (Air) are supplied from the top and bottom, respectively. The trace element is added into the anode gas (fuel gas) as hydride by a hydride generation device shown in Fig. 3 (a). In this device, the solution of As and Se reacts with hydrogen, and the gas hydride is generated. For As, for example, the following chemical reactions occurs in this device. NaBH4 + HCl + 3H2O → H3BO3 + NaCl + 8H
(1)
As + 8H → AsH3 + 5/2H2
(2)
A standard solution of As and Se, a hydrochloric acid solution (HCl) and a sodium boron-hydride solution (NaBH4) are supplied to the device with a pump. Then, the hydride compound of the trace element is generated by the reactions above-mentioned. A humidifier for the anode gas is installed in the fuel gas line. The anode gas is kept at 333 - 353 K with a ribbon heater after a humidification of the anode gas. Air compressed in a gas cylinder is supplied as the cathode gas. The evaluation and examination device for the fuel cell, shown in Fig. 3 (b), is used during the power generation experiment. The supply lines of the anode gas, the cathode gas and an exhaust gas are made of alumina. The temperature of the button type cell is controlled by using an electric furnace. Electricity generated in the button-type cell is collected by a Pt mesh, and is measured by an electrochemistry weighing device, shown in Fig. 3 (c). In this experiment, method of the electric current measurement at the constant voltage is applied for the evaluation of the fuel cell, changing the power load to generate a constant voltage in the fuel cell.
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b
a
c
Fig. 3 Schematic diagram of an experimental apparatus
2.3 Experimental procedure and conditions Figure 4 shows the experimental procedure. The button type cell is set up in the fuel cell evaluation and examination device. The temperature rises up to 1173 K in about 1.5 h. After that, N2 and air are introduced in the anode and the cathode, respectively. The anode gas is switched to H2 at 1173 K, and the anode is reduced for about 2 h under the condition of the infinite electric load (insulating state). The reason for this process is to remove the oxide film on the anode surface of the button-type cell. Afterwards, the measurement condition of the electrochemistry weighing device is changed to a constant voltage condition (0.75V). Finally, power generation by H2 begins. After attaining the steady state, the power generation experiments are conducted under each experimental condition. Experimental conditions and gas compositions are shown in Tables 1 and 2, respectively. Compositions in the simulated coal gasified gas, which refers to the gas compositions reported in the NEDO national project in Japan [1, 2]. The addition of trace element into the simulated gas is conducted after the current value attains the Submit before 31 May 2011 to
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Installation of the button type cell Anode: N 2, Cathode: Air Rising temperature to 1173K in 1.5 hour Reduction of the cell surface by H 2
Anode: H 2, Cathode: Air Open-circuit at 1173K in 2 hours Power generation of the cell by H 2 Anode: H 2, Cathode: Air Confirmation of stable current output under constant voltage (0.75V) condition Test for each experimental condition Fig. 4 Experimental procedure of power generation experiments of the button type cell
steady state. The trace element is added continuously for about 10 h. Afterwards, in order to observe the power generation recovery, the power generation experiment under the condition 2 is carried out again. To accelerate the degradation behavior of the cell by the trace element (As, Se), the high concentration of As and Se is added into the simulated coal gasified gas. After the power generation experiment, the anode surface of the cell is analyzed by a SEM/EDX for a deterioration evaluation by those trace elements.
Table 1 Common experimental conditions
Button type cell
Ni-YSZ/YSZ (10mm anode diameter)
Temperature
1173K
Gas flowrate in the anode
100mL/min
Gas flowrate in the cathode
100mL/min
Moisture in the anode
20% (Saturation vapor at 338K)
Pre-heating of anode gas
423K
Operation mode
Constant voltage 0.75V
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Table 2 Gas compositions for each experimental condition Anode gas (dry base) Condition 1 H2 power generation
H2:100%
Condition 2 Coal syn gas power generation
H2:20%, CO:50%, CO2:4%, N2:26%
Condition 3 Coal syn gas power generation with Se doping
H2:20%, CO:50%, CO2:4%, N2:26% H2Se:10ppm
Condition 4 Coal syn gas power generation with As doping
H2:20%, CO:50%, CO2:4%, N2:26% AsH3:10ppm
Cathode gas
Air:100%
3. Experimental result and discussion 3.1 Results of power generation experiments of the button type cell Results of the power generation experiments on condition 1 (H2) and condition 2 (simulated coal gasified gas) is shown Figs. 5 and 6, respectively. In these graphs, the horizontal axis and the vertical axis indicate an exposure period and a current output value at the constant voltage of 0.75V, respectively. The power generation period is about 20 h. From both the figures, the electricity generated is stable under the both conditions. Figures 7 (a) and (b) show the result of the power generation experiment under condition 3 and 4 (Se and As addition), respectively. For the Se addition, the current output value gradually decreases. The current output value of 20 % decreases in about 10 h. After stopping the Se addition, however, the current value almost recovers. For the As addition, on the other hand, the current output also decreases by adding As. The current value of 30 % decreases in about 10 h. However, the current value does not recover to the initial value. These results suggest that the degradation mechanisms for the Se addition will differ from that for the As addition.
3.2 Observation of anode surface of the button-type cell by SEM/EDX SEM images of the anode surface of the button-type cell are shown in Fig. 8. The anode surfaces after (b) H2 reduction, (c) H2 power generation and (d) the simulated coal gasified gas power generation are almost similar structure to that of (a) initial cell. However, the anode surfaces after (e) the Se addition and (f) the As addition change Submit before 31 May 2011 to
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0.30
0.30
0.25
0.25
0.20
0.20
Current [A]
Current [A]
Oviedo ICCS&T 2011. Extended Abstract
0.15 0.10
0.15 0.10
0.05 0.00
0.05 0
5
10
15
0.00
20
0
5
Time [h]
10
15
20
Time [h]
Fig. 5 Current output with time by H2
Fig. 6 Current output with time by the
(Condition 1)
the simulated gas (Condition 2). 0.30
0.30
Condition 2
0.25
Condition 3 (Se doping)
Condition 2
0.25 0.20
Current [A]
Current [A]
0.20 0.15 0.10 0.05 0.00
0.15
Condition 2
0.10
Condition 4 Condition 2 (As doping)
0.05
0
5
10
15
20
0.00
0
Time [h]
(a)
5
10
15
20
Time[h]
(b)
Fig. 7 Current output with time during power generation by the simulated coal gasified gas doped (a) Se (Condition 3) and (b) As (Condition 4)
greatly. For the Se addition, some pores in the anode are buried, compared with that after the H2 power generation and the simulated coal gasified gas power generation. For the As addition, on the other hand, the surface structure of the anode becomes disorder. This may be caused by the reaction of As with the anode material of Ni-YSZ cermet. Figure 9 shows the mapping analysis of Se and As on the anode surface by EDX. As the signal intensity of Se is very low, Se may not deposit on the surface. For As, on the other hand, As is detected on the anode surface. This suggests that an adhesion of As on the anode surface will affect the degradation of the cell performance.
4. Thermodynamic equilibrium calculation 4.1 Calculation condition To elucidate the chemical interaction between the trace elements of As and Se and Submit before 31 May 2011 to
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15µm
15µm
(a) Before test
(b) After H2 reduction
15µm
15µm
(c) After H2 power generation (Condition 1)
(d) After coal syn gas power generation (Condition 2)
15µm
(e) After coal syn gas power generation with Se doping (Condition 3)
15µm
(f) After coal syn gas power generation with As doping (Condition 4)
Fig. 8 SEM images of the anode surface of the cell after each experimental condition Se
As
15µm
(a) After coal syn gas power generation with Se doping (Condition 3)
15µm
(b) After coal syn gas power generation with As doping (Condition 4)
Fig. 9 SEM-EDX mapping on the anode surface of the cell after each experimental condition
the anode materials, the thermodynamic equilibrium calculation was carried out, using
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FactSage version 6.1 [3, 4]. The calculation conditions are shown in Table 3, which is almost the same as the power generation condition in this work.
Table 3 Equilibrium calculation conditions for SOFC power generation condition by the simulated coal gasified gas -
Component
Input [mol]
Concentration
Anode material
Ni
2.556x10-4
-
CO
1.34
50%
CO2
0.107
4%
H2
0.536
20%
N2
0.696
26%
H2O
0.536
20%
Cathode gas
O2
0.01876
-
Trace elements
H2Se or AsH3
2.68x10-5
10ppm
Anode gas
4.2 Calculation results and discussion Figure 10 (a) and (b) show the calculation results of the H2Se and AsH3 addition, respectively. In these figures, the vertical axis indicates a mole fraction of the compounds including Se or As. From Fig. 10 (a), Se will mainly exist as a gas phase of H2Se since as SOFC generally operates at 1073 – 1173 K. Therefore, Se will not react with Ni on the anode surface. It means that the degradation by Se addition will be caused by physical adsorption of Se compounds on the anode surface. Therefore, the power generation performance recovered, as shown in Fig. 7 (a). For As, on the other hand, Ni will be able to react with As to form the solid phase of NiAs. This result suggests that the anode degradation shown in Fig. 7 (b) will be caused by the chemical reactions between As compounds and the anode materials. This is one of the reasons for the irreversible degradation obtained by the experiment.
5. Conclusions The power generation experiment by the button-type fuel cell (SOFC) with the simulated coal gasified gas, that contained the trace element (Se, As) as well as the thermodynamic equilibrium calculations were carried out to elucidate the degradation characteristics of SOFC by the trace elements. The following results were obtained. In the power generation experiment by the simulated coal gasified gas with Se and Submit before 31 May 2011 to
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0.8 0.6 0.4
Se (g) Se2 (g) H2Se (g)
0.2 0.0 1000
1100
1200
Mole fraction of As [-]
Mole fraction of Se [-]
1.0
1300
0.8 0.6 0.4
As (g) As2 (g) As4 (g) AsN (g) NiAs (s)
0.2 0.0 1000
Temperature [K]
1100
1200
1300
Temperature [K]
(a)
(b)
Fig. 10 Mole fractions of (a) Se compounds and (b) As compounds under the SOFC power generation condition by the simulated coal gasified gas
As, the degradation behavior of the anode by Se and As was reversible and irreversible, respectively. For the Se addition, the anode would be degraded by the physical process. For the As addition, on the other hand, As was chemically captured on the anode surface, based on the SEM/EDX observation and the thermodynamic equilibrium calculations.
References [1]
Suzuki E. Proceedings of 2003 Gasification Technologies Conference (SanFrancisco, October 12–15), Gasification Technologies Council, Arlington, USA, 2003, 11 pp.
[2]
Ohtsuka Y, Tsubouchi N, Kikuchi T, Hashimoto H. Recent progress in Japan on hot gas cleanup of hydrogen chloride, hydrogen sulphide and ammonia in coalderived fuel gas. Powder Technology 190 (2009) 340–347.
[3]
FACT, www.crct.polymtl.ca
[4] C.W. Bale, P. Chartrand, S.A. Decterov, G. Eriksson, K. Hack, R. Ben Mahfoud, J. Melançon, A.D. Pelton and S. Petersen. FactSage Thermochemical Software and Databases. Calphad Journal 62 (2002) 189-228.
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Coupling gasification and solid oxide fuel cells: effect of tar on anode materials M. Millan1, E. Lorente2, J. Mermelstein1, C. Berrueco1, N.P. Brandon2 1
Department of Chemical Engineering, Imperial College London South Kensington Campus, London SW7 2AZ (UK) 2 Department of Earth Science and Engineering, Imperial College London South Kensington Campus, London SW7 2AZ (UK) email of corresponding author:
[email protected] Abstract The combination of gasification with solid oxide fuel cells (SOFC) has the potential to become an attractive technology for the production of electricity and heat. However the impact of tars, formed during gasification, on the performance and durability of SOFC anodes has not been well established experimentally. This study reports on an experimental study of the effects of carbon formation on anode materials of SOFC from synthetic model tars and real tars arising from the gasification of coal.
1. Introduction The combination of gasification with solid oxide fuel cells (SOFC) is a highly efficiency route of producing electricity and heat. Combined heat and power processes based on SOFCs and coal/biomass gasification have the potential to achieve efficiencies higher than 85% [1]. Solid oxide fuel cells operating at high temperature are able to internally reform a wide range of fuels, including syngas derived from coal gasification. The high catalytic activity of nickel-based anodes allows SOFCs to internally reform hydrocarbons such as methane and make use of CO as a fuel, making SOFCs the most fuel flexible of the different fuel cell types. However, when operating on hydrocarbon fuels (most significantly above C4), nickel-based SOFC anodes are susceptible to significant deactivation from carbon formation, which deteriorates the catalytic activity of the anode and as a consequence causes cell degradation [2]. In particular, aromatic hydrocarbons and tars, which is a complex mixture of organic compounds mostly of aromatic nature that derive from pyrolisis products and secondary reactions [3], may favour the development of carbon deposits. The allowable tar content in the fuel gas is
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one of the key research questions for upcoming fuel cell concepts with integrated gasification, since it determines the gas cleaning requirements. Although recent studies have shown the feasibility of using syngas in SOFCs, the effect of tars on the performance and durability of SOFCs has not been well established [4,5]. Experimental studies designed to obtain a clearer picture on how tars can lead to carbon formation and deposition on SOFC anodes have been carried out. An initial approach was based on the use of model compounds (benzene, toluene, naphthalene) as tars [6,7], which enabled the impact of operating conditions such as current density, steam and tar content and overall gas composition on anode degradation to be established. This work has been further expanded to investigate the impact of an actual gasification tar on two commercially available fuel cell anodes, Ni/YSZ (yttria stabilised zirconia) and Ni/CGO (gadolinium doped ceria). The effect of exposing the catalysts to real tars, as compared to model tars, will be assessed experimentally in terms of the amount of carbon deposition.
2. Experimental section 2.1. Materials Two types of anode catalysts, NiO/YSZ (yttria stabilised zirconia) and NiO/CGO (gadolinium doped ceria), were used in this study. The main characteristics of the powders, supplied from Fuel Cell Materials, are shown in Table 1. Prior to the carbon deposition tests, the anode materials were calcined at 1300 ºC in air for 1h. The calcined powders were then sieved to a particle size of 125-250 μm.
Table 1. Main properties of the SOFC anode materials Anode Material
NiO content (wt%)
BET surface area (m2/g)
NiO/YSZ
66
6.21
NiO/CGO
60
5.60
Toluene and benzene (HPLC grade, DBH, UK) were used as model tars. The real tar sample consisted in a tar obtained from an industrial coal gasifier. The profile of volatilisation temperature of the sample, which is shown in Figure 1, was obtained by a TGA-based weight loss determination [8]. A temperature of 350 °C was
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chosen for the injection of tar, since a high percentage of the sample (around 96%) is volatilised at that temperature. 100
Fraction of tar volatilised (%)
90 80 70 60 50 40 30 20 10 0 50
100
150
200
250
300
350
400
450
500
550
600
Temperature (°C)
Fig. 1. Profile of volatilisation temperature of coal gasification derived tar
2.2. Carbon deposition experiments In order to test the carbon deposition characteristics of the nickel oxide based anode materials due to tars present in syngas, a fixed bed flow reactor under atmospheric pressure was used. Typically, 40 mg of powder material was placed on a piece of quartz wool in the 6 mm OD quartz tube reactor. The material was heated to a typical SOFC operating temperature of 765 °C at a rate of 10 °C/min in dry nitrogen. Reduction was carried out for 90 min, by exposing the catalysts at temperature in a 2.5% H2O/H2/N2 mixture, with increasing concentrations of H2, from 5% to 25%, over the reaction period. The gaseous mixture was then changed to the experimental operating conditions of 15% H2 and 2.5% H2O (N2 balance). Tar was injected via a syringe pump (KD Scientific) at a rate of 100 μL/h, producing a tar concentration of 15 g/m3. The feed line was heated to an adequate temperature (around 150 °C for toluene experiments, and around 350 °C for the experiments with real tar) to allow for vaporization of the tar species into the gas phase, and subsequent mixing with the incoming gas. The total flow rate during heating, reduction and reaction was fixed at 100 ml (STP)/min. Anode catalyst samples were exposed to tar for 1h. The amount of deposited carbon (Wcarbon) on the anode materials was measured by weight difference of the samples before and after reaction (Winitial and Wfinal,
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respectively), taking into account the weight loss due to the reduction of NiO to Ni (ΔWreduction), according to Eq. 1. Wcarbon = Wfinal - (Winitial - ΔWreduction)
(1)
3. Results and Discussion The degree of carbon formation on the anode materials, Ni/YSZ (yttria stabilised zirconia) and NiO/CGO (gadolinium doped ceria), exposed to real tar was examined at the experimental conditions described in section 2. The samples were treated at 765 °C in a gas stream of 15 % H2, 2.5% H2O and 15 g/m3 tar for 1 h. To isolate the carbon formation from tars, other gases present in gasification syngas (CO, CO2, methane) were not used in this study. For comparison purposes, the impact of toluene and benzene as model tars were also studied at the same conditions. Figure 4 shows the results obtained in the carbon deposition experiments, in terms of amount of carbon formed over the catalysts materials. It can be observed that Ni/CGO presents a better performance (less carbon formation) than Ni/YSZ in the presence of both model and real tars. This result is in agreement with the expected behaviour of ceria-based anodes, which have been recognised to be effective in suppressing carbon deposition due to the redox nature of ceria [9]. Regarding the comparison between the model compounds and real tar, it can be seen in Figure 4 that the use of the real gasification tar resulted in an intermediate value of carbon deposition as compared with the experiments performed with toluene and benzene. Furthermore, in the case of Ni/YSZ, a sharp decrease is observed in the degree of carbon formation due to the real tar, in comparison with the amount of carbon formed over the catalyst exposed to toluene. The fact that benzene has considerably less impact on the nickel-based anodes degradation than toluene can be related with the higher stability of this compound [10, 11]. As it has been stated before a real tar is a complex mixture of organic compounds mostly of aromatic nature. Therefore, the effect of tar on carbon deposition over the anodes is expected to have a more complex influence than that of model compounds such as toluene and benzene. The results of the present study show the relevance of testing the anode materials with real tars, as the tolerance level of anode materials is highly
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influenced by the model tar selected for the study.
1.00
Toluene Real tar Benzene
Carbon deposited (mg C/mg reduced sample)
0.90 0.80
0.08 0.06 0.04 0.02 0.00
Ni/YSZ
Ni/CGO
Fig. 2. Amount of carbon deposited over Ni/YSZ and Ni/CGO, exposed to 2.5% humidified steam, 15 % H2, and 15 g/m3 tar for 1 h at 765 °C 4. Conclusions The impact of toluene and benzene as model tars and a real tar present in coal gasification syngas on the performance of two commercially available SOFC anode materials has been investigated. Carbon deposition measurements indicate that less degradation of the anode catalysts by carbon formation occurs when the anodes are fed with humidified hydrogen gas containing the real gasification tar or benzene, as compared with toluene. The results presented here are considered as a first step in the detailed studies required for full understanding of the influence of gasification tars on short- and long-term SOFC performance.
References [1] Zhang X, Chan SH, Li G, Ho HK, Li J, Feng Z. A review of integration strategies for solid oxide fuel cells. J Power Sources 2010;195:685-702. [2] Offer GJ, Mermelstein J, Brightman E, Brandon NP. Thermodynamics and Kinetics of the Interaction of Carbon and Sulfur with Solid Oxide fuel Cell Anodes. J Am Ceram Soc 2009;92:763-780.
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[3] Milne TA, Evans RJ, Abatzoglou N. NREL/TP-570-25357, 1998 [4] Mermelstein J, Millan M, Brandon NP. The impact of carbon formation on Ni-YSZ anodes from biomass gasification model tars operating in dry conditions. Chem Eng Sci 2009;64:492-500. [5] Singh D, Hernandez-Pacheco E, Hutton P, Patel N, Mann MD. Carbon deposition in an SOFC fuelled by tar-laden biomass gas: a thermodynamic analysis. J Power Sources 2005;142:194-9. [6] Mermelstein J, Brandon NP, Millan M. Impact of steam on the interaction between biomass gasification tars and nickel-based solid oxide fuel cell anode materials. Energy Fuel 2009;23:5042-8. [7] Aravind PV, Ouweltjes JP, Woudstra N, Rietveld G. Impact of biomass-derived contaminants on SOFCs with Ni/Gadolinia-doped ceria anodes. Electrochem Solid St 2008;11:B24-8. [8] Adegoroye A, Paterson N, Li X, Morgan T, Herod AA, Dugwell DR, Kandiyoti R. The characterisation of tars produced during the gasification of sewage sludge in a spouted bed reactor. Fuel 2004;83:1949-1960. [9] Zhu WZ, Deevi SC, A review on the status of anode materials for solid oxide fuel cells, Mater Sci Eng 2003;362:228-239. [10] Ellig DL, Lai CK, Mead DW, Longwell JP, Peters WA. Pyrolysis of volatile aromatic hydrocarbons and n-Heptane over calcuium oxide and quartz. Ind Eng Chem Process Des Dev 1985;24:1080-7. [11] Coll R, Salvado J, Farriol X, Montane D. Steam reforming model compounds of biomass gasification tars: conversion at different operating conditions and tendency towards coke formation. Fuel Process Technol 2001;74:19-31.
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Explosions in Coal Mines due to Emission of Molecular Hydrogen via Atmospheric Weathering Processes 1,2
Haim Cohen 1-
,
Department of Biological Chemistry, Ariel University Center at Samaria, Ariel, 40700 Israel, phone: 00972-524306878, fax: 00972-8-9200749, email:
[email protected] 2-
Chemistry Department, Ben-Gurion University of the Negev, Box 653 Beer Sheva , Israel, email:
[email protected] Abstract Explosions in coal mines are attributed to methane gas concentrations above the LEL or accumulation of fine coal dust which can undergo fast radical reactions. In order to avoid occurrence of such conditions in deep coal mines, methane detectors are installed and good ventilation is required. Still the annual death toll due to explosions in coal mines is ~ 5,000, mainly in China. Bituminous coals in contact with atmospheric oxygen undergo autocatalytic heating via exothermic oxidation of atmospheric oxygen to produce carbon dioxide, carbon monoxide, low molecular weight organic molecules (C1-5) and water. It has been established that molecular hydrogen is also produced. The hydrogen is produced via oxidative decomposition of formaldehyde groups with surface hydroperoxides and is catalyzed by the coal surface. Thus accumulation of hydrogen in a crack in the coal seam in a underground mine above 4.1% (LEL in air) might initiate an explosion. Indeed in the last decade several unexplained explosions have been reported in coal mines. We have checked if accumulation of hydrogen in a deep coal mine might reach the LEL and found that indeed such a situation might occur. These observations indicate that molecular hydrogen accumulation in confined spaces might be another source for unexplained explosions in coal mines and that installation of hydrogen detectors in coal mines is essential to reduce the risk of occurrence of explosions in coal mines.
Keywords: heating
coal mines, explosions, coal weathering, hydrogen explosions, self
1
1. Introduction Coal serves today as the largest source of fossil fuel and is expected to continue as a major energy supply in the next century. Thus, coal mining is an important and vital industry in the global economy. One of the major problems in underground coal mining is the occurrence of explosions in coal mines. The death toll due to these explosions accounts for thousands of human lives annually1. The main source observed for explosions in coal mines (and also confined storage facilities containing coal) stems from 2 sources: (i) Accumulation of methane gas (coal bed methane) released from the inner pores of the coal upon mining and exposure to atmospheric oxygen. The LEL (Lower Explosion Limit) of methane in air is 5.3% and (ii) Accumulation of fine coal dust in the air of the mine because of the mining. This dust has a very large surface area and thus it is available for radical reactions. Both processes emerge because of fast radical reactions that can be initiated by several sources (such as static electrical charge, random spark etc.). As these reactions are very fast (diffusion controlled rate, rate constants approaching 1x1012 M-1s-1 order)) and very exothermic the result can be a devastating explosions. In order to minimize the occurrences of such explosions in underground coal mines several measures are taken. Methane monitors are installed in the coal mines to indicate accumulation of methane gas which might approach dangerous levels. As well as efficient ventilation of the atmosphere of the mine in order to dilute dangerous gas concentrations and filter the fine coal dust which is emitted during mining. Still the death toll approaches 5,000 per year, the majority of which are in the Peoples Republic of China which is both the biggest consumer and producer of coal in the world. The main reason could be human negligence in the maintenance and operation of the mines. However, in several cases the operation of the mine was according to all safety measures and still unexplained explosions did occur. In the last 30 years, Israel has started to use bituminous coal as the major fossil fuel for power production in utility plants and at present 13 Mtonns of coal are consumed annually at 4 power stations producing ~55% of the electricity consumed in Israel. As Israel has no coal of it's own, it has to import the coals mainly from South Africa but also from Russia, Indonesia, Australia and Columbia which is transported via large ships. Also large coal piles (more than 1 Mtonnes are stored in two storage facilities in Ashkelon and Hadera. Coal, like any other organic material in contact under atmospheric conditions, undergoes surface oxidation/weathering processes which might result in autocatalytic heating of the coal pile if the heat formation in the pile is faster than the heat dissipation from the pile2. The process is dependant on coal rank and properties As a result, lignite coals undergo deterioration due to weathering processes in a matter of days while it can take bituminous coals several weeks to reach the same state. This multistage mechanism is quite complicated and even today it is not fully understood. The first stages involve physical adsorption and chemisorption of atmospheric oxygen. The second stage is the formation of surface oxides and hydroperoxides which can partially decompose to yield low molecular weight inorganic gasses like carbon oxides (CO, CO2), water, hydrogen (H2) and some organic gases (C1-5)3. The observation that hydrogen gas is evolved during the weathering process is quite novel and was extensively studied in our group in the last 2
30 years. It is observed that the release of H2 (that is considered as an reduction product) is linearly dependant on the atmospheric O2 consumed by the coal (which is an oxidative process!!!)3,4. The mechanism of this complex reaction is under study and involves reaction of formaldehyde CH2O release from the coal (via the weathering process) with hydroperoxide –COOH groups at the coal surface to yield dioxirane, H2CO2 as intermediate which further decomposes to yield molecular hydrogen, H2 as a product5. We have decided to check the possibility that accumulation of molecular hydrogen in mines could be the source of unexplained explosions in underground mines and to suggest means to monitor that possibility in confined spaces containing coal.
2. Experimental All chemicals and gases used throughout the study were of AR grade and supplied by Aldrich, Fluka, Merck or Maxima. The water used throughout this study was purified water (via ion exchange columns). Coal. Experiments in this work were carried out with three classes of coals; bituminous, sub-bituminous and lignite. The bituminous coal was from South Africa (denoted as SA) and the sub-bituminous coals from Indonesia (denoted as INA) and the USA (denoted as BAI). The South African bituminous coal used in this work serves as the major fossil fuel in coal fired power plants in Israel (more than 60% of the coal consumption). However the Sub-Bituminous Indonesian coal and the BAI USA coals are also fired in the Israeli utilities. The properties of all the coals are presented in Table 1. The experiments were performed in sealed glass vials (40 ml) used as batch reactors. The reactors were charged with coal (particle size 74µ ≤ X ≤ 250µ) in an air &&ve oven model FT 300. atmosphere and heated at 55-95C for various periods in a nu The effect of the oxygen concentration has on the processes was also studied under an atmosphere of pure argon or pure oxygen. All the coals in the present study were prepared by grinding them down and separating them by grain size via sieves. The coal samples were then dried in a Heraeus vacuum oven model VT6060 for 24 hours at 60C. Gas Chromatography. The amount of the gases (CO2, CO,, N2, O2, hydrocarbons) in the reactors was determined using a gas chromatograph (Varian model 3800) equipped with a thermal conductivity detector & a flame ionization detector connected in series. The gases were separated on a Carbosieve B 1/8”, 9’ ss column using a temperature programmed mode. The experimental error in the G.C. determination is ±5%. The gaseous atmosphere was sampled (1ml samples) after the reaction, with gas tight syringes (Precision Syringes, model A2) and the composition was determined in the gas chromatograph. The gases that could be determined are hydrogen, nitrogen, oxygen, carbon dioxide, carbon monoxide, methane & ethylene. The argon gas present is not separated from oxygen in the GC column, thus the value determined for oxygen includes ~0.93% argon gas. As the reactions studied are gas/surface reactions, the reproducibility of the results is not good. Therefore, each experiment has been carried out with duplicates in order to reduce the total experimental error. However, the error is ±15%, mainly due to the nature of the heterogeneous reactions studied in the experiments. 3
Table 1. Properties of Coalsa type
a b
proximate analysis (wt %) ashdb
VMdaf
SA
moisture 1.20
13.60
IN
2.61
BAI
5.87
ultimate analysis (wt %, daf) CV( J ⋅ g
H 4.05
O
S
27.93
C 73.3
5.52
0.46
28,416
10.37
35.43
71.3
4.51
8.81
0.66
28,564
7.78
37.20
78.1
5.18
NA
1.50
28,898
VM = volatile matter; CV = calorific value; daf = dry ash free. db – dry basis SA = South Africa; IN = Indonesia; BAI- USA.
3. Results and Discussion Release of Molecular Hydrogen- Effect of Coal Type We have decided to measure the effect of coal type on the release of molecular hydrogen via the weathering process. Thus, simulation experiments with the three coals have been carried out in small (100ml) glass reactors containing 5 grams coal at the temperature range 55-95C heated for 24 hours under isothermal conditions were performed, the results are given in Table 2. Table 2. Emission of molecular hydrogen – simulation weathering Rate of H2 emission at 55C Rate of H2 emission at 95C b coal ppmv/gram coal x hour 0.615 SA 12.9
a b
IN
0.826
15.0
BAI
1.51
24.5
carried out in 49ml sealed glass reactors heated at different temperatures for 24 hours SA = South Africa; IN = Indonesia; BAI- USA.
As can be clearly seen the emission of molecular hydrogen is dependent on the properties of the coal. However all the bituminous coals studied do release H2 upon weathering and the process is temperature dependent. In order to asses the possibility of accumulation of molecular hydrogen in an underground coal mine we have envisaged the following scenario: A 2.0 cubic meters volume of a confined space (crack) occurring in contact with a coal seam where the temperature of the coal is 55C and the coal is under atmospheric conditions. At these conditions the emission is at a rate of 0.615; 0.826 or 1.51 ppmv H2/gram coal x hour for SA, IN or BAI coal respectively. If the size of the surface coal approaches 1,000 Kg around the crack (probably this is only a lower limit) and the weathering process endures for 30 days at least than the amount of molecular hydrogen release assuming total accumulation (without ventilation in the crack) to the crack from the surface of the coal walls into the crack 4
−1
)
is 44 ; 56 and 102 L for the three coals. This corresponds to 2.2 ; 2.8 and 5.1 %vol which is higher (for the BAI coal) and very close (for the South African and the INIndonesian coals) to the 4.0% LEL level (lower explosion limit) in air of molecular hydrogen!!!. Thus this very simple estimate indicates that accumulation of molecular hydrogen, H2, produced via weathering low temperature oxidation of bituminous coals might be the main cause for unexplained explosions in underground coal mines.
4. Conclusions The results of this approximation and the conclusions are very simple. (i)
(ii)
(iii)
In order to prevent the risk of initiation of explosions via the accumulation of molecular hydrogen H2 in underground coal mines due to the low temperature oxidation (weathering) of bituminous coals it is recommended to install in addition to methane gas monitors also H2 detectors which are simple and cheap in order to follow up such possibility and to have alarms if H2 levels are rising in the mine. Furthermore it is also reasonable to install such monitors in confined spaces such as coal ship holds or bunkers in which coals are being stored for period of weeks and longer. This operation will increase the safety measures in the coal mining industry and will probably reduce the death toll appreciably in this industry.
5. References 1. . a. A. W.Davies and A. K. Isaac, Coal dust explosions: a continuing menace, Inst. Mining and Mettallurgy Trans. Sect. A: Mining Industry, 108, 85, 1999. b. G. L. Smith and J. J. du Plessis, J. South African Inst. Mining and Metallurgy, 99, 117, 1999. c. R. McGregor, Miners pay high price for China’s coal, Financial Times, July 17th, 2002. d. Coal mine explosion kills 48 in China, nd www.annanova.com/news/story/sm268418, 22 April, 2001. 2. C.R. Nelson, Chapter 1, “Chemistry of Coal Weathering”, C. R. Nelson editor, Elseiver (1989). 3. a. S. L. Grossman Ph.D. Thesis, “Low Temperature Atmospheric Oxidation of Coal”, Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel, (1994). b. S. L. Grossman, S. Davidi and H.Cohen, Fuel, 70, 897 (1991). c. S. L. Grossman, I. Wegener, W. Wanzl, S. Davidi and H.Cohen, Fuel, 73, 762 (1994). 4.
S. Davidi, S. L. Grossman and H.Cohen, Fuel, 74, 1357 (1995).
5.
U. Green and H. Cohen, Energy & Fuels 9 23 (6), pp 3078–3082 (2009).
5
Oviedo ICCS&T 2011. Extended Abstract
Pyrolysis and Combustion kinetics using the Distributed Activation Energy Model
F. Saloojee1, S. Kauchali2, N. Wagner
University of Witwatersrand, Johannesburg 1
[email protected] 2
[email protected] Oviedo ICCS&T 2011. Extended Abstract
Abstract In this work, the kinetics of pyrolysis and combustion of coal have been studied. Thermo-gravimetric experiments were simulated for these reactions at constant and variable heating rates. The results were used with an appropriate model in order to determine the reaction kinetics. The Distributed Activation Energy Model (DAEM) is commonly used to describe the coal pyrolysis process [1]. The model states that coal devolatilizes according to a number of first order reactions, each with unique activation energy. An algorithm has been developed to calculate the kinetic parameters of each reaction using the DAEM [1]. The algorithm was tested on simulated TGA data for pyrolysis reactions at constant and variable heating rates. Results show that this is a robust method for calculating the kinetic parameters of first-order reactions. Further scrutiny of the inversion algorithm has shown that the calculation of the activation energy is a model-free method. The algorithm was applied to simulated TGA data for coal combustion following the shrinking core model. Results show that the DAEM can be used as a model-free method to calculate the activation energy of coal combustion. However, the calculation of the pre-exponential factor requires the use of an appropriate structural sub-model.
Oviedo ICCS&T 2011. Extended Abstract
1. Introduction The conversion of coal to provide energy is one of the major causes of South Africa’s contribution to greenhouse gas emissions. These emissions can be reduced by correct design and efficient operation of coal conversion equipment. In order for this to be achieved, kinetics of coal conversion reactions need to be easily available. This was the motivation for the work which has been presented here. The Distributed Activation Energy Model (DAEM) has been used to model pyrolysis reactions of coal [1,2,3]. This model describes pyrolysis as a series of first-order Arrhenius reactions, each uniquely characterised by its activation energy. The rate equation can be expressed as follows:
!" #$%,
, exp exp
&1(1
Where M(t) is the mass of the fuel at time t, M0 is the initial mass of the fuel and w is the fraction of ash in the fuel. For each component in the fuel which reacts, fi,0 is the initial mass fraction of that component in the fuel, Ei is the activation energy of the reaction and Ai is the pre-exponential factor of the reaction. Based on this model, Scott et al. (2006) [1] developed a method of calculating the Ei, Ai and fi,0 for each reaction. This calculation requires data from TGA experiments at two different heating rates. For each devolatilization reaction occurring, the rate equation can be written as: exp
2
Integration of the above expression gives:
, exp exp B
3
where B is the heating rate and the exponential term can be expressed as Ψ. At a given conversion, the value of fi is always the same. Therefore, the right hand sides of Equation 3 can be equated for any two heating rates to calculate Ei. It is then assumed
Oviedo ICCS&T 2011. Extended Abstract
that each reaction reaches a conversion of 63.21 % [1] and the value of Ei is used to calculate the Ai for each reaction. If Equation 1 is written in Matrix form as: Ψ- Ψ. 1 Ψ 1
-, $ 1 ,- / 0Ψ- - Ψ. - 1 Ψ$ - 12 3 , ., / 1
4, . Ψ- . Ψ. . Ψ$ . 1
4
then inversion of the matrix equation provides the values of fi,0. The aim of this work was to use the method developed by Scott et al. (2006) as a modelfree method to calculate the activation energy of coal char combustion. 2. Pyrolysis Modelling The first step in this work was the testing of the algorithm on simulated TGA curves. Curves were created with specific E’s and A’s for different types of reactions. The DAEM algorithm was applied to these curves to test whether the parameters used for the simulations could be regenerated. The calculated kinetic parameters were then used to model the reactions for comparison with the original curves. 2.1 Simulated single, first-order reaction with constant heating rate For pyrolysis, a curve was created for a single first-order reaction with the kinetic parameters provided in Table 1. The DAEM was able to correctly calculate the kinetic parameters used and model the curves at the two heating rates used for the calculation. It was also able to extrapolate these predictions to higher and lower heating rates. The kinetic parameters calculated by the DAEM are presented in Table 1 as well. The simulated curves and model fits for the case of the single reaction are presented in Figure 1. Table 1: Comparison of original kinetic parameters and those recovered by the DAEM for a single, first-order reaction with constant heating rate Parameter
Recovered Value
Original Value
% Error
f0
0.9999
1
0.01
E (KJ/mol)
135.1974
135.2
0.0019
A(min-1)
1.13×1010
1.1001×1010
2.8
Oviedo ICCS&T 2011. Extended Abstract
1 0.001 K/min 10 K/min 1000 K/min 10000 K/min 0.001 K/min model 10 K/min model 1000 K/min model 10000 K/min model
0.9
Mass Fraction Remaining
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 300
400
500
600
700 800 900 Temperature (K)
1000 1100
1200
Figure 1: Simulated TGA curves for a single, first-order reaction at different heating rates, with model predictions for each of these heating rates 2.2 Seven simulated first-order reactions with constant heating rates For the second pyrolysis test, TGA curves were created for seven first-order reactions, using the kinetic parameters in Table 2. The DAEM again proved capable of calculating the correct kinetic parameters, as shown in Table 2, and of modelling the curves at the different heating rates. The simulated curves and model fits are presented in Figure 2. Table 2: : Comparison of original kinetic parameters and those recovered by the DAEM for seven first order reactions at constant heating rates
Reaction
Sum of f0
Original f0
Average E
Original E
Average A
Original A
1
0.1436
0.142857
150.1595
150
1.035E+15
1E+15
2
0.1432
0.142857
176.6007
175
1.552E+15
1E+15
3
0.1398
0.142857
192.6182
190
1.619E+15
1E+15
Oviedo ICCS&T 2011. Extended Abstract
4
0.145
0.142857
200.2781
200
1.056E+15
1E+15
5
0.1431
0.142857
225.9348
225
1.21E+15
1E+15
6
0.1426
0.142857
251.253
250
1.277E+15
1E+15
7
0.143
0.142857
274.7396
275
9.675E+14
1E+15
1 0.001 K/min 10 K/min 1000 K/min 10000 K/min 0.001 K/min model 10 K/min model 1000 K/min model 10000 K/min
0.9
Mass Fraction Remaining
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 300
400
500
600
700 800 900 Temperature (K)
1000 1100
1200
Figure 2: Simulated TGA curves for seven first-order reactions at different heating rates, with model predictions for each of these heating rates 2.3 Simulated first-order reaction with non-constant heating rate It was noted that in real TGA experiments, the heating rates of the sample are not always constant. Curves were then created for the heating rate profiles shown in Figure 3. The algorithm was modified to use instantaneous values for the heating rate at each temperature, as opposed to a constant value. In this case, the DAEM algorithm was again capable of calculating the correct kinetic parameters, as shown in Table 3.
Oviedo ICCS&T 2011. Extended Abstract
70
45 Constant Heating Rate Variable Heating Rate
60
Constant Heating Rate Variable Heating Rate
40 35 Heating Rate (K/min)
Heating Rate (K/min)
50 40 30 20
30 25 20 15 10
10 0 300
5 400
500
600
700 800 900 Temperature (K)
1000 1100 1200
0 300
400
500
600
700 800 900 Temperature (K)
1000 1100 1200
Figure 3: Heating rates vs. temperature profiles used for simulation of TGA data Table 3: Original and Recovered Kinetic Parameters from DAEM for a first-order reaction with variable heating rates Parameter
Recovered Value
Original Value
f0
0.9965
1
E (KJ/mol)
135.212
135.2
A(min-1)
1.1×1010
1.1001×1010
3. Model-free kinetics using the DAEM Examination of this method indicates that the calculation of E is a “model-free” method, while the calculation A is based in the assumption of a first order reaction. The aim of this work was to use the method developed by Scott et al. (2006) as a model-free method to calculate the activation energy of coal char combustion. The rate equation for a particular component in coal can be expressed as: exp 6
5
where g(fi) is a function describing the reaction model of component i. If a heating rate B is used, Equation 5 can be written as: = exp < =; 89.; 6 89
6
Integrating both sides of Equation 6: ? ?@ , A ln ΨB, T
7
Oviedo ICCS&T 2011. Extended Abstract
Integrating both sides of Equation 6: ? ?@ , A ln ΨB, T
7
Where G(fi) – G(fi,0) represents the integral on the right hand side of Equation 7 between limits fi and fi,0, and Ψ is as described previously [1]. At a specific conversion, the values of fi for any two heating rates are equal [1], so: ln ΨB- , T- ln ΨB. , T.
8
From Equation 8, the value of Ei can be calculated, proving that the method is indeed a model-free method. 3.1 Model-free combustion kinetics A combustion reaction was simulated according to the shrinking core model [4] and the data was fed into the algorithm. The DAEM was able to recalculate the activation energy used for the simulation. However, the value of A calculated by the algorithm was incorrect. The correct value was calculated by integrating the shrinking core rate expression and using the calculated value of E. Using these parameters, the shrinking core model was able to predict the reaction at the two heating rates used in the algorithm and at higher and lower heating rates, as seen in Figure 4.
Oviedo ICCS&T 2011. Extended Abstract
1 1 K/min 10 K/min 1000 K/min 10000 K/min 1 K/min model 10 K/min model 1000 K/min model 10000 K/min model
0.9
Mass Fraction Remaining
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 300
350
400
450 500 550 Temperature (K)
600
650
700
Figure 5: Simulated TGA curves for shrinking core reaction at different heating rates with model predictions for each of these heating rates
4. Conclusion The simulation of TGA data provides a test of how well the algorithm is able to perform for different types of reactions. The effects of multiple reactions, non-constant heating rates and a non first-order reaction mechanism were investigated. It has been found that the DAEM inversion algorithm is a model-free method of calculating the activation energy of coal pyrolysis and combustion. If the reaction mechanism is not first-order, the calculated value of E must be used in conjunction with an appropriate model to calculate the pre-exponential factor of the reaction.
Oviedo ICCS&T 2011. Extended Abstract
Acknowledgement University of Witwatersrand, Johannesburg Eskom, South Africa References [1] Scott, S.A., Dennis, J.S., Davidson, J.F. & Hayhurst A.N., 2006. An algorithm for determining
the
kinetics
of
devolatilisation
of
complex
solid
fuels
from
thermogravimetric experiments, Chemical Engineering Science, 61, p. 2339-2348 [2] Pitt, G.J., 1962. The kinetics of the evolution of volatile products from coal, Fuel, 41, p. 267-274 [3] Donskoi, E. & McElwain, D.L.S., 2000. Optimisation of coal pyrolysis modelling, Combustion and Flame, 122, p. 359-367 [4] Everson, R.C., Neomagus, H.W.J.P., Kasaini, H. & Njapha D, 2006a. Reaction kinetics of pulverized coal chars derived from inertinite-rich coal discards: Characterisation and combustion, Fuel, 85, p. 1067-1075
Oviedo ICCS&T 2011. Extended Abstract
A Graphite Furnace Atomic Absorption Spectrometer as an Experimental Platform for Studying Matrix Effects in Trace Element Vaporization during Coal Combustion E. I. Kozliak, O. V. Klykov, A. A. Raeva, D. T. Pierce and W. S. Seames The Sustainable Energy Research Initiative Program (SUNRISE), University of North Dakota, Departments of Chemistry and Chemical Engineering, 151 Cornell St., Mail Stop 9024, Grand Forks, ND 58202 USA,
[email protected] Abstract To date, no direct method is available to assess the partitioning of toxic trace elements (TTE) between the gas and condensed phases during coal combustion. Such a method was developed by us based on the use of a graphite furnace atomic absorption spectrometer (GFAAS) as the experimental platform, with the capability of generating data for temperatures up to 2800 °C. While our prior work reported on the previous ICCS&T meeting introduced to GFAAS small amounts of pure TTE standards to emulate the coal particle pyrolysis (reducing environment, high in carbon), the current study addressed the partitioning of TTEs entrapped in inorganic inclusions, introduced as TTE-doped aqueous solutions. The TTE (arsenic, antimony and selenium) atomization activation energies were determined with and without matrices to assess the matrix effects. Two cationic matrices, iron(III) and, particularly, calcium(II), significantly increased the atomization/vaporization activation energies indicating the increased TTE retention in the solid phase. By contrast, anionic matrices, e.g., acetate and aluminate, did not alter the activation energies, as expected. Unexpectedly, one more anionic matrix, silicate, decreased the atomization/energy for selenium while reducing its atomic absorption signal. Apparently, this matrix non-specifically blocked the TTE access to carbon resulting in its evaporation in the molecular rather than elemental form. Thus, several inorganic matrices were shown to alter the concentration and occurrence of TTEs in the gas phase at high temperatures characteristic for coalfired furnaces.
1
Oviedo ICCS&T 2011. Extended Abstract
1. Introduction Accurate modeling of the partitioning of trace elements (TE; e.g., As, Se and Sb) during pulverized coal combustion is an important step in understanding the impacts these TEs have on the environment for traditional PC combustors1 and on downstream process systems for gasification2-4 and oxy-coal combustion systems. Previous methods are all based on using average or bulk phase conditions and thus do not account for the effects of the microenvironment/matrix surrounding TEs. In our previous work, we used a graphite furnace atomic absorption spectrometer (GFAAS) to simulate in situ the microenvironment similar to that observed during coal combustion (i.e. reducing, high temperature microenvironment). Aqueous solutions of As, Se and Sb oxides were introduced into the furnace to model organically associated TEs.5 Then, the activation energies of TE vaporization/atomization in the furnace were calculated. It has been shown that the activation energies determined this way are independent from operational parameters of the instrument (TE concentration, Ar gas flow rate, ashing temperature, and atomization temperature).5 In the current study, TEs present as mineral inclusions were modeled by introducing the TE solutions together with various organic and inorganic matrices into GFAAS. The use of water soluble matrices allowed for a homogeneous mixing of the given TE and matrix, yet enabling the inherent accessibility of carbon. Matrices such as Ca(OAc)2, Fe(NO3)3, K2SiO3 and NaAlO2 were used. Upon heating, Ca(OAc)2,and
2
Oviedo ICCS&T 2011. Extended Abstract
Fe(NO3)3 decompose into CaO and Fe2O3 respectively, which are the major components of inorganic fraction of coal.6 K2SiO3 and NaAlO2 were also used as matrices to determine if there is any retention of TEs by mineral deposits formed on the walls of the boilers; their major components include potassium and sodium aluminosilicates.7
2. Experimental section Temperature measurements and instrument modification. A Modline 5 infrared (IR) thermometer (Model 52-3024 with 2B lens, IRCON, Niles, IL, USA) was positioned above the furnace to measure temperatures of the furnace wall. The thermometer provided a RS-485 digital output of factory-calibrated temperatures to a host computer. Factory calibration was traceable to NIST blackbody standards. Operated in this manner, the IR thermometer was capable of measuring accurate temperatures over a range of 750 – 3000 °C within a focal distance of 152 – 305 mm, and with a response of 6.6 ms to 60 s. The Hitachi Z-2000 AA spectrometer was modified (as described elsewhere5) to provide simultaneous and precisely synchronized absorbance and temperature measurements. The precise synchronization of absorbance and temperature measurements was achieved by recording and aligning (in time) optically-encoded signals embedded within the AA output and recorded along with the thermometer analog current output. Calculation of activation energies. Activation energies were calculated using the method described by Smets.8 This method is based on the calculation of rate constants
3
Oviedo ICCS&T 2011. Extended Abstract
of atom formation:
k1 =
n(t ) ∞
=
A(t ) ∞
(1)
∫ n(t )dt ∫ A(t )dt t
t
where k1 is the first-order rate constant, n(t) is the number of TE atoms at time t, and A(t) is the absorbance value at time t. Absorbance vs. time profiles from the Hitachi ∞
AA software were used to find A(t). The integrated absorbances ( ∫ A(t )dt ) were t
calculated using OriginPro 8.1. The portion of the absorbance vs. time curve with a positive slope (i.e., the atom formation part of the peak as opposed to its dissipation) was used to construct the Arrhenius plot. The points taken were from the part of the curve between 10×noise to 0.9×Amax. When an absorbance profile contained double peaks (which was the case for some of the experiments with matrix), the multiple peak fit function in OriginPro 8.1 was used for peak deconvolution. The fit used was Gaussian. Temperature vs. time data were obtained using a Modline 5 IR thermometer as described above. Activation energies were calculated from the slope and pre-exponentials were calculated from the intercept of Arrhenius plots (log k1 vs. 1/T).
3. Results and Discussion The effect of two representative inorganic matrices, NaAlO2 and Ca(OAc)2, on the activation energies for As, Sb, and Se atomization was determined (Table 1).
4
Oviedo ICCS&T 2011. Extended Abstract
Table 1. The effect of two representative inorganic matrices on the atomization activation energies for As, Sb, and Se.
Activation energy, kcal·mol-1 0.01 – 0.1 M
TE
No
0.01 M
matrix
NaAlO2
Ca(OAc)2* Peak 1
Peak 2
As
60 ± 5
61 ± 2
51 ± 2
70 ± 8
Sb
37 ± 2
34 ± 3
41 ± 3
65 ± 5
Se
69 ± 5
57 ± 7
136 ± 9
* Ca(OAc)2 concentration was 0.01 M for As and Se and 0.1 M for Sb
0.01 M NaAlO2 did not exhibit any statistically significant effect on the activation energies for all three elements. Figs. 1 - 3 show that neither the peak shapes nor temperatures at which the peaks start rising depend on whether this matrix is present. This observation indicates that aluminates are not expected to influence the partitioning of these three TEs. 0.35
0.25
No matrix
A
NaAlO2
-0.05
0
t, s
2
No matrix
A
NaAlO2
-0.05 0
1.5
t, s
Figure 1. Absorbance profile
Figure 2. Absorbance profile
for 100 ppb As with and
for 100 ppb Sb with and without
without 0.01 M NaAlO2.
0.01 M NaAlO2. 5
Oviedo ICCS&T 2011. Extended Abstract
0.2
0.35
NaAlO2
0 -0.05
No matrix
No matrix
A
2
t, s
Figure 3. Absorbance profile
A
Ca(OAc)2
-0.05 0
1.5
t, s
Figure 4. Absorbance profile
for 100 ppb Se with and without for 150 ppb Sb with and without 0.01 M NaAlO2.
0.1 M Ca(OAc)2.
In contrast to aluminate, calcium showed a significant effect on the activation energies for As, Sb, and Se. The largest effect was observed for Se; its activation energy increased by 86 kcal·mol-1 in the presence of this matrix. A higher activation energy indicates significant chemical interactions between the TE and this matrix, which is supported by the literature. Note that Ca(OAc)2 readily decomposes upon heating to CaO. Thus, CaO is expected to retain Se in mineral exclusions unless high temperatures (around 2300 °C) are reached. Then, if this TE is released to the vapor phase, it will be in its elemental form rather than its oxide. For As and Sb, two absorbance peaks instead of one were observed. Activation energies were calculated separately for each peak upon their deconvolution, as described in the Experimental section. Their occurrence suggests the existence of two competing atomization mechanisms for each TE. The activation energy calculated using the data points of the first peak matched that obtained without a matrix, thus indicating that this peak is likely due to the interaction of TE vapors with carbon. By contrast, the activation energy calculated using the second peak’s data points was significantly higher, apparently reflecting the TE’s interaction with the given inorganic matrix, i.e., calcium. This increase in Ea indicates a significant TE retention by CaO. However, the retention for As and Sb was not as strong as in the case of Se. Perhaps, 6
Oviedo ICCS&T 2011. Extended Abstract
this effect is due to the difference in preferred forms of occurrence of TEs in the vapor phase. Since Se evaporates in the form of its acidic oxide, its retention by basic CaO is expected. By contrast, if other TEs, e.g., As, vaporize mostly as atoms, a less pronounced influence of CaO is expected. Indeed, even though two peaks were observed for As in the presence of calcium, the activation energies calculated with and without this matrix were similar (Table 1). The slight influence of CaO on the evaporation of Sb, along with the occurrence of two peaks, indicates that this TE may still evaporate in both atomic and molecular forms, although the atomic form is dominant. An explanation for this effect is that vaporization combined with atomization occurs via multiple evaporation/ condensation cycles, some of them being coupled with atomization. This would explain the occurrence of two peaks for Sb, as in Figure 4. The main peak is similar to that obtained using the unlined graphite tube, i.e., it is due to both the atoms’ sorption on any surface and the oxides’ sorption on carbon. The second, smaller, peak observed only in the presence of the matrix, is due to the sorption of oxides on basic CaO, resulting in hindered TE atomization. The effect of iron on Ea was similar to that of calcium, thus proving that the increase of Ea was due to the TE oxide interactions with a catión. However, replacement of aluminate with another anionic matrix, silicate, unexpectedly resulted in a significant decrease of Ea for Se and Sb to 26-30 kcal/mol, whereas that for As remained unchanged. Based on this observation, the mechanism of As atomization and, therefore, its partitioning during coal combustion do not appear to be affected by the presence of 0.01 M K2SiO3. By contrast, for Se and Sb, silicates appear to either facilitate the rate-limiting step of their atomization or alter the atomization path resulting in a different rate limiting step of a lower activation energy. Additional mechanistic information was obtained when analyzing the atomic absorbance signal intensity. For all three TEs, the analytical signal was significantly suppressed in the presence of this matrix. The signal suppression of the elemental TE was most pronounced for Se; this feature provided an opportunity to obtain information on the TE speciation in the vapor phase. Apparently, in the presence of silicate, compared to the matrix-free case, the vaporized Se was produced in larger amounts in its molecular form, not ‘seen’ by the GFAAS detector. So, its sizable fraction left the 7
Oviedo ICCS&T 2011. Extended Abstract
furnace prior to atomization (only the target atoms are detected by GFAAS). The importance of this observation to coal combustion is that the presence of silicates appears to promote selenium evaporation without its atomization, thus stabilizing molecular species, e.g., selenium oxides. Blocking the selenium access to elemental carbon as a reducing agent could be the chemical reason for this effect.
4. Conclusions According to the developed method allowing for in situ measurements, exclusive evaporation in the elemental form occurs for selenium only in the presence of calcium whereas arsenic is expected to evaporate predominantly in its elemental form, either with or without matrix. By contrast, selenium (in the absence of a cationic matrix) and, particularly, antimony (with or without matrices) may evaporate as oxides followed by their subsequent atomization upon reactions with carbon. Cationic matrices bind selenium and antimony oxides thus significantly reducing the partitioning of these TEs into the gaseous phase.
Acknowledgement Funding for this study was provided by the U.S. Department of Energy (Grant DEFG02-6ER46292).
References [1] Seames WS, Wendt JOL. Partitioning of arsenic, selenium, and cadmium during the combustion of Pittsburgh and Illinois #6 coals in a self-sustained combustor. Fuel Process Technol 2000;63:179-96. [2] Frandsen F, Dam-Johansen K, Rasmussen P. Trace elements from combustion and gasification of coal-An equilibrium approach. Prog Energy Combust Sci 1994;20:115-38. [3] Kalfadelis CD, Magee EM. Ind Eng Chem Fund 1977;16(4): 489. 8
Oviedo ICCS&T 2011. Extended Abstract
[4] Erickson TA, Galbreath KC, Zygarlicke CJ, Hetland MD, Benson SA. Trace Element Emissions, Final Technical Progress Report, Prepared for U.S. Department of Energy, DE-AC21-92MC28016, October 1998. [5] Raeva AA, Pierce DT, Seames WS, Kozliak EI. A method for measuring the kinetics of organically associated inorganic element vaporization during coal combustion. Fuel Process Technol 2011;92:1333-9. [6] Bool LE, Helble JJ. A laboratory study of the partitioning of trace elements during pulverized coal combustion. Energy Fuels 1995;9:880-7. [7] Thompson D, Argent BB. Mobilisation of sodium and potassium during coal combustion and gasification. Fuel 1999;78:1679-89. [8] Smets B. Atom formation and dissipation in electrothermal atomization. Spectrochim. Acta 1980:35: 33–41.
9
Oviedo ICCS&T 2011. Extended Abstract
Organic sulphur alterations in consecutively chemically and biotreated lignites 1
1
2
2
L.Gonsalvesh1, S.P.Marinov , M.Stefanova , R.Carleer , J.Yperman 1
Institute of Organic Chemistry, Bulgarian Academy of Sciences, bl. 9, Sofia 1113, Bulgaria,
[email protected] 2
Research group of Analytical and Applied Chemistry, CMK, Hasselt University, Agoralaan – gebouw D, B-3590, Diepenbeek, Belgium,
[email protected] Abstract There are a variety of chemical, physical and biological desulphurization methods for inorganic sulphur removal. Recently, biological approaches received special attention as a potential technique to reduce organic sulphur under mild experimental conditions at lower operating and capital costs. The aim of the present study is to apply combination of desulphurization methods (chemical and microbial) toward inorganic and organic sulphur functional forms removal in coal. In the current study, one Bulgarian coal sample from “Maritza East” lignite deposit, which is with a significant role in the total energy supply for the country, is used. In order to improve the organic desulphurization effect and to concentrate efforts on a deeper research of organic sulphur changes, investigated sample is preliminary chemically treated. The following products are subjected to biodesulphurization with Pseudomonas Putida bacteria: initial coal, preliminary oxidized coal under atmospheric air and high temperature, demineralized coal, demineralized and oxidized coal, demineralized and depyritized coal, as well as demineralized, depyritized and oxidized coal. Maximum total (71.0 %), pyritic (90.6 %) and organic (49.4 %) sulphur desulphurization effects are achieved for the last sample. Temperature programmed reduction at atmospheric pressure coupled with mass spectrometry (AP-TPR/MS) is used to specify the organic sulphur forms in coal and to assess the changes in organic sulphur that occur as a result of applied treatments. The following organic sulphur types are specified in comparison with model compounds: thiols, organic sulphides, thiophenes, organic sulphonic acids, sulphoxides and sulphones. 1
Oviedo ICCS&T 2011. Extended Abstract
1. Introduction Clean coal utilization is a challenge for higher energy consumption and global ecological impact. Coal is under particular inspection, as during combustion a huge amount of pollutants is produced. Burning of sulphur-containing compounds in fossil fuels evolves sulphur oxides, provoking harmful effects on health, environment and economy. Since there are a variety of chemical, physical and biological desulphurization methods for inorganic sulphur removal, biotreatment received special attention as a potential approach to reduce organic sulphur in mild experimental conditions at lower operating and capital costs. Maritza East lignites are the main Bulgarian deposit with low rank coal. They are characterized by high ash and sulphur contents but a great part of the energy production of the country is based on them. The aim of the present study is to apply a combination of desulphurization methods (chemical and microbial) with an expressed desulphurization potential toward inorganic sulphur and organic sulphur functional forms removal in lignites. In order to increase the total desulphurization effect initial sample is preliminary chemically treated as follow: i) demineralization; ii) demineralization and depyritization; iii) oxidation under heating in air flow. Temperature programmed reduction at atmospheric pressure (AP-TPR) coupled with mass spectrometry (AP-TPR/MS) is used to specify the organic sulphur functional forms in lignites and to evaluate the changes in organic sulphur occurring as a result of applied treatments.
2. Experimental 2.1. Coal samples preparation Bulgarian lignites from Maritza East deposit (Trojanovo-North mine) is selected due to its high inorganic and organic sulphur contents and energy significance. Technological sample of freshly mined lignites is air dried, milled and sieved, < 0.25 mm.
2.2. Chemical treatments
2
Oviedo ICCS&T 2011. Extended Abstract
Demineralization of initial lignite sample is carried out by the Radmacher method – consecutively treatment with 5% HCl, 40 % HF and 35 % HCl at ambient temperature. Subsequently the sample is treated by diluted nitric acid (17 %) for depyritization [1]. Oxidation with atmospheric air is carried out in an electrical oven at 150 oC, for 45 h [2]. Samples placed in thin layer in quartz crucible are oxidized with air flow of 150 ml min-1.
2.3. Microbial desulphurization It is known that Pseudomonas putida (PP) bacteria are effective microbial culture capable to decrease coal organic sulphur [3]. In the present study PP bacterial strain is isolated from soils polluted with crude oil. These microorganisms are grown on Raymond nutrient medium at pH 6.8, temperature 28 oC and 30 days duration. The following products are subjected to biodesulphurization with PP bacteria: initial coal (In), preliminary oxidized coal under atmospheric air and high temperature (In-oxy), demineralized coal (AF), demineralized and oxidized coal (AF-oxy), demineralized and depyritized coal (APF), as well as demineralized, depyritized and oxidized coal (APF-oxy). After biotreatment, "PP" is added to the abbreviation of the corresponding sample. Laboratory scale shake-flask experiments are carried out at pulp density 10% (w/v), at 28 oC for 15 days. The biotreated samples are separated from the media by filtration and consequently washed with 5% HCl solution, and hot distilled water. The dried samples at 105 o
C are stored in inert atmosphere for analyses.
The data characterizing coal samples are given in Table 1.
2.4. AP-TPR/MS technique To specify the organic sulphur forms in coal and to assess the changes in organic sulphur that occur as a result of applied biotreatments, AP-TPR coupled “on-line” with mass-spectrometry (AP-TPR/MS) in different gas media (H2 and He) is used. Apparatus and experimental procedure of the AP–TPR are described elsewhere [4]. In each experiment, approximately 40 mg of sample mixed with 25 mg of fumed silica are placed in the reactor under a 100 ml min-1 flow of pure hydrogen or helium. A linear temperature program of 5 °C min-1 from ambient temperature up to 1025 °C is followed. TPR reactor is coupled “on-line” with a mass 3
Oviedo ICCS&T 2011. Extended Abstract
spectrometer (FISONS-VG Thermolab MS) through a capillary heated at 135 °C. The mass spectrometer equipped with a quadruple analyzer is set at an ionizing voltage of 70 eV. The MS signals m/z 10 ÷ 160 are “on-line” monitored.
3. Results and discussion 3.1. Bulk characteristics Ultimate analysis of the initial lignite sample in Table 1 shows its high organic and inorganic sulphur contents. In order to increase total desulphurization effect and to concentrate efforts on organic sulphur study, initial sample is subjected to chemical (demineralization, depyritization) and thermochemical (oxidation under heating in air flow) treatments prior to biotreatment with PP bacteria. It is known that mild oxidation with atmospheric air under heating is suitable for desulphurization of low rank coal with high pyrite content [2]. This dry oxidative method is based on pyritic sulphur transformation into sulphate sulphur by air oxidation of coal heated before combustion. Advantages of the technique are the lack of liquid phase, absence of expensive oxidative reagents and simplicity. It is necessary to emphasize that the generated sulphatic sulphur is retained by the slag and does not transformed into SOx during combustion. In the present study maximum total (71.0 %), pyritic (90.6 %) and organic (49.4 %) sulphur desulphurization effects are achieved for APF-oxy-PP sample. Total sulphur removal for InPP and In-oxy-PP samples is respectively 28.4 and 39.5 %. There is no appreciable difference in pyritic sulphur desulphurization effect registered for the last two samples, but in the case of In-oxy-PP organic sulphur is more attacked. Concerning demineralized samples, i.e. AF-PP and AF-oxy-PP, total sulphur removal is 43.9 %. Differences in pyritic sulphur and organic sulphur desulphurization for AF-PP and AF-oxy-PP samples are negligible. Table 1. Characteristics of the coal samples. Proximate analysis (%)
S content (%), daf
Desulphurization (%)
Sample W
VM
Cfix
Ash
St
Ss
Sp
So
∆St
∆Ss
∆Sp
∆So
In
8.40 31.30
28.20
32.10
9.48 1.65
3.19
4.64
-
-
-
-
In-PP
7.90 31.90
29.20
31.00
6.79 0.21
2.45
4.13
28.4
87.3
23.2
11.0
In-oxy-PP
5.00 28.50
31.10
35.40
5.74 0.16
2.37
3.21
39.5
90.3
25.7
30.8
4
Oviedo ICCS&T 2011. Extended Abstract AF-PP
5.90 47.10
43.10
3.90
5.32 0.08
2.35
2.89
43.9
95.2
26.3
37.7
AF-oxy-PP
6.20 38.80
49.40
5.60
5.32 0.10
2.30
2.92
43.9
93.9
27.9
37.1
APF-PP
3.40 49.50
44.70
2.40
2.87 0.02
0.31
2.54
69.7
98.8
90.3
45.3
APF-oxy-PP
8.00 35.30
54.90
1.80
2.75 0.10
0.30
2.35
71.0
93.9
90.6
49.4
St – total sulphur; Ss – sulphatic sulphur; Sp – pyritic sulphur; So – organic sulphur
3.2. AP-TPR experiments coupled “on-line” with MS detection 3.2.1. In H2 atmosphere The H2S kinetograms of AP-TPR/MS in H2 atmosphere of samples under consideration are visualized in Fig.1. Only m/z 34 ion profile is shown as m/z 34 (H2S+) and m/z 33 (HS+) demonstrate the same evolution. There are always two dominant peaks in m/z 34 profiles of In, In-PP and In-oxy-PP samples: the first one with Tmax at about 400 °C is attributed to dialkyl and alkyl-aryl sulphides; second peak at about 600 °C refers to the presence of di-aryl sulfides and more complex thiophenic structures. This assumption is based on the model compound approach and also on AP-TPR/MS profiles of typical aliphatic and aromatic fragments for investigated samples [4]. Structures discussed in AP-TPR/MS kinetograms are illustrated in Fig. 2. Despite of high pyrite content of In sample, individual peak corresponding to pyrite presence is not observed. Nevertheless it is noteworthy that the peak with maximum at about 650 °C is slightly asymmetric and starts at about 500 °C. This could be related to pyrite reduction/hydrogenation. In m/z 34 profile of In sample a weak shoulder at 300 °C can be recognized. It is more pronounced in the In-PP sample. This is explained by aliphatic mercaptans hydrogenation. The shoulder under consideration disappears in m/z 34 profiles of In-oxy-PP sample inasmuch as mercaptans are oxidized. Since the shoulder for thiols hydrogenation is observed in m/z 34 profile of In-PP sample, the oxidation of thiols is rather due to preliminary oxidation with atmospheric air than to biotreatment. It is known that thiols can be oxidized to disulphides under mild air oxidation, while under more severe condition, they can be oxidized to sulphonates [5]. Two peaks are observed in AP-TPR/MS m/z 34 kinetograms of AF-PP and AF-oxy-PP samples. The peaks are attributed in the same way as the peak assignment in m/z 34 profile for In sample. Since a well shaped shoulder (in the first peak) is observed at 300 ºC in m/z 34 profile of AF-PP sample, the aliphatic mercaptans presence is more pronounced. The 5
Oviedo ICCS&T 2011. Extended Abstract
emergence of this emphatic shoulder is explained by the reduced content of mineral components. It is proven that more reliable information with AP-TPR/MS can be achieved for demineralized samples. It is because mineral components (such as siderite) capture H2S and obtained H2S profile is less detailed [6]. The shoulder at 300 ºC again disappears in m/z 34 profile of AF-oxy-PP sample. The presence of pyrite influences the second peak in different manner: for AF-PP an asymmetric profile is generated towards the lower temperature region; for AF-oxy-PP a well expressed shoulder is recognized around 550 °C.
In In-PP In-oxy-PP
Intensity (mbar)
3.00E-012
2.00E-012
1.00E-012
0.00E+000
100
200
300
400
500
600
700
800
900
1000
Temperature (°C)
AF-PP AF-oxy-PP
Intensity (mbar)
3.00E-012
2.00E-012
1.00E-012
0.00E+000
100
200
300
400
500
600
700
800
900
1000
Temperature (°C)
6
Oviedo ICCS&T 2011. Extended Abstract
APF-PP APF-oxy-PP
Intensity (mbar)
1.20E-012
8.00E-013
4.00E-013
0.00E+000
100
200
300
400
500
600
700
800
900
1000
Temperature (°C)
Figure 1. AP-TPR/MS (H2), m/z 34 kinetograms for investigated coal samples. O R1,2
Thiols
SH
R1,2
S
O
Sulphonic acids
OH
R1,2
S
R1,2 Sulfides R1,2 S R1
S
O
R1,2
Thiophenes R1,2
O S
R1 - alkyl R2 - aryl
Sulphoxides
R1,2
Sulphones
O
Figure 2. Structural formulae of organic sulphur functional forms discussed in the text.
A broad signal (in the range of 200-800 ºC) with indications for apexes at 300 ºC, 400 ºC, 550 ºC and 650-700 ºC can be seen in AP-TPR/MS m/z 34 profile of APF-PP. No well formed peaks can be observed in this profile. This is probably due to low organic sulphur content and the modified coal matrix. Nevertheless interpretation of the apexes at 300 ºC, 400 ºC and 650700 ºC can be attributed in the same way as the interpretation of H2S profile of In sample. The apex at 550 ºC is probably related to hydrogenation of “new” organic sulphur species formed during depyritization and biodesulphurization of ash pyrite free coal. Other explanation is that some organic sulphur compounds could be more visible due to changes in the coal matrix as a result of the treatments. In m/z 34 profile of APF-oxy-PP again a broad 7
Oviedo ICCS&T 2011. Extended Abstract
signal is observed. It starts at higher temperature (~300 ºC) compared to APF-PP because of thiols oxidation. The maximum of the signal is at 550 ºC. Similar to APF-PP it is attributed to hydrogenation of new formed organic sulphur species of oxidative origin which are more dominating. 3.2.2. In He atmosphere AP-TPR pyrolysis in inert atmosphere is performed to receive more information for the nature of oxidized sulphur species. Fig. 3 gives SO2 evolution in He for samples under consideration. In it, only m/z 64 profiles are shown since they exhibit the same evolution pattern as m/z 48 profiles. Two peaks appear in m/z 64 kinetograms of In, In-PP and In-oxy-PP samples. The first broad peak is registered at lower temperature up to 400 ºC. Based on model compounds approach and also on AP-TPR/MS (He) profiles of typical aliphatic and aromatic fragments it can be attributed to organic sulphonic acids. The second peak maximizing at 490 ºC can be assigned to iron sulphates, sulphoxides and sulphones. Presently to distinguish last three types of sulphur containing compounds additional research is needed. Inasmuch as In-PP and Inoxy-PP samples have low content of sulphatic sulphur (see Table 1), the second peak could be mainly referred to sulphoxides and sulphones. It should be noted that in the case of In-oxyPP sample, the intensity of the second peak increases compared to the first one, confirming the increased presence of oxidized organic sulphur compounds. In AP-TPR/MS (He), m/z 64 profiles of AF-PP and AF-oxy-PP samples again two peaks are registered. These peaks are interpreted in the same way as the assignment of m/z 64 profiles for In-PP and In-oxy-PP samples. Again, due to the chemical treatment, the coal matrix is altered and thus the shape of the registered profiles is influenced. For the APF-PP profile a further shift towards lower temperature compared to the AF-PP profile is noticed, due to the additional chemical treatment. Further oxidation did occurred for APF-oxy-PP sample, resulting in the removal of already oxidized organic sulphur compounds and thus a clear change in the obtained profile compared with the one for APF-PP is registered.
4. Conclusions A combination of chemical and microbial desulphurization methods are applied for inorganic and organic sulphur removal in low rank coal, Bulgarian lignites. Maximum total (71.0 %), pyritic (90.6 %) and organic (49.4 %) sulphur desulphurization effects are achieved for 8
Oviedo ICCS&T 2011. Extended Abstract
preliminary chemically treated (demineralized, depyritized and oxidized) biodesulphurized sample APF-oxy-PP. Qualitative specification of a broad range sulphur and oxygen-sulphur functional forms is done by using AP-TPR/MS technique. Some changes are depicted as well: thiols disappear in all oxidized and biotreated samples; new formed sulphur containing compounds are observed after some treatments. Semi-quantitative appraisal of current desulphurized coals will be a target of future study.
1,20E-011
Intensity (mbar)
In In-PP In-oxy-PP
8,00E-012
4,00E-012
0,00E+000 100
200
300
400
500
600
700
800
900
1000
Temperature (°C)
3.00E-012
Intensity (mbar)
AF-PP AF-oxy-PP
2.00E-012
1.00E-012
0.00E+000 100
200
300
400
500
600
700
800
900
1000
Temperature (°C)
9
Oviedo ICCS&T 2011. Extended Abstract
6.00E-012
Intensity (mbar)
APF-PP APF-oxy-PP
4.00E-012
2.00E-012
0.00E+000 100
200
300
400
500
600
700
800
900
1000
Temperature (°C)
Figure 3. AP-TPR/MS (He), m/z 64 kinetograms for investigated samples.
Acknowledgements The study was performed within the framework of Cooperation agreement for joint supervision and award of a doctorate between Hasselt University, Belgium and Bulgarian Academy of Sciences, BAS-Bulgarian bilateral project with Hasselt University, FWOFlanders.
References [1] Marinov SP, Stefanova M, Stamenova V, Carleer R, Yperman. Sulphur functionality study of stream pyrolyzed “Maquinenza” lignite using reductive pyrolysis technique coupled with MS and GC/MS detection systems. Fuel Process Technol 2005;86:523-34. [2] Rustchev D, Bekyarova E, Patent №36265 MPK CL 10 9/06 (1983). [3] Rai,C. & Reyniers, J.P., Biotechnol Prog 1988;4: 225-30. [4] Mullens S, Yperman J, Reggers G, Carleer R, Buchanan III AC, Britt PF, et al. A study of the reductive pyrolysis behaviour of sulphur model compounds. J Anal Appl Pyrolysis 2003;70:469-91. [5] Tsai CS. Fundamentals of Coal Beneficiation and Utilizations. Coal Science and Technology 2, Elsevier, Amsterdam, 1982. 10
Oviedo ICCS&T 2011. Extended Abstract
[6] Maes II, Gryglewicz G, Yperman J, Franco DV, Haes JD, D`Olieslaeger M, et all. Effect of siderite in coal on reductive pyrolytic analyses. Fuel 2000;79:1873-81.
11
Oviedo ICCS&T 2011. Extended Abstract
Rank-dependent formation enthalpy of coal
M. Sciazko Institute for Chemical Processing of Coal, Zabrze, Poland,
[email protected] Abstract The final state of the geochemical transformation of plant debris is coal, which is a complex organic matter contaminated with dispersed mineral substances. These chemical changes led to the formation of a specific coal structure, dependent mainly on original substance composition and temperature-pressure history of its transformation. Coal organic matter is not described as a defined chemical compound but rather as a model form is used depending on the rank of coal investigated. Thus, coal may be characterized by a defined thermodynamic state at standard conditions of pressure and temperature. That quantity is called enthalpy of formation and is easily determined for pure species by using the proper thermodynamic tables or measuring suitable heats of reactions. This is not the case for coal due to the complexity of its composition. Considering the particular chemical structure of coal as a result of a specific reaction, one can assume that it may be also characterized by a defined thermodynamic state such as enthalpy of formation. In this work, a method to calculate enthalpy of formation for coal was developed over the entire rank range. Here, enthalpy of formation for a complex chemical compound was defined as the difference between the experimentally determined heat of combustion and thermodynamically calculated heat of combustion reaction of elementary substrates. A boundary condition for that approach is defined by the value of enthalpy of formation of graphite. The above-described method should produce a value of zero for graphite. Using the correlation for enthalpy of formation developed, this manuscript proposes a model of coal classification via a thermodynamic quantity reflecting its structure and technological suitability. Based on the analysis of enthalpy of formation with respect to coal composition, enthalpy of formation may have both negative and positive values, depending on the type of fuel. Furthermore, a change in formation enthalpy is continuous but corresponds to different chemical structures of coals.
1
Oviedo ICCS&T 2011. Extended Abstract
Comparing previous coal classification data with their corresponding values for enthalpy of formation suggests that the enthalpy of formation can be used to classify solid fuels. Various types of fuels are characterized, and the following values for enthalpy of formation are reported: anthracite (+250 kJ/kg), peat (< -3200 kJ/kg) and medium volatile bituminous coal ca. zero.
1. Introduction Established classification systems guide the interpretation of scientific research results and allow for the comparisons of operating conditions and coal selection for chemical processing. However, the analysis of such classification and the resulting parameters indicate that the system is inconsistent. In addition, when classifying coal types for processing in the chemical and power industries, the technological needs are not directly reflected, and the focus is rather on operational parameters such as caking ability, ash content or caloric content [1], [2]. Analysis of existing classification systems suggests that they are not related to the thermodynamics that characterize the work potential. This paper identifies a key thermodynamic parameter (enthalpy of formation) to characterize coals and relates it to coal properties. The enthalpy of formation represents the energy resulting from the reactions that created coal. For pure substances, the enthalpy of formation is a single defined value. Due to the various chemical structures of coal, however, the enthalpy of formation will depend on the rank of coal and on the structure specific for a given type of coal. The enthalpy of formation may thus characterize the coal with an accompanying classification system. To maintain consistency with chemical thermodynamics, a nascent model should consider that coals of increasingly high metamorphism approach the structure of graphite, in which the heat of calorimetric combustion and the thermodynamic enthalpy of combustion reaction are equal.
2. Experimental section The objective of this study is to determine the influence of coal (described by elemental composition) on the change of the enthalpy of its formation. This assumes that the enthalpy of formation for coal, which is a complex fuel, will be defined as the difference between the measured heat of combustion and thermodynamically calculated heat of combustion of coal elements. The difference between the measured heat of combustion 2
Oviedo ICCS&T 2011. Extended Abstract
and the calculated thermal effect of combustion reaction is based on 224 sets of data describing properties of Russian [3], American [4] and Polish [5] coals and chars/cokes. For computational and comparative purposes, all the elemental composition data have been converted into a dry and ash-free condition; the heat of combustion was treated similarly. The oxygen content is obtained by subtracting the determined contents from the other elements, where sulphur exists as combustible sulphur. The database comprised a very wide spectrum of fuel properties, and their ranges are presented in Table 1. Table 1. The range of elemental composition and of heat of combustion values. Parameter
Min. value
Max. value
C
69.87
91.26
H
2.61
6.66
O
2.08
23.08
N
0.07
2.53
S
0.39
9.37
Qsdaf, MJ/kg
27.27
36.98
Content, % (daf)
3. Results and Discussion Assuming that the enthalpy of coal formation is equal to the difference between enthalpy of combustion reaction of coal component elements in the standard state and the determined heat of combustion [6], the consistency of both methods for the determination of fuel calories should lead to the same result. In the case of elemental carbon represented by graphite, the standard enthalpy of formation is zero. Unfortunately, all known relationships for the calculation of the heat of combustion do not have such a feature [7]. Calculating the enthalpy of combustion reaction of coal as a dry and ash-free acc. to the general relationship (1) we have: ∆c H
0 , daf
C daf H daf S daf 0 0 0 = ∆ f H CO2 + ∆ f H H 2O ( l ) + ∆ f H SO 2 MC 2M H MS
(1).
Here, the symbols of elements stand for their weight fraction in coal organic matter divided by their atomic mass, which are multiplied by the appropriate molar enthalpies of formation for the individual products of element combustion as adopted from thermodynamic tables.
3
Oviedo ICCS&T 2011. Extended Abstract
After introducing the value of standard enthalpy of suitable components formation and assuming that the element fraction is a percentage, the equation becomes the following: ∆ c H 0 = −327,633C daf − 1417,892H daf − 92,768S daf kJ/kg(2) c Taking into consideration the variation between the values of enthalpy of combustion reaction and the calorimetric heat of combustion, it is critical to determine the key differences between them. Based on elemental analysis, the effect of hydrogen and oxygen on the heat of combustion of coal suggests that the latter has a stronger and more consistent effect. Therefore, applying the definition of the enthalpy of coal formation expressed by equation (3), it is necessary to correlate the thermodynamic heat of combustion with the enthalpy of combustion reaction. Analyzing equation (3), the convention is that the heat of combustion is always positive and the enthalpy of combustion reaction is negative due to an exothermic effect. ∆ f H 0 = Qs + ∆ c H 0
(3)
In general, the relationship between the heat of combustion and calorimetric heat of combustion may have the following form: Qs = (−1)∆ c H 0 f (θ)
(4).
Here, f(θ) is a function that modifies the enthalpy of combustion reaction, defining the ratio of absolute values of the heat of combustion and the enthalpy of combustion reaction. This is a normalized heat of combustion. Based on the elemental analysis, the influence on a change of the heat of combustion, an assumption was made that the correcting function f(θ) is defined by the oxygen content in coal (Oddaf ), expressed in wt.%. Analogous to an ideal gas virial equation of state, in the first approach, the following form of the correcting function was assumed:
f (θ) = 1 + a1θ + a2θ 2 + a3θ 3 + a4θ 4 ...
(5).
It is necessary to consider that the enthalpy of combustion reaction has a sign opposite to the thermodynamic heat of combustion, and thus, the factor of -1 is added in (4). The experimental data lead to the results presented in Table 2.
Table 2. Coefficients in correcting equation (5). Coefficient Value
a1 4.852·10
a2 -3
-1.437·10
A3 -3
8.467·10
A4 -5
-1.66·10-6
4
Oviedo ICCS&T 2011. Extended Abstract
The heat of combustion calculated this way has a mean error of +/-502 kJ (1.5%). Using a Student’s t test, the mean was x = 1.000, and the standard deviation s(x)=0.015. The correctness of assuming the zero hypothesis H0:x = 1 has been confirmed at the significance level of 0.05 by the result t = 0.128. The equation should be used with fourth-degree virial terms because the accuracy of the heat of combustion is computed in relation to the enthalpy of combustion reaction at an oxygen content below 5%, in the area of the enthalpy of formation sign change (Fig. 1). The correcting function was derived for the (daf) coal condition, and for this, reason it is valid only for this condition. 1,04
experimental data calculated data
Normalized heat of combustion
1,02 1
0,98 0,96 0,94 0,92 0,9
0,88 0
5
10
15 Oxygen content, %
20
25
30
Fig. 1. Normalized heat of combustion vs. oxygen content. As a result of the model, the enthalpy of any coal formation ∆fH0w is described by equation (6) resulting from the combination of equations (3) and (4). ∆ f H w0 = ∆ c H w0 [1 − f (θ)]
(6)
Because the enthalpy of formation values in the positive area are lower than 200 kJ/kg (with a mean correlation error for the heat of combustion of 500 kJ/kg), the Student’s t test offers additional credence to the results. All results of the (Qs/∆cH0) ratio that are higher than one were analyzed. Overall, this comprised 40 data points corresponding to anthracites, cokes and chars produced by coal pyrolysis. For this population, the mean was 1.004. Assuming the level of significance is 0.05 and checking the hypotheses H0:x =µ, H0:xµ consecutively for values of µ 1, respectively, the results support the following hypothesis: the positive values do not result from a measurement or calculation error but are a physical feature of coal or its solid products. These results were also confirmed by bond enthalpy analysis in model coals [8].
5
Oviedo ICCS&T 2011. Extended Abstract
4. Coal classification This model for enthalpy of coal formation calculation has a generalized nature because it unifies calorimetrically the determined heat of combustion and thermodynamic heat of coal combustion. Because of the continuity of coal composition changes and the presence of all individual element contents in the range studied, the relationships derived allow explicit determination of the enthalpy of formation for a given coal. In addition, the standard enthalpy of coal formation is determined for the reference state of temperature and pressure, which allows for comparisons of the results to the enthalpies of formation of other chemical compounds tabulated in thermodynamic handbooks. In turn, their tabulation enables comparison and ranking of individual coals. Calculations of the enthalpy of formation conducted for reference fuels adopted in this paper according to Jasienko [9] with the use of (6) lead to the results presented in Fig. 2. These are in line with the American classification (Fig. 2). The following information results: characteristic ranges of the enthalpy of formation may be distinguished depending on the solid fuel type; and range differentiation allows for the assumption that the enthalpy of formation may be a classification parameter for solid fuels. Considering the above, individual fuel types feature the following values for the enthalpy of formation according to the Polish classification: •
anthracite: 250 kJ/kg,
•
semi-coking coal, type 37: 125 kJ/kg,
•
ortho-coking coal, type 35: 0 kJ/kg,
•
gas coal, type 33: -600 kJ/kg,
•
flame coal, type 31: -1300 kJ/kg,
•
brown coal: -2500 kJ/kg,
•
peat: below -3200 kJ/kg.
The above specification is a type of thermodynamic classification of coals and chars, i.e., pyrolysis products. Chars and cokes usually contain less than 2% oxygen, which is less than that contained in anthracites. Thus, an assumption may be made that they constitute a group of fuels for which the enthalpy of formation is lower than 250 kJ/kg and higher than zero.
6
Oviedo ICCS&T 2011. Extended Abstract 500
Enthalpy of formation, kJ/kg
Lignite
Subb. B
HVB C
HVB B
HVB A
0 MVB
LVB
Anthracite
-500
-1000
-1500
-2000
-2500 Type of coal
Fig.2. Thermodynamic classification of solid fuels referred to the American Standards classification. The heat effect of coking coal formation, in which the enthalpy of formation is close to zero, can explain their ability to form good coke. The process of coke formation in general is not accompanied by any internal thermal effect. This is an important indication in the preparation of a blend for coal coking. A positive influence of the lack of thermal effect may be due to the fact that the coke formation basically starts in the coal plastic phase. Both the endothermic and exothermic effects are harmful to the formation of a homogeneous coke structure because of the shortening of the plastic phase. At the exothermic effect, the pyrolysis and volatiles evolution are more sudden. The residence time of coal shortens the plastic phase. In the case of the endothermic effect, the plastic layer is internally cooled, and its duration is reduced. In the coking conditions, this time translates to diminished thickness of the plastic layer. Concurrently, it is necessary to bear in mind that the thermal effect of the conversion is opposite to the calculated enthalpy of coal formation. When the enthalpy of formation has a negative value, this means that in the process of coal organic matter formation, an equivalent amount of heat is released as a result of formation of bonds between oxygen and hydrogen. In the case of anthracite coals, a positive result means that a supply of heat was necessary for their formation. An equivalent amount of heat will be released in their decomposition.
5. Conclusions Analysis of existing classification systems suggests that they fail to consider crucial issues in the reaction thermodynamics of coal evaluation. This paper deals with the selection of a key thermodynamic parameter, enthalpy of formation, to characterize coal and to relate it to coal properties. Enthalpy of formation was evaluated for the entire range of solid fuels, and a correlation proposed. The value of enthalpy of formation 7
Oviedo ICCS&T 2011. Extended Abstract
indicates the state of coal metamorphism and is thus directly related to coal structure and bond characteristics. Enthalpy of formation can be used for coal classification and is also necessary for the energy balance of the coal conversion systems.
References [1] Speight JG: Handbook of Coal Analysis. Jon Wiley&Sons, Inc., Hoboken. New
Jersey; 2005. [2] International codification system of hard coals by type; 1956
http://www.unece.org/energy/se/pdfs/coal6/coedhard.pdf. [3] Gagarin SG, Gladun TG. Evaluation of enthalpy of formation of coal organic matter
(in Russian). Chemia Tvierdovo Topliwa 2003;4:3-23. [4] Coal Conversion Systems Technical Data Book, section IA.50.1; 1982, vol.2. [5] Sciazko M, et al. Balancing of coking process. IChPW Report 2010;30. [6] Annamalai K, Puri IK. Combustion science and engineering. CRC Press, Taylor & Francis Group, Boca Raton, FL; 2005, p.169. [7] Channiwala SA, Parikh PP. A unified correlation for estimating HHV of solid, liquid and gaseous fuels. Fuel 2002;81:1051-1063. [8] Sciazko M. Models of coal classification in terms of thermodynamics and kinetics (in Polish). Krakow: AGH; 2010. [9] Jasienko S. Chemistry and physics of coal (in Polish). Wroclaw: University Press.; 1995.
8
Oviedo ICCS&T 2011. Extended Abstract
Ion beam tomography for coal characterization *
A. Bhargava1, P.J. Masset1, N. Gordillo2, C. Habchi2, P. Moretto2
1
TU Bergakademie Freiberg, Centre for Innovation and Competence – Virtuhcon, Freiberg -Germany, D-09599 2
Université Bordeaux 1, CNRS/IN2P3, Centre d’Etude Nucleaires de Bordeaux Gradignan, CENBG, Chemin du Solarium , BP 120, 33175 Gradignan, France Abstract 3D Scanning Transmission Ion Microscopy-Tomography (STIM-T) of German brown coal was carried out using a proton beam as a nuclear probe at the energy of 2.8 MeV at the nanobeam line of CENBG. Each scan produced series of images which were later stacked together numerically using computer algorithms to produce virtual cut sections across the scanned volume, revealing the internal structure. The STIM-T images were obtained with a spatial resolution in the sub-micrometer range. The analysis showed local density variations due to the presence of pores, minerals, cleats and fractures. The colour image analysis enabled the visualization of the internal microstructure of coal showing fair contrast among fractures and pores. These experiments were complemented by 2D Particle Induced X-ray Emission-Tomography (PIXE-T) for rapid non destructive chemical analysis showing spatial distribution of mineral matter in the selected coal slices. All experiments were done in vacuum (~ 5x10-6 mbar) to maintain a high degree of sensitivity for light elements.
Keywords: Coal characterization, Ion beam analysis, PIXE and STIM tomography
1. Introduction The world has witnessed rapid consumption of fossil fuels over last several decades to mitigate global energy demands. Among major fossil fuels, coal continues to hold a dominant share in the world’s energy spectrum. There are an estimated 275 billion tonnes of coal reserves in USA alone as compared to 4 trillion tonnes of coal resources [1]. Because of high abundance of coal reserves in many countries of the world, and enormous plant replacement costs as compared to other alternatives, coal fired power plants are here to stay for long time. Amidst rising energy demands and increasing oil prices, clean coal *Corresponding author:
[email protected] Oviedo ICCS&T 2011. Extended Abstract
technologies have gained significant attention. Of particular importance is, Integrated Gasification Combined Cycle (IGCC) power plants that have attracted considerable interest to provide clean energy from coal. The present challenge before the power generation industry is to meet emission norms and to reduce green house gases by CO2 sequestration methods. The heart of such a process unit lies in the gasifier reactor where multiphase reactions between coal (solid phase), oxygen (gas phase) and steam take place at elevated pressure (up-to 45 bars) and temperature (up-to 1500 ºC) under partial oxidation conditions. In last several decades a number of experimental, modelling and simulation studies have been reporting these dynamic heat and mass transfer processes at the particle level [2] [3]. However, few of them have been able to show the physiochemical aspects of gas-solid reactions at the reacting inter-phase through experiments. Previous attempts using X-ray computed tomography (X-ray-CT) were made by Mathews [5] and Yao et.al [6]. Also, Van Geet et. al. [7] used similar techniques with SEM –EDX to validate the presence of minerals like liptinite and vitrinite. The scope of this work aims to track and to explore the physio-chemical properties of only solid phase (coal) involved in the reaction, using ion beam technologies such as particle induced X-ray emission (PIXE) and scanning transmission ion microscopy-tomography (STIM-T). As far as we know, few attempts were made in early 1990s with ion beam techniques for coal and coal ash analysis [4]. Like, X-ray-CT, the STIM-T is also a non destructive method which allows the 3D sample visualization with a sub-micrometric lateral resolution [8]. Hence, very accurate spatial positioning and material characterization analysis is possible to ascertain coal matrix slice composition. 2. Experimental methods
2.1
CENBG nanobeam line and the analysis chamber
All experiments were performed at the nano-beamline of the AIFRA (Applilcation Interdisciplinaire des Faisceaux d’Ions en Aquitaine) facility at the CENBG using ultra – stable single–ended HVEE 3.5 MV SingletronTM accelerator. A proton beam at 2.8 MeV was used as a probe for all the analysis. The beam line attains a resolution of 300 nm in the STIM mode with a current of few thousands of counts per second and about 1μm when working in PIXE configuration with a current of few pA upto hundreds of pA. Fig. 1 shows the overview of the experimental setup.
Oviedo ICCS&T 2011. Extended Abstract
a)
b)
c)
FC STIM
RBS
microscopes goniometer
Fig. 1. a) The analysis chamber. b) The goniometer, microscopes and detectors. The red line indicates the beam direction. c) The top-view of the mounted sample on the goniometer.
The target chamber is equipped with three microscopes, one viewing the incoming beam (front side) and the others viewing the sample (backside). The sample holder is driven by a X, Y, Z motorized stage (NewportTM) allowing careful sample positioning in three directions. Additionally, a goniometer is provided to enable rotational motion of the sample. Detailed description of the experimental facility is beyond the scope of this paper and indicated references may be consulted [8], [11].
2.2
Sample Preparation
For this work two types of samples were chosen. Sample A grains were German lignite coal particles obtained from feed used in the local coal fired power plant. While, sample B were coal char particles, prepared by heating sample A to 450 ºC in the presence of nitrogen to remove the surface moisture. Sample B was then diluted in formvar (liquid polymer) solution and later, wires were stretched out of this solution and dried in air during one day. The size of these particles was about 25 μm. These formvar wires containing coal particles were inserted into a glass capillary of diameter ~150 μm and further inserted into a needle of ~400 μm. The whole assembly was mounted on the goniometer sample holder. Similarly, sample A of about 120 µm was glued using AralditeTM on the tip of the capillary glass of about 200 µm and mounted on the goniometer in the similar way.
Oviedo ICCS&T 2011. Extended Abstract
2.3
Scan settings
For 3D-STIM-T experiments a rectangular scan of 160 x 80 µm2 with a resolution of 1.25 µm/pixel was chosen for sample A, meanwhile the area of 100 x 50 µm2 with a resolution of 0.79µm/pixel was selected for sample B. Scan rate was about ~70 scans/projection for both samples and, a total of 100 projections were recorded in 180 degrees. For PIXE-T analysis two slices of 160 µm in width were selected from sample A, wherein the two large grains were including and, one slice in the case of sample B of 100 µm. This, allowed us to study the chemical distribution in the coals. The scan rate was 3000 scans per projection. And, the scan speed during the analysis was 100 μs/pixel for PIXE-T experiments and 200 μs/pixel for STIM-T experiments. Fig. 2 shows the sample images obtained by the camera and the microscope after mounting on the goniometer. a)
b)
Analyzed region
Analyzed region
50 µm
Optical Image
100 µm Sample A
Optical Image
Sample B
Fig. 2. a) A coal grain of about 200 μm was glued using AralditeTM on top of the tip of a glass tube of diameter 200 μm, which was further inserted in the needle of diameter 400 μm. b) Sample B: The analytical coal grains of about 20-30 μm were included in a formvar capillary (~150 μm diameter) which was then inserted into a glass tube of 200 μm and further into the needle of 400 μm.
After all the adjustments were made and the precise beam spot size on the sample was obtained, H+ beam as a microprobe was used to scan the chosen areas. The transmitted ions were collected in passivated implanted silicon lithium detector (Canberra PIPS detector. 25mm2, 12 keV energy resolution). The X-rays emitted from the sample were detected using a Si-Li X-Ray detector (Sirius/80/Be/PIXE, 140 eV energy resolution) placed at 45º backwards from the ion direction and at 22 mm distance from the sample.
Oviedo ICCS&T 2011. Extended Abstract
3. Results
3D – STIM Reconstruction and PIXE analysis
3.1
Series of 2D projections were stacked to create the complete 3D volume matrix. Tomorebuild code, developed at CENBG, was used to convert this data (energy sinogram) into 3D images using a filtered back projection algorithm [9]. These energy sinograms were reconstructed into 3D images as shown in Fig. 3 a) and Fig. 4 a) for sample A and B, respectively.
a)
3D STIM-T reconstruction: Sample A STIM Slice n° 4
Selected slice for PIXE-T
3 2 1
10 µm
b)
STIM slice n°:
10 µm
1
10 µm
2
3
4
max
g/cm3
10 µm
c)
0
STIM (black and white) + PIXE (color) overlapped
1.20
STIM slice
1
Ca
0.14
0.021
Mn
Fe
0.43
Ti
g/cm3
Ratio Z/Ca
50 µm 0
50 µm
50 µm 0
50 µm 0
50 µm 0
0
Fig. 3. a) 3D-STIM -T reconstruction of sample A where different cross sections are indicated as STIM-T slices and also the selected PIXE-T slice for the chemical is shown. b) Corresponding cross section from the selected STIM-T slices. c) PIXE-T slice (colour) overlapped with the STIM-T slice (black and white) in order to show the element distribution. Colour scale bar are normalized to the Ca element.
The colour contrast shows the local density variations in the 3D image post reconstruction. Several lateral planes show the virtual slicing of the selected grain. The qualitative nature of the various pores and fractures is visible from each cut away section using colour
Oviedo ICCS&T 2011. Extended Abstract
contrast, also shown in Fig. 3 (b). The darker regions show areas having lower densities possibly related with the fractures and pores, while the lighter areas show higher density indicating presence of mineral matter, such as calcium based compounds and other elements as shown in Fig. 3. (c). In this figure, PIXE-T slices are overlapped with the STIM-T slices. All gas – solid reactions take place on the surface and in the interior of these particles and these pores and fractures often allow the channeling effect of the reactant gas during the mass transport (diffusion) within the coal particle. The average density calculated for the coal grain (sample A) was 1.35 g/cm3, which is in fair agreement with the values published by Bell et. al [1].
a)
3D STIM-T reconstruction: Sample B Selected slice for PIXE-T Selected slice for n° 1 PIXE-T
n° 2 20 µm
20 µm
STIM (black and white) + PIXE (color) overlapped: slice n° 1
b)
1.17
0.15
Fe
0.57
S
1.00
Ca
g/cm 3
Ratio Z/Ca
20 µm
20 µm
0
20 µm 0
20 µm 0
0
STIM (black and white) + PIXE (color) overlapped: slice n° 2
c) 1.18
0.09
Fe
0.60
S
1.00
Ca
g/cm 3
Ratio Z/Ca
20 µm 0
20 µm
20 µm 0
20 µm 0
0
Fig. 4. a) 3D-STIM-T reconstruction of sample B where the named coal grains are represented in green and the two PIXE-T slices selected for the analysis are shown. b) STIM-T (black and white) and PIXE-T (colour) slice overlapped for the slice nº1. b) STIM-T (black and white) and PIXE-T (colour) slice overlapped for the slice nº2. The red circles are to stand out the high density of the two big grains chosen. Colour scale bar are normalized to the Ca element.
The 3D reconstruction corresponding to coal char (sample B) is shown in Fig. 4 a). The small green particles may be related with the various impurities (included in the formvar solution) as well as crushed grains. In this case the average density of the grains plus
Oviedo ICCS&T 2011. Extended Abstract
formvar solution was 1.08 g/cm3. The reason for deviation from these values is due to low density of both grains and formvar which, makes it difficult to have a better image contrast. Also, shown in Fig.
4 b) and Fig.
4 c) are series of images showing a
combination of STIM-T and PIXE-T results displaying elemental distribution with the density contrast, in the selected slices. The higher density material is indicated by the light colour areas (in STIM-T slices) showing mineral matter or hard fractures. The chemical element distribution obtained with the PIXE-T analysis verifies the presence of the grains when they are overlapped with the STIM-T slices. 4. Discussion In view of the heterogeneous composition of the coal matrix, several samples and experiments are required to ascertain the effect of randomly distributed mineral matter in mass transport of the reacting species in the solid phase. Since, the mineral matter is nonporous; it acts as a hindrance in the transportation of diffusing chemical species to the active carbon sites. As the temperature increases the solid phase gets consumed vis a vis bulk gaseous reactants. The inherent mineral matter acts as a barrier in the diffusion of chemically reactive species. It often, alters the trajectory of the diffusing gaseous specie (oxygen/carbon dioxide), delaying their availability at the reacting inter-phase resulting in incomplete reaction, or sluggish kinetics, also termed as diffusion limitation. Thus considering rather a practical case, in which the reaction between coal and a reactive gas is controlled by not only by a single transport phenomenon but rather a mix of several phenomenon (such as adsorption, chemical reaction and desorption). The spatial location of the mineral matter may significantly affect the kinetics of high temperature reaction (gasification/pyrolysis). Several existing models do not incorporate the effect of these mineral matter constituents in heat and mass transport due to their random presence in the coal matrix. In fact many of them make an assumption of non – existence of any hindrance to such pathways inside coal particle to maintain the simplicity of the mathematical nature of the model, overlooking the impact it could have on gasification kinetics. The authors do believe that the complexity of such a model may increase upon incorporating such assumptions; however it will certainly give illuminating reasons for lower conversions caused due to diffusion limitation at elevated temperatures. Thus, such effects should not be neglected and due attention should be paid to incorporate inhomogeneous nature of coal.
Oviedo ICCS&T 2011. Extended Abstract
5. Conclusions
The 3D-STIM –T and PIXE-T experiments provide accurate elemental maps of the analysed coal samples showing various components. Also, examined and corroborated with XRD experiments, in previous study [12]. The ion beam techniques can be used to characterize the local cleat, fractures and density variations along with the elemental mapping in the solid reactant phase. The results show the spatial distribution of mineral matter in the analysed coal slice. The images obtained using this technique will provide an additional experimental validation tool for several gas solid heterogeneous multiphase reactions in which the reaction rate is controlled by the processes occurring in the solid phase. Also, it is to be noted is that due to experimental limitation extending the scalability of such a technique from particle to bulk sample is questionable. This will also be discussed in the forth-coming publications, wherein quantification of various physical parameters controlling the mass transfer phenomenon in coal matrix is likely to be presented. In view of the present study, it is proposed that if the results of such experiments are accompanied with high temperature in-situ analytical techniques such as those with scanning confocal laser microscopy and hot stage microscopy it would be prove to be an important step in the validation of tracking inter-phase gas solid reactions.
Acknowledgements
The authors are grateful for the support provided by the European Communities as an integrating activity for the “Support of Public and Industrial Research Using Ion Beam Technologies (SPIRIT)” under transnational access activities. Also, the authors thank the BMBF (Fedral ministry of higher education, Government of Germany) to provide financial support under the framework of project Virtuhcon.
References [1] David A. Bell. (First edition 2011). “Coal Gasification and its Applications” Elsiever [2] Sadhukhan, A. K., P. Gupta, et al. (2010). "Modelling of combustion characteristics of high ash coal char particles at high pressure: Shrinking reactive core model." Fuel 89(1): 162-169.
Oviedo ICCS&T 2011. Extended Abstract
[3] Zhu, W. C., C. H. Wei, et al. (2011). "A model of coal-gas interaction under variable temperatures." International Journal of Coal Geology 86(2-3): 213-221. [4] Wang, X., X. Shen, et al. (1993). "PIXE study on effects of coal burning in a coal-fired power station on atmospheric environmental pollution." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 75(1-4): 273-276. [5] Mathews, J. P., J. D. N. Pone, et al. (2011) “High-resolution X-ray computed tomography observations of the thermal drying of lump-sized subbituminous coal.” Fuel Processing Technology 92(1): 58-64. [6] Yao, Y., D. Liu, et al. (2009). “Non-destructive characterization of coal samples from China using microfocus X-ray computed tomography.” International Journal of Coal Geology 80(2): 113-123. [7] Van Geet, M., R. Swennen, et al. (2001). “Quantitative coal characterization by means of microfocus X-ray computer tomography, colour image analysis and back-scattered scanning electron microscopy.” International Journal of Coal Geology 46(1): 11-25. [8] Barberet, P., S. Incerti, et al. (2009). "Technical description of the CENBG nanobeam line." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 267(12-13): 2003-2007. [9] Michelet-Habchi, C., S. Incerti, et al. (2005). "TomoRebuild: a new data reduction software package for scanning transmission ion microscopy tomography." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 231(1-4): 142-148. [10] Barberet, P., L. Daudin, et al. "First results obtained using the CENBG nanobeam line: Performances and applications." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms doi:10.1016/j.nimb.2011.02.036. [11] N. Gordillo et al., Technical developments for computed tomography on the CENBG nanobeam line, Nuclear Instruments and Methods. B (2011), doi:10.1016/j.nimb.2011.02.032 [12] A.Bhargava, P.J. Masset, “Ash fusibility studies in high temperature oxidising/reducing atmospheres”, 4th International Freiberg Conference on IGCC & XtL Technologies - 3-5th May, 2010.
The potential to upgrade petroleum cokes using high temperature processing Mohamed Ismail, John W Patrick, Ed Lester School of Chemical and Environmental Engineering, The University of Nottingham, University Park, NG7 2RD Nottingham, United Kingdom
[email protected] Abstract Metallurgical coke is used primarily as a reducing agent for the reduction of iron in the blast furnace. Due to the high cost, high demand and reduced availability of the high quality coking coals used in the production of this coke, alternative resources are being sought fulfill the role of this coke. One possibility is to make use of petroleum coke. The encouraging aspects for this use of petroleum coke include higher calorific value than traditional coke, relatively low cost, low ash content and ready availability. On the other hand, petroleum coke may not meet the requirements as regards mechanical strength and reactivity due to the influence of in both the macro and micro structures. In this study three samples have been examined for potential use of petroleum coke as a replacement for blast furnace coke. Two of these samples were green petroleum cokes and third one was a good quality metallurgical coke used for the purpose of comparison. These samples were subjected to microstructure analysis before and after heat treatment by X-ray computed tomography which is a non destructive test to explore the internal structure of these samples. In this preliminary work heat treatment up to 900 C led to increased densities of the petroleum cokes from about 1.4 to 1.8g/cm3 and these changes were reflected in the decreased voidage as demonstrated by the X ray computed tomography. The heat treated petroleum coke had a similar voidage to the good quality blast furnace coke indicating that heat treated petroleum coke may be a possible substitute for blast furnace coke. 1. Introduction Petroleum coke is a residual by-product of the cracking process in oil refineries. It may be described as a carbonaceous solid that serves various applications after suitable processing [1]. In recent years, crude oils have become heavier resulting in heavier coker lower case feeds [2]. There are many factors which affect the structure of petroleum coke such as the properties of crude oils and the processing conditions of the cokes such as temperature and pressure. Petroleum coke is mainly used as fuel in power plants and cement factories as a construction material for anodes for aluminum production, lime kiln firing, and specialty
applications, such as dry cells and electronics. It has been used as an additive to coal blends which are used in the production of metallurgical coke. However, it has not been used directly for the reduction of iron ore in a blast furnace. Petroleum coke offers some advantages over traditional metallurgical coke such as higher calorific value, relatively low cost, lower ash, ready availability, and for some types of petroleum coke, low sulfur content [1]. The objective of this study is to gain a thorough understanding of the structure of petroleum coke before and after heat treatment with the aim of assessing the possibility of changing the structure through heat treatment to enable the coke to be considered as a blast furnace coke substitute. 2. Experimental work
Coke materials used
One sample of a good metallurgical coke (BFC) was used as a standard for the purpose of comparison with two samples of petroleum coke, cokes K and RG. These three samples were prepared in the form of disc lumps with the dimensions of 5 to 7 mm diameter and 3 to 4 height.
Techniques
In order to assess the feasibility of petroleum cokes for conventional heat treatment, their physical properties were characterized using helium pycnometry and X ray computed tomography. Chemical properties were assessed using thermal gravimetric analysis (TGA), elemental analysis and bomb calorimetiry.
Procedure
In order to produce a means of distinguishing the microstructure of petroleum cokes from that of industrial metallurgical cokes, the three samples were scanned by X-ray computed tomography before and after treatment. XRCT is a non destructive technique which can be used to obtain digital information about the microstructure of the specimen in three dimensions [3], the images then being analyzed by using ImageJ software [4]. The specimens of petroleum coke were subjected to the heat treatment in an inert atmosphere (N2) using TGA with a variety of ramp rates and maximum temperatures. After initial heating rate of 50 C/min to 105C, the samples were held for 5 minutes and then heated again to a final temperature of 700C or 900C using a ramp of 10C/min, 30 C/min or 50C/min. the samples where then held at the chosen temperature for 20 minutes.
3. Results and Discussions Table 1 and 2 show that the carbon content in the petroleum cokes (K and RG) is greater than that of the traditional metallurgical coke (BFC). As a result, of that the heating value of K and RG is greater than that of BFC; this is shown in Table 3. Sample Name
Moisture VM, C, wt% wt% wt% 1.5 8.6 79.8 1.4 9.7 90.8 1.8 10.6 86.0 Table 1 Proximate analysis of cokes
BFC K RG
Ash, wt% 10 1.3 1.7
Sample Name N ,wt% C ,wt% H, wt% BFC 0.00 79.45 2.36 K 1.47 90.84 3.76 RG 0.00 83.96 3.66 Table 2 Elemental analysis of coked
S ,wt% 0.9 0.0 0.0
Sample Name BFC K Calorific Value, MJ/kg 28.82 36.20 Table 3 Gross calorific values of cokes
GR 36.48
Table 4 shows that for petroleum coke K there is a clear effect due to the increase in temperature between 700C and 900C but the rate of heating between 10C/min and 50C/min had little effect. The percentage weight loss at 700C was of the order of 4.4% and 7.25% at the final temperature of 900C. Ramp, Maximum Initial Wt, g Wt loss % C/min Temp, C K1 10 700 134.47 4.35 K2 30 700 98.40 4.53 K3 50 700 127.84 4.20 K4 10 900 132.03 7.11 K5 30 900 107.60 7.32 K6 50 900 127.88 7.31 Table 4 the effect of temperature and heating rate on the specimens of petroleum coke K Sample
As a result of these values petroleum coke sample RG was heat treated to 900C and a ramp rate of 50C/min. the data for this coke and the corresponding data for the petroleum coke K are given in Tables 5 and 6. The thermogravimetric analyser measured the weight change with temperature and the density of the samples was obtained by helium pycnometry. The data in these tables represented samples of the two cokes and provide an indication of repeatability. Tables 5,6 show the change in density of petroleum cokes K and RG. Before Treatment
Sample K7 K8 K9 K10 K11
After Treatment
Wt, g
, g/cm3
Wt, g
, g/cm3
wt%
0.377
1.447
0.344
1.873
8.775
0.326
1.455
0.297
1.897
8.812
0.402
1.452
0.370
1.858
8.085
0.398
1.447
0.366
1.862
8.073
0.294
1.461
0.270
1.873
8.325
Table 5 Green Petroleum Coke (K1) before and after heat treatment
In comparison of petroleum coke after heat treatment with good quality of blast furnace coke from Tables 5 & 6 and Figures 1, 2 & 3 show that the density is increased consequently as voidage is decreasing. Before Treatment
Sample RG1 RG2 RG3 RG4 RG5
After Treatment
Wt, g
, g/cm3
Wt, g
, g/cm3
wt%
0.316
1.492
0.293
1.873
7.378
0.348
1.463
0.322
1.860
7.533
0.399
1.448
0.370
1.871
7.336
0.334
1.482
0.310
1.868
7.269
0.362
1.452
0.335
1.847
7.386
Table 6 Green petroleum coke (RG) before and after heat treatment
Table 7 shows Image J data analysis for K1 specimen before and after heat treatment. Table 7 K1 petroleum coke Before heat treatment After heat treatment Blast Furnace Coke BFC
Total Area, mm2 15.5 8.1 12.1
Voids Area Fraction % 21.6 11.5 13.0
Figure 1a shows the scanned specimen of petroleum coke by X ray CT. X ray scanning parameters for a good quality image were determined by adjusting the energy of X rays, intensity of the beam and primary and secondary filters. Figure 1b shows the threshold of the image using software to analyze the data, the threshold being applied to characterize the components according to density and then converts the representative grey scale of a component into value. 1c is the analysis of image which is the extraction of void areas in pixels.
a
b
c
Figure 1. XRCT Image of Petroleum coke k1 before heat treatment
a
b
Figure 2 XRCT Image of petroleum coke K1 after heat treatment
c
a
b
c
Figure 3 XRCT Image of a good quality of blast furnace coke BFC 4. Conclusions Heat treatment of the petroleum coke samples results in a relatively small weight loss of approximately 4-8% depending on the maximum temperature. The heating rate appears to have little effect on the final weight loss. The void area fraction of pet coke K, from XRCT, appears to decrease to a similar value to that seen in the standard blast furnace coke BFC. The weight loss for Green petroleum coke RG appears to be higher, in all cases, than for pet coke K. the increase in density (from approximately 1.5 g/cm3 to 1.9 g/cm3), as a result of that heat treatment, also appears to be similar regardless of heating rate or maximum temperature. Understanding the microstructure of petroleum coke is vital in order to assess the feasibility of heat treating petroleum coke lumps. Acknowledgements This project is funded by the IDB bank for developing countries, under the Development Solutions Program and the University of Nottingham and also special thanks to Mr Michael for X-ray CT. References [1] Ellis, P.J., and Paul, C.A., ‘Petroleum Coke Calcining and Uses,’ Proc. 3rd Int.Conf. on Refining Processes, Delayed Coking, Atlanta, Ga , (2000) [2] Adam H. A. In: Marsh H., Heintz E., Rodiriguez-Reinoso F., editors.’ Introduction to carbon Technology’. Alicante 1997. Ch. 10. [3] Ketchum, R.A, Carlson, W.D,’Acquisition, Optimisation and Interpretation of X-Ray Computed Tomographic Imeagery: Applications to the Geoscience’ Computers and Geosciences 27,2001,pg 381-400 [4] ImageJ, http://rsb.info.nih.gov/ij/ software download and manual, accessed 30/10/2008
Oviedo ICCS&T 2011. Extended Abstract
A study of the feasibility of an anthracene oil-based pitch for isotropic carbon fibres preparation N. Díez, P. Álvarez, R. Santamaría, C. Blanco, R. Menéndez and M. Granda. Instituto Nacional del Carbón, CSIC. P.O. Box 73, 33080-Oviedo, Spain
[email protected] Abstract A new environmentaly friendly pitch, obtained from anthracene oil, is used for the preparation of isotropic carbon fibres. The pitch exhibits an adequate thermal behaviour and is free of solid particles. Green carbon fibres were obtained by means of a meltspinning process with no filtering step, and subsequent stabilization and carbonization. For the optimization of the melt-spinning process, the influence of the spinning temperature, extrusion pressure, spinneret hole size, winding speed and the interrelationship of these factors upon the microstructure and diameters of the fibres was studied.
1. Introduction Isotropic pitch-based carbon fibres are usually produced by melt-spinning [1]. One of the most important factors to be taken into account in their preparation is the specific characteristics of the precursors, in particular their softening point, carbon yield or the presence of solid particles -including mesophase spheres- [2,3]. The use of commercial pitches (coal-tar pitches and petroleum pitches) as carbon fibres precursors usually requires certain pre-treatments in order to adjust some of their characteristics [4]. This is because these pitches are mainly produced for use as binder and impregnating agents in aluminium and graphite industries. Industrial anthracene oil, obtained as a distillation fraction from coal tar, can be employed as raw material for the preparation of pitches on an industrial scale, since it is readily available (it represents ~ 30 wt. % of coal tar) and chemically consistent (polycyclic aromatic hydrocarbons of 3-5 rings [5]). This raw material is considered nowadays a good alternative for producing pitches, with a controllable softening point, a high carbon yield and no solid particles [6]. Among the unique characteristics of these pitches is their low environmental impact, derived from the low content in polycyclic aromatic hydrocarbons (PAH) catalogued as carcinogenic [7]. Furthermore, the preparation process (oxidative thermal condensation followed by thermal treatment) is
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Oviedo ICCS&T 2011. Extended Abstract
very versatile as it enables parameters such as the softening point of the pitch, to be easily controlled during the final steps of the preparation procedure [8]. In this paper we report on the feasibility of using novel anthracene oil-based pitches for the preparation of isotropic carbon fibres at laboratory scale. The main goals of the study are: (i) To characterize the anthracene oil-based pitch in order to determine the parameters that are relevant to its subsequent transformation into a carbon fibre (e.g., composition and pyrolysis behaviour) and (ii) to determine and optimize the main variables (spinning temperature, extrusion pressure, spinneret hole size and winding speed) that most affect the melt-spinning process. After stabilization and carbonization, the mechanical properties of the fibres (i.e., tensile strength) are determined.
2. Experimental section The carbon fibres precursor used in this work was an isotropic anthracene oil-based pitch (AOP) supplied by Industrial Química del Nalón, S.A. This pitch was obtained from anthracene oil [6] by a recently reported procedure consisting of oxidative thermal condensation and subsequent thermal treatment / distillation. This second processing step was adjusted until the desired softening point was reached (~ 250 °C). AOP pitch was characterized in terms of elemental composition, solubility tests, softening point and Fourier-transformed infrared spectroscopy. The thermal stability of the pitch was studied by means of a standard industrial test. The pitch was heated up to 45 ºC above its softening point for 20 h in an airtight device. The softening point of the product was then measured and compared with that of the parent pitch. AOP was melt-spun into fibers in a stainless steel reactor, equipped with stainless steal spinnerets of diameter 300 μm and 500 μm. The spinning temperatures chosen ranged btween 260 °C and 285 °C. Once the spinning temperature was optimized, different nitrogen extrusion pressures (from 1 bar to 5 bar) and winding speeds (from 50 cm s-1 to 250 cm s-1) were used to obtain fibres of different diameters. The green fibres were stabilized in an oven under an air flow of 20 L h-1, using the following multi-step program: heating at 1 °C min-1 from room temperature to 150 °C, maintaining this temperature for 4 h, and then heating at 1 °C min-1 to 160 °C, 180 °C, 200 °C, 220 °C, 250 °C and 270 °C, with 1 h of residence time at each of these temperatures. The stabilized fibres were then carbonized in a horizontal furnace, under a
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Oviedo ICCS&T 2011. Extended Abstract
nitrogen atmosphere, at 2 °C min−1 to 900 °C and 30 min of soaking time at this temperature. The texture and the diameter of the green, stabilized and carbonized fibres were studied by scanning electron microscopy (SEM). The tensile strength of the fibres was measured according to the ASTM D3379-75 Standard for single-filament materials.
3. Results and Discussion The anthracene oil-based pitch used comprises a series of characteristics that makes it highly suitable as a precursor for the preparation of carbon fibres (Table 1). The pitch is totally ash free. Therefore, its toluene and N-methyl-2-pyrrolidinone insolubles contents (TI and NMPI, respectively) are due exclusively to the presence of molecules with a high condensation degree, which makes them insoluble in these solvents. Table 1. Characteristics of the anthracene oil-based pitch.
AOP
Elemental Analysis (wt.%) C H N O S
IAr1
Ash 2
TI3
NMPI4
SP5
93.3
0.68
0.0
58
23
247
4.1
1.4
0.8
0.4
1
Aromaticity index determined by FTIR. Ash content ( wt. %). 3 Toluene insolubles content ( wt. %). 4 N-methyl-2-pyrrolidinone insolubles content ( wt. %). 5 Mettler softening point (ºC) 2
AOP is mainly composed of carbon (> 93 %) and, to a lesser extent, hydrogen, nitrogen and oxygen. The hydrogen is mainly aromatic, as indicated by its high aromaticity index. The low oxygen content (0.8 wt. %) proves that the oxygen groups introduced during the oxidative thermal condensation step were successfully removed during the subsequent thermal treatment. Another important feature is the low sulphur content of this pitch (less than 0.4 wt. %). Thermogravimetric analysis shows that below ~ 350 °C, weight loss is negligible (< 3 wt.%) as could be expected from a pitch with low volatiles content. Weight loss which mainly occurs between ~ 350 ºC and ~ 600 ºC yields a carbonaceous residue at 1000 ºC of 62 wt. %. These results indicate that the pitch could be heated above its softening point (required step for melt-spinning the pitch) up to ~ 350 °C without undergoing any significant loss of volatiles. In addition, the high carbon residue obtained is indicative of the high carbon yield of this pitch at high temperature.
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Oviedo ICCS&T 2011. Extended Abstract
The thermal stability of the precursor was studied according to the industrial procedure described in the experimental section. After 20 h at 292 °C, the softening point of the pitch increased by only 0.5 ºC. Furthermore, the thermogravimetric curve of the pitch after the test almost exhibited the same pattern than that of AOP, indicating that the pyrolysis behaviour of the pitch had not undergone any significant changes during the experiment. From these results it can be inferred that AOP would be especially suitable for use as a carbon fibre precursor. Having established that anthracene oil-based pitches do not require any pre-treatment prior to melt-spinning, we next evaluate the feasibility of this pitch for melt-spinning. For this purpose, a laboratory-scale apparatus that uses nitrogen pressure to extrude the pitch through a mono-hole spinneret was employed. Among the parameters involved in the pitch melt-spinning process, spinning temperature, extrusion pressure, winding speed and spinneret hole size are the most important, requiring optimization and analysis in detail [9,10]. Spinning was carried out at different temperatures using a 300 µm monohole spinneret, a nitrogen extrusion pressure of 5 bar and a winding speed of 250 cm s-1. The extrusion of the pitch only occurs at temperatures above 260 ºC, but spinning temperatures higher than 265 ºC are necessary to achieve a continuous flow of pitch through the spinneret. Examination of the green fibres by SEM (Figure 1) revealed that only spinning temperatures higher than 280 ºC (~30 ºC above their softening point) lead to green fibres with smooth and defect-free surfaces (Figure 1a). Below this temperature (Figure 1b, position A) the presence of defects on the surface of the fibres was detected. a
b
20 µm
Figure 1. SEM images of green fibres spun at (a) 275 and (b) 280 ºC. In order to study the effect of the extrusion pressure and winding speed on the diameter of the green fibres, several experiments were carried out using different nitrogen pressures (3 to 5 bar) and winding speeds (50 to 250 cm s-1), while the spinning temperature (280 ºC) and spinneret hole size (300 µm) were kept constant (Figure 2).
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Oviedo ICCS&T 2011. Extended Abstract
100
Diameter (µm)
80 60
5 bar 4 bar 3 bar
40 20 0 0
50
100
150
200
250
-1
Winding speed (cm s )
Figure 2. Variation of green fibres diameter with winding speed and nitrogen pressure. The results show that only nitrogen pressures between 3 and 5 bar allow a continuous flow of pitch resulting in correctly spun fibres. Thus, whereas nitrogen pressures lower than 3 bar fail to produce extrusion of the pitch, pressures higher than 5 bar do not allow the pitch to be stretched and wound correctly. Variation in the diameter of the green fibres with the winding speed confirms that the fibre diameter decreases with the increase in winding speed, possibly because the filament is more easily stretched. It was also observed that an increase in the extrusion pressure does not exert any significant influence on the average diameter of the extruded fibres. The thinnest fibres (average diameter of ~25 µm) were obtained at a nitrogen pressure of 3 bar and a winding speed of 250 cm s-1. The average diameter of the fibres obtained with the 500 µm spinneret (under a nitrogen pressure of 3 bar and a winding speed of 250 cm s-1) is slightly higher than that achieved with the 300 µm spinneret. Thus, at 3 bar and 250 cm s-1 the pitch that is spun through the 500 µm spinneret shows an average diameter of ~30 μm, ~10 μm larger than that spun with the 300 µm spinneret diameter. However, when a spinneret of a larger size was used, green fibres with diameters as low as ~ 20 μm were obtained because it was possible to apply lower extrusion pressures (up to 1 bar). Once spun, the green carbon fibres must be stabilized prior to carbonization in order to render the fibre infusible. The green fibres obtained at a spinning temperature of 280 °C,
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Oviedo ICCS&T 2011. Extended Abstract
a nitrogen pressure of 1 bar and a spinneret hole size of 500 μm (conditions that led to the green fibres with the smallest diameters) were stabilized, using the temperature/time program given in the experimental section, and then carbonized at 900 °C for 30 min. SEM observations showed that neither stabilization nor carbonization produced any defect on the surface of the fibres. Moreover, the microstructure of the carbon fibre remains completely isotropic whereas the morphology of the fibres, especially their diameter, undergoes substantial changes. Thus, stabilization causes a slight increase in the diameter of the fibres, which may be related to the uptake of oxygen during the process. Subsequent carbonization produces shrinkage that results in a decrease in the diameter of the fibre. This shrinkage leads to carbon fibres that have an even smaller diameter than that of the green fibre (~ 15 μm). The mechanical properties of the carbon fibres were evaluated in terms of their tensile strength (Figure 3).
Tensile strength (MPa)
1200 1000 800 600 400 200 0 10
20
30
40
50
60
Diameter (µm)
Figure 3. Variation of the tensile strength with carbon fibre diameter. As expected, tensile strength increases exponentially as the carbon fibre diameter decreases, from ~ 200 to > 1100 MPa (for carbon fibres with an average diameter of ~ 40 μm and 15 μm, respectively). These values are comparable to those reported in the literature for isotropic carbon fibres, even for other prepared from petroleum derivatives [11,12] which confirms the suitability of the pitch for high quality isotropic fibres preparation.
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Oviedo ICCS&T 2011. Extended Abstract
4. Conclusions A novel anthracene oil-based pitch of high softening point was successfully transformed into isotropic carbon fibres by melt-spinning. Analysis of the mechanical strength of the carbon fibres demonstrated that the isotropic precursor (anthracene oil-based pitch) and the procedure used in this study leads to carbon fibres with a tensile strength comparable to that of typical pitch-based isotropic carbon fibres produced from standard pitches. This demonstrates that the production of carbon fibres from this novel precursor represents an alternative to the ones available nowadays in the market.
Acknowledgement. The research leading to these results has received funding for the European Union’s Research Fund for Coal and Steel research programme under Grant Agreement number RFCR-CT-2009-00004. Dr. Alvarez also gratefully acknowledged Spanish Ministry of Science and Education by her Ramon y Cajal contract.
References [1] Derbyshire F, Andrews R, Jacques D, Jagtoyen M, Kimber G, Rantell T. Synthesis of isotropic carbon fibers and activated carbon fibers from pitch precursors. Fuel 2001;80:345-56. [2] Zeng SM, Maedaa T, Tokumitsua K, Mondoria J, Mochida I. Preparation of isotropic pitch precursors for general purpose carbon fibers (GPCF) by air blowing—II. Air blowing of coal tar, hydrogenated coal tar, and petroleum pitches. Carbon 1993;31:41319. [3] Mora E, Blanco C, Prada V, Santamaría R, Granda M, Menéndez R. A study of pitch-based precursors for general purpose carbon fibres. Carbon 2002;40:2719-25. [4] Alcañiz J, Cazorla D, Linares Solano A, Oya A, Sakamoto A, Hoshi K. Preparation of General Purpose Carbon Fibres from coal tar pitches with low softening point. Carbon 1997;35: 1079-87. [5] Fernandez JJ, Alonso M. Anthracene oil-based pitches. Light Metals 2004;449-50. [6] Álvarez P, Granda M, Sutil J, Santamaría R, Blanco C, Menéndez R, Fernández J J, Viña JA. Preparation of Low Toxicity Pitches by Thermal Oxidative Condensation of Anthracene Oil. Environ. Sci. Technol. 2009;43:8126–32.
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Oviedo ICCS&T 2011. Extended Abstract
[7] USEPA, Provisional Guidance for Quantitative Risk Assessment of PAH, EPA/600/R-93/089, United Status Environmental Protection Agency (1993). [8] Álvarez P, Granda M, Sutil J, Menéndez R, Fernández JJ, Viña JA, Morgan TJ, Millán M, Herod AA, Kandiyoti R. Characterization and Pyrolysis Behavior of Novel Anthracene Oil Derivatives. Energy & Fuels 2008;22: 4077–86. [9] Eddie DD, Dunham MG. Melt spinning pitch-based carbon fibres. Carbon 1989;27: 647-55. [10] Kase S, in: A.Ziabicki and Kawai H (Eds.), High-Speed Fibre Spinning, Wiley Interscience, New York, 1985, pp. 67-113. [11] Yang KS, Lee DJ, Ryu SK, Korai Y, Kim YJ, Mochida I. Isotropic carbon and graphite fibres from chemistry modified coal-tar pitch. Korean J. Chem. Eng. 1999;16: 518-24. [12] Wazir AH, Kakakhel L. Prepartion and characterization of pitch-based carbon fibres. New Carbon Materials 2009;24: 83-88.
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Oviedo ICCS&T 2011. Extended Abstract
Advanced characterisation of liquid hydrocarbons from South African high volatile bituminous coal M.H. Makgato1, H.W.J.P Neomagus1, R.C Everson1, J.H.L. Jordaan1, H.H. Schobert2 1
Chemical Resource Beneficiation (CRB), School of Chemical and Minerals Engineering, North-West University, Private Bag X05, Potchefstroom 2531, South Africa 2 The EMS Energy Institute, Penn State University, University Park, PA 16802 USA Abstract Detailed characterisation of liquid products from the first step of a two stage non catalytic direct liquefaction of a South African vitrinite-rich bituminous coal is reported. Elucidation of the composition, structural properties and molecular mass distribution of coal-derived liquids was carried out by GC/MS, NMR spectroscopy and Maldi-MS. Methylated-decane and cosane derivatives are the most predominant aliphatic hydrocarbons whereas alkylated derivatives of naphthalene, phenanthrene, pyrine, anthracene and pyrilene are the backbone aromatic structures. Of the five hydrocarbon classes identified, major changes were observed on the distribution of aliphatics and aromatics whereas the more polar compounds remain unchanged on solvent extraction.
Corresponding Author: +27 (0) 18 299 1991; E-mail address:
[email protected] 1. Introduction When coal is subjected to catalytic hydrogenation in direct liquefaction, it yields valuable organic products that could be used as feedstock for the preparation of petrochemicals, stable jet fuels and automotive fuels [1; 2]. To make coal a valuable feedstock for fuel engine and useful chemical addition of hydrogen or carbon removal is required [3, 4] to increased the H/C ratio from 0.8 in bituminous coals to 1.3-2.0 in petroleum crude oil, gasoline and diesel [5] preferably by direct coal liquefaction [6].
Previous studies [7, 8] on coal extraction of South African coals were mainly aimed at elucidating the structural properties of coal relative to its extracts or studying the swelling behavior of the coals without detailed characterization of the extracts. The data presented in this paper is results from the technical experiments on elucidation of the
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Oviedo ICCS&T 2011. Extended Abstract
chemical and structural compositions of the coal liquid derived extraction of coal with residue oil.
2. Experimental section 2.1 Material studied Proximate compositions of the vitrinite-rich Waterberg coal of interest were: 2.4% moisture, 37.1% volatile matter, 52.0% fixed carbon and 10.5% ash on dry basis whereas the ultimate analysis were 74.4% C, 5.3% hydrogen and 7.3% oxygen whereas nitrogen and total sulfur compositions were 1.5% and 0.99% on dry ash free basis. The tar distillate oil from gasification plants in Sasol Secunda, South Africa used as solvent showed the chemical class type analysis as 11% paraffins, 89% aromatic and less 0.1% cycloparaffins with the boiling range between 110-451°C at 0.5-95% weight loss.
2.2. Methods and techniques 2.2.1. Procedure for coal extraction Batch extraction experiments were carried out in a 2500 ml stirred autoclave at a temperature of 370°C, 7 bar final pressure, 2 hours resident time and solvent and coal ratio of 5:1 and 10:1 under initial N2 pressure and a constant 400 rpm stirring. After separation of residue coal from the coal extract, the degree of coal conversion was determined by weight loss between the feed coal and the residue coal on dry ash free basis using equation (1) and (2).
% Total conversion (daf) = 100 × %x Extraction (db) = 100 ×
1−Residue weight (g)/Coal weight (g) 1−Ash (wt %, db )/100
Coal weight (g) ∙ % x C −Residue weight (g)∙ % 𝑥𝑥 𝑅𝑅𝑅𝑅 Coal weight (g) ∙ % x C
(1)
(2)
2.2.2. Advanced characterization of products All solid materials, including the raw coal were analysed for proximate and ultimate compositions according to the South African Bureau of Standards (SABS) and ISO standards for coals and cokes analysis. In addition, spectroscopic techniques such as XRD, laser desorption mass spectroscopy and solid state NMR were used to examine the structural composition. The liquid products after fractionation into solubility class
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Oviedo ICCS&T 2011. Extended Abstract
distribution were characterized by GC-MS and liquid NMR spectroscopy.
3. Results and Discussion 3.1. Coal conversion The total coal conversion at constant 7 bar final pressure, 2 hours reaction time and 10/1 solvent to coal ratio increased from 45% at 350°C to 63 % at 360°C. Compared to other studies [9, 10, 11] that gave higher yield at either high solvent/coal ratios or catalytic hydrogen pressure, the yield reported here is from solvent extraction with low solvent composition and no catalyst of hydrogen pressure.
3.2. Advanced characterisation 3.2.2.1. Solubility fractionation Fractionation of residue oil and coal liquids extract with pentane, toluene and THF gave 80% pentane soluble fraction and no toluene insoluble fraction for residue oil while the coal liquid contains 50% of pentane soluble and 39% of toluene soluble while the toluene insoluble fraction was composed of 10% tetrahydrofuran soluble and only 4% insoluble residue.
2.2.2.2. Gas chromatography/Mass spectroscopy (GC-MS) Of the twenty most abundant aromatic compounds identified by GC-MS, pure compounds such as naphthalene, dibenzofuran and phenanthrene-derivatives are the most predominant, while cosine and decane-derivatives are the most predominant saturated hydrocarbons in both the residue oil and coal extract. Low molecular mass compound predominated phenols, benzene derivatives and high molecular mass region dominated C20 to C27 saturated hydrocarbons. A decrease in molecular mass from 522 m/z in the residue oil to 474 m/z in the extract were observed.
2.2.2.3. Nuclear magnetic resonance (NMR) Figure 3 shows summarises the structural parameters from 13C NMR spectra of residue oil and coal extract.
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Oviedo ICCS&T 2011. Extended Abstract
0.9 0.8
Relative distribution
0.7 0.6 0.5 0.4
RO
0.3
CEXT
0.2 0.1 0 fa*
fal
faP
faS
faH
faB
falH
Structural parameter
Figure 3. Distribution of structural chemical compositions of coal on solvent extraction
The coal liquid shows increased aromatic content (fa*), phenolic content (faP), alkyl substitution (faS). As with GC-MS, an increased fraction of alkyl-substituted aromatics in CEXT together with lower aliphatic fraction (fal) ring joining CH2 and CH due to depolymerisation was observed. Occurrence of depolymerisation and aromatisation was accounted in this case by the dissolution of more aromatic compounds from coal by residue oil while the substitution reactions occur between radicals from coal and residue oil as a result on breakage of CH2 and CH linkages. Khan, et al. [12] showed a decrease in the contribution of hydroaromatics and polyaromatics as well as an increase in substitution on extraction of Pakistani coal with benzene at 400°C using NMR as a characterisation tool.
2.2.2.4. Matrix-laser desorption ionisation mass spectroscopy (Maldi-MS) The Maldi-MS reflectron spectra analysis of residue oil and its coal extract showed that both samples contain a low mass envelope below 340 m/z and three maxima at 260, 370-400 and 550 m/z with the residue oil giving large abundance of low molecular weight compounds at 260 m/z than the extract.
4. Conclusions Advanced characterisation techniques such as NMR, GC-MS and Maldi-MS techniques were used to elucidate composition, structural properties and molecular mass distribution on coal extraction with residue oil. GC-MS analysis showed naphthalene, phenanthrene, pyrine, anthracene and pyrilene as backbone structures for alkyl-
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Oviedo ICCS&T 2011. Extended Abstract
aromatics and polycyclic hydrocarbons (PAH), with methyl-naphthalene been the most dominant aromatic hydrocarbon with up to 3 methyl substitutions. The study has established that although depolymerisation occurs on solvent extraction the composition of aromatic compounds also increases, which accompanied by a decrease in the molecular mass from 522 m/z in residue oil to 474 in coal extract. It was also found that long chain aliphatic hydrocarbon rather than aromatic compounds form major composition of the high molecular mass species, whereas phenols are the most abundant low molecular mass compounds.
Acknowledgement The authors wish to acknowledge financial support for this research from the South African National Research Institute (SANERI). Exxaro R&D and Sasol R&D for supplying the coal samples and residue oil provided respectively.
References [1] Schmid, B.K. Jackson, D.M. 1981. The SRC-II process. Phil. Trans. R. Soc. Lond. A, 300: 129-139. [2] Burgess, C.E., Schobert, H.H. 2000. Direct liquefaction for production of high yields of feedstock for specialty chemicals or thermally stable jet fuels. Fuel Process. Technol. 64: 57-72. [3] Whitehurst, D.D., Mitchell, T.O., Farcasiu, M. 1980. Coal Liquefaction: The chemistry and technology of thermal processes, Academic Press, London. P. 206-270. [4] Gorin, E.G. 1981. “Fudamentals of coal liquefaction” Chapter 27 of Chemistry of coal utilization, 2nd supplementary volume. Ed. Elliott, M., John Wiley & Sons. [5] Williams, R.H. & Larson, E.D. 2003. A comparison of direct and indirect liquefaction technologies for making fluid fuels from coal. Energy for Sustainable Development, 7: 103-129. [6] Huang, H., Wang, K., Wang, S., Klein, M. T., Calkins, W. H. 1996. Kinetics of Coal Liquefaction at Very Short Reaction Times. Energy Fuels, 10: 641-648. [7] Larsen, J.W., Green,T.K. Kovac, J. 1985. The nature of the macromolecular network structure of bituminous coals. J. Org. Chem. 50: 4729-4735. [8] Iino, M. 2000. Network structure of coals and association behaviour of coal-derived materials. Fuel 62: 89-101.
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[9] Okuyama, N., Komatsu, N., Shigehisa, T., Kaneko, T., Tsuhuya, T. 2004. Hypercoal process to produce the ash-free coal. Fuel Process. Technol., 85: 947-967. [10] Miura, K., Nakagawa, H., Ashida, R & Ihara, T. 2004. Production of clean fuels by solvent skimming of coal at around 350°C. Fuel, 83: 733-738. [11] Burgess Clifford, C., Schobert, H.H., Escallón, M. & Griffith, J. 2007. Effects of coal rank and reaction conditions on production of two-ring compounds for coal-based jet fuel. (Paper presented at International Conference on Coal Science and Technology held in August 2007.) Nottingham, UK. [12] Khan, M.A. Ahmad, I. Ishaq, M., Shakirullah, M. (2003) Spectral characterisation of liquefied products of Pakistani coal. Fuel Process. Technol. 85, 63-74.
6
A thermo-petrographic method to identify coals prone to self-oxidation Claudio Avila and Edward Lester Department of Chemical and Environmental Engineering, University of Nottingham. University Park, Nottingham (NG7 2JT). United Kingdom.
[email protected] Abstract The self oxidation of coal at low temperature is a significant problem for the coal industry. It is important not only because the economical losses associated to the reduction of the calorific value and the emission of noxious gases to the atmosphere; it is also relevant because it can lead to a bigger problem: the spontaneous combustion of a coal stockpile and a major fire. Although there have been created a number of methods to forecast this unwanted reaction, these are not reliable enough for many in the coal industry. Most of these tests are based on the measurement of heat release and oxygen consumption rate, with a significant variability in the results, depending of the testing procedure. This paper presents an alternative test based on the visual quantification of thermal alteration by means of combined petrographic and image analysis techniques. The experimental test heats up small coal samples at a low ramp rate (0.5oC min-1) under an oxidative atmosphere, starting from room temperature up to 250oC. Then, changes in the optical properties of fresh and oxidized material such as light reflectance, morphology and textural attributes are assessed by oil immersion microscopy and image analysis processing. Results showed a notable difference between the reflectance histograms of fresh and oxidized samples that relate directly to the reactivity of samples and to the coals susceptibility to spontaneous combustion. Also some physical alterations were detected and quantified such as oxidation rims, micro fractures, and changes in porosity that are key features with prone samples. Finally, a standardized procedure is proposed for propensity assessment.
1. Introduction The natural oxidation of coal is a phenomenon that begins immediately when coal come into contact with an oxidative atmosphere. This oxidation process is a set of several chemical reactions (in series and in parallel), with an overall net energy output. Under specific conditions, a thermal runaway can take place when the heat released during oxidation exceeds the dissipation rate of the material into the environment [1,2]. It is a slow process that takes days or months, and it is a particular problem when the material is stored at large
scale. The causes of spontaneous combustion are well known [3,4,5,6], and several methods have been developed, using these mechanisms, to predict the spontaneous combustion potential. However, the self-oxidation reaction is a complex series of reactions and accurate prediction is still difficult. Despite the advances in the understanding of the problem, the different experimental tests can deliver contradictory results [7,8]. Among the methods developed to predict this reaction, thermal methods are the most commons. In this case, these are based in the measurement of changes in the temperature of the sample, the heat released, and the change in the gas concentration produced by the emission of gaseous products and due to the oxygen adsorption [9,10,11]. However, these tests do not consider some relevant coal properties such as the weight evolution, the maceral composition and the optical properties of coals (random reflectance). This is relevant because these properties are frequently used by the coal industry to assess the coal reactivity, representing an opportunity to use a well known source of information available to predict this unwanted phenomenon. The use of petrographic information obtained from samples before, during, and after a thermal ‘event’ could result in a relevant contribution to improve the current tests, or to lead to a new generation of testing procedures. This paper presents the experimental results obtained from several coals, including well known spontaneous combustion coals, which have been exposed to different non isothermal programs in a thermal reactor. The paper evaluates changes in reactivity, based on the different morphotypes generated after the heating process, and the change in reflectance of the sample as a whole.
2. Materials and methods For this study, 25 coal samples from different parts of the world have been used, including at least 3 well-known spontaneous combustion coals. All experiments used fresh sample that were pulverized and then sieved into the size range 53-106µm. Each sample was characterized petrographically (random reflectance, morphologic characterization and maceral content), before and after thermal treatment. Finally, the optical characteristics are compared for the raw and treated material, which are also linked to the thermal response observed during the thermal treatment.
2.1 Coal thermal treatment A reactor has been designed to study the thermo-chemical behaviour of the samples under a controlled slow heating environment. In this reactor, the weight loss of the sample was measured simultaneously along with the temperature at different positions (diagram shown in Figure 1). The experimental procedure is described as follows: 100g of sample is placed into the sample holder and connected to the digital balance. Thermocouples are connected to the main PC unit which recorded all measured variables including weight and temperatures at each location. A gas flow of 80 ml/min through the centre of the reactor was set up to flow into the gas analyzers. After that, a heating ramp of 0.5oC min-1 starts to heat the furnace from room temperature to 250oC. When temperature reaches 250oC, all recorded signals are stopped, the sample holder is removed from the furnace, and the remaining material is prepare for petrographic analysis. 2.2 Sample analysis An automated light microscopy system consisting of a Zeiss Leitz Ortholux II POL-BK microscope, with oil-immersion objectives in the range of 10 to 32X magnification attached to colour digital camera Zeiss AxioCam is used for petrographic analysis. For these, polished blocks were prepared using carnauba paraffin wax to embed coal particles. After that, petrographic blocks were polished following the ASTM standard, at a final resolution of 0.04 µm. Finally, random reflectance measurements and maceral analysis were performed on all samples following the ISO for petrographic analysis of bituminous coals. Mosaic images were also obtained for all coal samples in order to identify and quantify the different morphotypes generated after the heating.
Figure 1: Diagram of experimental reactor designed to determinate experimentally the crossing point temperature values (CPT), to observe the transient thermal profiles of coals in a bulk sample, and to obtain the material needed for petrographic analysis.
3. Results 3.1 Thermal profiles Characteristic thermal profiles were recorded using the experimental reactor. In Figure 2, shows the data for two well known coals that are prone to spontaneous combustion. In this case, the high water content present in both samples (~15%) produced an inflection in the temperature profiles around 100oC. As can be seen by comparison with the Figure 3, in which are from a medium reactive coal (El Cerrejon, ~3.5% moisture content) and a low reactive coal (Pocahontas, ~0.6% moisture content), the effect of the water content in the thermal profiles is evident. The effect in the water content during the reaction also has been previously considered as a key self-heating mechanism [6]. From the experimental profiles, it is possible to observe that the temperature in the centre of the sample exceeds the temperature in the surroundings slightly (inside the sample), when the profile is close to 100oC. It is relevant because this suggests that heat production in the centre is not dissipated by the system fast enough to keep a flat profile, and this can be the beginning of a hotspot in a larger system.
Figure 2: North Dakota coal (left) and Fenosa coal (right). Both are extremely high reactive at low temperature.
Figure 3: El Cerrejon coal (left) and Pocahontas coal (right). The influence of the water content in the thermal profiles is clear.
Figure 4 shows a comparison of the Ignition temperature as predicted by various methods, including the classical crossing point temperature test [8] and the new crossing point temperature test, which is an improvement of the previous test introduced by Chen [10]. From this figure it is possible to see the discrepancies between the different approaches.
However, from previous historical evidence from these coals, the CPT value obtained using the Chen approach provide the closest indication of self heating potential.
Figure 4: Comparison of thermal parameters used to identify coals prone to spontaneous combustion. Among these, the most accepted is the CPT value obtained using the Chen correction [10], which delivers the minimum crossing temperature.
3.2 Reflectance comparison for fresh and oxidized coals As it can be seen from Table 1, the change in the reflectance value depends of the original sample reflectance. Low rank coals show larger changes than high rank coals. However, these variations are not directly related to the crossing point values recorded, and also they do not agree with previously reported tests of reactivity at low temperature [12]. Nevertheless, the change in the overall reflectance has a close relationship with the concentration of morphotypes presented in the sample (these are described in the next section) i.e. particles from highly reactive coals show a homogeneous change in reflectance whereas high rank or unreactive coals tend to show large amounts of “oxidation rims” and “high reflectance particles”. Clearly the reflectance change of the sample is linked to the kind of alteration formed, which is also related to the thermal profiles.
Table 1: Reflectance comparison for fresh and oxidized coals Coal
Reflectance Raw coal
Reflectance Treated coal
Change
North Dakota
0.41
0.59
0.18
% Change 45.0
Nadins
0.68
0.90
0.23
33.4
Fenosa
0.39
0.53
0.13
32.5
Hambach
0.32
0.42
0.10
31.9
Indo
0.62
0.78
0.16
25.6
Daw Mill
0.55
0.67
0.12
22.0
Kaltim Prima
0.54
0.65
0.11
20.4
Kleinkopje
0.76
0.89
0.13
17.8
La Loma
0.54
0.64
0.09
17.4
Asfordby
0.52
0.61
0.09
17.1
Zondag 1
0.61
0.71
0.10
15.5
Hunter Valley
0.77
0.89
0.11
14.3
Goedehoop
0.59
0.67
0.08
12.9
Cerrejon
0.57
0.63
0.06
11.2
Ironbridge
0.56
0.62
0.06
10.5
Lea Hall
0.60
0.66
0.06
10.3
Indiana EDF
0.68
0.75
0.07
10.1
Illinois 6
0.41
0.45
0.04
10.1
Littleton
0.65
0.71
0.06
10.0
Bentink
0.76
0.82
0.07
8.6
La Jagua
0.56
0.61
0.05
8.1
Yanowice
0.67
0.73
0.05
8.1
Pocahontas
1.33
1.36
0.03
2.4
Blue Creek
0.96
0.98
0.02
2.3
Deep Navigation
1.64
1.68
0.03
2.1
3.3 Morphologic characterization After heating, several characteristics in the coal particles were identified. The most common morphotypes are classified and described as follow: Homogeneous change of reflectance: This is the most common morphotype identified. These are produced when the oxidation reaction takes place over the whole particle, changing the reflectance uniformly. Whilst this kind of particle can be present in low rank and high porosity coal samples, there are significantly more with spontaneous combustion coals. Oxidation rims: This is the second most common morphotype identified. These are produced by a strong oxidation over the coal surface but not internally within the particle. In this case, these alterations are occur when the oxidation reaction is strongly controlled by oxygen diffusion. Cracks and micro fractures: These fractures were less significant or evident, and were produced by the shrinkage of particles induced by the temperature change and the volatile release. These particles were characterized by their perpendicular edges, which could also be perpendicular to a main fracture. High reflectance particles: These morphotypes are produced when the oxidation reaction take place over the whole particle changing the reflectance uniformly, but also inducing a plastic transformation, which increase the reflectance of the whole particle. These kinds of particles are mainly produced by high rank coals.
3.4 Spontaneous combustion assessment A standard assessment is proposed to predict the spontaneous combustion propensity of a coal sample, using automated image capture and manual post processing of images. Grey scale histograms from a specific fresh sample is compared with the oxidized material after the thermal treatment. The fresh histogram is subtracted from the oxidised histogram to highlight the material that has disappeared and the new material that has been generated during heating. Figure 5 shows an example of the results obtained for a highly reactive coal that is prone to self-heating. In this case, this sample is characterized for a high percentage of particles with a homogeneous change in reflectance. The histogram of the treated sample is similar to that of the fresh material profile, but with a higher reflectance peak position (Figure 5, graph i). Additionally, it also can be seen a slight change in the peak magnitude, which is produced by a percentage of particles with oxidations rims in the surface (Figure 5, graph i). Subtracting
the two profiles produces graph ii), to identify the position of the changes. The magnitude of this change is a clear indication of the scale of the change, which is a potential indicator of propensity.
i)
ii)
Figure 5: Histogram analysis of Fenosa coal, a well known coal prone to spontaneous combustion. In this case, the reflectance of the treated sample changes about 80% with regards to the original material.
4. Conclusions An experimental reactor has been designed and implemented in order to quantify thermochemical response of samples under a slow heating ramp rate, simulating a self-heating process. This instrument has enabled the measurement of the crossing point temperature values for a set of coals, as well as several temperatures inside the sample holder (at different positions), in order to estimate the reactivity at low temperature of the samples under study. At the same time, the reactor has been used to produce oxidized material in order to study the change of optical properties of coals as a result of the heating process. The change of reflectance has been studied using petrographic methods, and several different morphotypes have been identified, some of which appear to be characteristic of self-oxidized coals. Finally, the reflectance change measured between the fresh and the oxidized material has been linked with the thermal profiles during heating. This information has been also related to the
concentration of specific thermal alterations (morphotypes) present in each coal. Results indicate that an experimental procedure could potentially estimate the potential of coals to develop a thermal runaway using petrographic analysis and image analysis techniques.
5. References 1 Feng, K., Chakravo, R., and Cochrane, T. Spontaneous Combustion - Coal Mining Hazard. Canadian Institute of Mining Bulletin, 66 (1973), 75-84. 2 Parr, S. and Kressman, F. The spontaneous combustion of coal. The Journal of Industrial and Engineering Chemistry (1911), 152-158. 3 Bhattacharyya, K. The role of sorption of water vapour in the spontaneous heating of coal. Fuel , 50 (1971), 367-380. 4 Carpenter, D. and Sergeant, C. The initial stages of the oxidation of coal with molecular oxygen III-effect of particle size on rate of oxygen consumption. Fuel, 45 (1966), 311-327. 5 Gethner, J. The mechanism of the low temperature oxidation of coal by O2: observation and separation of simultaneous reactions using in situ FT-IR difference spectroscopy. Applied Spectroscopy, 41 (1987), 50-63. 6 Wang, H., Dlugogorski, B., and Kennedy, E. Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling. Progress in Energy and Combustion Science, 29 (2003), 487-513. 7 Gouws, M. and Wade, L. The self-heating liability of coal: Predictions based on composite indices. Mining Science and Technology, 9 (1989), 81-85. 8 Gouws, M. and Wade, L. The self-heating liability of coal: Predictions based on simple indices. Mining Science and Technology, 9 (1989), 75-80. 9 Jones, J. Recent developments and improvements in test methods for propensity towards spontaneous heating. Fire and Materials, 23 (1999), 239–243. 10 Chen, X. On basket heating methods for obtaining exothermic reactivity of solid materials: The extent and impact of the departure of the crossing-point temperature from the oven temperature. Trans IChemE, 77 (1999), 187-192. 11 Nugroho, Y., Mcintosh, A., and Gibbs, B. Using the crossing point method to assess the self-heating behaviour of Indonesian coals. Twenty-Seventh Symposium on Combustion, The Combustion Institute (1998), 2981-2989. 12 Avila, C. Study of spontaneous combustion of coals by means of Thernogravimetric analysis. (Berlin 2010), Proceedings of the Second International Conference on Coal Fire Research.
Monitoring Hot Spots in Bituminous Coal Stored at Atmospheric Conditions 1,2
,1
Haim Cohen , Uri Green , Franz Gildemeister 4b Shay Wasserman 12345-
1,3
5
4a
Lionel Metzger , Moshe Pesimberg
and
Department of Biological Chemistry, Ariel University Center at Samaria, Ariel, Israel Chemistry Department, Ben-Gurion University of the Negev, Beer Sheva, Israel TU Bergakademie Freiberg, Fakultät 4, Institut für Energieverfahrenstechnik und Chemieingenieurwesen 09599 Freiberg, Germany. a. Rutenberg Power Station, b. Orot Rabin Power Station, Israel Electric Environmental Protection & Licensing Unit, Israel Electric
Abstract Large coal piles (50-150,000 tons) undergo weathering processes during long term storage in open air. Exothermic chemisorption of atmospheric oxygen, formation of surface oxides and the decomposition of inherent coal structure result in release of organic and inorganic gases (e.g. Methane- CH4, Ethylene- C2H4, Ethane-C2H6 Carbon dioxide- CO2, Carbon monoxide- CO and Hydrogen - H2). Some of these reactions are exothermic and when the rate of heat dissipation in the pile is less than that of its formation, a significant increase in temperature can be registered at the locality. These localities are termed "hot spots" where in extreme cases can result in a fire. Monitoring of hot spots at the 2 main coal storage sites of bitumineous coal, Orot Rabin (Hadera) and Rutenberg (Ashkelon), of the Israel Electric Company have been conducted. A unique monitoring unit that can penetrate up to 8 meters into the coal pile and sample gases and measure the temperature was used. The study has shown that the hot spots are formed only in isolated spots and in extreme cases, open fires have been observed. The maximal temperature measured in the hot spots was 330C. Keywords: Coal Weathering, Self Heating, Coal Fires
Introduction In Israel, bituminous coal serves as the main fossil fuel for power generation (>60% electricity production in 2010) in utilities. At present the annual coal consumption is ~13 M tons of coal in these two power stations. As Israel has no coal available the coal is imported by large ships from South Africa (main source), Indonesia, Russia, Australia and Columbia. Furthermore, more than 1 M tons of coal serve as strategic supply in two storage facilities. Like any organic fossil fuel, large coal piles stored under open air undergo weathering processes during long term storage prior to combustion in utility plants. The weathering process is relatively fast and is dependent on the rank of the coal and storage conditions (wind direction, coal pile structure etc.). The geographical location of the mine also proves an important factor as the composition of the coal can differ from mine to mine and weathering is affected appreciably by the coal properties. Weathering processes involve physical adsorption and chemisorption of atmospheric oxygen subsequently forming surface oxides and hydroperoxides which can partially decompose to yield low molecular weight inorganic gases
like carbon oxides (CO, CO2), water, hydrogen (H2) and some organic gases (C1-5) . If the heat formation (due to exothermic processes) is greater than the heat dissipation, self heating of the pile might occur to form hot spots in the pile in which in extreme cases results in fire eruptions(3) as seen in Figure 1.
Figure 1: Photo of stockpiles in Ashkelon storage site affected by open fire and several hot spots
The major product that is released from coals undergoing low temperature aerial oxidation processes is carbon dioxide. This poster presents the monitoring results of temperatures and gases emitted from the storage piles in Ashkelon, in the Rutenberg Power Station of The Israel Electric Company
Experimental Monitoring and measurement of hot spots in Ashkelon Storage piles were conducted in order to obtain a deeper understanding about size and development of hot spots, as well as the determination of existing temperatures and generated gases. Temperature measurement. was conducted both with an Extech IR thermometer (model 42515) coupled with an 8 meter long thermocouple for depth measurements. In order to determine temperatures from within the coal piles, stainless steel pipes with a tailored membrane at the tip were pushed inside the pile and the thermocouple was inserted inside the pipe to measure the temperatures. In order to sample gases from the pile a vacuum pump connected by rubber tubing to a glass sampling cylinder was attached to the protruding stainless steel, the developed measuring unit for monitoring coal piles is presented in Fig 2.
Fig. 2: measuring system for monitoring stockpiles The work at the coal piles is usually divided into two steps. The first step is surface temperature measurements in order to get an overall picture of the apparent thermal status of the coal pile. Smoke releasing chimneys were clear indication of a forming hot spot. After plotting the apparent surface temperature of the pile penetration measurements were conducted in order to determine a more accurate temperature profile of the pile. At several localities the gas phase was sampled by the method described above and analyzed using the following methods. Gas Chromatography. The concentrations of the gases (CO2, CO,, N2, O2, hydrocarbons) in the reactors were determined using a gas chromatograph (Varian model 3800) equipped with a thermal conductivity detector & a flame ionization detector connected in series. The gases were separated on a carbosieve B 1/8”, 9’ ss column using a temperature programmed mode. The experimental error in the G.C. determination is ±5%. The gaseous atmosphere was sampled (1ml samples) after the reaction, with gas tight syringes and measured in the gas chromatograph.
Results A temperature profile of a coal pile in Ashkelon is shown in Fig 3. The temperature line of 55°C was added in order to dist inguish between cold areas and hot spots (T 55°C). A short summary of occurring temperatures i s presented in table 2-3 .
Fig. 3: Temperature profile of coal pile in Ashkelon (2.12.2010)
Distance from epicenter
Fig. 4: Temperature profile of coal pile in Ashkelon (23.1.2011)
Distance from epicenter
Table 1: Occurring temperatures from monitored hot spots
highest median median temp. temp. temp. date hot spot spread hot spot total [m] [°C] [°C] [°C] Ashkelon Dec/10 west 1 105 300 93 east 20 100 240 Jan/11 21,7 160 353 136 On both dates hot spots were detected and the gas content of these spots were sampled and analyzed. The results are presented in Tables 2,3 Table 2: Composition of the gas samples from two hot spots - Ashkelon (2.12.2011)
Sampling depth Temperature [m] [°C] hot spot 1 0.20 167 hot spot 2 0.20 135 1 n.d. = not detected name
CO [vol.-%] 8.97 1.27
CO2 [vol.-%] 12.47 9.75
H2 [vol.-%] 0.30 n.d.
Table 3: Composition of gas samples in Ashkelon taken with at increasing depth in the pile(23.1.2011)
depth temperature O2 CO CO2 H2 [m] [°C] [vol.-%] [vol.-%] [vol.-%] [vol.-%] 0 136 13.1 2.40 13.0 0.14 0.9 179 15.9 1.01 10.7 n.d. 1.5 140 9.6 1.11 12.7 0.03 3.5 136 4.3 1.39 15.8 n.d. 1 n.d. = not detected It is interesting to notice that the highest CO2 concentration of approximately 16 % is found at a depth of 3.5m at 136°C. It can b e assumed that diffusion of gases from the surface to deeper colder layers of the stockpile occurs because of temperature gradients or fluctuations in compaction. The higher concentration of remaining oxygen near the surface is reasonable because of the higher partial pressure of oxygen due to quick setting equilibrium between pile and surrounding air and wind. The highest CO amounts were measured at the pile surface. The Ashkelon stockpiles exhibited a large number of hot spots and several open fires. Such propensity to LTO has not been observed in the Hadera coal storage piles. As a climate comparison (table 4) shows no appreciable difference the reason for this propensity for the Ashkelon piles cannot be attributed to climatic factors. Table 4: Climatic characteristics in Ashkelon and Hadera
Precipitation Dec-Jan 2010/11 [cm/month] Average Temperature Dec-Jan 2010/11 [°C]
Ashkelon
Hadera
4.01
3.25
8 – 32
10 – 30
One of the most noted differences between the coal piles is their relative degree of compaction. The density of a less – compacted stockpile as found in Ashkelon is 850 whilst in Hadera the piles are compacted to within 950 to 1,250 .
[1]
This difference in compaction degrees is due to the different
storage operation equipments used: stacker-reclaimer in Ashkelon PS and bulldozers in Hadera PS. Thus, oxygen diffusion is appreciably slower in the Hadera coal pile is as compared to the Ashkelon storage site.
Conclusion It is clear that besides other existing parameters the different level compaction of the stockpiles has a significant high effect on coal stockpiles undergoing LTO. Furthermore, it is obvious from the above results that the behavior of the carbon oxide formation and equilibrium in the coal piles is extremely interesting and warrants further investigation.
Acknowledgment Financial support acknowledged
1
by
the
Israeli
Electric
Corporation
is
gratefully
. L. Grossman Ph.D. Thesis, “Low Temperature Atmospheric Oxidation of Coal”, Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel, (1994)
REDUCING THE ENVIRONMENTAL IMPACT OF SPONTANEOUS COAL COMBUSTION IN COAL WASTE GOBS X. Querol1, X. Zhuang2, Jing Li2, O. Font1, M. Izquierdo1, A. Alastuey1, B.L. van Drooge1, T. Moreno1, J. O. Grimalt1, F. Plana1 1
Institute of Environmental Assessment and Water Research, CSIC, C/ LLuis Solé Sabarís s/n, 08028 Barcelona, Spain, 2Institute of Sedimentary Basin and Mineral, Faculty of Earth Resources, China University of Geosciences, Hubei, 430074, People's Republic of China
[email protected] ABSTRACT The environmental characteristics of burning coal gangue dumps Shanxi Province, one of the major coal producing area in China and the world, were investigated in this study with the aims of obtaining relevant conclusions on: a) the major air and water quality impacts, as well as b) on remediation strategies. The mineralogy and composition of the original coal gangue, burned wastes and condensates from gaseous emissions, as well as their leaching properties are characterized in 4 different gobs with very diverse degree of reclamation. The results show that the combustion temperature could reach 1200oC in the burning core. Around this core a degasification aureole is formed with temperatures gradually being reduced down to around 100oC near the vents. During combustion in the burning core and degasification of the aureole, elements such as S, F, C, Cl, F, S, N, As, Cd, Hg, Pb, Sn, Ge and Se, and a number of organic pollutants are emitted into the atmosphere. Condensation processes account for the partial trapping of gaseous emissions of PaH, As, S, N, Hg, Pb and Se, among others. Thus, condensates of tar and mineralizations of elemental sulfur and a large variety of salts, including ammonium bearing species, enriched in Hg, Se, As and other trace elements are frequent in the gas vents. Leachates arising from the condensates reach strong acidity or mild alkalinity, depending on the condensate material, posing a serious threat to the environment. The findings show a condensation sequence model for coal gangue fires that may be generalized for most spontaneous combustion of waste gobs, and probably coal dumps and natural coal fires. It was found that covering the coal waste dumps with a layer of compacted soils of around 25 to 50 cm appears to be an excellent cost-effective method to reduce frequency and magnitude of spontaneous combustion. Furthermore, this cover is scavenging or trapping pollutants from gaseous emissions, and minimizing risks associated with the leaching of readily soluble salts condensed on the surface. KEY WORDS: Shanxi coal, China. Geochemistry, spontaneous combustion, leaching
INTRODUCTION The main coal-bearing units in the Datong and Yangquan mining districts belong to Shanxi and Taiyuan (Early Permian) and Datong (Middle Jurassic) formations. During Early Permian time this area was located in the northern part of the North China interior epicontinental sea basin[1]. This was the cause of the relatively high sulfur contents in the Permian coal from the districts[2]. The mining of these coals initially focused mainly on the relatively shallow-lying Jurassic deposits, but these have already been mined out in most mines. Current activity therefore focuses on the deeper and high-sulfur Permian carbonaceous deposits, which calls for special measures to prevent coal fires. Spontaneous combustion of coal may take place when the rate of heat generated by the oxidation of organic matter exceeds the rate of heat dissipation[3]. Most studies point to oxidation of organic matter as the main cause of coal self-ignition (seams or waste), but also other factors such as the heat from the oxidation of inorganic coal-bearing phases e.g. pyrite, could be a key factor in attaining the necessary heat for self-ignition[4]. Prior studies[4-7] have shown that the factors playing a major role in promoting coal oxidation are (a) increase in ambient air temperature, (b) thermal conductivity of coal; (c) grain size of coal and (d) the coal rank. Spontaneous combustion in coal waste dumps from Shanxi was common in the past, however currently most coal waste dumps had been compacted and covered with a layer of compacted soil to the point that it was not easy to find active vents. The land reclamation measures have drastically reduced the occurrence of spontaneous combustion, being thereafter restricted to sporadic and deep fires in the sliding faults developed at the front of coal-waste dumps covered with soil. The spontaneous combustion may take place in coal and coal waste dumps, coal mines, in coal outcrops, in ships transporting coal, and even in peat bogs. These fires constitute an important source of emissions of a large variety of volatile organic and inorganic atmospheric emission of pollutants, mainly CO2, and CO, NO, NO2, SO2, H2S, HF, NH3, HCl, n-alkanes, n-alkenes, sugars, alcohols, PAH, Hg, As, Pb and Se. After volatilization from coal gangue and owing to the sharp fall in temperature, these gaseous organic and inorganic species may condense or chemically interact with the overlying material giving rise to condensates enriched in the above pollutants. Thus, spontaneous coal combustion in coal waste gobs concentrates a number of toxic components in the surface of the gobs by mobilizing them by combustion (in the burning core) and de-gasification (in the thermally altered aureole) of coal and by subsequent condensation on the surface when temperature drops drastically. These pollutants are ready to be leached by rain with the consequent impact on water quality. With this in mind, in this study, coal fires at for different and representative coal mining waste dumps covering a variety of reclamation conditions were investigated concerning the
degree of land reclamation to identify possible threats to the environment and to devise remediation strategies. METHODOLOGY Four coal gobs, with (2) and without (2) top soil reclamation were sampled in terms of the original coal gangue, burned wastes, condensates from gaseous emissions in vents and top soils, and the chemical and mineralogical composition of the samples was determined by ICP-MS, ICP-AES and XRD. Furthermore, leaching experiments using the European Standard leaching test EN-12457 were carried out to all the above samples to determine the leaching potential of major, and trace elements. The pH and ionic conductivity of the leachates were determined by conventional methods. The content of major and trace elements of the leachates were determined by ICP-AES and ICP-MS. The content of Hg was determined directly on leachates by the same procedure as for the solid coal samples using GA-AAS. The content of ammonium was determined in the leachates by using a specific electrode. MAIN RESULTS 1. Based on the mineralogy of the burned wastes (mullite, cordierite, mullite, augite, diopside, amphiboles) in the fire core, we conclude that the combustion temperature could reach up to 1200oC in all 4 cases. 2. Around the core a degasification aureole is formed with temperatures gradually being reduced down to around 100oC near the vents. Thus, thermally altered or degasified coal wastes are found between the fire core (with oxidized combustion wastes) and the surface. 3. During combustion in the burning core and degasification of the aureole, elements such as S, F, C, Cl, F, S, N, As, Cd, Hg, Pb, Sn, Ge and Se, and a number of organic pollutants are emitted into the atmosphere. 4. Mercury tends to be highly enriched (up to 100 ppm) in high ammonium sulfate, ammonium chloride and Al-sulfate condensates, together with Se. 5. Close to the surface of the gob, condensation processes account for the partial trapping of gaseous emissions of PaH, As, S, N, Hg, Pb and Se, among others. Thus, condensates of tar and mineralizations of elemental sulfur, a large variety of Ca, Al-K-Fe sulphates, ammonium sulfate and ammonium chloride, highly enriched in Hg, Se, As and other trace elements are frequent in the gas vents. 6.
Organic condensates have extremely high concentrations of PaH and n-alkanes.
7. After deposition and condensation these unstable organic and inorganic species, these suffer important oxidation giving rise to gypsum crusts with low contents of organic matter.
8. In the two gobs with soil cover, both organic and inorganic condensates are found in the top surface of the buried gob, but in the soil top only ca sulfate (gypsum) was detected as a condensate material. This means that the most of volatile species have condensate in depth and that only SO2 is reacting with the top soil. Consequently, a 25 to 50 cm top soil is probably not only diminishing spontaneous combustion by diminishing the oxygen flux, but also reducing the emissions of gaseous pollutants. 9. Al, K, and Fe-bearing sulfates condensing at gas vents are regarded as the main concern in terms of leaching due to strongly acidic leachates (down to 1.6 pH) and environmentally relevant releases of potentially harmful elements (Al3+, Hg, As, Se, among others). Locally, the occurrence of ammonium chloride yields alkaline leachates up to 8.6 pH. The overall leaching of trace pollutants and sulfate would account for severe inputs to surface and groundwater. Minimizing the exposure of condensates to direct rainfall should be a major target of reclamation activities, thus the top soil also diminish leaching of the condensates. 10. It was found that covering the coal waste dumps with a layer of compacted soils of around appears to be an excellent cost-effective method to reduce frequency and magnitude of spontaneous combustion. Furthermore, this cover is scavenging or trapping pollutants from gaseous emissions, and minimizing risks associated with the leaching of readily soluble salts condensed on the surface. ACKNOWLEDGEMENT This study had financial support from the National Natural Science Foundation of China (Nos. 40572089 and 40972104). REFERENCES (1) Han, D., Yang, Q. Coal Geology of China. Second volume, , 1980, Coal Industry. (2) Mao, J., Xu, H. Evaluation and prediction of Chinese coal resources. Beijing: Science Press, 19991–465 (In Chinese). (3) Misra, B.K., Singh, B.D. Int. J. Coal Geol., 1994, 25, 265-286. (4) Pone, J.D.N., Hein, K.A.A., Stracher, G.B., Annegarn, H.J., Finkelman, R.B., Blake, D.R., McCormack, J.K. Schroeder, P. Int. J. Coal Geol., 2007, 72, 124-140. (5) Querol, X., Izquierdo, M., Monfort, E., Alvarez, E., Font, O., Moreno, T., Alastuey, A., Zhuang, X., Lu, W. Wang, Y. Int. J. Coal Geol., 2008, 75, 2, 93-104.
Plasma Supported Coal Ignition and Combustion V.E. Messerle1, E.I. Karpenko2, A.B. Ustimenko3 1 2
Research Department Plasmotechnics, Almaty, Kazakhstan
Research Institute of Experimental and Theoretical Physics al-Farabi Kazakh National University, Almaty, Kazakhstan 2
Ulan-Ude Division of the Institute of Thermophysics of SB RAS Ulan-Ude, Russia E-mail:
[email protected] Abstract This work presents new plasma technology for solid fuel ignition and combustion. It promotes more effective and environmental friendly low-rank coal ignition and combustion. To realise this technology at coal fired power plants plasma-fuel systems (PFS) were developed. PFS is pulverized coal burner equipped with arc plasmatron. Temperature of the flame from the plasmatron is varied from 5000 to 6000 K. The base of the PFS technology is plasma thermochemical preparation of coal for burning. It consists of heating of the pulverized coal and air mixture by arc plasma up to temperature of coal volatiles release and char carbon partial gasification. In the PFS coal-air mixture is deficient in oxygen and carbon is oxidised mainly to carbon monoxide. As a result, at the PFS exit a highly reactive mixture is formed of combustible gases and partially burned char particles, together with products of combustion, while the temperature of the gaseous mixture is around 1300 K. Further mixing with the air promotes intensive ignition and complete combustion of the prepared in the PFS fuel. PFS have been tested for boilers start up and pulverized coal flame stabilization in different countries at 30 power boilers of 75 to 950 t/h steam productivity. They were equipped with different types of pulverized coal burners: direct flow, muffle and swirl burners. At PFS testing power coals of all ranks (lignite, bituminous, anthracite and their mixtures) were incinerated. Volatile content of them was in range of 4 to 50%, ash varied from 15 to 48% and heat of combustion was from 1600 to 6000 kcal/kg. To show the advantages of the plasma technology before conventional technologies of coal combustion numerical investigation of plasma ignition, gasification and thermochemical preparation of a pulverized coal for incineration in a power boiler was fulfilled. Two computercodes were used for the research. The numerical experiments were conducted for low-rank
bituminous coal of 40% ash content incinerated at the boiler of 420 ton per hour steam productivity. Comprehensive image of plasma activated coal combustion processes in a furnace of pulverized coal fired boiler was obtained. Both analysis of the numerical experiment and experience of PFS industrial use showed ecological efficiency of the plasma technology. When the plasmatron operates in the regime of plasma stabilization of pulverized coal flame, NOX emission is reduced twice and amount of unburned carbon is reduced four times. 1. Introduction To improve efficiency of solid fuels use, to decrease fuel oil rate in fuel balance of thermal power plants (TPP) and to minimize harmful emissions a plasma technology of coal ignition, gasification and incineration was developed [1, 2]. This technology is plasma thermo-chemical preparation of coal for burning. In the framework of this concept some portion of pulverized solid fuel (pf) is separated from the main pf flow and undergone the activation by arc plasma in a special chamber with plasmatron – PFS (Figs.1 and 2). The air plasma flame is a source of heat and additional oxidation, it provides a high-temperature medium enriched with radicals, where the fuel mixture is heated, volatile components of coal are extracted, and carbon is partially gasified. This active blended fuel can ignite the main pf flow supplied into the furnace. This technology provides boiler start-up and stabilization of pf flame and eliminates the necessity for additional highly reactive fuel.
Figure 1. Sketch of the plasmatron.
Figure 2. Sketch of the Plasma-Fuel System (PFS).
2. Plasma-Fuel System The plasma thermo-chemical preparation of coal is schematically illustrated in Fig. 2. The arc plasmatron (Fig. 1) consists of copper water-cooled electrodes (cathode and anode)
through which the plasma forming air is blown. The plasmatron power is varied from 100 to 200 kW. Its height is 0.4 m, diameter – 0.25 m, and its weight is 25 kg. The measured energy conversion efficiency of the plasmatron is some 85%. Features of fuel-air mixture interaction with arc plasma in the PFS are given in Fig. 3. Across the plasma flame, coal particles with an initial size of 50-100 µm experience ‘heat shock’ and disintegrate into fragments of 5-10 µm. This increases the active interface of the particles, significantly accelerating the devolatilisation (CO, CO2, H2, N2, CH4, C6H6 and others) and 3-4 times accelerates the process of oxidation of fuel combustibles.
Figure 3. Features of arc plasma interaction with air-fuel mixture in the PFS. 3. PFS Industrial Tests PFS have been tested for boilers plasma start-up and pf flame stabilization in different countries at 30 power boilers steam productivity of 75 to 950 ton per hour equipped with different type of pulverized coal burners [2]. At PFS testing power coals of all ranks (lignite, brown, bituminous, anthracite and their mixtures) were used. Volatile content of them varied from 4 to 50%, ash - from 15 to 48% and calorific values - from 6700 to 25100 kJ/kg. For example, the PFS have been implemented in the furnace of a 640 t/h steam full-scale steam raising boiler (Gusinoozersk TPP, Eastern Siberia, Russia). A schematic view of the furnace equipped with the PFS, along with its main dimensions, is shown in Fig. 4. The furnace consists of two symmetrical combustion chambers (semi-furnaces), each provisioned with 8
tangentially directed pf burners in two layers. The combustion chambers are interconnected by a central section. Each burner comprises a primary air/pf delivery section and a secondary air section. Four PFS take the place of the four lower layer burners as shown on the right side of Fig. 4. The plasmatrons operate during the boiler start-up period and in the case of an unstable flame. When the boiler performance is stabilised, the plasmatrons are switched off and the PFS continue to function as conventional pf burners. In the case of flame instability, the plasmatrons are restarted. The fuel was Tugnuiski bituminous coal of 20 % ash content and 35 % of volatile matter. In total, four of the combustors of this TPP were equipped with sixteen PFS. It is estimated that, since 1995, more than 20000 tons of fuel oil has been saved in this facility. This corresponds to a reduction in the emissions of nitrogen and sulphur oxides, carbon monoxide and
7.744 m
33.596 m
vanadium pentoxide of some 13000 tons per year.
18.176 m
Figure 4. Scheme of the industrial furnace of BKZ 640-140 boiler and the boiler furnace equipped with four PFS (top view). Fig. 5 illustrates the scheme of arrangement of the PFS on the boiler combustor BKZ-420 in Ulan-Bator TPP-4 (Mongolia). According to the boiler construction twelve corner-fired burners are placed at three elevations. Two PFS were mounted cornerwise on the lower layer. All eight boilers of the power plant were equipped with PFS for fuel oil free boiler start-up. In 2-3 seconds after light-up with the PFS, the temperature of both pulverised coal flames increased up to 1100-1150 OC. In one hour, the temperature of the flames had achieved 1260-1290 OC and their length reached about 7 - 8 m. In accordance with the operating instructions, the total duration of the boiler start-up was 4 hours.
Fig. 6 demonstrates a scheme of arrangement of three plasma torches on a direct-jet flat-flame pulverised-coal burner of the low layer of BKZ-640 boiler at Gusinoozersk TPP (from the left it is the top view; from the right it is the cross section).
Figure 6. Scheme of arrangement of burners and PFS on BKZ-640 boiler.
1.1
4.0
1.0
3.5 Unburned carbon, %
NOx concentration, g/Nm
3
Figure 5. BKZ-420 boiler furnace equipped with two PFS (top view).
0.9 0.8 0.7 0.6 0.5 0.00
3.0 2.5 2.0 1.5 1.0
0.05
0.10
0.15
0.20
Specific power consumptions, kW h/kg of coal
0.00 0.05 0.10 0.15 0.20 Specific power consumptions, kW h/kg of coal
Figure 7. Specific power consumption influence Figure 8. Specific power consumption onto reduction of nitrogen oxides concentration influence onto reduction of unburned carbon at at plasma aided pulverised coal combustion. plasma aided pulverised coal combustion. Knowledge of the specific power consumption of a plasmatron is required to estimate PFS efficiency. This parameter is defined as the ratio of plasmatron electric power to pf consumption in the PFS. Figs. 7 and 8 present experimental results for NOX reduction and the decrease of unburned carbon during PFS operation versus specific power consumption for the plasmatron. It is seen that the NOX concentration is halved, and the amount of unburned carbon is reduced by a factor of 4. The NOX decrease is caused by the fact that the fuel nitrogen, released from the coal inside the PFS in conditions of oxygen deficiency, forms molecular nitrogen in the gas phase.
Since the fuel nitrogen is evolved inside the PFS and converted to molecular nitrogen there, mainly thermal nitrogen oxides are formed within the combustor volume. However, fuel nitrogen is the main source of nitrogen oxide emission from conventionally-fired pf combustors [3]. As to unburned carbon (Fig. 8), its decrease indicates a fuel reactivity increase which is explained by enlargement of the coal particles reactive surface due to ‘heat explosion’ and fragmentation resulting their interaction with arc plasma. 4. Numerical experiment Results of PFS application at a boiler BKZ-420 of 420 t/h steam productivity of Almaty TPP-2 (Kazakhstan) are presented in this section (Fig. 9). PFS for the boiler BKZ-420 are based on three main burners: two outer burners of the lower layer and a middle burner of the upper layer. PFS are placed in the burner instead of the channel of the primary air-fuel mixture (the inner channel of air-fuel mixture) (Fig. 10). PFS were designed and engineered using two computer-codes, one-dimensional Plasma-Coal [4], that takes into account plasma source and the detailed kinetics of the thermochemical transformations of fuel in two-phase flow, and three-dimensional Cinar ICE [5], that takes into account the geometry of the combustion chamber, the turbulence environment, radiation heat transfer and combustion of coal particles by the model of fast chemistry. Two modes of the boiler operation were chosen for the numerical studies. The first one was traditional regime, using six pulverized-coal burners, and the second one was regime with plasma activation of combustion, using the replacement of three pulverized-coal burners onto PFS. Parameters of highly reactive two-component fuel, derived from the air-fuel mixture in the PFS, were calculated using Plasma-Coal code. They were taken as initial parameters for the three-dimensional calculation of boiler’s furnace equipped with PFS, which were carried out by the program Cinar ICE. Dust of Ekibastuz bituminous coal of 40 % ash content, 24 % volatile, 5 % wet and calorific value of 4000 kcal/kg is burned in the boiler. Fineness of the coal grinding is R90=15 %. It means that averaged diameter of the particles is 60 µm. Initial data for calculation of the PFS by Plasma-Coal program are given in Table 1. As a result of the calculation distribution of temperature and velocity of gas and particles, concentrations of gas-phase components, degree of gasification, and carbon concentration in the coke residue were calculated.
Figure 9. Layout of the pf burners (1) and PFS (1) in the boiler BKZ-420 of Almaty TPP-2. Figure 10. Scheme and layout of two stage PFS for the boiler BKZ-420 of Almaty TPP-2: 1 – channel of the external flow of pf, 2 – secondary air duct, 3 - inlet of pf external flow, 4 – inlet of pf internal flow, 5 - plasmatron, 6 – chamber for pf flow turning, 7 – chamber for plasma chemical preparation of fuel for combustion, 8 - chamber for mixing and thermochemical preparation of fuel, 9 - furnace. Table 1. Initial parameters for PFS computation. Parameter Plasmatron power, kW Air-coal mixture temperature, К Consumption of coal through PFS or internal channel of burner, kg/h Primary air rate, kg/h PFS length, m Pulverized coal composition, mas. % Ash C H2 H2O CO CO2 40.0 46.18 2.63 1.84 3.95 1.4
Value 200 362 6000 8955 3.687 CH4 0.55
C6H6 3.45
It can be seen (Fig. 11) that in the initial part of PFS (X < 0.3 m) gas temperature exceeds the temperature of the particles due to the initial heat exchange of the plasma source with the gas phase. In this case, gas and particles velocities do not increase, almost without distinguishing between them. Later on the heated coal particles devolatilization with simultaneous gasification of carbon coke residue is observed (Fig. 12). Due to oxidation of carbon on the surface of the particles their temperature increases to 1350 K, exceeding the temperature of gas on 400 degrees
(X = 0.5 m). At the PFS exit between gas and particles thermal equilibrium is reached at a temperature of 1025 K and the gas flow velocity reaches 49 m/s, exceeding the particle velocity on 1 m/s (Table 2). Note that the flow velocity at the exit of PFS is much higher than the velocity of air-fuel mixture at the exit of traditional pf burners. Concentration of combustible components (CO, H2, Н, CH4, C6H6) increase with the PFS length, reaching its maximum (10%) at the PFS exit. The concentration of oxidizing agents (CO2, H2O, O2) at the PFS exit is 19.2%. The degree of gasification of coal along the length of PFS increases, reaching 48% at the exit, which is sufficient to produce highly reactive fuel. 100
N2
1400 1200
Ci, %
T, K
1000 1 800
H2
1
CO H2O
O2
C6H6 CH4
600 400 0.0
CO2
10
2
0.1 0.5
1.0
1.5
2.0
2.5
3.0
3.5
X, m
Figure 11. Gas (1) and particles (2) temperature (T) distribution along the PFS (X).
0.01 0.0
0.5
1.0
1.5
2.0 X, m
2.5
3.0
3.5
Figure 12. Gas components concentration (Ci) distribution along the PFS (X).
Table 2. Composition of highly reactive fuel at the PFS exit. Composition of gaseous phase, vol. % H2 CO CH4 C6H6 CO2 H2O N2 1.05 7.75 0.3 0.77 15.6 3.55 70.84 Gas temperature, К Solids temperature, К 1025 1025
O2 0.15
Ash, kg/h Carbon, kg/h 1518 261 Flow velocity, m/s 48.2
The integral characteristics of plasma-chemically prepared fuel for combustion at the exit of PFS (Table 2) were used as initial parameters for the three-dimensional numerical simulation of pf and highly reactive fuel co-combustion in the furnace of power boiler BKZ-420 (Fig. 9) with the aid of the program Cinar ICE. The results of the calculation of the furnace are shown in Fig. 13. There is a difference of temperature fields in two modes of coal combustion in the furnace. At conventional incineration
of coal six pf flames with a maximum temperature of 1852 OС are formed. In Fig. 13 (right) PFS is located on top layer in the center (longitudinal section of the furnace). Effect of PFS appears to change the shape of the flame of highly reactive fuel. High temperature cores of the flames with a maximum temperature of 1588 OС are shifted closer to the burner embrasures and the PFS, as well as to the upper part of the furnace.
Figure 13. Temperature field in the plane of the central burners and the PFS at conventional incineration of coal (on the left) and using three PFS (on the right). Concentration of unburned carbon, which characterizes the completeness of coal burnout, at the outlet of the furnace 16% less in the case of plasma activated regime of pf combustion using three PFS in compare with traditional coal burning. Fig. 14 shows average concentration of carbon dioxide distribution along the furnace height. While using three PFS concentration of CO2 is higher over the entire height furnace and at the furnace exit this excess amounts to 1%. It confirms high efficiency of coal combustion because of its more complete burnout. PFS also improves the environmental characteristics of pf combustion due to 33% reduction of nitrogen oxide emissions. 5. Conclusions Developed, investigated and industrially-tested plasma-fuel systems improve coal combustion efficiency, while decreasing harmful emission from pulverized-coal-fired Thermal Power Plants. NOx and unburned carbon concentrations decrease improves eco economic indexes of TPP.
PFS eliminate the need for expense gas or oil fuels on start-up, stabilisation of pulverized-coal flame and stabilization of liquid slag output in furnaces with liquid slag removal. Power consumption for PFS does not exceed 2% from heat capacity of the reequipped pulverized coal burner and payback period is not more than 18 months.
Figure 14. Averaged СО2 concentration distribution along the furnace height of the boiler BKZ-420: 1 – regime with PFS, 2 – conventional regime of coal incineration. References [1] Karpenko EI, Messerle VE, Ustimenko AB. Plasma-Aided Solid Fuel Combustion // Proceedings of the Combustion Institute, 2007, V.31, Part II, P.3353-3360 [2] Karpenko EI., Karpenko YuE, Messerle VE, Ustimenko AB. Using Plasma-Fuel Systems at Eurasian Coal-Fired Thermal Power Stations // Thermal Engineering, 2009, V.56, N 6. – P.456-461 [3] Tike DH, Slater SM, Sarofim AF, Williams JC. Nitrogen in Coal as a Source of Nitrogen Oxide Emission from Furnace. // Fuel, 1974, 53, P. 120-125 [4] Kalinenko RA, Levitski A.A., Messerle V.E., Polak L.S., Sakipov Z.B., Ustimenko A.B. Pulverized of Coal Plasma Gasification // Plasma Chemistry and Plasma Processing. V. 13. N 1, 1993, P. 141-167. New-York, London, Paris. [5] Messerle VE, Ustimenko AB, Askarova AS, Nagibin AO. Pulverized Coal Torch Combustion in a Furnace with Plasma-Coal System // Thermophysics and Aeromechanics, 2010, V. 17, N 3, P. 435-444
Oviedo ICCS&T 2011. Extended Abstract
Diffuse soil CO2 flux to assess the reliability of CO2 storage in the Mazarrón-Gañuelas Tertiary basin (Spain) J. Rodrigo-Naharro1 *, O. Vaselli2,3, B. Nisi4, M. Lelli4, R. Saldaña1, C. Clemente-Jul5, L. Pérez Del Villar1 1
Environmental Department. CIEMAT. Avda. Complutense, 22. 28040 Madrid (Spain) Department of Earth Sciences, Via G. La Pira, 4. 50121 Florence (Italy) 3 CNR-IGG Institute of Geosciences & Earth Resources, Via G. La Pira, 4. 50121 Florence (Italy) 4 CNR-IGG Institute of Geosciences and Earth Resources, Via G. Moruzzi, 1. 56124 Pisa (Italy) 5 Department of Chemical Engineering and Fuels. ETS Ingenieros de Minas. Universidad Politécnica de Madrid (UPM), Alenza 4. 28003 Madrid (Spain) 2
Abstract Geological storage of CO2 is nowadays internationally considered as the most effective method for greenhouse gas emission mitigation, in order to minimize its effects on the global climatology. One of the main options is to store the CO2 in deep saline aquifers at more than 800 m depth, because it achieves its supercritical state. Among the most important aspects concerning the performance assessment of a deep CO2 geological repository is the evaluation of the CO2 leakage rate from the chosen storage geological formation. Therefore, it is absolutely necessary to increase the knowledge on the interaction among CO2, storage and sealing formations, as well as on the flow paths for CO2 and the physico-mechanical resistance of the sealing formation. Furthermore, the quantification of the CO2 leakage rate is essential to evaluate its effects on the environment. One way to achieve this objective is to study of CO2 leakage on natural analogue systems, because they can provide useful information about the natural performance of the CO2, which can be applied to an artificial CO2 geological storage. This work is focused on the retention capacity of the cap-rock by measuring the diffuse soil CO2 flux in a site selected based on: i) the presence of a natural and deep CO2 accumulation; ii) its structural geological characteristics; and iii) the nature of the cap-
Oviedo ICCS&T 2011. Extended Abstract
rocks. This site is located in the so-called Mazarrón-Gañuelas Tertiary Basin, in the Guadalentin Valley, province of Murcia (Spain)
Therefore the main objective of this investigation has been to detect the possible leakages of CO2 from a deep saline aquifer to the surface in order to understand the capability of this area as a natural analogue for Carbon Capture and Sequestration (CCS).
The results obtained allow to conclude that the geological sealing formation of the basin seems to be appropriate to avoid CO2 leakages from the storage formation.
1. Introduction The scientific community has general accepted that long-term extrapolation in terms of safety of a deep geological storage of toxic industrial wastes, such as high activity radioactive wastes, industrial and mining wastes and even greenhouse gases, can not be satisfactorily done on the basis of short term researches in the laboratory [1]. Therefore, countries affected by these problems have developed methods of investigation which include both short-term tests in the laboratory, where the variables are controlled, as the study of natural analogues.
Although the studies about CO2 natural accumulations are not yet sufficiently developed, some authors [2,3] have included in their works the existing CO2 reservoirs in the world and the experimental reactions between CO2 and the storage formations [4]. Moreover, in the last decade there are many works focused on the evaluation of the safety of a CO2 geological storage by means of the study of CO2 leakage natural analogues [5-11]. Regarding Spain, there’s one current important project cofunded by the Ministry of Science and Innovation and FEDER European Funds, whose main objective is the global study of the several CO2 natural analogues in all over the country. Among them, the natural analogue of storage, and natural and artificial leakage of CO2 located in the – Gañuelas-Mazarrón Tertiary basin (Province of Murcia) is being studied by the CIEMAT reseach team (Fig. 1). The CO2 diffuse flux in the soil by means of a WEST-
Oviedo ICCS&T 2011. Extended Abstract
SYSTEMS fluxmeter has been performed in the above-mentioned site, in order to know whether the cap-rock is able to retain possible escapes of CO2 at the surface.
Fig. 1. Geographical location of the study area (red square)
2. Experimental section In the Gañuelas-Mazarrón Tertiary basin, according to the structural geological features [12,13], four areas were selected for a comprehensive CO2 flux study. They are located at the intersection of high density lineaments (Fig. 2) that should likely correspond to preferential leakage paths of deep-seated CO2. These areas are: Las Moreras, La Majada and Leiva (Fig. 3), which are at the contact between the Tertiary basin and the Triassic surroundings mountains, and the El Saladillo place, situated inside the GañuelasMazarrón basin.
The equipment used for CO2 flux measurements is that licensed by West-System and consists in an accumulation chamber from where the soil gas is forced to be pumped through an IR cell set at the wavelength of CO2. The increase of CO2 with time allows the measurement of the flux by means an algorithm that takes into account the pressure and temperature data collected in the field [14].
Oviedo ICCS&T 2011. Extended Abstract
The CO2 soil fluxes were carried out in September 2009 and March 2010 during dry and meteorologically stable periods in order to avoid the possible influence of variations induced by environmental parameters on soil degassing. Laboratory experiments were performed to assess both, the reliability of CO2 flux measurements and the calibration of the instrument [14].
QUATERNARY. Conglomerates, sands, slimes and clays
Figs. 2 and 3. Location of the areas where it has been measured the CO2 flux (left) [13] and their respective schematic geological situation (right)
NEOGENE. Volcanic Rocks: dacites and andesites NEOGENE. Carbonates and marls NEOGENE. Limestones
3. Results and Discussion
In September 2009 the CO2 flux soil was computed for a surface of ~52,700 m2 in Las Moreras; ~86,800 m2 in La Majada; ~179,600 m2 in Leiva; and ~136,000 m2 in El Saladillo. In these areas, 127, 277, 257 and 187 evenly distributed measurements were done, respectively. In March 2010, the investigation in La Majada and Leiva areas was enlarged with 93 and 94 measurements, covering additional surfaces of ~39,000 m2 and 30,000 m2, respectively. The measured φCO2 at Las Moreras oscillates from 0.007 to 0.929 moles m-2 day-1, with an average value of 0.262 moles m-2 day-1, while at El Saladillo they were spanning between 0.020 and 1.103 moles m-2 day-1, with an average value of 0.353 moles m-2 day-1. At La Majada a large interval of variation was observed in September 2009, ranging from
Oviedo ICCS&T 2011. Extended Abstract
0.007 to 7.503 moles m-2 day-1, with an average value of 0.877 moles m-2 day-1; whereas, in March 2010, a lower interval, between 0.025 and 1.425 moles m-2 day-1, was observed, being its average value of 0.456 moles m-2 day-1. Finally, at Leiva the φCO2 values varied between 0.024 and 1.490 moles m-2 day-1, with an average value of 0.391 moles m-2 day-1 (September 2009) and between 0.041 and 1.074 moles m-2 day-1 with an average value of 0.310 moles m-2 day-1 (March 2010). In order to better constrain the total φCO2 and the CO2 spatial distribution overall the investigated areas, the values are divided in populations according to the method proposed by Sinclair [15]. The diffuse φCO2 values in the four investigated areas were lower than 1.0 moles m-2 day-1, whereas values up to 7.5 and 1.49 moles m-2 day-1 were measured in September 2009 at the La Majada and Leiva areas, respectively. It is worthy to mention that φCO2 values higher than 1 moles m-2 day-1 were only sporadically recorded. 4. Conclusions On the basis of the diffuse soil CO2 degassing surveys carried out in September 2009 and March 2010, the general picture emerging from the present study is that in the area under study, although characterized by a complex geological setting, the efficiency of the cap-rock, as sealing formation, in the Gañuelas-Mazarrón Tertiary basin does not allow any relevant CO2 leakages at the surface. That is, in terms of CO2 soil flux, the Tertiary sedimentary deposits filling the basin act then as an impermeable layer through which the escape of CO2 is not jeopardized. This is strongly supported by the measurements of the φCO2 carried out by means of the accumulation chamber method. The investigated areas have generally low φCO2. They are basically comparable to those observed in cultivated areas worldwide, with very few exceptions that can possibly be related to structural weakness or fault zones. Nevertheless, this statement is not sufficiently supported by the available data. It is however matter of fact that the geological sealing formation results to be effective and efficient in case of any leakage of CO2.
Oviedo ICCS&T 2011. Extended Abstract
Acknowledgements We wish to thank to the Ministry of Science and Innovation of Spain and the European Union FEDER Funds for supporting this study. This work was carried out within the Project PSE-CO2, whose objective has been the development of the Carbon Capture and Storage (CCS) Technologies. References [1] Petit JC. Reasoning by analogy : rational foundation of natural analogue studies. Appl. Geochem 1992; Supplementary Issue 1:9-12. [2] Czernichowski-Lauriol I, Sanjuan B, Rochelle C, Bateman K, Pearce J, Blackwell P. The underground disposal of carbon dioxide. In: Holloway S, editor. Inorganic Geochemistry. Final Report of Joule II Project Nº CT92-0031. [3] Pearce JM, Holloway S, Wacker H, Nelis MK, Rochelle C, Bateman K. Natural occurrences as analogues for the geological disposal of carbon dioxide. Energy Converse and Management 1996;37:6-8. [4] Pearce JM, Rochelle C. CO2 storage: mineral reactions and their influences on reservoir permeability. A comparison of laboratory and field studies. Elsevier; 1999. [5] Czernichowski-Lauriol I, Pauwels H, Vigouroux P, Le Nindre YM. The french carbogaseous province: an illustration of natural processes of CO2 generation, migration, accumulation and leakage. Greenhouse Gas Control Technologies. Vols I and II, Proceedings 2003;411-416. [6] Hawkins, DG. No exit: thinking about leakage from geologic carbon storage sites. Energy 2004;29:1571-1578. [7] Beaubien SE, Lombardi S, Ciotoli G, Annuziatellis A, Hatziyannis G, Metaxas A et al. Potential hazards of CO2 leakage in storage systems-Learning from natural systems. Greenhouse Gas Control Technologies 2005;7:551-560. [8] Nordbotten JM, Celia MA, Bachu S, Dahle HK. Semianalytical solution for CO2 leakage through an abandoned well. Environmental Science & Technology 2005;39: 602-611. [9] Oldenburg CM, Lewicki JL. On leakage and seepage of CO2 from geologic storage sites into surface water. Environmental Geology 2006;50:691-705. [10] Riding JB. The IEA Weyburn CO2 monitoring and storage project - Integrated results from Europe. Advances in the Geological Storage of Carbon Dioxide: International Approaches to Reduce Anthropogenic Greenhouse Gas Emissions 2006;65:223-230.
Oviedo ICCS&T 2011. Extended Abstract
[11] Lewicki JL, Birkholzer J, Tsang CF. Natural and industrial analogues for leakage of CO2 from storage reservoirs: identification of features, events, and processes and lessons learned. Environmental Geology 2007;52:457-467. [12] Pérez del Villar L, Pelayo M, Recreo F. Análogos Naturales del Almacenamiento Geológico de CO2 (Fundamentos, Ejemplos y Aplicaciones para la Predicción de Riesgos y la Evaluación del Comportamiento a Largo Plazo). CIEMAT; 2007. [13] Pérez del Villar L. Memoria Científico-Técnica del periodo 2008-2009 del PSE120000-2008-6 (PSS-120000-2008-31). Línea de Análogos Naturales: "Resultados preliminares del estudio de los análogos naturales estudiados en: la región de La Selva (Girona), Valle del Alto Guadalentín (Murcia-Almería), Alicún de las Torres (Granada), Alhama de Aragón-Járaba (Zaragoza) y Castilla León” CIEMAT; 2009. [14] Nisi B, Vaselli O, Lelli M, Tassi F, Rodrigo-Naharro J, Pérez del Villar L. Diffuse CO2 flux and dissolved gases in the Mazarrón-Gañuelas area (Guadalentin Valley). Report PSE; 2010. [15] Sinclair AJ. Selection of threshold values in geochemical data using probability graphs. Geochem. Expl. 1974;3:129-149.
Carbon and Storage by pH swing aqueous mineralisation using a mixture of ammonium salts Aimaro Sannaa,b *, Marco Dri a,b, Xiaolong Wang a, Matthew R Hall b, Mercedes Maroto-Valer a a
National Centre for Carbon Capture and Storage, The Sir Colin Campbell Building, Innovation Park, University of Nottingham, Nottingham, NG7 2TU, UK
b Nottingham Centre for Geomechanics, Division of Materials, Mechanics and Structures, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, UK
Corresponding author: Aimaro Sanna, Energy and Sustainability Research Division, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, UK, Tel: +44 (0)115 9514198,
[email protected] ; Other authors: Marco Dri, Energy and Sustainability Research Division, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, UK, Tel+44 (0)115 9514198,
[email protected] ; Xiaolong Wang, Energy and Sustainability Research Division, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, UK, Tel+44 (0)115 9514198,
[email protected] ;Matthew R Hall, Division of Materials, Mechanics and Structures, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, UK, Tel: +44 (0)115 846 7873, Fax: +44(0)115 951 3159,
[email protected] ; Mercedes Maroto-Valer, Head of Energy and Sustainability Research Division, Faculty of Engineering Director of Centre for Innovation in Carbon Capture and Storage (CICCS), University of Nottingham, University Park, Nottingham NG7 2RD, UK, Tel: +44 115 846 6893, Fax: +44 115 951 4115,
[email protected].
Abstract
Carbon capture and storage by mineralisation (CCSM) focuses on mixing the carbon dioxide (CO2) in the flue gases with rocks rich in magnesium oxide. The oxides react with CO2 producing solid mineral carbonates, which are stable solids and can provide safe storage capacity on a geological scale. The aim of this work was to optimize a pH swing mineralisation processes developed at the University of Nottingham that uses recyclable ammonium salts to widespread implementation of the technology. Carbonation using a mixture of NH4HCO3 and (NH4)2CO3 under different temperatures was investigated considering that these solids are the expected intermediate solid products of the chilled ammonia capture process. The highest carbonation efficiency was 61.5% and this value is lower than that obtained when using only NH4HSO4 (70-80%).
1. Introduction
Carbon capture and storage (CCS) by geological storage has the potential to sequester about 50% of the CO2 emission per year in Europe by 2030 [1]. The state of the art indicates that this process can be applied mainly to large emitters, while it is less appropriate for smaller emission sources [2]. CCS by mineralisation (CCSM) can sequester CO2 by mixing the CO2 from flue gases with industrial solid waste rich in oxides or rocks rich in magnesium or calcium oxides. The oxides react with CO2 producing solid mineral carbonates, which are
stable and can provide safe storage capacity on a geological scale. It is estimated that the global magnesium silicate rock deposits are enough to sequester the CO2 generated by all the fossil fuels resources. CCSM can therefore contribute to decrease of CO2 emissions in areas where geological storage cannot be deployed and also can be applied to small industrial emitters [2]. The aim of this work is to investigate the technical barriers for the deployment of CCSM, such as the high energy demand for pre-treatment of the minerals and the slow kinetics of direct gas-solid reactions. Indirect CCSM by pH swing using ammonium salts has been recently investigated to enhance the efficiency of both dissolution and carbonation, resulting in 70-80% CO2 sequestered [3]. The process shown in Figure 1consists in 3steps: first, the dissolution of minerals rich in magnesium bringing it in the solution as MgSO4. Second, the removal of the impurities (Fe, Al, Mn etc.) by increasing the pH from acidic to basic and finally, the carbonation of the MgSO4 with ammonium carbonates coming from the CO2 capture stage producing hydromagnesite. Furthermore, this method can recycle most of the chemicals used during the process. In this study, further research is conducted in this process with the objective of optimise the operating variables. CO2
NH3
Capture
NH4HSO4
NH4HCO3 (NH4)2CO3 Serpentine H2O
Dissolution Silica
pH swing
MgSO4
Impurities (Fe, Al, Mn, etc.)
Regeneration
(NH4)2SO4
Carbonation Hydromagnesite
Figure 1 Scheme of the pH swing process used in this work.
The capture of CO2 by ammonia-based wet scrubbing is similar to the capture process using amines. Ammonia and its derivatives react with CO2 and water to form different solids at temperature below 10°C [4]. This process can precipitate several ammonium carbonate compounds in the absorber, mainly ammonium bicarbonate (NH4HCO3) and ammonium carbonate ((NH4)2CO3). Under CO2 loadings higher than 0.5 both ammonium salts are
present, while when the CO2 loadings is lower than 0.5 the only solid is ammonium carbonate [5]. Therefore, the chilled ammonia process is likely to produce a mixture of ammonium carbonate and bicarbonate. Therefore, this study wants investigate the carbonation of CO2 in presence of both salts at different temperatures and to compare with previous studies carried out using ammonium bisulphate. A series of dissolution and carbonation experiments were performed in a batch reactor under different temperatures (50, 70, 100°C) to evaluate its effect on the dissolution of serpentine mineral (1st reaction limiting step) and on the silica product layer diffusion (2nd reaction limiting step). The products of the reaction were then analysed to establish the mass balance and the overall CO2 sequestration efficiency compared with previous work [3,6]. 2. Experimental section
200g of serpentine with particle size ranging from 75 to 150μm were added into 4000mL 1.4M NH4HSO4 solution for a 1:20 solid liquid ratio after the solution temperature was stabilised at 100°C. A solution sample was extracted after 5, 10, 15, 30, 60, 120 and 180 minutes to establish the content of Mg and other ions in the solution by ICP-MS. After dissolution, the flask content was filtered with a 0.7μm Pall syringe filter and the solid was dried for 24 hours at 105°C and then analysed at the TGA. After the dissolution experiments, the impurities were removed by adding ammonia-water to rise the initial acid pH of the solution to neutral state and then to precipitate all the impurities such as iron, manganese and aluminium [3]. The carbonation experiments were carried out at 50, 70 and 100°C using the set-up shown in Figure 2. 200mL of the solution produced in the dissolution experiments was poured into a 250mL 3-necks flask and heated up at the required temperature by a silicon-oil bath under continuous stirring at 800rpm. As soon the temperature was stabilised and the pH was higher than 8, the stoichiometric mixture of 50% (NH4)2CO3 and 50% NH4HCO3 was added to the solution to start the carbonation reaction. Sampling and solutions analysis were done as for the dissolution experiments [3]. The carbonate content in the starting serpentine and final products was investigated by a TGA analyses were performed using a thermal gravimetric analyzer (TGA Q500, TA Instrument). The weight loss in the temperature region of 350°C to 500°C was determined to be carbonates [6]. The elemental composition of the serpentine used in this work was obtained from the literature [7, 8].
5
6
4 3
7
2 1 Figure 2 Carbonation set-up. 1 Temperature controller, 2 silicon-oil bath, 3 3-necks flask, 4 pH electrode, 5 thermo-couple, 6 cooling system, 7 sampling point.
3. Results and Discussion
Figure 3 shows the extraction of magnesium and iron carried out in triplicates. The higher magnesium extraction was obtained after 3hrs with 85% of the Mg removed from the serpentine particles. The three runs present the same dissolution trend indicating that a fast extraction occurs in the first 30 minutes with sequent slower dissolution afterwards. In fact, 70% of the magnesium is extracted in 30 minutes and only 15% more is extracted after 2 hours. The 3rd hour does not enhance the serpentine dissolution in a sensible way as can be seen in Figure 2. Therefore, 2 hours is the optimal dissolution time to reach the higher Mg extraction. However, 30 minutes might be preferred for a full scale mineral carbonation plant considering the trade off between the lower capital costs associated with faster kinetics [6] and the lower efficiency (70%) after 30 minutes extraction. It should be noted that the leaching of 200g of serpentine resulted in a lower extraction efficiency compared to the previous dissolution experiments carried out using 20g of serpentine [3]. This may be due to the different particle size distribution compared to previous work. The second stage of the overall process was the pH swing from acidic (pH 0.2) to neutral (pH 7) (reaction ii) and then basic (pH ≥8) by addition of ammonia water to remove all the impurities (Fe, Al, Zn, Ni, Cu, Mn etc.) from the solution.
Mg‐1
Mg‐2
Mg‐3
Fe‐1
Fe‐2
Fe‐3
90 80
Mg, Fe, %
70 60 50 40 30 20 10 0 0
40
80
120
160
200
Time, min
Figure 3 Magnesium and iron extraction efficiency during the 3hrs experiment.
Figure 4 shows the concentration of Fe, Al and Mn as a function of the pH. About 20% of Fe and Mn and 10% of Al precipitated when the pH increased from 0.2 to 2.5. The concentration of Fe, Mn and Al remained stable until pH approached 8. Then, at pH higher than 8 all the other Fe, Al and Mn precipitate as hydroxides leaving the solution of MgSO4 ready for the carbonation reaction. Fe
Al
Mn
80 70
Fe, Al, Mn, %
60 50 40 30 20 10 0 0
2
4
6
8
10
pH
Figure 4 Precipitation of iron, manganese and aluminium in function of the pH.
The last step of the process was the carbonation of the MgSO4 solution using a 50/50 mixture of NH4HCO3 and (NH4)2CO3.
Figure 5 shows how the concentration of magnesium in the solution decreases during the carbonation experiments due to the precipitation of the final product (MgCO3 Mg(OH)2 H2O). Only 10% and 30% of the total Mg precipitated in the first 5 minutes of the reaction in the experiments at 50 and 70°C, respectively. On the contrary, just after 5 minutes 80% of the total Mg in solution was precipitated at 100°C. This indicates that the temperature significantly influence the carbonation reaction. Figure 5 was also used to calculate the carbonation efficiency at the different temperatures. An efficiency of 51.6%, 58.5% and 76.5% was calculated considering the dissolved and precipitated magnesium. However, not all the magnesium was converted into carbonate. 50°C
70°C
100°C
120
Mg, wt%
100 80 60 40 20 0 0
10
20
30 Time, min
40
50
60
Figure 5 Variation of the magnesium concentration during carbonation at different temperatures.
The final carbonation efficiency (Mg in MgCO3 (after carb.) – Mg in MgCO3 (before carb.) / Mg in Serpentine *100) at 100°C was 61.5% that was much higher than at 50°C (39%) and at 70°C (41%). Therefore, the mineral carbonation at 100°C would require a low amount of starting serpentine (4.8t/tCO2) compared to that required at 50 and 70ºC. However, the carbonation efficiency using only NH4HCO3 under the same conditions was found higher (70-80%) [6], indicating that the carbonation using (NH4)2CO3 might require higher process conditions to reach similar efficiencies.
4. Conclusions
The results indicate that the pH swing process can be used to carbonate the CO2 trapped in the mixture of NH4HCO3 and (NH4)2CO3 produced during the chilled ammonia capture
process. However, the efficiency of the overall capture and storage process using the salts mixture resulted lower compared to that obtained by using only NH4HCO3.
Acknowledgements The work presented here was funded by the Centre for Innovation in Carbon Capture and Sorage (EPSRC grant EP/F012098/1). References
[1] Stangeland A, A model for the CO2 capture potential, International Journal of Greenhouse Gas Control, 1, 2007, 418-429. [2] IPCC, 2005: IPCC Special Report on Carbon Dioxide Capture and Storage. Prepared by Working Group III of the Intergovernmental Panel on Climate Change [Metz, B., O. Davidson, H. C. de Coninck, M. Loos, and L. A. Meyer (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 442 pp. [3] Wang X and Maroto-Valer M.M, Dissolution of serpentine using recyclable ammonium salts for CO2 mineral carbonation, Fuel 90 (2011) 1229–1237. [4] Figueroa J.D, Fout T, Plasynski S, McIlvried H, Srivastava R.D, 2008, Advances in CO2 capture technology—The U.S. Department of Energy’s Carbon Sequestration ProgramS, International journa l of greenhous e gas control , 2, 9-20. [5] Darde V, Thomsen K, van Well W and Stenby E, Chilled ammonia process for CO2 capture, Preprint – ICPWS XV Berlin, September 8–11, 2008 [6] Wang X and Maroto-Valer M, Integration of CO2 capture and storage based on pH– swing mineral carbonation using recyclable ammonium salts, Energy Procedia 4 (2011) 4930–4936. [7] Gerdemann S J, Dahlin D C, O’Connor W K and Penner L R, Carbon dioxide sequestration by aqueous mineral carbonation of magnesium silicate minerals, DOE-ARC, 2003, 018, http://www.osti.gov/bridge/ [8] Teir S, Revitzer H, Eloneva S, Fogelholm K-J, Zevenhoven R, Dissolution of natural serpentinite in mineral and organic acids, Int. J. Miner. Process. 83 (2007) 36–46.
New equipment for characterization of rocks for geological CO2 storage in coal seams Cienfuegos, P. & Loredo, J. Mining and Exploration Department – University of Oviedo - SPAIN
[email protected] Abstract The geological storage of CO2 in coal seams is an emerging option in the portfolio of mitigation actions for reduction of atmospheric greenhouse gas concentrations. A background study focused to the selection of favorable sites for CO2 geological storage are necessary steps, and in the selection of reservoirs for CO2 sequestration a complete petrophysical characterization of the sample is necessary. To complement the classical petrophysical parameters measured on the rocks of the geological formation with potential to be used to store the injected CO2, a new equipment has been designed and constructed to simulate at a laboratory scale the interaction between the rock and the injected CO2, at different pressure conditions simulating depths of the geological formations up to 1 000 meters. Essays focused to study the alterability of the rock in contact with CO2 either in subcritical or supercritical state, as well as essays for CO2 injectivity on the rock can be accomplished. 1. Introduction Tests and studies on characterization of rocks have been used to understand the interaction between physical properties, the chemical composition of the rock and the industrial use. The aim is to determine the measurable properties of the rock with special interest in this new industrial application. Two more interesting aspects of the geometry of space are porosity and the study of the interaction of the rock with supercritical CO2 (storage conditions). Therefore, we must consider the status of the rock before and after its contact with CO2, and its behavior, as it is important to determine the new conditions. The first phase consisted on the characterization of technology of fresh rock samples, and in the second phase, will be identical characterization changes after the test. The research began with a petrological study indicates that rock your petrographic analysis, microfractographic, morphological and chemical. Subsequently, we tests of water and mechanical properties parallel. These tests allow us to obtain the value of open porosity of the sample and its degree of saturation, deducted as well as important information geometry its empty spaces (pores and fissures) of great interest in the geological storage of any fluid. The period for the completion
of these tests can vary from one to three months, depending on the type of rock. Mechanical tests are faster and they get information that allows determining the elastic constants of tested rocks. New test equipment was necessary to develop the interaction of the rock with CO2. 2. 2. Experimental section: Design of a new equipment for complementary petrophysical characterization of rocks New equipment, called RockTestCO2, has been designed to carry out the study of the interaction of CO2 in rocks at high pressure conditions, simulating the process that occurs during the injection of CO2 in underground geological formations (figure 1).
Figure 1. Photogram and diagram of operation of test equipment named ROCKTESTCO2. The central part of the equipment consists of a AISI 304 stainless steel chamber with internal dimensions of 320x320x320 mm, 40 mm thick and an approximate weight of 200 kg. A sample rock is introduced with approximate dimensions of 270x270x270 mm. It also provides two 280x280 mm racks of stainless steel AISI 304 for the fixing of prismatic test specimens of 50 mm square and cylindrical samples with a diameter of 54 mm (figure 2).
Figure 2. Details of stainless steel chamber.
The CO2 is introduced into the chamber by a rod directly embedded into a drill that will have been previously done on the rock (figure 3, left), and it is inserted through the central part. The water enters the bottom of the camera. There are two metering pumps Dosapro mark MILTON ROY, with a flow rate up to 7.5 L / h, a pressure up to 300 bar and a AISI 316 L stainless steel dispenser (figure 3, right). These two pumps are lubricated in oil in a waterproof cap and speed reducers are built into the mechanics.
Figure 3. Details for two metering pumps “Dosapro”. The closing of this camera is achieved through the action of a hydraulic cylinder, and the end of this cylinder has a tray on which the rock is placed to study, so that the action of hydraulic cylinder allows both entering the rock inside the camera and closing it. As a safety feature, there is a switch that lets you keep closing pressure of the chamber throughout the procedure, preventing accidental opening of the system. It also has a ruptured disk and additional elements for protection and security. A camera 10 is coupled 180 W resistors and two 200 W resistors to heat the interior of it until the desired temperature, using a temperature sensor and a digital controller. The hydraulic closure is capable of exerting a force of over 95 tons, and it consists of a hydraulic cylinder of 200x140 mm and 500 mm in length, a tank with its accessories, filter screens, levels, etc. There is a motor-group with two pumps, and the low pressure gives the flow required for rapid movement and a pressing cylinder for 320 bar, as well as control valves and the associated control. The entire assembly approximately weighs 1 300 kg. This equipment includes a cabinet where both switches activation of different elements by the user, such as electrical control elements and protections necessary to ensure the safety of the people and the equipment according to current regulations (figure 4).
Figure 4. ROCKTESTCO2 test equipment. Basically, the new test consists of contacting the rock sample with CO2 in the natural reservoir conditions of pressure and temperature. The operational parameters of this equipment allow simulating in the laboratory the geological storage of CO2 in the natural conditions of pressure, temperature and salinity. 3. Results and Discussion Five samples of rocks (carbonates and sandstones) are used in initial tests. It is necessary to know the physical properties of these rocks in their natural state. For this study performed petrological and petrophysical studies and chemical and morphological analysis. Subsequently, subjected to interaction with CO2 for a variable duration from weeks to months, and finally, it is necessary to re-make all petrophysical tests chemical and morphological analysis to obtain differences by comparison of the physical properties and chemical composition of rocks (table 1). The physical properties are possible to observe the variation in short term tests of several months. Possible variations in chemical composition need more time. Table 1. Data indicate changes in parameters of physical properties as density and porosity. PARAMETER Density mean , ρd Desv. (Kg/cm3) Open mean porosity, no (%) Desv.
A 2638.24
ACO2 2629.73
B 2491.10
SAMPLES BCO2 C 2487.37 2614.37
CCO2 2577.11
D 2771.86
DCO2 2756.24
7.19
8.79
8.26
8.70
39.68
33.96
4.46
4.40
4.62
4.99
7.71
8.89
4.54
6.42
0.56
1.80
0.43
0.48
0.21
0.73
0.82
1.30
0.06
0.08
Preliminary results of petrophysical properties confirm those obtained by other laboratories [1], [2]. It shows a slight increase in effective porosity and a decrease in the mechanical strength.
4. Conclusions The design and construction of this equipment ROCKTESTCO2 allows us to investigate known physical and chemical processes that occur between the rocks store/seal and the CO2 injected into geological storage of CO2. Simulation of storing CO2 deep is essential to know the behavior of rocks (store or seal) in its interaction with the CO2. Finally, besides the mathematical modelling, it is necessary to develop a new petrophysical characterization equipment to simulate the pressures and temperatures at which rocks are the target of a geological storage of CO2. References 1.
Benson, S.M., L. Tomutsa, D. Silin, T. Kneafsey and L. Miljkovic: Corescale and Porescale Studies of Carbon Dioxide Migration in Saline Formations, Proceedings of 8th International Conference on Greenhouse Gas Control Technologies (GHGT8), IEA Greenhouse Gas Programme, Trondheim, Norway, June 19-22, (2006).
2. Hovorka, S.D., C. Doughty, S.M. Benson, K. Pruess, and P.R. Knox: “The Impact of Geological
heterogeneity on COB2B Storage in Brine Formations: A Case Study from the Texas Gulf Coast,” Geological Storage of Carbon Dioxide, S.J. Baines and R.H. Worden (eds.) Geological Society, London Special Publications, 233, p. 147-163. (2004).
Oviedo ICCS&T 2011. Extended Abstract
The Current State of Affairs of Coal Research in U.S. Universities Jonathan P. Mathews1, Bruce G. Miller1, Chunshan S. Song1, Harold H. Schobert1, Francois Botha2, and Robert B. Finkleman3 1
John and Willie Leone Family Department of Energy & Mineral and EMS Energy Institute, 126 Hosler Building, The Pennsylvania State University, University Park 16802, USA.
[email protected] 2 Illinois Clean Coal Institute, 5776 Coal Drive, Suite 200, Carterville, IL 62918, USA 3 University of Texas at Dallas, Richardson, TX 75080, USA Abstract An ISI Web of Knowledge (using the web of science database) evaluation of journal articles with “coal” in the title (in English-language journals) was performed, for the periods 1970 to 2010 and 2000 to 2010, as one approach to evaluate the historically and currently active research centers in coal science. The approach underestimates the contributions but provides a basis for comparisons. Contributions were broken down by research institutions and by countries of contributing authors using analysis tools within ISI Web of Knowledge. The United States has 30% of the publications (between 1970 to 2010), with Japan contributing 7.8% and the People’s Republic of China 7.5%. England, Australia, India, Canada, Poland, Spain, Germany, and France contributed between 5 to 2% each. However, China has been leading the publication production since 2006. Japan’s publications are relatively steady while U.S. publications have declined after a high point during 1984-2002 when a small resurgence occurred. This paper reports on the coal science contributions of U.S. universities and determines journal article publication activity level and focus. The leading academic institutions’ publication records were evaluated using Wordle to visually determine research focus areas through word frequency analysis of the journal article titles. Similarly, active authors (for the period of analyses) were identified using this approach. There has been a significant decline in the U.S. academic institutions that are active in coal science. Among the academic entities, the leading institutions (quantity of journal articles) were The Pennsylvania State University (Penn State), Kentucky, West Virginia, Southern Illinois, MIT, Utah, Brigham Young, Pittsburgh, Illinois, Ohio State, Virginia Tech, Wyoming, Auburn, Carnegie Mellon, North Dakota, Iowa, California at Berkeley, Tennessee, Texas, Purdue, Texas A&M, Missouri, Georgia, and Western Kentucky. Of these, about half are still “active” in “coal science” as defined as 15 coal science publications (by this search approach) between 2000 to
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Oviedo ICCS&T 2011. Extended Abstract
2010 where the focus is science and engineering research on coal but does not include coal-related areas such a post-combustion pollution control or the various catalytic aspects of coal gasification products. 1. Introduction The U.S. is second only to China in the amount of coal produced and consumed, with about 1.1 billion short tons consumed annually. Projections estimate a 6% increase in coal use between 2008 and 2035 [1]. Even if constraints on CO2 emissions were to be mandated in the U.S., substantial amounts of coal will still be used for the foreseeable future. Coal remains the only strategically secure major source of energy in the U.S. If energy security concerns are high or oil prices rise, higher projections are likely [1]. Although coal science is a relatively mature field new perspectives and more detailed understanding of coal characteristics are necessary to address new or alternative mining approaches, beneficiation, clean(er) combustion technologies, growing environmental concerns, the use of lower quality coals, and various emerging societal issues. In short, coal science can help to ensure the efficient, cost effective, environmentally compatible use of the abundant coal resources domestically and internationally. Coal research is faced with very significant challenges: substantial retirements of senior scientists, the cyclic nature of funding; traditionally conservative attitudes of the mining industry; and shifts in government funding towards renewable energy research. Many coal researchers, who started their careers in the energy crisis of the 1970s are now retired or soon will be. The mass influx of these coal researchers in the late 1970s and early 1980s has resulted in a ‘missing generation’ of coal scientists as most available coal-related research and academic positions have been filled by these researchers for the past 30 years. This imminent loss of expertise is significant for the continued progression and retention of the institutional memory without which the ‘wheel will be reinvented’. Funding cycles also strain the talent pool as researchers move into the “hot” funding areas without returning to the coal arena. This paper examines the current state of affairs for U.S. coal science academic centers. Here coal science is defined as the science and engineering research on coal – uses (primarily combustion and coking), occurrence, distribution, properties, technology options, environmental and health impacts, beneficiation, and ash chemistry but does not include coal-related areas such a post-combustion pollution control or the various catalytic aspects of coal gasification products.
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Oviedo ICCS&T 2011. Extended Abstract
2. Methodology An ISI Web of Knowledge (using the web of science database) evaluation of journal articles with “coal” in the title (in English-language journals) was performed, for the periods 1970 to 2010 and 2000 to 2010, as one approach to evaluate the historically and currently active research centers in coal science. The ISI Web of Knowledge tools were used to evaluate the contribution of countries as well as the academic entities in the United States. The U.S. data were transferred into an Endnote library that was used to generate an authors list and a journal titles listing for evaluation with Wordle [2]. Wordle creates a visual representation of text frequency. Note: the publications of U.S. federal and state agencies are not included in this survey. 3. Results and Discussion Table 1 provides one indication of global institutional historic productivity, which consists of the number of journal records for each institution with “coal” in the title of journal articles using the ISI Web of Knowledge [3] selecting only the Web of Science (Science Citation Index Expanded) database for English language publications between 1970 and 2010. While this will also include coal mining, mine reclamation, CO2 climate change, energy policy, etc., those are expected to be a relatively small portion of the coal research for most institutions. This approach however, is one measure to identify those centers that have produced copious coal-related English-language research publications. The search resulted in >22,700 journal publications. The top 100 entities were analyzed (shown in Table 1) and a breakdown of the total publications by country of origin obtained is shown in Fig. 1. Those entities listed in Table 1 that are shown in bold had >15 publication in the last decade (2000 to 2010). These values are certainly an underestimation of research productivity (this research approach found only 10 of the lead authors 18 mostly-recent applicable papers); however it is a useful means of comparing institutions. Several notable institutions have clearly moved away from coal research during this period. Fig 1. also shows the analysis of publication frequency per year for the United States (30%), Japan (7.8%), and China (7.5%) the three leading countries publishing English language coal research papers. For the U.S., there was a rapid increase in coal articles after the first energy crisis, peaking in 1984 with a general decline until 2002 where publication quantities were on par with Japan and China. Since 1983, Japans publication rate has been relatively steady. China’s publications, however, have rapidly increased since the late 1990s and have now significantly surpassed those
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Oviedo ICCS&T 2011. Extended Abstract
of the U.S. Thus, what were/are the active U.S. academic centers and their areas of focus? Table 1. Universities and Institutions Sorted by Frequency of “Coal” in Journal Article Titles (1970-2010)*
*English language, excluding DOE and Geologic Surveys. Brackets represent article count (estimates). Those in bold had >15 papers in the last decade (2000-2010) (date of analysis December 2010)
Figure 1. Journal article by country of origin (note authors of collaborative works are counted in the percentage of each country) between 1970 and 2010 and the publication frequency per year for the United States, China, and Japan The Pennsylvania State University is one of the few academic centers where there are formal education opportunities in coal science. Historically this has been through the Fuel Science program. The current iteration of this program is the Fuel Science option Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
within the graduate program of the Department of Energy and Mineral Engineering [4]. Over 200 research degrees (M.S. and Ph.D.) have been awarded with coal in the title between 1970 and 2010 in various departments. Much of the coal research is within the Earth and Mineral Sciences (EMS) Energy Institute [5]. Figure 2 shows the Wordle analysis of those journal titles with the relative frequency of occurrence being illustrated by font sizes (color use is decorative). The analysis shows the expected trend of activity in nearly all aspects of coal science, notably coal liquefaction (including coal to jet
Figure 2. Wordle generated image of the frequency of journal article titles (coal has been omitted) for Penn State (1970-2010). Frequency of “liquefaction” = 30. fuel), combustion (bench and pilot-scale) and gasification, mineral matter or ash characterization and behavior, coal characterization, structure and behavior, coal structural modeling, coking, petrology, coal cleaning and preparation, CO2 sequestration in coal, and coal-water slurry research. All coal ranks are represented and the EMS Energy Institute houses the Penn State Coal Sample Bank and Database [6, 7]. Over the review period the most active coal scientists were Drs. H.H. Schobert (author and H.H. Storch Award recipient), P. Painter, A. Davis (retired), P.L. Jr. Walker [8-10] (deceased), P. Given [11] (deceased), R.G.L. Austin (retired), P.G. Jenkins (retired), A.W. Scaroni (no longer active—administration), J.P. Mathews (author), M.M. Coleman (retired), W. Spackman (retired), G.D. Mitchell, P.G. Hatcher (currently at Old Dominion University), M. Sobkowiak, S. Falcone Miller, C.S. Song (author, EMS Energy Institute Director, and H.H. Storch Award recipient), and C. Burgess-Clifford, among many others. The University of Kentucky houses the Center for Applied Energy Resources (CAER) [12] and several noted coal scientists: Drs. J. Hower (former editor of International Journal of Coal Geology), G.P. Huffman (retired), F.E. Huggins, C.F. Eble, B.H. Davis, Submit before May 15th to
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N. Shaw, and F. Derbyshire (deceased, former CAER director) [13, 14] , among others. A concentrated location of coal science that has focused on coal petrology and geology (often in collaboration with the state Geologic Survey), coal liquefaction, combustion, coal processing/upgrading, mineral matter and ash issues, carbon materials, and waste combustion product uses. Still very active, CAER has produced 106 journal articles addressing coal in the last decade. These articles cover a wide range of activities. West Virginia University houses the National Research Center for Coal and Energy [15]. The interests are in coal liquefaction, combustion, gasification (both traditional and underground) and coal analysis, coal waste use, and coal-derived carbons. The university also has a large mining program with a publication concentration in mining health, as well as coal beneficiation. Recently coal-bed methane and CO2 sequestration in coal are also active research areas. The active coal scientists (not including authors involved in coal workers health-related research) during the period of analysis were: D. B. Dadyburjor, J.W. Zondlo, M.S. Seehra, A.H. Stiller, C.Y. Wen, and R.G. Ames, among others. Southern Illinois University houses the Coal Research Center formed to stimulate and coordinate the efforts to improve coal mining and coal use [16]. The Department of Geology also houses the Coal Characterization Laboratory (mostly petrology orientated). Illinois has the largest of the U.S. bituminous coal fields but faces the very significant challenge of utilizing high-sulfur coal. There is a wide range of activity with the obvious focus of coal cleaning, desulfurization, combustion, and petrology. The active individuals during the period of evaluation were noted coal petrologist J.C. Crelling (semi-retired), S. Lavani, M.K. Mohanty, C.B. Muchmore, R. Honakar, and S. Harpalania, among others. A recent addition is the petrologist S. Rimmer. Massachusetts Institute of Technology was very active in coal research between 1980 and 1995. The Wordle analysis shows a concentration in combustion and (rapid) pyrolysis [17]. This is no surprise given the notable coal scientists: A. Sarofim (no longer at MIT), J.B. Howard (deceased) [18], W.A Peters, J.M. Beer, among others. MIT published the influential future of coal report [19], and is very active in clean coal aspects, specifically carbon capture and sequestration [20]; however, it has not been as active as a coal research center, in coal science as defined here, beyond a few individuals. University of Utah is notable for both pilot/lab-scale coal combustion (often in collaboration with Brigham Young University) and quantitative NMR applications to Submit before May 15th to
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coals and coal-related solids/liquids, pyrolysis mass-spectroscopy, among other areas. They run an active Clean Coal Program [21]. There is an active educational component in the former Department of Chemical and Fuels Engineering [22] but now the renamed Department of Chemical Engineering. There remains an active interest in energy and fuels. The coal scientists active during the period of the analysis were R. Pugmire (active in both research and administration), H.L.C. Meuzelaar (not recently active), W.H. Wiser (retired), D.M. Grant (retired?), L.L. Anderson, J.M. Veranth, A.F. Sarofim, and M.S. Solum, among many others. This institution is particularly noteworthy due to its broad collaborative record. Brigham Young University is relatively small in comparison to a number of the other universities but has a coal combustion focus housing the Advanced Combustion Engineering Research Center [23], often in collaboration with the University of Utah. Interests are pulverized coal combustion, pyrolysis, gasification, and modeling, among a wide range of topics. The authors active in the period of evaluation were: the noted combustion scientists: L.D. Smoot and T.H. Fletcher, P.O. Hedman, and M.L. Lee, among others. The University of Pittsburgh: was the home to very notable coal research in the “golden era” under Dr. I. Wender [24]. Currently the university is noted for running the successful Pittsburgh Coal Conference [25]. There was a focus on liquefaction from the 1980s to 1990s, along with coal-dust characterization and coal processing, among others. Active authors were Y.T. Shah, G.E. Klinzing (no longer active – administration), J.W. Tierney (retired), and I. Wender (retired and H.H. Storch Award recipient), among many others. There has been only limited activity recently. University of Illinois at Urbana-Champaign’s history in coal research started in 1901 when S. Parr founded the now Department of Chemical and Biomolecular Engineering. UI also houses the state’s Geological Survey, where the ISGS Coal Section is primarily concerned with the study of coal bearing Pennsylvanian rocks in the Illinois coal fields [26]. UI was active in combustion, coal geology, gasification, ash, petrology, and characterization, broadly defined. Recent activity has included CO2 sequestration in coal. Ohio State University: The state of Ohio is one of the six leading states for coal production. Much of the historic work in the period evaluated was related to combustion, which is defined broadly due to the presence of noted scientist Dr. R. Essenhigh (formally of Penn State). Work includes generation and use of coal bySubmit before May 15th to
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products [27]. Clean coal research has continued under Dr. L.S. Fan on coal gasification and chemical looping combustion, while much of the other coal-related publications are focused on environmental, watershed, and mine reclamation issues. Virginia Polytechnic Institute and State University: Virginia Tech houses the Virginia Center for Coal and Energy Research [28] and the Department of Minerals and Mining Engineering [29] and has a long history of coal research. The Wordle analysis shows a concentration in ash, combustion, coal cleaning, solvent-refined coal, and a variety of environmental interests. For example, much of the ash interests are heavy metals and watershed issues. This is another institution where coal-science work has dwindled to only a few applicable papers (as defined here) in the last decade. Those who were active: D. S. Cherry, L.T. Taylor, and R.K. Guthrie, among others. University of Wyoming: Wyoming produces more coal than the next five leading states combined [30]. As such, it would be expected to be a center of coal research. The University of Wyoming [31] and the Western Research Institute [32] are separate entities but have a strong history of collaboration with a clear and expected focus on the strategic use of the large subbituminous coal reserves with a focus on liquefaction, gasification, coal liquids characterization, coalbed methane, among others. Those active in the period evaluated here are: R.J. Hurtubise, H.F. Silver, H.W. Haynes, and others. The university has a strategic partnership with the university of Queensland Australia and houses biannual conferences alternating between those locations [33]. The state has made strategic investments in subbituminous coal broadly with the creation of the Clean Coal Research Account [34] and thus coal research activities are expected to increase. Dr. J. G. Speight also generated a number of coal books here during this period [35, 36]. Auburn University: houses the Coal and Energy Laboratory [37] and was active in liquefaction, co-processing, combustion. Recent activity (last decade) has mostly been focused on environmental exposure issues. Those active in the time frame evaluated were: C.W. Curtis, J.A. Guin, and A.R. Tarrer among others. Carnegie Mellon University (Pittsburgh) is active in coal research although much of the current activity is system analysis and economic modeling with a focus on energy policy. The university houses the relatively unique Engineering and Public Policy department in the College of Engineering [38]. There are also interests in coal tar and water interactions, as well as mathematical modeling of devolatilization and heat and mass transfer. Leading authors during the period of evaluation were: E. Rubin (policy related) and R.G. Luthy, among others. Submit before May 15th to
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University of North Dakota is located near the lignite deposits of the Fort Union Region. UND houses the Energy and Environmental Research Center (EERC) [39]. They are active in gasification, combustion, ash chemistry, and emissions control, with an emphasis on mercury capture. UND’s research started by studying the state’s vast lignite resources and investigating potential uses for them; however, over the years they became a leading institution on low-rank coal science and technology, and currently are active in studying all ranks of coal. Active authors during this period were: J.W. Nowok (retired), S.A. Benson, among others. Iowa State University [40] was very active in coal research in the 1980s and somewhat active in the 1990s but has had little recent coal-science activity. The Wordle evaluation showed a concentration in combustion, mostly considering emissions and waste material, with a wide range of interests from microwave applications, fine coal agglomeration, to exploring new characterization techniques. Those active during the period of analysis were: R. Markuszewski, T.D. Wheelock, and C.D. Chriswell among others. Ames Laboratory [41] is also located here and specializes in materials for energy application. University of California at Berkeley has been active in coal research in a variety of fields. The coal interests have ranged widely from coal liquids, particulates/surfaces, and trace elements. Those active in the period of analysis were: D.W. Fuerstenau, L. W. Tian (now in Hong Kong), and A.T. Bell, among others. There has been recent activity in the areas of particulate matter and permeability. University of Tennessee [42] is close to the Appalachian bituminous coal basin but the production of coal from this state is small, producing the least amount of coal in the basin, only 2% of the production of the leading state (West Virginia) in this region [42]. However, the state is a significant user of coal and is located close to Oak Ridge National Lab [43], which was also active in coal research. The Worlde analysis showed a range of interests including PAH, toxicity, catalytic gasification, among others. Those active in the period of analysis were: G. Mamantov, E.L. Wehry, and J.W. Larsen (now retired from Lehigh University), among others. University of Texas is a multi-campus university with the coal research being mostly in Austin [44] with some work in Dallas [45]. Texas has both lignite and bituminous coal deposits, is the leading coal producing state for the Interior basin, is the state that uses the most coal in the U.S. [46], yet the quantity of coal science research is not in proportion to its extensive coal use. The Wordle analysis showed an interest in Submit before May 15th to
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underground gasification (modeling), ash chemistry (water contamination and trace elements), among others. Those active in the period of analysis were: T.F. Edgar, R.K. Guthrie (retired), and D.D. Cherry among others. A relatively new addition to the Dallas campus is R. B. Finkelman (author, formally with USGS). Purdue University houses the Center for Coal Technology Research [47]. It was formed as a state agency in 2004 to “promote the use of Indiana's coal reserves in an economically and environmentally sound manner”. The bulk of the coal work was in the 1980s with only a few publications in the 1990s. Activity has increased however in the last decade. The Wordle analysis showed that there was a concentration in coal structure characterization (often solvent swelling related). Those active in the period of analysis were: N.A. Peppas, L.M. Lucht, and C.K. Chao, among others. Texas A&M: The Wordle analysis shows an interest in co-firing (biomass and other material), coal-water slurry, and coal liquids, among others. Those active in the period of analysis were: K. Annamalai and J.M. Sweeten, among others. The Missouri Education System has two universities. The Missouri University of Science and Technology (Missouri S&T), formally The University of Missouri-Rolla [48]) and the University of Missouri at Columbia (Mizzou) both active in coal research, There was activity in coal-log transportation (Mizzou), ash and inorganics, with an emphasis on trace elements (Missouri S&T). The University of Georgia the university [49] has coal-research centered around trace elements and exposure. As most of the work is removed from coal-science, as defined here, it is not a coal center but is included for completeness. University of Western Kentucky: This university is of note for the minor in coal chemistry and a Masters of Science option within the chemistry department and the Institute for Combustion Science and Environmental Technology [50]. The bulk of their activity has been in the last decade. Their focus is on combustion and mercury speciation/emissions/capture and co-firing biomass (often chicken litter) with coal, among other research interests. Those active in the period of analysis were: W.P. Pan, Y. Cao, C.W. Chen, and J.T. Riley, among others. Others academic centers: Colorado State University was active in fly-ash chemistry and NMR spectroscopy with G.E. Maciel, D.F.S. Natusch, and A. Jurkiewicz being active among others. Lehigh University has been a center for coal science due to the combination of the work of noted coal scientist J. Larsen (retired—former editor of Energy & Fuels) and their Energy Center [51] with a focus on process optimization, Submit before May 15th to
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combustion, and processing. Brown University has a long history of coal science with several coal scientists: E. Suuberg (editor of the journal Fuel), R. Hurt, and J. Calo. The University of Ohio houses the Ohio University Coal Research Center in the Russ College of Engineering and Technology [52]. The focus there being air quality issues rather than coal science (as defined here). The University of Chicago was active in coal science under L. Stock and his colleagues (Dr. Stock’s journal articles alone numbered 50 publications between 1970 to 1997). 4. Conclusions There has been a notable rise and decline of coal-science publications from the U.S. Currently, the U.S. generates fewer journal articles than China and no more than half of the historically active coal science centers are still active. Wordle analyses were used to determine focus areas and authors for U.S. academic entities. Among the U.S. academic entities the leading institutions (quantity of journal articles) were Penn State, Kentucky, West Virginia, Southern Illinois, MIT, Utah, Brigham Young, Pittsburgh, Illinois, Ohio State, Virginia Tech, Wyoming, Auburn, Carnegie Mellon, North Dakota, Iowa, California at Berkeley, Tennessee, Texas, Purdue, Texas A&M, Missouri, Georgia, and Western Kentucky. References [1] EIA/DOE Annual Energy Outlook. http://www.eia.doe.gov/oiaf/aeo/index.html [2] Feinberg J Wordle. http://www.wordle.net/ [3] Thiomson Reuters ISI Web of Knowledge. http://apps.isiknowledge.com/ [4] The Pennsylvania State University Department of Energy and Mineral Engineering. http://www.eme.psu.edu/ [5] The Pennsylvania State University The EMS Energy Institute. http://www.energy.psu.edu/ [6] The Pennsylvania State University Penn State Coal Sample Bank and Data Base. http://www.energy.psu.edu/copl/index.html [7] Glick DC, Davis A, Operation and composition of the Penn State Coal Sample Bank and Data-Base. Organic Geochemistry 1991, 17, (4), 421-30. [8] 1969 Storch award: Dr Philip L. Walker, Jr. Fuel 1970, 49, (1), 102-3. [9] Philip L. Walker Jr. Publications. Carbon 1991, 29, (6), 693-701. [10] Marsh H, A tribute to Philip L. Walker. Carbon 1991, 29, (6), 703-4. [11] Derbyshire FJ, Obituary: Dr Peter Given. Fuel 1988, 67, (8), 1167-. [12] University of Kentucky Center for Applied Energy Research. http://www.caer.uky.edu/ [13] 1996 Storch Award—Frank J. Derbyshire. Fuel 1997, 76, (2), 99-. [14] 1997 Henry H. Storch Award—Frank Derbyshire. Fuel 1997, 76, (1), 1-. [15] West Virginia University National Research Center for Coal and Energy. http://www.nrcce.wvu.edu/about.cfm [16] Southern Illinois University at Carbondale Coal Research Center. http://www.crc.siu.edu/ [17] Mechanical Engineering at MIT Energy Science and Engineering. http://web.mit.edu/ese/ (Accessed February 22nd, 2006), [18] 1983 Storch Award—Jack Howard. Fuel 1983, 62, (9), 1101-. [19] MIT The future of coal, an interdisciplinary MIT study; 2007.
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Oviedo ICCS&T 2011. Extended Abstract [20] Massachussetts Institute of Technology (MIT) Carbon Capture & Sequestration Technologies. http://sequestration.mit.edu/research/index.html [21] The Utah State University Clean Coal Program. http://www.cleancoal.utah.edu/ [22] The University of Utah Department of Chemical Engineering (formaly Department of Chemical and Fuels Engineering). http://www.che.utah.edu/index.php [23] Bringham Young University Advanced Combustion Engineering Research Center. http://www-acerc.byu.edu/ [24] Wender I, Coal science in a changing world. Fuel 1985, 64, (8), 1035-8. [25] IPCC International Pittsburgh Coal Conference,. http://www.engr.pitt.edu/pcc/ [26] Illinois Geological Survey Illinois Geological Survey. http://www.isgs.illinois.edu/aboutisgs/about.shtml [27] Ohio University Ohio Coal Research Center. http://www.ohio.edu/ohiocoal/ [28] Virginia Center for Coal and Energy Research Virginia Tech. http://www.energy.vt.edu/ [29] Virginia Tech Department of Mining and Minerals Engineering. http://www.mining.vt.edu/ [30] EIA Domestic distribution of U.S. coal by origin state, consumer, destination and method of transportation. http://www.eia.doe.gov/cneaf/coal/page/coaldistrib/a_distributions.html [31] Clean Coal Technology Center University of Wyoming. http://www.uwyo.edu/ser/info.asp?p=3737 [32] Western Research Institute History. http://wri.uwyo.edu/about.aspx [33] Com. ACCD Advanced Coal Technologies Conference. http://www.advancedcoalconference.com/ [34] The University of Wyoming Clean Coal Technology Fund. http://www.uwyo.edu/ser/research/clean-coal/index.html [35] Speight JG, Knovel (Firm), Handbook of coal analysis. In Chemical analysis v. 166, Wiley-Interscience: Hoboken, N.J., 2005; pp x, 222 p. [36] Speight JG, The chemistry and technology of coal. 2nd ed.; M. Dekker: New York, 1994; p xi, 642 p. [37] Auburn University Coal and Energy Laboratories. http://www.eng.auburn.edu/research/dept-research/chen.html [38] Carnegie Mellon University Engineering and Public Policy. http://www.epp.cmu.edu/ [39] University of North Dekota Energy & Environmental Research Center. http://www.undeerc.org/ [40] Iowa State University http://www.vpresearch.iastate.edu/institute/ [41] Ames Laboratory (DOE) Ames Laboratory. http://www.ameslab.gov/research [42] Freme F Energy Information Administration U.S. coal supply and demand 2009. [43] Oak Ridge National Laboratory Oak Ridge National Laboratory. http://www.ornl.gov/ [44] University of Texas at Austin University of Texas at Austin. http://www.utexas.edu/ [45] University of Texas at Dallas University of Texas at Dallas. http://www.utdallas.edu/ [46] DOE/EIA Annual coal report 2008. http://www.eia.doe.gov/cneaf/coal/page/acr/acr_sum.html [47] Purdue University Center for Coal Technology Research. http://www.purdue.edu/dp/energy/CCTR/ [48] University of Missouri University of Missouri. http://www.missouri.edu/ [49] University of Georgia http://www.uga.edu/ [50] University of Western Kentucky Institute for Combustion Science and Environmental Technology. http://www.wku.edu/ICSET/comblab.htm [51] Lehigh University Energy Research Center. http://www.lehigh.edu/energy [52] Ohio Coal Research Center Ohio University. http://www.ohio.edu/ohiocoal/
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The Current State of Coal Research In The United Kingdom, Germany, Australia, and South Africa Jonathan P. Mathews1, Bruce G. Miller1, Chunshan S. Song1, Harold H. Schobert1, Francois Botha2, Robert B. Finkleman3, Alan Chaffee4, 1
John and Willie Leone Family Department of Energy & Mineral and EMS Energy Institute, 126 Hosler Building, The Pennsylvania State University, University Park 16802, USA.
[email protected] 2 Illinois Clean Coal Institute, 5776 Coal Drive, Suite 200, Carterville, IL 62918, USA 3 University of Texas at Dallas, Richardson, TX 75080, USA 4 Monash University, Victoria 3800, Australia 1. Introduction As indicated in an earlier paper [1] there is about to be a significant decline in coal science capability, for certain countries, as key experienced individuals retire and institutions refocus. It was therefore desirable to determine those locations with a coal focus, their research interests and level of current activity based on journal article publication record. Of the 22717 journal articles with coal in the title from an ISI Web of Knowledge English language evaluation using the web of science database: the leading publishing countries between 1970 and 2010 were: United States (30%), Japan (7.8%), China (7.5%) and England (5%). Australia (5%), India (4%), Canada (4%), Poland (4%), Spain (3%), Federal Republic of Germany (3%), France (2%), Turkey (2%), Russia (2%), South Africa (1%) and the Netherlands (1%). These countries have very different general trajectories in the frequency of coal-science focused publications: declining (USA, UK, Germany), consistent (Japan), or rapid rise (China). This paper focuses on the United Kingdom, Germany, Australia and South Africa.
2. Methodology An ISI Web of Knowledge (using the web of science database) evaluation of journal articles with “coal” in the title (in English-language journals) was performed, for the periods 1970 to 2010 and 2000 to 2010, as one approach to evaluate the historically active and currently active research centers in coal science. The ISI Web of Knowledge tools were used to evaluate the contribution of countries and research entities. The data were transferred into an Endnote library that was used to generate an authors list and the journal titles listing for evaluation with Wordle [2]. Wordle creates a visual
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representation of text frequency for the determination of key phrases and topics in titles and contributing authors.
3. Results and Discussion Fig. 1 shows the frequency of journal articles, with coal in the title of English-language journal articles (web of science database), versus year for the UK (here England, Scotland, and Wales), Australia, Germany, and South Africa. There is a general peak for all countries between 1980 and 1985, a decline from the peak until around 1991. For both the UK and Germany current output of articles is half of the historic high. Australia has a more prominent cyclic nature peaking in 2000 and 2009 presumably in response to funding opportunities. South Africa produced an average of only 2 papers per year in the 1970’s, 8 in the 80’s, 6 in the 90’s, with a significant increase after 2003.
Figure 1. Publication frequency of journal articles with coal in the title by country of author contribution(s) United Kingdom The United Kingdom was the birthplace of the coal-fueled industrial revolution. It is of no surprise that it was also a center of excellence for coal science over much of the history of coal science research. The UK has produced many noted coal scientists such as P. Given [3], F. Derbyshire [4], H. Marsh, and C. Snape [5]. Previously very active coal centers such as Newcastle and Sheffield Universities have refocused their interests as coal became of marginal interest regionally. Coal production had dropped to 12%
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(1999) of the 1913 peak output with a relatively steady decline since 1960 [6]. Those universities of note for coal science centers are now Nottingham, Leeds, and Imperial College London. There is a generally reduced level of interest in coal science concurrent with reduced domestic coal production.
Imperial College London has coal research within the Energy Engineering group of the Chemical Engineering and Chemical Technology department [7]. There activities are focused on the range of solid fuel processing technologies (combustion, gasification, pyrolysis, liquefaction) for the main utilization industries (power generation, fuel production, and chemicals production). Key individuals are: R. Kandiyoti, P. Fennell, M. Millan, N. Paterson, A. Herod (retired) [7]. One particular specialty of this group has been the characterization (advanced analytical analyses) of heavy coal liquids.
Nottingham University [8] has one of the largest concentrations of coal scientists in the UK, although not all are currently active in the field, and several are relatively recent additions (thus their research productivity is dissipated among their previous institutions and universities by the approach utilized here). Activities have traditionally been focused on combustion, liquefaction, structural analyses (coal, trace elements, and mineral matter), processing, and beneficiation. Of particular note is their work on coal petrology (including chars and image analysis) and microwave applications to coal (housing the National Center for Industrial Microwave Processing [9]). The coal scientists include: M. Cloke (administration), K. Steel (now at the University of Queensland, Australia), C. Snape [5] (administration - Director Energy Technologies Research Institute [10]) but still active in research, N. J. Miles, J. P. Wright, E. Lester, J. Patrick (special professor status, semi-retired but still active), S. Kingman, among others (such as M. Maroto-Valer, and J. Andrésen who are not currently active in coal). This latter group, along with C. Snape is also known for applying NMR analyses to coal although much of that work occurred in other institutions. Nottingham hosted the 2007 International Conference on Coal Science and Technology.
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Figure 1. Wordle view of the frequency of journal article titles 1970-2010 for Nottingham University Leeds University used to have the Department of Fuels and Energy. It changed and merged with other departments around 2004 into the School of Process, Environmental and Materials Engineering and offers Chemical Engineering and Energy Engineering degrees (among others) with research endeavors within the Energy and Resources Research Institute [11]. Their focus is combustion, pollution abatement, and biomass energy with strong ties still to coal science. Their stated vision is "to be recognized for internationally leading research in the sustainable development of natural resources, the sustainable use of fossil fuels and the development of renewable and future fuels."
Others: While not an academic institution, the IEA Clean Coal Center is also located in the UK and is worthy of mention, specifically for the high quality publications addressing many coal issues [12]. Strathclyde University, has P. J. Hall, (formerly C. Snape) and is also active in coal-based sequestration research.
Germany An industrial powerhouse, coal fueled the Germany economy and industrial complex. Hard coal production has declined from a peak in 1958 to producing 17% of that value
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in 2005 [13]. Underground coal mining is potentially slated to end in 2018 with the removal of coal subsidies. There are however large lignite reserves and Germany has been the leading producer of lignite coal doubling the U.S. production and almost doubling China’s [14]. Much of the coal science work is related to brown coal, coal-tar, gasification, and combustion.
Bergbau Forschung GMBH: An industrial company now named CarboTech AC GmbH specializing in activated carbon, activated cokes, and carbon molecular sieves from coal [15]. Activity stopped in the 1990’s under this name but with little activity since. A review of the petrology work at this laboratory is available [16].
The Max-Planck Institute for Coal Research: The Institute was formed in 1912 to study the chemistry and uses of coal. While it currently still retains the coal in the title, the focus is basic research in organic and organometallic chemistry, catalysis, and theoretical chemistry [17]. An evaluation of papers published between 2005-2008 showed that out of about 700 papers less than 10 contained coal in the title. However, historically the Institute was certainly an important center of coal research with pioneering gasification based coal-liquefaction research and the well-known FisherTropsch synthesis [18]. With the retirement of M. Haenel (2009) it is likely the end of coal research at this “coal” institution.
University of Stuttgart: The university houses the Institute of Combustion and Power Plant Technology [19], which was established in 1958 (as the Institute of Process Engineering and Power Plant Technology until a name change in 2009) with research focusing on combustion and gasification of solid fuels, air quality control, and various aspects of power plant technology. Recent activities include CO2 mitigation through oxyfuel, pre- and post-combustion capture processes, and renewable energy research including biomass co-firing and gasification. A key individual has been K. Hein (emeritus and past director of the Institute) now in Australia.
Others Institute of Geology and Geochemistry of Petroleum and Coal at RWTH Aachen University, specializes in coal petrology, coal-based sequestration and other coal aspects [20]. B. M. Kroos and several others are active. Technical University of Freiberg Submit before May 15th to
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(Saxonia) coal combustion and gasification research in the Institute for Energy Process Engineering and Chemical Engineering (Prof. Bernd Meyer) [21]. With core themes of geosciences, materials, energy and environment as well as a strategic partnership with the University of North Dakota coal-related science may increase. Engler-BunteInstitute of the Technical University of Karlsruhe [22]: coal and biomass conversion Prof. Rainer Reimert (retired).
South Africa South Africa ranks 6th in terms of global coal production (2009), is a significant coal exporter, and user of coal [14]. Coal is the major source for electricity and a coal-toliquid fuels and coal-to-chemicals industry (Sasol via gasification and Fisher-Tropsch synthesis) uses about 20% of the coal consumed [23]. After many years of relatively low-productivity of published coal research, relative to the importance of coal, South African coal science has seen a rebirth and increased activity. Much of this work is centered around Witwatersrand University and increasingly at University of the North West “Potch” campus. Cape Town held the 2009 International Conference of Coal Science and Technology, with a strong South African presence. There has also been expertise in gasification, combustion, and coal beneficiation due to the presence of high “ash” coals [24].
Witwatersrand University (Witts) located in Johannesburg has its origins as the South African School of Mines. While hard rock mining is still prominent at this institution, the bulk of the coal research has focused on coal fires, petrology, and coal quality issues of the inertinite-rich coals. There was also some coal mining: productivity, safety and health-related work. Those active in the period of evaluation were: D. Glasser, and R. M. S. Falcon (South African National Energy Research Institute Chair in Clean Coal Technology), among others. N. Wagner (petrologist) has recently (2007) joined the university’s Coal and Carbon Research Group [25] and thus the expansion of coal science is on going.
The University of Cape Town [26] is active in coal preparation, ash/waste, and coal cleaning issues. Academic offerings include a course on Fuels and Chemicals from Coal and Syngas. Active authors were: J. P. Franzidis, M. C. Harris, and P. Stonestreet among others. Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
Sasol is the major producer of coal-to-liquids and does so via in-direct liquefaction approaches. Thus as expected, there is considerable expertise in Fisher-Tropsch chemistry that is not covered in this analysis. Sasol also has been increasingly active in publishing since 2003 (gasification issues, mineral matter/ash transformation etc., notably J. C. van Dyk, among others).
Potchefstroom Campus of the University of the North West [27], while this university does not appear in Table 1 it has undergone considerable expansion/investment in coal research recently. Currently active in beneficiation, combustion/gasification (especially kinetics), coal handling, and coal chemistry. Those active are J. R. Bunt (formally with Sasol), R. C. Everson, and Q. P. Campbell among others. Graduate students currently active in coal science number around 8. Thus expectations are for a significant increase in coal science contributions from this institution.
Australia Australia has very significant national reserves of both brown and black coal [28] providing > 80% of its electricity. Australia is the world’s leading coal exporter and black coal is also its largest commodity export, ~23% of total exports [29]. As such, research associated focussed towards the efficient recovery and environmentally sustainable utilistation for this resource is of particular national significance. Organizations active in coal research have included the Commonwealth Scientific Industrial Research Organisation (CSIRO), several universities, a small number of industry research laboratories and, in respect of the brown coal in Victoria, the Herman Research Laboratory (HRL). There was a peak of activity during the 1980s, through the ‘oil crises’ of that period, as extensive funding was directed towards coal liquefaction. Whilst coals from around the country were investigated extensively, the work on Victorian brown coal was carried through to the successful demonstration of the 50 ton dry-coal/day BCL (Brown Coal Liquefaction) pilot plant at Morwell [30]. Victoria. Research activity has accelerated again in the last approximately 5 years with a focus on reducing the carbon emissions associated with coal-based electricity generation. Research has blossomed in aspects that can be related (a) to the development of improved process configurations for electricity generation and (b) to technologies for carbon capture and sequestration. Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
Federal and state government funding foster these activities. In the late 1970s the federal government introduced a research levy of 5 cents per tonne of saleable coal and established the National Energy Research, Development and Demonstration Council (NERDDC) to allocate the research funds.. In 1992, the State Electricity Commission of Victoria (SECV), of which HRL was a part, was privatized. The considerable downsizing that occurred as a result of industry restructuring led to considerable loss of Brown coal expertise and significantly reduced funding. Australia’s unique system of cooperative research centres (CRC) - joint ventures between government, industry and universities – was able to foster much of the coal research around the turn of the century. Black coal research (2001-2008) was carried out as part of the CRC for Coal in Sustainable Development [31]. Brown coal research was advanced in the CRC for New Technologies for Power Generation from Low-Rank Coal, which later became known as the CRC Clean Power from Lignite (1993-2006). Although they carried out some research ‘in-house’, these organizations supported a large proportion of the work occurring at the universities through this period. Currently (since 2003) the CRC for Greenhouse Gas Technologies (CO2CRC) funds a number of research and pilot projects associated with CO2 capture and sequestration. The Australian National Low-Emissions Coal Council Research and Development (ANLEC R&D) Ltd. was established (2009) by the federal government to foster research to assist with the deployment of Low Emission Coal Technology [32]. In 2010, the Victorian government established Brown Coal Innovation Australia (BCIA) [33] to invest in the development of technologies and people that broadens the use of brown coal for a sustainable future. Other state governments have more general funding schemes that encompass R&D funding for coal-based projects. Most now have primary emphasis on lowering the emissions associated with its use.
CSIRO [34] has been intensively involved in coal R&D since the establishment of its Coal Research Section soon after the conclusion of the second world war. During the 1980s, its Divisions of Fossil Fuels and Energy Chemistry (which later united to form the Division of Coal Technology) were very active in research on coal conversion to liquids by both direct and indirect means, but interest in this topic waned as the oil crises of that decade subsided. Specialists in coal petrology (Shiboka), mineralogy Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
(Swaine), geochemistry (Wilson), chemistry (Durie, Wailes, Lynch, Schafer) and combustion (Mulcahy, Smith, Duffy) made major contributions to understanding the variability in coal structure and properties. Coalscan was developed to provide real time information regarding the mineral, moisture and “ash” content of the coal and its products during the mining and recovery. Projects for producing ‘ultra-clean’ coal developed. More recently, the current Division of Energy Technology has focused on carbon capture and storage systems, coal gasification for higher efficiency energy production and the direct use of coal in engines. Fundamental work regarding the nature of methane interactions with coal seams has relevance to coal mine safety in addition to CO2 sequestration. Industry Research Laboratories: During the 1980s, the corporate research laboratories of BHP Ltd. (both in Melbourne and Newcastle), CSR Ltd. as well as the The Australian Coal Industry Research Laboratory (ACIRL) built up impressive facilities within their respective laboratories and substantially contributed to national sponsored studies of coal liquefaction. Herman Research Laboratories (HRL): As part of the SECV prior to 1992, HRL was particularly well equipped and played a preeminent role in research and development regarding all aspects Victorian brown coal characterization and use. Most of the prominent specialists at HRL at the time contributed chapters to a monograph entitled ‘The Science of Victorian Brown Coal’ [35] where their many significant contributions in relation to brown coal structure, mineralogy, dewatering, liquefaction, combustion and industrial applications are well presented. From 1992 HRL diversified to provide consultancy and contract research services to a broader industry base. Currently, it promotes a high efficiency process configuration for electricity production from brown coal, known as IDGCC (integrated, driving and gasification combined cycle).
Monash University: This university, named after Sir John Monash under who’s leadership the SECV began the development of Victoria’s enormous brown coal reserves, has played a major role in brown coal research. The steam fluidized bed drying process, originally developed by Potter in the 1970s, has seen further development and growing applications over recent years. In the 1980s, both the School of Chemistry (Jackson, Larkins) and the Department of Chemical Engineering (Agnew, Sridhar) were involved in coal liquefaction studies. Later, research into non-evaporative methods for Submit before May 15th to
[email protected] 9
Oviedo ICCS&T 2011. Extended Abstract
dewatering and remediation of the product water (Chaffee, Hoadley) as well as on catalytic aspects of pyrolysis/gasification/combustion (Li, then Bhattacharya) developed [36]. An updated monograph, ‘Advances in the Science of Victorian Brown Coal’ was produced by Li 2004 [37]. A new wave of activity is now underway with the recent appointment of two professorial BCIA Research Leadership Fellows [33] and the commencement of substantial new programs addressing oxy-fuel combustion, spontaneous combustion, etc.
University of Newcastle: For over 30 years Prof Terry Wall, in collaboration with Gupta, Lucus, Bryant, Moghtaderi and many others, has played a preeminent role in combustion research, principally on bituminous coals and ash chemistry [38]. He led the development of significant studies into coal blending which has been important for Australia’s export industry. Claus Diessel, (now emeritus) made substantial contributions to the petrology of Australian coals.
University of Melbourne [39]: Through the 70s and 80s, the Department of Chemical Engineering became well known for its fundamental work on the swelling characteristics of brown coal (Evans, Allardice), the rheological behaviour of coal-water slurries (Boger) and coal drying (the Evans-Siemon process). In the School of Chemistry, an evaporative drying process (densified coal) and fundamental work on the organic geochemistry of brown coal was pursued. Both departments also pursued liquefaction studies. Johns, Verheyen, Larkens, and others were also active.
University of Queensland: Active in Fluidized bed gasification (Rudolph). Stanmore was also active in combustion-related work. A program on dynamic fluid transport properties and permeability of in-situ coal (Massarotto and colleagues) is being applied to reservoir simulation studies for coalbed methane (CBM) extraction, coal mine demethanation (CMM) and carbon dioxide geosequestration in coal seams. The university is active in mineral processing [40].
Others: The geology/petrology lab of Colin Ward at the University of New South Wales [41] has worked extensively on the occurrence and transformation of mineral phases during coal utilization. Much of this has been in collaboration with CSIRO (French) making use of the powerful QEMSCAN analysis system. At the University of Adelaide, Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
Ashman and Mullinger have led a group investigating the gasification potential and combustion characteristics of South Australian lignites with a view to their eventual utilisation. At Curtin University, Li (who moved from Monash) and colleagues have recently established the Fuels and Energy Technology Institute (FETI) which is investigating the production of fuels and chemicals from lignite as well as gasification and oxyfuel combustion of Western Australian lignites [42, 43]. Acknowledgements The authors thank the following individuals who contributed to our ability to evaluate the current state of coal capabilities: Drs. Haenel (Max-Planck Institute for Coal Research), and J. M. Jones (University of Leeds) and others for helpful conversations. This project was funded by the Illinois Clean Coal Institute with funds made available through the Office of Coal Development of the Illinois Department of Commerce and Economic Opportunity. References [1] Mathews JP, Miller B, Song C, Schobert HH, Botha F, Finkelman RB, The current state of affairs of coal research in U.S. Universities, International Conference on Coal Science and Technology, 2011, Oviedo, Spain, [2] Feinberg J Wordle. http://www.wordle.net/ [3] Derbyshire FJ, Obituary: Dr Peter Given. Fuel 1988, 67, (8), 1167-. [4] 1996 Storch Award—Frank J. Derbyshire. Fuel 1997, 76, (2), 99-. [5] 2006 Henry H. Storch Award in Fuel Chemistry goes to Colin Snape. Fuel 2007, 86, (1-2), 1-2. [6] Hicks J, Allen G House of Commons Research Paper: A century of change: Trends in UK statistics since 1900. www.parliament.uk/commons/lib/research/rp99/rp99-111.pdf [7] Imperial College London Energy Engineering Research Group, Department of Chemical Engineering and Chemical Technology. http://www3.imperial.ac.uk/chemicalengineering/research/researchthemes/researchfocusareas/e nge [8] Nottinham University Chemical and Environmental Engineering. http://www.nottingham.ac.uk/Engineering/Departments/Chemenv/People/index.aspx [9] Nottinham University National Center for Industrial Microwave Processing. http://www.nottingham.ac.uk/ncimp/research.php [10] Nottingham University Energy Technology Research Institute. http://research.nottingham.ac.uk/NewsReviews/ExpertiseResults.aspx?id=3417 [11] University of Leeds Energy and Resources Research Institute. http://www.engineering.leeds.ac.uk/erri/ [12] IEA Clean Coal Center http://www.iea-coal.org.uk/site/ieacoal/about/history [13] Energy Watch Group Coal: Resources and future production. www.energywatchgroup.org/.../EWG_Report_Coal_10-07-2007ms.pdf [14] EIA Coal Statistics (2008 data). http://www.eia.gov/coal/data.cfm#reserves [15] CarboTech AC GmbH Company history. http://www.carbotech.de/en/history.php [16] Steller M, Arendt P, K¸hl H, Development of coal petrography applied in technical processes at the Bergbau-Forschung/DMT during the last 50 years. Int. J. Coal Geol. 2006, 67, (3), 158-70.
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Oviedo ICCS&T 2011. Extended Abstract [17] Max-Planck Institute for Coal Research http://www.mpimuelheim.mpg.de/kofo/english/mpikofo_home_e.html [18] Haenel MW, History of the Max-Planck-Institut für Kohlenforschung. 2008. [19] University of Stuttgart Institute of Combustion and Power Plant Technology. http://www.ifk.uni-stuttgart.de/index.en.html [20] University RA Institute of Geology and Geochemistry of Petroleum and Coal. http://www.lek.rwth-aachen.de/cms/index.php?id=12&L=2 [21] Technical University of Freiberg (Saxonia) Institute for Energy Process Engineering and Chemical Engineering. http://tu-freiberg.de/index.en.html [22] Karlsruhe Institute of Technology Engler-Bunte-Institute. http://ceb.ebi.kit.edu/english/index.php [23] Ebergard A The future of South African coal: markets, investment, and policy changes. http://pesd.stanford.edu/publications/ [24] de Korte GJ, Coal preparation research in South Africa. Journal of the South African Institute of Mining and Metallurgy 2010, 110, (7), 361-4. [25] Witwatersrand University Center for Coal Research. http://web.wits.ac.za/Academic/EBE/ChemMet/ResearchUnits.htm [26] The University of Cape Town http://www.uct.ac.za/ [27] North West University PC Energy Systems, The Coal Group. http://www.nwu.ac.za/pfe/currentres.html [28] Geosciences Australia (Australian Government) Coal resources. http://www.ga.gov.au/energy/coal-resources.html [29] Australia Coal Association The Australian Coal Industry- Coal Exports. http://www.australiancoal.com.au/the-australian-coal-industry_coal-exports.aspx [30] Okuma O, Sakanishi K, Liquefaction of Victorian Brown Coal. In Advances in the Science of Victorian Brown Coal, Li, C.-Z., Ed. Elsevier: New York, 2004; pp 85-133. [31] Cooperative Research Center for Coal in Sustainable Development http://www.ccsd.biz/index.cfm [32] ANLEC R&D http://www.anlecrd.com.au/ [33] Brown Coal Innovation Australia http://www.bcinnovation.com.au/ [34] CSIRO Energy from coal. http://www.csiro.au/science/Coal.html [35] Durie RA, The Science of Victorian brown coal: structure, properties, and consequences for utilization. Butterworth-Heinemann: Oxford, 1991. [36] Monash University Clean Energy Technology. http://www.eng.monash.edu.au/research/strengths/clean-energy-technologies/ [37] Li C-Z, Advances in the Science of Victorian Brown Coal. Elsevier: New York, 2004. [38] University of Newcastle Low emission coal. http://www.newcastle.edu.au/researchcentre/energy/research/low-emission-coal.html [39] University of Melbourne University of Melbourne. http://www.unimelb.edu.au/ [40] University of Queensland http://www.chemeng.uq.edu.au/Mineral-Processing-InterfacialProcesses [41] University of New South Wales http://www.unsw.edu.au/index.html [42] Curtin Univeristy Curtin Univeristy. http://www.curtin.edu.au/ [43] Curtin Univeristy Curtin Centre for Advanced Energy Science and Engineering. http://energy.curtin.edu.au/
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Oviedo ICCS&T 2011. Extended Abstract
Adsorption Behavior and Biogasification of Soma Lignite Mustafa Baysal1, Sedat İnan2, Fırat Duygun2 ,Yuda Yürüm1 1
Faculty of Engineering and Natural Sciences, Sabanci University, Orhanli, Tuzla, Istanbul 34956, Turkey 2 TÜBİTAK Marmara Research Centre, Earth and Marine Sciences Institute, GebzeKocaeli, Turkey Corresponding author: e-mail:
[email protected] Abstract Coal bed methane (CBM) can arise from both thermogenic and biogenic activity on the coal beds and adsorb on the porous matrix of the coal. Therefore, investigation of pore structure and gas capacity of the coal is essential for accurate estimations of coalbed gas potential. Coal samples of lignite to sub-bituminous rank were obtained from different depths of Soma basin and were characterized by low pressure CO2 adsorption isotherms at 273 K. Micropore surface areas of the samples were calculated by using D-R model, changed from 232,653-274,73 m2/g. Micropore volume and capacity were determined by D-R equation to vary between 0.075 cm3/g and 0.92 cm3/g and between 40.63 cm3/g to 47.92 cm3/g, respectively. Pore widths of all samples were below 1 nm; suggesting that micropore ratios of the samples are very high. On the other hand, high pressure (up to 1 MPa) nitrogen and methane adsorption isotherms were determined by using Hiden Isochema Intelligent Gravimetric Analyzer (IGA-001) at room temperature. Results showed that methane adsorption on the samples increased with increasing micropore ratio. Effects of outgas temperature, organic carbon content on gas adsorption capacity of the samples were determined. Carbon isotope analyses of the coal gas desorbed from coal core samples of the Soma lignite basin in Turkey suggest bacterial origin. For purpose of better understanding of secondary biogenic gas potential of the samples biogasification experiments have been started. Firstly, coal samples were solubilizied by using Lewis bases. At moderate pH levels at moderate pH (9≥pH≥5) level carbonate and phosphate systems could solubilize coal efficiently. In the biogasification process, coal samples which were ground properly were incubated in anaerobic media with carbonate solution with microorganisms. After determination of optimal gasification parameters, methane generation due to the microbial activity will be calculated on daily basis.
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Oviedo ICCS&T 2011. Extended Abstract
1. Introduction Energy demand of the world is increasing constantly. At present, coal still keeps its value as one of the primary sources of energy to supply this demand. However, utilization of coal as an energy source has lots of negative impacts on the environment. For this reason, scientists have investigated alternative processes to produce clean energy from coal. In order to achieve that, extraction and production of natural gas from coal has become a more significant subject for the energy providers. Coal bed methane (CBM) production is a large and clean energy source with many advantages. In the USA, %10 percent of natural gas demand has been supplied by CBM [1]. CBM may have thermogenic or biogenic origin and the coal gas is adsorbed in the porous coal surface. In the last two decades, production of the secondary biogenic methane by utilization of additional microorganisms has been studied by scientists aiming to obtain more of clean energy from coal. In this study, our primary objective is to understand CBM capacity of the Soma coal basin. For this reason, porosity of the coal samples must be determined [2]. Usually, surface area and the porosity of the materials can be calculated through the N2 physical sorption experiment, in this method entire relative pressure range (10-8 to 1) can be analyzed without using high pressure equipments [3]. However, for microporous materials like carbon materials and zeolites physical sorption occurs at very low relative pressure ranges (10-8 to 10-3) and experiments that are conducted with N2 are less reliable due to the low diffusion rate and adsorption equilibrium in the pores between 0,5 to 1 nm at 77 K. It is also known that specifically for carbon materials experiments that are conducted at low temperatures such as N2 sorption causes pore shrinkage that leads to the low sorption equilibrium ([4,5,6]). Most important factors that affect physical interaction between absorbent and the absorbate are dynamic radius of the absorbate, temperature and solubility parameters of the materials. In the literature, there are many examples where carbon dioxide gas was used for microporous materials instead of nitrogen [7]. Since, dynamic radius of the CO2 is relatively smaller than that of N2 (CO2: 3,3 angstrom, N2: 3,6 angstrom [8,9]), also solubility parameter of the CO2 is far greater than nitrogen ( for CO2 δ=6.1 cal0.5cm1.5
, for N2 δ=2.6 cal0.5cm-1.5 ). Owing to these superior properties, interaction between
coal and the CO2 is better than N2-coal interaction [10, 11]. The last and the most important parameter is the temperature, for physical adsorption of the CO2, measurement
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Oviedo ICCS&T 2011. Extended Abstract
temperature of the isotherm can be 273 K or 298 K which means that we can avoid slow adsorption equilibrium, diffusion limitations at 77 K, also pore shrinkage of the coal at low temperatures can be overcome by using CO2 for the micropore characterization of the coal. Therefore, CO2 can reach narrow and wavy micropore structure of the absorbates due to the high diffusion rate which is called activated diffusion [12, 13]. With all these advantages, coal micropore characterization has been determined by CO 2 since 1964 [14, 15]. In 1984, Smith and Williams reported a relation between high pressure methane adsorption capacity and low pressure CO2 adsorption of coal by comparing the results of these experiment and observed close results which means that low pressure CO2 adsorption also gives idea of the CBM potential [16]. In 1982, Cohen & Gabrielle published the first report on the biological conversion of the coal by microorganisms [17]. Since that time, biological conversion of the coal has been a major area of interest for scientists. Biological treatment of the coal can be divided into two categories; first one is the removal of the sulfur, nitrogen, metals and other unwanted components of the coal and the second one is the conversion of the coal like liquefaction, microbial gasification and microbial pretreatment [18]. Usually, biological treatment of the coal takes place under mild conditions at low temperature and pressure unlike the classic thermo-chemical processes. For instance, during the thermo-chemical processes, formation of the gas products and liquid hydrocarbons from the coal have been carried out by the thermo catalytic breakdown of deeply buried organic matter at relatively high temperatures (> 80oC). On the other hand, in the anoxic biogasification processes, microorganisms cause degradation of the organic content (aromatic hydrocarbons) of the coal to produce gas and other hydrocarbons. 2. Experimental section For this study, coal samples collected from different depths of Soma basin were used. In order to understand the basic characteristic of our samples ultimate and proximate analysis were performed in TÜBİTAK Marmara Research Center (MRC) Energy Institute; results are shown in Table 1. Rock-eval pyrolysis was conducted for determination of level of maturity and type of the organic matter contained. Petrographic analysis yielded maceral types and huminite/vitrinite reflectance was also measured. All these results are given in Table 2. To understand origin of the coal bed gas,
13
C isotope
analyses were conducted by using Continuous Flow Gas Chromatography—Isotope Ratio Mass Spectrometer (GC-IRMS) at TÜBİTAK Marmara Research Center (MRC)
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Oviedo ICCS&T 2011. Extended Abstract
Earth and Marine Sciences Institute (EMSI). Low pressure CO2 micropore surface area and micro porosity experiments were conducted at 273 K by using Quantachrome Autosorb Automated Gas Sorption System. Samples were outgassed at 373 K for 6 h prior to measurements, this temperature was chosen due to the fact that high temperature could cause the collapse of the organic matrix of the coal and also low temperature cannot remove water molecules from pores. High pressure gas adsorption experiments were performed by using Hiden Isochema Intelligent Gravimetric analyzer (IGA-003) with nitrogen and methane. The IGA has a fully automatic microbalance system that allows measuring the weight change as a function of time, gas pressure and the sample temperature. The precision of the measurement can be controlled by a PC. Long term stability of microbalance is 0.1µg with a weighting resolution of 0.2 µg and temperature stability is 0.1oC. For nitrogen adsorption experiments samples were outgassed at 105oC 3 hours under 10-6mbar vacuum, for methane experiments samples were only outgassed under vacuum without any heat treatment. In order to understand the effect of outgas temperature to methane adsorption capacity of the coal, only one sample was outgassed at 105oC 3 hours. For nitrogen experiments, linear driving force mass transfer model was used to get asymptotic uptake for every pressure point at 298 K up to 9 bar. For methane experiment only 6 hours interaction time was used to get thermodynamic equilibrium at 298 K up to 9 bar without using PC control asymptotic uptake value. For demineralization experiments, first samples were stirred with 6N HCl for 24 h under nitrogen atmosphere, then filtered and washed with distilled water until the filtrate became neutral, immediately followed by %40 HF addition to HCl washed coal and stirred for 24 h under nitrogen gas in a nalgene beaker then filtered and washed with water [19]. Demineralized samples will be used for methane adsorption experiments to understand mineral matter effect. For biogasification experiment, anaerobic medium, that contains sodium carbonate and phosphate as Lewis bases for degradation of the complex structure of the coal matrix, was prepared. Then methanogenic bacteria will be added to the coal-anaerobic media to understand bioavailability of Soma lignite. 3. Results and Discussion Coal samples extracted from Soma basin are considered as low rank (lignite to subbituminuous) with high content of vitrinite /huminte maserals, high organic carbon
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Oviedo ICCS&T 2011. Extended Abstract
amount and low mineral matter. Results are shown in Table-1 and Table-2, therefore they have high micro porosity and high adsorption capacity compared to the other coal samples with the same rank. Vitrinite reflectance (%Ro) values of the samples vary between 0.42 and 0.48 and Pyrolysis Tmax values of the samples are between 393 and 412oC; both values suggest that coal samples are immature with respect to thermogenic gas generation (Table 2). Table 1. Ultimate and Proximate Analysis of the Samples Sample No JK - 1122 JK-1126 JK-1135 JK-1137
Original sample C% H%
N%
67,91 66,75 59,45 65,56
0,58 1,48 1,89 0,93
5,85 4,8 5,79 6,23
S%
Dry sample C% H%
N%
S%
O%
2,18 1,01 1,23 1,88
74,94 72,07 63,62 70,53
0,64 1,6 2,02 1
2,41 1,09 1,32 2,03
12,82 14,71 12,69 10,79
Sample No JK - 1122
Original sample Volatile Moisture % Matter % 9,37 3,52
Ash %
JK-1126
7,38
JK-1135 JK-1137
5,29 4,29 5,41 5,86
33,88
Fixed Carbon % 53,23
Dry sample Volatile Ash % Matter % 3,88 37,38
Fixed Carbon % 58,74
5,76
36,01
50,85
6,21
38,87
54,92
6,56
13,93
37,63
41,88
14,91
40,27
44,82
7,04
9,1
42,3
41,56
9,78
45,5
44,72
Table 2. Rock-Eval and Maceral Analyses Results Sample No JK -1122 JK-1126 JK-1135 JK-1137
Depth (m) 793.50-793.70 826.65 725.90-726.20 736.70-736.90
Tmax (oC) 396 412 408 393
Organic Carbon % 67.55 68.31 61.3 66.37
Huminite (%) 96 87 78 82
Liptinite (%) 2 1 19 16
Inertite (%) 2 12 3 2
Ro (%) 0.46 0.48 0.42 0.44
The desorbed gas from the coal samples were collected and used for the determination of the carbon isotopic ratio of the gasses. Results are shown in Figure 1. According to the results, majority of the collected samples are in biogenic region, represented as a green dot on the Figure 2, also one of the samples is in the mixed gas region but very close to the biogenic part, which is shown by red dot on the figure. These results confirm that origin of the CBM is the result of the bacterial activity [20].
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Oviedo ICCS&T 2011. Extended Abstract
Figure 1. Differentiation of biogenic and thermogenic gas Usually coal samples have high micro porosity therefore methane is adsorbed in this micropore structure. In order to understand primary biogenic methane potential of the Soma basin, porosity and micropore surface area of the samples were determined by CO2 sorption experiments. Adsorption isotherms obtained in this study are shown in Figure 2. D-R micropore surface area, micropore volume and micropore capacity are given in Table 3. CO2 isotherms indicate that micropore area and adsorption capacity of JK-1126 is 274,73m2/g and 47,92, respectively; the highest of all samples, . This result indicates that coal samples with high organic carbon ratio and high Ro values have greater micro porosity, and thus, gas adsorption capacity. Pore size distribution of all four samples show that micro pore size of the Soma lignite is reported below 1 nm (Figure 3.). Table 3. CO2 surface characterization results at 273 K Sample No JK - 1122 JK-1126 JK-1135 JK-1137
Organik Karbon % 67,55 68,31 61,3 66,87
DR surface 2
area (m /g) 248,891 274,73 224,909 232,653
DR micropore volume 3
DR micropore capacity (m3/g)
(m /g) 0,083 0,092 0,075 0,078
43,23 47,92 39,06 40,63
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Oviedo ICCS&T 2011. Extended Abstract
Figure 2. CO2 Adsorption Isotherms
Figure 3. Pore size distribution of the samples Nitrogen sorption in coal is a diffusion limited process, uptake is very low compared to methane and CO2. Nitrogen Isotherms up to 9 bar by using asymptotic values show that JK-1126 also has higher adsorption capacity than the others (see Figure 4.). Methane adsorption is far greater than nitrogen adsorption to the coal due to the strong interaction of the C-C Van der Waals forces and easy access (i.e.: smaller dynamic radius) to the micropore structure of the coal (see Figure 5). JK-1126 has the highest organic carbon ratio, as well as the highest adsorption capacity. Therefore, micropore structure of the coal is strongly related to the organic carbon pattern, adsorbent finds available sites in these organic patterns.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 5. Methane adsorption isotherms at 298 K In the literature, there are many arguments about outgas temperature of coal, therefore outgas effect on the methane adsorption capacity of coal were investigated as shown in Figure 6., One sample was outgassed in vacuum at 105oC prior to adsorption, other sample was outgassed only in vacuum. Results show that vacuum outgassed sample has higher methane adsorption capacity than the other; this is taking to suggest that temperature could cause a collapsed micropore structure of coal, and disturbed structure cannot adsorb methane efficiently.
Figure 6. JK-1137 adsorption isotherms at 298 K with and without temperature outgas prior to experiment. After demineralization, methane sorption experiment will be performed.
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Oviedo ICCS&T 2011. Extended Abstract
Also, to understand bioavalibilty of the samples, biogasification experiments with the specific organisms have still been continued. 4. Conclusions The isotherm up to 9 bar shows that methane adsorption on coal is greater than the nitrogen adsorption isotherms. Micro porosity is strongly related to organic carbon ratio of the coal, moreover, gas adsorption capacity is directly proportional to micro porosity. 105oC is too high for the outgas process of coal, since temperature most likely cause collapse of the micropore structure. Lower temperature must be applied to get maximum gas adsorption capacity. References [1] Harris S.H. et al, Microbial and chemical factors influencing methane production in laboratory incubations of low-rank subsurface coals. International Journal of Coal Geology 2008;76:46–51 [2] Rolando M. A. Roque-Malherbe. Adsorption and Diffusion in Nanoporous Materials,CRC press, (2007) [3] Lozano-Castelló D., Cazorla-Amorós D., Linares-Solano A. Usefulness of CO2 adsorption at 273 K for the characterization of porous carbons. Carbon 2004;42:1231–1236 [4] Lowell S., Shields, J. E. Thomas Martin A.; Thommes M., Characterization of Porous Solids and Powders: Surface area, Pore Size and Density, Springer, (2004) [5] Anderson R. B., Bayer J., Hofer L. J. E., Determining surface areas from carbon dioxide isotherms. Fuel 1965;44:443-452 [6] Walker P. L. Jr., Geller I. Change in surface area of anthracite on heat treatment. Nature (London) 1956;178:1001[7] Mastalerz et al. Meso- and Micropore Characteristics of Coal Lithotypes: Implications for CO2 Adsorption. Energy & Fuels 2008;22, 4049–4061 [8] Breck D.W. Zeolite Molecular Sieves Wiley, New York (1974),p. 634 [9] Kenneth S.W.Sing, Ruth T.Williams, Review: The Use of Molecular Probes for the Characterization of Nanoporous Adsorbents. Part. Part. Syst. Charact. 2004;21:71 – 79 [10] Reucroft P. J., Sethuraman A. R. Effect of pressure on carbon dioxide induced coal swelling. Energy & Fuels 1987;1:72-75 [11] Barton A. F. M. Handbook of Solubility Parameters and Other Cohesion Parameters; CRC Press: Boca Raton, FL, (1983) [12] Nandi S. P., Walker P. L. Jr. The diffusion of nitrogen and carbon dioxide from coals of various rank. Fuel 1964;43:385-93 [13] Cazorla-Amoro´s D. et al. CO2 As an Adsorptive To Characterize Carbon Molecular Sieves and Activated Carbons. Langmuir 1998;14:4589-4596 [14] Marsh H. Determination of Surface Areas of Coals - Some Physicochemical Considerations. Fuel 1965;44:253-68 [15] Marsh H., Siemieniewska T. The surface area of coals as evaluated from the adsorption isotherms of carbon dioxide using Dubinin–Polanyi equation. Fuel 1965; 44:355-67 [16] Smith D. M., Williams F.L. Coal Sience and Chemistry(A. Volborth, Ed.), Elsevier,Amsterdam 1987, p:381
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Oviedo ICCS&T 2011. Extended Abstract
[17] Cohen M.S., Gabriele P.D. Degradation of coal by the fungi Polyporus versicolor and Poria monticola. Applied and Environmental Microbiology 1982;44:23-27 [18] Narayan R., Ho N.W.Y. Objectives of coal bioprocessing and approaches. Am. Chem. SOC., Div. Fuel Chem. Prep. 1988;33:487-495 [19] Altuntaş, N.;Yürüm, Y. Effect of Catalysts on the Pyrolysis of Turkish Zonguldak Bituminous Coal. Energy & Fuels 2000;14:820-827 [20] İnan S. Et al., Coalbed Gas Potential In the Miocene Soma Basin (Western Turkey). 27th Pittsburgh Coal Conference 2010; Abstract Booklet:pp.21
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Oviedo ICCS&T 2011. Extended Abstract
Decoupling in Thermochemical Conversion: Approach and Technologies Guangwen Xu, Juwei Zhang, Yin Wang, Shiqiu Gao State Key Laboratory of Multi-phase Complex System, Institute of Process Engineering,Chinese Academy of Sciences, P. O. Box 353, Beijing 100080, P. R. China : Tel/Fax：+86-10-62550075, E-mail:
[email protected] Abstract All thermochemical conversion processes for coal, biomass and solid wastes involve a series of chemical reactions as well as physical variations including fuel drying/pyrolysis, char gasification, tar reforming/cracking, combustible matter combustion, water gas shift and so on. These reactions are mutually interactive to form a complicated reaction network.
In the conventional thermochemical conversion
technologies (processes), these reactions are coupled together to implement the conversion in a single reaction vessel, which may result in some undesirable effects such as low efficiency, low-value/quality products, and high pollutant emission.
The
“decoupling” means to control the interactions among different reactions to facilitate the beneficial interactions or to suppress the undesirable interactions to optimize the performances of thermochemical conversion, including facilitating the conversion for higher efficiency, improving product quality/value, increasing fuel adaptability, suppressing pollution emission, realizing poly-generation and any other benefits. The implementation of “decoupling” comprises first the breakage of inter-linked reactions to separate one or more interacted reactions and then reorganization of the separated reactions. This article highlighted the decoupling principle, and both “isolating” and “synergizing” were generalized as the two different approaches of decoupling. On the basis of the decoupling approaches, a series of decoupling thermochemical conversion (DTC) technologies were highlighted to understand their process principle and realize technology superiorities. In turn, an overview on the progress of a few typical DTC technologies under development in Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) was presented to summarize the major results in both fundamental studies and pilot or demonstration tests. The technologies referred to in the article included the dual fluidized bed gasification (DFBG), dual bed pyrolysis Submit before January 15th to
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gasification (PG), two-stage gasification (TSG), topping combustion (TC), low-NOx fluidized bed combustion (LFBC) and decoupling combustion (DC). This summarization validated that the decoupling can provide a viable idea and practical approach of technology innovation for developing new conversion technologies that overcome the inherent disadvantages of the traditional conversion technologies and thereby realize the decoupling effects of, for example, high efficiency, poly-generation, high quality/ value of products, wide fuel adaptability, and low pollutant emission etc. 1. Introduction The thermochemical conversion supplies the major technical approaches for utilizing solid carbonaceous fuels including coal, biomass and municipal wastes. It is shown generally via three different conversion patterns: pyrolysis (carbonization or coking), gasification and combustion. In the process of each of these conversion patterns, not a single but a series of reactions occur to incur the explicit chemical changes. Figure 1 highlights the chemical behaviors involved in the thermochemical conversion of solid fuels. It is noteworthy that in Fig. 1 the words or terminologies pyrolysis, gasification and combustion refer to their individual reactions in the middle rectangle box rather than to their macro processes in the last column of the figure.
Solid fuel Oxidant (O2) Reagent (H2O, CO2, H2)
(1) Drying (2) Pyrolysis (3) Cracking/ decompositon (4) Polymerization (5) Hydrogenation (6) Gasification (7) Combustion (8) Reforming (9) Water gas shift …….
Sufficient O2 Enough long t and high T
Combustion: CO2, H2O, heat
Insufficient O2 Enough long t and high T
Gasification: CO, H2, CmHn
Lean in O2 Short t and low T
Pyrolysis: C (char), CO, H2 CmHn, (C6Hm)xOy
Fig.1 Chemical behaviors of solid fuels during the thermochemical conversion process
The reactions in the rectangle box are inter-correlated or interactive, and some are even sequential in occurrence. Under heating, the solid fuel is first dried and pyrolyzed to produce char, tarry oil (tar), steam and uncondensable pyrolysis gas consisting mainly of H2, CO, CO2, and CH4. In turn, the other reactions in box start to occur and lead to a series of interactions between/among the product/products of some reactions with the other reactions. These interactions make the involved reactions in the thermochemical
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conversion process, such as those listed in the rectangle box in Fig.1, closely intercorrelated to form a complicated reaction network described in a previous publication of ours [1].
Of these interactions, some can facilitate the conversion to lead to high
efficiency, low pollution emission and high product quality, whereas the others are not. Therefore, it deserves to control the interactions for optimizing the thermochemical conversion process.
In most commercialized as well as in-developing processes of
pyrolysis, gasification and combustion, all such reactions are arranged into a single reaction space and it is thus impossible to control any individual reaction and its interactions with the other reactions. This causes the problems related to low product quality or value, low conversion efficiency, poor fuel adaptability, high pollutant emission and so on. In order to manipulate individual reaction to avoid or weaken the undesired but strengthen the desired interactive effects, separation of the related reactions and in turn rearrangement of the separated reactions is necessary and worthwhile. This idea of reaction control has been termed “decoupling” in our previous publication [1]. Two implementation approaches for decoupling, isolating and synergizing, have been also developed and through their applications to gasification it has been found that the “isolating” and “synergizing” approaches correspond rightly to the conversion technologies based on “dual bed” and “staging”, respectively. Figure 2 summarizes the preceding inter-correlations among the reactions involved in the thermochemical conversion process, two implementation approaches of the decoupling, their implicated characteristic conversion technologies and the expected technical effects from implementing the decoupling. As one may image, the implementation of the decoupling consists of two sequential actions upon the involved reactions, separation of one or more reactions from the inter-correlated reaction network (see Ref. [1]) by breaking the linkages of the reaction or reactions with the others, and rearrangement of the separated or decoupled reactions according to the needs of reaction control. If the decoupled reactions are arranged into isolated reactors to separate their products and fully suppress the interactions between their products, the resulting decoupling is the “isolating” and the technology is dual bed conversion, realizing consequently the effects of poly-generation, high efficiency, high product quality, and wide fuel adaptability.
If the decoupled
reactions are reorganized to facilitate the beneficial interactions or to suppress the undesired interactions, the utilized decoupling is the so-called “synergizing” and the corresponding conversion technologies are usually related to “staged” shown explicitly as Submit before January 15th to
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two-stage processes, fuel staging and reactant-staging. technologies
These staged conversion
are most effective to lowering pollution emission, raising efficiency and
product quality, and allowing wide fuel adaptability. In practice, the decoupling may be also implemented by executing both “isolating” and “synergizing” to have the creatively new designs for thermochemical conversion technologies. Combustion Reaction network
Fuel
Char
Residua Char
Pyrolysis
Gasification Break
Decoupling approach
Isolating (reacting independently isolated product stream)
Synergizing (Re-organization one product stream)
Derived technology
Dual-bed conversion
Staged conversion
Decoupling effect
Poly-generation High efficiency High product quality Wide fuel adaptability
Low pollution High efficiency High product quality Wide fuel adaptability
Fig. 2 Two decoupling approaches applied in the reaction network of thermochemical conversion process (taking the simple reaction network of pyrolysis, gasification and combustion for example))
In succession to our previous publication [1], this article is devoted to generalizing the conception and applications of the decoupling to all types of thermochemical conversion technologies or processes. Table 1 summarizes some typical and well-known thermochemical conversion technologies based on decoupling and their realized major decoupling effects (i.e., technology advantages). These technologies mainly involve three types of thermochemical conversion process: pyrolysis, gasification and combustion, and here pyrolysis includes also coking. It can be seen that all of these technologies have been commercialized or in the progress toward commercialization. Herein, an overview on the progress of a few typical decoupling thermochemical conversion (DTC) technologies under development in Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) was presented to summarize the major results in both fundamental studies and pilot or demonstration tests. The technologies referred to in the article included the Submit before January 15th to
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dual fluidized bed gasification (DFBG), dual bed pyrolysis gasification (PG), two-stage gasification (TSG), topping combustion (TC), low-NOx fluidized bed combustion (LFBC) and decoupling combustion (DC). Table 1 Typical thermochemical conversion technologies with different decoupling approaches and corresponding effects Process
Decoupling approach
isolating
pyrolysis isolating
isolating and synergizing
isolating
gasification
isolating
synergizing
isolating
combustion
synergizing
synergizing
Decoupling effects Using heat of exhaust gas to regulate the moisture in coal and realize utilization of poor-coking coal, high productivity, energy saving Rapid preheating of the coal charge to realize utilization of weak-caking coal, high productivity, energy saving Multi-stage pyrolysis to improve high product quality and fuel adaptability of the technology Avoiding dilution of produced gas by N2 and combustiongenerated CO2 to produce middle-caloric fuel gas using air as a gasification reagent Co-producing pyrolysis oil and fuel gas or syngas to use coal hierarchically Reforming/cracking of tar and pyrolysis gas by catalysis of char to produce fuel gas or syngas with little tar Co-producing pyrolysis oil, pyrolysis gas, steam and elecitricty to use coal hierarchically Reduction of NO by char and pyrolysis gas to lower NO emission in the flue gas Introduction of pyrolysis gas into char bed to lower NO and CO emission in the flue gas
Main decoupled reaction (s)
Typical technology
drying
CCMC
commercialization
drying and pyrolysis (low extent)
SCOPE21
commercialization
pyrolysis (low extent)
COED
commercialization
combustion
DFBG
demonstration
pyrolysis
PG
pilot
pyrolysis
TSG
pilot
pyrolysis
TC
pilot
pyrolysis
LNFC
pilot
pyrolysis
DC (grate furnace)
commercialization
Application stage
a
a
The full names of the typical DTC technologies are coking with coal moisture control (CCMC) [2], super coke oven for productivity and environmental enhancement toward the 21st century (SCOPE21) [3], char oil energy development (COED) [4], dual bed gasification (DBG) [5], pyrolysis gasification (PG) [1], two-stage gasification (TSG) [6], topping combustion (TC) [7], low-NOx fluidized bed combustion (LFBC) and decoupling combustion (DC) in grate furnace [8].
2. Application to Gasification The gasification technologies based on the decoupling have been named the decoupling gasification (DCG) technologies in our previous publication [15]. By far, the decoupling has been widely applied to the development of gasification technologies, and Fig. 3 highlights the process principles of three typical DCG technologies developed in IPE. Of them, the DFBG and PG adopted the “isolating” decoupling approach, while the
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TSG is based on “synergizing” decoupling approach. As illustrated in Fig. 3, the DFBG was created by decoupling the char combustion from all the other gasification reactions, While the PG and TSG were born from decoupling and in turn reorganization of the pyrolysis reaction. Table 1 also briefs the realized decoupling effects for all the mentioned DCG technologies, and these effects, as detailed in our previous publication [1], have been well validated through pilot or bench tests or demonstration applications. This results in the demonstration of that the DCG technologies innovated with either isolating or synergizing approaches or both of them can effectively lower emission, raise efficiency, increase product quality or/and allow wide fuel adaptability. Flue gas
Product gas
Pyrolysis gas+tar
Riser gasifier
Riser combustor
Product gas
Fuel BFB gasifier
Fuel Distributor
Pyrolyzer
Ash
Pyrolysis gas or N2
Steam+air Air
Air (a) DFBG
(b) PG
(c) TSG Fig. 3 Schematic diagram of three DCG technolgies
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3. Application to Combustion As far, there are some application examples of decoupling approaches for the combustion process, and many of them are developed in China [7-12]. Both the isolating and synergizing approaches have been used in these combustion technologies. 3.1. Principle Figure 4 (a) shows the principle diagram of one typical combustion technology using the isolating approach. This technology was named “topping combustion (TC)” which originated from the conception of “topping” in petroleum industry and it was proposed at the Institute of Process Engineering (IPE), Chinese Academy of Science (CAS). The TC is a poly-generation technology which can co-produce light oil, pyrolysis gas, heat, and electricity. As shown in Fig. 4 (a), the linkage between pyrolysis and char combustion is broken, and these two reactions proceed in the separated reactor, which indicates the isolating approach is used. The fuel (coal) is pyrolyzed quickly in a downer reactor after mixing with the hot sand from the char riser combustor, then the produced gas (volatiles) is separated from the solid and quenched quickly to extract the light oil (the conception of “topping” is manifested here) while the secondary reactions are minimized. For this technology, the key to achieve success is the word “fast” including the fast mixing of coal with the hot sand particles, fast gas-solid separation, and the fast cooling of the volatiles. In the combustion process, the effect of low NOX emission can generally be realized through the synergizing approach, as shown in Fig. 4 (b). From Fig. 4 (b), it can be seen that after the linkage between the pyrolysis and char combustion is broken, the pyrolysis gas is introduced into the char combustion zone to make use of the interaction between the pyrolysis gas and char or the products of char combustion. Perhaps the most important interaction is the NO-char reaction whose fundamentals have been investigated in many studies in fixed beds [13] and entrained flow reactors [14] for both coal char and biomass char. Besides, the NO from char combustion can also be reduced by the reductive components such as CH4, H2 and CO in pyrolysis gas [15]. The NO formed in both pyrolysis reaction and char combustion (i.e., the NO formed from char-N and volatile-N) can be obviously decreased, compared to regular combustion technologies in which the pyrolysis reaction and char combustion proceed in a single reactor.
Combustion process (isolating) Flue gas
Hot sands Break
Combustion Pyrolysis Submit before January 15 to
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th
Air Cold sands +char
7 Fluidization gas
Oviedo ICCS&T 2011. Extended Abstract
3.2. Topping combustion The process diagram of TC technology is shown in Fig. 5(a). The TC system mainly includes a solid-solid mixer, a downer pyrolyzer, a gas-solid separator, and the riser combustor. The product distribution of the produced gas from the downer pyrolyzer was investigated in a lab-scale (8 kg/h) electricity-heated TC apparatus in which the downer pyrolyzer and riser combustor have the inner diameters of 0.039 m and 0.086 m. The details of this apparatus and experimental procedures can be referred to literature 7. A Chinese lignite which had 6.0% moisture, 36.2% volatiles, 33.5% fixed carbon, and 24.3% ash by weight (dry basis) was used. The yields of liquid including tar, light tar and water were increased with the increasing of pyrolysis temperature and the yield of light tar could reach 7.5% when the pyrolysis temperature was about 930 K. The light tar mainly consisted of acid group, aliphatic, aromatic, and polar & basic group, and their yields were 4.3%, 1.0%, 1.6%, and 0.6%, respectively.
These results indicate the high-value
compounds contained in coal can be utilized with high efficiency in the TC technologies. At present, a 5 ton/h pilot-scale TC apparatus has been built in IPE and the experiments are in progress. Submit before January 15th to
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Flue gas + ash Fuel Mixer
Riser combustor
Secondary air
Pyrolyzer (downer) Product gas
Gas-solid separator
Cooler
Char + hot sands
Tar Fluidization gas
Primary air (a) TC Flue gas
Secondary air
Riser combustor
Flue gas
Pyrolysis gas
Pyrolysis
Postcombustion
zone
Fuel Combustion zone
Pyrolyzer Char + hot sands
Fluidization gas (N2+air)
Secondary air Primary gas
Primary air (b) LFBC
(c) DC
Fig. 5 Schematic diagram of three combustion technologies with decoupling approaches
3.3. Low-NOx combustion Figure 5(b) and (c) show the process diagrams of two low-NOx combustion technologies in fluidized bed and grate furnace (fixed bed) with synergizing approaches respectively, and they were both proposed in IPE. The fluidized bed low-NOx combustion system, as shown in Fig. 5 (b), mainly consists of a bubbling fluidized bed pyrolyzer and a riser char combustor. This system is actually modified from the 50 kg/h pilot-scale PG apparatus shown in Fig. 3 (b) by introducing the produced pyrolysis gas from pyrolyzer
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into the middle of the riser char combustor (i.e. char gasifier in PG), resulting in NOx reduction by char and pyrolysis gas. In order to validate the decoupling effects of this low-NOx combustion technology, the experiments of both regular CFB combustion (i.e., the pyrolysis reaction and char combustion both occur in the riser) and low-NOx combustion were performed using a Chinese lees which had 43.8% moisture, 39.7% volatiles, 9.4% fixed carbon, and 7.1% ash by weight. Figure 6 compares the volume fractions of the main flue gas components produced from regular combustion with that from low-NOx combustion.
Compared with the regular CFB combustion, the NOx
concentration can be decreased from 800 ppm to 100 ppm, indicating the remarkable NOx reduction effects of decoupling in combustion process with synergizing approach. O2
CO
25
900
20
750 600
15
450 10
300
5 0
150 0
5
10 15 Time (min)
20
30
1050
CO2 25
NOx
O2
CO
600
20
450
15
300
10
150
0
5 0
0 0
(a)
20
40 60 Time (min)
80
NOx concentration (ppm)
NOx
Gas composition (vol.%)
Gas compositon (vol.%)
CO2
NOx (ppm)
30
100
(b)
Fig. 6 Volume fractions of the main flue gas components produced from: (a) Regular CFB combustion; (b) fluidized bed low-NOX combustion with synergizing approach
The low-NOx combustion can also be implemented in grate furnace [8], as shown in Fig. 5 (c). This type of combustion technology is generally called decoupling combustion (DC) [8]. The furnace is divided into pyrolysis zone, combustion zone (above grate), and burnout zone. The fuel are pyrolyzed quickly in the pyrolysis zone, and the produced char and pyrolysis gas enter into the char combustion zone where the NOx reduction by char and pyrolysis gas occur, then the residual char and gas move into the burnout zone to burn with secondary air. Dong et al. [16] measured the concentration of gas composition in flue gas and the averaged temperature in a 4.5 kg/h DC grate furnace and a 3 kg/h regular combustion grate furnace using a blend of 50% rice husk and 50 % coal by weight, the results are presented in Fig. 7. The two combustion patterns have a same excess air ratio. It can be obviously seen that the DC has a lower NO, lower CO emission level, and higher furnace temperature than regular combustion.
The higher CO emission for regular
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combustion can be attributed to that the fuel pyrolysis occurs above the char bed and the produced volatiles are easy to escape directly with flue gas without experiencing the high temperature char bed. Via DC, the NO concentration is reduced by 19% compared to regular combustion, though the higher CO concentration and temperature facilitate the NO formation [17, 18]. All these results justify the decoupling effects of low pollution, high efficiency and stable combustion via DC. It should be noted that the DC can be easily employed by modifying the existing grate boiler. Currently, the 1 t/h (evaporation) DC grate boiler has already been commercialized and the scale-up works (2-10 t/h) are in progress. 10000
DC RC
150
1200 8000
1000
6000 90 4000 60
800 CO (ppm)
NO (ppm)
120
600 400
2000
30 0
0 NO
CO
Averaged temperature
180
200 0
Temperature
Fig. 7 Performance comparisons between DC with synergizing approach and regular combustion (RC) in grate furnace [16]
4. Conclusions Based on the DCG proposed in our previous paper, the conception of decoupling has been extended to more general process: thermochemical conversion which commonly includes pyrolysis, gasification and combustion process.
When the decoupling
approaches are applied in the typical processes of thermochemical conversion, various types of novel technologies can be formed. In order to generalize the application of decoupling in the thermalchemical conversion and justify the superiority of the decoupling approaches, some typical decoupling application examples developed in IPE are introduced and the related experimental results are reanalyzed. As for combustion technologies, the principle of TC are based on the isolating of pyrolysis reaction from other reactions in the whole combustion process to separate the
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pyrolysis products to realize the decoupling effects of poly-generation and high product quality, and the principle of low-NOX combustion in both fluidized bed and grate furnace is based on the decoupling of pyrolysis reaction from the whole combustion process to take advantage of the interactions among pyrolysis gas, char and NO to realize the decoupling effects of low pollution. Based on these result analyses, the terminology of decoupling thermochemical conversion (DTC) was proposed to distinguish the conversion technologies based on decoupling from the conventional thermochemical conversion technologies. It is anticipated for this paper that more and more DTC technologies would be derived from the conception of decoupling, since the DTC technologies can realize lots of desired decoupling effects which could not be easily obtained in the conventional thermochemical conversion technologies. Acknowledgement The authors are grateful to the financial support of the Natural Science Foundation of China (contract No: 21006110,) and Key Projects in the National Science & Technology Pillar Program (contract No: 2009BAC64B05). References [1] Zhang JW, Wang Y, Dong L, Gao SQ, Xu GW. Decoupling gasification: approach principle and technology justification. Energy Fuels 2010;24:6223–6232. [2] Kenji K, Seiji N. Coal pretreating technologies for improving coke quality. Proceeding of the 5th Internationall Congerss on the Science and Technology of Ironmaking, Shanghai, China, 2009, 361–366. [3] Taketomi H, Nishioka K, Nakashima Y, Suyama S, Matsuura M. Research on coal pretreatment process of SCOPE21. 4th European Coke and Ironmaking Congress Proceedings, Paris, France, 2000, 640–645. [4] Strom AH, Eddinger RT. COED plant for coal conversion. Chemical engineering progress 1971;67:75–80. [5] Xu GW, Murakami T, Suda T, Matsuzawa Y, Tani H. Gasification of coffee grounds in dual fluidized bed performance evaluation and parameter influence. Energy Fuels 2006;20: 2695–2704. [6] Henriksen U, Ahrenfeldt J, Jensen TK, Gobel B, Bentzen JD, Hindsgaul C, Sorensen LH. The design, construction and operation of a 75 kW two-stage gasifier. Energy 2006;31:1542–1553. [7] Wang JD, Lu XS, Yao JZ, Lin WG, Cui LJ. Experimental study of coal topping process in a downer reactor. Ind. Eng. Chem. Res. 2005;44:463–470. [8] Li JH, Bai YR, Song WL. NOx-suppressed smokeless coal combustion technique. Proceedings of International Symposium on Clean Coal Technology, Xiamen, China, 1997, 344–349.
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Oviedo ICCS&T 2011. Extended Abstract [9] Fang MX, Wang QH, Yu CJ, Shi LZ, Luo ZY, Cen KF. Development of gas steam and power multi-generation system. Proceedings of the 18th International Conference on Fluidized Bed Combustion, Toronto, Ontario, Canada, 2005, 22–25. [10] Fang MX, Cen JM, Wang QH, Shi ZL, Luo ZY, Cen KF, 25 MW circulating fluidized bed heat-power-coal gas poly-generation installation. Journal of Power Engineering (in Chinese) 2007;27:665–639. [11] Chinese Patent 01218480.2. [12] Yao JZ, Wang XQ, Lin WG, Li JH, Kwauk MS. Coal topping in a fluidized bed system. 16th International Conference on Fluidized Bed Combustion, Reno, NV, 2001, 13–16. [13] Dong L, Gao SQ, Song WL, Xu GW. Experimental study of NO reduction over biomass char. Fuel Processing Technology 2007;88:707–715. [14] Sun SZ, Zhang JW, Hu XD, Wu SH, Yang JC, Wang Y, Qin YK. Studies of the NO-char reaction kinetics obtained from drop tube furnace and thermogravimetric experiments. Energy Fuels 2009;23:74–80. [15] Giral I, Alzueta MU. An augmented reduced mechanism for the reburning process. Fuel 2002;81:2263–2275. [16] Dong L, Gao SQ, Song WL, Li JH, Xu GW. NO reduction in decoupling combustion of biomass and biomass-coal blend. Energy Fuels 2009;23:224–228. [17] Zevenhoven R, Hupa M. The reactivity of chars from coal, peat and wood towards NO, with and without CO. Fuel 1998;77:1169–1176. [18] Aarna I, Suuberg EM. The Role of Carbon Monoxide in the NO-carbon Reaction. Energy Fuels 1999;13:1145–1153.
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Integrated Process of Coal Pyrolysis with CH4/CO2 Activation by Dielectric Barrier Discharge Plasma Xinfu He, Haoquan Hu*, Lijun Jin, Yunpeng Zhao State Key Laboratory of Fine Chemicals, Institute of Coal Chemical Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, P. R. China, *
[email protected] Abstract An integrated process to combine coal pyrolysis with CH4/CO2 activation by dielectric barrier discharge (DBD) plasma was reported. Coal pyrolysis was carried out under seven atmospheres, including N2, H2 and different plasma of H2, CH4, CH4/H2, CO2/H2, CH4/CO2/H2 (MG) to confirm the effect of integrated process of coal pyrolysis with CH4/CO2 activation by DBD plasma on improving tar yield. The results showed that the effect of seven atmospheres on tar yield generally has the following order: MG plasma > CH4 plasma ≈ CH4/H2 plasma ≈ CO2/H2 plasma > H2 plasma > H2 > N2, especially at low temperature range. The effect of discharge power on product yields were also investigated. The results showed that the tar yield of Shenmu coal under optimum condition is about 2.0 and 1.8 times as that under N2 and H2 at 400 °C, respectively.
1. Introduction Coal tar from low temperature pyrolysis of coal could be one of the most important sources of fuel oil and chemicals. In general, the tar yield in coal pyrolysis process is low. To improve the tar yield, many methods, including changing the pyrolysis atmosphere, [1-6] pre-treatment of coal, [7] catalytic pyrolysis [4, 7] and catalytic hydropyrolysis [4, 8] were explored. Our recent studies indicated that tar yield could increase remarkably by integrating the coal pyrolysis with partial oxidation [9] or carbon dioxide reforming [10, 11] of methane (POMP or CRMP). However, POMP process is restricted for safety concern, while CRMP process has to be operated at above 800 °C because CH4 is hard to be activated, which is higher than the optimal coal pyrolysis temperature range for high tar yield (500-600 °C), resulting in the formation of large amount of water. Many studies have been carried out using dielectric barrier discharge (DBD) plasma for methane conversion [12-15] because it can be operated at ambient temperature and atmospheric pressure, and can be initiated in large scale. In this work, DBD plasma was
1
Oviedo ICCS&T 2011. Extended Abstract
used for activating CH4/CO2 to find out whether the integrated process of coal pyrolysis with CH4/CO2 activation by DBD plasma could improve the tar yield.
2. Experimental Coal Sample Two Chinese coal samples, Huolinhe (HLH) lignite and Shenmu (SM) subbituminous coal, were crushed and sieved to 40-60 mesh for pyrolysis. The proximate and ultimate analyses of the coal samples are shown in Table 1.
2.2 Apparatus and Procedures. The schematic diagram of the experimental setup and the reactor as well as the method for measuring discharge power was described elsewhere. [16] The feed gas includes N2, H2 and different plasma of H2, CH4, CH4/H2 (1:2), CO2/H2 (1:2), CH4/CO2/H2 (1:1:2, denoted as MG) at atmospheric pressure. During the experiment, the feed gas was first introduced to the reactor for several minutes, then gas discharge was initiated and the reactor was loaded into the center of the preheated furnace (400 to 650 °C). The heating time from ambient temperature to desired pyrolysis temperature was about 3 min and the reactor was held at the temperature for a desired time. The liquid products, tar plus water, were collected in a cold trap at -10 °C, and then the water in the liquid products was separated according to ASTM D95-05e1 (2005) using toluene as solvent. In this way, tar and water yield could be calculated, respectively.
3. Results and Discussion 3.1 Effect of Temperature under Different Atmospheres. The effect of pyrolysis temperature on char, tar and water yields under N2, H2 and different plasma atmospheres are shown in Figure 1. It can be seen that char yield is the highest while tar and water yields are the lowest under N2 at the investigated temperature range, and it is the same trend as those under H2 at low temperature range.
2
Oviedo ICCS&T 2011. Extended Abstract
Coal conversion as well as tar and water yields under H2 is higher compared with those under N2 when temperature exceeds 550 °C. H2 at low temperature range is an inert gas equivalent to N2 and has no effect on coal conversion, but as the temperature increases, it can be activated and has effect on stabilizing the free radicals cracked from coal, resulting in the increase of tar and water yields. When plasma discharge was introduced, H2 can be activated or dissociated to H, H+, H2+, H3+, etc., which have higher reactivity than molecular hydrogen, [17] that’s the reason for the lower char yield and higher tar yield under H2 plasma than that under H2 at low temperature range. However, H2 molecule can be activated thermodynamically at high temperature range, which can explain why char and tar yields have little difference under H2 plasma compared with that under H2 at high temperature range. Higher water yield under H2 plasma may be ascribed to the high-energy H species excited by discharge, which has higher ability to react with oxygenous groups in coal.
90
25
N2
CH4 P
H2
CH4/H2 P
H2 P
CO2/H2 P MG P
80 70 60
400
450
500
550 o
Temperature( C)
600
6
(b)
650
Water yield(wt%,daf)
Char yield(wt%,daf)
(a)
Tar yield(wt%,daf)
100
20 15 10 5 0
400
450
500 550 600 o Temperature( C)
650
5
(c)
4 3 2 1 0
400
450
500 550 600 o Temperature( C)
650
Figure 1. Effect of temperature on char (a), tar (b) and water (c) yield under different atmospheres (240 ml/min, holding time: 7 min, Pdis: 40 W) Other plasma atmospheres showed positive effect on coal conversion and displayed lower char yield than that under H2 plasma at low temperature range (400-500 °C). Higher tar yield can be achieved in the integrated process of coal pyrolysis with gas activation by DBD plasma than that in the single process of coal pyrolysis under N2 or H2. Tar yield under the studied atmospheres generally has the following order: MG plasma > CH4 plasma ≈ CH4/H2 plasma ≈ CO2/H2 plasma > H2 plasma > H2 > N2. CH4 was dissociated to ⋅CH3, ⋅CH2, ⋅CH, ⋅C and H⋅ species in CH4 plasma, [18] these activated species combined with free radicals ruptured from coal lead to the increase of tar yield at low tamperature range, as can be seen in Figure 2(b). However, CH4 is mainly dissociated to ⋅C and H⋅ when temperature exceeds 500 °C, and will cause serious carbon deposit which can further affect the discharge. So, tar yield under CH4 plasma approaches to that under N2 while water yield approaches to that under H2 plasma when the temperature is higher than 500 °C. The addition of H2 to CH4 has the
3
Oviedo ICCS&T 2011. Extended Abstract
effect on increasing tar yield and decreasing water yield compared with that under CH4 plasma at high temperature range because H2 can eliminate carbon deposit and maintain a steady DBD. [19, 20] Tar yield under CO2/H2 plasma is about the same as that under CH4/H2 plasma when temperature is below 500 °C, but approaches to that under N2 when temperature is above 500 °C. Water yield under CO2/H2 plasma is the highest in all the experiments and keeps increasing with the increase of temperature. It’s about several times more than that under N2 and H2 at low temperature range but it’s still no more than 6 %. The high tar under CO2/H2 plasma may ascribed to the combination of oxygenous radicals and CHx radicals formed in CO2/H2 plasma [21-23] and those from coal, while high water yield due to the reverse water gas shift reaction and methanation reaction which can easily occur under the experiment conditions. MG plasma has both the advantages of CH4/H2 plasma and CO2/H2 plasma. Tar yield under MG plasma is the highest compared with that under other atmospheres, and it’s about 100 % and 77 % more than that under N2 and H2 at 400 °C, respectively. The increase of tar yield under MG plasma is more evident at low temperature range, which can be seen from Figure 2(b) that tar yield under MG plasma is about 2 and 1.1 times as that under N2 at 400 °C and 600 °C, respectively. While water yield under MG plasma is lower than that under CO2/H2 plasma though it’s higher than that under any other atmospheres. HLH SM
75 70 65 30
40
50
60
Discharge power(W)
Water yield(wt.%,daf)
80
60
10
24 (a)
Tar yield(wt.%,daf)
Char yield(wt.%,daf)
85
(b)
22 20 18 16 14
30
40
50
Discharge power(W)
60
(c)
8 6 4 2 0
30
40
50
60
Discharge power(W)
Figure 2. Effect of discharge power on char, tar and water yields under MG plasma atmosphere (500 °C; 240 ml/min; 7 min) 3.2 Effect of Discharge Power. The effect of discharge power on char, tar and water yields under MG plasma is shown in Figure 2. With increasing discharge power, both coal conversion and water yield increase in varying degrees. However, tar yield of HLH coal increases first, then decreases and has a maximum at discharge power of 40 W, while that of SM coal keeps
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Oviedo ICCS&T 2011. Extended Abstract
increasing. Discharge power is one of the most important factors affects the activation level of the feed gas. The energy and the number of the electrons in the discharge zone are directly determined by the input energy which is depending on discharge power. As the discharge power increasing, the number of high-energy electrons and the collision frequency between electron and gas molecular increases, leading to formation of more activated species [24-26] and finally resulting in the increase of volatiles. However, carbon deposit which can seriously affect the discharge is unnegligible when increasing the discharge power. Tar yield could be significantly increased by increasing discharge power on condition that the discharge is uniform and stable.
4. Conclusions Experimental results showed that coal pyrolysis coupling with gas activation through DBD plasma has effects on coal conversion and product yield, especially at low temperature range. Compared with that under H2 atmosphere, tar yield has little change but water yield shows a significant increase under H2 plasma, while tar yield increases remarkable and water yield decreases under CH4 plasma at low temperature range. CH4 plasma discharge was difficult to be maintained stable and uniform at above 500 °C because of the carbon deposit. Decreasing temperature and addition of H2 and/or CO2 into CH4 can stable the discharge and lead to the increase of tar yield. Tar yield under MG plasma is about two times of that under N2 at 400 °C. CO2/H2 plasma can also increase tar yield, but has the highest water yield in all the experiments. Increasing discharge power can improve tar yield, but water yield has the same trend. Acknowledgement. This work was performed with support of the National Natural Science Foundation of China (20576019 and 20776028), and the National Basic Research Program of China (973 Program), the Ministry of Science and Technology, China (2011CB201301).
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Oviedo ICCS&T 2011. Extended Abstract 1995; 74:17-9. [4] Zhou Q, Hu HQ, Liu QR, Zhu SW, Zhao R. Effect of atmosphere on evolution of sulfurcontaining gases during coal pyrolysis. Energy Fuels 2005; 19:892-7. [5] Qin ZF, Maier WF. Coal Pyrolysis in the Presence of Methane. Energy Fuels 1994;8:1033-8. [6] Sakaguchi M, Laursen M, Nakagawa H, Miura K. Hydrothermal upgrading of Loy Yang Brown coal - Effect of upgrading conditions on the characteristics of the products. Fuel Process Technol 2008; 89:391-6. [7] Hu HQ, Bai JF, Wang Y, Guo SC. Catalytic Liquefaction of Coal with Highly Dispersed Fe2S3 Impregnated in-Situ. Energy Fuels 2001; 15:830-4. [8] Li BQ, Braekman-Danheux C, Cyprès R. Catalytic hydropyrolysis by impregnated sulphided Mo catalyst. Fuel 1991; 70:254-8. [9] Liu QR, Hu HQ, Zhu SW. Integrated process of coal pyrolysis with catalytic partial oxidation of methane. International Conference on Coal Science and Technology. Okinawa, Japan, 2005. [10] Liu JH, Hu HQ, Jin LJ, Wang PF, Zhu SW. Integrated coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst for improving tar yield. Fuel Process Technol 2010; 91:41923. [11] Liu JH, Hu HQ, Jin LJ, Wang PF. Effects of the Catalyst and Reaction Conditions on the Integrated Process of Coal Pyrolysis with CO2 Reforming of Methane. Energy Fuels 2009; 23:4782-6. [12] Drost H, Rutkowsy J, Mach R, Klotz HD, Schulz G. Plasma-chemical methane conversion under nonthermal and thermal conditions: an attempt toward uniform kinetic modeling. Plasma Chem Plasma Process 1985; 5:283-91. [13] Zhou LM, Xue B, Kogelschatz U, Eliasson B. Partial oxidation of methane to methanol with oxygen or air in a nonequilibrium discharge plasma. Plasma Chem Plasma Process 1998; 18:375-93. [14] Liu CJ, Xue BZ, Eliasson B, He F, Li Y, Xu GH. Methane conversion to higher hydrocarbons in the presence of carbon dioxide using dielectric-barrier discharge plasmas. Plasma Chem Plasma Process 2001; 21:301-10. [15] Rico VJ, Hueso JL, Cotrino J, González-Elipe AR. Evaluation of different dielectric barrier discharge plasma configurations as an alternative technology for green C1 chemistry in the carbon dioxide reforming of methane and the direct decomposition of methanol. J Phys Chem A 2010; 114:4009-16. [16] He XF, Hu HQ, Jin LJ, Zhao YP. Prepr Pap - Am Chem Soc, Div Fuel Chem 2010;55:17-8. [17] Zhang YW, Ding WZ, Guo SQ, Xu KD. Reduction of metal oxide in nonequilibrium hydrogen plasma. Chin J Nonferrous Met 2004; 14:317-21. [18] Kadao S, Urasaki K, Sekine Y, Fujimoto K, Nozaki T, Okazaki K. Reaction mechanism of methane activation using non-equilibrium pulsed discharge at room temperature. Fuel 2003; 82:2291-7. [19] Dai B, Zhang XL, Gong WM, He R. Effects of Hydrogen on the Methane Coupling under Non-equilibrium Plasma. Plasma Sci Technol 2001; 3:637-9. [20] Cui JH, Xu GH, Han S. Eliminating Coke Formed in CH4 Coupling under Plasma via Pure H2 Discharge in the System. Acta Phys-Chim Sin 2002; 18:276-8. [21] Liu CJ, Xu GH, Wang TM. Non-thermal plasma approaches in CO2 utilization. Fuel
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Oviedo ICCS&T 2011. Extended Abstract Process Technol 1999; 58:119-34. [22] Maya L. Plasma-assisted reduction of carbon dioxide in the gas phase. J Vac Sci Technol A 2000; 18:285-7. [23] Eliasson B, Kogelschatz U, Xue BZ, Zhou LM. Hydrogenation of Carbon Dioxide to Methanol with a Discharge-Activated Catalyst. Ind Eng Chem Res 1998; 37:3350-7. [24] Zhu AM, Gong WM, Zhang XL, Zhou J, Shi H, Zhang BA. Investigation on pulsed corona induced plasma for coupling of methane. Nat Gas Chem Ind 1997; 2:1-5. [25] Dai B, Zhang XL, Zhang L, Gong WM, He R, Lu WQ, Deng XL. Methane coupling under hydrogen plasma. Sci China Ser B 2001; 31:174-7. [26] Wang BW, Zhang X, Liu YW, Xu GH. Conversion of CH4, steam and O2 to syngas and hydrocarbons via dielectric barrier discharge. J Nat Gas Chem 2009; 18:94-7.
7
Effect of Steam Treatment of a Sub-bituminous Coal on Its Caking and Coking Properties Shui Hengfu
Shan Chuanjun Chang Hongtao Wang Zhicai Ren Shibiao and Kang Shigang
Lei Zhiping
School of Chemistry & Chemical Engineering, Anhui Key laboratory of Coal Clean Conversion & Utilization, Anhui University of Technology Ma’anshan 243002, Anhui Province, P.R. China
[email protected] (Shui H.) Abstract A Chinese sub-bituminous coal i.e. Shenfu (SF) coal was steam treated at different temperatures and the caking and coking properties of the treated coals were evaluated by caking indexes (G indexes) and crucible coking determinations. The results show that steam treatment can obviously increase the G index of SF coal and modify the crucible coke quality made from the steam treated SF coal blends. For the steam treated coals used in the coking coal blends instead of the SF raw coal, the micro-strength index (MSI) of the coke and particle coke strength after reaction (PSR) increased, and particle coke reactivity index (PRI) decreased, which are beneficial for metallurgical coke to increase the gas permeability in blast furnace. The removal of oxygen functional groups especially hydroxyl group thus dissociating the aggregated structure of coal during steam treatment maybe responsible for the modifying results. 1. Introduction
The rapid developing of iron-making by blast furnaces promotes the developing of coke-making industry. This is leading to the increased requirement to the coking coals. More than 300 millions tons coke productivity consumes about 400 millions tons coking coals per year in China, resulting in the shortage supply of the coking coals. Therefore opening coking coal resources is becoming one of most interesting issues in coke-making industry. On the other side, the reserve of sub-bituminous coals in China is abundant. Shengfu (SF) coal is one of the sub-bituminous coals and it has low contents of sulfur and ash. Therefore it is effective for lowering the contents of sulfur and ash in coke if SF coal can be used in coal blends. In order to modify the
caking propensity and decrease volatile material content thus increasing the amount of non-coking coals used in coke-making coal blends, many of effective methods have been carried out as pretreatment such as thermal and hydrothermal treatments [1-3]. Mukherjee et al [2] found that hydro-thermal treatment promoted the formation of a coke-like mass for non-coking coal and the relative decreases of total oxygen and hydroxyl oxygen were greater in hydro-thermal treatment than in thermal treatment without water for coal. Iino et al [3] found that water treatments of three Argonne Premium coals at 600 K increased their extraction yields greatly. We have also found that hydro-thermal treatment at proper conditions can increase the extraction yields of bituminous coals [2]. Hydrothermal treatment (liquid water or steam) researches by pioneers are all carried out at higher pressure, normally more than 20 atm, and the hydrothermally treated coals are characterized by solvent extraction. It can speculate that hydrothermal treatment of coal by steam at atmosphere maybe more beneficial for removal volatile maters and easy to be realized in industry, especially for sub-bituminous coals. In this study a Chinese sub-bituminous SF coal was steam treated at atmosphere, and the caking and coking properties of the treated coals were evaluated by crucible coking determinations. The results are positive and the steam treated SF coal can be used in coal blends of coke-making. 2. Experimental 2.1. Coal sample A Chinese sub-bituminous coal i.e. SF coal was used in this study. The properties of SF coal are shown in Table 1. The coal sample was ground and sieved passing through 200 meshes, stored under a nitrogen atmosphere and dried for 12 h under vacuum at 80℃ before use. Table 1 Ultimate and proximate analyses of SF coal
SF Coal *
Proximate analysis(wt%)
Ultimate analysis（wt %, daf）
Sample
*
C
H
N
S
O
Ad
Vdaf
Mad
78.67
5.01
1.21
0.45
14.66
5.2
38.3
10.1
by difference.
G 0
2.2. Steam treatment The steam treatment of coal was performed at a fixed bed reactor at atmospheric pressure. The reactor was constructed of 2.6 cm i.d. 314 stainless-steel pipe and was 26 cm in length. In each run, 70 g of dried coal sample was charged into the reactor then saturated steam in 100 oC was induced flowing through the coal sample in the reactor with a rate of 5ml/min. The reactor was heated by a two half external furnace to the desired temperature, maintained for 1h, then cooled down to room temperature in 1-2 h by opening the two half furnace and stopped steam flowing. The treated coal was taken out from the reactor, and then dried under vacuum at 80℃ for 12 h. 2.3. Caking index measurement The caking index (G index) was used to characterize the caking property of coal. The measurement was carried out according to National Standard of China (GB5447-85), which is based on that of Roga index. Briefly, 1g of coal was mixed with 5g of standard anthracite (Ruqigou，China). The mixture was carbonized in an inert atmosphere at 850°C for 15 min. The coke obtained was subject to the drum tests for twice, which is slightly different from the Roga index testing requiring drum tests for three times. The coal sample preparation, stirring, carbonization and drum test are all the same as those of the Roga index measurement, and the caking index G was calculated as: G= 10 +
30m1 + 70m2 m
Where m is the weight of coal sample (g), m1 and m2 are the weight (g) of the coke fraction (>1mm) after the first and second drum test respectively. 2.4. Coal extraction Coal extraction was carried out at room temperature. A mixed solvent of carbon disulfide/N-methyl-2-pyrrolidinone (CS2/NMP, 1:1 by volume) was used as solvent, as described in details elsewhere [4]. The extraction yield was then determined from the weight of the residue: Extraction yield =
1 − M r / M coal × 100 % (100 − A d ) / 100
Where, Mr is the weight of dried residue (g), Mcoal is the weight of dried coal (g), and Ad is the ash content of coal (db,%). 2.5. Crucible coking determination The carbonization experiments were carried out in an electrically-heated oven using a 300ml crucible. 300g coal blends (SF raw coal or its steam treated coal 8%, gas coal 27 wt%, coking coal 35 wt%, lean coal 10 wt% and rich coal 20 wt%) with a particle size less than 1.25mm were loaded into the crucible. An iron cake of 500g was put on the coal sample to maintain the bulk density of coal feed. The filled crucible with a cover was placed in the oven in an inert atmosphere and heated at the rate of 5~7°C/min to 400 °C, at 3 °C/min to 950°C, and held at 950°C for 30min, then cooled down to room temperature in about 12 h. The coke produced was subject to further evaluations. 2.6. Coke reactivity towards CO2 The reactivity towards CO2 of coke product was measured following a procedure based on the reported method [5]. Briefly, 20 g of cokes (3–6 mm in size) were reacted at 1100°C for 2 h with CO2 at a flow rate of 150 ml/ min. The particle coke reactivity index (PRI) was calculated as the percentage of weight loss after the reaction. Replicate runs were conducted, and the error was within 3%. PRI reported in this study are the average value of the 2 runs. 2.7. Coke mechanical strength Micro-strength of coke was determined according to the Ragan and Marsh method [6]. Briefly, two charges of coke (2 g; particle size between 0.6 and 1.2 mm) were charged into two separate cylinders (25.4 mm i.d and 305 mm long) sealed by steel dust caps, and each contained 12 steel ball-bearings (8 mm diameter). While the cokes from the crucible coking experiments were subjected to 800 rotations at a speed of 25 rpm, the weight percent of coke particles (>0.2 mm in size) was used as the indicator of the micro-strength index (MSI) of the coke. The micro-strength index of the coke after reactivity measurement is defined as particle coke strength after reaction (PSR). The MSI and PSR were reported as the average value of 2 runs. 2.8. FTIR measurement
FTIR were measured on a PE-Spectrum One IR spectrometer at a resolution of 4 cm-1. Samples for the FTIR measurement were prepared by mixing the coal sample with KBr and the mixture was pressed to form a pellet. The difference spectra between raw and treated coal were also obtained using the absorption of C=C bond stretching of aromatic rings at 1600cm-1 as a standard peak.
3. Results and Discussion 3.1. Effects of steam treatment on the caking property and extraction yield of SF coal. Table 2 shows the G indexes and extraction yields of raw and steam treated coals at different temperatures. Because SF coal is a non-caking coal, its G index is 0 as shown in Table 1. In order to differentiate varieties of G index after steam treatment, SF coal or its steam treated one was mixed with an equivalent rich coal (G index is 98) and the mixed coal was used to determine G index instead of SF raw coal or its steam treated ones. Table 2 shows that steam treatment of SF coal can increase its G index and modify its caking property. The maximal G index of 42.4 was obtained at 150℃ steam treatment, which is much higher than that of raw coal 34.6. Further increasing the steam treatment temperature the G index had a decreased tendency. The change of extraction yield after steam treatment is similar with that of G index as shown in Table 2. The extraction yield of SF raw coal is low (4.8%). After steam treatment the extraction yield increased obviously and the maximal extraction yield of 16.0 % was obtained at 200℃ steam treatment. At the range of 150-250℃ the steam treated coals gave similar extraction yields but were much higher than that of raw coal. We have reported [7,8] that the amount and composition of extractible constituents in the CS2/NMP mixed solvents have a great effect on the caking property of coal. With the increase of the extraction yield in the mixed solvents, the caking index of the coal increases. A little decrease in G index after 200℃ steam treatment maybe due to the more content of light constituents in the extractible constituents compared to those of
the coal steam treated at 150℃. It can also be observed from Table 2 that with steam treatment temperature increasing, the volatile yield continuously decreases. Table 2 Effect of steam treatment on the G index, extraction yield and volatile yield of SF coal with different temperatures G
Extraction yield (daf, wt%)
V (daf, wt%)
Raw coal
34.6
4.8
38.3
100
38.4
10.3
36.5
150
42.4
15.2
31.4
200
41.2
16.0
30.2
250
39.2
15.6
28.7
Temperature (℃)
3.2. Characterization of steam treated coal. Table 3 shows the elemental compositions of SF raw coal and its steam treated ones. It can be observed from Table 3 that the changes of N and S after steam treatment are negligible. An obvious decrease in O contents for the steam treated coals compared to that of SF raw coal could be observed. With the increasing of steam treatment temperature the O content of the treated coal kept the decreased tendency. For example, O content decreased from 14.66% of SF raw coal to 13.62% of 150℃ and further to 13.10% of 250℃ steam treated ones. This suggests that steam treatment can promote the removal of the oxygen groups in coal molecules although it has little effect on the removal of S and N heteroatoms. It is very interesting that H/Cs of steam treated coals almost keep the same as that of raw coal 0.76 as shown in Table 3. It is easy to understand that H content in volatile mater in higher than that in raw coal. Steam treatment promotes to release the volatile metters from the treated coal bringing much of light constituents to be rich in hydrogen. Table 3 Elemental analyses of SF raw coal and its steam treated ones (wt %, daf) C
H
N
S
O*
H /C
Raw coal
78.67
5.01
1.21
0.45
14.66
0.76
100
79.36
5.04
1.27
0.42
13.91
0.76
150
79.65
5.08
1.26
0.38
13.62
0.76
Temperature
(℃)
200
79.80
5.06
1.29
0.41
13.44
0.76
250
80.13
5.04
1.29
0.44
13.10
0.75
* By difference. In order to probe the mechanism for the G index and extraction yield enhancements of coal by steam treatment, FTIR measurement was used to discover the structural change of coal by the steam treatment. Figure 4 shows the FTIR spectra of SF raw coal, its steam treated one at 200 ℃ and their difference spectrum. The difference spectrum shows a decrease in intensity of bands near 3400 and 1650 cm-1 for steam treated coals, which are assigned to self-associated OH hydrogen bonds and carbonyl band (C=O) stretching in coal respectively. The decreases in intensity of bands near 3400 and 1650 cm-1 in difference spectra show the decreases in the self-associated OH hydrogen bonds and carbonyl bands of steam treated coals. That is to say one of the mechanisms of steam treatment of coal is to remove OH and carbonyl groups, therefore to decrease self-associated OH hydrogen bonds resulting in G index and extraction yield enhancements of treated coal. The removal of oxygenated a
functional groups including hydroxyl
A
b
oxygen
is
beneficial for the caking property of coal because
c
oxygenated 4000
3500
3000
2500
2000
Wavenumber /cm
1500
1000
functional
500
-1
groups during coal pyrolysis consume much amount of
Fig. 1 FTIR spectra of steam treated coal at 200 (a), SF
raw coal (b)
and the difference b-a (c)
active hydrogen, resulting in the formation of cross-linked
chars.
3.3. Crucible coking determination. Normally, the use of coal blends is a common practice in the coke manufacture
industry. And also SF coal is a non-caking coal, it can not be singly used in coke-making. As such, coal blends were used in crucible coking determinations in this study instead of a single coal. The standard coal blends used in this study were gas coal 35 wt%, coking coal 35 wt%, lean coal 10 wt% and rich coal 20 wt%. In the case of SF coal used in the coal blends, the amount of SF raw coal or its steam treated one was 8 wt% instead of 8 wt% gas coal, i.e. the amount of gas coal used in the coal blends decreased to 27%. The coke micro-strength index (MSI), the particle coke reactivity index (PRI) towards CO2 and particle coke strength after reaction (PSR) of the cokes produced in crucible coking experiments were used to assess the coke properties, as shown in Table 4. Table 4 Crucible coking determination results Coal Blends
MSI,%
PRI, %
PSR,%
Standard coal blends
63.4
41.0
49.5
SF raw coal
54.6
48.6
42.9
150
hydro-thermally treated coal
61.3
42.8
45.9
200
hydro-thermally treated coal
62.0
41.4
50.0
250
hydro-thermally treated coal
61.0
42.9
49.1
It can be observed that comparing with standard coal blends, using 8 wt% SF raw coal instead of equivalent amounts of gas coal caused an obvious decrease in MSI and increase in PRI, resulting in great decrease in PSR. Currently perhaps the two most important parameters, used and worldwide to evaluate the performance of a metallurgical coke in the blast furnace and to define the quality of coke, are the reactivity to CO2 at high temperature (coke reactivity index) and the post-reaction mechanical strength (coke strength after reaction index) [9, 10] . This result suggests that as a sub-bituminous coal, SF raw coal is disadvantage in coal blends compared to gas coal because of its non-caking property and high content in volatile yield. Table 3 shows that steam treated coals give much higher quality of cokes compared to SF raw coal. The PRIs of the cokes from steam treated coals decreased obviously compared with that of SF raw coal, and the corresponding PSRs were also higher than that of SF raw coal. The coke with the largest values of MSI, PSR and lowest value of PRI was obtained from 200
steam treated coal, and it had got to the quality of coke from
standard coal blends. The results strongly demonstrate that steam treatment is a very effective method for sub-bituminous SF coal to modify its caking and coking properties. The crucible coking determination results of steam treatment are consistent with the changes of G and solvent extraction yield shown in Table 2. The steam treated coals with increased values of G and extraction yield gave higher quality of coke when they were used in coal blends. It is well known that [2] oxygen groups, especially for hydroxyl oxygen in coal molecules are responsible for the generation of cross-link and consumption of active hydrogen, thus shortening the plastic temperature range. Steam treatment can promote the removal of OH group (indicated by elemental analyses and FTIR), thus dissociating the aggregated structure of coal and making the treated coal to be with less aggregated structure and much more amount of light fragments. These are beneficial for SF coal to modify its caking and coking properties, resulting in a higher quality coke formed. 4. Conclusions Comparing with thermal treatment, steam treatment of sub-bituminous SF coal can obviously increase its G index and solvent extraction yield and decrease its volatile yield by promoting the thermolysis of SF coal and making much more volatile matters to be released. Steam can swell the coal and dissolve the mobile, thermolytic fragments, especially for oxygen-containing materials, resulting in more light fragments existed in the steam treated coal and improved transfer of internal donatable hydrogen. Steam treatment of SF coal can promote the removal of oxygen groups, especially OH group in coal molecules. This will decrease self-associated OH hydrogen bonds in macromolecular network of coal, thus making the treated coal to be with less aggregated structure, resulting in the G index and extraction yield enhancements of the treated coal. Steam treatment is an effective method to modify the caking and coking properties of SF sub-bituminous coal. Crucible coking tests suggest that steam treatment can greatly increase the MSI, PSR and decrease the PRI of the coke when the steam treated SF coal is used in the coal blends instead of SF raw coal. The quality
of the coke obtained from 8% 200℃ steam treated SF coal in coal blends gets to that of the coke obtained from the standard coal blends, which there is no SF coal addition in the coal blends.
Acknowledgment.
This work was supported by the Natural Scientific Foundation
of China (20876001, 21076001, 20936007), and National Basic Research Program of China (973 Program, 2011CB201302). Authors are also appreciative for the financial support from the Provincial Innovative Group for Processing & Clean Utilization of Coal Resource. References [1] Saikiaa BK, Boruaha RK, Gogoib PK, Baruaha BP. A thermal investigation on coals from Assam (India). Fuel Processing Technology 2009; 90:196–203. [7] Shui HF, Lin CH, Zhang M, Wang ZC, Zheng MD. Comparison of the associative structure of two different types of rich coals and their coking properties. Fuel 2010; 89:1647–1653. [2] Mukherjee DK, Sengupta AN, Choudhury DP, Sanyal PK, Rudra SR. Effect of hydro-thermal treatment on caking propensity of coal. Fuel 1996;75: 477-482. [4] Shui HF, Wang ZC, Wang GQ. Effect of hydro-thermal treatment on the extraction of coal in the CS2/NMP mixed solvent. Fuel 2006; 85:1798-1802. [3] Iino M, Takanohashi T, Li C, Kumagai H. Increase in extraction yields of coals by water treatment. Energy & Fuels 2004; 18: 1414-1418. [5] Wietlik US, Gryglewicz G, Machnikowska H, Machnikowski J, Barriocanal C, Alvarez R, Dı´ez MA. Modification of coking behaviour of coal blends by plasticizing additives. Journal of Analytical and Applied Pyrolysis 1999; 52: 15–31. [6] Ragan S, Marsh H. Carbonization and liquid-crystal (mesophase) development. 22. Micro-strength and optical textures of cokes from coal-pitch cocarbonizations. Fuel 1981; 60:522–528. [8] Shui HF, Zheng MD, Wang ZC, Li XM. Effect of coal soluble constituents on caking property of coal. Fuel 2007; 86 : 1396–1401.
[9] Koszorek A, Krzesińska M, Pusz S, Pilawa B, Kwiecińska B. Relationship between the technical parameters of cokes produced from blends of three Polish coals of different coking ability. International Journal of Coal Geology 2009; 77:363-371. [10] Pis JJ, Menendez JA, Parra JB, Alvarez R. Relation between texture and reactivity in metallurgical cokes obtained from coal using petroleum coke as additive. Fuel Processing Technology 2002; 77–78: 199– 205.
International Conference on Coal Science and Technology (ICCS&T), October 2011 ABSTRACT THE ROLE OF COAL SCIENCE IN DEVELOPMENT AND DEPLOYMENT OF HIGH EFFICIENCY ENERGY TECHNOLOGIES D. J. Harris and D. G. Roberts CSIRO Energy Technology PO Box 883 Kenmore, Queensland, 4069, Australia
[email protected] World coal consumption is projected to grow by approximately 55% between 2007 and 20351. The non-OECD Asian nations (predominantly China and India) are expected to account for 95% of this projected growth, with China to increase its coal-fired electricity generation capacity from approximately 500 GW (2007) to approximately 1250 GW by 2035. While coal use in OECD countries is expected to increase relatively slowly over this period, and coal’s share of electricity generation in these nations is expected to fall, increased generation from coal-fired power plants is still significant: in the US it is expected to account for 26 percent of the growth in total electricity generation from 2007 to 2035. Another important factor in some OECD countries (particularly the US and Australia) is the need for new plant to replace aging installations which have relatively low efficiencies and are expected to be unattractive for retrofit of CO2 capture technologies to meet likely future greenhouse-gas emissions requirements. The research challenges needed to advance the development of low emissions coal-based power generation technologies are clearly associated with increasing efficiencies and reducing greenhouse gas emissions at large scale and low cost. In the face of strongly increasing world coal use, new technologies will be needed in the future to increase the efficiency of coal fired power generation significantly above the levels of current best practice and to facilitate the capture of CO2 for long term storage. Low Emissions Coal: Efficiency is King The average efficiency of coal-fired plants globally is currently only about 28% (HHV) with the most efficient ultra-supercritical steam plants and new IGCC demonstration technologies achieving about 45%2. The current large worldwide growth in new capacity provides an important opportunity in both developing and developed nations for development and deployment of advanced, high efficiency power generation technologies which can provide a suitable technology platform for further efficiency and cost improvements to meet the requirements for increasing levels of CO2 emissions abatement. Repowering existing coal-fired plants, where possible, to improve their efficiency, coupled with installation of new and more efficient plant, will provide significant reductions in CO2 emissions. However, to achieve very high levels of CO2 emissions reduction from fossil fuel based power generation technologies, it will be increasingly important to have in place conversion technologies with the highest possible efficiencies which are capable of reducing the amount of CO2 that must eventually be captured and stored. Due to the significant energy demands and costs associated with CO2 capture and storage (CCS), deploying the most efficient plant possible is a critical prerequisite to enable these plants to be capable of being fitted with CO2 capture technologies, either from new or as a staged retrofit in the future. The presentation will discuss research needs and technology development pathways in the areas of high efficiency, low emissions coal technologies. Particular emphasis will be on coal gasification and the important downstream syngas conversion and gas separation technologies necessary to facilitate CO2 capture and hydrogen production at a scale and cost acceptable to the power industry. Based on current Australian RD&D programs, the presentation will also include an overview of current pilot and demonstration-scale research on post combustion capture (PCC) of CO2 from conventional pulverised coal power technologies. 1
US Energy Information Administration, International Energy Outlook 2010 World Coal Association, 2011: http://www.worldcoal.org/coal-the-environment/coal-use-theenvironment/improving-efficiencies/ 2
1
Ultimately, even higher efficiency systems will be required. This presentation will also introduce examples of some novel future technologies, such as direct injection coal engines using coal water fuels and direct carbon fuel cells, which have the potential to achieve step increases in power generation efficiency with consequent reductions in the amount of CO2 that would be emitted or collected for storage. The emphasis here will be on the impact of coal properties and behaviour on the performance of these technologies and the role of coal science and associated R&D in facilitating their rapid development and uptake to meet environmental, cost and performance goals during the next 5-20 years of rapid energy demand growth. Post Combustion Capture: Starting From Where We Are While next generation, high efficiency technologies are clearly needed to meet longer term needs, post combustion capture (PCC) of CO2 from conventional pulverised coal power technologies is an important transition technology and focussed research and demonstration programs are required to support early adoption of these technologies on the most appropriate existing and new pf plant. While solvent based technologies for CO2 capture are well established in the chemical and process industries, the key challenges associated with PCC technology are associated with reducing the capital cost, energy efficiency penalties and potential environmental impacts of these large scale solvent based systems. For current systems, the efficiency penalties associated with PCC on conventional plant can be up to 10 percentage points and this major loss of efficiency (and capacity) represents the most challenging aspect for retrofit and new build applications of this technology. On the most modern pf plants, which already have high levels of flue gas treatment, coal property impacts on PCC systems are relatively minor and much of the required R&D is focussed on developing improved solvents and reducing the energy requirements of CO2 recovery. However, many existing coal fired plant, with little or no flue gas treatment, face additional constraints as coal specific contaminants can interact deleteriously with the most common solvents and further work is required to develop alternative materials and processes. IGCC: a High-Efficiency Platform for CCS IGCC technology presently achieves similar efficiency to latest PC technology (~40–45% HHV basis) but at a slightly higher capital cost. However, substantial improvements in IGCC efficiency (~ + 8 percentage points) along with significant reductions in capital cost are projected through new and improved process blocks now under development internationally. As for all power technologies, the introduction of CCS decreases the overall efficiency and increases costs of power generation. For IGCC systems, efficiency losses with currently-available (precombustion) CO2 capture technologies are expected to be approximately 6–8 percentage points and capital costs are likely to increase by up to 40%. Carbon capture technologies for IGCC applications are still early in their learning curve; therefore, as with the main IGCC plant, significant improvements to the process components can be envisaged and development of these will substantially reduce the cost and efficiency penalties associated with CCS. As IGCC and IGCC-CCS technologies begin to be implemented, initially at the commercial demonstration scale, a critical factor in the success of these projects, and in the subsequent wider deployment, will be stakeholder confidence. It is important that governments, technology developers, vendors, operators and the community can see that such technologies can operate reliably at the required scale with high availability, safety and environmental performance while meeting the necessary CO2 emissions requirements. Ongoing research is therefore required to continue to support development and deployment of large-scale IGCC and IGCC-CCS systems. Many of the major technical issues associated with the success of these initial projects, and which will underpin continued improvement of the efficiency and performance of IGCC with CCS, will rely on a detailed understanding of the behaviour of coals in the gasification process and of the resultant impacts on downstream unit operations associated with syngas cleaning, processing, separation and CO2 storage or utilisation. For example: •
Knowledge of coal gasification reactivity and conversion behaviour under conditions relevant to the specific technology and operating environment is a critical factor in efficient gasifier design and operation to ensure complete and efficient coal conversion to maximise efficiency and reduce carbon in slag to acceptable levels;
2
•
Appropriate coal characterisation, selection and preparation are key factors which define the ability of the mineral matter component of coals to form suitable slags that do not compromise gasifier operation and ensure high availability. Of particular importance in this regard is the impact of poor slagging behaviour of coals on the entire system operation. Most notably the need to operate the gasifier at higher temperatures or with excessive fluxing to successfully manage the slag in the gasifier. This has direct implications on gasifier efficiency and on oxygen demand (and costs) and can directly limit plant capacity. Excessively high operating temperatures also affects plant life and maintenance requirements – both within the gasifier and in downstream gas cooling and cleaning systems
•
In any system where coal-derived syngas is used as the basis for power generation, chemicals production, or in the manufacture of liquid fuels, the syngas must be cleaned to standards acceptable by the downstream plant. In coal gasification derived systems the contaminants include fine particles of fly ash, gaseous species containing sulphur, chlorine, fluorine, alkali metals and trace elements. Coal properties and gasification behaviour under the relevant process conditions profoundly affect syngas composition which specify development criteria for improved and breakthrough technologies to reduce the costs and energy penalties associated with syngas cleaning and processing, gas separation and CO2 capture systems
Coal Impacts on Gasification Performance Conditions inside an entrained flow gasifier are extreme: pressures are high (20–40 bar or sometimes greater) and temperatures are high (flame temperatures often over 1800 K). The ratio of oxygen to fuel is significantly lower than those used in coal combustion technologies, and the mineral matter in the coal is required to melt and flow out of the gasifier continuously. Steam is sometimes included in the feed streams to the gasifier, and some gasifiers are designed to feed coal as a coal-water slurry. These aspects of gasification mean that the extensive literature and understanding of coal performance in pf boilers has little direct application to understanding and prediction of coal performance under gasification conditions. Results of ‘standard’ combustion tests do not translate to gasification performance—new approaches, facilities, techniques, and knowledge are required. A striking point to emerge from analysis of coal performance in the complex environment in these high pressure, high temperature reaction systems is the potential impact of relatively fundamental coal properties on many of the process operations comprising the IGCC system. Even seemingly simple factors such as inherent moisture, mineral matter composition, high temperature volatile yield, char reactivity and structure, grinding behaviour, slurrying characteristics, sulphur content etc can become particularly important as they may create issues that cannot be accommodated through simple changes to operating conditions. Such issues therefore become limiting factors for the fixed plant design (eg size of ASU, gasifier, syngas cooler etc). Managing these and other coal related issues can incur significant costs and/or operating boundaries that can seriously affect plant capacity, efficiency and performance. To allow practical and reliable application of a sound fundamental understanding of gasification science to the solving of real industrial problems, knowledge of coal pyrolysis, char formation, char reactivity, slag formation and flow, and coal gasification behaviour needs to be integrated in a form that is applicable to a range of gasification technologies and, eventually, gasification-based energy systems. Fundamental, experimental gasification research needs to be undertaken in parallel with the development of detailed coal reaction and conversion models designed to allow more widespread application of the outcomes through, for example, relevant gasifer and integrated process models of the entire coal conversion, slag handling, syngas processing and gas separation systems. This can only be done effectively through close collaboration of researchers, industrial technology developers, vendors and operators. From Refineries to Power Generation: Advanced Syngas Processing for High Efficiency CCS In the chemicals and refinery industries, coal gasification, and capture of CO2 from syngas is commercially mature. A research strategy to support the rapid development and application of advanced syngas processing and gas separation technologies in the power sector will require a combination of fundamental materials development and testing programs, laboratory scale experiments, modelling projects, larger ‘research gasifier’ scale measurements and screening tests. This work would be complemented with appropriately targeted pilot plant and slipstream tests utilising syngas slipstreams such as those available from a number of international IGCC commercial, 3
demonstration and research projects. An example of a commercial facility that currently operates in this way is the Puertollano demonstration IGCC project in Spain which has a slipstream of up to approximately 2% of the syngas available for advanced technology development projects such as gas cleaning, shift and gas separation concept development, materials testing etc. Improved technology components and concepts fitting within the IGCC process flow sheet that have been identified to date, and in some cases tested using simulated syngas environments at laboratory scale, include: •
new water gas shift catalysts optimised for coal syngas and suitable for use with membrane reactor systems at higher temperatures (up to 600°C);
•
integrated high temperature (~600°C) dry syngas cleaning systems;
•
trace element capture integrated with high temperature syngas cleaning;
•
metal and ceramic membrane based Hydrogen/CO2 separation technologies;
•
integrated water gas-shift/metal membrane catalytic reactor concepts capable of enhancing hydrogen production and separation at high temperatures;
•
ion transport membrane air separation technologies have been in development for almost two decades and are now are nearing commercial availability at tonnage scales.
Further opportunities to significantly increase efficiencies are expected as syngas and hydrogen based fuel cells reach commercial availability. While these are unlikely to be available at the scale and reliability required for large scale power generation within the next 15-20 years they provide an attractive development pathway for the core, high efficiency technology platforms that are being developed and demonstrated today.
4
Gas adsorption capacity of coaly shales from Japan and USA - Implications for CO2 storage in coal-bearing formation S. SHIMADA1, Y. NISHIIRI1, N. SAKIMOTO1, K. OHGA2 and Y-S. JUN3
1
Graduate School of Frontier Sciences, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8563 Japan,
[email protected] 2
Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 3, Kitaku, Sapporo 060-8628, Japan 3
Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis
One Brookings Drive, Campus Box 1180, St. Louis, MO 63130-4899, USA Abstract The adsorption capacity of CO2 and CH4 with coaly shales was measured by the volumetric method at 35°C and 50°C, with a pressure range up to 9 MPa. The coaly shale samples were obtained from Yubari (Japan), Kusiro (Japan), Bibai (Japan), and Illinois(USA) and a gas shale sample came from Pennsylvania (USA). Adsorption capacity of the shale samples varied widely. In particular, Yubari coaly shale exhibited the largest CO2 adsorption capacity of 14 cc/g at 35°C and 5 MPa. This value is equivalent to the adsorption amount of general coal with medium CO2 adsorption capacity. The above result suggests that CO2 adsorption in shale is not negligible during CO2 storage in coal bearing formation. This study provides information about the potential challenges on low injectivity (low permeability) of coaly shale CO2 storage operation and can aid developing effective and safer CO2 storage in ECBMR. 1. Introduction Geological CO2 storage is a promising method to reduce CO2 emissions to the atmosphere in abating global warming. ECBMR (Enhanced Coalbed Methane Recovery) is a unique technology to enhance methane recovery from coal seams while storing CO2. However, the coal seam as a target formation of geological CO2 storage has a disadvantage that the coal seams are thinner compared to aquifers, while thicker formation is preferred to ensure larger CO2 storage capacity. The coal-bearing formation consists of coal seams and aquifer components (shale, sandstone and brine etc.). Therefore, from the view point of CO2 storage, the coal-bearing formation can be a very attractive target formation. The storable CO2 amount in coal seams is calculated by the sum of adsorbed gas in the 1
coal matrix and free gas in cleats. For the aquifer component, the storage amount has been calculated by the sum of free CO2 gas in pore space and CO2 dissolution in aquifer brine. The adsorption mechanism is usually not considered in aquifer components. Shales and coaly shales composing the coal-bearing formation have very fine pores and might exhibit the adsorption phenomena with CO2. Therefore, when coal-bearing formation is considered for potential CO2 storage, the CO2 adsorption contribution in formation may not be negligible in the calculation of storable CO2. Moreover, shale has sealing capacity in geological CO2 storage. As a storage site, either for depleted oil and gas field or an aquifer, one of the most important tasks for operation is to verify the sealing integrity of CO2 by cap rock of the reservoir. In Sleipner monitoring project, when CO2 is injected into the aquifer formation, the buoyancy increases and the majority of CO2 has accumulated at the bottom of the cap rock. In this case, the adsorption phenomenon is believed to occur between CO2 and the shale that located in the cap rock. Nevertheless, this kind of trapping mechanism for adsorption has not been seen from any reservoir simulator so far. However, if the CO2 adsorption can be fixed stably, it is not just contribute to the increment of capacity of storage potential, but also can be anticipated for decreasing the CO2 leakage rate as well [1, 2]. In addition, recent increasing shale gas development in the United States also promotes the importance of research regarding CH4 adsorption on shale, which previously not really given much attention. Although it is known that shale gas exists as free gas or adsorbed gas inside shale, there are not many research related to experiment of adsorbed gas, and also there is still many unclear things related to adsorption mechanism using possible adsorption model equation. The significance of research regarding special characteristic of CO2 and CH4 adsorption is also based on the idea of that similar advanced CH4 capture method for CO2 injection into coal seam might be applicable for shale gas production as well. Therefore, in this study, an experiment of CO2 and CH4 adsorption in shale has been carried out, verifying the possible adoption of the adsorption model equation for four coaly shale and a gas shale samples. 2. Experimental Method 2.1 Outline A series of experiments to measure the amount of CO2 and CH4 adsorption by using volumetric method have been carried out in this study. The method is to calculate the molar amount of gas from gas pressure injected to the cell and determines the adsorbed amount from the difference of the molar amount in gas before and after adsorption. The measuring device of volumetric method is shown in Figure 1. In order to verify the supercritical adsorption properties, experimental condition was set to be 35°C or 50°C, and up to about 9 MPa. 2
Figure 1 Schematic diagram of experimental apparatus. (a) Reference cell, (b) Sample cell, (c) Water bath for temperature control, (d) Pressure transducer, (e) Gas cylinder, (f) Vacuum pump, (v-1) and (v-2) valves By using the adsorbed amount obtained from the experiment, the amount of excess adsorption is calculated by the nth of differential excess adsorption ∆n (nexc) of the following Eq. 1,
∆n
(n) exc
Pi ( n )VR Pf( n −1)VV Pf( n ) (VR + VV ) − = + RTZ ( n ) RTZ ( n −1) RTZ (f n ) i f
(1)
where i and f are the initial and final conditions of adsorption equilibrium, respectively, at each step, VR is the reference cell volume, VV is the void volume of sample cell, Z is the compressibility factor. Regarding the compressibility factor of Z in Eq. 1, the value for CO2 was obtained from Span and Wagner equation [3] and CH4 from Setzmann and Wagner equation [4]. The nth excessive adsorbed amount was calculated by using Eq. 2 below n
(n) exc
n
(k ) = ∑ ∆nexc k =1
(2)
In this calculation, the initial value of the void volume of sample cell is calculated as constant since it is deviated due to the larger volume of adsorbed surface in the sample, which increases the amount of adsorption when pressure is high. Therefore, the value of the absolute amount of adsorption, which was taken from the volume of adsorption layer, is converted to Eq. 3. In this study, the adsorbed phase density is calculated as equal to the liquid density at normal boiling temperature for CH4 and liquid density of triple point for CO2. The value for CO2 and CH4 is 1.178[g/ml] and 0.422[g/ml], respectively.
ρg nexc = nabs 1 − ρ ad
(3)
where nabs is the absolute adsorbed amount, ρg is the gas density, and ρad is the adsorbed phase density. 3
2.2 Shale Samples The following five shale samples were used in this study: PA-GS (gas shale taken from shale gas development area in Pennsylvania, USA) Illinois (coaly shale collected from the coal-bearing formation of a coal mine in Illinois, USA) Yubari (carbonaceous shale of Yubari area, Japan) Bibai (coaly shale from Bibai coal mine, Japan) Kushiro (coaly shale from Kushiro coal mine, taken from under sea formation) In order to reduce the time to reach the equilibrium, the shale sample was crushed to 75~150 μm size. For the pre-treatment before the experiment, the sample is vacuumed for 24 hours at 60°C. 2.3 Adsorption Model Equation In this study, the measured values are fitted with four adsorption formulas shown below. [5, 6, 7, 8] Langmuir Equation (Surface adsorption model)
n=
n0 KP 1 + KP
(4)
Freundlich Equation (Surface adsorption model)
n = KP1/ t
(5)
Modified Dubinin-Radushkevich (DR) Equation (Pore-filling model)
ρ n = n0 exp − D ln ad ρg
2
(6)
Modified Dubinin-Astakhov (DA) Equation (Pore-filling model)
ρ n = n0 exp − D ln ad ρg
m
(7)
where n is the absolute adsorbed amount, n0 is the maximum adsorbed amount, and K, t, D are constants. The Langmuir and Freundlich equations are surface adsorption models, and modified DR and DA equations are pore-filling models. In the modified DA equation, the values of m are coefficients related to the pore size of the sample. Also m=2 in the modified DR equation, is mainly considered to be suited for a microporous (< 2nm) sample, and for 1 < m < 2 is for the mesoporous (2~50nm) sample in case of CO2 and CH4 adsorption. 4
3. Results 3.1 CO2 and CH4 Adsorption Measurement Figure 2 (a)-(e) shows measurement results on absolute adsorption amount for each sample. The ratio of absolute adsorption for CO2:CH4 is about 2-3 for all samples. This number is similar to the adsorption of bituminous coals. Especially for PA-GS, which was collected from shale gas (CH4) exploration fields, it might be suggested that CH4 enhanced recovery by CO2 injection is possible and similar to the enhanced coalbed methane recovery. The difference of adsorption amount at 35°C and 50°C is smaller for CH4 than CO2.
(a) PA-GS
(b) Illinois
(c) Yubari
(d) Bibai
(e) Kushiro Figure 2 Absolute adsorption amount (mmol/g) on various shale samples. 5
Figures 3 and 4 describe the absolute adsorption amounts of CO2 and CH4 at 35°C, respectively. The reversible adsorption reaction was observed (not mentioned in details here), so adsorption on shale is considered to be a physical adsorption. The adsorption behavior tended to increase linearly with increasing pressure. In addition the rapid increase of adsorption amount like coal sample in low-pressure as often described by Langmuir adsorption model was rarely seen. The increment of adsorption amount has been attributed to the micropore filling. Thus, it was suggested that the development of microporous structure similar to coal sample cannot be seen in shale sample. The result also showed that for both CO2 and CH4, Yubari exhibited the highest adsorption amount and Illinois exhibited the lowest.
Figure 3 Absolute adsorption amount
Figure 4 Absolute adsorption amount
(CO2, 35°C)
(CH4, 35°C)
3.2 Verification of Adsorption Model Equations The following Eq. 8 is used as an indicator to verify the actual value and the degree of expression for four adsorption models described in section 2.3. Figures 5 and 6 show the error comparison of CO2 and CH4 adsorption measurement results for each sample and temperature.
Error =
1 N
nexp ,i − ncal ,i ∑ nexp ,i i =1 N
2
(8)
where N is the number of data, nexp is the measured value, and ncal is the calculated value. According to the results of Figures 5 and 6, the Langmuir equation showed huge errors for CO2, while the Freundlich equation expresses the adsorption isotherms well. On the other hand, it has been observed that the Langmuir equation could fit better in CH4 than CO2. The Langmuir equation can be used for assuming that there is no interaction between adsorbed molecules, in fact, there is an intermolecular force such as dispersion force especially in CO2. Thus, it was assumed that the error in curve fitting of CO2 was higher 6
than CH4 due to this force. Furthermore, both modified DR and DA equations, which are pore-filling models, have described adsorption behavior of each sample of CO2 and CH4 accurately as opposed to than surface adsorption models. The m value that is related to the pore size in the DA equation has also been calculated. Each value falls within the range of 1.5 < m < 2. From here, it has been inferred that the microporous structure in the shale has not developed too much, but rather as a relatively small pore; that is to say, a mesoporous structure has developed.
Figure 5 Error comparison (CO2)
Figure 6 Error comparison (CH4)
4. Discussion A calculation was performed to estimate how much CO2 can be stored in the shale by adsorption. In this estimation, Illinois sample, which has the least adsorption amount, was used. In this calculation, the assumed conditions of shale formation (1m3) have been filled with 100% CO2. The amount of storage CO2, G1 is calculated using the traditional model for fluid stored in the pore spaces of shale without respect to adsorption. G2 is calculated as the adsorption amount from this experimental result. In addition comparison examination has been performed between G1 and G2. In various calculations, the following values were used; CO2 density ρCO2 = 286.914 [kg/m3], adsorbed amount nCO2 = 4.629 [kg/ton], shale porosity measured by mercury porosimeter φ shalee= 3.608%, pressure 9MPa and temperature 50°C. As the result, G1 = Vshale × φshalee × ρCO2 = 10.352 [kg/m3] and, G2 = Vshale × (1- φshale) × ρshale × nCO2 = 12.146 [kg/m3] were obtained. As a consequence, the amount of storage in coaly shale by adsorption is more than that stored in pores. Thus, it is worthwhile to consider the adsorption in shale as a storage mechanism, which has not been considered until now. 5. Conclusion 7
Through the adsorption amount measurement for five types of shales, the physical adsorption of CO2 and CH4 in shale has been accurately described by the pore-filling model equations than surface adsorption model. The absolute adsorption amount in coaly shale is relatively large enough to be included in the storage amount in the coal bearing formation. Acknowledgement This study is partly supported by the CCCU (Consortium for Clean Coal Utilization) of Washington University St. Louis, USA. The authors would like to express deeply our thanks for the research fund. References [1] Busch, A., et al.; “Effects of physical sorption and chemical reactions of CO2 in shaly caprocks”, Energy Procedia 1, 2009, 3229-3235. [2] Busch, A. et al.; “Carbon dioxide storage potential of shales”, INITERNATIONAL JOUNAL OF GREENHOUSE GAS CONTROL 2, 2008, 297-308 [3] Span, R., Wagner, W.; “A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple-Point Temperature to 1100K at Pressures up to 800MPa”, J. Phys. Chem. Ref., 1996, Vol. 25, No. 6. [4] Setzmann, U., Wagner, W.; “A New Equation of State and Tables of Thermodynamic Properties for Methane Covering the Range from the Melting Line to 625 K at Pressures up to 1000 MPa”, J. Phys. Chem. Ref. Data, 1991, Vol. 20, No. 6. [5] Cipolla, C.L., et al.; “Modeling Well Performance in Shale-Gas Reservoirs”, 2009, SPE125532 [6] Nuttall, B.C., et al., “Analysis of Devonian Black Shales in Kentucky for Potential Carbon Dioxide Sequestration and Enhanced Natural Gas Production, Final Report”, 2005 [7] Fujii, T. et al.; “Evaluation of CO2 sorption capacity of rocks using gravimetric method for CO2 geological sequestration”, Energy Procedia 1, 2009, 3723-3730. [8] Sakurovs, R., Day, S., Weir, S., and Duffy, G.; “Application of a Modified Dubinin-Radushkevich Equation to Adsorption of Gases by Coals under Supercritical Conditions”, Energy & Fuels, 2007, 21, 992-997
8
Relationships between the sorption capacity of methane, carbon dioxide, nitrogen and ethane on bituminous coals. R. Sakurovs, S. Day and S. Weir CSIRO Energy Technology PO Box 330 Newcastle 2300 Australia
[email protected] Abstract Sequestration of carbon dioxide in coal seams can reduce atmospheric emissions of carbon dioxide. If such sequestration simultaneously results in enhanced coal bed methane (ECBM) production, some of the sequestration costs can be recovered by the value of the methane produced. This requires knowledge of both the carbon dioxide and methane sorption behaviour of coal at high pressures. In order to elucidate the connection between them, we compared the sorption of carbon dioxide, methane, ethane and nitrogen at 55 °C at pressures up to 20 MPa for a number of coals. Sorption isotherms were fitted by a modified DubininRadushkevich model. The relationship between methane and nitrogen maximum sorption capacity was particularly close: on a volume basis, the maximum sorption capacity of all coals examined for methane was twice that of nitrogen. We confirm that the ratio of maximum sorption capacity of carbon dioxide and methane decreased linearly with increasing carbon content. However, this does not necessarily indicate that low rank coals had a specific interaction with carbon dioxide not observed by methane, since similar trends were observed with the ethane/methane sorption ratio.
1. Introduction Unmineable coal seams are one option for sequestration of carbon dioxide, because they can store 6-12 % by weight of carbon dioxide [1]. Often coal seams contain methane. If carbon dioxide can be sequestered in such coal seams and the process simultaneously results in enhanced coal bed methane (ECBM) production, some of the sequestration costs can be recovered in the value of the methane produced [2].
It has long been known that coals can sorb more carbon dioxide than methane [3] although published values for the ratio of molar sorption capacity for coals vary from 2:1 to 10:1 [4]. This variation is partly because the ratios were measured at pressures below saturation and
1
carbon dioxide is adsorbed more strongly than methane, which would increase the ratio especially at very low pressures. However, of more fundamental interest is the maximum adsorption capacity of the two gases, which has not been so intensively investigated.
From basic monolayer sorption models it would be expected that, on a volume basis, the maximum adsorption capacities of gases should be roughly the same since the surface area and pore volume of the coal should be constant. Simple pore-filling models would also reach a similar conclusion. While it is true that larger molecules may not penetrate some pores that are accessible to smaller molecules [5] and that coals swell to some extent when exposed to gases that are strongly sorbed [6], which could change surface area and micropore volume, the difference in the maximum sorption capacity between methane and carbon dioxide is too great to be explained by either hypothesis. Others have suggested that there could be a specific interaction between carbon dioxide and coal that does not exist between methane and coal [2].
Sakurovs [7] found an approximately proportional relationship between the maximum sorption capacity of a coal for gases and their critical temperature if the gases accessed the coal structure equally well. This was used to explain why the maximum (volumetric) adsorption capacity for carbon dioxide is greater than that of methane by about a factor of two: the critical temperature of carbon dioxide is greater than that of methane by about a factor of two. We extend this study here to a range of bituminous coals to determine if the relationships found previously are general.
2. Experimental The excess sorption measurements of twenty-three bituminous and subbituminous coals using methane, carbon dioxide and nitrogen were determined using a gravimetric system [8]. Ethane measurements were performed on ten coals. The coals (analytical data in Table 1) were crushed with minimum fines to less than 1 mm, and the 0.5 mm - 1mm size fraction was used for all characterisation. Prepared samples were dried overnight under vacuum at 60 °C.
Sorption measurements were made using a nominal sample mass of 200 g at pressures up to 20 MPa (accurate to 0.01 MPa) and at a temperature of 55(±1) °C. Samples were maintained at each pressure step for sufficient time to allow equilibrium to establish. Gas densities at each pressure were measured using a reference cell in the isotherm apparatus. In this study, 2
the coal samples were exposed to the various gases one after the other, with carbon dioxide being the first in the series in all cases.
The densities of the coals were measured using a Quantachrome Ultrapycnometer 1000 helium pycnometer. Corrections to cell volume as a consequence of coal swelling were not applied; we assumed that the coal volume inaccessible to the gas remains constant on swelling [9, 10].
Excess sorption (Wads) was fitted to the modified Dubinin-Radushkevich equation [11]
Wads = W0 (1 − ρG / ρ L )e
−[ln ( ρ L / ρG ) RT / E ]2
+ kρG
Equation 1
where W0 is the maximum sorption capacity of the coal, ρG is the density of the gas at the temperature and pressure, ρL is the condensed gas density (assumed to be the van der Waals density of the gas [7]), R is the gas constant, T the temperature, E the apparent heat of sorption and k is the volume accessibility of the coal by the gas compared to that accessed by helium [10]. The term (1 – ρG/ρL) is the correction for the volume of gas displaced by the concentrated surface phase.
3
Table 1 analytical data for coals CH4
CO2 coal
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
ash density C H VM Rv,max db daf daf daf % g/cc % % % % 17.6 1.519 83.86 4.55 28.4 0.81 18.7 1.505 83.52 4.77 31.1 0.80 9.7 1.449 72.76 4.83 49.7 0.25 7.7 1.422 82.99 4.66 31.7 0.69 20.3 1.552 80.70 3.90 31.2 0.62 8.3 1.387 85.60 4.90 30.0 0.90 9.1 1.368 89.22 5.37 27.7 1.21 5.6 1.313 84.11 5.73 36.1 0.95 15.48 1.446 77.67 5.00 47.3 0.46 7.4 1.331 83.59 5.40 37.3 0.89 5.3 1.324 84.37 5.55 38.5 0.90 16.9 1.481 88.93 4.55 21.7 1.40 11.4 1.365 83.30 5.25 35.6 0.80 25.5 1.471 82.68 5.11 34.9 0.80 4.9 1.319 84.12 5.29 35.9 0.80 5.8 1.329 83.76 5.22 35.6 0.80 8.8 1.367 88.82 5.01 23.4 1.43 4.8 1.363 91.07 4.44 19.5 1.68 24.8 1.542 81.78 5.32 38.8 0.81 3.6 1.353 67.95 4.72 47.3 2.2 1.354 74.30 5.00 44.3 3.5 1.395 71.40 4.60 41.4 3.7 1.340 72.60 5.40 51.4
Vit mmf % 10.6 20.2
Lipt mmf % 5.0 4.9
29.7 23.9 33.9 85.4 82.7 85.0 88.7 89.4 28.1 64.0 40.3 64.3 59.5 76.7 89.0 28.7
3.9 1.6 2.3 0.3 4.1 5.0 2.2 3.5 0.0 1.6 1.3 3.0 1.3 0.0 1.0 6.7
W0 db kg/t 81.0 77.7 89.0 110.1 103.3 74.1 70.5 67.0 96.3 68.2 58.5 53.8 73.6 65.0 79.9 78.5 63.7 67.8 45.4 96.8 144.4 144.1 126.5
W0 rms vol db % kg/t 12.0 0.5 11.4 0.5 12.5 1.1 15.2 0.9 15.6 0.7 10.0 0.6 9.4 0.5 8.6 0.2 13.5 1.0 8.8 0.3 7.5 0.7 7.8 0.8 9.8 0.8 9.3 0.3 10.2 0.9 10.2 0.6 8.5 0.4 9.0 0.6 6.8 0.5 12.7 0.8 19.0 1.7 19.6 1.8 16.5 2.0
W0 vol % 7.1 7.1 4.8 7.1 8.6 6.6 6.3 5.3 7.4 5.4 5.2 5.4 6.0 5.6 6.9 5.7 5.7 6.2 4.0 6.3 8.7 9.1 6.6
N2 Ethane W0 vol % 4.0 3.7 2.7 4.7 3.4 3.3 2.6 3.4 2.7 2.8 3.3 2.5 3.4 2.8 3.3 3.4 2.0 4.2 4.7 3.5
W0 vol % 11.0
13.6 9.7 9.4 8.4 8.5
8.7
17.8 16.7 12.7
4
3. Results and Discussion
Figure 1. Relationship between volume sorption capacities of coals for methane versus volume sorption capacity for carbon dioxide
Figure 1 shows that the sorption capacity of coals for methane increases with the sorption capacity for carbon dioxide, though the relationship is not a proportional one.
Figure 2 Relationship between volume sorption capacities of coals for nitrogen versus volume sorption capacity for methane
5
Figure 2 shows that the sorption capacity for nitrogen is proportional to that of methane; all coals examined can sorb about twice as much methane as nitrogen (by volume).
a)
b) Figure 3. Relationship between volume sorption ratio and rank for a)CO2/CH4 and b)Ethane/CH4.
6
Figure 3 shows that the ratio of maximum sorption capacity between carbon dioxide and methane decreases, with increasing carbon content, from 2.5 to 1.5 over the range investigated here. This shows that proportionally more carbon dioxide, compared to methane, can be sorbed into lower rank coals than higher rank coals. A similar trend is evident for the ethane/methane sorption ratio. These results suggest that the relationship between sorption capacity for a gas and critical temperature observed previously[7] is only approximate, and other factors specific to coals can affect this result. It also shows that the effect is not specific to carbon dioxide, but occurs with ethane as well. This means that the reason the ratio of maximum sorption between carbon dioxide and methane decreases with increasing rank is not due to a specific interaction of the coal with carbon dioxide.
4. Conclusions Investigation of the sorption of a range of bituminous coals with different gases under supercritical conditions has shown the following: 1. There is a good correlation between the maximum sorption capacities of different gases on coals. The maximum sorption capacity of coal for nitrogen is proportional to its sorption capacity for methane. 2. The ratio of sorption of carbon dioxide to methane increases with decreasing rank and increasing sorption capacity. This variation is not due to a specific interaction of the coal with carbon dioxide since ethane, which on a volume basis is sorbed by coal about as well as carbon dioxide, has a similar effect. References [1] S. Day, G. Duffy, R. Sakurovs, S. Weir, Effect of coal properties on CO2 sorption capacity under supercritical conditions, International Journal of Greenhouse Gas Control, 2 (2008) 342-352. [2] C.M. White, D.H. Smith, K.L. Jones, A.L. Goodman, S.A. Jikich, R.B. LaCount, S.B. DuBose, E. Ozdemir, B.I. Morsi, K.T. Schroeder, Sequestration of carbon dioxide in coal with enhanced coalbed methane recovery - A review, Energy & Fuels, 19 (2005) 659-724. [3] I. Ettinger, Chaplins.A, E. Lamba, V. Adamov, Natural factors influencing coal sorption properties .3. Comparative sorptionof carbon dioxide and methane on coals, Fuel, 45 (1966) 351-&. [4] S. Harpalani, B.K. Prusty, P. Dutta, Methane/CO2 Sorption Modeling for Coalbed Methane Production and CO2 Sequestration, Energy & Fuels, 20 (2006) 1591-1599. [5] O.P. Mahajan, CO2 surface area of coals - the 25-year paradox, Carbon, 29 (1991) 735742.
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[6] S. Day, R. Fry, R. Sakurovs, Swelling of Australian coals in supercritical CO2, International Journal of Coal Geology, 74 (2008) 41-52. [7] R. Sakurovs, S. Day, S. Weir, Relationships between the Critical Properties of Gases and Their High Pressure Sorption Behavior on Coals, Energy & Fuels, 24 (2010) 1781-1787. [8] R. Sakurovs, S. Day, S. Weir, G. Duffy, Application of a modified Dubinin-Radushkevich equation to adsorption of gases by coals under supercritical conditions, Energy & Fuels, 21 (2007) 992-997. [9] S.A. Mohammad, J.S. Chen, J.E. Fitzgerald, R.L. Robinson, K.A.M. Gasem, Adsorption of Pure Carbon Dioxide on Wet Argonne Coals at 328.2 K and Pressures up to 13.8 MPa, Energy & Fuels, Accepted (2009). [10] R. Sakurovs, S. Day, S. Weir, Causes and consequences of errors in determining sorption capacity of coals for carbon dioxide at high pressure, International Journal of Coal Geology, 77 (2009) 16-22. [11] R. Sakurovs, S. Day, S. Weir, G. Duffy, Temperature dependence of sorption of gases by coals and charcoals, International Journal of Coal Geology, 73 (2008) 250-258.
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Oviedo ICCS&T 2011. Extended Abstract
CIUDEN CO2 Transport Test Rig: Technical Description and Experimental Plan B. Navarrete 1; P. Otero; I. Llavona; M.A. Delgado; Fundación Ciudad de la Energía CIUDEN, II Avenida de Compostilla nº2 Ponferrada, Spain.
[email protected]: Abstract Fundación Ciudad de la Energía (CIUDEN), a public Foundation created by the Spanish Government, is currently designing an experimental installation to study the main issues related to CO2 pipeline transport, within CIUDEN’s Technology Development Centre for CO2 Capture es.CO2. This paper describes CIUDEN´s CO2 Transport Test Rig, currently under development of the detailed engineering design and R&D program, prior to the immediate start of the construction of the Installation. The main technical characteristics of the process units are the following: (a) Pumping system to transport CO2. (b) High pressure vessel. (c) Recirculation pump and heat exchanger system in order to set operation pressures and temperatures within the range of 80 -110 barg and 10 - 30 ºC respectively. (d) Dosing equipment to injecting impurities in the CO2 flow. (e) Tube coils with variable lengths and different materials. (f) Test zones. CIUDEN has designed a complete test campaign, mainly focused on the evaluation of the effect of impurities and contaminants on the mechanical behaviour of different steels and other materials, equipment and instrumentation. It will also be studied the influence of different compositions of CO2 on the flow assurance, as well as CO2 sudden depressurization and its effects on the pipeline, equipment and instrumentation. Due to the semi-industrial size of the installation and the flexibility of its design, the results are expected to be particularly valuable for the design and construction of commercial CO2 transport pipelines and auxiliary equipments. Additionally, the facility could be used as a test facility for manufacturers of industrial transport and storage injection equipments and auxiliaries and training–room for operators in charge of the operability/maintenance of the industrial CO2 pipelines.
1
Oviedo ICCS&T 2011. Extended Abstract
1. Introduction
Earlier work by Svensson et al. [1] identified pipeline transport as the most practical method to move large volumes of CO2 overland and other studies have affirmed this conclusion [2]. There is considerable experience in the transport of CO2 by pipeline primarily for use in enhanced oil recovery (EOR) operations [2, 3]. An important number of studies have been carried out in order to define sizing of CO2 pipelines and estimate the capital cost of pipeline transport. Also, models have been developed for pipelines engineering-economic evaluations [4]. However further investigations are necessary in order to solve the uncertainties related to the effect of impurities on the behavior of the fluid and their consequences upon the pipeline design and operation [5]. Fundación Ciudad de la Energía, a public Foundation created by the Spanish Government, is involved on the construction of a Technology Development Centre for CO2 Capture, hereinafter, the Centre or “es.CO2”. The main objectives of the Centre are the research, development and demonstration of efficient, cost effective and reliable carbon capture and storage technologies (CCS) [6]. The main units of the es.CO2 Centre, are the following: - Fuel Preparation unit. - Pulverized coal boiler (20 MWth) capable of operating from air-mode to full oxycombustion-mode. - Circulating fluidized bed boiler (15 MWth in air-mode, 30 MWth in oxymode). - Comburent preparation system. - Flue gas cleaning train to remove dust, NOx and SOx. - CO2 compression and purification unit (oxymode). - CO2 transport experimental installation. In addition, es.CO2 includes a biomass gasification unit of 3 MWth, as part of another initiative of the Spanish Government. Figure 1 shows a diagram of the installation [7, 8, 9]. Focused on the CO2 Transport Experimental Facility activity, the main goals will be the evaluation of the effect of impurities and contaminants and the study of the thermodynamic conditions of the CO2 on the mechanical behavior and corrosion of different steels and other materials, as well as on the flow assurance. It will also be used for industrial equipment and instrumentation testing and is suitable to study the CO2 depressurization and its effects on the pipeline and equipment.
2
Oviedo ICCS&T 2011. Extended Abstract
Figure 1.- Schematic process diagram of es.CO2
2. Experimental section The CO2 Transport Test Rig at the es.CO2 Centre, , includes the following main units, as shown in Figure 2: (a) Pumping system to transport CO2 either from storage vessels (commercial quality) or the CPU (Compression and Purification Unit) of the Centre. (b) High pressure vessel to avoid fluctuations in the flow. (c) Recirculation pump and heat exchanger systems in order to set operation pressures and temperatures within the range of 80 -110 barg and 10 - 30 ºC respectively. In order to operate the test rig in thermal conditions similar to those expected in CO2 transport pipelines (mainly buried), the facility will be located inside a highly thermal isolated building with thermal control. Dimensions of the industrial building are 23x19x10 m3. It is designed considering that has to be capable of maintain isothermal conditions in the interval of 15 to 18 ºC, as well as to deal with possible enlargements and safety issues as a consequence of the use of the CO2 flow. To achieve these requirements, the building will include a heater/cooler system that will make the most of the steam produced in the es.CO2- The building will be made of pre-fabricated concrete and will have an effective ventilation system to avoid sub-oxygenated atmospheres.
3
Oviedo ICCS&T 2011. Extended Abstract
Figure 2.- Block diagram of CO2 Transport Test Rig (d) Dosing equipment to add impurities and contaminants to simulate different CO2 streams composition expected to be captured in the industry: H2O, NOx, SOx, N2, O2, Ar, CO, H2, H2S, CH4. It is important to point out that besides the es.CO2 was conceived considering the development of oxycombustion processes, the CO2 transport experimental facility will test CO2 streams including typical contaminants of precombustion processes, such as CO, H2, H2S and CH4. (e) Tube coils with variable length and different materials: each coil has an equivalent length of approximately 500 m and a nominal diameter of 2 inches. Considering the number of tube coils, the length of the whole test rig will exceed 5,000 meters. It is also possible to by-pass one or several tube coils in order to be adapted to specific conditions. (f) Test zones with pipes of different diameters in order to install new equipment or instrumentation to be tested in real conditions of CO2 transport. The number of test zones is designed considering the different tests that will be carried out (see Table 1)
4
Oviedo ICCS&T 2011. Extended Abstract
Figure 3. 3D simulation of the Test Rig where it can be seen the tube coils and some of the test zones [10] 3. Test campaign and test matrix To achieve the aforesaid objectives, a set of specific testing campaigns has been designed focused on the data acquisition for scaling-up the system, operator training and CO2 safety operation.Table 1 shows the type of test that will be carried out and the independent variables that will be modified during the tests duration. Table 1. Summary of the test campaign. ID
Type of test
1
Corrosion rates in different materials.
2
Flow assurance (depressurization in the line).
3
Installation of industrial instrumentation or equipment.
4
Release studies.
Independent variable Pressure, Temperature. CO2 quality. CO2 velocity. Pressure, Temperature. CO2 quality. CO2 velocity. Diameter. Pressure, Temperature. CO2 quality. TBD.
4. Conclusions
5
Oviedo ICCS&T 2011. Extended Abstract
The CIUDEN´s CO2 Transport Test Rig that is installed in the CIUDEN´s Technology Development Centre for CO2 Capture will provide real basis for the design, maintenance and operation of industrial CO2 pipelines. The designed test campaigns will generate valuable information to material selection, impure CO2 behavior, depressurization and CO2 safety operation; besides this and considering that the installation is located inside a building, it will be possible to test CO2 small releases in order to study or validate dispersion models. Acknowledgement Part of the research work presented in this paper is co-financed by the European Union´s European Energy Programme for Recovery programme. The sole responsibility of this publication lies with the author. The European Union is not responsible for any use that may be made of the information contained therein. References [1] Svensson, R., et al., Transportation systems for CO2-application to carbon capture and storage. Energy Conversion & Management, 2004. 45: p. 2343-2353. [2] Doctor, R., et al., Transport of CO2, in IPCC Special Report on Carbon Dioxide Capture and Storage, B. Metz, et al., Editors. 2005, Cambridge University Press: Cambridge, U.K. [3] Gale, J. and J. Davidson, Transmission of CO2- Safety and Economic Considerations. Energy, 2004. 29: p. 1319-1328. [4] Bock, B., et al., Economic Evaluation of CO2 Storage and Sink Enhancement Options. 2003, TVA Public Power Institute: Muscle Shoals, AL. [5] IEA Greenhouse R&D Programme, Impact of impurities on CO2 Capture, Transport and Storage, PH4/32, august 2004.
[6] Cortes V J. State of development and results of oxy-coal combustion research initiative by CIEMAT in Spain. 2nd IEAGHG International Oxy-Combustion Network Meeting. Windsor, USA. January 2007. [7] Cortes V J, Navarrete B. Test Facilities for Advanced Technologies for CO2 Abatement and Capture in Coal Power Generation. 3rd IEAGHG International Oxy-Combustion Network Meeting. Yokohama, Japan. March 2008. [8] Lupion M, Navarrete B; Otero P; Cortes V J. CIUDEN CCS Technological Development Plant on oxycombustion in Coal Power Generation. 1st International Oxyfuel Combustion Conference. Cottbus, Germany. September 2009 [9] Lupion M. CIUDEN Carbon Capture Technology Development Plant. Second APP Oxy-fuel Capacity Building Course. Beijing, China. March 2010 [10] ISOLUX CORSÁN. Technical proposal for CIUDEN´s bidding process LT-2010/02
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Oviedo ICCS&T 2011. Extended Abstract
Viscosity behaviour of slags from coal-petroleum coke blends
Alexander Ilyushechkina and Marc Duchesneb a
CSIRO Energy Technology, Queensland Centre for Advanced Technologies,
Technology Court, Pullenvale QLD 4069, Australia b
CanmetENERGY, 1 Haanel Drive, Ottawa ON K1A1M1, Canada
Abstract The slagging behaviour of petroleum coke and coal blends must be known to determine suitable blending requirements for entrained-flow slagging gasification. In the present study, the viscosities of petcoke ash blended with Australian and Canadian coal ashes were measured in the temperature range of 1200-1550ºC. The effect of compositional changes in the blends on viscosity behaviour was investigated in terms of solids precipitation. At high temperatures, increasing the amount of petcoke ash (up to 100% of the coal ash weight) gradually reduces the viscosity of the blends used in this study. This reduction in viscosity is likely associated with changes in slag composition, particularly for the major components CaO, SiO2, Al2O3, and FeOx. These changes decrease the liquidus temperature, increase the amount of CaO, and decrease the Si/Al ratio. However, increasing the petcoke content in the blends may increase the temperature of critical viscosity. Slag quenching experiments indicate that the presence of vanadium in petcoke containing slags stimulates solids precipitation, which increases viscosity dramatically at lower temperatures.
1. Introduction Production of petroleum coke (petcoke), a by-product of the oil refining industry, has been and is expected to continue increasing [1]. Major factors driving this increase include the rising demand for transport fuels, the use of heavier crude oils and new environmental regulations pushing for reduced waste and highly refined fuels. Due to petcoke’s high heating value and low cost, there is much interest in its use as a primary fuel or in a coal-petcoke blend. Oil sands petcokes have been found to be particularly unreactive, with reactivities comparable to high rank coals such as anthracites [2]. In
Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
addition, the high sulphur (5–6%) and metals (particularly V and Ni) content of the petcokes cause concern for downstream treatment and residue disposal. One method of mitigating undesirable aspects of the petcoke as a fuel is to blend it with other fuels, such as lignite, sub-bituminous coals and bituminous coals. The higher volatile content of these fuels could potentially make gasification of the petcoke more reliable by lowering ignition and ash fusion temperatures (for slagging gasifiers). The majority of gasifiers in operation today are of the entrained-flow type. In this type of gasifier, most of the inorganic component of the fuel (ash) is partially or fully melted, sticks to the reactor wall and flows to the bottom as slag. To determine the suitability of a fuel and appropriate operating conditions for gasification, it is important to know its slagging properties. A slag which is too viscous may accumulate on the reactor wall till the reactor is plugged, ceasing operation. As a rule of thumb, slag viscosity should not exceed 25 Pa s at the slag tapping temperature [3, 4]. The petroleum coke ash can contain high concentrations of vanadium, nickel, and iron. Vanadium oxide is a major impurity in the petcoke slags which is not found in coal ash. The oxidation state of vanadium depends upon the temperature and partial pressure of oxygen [5]. Because of the low oxygen partial pressure existing in a gasifier, a VO x phase can precipitate under reducing conditions during gasification. Previous studies have identified karelianite (V2O3) in slag which can increase the viscosity of a coal/petcoke mixture [6]. In order to prevent V2O3 from accumulating inside the gasifier, the slagging behaviour of petroleum coke and coal ash blends has to be understood. In the present study, the viscosities of Australian and Canadian coal ashes blended with petcoke ashes were measured in the temperature range 1200-1550ºC. Microstructural analysis of quenched slag was conducted to investigate a link between solid phase formation and viscosity behaviour.
2. Experimental 2.1 Coal and petcoke selection Several coal ashes and petcoke ashes were used in this study. Compositions are given in Table 1. C1 is an artificial coal ash, for which the composition is based on the major and minor oxides analysis of Genesee coal, a western Canadian sub-bituminous coal. C2 is a slag obtained from the gasification of a low-rank (sub-bituminous) coal from Western Australia. C3 is a slag obtained from gasification of an Australian high volatile bituminous coal from the Hunter Valley in NSW. Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
P1 is real ash produced from Suncor petcoke by ashing at 700-750 ºC for 20-30h. P2 is artificial Suncor petcoke ash; its composition is based on the major and minor oxides analysis of Suncor petcoke, excluding sulphur. Artificial coal and petcoke ashes were prepared by mixing laboratory or analytical grade Al2O3, CaO, Fe2O3, K2CO3, MgO, Na2CO3, NiO, S, SiO2, TiO2 and V2O5 powders. Slag samples were collected from the quench vessel of Siemens pilot plant gasifier [7].
Table 1. Composition of ashes and slags (wt.%) used in this study Samples C1* C2 C3 P1 P2* SiO2
58.02
49.62
47.73
37.77
40.66
Al2O3
23.47
18.22
24.07
16.6
17.87
Fe2O3
4.55
24.36
15.41
7.35
7.91
TiO2 CaO MgO
0.53 5.63 1.57
1.17 3.27 1.62
1.49 8.25 0.97
1.1 15.82 3.87
1.19 17.03 4.17
Na2O
2.34
0.55
0.28
1.67
1.8
K2O
0.58
0.45
0.3
0.96
1.03
V2O5 NiO
0 [36,37,40]. Pore coalescence was therefore the dominant structural mechanism during the initial stage of gasification for chars B, C and C2. On the other hand, pore growth was more significant during the initial period of char C2 gasification reaction.
(i)
(ii)
Figure 3: RPM fitting to experimental results: (i) Char C conversion at 75% CO2, 0.875 bar, (ii) Char C2 conversion rate at 25% CO2 concentration, 0.875 bar
5.0
Conclusion
The four parent coals were characterised as high ash and inertinite-rich. The transition from coal to char led to the formation of various char carbon forms in the chars. The total reactive components (TRC) generally decreased from coals to the chars, while the total inert components (TIC) exhibited gains in the transition. Except for the maceral contents and inertinite-vitrinite ratios, significant changes in properties were not observed in the four original coals. The subsequent chars, however exhibited differences, both amongst the chars and from the parent coals. Results from the carbon crystallite analysis revealed that the chars are more structurally ordered, more compact and condensed (smaller in size) than the original coals. The increasing orders of magnitude of both the fraction of amorphous carbon and structural disorderliness was found to change from coals to chars. CO2 gasification reactivity of the four chars was found to increase with increasing temperature as well as CO2 composition in the reaction gas mixture. Comparison of the 9
reactivity of the four chars shows that, the reactivity of the chars generally increases in the order: char C2 < char C < char B < char D2. The reactivity of char D2 was found to be higher than the reactivity of the other three chars by a factor > 4. Correlation of the parent coal petrographic properties to the reactivity of the respective chars gave insignificant trends except for the rank parameter, the vitrinite reflectance. Correlation of char properties with char gasification reactivity show systematic and significant trends. Kinetic parameters were determined using the RPM. The activation energy obtained for the char-CO2 gasification reactions were between 163.3 kJ·mol-1 to 235.7 kJ·mol-1; while the order of reaction with respect to CO2 concentration ranged from 0.52 to 0.67. The investigated char-CO2 gasification reactions within the specified operating conditions were found to be kinetically chemical-reaction controlled and were satisfactorily described by the RPM (Regime I).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
[11] [12] [13] [14] [15]
Laurendeau NM. Heterogeneous kinetics of coal char gasification and combustion. Progress in Energy & Combustion Science 4: 221-270; 1978. Watkinson AP, Lucas JP and Lim CJ. Fuel 1991; 70: 519-527. Yu J-L, Lucas J, Wall T, Liu G, and Sheng C. Modelling the development of char structure during rapid heating of pulverised coal. Combustion and Flame 136: 519-532; 2004. Du Cann VM. Test Report- PSA 2007-016, Petrographics SA, Pretoria, South Africa; 2007. Du Cann VM. Test Report- PSA 2008-040, Petrographics SA, Pretoria, South Africa; 2008. Everson RC, Neomagus HWJP, Kaitano R, Falcon R, Van Alphen C. and du Cann VM. Fuel 2008; 87: 3082-3090. Lu L, Sahajwalla V, Kong C and Harris D. Quantitative X-ray diffraction analysis and its application to various coals. Carbon 39: 1821-1833; 2001. Davis KA, Hurt RH., Yang NYC and Headley TJ. Evolution of char chemistry, crystallinity, and ultrafine structure during pulverized-coal combustion. Combustion & Flame 100:31-40; 1995. Takagi H, Maruyama K, Yoshizawa N, Yamada Y and Sato Y. Fuel 2004; 83: 2427-2433. Trejo F, Ancheyta J, Morgan TJ, Herod AA. and Kandiyoti R. Characterization of asphaltenes from hydrotreated products by SEC, LDMS, MALDI, NMR, and XRD. Energy & Fuels 21:2121-2128; 2007. Maity S and Mukherjee P. X-ray structural parameters of some Indian coals. Current Science 91: 337-340; 2006. Lu L, Kong C, Sahajwalla V and Harris D. Fuel 2002; 81: 1215-1225. Lu L, Sahajwalla V, Kong C and Mclean A. Char structural ordering during pyrolysis and combustion and its influence on char reactivity. ISIJ International 42: 816-825; 2002. Franklin RE. The interpretation of diffuse X-ray diagrams of carbon. Acta Crystallographica 3: 107121; 1950. Ergun S and Tiensuu VH. Fuel 1959; 38: 64-78.
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[16]
[17] [18] [19] [20] [21] [22]
[23]
[24] [25] [26]
[27] [28] [29] [30] [31]
[32] [33] [34] [35]
[36] [37] [38] [39] [40]
Webb, P. A. (2001). Volume and density determination for particle technologist. Micromeritics Instrument Corp., Norcross, Georgia, USA. http://www.micromeritics.com/Repository/files/density-determination.pdf. (Accessed 22-08-2010). Dutta S, Wen CY. and Belt RJ. Reactivity of coal and char: I. In carbon dioxide atmosphere. Ind. Eng. Chem. Proc. Des. Dev. 16: 20-30; 1977. Hampartsoumian E, Murdoch PL, Pourkashanian M and Trangmar DT. The reactivity of coal chars gasified in a carbon dioxide environment. Combustion Science and Technology 92: 105-121; 1993. Kyotani T, Kubota K, Cao J, Yamashita H and Tomita A. Combustion and CO2 gasification of coals in a wide temperature range. Fuel Processing Technology 36: 209-217; 1993. Ye DP, Agnew JB. and Zhang DK. Fuel 1998; 77: 1209-1219. Zhang L, Huang J, Fang Y and Wang Y. Gasification Reactivity and Kinetics of Typical Chinese Anthracite Chars with Steam and CO2. Energy & Fuels 20: 1201-1210; 2006. Çakal GÖ, Yücel H and Gürüz AG. Physical and chemical properties of selected Turkish lignites and their pyrolysis and gasification rates determined by thermogravimetric analysis. J. Anal. Appl. Pyrolysis 80: 262-268; 2007. Zhang J-W, Zong Z-M, Wang T-X, Xie R-L, Ding M-J, Cai K-Y, Huang Y-G, Gao J-S, Wu Y-Q and Wei X-Y. Reactivities of Shenfu chars towards gasification with carbon dioxide. Journal of China University of Mining & Technology 17: 197-200; 2007. Everson RC, Neomagus HWJP, Kasaini H and Njapha D. Fuel 2006; 85:1076-1082. Everson RC, Neomagus HWJP, Kaitano R, Falcon R and du Cann V M. Fuel 2008; 87: 3403-3408. Wu S, Gu J, Zhang X, Wu Y and Gao J. Variation of Carbon Crystalline Structures and CO2 Gasification reactivity of Shenfu coal chars at elevated temperatures. Energy & Fuels 22: 199-206; 2008. Czechowski F and Kidawa H. Reactivity and susceptibility to porosity development of coal maceral chars on steam and carbon dioxide gasification Fuel Processing Technology 29: 57-73; 1991. Senneca O, Salatino P and Masi S. Fuel 1998; 77: 1483-1493. Kajitani S, Suzuki N, Ashizawa M and Hara S. Fuel 2006; 85: 163-169. Zhang Y, Hara S, Kajitani S and Ashizawa M. Fuel 2010; 89: 152-157. Radovic LR, Steczko K, Walker PL Jr. and Jenkins RG. Combined effects of inorganic constituents and pyrolysis conditions on the gasification reactivity of coal chars. Fuel Processing Technology 10: 311-326; 1985. Matsui I, Kunii D and Furusawa T. Study of char gasification by carbon dioxide: I. Kinetic study by thermogravimetric analysis. Ind. Eng. Chem. Res. 26: 91-95. Fu W-B and Wang Q-H. A general relationship between the kinetic parameters for the gasification of coal chars with CO2 and coal type. Fuel Processing Technology 72: 63-77; 2001. Ochoa J, Cassanello MC, Bonelli PR and Cukierman AL. CO2 gasification of Argentinean coal chars: a kinetic characterization. Fuel Processing Technology, 74: 161-176; 2001. Sinağ A, Sinek K, Tekeş AT, Misirlioğlu Z, Canel M and Wang L. Study on CO2 gasification reactivity of chars obtained from Soma-Isıklar lignite (Turkey) at various coking temperatures. Chemical Engineering and Processing, 42: 1027-1031; 2003. Bhatia SK, and Perlmutter DD. A random pore model for fluid-solid reactions: I. isothermal, kinetic control, AIChE Journal, 26: 379-386; 1980. Murillo R, Navarro MV, López JM, García T, Callén MS, Aylón E and Mastral AM. Activation of pyrolytic lignite char with CO2- kinetic study. Energy & Fuels, 20: 11-16; 2006. Cloke M and Lester E. Fuel 1994; 73: 315-320. Sakawa M, Sakurai Y and Hara Y. Fuel 1982; 61: 717-720. Liu G, Benyon P, Benfell KE, Bryant GW, Tate AG, Boyd RK, Harris DJ and Wall TF. Fuel 2000; 79: 617-626.
11
CHARACTERISATION AND CARBON DIOXIDE GASIFICATION KINETICS OF HIGH ASH INERTINITE RICH SOUTH AFRICAN COALS Rufaro Kaitano*1, Raymond C Everson1 and Hein W J P Neomagus1, 1
Energy Systems Research Group, School of Chemical and Minerals Engineering, North-West University, Potchefstroom Campus, Private Bag X6001,Potchefstroom 2520, South Africa * Corresponding author: Tel: + 27 18 299 1664 Fax: + 27 18 299 1535 E-mail:
[email protected] Keywords: High ash Coal; Inertinite, Charaterisation. Dense Chars and Random Pore Model ______________________________________________________________________________ Abstract Characterisation and carbon dioxide-char reaction kinetics of a typical South African low grade coal with an ash content of an average of 35 wt % studies were conducted. Fundamental knowledge of the reaction kinetics for char conversion at reactions conditions typical of fluidised bed gasification and combustion was obtained.The random pore model was used to describe the experimental results and the reaction rate is chemical reaction controlled. Introduction South Africa has several millions of tons of low grade coal discards which are thought to play a significant role in the country’s energy mix. However, it has been suggested that to meet the current ever tightening fossil fuel usage conditions, the route to be followed in utilisation these coal deposits is gasification. A number of gasification experiments have been identified for investigation in the laboratory, (steam, and carbon dioxide); this work investigates the behaviour of these coals in the presents of different concentrations of carbon dioxide/nitrogen. To have an insight into the characteristics of the coal traditional and advanced charaterisation investigations were carried out. Experimental The experimental apparatus used for the determination of the reactivity of the chars in this investigation was a TGA, model Bergbau-Forshung GMBH7, supplied by Deutsche Montan Technologie (DMT), Germany. This apparatus has also been used with success by many other investigators for coal/char conversion studies (Johnson J.L., 1981, Calo and Suuberg, 1999; Kajitani, 2006). The gas mixtures were varied between 100% and 20% CO2, balance N2. Advanced characterisation was carried out by various accredited laboratories in South Africa such as Secunda Coal Laboratory of South African Bureau of Standards Laboratories (SABS) and petrographic analysis was carried out by Coal and Mineral Technologies (Pty) Ltd,
Data acquisition
Microbalance
Purge
Sample lock
Gas mixer
Mass Flow Controllers
F
F
F
Pressure control
Reactor
valve
O2
CO 2
N2
Figure 1.1 Schematic presentation of the experimental set-up Results and discussion A typical experimental result obtained from the Thermogravimetric analyser at 900°C, 87.5 kPa and 100% carbon dioxide is given in Figure 1.2, where both the mass of the char sample and the reaction temperature are given as a function of time. 25 900
Mass (mg ) Temp.
Carbon
600
o
15
Temp ( C)
Char Mass (mg)
800
20
400
10 Ash
5
200
0 0
50
100 Time, t (min)
150
200
Figure 1.2: Isothermal gasification of coal char at 900˚C in 100% CO2 at 87.5kPa Model equations The overall reaction rate is: (Bhatia and Perlmutter, 1980)
dX rs (1 − X ) S o 1 − ψ ln(1 − X ) = (1 − ε O ) dt
(1.1)
ψ being the structural parameter characteristic of the initial char structure and defined as:
ψ=
4π L 0 (1 − ε ) ο 2 S ο
(1.2)
By introducing a dimensionless parameter τ , defined by Kaitano, (2007) and Everson et al., (2008a) as: r S t τ= s o 1- ε o
(1.3)
Equation (1.1) can be rewritten in the dimensionless form as follows: dX = (1 − X) 1 − ψln(1 − X) dτ
(1.4)
Integration of Equation 1.4 gives the carbon conversion X, as a function of time t, or the dimensionless time τ (implicit and explicit).Relationships for carbon conversion X in terms of time t or dimensionless time τ (implicit and explicit) obtained by integration of the above equations are as follows: In terms of time t: t=
2(1 − ε o ) ( 1 − ψln(1 − X) − 1) rs S o ψ
(1.5)
In terms of dimensionless time τ τ=
2
ψ
( 1 − ψ ln(1 − X ) − 1)
(1.6)
and explicitly as X = 1 − exp[−τ (1 +
Defining the time factor as:
ψτ 4
)]
(1.7)
tf =
rs S O (1 − ε O )
(1.8)
Equation (1.6) in terms of time t becomes X = 1 − exp[ −t f t (1 +
ψt f t 4
)]
(1.9)
A reduced time t / t X with t X the time for a fractional conversion of X, being the upper limit for reliable experimental results, can be defined, which is independent of the parameters appearing before the square root term (Equation (1.5)) and only dependant on ψ as shown in equation (1.10) where t 0.9 is the time for 90% conversion. Thus, all results for a particular coal-char gasified or combusted should be the same, which enables this property to be used for determination of the structural parameter. The numerical value of the structural parameter can be evaluated by regression of the experimental data using equation 1.10. Solver was used to iterate the value of ψ . t t 0.9
=
It should be noted that
1 − ψ ln(1 − X − 1 1 − ψ ln(1 − 0.9) − 1 t t
0.9
=
(1.10)
τ τ
0.9
Intrinsic reaction rate equation rs given by Equation (1.11) for both gasification and combustion based on an nth order power rate relationship as discussed in Section 1.2 was used. In this investigation the dependence for gasification and combustion were based on the partial pressure of carbon dioxide and oxygen concentration respectively. The equations are: Gasification:
rs = k SO exp(− E / RT ) p n
Combustion:
rs = k SO exp(− E / RT )C n
(1.11)
Figure 1.4 shows a comparison between experimental results and model predictions, a plot of conversion, X vs t/t0.9 shows that the structural parameter value is valid for description of the experimental data.
1
Conversion, X (-)
0.8
0.6
0.4 0.2 0 0
0.2 M odel 87.5kPa 87.5kPa 87.5kPa 87.5kPa 87.5kPa 87.5kPa
0.4
t/t0.9
100% 863C 100% 875C 60% 875C 80% 888C 80% 900C 40% 900C
0.6 87.5kPa 87.5kPa 87.5kPa 87.5kPa 87.5kPa 87.5kPa
0.8
1
80% 850C 80% 863C 80% 875C 100% 888C 100% 900C 60% 900C
Figure 1.4: Comparison of gasification experimental and model results at 87.5 kPa
Table 1.1 gives the evaluated parameters which are comparable with literature on gasification available, Kajitani, 2006. Table 1.1: Intrinsic reaction rate parameters of carbon dioxide gasification Kinetic Parameter Calculated Value Activation energy, E
229 (±37) kJ mol-1
Pre-exponential factor (lumped), kso
9.6·108(±2) s-1kPa-1
Partial pressure dependency, n
0.50(±0.05)
Structural parameter, ψ
1.04(±0.39)
Conclusion The results are consistent with carbon dioxide gasification literature. It was found that the reaction rate increases with increasing temperature, increasing pressure and increasing carbon dioxide concentration. The char conversion kinetics could well be described with the random pore model in the absence of diffusion limitation with a structural parameter, ψ equal to 1.04. The structural parameter was
determined by a regression technique using a reduced time parameter, which eliminates the effect of intrinsic reaction rate kinetics. The intrinsic kinetics could be accurately described with a nth order power law in combination with the Arrhenius equation and an order in carbon dioxide of 0.5, an activation energy of 229 kJmol-1, and a pre-exponential factor of 9.6·108 s-1kPa-1 were determined. The activation energy is relatively high which could be attributed to the high inertinite content of the coal. Although the ash content was high, no significant catalytic effect of the ash could be observed.
Acknowledgements Eskom and the National Research Foundation (NRF - financial support for this project. Mr. Jan Kroeze, Mr. Hennie van Zyl and Mr Adrian Brock - experimental apparatus maintenance. Ms Vivien du Cann and Dr Chris van Alphen - characterisation work and the interpretation thereof.
References: BHATIA, S.K. AND PERLMUTTER, D.D. (1981). A random pore model for fluid solid reactions: II. Diffusion
and Transport Effects, AIChE Journal 27(2):247. CALO, J.M. AND SUURBERG, E.M. (1999). High pressure/temperature thermogravimetric apparatus report. Brown University. U.S.A. EVERSON, R.C., NEOMAGUS, H.W.J.P., KAITANO, R., FALCON, R. AND du CANN, V. M. (2008a). Properties of high ash coal-char particles derived from inertinite-rich coal: II. Gasification kinetics with carbon dioxide. Fuel, 87: 3403-3408. JOHNSON J.L. (1981). Fundamentals of coal gasification, In: Chemistry of Coal Utilisation, Second Sup. Volume, Wiley Inter-science, New York: 1591-1598. KAITANO, R. (2007). Characterisation and reaction kinetics of high ash chars derived from inertinite–rich coal discards. Doctoral thesis. North-West University, South Africa. KAJITANI, S. SUZUKI, N. ASHIZAWA, M. AND HARA, S. (2006). CO2 gasification rate analysis of coal char in entrained flow coal gasifier. Fuel 85:539
Program topic: Coal gasification Gasification kinetics of coal char using direct measurement of particle temperature Ryanggyoon Kim1, Ho Lim2, Cheoloong Kim3, Juhun Song4, and Chunghwan Jeon*
1. Presenter, Doctoral Course, School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-3035, Fax: 82-51-582-9818, Email:
[email protected] 2. Doctoral Course, School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-3035, Fax: 82-51-582-9818, Email:
[email protected] 3. Senior Researcher, Energy Technology Team, GS Engineering & Construction CO., Ltd., Republic of Korea, Ph: 82-2-728-3276, Fax: 82-2-728-3544, Email:
[email protected] 4. Assistant Professor, School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-7330, Fax: 82-51-512-5236, Email:
[email protected] * Corresponding author, Associate Professor, School of Mechanical Engineering, Pusan National University, Pusan Clean Coal Center, Republic of Korea, Ph: 82-51-510-7324, Fax: 82-51-5829818, Email:
[email protected] Gasification kinetics of coal char is obtained by using the semenov’s thermal spontaneous theory. The critical condition of thermal ignition occurs when the rates of heat generation and heat loss are equal and, in addition, when the derivatives of both these rates with respect to temperature are also equal. Especially, rate of heat generation and rate of heat loss are increased at the same time under elevated ambient pressure condition due to high density of ambient gas around coal char. Thus, in order to describe effect of elevated total system n pressure at rate of generation, the nth-order rate equation( R = kPCO 2 ) was modified to be n m R = kxCO 2 Ptotal where the correlation exponent, m, to modify the effect of the pressure was determined by linear fitting. Convection and radiation were used to explain the rate of heat Gr = ( P∞ ρ D 2 / μ 2 )1/ 2 loss which was considered by using the modified Grashof number( ,m ) under natural convection which is developed to describe the effect of elevated ambient pressure on heat loss. The ignition temperature of coal char particle is obtained by a direct measurement of the particle temperature with photo detector as well as by means of a solid thermocouple which is used as both a heating and a measuring element. The ignition temperatures for subbituminous coal wira of 0.8mm diameter have been measured at 7 different ambient pressures in the ranging from 1 to 15bar in constant volume chamber. The result shows that the coal char ignition temperature deceases with increasing ambient pressure up to the critical pressure condition(15bar) due to an enhanced rate of heat generation. This kinetics is in much closer agreement with the results of other investigators.
Oviedo ICCS&T 2011. Extended Abstract
DIRECT CTL: Innovative Analyses for High Quality Distillates A. Quignard, N. Caillol, N. Charon, M. Courtiade, D. Dendroulakis IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, 69360 Solaize, France Contact Information:
[email protected] Abstract Distillate liquid yields from high hydrogen pressure catalytic conversion of coal processes, called Direct Coal Liquefaction (DCL), are typically high at 4 to 5 bbl/T coal on a dry ash free basis for the best available DCL processes, making them an attractive option to produce transportation fuels from coal. These yields are significantly higher than using the so called Indirect Coal to Liquid (ICL) route, i.e. gasification plus Fisher Tropsch (FT) synthesis. Nevertheless, DCL products are often considered as relatively low quality products and their chemical structure is not well known.
This work focuses on the physical / chemical standardized analyses and innovative detailed characterization of the properties and the unique composition of jet fuel and Diesel cuts obtained by DCL before and after hydroprocessing. It shows that 100% high quality fully desulphurized Jet A, Jet A-1 or JP-8 aviation fuels could be obtained when using the appropriate hydrocracking conditions. It also shows that the Diesel cut obtained from the same upgrading process can be used as a high quality base for transportation fuels with less than 5 ppm sulfur, excellent cold flow properties and good combustion characteristics, with a very specific chemical structure. This innovative detailed characterization of hydroprocessed DCL jet fuel and Diesel cuts was provided using a GCxGC method developed within IFP Energies nouvelles (IFPEN) laboratories.
1. Introduction The worldwide demand of fuels has been intensified in recent years and is expected to continue growing. To satisfy these energy requirements and diversify the source of fuels, the energy industry has to face the challenge of using alternative resources in order to produce transportation fuels while ensuring an increased predicted demand of aviation fuels and Diesel. Direct Coal Liquefaction (DCL) process, such as Axens H-CoalTS,
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Oviedo ICCS&T 2011. Extended Abstract
enables higher liquid yields than the Indirect Liquefaction (ICL) process (syngas production via coal gasification followed by Fisher Tropsch synthesis). Nevertheless, DCL products are often considered as relatively low quality products and their chemical structure is not well known. DCL main simplified process is presented in Figure 1. Usually in a typical mouth mine DCL unit, the hydrogen required for the coal high pressure catalytic hydroconversion unit and the downstream hydroprocessing of the DCL products is produced from a coal gasification unit. Figure 2 reminds a typical DCL product upgrading route with a high pressure catalytic hydroprocessing (typically hydrotreatment plus hydrocracking) of the full DCL product followed by reforming and isomerization of the hydroprocessed naphtha cuts. This work focuses on the characterization of physical and chemical properties and composition of jet fuel and Diesel cuts obtained by DCL before and after hydroprocessing using high pressure hydrotreatement (HDT) and hydrocracking (HCK), and how analytical and correlative methods are modified or completely changed by using new innovative analytical techniques. It also shows that high quality fuel components can be obtained using appropriate hydrotreating or hydrocracking conditions [1-3]. Product Treating
Coal
Sulfur Ammonia
Coal Liquefaction
Coal Preparation
Gasification/ASU
H2
Liquid Product
Product Upgrading
CO2 Capture
Figure 1. DCL main process block Raw DCL products H2
Isomerization
HDT/HCK
Catalytic Reforming
ULS Gasoline
Gasoline Blending
Butanes EtOH ULS Diesel (CN > 50) High Quality Jet Fuel
Figure 2. DCL upgrading scheme via hydroprocessing
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Oviedo ICCS&T 2011. Extended Abstract
2. Experimental section The upgrading of rough direct coal liquefaction effluents (C5-350/450°C DCL cuts) was carried out in a 1L bench unit at IFPEN facilities. The upgrading experiments were run uninterrupted under severe HDT and HCK operating conditions: total pressure of more than 120 bar, relatively moderate temperatures and quite low hourly space velocities (LHSV). The used LHSV are among the lower ones used for HDT/HCK processes in order to enhance the hydrogenation activity on such a specific feedstock with high aromatic molecules and impurities (i.e; N and O) contents. IFPEN HDT/HCK bench unit well correlates with industrial reactors, as previously demonstrated. The industrial HDT and HCK catalysts used in these experiments were base metal catalysts, in situ sulfided on the unit . After reaction, effluents were cooled, condensed and separated into a gas phase and a liquid phase. Liquid phase effluents were distilled by physical distillation (True Boiling Point - TBP) according to ASTM D2892 method and characterized using standard petroleum analyses and multidimensional gas chromatography (2D-GC or GCxGC) equipped with a flame-ionization detector (FID) and a cryogenic system [4].
3. Results and Discussion 3.1 Physical and chemical properties of DCL products. The main physical and chemical analyses of an IBP-380°C rough DCL cut, before and after high pressure HDT as well as after HCK are presented in Table 1. The rough DCL product contains a high level of nitrogen and oxygen with about 50% aromatics, almost no paraffins, resulting in a relatively low hydrogen level at 11.2 wt%. On the other hand, HDT and HCK total liquid products exhibit a much higher hydrogen content with no impurities and a much lower aromatic content. These cuts are almost made of cyclo-paraffins with 80wt% or more napthenes and a remaining low normal + iso-paraffin content. The hydrogen level is enhanced up to 13.3 wt% on the HCK product. This is a unique structure, never seen in petroleum products, with maybe the exception of hydrocracked light cycle oil (HCK LCO) from catatytic cracking (FCC).
Table 1. Physical and chemical properties of raw DCL, HDT and HCK products Cut
Unit
DCL C5380°C
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HCK
3
Oviedo ICCS&T 2011. Extended Abstract
C5+
DCL C5+
0.9255
0.8805
0.8685
d154
g/cc
Kinematic viscosity at 20°C
mm2/s
8.05
5.2
4.05
Carbon
wt %
87.26
87.3
86.72
Hydrogen
wt %
11.24
12.7
13.28
Oxygen
wt %
1.28
1500 1420 1260 a
ND not detected
b c
Trace elements (e.g. Sr, Mn, V, Zr, Y, Zn, Cu,Rb) were ignored.
b=%Fe2O3+%CaO+%MgO+%Na2O+%K2O; a=%SiO2+%Al2O3+%TiO2
d
ST as softening temperature; eHT as hemispherical temperature fFT as fusing
temperature. 3.2 XRD analyses Compositional and structural transitions of primary minerals in coal ashes and slags were systematically investigated at a temperature range of 300 oC to1600 oC. Kaolinite and/ or illite, quartz, pyrite, siderites, and ankerites etc., are the mainly composed minerals in a majority of coals as low temperature crystalline minerals. The transitions of such primary minerals with increasing temperature (300-1000oC) are principal decomposition and crystal transition at low temperature region. D ash with high SiO2 content underwent the transformation of quartz to cristobalite and mullite through the solid reaction of agglomerated silica and alumina. In contrast, M ash with high Fe2O3, these transformations were carried out through the reactions among silica, alumina
and
iron
oxide
to
Fe-rich
spinel.
Ca-rich
mineral
(primary
anorthite-CaAl2Si2O9) in A ash formed the low temperature eutectic. Rapid quenching
Oviedo ICCS&T 2011. Extended Abstract-Poster
slags show the states of amorphous glasses and mixed structures with some solid minerals, which make it difficult to identify their compositions by using XRD technique as shown in Fig.1. Moreover, three broad peaks were formed in the different regions. According to the components of ashes, we assumed that the broad peak at 13-33o in slag D is ascribed to the amorphous alumina-silicate and silica; broad peak at 15-35o in slag M is attributed to the amorphous iron-rich minerals and alumina-silicate; moreover, the broad peak at 17-37o in A ash is considered to be the amorphous (Ca, Mg)-bearing minerals that from the destruction of crystal structure by the rapid quenching.
Intensity (a.u.)
(a)
(b)
(c)
10
20
30
40
50
60
2 theta (deg.)
Fig.1. XRD patterns of (a) D, (b) M and (c) A Slag as received. 3.2 Molten structural of ashes with different compositions In the present study, the structural analyses were carried out by using multi-nuclear solid state NMR. Some of the amorphous matters derived from decompositions of minerals (such as alumina and meta-kaolinite) were detected by NMR analyses. Due to the complicated mixing states of mineral components, molten ashes and slags showed the relatively broad resonance signals. Resonances in A ash was obviously shifted to low magnetic field, reflecting the effect of the Ca2+ cutting of the large polymeric structure to segments (Fig. 2a). Different effects of Ca and Fe are considered as follows: Fe ion may only influence on the Si-O-Al chain of framework that result in the less shift of 29Si resonance in M molten ash (Fig. 2b). In contrast, Ca
Oviedo ICCS&T 2011. Extended Abstract-Poster
ion cut the network of Si-O-Si and Si-O-Al to result in the apparent shift of 29Si peaks to low magnetic field. 60
Fraction (%)
50
D1600 M1600 A1600
Si
(a)
2+
Ca O O
O
30 O
Al
O
O
10 0 -80 -85 -90 -95 -100 -105 -110 -115 -120 Chemical shift (ppm)
O
Ca2+O
Si
Q3
O
Major in A ash
40
20
Q2
O
Si O
O
Si
O
Si
O
O
Al O
Si
O Ca2+ O
O Si
O
Al
(b) OCa 2+
O Fe 2+
O O
Si
Q4
Major in M ash
Major in D ash
O
Fig.2. Structural analyses of ashes (a) Chemical shift as a function of structural fraction of ashes prepared at 1600 oC and (b) prediction of structural distribution in melting ashes. 3.3 Flow properties of ashes with correlate with structures Due to the co-existing of various micro-structures in melting ashes, they show different rheological behaviors at different temperatures. Fig. 3a shows the relationships between the viscosity and the composition of molten ashes. Molten D ash with high amounts of solids and/or crystal showed high viscosity, in which the melting matters were thought as silica and mullite eutectic. The isolated amorphous alumina was considered significantly increased the viscosity. A and M ashes have similar b/a ratio that contributed to high Ca and Fe contents, respectively. However, they show different viscosity tendencies. The distinctions should be caused by the different effects of Ca and Fe ions in the network of melting ashes. The combining force of alkaline and alkaline-earth must be stronger than that of iron, because the iron ions are considered to combine principally with Al tetrahedrons. Hence, alkaline and alkaline-earth cations decrease the viscosity and melting temperature of ash more effectively. Fig. 3b shows the effect of shear rate on the sensitivity of the melting viscosity to temperature variation. At low temperature, viscosity decline rapidly with the
Oviedo ICCS&T 2011. Extended Abstract-Poster
increasing of shear speed. This change performed less at high temperature after majority liquid phase forming. [2] Viscosity constant regardless with shear rate at high temperature region was considered totally liquid with relate to short molecule or chain structure (such as anorthite in A ash); moreover, viscosity became more distinct with shear rate changes may be induced by the layer structure in M ash (such as Fe-rich spinel) and framework structure in D ash (such as mullite).
140
60 40
A ash
B/A=0.85 High Fe
B/A=0.19 High Si+Al
B/A=0.90 High Ca
40 30 20 10
o
1200 C o 1250 C o 1300 C o 1350 C o 1400 C o 1450 C o 1500 C o 1550 C o 1600 C
10001100120013001400150016001700 o Temperature ( C )
00 1 2 3 4 5 6 Sh e a
r rat
( Co
0
)
20
7
e (S -1 )
8
9
o
1650 C
10
pe ra tu re
80
(b)
D ash Mash
100
Te m
(a)
Viscosity (Pa.s)
Viscosity (Pa.s)
120
0 6.250 12.50 18.75 25.00 31.25 37.50 43.75 50.00
50
Fig.3.Viscosity of (a) tendencies correlation with compositions and (b) as a function of shear rate at different temperatures. 4. Conclusions
In present works, various structure transitions were found with strong relationship to the ash properties, especially the fluidity behaviors at melting stage. Alkaline-earth ions certainly cut the framework to segments corresponding to the shift of 29Si spectra. Large frame work structure shows non-Newtonian flow and strong shear-thinning behavior; In contrast, segmental structures hold the Newtonian flow till low temperature and it contributes less shear-thinning behavior. Acknowledgement
The authors are grateful to the financial support from new energy development organization (NEDO) and globe center of excellence (GCOE). References
[1] Harold H. Schobert, Robert C. Streeter, Erle K. Dieh. Flow properties of low-rank coal ash slags: Implications for slagging gasification, Fuel 1985; 64:1611-1617.
Oviedo ICCS&T 2011. Extended Abstract-Poster
[2] Wenjia Song, Lihua Tang, Xuedong Zhu, et al., Flow properties and rheology of slag from coal gasification Fuel 89 (2010), pp. 1709-1715.
Oviedo ICCS&T 2011. Extended Abstract
Nanominerals and ultra-fine particles within coal ashes
Luis F. O. Silvaa; Frans Waandersd; Marcos L. S. Oliveiraa; Kátia da Boita a
Catarinense Institut of Environmental Research and Human Development – IPADHC,
Brazil. b
School of Chemical and Minerals Engineering North West University (Potchefstroom
campus) Potchefstroom 2531, South Africa * Corresponding author. E-mail address:
[email protected] (L.F.O. Silva)
Abstract Environmental and human health risk assessments due to nanoparticle effects from coal and coal ashes require thorough characterization of the nanoparticles and their aggregates. In this paper the nanosized particles from coal combustion sources are investigated and the complex micro mineralogy of these airborne combustion-derived nanomaterials are characterised. The investigation forms part of a larger experiment on the technical feasibility and environmental impacts of combustion in a Brazilian coalfired power station which uses coal with many potential damaging elements and pyrite, producing a high ash. The combination of Optical Microscopy with instrumental microscopic techniques like Electron Microscope coupled to Energy Dispersive X-Ray Spectroscopy (EDS), Confocal Microscopy and Micro-Raman Spectroscopy have demonstrated to be useful tools for the research of the mineralogical composition of coal ashes. Nanometre-sized crystalline phases in fly ash were characterised using FE-SEM, HR-TEM, and EDS. HR-TEM data reveal nanoscale C-deposits juxtaposed with and overgrown by slightly larger aluminosilicate glassy spheres, oxides, silicates, carbonated, phosphates, and sulphates. The nanoparticles include iron-rich oxide, Fesulphate, and Fe-aluminosilicate glass. Individual metalliferous nanoparticles have a heterogeneous microstructure in which elements such as iron, aluminium and silicon are not uniformly distributed. Iron oxides (mainly hematite and magnetite) are the main coal ashes products of the oxidation of pyrite, sometimes via intermediate pyrrotite formation. The presence of iron oxide nanocrystals mixed with silicate glass particles emphasises the complexity of coal and bottom ash micro mineralogy. Given the
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potentially bio reactive nature of such transition metal-bearing materials, there is likely to be an increased health risk associated with their inhalation. The techniques provide a fast and powerful analytical technique in the study of fly ash nanoparticles, providing a better understanding of the detailed chemistry of this potentially strongly bio reactive component of atmospheric particulate matter, non-destructive and highly-selective analysis of both the surface and the coal inner bulk, and through chemical modelling simulations give the required information to confirm the stability of secondary minerals detected in the samples and helps to diagnose the potential environmental risks associated to their weathering.
1.
Introduction
The combustion of coal by amongst others power plants generate large quantities of fly ash that can have a significant impact on the environment. Although fly ash particles with sizes ranges between 1-10μm diameter, are readily identified using analytical electron microscopy and well documented in the literature [1, 2], there is relatively little information available on ultrafine (< 100 nm) particles, even though these are abundantly present in coal fly ash. The greater surface areas of ultrafine particles compared with larger particles with the same chemical compositions make them more environmentally active with respect to bio-uptake and associated health risks [1, 3-5]. In this paper it is demonstrated how FE-SEM, HR-TEM, and EDS can be used to investigate the elemental distribution, morphology, crystalline phase and electronic structure of individual coal fly ash particles, with emphasis on the ultrafine particles that may have the greatest impact on human life.
2.
Experimental
The coal ash and fly ash samples for this study were collected at the principal Brazilian power plant in the Santa Catarina, State, which uses coal for the generation of electricity. The incineration temperature in the combustion chamber varies between 1 000 ºC and 1 500ºC, and almost 98% of the fly ash is captured in the electrostatic precipitators, which then is then used in the cement industry. The composition of the crystalline minerals in the coal and coal ash were determined by means of a Siemens model D5005 X-ray diffractometer. Qualitative chemical analysis were performed with a LEO-435VP scanning electron microscope (SEM) fitted with an Oxford EDS with a resolution > 133eV. HR-TEM analyses were conducted on particles Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
suspended in hexane. The suspension was stirred for ~1 min and subsequently pipetted onto lacy carbon films supported by Cu grids. The suspension was left to evaporate before inserting the sample into the TEM. The samples were studied by means of a 200 keV JEOL-2010F field-emission HR-TEM equipped with an Oxford energy dispersive X-ray detector (EDS) unit. EDS spectra were recorded in TEM image mode and then quantified using ES Vision software which uses the thin foil method to convert X-ray counts of each element into atomic or weight percentages.
3.
Results and Discussion
The common minerals and phases identified in the fly ash mainly contain inert silicates, oxides, and amorphous phases, and to a lesser extent, carbonates, sulphates, and hydroxides, which formed during heating. They are a result of some additional volatilization of elements and induced alteration, decomposition, crystallization, recrystallization, or amorphization of the actual minerals and phases present [6]. The energy-dispersive X-ray spectrometer data and high-resolution transmission electron microscopy (HR-TEM) images revealed the presence of fine crystalline phases, such as iron-rich oxide spinels and a Fe-aluminosilicate glass. The fate of such nanominerals during coal combustion is determined by competitive processes by which different iron compounds are produced and they typically exist either in iron-oxide form or in combination with other elements, forming multi-element oxides
Figure 1: HR-TEM image and EDS spectrum showing very-fine ordered Hematite structures in fly ash particles [7].
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Figure 1: (A) Jarosite pseudomorph (pyrite-sulphur-jarosite assemblage) from fly ash (TEM image and EDS); (B) Hematite present in fly ash (TEM image) [8].
Fig. 4 (a) HR-TEM and Fourier transformation (FFT) confirm the size of a nanoquartz sphere; (b) FE-SEM of submicroscopic spheres, containing Zr, Ni, Mg and Al [1] 4.
Conclusions
The combination of FE-SEM and HR-TEM/ EDS as used in this study provides a powerful technique to characterise nanoparticles in coal ash and further demonstrates the complexity of mineralogical relationships between nanominerals present in coals and bottom ashes produced during coal combustion, yielding observations which are impossible to make using more traditional characterisation methods such as optical
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Oviedo ICCS&T 2011. Extended Abstract
petrography. Iron was found to be the most abundant transition metal in ambient particulate especially around the Santa Catarina power plant.
Acknowledgements One of the authors (FW) is greatly indebted to the main author (LFOS) who provided the information needed for this presentation.
The NWU and THRIP are thanked for
financial support to attend the conference.
References 1.
Silva, L.F.O. and da Boit, K.A. Nanominerals and nanoparticles in feed coal and bottom ash: implications for human health effects. Environ Monit Assess (2011) 174:187–197.
2.
Ribeiro, J., Flores, D., Ward, C.R., Silva, L.F.O., Identification of nanominerals and nanoparticles in burning coal waste piles from Portugal. Science of the Total Environment 408 (2010) 6032–6041.
3.
O’Connor, G.M., Dick, S., Miller, C., Linak, W. (2004). Differential pulmonary inflammation and in vitro cytotoxicity of size-fractionated fly ash particles from pulverized coal combustion. Journal of the Air & Waste Management Association, 54, 286–295.
4.
Oberdoerster, G., Oberdoerster, E., Oberdoerster, J. (2005).Nanotoxicology: An emerging discipline evolving studies of ultrafine particles. EnvironmentalHealth Perspectives, 113, 823–839.
5.
Xia, T., Lovochick, M., & Brant, J. (2006). Comparisons of the ability of ambient and manufactured nanoparticles to induce cellular toxicity according to an oxidative stress paradigm. Nano Letters, 6, 1794–1897.
6.
Vassilev, S.V., Vassileva, C.G., 2005. Methods for Characterization of Composition of Fly Ashes from Coal-Fired Power Stations: A Critical Overview. Energy Fuels, 19 (3), 10841098.
7.
Silva, L.F.O., Querol, X., da Boit, K.M., de Vallejueloc; S.F-O., Madariaga, J.M. Coal Mining Residues and Sulphides Oxidation by Fenton´s Reaction: an accelerated weathering procedure to evaluate the impact for environment and human health to be published in Science of the Total Environment (2011) Manuscript Number: STOTEN-D-10-00124
8.
Silva, L.F.O., Macias, F., Oliveira, M.L.S., da Boit, M.K., Waanders, F. Coal cleaning residues and Fe-minerals implications Environ Monit Assess (2011) 172:367–378.
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Oviedo ICCS&T 2011.
Properties Of Fly Ash From Biomass Combustion R. P. Girón, I. Suárez-Ruiz, B. Ruiz, E. Fuente, R. R. Gil Instituto Nacional del Carbón, CSIC. Francisco Pintado Fe, 26, 33011 Oviedo, Spain,
[email protected], phone: +34985119090, FAX: +34985297662
Abstract Nowadays the use of biomass as renewable energy source is increasing, however this application has the disadvantage that it produces large quantities of fly ash. The type of ash is different depending on the biomass source and combustion conditions. In this work fly ashes derived from fixed combustion and from fluidized bed combustion systems of forest biomass have been investigated. The raw fly ashes have been dry sieved, and then both the raw sample and the fractions were exhaustively characterized.
1. Introduction The increased demand for energy and the polluting nature of current sources of fossil fuel energy demonstrates the need for new energy technologies, which can offer greater efficiency and minimal environmental impact. Biomass combustion worldwide has a significant potential to meet this demand and great importance as regards global warming since the CO2 generated is considered neutral, for example, in regard to forestry wastes, wood chips, sawdust and bark as fuel will contribute to the conservation of fossil fuel resources and reducing greenhouse gas emissions [1, 2]. However, the disadvantage of incineration is that it produces large amounts of fly ashes. Landfill disposal has traditionally been the most widely used method of disposal in waste management. With the recent increase in the cost, acquisition and development of new waste disposal sites, the management of this fly ash represents a purpose today in energy generation. Biomass fly ashes have a predominantly inorganic fraction and an organic fraction (unburned carbon) minority. The proportion of both fractions is dependent on different parameters and conditions of the combustion process, such as the type of biomass, the load, the combustion, gasification and operating conditions. There are several types of combustion, industrial biomass combustion systems employ fixed bed and fluidized bed appliances. Fixed bed furnaces usually entail lower investment and operating costs for smaller power plants [3]. On the other hand, fluidized
1
Oviedo ICCS&T 2011.
bed furnaces combine high fuel flexibility, good mixing and temperature control, with high conversion efficiencies and low pollutant emissions. This work aims to characterize of two types of fly ash obtained from burning forest biomass: i) fly ash obtained from a combustion furnace (750 ºC) and ii) in fluidized bed gasifier (550 °C). The objective of this characterization is to determine the possible uses of each of the fractions; for example, fractions with a high unburned carbon content can be used as precursors for obtaining activated carbons whereas fractions with a low unburned carbon content can be used as nutrient in ground.
Experimental section For this research, fly ashes were obtained from combustion of forest biomass in a paper mill industry located in northern Spain. The biomass used consisted of bark and chips of Eucaliptus globulus. The fly ashes were sampled in electrostatic precipitators, one from the fixed bed system that operates at a temperature of 750 ºC, referred to in this study as A and the second from fluidized bed at a working temperature of 550 ºC, called B. From the total sample (20 kg) representative subsamples were obtained for a quarter. The raw fly ashes samples were dry sieved yielding the following fractions: >500 μm, 500-212 μm and > 212 μm. Each fraction was labelled as follows; the fly ash from which it was derived followed by a subscript for the size fraction, thus the fraction >500 μm from A is referred to as A5. To characterize of the raw samples and the corresponding fractions a set of different techniques were used following in most cases the standard procedures. These techniques were: petrographic analysis for volumetric composition; XRF, atomic absorption and XRD for mineral matter characterization, and thermogravimetric analysis under N2 atmosphere for thermal behaviour.
2. Results and Discussion Petrographic composition. Table 1 shows the dry sieved yield and the total unburned carbon and mineral material contents in the raw fly ashes, A and B, and their fractions. The highest concentrations of unburned carbons were found in the two fractions >500 μm, but if the fly ash fractions are compared, the B5 content lower volume of unburned carbons. Fly ash B and its fractions have a higher mineral content, because the conditions provided by fluidized bed combustion appear to be more efficient than those
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Oviedo ICCS&T 2011.
of fixed bed combustion. Table1. Petrographic composition and dry sieved yield Dry Sieved Yield (%) Unburned (% vol.) Mineral Matter (% vol.)
A
A5
A2-5
A2
B
B5
B2-5
B2
16,0 84,0
2,17 95,2 4,8
4,17 9,5 90,5
93,66 7,6 92,4
4,0 96,0
4,01 28,4 71,6
8,63 4,0 96,0
86,76 1,7 98,7
With respect to the unburned carbons, Figure 1 and Figure 2 show the images obtained by both optical microscopy and SEM. Two types were identified: i) unburned carbons with a low level of transformation retaining the cellular structure of biomass, and ii) unburned carbons that are transformed, passing through a molten phase during which a large amount of volatiles are evolved resulting in a abundance of macroporosity. This pattern is repeated in both fly ash, A and B.
Fig 1. Unburned carbon weakly transformed
Fig 2. Unburned carbon transformed.
Chemistry and inorganic composition of fly ashes. The crystalline mineral species in fly ashes identified by XRD analysis are illustrated in Table 2. In both cases the inorganic fractions are dominated by Ca and Si, forming carbonates, sulphates and silicate components. The inorganic elements contents, expressed as oxides, are shown in Fig. 3. Both fly ashes are rich in Ca and Si, in B and their fractions the Si content is due to SiO2 which is part of the bed and is dragged together with fly ash. It is noted that the composition of the fraction of 700 ºC) weight loss is due to the decomposition of calcium carbonate and other carbonates. 3. Conclusions The results of the comparison of the two fly ash samples show that the unburned carbon content in fly ash from the fixed bed combustor is greater than that of the fluidized bed leading us to conclude that combustion is more effective in the second type of combustor. In both cases there are two types of unburned carbon, one type some more transformed than other. These unburned carbons will be investigated for potential precursor materials of activated carbons. The majority species in the fly ash are Ca and Si, in the case of A the predominant species is Ca in the form of CaCO3, and in B the predominant species is Si in form of SiO2. Acknowledgement. The financial support for this work was provided by research project from the PRIAsturias, PC 07-015.The Phstudent thanks the CSIC for a predoctoral research grant JAE (ref. PR2005-0168).
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Oviedo ICCS&T 2011.
References [1] Green, C., Byrne, K.A., Cutler, J.C. Biomass: Impact on Carbon Cycle and Greenhouse Gas Emissions. Encyclopedia of Energy. New York: Elsevier 2004:223-36. [2] Petersen Raymer, A.K. A comparison of avoided greenhouse gas emissions when using different kinds of wood energy. Biomass and Bioenergy 30, 605-17 (2006). [3] Warnecke, R. Gasification of biomass: comparison of fixed bed and fluidized bed gasifier. Biomass and Bioenergy 18, 489-97 (2000).
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Oviedo ICCS&T 2011. Extended Abstract
Characteristics of Crush Strength in Coal Briquette Molded with Polymer as a Binder Seung-Hyun Moon1, Seung-Jae Lee1, In-Soo Ryu1, Yong-Woo Kim1, Tae-In Ohm2 1
Korea Institute of Energy Research, 71-2 Jang-dong Yuseong-gu Daejeon, S.Korea. E-mail :
[email protected] 2 Hanbat National University, San 16-1 Duckmyung-dong Yuseong-gu Daejeon, S.Korea. Abstract A rapid increase in energy price makes low grade fuel to be a more promising one. The lower grade fuels containing high contents of moisture, ash and sulfur cause many problems in combustion such as low calorific value, particulate and sulfur dioxide. The problems by ash and sulfur can be solved by flue gas treatment technologies. High content of moisture in low rank coal is related to combustion efficiency as well as transportation. Therefore, low rank coal should be dried before transportation. As a mere drying of low rank coal tends to cause spontaneous ignition during mass storage, the coal has been dried by oil frying method and made in a form of briquette. In this study, we compared crushing strength of coal briquette in which polymer such as polyethylene and polypropylene is used as a binder. Indonesian low rank coal was fry-dried in the kerosene containing 0.5% polymer. A certain amount of the fry-dried coal was put into the mold, heated up to 60-100oC. Molding pressure and molding duration were varied to find optimum conditions. The crushing strength of a briquette formed from the fry-dried coal increased along with the content of polyethylene. The higher fry-drying temperature influenced to lower the briquette strength. Molding pressure had an optimum condition at 100 kgf/cm2 showing stronger briquette than the others molded at 80 kgf/cm2 and 120 kgf/cm2. Briquette strength increased with a mold temperature, indicating that heat is necessary to evenly disperse a binder between coal particles. Molding duration was varied from 20 to 60 seconds, besides which conditions briquette strength was much weakened. In conclusion, polymer could be used as a binder for coal briquette and conditions such as drying temperature and temperature, pressure and duration in molding should be optimized to obtain proper briquette strength.
Key Words: Low-rank coal, Coal briquette, Polymer binder, Crush strength
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1. Introduction A sharp increase of oil price made coal, especially low-rank coal, to be more important. Low-rank coal cannot be used as itself because of lower heating value without upgrading process. The coal with high content of moisture brings about several problems in transportation and combustion. Thus, the coal has been effectively upgraded by drying processes such as UBC (upgrading brown coal), BCB (bindless coal briquette), MTE (mechanical thermal expression), HWD (hot water drying), K-fuel, Syn-coal and so on. However, even after drying the coal, the dried coal tends to re-adsorb moisture from atmosphere during transportation and storage, which can cause various problems in processes of mixing, pulverizing and screening as well as in transportation [1]. Many efforts have been made to prevent the dried coal from re-adsorbing moisture. One of promising technologies is the fry-drying process in oil, well known as the UBC process [2], where the pore surface of the dried coal is coated with oil component e.g. a mixture of kerosene with asphalt. The heavy oil component of asphalt can mainly play roles of the avoidance of moisture re-adsorption on the coal and as a binder for coal-molding process [3]. However, the developed process is disadvantageous in high energy consumption required to transfer moisture and heavy oil component in the coal pores. Recently, our research group has developed a novel coal-drying process (non-fried carbon briquetting process: NFCB process) lowering drying temperature, where vinyl and plastic wastes, asphalt and palm oil are utilized as a heavy oil component to avoid moisture readsorption of coal. Thus, this study deals with mechanical characteristics of briquettes molded with coal dried by the NFCB process with a polymer.
2. Experimental Coal sample used in this study is Indonesian lignite containing higher than 30 wt.% of moisture, which is summarized in Table 1 with the results in composition analysis and calorific value of the coal sample using Tru Spec Elemental Analyzer (LECO Co., USA), SC-432DR Sulfur Analyzer (LECO Co., USA) and TEA-701 Thermogravimeter (LECO Co., USA). Lump coal of Indonesian lignite was crushed by a hammer mill and then by a conventional grinder. 1~3 mm of coal granules obtained using sieve tray were sealed in a plastic bag and then stored in a globe box in order to maintain the moisture content of the
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coal. The coal granules were dried by the non-fried carbon briquette (NFCB) process developed by our research group, where kerosene and polyethylene polymer were utilized as light and heavy oil components, respectively.
Table 1. Summary of composition and calorific value of Indonesian Lignite. Moisture 34.27
Proximate Analysis (wt%) Volatile matter Ash Fixed carbon 33.64 2.01 29.99
Elemental Analysis (wt%) C H N O S 70.50 5.14 0.99 21.33 0.03
15 g of dried coal granule was mounted in a heated molder as shown in Figure 1, and then was pressurized by using hydraulic cylinder for a fixed period. Crushing strength of molded coal sample was measured by using an instrument with a load cell as shown in Figure 2.
(a)
(b)
Figure 1. Hydraulic molding machine for dried coal granule: (a) coal molder and (b) molded coal.
Figure 2. An instrument measuring crushing strength measuring of molded coal sample.
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In order to examine an effect of polymer content of molded coal on crushing strength, polymer content was varied from 0.2 wt.% ~ 0.8 wt.% of total coal weight, where dried coal sample for molding was prepared with 100 g of coal and 100 g of kerosene by the NFCB process heating up to 135 oC for 30 min followed by evaporation of kerosene in oven at 130 o
C for 15 min. The dried coal was pressed to 100 kgf/cm2 of pressure, and was heated up to
80 oC for 40 sec. After 20 min of cooling time, the molded coal sample was taken out from the molder for measurement of crushing strength. Temperature for kerosene evaporation in the NFCB process was also varied form 110 oC to 150 oC. Molding pressure was adjusted in a range of 80 kgf/cm2 and 120 kgf/cm2, and molding time was increased from 20 sec to 60 sec. On the other hand, molding temperature was raised from 60 oC to 100 oC. Finally, cooling time after molding the dried coal was increased by 10 min. The conditions except each molding variable was fixed to the same values mentioned above.
3. Results and Discussion When 100 g of coal and 100 g of kerosene were used in the NFCB process, the increase of vinyl content can generally enhance crushing strength of molded coal samples (see Figure 3).
Figure 3. Crushing strength of the coals molded with various vinyl contents
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Oviedo ICCS&T 2011. Extended Abstract It is expected that heating the dried coal to 100 oC of molding temperature would melt vinyl in the dried coal to pass through the gaps between coal particles and block their contact to air, which could lead to improve the binding strength of coal particles. It is also worth noting that 0.5 wt% and 0.8 wt% of vinyl content do not significantly increase crushing strength of molded coals, which reveals that there should be the maximum of vinyl content over which the crushing strength of molded coal is not affected as much as the addition of vinyl. An effect of kerosene evaporation temperature is displayed in Figure 4. It seems that the coal samples evaporated at 110 oC and 130 oC are not significantly influent on the crushing strength. On the other hand, the coal prepared at 150 oC of the evaporation temperature exhibits relatively lower crushing strength than the other samples. Thus, the enhancement of the crushing strength of the molded coal samples can be assisted by the presence of some oil component of kerosene rather than complete removal of kerosene from the dried coal.
Figure 4. Effect of the oil evaporation temperature in the NFCB process. As shown in Figure 5, 100 kgf/cm2 of molding pressure can produce briquettes having the
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Oviedo ICCS&T 2011. Extended Abstract highest crushing strength. It is considered that molding pressure below 100 kgf/cm2 is difficult to get properly together coal particles. However, molding pressure over 100 kgf/cm2 may stress coal particles in molder out to lower crushing strength of molded coal samples.
Figure 5. Crushing strength of the coals molded under various molding pressure.
In the variation of molding time, 40 sec of molding time can achieve the highest crushing strength of coal briquette. Thus, it is not necessary to delay molding time too much in a view point of crushing strength of the briquette. The crushing strength can increase with increasing molding temperature in a range between 60 oC and 100 oC, implying that the mobility of oil component and vinyl present in the dried coal can rise with molding temperature to bind strongly coal particles. On the other hand, it is observed that the crushing strength is maximized at 20 min of cooling time after molding, and is not significantly changed at longer than 20 min of the cooling time. Thus, it is suggested that coal briquette heated during the molding process should be cooled down in atmosphere for longer than 20 min in order to form strong coal briquette in crushing. Moisture re-adsorption of the coal briquettes prepared with various oil components is
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Oviedo ICCS&T 2011. Extended Abstract
exhibited in Figure 6. As-molded coal briquettes have less than 3 wt.% of water, but water content of the samples left in atmosphere for 10 days goes up to 8 wt.%. It is obviously observed that the addition of oil components such as kerosene, asphalt and vinyl can retard moisture re-adsorption of the briquette, even though the samples with the oil component are saturated with water at the same water content of the sample without the oil component.
Figure 6. Moisture re-adsorption of briquettes of coals dried with various oil components.
4. Conclusions It is certain that the addition of vinyl as a heavy oil component in the NFCB process is favorable to increase the crushing strength of the product of coal briquette. Moreover, it is suggested that evaporation temperature of kerosene as light oil component in the NFCB process should not exceed 130 oC, and thus kerosene left in the dried coal particles can help to increase binding strength during the molding process of the dried coal. Crushing strength of coal briquette can be affected by several molding conditions such as time, pressure and temperature, which should be controlled to be 40 sec, 100 kgf/cm2 and 100 oC, respectively,
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in order to obtain the proper strength. Furthermore, the heated coal briquette should be cooled down for longer than 20 min in atmosphere to maintain the crushing strength. Finally, it is confirmed that the coal briquette having oil components can retard moisture re-adsorption in the exposure of the sample to atmosphere.
Acknowledgement We acknowledge funding from Korea Institute of Energy Technology Evaluation and Planning (KETEP) for a project of power generation & electricity delivery.
References [1] Moon, S.-H. and Lee, I.-C., Moisture control in application of coal, Korea Institute of Energy and Resources (1990) in Korean [2] Chun, B.-S., Kumar, S., Park, Y.-S., Kim, J.-Y., Shin, S.-U., Shin, B.-W., Do, J.-N. and Kim, Y.-I., Application of Alternative Materials for a Fossil Fuel of Fuel by Vacuum Frying, Korean Geo-Environmental Conference Sep. 19 (2008) 107 in Korean [3] Sugita, S., Deguchi, T. and Shigehisa, T., UBC (Upgraded Brown Coal) Process Development, Kobe Steel Engineering Reports 53(2) (2003) 41-45 in Japanese [4] Hickey H., MacMillan B., Newling B., Ramesh M., Eijck, P.V. and Balcom B., Magnetic resonance relaxation measurements to determine oil and water content in fried foods, Food Research International 39 (2006) 612 [5] Li X.; Song H., Wang Q., Meesri C., Wall T. and Yu J., Experimental study on drying and moisture re-adsorption kinetics of an Indonesian low rank coal, Journal of Environmental Sciences Supplement (2009) 127 [6] Peregrina C., Arlabosse P., Lecomte D. and Rudolph V., Heat and mass transfer during fry-drying of sewage sludge, Drying Technology 24 (2006) 797 [7] Farkas B.E., Singh R.P. and Rumsey T.R., Modeling heat and mass transfer in immersion frying I. Model development, Journal of Food Engineering 29 (1996) 211 [8] Peregrina C., Rudolph V., Lecomte D. and Arlabosse P., Immersion frying for the thermal drying of sewage sludge: An economic assessment, Journal of Environmental Management 86 (2008) 246
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Oviedo ICCS&T 2011. Extended Abstract
Characteristics of dried low-rank coal by hot oil immersion drying Method for the upgrading Tae-In Ohm1, Jong-Seung Chae1, Seung-Hyun Moon2 1 Hanbat National University, San 16-1 Duckmyung-dong Yuseung-gu Daejeon, 2
S. Korea. E-mail :
[email protected] Korea Institute of Energy Research, 71-2 Jang-dong Yuseung-gu Daejeon, S. Korea.
Abstract Coal is the most abundant fuel on earth, and Low-rank coal (LRC) such as subbituminous coal and lignite makes up about half of all coal deposits. LRC is inconvenient to use due to its low caloric value and high moisture content, and because these oxygen-rich coals tend strongly toward spontaneous combustion. Solving these problems would substantially improve the efficiency of LRC use. In this study, we describe a drying technique utilizing hot oil immersion. This upgrading process may be executed under relatively low temperature and pressure, greatly reducing its energy cost. Drying tests of Indonesian lignite were performed with refined oil and B-C heavy oil, which were heated to 120 °C, 130 °C or 140 °C. Following 10 min of treatment, the moisture content of the upgraded coal was improved from 32 wt.% to 2.0-3.2 wt.%, and its high heating value from 12,500 kJ/kg to 25,100 kJ/kg. The coal drying curve shows that most of the moisture evaporated within about 5 minutes at an oil temperature of 140 °C, much more rapidly than occurs using heated gas drying methods. Further, there was a stepwise reduction in weight indicating rapid moisture evaporation to its final level. This occurred because moisture was boiled off at the same time that high temperature and vapour pressure in the coal led to hardening and carbonization. BET analysis indicated that moisture occupying fine pores was replaced by oil after the drying process, and that pore diameter, surface area and volume were all reduced. In the drying process using high viscosity B-C heavy oil, oil absorption became more significant as coal size decreased. This was due to absorption of the viscous oil in the pores of the smaller particles, which on a relative basis have a wider surface area. Coal size had less influence on the absorption of refined oil, which was more readily recovered from the smaller coal by centrifugal separation. Key Words: Low-rank Coal, Coal Drying, Oil Immersion Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
1. Introduction A stable security plan requires low-cost energy sources, but the present substantial demand for energy has elevated the prices of gasoline as well as coal. The upgrading of Low-rank coal (LRC) offers a means to reduce total energy costs. LRC accounts for about half of the world's coal deposits, and is relatively inexpensive at just 20-30% of the price of high-rank coal. However, the use of LRC has been extremely limited for several reasons. Its high moisture content of 30-70% makes it more difficult to transport over long distances, and its heating value is only 4,500 kcal/kg at best. Also, due to its high porosity and high carbonyl content, LRC has a strong tendency toward spontaneous combustion during long-term storage. Overcoming these disadvantages through an upgrading process would confer a significant economic benefit. In LRC upgrading processes, water is evaporated from surface and interstitial spaces, the moisture being replaced with oil. Hence, the heating value of LRC is increased, and the conversion from a hydrophobic to hydrophilic condition serves to stabilize it[2,3,4,5]. Coal drying technologies can be categorized as evaporative or nonevaporative, the latter category including processes known as the K-Fuel process (U.S.A.), the Binderless Coal Briquettes process (Australia) and the Upgrading Brown Coal process (Japan). In this study, the technique of immersion in hot oil was used to dry LRC through heat and mass transfer mechanisms. Coals were added to oil heated above the evaporation temperature of moisture, generating a strong turbulent flow on the coal surface by boiling. Through heat transfer, both surface water and interstitial water evaporated rapidly. By this drying technique, hereinafter called 'fry drying', LRC could be upgraded to a moisture content of 5% or less and a heating value of 6,000 kcal/kg or more, owing to replacement of moisture in the coal with oil.
2. Experiment Deposits of Indonesian lignite are abundant, and its advantageous geographic distribution helps to keep transportation costs low. For these reasons, Indonesian lignite was selected as the test sample to be upgraded. For use in experiments, block coals were mechanically crushed and then passed through 2-3 mm, 6-7 mm and 10-11 mm screens, such that specific coal sizes could be tested. Basic characteristics of coal samples were measured using a Truspec CHN Elemental
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Oviedo ICCS&T 2011. Extended Abstract
Analyzer (LECO), SC -432DR Sulfur Analyzer (DIONEX), Analyze (LECO), IC-2000 Analyze (LECO) and TG A-701 Proximate Analyzer. Results of proximate, ultimate, and heating value analyses are shown in Table 1. Table 1. Characteristics of Indonesian Low Rank Coal. Proximate Analysis (as received base) Moisture (wt%)
Ash (wt.%)
Fixed carbon (wt.%)
Volatile matter (wt.%)
32.3
2.0
34.6
31.1
Ultimate Analysis (as received base) C (wt.%)
H (wt.%)
O (wt.%)
N (wt.%)
S (wt.%)
Cl (ppm)
43.5
4.1
17.5
0.6
not done
not done
Calorific Values High calorific value (kcal/kg)
Low calorific value (kcal/kg)
3,230.8
2,864.2
Refined waste oil and B-C heavy oil were used as drying media. Refined oil is recycled waste oil from which moisture, ashes, heavy metals and other contaminants had been removed. B-C heavy oil, the most viscous of the heavy oils with a minimum viscosity of 50 cst (50 °C), is used as fuel for burners equipped with a preheating and warming apparatus, such as large-scale boilers and low-speed diesel engines. The refined oil used in this study had a boiling point of approximately 340 °C and a specific gravity of 0.856-0.86; the B-C heavy oil had a boiling point of about 340 °C and a specific gravity of 0.92-0.95. Fig. 1 shows the design for a batch-type coal drying apparatus. The cylindrical reactor (height 23 cm, diameter 20 cm) and a square mesh net receptacle for coals to be fed into the reactor (width 10 cm, length 10 cm, height 2.5 cm) were made of stainless steel. The weight of the oil in the reactor was measured with an electronic scale placed under the drying apparatus. An automatic temperature controller was provided to precisely control the reactor temperature. A notebook computer recorded changes in temperature and weight as functions of heating time of the oil and drying time of the coal. The oil was preheated to a stable temperature of 120 °C, 130 °C, or 140 °C before the Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
addition of 50 g of coal per litre of oil. Each fry-drying experiment was performed for 10 minutes. After drying, coals were transferred to a centrifugal separator for 10 minutes, and the amount of separated oil was then measured. To assess drying efficiency under each reaction condition, moisture content was measured by electric oven in samples collected before and after the drying process, and crushed to a uniform size of 0.25 mm. Moisture measurements were completed the same day to preclude changes in moisture content. For all parameters measured, the arithmetic mean of three experiments was calculated.
Fig. 1. Batch-Type Coal Drying Apparatus.
3. Results and Discussion 3.1 Drying curves The drying process of a general solid can be divided into three periods, namely, a preheating period, a constant-rate drying period and a falling-rate drying period. In the brief preheating period, the solid initially warms and the moisture content slowly decreases. In the subsequent constant-rate drying period, the evaporation rate at the surface of the solid is equal to the internal diffusion rate, and there is an abrupt, linear decrease in moisture content. Lastly in the falling-rate drying period, the evaporation rate at the surface increases while the internal diffusion rate diminishes, and thus moisture content decreases slowly until a minimum is reached. This scenario will vary according to the shape of the solid and conditions of the heated gas such as temperature and humidity.
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Oviedo ICCS&T 2011. Extended Abstract
A drawback in the use of heated gas for solid drying is the length of time required for both the constant-rate drying period and the falling-rate drying period. To solve this problem, in this study we have investigated the drying characteristics of an alternative process that utilizes boiling heat transfer. The coal drying curve in Fig. 2 shows that most of the moisture evaporated within about 5 minutes at an oil temperature of 140 °C, much more rapidly than occurs using heated gas drying methods. Further, there was a stepwise reduction in weight indicating rapid moisture evaporation to its final level. This occurred because moisture was boiled off at the same time that high temperature and vapour pressure in the coal led to hardening and carbonization. 860 850
Weight(coal+oil)
840 830 820 coal input
810
coal diameter : 2-3mm coal weight : 50g oil temp : 140 C
800 790 780
0
2
4
6
8
10
12
14
16
18
20
Fry-dry time (min)
Fig. 2. Drying Curve of Raw Indonesian Lignite. 3.2 Results of TGA analyses Coals 2-3 mm in diameter, before and after drying in B-C oil at 140 °C, were TGAanalyzed in nitrogen or in air at a heating rate of 20 °C /min. The results are shown in Figs. 3. Raw coal lost mass in either nitrogen or air both before reaching a temperature of 100 °C and after, as moisture phase-changed to vapour. In contrast, coal first subjected to the drying process lost mass gradually over a temperature range of 100150 °C. This was apparently caused by decomposition of organic material present in the coal. The reduction of mass in coal dried in B-C oil took place at slightly higher temperatures than with coal dried by refined oil, due to the characteristically high viscosity and high density of B-C heavy oil.
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Oviedo ICCS&T 2011. Extended Abstract
90
90
80
80
70
70
Weight (%)
100
Weight (%)
100
60 50 40 30
0
0
100
200
300
60 50 40
20
Temp : 20 oC / min Gas : N2
10
Temp : 20 oC / min Gas : air
30
raw-coal B-C oil drying Refined-oil drying
20
raw-coal B-C oil drying Refined-oil drying
10
400
500
600
700
800
0
900
0
100
200
300
400
500
600
700
800
900
Temperature ( oC)
Temperature ( oC)
Fig. 3. TGA Curves of Raw and Upgraded Indonesian Lignite in N2(left) and Air(right) (Heating rate 20 °C /min). 3.3 Effectiveness of fry-drying The coal contained 27-30% moisture before the drying process; moisture contents determined after the fry-drying process are shown in Fig. 4. Moisture content was reduced to 2.6-9% after drying with B-C oil, and 2-7% when dried with refined oil. The effectiveness of fry-drying was greater at higher oil temperature and with smaller coal size. 10
10 2-3mm
9
9
2-3mm
4-5mm 10-11mm
8
Moisture(%)
Moisture(%)
10-11mm
7
7 6 5 4
6 5 4
3
3
2
2
1
1
0
6-7mm
8
120
130
B-C Oil Temperature ( o C )
140
0
120
130
Refined Oil Temperature ( oC ) C
140
Fig. 4. Moisture Contents of Upgraded Coal Dried in B-C Oil (upper panel) or in Refined Oil (lower panel). 3.5 Oil absorption by coal In the drying process using high viscosity B-C heavy oil, oil absorption became more significant as coal size decreased (Fig. 5). This was due to absorption of the viscous oil in the pores of the smaller particles, which on a relative basis have a wider surface area. Coal size had less influence on the absorption of refined oil, which was more readily recovered from the smaller coal by centrifugal separation. Submit before May 15th to
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12
12
10
10
Oil Absorption Amount (g)
Oil Absorption Amount (g)
Oviedo ICCS&T 2011. Extended Abstract
8
6
4
2-3mm
2
8
6
4
2-3mm
2
6-7mm
6-7mm
10-11mm
0
120
130
o C ( C ) B-C Oil Temperature
10-11mm
0
140
120
130
Refined Oil Temperature ( o C)
140
Fig. 5. Amount of Oil Absorbed by Coal Upgraded in B-C Oil (upper panel) and in Refined Oil (lower panel). 3.6 Oil recovery rate and net oil consumption Oil was recovered from dried coal by centrifugal separation for 10 minutes. B-C heavy oil could not be recovered due to its high viscosity. Rates of refined oil recovery and net consumption are shown in Fig. 6. The rate of recovery was independent of both drying temperature and coal size. Net oil consumption increased with drying temperature, regardless of the coal size. 2
2 2-3mm 6-7mm
Net Oil Loss Rate (%)
Oil Seperation Rate (%)
10-11mm
1.5
1
0.5
1.5
1
0.5 2-3mm 6-7mm 10-11mm
0
120
130
Refined Oil Temperature ( o C)
140
0
120
130
Refined Oil Temperature ( o C )
140
Fig. 6. Oil Recovery Rates (upper panel) and Net Rates of Consumption (lower panel) for Centrifugal Separation of Refined Oil. 4. Conclusions We have developed a new, rapid method for the upgrading of LRC. Drying tests were performed on Indonesian lignite (moisture content 32%, high heating value 3,000 kcal/kg) using immersion in either refined oil or B-C heavy oil that had been heated to a
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Oviedo ICCS&T 2011. Extended Abstract
temperature of 120 °C, 130 °C or 140 °C. Using this fry-drying process, it was possible to obtain upgraded coal with a moisture content of 3% or less and a high heat value of approximately 6,000 kcal/kg.
Acknowledgement. This work was supported by the New & Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) grant funded by the Korea government Ministry of Knowledge Economy(No. KETEP : 20103020100010).
References [1] Sakaguchi, M. et al., Hydrothermal upgrading of Loy Yang Brown Coal - Effect of upgrading conditions on the characteristics of the products, Fuel Processing Technology 89 (2008) 391-396 [2] Renfu, X. et al., Effects of chemicals and blending petroleum coke on the properties of low-rank Indonesian coal water mixtures, Fuel Processing Technology 89 (2008) 249-253 [3] Nugroho, Y. and McIntosh, A., Low-temperature oxidation of single and blended coals, Fuel 79 (2000) 1951-19 61 [4] Küçük, A. and Kadioglu, Y., A study of spontaneous combustion characteristics of a Turkish lignite; particle size, moisture of coal, humidity of air, Combustion and Flame 133 (2003) 255-261 [5] Sonata, W. and Zhang, D., Low- temperature oxidation of coal studied using wiremesh reactors with both steady-state and transient methods, Combustion and Flame 117 (1999) 646-6516. Sugita, T. et al., UBC (Upgraded Brown Coal) Process Development, in, Kobe Steel Engineering Reports, p. 53, 2003 [6] Katalambula, H. et al., Low-Grade Coals, A Review of Some Prospective Upgrading Technologies, Energy & Fuels 23 (2009) 3392-34058. Morimoto, M. et al., Hydrothermal extraction and hydrothermal gasification process for brown coal conversion, Fuel 87 (2008) 546-551 [7] Lee, S. J., Shin, H. Y, Bae, I. K., Chae, S. C., Report on upgrading technology for low-rank coal, Journal of the Korean Society for Geosystem Engineering 45 (2008) 276 -282 [8] Ohm, T., Chae, J., Kim, J., Kim, H. and Moon, S., A study on the dewatering of the industrial waste sludges by fry-drying technology, Journal of hazardous materials 168 Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
(2009) 445-450 [9] Ohm, T. I., Chae, J. S., Kim, H. K., Lim, K. S., Kim, M. J., Moon, S. H., An experimental study on the drying characteristics of the sludge in the EDIHO using drying curve, Journal of Korea Society of Waste Management 26 (2009) 312- 318 [10] Ohm, T. I., Chae, J. S., Kim, J. E., Kim, H. K., Moon, S. H., A study on dewatering characteristics of the industrial waste water sludge using fry-drying technology, Journal of Korea Society of Waste Management 25 (2008) 225-231 [11] Ohm, T. I., Chae, J. S., Kim, J. E., Kim, H. K., Lim, K. S., Moon, S. H., A study on the characteristics of evaporative drying in immersed hot oil for summer and winter sewage sludge, Journal of Korea Society of Waste Management 26, (2009) 78-85
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ENERGY AND EXERGY ANALYSIS OF CONTINUES MICROWAVE DRYING OF COAL M. B. Alvarado1∗, E. J. Muñoz1, S.C. Navarro2∗∗, F. Chejne1, H. Velazquez1 1 Grupo de Termodinámica Aplicada y Energías Alternativas, Escuela de Procesos y Energía, Universidad Nacional de Colombia, Sede Medellín, 2 Investigación y Desarrollo de Tecnologías y Procesos, Cementos ARGOS.
Abstract The aim of this study is evaluate the energetic and exergetic efficiency of coal drying process in a microwave tunnel-type oven, using a Colombian coal for the experiments. The sample has moisture content around 20% and the process remove an 8% by weight, it is assumed that the carbonaceous material does not vary in elemental composition, dielectric and physicochemical properties with increasing temperature and moisture change due to microwave radiation. The design parameters of the equipment taken for analysis are based on data from a research group TAYEA of the Universidad Nacional de Colombia associate with Investigación y Desarrollo de Tecnologías y Procesos,ARGOS Company and financed by them. It was found that the energy drying process efficiency is equal to the second law around 69% which is explained by the quality of electromagnetic waves exergy. Keywords: Microwave, coal, exergy, energy.
1. INTRODUCTION The moisture content in coal is an important parameter that affects the thermal combustion efficiency, handling and transportation cost, and allocation of the price. Some parameters affect the amount of moisture reduction with microwave treatment such as: density, particle diameter, mass processing, temperature, location in the dry chamber, material composition where are considering the water, ash and minerals amount, the presence of metallic elements, and volatile matter [11].
∗
Corresponding author:
[email protected] [email protected] ∗∗
Pyrite as water are the main source of heating of the carbonaceous structure during microwave exposition [2]; Microwave heating can lead fractures due to thermal stresses between the present phases in the material. Thermal stresses are result of the different capacities of absorber microwave in coal’s materials that generate differentials of temperatures inside the material. Electric permittivity and magnetic permeability of each phase are the properties that produce these differences. Coal is not a good microwave absorber because their relative electrical permittivity as a volumetric material is lower than 0.1 (at 2.45GHz and 25°C), otherwise for water is around 12 at the same conditions resulting more susceptible to microwave heating than coal [12]. The density of energy carried by microwaves is proportional to the square of electric field magnitude incident to the material and is represented by Lambert-Beer equation [9] Equation 1), therefore the physical strength ( between coal particles can be increased when high density of microwave energy is applied, this effect generates large intermolecular tensions that eventually cause fractures within coal matrix [13][2]. Equation 1 The instantaneous power in an electromagnetic wave is described by the Poynting vector, whose value at the material surface takes the form of Equation 2, which depends on the maximum field value. Equation 2 The attenuation factor β of heat generation presented in Equation 1 is determined by Equation 3: Equation 3 Where (
the frequency of electric field ( ), ), is the electric permittivity and
is the light speed in vacuum space indicated such a material can be
penetrated by an electric field, causing it to warm up, and as this heat is dissipated (
).
For the coal and indicates the electrical energy distribution within a microwave irradiated material and affects the efficiency of energy transfer from the microwave oven to the product. Thus the attenuation factor will determine the energy distribution of energy within a material [10]. The thickness of the depth of penetration ( ) of the applied power depend on the dielectric properties of the material [1], to coal it takes a value of 0.05m.
Previous studies have found coal drying efficiencies around 83%, in tunnel-type microwave oven where coal sample passes through a conveyor belt, equipped with insulation systems and Remote control [12]. The selection of this application depends on the market behavior of coal and the use the use will be given to it: pyrolysis, gasification, desulfurization, substance or catalyst absorber, etc. The Colombian coal provided by ARGOS has been studied in particle sizes less than 38mm, finding moisture removal up to 6% in times of 8 minutes without degrading other properties such as calorific value, Hard Grove Index, ash and sulfur content. We found that larger particles are those with higher moisture removal [14]. The interest aroused by the use of microwaves for drying coal justified the study of energy and/or exergy benefits in the process. The coal can be treated as a flow stream in the exergetic analysis of the process and also is discuss how the coal price affects the use of this technology; the above in order to stimulate the comparison of this technology with others conventional existing for drying coal. Some advantages of microwave heating application have been discussed through the literature: - Substantial reduction of heating times and energy costs. Heating times may be even reduced at less than one percent required by conventional diffusive or convective heating techniques [3]. - Possibility of selective heating depending on the responses of different phases present in a material [5] [6]. - Ability to improve product quality and improved chemical synthesis [7], [8]. The evaluating system of this study is presented in the Figure 1 where could see mass and energy flows involved in the microwave dry process.
Figure 1. Scheme of microwave dryer tunnel-type. Due to the difference in the effects occurred between water and carbonaceous structure present in the coal flow on the conveyor belt at the Figure 2 it was divided into two streams, one for water
(mWo) and the other for the carbonaceous mass (mCo) even when there are at the same temperature (To). To the operation, the conveyor belt requires a voltage (V2) and a current (I2) and due to energetic inefficient heat (QC2) is released. The magnetron for generating microwave power (Po) requires a electrical consumption of voltage (V1) and current (I1), overheating is product of the energy inefficiency of the magnetron to prevent it and damage the equipment the Fan 2 is used, which circulates air mass (mAf) through a T0 temperature to Tf2 releasing heat (QC4) and has a energy consumption of voltage (V4) and current (I4). The power output (Po) is supplied to the drying chamber, in which one part is absorbed by the coal moisture on the conveyor belt causing the warming of the material to the outlet temperature (Tf) and evaporation of water which gives result an outflow (mcf + mWf) and the other part is considered like lost power (Pp). Fan 1 is used to remove water vapor generated (mVf) to a temperature (Tf1), consuming a power voltage (V3) and current (I3) and heat loss (QC3). All equipment of the drying system operating at the same voltage, so V1 = V2 = V3 = V4 = V = 220V.
2. MODELO TERMODINAMICO Y TERMOECONOMICO
2.1.
PARÁMETROS USADOS EN EL MODELO
The coal mined present a moisture of W0=20% and the process is able to removed until the 8%, the environment temperature is set at 25°C. The thermodynamic properties of the materials involved in the process are summarized in Table No 1 which were taken to 25°C of temperature and 1atm of pressure using Enginnering Equation Solver program (EES 8.609) licensed by Universidad Nacional de Colombia [15]. 50% was added to latent heat of vaporization which refers to the energy required to break the interaction of coal-steam and calculation thus find a latent heat of sorption. The energy magnetron efficiency was considered 70%, and this is fed with a voltage of 220V. Table No 1. Materials properties. Water Air Coal (kJ/kg °C) 3.979 1.005 1.260 PCI (kJ/kg) (kJ/kg)
----2256.8
-------
24000 ----
Efficiencies were evaluated for microwave drying system. Energetic efficiencies for microwave
drying and to the system are shown in Equation 4 and
Equation 5. Equation 4 Equation 5
Exergetic efficiencies for microwave drying and to the system are shown in Equation 6 and Equation 7. Equation 6 Equation 7
2.2.
THERMODYNAMIC MODEL
2.2.1. Mass Balance To the solution is necessary to perform the mass balance in the drying chamber for water, because the carbonaceous mass is unchanged as shown in Equation 8: Equation 8 Is necessary to specify that this mass of water is equal to the percentage of moisture present on coal . (
2.2.2. Energy Balance The energy balance considering the system shown in Figure 1 is presented by
Equation 9:
Equation 9 Where are the current consumed by the microwave generator, fan 1, fan 2 and the conveyor belt, respectively. The second and third term on the left side of the equation refers to the energy contained in the stream of wet coal and air input to the system. The first, second and fourth term of
Equation 9 represents the energy contained in the air, water and dry coal respectively. The third term on the right side of the equation is the energy consumed in water evaporation. The following terms represent the heat lost in the magnetron, the fan 1, fan 2, the conveyor belt and the drying chamber, respectively, due to the inefficiencies of the equipment. The two main parts (magnetron and dryer chamber) is necessary to present the energy balance as shown in Equation 1011
Equation 12 and 12, respectively: Equation 10
Equation 11 Where, is the maximum power capable to produce by the magnetron. 2.2.3. Exergy Balance Exergetic balance taking to account the system presented in Figure 1 is showing by Equation 13:
Equation 12 The Equation 12 present the physic and chemical exergy associated with the initial and final state of coal and air, and the steam stream at the outlet of the dryer chamber. The last term is associated with the exergy destroyed accounted for the losses associated with the system irreversibilities. The physical exergy of air is calculated as shown in equation 14: Equation 14
Equal to energy balance is necessary to perform an exergetic balance for the two main parts (Magnetron and Dryer Chamber) presented in Equation 135 and 16, respectively: Equation 135 Equation 146
2.2.3.1.
Chemical Coal Exergy
The total chemical exergy [4] is calculated by equation 17: Equation 157 The
chemical
fuels
exergy
(coal)
was
calculated
by
the
Equation 168 for elemental analysis free of ash and moisture
Equation 168 Where the temperature should be in Kelvin degrees, PCS is the caloric value of coal and mole fractions of each component which are calculated using the following relationships:
The
entropy
and
caloric
value
of
coal
[4]
are
is
described
by
Equation
17
and 20: Equation 179 Equation 20 The Table No 2 shows the elemental analysis performed at the coal sample before and after drying using a microwave oven with reference LG MS-1146SQP, tests were made in the laboratory of the Universidad Nacional de Colombia using an elemental analyzer (CHN) marks Exeter. Water vapor exergy was calculated with Equation .
Equation 21 Table No 2. Ultimate Analysis Output Element Input H 0.0484 0.0531 O 0.1314 0.1441 S 0.0222 0.0243 C 0.5387 0.5910 Ash 0.0477 0.0526 H2O 0.1974 0.1196 N 0.0112 0.0123
3.
RESULTS Y DISCUSSION
The results of mass, energy and exergy balance with maximum power input conditions are
¡Error! No se encuentra el origen de la referencia.
shown
in
and 4.
Table No 3. Energy Results Energy fluxes Value (kW) 10,00 VIMW
Table No 4. Exergy Results Exergy Fluxes Value (kW) 459,40
3,00
QS QD QP
4,81 0,57 0,35 1,32
Po
10,00 7,00 0,27 464,20
Figure 2 and 3 represent the energy and exergy Sankey diagram for the coal microwave dryer working at full power (10.00 kW).
Figure 2. Sankey diagram of energy fluxes Figure 22 present the energy flows of streams involved in coal drying process, showing that most of the input energy is needed to evaporate the water contained in coal matrix, in addition the magnetron dissipates a significant amount of energy that is fed into the system, the system efficiency of the drying process according to Equation 5 is 48%, while the process efficiency of the drying chamber according to Equation 4 is 69% . This indicates that much of the microwave energy is transferred to the vapor and the rest is stored as heat in the coal.
Figure 3. Sankey Diagram of Exergy Flux Figure 3 present the Sankey diagram associated with exergy flux in the microwave drying system, where it is clear that the useful stream is associated with the exergy contained in coal, the system is able to process 70kg/h; according by Equation 7, the exergetic efficiency of microwave drying process is 48%, and the exergetic efficiency in the dryer chamber is 69% (Equation 6). It is remarkable that energetic and exergetic efficiencies are equal, which is understandable due to the exergetic forms that interact within the system have quality 1, and this makes the exergy equal to the energy transport by streams getting the maximum benefit, that is a maximum energy efficiency.
4.
CONCLUSIONS
Equality between energetic and exergetic efficiencies of microwave drying process occurs because the exergy of the microwaves is equivalent to its energy content, which does not happen with conventional convective or conductive drying processes, where required heating dry air or other conductive material. These do not transfer all the energy contained in the process, which reduces significantly the efficiencies of these processes, also microwave drying has another advantage because it does not require long times to reach operating conditions necessary to initiate the process. Acknowledgement Authors acknowledge the financial support of INCARBO, Investigación y Desarrollo de Tecnologías y Procesos, ARGOS and Universidad Nacional de Colombia. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
A. Datta, Handbook of microwave technology for food applications. New York: M. Dekker, 2001. Marland, S., A. Merchant, and N. Rowson, Dielectric Properties of coal. Fuel, 2001. Meredith, R., Engineers' Handbook of Industrial Microwave Heating. The Institution of Electrical Engineers, London, 1998. A. Bejan, Thermal design and optimization. New York: Wiley, 1996. Harutyunyan, A.R., et al., Purification of single-wall carbon nanotubes by selective heating of catalyst particles. The journal of physical chemistry B, 2002. 106(34): p. 8671-8675. Wang, Y., E. Forssberg, and M. Svensson, Microwave assisted comminution and liberation of minerals. Mineral processing on the verge of the 21st century, 2000. Jones, D.A., et al., Microwave heating applications in environmental engineering - a review. Resources, Conservation and Recycling, 2002. 34: p. 75-90. Whittaker, G. and D.M.P. Mingos, The application of microwave heating to chemical syntheses. Journal of microwave power and electromagnetic energy, 1994. 29(4): p. 195219. Swami, S., Microwave heating characteristics of simulated high moisture foods. 1982, MS thesis, University of Massachusetts: Amherst, MA, USA. Ayapa, K.G., et al., Microwave heating: an evaluation of power formulations. 1991, Editorial Pergamon Press plc. Vol. 46, No. 4: Gran Bretaña. p. p. 1005 -1016. Ponte, D.G., et al., Determination of moisture content in power station coal using microwave. 1995, Oviedo University: Spain. Kalra, A., Dewatering of fine coal slurries by selective heating with microwaves. 2006, College of Engineering and Mineral Resources West Virginia University: Morgantown, United States. Yag˘mur, E., S¸ims¸ek, E. H., & Taner Tog rul, Z. A., Effect of demineralization process on the liquefaction of Turkish coals in tetralin with microwave energy: Determination of particle size distribution and surface area. Fuel, 2005. 84: p. 2316–2323. M. Alvarado, J. Mejia, M. Vanegas, L. Hernandez. Estudio de secado con Energía Microondas del Carbón de Bijao–Córdoba, in Programa de Ingeniería Química. 2009, Universidad del Atlántico: Barranquilla, Colombia.
[15]
Robert Perry, Perry's chemical engineer's platinum edition Perry's chemical engineers' handbook, 7th ed. (New York: McGraww-Hill ;, 1999). [16] Anual Energy Review, 2009
NOMENCLATURA B BD W Cp Emax PCI
c
Exergía Exergía Destruida Humedad Capacidad calorífica (kJ/kg K) Campo eléctrico máximo (V/m) Calor latente de vaporización del agua (kJ/kg) Poder calorífico inferior Potencia absorbida Potencia aplicada inicial Distancia de penetración de la onda microonda Constante dieléctrica relativa (habilidad para almacenar energía eléctrica) Perdida dieléctrica relativa (habilidad para disipar energía eléctrica) Frecuencia de aplicación de la microonda Velocidad de la luz en el vacio Permitividad de la luz en el vacio Masa del carbón húmedo Masa del carbón seco Masa de agua a la entrada Masa de vapor evaporado Masa de agua que sale con el carbón Masa de aire a la salida del ventilador 2
Eficiencia energética Eficiencia exergética Calor perdido por la ineficiencia del magnetrón Calor perdido por la ineficiencia del ventilador 1 Calor perdido por la ineficiencia del ventilador 2 Calor perdido por la ineficiencia de la banda transportadora Calor perdido por las ondas no absorbidas en la cámara de secado Fracción molar T Temperatura (C) Subíndices w agua MW Generador de microondas A aire V1 Ventilador 1 C coal V2 Ventilador 2 S vapor (steam) CB Banda Transportadora DC Cámara de secado 0 inicial f final
Moisture Re-Adsorption Characteristics of Coal Samples Dried by a Pneumatic Dryer
Sangdo Kim, Youngjun Rhim, Sihyun Lee:
Clean Coal Center, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, South Korea (305-343):
[email protected] Deposits of low rank coal (LRC) represent nearly half of the estimated coal resources in the world. However, LRC is difficult to use in thermal power plants for two reasons: high moisture content (30% or more) and capacity for spontaneous combustion. To avoid such problems, upgraded technology to reduce the moisture content of low rank coal has been developed; however, dried coal can re-adsorb moisture when exposed to outside air. This paper discusses the results of moisture re-adsorption of coal samples dried by a pneumatic dryer. In addition, the results on moisture re-adsorption and BET surface area of coal samples after drying and equilibrium moisture content are discussed. The moisture content of coal samples past 25 days did not change greatly compared to the moisture content of coal samples measured after drying. BET surface area of the dry coal was decreased compared to raw coal, and the equilibrium moisture content was lower than that of raw coal.
1. Introduction Lignite and sub-bituminous coal are classified as low rank coal, and their reserve is so abundant as to represent more than half of the entire coal deposits in the world. However, only about a quarter of the low rank coal reserve is currently in use or production. This is because of the low power-generating efficiency of low rank coal due to high moisture content; furthermore, a great deal of energy is required to dry low rank coal in a power plant setting. In addition, low rank coal has a high risk of spontaneous combustion, and hence has restrictions regarding its long-term storage and transport. To resolve this problem, many studies have been undertaken to dewatering low rank coal[17]. These include Australia's BCB (Binderless Coal Briquetting) [1-2], which uses pneumatic drying; Japan's UBC (Upgrading Brown Coal) [3-5], which uses drying in the oil phase; Germany's WTA (fluidized-bed drying with internal water heat utilization)[6], which uses a fluidized-bed of steam; and the DryFineTMprocess[7] of the U.S., which uses a fluidized-bed.
Dried coal tends to re-adsorb moisture, which can be critical for the long-term storage and transport of dried coal. Kartikeyan [8, 9] conducted research on the moisture re-adsorption characteristics of dried coal and explored how to minimize re-adsorption. Xianchun [10] carried out an experimental study on drying and moisture re-adsorption kinetics of low rank coal from Indonesia. This research examines moisture re-adsorption characteristics of coal dried by a pneumatic dryer.
2. Experimental 2-1 Experimental Equipment For the experiment, Meng Tai coal from Inner Mongolia was used. Table 1 describes the results of the proximate, ultimate, and heating value analysis. The moisture content and heating value were 29.74 wt% and 4,270 kcal/kg in ARB(as received base) condition, respectively. Through a pulverizing and distributing processes, the coal particles had a size of 100~2,000 ㎛. Figure 1 illustrates a pneumatic dryer used in the experiment, consisting of five parts: (1) an LPG burner to provide high-temperature gas, (2) a feeder to provide raw coal, (3) a riser tube to dry coal with high moisture content, (4) a cyclone to separate gas and solid matters, and (5) a bag filter. The diameter and height of the riser tube were 40 mm and 5,000 mm, respectively. The coal was provided at the rate of 5 kg/hr. Drying temperature was measured at the mouth of the feeder providing the coal. The temperature of inlet gas was 400~600 ℃, and the flow rate of the gas in the riser tube was set at 20 m/sec. During the experiment, the LPG burner generated high temperature gas, and when it reached a certain temperature, raw coal was supplied. The coal went through the riser tube and was dried. The dried coal was separated from the high-temperature gas in the cyclone and stored in the storage tank to be discharged. The dried coal was then put in containers: one sample was stored with a cover, and the other samples were stored indoors with their covers open. Although the storage conditions varied slightly, the humidity was kept at 60-80 % and the temperature at 20-25 ℃.
To measure moisture content of the raw coal and the dried coal, 841 KF Titrando (Metrohm, Switzerland) with Karl Fischer method was used.
Table 1. Analyses of coal sample. Coal Name
Meng Tai
Proximate analysis (wt%, ARB) Moisture
29.74
Volatile matter
27.83
Ash
10.51
Fixed carbon
31.92
Ultimate analysis (wt%, ADB) Carbon
62.73
Hydrogen
4.11
Nitrogen
0.95
Oxygen
21.42
Sulfur
0.28
Heating value analysis (kcal/kg) ARB
4,270
ADB
5,730
Note: ARB - as received base, ADB - air dried base
2-2 Measurement of Equilibrium Moisture To examine the characteristics of moisture re-adsorption, equilibrium moisture was measured. Equilibrium moisture is the moisture coal can hold in a humid atmosphere; it is effectively the sum of adsorbed moisture filling micro-pores and moisture filling large pores by capillary action[11]. For this research, equilibrium moisture was measured according to the ASTM D 1412-07 standard method; the measuring method is shown in Fig. 2. Five grams of coal with diameters less than 1.18mm were used, and the experiment was conducted at an absolute humidity of 96-97 % and temperature of 30 ℃.
Fig. 1 Experiment equipment.
Fig. 2 Measuring method of Equilibrium moisture
3. Results and Discussion Dried coal tends to re-adsorb moisture. For this reason, it is very important to study the readsorption characteristics of coal in order to ensure effective storage and transport. Table 2 shows the results of the ultimate, proximate, and heating value analysis for the coal dried by pneumatic dryer. After the experiment, the moisture content of the raw coal dropped below 7 wt%. Kartikeyan [8] conducted moisture re-adsorption experiments after completely drying the coal at temperatures 75 ℃, 100 ℃ and 150 ℃. Re-adsorption experiment is under an ambient environment of about 80% humidity at room temperature of 27℃. According to the experiment result, the moisture content of dried coal increased by 10-13% in two to four days, due to readsorption, and the amount depended on drying temperature. The moisture content did not change any more after 15 days. Xianchun [10] noted that the moisture desorption and re-adsorption isotherms of coal showed irreversibility in the desorption-adsorption cycle, indicating that irreversible coal structure changes occurred due to the shrinkage of the coal that took place during thermal drying, which is dependent on drying temperature. In addition, the higher the drying temperature, the more intensely the pore structure of coal collapsed, resulting in less surface area on coal particles to re-adsorb the moisture from the surrounding atmosphere [10]. Fig. 3 shows the results of re-adsorption moisture content when the dried coal was stored in closed condition. Dried with inlet gas at a temperature of 400℃, the coal re-adsorbed 30% of the moisture in two days; afterwards, the moisture content did not alter significantly. At drying temperatures of 500℃ and 600℃, the dried coal re-adsorbed some 5% of moisture, even after 24 days had elapsed. Fig. 4 shows the results of re-adsorption moisture content when the dried coal is in atmospheric condition. Dried with inlet gas at a temperature of 400℃, the coal re-adsorbed 55% of moisture in two days. After 24 days, about 75% of moisture was re-adsorbed. At drying temperatures of 500℃ and 600℃, there was no initial re-adsorption of moisture, but the moisture content gradually increased up to 55%.
The results of re-adsorption moisture content for dried coal showed similar results as the research outcome of Kartikeyan [8]. It was also shown that re-adsorption moisture content depended on drying temperature. Table 2. Analyses of dried coal. Inlet gas temperature(℃)
400
500
600
Proximate analysis (wt%, ARB) Moisture
6.61
6.54
6.1
Volatile matter
38.1
38.19
38.74
Ash
14.16
15.17
14.64
Fixed carbon
41.13
40.1
40.52
Ultimate analysis (wt%, ADB) Carbon
61.05
60.05
61.45
Hydrogen
4.05
4.03
4.22
Nitrogen
1.08
1.08
1.10
Oxygen
19.56
19.56
18.5
Sulfur
0.1
0.11
0.09
Heating value analysis (kcal/kg) ARB
5,537
5,586
Note: ARB : as received base, ADB : air dried base Fig. 2 Measuring method of Equilibrium moisture
5,636
Fig. 3. Re-adsorption moisture content of dried coal in closed condition.
Fig. 4. Re-adsorption moisture content of dried coal in atmospheric condition.
Table 3 shows the results of equilibrium moisture measurement. Five types of samples were used: raw coal, coal dried for 1 hour in the oven at 107℃, and three more samples dried with a pneumatic dryer at different temperatures. For the first two samples, the equilibrium moisture content was similar, at 25wt%. For the rest of the samples, the equilibrium moisture content decreased with rising gas temperature.
Table 3. Equilibrium moisture. Sample
Equilibrium moisture content (%)
Raw coal
25.52
Oven drying coal
25.06
400℃ dried coal
18.66
500℃ dried coal
18.59
600℃ dried coal
17.43
As Xianchun [10] presented, the equilibrium moisture content decreased compared to raw coal, because of internal structural changes that take place in coal dried with a pneumatic dryer. To verify this, BET surface areas of raw coal and dried coal were measured (Table 4). Coal dried with a pneumatic dryer showed greater decrease of BET surface area than raw coal. The amount of decrease also depended on drying temperature, which indicates that surface area shrinks as moisture rapidly evaporates upon contact with high-temperature gas.
Table 4. BET surface area. Coal sample
BET surface area(m2/g)
Raw coal
11.7035
400℃
6.9129
500℃
6.3596
600℃
5.5317
Conclusion In this research study, moisture re-adsorption characteristics of coal dried with a pneumatic dryer were examined. Compared with the initial moisture content, the dried coal re-adsorbed more than 55% of moisture, but after 24 days the overall moisture content did not change substantially. The equilibrium moisture content of dried coal was below 18.6wt%, and that amount decreased with higher gas inlet temperature. As the drying temperature increased, BET surface area decreased, because the moisture in the coal evaporated rapidly upon contact with the high-temperature gas of the pneumatic dryer. The experiment results suggest that, when dried high moisture content coal with a pneumatic dryer, the internal structural change of coal can help to effectively prevent moisture re-adsorption.
Acknowledgement This work was supported by the Power Generation & Electricity Delivery of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government Ministry of Knowledge Economy.
References 1. Mangena, S.J., Korte, G.J., McCrindle,R.I. and Morgan, D.L., "The amenability of some Witbank bituminous ultra fine coals to binderless briquetting", Fuel Processing Technology, 85, 1647–1662(2004) 2. Keith C., "Commercial scale low rank coal upgrading using the BCB process", 2nd Coaltans Upgrading Coal Forum, Presentation(2010) 3. Sugita, S., Deguchi, T. and Shigehisa, T., "Demonstration of a UBC process in Indonesia", 神戸製鋼技報, 56(2), 23-26(2006) 4. Drtin, F.U., Hiromoto U. and Bukin, D., "Change of combustion characteristics of Indonesian low rank coal due to upgraded brown coal process", Fuel Processing Technology, 87, 10071011(2006) 5. Yukio A., "UBC Process - Upgrading the Future", 2nd Coaltans Upgrading Coal Forum, Presentation(2010)
6. Klutz, H.J., Moser, C. and Block, D. “WTA Fine Grain Drying – Module for Lignite-Fired Power Plants of the Future”, VGB Power Tech Report 11(2006) 7. Sarunac, N. Ness, M. and Bullinger, C., "One year of operating experience with a prototype fluidized bed coal dryer at coal creek generating station", National energy technology laboratory. 8. Karthikeyan, M and Mujumdar, A.S., "Factors affecting quality of deiced low rank coal", Drying Technology, 25(10), 1601-1611(2007) 9. Karthikeyan, M and Mujumdar, A.S., "Minimization of Moisture Re-adsorption in Dried Coal Samples Drying Technology", Drying Technology, 26(7), 948-955(2008) 10. LI Xianchun, Song Hui, Wang Qi, Meesri Chatphol, Wall Terry and YU Jianglong, "Experimental study on drying and moisture re-adsorption kinetics of an Indonesian low rank coal", Journal of Environmental Science Supplement, S127-S130(2009). 11. Barry Ryan, “A discussion on moisture in coal implications for coal bed gas and coal utilization”, ISSA(International Social Security Association), Summary of Activities, 139-149, 2006
Oviedo ICCS&T 2011. Extended Abstract
Moisture Readsorption Characteristics of Upgraded Low Rank Coal Hokyung Choi, Sangdo Kim, Jiho Yoo, Donghyuk Chun, Jeonghwan Lim, Youngjoon Lim, Sihyun Lee Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea:
[email protected] Abstract This study reports the moisture readsorption characteristics of dried coal produced from low rank coal using the upgraded brown coal (UBC) process. The moisture readsorption ratio rapidly increased only during the first 10 hours and formed equilibrium at a certain level thereafter. Raw coal showed the highest moisture readsorption ratio among the samples to form equilibrium at around 14 %. In the case of dried coal, as the amount of asphalt increased, the moisture readsorption ratio decreased. The appropriate portion of asphalt added during drying process is around 1.0 %. Further, increasing drying pressure negatively affects moisture readsorption characteristics of dried coal.
1. Introduction Low rank coal sees little use in spite of its large reserves and low price because it has high moisture content and low heating value. However, the recent high price of oil and high rank coal has encouraged many industries to use low rank coal. Upgraded brown coal (UBC), a well-known coal drying process, enables the utilization of low rank coals. The UBC process removes moisture in the coal using the slurry dewatering process, which involves the evaporation of moisture in the slurry of coal and light oil containing a small portion of heavy oil (such as asphalt) at temperatures of 130–160 °C under a pressure of 0.4 to 0.45 MPa [1,2]. Moisture in the air generates heat when adsorbed or condensed by coal, and this leads to temperature increases of the coal, promoting its spontaneous combustion. Drying coal usually improves the susceptibility to the spontaneous combustion of coal. However, moisture readsorption on the coal inevitably occurs in the absence of a stabilization treatment and causes the loss of the drying effects. To explore the efficient use of low rank coal, this study investigated the moisture readsorption characteristics of upgraded low rank coal produced by the coal-oil slurry dewatering process. To this end, proximate properties, BET surface area, and moisture readsorption characteristics of the coal were analyzed. Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
2. Experimental This study used an Indonesian lignite (KBB coal) as raw coal. The raw coal was upgraded as follows, referring to the procedure of the UBC process [3]. The raw coal was ground and sieved to obtain 0.5–1.3 mm particle size. It became slurry by mixing with kerosene solvent. Up to 4.0 wt% of asphalt, as a heavy oil additive, was added to the slurry. The weight ratio of the solution (kerosene + asphalt) and the raw coal was adjusted to 1:1. The slurry was retained at 140 °C for 30 minutes to evaporate the moisture in the coal. The pressure of the reaction vessel varied in the 0.1–0.3 MPa range. After the evaporation, the solid coal was filtered and dried in an oven at 130 °C to remove the remaining solvent. Before the analyses, other than proximate analysis and BET surface area analysis, raw coal and upgraded coal samples were dried again at 105 °C for 5 hours in nitrogen to remove the moisture that might have been adsorbed while the sample was being preserved. The moisture readsorption of a coal sample was characterized by monitoring a weight change of the coal sample caused by moisture readsorption in a humidity chamber and expressed as a ratio of the changed weight to the initial weight of the coal sample. The coal sample was placed in the chamber and maintained at a temperature of 30 °C and a relative humidity of 100 %. The weight change was monitored every hour for the first 10 hours and then every 24 hours for the following five days.
3. Results and discussion Table 1 shows the results of proximate analysis and BET surface area analysis of coal samples. In the table, the upgrading pressure refers to the pressure of the moisture evaporator in the upgrading process and the asphalt concentration denotes the weight percentage of the asphalt from the total weight of the slurry. Significantly, while going through the UBC process, the moisture content in the coal decreased from 15.96 % in the raw coal to 3.22 % at the minimum in the upgraded coal. As the moisture content in the coal decreased, the heating value of the coal increased from 5448 kcal/kg in the raw coal to 6623 kcal/kg at the maximum after upgrading. As upgrading pressure increased, the moisture content of the upgraded coal slightly increased. This occurs because of the increase in boiling temperatures along with the increase in upgrading pressure.
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Oviedo ICCS&T 2011. Extended Abstract
Table 1. Proximate and BET surface area analysis results of coals (air dried basis). Coal type
Upgrading pressure (MPa)
Asphalt concentration (%)
Moisture
Ash
(%)
raw
-
-
0.1
upgraded
0.2
0.3
(%)
Volatile matter (%)
Fixed carbon (%)
Heating value (MJ/kg)
BET Average surface pore width (m²/g) (nm)
15.96
4.25
46.78
33.01
27.14
26.20
10.31
0.0
9.45
4.30
49.94
36.31
28.57
20.11
13.09
0.5
4.41
4.63
52.65
38.31
28.31
17.70
13.80
1.0
4.11
4.48
52.91
38.50
28.35
16.13
14.23
2.0
3.26
4.56
53.72
38.46
28.22
12.18
15.59
4.0
3.22
5.08
53.56
38.14
28.65
10.71
16.09
0.0
9.53
4.43
50.06
35.99
27.61
21.21
11.55
0.5
4.85
4.41
52.60
38.14
27.67
17.68
12.57
1.0
3.92
4.99
53.61
37.48
27.68
16.85
12.61
2.0
3.87
4.17
53.95
38.01
27.85
10.92
14.56
4.0
3.79
4.80
53.56
37.85
27.95
8.99
15.20
0.0
9.96
4.38
50.11
35.55
27.67
17.00
12.79
0.5
5.58
4.93
52.21
37.29
27.54
15.67
12.01
1.0
5.41
4.25
53.07
37.27
27.20
13.83
12.38
2.0
5.35
4.05
52.71
37.89
27.46
9.20
14.10
4.0
5.33
4.53
52.37
37.77
27.44
8.68
14.45
When comparing changes in moisture content after adding the different amounts of asphalt, whereas the moisture contents ranged around 9–10 % in the case of the upgraded coal with no asphalt addition, they stayed lower than 6 % in all cases of upgraded coal with a 0.5 % or higher percentage of asphalt added. Upgraded coal with no asphalt addition shows high moisture content probably because of the readsorption of moisture in the process of handling after upgrading. The BET surface area of raw coal reached 26.2 m²/g. In upgraded coal, with the upgrading pressure at 0.1 MPa, as the amount of asphalt increased from 0.0 % to 4.0 %, the BET surface area decreased from 20.1 m²/g to 10.7 m²/g. In addition, the average pore size increased from 13.09 nm to 16.09 nm because the asphalt blocks the fine pores more easily than it blocks the larger pores. No large changes in BET surface area and pores resulted from increases in upgrading the pressure. Figure 1 shows the moisture readsorption characteristics of the raw and upgraded coal. As shown in the figure, the moisture readsorption ratio rapidly increased during the first 10 hours only and reached equilibrium at a certain level thereafter. Raw coal showed the highest moisture readsorption ratio among the samples to form equilibrium at around
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Oviedo ICCS&T 2011. Extended Abstract
1.140. In the case of upgraded coal, as the amount of asphalt increased, the moisture readsorption ratio decreased. This would take place because of the suppression of moisture readsorption by the asphalt with its hydrophobic nature. When the upgrading pressure increased, moisture readsorption ratios increased slightly even in the upgraded coal with asphalt added. When the content of the asphalt reached 4.0 %, the equilibrium moisture readsorption ratio of the coal upgraded at 0.1 MPa reached 1.104, that of the coal upgraded at 0.2 MPa reached 1.124, and that of the coal upgraded at 0.3 MPa reached 1.130. The effect of upgrading pressure on the moisture readsorption remains unclear. The drying pretreatment seemed to expose the adsorption sites of the upgraded coal to the air by removing moisture that had not been completely
Figure 1. Moisture readsorption ratios of coals upgraded at (a) 0.1 MPa, (b) 0.2 MPa, and (c) 0.3 MPa.
removed under enhanced pressure.
References [1] Sugita S, Deguchi T, Shigehisa T, Katsushima S, Makino E, Otaka Y. Demonstration of UBC process in Indonesia–Upgrading of low rank coal. Proc of the International Conference on Coal Science and Technology, Okinawa 2005. [2] Kinoshita S, Yamamoto S, Deguchi T, Shigehisa T. Demonstration of upgraded brown coal (UBC) process by 600 tonnes/day plant, Kobelco Technology Review 2010;29:93-98. [3] Umar DF, Usui H, Daulay B. Change of combustion characteristics of Indonesian low rank coal due to upgraded brown coal process. Fuel Processing Technology 2006;87:1007-1011.
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SOLAR DRYING TECHNOLOGY OF COAL IN THE OPEN IN THE IRON AND STEEL RESEARCH CENTER Authors: Andrey Leyva Mormul (
[email protected]) Ariel Díaz Castillo (
[email protected]) Oscar Sinecio Leyva González (
[email protected]) José Anival Trotman Gavilán (
[email protected]) Oscar Figueredo Stable (
[email protected])
Address: Centro de Investigaciones Siderúrgicas, Calle 72, No.8-F, S/C, La Pasa, Nicaro-Levisa, Mayarí, Holguín, Cuba
ABSTRACT The job presents the results achieved by the Iron and Steel Research Center after the implementation of solar drying of coal in the open air, prior to conventional drying oven or rotary drum cylinder. This has brought an increase drying efficiency in the production process, and involves a parallel decrease in the volume of products of combustion gases, propellants maximum greenhouse effect, acid rain and desertification of soils. From the quantitative evaluation, we determined that for each 1 % moisture lost by the coal exposed to sunlight, saves 4 liters of diesel fuel per ton of coal produced with the prior application of solar drying, systems, lowering the moisture content (W) of coal to be processed in about 8 % to reach equilibrium moisture content is 2 %, while minimizing the fuel consumption per ton of coal drying, 40 to between 19 and 22 l, and increase furnace productivity by 0.5 to 1.3 t/h, which brings economic benefit of 58215.46 USD over a year.
INTRODUCTION Energy education not only contributes to a better and more efficient use of fossil fuels available to mankind, but also a guarantee in the transition to a sustainable energy economy that rests on the available solar energy [Retired, et al ., 2007]. The coal used as loading, swelling and adjustment in the steel company José Martí Antilles Steel and Stainless Steel Enterprise ACINOX Tunas, is prepared mechanically in DSIT coal plant. Swelling coals and setting are subjected to the process of milling, sorting and drying in a rotary drum furnace for the removal of moisture contained in these materials, then incorporated into a crushing and screening equipment CMD 27, with which guaranteeing the fineness required by users. Among the most important aspect we have raised, in terms of reducing fuel consumption, is the efficient implementation of the drying process in the rotary cylinder. To contribute to this, we implemented the solar drying of coal in the open air, prior to drying in the oven rotating cylinder what has been successful with regard to the efficiency of the production process and obtain a higher quality product. Before proceeding to explain the procedure used and presents the results, some interesting elements are required:
•
In each square meter of Cuban territory, we have already received a daily amount of solar energy of 5 kWh, roughly equivalent to half a kilogram of fuel oil, average virtually unchanged throughout the year [Bérriz and Alvarez, 2008].
•
Coal, according to their physical characteristics, is a hygroscopic mineral, it has the ability to impregnate or exhale moisture depending on the environmental conditions in which they are placed, and is clearly black, which absorbs between 90 and 98 % sunlight without reflecting it later.
TECHNOLOGY FLOWS WITH AND WITHOUT SOLAR DRYING
Final Product Hopper
Hopper 2
Big Bag
Final Product Hopper
Big Bag
Balance
Hopper 1 Combustion Chamber
Sieve Shaker Dryer CM B E
Coal
CM: Cone Mill BE: Bucket Elevator
Fig 1. Preparation of coal without the application of solar drying.
Big Bag
Final Product Hopper
Hopper 2
Big Bag
Final Product Hopper
Big Bag
Big Bag
Balance
Hopper 1 Combustion Chamber
Sieve Shaker Dryer CM B E
Solar Radiation
Coal Coal
CM: Cone Mill BE: Bucket Elevator
Fig 2. Preparation of coal to the implementation of solar drying.
Comparing Figures 1 and 2, we can see that both the coal stacked in the reception area of mineral, receives solar radiation and air flow that promotes natural convection. But when the ore is spread in hours either early morning (Fig. 2), across the yard surface, forming a platform about 0.15 or 0.20 m tall, and is removed every 3 h until very Late in the afternoon, which is collected and stored in a conical pile in the shed, to the day after being subjected to drying in the oven rotating cylinder. There is a significant reduction of moisture in coal, which brings a minimization of fuel consumption per ton of dried material. Note: The recreation operations removal and collection of coal are performed by a loader TO-18 mark.
MATERIALS AND METHODS To take a representative sample, sufficient and minimal systematic sampling was used where an imaginary overlaid network and selected 30 points, which was taken the sample, it is an analysis of moisture in triplicate in glass test tubes 0.10 kg of coal inside. This procedure is performed three times a day (7:00 am, 12 am and 5:00 pm). In the development of work using various tools and materials allowed the execution of the experiments (oven 300 ºC C HOL 3524-5, dried and Analytical Balance BЛKT-500 gM). All tests were part of the moisture. To conduct the study in DSIT climate, were used the following equipment: ¾ SIC 100 Powermeter & Integrator (measure solar radiation and temperature) ¾ mercury thermometer -10 to 200 ºC (Measuring temperature) ¾ Fluke 62 Mini IR Thermometer (Measure temperature of solids)
RESULTS Figures 1 and 2 appear, it shows the results of changes Coal Moisture, Solar Radiation and Ambient Temperature. Observing the percentage decrease of the mass of coal as it dries in the course of time. 100
120 100
96
60 40
Moisture (%)
100·W/m 2
98 80
94 20 0 7:55 8:31
92 9:07 9:43 10:19 10:55 11:31 12:07 12:43 13:19 13:55 14:31 15:07 15:43 16:19 16:55 Hora (h) Solar Radiation
Coal Moisture
Graph 1. Variation of Coal Moisture and Solar Radiation vs. Time. 100
35 33
ºC
31 96 29 94
27 25 7:55
Moisture (%)
98
8:31
92 9:07 9:43 10:19 10:55 11:31 12:07 12:43 13:19 13:55 14:31 15:07 15:43 16:19 16:55 Hora (h) Ambient Temperature
Coal Moisture
Graph 2. Variation of Coal Moisture and Ambient Temperature vs. Time. The coal in the open air exposed to the sun, reduces its mass by drying, approximately 8%, reaching to achieve a 2% moisture content, and take a temperature of 60 ºC, lower by 5 °C the temperature reached coal to exit the rotary dryer. Note that rainy seasons and rainfall in the year, where the cloudiness does not allow a good stock rays of the sun on the mineral. During this period, coal remains piled in a cone-shaped battery and the main drying agent, an even
greater amount of solar radiation that is air. Normally in this geographical area of the Cuban archipelago, these seasons are not as significant, droughts are more representative. TABLE I. Comparative results of the efficiency of the dryer before and after implementing the previous solar drying of the mineral. Productivity (t/h)
Diesel consumption per ton of Quality of the product (acording to coal drying (l/t)
moisture %)
Before
0,5
≈ 40
0,8-1,3
After
1,3
≈ 22
0,8-1,3
Difference
+0,8
≈ -18
-
TABLE II. Environmental Analysis. Chemical concentration of the gases of combustion products [%] CO2 CO
O2
1 liter
11
0,2
6
40 liters
440
8
240 3312
22 liters
242
4,4
132 1821,6
Difference 198
3,6
108 1490,4
N2 82,8
The more dry the mineral is subjected to the oven, shorter it stays in it, resulting in lower emission of fines or dust into the atmosphere, among which the particles of aerodynamic diameter is less than 10 μm (PM10), these are very dangerous for the humans health, because they are able to reach the bottom of the lungs. TABLE III. Economic Impact. BEFORE Dry mass (t/day) Diesel consumption (l)
AFTER Cost (USD)
Dry mass (t/day) Diesel consumption (l)
Cost (USD)
1
40
22,46
1
22
12,36
18
720
404,35
18
396
222,39
OTHER COSTS
OTHER COSTS
Loader (l/day)
-
-
Loader (l/day)
40
22,46
Total
720
404,35
Total
436
244,86
Drying 18 t, our average production per day, currently has an economic cost equal to 244.86 USD per day. So every day we are saving 159.49 USD, that in a period of one year it would be 58215.46 USD.
CONCLUSIONS 1. The coal in the open air exposed to the sun, reduces its mass by drying, approximately 8%, reaching to achieve a 2% moisture content, and take a temperature of 60 ºC, lower by 5 °C the coal temperature reached the exit rotary dryer. 2. According to the analysis developed, it was determined that to each 1% moisture lost by the coal exposed to sunlight, saves 4 liters of diesel fuel per ton of coal produced. 3. With the prior application of solar drying in the rotary drum dryer has been an increase in productivity of 0.8 t/h, a significant reduction in diesel fuel, approximately half and the product presents the quality required by customers. 4. From an environmental perspective: •
The reduction of diesel consumption per ton of mineral drying brings parallel minimization of products of combustion gases (see Table II).
•
When using a coal with less humidity, less time is retained in the furnace, which contributes to the emission of fine powders, among which (PM10), there are particles of aerodynamic diameter less than 10 μm. This value has not yet been quantified.
5. The previous solar drying has resulted in the production process a significant economic impact, and now we are saving 159.49 USD daily in the period of one year, it would be 58215.46 USD.
BIBLIOGRAPHY 1. Arun S. Mujumdar. Handbook of Industrial Drying. Jerzy Pikon. Drying of Coal. Silesian Technical University. Gliwice, Poland. 2007. Págs. 977-981. 2. Bérriz Luis. Cuando el sol seca (Plantas medicinales). Energía y Tú. Nº 7. 1999. ISSN: 1028-9925. 3. Clariana Josep A.; Rougé Philippe; Arata Paola; Acevedo Sebastián; Segovia Javier. Postratamiento de Biosólidos en Era de Secado de la Estación Depuradora de Aguas Residuales El Trebal (Santiago de Chile). Tomado de: http://aca-web.gencat.cat/aca/documents/ca/jornadatecnica003/15_clariana_segovia.pdf (20/03/09 a las 14:30) 4. Corp Sergio. El secador solar de polen. Energía y Tú. Nº 15. 2001. ISSN: 1028-9925. 5. Cortéz Cádiz Elvira del Carmen. Fundamentos de ingeniería para el tratamiento de los biosólidos generados por la depuración de aguas servidas de la región metropolitana. Memoria para optar al titulo de Ingeniero Civil Químico. Año 2003. Tomado de: http://cabierta.uchile.cl/revista/21/articulos/pdf/rev3.pdf (23/03/09 a las 13:28) 6. Corvalan R., Horn M., Roman R., Saravia L. Ingeniería del Secado Solar. Ciencia y Tecnología para el Desarrollo CYTED. CDROM. Salta, República Argentina, abril de 2006. 7. Cuevas Fernando. Estrategia Energética Sustentable Centroamericana 2020. III Taller Contaminación Atmosférica vs. Desarrollo Sostenible. Ciudad de La Habana, CUBAENERGIA; 2008.
8. Helmer, W. A. and A. Abbas. nd. Solar drying of coal wastes from slurry ponds. Tomado de: http://pdf.aiaa.org/jaPreview/JE/1981/PVJAPRE62537.pdf. (19/05/08 a las 14:50) 9. Estenoz Severo; Espinosa Marianny; Pérez Niurka. Uso de energías renovables en la industria cubana del níquel. ECOSOLAR (Rev. Científica de las Energías Renovables), Nº 8, 2004. ISSN 1028-6004. 10. Fonseca Fonseca Susana, Abdala Rodríguez Jorge Luis, Ferro Fernández Victor R., Pantoja Enríquez Joel, Torres Yen Alonso. Estudio comparativo del secado solar de café en plazoletas tradicionales y ennegrecidas.
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http://www.uo.edu.cu/ojs/index.php/tq/article/view/520/392. (23/05/08 a las 08:00) 11. Lara Coira Manuel. Escenario Energético Mundial. DYNA 82(9): 471-478, 2007. 12. Leyva Andrey; Díaz Ariel; Leyva Oscar. Secado solar del carbón mineral a la intemperie. V Taller Internacional de Educación, Energía y Desarrollo Sostenible, Ciudad de La Habana; 2008. 13. Retirado Yoalbys; Góngora Ever; Torres Enrique; Rojas Arturo L. Comportamiento de la humedad durante el secado solar del mineral laterítico. Minería y Geología. Vol. 23, Nº 3, 2007. ISSN 1993 8012. 14. Suárez Rodríguez José A., Beatón Soler Pedro A. Estado y perspectivas de las energías renovables en Cuba.
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http://www.uo.edu.cu/ojs/index.php/tq/article/view/1255/916. (23/05/08 a las 08:00) 15. Teske Sven, Zervos Arthouros, Schäfer Oliver. Revolución energética. Perspectiva mundial de la energía renovable. Greenpeace Internacional, Consejo Europeo de Energías Renovables (EREC). Enero 2007. 16. Ficha Técnica (Secado Solar). Tomado de: http://www.itdg.org.pe/fichastecnicas/pdf/FichaTecnica13Secado%20solar.pdf. (17/05/08 a las 12:08) 17. La energía solar. Tomado de: http://www.dinero15.com/site_images/PDF/energiasolar.pdf. (19/05/08 a las 08:00) 18. 05 Desecación y deshidratación. Tomado de: http://www.caempa.com.ar/Presentaciones/05%20Desecaci%C3%B3n%20y%20deshidrataci%C3%B3n.pdf. (19/05/08 a las 08:06)
A New Supercritical Solid Acid for Breaking Car-Calk Bond in Di(1-naphthyl)methane Xiao-Ming Yue,† Xian-Yong Wei,†* Bing Sun,† Ying-Hua Wang,† Zhi-Min Zong, † and Zi-Wu Liu, ‡ †
Key Laboratory of Coal Processing and Efficient Utilization (Ministry of Education), China University of Mining & Technology, Xuzhou 221008, Jiangsu, China, and ‡School of Chemistry and Chemical Engineering, South China University of Technology, Wushan 381, Guangzhou 510640, Guangdong, China Introduction Catalysis in coal hydroliquefaction (CHL) has been exten- sively studied. Metal oxides, metal sulfides, metal halides, and acidic species, are well used as catalysts for CHL[1]. Rapid development in the area of carbocation chemistry began after the pioneering work of Olah, who utilized antimony pentafluoride as a strong Lewis acid[2]. Solid acids have advantages of corrosion resistance, higher safety than liquid acid and mineral acids, store, and handle easily and produce no wastes. Due to the increasing awareness of environmental protection and safety factors in industry, solid acid alternatives such as zeolites, heteropoly acids, acid clays, acid ion exchange resins, and sulfonated polystyrenes have been developed[3-8]. The complexity of coal structures leads to difficulty in understanding CHL mechanisms using coals themselves. Alternatively, the reactions of coal-related model compounds proved to be a powerful tool to reveal CHL mechanisms on the molecular level[9-12]. The cleavage of bridged bonds in coals is one of the most important reactions in CHL. Wei et al.[13] found that metal sulfides significantly catalyze the hydrocracking of di(1-naphthyl)methane (DNM) via monatomic hydrogen transfer. Activated carbon (AC) has similar catalysis in DNM hydrocracking but shows lower activity than metal sulfides[14]. In the present study, we investigated a new solid super- acid (SSA)-catalyzed DNM hydrocracking. Experimental Materials. DNM was synthesized by heating naphthalene with 1-chloromethylnaphthalene in the presence of zinc powder. Cyclohexane was commercially purchased and distillated before use. SbCl5, trimethylsilyl trifluoromethanesulphonate (TMSTFMS) and AC were also commercially purchased. SSA preparation and characterization. After being grounded to < 75 µm and dried for 24 h in a vacuum at 80 oC, AC was impregnated with SbCl5 and TMSTFMS under micro- wave irradiation. Then the mixture was magnetically stirred at room temperature for 12 h followed by filtration through a membrane filter with 0.45 μm of pore size and dried at 120 oC for 24 h. The SSA prepared was characterized with Nicolet Magna IR-560 FTIR, Hitachi S-3700N EDS/SEM, and TP-5000 II versatile adsorption detector with QIC-20 gas analysis system. General Procedure. DNM (1 mmol), catalyst (0.4 g), and cyclohexane (30 mL) were put into a 60 mL stainless, magnetically stirred autoclave. After being pressurized with hydrogen to 5 MPa at room temperature, the autoclave was heated to a reaction temperature (170-300 °C) in 15 min and maintained for a prescribed period of time (1 to 10 h). Then the autoclave was immediately cooled to room temperature in an ice-water bath. The reaction mixture were taken out from the autoclave and identified with HP 6890/5973 GC/MS and quantified with Agilent 7890 GC.
1500
1100
700
579.4
809.3 900
649.4
1040.7
1176.6 1300
1099.8
1358.0
Absorbance
1259.8
Results and Discussion The existing of sulfonic group, Si-O, and Si-C can be confirmed from the absorbances at 1040.7, 1099.8, 1176, 1259.8, and 1358.0 cm-1, while the absorbances at 579.4 and 649.4 could be related to the stretch vibration of C-Cl bond, as shown in Fig. 1, i.e., the reaction of SbCl5 with AC could occurred to some extend.
500
Wavenumbers (cm-1)
Fig. 1 FTIR spectrum of the SSA prepared
The SEM micrographs reveal the dispersion of active components on AC. As Fig. 2a displays, the surface of AC is smooth and slightly concave. However, the SEM micrograph of SSA (Fig. 2b) exhibits a rough surface. There were irregular grains with diameter less than 5 µm adhered to the surface of AC. The elemental composition from SbCl5 and TMSTFMS can be confirmed by EDS measurement (Fig. 3).
(a)
(b)
Fig. 2 SEM micrographs of AC (a) and the SSA (b) The TPD profile of SSA in Fig. 4 displays that one well-resolved desorption peak of NH3 appears at around 220 oC, which is attributed to NH3 adsorbed on weak acid sites. A narrow desorption peak at the range of 590–670 oC corresponds to the NH3 adsorbed on strong acid sites.
TPD signal
Cl
Sb C O
0
S
Si
F
1
2
Fig. 3
Sb Cl 3
Sb
Energy (keV)
4
5
EDS spectrum of the SSA
6
0
100
Fig. 4
200
300
400 500
600
Temperature (oC)
700 800
NH3-TPD profile over the SSA
As shown Table 1 and Fig. 5, the reaction of DNM over the SSA only afforded naphthalene and 1-methylnaphthalene (1-MN), indicating that the SSA specifically catalyzed DNM hydrocracking under the reaction conditions. Both raising reaction temperature and prolonging reaction time increase DNM conversion. Noteworthily, the yield of naphthalene is significantly higher than that of 1-MN in most of cases, suggesting that demethylation of the resulting 1-MN significantly occurred. As an acidic catalyst, the SSA may catalyze the heterolytic splitting of H2 to mobile H+ and immobile H-. The addition of mobile H+ to ipso-position of naphthalene ring induced DNM hydrocracking and subsequent 1-MN hydrocracking followed by stabilization of the resulting naphthyl-1-methyl and methyl cations with immobile H- (Scheme 1).
o
temp. [ C] 150 170 200 250 250 250 250 300 300 300 300
Table 1. The SSA-Catalyzed Hydrocracking of DNM yield [mol%] time [h] conv. [%] naphthalene 1-MN 3 0 0 0 3 0.1 0.1 0.1 3 6.4 11.1 1.7 1 8.7 12.9 4.5 3 9.1 13.9 4.3 6 10.2 15.1 5.3 10 10.5 15.2 5.8 1 20.9 21.6 20.2 3 50 58.4 41.6 6 69.3 75.1 63.5 10 74.9 82.4 67.4
DNM conversion (%)
50
50
40
40
30
30
20
20
10
10
0 120
Fig. 5
60
naphthalene 1-MN
160 200 240 280 Reaction temperature (oC)
320
Yield (mol%)
60
0
DNM conversions and product yields over the SSA at different temperatures for 3 h Scheme 1. Possible pathway for hydrogen transfer to DNM over the SSA H-
H
+
CH3
CH 4
+ + H+ - H+
H
+ +
+ H+ - H+ H-
Conclusions The SSA we prepared shows high activity and extremely high selectivity for DNM hydrocracking. The catalyst may heterolytically split H2 to mobile H+ and immobile H-. The addition of mobile H+ to ipso-position in DNM could be crucial step for DNM hydrocracking and subsequent steps include cleavage of bridged bond in hydroDNM cation, stabilization of the resulting naphthyl-1-methyl cation, mobile H+ to ipso-position in 1-MN, and stabilization of the resulting methyl cation. Acknowledgments. This work was subsidized by the Special Fund for Major State Basic Research Project (Grant 2011CB201302), National Natural Science Foundation of China (Grants 20936007 and 51074153), the Fund from the Natural Science Foundation of China for Innovative Research Group (Grant 50921002), the Program of the Universities in Jiangsu Province for Development of High-Tech Industries (Grant JHB05-33), and the Fundamental Research Funds for the Central Universities (China University of Mining & Technology, Grant No. 2010ZDP02B03 and 2010LKHX09). References [1] Matsuhashi H., Nakamura H., Arata K., Yoshida R., Maekawa Y. Fuel 1997; 76(10): 913-918. [2] Olah G. A., Praqkash G. K. S. Encyclopedia of Physical Science and Technology 2004: 175-188. [3] Smith G. V., Notheisz F. Heterogeneous Catalysis in Organic Chemistry. Academic Press, San Diego, 1999. [4] Sheldon R. A., van Bekkum H. Fine chemicals through hetero- geneous catalysis. Wiley-VCH, New York, Weinheim 2001. [5] Yadav J. S., Reddy B. V., Eeshwaraiah B., Srinivas A. Tetrahedron 2004; 60: 1767-1771. [6] Yadav J. S., Reddy B. V., Raju A. K., Guaneshwar D. Adv. Synth. Catal. 2002; 344: 938-940. [7] Thomas J. M., Raja R., Lewis D. W. Angewandte Chemie International Edition 2005; 44: 6456-6482. [8] Olah G. A., Iyer P. S., Prakash G. K. S. Synthesis 1986: 513-531. [9] Murata, S., Nakamura, M., Miura, M., Nomura M. Energy Fuels 1995; 9 (5): 849-854. [10] Zong Z. M., Wei X. Y. Fuel Process. Technol. 1994; 41 (1): 79- 85. [11] Grigorieva E. N., Panchenko S. S., Kovrobkov V. Yu. Kalechitz, I. V. Fuel Process. Technol. 1994; 41 (1): 39-53. [12] Kamiya Y., Ogata E., Goto K., Nomi T. Fuel 1986; 65 (4): 586- 590. [13] Wei X. Y., Hai N. Z., Zong Z. M., Lu Z. S., Chun X. Y., Wang X. H. Energy Fuels 2003; 17 (3): 652-657. [14] Sun L. B., Zong Z. M., Kou J. H., Zhang L. F., Ni Z. H., Yu G. Y., Chen H., Wei X. Y., Lee C. W. Energy Fuels 2004; 18 (5): 1500-1504.
Oviedo ICCS&T 2011. Extended Abstract
Briquetting of carbon-containing wastes from steelmaking for metallurgical coke production M.A. Diez, R. Alvarez, J.L.G. Cimadevilla Instituto Nacional del Carbón, INCAR-CSIC, Apartado 73, 33080-Oviedo. Spain.
[email protected] Abstract This work focuses on the manufacture of briquettes by using carbon-containing wastes from steelmaking as fillers and binders for use in coke ovens to produce metallurgical coke. Coal-tar sludges from the tar decanter of a by-products coking plant were used individually as a binder or combined with other wastes, such as oils from the steel rolling mills and deposits from the coke oven gas pipelines. Another objective of this study was to find alternative low-cost fillers such as the coal generated after routine cleaning operations in the coal stockyards, so as to reduce the overall cost of briquette manufacture. The feasibility of using carbon briquettes with different formulations produced in a roll-press machine was tested in a semipilot movable wall oven by adding them to a coking blend at a ratio of 10 wt%. The quality of the cokes produced was assessed by measuring of their reactivity towards CO2 and mechanical resistance before and after gasification with CO2. In general, the coke quality parameters did not show any significant deterioration as a result of the addition of carbon briquettes when the amount and the nature of the binder and the particle size of the filler are optimized. Partial briquetting of the charge enabled cokes to be produced according to the specific requirements of blast furnace.
Keywords: coal, wastes, briquetting, carbonization, metallurgical coke
1. Introduction Briquetting processes that use coal as filler and binders such as pitches and tars have been industrially implemented in the past for metallurgical coke production [1-4]. Due to increasingly stringent regulations governing waste disposal practices and the need to reduce fossil fuel consumption, cold coal briquetting is regarded as a useful technology for recycling low-value and carbon-containing wastes generated in steelmaking.
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Wastes generated in different parts of an integrated steel factory such as tar sludge and residual pitch from the benzol distillation column have been successfully used as minor components in coal blends or as binders in partial charge briquetting for metallurgical coke production [5]. The use of a combination of several heterogeneous carbon-containing wastes from steelmaking of different composition and origin to manufacture briquettes is proposed as an environmentally friendly way which has several advantages associated with a utilization of the wastes in situ and their removal in single operation making it unnecessary to dispose them. The objective of this work was to determine the effects of partial briquetting on the overall carbonization behaviour of the charge and on the quality of the resultant cokes in order to establish the viability of using several carbon-containing wastes to manufacture briquettes.
2. Experimental section Coal blend and wastes The coal blend P was prepared and supplied by ArcelorMittal-Spain. Coal blends are prepared every month by the company by mixing bituminous coals of different rank, thermoplastic properties and geographic origin. The main characteristics of the coal blend P are as follows: ash, 7.6 wt.% db, volatile matter, 25.5 wt.% db, S, 0.72 wt.% db, Gieseler maximum fluidity, 544 ddpm. Two wastes from different parts of the integrated steel installation were selected to be used in combination with coal-tar sludges from the tar decanter of the by-products coking plant (Mx) as a binder: oily wastes from the steel rolling mills (Lo) and deposits from the coke oven gas (COG) pipelines (Tu). Due to fluctuations in the composition of Mx, two different samples of Mxa and Mxb were used, the difference between them being the amount of waste which is soluble in powerful solvents such as quinoline. While Mxa contains about 47 wt% of quinoline soluble, Mxb has a very low content nearly 15 wt%. The coal generated during routine cleaning operations in the coal stockyards –B(a particle size of < 5 mm and a volatile matter content of 21 wt% db) was used as a low-cost filler.
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Manufacture and characterization of briquettes Carbon briquettes were produced in a Komarek B050 roll-press machine using different combinations of carbon-containing wastes from the steel industry (Table 1). All of the briquettes produced were pillow-shaped 39 mm long, 19 mm wide and 10 mm thick. The physical properties of the briquettes (density and mechanical strength) were measured in order to assess the effectiveness of the agglomeration process. The density of the briquettes was determined by water immersion at 20 ºC using 100 g briquettes. The mechanical strength of the briquettes was tested with an I-type rotating drum (the same to determine CSR and described below) applying a mechanical treatment of varying severity from 20 to 150 revolutions at a rotation rate of 20 rpm. After each set of rotations, the sieving process and weighing of the size fractions after which all of the material was returned to the drum. The amount of unbroken briquettes and broken briquettes with a size >10 expressed as a percentage of the initial weight of the briquettes was used as an indicator of the strength of the briquettes.
Semipilot carbonization tests The amount of briquettes added to the industrial coal blend P was 10 wt%. All the carbonization tests were carried out in an electrically-heated movable wall oven of about 17 kg capacity with the following dimensions: 790 mm height, 250 mm length and 150 mm width. During the carbonisation tests, the temperature of the wall was kept constant at 1010 ºC. The coking time was nearly 3 h 30 min, the temperature in the centre of the charge rising to 950 ºC. After the hot coke was pushed from the oven, it was quenched with a water spray. The oven used produces enough coke to enable it to be characterized by the standard procedures used by the steel industry. As the bulk density of the charge varies as a function of grain size and moisture content, both of these parameters were kept as close as possible in each carbonization test. The bulk density was kept at 782 ± 6 kg/m3 db.
Coke characterization The quality of the resultant cokes was evaluated in terms of their reactivity to CO2 (CRI) and the mechanical strength of the partially-gasified coke (CSR) by the NSC method, following the ASTM D5341 standard procedure. To determine CRI, 200 g of coke with a particle size between 22.4 and 19 mm was exposed to the action of CO2 at flow rate of
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5 L/min h at 1100 ºC for 2 h. The weight per cent of the initial coke mass lost during the reaction is defined as CRI. The mechanical degradation of the partially gasified coke (CSR) was measured as the weight of coke remaining on a 9.5 mm sieve after 600 revolutions at a rotation rate of 20 rpm in an I-type drum. In addition, the cold mechanical strength of the coke was evaluated from a sample of 10 kg with an initial size of > 50 mm, employing a JIS drum and rotating it for 150 revolutions at a rotating rate of 15 rpm (JIS K2151 standard procedure). Two indices were derived from this test: the DI150/15 and DI150/5 indices which are defined as the amount of coke with sizes >15 mm and 10 mm) after X revolutions in a I-type drum; nd: not determined, most of the briquettes disintegrate when immersed in water.
Partial briquetting carbonization and coke quality All the briquettes were carbonized with the industrial coal blend P at an addition rate of 10 wt%. To avoid the secondary effect of an increase in bulk density on coking pressure
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generation and metallurgical coke properties, the series of carbonization tests were carried out with only minor variations in bulk density. No relevant effect on the generation of coking pressure was observed during partial briquetting (1.4 kPa for the blend P vs. 0.8-1.4 kPa for carbonizations with partial briquetting). Thus none of the formulations used for briquetting were detrimental to cokemaking. When the cold mechanical strength indices (DI150/15 and DI150/5) of the resultant cokes are compared with those of the coke produced from the blend P, similar cohesion and abrasion indices are observed for cokes from the charges which contain Mxa (Table 3). In addition, the high-temperature properties of the cokes (CRI and CSR) remain constant, whether Mxa is used, individually or combined with the oily waste from the steel rolling mills (Lo). In contrast, the incorporation of the waste left behind in the COG pipelines (Tu) clearly produces a more reactive coke (CRI) and a less resistant coke after the reaction with CO2 (CSR). The increase in reactivity by about 3 points is attributed to the catalytic effects of the iron oxides present in the solid fraction of this waste.
Table 3. Characteristics of the cokes produced from the coal blend P and partial briquetting of the charge (briquette addition rate: 10 wt%). Coke
P P+10B30Mxa P+10B13Mxa13Tu P+10B13Mxa7Lo P+10B30Mxb P+10B15Mxb15Tu
DI150/15
DI150/5
CRI (%)
CSR (%)
P (%)
77.8 76.7 77.2 78.0 62.9 69.3
16.5 15.7 15.3 15.5 22.7 20.8
30.9 31.6 33.7 31.6 31.4 32.3
56.2 55.6 52.6 56.8 55.4 53.0
52.9 51.4 51.7 51.4 52.2 51.7
The poor agglomeration achieved in the briquettes manufactured using the low quinoline-soluble sludge Mxb is also reflected in the cold mechanical strength of the cokes. A loss of cohesion and resistance to abrasion in the coke is a result of the partial briquetting of the charge. However, the CRI and CSR indices are not greatly affected. Thus, variation of the high-temperature properties seems to be a consequence of the type of binder used in the manufacture of briquettes and not the degree of agglomeration achieved.
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4. Conclusions Partial briquetting can be considered as a recycling route for wastes of different types, origin and composition in an integrated steel factory. An evaluation of the amount of tar sludge necessary to act as binder in the briquette is essential to ensure that the cold mechanical strength of the cokes resulting from partial briquetting is adequate and to retain the amount of breeze coke. No negative effect was observed in the coke hightemperature properties, reactivity to CO2 and strength after reaction. By controlling the amount of effective binder used to make the briquettes, the partial briquetting of the coal charge will produce cokes with the desired characteristics for use in blast furnaces.
Acknowledgements The financial support provided by PCTI-Asturias-Spain through the research project PEST08-07 is gratefully acknowledged. We are also grateful to ArcelorMittal-Spain for its collaboration.
References [1] Akamatsu K, Nire H, Miyazaki T, Nishioka K, Influence of non-coking coal on the quality of metallurgical coke, Coal, coke and the blast furnace, The Metals Society, 1977:55-65. [2] Nakamura N, Togino Y, Adachi T, Philosophy of blending coals and cokemaking technology in Japan, Coal, coke and the blast furnace, The Metals Society, 1977:93-106. [3] Schinzel W, Briquetting. In: Chemistry of Coal Utilization, Second supplementary volume, Elliot MA (ed.), John Wiley and Sons, New York, 1981, Chap. 11, pp.609-664. [4] Braun NV, Glushchenko IM, Panchenko NI, Ivchenko AY, On the possibility of using coking plant wastes as a binder for briquetting a coal charge, Coke and Chemistry USSR 1986;5:28-33. [5] Álvarez R, Barriocanal C, Diez MA, Cimadevilla JLG, Casal MD, Canga CS, Recycling of hazardous waste materials in the coking process Environ. Sci. Technol. 2004;28:1611-15. [6] Clarke DE, Marsh H, Influence of coal/binder interactions on mechanical strength of briquettes, Fuel 1989:68:1023-30. [7] Clarke DE, Marsh H, Factors influencing properties of coal briquettes, Fuel 1989:68:1031-38. [8] Taylor JW, Hennah, The effect of binder displacements during briquetting on the strength of formed coke. Fuel 1991;70:873-76.
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Oviedo ICCS&T 2011. Extended Abstract
Co-carbonization behaviour of coal and biomass-derived products and its effect on coke structure and properties M.A. Diez1, R. Alvarez1 and M. Fernández2 1
2
Instituto Nacional del Carbón, INCAR-CSIC, Apartado 73, 33080 Oviedo, Spain Centro Nacional de Investigaciones Metalúrgicas, CENIM-CSIC, Avda Gregorio del Amo 8, 28040 Madrid, Spain.
[email protected] Abstract Co-carbonizations were carried out to study the feasibility of using biomass-derived products as additives to coking coals for the production of metallurgical cokes. Blends of a coking coal with Eucalyptus wood and the products resulting from its carbonization at 415 ºC (charcoal, light and heavy tars) were prepared at an addition rate of 2 wt%. Moreover, the effect of the biomass products was compared to that of wood constituents such as hemicellulose, cellulose and lignin which were used as reference additives. Wood biomass, its carbonization products and its model compounds were observed to reduce the Gieseler fluidity of the coal. In general, the overall effect of Eucalyptus wood and its carbonization products (char and tars) greatly resembled that of the parent biomass component. As regards coke quality, not all of the biomass-derived products affected the quality parameters in the same way. In general, the cokes were found to be less mechanically resistant and more reactive, but the degree of deterioration was depended on the type of additive. A common feature of these cokes was their higher total pore volume which was accompanied by a shift to smaller pores of 10-50 µm. These preliminary laboratory results may contribute to a better prediction of the behaviour of biomass/coal blends in the production of coke.
Keywords: coal, biomass, wood by-products, charcoal, co-carbonization, coke
1. Introduction The environmental benefits of wood or other forms of vegetable biomass are associated with the reduction of CO2 in the atmosphere due to their CO2-neutrality, their contribution to the preservation of natural resources by partially replacing coal in conversion processes and their flexibility in the production of solid, liquid and gaseous fuels. Biomass can be used to produce chemicals and liquid fuels, charcoal for use in
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metallurgy, carbon adsorbents from wood and biomass wastes and for co-firing with coal in energy generation [1-5]. Charcoal from hardwood species in small blast furnaces is employed for iron production in the Brazilian steel industry [1,2,6]. In the last few years, the use of charcoal from sustainable biomass in modern blast furnaces has opened up an environmentally friendly way to reduce CO2 emissions and the use of fossil fuels [7-9]. In the steel industry, charcoal is also seen as a potential additive to coal blends in the production of coke that is used to feed blast furnaces [9]. When hardwood or other types of biomass decompose by the action of heating in an oxygen-deficient atmosphere, a carbon material (char) is obtained together with a complex mixture of volatile products. These are allowed to escape as gases and other volatiles or they are condensed and converted to useful by-products (permanent gases and tar). The relative yields of each product (char, gas and tar) depend on the type of biomass, the design of the carbonization reactor and the carbonization conditions. When tar condensers are installed, two types of tar are recovered, a heavier tar that settles at the bottom of the column and a watery tar, the so-called pyroligneous acid that remains at the top. These tars account around 7 and 35 wt% of the initial wood, respectively, the raw material serving as a base for the vegetal carbochemistry [1-3,10]. The aim of the present work is to study the effects of biomass-derived carbonization products on the thermoplastic behaviour of coal and the structure and properties of the resulting cokes as a preliminary evaluation of the performance of coalbiomass blends in cokemaking. To understand the effects of Eucalyptus sawdust and its carbonization products on coal and coke properties, xylan –as being representative of different types of hemicelluloses-, cellulose and lignin were used as model additives.
2. Experimental section Coking coal A which was used to prepare the blends has a volatile matter content of 21 wt% db and a Gieseler maximum fluidity of 389 ddpm, yielding a high-temperature coke with a high mechanical strength and a low reactivity to carbon dioxide. Eucalyptus wood and its carbonization products obtained at 415 ºC (charcoal –Ch- and the two tar fractions -water-soluble tar, ST and water-insoluble tar, IT-) were added to coal A at an addition rate of 2 wt%. Three biomass model compounds (commercial xylan, cellulose and lignin from Sigma-Aldrich) were also tested.
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The thermoplastic properties of the coal and blends were tested in a constanttorque Gieseler plastometer, R.B. Automazione PL2000, following the ASTM D2639 standard procedure. This instrument measures the rotation of a stirrer inside a compacted 5 g sample of particle size 50 nm), mesopores (50 nm > dp > 5.5 nm). The microporore volume (dp C19), and a very low Submit before 31 May 2011 to
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proportion of the lighter fraction (C19) as the fluidity decreases (Figure 3). However, other chemical families present in the two tars A5HDPE and A5LUB should be considered to explain the different behaviour. 45
Amount of >C19 fraction (%)
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Figure 3. Variation of the amount of heavy fraction (>C19 ) in the tars obtained at 600 ºC with the parent blend fluidity.
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Oviedo ICCS&T 2011. Extended Abstract
The development of the fluidity of the coal in the presence of the additives clearly influences the structure of high-temperature cokes. The decrease in the Gieseler maximum fluidity in the parent blend results in a less organized carbon structure with various forms of structural defects and imperfections in the graphitic microcrystallites as is reflected by the increase in the D/G band ratio of the cokes obtained at 900 ºC (Figure 4). The exception to the general trend is the coke produced from the blend with the lubricating oil (A5LUB, not included in the graph). The increase in the fluidity of the coal blend from 312 ddpm to 684 ddpm when the lube oil gives rise to a coke with a similar carbon structure to that of the coal blend. 2.0 A5TUB
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Figure 4. Variation of the band area ratio (D/G) for cokes obtained at 900 ºC (D and G bands at 1320 and 1595 cm-1, respectively) with Gieseler maximum fluidity of the parent blends.
4.
Conclusions
All the additives tested increase the volatility of the products by limiting the cokeforming processes and consequently enhancing the formation of tar and gas fractions. Gray-King pyrolysis provides useful information on the effect of the additives on the distribution of coke, tar and gas. HDPE and lubricating oil mainly contributed to the formation of a tar with heavier hydrocarbons, whereas the other two additives are mainly recovered as the non-condensable fraction. The degree of inhibition in Gieseler fluidity induced by the additives is related to the more disordered structure of the cokes produced at high-temperature as was detected by Raman spectroscopy.
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Acknowledgements The financial support provided by PCTI-Asturias, Spain, through project PEST08-07 is gratefully acknowledged. We are also grateful to ArcelorMittal in Spain for its collaboration.
References [1]
Clarke DE, Marsh H, Mechanisms of formation of structure within metallurgical coke and its effect on coke properties, Erdöl und Kohle 1986;39:113-122.
[2]
Patrick JW. The coking of coal, Sci. Prog. 1974:61:375-399.
[3]
Loison R, Foch P, Boyer A (eds). Coke quality and production; Butterworth London; 1989.
[4]
Diez MA, Alvarez R, Barriocanal C, Coal for metallurgical coke production: predictions of coke quality and future requirements for cokemaking. Int. J. Coal Geology 2002;50:389-412.
[5]
Mochida I, Marsh H, Grint A. Carbonization and liquid-crystal (mesophase) development. 12. Mechanisms of the co-carbonization of coals with organic additives. Fuel 1979; 58:803-808.
[6]
Valia HS, Hooper W. Use of reverts and non-coking coals in metallurgical cokemaking, ISS Ironmaking Conf. Proc. 1994;53:89-105.
[7]
Menéndez JA, Pis JJ, Alvarez R, Barriocanal C, Fuente E, Diez MA. Characterization of petroleum coke as an additive in metallurgical cokemaking. Modification of thermoplastic properties of coal. Energy and Fuels 1996:10, 12621268.
[8]
Barriocanal C, Álvarez R, Canga CS, Diez MA. On the possibility of using coking plant waste materials as additives for coke production, Energy and Fuels 1998;12:981-989.
[9]
Diez MA, Alvarez R, Melendi S, Barriocanal C. Feedstock recycling of plastic wastes/oil mixtures in cokemaking, Fuel 2009;88:1937-1944.
[10] Cuesta A. Dhamelincourt P, Laureyns J, Martinez-Alonso A, Tascón JMD, Raman microprobe studies on carbon materials, Carbon 1994;32:1523-1532. [11] Miyazu T, The evaluation and design of blends using many kinds of coals for cokemaking. In: Int. Iron Steel Cong., Dusseldorf, 1974, Pap. 1.2.2.1. [12] Nakamura N, Togino Y, Adachi T. Philosophy of blending coals and cokemaking technology in Japan. In: Coal, coke and the blast furnace, The Metals Society, Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
1977, UK, p. 93-106. [13] Diez MA, Domínguez A, Barriocanal C, Alvarez R, Blanco CG, Casal MD, Canga CS, Gas chromatographic study for the evaluation of the suitability of bituminous waste material as an additive for coke production. Journal of Chromatography A, 1998;823:527–536. [14] Domínguez A, Blanco CG, Barriocanal C, Alvarez R, Diez MA. Gas chromatographic study of the volatile products from co-pyrolysis of coal and polyethylene wastes, Journal of Chromatography A 2001;918:135-144.
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Effect of volatile matter evolution on optical properties of macerals from different rank coals A. Guerrero, M.A. Diez, A.G. Borrego Instituto Nacional del Carbón (INCAR-CSIC). Francisco Pintado Fe, 26, 33011 Oviedo, Spain Abstract The behavior of coal macerals in carbonization has been a topic of research for many years since the early recognition that the macerals behaved differently during the coking process. In addition, the coke optical texture and the amount of unreactives in the coke matrix have shown to be related to parameters relevant for coke properties such as reactivity and strength. The coals involved in this study are Polish coals of the Upper Silesian coal basin ranging in rank from high volatile to medium volatile bituminous . The experimental approach used in this study consisted on analyzing both the raw coal and the heated coal using optical microscopy and reflectance analysis. For each measured spot, both the reflectance and the component identified were recorded. The coals were heated in a thermogavimetric analyser at slow heating rate under inert gas flow up to temperatures in the range 450 to 1000 °C. Once the sample reached the desired temperature the oven was cooled down to stop the reaction and the cokefied residue recovered for petrographic analysis. Only the coals with reflectance over 1.0 % passed through a fluid stage in which integrity of the particles was lost. The size of the optical texture of the re-solidified material increased with the rank of the parent coal. The reflectance of all the macerals increased with increasing heating temperature, being the treatment final temperature the most relevant factor in determining the reflectance of inertinite macerals. The higher the heating temperature, the higher the reflectance with little influence of the parent inertinite reflectance. For those coals in which vitrinite did not pass through a fluid stage the distinction between vitrinite- and inertinite-derived material in the heated samples was very difficult. Inertodetrinite was virtually indistinguishable, whereas only relic cellular structure allowed distinguishing between vitrinite and semifusinite.
1. Introduction The behavior of coal macerals in carbonization has been a topic of research for
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many years since the early recognition that the macerals behaved differently during the coking process (Shapiro and Gray 1964). In addition the coke optical texture and the amount of unreactives in the coke matrix has shown to be related to parameters relevant for coke properties such as reactivity and strength (Mackowsky, 1976). Despite the numerous studies dealing with the transformation of coal macerals upon heating, the issue is far from being solved. Different authors have identified as relevant factors determining the plastic behaviour of coal macerals the reflectance of the coal to which they belong (Taylor et al., 1967; Falcon and Snyman, 1986; Diessel and Wolff-Fischer, 1987), their individual reflectance (Diessel, 1983; Shapiro and Gray, 1960) or the characteristics of the whole coal reflectogram (Kruszewska, 1990). Other aspects not exclusively related with maceral reflectance are the type of maceral (Shapiro et al., 1965; Nandi et al., 1977) the fluorescence intensity (Diessel, 1985) or the degree of maceral association (Rentel, 1987), the latter recognized as related with the plastic properties of macerals. This topic is being revisited in a project of the European research fund for coal and steel focused on optimizing coking coal blends (RATIO-COAL).
2. Experimental section Six Polish coals in the rank interval of those used for metallurgical coke production and their cokefied products at different temperatures have been studied by optical microscopy. The experimental approach used is study consisted on performing a combined maceral-reflectance analysis at maceral level. For each coal 500 reflectance values were recorded and saved together with the corresponding maceral assignment. In this way detailed information of the maceral composition and also of maceral reflectance distribution is obtained. The coals were heated in a thermogavimetric analyser under a N2 flow of 5 0 mLmin-1 at a heating rate of 5 °Cmin-1. The maximum heating temperature ranged from 450 to 1000 °C. Once the sample reached the desired temperature the oven was cooled down to stop the reaction and the cokefied residue recovered for petrographic analysis. In the cokefied material around 250 instead of 500 reflectance points were recorded and also the corresponding maceral was identified. The degree of detail in the analysis of cokefied material was less than for the raw coal, first because the temperature obscured some of the maceral distinguishing features and also because the amount of sample recovered from the thermobalance was rather small.
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3. Results and Discussion The coals involved in this study are from the Upper Silesian coal basin (Fig. 1) ranging in rank from high volatile to medium volatile bituminous (Table 1).
Figure 1 – Upper Silesian Coal Basin map showing the location of the samples studied
The coals have ash content below 10% and low sulfur contents. The Giseler test indicated a very low fluidity for all the coals, lower than expected for their rank. It should therefore be considered that the coals have lost the plastic properties due to alteration or weathering. Fluidity is very sensitive to exposure of the coals to air and prolonged storage times.
Table1. Proximate, ultimate and petrographic analyses of the studied coals. Ash V.M. C H N Odif ST Fmax VRr V I L Ck db % daf % ddpm (%) vol % mmf MR 3.3 33.82 85.34 5.09 1.40 7.59 0.59 8 0.81 68.6 27.4 3.6 0.4 SZ 7.13 33.06 86.35 5.16 1.55 6.18 0.76 248 0.89 68.4 27.6 3.0 0.2 PW 6.98 25.85 89.03 4.81 1.44 4.13 0.59 120 1.12 65.4 33.0 1.2 0.4 ZF 7.31 25.21 89.11 4.73 1.41 4.19 0.56 93 1.14 62.6 32.0 2.4 3.0 BY 6.42 25.05 89.21 4.84 1.59 3.80 0.56 183 1.17 66.4 31.6 2.0 0.0 JS 7.16 21.28 90.28 4.60 1.29 3.33 0.50 63 1.29 50.4 46.4 1.0 0.2 VM=Volatile matter content, Fmax=Maximum Giseler Fluidity, VRr=Vitrinite reflectance, V=vitrinite, I=inertinite, L=liptinite; Ck=natural coke, db=dry basis, daf=dry-ash-free basis ddpm=dial divisions per minut,. vol= volume, mmf=mineral matter free basis
The maceral analysis of the coals indicated a moderately high vitrinite content for most of the coals (around 65%) and inertinite content around 30%, except for JS coal, which Submit before January 15th to
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Oviedo ICCS&T 2011. Extended Abstract
exhibited balanced inertinite and vitrinite contents. All the coals had low liptinite contents in all of them the presence of coke was detected in very low amounts.
Figure 2 shows the volatile matter lost at different temperatures of the studied coals (a) and the vitrinite reflectance reached as a function of the normalized volatile release (b). Three groups can be established with the thermal behavior of the studied coals: Those with vitrinite reflectance below 0.9% lose volatiles at lower temperature and exhibited a higher devolatilization rate. The coals with vitrinite reflectance between 1.12 and 1.17% exhibited nearly identical thermograms and have similar volatile matter content despite their difference in rank due to the differences in maceral composition. The lowest rank coal of the group having the highest inertinite content and viceversa. The highest rank coal released the volatiles at higher temperatures and with the lowest devolatilization rate. 35
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Figure 2. a).Volatile matter lost at different temperatures for the studied coals and b). Vitrinite reflectance reached as a function of the normalized volatile release (b). The effect of devolatilization on the reflectance of vitrinite is seen in Figure 2b. It is observed that there is a low increase in reflectance until the volatile release has not reached around 67-75%. Below this threshold vitrinite reflectance is maintained below 2% and above this threshold the reflectance raised quickly reaching values around 7% at 1000 ºC. Figure 3 shows an example of the aspect of coal JS and the same sample heated at 550 and 1000 °C. The main features found for the different samples can be summarized as follows: -
Vitrinite from ZF, PW, BY and JS fused upon heating passing through a plastic stage in which a mosaic structure was formed. The size of the mosaic-forming grains was
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Oviedo ICCS&T 2011. Extended Abstract
larger in JS than in the other coals. Coals MR and SZ did not melt and the individual grains maintained their integrity although significant changes occurred in the vitrinite whose reflectance approached to the inertinite reflectance. Incipient anisotropy was only observed in the highest temperature sample of the MR series, whereas in SZ series incipient anisotropy was observed in lower temperature samples. -
The reflectance of all the macerals increased with increasing heating temperature and the treatment final temperature was the most relevant factor in determining the reflectance of inertinite macerals. The higher the heating temperature, the higher the reflectance with little influence of the parent inertinite reflectance.
-
For those coals in which vitrinite did not pass through a fluid stage the distinction between vitrinite- and inertinite-derived material was very difficult. Inertodetrinite was virtually indistinguishable, whereas only relic cellular structure allowed distinguishing between vitrinite and semifusinite.
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In the lowest ranked coals it was observed the formation of a high relief and high reflectance, supposedly carbon-rich structure in the inner part of the vitrinite grains.
550 ºC Rr=1.29%
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i
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Figure 3. Appearance of Coal JS and its cokefied material at different temperatures. Rr=random reflectance, i=inertinite, v-d=vitrinite-derived. Optical micrographs under incident white light. The evolution of the two maceral groups reflectance which are identifiable during the whole heating process is shown in Figure 4. The figure clearly shows a convergence of the reflectance values of both maceral groups upon heating. Vitrinite and inertinite reflectances become very close at 550 ºC and typically at 1000 ºC the reflectances of vitrinite surpass that of inertinite. In addition, as observed in the case of vitrinite, the main factor determining the inertinite reflectance is the peak temperature at which the sample was heated. The increase in inertinite reflectance up to 550 ºC was rather low, but further increase in temperature resulted in a drastic increase in the reflectance values.
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Oviedo ICCS&T 2011. Extended Abstract
8
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Figure 4. Evolution of vitrinite and inertinite reflectances with temperature for the studied coals.
4. Conclusions ·The lowest rank coals (MR and SZ) did not pass through a fluid stage leading to the formation of a matrix, whereas coals with vitrinite reflectance 1.12-1.29% passed through a plastic stage forming an anisotropic matrix in which the size of the mosaics increased with the rank of the coals.
·The reflectance of all the macerals increased with increasing the treatment temperature obscuring some of the distinguishing features of the macerals. For vitrinite which is maintained isotropic, the distinction between vitrinite and inertinite is difficult in the heated samples and the formation of a carbon-rich secondary structure is observed in the highest temperature samples. Semifusinite loses part of the cellular structure from 550 ºC becoming difficult to distinguish from macrinite. In addition inertodetrinite is also difficult to distinguish from the matrix.
·The reflectance reached by both vitrinite and inertinite is more closely related to the treatment temperature than to the reflectance of the parent coal, nevertheless the vitrinite optical texture is very different for different coal ranks. The high volatile vitrinites lose faster their volatile matter remaining isotropic whereas the lower volatile vitrinite have more time to re-organize the carbonaceous residue to yield anisotropic ordered structures.
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Oviedo ICCS&T 2011. Extended Abstract
·The drastic increase in reflectance occurs from 550ºC and corresponds to a volatile loss of 67-75% of the coal volatile matter.
Acknowledgements: The research leading to these results has received funding from the Research Programme of the Research Fund for Coal and Steel (Grant Agreement number RFC-PR- 09024). I. Jelonek (U. Silesia) is gratefully acknowledged for providing the coal samples for this study.
References: Diessel C.F.K.., 1983. Carbonization reactions of inertinite macerals in Australian coals.. Fuel 62, 883-892 Diessel, C.F.K., 1985. Fluorometric analysis of intertinite, Fuel 64, 883–892. Diessel, C.F.K.; Wolff-Fischer, E., 1987. Coal and coke petrographic investigations into the fusibility of Carboniferous and Permian coking coals Int. J. Coal Geol. 9,87-. Falcon, R.M.S. and Snyman, C.P., 1986. An introduction to coal petrography: atlas of petrographic constituents in the bituminous coals of Southern Africa. Geol. Soc. South Afr. Rev. Paper 2, p. 27 Kruszewska K., 1989The use of reflectance to determine maceral composition and the reactive-inert ratio of coal components Fuel, 68, 753-757 Mackowsky, M-Th., 1976. Prediction methods in coal and coke microscopy. J. Microscopy. 109, 119-137 Nandi B.N., Brown T.D., Lee G.K. 1977. Inert coal macerals in Combustion Fuel, 56, 125-130. Rentel, K., 1987. The combined maceral-microlithotype analysis for the characterization of reactive inertinites. International Journal of Coal Geology, 9, 77-86 Schapiro N.; Gray, R.J. 1960 Petrographic classification applicable to coals of all ranks, Proc. Ill. Mining Inst., 68th Year 83–97. Schapiro, N., Gray, R.J., Eusner, G.R. (1965). Recent developments in coal petrography. Blast Furnace, Coke Oven and Raw Materials Committee, Proc, 20, 89-112. Schapiro, N.; Gray, R.J., 1964. The use of coal petrography in coke making, J. Inst. Fuel 37, 234–242. Taylor G.H., Mackowsky M.Th.; Alpern, B. 1967. The behaviour of inertinite during carbonisation. Fuel 46, 431–440.
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Oviedo ICCS&T 2011. Extended Abstract
Semi-pilot scale carbonization to assess blast furnace coke quality E. Díaz-Faes, R. Alvarez, C. Barriocanal, M.A. Díez Instituto Nacional del Carbón (INCAR), CSIC, Apartado 73, 33080 Oviedo. Spain
[email protected] Abstract A series of coals of different rank and geographical origin were carbonized in two movable wall ovens (MWO) of 320 kg (pilot oven) and 15 kg (semi-pilot oven) at INCAR. All the coals used were chosen from among those commonly employed by the cokemaking industry in blend preparation. The quality of the cokes obtained from the two MWO`s was assessed in terms of reactivity towards CO2 by the Nippon Steel Corporation test (NSC test) and the ECE-INCAR test. A good correlation was found between the reactivity to carbon dioxide as determined by the NSC and ECE-INCAR methods. Furthermore, using a semi-pilot oven in preference to large-capacity ovens yields valuable results due to the small amount of coal employed (15 kg vs. 300-400 kg) since it is quicker, more flexible and leads to lower costs.
1. Introduction Metallurgical coal is a macroporous material obtained from coking coals or blends of coals by heating them in the absence of oxygen. In the blast furnace, coke plays three roles: as a fuel, providing the energy necessary for the process; as chemical agent, acting as reducing agent of the iron ore and as a permeable support of the burden, allowing the gases to pass through the burden to the upper part of the blast furnace and enabling the liquids to pass down to the crucible. For the two first functions, coke can be replaced by other fuels and carbon sources such as pulverized coal, plastics, oils, etc. [1-3], but there is no other material that can fulfill the role of permeable support of a blast furnace charge. This substitution has led to a reduction of the coke rates in the blast furnace over recent years. In other words, the quality of the coke has acquired greater importance in our efforts to keep the blast furnace operating in optimal conditions [4]. One of the most important properties of coke is its ability to perform well in oxidizing conditions and at the high temperatures characteristics of a blast furnace [5]. Japanese industry has developed a method of measuring the reactivity of a coke towards carbon dioxide and the resistance to the abrasion of the partially gasified coke (NSC test, ASTM-D 5341). INCAR has been using a modification of the ECE reactivity test which 1
Oviedo ICCS&T 2011. Extended Abstract
requires a smaller amount of coke and is less expensive and time consuming. The aim of this work was to establish relationships between the quality of the cokes obtained at two different scales, semi-pilot and pilot, using two movable wall ovens (MWO) of different capacity, 15 and 320 kg, respectively and between reactivity indices determined by the ECE and NSC methods.
Experimental section 2.1. Carbonization tests at pilot and semi-pilot scale Carbonization tests at pilot scale were carried out in an electrically-heated moveable wall oven of 320 kg capacity (MWO320) with the following dimensions: 915 mm length, 840 mm height and 455 mm width. The initial coke-oven wall temperature during charging was 880 ºC, rising at a rate of 14 °C/h up to 1200 ºC by the end of the process and to 1050 °C in the centre of the charge. The coking time required was 18 h.
Coals were also carbonised in a semi-pilot moveable-wall oven of 15 kg of capacity (MWO15) fitted with electrical heating and having the following dimensions: 150 mm length, 750 mm height and 250 mm width. During the carbonisation tests, the temperature of the wall was kept constant at 1010 ºC. The coking time required to reach a temperature in the centre of the charge of 950 ºC was 3 hours. In the two-scale carbonizations tests, after the coke had been pushed from the oven, it was quenched with water. The moisture content of the coals to be carbonized in the two ovens was kept as close as possible to 5 wt%.
2.2. Coke quality 2.2.1. NSC test Coke reactivity towards CO2 (CRI) and coke strength after reaction (CSR index) were assessed by the test developed by the Nippon Steel Corporation (NSC) and standardized afterwards by ASTM D5341-99 (ISO 18894:2006). Briefly, a sample of coke (200 g) with a particle size between 19 and 22.4 mm was reacted at 1100 ± 5 ºC for 2 h with CO2 at a flow rate of 5 L/min. The partially gasified coke was weighed and subjected to the tumbler test. The CRI was calculated as the percentage of weight loss. The mechanical degradation of the coke after CO2 reaction (CSR) was measured as the weight of coke remaining on a 9.5 mm sieve after 600
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Oviedo ICCS&T 2011. Extended Abstract
revolutions at 20 rpm and it was calculated as the weight percentage of coke larger than 9.5 mm relative to the weight of the coke after the reaction with CO2. 2.2.2. ECE-INCAR reactivity test The procedure used is based on a recommendation by the European Commission in 1965. Whereby, reactivity is measured as the weight loss after 2 hours of reaction instead of by analysing the gas composition during the reaction [6]. To carry out the test a sample of 7 g coke with a particle size between 1 and 3 mm was introduced in a quartz reactor and kept at 1000 ºC in an electrical oven. The heating and cooling of the sample was carried out under N2. Once the temperature of the sample had stabilized, a flow of CO2 of 7.2 L h-1 was made to pass through the sample for 1 hour. After the reaction had finished, the sample was left to cool before being weighed. Coke reactivity was calculated as the percentage of weight loss.
2. Results and Discussion The coals were carbonized in two MWO`s available at INCAR with the aim of comparing the quality parameters of the cokes obtained using two scales: reactivity and hot mechanical strength. It is important to point out that the quality indices of the cokes produced in the semi-pilot oven did not numerically match those from the pilot oven, mainly due to wall effects and the different conditions applied during the coking process (i.e. coking rate). The relationship between the reactivity of the cokes produced in the two ovens yields good regression coefficients: 0.943 for reactivity assessed by means of ECE-INCAR reactivity test (Figure 1) and 0.965 for the CRI indices (Figure 2a), the values of MWO15 being slightly higher than those of MWO320. With some exceptions, the cokes produced in the semipilot oven are more reactive than those produced at pilot scale. The same trend was observed in the case of the mechanical strength of the partially gasified cokes (CSR indices), where the regression coefficient was 0.963 (Figure 2b).
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Oviedo ICCS&T 2011. Extended Abstract
18
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14 19 24 29 34 39 44 49 54 59 64 69 74 79 84
CSR (%), MWO15
Figure 2. Relationship between CRI (a) and CSR (b) indices for cokes produced in the two MWO`s. Relationships between the ECE-INCAR reactivities and CRI and CSR indices are shown in Figures 3 and 4 for the two moveable wall ovens. The best correlation coefficients are obtained when the ECE-INCAR reactivities and CRI indices are compared in the two MWO`s, a value of r = 0.952 being obtained for the cokes produced in the pilot oven and r = 0.911 for the cokes produced in the semipilot oven. The correlations are worse when CSR index is compared with ECE-INCAR reactivity index, a correlation coefficient of r = 0.882 being obtained for the cokes of the 320 kg capacity oven and r = 0.830 for the cokes of the 15 kg capacity oven. This is due to the influence that bulk density has on the strength of the partially gasified cokes during coking.
4
Oviedo ICCS&T 2011. Extended Abstract
70
90 80
a
50
CSR (%), MWO320
CRI (%), MWO320
60
40 30 20
r = 0.952
10
b
70 60 50 40 30
r = 0.882
20 10
0
0 2
4
6
8
10
12
14
16
18
2
4
6
RECE-INCAR (%), MWO320
8
10
12
14
16
18
RECE-INCAR (%), MWO320
Figure3. Relationship between the RECE-INCAR and CRI (a) and CSR (b) indices for the cokes produced in the pilot oven.
90
80
80
a
60
CSR (%), MWO15
CRI (%), MWO15
70
50 40 30 20
r = 0.911
10
b
70 60 50 40 30
r = 0.830
20 10
0
0 2
4
6
8
10
12
14
16
18
20
RECE-INCAR (%), MWO15
22
2
4
6
8
10
12
14
16
18
20
22
RECE-INCAR (%), MWO15
Figure4. Relationship between the RECE-INCAR and CRI (a) and CSR (b) indices for the cokes produced in the semi-pilot oven.
Conclusions The use of a semi-pilot carbonization oven enables coke quality to be determined by means of reactivity towards CO2 and coke strength after reaction and valuable results to be obtained with only a small amount of coal (15 kg vs. 320 kg). Additional advantages include a considerable saving of time, a reduction in cost and a more flexible process. ECE-INCAR test can be used as a guide to estimate coke quality in terms of its reactivity to CO2, although it cannot replace the NSC procedure. Acknowledgement. The authors thank the European Coal and Steel Community –ECSC- (project 7220PR/119) for financial support.
References [1] Cross, WB. The future of the European steel industry and its demand for coal. The Coke Oven Managers’ Association (COMA). Year-Book, Mexborough, United
5
Oviedo ICCS&T 2011. Extended Abstract
Kingdom, 1994, 97-108. [2] Asanuma M, Ariyama T, Sato M, Murai R, Nonaka T, Okochi I, Tsukiji H, Remoto K. Development of waste plastics injection process in blast furnace. ISIJ Int. 2000, 40: 244-251. [3] Ohji, M Production and technology of iron and steel in Japan during 1999. ISIJ Int. 2000, 40: 529-543. [4] Díez, MA, Álvarez R, Barriocanal C. Coal for metallurgical coke production: predictions of coke quality and future requirements for cokemaking. International Journal of Coal Geology 2002, 50: 389-412. [5] Sakawa M, Sakurai Y, Hara Y. Influence of coal characteristics on CO2 gasification. Fuel 1982, 61 (8): 717-720. [6] Menéndez JA, Álvarez R, Pis JJ. Determination of metallurgical coke reactivity at INCAR: NSC and ECE-INCAR reactivity test. Ironmaking and Steelmaking 1999: 117121.
6
Oviedo ICCS&T 2011. Extended Abstract
Fundamental Investigation Pyrolysis Behaviour of Low Rank Coals Tatsuro Harada1), Seiichiro Matsuda1), Nozomi Wada2), Yohsuke Matsushita2)*, Isao Mochida2) 1) Research Laboratory, Kyushu Electric Power Co., Inc, 12-1-47 Shiobaru, Minami-ku, Fukuoka, Fukuoka, 815-8520 Japan 2) Research and Education Center of Carbon Resources, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka, 816-8580 Japan Abstract Pyrolysis of cellulose, brown and bituminous coals were examined by TGA at variable heating rates of 50 to 999 k / m up to 1473K. The volatile contents of these samples were around 92.9 % of cellulose, 53.5 % of brown coal and 28.2 % of bituminous coal. The heating rates influence the contents. The temperature range of the pyrolysis was most large with Loy Yang coal, indicating that the contents of remaining volatile of the char produced from that coal which is believed very influential on the combustion reactivity of the char are easily controllable.
TGA data give us the
Arrhenius plot and kinetic of pyrolysis at the heating rates. Remaining volatile contents of the chars produced from Loy Yang were calculated from the kinetics at the variable pyrolysis temperature as the solid fuel at the fixed heating rate. According to the calculation, targeted char is suggested to be produced by controlling the temperature and time at the selected heating rate, although chemistry of volatiles and char are also needed to evaluate the combustion properties of char as the fuel for the pulverized coal combustion.
1. Introduction Low rank coals such as brown coal are largely deposited but their use is limited domestically or even locally. Their issues are low calorific values and instability of the coals, when dried, for spontaneously combustion. Supply of black coals will be restricted as their price will increase, reflecting on demand / supply balance. Hence it is very necessary for coal demanding countries to convert low ranking coals into handy fuel as solid fuel through low cost procedures. In the present study, pylolysis properties of Victorian brown coal were studied to find ways to convert it into power generation fuel in coal demanding countries. The three major issues are low calorific value due to huge water and oxygen contents, too much high reactivity to form long flame when burn in pulverized
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coal firing, and huge possibility of spontaneous combustion during the transportation of dried coal even of it is of low ash and contamination. The pyrolysis treatment of brown coal can solve to such issues. Hence we attempt to clarify the pyrolysis reaction of the brown coal among the natural resources, nature of the volatile as well as, pyrolytic kinetics to control structural characteristics and combustion properties of the char in comparison with the dried coal.
2. Experimental section
Table 1 summarizes the samples examined in this study. Brown coal, Loy Yang and bituminous coal Newlands came from Australia, Victoria and Queens land, respectively. Cellulose was a chemical regent and supplied by SigmaAldrich Corporation. Pyrolysis of the samples was measured by a thermogravidity analyzer (TGA, TG / DTA 200SA Bruker) at heating rates of 50 to 999 K/min and a final temperature up to 1473K. The samples were heated in an infrared furnace to vary the heating rate of a wide range. The sample tube was first vacuumed for 20 min and flushed with nitrogen flow for 30 min to lower the oxygen concentration less than 10 ppm. Table 2 summarizes the TGA conditions. Activation energy and pre-exponential factor of the pyrolysis were calculated by analyzing weight reducing profile at every heating rate. The volatile contents of products char were calculated at several temperatures based on the Arrhenius equation at the heating rate of 50 K / min.
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3. Results and Discussion 3.1 Pyrolysis profiles of cellulose, brown and bituminous coals The
final
weights
of
the
samples were basically around the fixed carbon amounts summarized in Table 1. The weight decreased markedly in order of Newlands < Loy Yang < Cellulose, reflecting oxygen and hydrogen contents since they are lost in principally forms of CO2, H2 and CH4. The larger heating rate tends to reduce the final weight, regardless the samples. Figure 1 shows weight loss profile of the samples relative to the final loss at 1473 K by heating rate at 50 K / min. Figure 1 indicates the regions of weight loss. Cellulose started weight loss at about 700 K and completed at 800 K, whole 95 % weight loss occurring in the range of 100 K. The very rapid weight loss was noted in a narrow range.
In contrast, Loy Yang coal lost its weight in a very broad
temperature range of 300 to 1473 K. The rapid weight loss was observed at 600 – 800 K where ca 40% was lost. Higher ranking coal of Newlands coal lost in a little narrower range. The principle loss was observed in the range of 600 to 800 K where 60% was lost. The brown coal appears to have the larger variety of components in comparison with both cellulose and Newlands, being located between them in the
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coalification progress. Figure 1 suggested feasibility for the control of remaining volatile contents in the product char from brown coal. The control of the remaining volatile content less than 30% is rather easy because its decrease is mild against the temperature in the range of 800 to 1423 K.
3.2 Arrhenius analysis of weight loss profile Figure activation
2
summarizes
energy
of
the
pyrolysis
weight loss at the heating rates. The activation energy increased with larger heating rate.
The
energy of Loy Yang coal ranged in 2.5×104 to 3.5×104 J / mole.
The
energy of Loy Yang coal is basically smaller than that of Newlands coal by 0.2 - 0.5×104 J / mole. The largest difference was observed at 400-600 K / min.
3.3 Product Char from Loy Yang Coal The amounts of produced gas & tar and char were ca 50.2 wt% and 49.8 wt%, respectively at 1173 K. Gaseous products consisted of CO2, CO, H2, CH4 and C2H6. Pyrolysis
of
Loy
Yang
Coal
changed its color from brown to black. The sizes of coal and char were mach the same although the large amount of volatile was lost according
to
the
pyrolytic
temperature and time. The char appears combusted in different character from those of row coal due to different amount of remaining volatile. The char looks still much more reactive than the Newland coal or its char. Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
3.4 Discussion The rate of pyrolysis is estimated from the Arrhenius plot by assuming the reaction order. Reaction rate was investigated by differential of weight loss profile at various heating rates.
Activation energy and frequency factor of pyrolysis
reaction were determined by the Arrhenius plots slope and intercept, respectively. Based on the rate equation, activation energy and frequency factors, the yield of char and its volatile content are calculated at the pyrolysis temperature and time by the fixed heating fate. Figure 2 summarizes the yield of char from the Loy Yang coal and its volatile content at every temperature and time on the heating by the rate of 50 K / min. The volatile content was 44.5 at 573K to 6.29 at 1173K where the necessary times of heating were 250 to 1,500 sec, respectively by heating at 50K / min. Table 3 summarized the remaining volatile contents of chars produced at several temperatures by variable heating rates. The contents of char produced at 573K increased slightly by increasing heating rate from 50 K/min to 999 K/min while those at 773 K were almost constant around 20%. The contents at 1173 K decreased significantly from 6.6 to 3.1 % according to the heating rate.
The combustion of char is influenced by the volatile contents and composition as well as char reactivity. The exact result and influence on the combustion may be useful to design the pyrolytic process to produce char to substitute steam for the current use of brown coal. Coal volatile products at a pyrolysis are also important to count the feasibility of the pyrolytic process because the volatiles are supplied to fuel and chemical industries as the wanted feedstock.
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4. Conclusions Pyrolytic characteristics of the Newlans coal of bituminous coal, the Victorian brown coal of low rank coal and the cellulose of a regent under the various heating rate from 50 to 999 K/min were investigated by using the thremogravimetry analyzer. Each sample’s characteristics of volatile matter released and pyrolytic reaction were investigated. The activation energy in the pyrolysis of Loy Yang coal was lower than that of anstandard bituminous Newlands coal. Our approach will contribute to the easy and economical use and transportation to accelerate the utilization of brown coals.
Accurate chemical analysis of pyrolytic reaction is
necessary to find ways of advanced utilization and safe transportation of brown coal. Our work suggests the possibility of expanding utilization of cheap young coal such as brown coal or lignite in the future. The results will be very useful to design advanced utilization of low rank coal.
Acknowledgement This research is partially supported by international advanced utilization of Victorian brown coal based on clean coal technology development project for fundamental international collaboration research in the energy innovation program funded by New Energy and Industrial Technology Development Organization (NEDO).
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Oviedo ICCS&T 2011. Extended Abstract
High pressure pyrolysis of different coal types – Influence of pressure on devolatilisation characteristics using TGA/MS M. Klinger, B. Meyer TU Bergakademie Freiberg, Department of Energy Process Engineering and Chemical Engineering, Fuchsmühlenweg 9 Haus 1, D-09596 Freiberg
[email protected] Abstract The influence of pressure on devolatilisation characteristics like yields and compositions of pyrolysis products was investigated using a combined thermo gravimetric/mass spectrometric device (TGA/MS). Six coals of different ranks, including German brown coals, German anthracite and two world-market sub-bituminous coals, were pyrolyzed at temperatures of up to 1100 °C with a constant heating rate of 5 K/min and system pressures of 1, 5, and 10 bar, respectively. Gas analysis involved permanent gases like H2, CO, CO2, N2, CH4, COS, H2S, H2O, O2, and Ar. The latter two were not taken into consideration, since both are no pyrolysis products. As expected, higher coal ranks lead to increased yields of char, whereas the influence of pressure is low but steady – increased pressure results in increased yields for all coal types investigated. Gas yields do not show a clear trend, since most coals display a minimum at 5 bar and a maximum at 10 bar. Also gas compositions fluctuate in terms of maxima values as well as start and peak temperatures of different gas species and coals.
1. Introduction Pyrolysis is a key process in the utilisation of solid fuels (e.g. coal, biomass) in energetic and non-energetic applications. It is not only relevant as an individual process for the production of char/coke or tar/oil and for fuel conditioning, but also as a sub-step of gasification and combustion. Pyrolysis is controlled by various parameters like process conditions (temperature, pressure, heating rate) and feedstock properties. The relevant parameters, which have an impact on gasification, are defined by the behaviour of the feedstock during pyrolytic decomposition [1]. Most important are char yield and reactivity [2] as well as the yield of gases/vapours and their composition. The former two have a significant effect on the carbon conversion and therefore on the gasification temperature (at fixed residence time), which is reflected in the efficiency of the gasifier.
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Oviedo ICCS&T 2011. Extended Abstract
The latter two, yield of gases/vapours and their composition, strongly influence the quality of the product gas and the formation of tars (in case of fixed and fluidised bed gasifiers). Since modern gasification plants are operating at elevated pressures [3][4], basic knowledge and understanding of thermal devolatilisation at those conditions are needed [5][6][7]. In the literature only few studies of combined TGA/MS investigations at high pressure can be found [5], and no research in that field has been done on German brown coals.
2. Experimental Section 2.1. Samples Six different coals, namely one brown coal from Lusatia, two brown coals from Rhineland, anthracite from Westphalia (all four Germany), a world-market subbituminous coal from Colombia and a low-rank coal from Puertollano (Spain) were investigated. Samples were milled and sieved to a fraction of < 100 µm and oven dried until a constant mass was reached. Proximate and ultimate analyses as well as the calorific values are given in Table 1. Table 1 Results of ultimate, proximate analysis and heating value determination of coal samples. Brown coal sub-bituminous coal/anthracite Lusatia Rhineland Rhineland Puertollano Westpahlia Colombia Germany Germany Germany Spain Germany Sample identification LB3 DK HKN KOL PSK IA Proximate analysis in wt.-% Moisture (r) 11.91 *) 49.59 51.12 14.97 13.55 3.95 Ash (d) 6.05 9.69 5.47 8.31 48.16 11.20 Volatile Matter (d) 52.30 48.41 50.70 38.79 21.67 6.07 Fixed Carbon (d) 41.65 41.90 43.83 52.90 30.17 82.73 Sum (d) 100.00 100.00 100.00 100.00 100.00 100.00 Ultimate analysis in wt.-% (daf) Carbon 68.27 68.88 69.04 79.10 77.43 93.31 Hydrogen 5.01 4.98 5.01 5.35 5.41 3.14 Nitrogen 0.74 0.81 0.79 1.58 1.82 1.19 Combustible Sulphur 0.30 0.02 0.05 0.71 1.32 0.99 Oxygen 25.68 25.31 25.11 13.26 14.02 1.37 Sum 100.00 100.00 100.00 100.00 100.00 100.00 O/C 0.376 0.368 0.364 0.168 0.181 0.015 H/C 0.074 0.072 0.073 0.068 0.070 0.034 Heating value in kJ/kg (d) HHV 25,059 23,975 25,267 29,125 15,714 31082 LHV
24,031
22,995
24,233
28,054
15,103
30,474
*) Coal was delivered as pulverized and dried sample.
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2.2. Pyrolysis The pyrolysis experiments were carried out in a TGA/MS-system, manufactured by the Rubotherm Company, which offers several benefits like temperatures of up to 1100 °C, pressures from atmospheric to 40 bar, and the use of different gases including corrosive ones. Due to a special magnetic coupling a closed reaction chamber and thereby contactless weighing can be afforded. For this study, argon was used as purge gas with adapted flow rates for each pressure – 1 bar: 15 ml/min, 5 bar: 63 ml/min, and 10 bar: 125 ml/min – to assure the same gas velocities. Approximately 1 g (±0.002 g) of tried and pulverized coal was sampled into an alumina crucible of 15 mm in diameter and 20 mm in height. After closing the reactor the whole system was evacuated for 20 min, where at the end a reference weight, without buoyancy effects, was taken. With a flow of 500 ml/min of argon, the system was refilled and pressurized to the selected values. The sample was heated from room temperature to 1100 °C with a heating rate of 5 K/min. The process and pyrolysis gases pass a two-stage cold trap operating at 0 °C (ice water) and -10 °C (cryostat), respectively. An automated pressure controlling valve keeps the system pressure at a defined and constant level. The mass spectrometer (MS) samples gas directly from the exhaust tube via a quartz capillary, 75 µm in diameter. For each run a blank measurement at the same conditions like the pyrolysis experiment (pressure, flow and heating rate) was recorded, to be subtracted from the TG curve.
2.3. Gas analysis The composition of the exhaust gas (pyrolysis gas + purge gas) was analysed by means of mass spectrometry. The MS is a quadrupole type (IPI GAM 200) with a secondary electron multiplier (SEM) detector to determine concentrations down to few ppm. Volume concentrations for single gas species were recalculated into ml/min for each temperature, knowing the volume flow of argon and the measured concentrations of all gas species. MS analysis was started simultaneously with the heating of the sample, enabling a temperature allocation to each gas concentration. Determination of time lag was carried out in pre-experiments using a tracer gas and taken into consideration.
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3. Results and Discussion 3.1. Char yield and mass loss rate The six coal samples show typical mass loss curves for each coal rank, whereas the three brown coals have lower char yields at 1100 °C than the sub-bituminous coals and the anthracite. The higher char yield of the hard coals results from a lower volatile content (compare Table 1). For LB3 an additional mass loss at around 800 °C can be observed, which may be assigned to mineral decompositions, like carbonates or sulphates. With increased pressure a slight increase in char yield can be observed within all coals, most prominent at LB3 and KOL. A pressure increase from 1 to 5 bar results in more significant changes then a further increase to 10 bar (see Figure 1 and Table 2). 100
100
80
90
b)
a)
80
70
70
IA 60
60
PSK
50
KOL
40
HKN DK
30
LB3
1 bar
50
5 bar
40
10 bar
30
char yield in g/g coal (d)
char yield in wt.‐% (d)
90
20
20 200
400
600
800
1000
LB3
DK
HKN
KOL
PSK
IA
temperature in °C
Figure 1 a) Mass loss curves for all coals investigated at 1 bar, normalized to a start weight at 250 °C to eliminate first mass loss effects due to water release. b) Char yields at 1100 °C for 1, 5, and 10 bar. Table 2 Char yields for different pressures and coals, normalized to a start temperature of 250 °C. pressure in bar LB3 DK HKN KOL PSK IA 1 41.8 53.1 53.2 61.9 79.8 91.0 5 51.7 – 52.4 65.3 81.8 88.9 10 54.0 55.2 54.8 66.8 82.7 93.3
Curves of mass loss rate (DTG) display two maxima (see Figure 2). The first (100– 200 °C) is related to primary decomposition like water release, whereas the second (300– 500 °C; 400–700 °C) reflects the main pyrolysis. Figure 2 b) shows a shift of main peak maxima to higher temperatures with increasing coal rank – from 350 to 400 °C for brown coals, up to 500–600 °C for sub-bituminous coal PSK and anthracite IA. With decreasing peak maxima a widening of peaks takes place, meaning that the decomposition reactions proceed over a broad temperature range, best seen at PSK and IA. In contrast, a sharp peak form arises from higher reactivity and thus from faster devolatilisation – thermal decomposition takes places in a narrow temperature range of just 250 K for all brown
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coals and the Colombian sub-bituminous coal KOL. This behaviour can be explained by a general higher amount of volatiles (see Table 1) and therefore of functional groups for low rank coals, compared to sub-bituminous or even higher rank coals. The influence of pressure is shown for Lusatian brown coal LB3, where an increase leads to a higher char yield, as already depicted. Additionally, the peak of main pyrolysis is shifted to lower temperatures (from ca. 350 to 300 °C) and rises with higher pressure. Again, the effect is more prominent for the pressure increase from 1 to 5 bar than further to 10 bar (see Figure 2 a). This trend is not seen significantly in all coals! Similar results were found by Yang et al. [6] and Yun & Lee [5] for one of their studied coals. In contrast, Tomeczek & Gil [8] found decreasing char yields with increasing pressure for rapid heating pyrolysis (20–100 K/s) of sub-bituminous coal. They listed other references showing similar trends to their results, but noted that a comparison of influence of pressure is difficult due to different types of coal and definitions of volatile matter (water and ash free or analytical state) – significantly different heating rates might also be mentioned as a reason for contrary trends. 0.50
a)
char yield in wt.‐%
80 70
1 bar
0.45
5 bar
0.40
10 bar
60
0.35 0.30
50
0.25
40
0.20
30
0.15
20
0.10
10
0.05
0.30 LB3
b)
0.25
DK HKN
0.20
KOL PSK
0.15
IA 0.10 0.05 0.00
0.00
0 0
200
400
600
800
1000
mass loss rate in wt.‐%/K
90
mass loss rate in wt.‐%/K
100
0
100
temperature in °C
200
300
400
500
600
700
temperatur in °C
Figure 2 a) Influence of pressure on mass loss curve and first derivate of brown coal LB3. b) First derivate of mass loss (DTG curves) of all coals investigated at 1 bar.
3.2. Gas yield and composition The start temperature of gas release indicates the beginning of the formation (≥50 ppm) of the assigned gas species. Total gas yield is calculated by summation of yields over temperature. In Table 3 values for start temperature and total yield for H2, CO, CO2, N2, and CH4 are given in respect of coal type and pyrolysis pressure.
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Table 3 Start temperature for the release of different gas species and their total yield, depending on type of coal and system pressure. T start in °C p in bar LB3 DK HKN KOL PSK IA 1 561 475 499 573 624 615 H2 5 656 – 648 652 808 618 10 0 631 594 638 0 689 1 329 351 360 417 525 641 5 379 – 374 407 440 673 CO 10 290 356 281 163 387 191 1 190 434 435 397 328 432 5 515 – 561 640 703 769 CO2 10 442 164 426 191 333 634 1 374 510 497 424 461 477 5 399 – 383 445 451 0 N2 10 310 463 325 159 139 148 1 379 380 398 387 448 510 5 346 – 361 390 429 461 CH4 10 325 331 322 347 387 488 total yield in ml/gcoal LB3 DK HKN KOL PSK IA 1 349.1 1090.3 1267.9 182.1 112.8 349.8 H2 5 180.8 – 131.2 291.6 44.6 1335.7 10 0 39.9 171.9 134.3 0 73.8 1 971.6 831.8 836.2 399.1 202.3 226.1 CO 5 358.8 – 418.5 362.2 263.8 94.9 10 326.3 865 607.1 1038.5 647.4 284.6 1 2422.5 183 195.4 585.7 447.1 375.8 CO2 5 275.5 – 219.1 123.1 76.5 98 10 339.9 2223.8 397.5 1711.3 1190.7 113.7 1 126.2 37.8 36 69.8 45.7 35.3 N2 5 199.8 – 268.9 106.9 223.1 0 10 117 189.1 136.9 572.9 582.3 311.2 1 260.1 262.9 316 273.2 127.5 103.6 CH4
5
206.6
–
197.8
301
107.6
136.1
10 191.8 218 248.2 287.3 117.5 85.5 As can be seen from Figure 3 gas yields for 1 bar do not correlate with the amount of volatiles for each coal (compare Table 1), but show rather similar values of around 15–20 wt.-%. LB3 describes an exception, since it produces significant higher yields (43 wt.-%), which arise from large yields in CO2 (see
Table 3 and Figure 4 a), which in turn can be attributed to carbonate decomposition. The influence of pressure on gas yields does not follow a clear trend. For most coals 5 bar experiments display a yield minimum (except anthracite IA), whereas 10 bar leads to significant higher values for DK, KOL, and PSK (see Figure 3 b). So no distinction between brown coals and hard coals can be drawn in terms of gas yields. That LB3 shows its highest amounts at atmospheric pressure can also be explained by carbonate decomposition, since higher pressure depresses the CO2 formation for this reaction.
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a)
yield in wt.‐%
45
50
b)
1 bar
45
40
LB3
5 bar
35
DK
10 bar
30
HKN
30
25
KOL
25
20
PSK
20
15
IA
15
40 35
10
10
5
5
gas yield in g/g coal
50
0
0 0
200
400
600
800
1000
LB3
DK
HKN
KOL
PSK
IA
temperature in °C
Figure 3 a) Gas yield curves for all coals investigated at 1 bar. b) Char yields at 1100 °C for 1, 5, and 10 bar. The gas yield minimum at 5 bar is also reflected in CO and CO2 yields (see
Table 3) for almost all coals investigated (except PSK, where 1 bar displays the lowest CO value). Nevertheless, CO2 contributes stronger to the total gas yield due to its higher density (ρCO2=1.98 g/l, ρCO=1.25 g/l). This can also be seen in case of sub-bituminous coal PSK, where the minimum for CO yield occurs at 1 bar and for CO2 at 5 bar – same as for the overall gas yield. Note that total gas yields are given in g/gcoal, enabling the direct comparison with char yields, whereas yields of gas species are given in ml/gcoal. Start temperatures of CO formation at 1 bar lie between 330 and 360 °C for brown coals, rising up to 410 (KOL), 440 (PSK), and 670 °C (IA) with increasing coal rank. CO formation temperatures for 5 bar show almost the same trend and values as for 1 bar, whereas 10 bar values are generally lower, but fluctuate strongly between 160 and 390 °C over all coals. Start temperatures of CO2 display a maximum at 5 bar (following the same trend of coal ranks as CO), but display no trend for 1 and 10 bar experiments. The influence of coal rank on CO and CO2 start temperature indicates different formation mechanism, depending on coal structure, e.g. volatile matter. In general, for 5 bar experiments CO2 formation temperatures are 100–250 K higher than those of CO. In contrast, Chen et al. [9] found for two coals (low rank and sub-bituminous) CO2 to be produced between 300 and 700 °C and CO at 500 to 1100 °C, showing that CO formation starts later than CO2, but over a wider range (at 1 bar). Compared to our data at 1 bar one can find lower start temperatures for CO2 than for CO, at least for the three hard coals (KOL, PSK, and IA).
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Sum PyGas H2
yield in (ml/min)/g Coal
2.5
1600 1 bar
a)
b)
5 bar
CO
1400 1200
10 bar
CO2
2.0
1000
N2
1.5 1.0
CH4
800
COS
600
H2S
400
H2O
0.5
H2 total yield in ml/g Coal
3.0
200 0
0.0 0
200
400 600 800 temperatur in °C
1000
LB3
DK
HKN
KOL
PSK
IA
Figure 4 a) Yield curves for singles gas species, exemplarily shown for LB3, 1 bar. b) Total hydrogen yields in respect of coal type and pressure. The hydrogen yield shows a strong influence of pressure for the brown coals, whereat 1 bar leads to higher amounts than 5 and 10 bar (e.g. HKN, see Table 3 and Figure 4 b), which is in good agreement with Tao et al. [7]. For sub-bituminous coals (KOL and PSK) H2 yields are not much affected by pressure. In contrast, anthracite shows a contrary behaviour than brown coals and produces most hydrogen at 10 bar (which depicts the highest value at all), followed by 1 and 10 bar. This shows that crucial different mechanisms for hydrogen formation take place. Maximum temperatures for H2 are almost in all cases at 1100 °C, only at 10 bar LB3, DK and IA have lower temperatures of 820, 720, and 780 °C, respectively. Porada [10] found the formation maximum of H2 to be at ca. 720 °C for a middle rank coal investigated at 1 bar, which is in contradiction to our 1 bar data. Hydrogen formation for 1 bar pyrolysis starts at 480–560 °C for brown coals with slightly higher values (570–620 °C) for hard coals (see
Table 3). With rising pressure start temperatures increase (650–810 °), but show its maxima at 5 bar for all coals (except the anthracite, where the highest H2 start temperature occur at 10 bar). Methane shows also an increase in start temperatures with higher coal ranks, but a contrary behaviour to hydrogen in respect of pressure influence. Lowest formation temperatures are found at 10 bar (320–490 °C) and highest at 1 bar (ca. 50 K above), whereas 5 bar values lie in between. Hence, a clear and steady influence of pressure on the formation temperature of CH4 can be detected. Methane formation displays a yield maxima, whose temperature decreases from approximately 800 to 700 to 600 °C with increasing pressure (1, 5, 10 bar, respectively) for all coals investigated (more or less independent on coal rank). Arenillas et al. [11] noticed the maximum at 550 °C, Porada 10[10] at 460 °C, and Jong et al. [12] at 605 °C, which are all at lower temperatures than our findings for 1 bar. CH4 yields at 1 bar are higher for brown coals (260–320 ml/gcoal) than for sub-bituminous coals and anthracite (100–130 ml/gcoal), whereas KOL shows with ca. 270 ml/gcoal also relative high amount (see
Table 3). This can be explained by the low state of coalification, reflected in the high volatile content of brown coals and KOL. Pressure increase leads to decreasing CH4 yields for most coals, except KOL and IA, whereas the effect of pressure is more prominent for brown coals. Sub-bituminous coal KOL and anthracite IA display a maximum in methane yield at 5 bar. Tao et al. [7] found slightly increasing CH4 amounts with higher pressure and explained that by methane formation reactions from CO2 + 4 H2. Since methane values in our study drop with increasing pressure, this homogeneous reactions cannot be taken into consideration. Furthermore, secondary reactions between
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Oviedo ICCS&T 2011. Extended Abstract
char and gas seem to be the reason, since increased pressure hinders gases to exhaust from the char particle. Other gases like N2, H2S, COS, or H2O show no clear trends in formation temperature and total yields or occur in too small concentrations to be evaluated in a good quality.
4. Conclusions The influence of pressure on devolatilisation characteristics, e.g. char and gas yields as well as gas composition was investigated at coals of different rank. Following conclusions can be made: The char yield increase with coal rank and with increasing pressure. Also the peak of mass loss rate becomes higher and is shifted to lower temperatures with increased pressure. Gas yields cannot be correlated to coal rank. Additionally, the impact of pressure fluctuates for the different coals in terms of gas yields. It can be stated that most coals display a yield minimum for 5 bar, but also highest values for 10 bar are found. So no clear trend in pressure effect on total gas yields can be drawn. Yields of CO and CO2 reflect the 5 bar minimum of the total gas yield with changing pressure dependencies for different coals. H2 yield is strongly affected by pressure in case of brown coals, where maximum values are found for 1 bar. Anthracite, in contrast, has its maximum and minimum at 10 and 5 bar, respectively. For methane an increase in pressure causes decreasing start and maximum temperatures. With higher coal rank the start temperature rises for all pressures investigated. It can be summarized that pressure affects char and gas yields as well as gas composition, whereas for the latter no consistent trends for coal ranks or gas species can be detected. Acknowledgement. The investigations were financially supported by the German Federal Ministry of Economics and Technology, EnBW, Eon, RWE, Siemens, and Vattenfall within the research project “HotVeGas”.
References [1]
Cai HY, Güell AJ, Chatzakis IN, Lim JY, Dugwell DR, Kandiyoti R. Combustion
reactivity and morphological change in coal chars: effect of pyrolysis temperature, heating rate and pressure. Fuel 1996; 75:15–24 [2]
Roberts DG, Harris DJ, Wall TF. On effects of high pressure and heating rate during coal
pyrolysis on char gasification reactivity. Energ Fuel 2003; 17:887–95
Submit before 31 May 2011 to
[email protected] 9
Oviedo ICCS&T 2011. Extended Abstract [3]
Roberts DG, Harris, DJ. Char gasification with O2, CO2 and H2O: effects of pressure on
intrinsic reaction kinetics. Energ Fuel 2000; 14:483–9 [4]
Wall TF, Liu G, Wu H, Roberts DG, Benfell KE, Gupta S et al. The effect of pressure on
coal reactions during pulverized coal combustion and gasification. Prog Energ Combust 2002; 28:405–33 [5]
Yun L, Lee GB. Effects of pressure in coal pyrolysis by high pressure TGA. Korean J
Chem Eng 1999; 16:798–803 [6]
Yang H, Chen H, Ju F, Yan R, Zhang S. Influence of pressure on coal pyrolysis and char
gasification. Energ Fuel 2007; 21:3165–70 [7]
Tao W, Zou YR, Carr A, Liu J, Peng P.Study of influence on enhanced gaseous
hydrocarbon yield under high pressure–high temperature coal pyrolysis. Fuel 2010; 89:3590–7 [8]
Tomeczek J, Gil S. Volatiles release and porosity evolution during high pressure coal
pyrolysis. Fuel 2003; 82:285–92 [9]
Chen L, Zeng C, Guo X, Mao Y, Zhang Y, Zhan X et al. Gas evolution kinetics oft wo
coal samples during rapid pyrolysis. Fuel Process Technol 2010; 91:848–52 [10]
Porada S. The reaction of formation of selected gas products during coal pyrolysis. Fuel
2004; 83:1191–6 [11]
Arenillas A, Ruberiea F, Pevida C, Pis JJ. A comparison of different methods for
predicting coal devolatilisation kinetics. J Anal Appl Pyrol 2001; 58–59:685–701 [12]
Jong W, Nola G, Venneker BCH, Spliethof H, Wójtowicz MA. TG-FTIR pyrolysis of
coal and secondary biomass fuels: determination of pyrolysis kinetic parameters for main species and NOx precursors. Fuel 2007; 86:2367–76
Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
Brown coal and rape cake co-pyrolysis products in the range 5 to 40 per cent Authors: Josef Vales, Jaroslav Kusy, Lukas Andel, Marcela Safarova Brown coal research institute j.s.c. Budovatelu 2830, 434 37 Most, Czech Republic Corresponding author:
[email protected], +420476208627
Abstract This article summarises experimental results of thermal reprocessing – co-pyrolysis of the mix of brown coal and defined biomass amount (rape cake) and its influence on the yield and quality of pyrolysis products – solid carbon semi-coke, liquid and gaseous products.
1. Introduction Decreasing resources of noble energy raw materials [1] make for searching for alternative energy source for the future. Domestic energy sources and their qualitative parameters are reassessed in relation to available and technologically effectively advanced procedures of their possible processing and using while respecting development trends of legislatively allowable limit loads of environment. Coal deposits become more important because of the size of geologic and mineable resources (240 years) [1], their homogenous distribution over all continents and because of their possible conversion to gas and liquid fuels. As a matter of fact, every carbonaceous raw material (coal, carbonaceous waste, and biomass) can be transformed to gaseous medium. Innovative ways of processing are oriented to thermal re-processing of coal mass together with hydrogen and carbon rich substances, so called co-processes [2, 3].
2. Experimental section Pyrolysis is a technological process of a thermal re-processing of suitable charge without air access. Solid pyrolysis residue (pyrolysate) is a product of the pyrolyse. Liquid phase created from a mixture of pyrogenous water, oil, or tar (organic liquid), and a mixture of reaction gases is the product of the pyrolysis. The technology was used for producing oil and paraffin of shale in France in 1832 [5]. The process was significantly developed technologically at liquid fuel production by tar hydrogenation of coal in Germany before 1940 [4]. Submit before May 31st to
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Oviedo ICCS&T 2011. Extended Abstract
Aim of experiments Experimental works were focused to the determination of yield changes during the thermal reprocessing (co-pyrolysis) of the mixtures of brown coal with the different additions of rape cake under the same conditions.
Experimental laboratory testing unit and raw materials Laboratory pyrolysis unit (figure 1) with a rectangle shaped retort, indirect electric heating, and electronically setting of temperature program run was used for testing [6]. Gaseous products are discharged through an outlet and cooler to collecting box. Uncondensed gas is combusted in a burner. Solid pyrolysis carbonaceous residue remains on the retort bottom. Samples of granularity prepared charge raw material, i.e. pressed rape cake, brown coal, and mass defined charge mixtures – coal: cake with 1000 g total mass were input individually to the retort and tested. Tests ran under the same process conditions: temperature increase gradient, final temperature and the delay time. Qualitative parameters were assigned to charge raw materials and products [7, 8, 9, 10, 11, 12, 13, 14].
Fig. 1: Laboratory pyrolysis unit with retort Submit before May 31st to
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Oviedo ICCS&T 2011. Extended Abstract
For the co-pyrolysis experiments, brown coal mined in the coal mine named Důl Československé armády (CSA) and rape cake from the pressing of oil seed rape from the Preol, Lovosice. Basic qualitative parameters of the input raw materials are summarized in the table 1. Determination of the yield of the low temperature distillation according to the standard CSN ISO 647 [7] was also made. Results are in the table 2. Table 1: Qualitative parameters of the input raw material Parameter Wa Ad Std Cd Hd Nd Od Vd Qs d Qi d
[wt. %] [wt. %] [wt. %] [wt. %] [wt. %] [wt. %] [wt. %] [wt. %] [MJ/kg] [MJ/kg]
brown coal, ČSA 5,98 4,06 0,75 72,30 5,65 0,88 16,36 54,83 31,34 30,11
rape cake, Preol a.s. 6,31 6,36 0,68 49,12 7,20 5,26 31,38 78,11 21,99 20,42
Table 2: Yield of the tar, water, gas and semicoke from the low temperature distillation sample Brown coal ČSA Rape cake Preol a.s
TsKd [wt. %] 25,39 34,08
sK
d
[wt. %] 57,31 29,82
WsKd [wt. %] 8,43 20,80
GsKd [wt. %] 8,87 15,30
Pure brown coal, pure rape cake and their blends with the ratio 5, 10, 15, 20, 30 a 40 wt. % were tested. All samples were pyrolised under the same conditions – initial temperature 25 °C, heating rate of 2,47 °C.min-1, terminal temperature 650 °C with the 60 min of delay on this temperature.
Yields of pyrolysis tests Yields of laboratory pyrolysis tests obtained from the experiments with laboratory testing unit are shown in the table 3. Gaseous products were not measured, but they are calculated as a balance between 100 % and the sum of another products.
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Oviedo ICCS&T 2011. Extended Abstract
Table 3: Yields of pyrolysis tests Pyrolysis product
Batch, % mixture of coal : rape cake related to the yields of pyrolysis products
[wt. %] C-
mixture
mixture
mixture
mixture
mixture
mixture
R-
brown
C:R
C:R
C:R
C:R
C:R
C:R
rape
coal
95 : 5
90 : 10
85 : 15
80 : 20
70 : 30
60 : 40
cake
solid carbon
49,79
51,80
50,58
49,50
45,43
43,49
40,75
27,16
pyrogenetic water
12,64
13,70
14,55
15,06
16,49
17,06
18,60
22,33
tar
18,44
17,85
17,75
18,57
17,43
18,46
19,17
31,63
gas + loses
19,13
16,65
17,12
16,87
20,65
20,99
21,48
18,88
100
100
100
100
100
100
100
Sum of the wt. %
Solid carbonaceous products were analysed
according
to
Czech
100
standards
[8,9,10,11,12,13,14]. Elementar analysis was made on the analyzer Elementar Vario EL 3. Results of these analyses are showed in the table 4. Table 4: Qualitative parameters of the solid carbonaceous products of co-pyrolysis Parameter
Qualitative parameters of the solid carbonaceous products of co-pyrolysis
of the solid carbonaceous
C-
mixture
mixture
mixture
mixture
mixture
mixture
R-
product
brown
C:R
C:R
C:R
C:R
C:R
C:R
rape
[wt. %]
coal
95 : 5
90 : 10
85 : 15
80 : 20
70 : 30
60 : 40
cake
0,08
100 600
26.5
43.4
37.0
>100
700
30.7
35.2
28.1
>50
800
32.2
30.7
18.8
7.8
Reaction conditions: 750 °C, 30 min, Ni/Al2O3-MgO catalysts with 8 wt.% MgO reduced at 850 °C.
Figure 2 presents the XRD patterns of Ni/Al2O3-MgO catalysts calcined at 500-800 °C.
4
Oviedo ICCS&T 2011. Extended Abstract
With increasing calcination temperature, the intensities of XRD peaks of NiO-MgO solid solution in the catalysts increase, and Ni/Al2O3-MgO catalyst calcined at 800 °C has the most NiO-MgO solid solution. The Ni particles reduced from the catalyst highly disperse on the catalyst surface, leading to high tar yield and low carbon deposition on the catalyst [7]. 3500
o 800 C
NiO-MgO Al2O3 MgAl2O4 and/or NiAl2O4
3000
o 700 C
Intensity (a.u.)
2500 2000
o 600 C
1500 1000
o 500 C
500 0
40
50 60 2θ (degree)
70
80
Figure 2 XRD patterns of Ni/Al2O3-MgO catalysts calcined at different temperatures
3.4. Effect of reduction temperature Figure 3 shows the effect of reduction temperature of Ni/Al2O3-MgO catalysts on tar, water yields and CH4 conversion of PS coal pyrolysis under CH4/CO2. The tar, water yields and CH4 conversion over the catalyst reduced at 550 °C is 23.0, 5.2 wt.% and 0.8%, respectively. With the increase of reduction temperature, the tar, water yields and CH4 conversion increase. The formation of NiO-MgO solid solution in the catalyst reinforces the interaction of NiO and support, which increases the reduction temperature
Yield (wt.%, daf) and conversion (%)
of catalyst and results in the high tar yield [7].
30
20
10
0
Tar yield Water yield CH 4 conversion
550 600 650 700 750 800 850 o Reduction temperature ( C)
Figure 3 Effect of reduction temperature on tar, water yields and CH4 conversion of PS coal pyrolysis under CH4/CO2 (Reaction conditions: 750 °C, 30 min, Ni/Al2O3-MgO catalysts with 8 wt.% MgO calcined at 800 °C)
5
Oviedo ICCS&T 2011. Extended Abstract
4. Conclusions The Ni/Al2O3 catalyst promoted by MgO presents higher tar yield and lower water yield, CH4 conversion and carbon deposition than the catalysts promoted by CaO and BaO. The tar yield over Ni/Al2O3-MgO catalyst with 8 wt.% MgO is higher than that over the catalyst with 1 wt.% MgO for the formation of more NiO-MgO solid solution in the catalyst. With increasing the calcination temperature, more NiO-MgO solid solution is formed in the catalyst, so Ni/Al2O3-MgO catalyst calcined at 800 °C provides the highest tar yield. With the increase of reduction temperature, more Ni particles are reduced from the catalyst and highly dispersed on the catalyst, which results in the improvement of catalyst activity. Acknowledgement This research was performed with the support of the National Natural Science Foundation of China (No. 20576019, 20776028), the National High-Tech R&D Program (863 Program), the Ministry of Science and Technology, China (No. 2008AA05Z307), and the National Basic Research Program of China (973 Program), the Ministry of Science and Technology, China (No. 2011CB201301). References [1] Egiebor NO, Gray MR. Evidence for methane reactivity during coal pyrolysis and liquefaction. Fuel 1990; 69: 1276-82. [2] Liao HQ, Li BQ, Zhang BJ. Co-pyrolysis of coal with hydrogen-rich gases. 1. Coal pyrolysis under coke-oven gas and synthesis gas. Fuel 1998; 77: 847-51. [3] Smith GV, Wiltowski T, Phillips JB. Conversion of coals and chars to gases and liquids by treatment with mixtures of methane and oxygen or nitric oxide. Energy & Fuels 1989; 3: 536-7. [4] Liu JH, Hu HQ, Jin LJ, Wang PF. Effects of the catalyst and reaction conditions on the integrated process of coal pyrolysis with CO2 reforming of methane. Energy & Fuels 2009; 23: 4782-6. [5] Horiuchi T, Sakuma K, Fukui T, Kubo Y, Osaki T, Mori T. Suppression of carbon deposition in the CO2-reforming of CH4 by adding basic metal oxides to a Ni/Al2O3 catalyst. Applied Catalysis A: General 1996; 144: 111-20. [6] Mehr JY, Jozani KJ, Pour AN, Zamani Y. Influence of MgO in the CO2-steam reforming of methane to syngas by NiO/MgO/α-Al2O3 catalyst. Reaction Kinetics and Catalysis Letters 2002; 75: 267-73. [7] Yamazaki O, Tomishige K, Fujimoto K. Development of highly stable nickel catalyst for methane-steam reaction under low steam to carbon ratio. Applied Catalysis A: General 1996; 136: 49-56.
6
Programme topic: Coal pyrolysis and liquefaction
Kinetics of co-pyrolysis of high- and low-sulfur coal blends with additives L. Butuzova1, R. Makovskyi1, V. Bondaletova1, D. Dedovets2, G. Butuzov1 1
Donetsk National Technical University, 58 Artema str., Donetsk 83000, Ukraine, tel. fax: +38(0622) 55-85-24,
[email protected] 2
[email protected] National Academy of Sciences of Ukraine, L.M. Litvinenko Institute of Physical Organic Chemistry and Coal
Chemistry, 70 R.Luxemburg str., Donetsk 83114, Ukraine
Abstract The thermogravimetric studies of a pyrolytic decomposition of blend based on low- and highsulfur coals with additives (components of coal-tar and radical polymerization initiator) were carried out. Thermokinetic analysis demonstrated that thermal decomposition of the chemically treated bland proceeds more intensely than for the original bland and permits variation in the gas evolution rate on the different stages of pyrolysis process. Keywords: sulfur coals, pyrolysis, kinetics 1. Introduction Previous investigations indicate that the dependence of the coal structure and reactivity on sulfur content is fairly strong [1-2]. But there no a comparative data in the scientific literature about the thermal behaviour of low- and high-sulphur coals of the same rank in coking blends and in presents of additives. Developments of pretreatment methods for sulfur coals are especially desirable for reduction of the sulfur content in pyrolysis products and for the control of caking ability. The components of coal-tar and radical polymerization initiator are deemed as the most effective additives for cokemaking and for a study of the pyrolysis mechanisms [3]. The effectiveness of such materials at the different stages of pyrolysis process was compared. The aim of this paper is a detailed study of the kinetic behaviour of low- and high-sulphur coals and their blend during pyrolysis with additives using thermogravimetry method and elucidation of usability of the thermokinetic analysis for coke properties determination. 2. Experimental Experiments were conducted on the pairs of petrographically homogeneous low- and highsulphur bituminous coals of Donets Basin. It was high-sulphur coal of J-Grade (JRC: Cdaf = 87,3; Vdaf =31,7; Sdt =2,81) and low-sulphur coal G-Grade (GLRC: Cdaf =85,1; Vdaf=36,0; Sdt =1,22) according to Ukrainian classification and their blend (50:50). The samples were treated by radical polymerization initiator (acrylic acid dinitrile - AAD) and by the components of coal tar (pitch, anthracene, phenanthrene). The radical polymerization initiator was introduced to affect the course of radical reactions. Other additives were used as possible analogues of the
components, of liquid semi-coking and coking products which are known to be responsible for synthesis reactions during coking. The thermal behaviour of coal blends were studied by thermogravimetric analyses and standard Sapozhnikov metods (GОSТ 1186-87). The thickness of plastic layer (y) and the contraction (x) by Sapozhnikov’s method was applied as characteristic of coal coking ability. Derivatogrammes were registered in a Q-1500D derivatograph of Paulic- Paulic-Erdei system at the rate 100C/min in a closed platinum crucible under the layer of quartz sand up to 10000C. The kinetic parameters, i.e. the activation energy E and the rate of decomposition in different periods of pyrolysis were calculated by the results of the continuous measurement of the weight loss. 3. Results and discussion Behaviour of the mass loss curves indicates that the blends decomposition process may be presented as a sum total of seven independent steps (linear parts on the curve TG). A Table 1, 2 shows the values of temperature intervals and corresponding mass loss for different steps of pyrolysis process. Table 1 – The temperature intervals for independent steps of coals pyrolysis process. The temperature intervals for different steps*, °C
Coals, blends
Additive
(50:50)
I
III
IV
V
VI
VII
J RC
–
100-140 350-415
415-480
480-595
595-867
867-930
G LRC
–
75-125
327-400
400-472
472-504
504-573
573-894
GLRC+JRC
–
70-140
328-400
400-477
477-542
542-700
700-900
GLRC+JRC
AAD
75-180
350-420
420-455
455-530
530-757
757-900
GLRC+JRC
pitch
60-150
340-400
400-485
485-542
542-720
720-880
GLRC+JRC
anthracene
30-110
190-395
395-480
480-588
588-700
700-885
GLRC+JRC
phenanthrene
50-110
170-400
400-473
473-573
573-700
700-900
* II step is occurred without mass loss
It can be seen from the Table 2, that the most intensive decomposition of J RC sample are occured at the IV-VI steps which is known to be related to formation of the main bulk of the semi-coking products. The periods of the most intensive decomposition of GLRC coal are the IV and VII steps. VII period (coking state) is characterized by a much higher rate of volatile products evolution from the solid phase as compared to the previous. Thermal decomposition of blend is characterized by a comparative deceleration of the mass loss at the V, VI steps in comparison with J RC.
Introduction of the radical polymerization initiator AAD results in acceleration of the gas evolution rate at the first - third steps (in a three or two-fold) and shift the temperature range of these stages to higher temperatures. Таблиця 2 – Kinetic of the mass loss during independent steps of coals pyrolysis process, %. Coals,
Additive
Mass loss at different steps Σ∆
I
III
IV
V
VI
VII
2
3
4
5
6
7
8
9
J RC
–
0,47
1,64
7,74
6,57
11,26
9,38
37,06
G LRC
–
2,11
3,29
8,92
1,41
5,87
15,96
37,56
GLRC+JRC GLRC+JRC GLRC+JRC GLRC+JRC GLRC+JRC
– AAD pitch anthracene
1,88 6,10 1,88 2,81 2,35
1,88 3,29 2,35 3,99 5,16
8,45 5,16 8,92 8,45 7,74
5,16 7,28 5,16 7,74 6,81
7,04 9,62 11,97 4,92 5,40
10,79 8,21 9,39 10,32 10,33
35,43 39,66 39,66 38,23 37,79
blend (50:50) 1
phenanthrene
There are reasons to believe that this acceleration appears due to scission of inter- and intramolecular bonds, including -C-S- bonds. This hypothesis is supported by the lowermost value for the activation energy for AAD-treated sample (Table 3). The removal of sulfur-and oxygen-containing groups causes a decrease in the rate of mass loss at the IV stage due to increases the thermostability of solid fuel. Decomposition rate increases at V and VI steps (semicoking) and decreases during coking (VII period) under the action of AAD. This is indicative of the formation of more condensed structures by polyrecombination reactions. Table 3 Thermokinetics parameters for the most intensive decomposition step in derivatograms of investigated coals and blends. Ee, kJ/mol
7,04
1,56
75,06
380-485
9,15
2,13
57,67
440
380-495
8,45
1,92
67,58
AAD pitch
430 450
380-512 390-505
11,03 8,92
2,57 1,98
40,20 54,66
GLRC+JRC
anthracene
440
400-505
10,79
2,45
42,29
GLRC+JRC
phenanthrene
440
395-512
11,26
2,56
40,81
Additive
Tm, Ka), °C
(Ti-Tf) b), °C
J RC
–
450
395-512
G LRC
–
430
GLRC+JRC
–
GLRC+JRC GLRC+JRC
blends (50:50)
a)
%
∆
r c) mg/(min ·g)
Coals,
Tm - temperature of maximum reaction/process rate; initial state; c) relative rate of thermal decomposition,
b)
at Tm
Tf - temperature of the final state, Ti - temperature of the
These data confirm that the addition of AAD to coal blend modifies the plastic layer: the thickness of plastic layer increases from 14.5 to 15.5 mm and the contraction increases
substantially from 27 up to 36 mm whereas the mechanical strength of coke is stable. As can be seen from Table 3, the influence of all additives results in a decrease the values of E and a change the ratio of the rates of destruction and synthesis reactions. The influence of pitch is more pronounced only at the VI step. The rate of organic sulfur decomposition was highest in the same temperature range [4]. Moreover the total sulfur content in the obtained cokes was less than 1.5 %. There are reasons to believe that the pitch intensifies desulphurization process and improves of the coking ability of blends. When anthracene and phenanthrene were added, an intensification of gas evolution processes at I, III and V stages and a significant deceleration of blend decomposition at VI stage are observed. The presence of these additives in the blend shifts the temperature region of the third stage to lower temperatures. Probably, highly condensed aromatic structures help to stabilize the free radicals present in reaction media with subsequent promotes of polyrecombination reactions at VI stage. Thermostability of linear structures is higher than angular. Therefore upon the effect of phenanthrene the conversion degree is increased from 1.88 to 5.16 at III stage. The reason for this is the lower value of the effective activation energy (Ee) in the process of vapour-gaseous products formation for phenanthrene in comparison with anthracene (depending on mutual arrangement of aromatic rings and variation in paramagnetic centers concentration). Thus, treatment with AAD, anthracene and phenanthrene has exerted considerable effects. Thermo-chemical destruction promotes impoverishment of solid products with sulfur- and oxygen-containing groups, i.e. it improves their quality. These reactants act as radical polymerization initiators, thus increasing the yield of semi-coke (Table 3) and coke (Table 2) as compared to untreated blend. Accordingly, there are many grounds for believing that these methods of coal pre-treatment are a promising for low quality coals processing. 4. Conclusions Chemical pretreatment has a considerable influence on the kinetics of co-pyrolysis of sulfur coalcontaining blends. The use of additives (components of coal-tar and AAD) shows the possibility to manage of the rate and mechanism of the separate stages of pyrolysis process. References [1] Butuzova, L., Safin, V., Marinov, S., Yaneva, N., Turchanina, O., Butuzov, G. The pathways for thermal decomposition of coals with high content of sulphur and oxygen Geolines, Academy of Science of the Czech Republic. 2009;22:15-9. [2] Mianowski A. Butuzova L., Radko T. Turchanina O. Thermokinetic analysis of decomposition of Ukrainian coals from Donets Basin. Bulletin of geosciences. 2005;80,№ 1:39-44. [3] Fernandez A.M., Barriocanal C., Diez M.A., Alvarez R. Influence of additives of various origins on thermoplastic properties of coal. Fuel. 2009;88:2365-72 [4] Gryglewicz G. Sulfur transformations during pyrolysis of a high sulfur Polish coking coal. Fuel. 2009;74,№ 3:356-61.
Oviedo ICCS&T 2011. Extended Abstract
Effect of elemental composition of various additives on the modification of coal thermoplastic properties
M.G. Montiano, C. Barriocanal, R. Alvarez
[email protected] Instituto Nacional del Carbón, CSIC, Apartado 73, 33080 Oviedo. Spain
Abstract A bituminous coal normally used in the cokemaking industry was selected as base coal for studying the modification of its thermoplastic properties due to the addition of two different sawdusts. 1. Introduction The iron and steel industry is a major greenhouse gas (GHG) emission source. The introduction of biomass into the steel industry either as a substitute for coal in the blast furnace or as a component of coal blends for coking has been considered as a way to reduce CO2 emissions [1-3]. Coal thermoplastic properties are considered to be of great importance for the formation of the structure of metallurgical coke and consequently their properties. The use of additives modifies this behaviour by either improving it or causing it to deteriorate [4,5]. The modification of thermoplastic properties of coal can be assigned to physical and chemical factors [4]. Our aim is to study the effect of the amount of heteroatms present in the biomass on the coal’s plastic properties. To that end, two waste sawdusts were heated up to 250°C in order to reduce their oxygen content and added to a bituminous coal to study the effect on coal thermoplasticity.
2. Experimental section 2.1.Materials One bituminous coal (G) and two waste sawdust were selected: chestnut sawdust (SC1) and oak sawdust (SR1). The Proximate analyses were performed following the ISO562 and ISO1171 standard procedures for volatile matter and ash content, respectively. The elemental analyses was carried out using a LECO CHN-2000 for C, H and N content (ASTM D-5773), a LECO S-144 DR(ASTM D-5016) for sulphur and a LECO VTF-900 for direct oxygen determination.
1
Oviedo ICCS&T 2011. Extended Abstract
2.2.Materials The TG/DTG analysis of the coal and the additives was carried out using a TA Instruments SDT 2960 thermoanalyser. Samples of 10-15 mg with a particle size of 98wt%) of anthracene and carbazole are required. Most of anthracene and carbazole are separated from coal tar now. And it is difficult to acquire high purity and high recovery rate. In this study, we developed a separation method to get the higher purity of anthracene and carbazole from crude anthracene: remove phenanthrene with xylene firstly, then refine anthracene and carbazole with solvent I (added 10% additive F) by using liquefying crystal. The result showed that with this new solvent separation method the recovery rate of anthracene and carbazole purity higher than 90wt% and 97wt% would be at more than 82% and 73% respectively in one pass. Besides, the developed solvent can be easily recycled, met with environmental requirements and is featured with products of good quality. Key words: coal tar; anthracene; carbazole; solvent; separation 1 Introduction Anthracene(An), phenanthrene(Phe) and carbazole(Car) are the important nonrenewable chemical resources for dyes, pharmaceuticals, photoelectric materials etc[1-3]. And their demands increased yearly. For fine chemicals manufacture, anthracene/carbazole with a purity >98% is required. Although anthracene and carbazole could be synthesized by chemical method now[4], they were separated and purified from crude anthracene of coal tar yet due to the cost and waste issues. So many researchers become concerned about the purity and recovery rate of products. And it is not an easy task to separate and collect them with high purity because the amounts of the main components of crude anthracene varied with the coals and coal processing, the purity of anthracene and carbazole could only reach about 97% at present. Most of the method used for getting high purity products must combine with solvent method. The key of solvent method is the selection for available and suitable solvent used in the processing. But so far, there are very few organic solvents used, such as benzole, dimethylformamide(DMF), pyridine and so forth, and a
few potential solvents were not reported. Furthermore, the essential difference between those solvents is lack of theoretical study. Here, we developed a separation method to get the higher purity of anthracene and carbazole from crude anthracene: remove phenanthrene firstly, then refine anthracene and carbazole by using liquefying crystal. The factors of having strong influences on the purity and recovery rate of products, such as solvent types, ratios of solvent, temperature of dissolution and crystallization were carefully investigated. 2 Experimental Refining of crude anthracene Crude anthracene used in this experiment is offered by One Steel factory, China (contained anthracene 40.94wt%, phenanthrene 21.01wt%, carbazole 18.94wt%). The solvent used here are acetophenone, DMF, xylene, methylene chloride (analytical grade) 200# solvent oil and oxygen containing solvent I. Add a certain amount of crude anthracene and solvent in flask equipped with blender, reflux condenser pipe and thermometer tubes with mixer, stir and heat until the solids are completely dissolved, heat up to a certain temperature and keep for 30min, then filter at about 40◦C under vacuum, and the cake was washed by solvent and dried under room temperature, and used for raw material of anthracene and carbazole. The filtrate was placed in a rotary evaporator (Buchi R-200, Switzerland) under vacuum until completely dry. And the residue used as raw material of phenanthrene. Gas chromatographic analysis. GC was performed on a Shellomadzu GC 2014 (Japan) with a Rtx®-5 (USA) capillary column (0.32mmх30m), wall-coated with 5% dipheny/95% dimethyl polysiloxane, film thickness 0.25µm. Using hydrogen flame ionization detector (FID). The temperature program was: 170◦C (0.4µL injection volume), keeping for 1min, then 3.5◦C/min to 200 ◦C, holding for 1min, then 10◦C/min to 250◦C. The internal standard curves method with fluorenone as internal standard substance is used for quantity. The chromatogram of the standards and the calibration curves is shown in Figure 1 and Figure 2, respectively.
200000
10.528 / Carbazole
50000
9.738 / Anthracene
100000
9.563 / Phenanthrene
8.780 / 9-Fluorenone
Intensity
150000
0 8
9
10
11
min
Figure 1 Gas chromatogram of the standard of anthracene, phenanthrene, carbazole and fluorenone
3.0
2.5
Anthracene Phenathrene Carbazole
Ai/As
2.0
1.5
1.0
yAn=1.6910x+0.0211 yPhe=1.9515x-0.0240 yCar=1.6206x-0.0321
0.5
0.0 0.0
0.2
0.4
0.6
0.8
1.0
R=0.99804 R=0.99918 R=0.99909 1.2
1.4
1.6
c ( mg/mL)
Figure 2 Calibration curves of anthracene, phenanthrene and carbazole 3 Results and Discussion 3.1 Choice of solvents By liquefying crystal, the separation and refining of anthracene, carbazole and phenanthrene is according to different solubility and volatility in different solvent. Phenanthrene has higher
solubility in most solvent, and it is easier to remove. And the solubility of anthracene is very low in almost all kinds of solvent; the solubility of carbazole is high in nirogen and oxygen cotaining solvents, such as DMF and N-methyl-2-pyrrolidone(NMP), but low in benzene solvent, so the separation of anthracene and carbazole depends on the solubility and selectivity. The purpose of using liquefying crystal is to remove the phenanthrene, fluorene and oil impurities to gather carbazole and anthracene components, so the problem is how to improve the solvent selectivity and dissolution of carbazole and anthracene. And the selectivity and solubility of the solvent could be reflected by the phase diagram and solubility curve. Carbazole o
A
0.0
45 C o 60 C o 70 C
1.0
0.2
0.8
0.4
0.6
0.6
0.4
ⅣⅣⅣⅣ ⅡⅡⅡⅡ
0.8
0.2 ⅠⅠⅠⅠ
1.0
DMF 0.0
0.0
0.2
0.4
0.6
0.8
1.0
Anthracene
Note: I- Crystallized area of anthracene, II –Crystallized area both of anthracene and carbazole, III- Crystallized area of carbazole, IV -Homogeneous area
Carbazole 0.94
B 0.95
o
30 C o 60 C
0.06 0.05
0.96
0.04
0.97
0.03
0.98
0.02
0.99
0.01
1.00
0.00
Xylene 0.00
0.01
0.02
0.03
0.04
0.05
Anthracene
0.06
Carbazole C
0.88
30oC 60oC
0.12
0.90
0.10
0.92
0.08
0.94
0.06
0.96
0.04
0.98
0.02
1.00 0.00
0.00 0.02
0.04
0.06
0.08
0.10
0.12
Acetophenone
Anthrancene
Fgure 3 Phase diagram of the ternary anthracene-carbazole-DMF(A)/ Xylene(B)/ Acetophenone(C) system In the ternary anthracene-carbazole-DMF system (Figure 3A), the crystallized area is large for both of anthracene and carbazole, especially for anthracene. And the selectivity of carbazole is higher than anthracene in acetophenone (Figure 3C). So DMF and acetophenone are relatively appropriate solvents to get high pure anthracene.
In the ternary anthracene-carbazole-xylene system (Figure 3B), the crystallized area is very small for both of anthracene and carbazole. Therefore, when using xylene, the necessary solvent ratio is very big. So xylene is not the ideal solvent for refining of anthracene. However, the crystallized area of carbazole is larger than that of anthracene, it could be used to refine carbazole. 3.2 Influence of the ratios of solvent for enrichment of anthracene and carbazole. The ratios of solvent affect the purity and recovery rate of products during processing[5], so we investigated the ratios of solvent from 0.5 to 3.0. The study used crude anthracene 50g, with xylene as solvent, dissolving at 100oC and crystallizing at 40oC, respectively. The results were presented in Table 1. With the ratios of solvent increasing, the purity of the products increased too. However, the recovery rate was maximum at 1.5. And it has a satisfactory result with xylene as solvent to remove phenanthrene in the first step, the contents of dried cake are as following: anthracene 57.72wt%, carbazole 27.92wt% and phenanthrene 14.33wt% in one pass. 3. 3 The selectivity of solvent I. The experiment had compared the refining effect of different solvent: DMF, acetophenone and solvent I (oxygen containing solvent). The results showed that (Table 2), when using solvent I, the purity of anthracene is slightly lower than using acetophenone and DMF, while the recovery rate is the highest. So we select solvent I for further study. Although the solvent I has good selectivity, the recovery rate of anthracene is still lower, about 69%. To make full use of anthracene resources and to improve the recovery rate of anthracene, amine additive (F) is introduced. And the addition proportion was investigated under two temperature of 70oC and 100oC. The results are as follows (Table 3). From Table 3, we can find when additive F is increased from 0%(V/V) to 5%(V/V), the recovery rate is increased about 10%, and the purity of anthracene is also increasing. The reason is probably that additive F can restrict the solubility of anthracene and increase the solubility of carbazole in solvent I [6]. Table 1 Influence of ratios of solvent on the purity and recovery rate of anthracene and carbazole Ratios of Solvent 0.5 1.0 1.5 2.0 3.0
An 45.32 53.56 57.72 59.65 63.15
Content/wt% Car 21.11 24.62 27.95 28.48 30.08
Phe 33.57 21.82 14.33 11.87 6.77
Recovery Rate /% An Car 79.15 75.78 88.85 83.95 92.22 91.82 80.67 79.17 70.06 68.60
Table 2 Experimental result of solvent I Heating temperature/◦C
Solvent Solvent I Acetophenone DMF
130 140 130
Recovery rate of An /%
Content/wt% An 84.56 86.42 85.64
Car 7.32 6.56 6.21
Phe 8.12 7.02 8.15
69.58 56.14 52.68
Table 3 The influence of addition of F in solvent I on refining anthracene F/% 0 5 10 0 5 10
Temperature/oC 70 70 70 100 100 100
Content/wt% 84.56 91.12 93.48 83.42 90.86 92.28
Recovery rate of An/% 69.58 80.42 83.86 68.32 79.84 82.72
Table 4 Refined effects of 200# solvent oil, methylene chloride and xylene for carbazole
No. of refining 1 2 3 Total
200# solvent oil Methylene chloride Recovery Recovery Content/wt% Content/wt% rate/% rate/% 53.10 89.00 71.40 52.90 88.90 86.50 80.60 78.60 90.80 88.40 87.50 86.70 62.49 33.10
Xylene Content/wt% 55.50 89.20 97.20
Recovery rate/% 96.70 91.90 89.20 72.78
3.4 Refining of carbazole. We used xylene to refine carbazole. The solvent ratio is 1.5 for the first pass, and the ratio increased to 2 for the second and third pass, with heating and filtering temperature at 40 oC, and the results are as follows (Table 4). The results suggested that the purity of carbazole is increased with the refining numbers. Meanwhile, the loss of carbazole is increased either. So the number of washing pass cannot be too many. When using xylene as the solvent, the purity of carbazole can reach 97.20% and total recovery rate is 72.78% after being washed three times. 4. Conclusions With the new solvent separation method: remove phenanthrene with xylene firstly, then refine anthracene and carbazole by solvent I with 10% additvie F using liquefying crystal, the recovery rate of anthracene and carbazole purity higher than 90wt% and 97wt% would be at
more than 82% and 73% respectively in one pass. And this new solvent system could improve the selectivity of anthracene and carbazole and changed their liquid-liquid partition. Besides, the developed solvent can be easily recycled, met with environmental requirements and is featured with products of good quality. Acknowledgment This work was supported by the Taiyuan Scientific and Technological project(11014907) and Jiangdu Refining Chemical Company. References [1] Zhang YD, Wada T, Sasabe H. J. Mater. Chem. 1998, 8(4), 809-828 [2] Grazulevicius JV, Strohriegl P, Pielichowski J, Pielichowski K. Prog. Polym. Sci. 2003, 28, 1297-1353 [3] Wang ZQ,Zheng CJ, Liu H,Ou XM, Zhang XH. Science China(Chemistry) 2011, 54(4), 666-670 [4] Vlčko M, Cvengrošová Z, Cibulková Z, Hronec M. Chinese Journal of Catalysis 2010, 31(12), 1439-1444 [5] Song YX, Hu ZQ, Gao JS. Coal Coversion 1999, 22(2), 94-96(In Chinese) [6] Gao JS, Zhou XP, Wang ZH, Hang YZ. Shanghai Chemical Industry 1994, 19(6), 1922(In Chinese)
STUDY OF COAL, CHAR AND COKE FINES STRUCTURS AND THEIR
PROPORTIONS
IN
THE
OFF-GAS
BLAST
FURNACE
SAMPLES BY X-RAY DIFFRACTION 1
A.S. Machado*, 2A.S. Mexias, 1A.C.F. Vilela, 1E. Osório.
1
Iron and Steelmaking Laboratory, UFRGS, Porto Alegre, Brazil.
2
X-Ray Diffractometry Laboratory, UFRGS, Porto Alegre, Brazil.
*
[email protected] Abstract Four dust samples were collected in the BF off-gas for this investigation, two at all coke and two at Pulverized Coal Injection (PCI) operations. The atomic structure of raw coke, chars and their parent coals used in PCI were investigated. This study has showed that the XRD technique could be used as a standard procedure to identify the char and coke structures. This technique was used to quantify the fines proportions of these carbonaceous materials in the BF flue dust samples. It was also showed the unexpected presence of coke fines in the flue dust fractions smaller than 63μm. The quantification of the carbonaceous material content in the BF off-gas samples could be used to improve the PCI performance in operating BF. Keywords: char, coke fines, X-ray diffraction, pulverized coal injection, Blast Furnace, graphitization.
1. Introduction The Blast Furnace (BF) is the most important technology for production of iron for steelmaking [1]. In the last decades, the PCI rates have increased in the most of BFs, achieving an injection rate between 150 — 220 kg/thm [2]. One of the problems during the PCI operation in BF, especially at high injection levels, is the increase in the formation of unburnt char, which could accumulate in the near raceway region. This material could harm the burden permeability. Higher char levels in the BF dust samples are related to insufficient coal combustibility and to an unstable furnace operation [3]. The quantification of the carbonaceous content in these samples could be used in the coal selection and to improve the PCI performance [3,4].
The BF off gas solid samples (flue dust and sludge) basically contain metallic oxides and carbonaceous materials. The carbon in BF dust samples is originated from coke fines, char and some unconsumed pulverized coal [4,5]. Chemical analyses in the BF dust samples do not reveal some carbonaceous material. Optical microscopy is used to study the off gas solid samples [5,6], but it can lead to some ambiguous results, since char mixed with ash are very fine and lack unique morphological features [3]. X-ray diffraction (XRD) technique has been utilized to determine the crystallite sizes (Lc, La, etc.) in carbonaceous materials [7]. Since the coke structure is more ordered than the char structure, it would be possible to quantify the proportion of these materials in the BF off-gas samples by chemical analysis in combination with XRD [3]. The aims of this work are to study coal, char and coke structures by XRD and to quantify carbonaceous components (char and coke fines) in the flue dust BF samples at all coke and PCI BF operations through the use of the XRD technique and ultimate analysis.
2. Experimental section The methodology conducted in this study is composed of: (1) chemical and granulometry analyses; (2) production of chars in a raceway simulator; (3) the chemical treatment used to demineralize the samples; (4) XRD and the mathematical characterization of their profiles to obtain Lc (average stacking height) values.
2.1 Raw and carbonaceous materials characterization Four flue dust samples collected in the BF off-gas (FD-AC1, FD-AC2, FD-AP1 and FD-AP2), three coal samples (CA, CB and CAB) and their laboratory produced chars (ChA, ChB e ChAB) and one metallurgical coke sample (CK), obtained from a Brazilian company, were selected for this work. The char ChAB and the coke fines of the 250-425μm fraction of the flue dusts (CKFD-AC1, CKFD-AC2, CKFD-AP1 and CKFD-AP2) were utilized as a standard for the quantification of the percentage of char and coke fines in the BF flue dust [4]. The char samples were made in a laboratory rig that simulates the behavior of fines injected into the raceway. The coal CAB is a mixture of coals CA and CB utilized in PCI. The flue dust samples FD-AC1, FD-AC2 were obtained from all coke BF operations and samples FD-AP1, FD-AP2 from PCI BF operations. Chemical analyses of the coal and coke samples were carried out. A granulometric analysis of coal CAB was conducted. The dust samples were mechanically separated in seven
different sizes ranging from 425μm [4]. The separation was conducted to verify how the carbonaceous particles are distributed in the dust and to identify the possible fractions composed by char or coke. All coals, coke and flue dusts fractions were demineralized to avoid the effect of mineral matter on the quantitative analyses by XRD.
2.2 X-ray diffraction – carbonaceous structure characterization XRD analyses were carried out on an X-ray Powder Diffractometer using CuKα over an angular range of 5–115° (0.05° x 4s). The XRD traces were subjected to a series of mathematical treatments and the Lc value was determined according to the Scherrer equation [9]. The carbonaceous average stacking height value (Lc or L002) has been used to characterize the dimension of the crystalline carbon (crystallites) in all samples. Since the coke structure is more ordered than the char structure, the percentage of these materials in the BF flue dust samples were quantified on the basis of a suitable calibration using char and coke standards combining XRD and carbon elementary analyses [3,4].
3. Results and discussion
3.1 Samples characterization Chemical analyzes of the coal and coke samples are summarized in Table 1. The granulometric analyses of the coal CAB showed practically no particles above 150μm, and its char particles will probably not exhibit sizes above 250μm as described in literature [8]. Table 1 — Summary of chemical analyzes of the selected coals and coke
Item Proximate: (dry base), %
Ultimate: (dry base), %
CA
CB
CAB
Coke
Volatile matter
24,46
14,42
19,04
1,21
Fixed carbon
66,11
74,24
70,22
89,18
Ash
9,43
11,34
10,74
9,61
Carbon
75,92
76,84
76,82
90,17
Hydrogen
6,26
5,60
5,69
0,11
Nitrogen
1,72
1,64
1,70
1,39
Sulfur
0,53
0,71
0,60
0,61
Oxygen
6,14
3,87
4,45
—
Carbon content and inorganic matter content of the selected flue dusts are provided in Table 2. BF flue dusts basically contain metallic oxides and carbonaceous materials. Carbon in BF dust samples originated from coke, char and some unconsumed PCI coal [4,5]. Table 2 – Carbon and inorganic matter contents of the flue dusts FD: AC1, AC2, AP1 and AP2
BF — all coke
Item
BF — PCI
FD-AC1
FD-AC2
FD-AP1
FD-AP2
Carbon (dry base), %
38,91
40,15
43,57
36,66
Inorganic matter (dry base), %
59,97
55,23
57,06
61,60
Figure 2 compares the distribution of the carbon content in each size range of dust samples FD-AC1, FD-AC2, FD-AP1 and FD-AP2. The proportion of carbon fines in the dust samples less than 63μm is insignificant, smaller than 1%. According to Gupta et al. [4], the high carbon content found in size ranges greater than 90μm are associated to a higher generation of coke fines in these samples. The authors considered that the size range greater than 250μm is composed exclusively by coke fines.
Figure 1 – Weight of carbon in seven size ranges of dust samples FD-AC1, FD-AC2, FD-AP1 and FD-AP2
3.2 X-ray diffraction — coal-char and coke fines quantification Figure 2a shows the reduced intensity of XRD profile of coal CAB and its char ChAB. The L002 of char ChAB was higher than its parent coal CAB indicating slightly higher crystalline order of carbon. Figure 2b shows the reduced intensity without the XRD
background of the standards ChAB, CK, CKFD-AC1 and CKFD-AP1. It is clear in the figure that the structure of coke samples are more ordered than char structure (narrow peak Æ bigger L002). The coke fines in the flue dust size fraction 250–425μm is the most graphitized fraction in the dust (Tab. 3), and according to Sahajwalla et al. [8] this size fraction is a better representative of the residual coke fines (coke standard) in the BF flue dust.
(a)
(b)
Figure 2 – a) Comparison of reduced intensity of XRD pattern of the CAB and ChAB; b) Comparison of X-ray spectra and profile of 002 carbon peaks for the standards ChAB, CK, CKFD-AC1 and CKFD-AP1
The XRD spectra and profile of (002) carbon peaks in seven size ranges of dusts samples FD-AC1 and FD-AP1 are shown in Figure 3. The L002 values of each size range of FD-AP1 are indicated in Table 3. Figure 3 shows a small but perceptive (002) carbon peak in the flue dust fractions smaller than 63μm. Demineralization process allowed to observe and to calculate the L002 values of these small fractions. The L002 of the small fractions (250µm were considered to be composed only by coke fines [8]. Table 3 – Char proportion in dust sample FD-AP1
FD-AP1 Dust particle size
L002
Total Carbon
PCI carbon —
Coke carbon
(µm)
(nm)
(wt, %)
Char (wt, %)
(wt, %)
< 38
2,55
0,08
0,03
0,05
38 – 63
2,91
1,05
0,24
0,81
63 – 90
2,93
1,98
0,42
1,56
90 – 180
3,18
11,7
1,08
10,62
180 – 250
3,32
12,62
0,31
12,31
250 – 425
3,37
7,75
—
7,75
> 425
3,12
5,22
—
5,22
FDtotal
3,28
40,4
2,08
38,32
Table 4 indicates the measured char and coke percentages in the dust samples FDAC1, FD-AC2, FD-AP1 and FD-AP2. The char content in dust samples (BF with PCI) was below 3%. The coke content in dusts samples ranged from 32% to 40% and was higher in flue
dust of the all coke BF. Considering the BF operational parameters and all BF off gas samples (flue dust and sludge), it would be possible to calculate the percentage of uncombusted char/thm (ton of hot metal). Table 4 – Summary of PCI and coke carbon in dust samples FD-AC1, FD-AC2, FD-AP1 and FD-AP2
Item
BF all coke
BF with PCI
FD-AC1
FD-AC2
FD-AP1
FD-AP2
Char (wt, %)
—
—
2,08
2,64
Coke (wt, %)
38,91
40,15
38,32
32,54
This study has showed that the XRD technique associated to chemical analyses could be used as a standard procedure to identify the coal-char and coke structures and to quantify the percentage of these carbonaceous materials in the BF flue dust samples. 4. Conclusions — The granulometric analyses of the coal CAB showed practically no particles above 150μm, and its char particles will probably not exhibit sizes above 250μm. — The L002 of char ChAB was higher than its parent coal CAB indicating slightly higher crystalline order of carbon. — The L002 of the small fractions ( 90%
Pure H2 flow
2 tonne/day
Purity of pure H2
99.99 %
Raw H2 flow
5 tonne/day
Purity of raw H2
77.4 %
The pilot plant consists mainly of the three following steps: 1st step – CO conversion with water steam (shifting unit)
The aim of this phase is to modify the clean gas composition in order to move the carbon contained in the CO to CO2, while maximizing the H2 content.
The syngas from the existing IGCC is fed in a sulphur removal reactor (Zn oxide based adsorber,
used only in sweet conditions) and mixed with saturated medium pressure water steam. The mixture is then heated up to 310 ºC to guarantee water-gas shift reaction conditions in a first catalytic reactor (the catalyst is been supplied by Johnson-Matthey) where the main conversion from CO to CO2 and H2 is produced. Since the reaction is exothermic, the first reactor gas outlet temperature is quite high (480ºC). An intermediate cooling stage is required (where IP steam is produced), after which the gas is sent to a second reactor where the final conversion is achieved. The outlet high temperature with which the gas comes out of the second reactor is used in a regenerative heat exchanger to heat up the first reactor inlet gas. Following to this, there is the gas three step cooling process to 45ºC (low pressure steam generator, air cooler and water cooler). 2nd step – CO2 and H2 separation unit (CO2 capture)
The target of this step is to separate CO2 and hydrogen, obtaining a hydrogen enriched gas and a CO2 product stream.
To this purpose, an amine solution (concretely aMDEA - active Methyl DiEthanolAmine) is used to capture the CO2 contained in the gas coming from the shifting unit. The CO2 capture rate is higher than 90%. The CO2 captured is recycled back to the IGCC process. Downstream the CO2 absorption, the resulting gas is a hydrogen enriched flow called raw hydrogen (77.4% of purity). This stream is split into two: 40% is sent to the H2 purification unit and the rest, approximately 5t/d, is recycled back to the IGCC plant.
The aMDEA is regenerated by means of temperature increase and pressure reduction. During this process the CO2 is desorbed, obtaining the CO2 pure product stream. Once the aMDEA is regenerated, it is conditioned (pressure increase and temperature decrease) to be re-used. 3rd step – Hydrogen purification unit
Pure hydrogen (99.99% purity,) is obtained in this step from the raw hydrogen coming from the previous step.
For this purpose, 40% of the hydrogen enriched flow, called raw hydrogen, is purified by means of a PSA unit (Pressure Swing Adsorption) supplied by LINDE. Impurities such as CO2, CO, N2,
Ar are trapped in an adsorption multi-bed system whilst the hydrogen passes through it. This purification unit consists of four stages: adsorption, decompression, regeneration and compression. This process is carried out in four adsorption beds, consisting each of them in activated carbon, alumina and molecular sieve. The pure hydrogen obtained is recycled back to the IGCC, but can be used for different applications in the future.
The capacity of this unit is 2 tonnes of hydrogen per day with 99.99% of purity, being the nominal hydrogen recovery 70%. The tail gas generated in this step is also recycled back to the IGCC, but could be used as heat source in other processes due to its high hydrogen content (>50%).
3. Results and Discussion
The first tonne of CO2 was captured on 13th September 2010 (thus becoming the first installation of this kind in the world) and the commissioning was accomplished by October 2010. Characterization tests are being carried out since November 2010 until June 2011, covering the two different feeding syngas conditions.
As a brief description of the main learning in project phase can be mentioned: the finance delay due to funding calls, delay in the main equipment supply -more than 12-14 months-, the detailed engineering was conditioned by suppliers and the pilot plant construction was also delayed due to internal safety working permits since it is installed in an operating plant, finally lack of experimented personnel implied a delay on the commissioning.
The first battery tests using the sweet catalyst were undertaken from Oct 2010 to Feb 2011. The table below shows the composition of the main streams, comparing the expected values and the analysed at ELCOGAS laboratory: Table 4. Main results obtained from pilot plant in sweet operation (dry base). ELCOGAS laboratory
Main learning in the sweet characterisation tests has been the high reactivity achieved in the first reactor of the shifting unit, near to 95% CO-CO2 conversion, what would make possible to consider a shifting process with only one step using the sweet catalyst.
So, the figure below shows how the CO concentration varies with the temperature in the shifting unit, both theoretically (blue line) and practice (pink line). 20,0
20/01/11 17:24-28:35
CO (%)
15,0
10,0
Theoretical equilibrium curve Practice equilibrium curve
Practice Theoretically
5,0
0,0 300,0
350,0
400,0
450,0
500,0
550,0
600,0
Temperatura (ºC) Johnson Matthey
De alta Tª
Practice
Theoretically
Theoretically equilibrium curve
Practice equilibrium curve
Figure 3. Shifting unit conversion – diagram of temperature influence
In the figure above, the conversion in the first shifting reactor is represented, reaching near 95% in the practical case. It is seen that the temperature achieved at this point (511ºC) is higher than expected (498ºC). The next step is the cooling stage (straight line), where the outlet theoretical temperature (347 ºC) is not achieved in practice (383ºC). The final conversion obtained after
second reactor is 98%, near to the expected one. In addition, the equilibrium curves have been represented for both cases.
In addition, auxiliary consumption was lower than estimated in design, being the integration of O&M in the existing IGCC very easy, the rate of CO2 captured is 91.7% and the cold gas efficiency is 89.5%. Finally, the pilot plant has provided very useful data to develop some calculations about the CO2 capture costs. For these studies, captured CO2 costs have been estimated as a quotient between capture plant costs -CAPEX (investment costs) and OPEX (operational costs)- and captured CO2 tonnes.
CO 2 capture cost, €/t CO 2 =
CAPEX + OPEX Captured CO 2 tonnes
[eq.1]
This point of view is singular and in addition, data to calculate the cost of captured CO2 in the established conventional way for new plants can be offered. Table 5 shows the values that have been fixed to define the base case for calculations.
Table 5. Base case data
Variables
Expected life
Bank interest
Bank fee
Scale factor
Operating hours (IGCC mode)
Data
25 years
3.0 %
0.5 %
0.75
6,500 h
Average load factor
0.92
Net efficiency of Electricity power plant price with CO2 capture
40 €/MWh
Treated gas
33%
100%
According to these data, the first estimation cost of avoided CO2 is approximately 25-30 €/t for the existing IGCC (retrofitting) with sweet catalyst processes, which has been obtained from the pilot plant data.
Moreover, using these results as a reference, some sensitivity analysis have been carried out to get how some parameters influence on the captured CO2 cost. Figure 4 shows the influence of the operating hours and IGCC plant efficiency with CO2 capture on the captured CO2 cost:
60
3.000 h 3.500 h
CO2 cost (€/t CO2)
50
4.000 h 4.500 h
40
5.000 h
30
5.500 h 6.000 h
20
6.500 h 7.000 h
10 27
28
29
30
31
32
33
34
35
36
37
7.500 h
IGCC plant efficiency w ith CO2 capture (%)
Figure 4. Influence of the IGCC plant efficiency on the CO2 capture cost depending on the operating hours
It can be observed that the slope is the same in all cases, which means that the influence of the efficiency on the CO2 capture cost is independent of the operating hours. Small efficiency decreases cause big variations on the the CO2 capture cost.
For the second battery tests (sour capture), which will take place from May to June 2011, the sour catalyst will be tested, expecting to get final results by the end of July 2011. These final results will include comparison of the pilot plant’s behaviour under the two different operation conditions, optimization of steam/gas ratio at shifting unit for the correct operation of the plant, optimization of energy balance and real costs obtaining of CO2 capture and H2 co-production.
4. Conclusions
With the aforementioned and taking into account the results to be obtained from the pilot plant, ELCOGAS has the opportunity to contribute to the optimisation of IGCC technology subsequently to optimisation of the clean coal technologies. So, improvements and processes, which are being set out for the design of new plants, can be tested and developed even at commercial scale, leading to ultra-efficient and zero-emissions energy plants based on gasification of low cost fuels.
Once the PSE project is finished, ELCOGAS proposal is to use the pilot plant as an R&D platform in order to develop new projects related to these research areas: optimisation of catalysts for shift reaction (including tests on a variety of different catalysts), development and
demonstration of new processes for CO2-H2 separation, demonstration of processes for CO2 treatment and the improvement of integration between the CO2 capture facility and the IGCC power plant to increase efficiency
Acknowledgement
It is worth to have an special mention to both Spanish Government, through the Spanish Science & Research Ministry and Regional Government, because of their contribution in the project funding it through the Strategic and Singular Project Programme (PSE).
The effect of minerals on the moisture adsorption and desorption properties of South African fine coal S.M. du Preez, Q.P. Campbell* School of Chemical and Minerals Engineering, North-West University, 2520, Potchefstroom, South Africa. *Corresponding author. Tel.:+27(0)18 299 1993, E-mail address
[email protected] The aim of this research was to study the influence of mineral matter content and type on the equilibrium moisture levels of South African coals under different environmental conditions.
Some of the moisture sensitive conditions to which
beneficiated and dried coals are exposed to, include open air stock piles subjected to heavy rainfall and varying climatic conditions. Under these conditions coal can experience an increase in moisture content which can result in extensive handling problems, the plugging of belt conveyors or even moisture contract penalties. A series of adsorption experiments were conducted to correlate the equilibrium moisture levels and different physical properties of different coal samples.
A climate chamber
varying the temperature and humidity of the environment in which the coal particles were placed produced the equilibrium sorption data. The equilibrium data obtained were then correlated with coal properties such as porosity, coal rank and more importantly mineral matter content.
1
1. Introduction Coal plays a key role in the South African economy and is a commodity responsible for approximately 77% of its primary energy production
[1]
. In 2007, South Africa
produced 247 million tons of coal, utilizing 182 million tons locally and exporting 68 million tons [1]. The response of coal moisture to changing environmental moisture levels are influenced by factors such as clay content and the percentage fines. Coal containing a significant amount of clay will potentially hold more moisture. This is particularly important as the mineral matter found in South African coals is predominantly clay minerals, largely in the form of kaolinite and illite.
The influence of varying
conditions can become particularly prominent when large quantities of coal are stored or transported over great distances. Various publications were found in the literature concerning the subject of water adsorption on coals as a function of vapour pressure [2, 3, 4]. Due to the heterogeneous nature of coal, it follows that several individual coal properties will influence the adsorption behaviour of coal. The extent of moisture adsorption is influenced by coal rank, mineral matter content, porosity, and that the specific adsorption sites are determined by oxygen functional groups. This study was done to determine the influence of the mineral matter content on the moisture adsorption properties of a specific coal. There is almost always a significant amount of mineral matter intimately associated with the coal, also referred to as inherent mineral matter. Inherent mineral matter cannot be effectively removed by the beneficiation process and is ever present in even the cleanest coal products [5]. It is imperative to take into account the effect of this mineral matter when assessing the coal’s behaviour during handling and storage. To better understand the mechanism of moisture adsorption and the subsequent influence of the mineral matter content on this mechanism it is also vital to understand the physical and chemical characteristics of the specific coal. Isotherms like the Dubinin-Astakhov equations are regularly used to characterize moisture adsorption on
2
carbonaceous materials. The results obtained from these isotherms can be used to characterize the chemical and physical properties of the coal surfaces, contributing to the understanding of the moisture adsorption mechanism on coal.
2. Experimental section Coal selection and preparation: Five coal samples from three different collieries in the major coalfields of South Africa were chosen for this study. These were the Waterberg (coal A), Witbank (coal B) and Free State (coal C) regions
[6]
. Coal samples from a Witbank - Highveld
colliery was taken from three different sampling points: the export product (B1), middling fraction (B2), and the discard stream (B3).
This was done to ensure a
variation in ash content while keeping most other coal properties constant, since that it was identified early in the study that coal rank is expected to have a major influence on the moisture adsorption properties of a specific coal. The export sample will also give better insight into the moisture adsorption properties of coal that will be transported to over 500 kilometres to the Richards Bay Coal Terminal, since the Witbank coalfield is a major source of steam coal for the export market [7]. The coal samples were milled and dry sieved in +1mm - 2mm size fractions. The main purpose of the milling was to reduce the particle size of the coal samples before sieving. A jaw crusher was specifically used to ensure that the particles break along their inherent lines of weakness, maximising the exposure of the finely dispersed mineral matter present in the coal particle. Climate chamber A climate chamber, where the relative humidity and temperature of the atmosphere can be independently controlled, was used to test the moisture adsorption and desorption properties of five selected coal samples. A load cell was installed inside the climate chamber to record the increase in mass due to moisture adsorption and any decrease in mass due to moisture desorption under varying climatic conditions.
3
The experimental procedure that was followed, involved the selection of about 70 grams of the coal sample. The sample was dried overnight in a vacuum oven at 105○C to ensure that all the moisture is excluded from the sample before each experiment. The sample was then placed into the climate chamber at a relative humidity (RH) of 20% at the specified temperature. The system was then allowed to reach equilibrium which was indicated by a constant mass reading. The humidity was the increased to 40%, 60% and 80% in turn, again allowing each step to reach equilibrium. After a maximum of 80% RH was reached the humidity was decreased in the same sequence as for the adsorption steps, from 80% to 60%, 40% and 20% RH while the temperature was kept constant. The overall time to complete an experiment was in the order of 70 hours to ensure complete equilibrium was reached in each step. Directly after each experiment was completed the sample was weighed and placed immediately in a vacuum oven for several hours after which the sample was weighed once again to determine the final moisture content of the coal sample using ISO and SABS standards. This data was used to back-calculate mass of adsorbed moisture per unit mass of coal. The humidity sequences were investigated at temperatures of 15◦C, 20◦C and 28◦C. A schematic representation of the experimental setup can be seen in Figure 2.1.
4
Figure 2-1: Schematic representation of the experimental setup The load cell continuously recorded the increase or decrease in mass during each experiment. These values and the relative humidity and temperature readings were continuously recorded by the computer.
3. Results and Discussion The proximate analysis of coal evaluates the moisture, ash, volatile matter and fixed carbon content was determined according to standard test methods.
The results
obtained from the proximate analysis can be seen in Table 3-1. Table 3-1: Proximate analysis*
Inherent moisture 5
%
A (ROM)
B1 (Export)
B2 (Middlings)
B3 (Discard)
C (ROM)
0.6
2.6
2.2
1.2
3.9
%
50.1
14.9
31.6
63.5
34.1
Volatile matter %
13.8
26.2
20.6
18.2
20.6
Fixed carbon
%
35.5
56.3
45.6
17.1
41.4
Total sulphur
%
0.42
0.33
0.48
6.99
0.14
Ash content
*Air dried basis, percentages reported as wt. %
According to the characterization results in Table 3-1 all the coal samples except for B1 export could be regarded as high ash coals. The percentage ash in coal A and coal B3 discard is noticeably higher than for the other coals. Coal C contains a distinctly higher amount of inherent moisture when compared to the other four coal samples, which is typical of Free State coals. According to the petrographic analysis conducted, coal A can be classified as a medium rank B coal where Coals B and C are reported to be medium rank C coals. All the coal samples are rich in inertinite except for coal A which is rich in vitrinite. In Table 3-2 the ash composition analysis results can be viewed for coal A, B1 Export, B2 middlings and B3 discard, as well as coal sample C. Table 3-2: Ash composition (XRF) analysis of coal samples* Inorganic species Al2O3
%
SiO2
%
CaO
%
6
A (ROM)
B1 (Export)
B2 (Middlings)
B3 (Discard)
C (ROM)
24.61
28.93
30.35
21.36
32.19
66.65
49.46
56.65
42.58
51.50
0.97
8.86
3.55
4.49
7.87
Fe2O3
%
2.71
1.81
2.61
22.38
2.37
K2O
%
2.45
0.49
0.54
0.7
0.48
MgO
%
0.53
1.32
0.75
1.44
0.71
Na2O
%
0.32
0.04
0.04
0.05
0.38
V2O5
%
0.16
1.61
0.28
0.22
0.1
TiO2
%
0.95
2.02
2.13
1.18
1.80
SO3
%
0.68
4.21
2.89
6.04
1.85
Other
%
0.25
1.25
0.27
0.36
0.39
100
100
100
100
100
Total
*All percentages are reported as wt. %
The results in Table 3-2 indicates that the ash is rich in Al2O3 and SiO2 which corresponds to high levels of quartz and kaolinite present in the coal. It can also be observed that the bulk of the ash for each of the five coal samples consists of SiO2 which is derived from quarts and clay minerals [8, 9]. The second largest contributor to the ash is Al2O3 which in turn corresponds to elevated amounts of clay minerals present. Fe2O3 can be related to the pyrite present in the coal samples. Coals A and B2 are the two coal samples containing the highest amount of clay minerals whereas B3 discard the least. The elevated levels of pyrite in the B3 discard sample are expected since pyrite is undesired in the final export product this also explains the low levels of pyrite present in the B1 export sample. A typical experiment conducted in the climate chamber with varying humidity at a constant temperature of 28○C can be seen in Figure 3-1.
7
Figure 3-1: A typical adsorption desorption experiment for coal C at 28○C. In Figure 3.1 the relative humidity was varied according to the sequence described in the experimental section.
The mass gain and loss for each step in the relative
humidity was recorded. A constant mass gain or loss indicated that equilibrium was achieved.
A temperature of 28○C was chosen as this is representative of the
environmental conditions that the coal will be exposed to in South Africa during summer. From the data obtained in Figure 3.1 the overall percentage moisture can be calculated. The moisture adsorbed at the equilibrium points can then be calculated as well as the amount of moisture adsorbed per amount of dry sample. Various models such as the Langmuir and Dubinin Astakhov can be fitted to the data. From these models, conclusions can be made about the maximum amount of moisture adsorbed as well as the degree of hysteresis that is present for each of the coal samples. Additionally, the dynamic part of each experiment can also be investigated and conclusions regarding the influence of mineral matter on the kinetic moisture adsorption can be drawn. The overall percentage moisture adsorbed is about 6.5% for coal sample C. It is also interesting to note that some form of hysteresis is present in this sample seeing that
8
the moisture adsorbed is not equal to the moisture desorbed. The hysteresis can clearly be seen in the adsorption and desorption isotherm illustrated in Figure 3-2.
Figure 3-2: Adsorption desorption isotherm of coal C A similar experiment was conducted on the B2 middlings sample and the percentage moisture adsorbed for this sample was 3.5%.
9
4. Conclusions •
The difference in the percentage moisture adsorbed between the B2 middlings and sample C can be attributed to the different minerals present in these samples since they are from the same rank the only other variable is the difference in mineral content. This statement will be further investigated and additional conclusions will be made regarding maceral content of each coal sample.
•
QEMSCAN results of the five coal samples will give further information regarding the amount and type of minerals present.
•
The hysteresis observed during the experiment can be attributed to capillary condensation and the ink bottle effect present during adsorption - desorption process.
In the very fine pores of the coal particle the mechanism of
adsorption is pore-filling rather than surface coverage. A possible explanation for low pressure hysteresis can be formulated in terms of swelling of the particles during adsorption. The swelling distorts the coal structure and opens up cracks which were previously inaccessible to adsorbate molecules. This can cause distortion that is not perfectly elastic and molecules can become trapped in the coal structure which cannot be released during desorption unless the temperature is elevated [10].
10
References [1] DEPARTMENT OF MINERALS AND ENERGY. 2008. South Africa’s Mineral Industry 2007/2008. Directorate: Mineral Economics Report, Pretoria, South Africa. [2] MAHAJAN, O.P. and WALKER, P.L. 1971. Water adsorption on coals. Fuel, Vol. 50, Issue 3. [3] UNSWORTH, J.F., FOWLER, C.S. and JONES, L.F. 1989. Moisture in coal: Maceral effects on pore structure. Fuel, Vol. 68, Issue 1. [4] MCCUTCHEON, A.L. and BARTON, W.A. 1999.
Contribution of mineral
matter to water associated with bituminous coals. Energy & Fuels 13, (1). [5] WARD, R.C. 2002. Analysis and significance of mineral matter in coal seams. International Journal of Coal Geology, Vol. 50: 135-168, 2 May. [6] JEFRFEY, L.S. 2005. Characterization of the coal resources of South Africa. The Journal of the South African Institute of Mining and Metallurgy. [7] MANGENA, S.J. and DE KORTE, G.J. 2004. Thermal drying of fine and ultrafine coal. [8] VAN DYK, J.C., and KEYSER, M.J.
2005.
Characterization of inorganic
material in Secunda coal and the effect of washing on coal properties. The Journal of the South African Institute of Mining and Metallurgy. Jan. [9] SPEARS, D.A. 2000. Role of clay mineral in UK coal combustion. Journal of Applied Clay Science, Vol. 16: 87-95. [10] GREGG, S.J & SING, K.S.W. 1982. Adsorption Surface Area and Porosity. 2nd ed. New York: Academic Press. 303p.
11
Structural Changes and Possible Modes of Interaction in Bituminous Coal Fly Ash Due to Treatments with Aqueous Solutions (Acidic and Neutral)
Roy Nir Lieberman,1, Roy Nitzsche,3, Haim Cohen1,2 123-
Department of Biological Chemistry, Ariel University Center at Samaria, Ariel, 40700 Israel, phone: 00972-52- 4306878, fax: 00972-8-9200749, email:
[email protected];
[email protected] Chemistry Department, Ben-Gurion University of the Negev, Beer Sheva, Israel email:
[email protected] TU Bergakademie Freiberg, Fakultät 4, Institut für Energieverfahrenstechnik und Chemieingenieurwesen 09599 Freiberg, Germany.
Abstract Coal fly ash is produced in Israel via the combustion of Class F bituminous coals. The bulk of coal fly ashes produced in Israel stems from South African and Columbian coals thus these ashes were the subject of the present study. It has been reported that the flyash can be used as a scrubber and fixation reagent for acidic wastes. Furthermore, the scrubbed product can serve as a partial substitute to sand and cement in concrete while the bricks have proved to be strong enough according to the concrete standards. Three possible modes of interaction were observed: cation exchange, chemical bonding and electrostatic adsorption of very fine precipitate at the flyash surface. In order to have a better understanding of the fixation mechanism we have decided to treat the flyashes with acidic (0.1M HCl) and neutral (DDW) solutions, thus changing the properties of the surface of the flyash particles. Surface analysis of the treated and untreated fly ashes have demonstrated that the treated flyashes have changed appreciably its' interactions with transition metal ions (e.g Cd2+, Cu2+). Introduction The major part of the electricity in Israel ( >60% in 20081) is produced by 4 bituminous coal fired power stations (the coals are imported mainly from South Africa Columbia, Indonesia, Russia and Australia2). Due to Israel strict environmental regulations the coal imported to Israel contains low content of sulfur and phosphorus. Thus, the fly ash produced in Israel has a highly basic reaction when exposed to water (pH >10), mainly because of the high content of CaO (and is defined as Class F). This means that the fly ash can act as a natural pozzolan. The present coal consumption is cal 13 MTons which yields ~1.3 MTons of Coal flyash. The fly ash particle size is in the range 3-250 μm and contains different types of glassy spheres. The first type are the Cenospheres (image 1A) which are glass bubbles and the second type are the Plerospheres (image 1B) which are also hollow glass bubbles filled with small particles inside. Both types are composed mainly of aluminates and silicates (>70%w). The fly ash has a large surface area which gives it the possibility to act as a potential fixation reagent. The chemical composition of the South African and Columbian fly ashes (SAFA, COFA respectively) is given in Table 1.
Table 1: the Major components and Minor elements in the SAFA and COFA of the South African and Columbian fly ashes COFA*
SAFA*
54.4 20.8 1.05 6.18 4.65 2.05 0.12 0.05 0.75 0.13 9-7
40.9 31.4 1.75 3.05 8.35 2.45 0.05 0.02 1.95 0.35 5-4
Component %Weight SiO2 Al2O3 TiO3 Fe2O3 CaO MgO K2O Na2O P2O5 SO3 C
Element COFA** SAFA** Ppm Ag 9.5 13.6 As 99.9999 vol%) at a rate of 3 °C/min up to 900 °C with a holding period of 10 min, and then cooled down to
ambient temperature at an average rate of 100–150 °C/min. The resulting coke was recovered and its dimensions and mass were measured. Mechanical strength of the coke was measured at ambient temperature by means of diametrical compression tests on a testing apparatus, Shimadzu EZ-L. The displacement and loading were measured during the compression at a displacement rate of 2.00 mm/min [19]. Assuming that the maximum loading at the breakage of the specimen corresponded to the maximum tensile stress, Pmax, it was determined based on an equation: Pmax = 2Lmax/πdl, where Lmax, d and l are the maximum loading, diameter and thickness of the specimen, respectively. Though not shown in detail, for all of the specimens tested, the loading (= stress) increased linearly with the displacement until its sudden drop. The coke samples prepared in the present study were thus broken obeying a brittle fracture mechanism. It was also confirmed that the coke samples cracked nearly equally into two semi-discs, which was a necessary condition in applying the above equation [20]. Fractured surfaces as well as top/bottom ones of some coke samples were observed by scanning electron microscopy (SEM) on a micrograph (Keyence, VE-9800). 3. Results and Discussion 3.1. Effects of briquetting temperature on properties of briquette and coke Effects of briquetting temperature, TB, were examined on the properties of resulting briquette and coke. The briquetting pressure, hereafter referred to as PB, was fixed at 128 MPa. The briquettes prepared at TB = 25, 70, 100 and 130 °C contained 6.6, 4.5, 2.4 and 0.5 wt% moisture, respectively, while less than 0.1 wt% for those at higher temperatures. Figure 1 shows the coke yield as a function of TB. The briquetting was effective for increasing the coke yield over the entire range of TB. Such increase was probably due to suppressed tar evolution caused by promoted cross-linking reactions and intra-particle charring of tar vapor. It was suggested that the briquetting at TB > 100 °C caused an additional positive effect on the suppression of tar evolution, implying changes in the coal structure at a molecular scale. The briquette density, ρB, was calculated on a moisture-free basis by an equation, ρB = (1 – w)ρ, where w and ρ were the residual moisture content and measured apparent density of the briquette, respectively. This equation is based on an assumption that the briquette undergoes little volumetric contraction in the final stage of moisture release [21]. As shown in Fig. 2, ρB greatly increases from 1.02 to 1.20 g/cm3 at 25–70 °C, and further but gradually to 1.26 g/cm3 at 230 °C. According to Higgins et al. [22] and Matsuo et al. [23], the true density and micropore volume of dry Loy Yang coal are 1.42 g/cm3 and 0.065 cm3/g, respectively. Assuming no meso-/macro-pores in the briquette, its density is 1.30 g/cm3. ρB for the briquettes prepared at 200–300 °C being as high as
1.24–1.26 cm3/g thus suggested that the briquetting at such temperature effectively eliminated inter-particle spaces by causing deformation of particles and their adhesion/coalescence and even loss of intraparticle macro/meso-pores. TB influenced the density of coke, ρC, in a way slightly different from ρB, i.e., there occured a minimum of ρC. The density of coke was a result from events causing increase or decrease in the density of carbonizing briquette. ρC had a minimum at TB = 130–160 °C. It was believed that during the carbonization ρC varied in three events; thermal relaxation of briquette, pore formation due to evolution of volatiles and densification of the nonporous part of the solid. No particular effects of applying TB = 130–160 °C was plausible on the second and third events so far as the result shown in Fig.1 was considered, and it was therefore suggested that the briquettes for TB = 130–160 °C underwent thermal relaxation that was associated with volumetric expansion in the course of reheating. In other words, the coal underwent a type of structural rearrangement during the briquetting at TB > 100 °C in a manner different from that at TB ≤ 100 °C. This hypothesis was consistent with the increase in the coke yield at TB > 100 °C, though the scale of such rearrangement is unknown. Another effect of applying TB > 100 °C on a coke property will be shown and discussed later. In Fig.3, the average tensile strength of coke, Pmax, is shown as a function of TB together with standard deviation, σ. Pmax is greater than those of conventional cokes, 2–6 MPa over the range of TB. It is also noted that Pmax steeply increases from 14 to 28 MPa at TB = 100–130 °C. Briquetting at TB > 100 °C was thus effective for preparing high strength coke with Pmax = 28–37 MPa. 3.2. Effects of briquetting pressure on properties of briquette and coke The effects of PB on ρB and ρC were investigated with TB = 200 °C. As seen in Fig.4, both ρB and ρC increase monotonously with PB in manners very similar to each other. ρB and ρC are also very close to each other. Figure 5 illustrates the effect of PB on the coke yield. Compared with the effect of applying TB = 200 °C on the coke yield (see Fig. 1), that of increasing PB was less significant. Figure 6 presents average Pmax as a function of PB. Pmax increases in a manner similar to that of ρC, and this indicates importance of ρC as a factor determining the tensile strength of coke. 3.3. SEM observation of coke samples Top/bottom and fractured surfaces of cokes prepared under different combinations of TB and PB were obserbed by SEM. Figure 7 displays SEM photographs of some selected coke samples. One of the features common among the coke samples was absence or
rarity of pores with sizes of 10 µm and greater, and this was a main reason why many of the present cokes had Pmax > 25 MPa. The fractured surfaces of a coke sample prepared with PB = 128 MPa and TB = 100 °C (see photos e and f) has morphology very similar to that of another coke from the same PB and TB = 200 °C (c and d) in terms of frequency of grain boundaries and size/frequency of pores. On the other hand, the fractured surface of a coke from TB = 200 °C and PB = 32 MPa (photos g and h) has clearly more grain boundaries and greater pores than that from PB = 128 MPa. The photographs c–f demonstrate that the briquetting leading to cokes with ρC > 1.2 g/cm3 successfully eliminated grain boundaries. It was found that the briquettes prepared at TB > 100 °C were tinged with black while the briquettes prepared at TB = 25 °C were dark-brown colored. This was an implication of that more or less amount of low-mass components of the coal was mechanically squeezed out of the macromolecular network, appeared on the particle surface and promoted its adhesion to another particle. It was also implied that such low-mass components, even inside the particle matrix, played a role of plasticizer, enhancing deformation of the particle. Some briquettes were crushed and then subjected to extraction with tetrahydrofuran (THF) at 30 °C and under ultrasonic irradiation. THF extracted material with 12.9 wt% of the briquette. This extraction yield was nearly equivalent with that from the starting coal, 13.6 wt%. The result was explained by that the mechanical extraction of low-mass components, if occurred, was not so extensive as the extraction with THF. 3.3. Factors crucial to mechanical strength of coke Figure 8 summarizes combined effects of TB and PB on the average Pmax assuming that ρC is a critical property for the mechanical strength of coke. Two different relationships between Pmax and ρC are seen in the figure. Pmax of the coke from briquetting at TB > 100 °C is a linear function of ρC over the ranges of ρC = 0.87–1.27 cm3/g and PB = 32–192 MPa. In case of TB ≤ 100 °C, Pmax is described by another linear function of ρC. Briquetting with TB > 100 °C was thus found to be necessary for preparing coke with Pmax > 15 MPa within the conditions examined so far. Each of the linear relationships are explained reasonably. Under an assumption that all of the cokes prepared in this work had similar true densities [24], difference in ρC among cokes from different conditions is attributed mainly to that in the porosity. Patrick and Stacey [24] showed that the tensile strength of coke was well described as a function of porosity. Arima [25] claimed that the strength of non-porous part of coke was not necessarily a function of coal rank/type and fusibility while frequencies of connected pores and non-adhesion grain boundaries were more crucial. ρC of the present
cokes, ranging from 0.87 to 1.27 cm3/g, are much higher than general blast furnace and foundry cokes. It was thus believed that such high density, in other words, low porosity was the primary reason of very high tensile strength of the cokes prepared in this work. Polished surface of a coke sample (TB = 200 °C, PB = 128 MPa) was observed by an optical polarized-light microscopy, which confirmed no progress of formation of optically anisotropic textures during the carbonization. A thermomechanical analysis of a briquette (TB = 200 °C, PB = 128 MPa) in a needle penetration mode revealed no softening/fusion of the briquette during the carbonization. These results are proofs of that high strength of the present cokes was not due to carbonization via mesophase formation. Here is discussed on the presence of two different ρC–Pmax relationships for the briquetting at TB > 100 °C and that at TB ≤ 100 °C. As shown in some photographs of Fig.7, it was difficult to explain the difference in the fractured surface between the cokes from briquettes with TB = 100 °C and 200 °C. The briquettes prepared at TB ≤ 100 °C contained 2.4 to 6.6 wt% moisture, which played a role of plasticizer and/or lubricant in the briquetting helping the formation of briquettes with ρB as high as 1.2 g/cm3. It was believed that low-mass components of the coal did not play important roles due to insufficiently high temperature for breaking hydrogen bonds and also the presence of water that was not necessarily a good solvent of such components. The briquetting at TB > 100 °C effectively removed water to a content below 0.5 wt% and also allowed mobilization of low-mass components. As shown in Fig.2, The densities of the briquettes with TB = 130 and 160 °C decreased upon the reheating (for the carbonization) to degrees much greater than those with TB ≤ 100 °C. This was probably arisen from thermal relaxation (volumetric expansion) of the briquettes with TB = 130 and 160 °C. Such thermal relaxation might release briquetting-induced mechanical stresses inside the briquettes, which could induce defects such as microcracks during the carbonization. Thus the thermal relaxation, if occurred, played a role of annealing in the early stage of the carbonization. For the briquetting at TB = 200–230 °C, the temperature would be high enough for the annealing within the period of briquetting. The resulting briquettes therefore underwent little or no density decrease (see Fig.2). 4. Conclusions Binderless briquetting of pulverized Loy Yang brown coal applying mechanical pressure of 32–192 MPa and temperature of 25–230 °C and subsequent carbonization with heating up to 900 °C successfully produced coke having tensile strength of 6–37 MPa. Such high mechanical strength of cokes was attributed mainly to low porosity. Briquetting at temperature over 100 °C caused plasticization/deformation of the coal
matrix due to low-mass components, and thereby promoting coalscence/adhesion of particles and eliminating inter-particle spaces and grain boundaries. Acknowledgement. This study was carried out as a part of a research project, “Scientific Platform of Innovative Technologies for Co-Upgrading of Brown Coal and Biomass”, which has been financially supported by MEXT, Japan in a Program of Strategic Funds for the Promotion of Science and Technology. The authors are also grateful to The Iron and Steel Institute, Japan (ISIJ), and Nippon Steel Corporation (NSC) for financial supports. Prof. Tsuyoshi Hirajima, School of Engineering, Kyushu University, and Dr. Seiji Nomura, NSC, are acknowledged for their technical advice. References [1] George AM, Mackay GH. Chapter 2: The Science of Victorian Brown Coal. Edited by Durie RA. 1991, Butterworth-Heinemann, Oxford. [2] Miyazu T. Proc. Int. Iron Steel Congress, Dusseldorf 1974;Paper 1.2.2.1. [3] Wornat MJ, Sakurovs R. Fuel 1996;75:867-871. [4] Sakurovs R. Fuel 2000;79:379-389. [5] Taylor JW, Coban A. Fuel 1987;66:1274-1280. [6] Rubio B, Izquierdo MT, Segura E. Carbon 1999; 37:1833–1841. [7] Paul SA, Hull AS, Plancher H, Agarwal PK. Fuel Processing Technology 2002;76:211-230. [8] Plancher H, Agarwal PK, Severns R. Fuel Processing Technology 2002;79:83-92. [9] Yip K. Wu H, Zhang Dk. Energy Fuels 2007;21:419-425. [10] Bayraktar KN, Lawson GJ. Fuel 1984:63;1221-1225. [11] Patrick JW, Stacey AE. Fuel 1972;51:81-87. [12] Patrick JW, Stacey AE, Wilkinson HC. Fuel 1972;51:174-179. [13] Patrick JW, Stacey AE. Fuel 1972;51:206-210. [14] Miyagawa T, Fujishima I. Nenryokyokai-shi 1975;54:983-993. [15] Miyagawa T, Fujishima I. Nenryokyokai-shi 1976;55:30-37. [16] Allardice, DJ. Chapter 3: The Science of Victorian Brown Coal. Edited by Durie RA. 1991, Butterworth-Heinemann, Oxford. [17] Miura K, Mae K, Sakurada K, Hashimoto K. Energy Fuels 1992;6:16-21. [18] Allardice DJ, Chaffee AL, Jackson WR, Marshall M. Chapter 3: Advances in Science of Victorian Brown Coal. Edited by Li CZ. 2004, Elsevier, Oxford. [19] Yamazaki Y, Hayashizaki H, Ueoka K, Hiraki K, Matsushita Y, Aoki H, Miura T. Tetsu-to-Hagané 2004;90:536-544. [20] Mellor M, Hawkes I. Engineering Geology 1971;5:173-225. [21] Evans DG. Fuel 1973;52:186-190. [22] Higgins RS, Kiss LT, Allardice DJ, George AM, King TNW. SECV Research and Development Department Report 1980, Report No. SC/80/17. [23] Matsuo Y, Hayashi Ji, Kusakabe K, Morooka S. Coal Science Technology 1995;24:929-932.
[24] Patrick JW, Stacey AE. Fuel 1978;57:258-264. [25] Arima T. Tetsu-to-Hagané 2001;87:274-281.
Coke yield, wt%-dry-coal
65 PB = 128 MPa 60
55
50
45
Char yield from pulverized coal
0
50
100
150
200
250
TB, °C
Figure 1. Effect of TB on the yield of resulting coke. 1.4 PB = 128 MPa
!B or !C, g/cm3
1.3 1.2 1.1 1
!Coke C
0.9 0.8
!Moisture-free briquette B
0
50
100
150
200
250
TB, °C
Figure 2. Effects of TB on ρB and ρC. 50
PB = 128 MPa
Pmax, MPa
40 30 20 10 0
2 sigma
0
50
100
150
200
TB, °C
Figure 3. Pmax as a function of TB.
250
1.4 TB = 200 °C
!B or !C, g/cm3
1.3 1.2 1.1 1
Coke
0.9 0.8
Moisture-free briquette 0
50
100
150
200
PB, MPa
Figure 4. Effects of PB on ρB and ρC.
Coke yield, wt%-dry-coal
65 TB = 200 °C 60
55
50
45
Char yield from pulverized coal
0
50
100
150
200
PB, MPa
Figure 5. Effect of PB on the yield of resulting coke. 50
TB = 200 °C
Pmax, MPa
40 30 20 10 0
2 sigma
0
50
100
150
PB, MPa
Figure 6. Pmax as a function of PB.
200
Figure 7. SEM images of fractures surfaces (a, c - h) and top/bottom surface (b) of coke samples. Images a, c and d: ΤΒ/PΒ; 200 °C/128 MPa. Images b, e and f: 100 °C/128 MPa. Images g and h: 200 °C/32 MPa. 50
Pmax, MPa
40 30
PB = 128 MPa TB = 200 °C
TB > 100 °C
20 10 0 0.8
TB ! 100 °C
0.9
1
1.1
1.2
3
!C, g/cm
Figure 8. Relationships between ρC and Pmax.
1.3
A Mechanism of improvement in coke strength by Adding a Solvent-Extracted Coal Noriyuki OKUYAMA, Takahiro SHISHIDO, Koji SAKAI, Maki HAMAGUCHI and Nobuyuki KOMATSU Coal & Energy Technology Dept., KOBE STEEL, Ltd, JAPAN
[email protected] Abstract: A coal extract, produced by thermal extraction and solvent de-ashing in the coal derived methylnaphthalene solvent, has an excellent thermoplasticity even though the parent coal appears no thermoplasticity. We named it “HPC, High Performance Caking additive”, and have been developing to utilize as a thermoplasticity accelerator to make strong coke for blast furnace. Significant improvement in the thermoplasticity of coal blends are observed by HPC addition, especially with high blending ratio of slightly caking coals. It improves other dominant factors in coke strength, increasing in the dilatation of coals, increasing in the anisotropic texture and decrease in the inert structure in the coke. It is confirmed that the improvement of dilatation is the most important factor to perform filling the inter particle voids of coals in the coking reaction, that brings strong adhesive of coal particles to form a lump strong coke. The increasing in the charging bulk density of coal is also an important factor to decrease in the inter particle voids. The changing in the coke strength is quantitatively investigated as the functions of those factors in this study. 1. Introduction We have been developing a noble coal upgrading process to make an ash-less coal by applying the solvent de-ashing technology1). Coal is extracted in the coal-derived methylnaphthalene solvent at 350-400 oC. The solution is separated from the extraction residue by the gravity settling. Solvent is recovered and recycled in the process. HPC appeals an excellent thermoplasticity even though the parent coal appeals no thermoplasticity2). HPC softens at low temperature (less than 300ºC), keeps a highly fluidity in a wide temperature range and resolidifies at high temperature, nearly 500ºC. Therefore, HPC is available as a caking additive to make strong coke for the blast furnace. We participate in a Japanese national project called COURSE50 (CO2 Ultimate Reduction in Steelmaking process by innovative technology for cool Earth 50), in which we aim to apply HPC
as a caking additive to make strong coke for the iron blast furnace, which maximize the use of hydrogen as a reductant, in order to minimize coke addition to the furnace. Thermoplasticity is one of the most important characteristics for coke making. Japanese coke and steel companies make blast furnace coke by blending various types of coals, but the strongly caking coals have to be the main components in the coal blends. On the other hand, increasing in the use of slightly caking coals is an important subject to manage the shortage problem of strongly caking coals and to reduce accommodation cost of coal. This study investigates the effects of HPC as a caking additive to increase coke strength. Improvements in the caking properties by HPC addition, such as thermoplasticity, dilatation and anisotropic texture are examined, and coke strength is quantitatively understood with relation of those factors in this study. 2. Experimental section 2.1 Materials Three kinds Australian strongly caking coals (A, B, C) and a slightly caking coal (D) were used in this study. Table 1 shows the results of proximate, ultimate analysis and Gieseler plastometry (JIS M8801, similar to ASTM procedure) of the materials, and Table 2 shows the coal blending ratio of each blending base and total reflectance (Ro), total inert (TI) of each base. Base-1 consists with 75 wt% of strongly caking coals, and Base-2 consists with 50 wt% of strongly caking coals, coal-A : B: C : D = 15: 30 : 5: 50. When HPC was added to coal blend, coal-C was exchanged with HPC in the case of Base-1, and coal-B was exchanged in the case of Base-2. HPC was produced using a continuous bench scale unit (BSU), 0.1 t/d of coal consumption. The feedstock for HPC was an Australian steaming coal (MO), extracted at 400ºC. Table 3 shows the properties of MO-coal and HPC, and Table 4 shows the composition of the recycling solvent of BSU. Table 1 Properties of blending coals Proximate analysis name
ash [wt%]db
A B
10.3 10.5
VM
C
1)
21.2 21.8
Ultimate analysis H
N
S Odiff.
Maceral analysis4) Thermoplasticity 3) ST MFT RT Log (MFD) Ro Exinite Vitrinite Inertinite
[wt%] ( daf 2) ) 90.2 4.6 2.0 0.6 2.6 89.6 4.7 1.6 0.3 3.8
433 432
[ddpm] [ºC] 481 502 1.43 474 505 1.08
[%]
[-] 1.46 1.29
0.0 0.0
86.0 75.0
TI [%]
14.0 25.0
20.7 28.4
C
8.0
35.5
85.7 5.4 2.2 0.6 6.0
383
443 476
3.27
0.91
1.6
85.2
13.2
16.5
D
10.0
28.0
87.0 4.8 2.0 0.6 5.7
422
455 473
1.00
1.00
0.4
75.2
24.4
30.8
1) dry basis, 2) dry and ash free basis, 3) Gieseler plastometry (JIS M8801), ST: Softening temp., MFT: Maximum fluid temp., MFD: Maximum fluidity RT: Resolidification temp. 4) JIS M8816， Ro: Mean reflectance, TI: Total inert
Table 2 Coal blending conditions
Table 3 Properties of coal extraction solvent
Blending ratio [wt%] Base blend A B C D Ro (calc.) TI (calc.) 1.11 23.8 15 26 (34) 25 Base-1 1.16 27.9 Base-2 20 (30) 0 50
Ultimate analysis Atomic ratio H/C O/C H N S Odiff. [wt%] 91.45 6.9 0.02 0.7 0.93 0.905 0.008 [wt%] Component 1-methylnaphthalene 54.23 2-methylnaphthalene 37.46 naphthalene 2.10 dimethylnaphthalene 1.92 biphenyls 0.32 benzenes (1-ring compounds) 0.68 alkanes 0.48 thiol (S-containing aromatics) 2.04 others 0.76
( ) ：Exchanging coal with HPC
C
2.2 Coal carbonization experiment The coal blends were carbonized according to the conventional metallurgical coke making procedures. Coals were pulverized under 3 mm and HPC was pulverized under 0.15 mm. Coal blends were charged into an iron-made container of 0.02 m3, at 800 kg/m3 of bulk density, and were heated to 1000 ºC at a rate of 3 ºC/min under inert atmosphere. Duration was 30 min. 9 containers were filled in a coke oven, which has 300 kg of coal charging capacity. Drum Test (JIS K2151) was carried out to measure the coke strength. This is common way to evaluate coke strength in Japan. A 10kg of coke sample of the +50mm square hole was placed in the tumble drum and rotated for 30 revolutions, removed, screened and replaced in the drum and given impacts by further 150 revolutions. The drum index, DI15015, means the percentage of remaining +15mm square hole after 150 revolutions. The larger number indicates the stronger coke. 3. Results and Discussion 3.1 Changing in coke strength with fluidity of coal blends Thermoplasticity of coal is improved by HPC addition. That effect strongly appeals with lower grade coal, such as none or slightly caking coal3). Figure 1 shows Gieseler curves of the coal blends and HPC additional cases. Base-1 has sufficient fluidity, but base-2 has insufficient fluidity since blending ratio of the slightly caking coal (Coal-D) is 50 wt%. When HPC is added, Gieseler curves expanded to wider range and higher fluidity. And those effects appear more strongly on Base-2. Figure 2 shows the relation between MF value and coke strength (DI15015), and other dominant factors for coke strength, total reflectance (Ro), total dilatation (TD) of coal blends and anisotropic texture of coke. The DI value was increased more over to 88 by increase in MF value, and decreased in reversely. In the case of Base-2, DI value was too weak to use for
blast furnace without HPC addition and strongly increased with increase in MF value by HPC addition. Looking at other dominant factors in coke strength, it can be said as follows; (a) Total reflectance of coal blends are not influenced in this study (b) Total dilatation is strongly increased with increase in MF value especially in Base-2.
Log (Fluidity/ddpm)
(c) Optical anisotropic texture is developed with HPC addition, and inert texture, which can be regarded as the start point of crack, is decreased. Base blend + HPC 5% + HPC 10% + HPC 15%
3 Base-1
Base-2
+ HPC 20%
2
1
0 380
420
460
420 500 380 Temperature [ºC]
460
500
(5)
Mean reflex ratio (10)
(0)
85
(15)
(20)
(5)
80 (
): HPC amount
75 0
1 2 3 Log (MF/ddpm) Base-1 Base-2’
1.3
60
(Ro)
1.1
(25)
(10)
(0)
Ro
90
Optical texture [%] Total dilatation [vol%]
Coke strength DI 150 15
Fig.1 Changing in Gieseler curves by HPC addition
4
Total dilatation
(TD)
40 20 0 80
Optical texture Anisotropic texture
60 40 20
Inertﾄ texture
0 0
1
2
3
4
Log (MF/ddpm)
Fig.2 Relation between the maximum fluidity (MF) of coal blend and coke strength, and Relation between MF and other dominant factors in coke strength
3.2 Dilatation property in HPC addition As mentioned above, the dominant factors were improved accordingly with increase in the fluidity by HPC addition. Especially, increase in the total dilatation was strongly appeared by HPC addition. Figure 3 shows the behaviors of shrinkage and dilatation of coal blend in the dilatometer tests using Base-1 and Base-2. Base-1 shows sufficient behavior, it indicates nearly 40 % of dilatation after shrinkage. The shrinkage means the increasing in bulk density of coal by softening and fluidizing. On the other hand, base-2 shows insufficient behavior, dilatation is not appeared after shirincage without HPC. It can be seen that the large difference of the dilatation behaviors between Base-1 and Base-2 causes the large difference of DI values of coke between Base-1 and Base-2, about 87 and 78 respectively. When HPC is added to Base-2, dilatation is strongly increased, and both shrinkage and dilatation temperatures are shifted to lower
300
350
400
450
500
Displacement [%]
dilatation
Base-1 Base-1 + HPC 5% Base-1 + HPC 10%
Total dilatation (TD)
25 20 15 10 5 0 -5 -10 -15 -20 -25
shrinkage
Displacement [%]
temperatures according to the changing in Gieseler curves. 25 20 15 10 5 0 -5 -10 -15 -20 -25 300
Temperature [ºC]
Base-2 Base-2 + HPC 5% Base-2 + HPC 10% Base-2 + HPC 20%
350
400 450 Temperature [ºC]
500
Fig.3 Shrinkage and dilatation behaviors of coal blends and HPC addition in the dilatation tests
Nomura, et al.4) reported that the coke strength largely depended on the effect of filling the void of coal. In the view point of that, the dilatation property of coal and the bulk density at the charging should be equivalent effect, and he defined the void filling ability as following equation; Void filling ability [-] = Specific dilatation volume [cm3/g]･Charging bulk density [g/cm3] In that equation, specific dilatation volume expresses the volume of a unit mass of coal after expansion using the dilatation rate in the dilatometer test (Fig.3).
In reference to that, we examined the contribution to the coke strength of the “void filling ability” by HPC addition. Figure 4 shows the changing in the coke strength as a function of the dilatation rate. Coke strength increases with increase in the dilatation rate, and the series of Base1 and Base-2 can be plotted on a same line. Looking at the same dilatation rate, the higher charging bulk density is plotted at higher coke strength. Figure 5 shows relation between the “Void filling ability” and coke strength. The influences of the dilatation and the bulk density can be expressed on a same line. Therefore, the increasing mechanism of coke strength by HPC addition can be also explained as the void filling ability. That result conforms to the principle of a coal blending theory to satisfy the enough conditions of caking properties. The relation can be approximated following quadratic equation in this study; DI15015 = -31.92・(Void filling ability-1.2)2 + 88.8 For example, when the coal charging density is 0.85 g/cm3, the highest coke strength (DI15015=88.8) will be obtained by setting a blending condition of HPC to give the dilatation rate at around 30 % in this study.
Coke strength , DI15015
90
0.95 0.80
85
0.72 Coal charging density (g/cm 3 )
80
Base-2
Base-1
75 -30 -20 -10
0
10
20
30
Dilatation [vol%] Fig.4 Changing in the coke strength as a function of the dilatation rate
Coke strength , DI150 15
90 Coal charging density g/cm3
85
Base-1 Base-1 Base-1 Base-1 Base-1 Base-2 Base-2
80
1.01 0.95 0.90 0.82 0.80 0.85 0.80
75 0.4
0.6 0.8
1.0
1.2 1.4
1.6
Void filling ability [-] Fig.5 Relation between the “Void filling ability” and coke strength 4. Conclusions Significant improvement in the thermoplasticity of coal blends are observed by HPC addition, especially with high blending ratio of none or slightly caking coals. HPC gives a large effect to filling void of coal by expanding. The changing in the coke strength is quantitatively investigated as the functions of that factor in this study. HPC is expected to be a high performance caking additive to widen the coal resources to lower rank coals for blast furnace coke. Acknowledgement This study has been carried out as a part of Japanese national project called COURSE50 (CO2 Ultimate Reduction in Steelmaking process by innovative technology for cool Earth 50). We thank NEDO for the support of this study. References [1] Okuyama N, Komatsu N, Kaneko T, Shigehisa T, Tsuruya S,: Fuel Processing Technology 85 (2004) 947967 [2] Okuyama N, Komatsu N, Kaneko T, Shigehisa T, Tsuruya S,: Coal Preparation, 25 (2005) 295-311 [3] Okuyama N, et al., Proceedings in the 27th Annual International Pittsburgh Coal conference, (2010), Istanbul [4] Nomura S, Arima T, Kato K, Yamaguchi K: NIPPON STEEL TECHNICAL REPORT No. 94 (2006)
Oviedo ICCS&T 2011. Extended Abstract
Coal Drying and Dewatering for Power Generation – Current status, Research and Development Needs David Stokie1, Jianglong Yu2, Anthony Auxilio1 and Sankar Bhattacharya1 1
Department of Chemical Engineering, Monash University, Victoria, Australia
[email protected] 2 Key Laboratory of Advanced Coking Technology, Liaoning Province, School of Chemical Engineering, University of Science and Technology Liaoning, Anshan (114051), P.R. China Abstract Around 45% of the world’s coal has either high-moisture or high-ash levels resulting often in inefficient power plants using these coals. There is a strong need to develop less energy-intensive coal drying technologies to improve the efficiency of plants using highmoisture coals. While some efforts in coal drying are in progress in Australia, Germany and the USA, accelerating these efforts into large-scale integrated demonstration is important. Success in developing more efficient coal drying and beneficiation technologies will promote the wider use of the high-moisture low-rank coals in efficient technologies such as either ultra-supercritical pulverised coal, and IGCC application for power and co-production of chemicals and fuels. This paper discusses the status of major drying technologies and identifies the key R&D needs for their wider commercial deployment. It does not deal with modelling of coal drying. 1. Introduction Low-rank coals containing high-moisture (30-70% on as-received weight basis) represent a significant resource worldwide. An estimated 45% of world’s coal reserves are lignites, some of which are referred to as brown coal. Most brown coals are cheap, are low in ash and sulphur contents, but have high moisture contents up to 70% on asreceived basis. Low-rank coals represent the major source for power generation in several countries – Australia (~50%), Germany (~75%), Greece (~90%), Poland (~55%), Russia (~45%), the USA (~10%) are examples. Figure 1 identifies the major countries that use high ash and/or high-moisture coals, and indicative ranges of moisture content, ash content and calorific values of lignites in those countries.
Coal pre-drying is an important step towards improving the efficiency of both existing and new pulverised coal-fired power plants using high-moisture coals. In general the efficiency of a unit using coal drops by about 4% point and 9% point when coal moisture content increases from 10% to 40% and 60% respectively. This is quite significant as 1%-point increase in efficiency can often result in up to 2.5%-point
1
Oviedo ICCS&T 2011. Extended Abstract
reduction in CO2 emission. Apart from efficiency reduction, high moisture increases coal handling feed rate, auxiliary power in coal handling systems and pulverisers, and plant operating and maintenance costs.
70 6
1 moisture content of raw coal, %
60 4 Mj/kg
5
9
3
50
7 8
2
40
12 30
8 Mj/kg
10
4
12 Mj/kg
20
16 Mj/kg
11 10
20 Mj/kg
0 0
5
10
15
20
25
30
ash content of raw coal, %
Figure 1: High-ash and/or High-moisture containing coals often termed as lignites – their location, and calorific values (LHV, Mj/kg); country labels as follows: 1: Australia; 2: Indonesia; 3: India; 4: USA (Texas, North Dakota); 5: Germany; 6: Greece; 7: Spain; 8: Poland; 9: Czech Republic; 10: China; 11: Turkey; 12: Romania Compiled from various sources
Figure 2: Illustration of boiler size variation with moisture content in coal (Allardice, 1991) However, drying high-moisture coals increases the risk of spontaneous combustion as, due to their high oxygen content, they are usually more reactive than hard coals.
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Oviedo ICCS&T 2011. Extended Abstract
Therefore, in most power plants using high-moisture coals, drying has to be carried out immediately prior to combustion, i.e. in and around the mill, by recirculating some of the flue gases from the upper part of the boiler. This requires the boiler to be substantially larger to cope with the water vapour; As illustrated in Fugure 2, the higher the moisture content, the larger the boiler. In addition, to handle the additional volume of water vapour, the fan power requirement would be higher resulting in higher auxiliary power requirement and reduced efficiency. If high-moisture coal could be pre-dried, the boiler size could be smaller; and if low grade or waste heat could be used for drying, the boiler efficiency could be higher as well. The objective of this short paper is to summarise the status of different coal drying and dewatering technologies, identify the technical challenges and the immediate needs for research and development. Modelling of coal drying is not discussed in this paper. 2. Water in brown coal, physical nature of brown coal, and major variables affecting drying Moisture occurs in the forms of: surface water – which is weakly attracted to the particle surface, capillary water – found in capillaries and cracks in the coal structure, interparticle water – found in the space between two particles and interior water – dispersed through the coal structure. This is highlighted in figure 3, taken from (Muthusamy 2009).
Figure 3: Different forms of water associated with coal. (Karthikeyan, 2009)
Moisture in coal can also be described as freeze-able and non-freeze-able water. Freezeable water is weakly bound to the coal surface and is found in the bulk phase and the pore water (Allardice 2004). In contrast non-freeze-able water is molecularly bonded to the coal. Through hydrogen bonding (in conjunction with acidic functional groups, such
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Oviedo ICCS&T 2011. Extended Abstract
as carboxylic acid) these bonds allow the moisture to be retained in the coal structure beyond the bulk water removal phase. While it varies from coal to coal, chemical bonding constitutes approximately 20% of the water in Victorian brown coal. Moisture removal from coal can be classified as evaporative (where the water comes out as vapour and can be condensed later) or dewatering, depending on how water is released from the coal matrix. Key parameters that affect drying rate and final moisture content of a dried brown coal include following: pressure and temperature of the drying process, flow rate of drying medium, relative humidity, residence time inside the dryer, size and physical natures of the particles to be dried. The kinetics of water removal depends on the moisture within the coal, as illustrated in figure 4. During the first phase, the surface and intermediate capillary water is evaporated. As moisture content decreases, the internal moisture has to be diffused out overcoming the capillary forces, and the drying rate decreases due to the increased binding forces.
Figure 4: Drying rate of coal with residual moisture content
Drying or dewatering rate and hence the design of a coal dryer is affected by several factors, apart from the the nature of the bonding between the organic matter and the water - the physical nature of coal and its porosity, particle size, pressure, temperature. Figure 5 shows the morphology of a brown coal particle in three micrographs; these clearly show the woody character as micrographs are taken at higher resolutions. Such particles are difficult to fluidize resulting in improper mixing in a steam fluidized bed dryer and therefore ineffective drying of the mass of coal inside the dryer. Woody particles constitute up to 5% of some Victorian brown coals.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 5: Morphology of some of the brown coals – from left to right the electron micrographs show progressively woody character of the coal surface. Figure 6 represents the effect of pressure and particle size on heat transfer during drying of German brown coal in a steam fluidized bed dryer. Higher heat transfer rate is always desirable, as it results in smaller dryers. Smaller particles and higher pressure in general tend to increase heat transfer. However, smaller particles are not always amenable to easier fluidization. Additionally, higher pressure inside the dryer can make fluidization difficult; it also means extraction of high pressure steam, which will reduce the overall efficiency of a process in which the dryer is integrated. Therefore, the choice of particle size, pressure and temperature is always a balance between the degree of drying and the overall efficiency of the overall process.
Figure 6: Effect of particle size and pressure on heat transfer during steam fluidized bed drying of German brown coal (Hoehne et al, 2009) 3. Major technologies - brief description and their status The major technologies for coal drying and dewatering include the following: •
Fluidized bed dryer – steam or hot air fluidized, heating could be steam or hot gas
•
Entrained flow dryer – with high volumes of low-oxygen containg flue or fuel gas
•
Mechanical thermal expression dewatering
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Oviedo ICCS&T 2011. Extended Abstract
•
Hydrothermal dewatering
The subsequent sections present further discussions on the above technolgies and their current status. 3.1 Steam fluidized bed drying High-moisture coals are prone to spontaneous combustion when dried. They should preferably be dried in the absence of oxygen – or, alternatively, at a low oxygen level at lower temperatures - in an inert medium such as steam, which is readily available in a power station. Steam fluidized bed drying with in-bed heating was invented by Professor Owen Potter at Monash University. Steam drying underwent extensive testing and development in Germany, and to a lesser extent in Australia, between 1990 and 2002 (von Bargen, 2007). Figure 7 shows the schematic of a steam fluidized bed dryer. In a steam fluidized bed dryer, raw coal is fluidized by steam, and heat is supplied through immersed tubes using high temperature steam. Usually, a temperature gradient of around 50°C between the heating steam and the dryer bed is preferred to ensure an optimum level of drying and drying time. This means for drying to be accomplished at atmospheric pressure (around 100°C saturation temperature in the bed), the heating steam has to be around 5bar. This steam can potentially be supplied from low-pressure turbines in a coal-fired plant. Variations of the process shown in Figure 7 are possible, e.g. the vapour compressor may be completely dispensed with and the vapour either released into the atmosphere or used for thermal recuperation. In such a case, the heating steam, which is in the immersed coil, could be sourced from the steam cycle of the plant. The volume of the dryer and the level of drying that can be achieved in a steam fluidized bed dryer depend on a number of factors, including: • The conditions of the steam used for heating • The particle size of raw coal feed, which would, in turn, affect the drying time • The fluidisation velocity, which is important to ensure maximum contact between the heating steam and the particles. There are also issues that would be important in scaling up the capacity of the dryer. For example, though finer coal size is conducive to faster drying, effective fluidisation is made more difficult, which influences the level of drying that can be obtained within a reasonable time. RWE of Germany holds the state of the art in both brown coal combustion plant and brown coal drying in its technology (abbreviated in German as
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BoA) with WTA steam fluidized bed pre-drying. In this process, raw coal is milled to a fine grain (0-2mm), which is then dried in a steam fluidized bed. Use of fine grain coal for drying reduces the size and, therefore, the cost of the dryer, it reduces the steam required to maintain fluidisation and it also requires slightly lower steam conditions than would be the case for drying coarser coal. The resulting dried coal contains 66% less than 90µm and less than 9% greater than 1mm (Klutz et al., 2006), while coal moisture content reduces from about 50% to between 10 and 18%, prior to feeding into the mills. Figure 7 shows the general schematic of the WTA steam fluidized bed dryer.
Large-scale demonstration of the WTA process is being carried out by RWE at one of their supercritical units, Niederaussem K, where 25% of Unit K’s input fuel is being treated; energy is saved by feeding only low-grade heat (120°C), in the form of low pressure steam, to fluidise and directly dry the coal. Much of the latent heat from the liberated water vapour is recovered in a heater and used in the system. Results indicate that the unit achieves a much better efficiency than previous lignite units because of the efficiency maximising measures of the plant’s ‘BoA’ or optimised efficiency technology system.
Figure 7: General schematic of WTA steam fluidized bed drying Courtesy RWE Power In addition to the demonstration at Niederaussem K, the WTA technology is also planned for demonstration at the Hazelwood Power Station in Victoria, Australia (Innocenzi, 2008). A WTA drier is planned for retrofitting to an existing 200MWe unit to dry 50% of the original feed of high-moisture coal, to reduce the moisture content 7
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from about 60% to 12%. The dried coal would then be co-fired with 50% high-moisture coal into the boiler. In addition to RWE, Vattenfal in conjunction with Brandenburgh Technical University is also known to develop this technology, although at a slightly positive pressure.
3.2 Hot Air (low temperature) fluidized bed drying Great River Energy (GRE) of the USA demonstrated the Lignite Fuel Enhancement System (LFES), which uses waste heat to dry fuel before being fed into the boiler. The LFES, illustrated in Figure 8, exploits the low-grade heat, which otherwise has little use. In the LFES, low temperature hot air (as opposed to steam in WTA) fluidises and heats the lignite to remove moisture from it. The air stream is cooled and humidified as it flows upward through the fluidized bed. The amount of moisture that can be removed is limited by the drying capacity of the air stream, which is supplemented by an in-bed hot water coil. GRE tested a number of lignites in a 2 tonnes/h pilot-scale dryer to evaluate the drying potential of different feedstocks. Tests confirmed the viability of coal drying and provided a basis for a larger-scale demonstration under the Clean Coal Power Initiative (CCPI). The CCPI-funded project (USDOE, 2008) progressed in phases. The full-scale integrated four-dryer system is designed to reduce the moisture content of all coal burned at the plant by 8.5%-points, from 38.5%.
Figure 8: A schematic of the Lignite Fuel Enhancement System, which uses waste heat from condenser water and flue gas Courtesy: Great River Energy 3.4 Entrained flow or flash drying In the Latrobe valley power stations, Victorian brown coals are dried by recirculating
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hot flue gas through the itegrated mill/drying systems. HRL, as part of its IDGCC process, developed an entrained flow dryer using hot pressurised fuel gas. CRC for Lignite trialled a pressurised entrained flow drier, up to 10 bar, (Ross et al., 2005) using hot flue gas with low oxygen content. Developed properly, this has the potential to be used at least in a two-stage drying process wher the first stage could be entrained flow dryer while the finaly drying can be accomplished in a steam-fluidized bed dryer. White Energy in Australia is another developer of this technology, mainly for sub-bitumnous coals. 3.5
Mechanical Thermal Expression (MTE) dewatering
The MTE process removes moisture from coal without evaporation (dewaters), and is one which builds on work that was undertaken at the University of Dortmund and Diffenbacher (Bergins, 2003) in the late-nineties. It was demonstrated that if coal is heated to 150-200°C, at saturation pressure to prevent evaporation, the water in coal can then be ‘squeezed’ out by applying mechanical pressure. Raising the temperature makes the coal easier to deform under compression and makes the water more mobile by reducing its viscosity and surface tension. A substantial amount of research and development work was undertaken over 12 years in Australia on MTE dewatering by the Cooperative Research Centre for Clean Power from Lignite. This included work at bench scale and then successful development work at the 1 tonne/h scale (McIntosh and Huynh, 2005), wherein the effect of process variables (pressure, temperature, coal type, duration of heating and compression) on the extent of dewatering and throughput were established. Numerous tests were carried out in continuous and cycling batch mode. With Victorian brown coals, it was demonstrated that approximately 70% of the original coal water could be removed at around 200 C and at compression pressures of 60 to 110bar. A 15 tonne/h rig was designed, constructed and operated at the Loy Yang Power (a utility) site in Victoria. No development work is currently in progress.
3.6 Hydrothermal dewatering In hydrothermal dewatering, combination of high temperature and pressure (300 C and 100 bar) decarboxylates the coal. As CO2 is ejected the coal physically shrinks, expelling liquid water from its interstices in the process. The decarboxylation reaction is exothermic and contributes energy to the process, which uses about 2% of the wet brown
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coal’s energy content for the overall process. Although hydrothermal dewatering has a long history of exploratory development, several key issues remain unknown. These include capital cost, scalability, treatment of discharged water. Australian company Exergen is currently the frontrunner in the development of this technology. Other companies working in related technologies are Ignite Energy Resources of Australia and Evergreen Energy of the USA. 3.7 Other drying technologies There are other drying technologies, which are under development or developed from small to medium scale. However, their application to large coal-fired plants for highmoisture coals is yet to be demonstrated. Some of these are: •
Rotary drier – It consists of a slightly tilted large rotating cylindrical shell which is slightly tilted from the feed to the discharge end. The drying medium can be superheated steam, inert gas or hot gas relatively free of oxygen. This is fed in either co-current or counter-current direction to the coal feed. Several companies such as Pinch Technologies and Keith Engineering from Australia and Tsukishima Kikai Ltd of Japan are front-runners of such developments.
•
Microwave drying – Most of the coals are usually transparent to microwave energy. As water is an absorbent of microwave energy, microwave energy if properly delivered can release both bound and free moisture in coal.
Table 1 shows the typical energy consumption and typical drying time for some of the major evaporative drying processes. Such information for the dewatering processes are not yet conclusively known. Table 1: Comparison of energy consumption and typical drying time for major drying processes (Wilson et al, 1992; Karthikeyan et al., 2009) Type of dryer
Steam fluidized dryer
Energy consumption, kJ/kg Drying time to water equilibrium moisture minutes 3100-400 30-40 Lower values achievable with process integration
Hot air or gas fluidized dryer Rotary dryer
3100 3700
1-5 15-40
4. Practical issues and R&D needs
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Coal drying technologies, once commercialised, will make the vast resource of low-rank coals of varying moisture contents much more attractive for utilisation in new power generation units or for co-producton purposes. Significant changes to the structure and physical properties of coal do happen depending on the drying process; chemical properties also get upgraded. However, most high-oxygen containing low-rank coals will remain prone to spontaneous combustion after drying. It is, therefore, likely that pre-drying would still be carried out close to the power stations to avoid problems relating to spontaneous combustion. Disintegration of particles during drying is also an important practical issue. Reduction of particle size depends on the drying process, drying temperature and the type of coal. Experience with pilot-scale hot-gas drying (Ross et al, 2005) indicate that up to 20% finer particle size incerase takes place during drying of Victirian brown coal. Finer particles theoretically dry at a faster rate, but elutriate away from the dryer spending less residence time in the dryer. They also widen the size distribution of the particles being dried, making the design and operation of a dryer difficult. Finer particles are also known to be more hygroscopic, affecting their storage and handling properties. Generation of fines during drying, moisture readsorption and spontaneous combustion are all inter-related issues. Singnificant work have been done (Fei et al, 2009) on spontaneous combustion, but targeted experiments as a function of drying processes (in particular hot-gas drying and steam fluidized bed drying) are required to assess these issues, and the design of appropriate dryers. Other major and immediate needs for development of drying are: •
a reliable feeding system at high pressure, >25 bar, for high-moisture coals to used in gasification systems
•
drying kinetics of fine coal particles using waste heat, low-oxygen flue gas, fuel gas or low-grade steam and changes in their physical structure during the drying process
While all of the aforementioned issues are being addressed to varying extents, there is an urgent need to test the technologies at full-scale on coal-fired power plant.
5. Concluding Comments Drying is the key process before high moisture coals can be used in any applications. There are plenty of drying options for different range of applications. The type of application - whether the application is integrated power generation requiring operation at high availability, or fuels and chemical production through gasification requiring low 11
Oviedo ICCS&T 2011. Extended Abstract
availability - determines the type of coal drying technology needed. It also depends on whether partial drying is acceptable in situation such as retrofit for power generation. If partial drying is acceptable in the first instance, water can potentially be recovered from the flue gas through membranes, which are still in the developmental stage. For power generation purposes, steam fluidized bed drying is decidedly the front-runner and its demonstration for drying of high-moisture coal (~60% moisture) to commercial scale should be vigorously pursued. However, there are certain factors wich will influence commercial success of any technology (Godfrey, 2010). These, apart from maturity and scalability mentioned earlier, include footprint of the drying plant, capital and operating cost, abd capability of integrating with the overall coal conversion process.
Despite significant fundamental research in drying for all sorts of solid materials, coal drying has not yet been fully commercialized to a large scale for power industry application. Scaling-up of steam fluidized bed dryer to large commercial scale appears to be the major stumbling block before its wider application in the power industry. The application of computational fluid dynamics modeling along with targeted measurements in smaller rigs will significantly help in this matter. It is also necessary to generate fundamental data on drying kinetics from a range of coals under different conditions of drying temperature, particle size and heating medium, in particular steam. While modeling effort will shed insights into further development, one should also consider different types of fluidized bed dryer, and two-stage drying. In two-stage drying, first stage could be an entrained-flow dryer using hot fuel or flue gas, while final drying will be carried out in a smaller fluidized bed dryer with less scaling-up and fluidization issues. Incentives are required to accelerate the development and commercialisation of coal predrying technologies to full scale. International cooperation is also important among technology developers and utilities that use high-moisture coals.
Acknowledgement The authors acknowledge the Department of Resource, Energy and Tourism, Australia for their support of this project under its Joint Cordination Group (JCG) Clean Coal Technology program. References
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D. Allardice, The water in brown coal, Chapter 3 in RA Durie (ed.) The Science of Victorian Brown Coal, Butterworth-Heinemann, Oxford 1991, pages 102-150. C. Bergins, Kinetics and mechanism during mechanical/thermal dewatering of lignite, Fuel, V83, 2004, pages 355-364 Y. Fei, A. Abd Aziz, S. Nasir, W.R. Jackson, M. Marshall, J. Hulston, A.L. Chaffee, The spontaneous combustion behavior of some low rank coals and a range of dried products , Fuel, Volume 88, Issue 9,2009, pages 1650-1655 B. Godfrey, Recent Development s in innovative drying technologies, International Lowrank Coal Symposium, Melbourne, April, 2010 O. Hoehne, S. lechner, M. Schreiber, HJ Krautz, Drying of lignite in a pressurized steam fluidized bed – theory and experiments, Drying Technology, V28, Issue 1, 2010, pages 5-19 M. Karthikeyan, J. Kuma, C. Hoe, D. Ngo, Factors affecting quality of dried low-rank coals, Drying Technology, V25, Issue 10, 2007, pages 1601-1611 M. Karthikeyan, W. Zhonghua, A. Mujumdar, Low-rank coal drying technologies – Current Status and new Developments, Drying Technology, V27, Issue 3, 2009, pages 403-415 M. Mcintosh and D. Huynh, Pre-drying of high moisture content Australian brown coal for power generation, Proc 22nd Annual International Coal Preparation and Aggregae processing Conference, Lexington, USA, 2005 D. Ross, S. Doguparthy, D. Huynh, M. McIntosh, Pressurised flash drying of Yallourn lignite, Fuel, Volume 84, Issue 1, January 2005, pages 47-52.
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Pre-combustion CO2 capture: Laboratory- and Bench-scale Studies of a Sweet Water-Gas-Shift Catalyst for H2 and CO2 production J.M. Sánchez, M. Maroño, D. Cillero, L. Montenegro, E. Ruiz CIEMAT, Combustion & Gasification Division, Avenida Complutense, 22, 28040 Madrid (SPAIN; corresponding author:
[email protected] Abstract CIEMAT is currently engaged in several R&D projects dealing with pre-combustion CO2 capture and H2 production studies. In the pre-combustion CO2 capture approach, the carbon of the fuel is removed prior to combustion by partial oxidation or gasification, followed by steam reforming and water-gas shift (WGS) so that a CO2 and H2-rich gas is produced. Both components are subsequently separated usually by means of chemical or physical scrubbing. High purity H2 production often includes a PSA unit. This “conventional” concept is now being proved at a 14 MWth pilot plant in ELCOGAS IGCC. Nonetheless, a lot of R&D effort is still required, specifically focusing on the effect of process conditions on the activity of shift catalysts and looking into enhanced technologies for the reaction. In the first section of this paper, the activity of an iron-chromium-based catalyst for the water-gas-shift reaction is studied. To meet the goals set in the PSE-CO2 projects, the influence on the activity of the sweet shift catalyst of the main operating parameters temperature, space velocity, excess steam, and gas composition- is studied at laboratory scale. Results are presented and discussed. Best operating conditions to maximize selective shift conversion of CO to CO2 and H2 are determined. Lab-scale results also provide base-case data for the CAPHIGAS and FECUNDUS projects, in which a hybrid system for CO2 capture with H2 production is being studied, comprising the WGS catalyst, a CO2-selective sorbent, and a selective membrane for hydrogen removal in a single reactor. Based on the results obtained at lab scale, the second part of this paper deals with subsequent WGS testing at bench-scale, as part of the activities conducted by CIEMAT in the PSE-CO2 project. Preliminary results of bench-scale studies are presented.
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1. Introduction In recent years, production of a hydrogen-rich gas from fossil fuels is attracting interest in power generation processes especially if coupled to CO2 capture. The approach is the so-called “pre-combustion fuel decarbonisation”, in which the carbon of the fuel is removed prior to combustion by partial oxidation or gasification, followed by steam reforming and water-gas shift (WGS) so that a CO2 and H2-rich gas is produced. Both components are subsequently separated and CO2 in the exhaust gas is captured using chemical or physical solvents (e.g. amine scrubbing). The water gas shift (WGS) reaction is, therefore, a key step on production of hydrogen and CO2-capture-ready streams from gasification. The water gas shift (WGS) reaction has been used industrially since the beginning of the 20th century in hydrogen production via coal gasification, as a part of ammonia synthesis by the Haber-Bosch process [1]. It is a mildly exothermic reaction, limited by chemical equilibrium, thermodynamically favoured at low temperatures, and kinetically favoured at high temperatures. To achieve a significant conversion at intermediate temperature, a catalyst is required. According to literature, WGS catalysts can be classified in three main groups: High temperature sweet shift catalysts, usually based on iron oxide with addition of chromium oxide, which operate at inlet temperatures in the range of approximately 320360ºC. Studies are being addressed to the identification of new promoters that are able to increase catalytic activity over larger range of temperature, such as copper [2], [3], rhodium, platinum, nickel, cobalt, manganese, palladium, [4] or to the formulation of Cr-free catalysts, replacing chromium e.g. by aluminium, manganese or cobalt [5] Low temperature sweet shift catalysts, typically based on a Cu/ZnO/Al2O3 or Cu/ZnO/Cr2O3 structure, which are used as second shift stage conducted in the temperature range from 150-250ºC for further decreasing of CO concentration and increasing hydrogen production. R&D efforts deal with the development of advanced catalysts, for instance transition metal supported-ceria (CeO2), including noble metal catalysts such as platinum, rhodium, palladium or gold [6-10]. Sulphur-tolerant WGS catalysts: During (co-)gasification of rich sulphur fuels, e.g. mixtures of coal and pet-coke, H2S concentration in the gas can be as high as 1% v/v. To prevent poisoning of Fe-Cr and especially Cu-Zn-Al catalysts, sulphur is removed before the water gas shift reactor. Shifting the sour gas, using sulphur-tolerant catalysts
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can be an attractive option. Explored catalysts include those based on cobaltmolybdenum compositions [11], the use of Pt/ZrO2 materials [12], [13] or the use of carbides as promising candidates such as molybdenum carbide [14]. In this paper, the activity of an iron-chromium-based catalyst for the water-gas-shift reaction is studied, first at laboratory scale and then at bench scale level.
2. Experimental section 2.1 Catalyst A commercial Fe-Cr-Cu-based sweet WGS catalyst in pellet form was selected for water gas shift studies. The catalyst was used as received in cylindrical tablets of 6x3 mm. For testing at lab scale, 5 g of fresh catalyst was used in every test. For the bench-scale studies the amount of catalyst loaded in the reactor was 2000 g. 2.2 Test rigs Activity of the catalyst was examined firstly at lab-scale in a Microactivity Pro Unit. The unit can work at up to 700ºC and 30 bar. Maximum operating gas flow rate is 4.5 Nl/min. A detailed description of the rig can be found elsewhere [15].
Figure 1. Picture of the bench-scale test rig For testing at bench-scale an existing bench-scale test rig was adapted to WGS studies. This plant had been used extensively for hot gas desulphurisation. It is a high temperature, high-pressure (HTHP) bench scale facility for sorbent and catalyst testing. The plant, shown in Figure 1, can treat up to 20 Nm3/h of a gas mixture simulating the
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composition of gasification gases. It is designed to operate at a maximum temperature of 700ºC and a pressure of 30 bar. Main modifications to the existing facility included a new pump with higher capacity to deliver the flow-rate of water/steam demanded by the WGS reaction and an automatic system for removal of the excess water, installed downstream the reactor. Complete description of the rig can be found in [16]. Gas composition at the reactor inlet and outlet was analysed by gas chromatography. 2.3 Experimental programme Studies at lab scale were focused on the optimisation of shift reactor operating conditions to maximise selective conversion of CO to CO2 and production of hydrogen while ensuring catalyst lifetime. The effect of main operating parameters on the activity and selectivity of the catalyst was determined in the following range: - Temperature, (T): From 250ºC to 380ºC - Gas hourly space velocity (GHSV): From 2500 h-1 to 5000 h-1 - Steam to CO molar ratio (R) between 1 and 3 Despite the fact that WGS is a moderately exothermic reaction, laboratory experiments presented in this work can be considered isothermal, because heat release was almost negligible, due to the small amount of catalyst and the low value of feed gas flow-rate. WGS tests were performed using different gas compositions as shown in Table 1. Table 1. WGS catalytic activity tests: Gas composition (% v/v dry basis) Component H2 CO CO2 N2
M1 23 60 4 13
M2 23 60 17 -
M3 60 40
M4 60 40 -
Under the scope of the PSE-CO2 and CAPHIGAS projects, M1 composition was set according to the gas composition expected for entrained flow oxygen gasification at ELCOGAS IGCC plant. M2 is similar to M1 but it contains more CO2 and is the composition expected for oxygen-carbon dioxide gasification in fluidised bed, which is the approach in the FECUNDUS project. For comparison purposes, M3 and M4 consist of binary mixtures of CO in N2 and CO2 respectively. Studies at bench scale focused on evaluating the performance and the activity of the catalyst at operating conditions which had proved to be successful in laboratory
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experiments. The study has included the effect of steam to CO ratio and the effect of gas composition on the performance of the catalyst. In contrast to the laboratory scale studies, runs conducted at bench-scale level proceeded adiabatically.
3. Results and Discussion 3.1 Laboratory-scale studies The catalyst started to be active around 280-300 ºC, depending on operating conditions and it did not require any activation or became active on-stream. CO conversion increased on increasing temperature and reached a maximum between 350 ºC and 380 ºC, as Figure 2 shows.
100 90
CO Conversion (% mol)
80 70 60 50
20bar
40 30 20 10 0 300
320
340
360
380
Temperature (ºC)
Figure 2. Effect of temperature on CO conversion (SV=4715 h-1, P= 20 bar, Gas composition (%v/v): N2 13 %, CO 60 %, H2 23 %, and CO2 4 %, R=3)
In all tests, despite the high CO content in the feed gas -60 % v/v dry basis- the catalyst showed very good performance at intermediate temperatures 320 ºC-380 ºC rising hydrogen content in the gas from 23%v/v (dry basis) at the reactor inlet to around 4850 %v/v at the reactor outlet and reducing CO concentration at the reactor outlet to less than 3 % v/v. Regarding the influence of space velocity, higher GHSV values led to lower CO conversion and a higher temperature was required to achieve a given CO conversion as shown in Figure 3.
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CO conversion for different GHSV values. Steam/CO=2 100 90
Equilibrium R=2
CO conversion (% mol)
80
-1
SV= 2885 h ; R= 2
70 60 -1
50
SV= 4715 h ; R= 2
40 30 20 10 0 -10 240
260
280
300
320
340
360
380
400
420
Temperature (ºC)
Figure 3. Effect of space velocity and on CO conversion Gas composition (%v/v): N2 13 %, CO 60 %, H2 23 %, and CO2 4 %
The effect of steam to carbon monoxide ratio was also evaluated. At least a steam to CO ratio of 1 is required to convert all CO into CO2. It is known, however, that running the WGS reaction at stoichiometric steam to CO ratio can promote undesirable secondary reactions, such as Boudouard reaction or methane formation. In order to prevent secondary reactions and to drive the reaction thermodynamically to the products side, excess steam is often used, though consequently, this poses a penalty on the energy efficiency of the process. In this study steam to CO ratio was varied from 1 to 3. Effect of excess steam on CO conversion 100
Equilib R=2
90
R=2 CO conversion (% mol)
80 70
R= 1
60 50 40 30 20
-1
Gas space velocity SV = 2885 h
10 0 240
260
280
300
320
340
360
380
400
Temperature (ºC)
Figure 4. Effect of steam to CO ratio on CO conversion Gas composition (%v/v): N2 13 %, CO 60 %, H2 23 %, and CO2 4 %, P=10 bar
At low space velocity a noticeable enhancement of catalytic activity is gained on doubling steam to CO ratio as Figure 4 shows. Secondary reactions such as methane formation was not found to be taking place, even when steam to CO ratio was set at the
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stoichiometric value (R=1). However at higher space velocities (SV> 4715 h-1) and low steam to CO ratio, R ≤ 2, carbon built on the surface of the catalyst and methane formation was detected, so that a steam to CO ratio above 2 is required. A further increase of the steam to CO ratio (R=3) did not result in significantly higher CO conversion. The effect of CO2 content in the feed gas on the activity of the catalyst is shown in Figure 5. Above 330 ºC, increasing the content of CO2 resulted in a decrease of CO conversion, which was directly related to CO2 content in the feed gas. At 300 ºC, there was not a clear relationship between CO2 content in the feed gas and CO conversion, what might indicate that the presence of H2 was also influencing CO conversion.
Influence of feed gas composition 100 -1
SV= 4715 h , R H2O/CO=3, P= atmospheric 90
xCO (% mol/mol)
80
70
CO 60%; N2 40% CO 60%; H2 23%; CO2 4%; N2 13%
60
CO 60%; H2 23%; CO2 17% CO 60%; CO2 40%
50
40 300
320
340
360
380
Temperature (ºC)
Figure 5. Effect of gas composition and CO2 content on CO conversion SV=4715 h-1, R=3, P=1 bar
3.2 Bench scale studies Several studies were performed to examine the activity of the catalyst at bench-scale. The system showed an adiabatic behaviour, with temperature increasing due to the exothermic nature of the WGS reaction. In all tests, CO conversion increases quickly as soon as the reaction starts, what happens around 310 ºC, and so does the catalyst bed temperature, though never exceeding 560 ºC, what ensures that the catalyst is not damaged due to sintering. As an example, Figure 6 shows the test carried out at SV=4715 h-1, R=3. As can be seen, temperature and CO conversión is stabilized and maintained over time.
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Oviedo ICCS&T 2011. Extended Abstract
100
540 520
90
500 480
Temperature (ºC)
70
440 Sv = 4715 h-1 R=3
420 400
60
Bed temperature CO Conversion
380 360
50 40
340 30
320 300
20
CO Conversion (% mol)
80
460
280 10
260 240 0
30
60
90
120
150
180
210
240
0 300
270
Time (min)
Figure 6. Evolution of temperature profile and CO conversion during WGS study at bench scale. Gas composition (%v/v d.b.): N2 13 %, CO 60 %, H2 23 %, and CO2 4 %, P=10 bar, SV=4715 h-1, R=3, inlet T= 331 ºC
The effect of steam to CO ratio on CO conversion was determined for three R values (R = 1.61, 2 and 3). As shown on Figure 7, slightly higher CO conversion is achieved on increasing steam to carbon as predicted by the laboratory study. Secondary reactions were not found to be occurring. CO concentration at the reactor outlet decreased to less than 5% when using R=3, and to less than 9% for R=1.61. Average increase of bed temperature (ΔT) ranged between 210 and 230ºC. Average ΔT
280 260 240
100
Average CO Conversion Sv = 4715 h-1 R = 1,61
Sv = 4715 h-1 R=2
Sv = 4715 h-1 R=3
80
200
ΔT (ºC)
180
60
160 140 120
40
100 80 60
20
CO Conversion (% mol)
220
40 20 0
0
Figure 7. Bench scale -WGS study: Effect of steam to CO ratio on bed temperature and CO conversion Gas composition (%v/v d.b.): N2 13 %, CO 60 %, H2 23 %, and CO2 4 %, P=10 bar, SV=4715 h-1, R=1.61, 2 & 3, inlet T between 294 and 344 ºC
4. Conclusions The activity for the water gas shift reaction of an iron-chromium-based catalyst has been studied on laboratory and bench-scale. Despite the high CO content in the feed gas, by
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Oviedo ICCS&T 2011. Extended Abstract
choosing the right shift reactor conditions, CO concentration at the reactor outlet reached values below 3%, whereas H2 increased up to above 50% v/v (dry basis). Isothermal tests conducted at laboratory-scale experiments show that increasing space velocity leads to lower CO conversion and a higher temperature is required to achieve a given CO conversion. A higher H2O/CO ratio leads to higher carbon monoxide conversion, and without undesired secondary reactions. Higher CO2 content in the feed gas inhibits slightly the activity of the catalyst, especially above 300 ºC. Adiabatic tests carried out at bench-scale level shows that with a gas temperature at the reactor inlet of about 310 ºC, the WGS proceeds successfully. In the less efficient case, CO content at the reactor outlet reaches values below 9% v/v (dry basis), that is overall conversion is about 85 % (%mol/mol). Maximum gas temperature due to the heat release of the WGS reaction stays below 560 ºC and therefore loss of activity due to sintering is not expected. As happened for laboratory scale experiments, increasing steam to carbon monoxide ratio leads to slightly higher CO conversion which makes possible to achieve a content of CO at the reactor outlet as low as 5%.
Acknowledgement This research is financed by the European Union, Research Fund for Coal and Steel, FECUNDUS project (RFCS-CT-2010-00009), and by the Spanish Ministry of Science and Innovation through PSE-CO2 project, (PSE-120000-2008-29) and CAPHIGAS project, (ENE2009-08002).
References [1] Topham SA. The history of the catalytic synthesis of ammonia. In: Anderson JR, Boudart M, editors. Catalysis Science and Technology, New York: Springer Verlag; 1985, p. 1–50. [2] Andreev A, Idakiev V, Mihajlova D, Shopov D. Iron-based catalysts for the water gas shift reaction promoted by first-row transition metal oxides. Appl Catal 1986;22:385–7. [3] Edwards MA, Whittle DM, Rhodes C, Ward AM, Rohan D, Shannon MD et al. Microestructural studies of the copper promoted iron oxide/chromia water gas shift catalyst. Phys Chem Chem Phys 2002;4:3902–8. [4] Lei Y, Trimm DL, Cant NW, Tran T. Novel Fe-Cr Oxide catalyst for water gas shift reaction. In: Coombs S, Dicks A, editors. Proceedings of the First Nanomaterials Conference. NSW, Australia; 2004, p. 21–23.
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Oviedo ICCS&T 2011. Extended Abstract [5] Natesakhawat S, Wang X, Ozkan US. High-Temperature Water-Gas Shift Reaction over CrFree Fe-Al Catalysts Promoted with First Row Transition Metals. In: AIChE editors ISBN 08169-0965-2. Proceedings of the AIChE Annual Meeting 2004. Austin, Texas; 2004, paper 24d. [6] Jacobs G, Patterson PM, Williams L, Chenu E, Sparks D, Thomas G et al. Water gas shift: in situ spectroscopic studies of noble metal promoted ceria catalysts for CO removal in fuel cell reformers and mechanistic implications. Appl Catal A-Gen 2004;262:177–87. [7] Tibiletti D, Bart de Graaf EA, Phen The S, Rothenberg G, Farrusseg D, Mirodatos C. Selective CO oxidation in the presence of hydrogen: fast parallel screening and mechanistic studies on ceria-based catalysts. J Catal 2004;225:489–97. [8] Luengnaruemitchai A, Osuwan S, Gulari E. Comparative studies of low-temperature watergas shift reaction over Pt/CeO2, Au/CeO2 and Au/Fe2O3 catalysts. Catal Commun 2003;4:215– 21. [9] Fu Q, Kudriavtseva S, Saltsburg H, Flytzani-Stephanopoulos M. Gold-ceria catalysts for low-temperature water gas shift reaction. Chem Eng J 2003;93:41–53. [10] Panagiotopoulou P, Kondarides DI. Effect of morphological characteristics of TiO2supported noble metal catalysts on their activity for the water gas shift reaction. J Catal 2004; 225:327–36. [11] Song C. Overview of hydrogen production options for hydrogen energy development, fuelcell processing and mitigation of CO2 emissions. In: Proceedings of the 20th International Pittsburgh Coal Conference. Pittsburgh, PA; 2003, paper Nº 40-3. [12] Xue E, O`Keeffe M, Ross JRH. Water gas shift conversion using a feed with a low steam to carbon monoxide ratio and containing sulphur. Catal Today 1996; 30:107–118. [13] Maroño M, Sánchez JM, Ruiz E, Cabanillas A. Study of the suitability of a Pt based catalyst for the upgrading of a biomass gasification syngas stream via the WGS reaction. Catal Lett 2008;126:396–406. [14] Patt J, Moon DJ, Phillips C, Thompson L. Molybdenum carbide catalysts for water gas shift. Catal Lett 2000;65:193–5. [15] Maroño M, Sánchez JM, Ruiz E. Hydrogen-rich gas production from oxygen pressurized gasification of biomass using a Fe–Cr Water Gas Shift catalyst. Int J Hydrogen Energy 2010;35: 37–45. [16] Sánchez JM, Ruiz E, Otero J. Selective Removal of Hydrogen Sulfide from Gaseous Streams Using a Zinc-Based Sorbent. Chem Eng Sci 2005;60:2977–89.
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Regeneration of used alkali carbonates for removal of gaseous sulfur compounds in gasification process Slamet Raharjo1, Yasuaki Ueki2, Ryo Yoshiie1 and Ichiro Naruse1 1
Department of Mechanical Science and Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, JAPAN 2 Energy Science Division, EcoTopia Science Institute, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, JAPAN
[email protected] Abstract Integrated gasification combined cycle system (IGCC) is expected to play an important role in one of high efficient coal conversion technologies. However, it is necessary to remove H2S and COS almost completely to supply the gasified gas into a gas turbine as a fuel. Although molten alkali carbonates of 43 mol-Na2CO3 + 57 molK2CO3 can completely absorb them even at high temperature, the regeneration of the used molten alkali carbonates is one of the important issues in enhancing the overall efficiency more in the gasification system. Therefore, the present work studies the regeneration of the used molten alkali carbonates by using CO2 and CO2 + steam as regeneration agents. As a result, only about 8 mass% and 5 mass% of sulfur were remained as solid sulfur after the regeneration at 900 K and 773 K by using CO2 and CO2 + steam as the regeneration agents, respectively. The steam addition contributed to decreasing the regeneration temperature. The dominant gaseous sulfur produced during the regeneration was COS and H2S for CO2 and CO2 + steam, respectively. Keyword: Molten alkali carbonates, Hot gas desulfurization, Coal gasification, Regeneration
1. Introduction Coal gasification processes emit pollutants of gaseous sulfur of H2S and COS, which are hazardous and corrosive [1]. H2S and COS contained in the gasified gas may cause some failures to the subsequent units such as a gas turbine and a fuel cell. Therefore, direct utilization of the gasified gas as a fuel or a chemical feed stock requires removal of H2S and COS in the gasified gas almost completely [2]. The integrated gasification fuel cell combined cycle (IGFC) operated under the EAGLE project in Japan currently uses the cold gas clean-up system to remove the gaseous
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Oviedo ICCS&T 2011. Extended Abstract
sulfurs [3]. However, integrating the hot gas desulphurization (HGD) system offers some potential benefits including improved thermal efficiency and environmental performance, reduced capital and operating costs, and the use of a more advanced, high efficiency gas turbine [2]. The hot gas desulfurization system by using molten alkali carbonates (43 mol-Na2CO3 + 57 mol-K2CO3) was studied in our previous work [4]. It suggested that the molten alkali carbonates could completely remove the gaseous sulfurs of H2S, COS and SO2 even at high temperature of 1173 K. Reactions between the molten alkali carbonates and the gaseous sulfurs result in formation of alkali sulfides (Na2S and K2S) mainly. However, they must be converted back to the alkali carbonates in order to recycle the used solvent into the gasification system. Therefore, the present work studies the regeneration of the used molten alkali carbonates by using CO2 and CO2 + steam as the regeneration agents.
2. Experimental First, the FactSage, which could estimate chemical equilibrium solutions, was used to determine the optimum regeneration condition for the regeneration experiments. The regeneration experiments were conducted by a tube reactor made of quartz. Figure 1 shows the schematic diagram of the tube reactor employed in this study. Steam generator Quartz tube reactor
Outlet
M2S sample N2 CO2
GC-FPD
Activated carbon
Waterpump EMIA-120
Residue
Ultrapure water
Fig. 1 Schematic of experimental apparatus Nitrogen gas was used as a purge gas prior to supplying the regeneration agent. The alkali sulfide sample set inside a ceramic boat was put into the quartz tube reactor. The first holding temperature was 383K in order to remove the moisture and the crystal
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Oviedo ICCS&T 2011. Extended Abstract
water in the sample. Then, the temperature was raised to the regeneration temperature, and was kept for 30 min under nitrogen atmosphere before switching to the regeneration agent of CO2 or CO2 + steam.
It kept 60 min for the regeneration. Solid sulfur
concentration remaining in the residue after the regeneration experiments was analyzed by using a sulfur analyzer, while the gaseous sulfur compositions in the exit gas were detected by a FPD gas chromatograph.
3. Results and Discussion 3.1 Chemical equilibrium calculations to estimate the optimum regeneration conditions Figure 2 shows the results of chemical equilibrium calculation for the regeneration process by CO2 as the regeneration agent. These graphs display the production fractions of (a) sodium carbonate and (b) potassium carbonate, which correspond to the regeneration efficiency. The higher amount of sodium or potassium carbonate means that the higher amount of sodium or potassium sulfide reacted with CO2. The variation in CO2 amount has minor effect to the production fraction of sodium carbonate, whereby, the relatively higher amount of CO2 would be favorable for potassium carbonate. Additionally, the simulations suggest that the optimum regeneration temperature lies between 600 K and 900 K. Figure 3 presents the results of chemical equilibrium calculation for the regeneration process by CO2 + steam under various ratios of CO2/steam. The various ratios of CO2/steam result in a little effect on sodium carbonate formation, while CO2/steam ratio of 1/2 exhibits the highest production fraction of potassium carbonate at low temperature. The optimum range of temperature would be between 500 K and 900 K. Based on those calculation results, the experimental conditions of regeneration experiments on the tube reactor for CO2 as the regeneration agent are shown in Table 1.
3.2 Regeneration experiments Figure 4 shows the remaining solid sulfur in the sample after the regeneration experiments for CO2 as the regeneration agent. As seen from the figure, around 900 K would be the optimum regeneration temperature. At this temperature, the remaining solid sulfur becomes only 8 mass% of the total sulfur content in the sample. Based on
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Oviedo ICCS&T 2011. Extended Abstract
this result, around 92 mass% of sulfur might have been vaporized as gaseous sulfurs during regeneration.
(a) Production fraction of sodium carbonate 100
Na2CO3 (s) [mole%]
80 60 40 Alkali sulfide/Carbon dioxide=1/4 (mole ratio)
20
Alkali sulfide/Carbon dioxide=1/50 (mole ratio) 0 470 510 550 590 630 670 710 750 790 830 870 910 950 990 Temperature [K]
(b) Production fraction of potassium carbonate 100 Alkali sulfide/Carbon dioxide=1/4 (mole ratio) Alkali sulfide/Carbon dioxide=1/50 (mole ratio)
K2CO3 (s) [mole%]
80
60
40
20
0 470 510 550 590 630 670 710 750 790 830 870 910 950 990 Temperature [K]
Fig. 2 Results of chemical equilibrium calculation of regeneration reactions for CO2 as a regeneration agent Further experiments for the mixture of CO2 and steam as the regeneration agent were also carried out by using the tube reactor. The experimental condition is provided
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Oviedo ICCS&T 2011. Extended Abstract
in Table 2. The ratio 1:2 of CO2/steam was chosen, based on the chemical equilibrium calculation result.
(a) Production fraction of sodium carbonate 100
Na2CO3 (s) [mole%]
80
60 Carbon dioxide/steam=1/1 (mole ratio) 40
Carbon dioxide/steam=1/2 (mole ratio) Carbon dioxide/steam=1/4 (mole ratio)
20
Carbon dioxide/steam=2/1 (mole ratio) Carbon dioxide/steam=4/1 (mole ratio)
0 450 490 530 570 610 650 690 730 770 810 850 890 930 970 1010 Temperature [K]
(b) Production fraction of potassium carbonate 100
K2CO3 (s) [mole%]
80
60
40
Carbon dioxide/steam=1/1 (mole ratio) Carbon dioxide/steam=1/2 (mole ratio) Carbon dioxide/steam=1/4 (mole ratio)
20
Carbon dioxide/steam=2/1 (mole ratio) Carbon dioxide/steam=4/1 (mole ratio)
0 450 490 530 570 610 650 690 730 770 810 850 890 930 970 1010 Temperature [K]
Fig. 3 Results of chemical equilibrium calculation of regeneration reactions for CO2 + steam as a regeneration agent
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Oviedo ICCS&T 2011. Extended Abstract
The remaining solid sulfur after the regeneration experiments by CO2 + steam is shown in Fig. 5. The result suggests that the lowest remaining solid sulfur of around 5 mass% of the total sulfur content in the sample can be achieved at the optimum regeneration temperature of 773 K. That means around 95 mass% of sulfur is expected to be vaporized during regeneration. Table 1 Experimental conditions of tube reactor for CO2 as the regeneration agent Sample
Na2S.9H2O + K2S
Na2S/K2S mole ratio
1/1
Atmosphere
N2, changed to the regeneration agent
Particle size
< 500 μm
N2 flow rate
1 L/min
CO2 flow rate
1 L/min
1st holding temperature
383 K for 8 min
2nd holding temperature
650 K or 925 K for 30 min
Regeneration temperature
650 K or 925 K for 60 min
Remaining solid sulfur [mass%]
50 45 40 35 30 25 20 15 10 5 0 650K
773K
873K
900K
925K
Temperature [K]
Fig. 4 Results of the remaining sulfur after the regeneration experiment by CO2 as the regeneration agent
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Oviedo ICCS&T 2011. Extended Abstract
Table 2 Experimental conditions of tube reactor for CO2 + steam as the regeneration agent Sample
Na2S.9H2O + K2S
Na2S/K2S mole ratio
1/1
CO2/steam mole ratio
½
Particle size
< 500 μm
N2 flow rate
1 L/min
H2O (l) flow rate
0.57 ml/min
CO2 flow rate
0.40 L/min
1st holding temperature
383 K for 8 min
2nd holding temperature
550 K or 873 K for 30 min
Regeneration temperature
550 K or 873 K for 60 min
Remaining solid sulfur [mass%]
20 17.5 15 12.5 10 7.5 5 2.5 0 550K
650K
773K
873K
Temperature [K]
Fig. 5 Results of the remaining sulfur after the regeneration experiment by CO2 + steam as the regeneration agent Comparing between Figs. 4 and 5, the regeneration process of the addition of steam results in lower regeneration temperature, compared to that without steam. It is obvious that the steam addition contributes to decreasing the optimum regeneration
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Oviedo ICCS&T 2011. Extended Abstract
temperature, which is favourable in enhancing the overall efficiency more in the gasification system.
(a) CO2 as the regeneration agent 60 Gas Concentration [ppmV]
Carbonyl sulfide 50 Hydrogen sulfide 40
Sulfur dioxide
30 20 10 0 15'
30'
45'
60'
Sample (minutes)
(b) CO2+steam as regeneration agents
Gas Concentration [ppmV]
110 100
Carbonyl sulfide
90
Hydrogen sulfide
80
Sulfur dioxide
70 60 50 40 30 20 10 0 15'
30'
45'
60'
Sample (minutes)
Fig. 6 Gaseous sulfur concentrations in the exhaust gas during regeneration
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Oviedo ICCS&T 2011. Extended Abstract
Figure 6 shows some gaseous sulfur concentrations including COS, H2S and SO2 in the exhaust gas during regeneration at 650 K under the conditions of (a) CO2 and (b) CO2 + steam as the regeneration agent. From this figure, COS is the dominant gaseous sulfur among others for CO2. Meanwhile, H2S is the dominant gaseous sulfur for CO2 + steam. Based on those results, the expected regeneration reaction scheme for both cases can be proposed as follows: With CO2 as the regeneration agent: Na2S[s] + K2S[s] + 4CO2[g] Æ Na2CO3[s] + K2CO3[s] + 2COS[g] With CO2 + steam as regeneration agents: Na2S[s] + K2S[s] + 2CO2[g] + 2H2O[g] Æ Na2CO3[s] + K2CO3[s] + 2H2S[g]
4. Conclusions The used alkali carbonates could be regenerated by using CO2 and CO2 + steam. The lowest remaining sulfur after regeneration of around 8 mass% of the total sulfur content in the sample was achieved at around 900 K by CO2 as the regeneration agent. Meanwhile, the regeneration by a mixture of CO2 and steam resulted in lower temperature between 650 K and 773 K. For the regeneration process by CO2, COS emitted as the dominant gaseous sulfur, while H2S was dominant for CO2 + steam as the regeneration agents.
References [1]
Lew S, Sarofim AF, Stephanopoulos MF. Sulfidation of zinc titanate and zinc oxide solids. Ind Eng Chem Res 1992;31:1890–1899 .
[2]
Mitchell SC. Hot Gas Cleanup of Sulphur, Nitrogen, Minor and Trace Elements. London: IEA Coal Research; 1998.
[3]
Kimura N. EAGLE project perspective on coal utilization technology. APEC Clean Fossil Energy Technical and Policy Seminar. Philippines; 2005, Jan.
[4]
Raharjo S, Ueki Y, Yoshiie R, Naruse I. Hot gas desulfurization and regeneration characteristics with molten alkali carbonates. International Journal of Chemical Engineering and Application 2010;1:96–102 .
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Step Change Adsorbents and Processes for CO2 capture “STEPCAP”
T.C. Drage1 A.I Cooper3, R Dawson3, J Jones3, C Cazorla Silva4, C.E. Snape1, L. Stevens1, X. Guo4, J. Wood2, J. Wang2 1
Department of Chemical and Environmental Engineering, Faculty of Engineering,
University of Nottingham, Nottingham, NG7 2RD, UK. Fax: 44 (0)115 951 9514115; Tel: 44 (0)115 9514099; E-mail:
[email protected]. 2
Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham, B15
2TT, UK. 3
Department of Chemistry, Crown Street, The University of Liverpool, Liverpool, L69
7ZD, UK 4
Department of Chemistry, University College London, London, WC1H 0AJ, UK.
Abstract STEPCAP is a multipartner consortium project, the aim of which is to develop a targeted range of novel CO2 adsorbents for carbon capture. This research into materials and process development is essential to achieve the potential cost and efficiency benefits offered by solid sorbents capture technologies over the current state of the art processes. Firstly, this paper will discuss the key materials and process challenges associated with developing solid sorbents. This will lead into a discussion of materials development in STEPCAP which is based on a fundamental understanding of adsorption processes to design and optimise material properties and form. The development and performance of the three classes of materials under development in this study, microporous polymers, surface modified hydrotalcites, and co-doped sorbents, which offer potential for a step change increase in adsorption capacity and performance over previously developed materials will be discussed. Modified hydrotalcites such as, amine modified layered double hydroxides (LDH’s) have been synthesized via the exfoliation and grafting route. In addition, novel conjugated microporous polymers synthesized through SonogashiraHagihara coupling have also been investigated and have demonstrated similar capacities. Critically, due to the hydrophobic nature of some of these adsorbents, identical performance has been observed in the presence of moisture, an advantageous property for operation in the water saturated environment of flue gases. This presentation will
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Oviedo ICCS&T 2011. Extended Abstract
also present data on the performance of these materials in simulated flue gases as well after simulated temperature swing regeneration cycles to assess the stability and lifetime of the sorbents.
1. Introduction Recognising that fossil fuels will continue globally as part of a diverse energy mix for some time[1], targets and strategies have been developed to reduce greenhouse gas emissions, for example the European Unions Sustainable Energy Technology (SET) Plan[2]. Rapid development and implementation of these strategies will be required if the warnings of potentially damaging climate change reported by the Intergovernmental Panel on Climate Change (IPCC) are to be avoided[3], a task that is made more challenging when set against the significant global increase in energy demand[1]. Europe is committed to an 80% reduction in greenhouse gas emissions by 2050[4] and similar emissions reduction targets have been proposed and committed to on a global scale[5]. The current state of the art technologies for post-combustion capture, amine solvent scrubbing, uses aqueous solutions of alkanolamines to achieve CO2 separation from flue gas[6-8]. Whilst this technology is the current state of the art and will be used in the first generation of carbon capture plant, the technology has a number of drawbacks in terms of complexity in operation, high pH solvents leading to corrosion of metal piping, and the energy-intensive regeneration of the solvents[6]. This high energy usage of this process has led to the proposal of a range of potentially more efficient and less energy intensive second and third generation capture technologies[9]. The development of a solid adsorbent capture technology is one of the most promising alternative capture technologies[9]. A key motivation for the development of solid adsorbents for carbon capture is the potential energy saving shown by theoretical studies. These studies suggest that an adsorbent system with a cyclic capacity approaching or better than 3 mmol g-1 could significantly reduce the energy requirement of post-combustion capture by 30-50% compared with amine solvent systems[10]. A wide range of materials have been developed for this application[11] and include, supported amines and immobilized amines[12-16] activated carbons[17-19], Hydrotalcites[20], zeolites[21], inorganicorganic hybrid materials such as Metal Organic Frameworks (MOFs)[22]. Of all the materials developed and tested the challenge still remains to develop materials that
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Oviedo ICCS&T 2011. Extended Abstract
achieve these performance targets and are fully stable under the conditions of postcombustion flue gases[23].
2. Experimental Adsorbent materials have been characterised and tested using a range of techniques. Characterisation of materials has focussed on determining the physical and chemical properties of the solid sorbent materials. This has been conducted using a range of techniques, for example, elemental analysis, powder x-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectra (DRIFTS), textural properties have been determined by N2 adsorption analysis . Thermogravimetric analysis (TGA) has been used to determine the thermal stability of the materials as well as measure CO2 adsorption capacity and cyclic capacity[14].
3. Results and Discussion To realise the potential of solid sorbent for carbon capture two developments are required, new porous materials and plant integration processes. The key challenges for materials development and requirements in terms of: operating conditions, gas composition, stability and lifetime required to make solid sorbents a viable large scale CO2 capture process are described in this presentation[24]. To date a wide range of materials have been developed and tested as part of the STEPCAP project. The key materials under development are, microporous polymers, surface modified hydrotalcites, and co-doped sorbents. Performance of these materials has been assessed under a range of conditions and will be presented. Current key developments are summarised as follows: Hydrotalcites and conjugated microporous polymers have been studied as potential adsorbents for CO2 capture[25, 26]. Modified hydrotalcites such as, amine modified layered double hydroxides (LDH’s) were synthesized via exfoliation and grafting route. The influence of primary and secondary amines on carbon dioxide adsorption was investigated. One hydrotalcite with
3-[2-(2-Aminoethylamino) ethylamino]propyl-
trimethoxysilane, containing both a primary and secondary amine functional groups showed a steady increase in CO2 adsorption capacity of 0.74 - 1.76 mmol g-1 from 25 80oC through the flue gas temperature range. Synthetic microporous polymers possess some of the highest reported surface areas[27]
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Oviedo ICCS&T 2011. Extended Abstract
and some preparative routes might in principle be applicable to CCS applications[28]. A key benefit of porous organic chemistries is the very diverse synthetic organic chemistry which is available, both in terms of the wide range of monomers that can be exploited either by direct incorporation[29-31] or by the possibility of post-synthetic modification of networks to include functional groups reactive to CO2. These routes to materials synthesis are being explored as part of the STEPCAP project.
Incorporation of
functional monomers has been shown to be useful in tuning the isosteric heat of adsorption of CO2 by these materials[32]. A further advantage of organic polymeric networks over other highly porous synthetic materials such as hybrid inorganic-organic materials is their high moisture stablility together with high thermal stability[27]. However, despite recent reports of uptakes of around 3 mmol g-1 at ambient temperatures[33] microporous organic polymers have yet to achieve high enough CO2 loadings under the required conditions to be commercialised.
4. Conclusions The development of solid sorbents for CO2 capture is an area of significant academic and industrial interest. The composition of the flue gases in post-combustion capture and the requirements for material performance to minimise the energy penalty of the capture process present a significant challenge for materials development. To date, a wide range of functional materials have been and will continue to be developed with potential to make breakthrough. Whilst at present the required cyclic capture capacities can be achieved, one of the main challenges still remains to develop materials that can operate reliably and over a large number of cycles in a flue gas environment, a challenge which will form the future focus of the STEPCAP project.
Acknowledgement. The authors would like to thank E.ON-EPSRC strategic call on CCS for funding the Step Change Adsorbents and Processes for CO2 Capture research programme EP/G061785/1.
References [1] World Energy Outlook 2008 Edition, International Energy Agency, 2009. [2] P. Capros, L. Mantzos, N. Tasios, A. De Vita, N. Kouvaritakis, EU energy trends to 2030Update 2009, 2010.
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Oviedo ICCS&T 2011. Extended Abstract
[3] E. Rubin, L. Meyer, H. de Coninck, IPCC Special Report: Carbon Dioxide Capture and Storage, 2005. [4] Department of Trade and Industry. Meeting the Energy Challenge: A White Paper on Energy, 2007. [5] United Nations Framework Convention on Climate Change (UNFCCC). Report of the Conference of the Parties on its sixteenth session, held in Cancun from 29 November to 10 December 2010. Part one: Proceedings., 2011. [6] C.L. Leci, Financial implications on power generation costs resulting from the parasitic effect of CO2 capture using liquid scrubbing technology from power station flue gases, Energ Convers Manage, 37 (1996) 915-921. [7] H.J. Herzog, E.M. Drake, Greenhouse Gas R&D programme. IEA/93/oE6, (1993). [8] R.M. Davidson, Post-combustion carbon capture from coal fired plants - solvent scrubbing. IEA Clean Coal Centre, 2007. [9] J.D. Figueroa, T. Fout, S. Plasynski, H. McIlvried, R.D. Srivastava, Advancesn in CO2 capture technology - The US Department of Energy's Carbon Sequestration Program, Int J Greenh Gas Con, 2 (2008) 9-20. [10] M.L. Gray, K.J. Champagne, D. Fauth, J.P. Baltrus, H. Pennline, Performance of immobilized tertiary amine solid sorbents for the capture of carbon dioxide, Int J Greenh Gas Con, 2 (2008) 3-8. [11] R. Davidson, Post-combustion carbon capture – solid sorbents and membranes. IEA CLean Coal Centre, 2009. [12] X.C. Xu, C.S. Song, J.M. Andresen, B.G. Miller, A.W. Scaroni, Novel polyethylenimine-modified mesoporous molecular sieve of MCM-41 type as high-capacity adsorbent for CO2 capture, Energ Fuel, 16 (2002) 1463-1469. [13] X.C. Xu, C.S. Song, J.M. Andresen, B.G. Miller, A.W. Scaroni, Preparation and characterization of novel CO2 "molecular basket" adsorbents based on polymer-modified mesoporous molecular sieve MCM-41, Micropor Mesopor Mat, 62 (2003) 29-45. [14] T.C. Drage, A. Arenillas, K.M. Smith, C.E. Snape, Thermal stability of polyethylenimine based carbon dioxide adsorbents and its influence on selection of regeneration strategies, Micropor Mesopor Mat, 116 (2008) 504-512. [15] P.J.E. Harlick, A. Sayari, Applications of pore-expanded mesoporous silicas. 3. Triamine silane grafting for enhanced CO2 adsorption, Ind Eng Chem Res, 45 (2006) 32483255. [16] R. Serna-Guerrero, E. Da'na, A. Sayari, New Insights into the Interactions of CO2 with Amine-Functionalized Silica, Ind Eng Chem Res, 47 (2008) 9406-9412. [17] C. Pevida, T.C. Drage, C.E. Snape, Silica-templated melamine-formaldehyde resin derived adsorbents for CO2 capture, Carbon, 46 (2008) 1464-1474. [18] A. Arenillas, K.M. Smith, T.C. Drage, C.E. Snape, CO2 capture using some fly ashderived carbon materials, Fuel, 84 (2005) 2204-2210. [19] T.C. Drage, A. Arenillas, K.M. Smith, C. Pevida, S. Piippo, C.E. Snape, Preparation of carbon dioxide adsorbents from the chemical activation of urea-formaldehyde and melamineformaldehyde resins, Fuel, 86 (2007) 22-31. [20] S. Walspurger, L. Boels, P.D. Cobden, G.D. Elzinga, W.G. Haije, R.W. van den Brink, The Crucial Role of the K+-Aluminium Oxide Interaction in K+-Promoted Alumina- and Hydrotalcite-Based Materials for CO2 Sorption at High Temperatures, Chemsuschem, 1 (2008) 643-650. [21] P. Xiao, J. Zhang, P. Webley, G. Li, R. Singh, R. Todd, Capture of CO2 from flue gas streams with zeolite 13X by vacuum-pressure swing adsorption, Adsorption, 14 (2008) 575582.
Submit before 31 May 2011 to
[email protected] 5
Oviedo ICCS&T 2011. Extended Abstract
[22] A. Torrisi, R.G. Bell, C. Mellot-Draznieks, Functionalized MOFs for Enhanced CO2 Capture, Cryst Growth Des, 10 (2010) 2839-2841. [23] S. Sjostrom, H. Krutka, Evaluation of solid sorbents as a retrofit technology for CO2 capture, Fuel, 89 (2010) 1298-1306. [24] T. Drage, C. Snape, L. Stevens, J. Wood, J. Wang, A. Cooper, R. Dawson, G. Guo, C. Satterley, R. Irons, Materials challenges for the development of solid sorbents for postcombustion carbon capture, Journal of Materials Chemistry, (In Prep). [25] J. Wang, L. Stevens, T. Drage, J. Wood, Preparation and CO2 adsorption of amine modified Mg-Al LDH via exfoliation route, Chem Eng Sci, (In Press). [26] J. Wang, L. Stevens, T. Drage, J. Wood, Preparation and CO2 adsorption of amine modified layered double hydroxide via anionic surfactant-mediated route (In Prep). [27] H. Ren, T. Ben, E.S. Wang, X.F. Jing, M. Xue, B.B. Liu, Y. Cui, S.L. Qiu, G.S. Zhu, Targeted synthesis of a 3D porous aromatic framework for selective sorption of benzene, Chem. Commun., 46 (2010) 291-293. [28] C.D. Wood, B. Tan, A. Trewin, H.J. Niu, D. Bradshaw, M.J. Rosseinsky, Y.Z. Khimyak, N.L. Campbell, R. Kirk, E. Stockel, A.I. Cooper, Hydrogen storage in microporous hypercrosslinked organic polymer networks, Chem Mater, 19 (2007) 2034-2048. [29] R. Dawson, A. Laybourn, R. Clowes, Y.Z. Khimyak, D.J. Adams, A.I. Cooper, Functionalized Conjugated Microporous Polymers, Macromolecules, 42 (2009) 8809-8816. [30] R. Dawson, A. Laybourn, Y.Z. Khimyak, D.J. Adams, A.I. Cooper, High Surface Area Conjugated Microporous Polymers: The Importance of Reaction Solvent Choice, Macromolecules, 43 (2010) 8524-8530. [31] J.-X. Jiang, A.I. Cooper, Microporous organic polymers: design, synthesis and function, Topics Curr. Chem., 293 (2009) 1-33. [32] R. Dawson, D.J. Adams, A.I. Cooper, Chemical tuning of CO2 sorption in robust nanoporous organic polymers, Chemical Science, (2011). [33] M.G. Rabbani, H.M. El-Kaderi, Template-Free Synthesis of a Highly Porous Benzimidazole-Linked Polymer for CO2 Capture and H2 Storage, Chemistry of Materials, 23 (2011) 1650-1653.
Submit before 31 May 2011 to
[email protected] 6
Oviedo ICCS&T 2011. Extended Abstract
Development of a new synthesis gas production process from coal by catalytic gasification of HyperCoal using steam-CO2 as gasifying agent
Atul Sharma and Toshimasa Takanohashi Advanced Fuel Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, 16-1, Onogawa, Tsukuba, Ibaraki, JAPAN. Corresponding author:
[email protected] Abstract Growing energy costs and demand for fossil fuels because of rapid industrialization of emerging economies have revived the interest in coal gasification as a clean coal technology. Gasification can be used for both power generation and for production of liquid fuels/chemicals. To overcome the major drawbacks; high capital and/or operating cost, new advanced gasification processes have to be developed for more efficient and clean gasification of coal. Low temperature catalytic gasification of coal is a highly efficient way to convert coal to fuel gases but has never become a commercial process due to technical and economical factors. Primary reason is the loss of catalyst due to deactivation. In addition, due to the catalytic effect, the control of product gas composition is not easy. We developed a new process to clean coal before use, called HyperCoal process to produce ash less coal. With HyperCoal as feedstock, the loss of catalyst due to deactivation can be overcome and catalyst can be recycled and reused. For indirect production of liquids/ chemicals from coal, FT synthesis process is a primary process. However, a H2/CO ratio of 1 for direct DME production and 2 for methanol production is needed. From conventional high temperature coal gasification, synthesis gas with desired H2/CO can not be produced in a single step. The process is a two step process and efficiency is about 38~42%. In case of catalytic gasification, product gas is mainly H2 and CO2 at atmospheric pressure and methane rich at high pressure. The main highlight of the present study is the production of the synthesis gas from catalytic gasification at 650~700 oC temperature by gasifying HyperCoal in H2O/CO2 mixed environment and controlling its composition by adjusting the composition of the gasifying agent. Using this approach synthesis gas was produced with H2/CO ratio of 1~3 at 650~700 o
C in a single step which can be directly used as feedstock for DME and methanol production by FT
synthesis process.
1
Oviedo ICCS&T 2011. Extended Abstract
1. Introduction Growing understanding to reduce CO2 emissions and at the same time growing energy costs because of increased demand for fossil fuels due to rapid industrialization of emerging economies have revived the interest in coal gasification as a clean coal technology. Gasification can be used for both power generation and for production of liquid fuels/chemicals. However, for commercial acceptance, it has to economically compete with oil based industries. The major drawbacks such as high capital/operating cost and low efficiency have to be overcome. And for that, new advanced processes for more efficient and clean gasification of coal have to be developed. Low temperature catalytic gasification of coal is a highly efficient way to convert coal to fuel gases but has never become a commercial process due to technical and economical factors. Primary reason is the loss of catalyst due to deactivation. In addition, the primary gas at atmospheric pressure is hydrogen and at high pressure is methane. Therefore, the control of product gas composition is not easy. We developed a new process called HyperCoal process to produce ash less coal. With HyperCoal as feedstock, the loss of catalyst due to deactivation can be overcome and catalyst can be recycled and reused. For indirect production of liquids/ chemicals from coal, FT synthesis process is a primary process. However, a H2/CO ratio of 1 for direct DME production and 2 for methanol production is needed. From conventional high temperature coal gasification, synthesis gas with desired H2/CO can not be produced in a single step. The process is a two step process and efficiency is about 38~42%. In case of catalytic gasification, product gas is mainly H2 and CO2 at atmospheric pressure and methane rich at high pressure. The main highlight of the present study is the production of the synthesis gas from catalytic gasification at 600~700 oC temperature by gasifying HyperCoal in H2O/CO2 mixed environment and controlling its composition by adjusting the composition of the gasifying agent. Using this approach synthesis gas was produced with H2/CO ratio of 1~3 at 650~700 oC in a single step which can be directly used as feedstock for DME and methanol production by FT synthesis process.
2. Experimental A subbituminous coal, Pasir (PAS) from Indonesia was selected for the investigation. HyperCoal production method has been described in detail elsewhere. Briefly, HyperCoal (HPC) was produced by the solvent extraction of the coal with 1-methylnaphthalene at 360 C and subsequently separating the extract (HyperCoal) from the solvent. The extraction yield was 51 % for Pasir coal. The properties of the Pasir coal and HyperCoal produced from Pasir coal are shown in Table 1.
2
Oviedo ICCS&T 2011. Extended Abstract
Table 1: Properties of coal and HyperCoal. Coal
Ash
Elemental analysis (wt % daf)
(wt %, db) C
H
N
S
O
Pasir coal
4.2
68.2
5.4
1.1
0.16
25.14
Pasir HyperCoal
0.01
79.5
5.9
1.1
0.29
13.21
HyperCoal has nearly no mineral matters. Because of almost no mineral matter, all the inorganically associated sulfur will be removed. The only sulfur in HyperCoal will be the organically associated sulfur. A detailed characterization of catalyst, HyperCoal, original coal, and chars using XRD, NMR, and SEM-EDX mapping techniques had been carried out and reported elsewhere. The experimental setup is shown in Figure 1.
Ar/O2 mixer
Purge gas /(Ar+O2) gas Steam generator 3-way valve
4-way valve
Sample
water TG carrier gas
Flow controller
TGA
Ice Trap
Ar
CO2
Ar
O2
HPLC pump
Gas out
Flow meter
CO2
µGC
Figure 1. Schematic of experimental set up for catalytic steam gasification of HyperCoal.
Samples for catalytic gasification experiments were prepared with 50 % catalyst loading. Catalyst loading was on dry and ash free wt % basis of coal and HPC. Catalyst mixing method has been described in detail elsewhere. Briefly, a desired amount of K2CO3 was added on the top of a measured sample already loaded into a test crucible as solid particles and stirred with a small spatula until white K2CO3 disappears by capturing moisture from the air. The particle size of coal and HyperCoal sample was under 75 µm. The gasification experiments were carried out with and without K2CO3 as a catalyst at 700, 650 and
3
Oviedo ICCS&T 2011. Extended Abstract
600 C with different steam to carbon dioxide (H2O/CO2) ratios as gasifying agent. Experiments were carried out in a thermogravimetric (TG-DTA 2020S, MAC) apparatus. A desired amount of water was pumped by a HPLC pump to a steam generator held at 250 C. CO2 was flowed to the steam generator as a steam carrier gas. By changing the amount of water pumped by the HPLC pump to the steam generator and the flow rate of CO2 as the carrier gas, different steam to CO2 ratio were achieved. For pure steam gasification, argon gas instead of CO2 was used as carrier gas. In case of steam and CO2 only conditions, partial pressure of steam and CO2 were kept at 0.5 atm by mixing argon gas. A 4-way valve at the inlet of the TG-DTA was used to change (Ar+O2) flow to (CO2+steam) flow. The flow lines were kept at 250 C by using ribbon heaters. First, a desired amount of sample was heated to 200 C and held in pure argon flow for 60 min to remove moisture and O2 from the reaction zone. After 60 min hold, the sample was heated to the desired temperature at 20 C /min in pure argon. When the desired temperature was reached without any hold time the pure argon gas was switched to the preset steam/CO2 gas mixture. The steam+CO2 mixture flowing from top comes into contact with the sample in the crucible. The evolved gases flow out together with the purge gas from the side into an ice cooled tar trap to remove tar before injecting to the micro gas chromatograph (Agilent 3000A). The total gas flow rate at the outlet was measured every 3 min by a film flow meter. 800
20
Weight [ mg]
16
700
Ar (100%) Steam + CO2 50 + 50
12
600 500 400
8
300
Temperature [C]
Ar + O2
200
4
100 0
0 0
30
60
90
120
150
Time [min]
Figure 2. Weight loss profile of HPC pyrolyzed in argon up to 700 C followed by steam+CO2 gasification.
4
Oviedo ICCS&T 2011. Extended Abstract
3. Results and Discussion Figure 2 shows a typical weight loss curve for HPC+50 % K2CO3 sample pyrolyzed in argon up to 700 C followed by gasification with [50% steam+50% carbon dioxide (vol/vol)] as gasifying agent (from hereon in this manuscript steam to carbon dioxide ratio will be addressed as H2O/CO2). In a previous study gasification rate and gas composition was investigated at 10, 20, 40, and 50 % catalyst mixing ratio. It was reported that gasification rate was affected by the catalyst amount up to 50 % loading and above this catalyst loading rates were almost independent of catalyst amount. All experiments were carried out at atmospheric pressure. The weight loss curve can roughly be divided into three stages; moisture removal or drying stage, devolatilization stage and fixed-carbon gasification stage. The initial weight loss (up to 200 C) during heating from room temperature to 200 C in O2+Ar mixture is mainly due to moisture captured from air. Pre-oxidation was done to reduce the extremely high swelling propensity of HyperCoal. After pre-oxidation stage, sample was switched to 100 % argon for 60 min. The coal/HPC conversion on dry, ash, catalyst and volatile free basis (dacvf) (from hereon called char conversion) was calculated during the fixed-carbon gasification stage by the following equation: X (char conversion, % dacvf) =
W0 W 100 W0 (1 Wash Wcat )
[1]
where W0 is the weight when the gasification begins (db, mg) (weight at t= 45, 41 and 39 min for T= 700, 650 and 600 C, respectively), W is weight at any gasification time (db, mg, >39 min), Wash is weight fraction of ash content in coal or HPC, Wcat is weight fraction of catalyst content. Results of gasification rate and gas composition only in the char gasification stage will be discussed further. Figure 3 shows the gasification profile, gas composition and H2/CO ratio of produced gas from K2CO3 catalyzed coal and HPC at 700 C as a function of H2O/CO2 ratio. In general, rate decreased with increasing CO2 fraction in the gas mixture. Similarly, H2 decreased and CO increased with increasing CO2 fraction in the gas mixture. Under H2O/CO2 mixed gas environment, three reactions as shown below: C-H2O reaction (1), C-CO2 reaction (2) and water-gas shift (WGS) reaction (3) are expected to take place. C
+
H2O
→
CO
C
+
CO2
⇌
2CO
CO +
H2O
⇌
H2
+
H2
[1] [2]
+
CO2
[3] 5
Oviedo ICCS&T 2011. Extended Abstract
100
100/0
Char conversion [ %, dacvf]
Char conversion [ %, dacvf]
100 80 60
0/100
30/70 50/50
40
60/40
(a)
70/30
20
COAL＋K2CO3 T= 700
100/0 80 30/70
60
50/50
0 0
10
20
30
40
50
60
70
80
0
90
10
20
COAL＋K2CO3
125 100 75 50 25
Gas yield [mmol/g-char]
Gas yield [mmol/g-char]
175
CO H2
(b) T= 700
150
60
70
80
90
(e)
CO H2
T= 700
HPC＋K2CO3
100 75 50 25
50/50 30/70 0/100
100/0 70/30 60/40
Gasifying agent, H2O/CO2, (vol/vol)
50/50 30/70 0/100
Gasifying agent, H2O/CO2, (vol/vol) 30
29.5
(c)
25
27.1
15 10
10 4.4
2.8
2.1
1.0
0.1
HPC＋K2CO3 T= 700
20
H2/CO
15
(f)
25
COAL＋K2CO3 T= 700
20
H2/CO
50
0 100/0 70/30 60/40
5
40
125
0
30
30
Gasification time [min]
Gasification time [min]
150
(d) HPC＋K2CO3 T= 700
70/30 20
0
175
0/100
60/40
40
5
5.0
3.2
2.5
1.3
0.1
0
0 100/0 70/30 60/40 50/50 30/70 0/100 Gasifying agent, H2O/CO2, (vol/vol)
100/0 70/30 60/40 50/50 30/70 0/100 Gasifying agent, H2O/CO2, (vol/vol)
Figure 3. Effect of H2O/CO2 ratio of the gasifying agent on (a, b) gasification profiles, (c, d) gas yields and (e, f) H2/CO ratio of K2CO3 catalyzed coal and HyperCoal at 700 C.
Figure 3(a, d) shows the gasification profile of HPC and coal with 50 wt % catalyst in steam and carbon dioxide (H2O/CO2) mixed environment at 700 C. The H2O/CO2 ratios selected are H2O/CO2=100/0, 70/30, 60/40, 50/50, 30/70, and 0/100. H2O/CO2=70/30 means 70 % H2O and 30 % CO2 on volume basis. The gasification rates were high enough for commercial application. Figure 3(b, e) shows H2 and CO amount in the produced gas at different H2O/CO2 for coal and HPC at 700 C. At H2O/CO2=100/0, produced gas contained mainly H2 and very little CO. As H2O/CO2 changed to 70/30, 60/40, 50/50 and 30/70, H2 decreased and CO increased. At H2O/CO2=0/100, produced gas contained mainly CO and very little H2. Figure 3(c, f) shows change in H2/CO ratio with H2O/CO2 ratio of the 6
Oviedo ICCS&T 2011. Extended Abstract
gasifying gas. Results show that by changing H2O/CO2 ratio of the gasifying agent, H2/CO ratio of the produced gas can be controlled. These results show that synthesis gas with H2/CO ratio from 1~3 can be produced by gasification of coal in a single step by changing the H2O/CO2 ratio of the gasifying agent. Synthesis gas with H2/CO=1, 2 and 3 can be used as feedstock for FT synthesis process to produce DME, methanol, methane and other chemicals. For commercial application a high gasification rate or short gasification time is required. Considering the scale of operation of a coal gasifier typically about thousand tons per day, a long gasification time means large residence time leading to huge gasifier size in addition to additional energy requirements. Figure 4 shows a correlation between H2/CO ratio of synthesis gas, gasification time and H2O/CO2 ratio of the gasifying agent at 700, 650 and 600 C. A gasification rate of about 0.3 h-1 (18 min) at temperature 700 C and below would be necessary for commercial application. From Figure 4 it can be seen that synthesis gas with H2/CO=1~3 can be produced in a single step from catalytic coal gasification at 700 C with gasification time CeO2-La2O3-based Cu catalysts > CeO2-La2O3-Al2O3-based
Cu catalysts. Whilst it is possible to operate at reduced steam to carbon ratios, additional water (taking the steam to carbon ratio up towards a value of 3:1) is often required to suppress catalyst deactivation due to metal sintering and carbon formation on the catalyst surface. Operation at low steam to carbon ratios would be attractive as it would reduce steam requirements and lead to potentially improved operating efficiencies through reduction the energy penalties associated with generating excessive quantities of steam over and above the stoichiometric requirements for the WGS reaction. This paper presents data from over 2000 hrs of laboratory-scale reactor operation with a CeO2-La2O3based Cu catalyst for the water-gas shift conversion of CO in coal-derived syngas conditions over a range of steam to carbon ratios.
2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
2
2. EXPERIMENTAL The specifications for the water-gas-shift catalysts and the experimental conditions used in this study are listed in Table 1: The HT2 commercial catalyst is used as a reference throughout our studies as it is the state of the catalyst for the water-gas shift reaction. Table 1 - Materials and experimental conditions
WGS Catalyst
HT2 Commercial – Fe2O3 (80-95%), Cr2O3 (5-10%), CuO (1-5%) Copper Ceria Catalyst - (10at%Cu)/Ce(30at%La)Ox Weight: 0.20 ± 0.005 g; Fraction: 53 – 150 µm
Inert Packing
Alpha alumina, Weight - 1.00 ± 0.005g, Fraction 53 – 150 µm
Syngas Inlet composition (vol %)
65% CO; 30% H2 ; 2% CO2; 3% N2
Temperature / Pressure
450-600oC / 1atm
H2O:CO molar ratio (S/CO)
3.09, 2.71, 2.32, 1.93, 1.55, 1.25, 1.00 /1
Feed flow rate (dry basis)
797ml/min
2.1 Catalyst preparation The ceria-lanthana-based catalyst was synthesized using the urea method [4]. Pre-determined amounts of (NH4)2Ce(NO3)6, La(NO3)3.6H2O, Cu(NO3)2.2.5H2O
or
Cu(NO3)2.2.5H2O plus
Fe(NO3)3.9H2O and urea were dissolved in distilled water and then heated to 100°C while stirring vigorously. The mixture was kept at this temperature with periodic addition of water for 8 hours. The resulting solution was filtered and washed with hot distilled water twice, followed by drying at 100°C overnight and calcining in flowing air at 650°C for 5 hours.
2.2 Water Gas Shift Reactor System Experiments were undertaken in a laboratory scale fixed bed differential reactor where CO conversion was ~10%. This level of conversion was achieved by using low catalyst loadings and high gas flows of 797 ml/min (NTP, dry basis) to allow discrimination of both catalyst activity and stability. The simulated synthesis gas was fed into the reactor through individual gas lines for CO, H2, CO2 and H2. The inlet gas composition was adjusted through individually controlled mass flow controllers. The gas was electrically heated and maintained at ~180oC prior to entry to the furnace. A steady flow of de-ionised water was metered by a HPLC pump (Shimadzu LC 20-AT) and was vaporised inside an electrically-heated pre-heating tube and mixed with the gases prior to entering the 15mm ID stainless steel reactor. Inside the reactor 0.20 ± 0.005 g of catalyst was mixed with 1.00 ± 0.005 of inert α-Al2O3 and packed into the reactor between two ceramic sheets and a loose packing of quartz wool was placed at the inlet. Steam in the product gas was trapped using a water2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
3
cooled condenser and outlet gases were analysed by a micro gas chromatograph (Varian CP-4900). Four components (CO, H2, CO2 and N2) were measured every third minute during the experiment and accurate carbon balances were observed throughout.
3 RESULTS AND DISCUSSION 3.1 Preliminary Formulation Studies Figure 1 shows the conversion of the commercial reference HT2 catalyst at 450°C and 600°C. At the 450°C operational temperature limit of this catalyst, its performance is observed to stabilise to a conversion of 15.2 ± 0.1 % or a conversion rate of 2.85E-04 mol/g/s. Whilst there is some variation in the conversion stability, the level is in agreement with its previously observed performance given the duration of exposure and stabilisation time. The system temperature was then ramped beyond the specified catalyst operating temperature at a rate of 2°C/min to the desired elevated temperature limit of 600°C. The conversion is observed to increase dramatically to ~80% which approaches the equilibrium value for these operating conditions (black line). Following this and after three days testing, the performance is observed to degrade asymptotically to a value of ~3%. This conversion is slightly higher than the 1.72 ± 0.05% background level (due to the gas phase reaction) indicating a small amount of residual activity. The key result is that HT2 has been shown to be unstable at the high temperature, with its performance degrading to very low levels at 600°C. The inlet gas concentration is shown for reference (dashed line).
Following observation of the commercial catalysts operational limit, the performance of the highly active WGS ceria based catalyst was measured at 600oC. The conversion result, shown in Figure 2 for the S/CO ratio of 3.09/1, demonstrate its stability over a 4 day period at a level of 15.0 ± 0.2%. 3.2 Kinetic and Reaction Order Study A new sample of ceria catalyst was loaded in the reactor and a kinetic study performed over a three day period. Following activation in 150ml/min of H2 at 650°C at 1atm over a 2hr period, the conversion profile trended downwards from 21-22% to a stable 15% over a 2 day period. This trend was consistent with previous observations of catalysts conditioning and was re-assuring as it confirmed the reproducibility of both the catalyst preparation procedure and the experimental technique used in this study. Next, a program of 22 feed gas compositional changes with a constant wet gas velocity was conducted to quantify the effects of CO, H2O, CO2 and H2 concentration on the WGS reaction rate. Nitrogen was used to supplement the presence of one component in the stream whilst allowing the other components to remain at the same concentration. To obtain the 2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
4
apparent activation energy, an experiment was carried out where the temperature was ramped from 550 to 600°C with a heating rate of 0.4°C/min. The results are shown in Table 2 relative to a high temperature commercial catalyst evaluated in a separate study [5] . Over the temperature range of 550-600°C, the reaction order for CO was found to be around 1, the reaction rate retarded by increasing CO2 concentration and increasing H2 concentration according to the reactions orders shown in Table 2. The effect of varying H2O concentration on WGS reaction rates was found to be insignificant (reaction order close to zero) when the steam to CO ratio was between 3.09/1 and 1.55/1. This is similar behaviour to the commercial high temperature catalysts but at the higher operating temperature. The conversion profile (not shown) shows an increase from 4.0% to 15% over the temperature range 550°C to 600°C. The strong increase in reactivity with temperature begs the question of maximum operating temperature and maximum conversion level, however this was not pursued in this study as 600oC is likely the be the operating limit for any membrane separator in the foreseeable future. The stable conversion of 15.0 ± 0.2 % was achieved over a run that lasted for a further 2 days, indicating the excellent stability of ceria catalyst at the operating conditions. Table 2 - Reaction orders of gases components over the ceria based copper catalyst at 600°C and high t emperature commercial catalyst at 450°C Catalyst
Apparent Reaction Order
E (KJ mol-1)
Source
a [CO]
b [H2O]
c [CO2]
d [H2]
Ceria-Cu
0.95 ± 0.04
0.00 ± 0.18
-0.06 ± 0.04
-0.08 ± 0.03
92.3 ± 2.0
This study
HT
1.00 ± 0.03
0.00
-0.36 ± 0.04
-0.09 ± 0.007
111 ± 2.6
[5]
Figure 3 shows the plot of logarithmic values of reaction rates versus inverse temperature and the apparent activation energy was found to be 92.3±2.0 kJ mol–1. This level is consistent with our previous investigations on the high temperature commercial catalyst [5]. 3.3 Steam to CO Study A study of the effect of feed gas steam to CO ratio was undertaken using the stable ceria catalyst sample in the kinetic study. The gas flows shown Table 3 were maintained over the catalyst whilst the H2O:CO ratio was varied from 3.09/1 the ratio of 1.00/1. Each ratio was held for 12-18 hrs.
2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
5
Table 3 - Water %, S/CO Ratio and Gas and Water flows for the Steam to CO Study. The H2O flow is liquid. The italicised values were those changed during the experiment. H2O (%)
67
59
50
42
33
27
22
H2O:CO ratio (S/CO)
3.09
2.71
2.32
1.93
1.55
1.25
1.00
CO Flow (ml/min)
518
518
518
518
518
518
518
H2 Flow (ml/min)
239
239
239
239
239
239
239
CO2 Flow (ml/min)
16
16
16
16
16
16
16
N2 Flow (ml/min) H2O Flow (ml/min)
24
224
424
624
824
974
1104
1.288
1.17
0.966
0.805
0.643
0.523
0.418
Figure 4 shows the stable CO conversion levels at each S/CO ratio. The results show conversion at the starting S/C ratio of 3.09/1 to be the equivalent to the stabile level at the end of the kinetic study. Next an increase to ~19% was observed for the 2.32/1 ratio. The conversion for the 2.71/1 ratio was noted to be less than fully stabile, however our focus was the lower S/CO ratio gas conditions. At the lower S/CO ratios of 1.93, 1.55 and 1.25 to 1 the CO conversion is seen to be consistent and stable at around 16-17%. These results indicate good stability over appreciable periods of time on the laboratory scale at lower S/CO ratios. The ratio of 1.0/1 was then considered even though it is impractical in real world applications as it would be most probably to lead to the formation of carbon through the bed and downstream in the system. While stable conversion was observed at this ratio, a return to 3.09/1 revealed degradation in performance down to 10% conversion and below over the final two days of testing (not shown). Post run inspection revealed that carbon had formed in the bed indicating that the system had been pushed beyond its designed operating window in terms of S/CO ratio. However, the ceria based catalyst had demonstrated stable performance at 600oC with low steam to carbon ratios over an extended period of operation. 4. CONCLUSIONS
In this paper results from a novel ceria-based catalyst have been presented. The catalyst demonstrated good stability and strong conversion performance at 600oC, well beyond the 450oC operating temperature of the commercial catalyst HT2. The comparison was conducted at a S/CO ratio of 3.09/1 and over a period of 4-5days. In a subsequent kinetic study reaction orders for CO, H2O, CO2 and H2 were determined as was an activation energy value of 92.3 ± 2.0 kJ.mol-1. The values obtained were consistent with those observed in our previous high temperature catalyst work. A detailed steam to carbon ratio study with 12-18 hr exposure periods revealed stable conversion performance down to S/CO ratios as low as 1.00. The results are encouraging as elevation of the processing temperature and reduction in the amount of steam required could lead to 2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
6
improvements in both the efficiency and cost of an IGCC plant. Detailed modelling would be required to calculate the the optimum system steam to carbon ratio and the effect of reduced steam consumption on the overall process performance and economics. ACKNOWLEDGMENTS The authors wish to acknowledge the financial support of the Centre for Low Emission Technologies.
2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
7
Figure 1 - Conversion of 0.20g of HT2 catalyst over a 5day period; H2O/CO /CO ratio of 3.09/1 at the operating maximum of 450°C then 600oC. The inlet gas concentration of 65% CO, 30% H2, 2% CO2, 3% N2 (dashed) and empty reactor conversion levels (orange) are shown for reference. The inlet concentration was confirmed at the end of the experiment. experiment
CO Conversion (%)
30
20
Ceria Based Cu
15.0 ± 0.2%
Blank
1.72 ± 0.05%
10
0 0
1
2
3
4
Duration (days)
Figure 2 - Water-gas gas shift performance of synthesized catalysts with the H2O/CO CO ratio of 3.09/1. The ceria based copper catalyst produced a stable conversion of 15.0 ± 0.2% at the elevated temperature of 600°C. This compares with the background level of 1.72% and the commercial 450°C 450 limited catalysts performance of ~3%.
2011 ICCS&T Oviedo, Spain A CeO2-La2O3 La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
8
-8.0 Ln(CO rate)
Ln (reaction rate)
-8.2 -8.4
600oC
-8.6 -8.8
Activation Energy = 92.3 ± 2.0 kJ.mol-1 -9.0
550oC -9.2 1.14E-03
1.16E-03
1.18E-03
1.20E-03
1.22E-03
1/T (1/K)
Figure 3 - The Arrhenius plot for the WGS reaction over ceria based catalyst with a synthesis gas representative of coal derived synthesis gas (65% CO, 30% H2, 2% CO, 3% N2), temperature of 550 - 600oC and H2O:CO ratio of 3.09/1. 25
19.4
20
16.7
Conversion (%)
16.5
17.8
15.2
15.9
15.5
1.25/1
1.00/1
15
10
5
0 3.09/1
2.71/1
2.32/1
1.93/1
1.55/1
Steam to CO ratio (S/CO)
Figure 4 - Conversion performance of the ceria based catalyst as a function of H2O:CO ratio at 600oC. Error bars shown are the standard deviation in the final 2 hours of data from each S/CO ratio.
2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
9
REFERENCES [1]
[2]
[3]
[4]
[5]
Sun, Y., et al., A comparative study of CeO2-La2O3-based Cu catalysts for the production of hydrogen from simulated coal-derived syngas. Applied Catalysis A: General, 2010. 390(1-2): p. 201209. Sun, Y., et al., High temperature water-gas shift Cu catalysts supported on Ce-Al containing materials for the production of hydrogen using simulated coal-derived syngas. Catalysis Communications, 2010. 12(4): p. 304-309. Sun, Y., et al., Effect of Ce on the structural features and catalytic properties of La(0.9-x)CexFeO3 perovskite-like catalysts for the high temperature water-gas shift reaction. International Journal of Hydrogen Energy, 2011. 36(1): p. 79-86. Qi, X. and M. Flytzani-Stephanopoulos, Activity and Stability of Cu−CeO2 Catalysts in HighTemperature Water−Gas Shift for Fuel-Cell Applications. Industrial & Engineering Chemistry Research, 2004. 43(12): p. 3055-3062. Hla, S.S., et al., Kinetics of high-temperature water-gas shift reaction over two iron-based commercial catalysts using simulated coal-derived syngases. Chemical Engineering Journal, 2009. 146(1): p. 148-154.
2011 ICCS&T Oviedo, Spain A CeO2-La2O3 based Cu catalyst for application in high temperature water gas shift reaction.
10
Coal plasma gasification for clean synthesis gas production V.E. Messerle1, A.B. Ustimenko1, N. Slavinskaya2, O.A. Lavrichshev3, E.F. Ossadchaya3 1 2 3
Research Department Plasmotechnics, Almaty, Kazakhstan
Institute of Combustion Technology, German Aerospace Centre, Stuttgart, Germany
Research Institute of Experimental and Theoretical Physics al-Farabi Kazakh National University, Almaty, Kazakhstan E-mail:
[email protected] Abstract This paper describes numerical and experimental investigation of coal gasification in combined arc-plasma reactor. The gasifier is an entrained flow reactor. The experimental installation is intended for work in the electric power range of 30-100 kWe, mass averaged temperature 1800-4000 K, coal dust consumption 3-10 kg/h and gas-oxidant flow 0.5-15 kg/h. The numerical experiments were conducted with the aid of PLASMA-COAL computer code. It was designed for computation of the processes in the plasma gasifier. This code is based on one-dimensional model, which describes two-phase chemically reacting flow with an internal plasma source. The thermo chemical conversion of coal-oxidant mixture is described through formation of primary volatile products, conversions of evolved volatile products in the gas phase and the coke residue gasification reactions. Kazakhstan Kuuchekinski bituminous coal of 40% ash content, Germany Saarland bituminous coal of 10.5% ash content and 14% ash content bituminous coal from the Middleburg opencast mines, South Africa, were used for the investigation. The investigation demonstrated that high quality synthesis gas can be produced using different power coals and plasma assisted technology. 1. Introduction Coal is the major source of energy. It provides 24% of thermal generation and 40% of electric energy in the world [1]. The share of coal in the world's proven reserves of fossil fuels is about 64% [2]. In particular, Kazakhstan is ranked eighth in the world in coal production, and its proven reserves reach 177 billion tons. In the near future increase of coal use is expected. According to forecasts [3] by 2020 the share of coal in the global fuel balance will be 56%.
Coal, being one of the most complex composition fossil fuels, is the richest source of valuable chemical products. In addition to power generation in world practice technologies are mastered by which from coals more than 500 products (synthesis gas, fuel oil, methanol, sorbents, etc.) are obtained. One of the new promising technologies for processing of coal is its plasma gasification [46], intensively developed in Kazakhstan. This paper considers numerical and experimental studies of plasma gasification of three kinds of coals: Ekibastuz coal (EC), ash content 40% (Kazakhstan), Saarland coal (SC) ash content of 10.5% (Germany) and Middleburg coal (MC), ash content 14% (South Africa). Experimental studies of plasma gasification were carried out by the example of EC (Table 1). Then we calculated its plasma gasification on the kinetic program PLASMA-COAL and compared the results of calculations with experiment. Then, using the verified program PLASMA-COAL comparative numerical study of plasma gasification of the three above coals was performed. Table 1. Chemical composition of Ekibastuz bituminous coal, mass. % Аd
С
О2
Н2
N2
S
40
48.86
6.56
3.05
0.8
0.73 23.09
SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O 13.8
2.15
0.34
0.31
0.16
0.15
Higher calorific value of coal on dry weigh Qd=16632 kJ/kg, moisture of coal Ww= 5.8%, Аd – ash on dry weight of coal
2. Experiment Experiments and further numerical calculations were performed applied to a plug flow plasma gasifier of the combined type of 100 kW nominal electrical power. The experimental setup is shown in Fig. 1 [4]. The electric arc is ignited between the rod and ring graphite electrodes in the combined plasma reactor 1, Fig. 1. The inner diameter of the reactor (i.e. of the graphite lining) is 0.15 m and its height is 0.3 m. The arc rotates under the influence of the magnetic field. The coal dust is fed to the reactor from dust feeder 7 through ejectors in the top cover of the reactor. Dust is sprayed in the reactor arc zone by plasma-forming gas (steam or air), also introducing into the reactor through injectors in the top cover. The oxidant-pulverised coal mixture entering the arc zone is heated to high temperatures by the rotating arc to produce a twophase plasma flow where the coal gasification process occurs. The gaseous products are derived through the slag and gas separator chamber 2, the chambers of synthesis gas cooling 4 and
hydration 6. The solid residue is removed through the diaphragm 2 into slag catcher 3. The distance from the top cover of the plasma reactor 1 to the exit of the gasifier (orifice 5) is 0.9 m. As a result of experiments on the basis of material and heat balancing of the plant, the main parameters of the plasma gasification of coal were measured. They are mass averaged temperature, coal gasification degree, specific power consumptions, synthesis gas yield. To conduct high temperature measurements in the reactor optical pyrometers were used. They allowed measuring the temperature to 4000 K. Sieve analysis of dust showed that the average particle size of coal was 75 microns. Fig. 1. Laboratory scaled plant for plasma gasification of coal: 1 – plasma reactor; 2 – orifice, synthesis gas and slag separator chamber; 3 – slag catcher; 4 – synthesis gas cooling chamber; 5 – orifice; 6 – hydration chamber; 7 – dust feeder; 8 – cooling water system; 9, 10 – power supply system; 11, 12 – rod electrode moving system; 13 – steam generator; 14 – safety valve; 15 – slag catcher elevator. The experimental results, obtained for EC, are summarized in Table 2. Reactor power (P) has been ranged from 25 to 52.8 kW. The measured efficiency of the reactor was 76%. The process specific power consumption (Qsp) is related to one kilogram of the reacting mass. As it is seen from Table 2, experiments No 1 and 2, coal gasification degree (Xc) at plasmaair gasification of coal increases from 89.6 to 95.8% with power consumption elevation from 2.1 to 3.3 kW·h/kg. The yield of synthesis gas varies from 43.3 to 56.3%. In plasma-steam gasification of coal, Table 2, experiments No 3 and 5, the specific power consumption is higher: 4.2 - 7.7 kW·h/kg. The degree of gasification remains at a high level, 92.0 – 94.2%. It is significant that the yield of synthesis gas is much higher, 90.0 – 97.3%, at plasmasteam gasification of coal. 3. Verification of computer-code PLASMA-COAL Computer-code PLASMA-COAL was designed for computation of the processes of moving, heating, and kinetics of thermochemical conversion of a coal–oxidant mixture in a plasma
gasifier alike, as shown in Fig. 1. This code is based on 1-D which describes a two phases (coal particles and gas oxidizer) chemically reacting flow in a reactor with an internal heat source (electric arc) [5, 6]. Coal particles and gas are admitted into the reactor with equal temperatures. There is a heat–mass exchange, particle-to-particle exchange, gas-to-particle exchange and gasto-electric arc exchange. In addition, heat and impulse exchange between the flow and the wall of the reactor is accounted for. Some chemical fuel transformations are also considered. They are the formation of primary volatile products, the conversation of evolved volatile products in the gas phase and the coke residue gasification reactions. Table 2. The main indices of Ekibastuz coal plasma gasification. Consumption, kg/h
N 1
EC Steam 8.0 -
Air 8.0
2
4.0
-
3
4.0
4 5
P, kW
Q, T, K kW·h/kg
CO
H2
N2 55.3
89.6
XC, %
33
2.1
2100
27.4
Vol. % 15.9
5.1
30
3.3
2850
38.1
18.2
43.7
95.8
1.9
-
25
4.2
3100
41.6
55.7
2.7
94.2
6.5
3.0
1.9
52.8
4.6
3150
38.6
51.4
9.8
92.0
4.0
2.44
0.43
52.3
7.7
3500
41.5
55.8
2.7
93.7
The plug flow assumption was applied to the entrained flow reactor. The resulting set of ordinary differential equations includes equations for species concentrations (chemical kinetics equations) in conjunction with the equations for gas and particle velocities and temperatures, respectively. The energy contribution from the plasmas had been found empirically and included into the energy equation as an internal heat source. Moreover, the model was distinguished by its detailed description of the chemical reactions previously mentioned [5, 6]. Kinetic scheme consists of 51 chemical reactions. Arrhenius equation describes the temperature dependence of
Ej n ⋅ T , where n is the temperature the rate constants of chemical reactions: k j = A j ⋅ exp − RT factor, A is the preexponential factor, Ej is the activation energy, and index j is the number of the reaction. The coal composition is presented in the model by its organic and mineral parts. The organic mass of coal is specified by the set of the functional groups (CO, CO2, CH4, H2O, and tar) and
Table 3. Kinetic parameters of the reactions of coal gasification. LgA b)
n
E
LgA b) n
E
1 [H2]S = H2
18.2
0
88.8
26 H+O2= O+OH
11.27 0
16.8
2 [H2O]S =H2O
13.9
0
51.4
27 H+H2O= H2+OH
10.98 0
20.3
3 [CO]S = CO
12.3
0
44.4
28 H2+O=H+OH
7.26 1.0
8.9
4 [CO2]S =CO2
11.3
0
32.6
29 H2O+M= H+OH+M
13.3
0
105.0
5 [CH4]S =CH4
14.2
0
51.6
30 H2O+O= OH+OH
10.53 0
18.3
6 [C6H6]S =C6H6
11.9
0
37.4
31 CO+OH= CO2+H
4.11 1.3 -0.77
7 C+H2O= CO+H2
11.32
0
60.8
32 CO+O2= CO2+O
11.5
8 C+CO2= CO+CO
13.2
0
83.6
33 CO2+H= CO+OH
6.15 1.3 21.6
9 C+O2=CO2
9.42
0
38.0
34 CO+O+M= CO2+M
12.77 0
10 C+C+O2= CO+CO
9.72
0
41.8
35 C2H2+M= C2H+H+M
11.0
0
114.0
11 CH4+H= CH3+H2
11.1
0
11.9
36 C2H2= C+C+H2
6.0
0
30.0
12 CH4+OH= CH3+H2O
0.54
3.1
2.0
37 C2H2+O2= HCO+HCO
9.6
0
28.0
13 CH4+M= CH3+H+M
14.15
0
88.4
38 C2H2+H= C2H+H2
11.3
0
19.0
14 CH4+O= CH3+OH
10.2
0
9.2
39 C2H2+OH= CH3+CO
9.1
0
0.5
15 CH3+H2O= CH4+OH
9.84
0
24.8
40 C2H2+O= CH2+CO
10.83 0
4.0
16 СH3+H2= CH4+H
9.68
0
11.4
41 CH2+H2O= CH2O+H2
11.0
0
3.7
17 CH3+M= CH2+H+M
13.29
0
91.6
42 CH2+O2= HCO+OH
11.0
0
3.7
18 CH3+O2= CH30+O
10.68
0
29.0
43 C2H+O2= HCO+CO
10.0
0
7.0
9.6
0
0
44 C2H+H2O= CH3+CO
9.08
0
0.5
20 СH3+O= CH2O+H
11.11
0
2.0
45 C6H6=C2H2+ C2H2+C2H2 12.0
0
85.0
21 CH3O+M=CH2O+H+M
10.7
0
21.0
46 OH+OH= H2O+O
0
1.1
22 CH2O+M= HCO+H+M
13.52
0
81.0
47 H+OH+M= H2O+M
10.56 0
0.0
23 HCO+M= H+CO+M
11.16
0
19.0
48 H+H+M= H2+M
9.56
0
0.0
24 O2+M= O+O+M
12.7
0
115.0
49 CH2O+OH= HCO+H2O
10.5
0
1.5
25 H2+M= H+H+M
11.34
0
96.0
50 H+OH= H2+O
9.84
0
7.04
51 H2+OH= H2O+H
11.4
0
10.0
j
Reaction a)
19 CH3+OH= CH2O+H2
j
Reaction a)
9.5
0
37.6
4.1
a)
Equations 1-6 are the devolatilization reactions. Dimensions of Aj are [s-1] for the first-order reactions and [10-3m3mol-1s-1] for the second-order reactions, and dimension of E is [kcal mol-1]. b)
carbon. According to the assumed scheme, the first chemical stage of the process is coal thermal destruction (reactions 1–6 in Table 3). Heating the coal particles generate volatile and tar components, which are presented by benzol C6H6 [6]. The interactions between the char carbon
and water vapor, oxygen, and carbon dioxide (reactions 7–10) are the rate-limiting stages of the process. These reactions present the complex heterogeneous processes, which include the different elementary stages: a reagent adsorption on the particle surface, dissociation, the reactions in the gaseous phase, desorption, etc. The detailed mechanism of these processes is not known at today, but such presented global steps can describe the main feature of the processes based on the empirical information about the rates of reaction paths. To verify the program PLASMA-COAL variant 5 from the Table 2 was calculated. Results of the comparison are presented in Table 4. Note that in the calculation the experimentally observed air leak at a rate of 0.43 kg / h was taken into account. It is seen that discrepancy in the concentrations of gas phase components is not more than 4 %, coal gasification degree – 1 % and mass average temperature at the exit of plasma reactor – 2 %. Such a relatively small discrepancy of the computed and experimental data confirms validity of the accepted physical and mathematical models and legitimacy of the kinetic code PLASMA-COAL application for numerical investigation of coal plasma gasification. Table 4. Comparison of the numerical results on PLASMA-COAL code with experimental one. Gas composition at the exit of gasifier, vol. % Method
X c, %
T, (K)
0.0
93.7
3500
0.0
93.9
3559
H2
CO
N2
О2
Experiment
55.8
41.5
2.7
Computation
53.5
42.1
2.71
4. Numerical simulation of the coals plasma gasification Three widely used in the energy sector of Kazakhstan and Germany coals were selected for the numerical study. They are Kazakhstan EC, German SC and the South African MC. Their characteristics are given in Table 5. For all the variants power of the plasma reactor was 52.3 kW, coal consumption – 10 kg/h, steam consumption was selected from an evaluation of the complete coal gasification. It was 7, 9.2 and 9.7 kg/h for EC, SC and MC respectively. Results are presented in Figs. 2 - 9. Figs. 2 - 4 show the composition of gases obtained by the coals plasma gasification. It is evident that high-quality synthesis gas is obtained from all three coals. Concentration of the synthesis gas at the outlet of the gasifier is 98.7, 96.4 and 97.15 vol. % for EC, SC and MC, respectively. In all variants of the calculation concentration of
hydrogen (H2) significantly exceeds that of carbon monoxide (CO). This excess is for EC 12.23%, for SC - 5.42% and for MC - 4.35%. Note that in the products of SC and MC gasification there is methane (CH4), 1.53 and 1.27 % respectively, whereas there is no methane at the outlet of the gasifier at EC gasification. Typically there is a methylene radical (CH2) , in the products of the coals plasma gasification with a concentration in the range of 1 to 2 %. The concentration of oxidant (H2O) to the plasma reactor exit (X = 0.3 m) tends to zero. The gasifying agent (water vapor) flow rate increasing can lead to an increasing in the yield of the synthesis gas due to the conversion of hydrocarbon impurities (CH4 and CH2). Table 5. Coals characteristics, mass. %. Coal
Ad
C
H2
H2 O
CO
CO2
СH4
C6H6
Vdaf
Qd, kJ/kg
EC
40.0
46.18
2.63
1.84
3.95
1.4
0.55
3.45
34.55
16632
SC
10.5
57.28
1.95
4.5
9.67
1.6
2.58
11.92
32.22
29277
MC
14.0
60.2
1.5
2.9
7.7
1.3
2.1
10.3
25.8
27321
100
100
H2 CO
10
10
Ci, vol.%
Ci, vol.%
H2O CH2 1
H2 CO
H2O
CH4
CH2
1
CH4
H
H
C6H6 C6H6 0.1 0.0
0.2
0.4
0.6
0.8
X, m
0.1 0.0
0.2
0.4
0.6
0.8
X, m
Fig. 2. Distribution of gas composition
Fig. 3. Distribution of gas p composition
along the gasifier at EC gasification.
along the gasifier at SC gasification.
The coals gasification degree (Fig. 5) increases with the length of the gasifier and at the reactor output it is 100%. This indicates the completion of the gasification process of all three coals. Complete conversion of EC is reached faster than for SC and MC, which is associated with higher temperatures (Fig. 6), and, accordingly, the specific power consumption for the gasification of EC (Fig. 7).
Fig. 6 shows that all curves have a maximum temperature in the range 2000 - 2600 K at the exit of the reactor (X = 0.3 m). Moreover, for all the coals gas temperature near the maximum exceeds the temperature of coal particles by 250 - 300 degrees. This is due to the dominance of the heterogeneous endothermic reactions (7) and (8) over exothermic reactions (9) and (10), Table 3, at the coals plasma-steam gasification. At the gasifier exit the difference between gas and particles temperature decreases to 40-60 degrees, the temperature of gasification products is reduced to 1270 - 1400 K.
100
100
H2 CO
H2O
1
80
2 3
CH4
60
Xc, %
Ci, vol.%
10
CH2
40
1
0.1 0.0
20
H
C6H6 0.2
0.4
0.6
0 0.0
0.8
0.1
X, m
0.2
0.3
X, m
Fig. 4. Distribution of gas composition along
Fig. 5. Coal gasification degree distribution
the gasifier at MC gasification.
along the gasifier: 1 – EC, 2 – SC, 3 – MC.
3.0
1
2500
1
2
2.5
2
T, K
6
3 5
4
1500
Qsp, kW ⋅h/kg
2000
1000
3
2.0 1.5 1.0 0.5
500 0.0
0.2
0.4
0.6
0.8
X, m
0.0 0.0
0.1
0.2
0.3
0.4
X, m
Fig. 6. Gas (1, 3, 5) and coal particles (2, 4, 6)
Fig. 7. Specific power consumption
temperature distribution along the gasifier: 1,
distribution along the gasifier: 1 – EC, 2 –
2 – EC; 3, 4 – SC; 5, 6 – MC.
SC, 3 – MC.
Specific power consumption (Fig. 7) increases in the length of the gasifier, reaching a maximum at the exit of the reactor (X = 0.3 m). Specific power consumption for EC gasification reaches 2.75 kW·h/kg, which is considerably higher than for SC and MC gasification (2.45 and 2.39 kW·h/kg, respectively). Specific yield of the gas determined as the ratio of flow of product gas to coal consumption, increases along the gasifier, peaking toward the exit of the reactor (Fig. 8). The yield of gas for low ash content coals (SC and MC) is 30 % higher than for the high-ash EC, although even in the latter case, 1.3 kg of gas is produced from 1 kg of coal. It follows from Fig. 9 that calorific value of the product gas for all three coals reaches a considerable value at the gasifier exit and varies in the range of 4,358 - 4,555 kcal/kg. Greater calorific value of gas produced at the high-ash EC plasma gasification is associated with a higher concentration of hydrogen in the obtained synthesis gas, in comparison to those obtained from SC and MC (Figs. 2 - 4).
5000
3 2
1.6
4500
1.4
Qg, kcal/kg
Gas Yield, kg/kg
1.8
1
1.2 1.0
1 2 3
4000
3500
0.8 0.0
0.2
0.4
0.6
0.8
3000 0.0
0.2
X, m
0.4
0.6
0.8
X, m
Fig. 8. Specific yield of gas distribution
Fig. 9. Gas calorific value distribution along
along the gasifier: 1 – EC, 2 – SC, 3 – MC.
the gasifier: 1 – EC, 2 – SC, 3 – MC.
5. Conclusions Numerical and experimental investigations of three different power coals plasma gasification showed the possibility to produce the high-quality synthesis gas, regardless of the quality of the gasified coal. The produced gas can be used as a high-energy gas, high potential gas – reducing agent and as a raw material for methanol and dimethyl ether synthesis.
Performed verification of the computer-code PLASMA-COAL confirmed its validity for simulations of solid fuels plasma gasification. Numerical simulations have shown that the synthesis gas concentration at the outlet of the gasifier reaches high values for all studied coals and varies in the range of 96.4 - 98.7%, whereas specific power consumption for the gasification process does not exceed 2.75 kW·h/kg. Regardless of the coal quality, its steam plasma gasification provides the high calorific value gas (4358 - 4555 kcal/kg) at the gas specific yield of 1.3-1.83 kg/kg. References [1] Key World Energy Statistics 2003 Edition, International Energy Agency, OECD/IEA, Paris, www.iea.org [2] British Petrol Statistical Review of World Energy, June 2002, British Petrol, London, www.bp.com [3] Cletcins K. World power policy. Using a technology of a three-stage combustion for NOx suppression on solid fuel boilers in Europe and CIS // Opening Rep. Europ. Commission for Power Engineering and Transport. – Moscow: Russian J.S.Co. “United Power System of Russia”. All-Russian Technical Institute. 2000. P. 4-17. [4] Messerle V.E. Ustimenko A.B. Solid Fuel Plasma Gasification. // Advanced Combustion and Aerothermal Technologies, N.Syred and A.Khalatov (eds.), Springer. 2007. P.141-156. [5] Gorokhovski M., Karpenko E.I., Lockwood F.C., Messerle V.E., Trusov B.G., Ustimenko A.B. Plasma Technologies for Solid Fuels: Experiment and Theory. // Journal of the Energy Institute. 78 (4), 2005. P. 157-171. [6] Kalinenko RA, Levitski A.A., Messerle V.E., Polak L.S., Sakipov Z.B., Ustimenko A.B. Pulverized Coal Plasma Gasification // Plasma Chemistry and Plasma Processing. V. 13. N 1. 1993. P. 141-167. New-York, London, Paris.
Oviedo ICCS&T 2011. Extended Abstract
Coprocessing of Low-Rank Coal and Biomass Utilizing Mild Solvent Treatment at around 350°C X. Li1, J. Wannapeera2, N. Worasuwannarak2, R. Ashida1 and K. Miura1* 1
Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan The Joint Graduate School of Energy and Environment, King Mongkut's University of Technology Thonburi, 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok, 10140, Thailand *e-mail:
[email protected] 2
Abstract The authors have been proposing methods to dewater, and fractionate coal by using the sequential thermal solvent extraction. They have recently showed that the degradative extraction at around 350°C using a non-polar solvent such as 1-methylnaphthalene under 10 MPa is effective to recover several fractions having similar chemical and physical properties from a wide range of low-rank coals. In this paper the applicability of the method to much lower grade carbonaceous resources is examined. Two biomasses, cellulose, lignite, a peat and four low rank coals, and mixed samples of biomass and two coals were treated by 1-methylnaphthalene at 350°C to upgrade and to fractionate the raw materials into several fractions having similar chemical and physical properties. The extracted fractions, Solubles and Deposits, were very close to each other in elemental composition, chemical structure, molecular weight distribution, pyrolysis behavior, and softening/melting behavior.
Thus, the proposed degradative solvent
extraction method was found to be effective to convert low grade carbonaceous resources into solid fuels having higher heating values and significantly upgraded compounds having similar chemical and physical properties.
1. Introduction It is beyond question that coal is a valuable resource expected as not only fuels but also chemical feedstocks in this century. On the other hand, the minable reserves of high grade coal, bituminous coal, have been depleting very rapidly due to rapid increase of worldwide coal consumption. This inevitably requests to utilize low-rank coals, brown coal/lignite and sub-bituminous coal, instead of high grade coal, because the minable reserve of the low-rank coals is as large as that of high grade coal. Peat being distributed worldwide and biomass wastes are also low-grade but valuable carbonaceous resources that must be utilized effectively
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Oviedo ICCS&T 2011. Extended Abstract
These low-grade carbonaceous resources contain a large amount of water (~ 60 %) in general, resulting in low calorific value. This means that dewatering or drying is essential when these resources are transported and stored to be utilized. Dewatered samples unfortunately tend to have high spontaneous combustion tendency as compared to non-dewatered raw materials.
It is required to reduce the amount of oxygen
functional groups to suppress the spontaneous combustibility. The process to reduce the oxygen functional groups is called upgrading.
Therefore, both dewatering and
upgrading are necessary to utilize these resources more effectively even as just fuels. If we utilize these resources as feedstocks of chemicals and materials, we might have to develop methods that enable us to effectively recover precursors of chemicals and/or materials from the raw low-grade resources. The authors have been proposing methods to dewater, and fractionate coal by using the sequential thermal solvent extraction (1-4). They have recently showed that the degradative extraction at around 350°C using a non-polar solvent such as 1methylnaphthalene (1-MN) under 10 MPa is effective to recover several fractions having similar chemical and physical properties from a wide range of low-rank coals (5, 6). In this paper the applicability of the method to much lower grade carbonaceous resources is examined.
2. Experimental section 2.1 Samples and solvents used Table 1 summarizes the ultimate and proximate analyses of the samples used. Reagent grade cellulose (Cell) and lignin (LN), two biomasses (leucaena (LC) and rice straw (RS) from Thailand), a peat (PE) from Belarus, a lignite from Thailand (Mae Moh; MM), and brown coals from Indonesia (WA and BB) and Australia (LY) were employed as low-grade carbonaceous resources. LC and RS were pre-dried, PE and coal samples contained water by more than 12.2 %. Four combinations of one to one mixed samples of biomass and coal, LC/MM. RS/MM, LC/LY, and RS/LY were also used as samples to examine their synergetic effect during the solvent treatment. 1-methylnaphthalene (1MN) was used as a non hydrogen donor solvent for the degradative extraction. 2.2 Experimental procedure Since the treatment at around 350°C was found to be effective to upgrade various low rank coals in the previous works, the degradative extraction of the sample was Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
Table 1. Analyses of samples used Sample (abbreviation) Cellulose (CELL) Lignin (LN) Leucaena (LC) Rice straw (RS) Peat (PE) Mae Moh (MM) Loy Yang (LY) Wara (WA) Berau BInungan (BB)
Ultimate analysis (wt%, d.a.f.) C H N O+S(diff) 41.2 6.1 0.3 52.4 60.3 4.9 0.3 34.5 49.5 5.9 0.8 43.9 45.7 5.9 0.9 47.5 59.7 4.4 2.2 33.7 66.4 3.9 1.9 27.8 66.7 4.7 0.9 27.7 67.1 5.1 1.0 26.9 71.0 4.9 1.3 22.8
Proximate Analysis (wt%, d.b.) VM FC Ash 92.4 7.6 0.0 66.1 20.6 13.3 85.1 14.1 0.8 69.5 11.4 19.1 46.1 40.2 13.6 50.2 24.0 25.8 51.5 47.0 1.5 50.5 47.9 1.5 43.4 52.5 4.1
Moisture [wt%] 0.0 13.0 3.3 5.5 32.4 12.2 56.3 37.0 21.9
performed using a stainless steel autoclave (350 cm3, 55 mm I.D.) at 350°C. The autoclave was charged with samples (13 g on dry basis) and 310 cm3 of 1-MN. A stainless filter (65 mm O.D. and 0.5 µm opening) was equipped at the bottom of the autoclave. After sufficiently purging the autoclave with N2, the autoclave was heated up to 350°C, where it was kept for 60 min. The extract and the residue (Residue) were separated by opening the valve connected below the filter at the extraction temperature. The extract with the solvent was collected in a stainless steel vessel equipped under the valve which was cooled by water. The solvent containing the extract was filtrated using a PTFE membrane filter (0.5 μm opening) to separate the extract into the extract that precipitates at room temperature (Deposit) and the extract soluble in solvent even at room temperature. The latter fraction was treated by a rotary evaporator at around 140°C under reduced pressure to remove 1-MN and to recover the extract in this fraction as solid. The extract recovered as solid was called “Soluble” and that evaporated with 1MN was called “Liquid”. The yields of Residue, Deposit, and Soluble were determined by weight, and the Liquid yield was estimated by difference. The yield of H2O formed was determined by the oxygen balance.
3. Results and Discussion 3.1 Yields of products As stressed in the previous works, the water in the sample was completely removed while the sample was heated up to 350°C without phase change. The water removed is easily separated from solvent by decantation. Figure 1 shows the yields obtained for the nine samples through the degradative extraction on weight basis. The yields were all represented on the basis of free from ash and water (d.a.f.). The yields of Liquid look very large for Cell, LC, and RS. Elemental Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
CO2
Yield [wt%, d.a.f.]
80
100
Carbon distribution [wt%, d.a.f.]
Other gas 100
H2O Liquid (diff.)
60
40
Soluble Deposit
20
CO2
60
Soluble 40
Deposit 20
Residue
Residue 0
0 Cell
LN
LC
RS
PE
MM
LY
WA
Figure 1 Yields of the products.
BB
Liquid
Other gas 80
Cell
LN
LC
RS
PE
MM
LY
WA
BB
Figure 2 Carbon distributions in the products.
balance shows, however, the Liquid consists mostly of oxygen. The Liquid from Cell, for example, consists 8.2 kg of C, 3.8 kg of H, and 42.5 kg of O on the basis of 100 kg of d.a.f Cell. This suggests that the yield of organic compound in Liquid is very small and that most of Liquid is H2O. Then from both practical and fundamental viewpoints the distribution of carbon in the product is more informative than the yield on weight basis. The yields shown in Figure 1 were then converted to the carbon distribution to the product, and they are shown in Figure 2. The formation of CO2 and hence the loss of carbon as CO2 is inevitable, because the treatment is intended to remove oxygen functional groups as CO2 and H2O. The losses of carbon as CO2 were around 5 % for Cell, LN, and biomasses, and less than 3 % for coals. About 20 % of carbon was recovered as Liquid for Cell and LC, but only 2.6 % as Liquid for LN. These results show that most of the products are recovered as solids. The largest extract faction is Soluble for every sample. The carbons in Soluble were respectively as large as 58 %, 49 %, and 42 % for Cell, RS, and LC and were 20 to 30 % for other samples. Figures 3 and 4 respectively show the yield of each product and the carbon distribution in the product for the four mixed samples. The experimental results are compared with the distribution calculated assuming no interaction. The experimental and calculated distributions are slightly different for all of the samples, showing the existence of some interaction during the solvent treatment.
The amounts of
experimentally obtained extract were larger for LC/MM and RS/MM and smaller for LC/LY and RS/LY than the calculated ones. More detailed examination is necessary to estimate the importance of the interaction.
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Oviedo ICCS&T 2011. Extended Abstract
Other gas
CO2
[wt%, d.a.f.] Yield
80
60
40
100
Carbon distribution [wt.%, d.a.f.]
100
Liquid (diff.)
Soluble Deposit
20 Residue 0 Exp. Cal. LC/MM
Exp. Cal. RS/MM
Exp. Cal. LC/LY
Other gas
Liquid
CO2
80
Soluble 60 Deposit 40 Residue
20 0
Exp. Cal. RS/LY
Exp. Cal. LC/MM
Exp. Cal. RS/MM
Exp. Cal. Exp. Cal. LC/LY RS/LY
Figure 4 Carbon distribution in the product for the mixed samples.
Figure 3 Yields of the products for the mixed samples. 3.2 Properties of products
The carbon contents of the Solubles were as large as 80.0-84.9 % and the hydrogen contents were as large as 6.4-7.8 % on d.a.f. basis. Figure 5 shows the elemental compositions of the raw materials, Solubles, Deposits, and Residues on the H/C vs. O/C diagram. For the Solubles, all of the data points converged. It was also the case with the Deposits. These results show that the proposed degradative extraction can convert the wide range of low grade carbonaceous resources into Solubles and Deposits that have respectively similar elemental compositions. Figure 6 compares the higher heating values (HHV) between raw material and the product (sum of HHV of Soluble, Deposit and Residue on raw material basis). The HHV of the product was slightly larger than that of raw material. This indicates that the 2.0
30
RS LC
1.5
H/C
Soluble 1.0
RS+MM
Lignin
Deposit
LC+MM Peat
Coal
Raw coal Residue Deposit Soluble
0.5 Biomass and BM + Coal 0.0 0.0
0.2
0.4
0.6
Raw Material Residue Deposit Soluble 0.8
HHV [MJ/kg-Raw material, d.a.f.]
Cell
1.0
Raw Material Liquid Soluble Deposit Residue
25 20 15 10 5 0
Cell
LN
LC
RS
PE
MM
LY
WA
BB
O/C
Figure 5 Elemental compositions of raw coals and extraction products on the H/C vs. O/C diagram.
Figure 6 Comparison of higher heating values (HHV) between raw coals and upgraded coals.
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Oviedo ICCS&T 2011. Extended Abstract
Cell LN LC
RS LC/LY RS/LY PE MM LY
Normalized displacement [-]
RS/MM
0.0
WA
-0.2
1000 1500 2000 Mass/Charge
Soluble 0.8
MM RS/MM
-0.4
RS -0.6
LY
-0.8
0.6
LC WA
0.4
LC/LY 0.2
RS/MM
Cell -1.0
0
100
200
300
400
500
0.0 600
o
BB
500
1.0
BB PE LN RS/LY
Relative weight [kg/kg-sample, d.a.f.]
Intensity [a.u.]
LC/MM
Temperature [ C]
Figure 8. TG curves (right) and TMA profiles (left) of the Solubles.
Figure 7 Molecular weight distributions of the Solubles. proposed degradative extraction is an endothermic process for these samples, which means the treatment does not lose heating value of raw materials. Figure 7 shows the molecular weight distributions (MWDs) measured by LDTOFMS of the Solubles. The MWDs are very close to each other, and the Soluble consisted of low-molecular-weight compounds of less than 500 in MW. The MWDs of Deposits are also rather close to each other, and Deposit consisted of compounds having less than 800 in MW. Figure 8 shows thermogravimetric (TG) curves (right axis) and thermomechanical analysis (TMA) profiles (left axis) of the Solubles during the heating to 900°C at a heating rate of 10 K/min. Both TG curves and TMA curves were respectively so close to each other.
Since the weight decrease below 400°C was judged to be due to
devolatilization, the Solubles are judged to consist of components having low-molecular weights. All of the Solubles completely melt at less than 100°C before devolatilaization starts. All of the Deposits have similar properties, but they melted at around 250°C.
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Oviedo ICCS&T 2011. Extended Abstract
4. Conclusions Two biomasses, cellulose, lignite, a peat and four low rank coals, and mixed samples of biomass and two coals were treated by 1-methylnaphthalene at 350°C to upgrade and to fractionate the raw materials into several fractions having similar chemical and physical properties. The Solubles and Deposits were very close to each other in elemental composition, chemical structure, molecular weight distribution, pyrolysis behavior, and softening/melting behavior. Thus, the proposed degradative solvent extraction method was found to be effective to convert low grade carbonaceous resources into solid fuels having higher heating values and significantly upgraded compounds having similar chemical and physical properties.
References [1] Miura K, Shimada M, Mae K. Extraction of coal at 300 to 350°C to produce
precursors for chemicals. Proceedings of the 15th Pittsburgh Coal Conference, Pittsburgh, 1998, Paper No. 30–1. [2] Miura K, Shimada M, Mae K, Huan YS. Extraction of coal below 350°C in flowing non-polar solvent. Fuel 2001;80:1573–82. [3] Miura K, Nakagawa H, Ashida R, Ihara T. Production of clean fuels by solvent skimming of coal at around 350°C. Fuel 2004;83:733–8. [4] Miura K, Mae K, Ashida R, Tamura T, Ihara T. Dewatering of coal through solvent extraction. Fuel 2002;81:1417–22. [5] Ashida R, Umemoto S, Hasegawa Y, Miura K, Kato K, Saito K, Nomura S. Upgrading of low rank coal through mild solvent treatment at temperatures below 350°C. Proceedings of the 26th Annual International Pittsburgh coal conference, Pittsburgh, 2009, 51/1–51/12. [6] Li X, Hasegawa Y, Morimoto M, Ashida R, Miura K. Conversion of low-rank coals into upgraded coals and extracts having similar chemical and physical properties using degradative solvent extraction. Preprints of Symposia - American Chemical Society, Division of Fuel Chemistry 2010;55:212–3.
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Upgrading and dewatering of low rank coals realizing the suppression of self-ignition tendency through solvent treatment at around 350°C H. FUJITSUKA, R. ASHIDA, and K MIURA Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan
[email protected] Abstract We have recently presented a novel method which can not only dewater but upgrade low rank coals under rather mild conditions. The method treats coal in non-polar solvents, such as 1-methylnaphthalene, at temperatures below 350°C. One of the remaining important questions to be considered for the method is if the self-ignition tendency can be suppressed by this solvent treatment method. In this study, self-ignition tendencies were examined for the samples prepared from an Australian brown coal by the proposed treatment. It was found that the treated coals obtained by the solvent treatment had little moisture content and had the heating values corresponding to subbituminous or bituminous coal. The self-ignition tendencies of the extracted fractions were significantly suppressed because of their small pore surface areas. The suppression of self-ignition tendency of the solvent treated coal was also explained by its small pore surface area which was probably caused by the coating of the extracted fractions. Thus, the validity of the proposed solvent treatment method as the dewatering and upgrading method of low rank coal was clarified.
1. Introduction Low rank coals such as brown coals and lignites, abundantly deposited and distributed worldwide, must be important resources for both energy and chemicals in this century. Low rank coals, however, have not been used on a large scale except for at mining sites. This is because low rank coals contain a large amount of water and show high self-ignition tendency when dewatered, which makes their transportation and storage extremely difficult. Therefore, not only dewatering but suppressing spontaneous combustibility of low rank coals is essential for their transportation and storage. Moreover, increasing their energy density, in other words increasing heating values on weight basis, is also needed for their transportation. The last process is generally called
upgrading. Thus, dewatering, upgrading, and suppression of self-ignition tendency are requested for effective use of low rank coals. We have recently presented a novel method which not only dewaters but upgrades low rank coals [Ref. 1, 2]. The method treats coal in non-polar solvents, such as 1-methylnaphthalene, at temperatures below 350°C, and separates the coal into extract, residue, and gaseous product consisting of CO2 and a negligible amount of hydrocarbon gases at the treatment temperature. Inherent water and water produced are almost completely removed from coal as liquid without phase change and separated from solvent by decantation at room temperature. The extract is further separated into solvent-soluble fraction, Soluble, and solvent-insoluble fraction, Deposit, at room temperature. The whole process of this treatment is therefore an efficient dewatering and removal of most of oxygen functional groups as either CO2 or H2O without affecting hydrocarbon moieties of coal. Then all of the three fractions obtained have the heating values corresponding to subbituminous or bituminous coal. Furthermore, the sum of the heating values of the three fractions multiplied by their yields slightly exceeds the d.a.f. basis heating value of original coal. Thus the proposed method was found to be an effective dewatering and upgrading method of low rank coal. One of the remaining important factors to be considered is if the self-ignition tendency of the three fractions obtained is suppressed. In this study self-ignition tendencies were examined for the three fractions and their mixture obtained from an Australian brown coal by the proposed method. Then factors affecting their self-ignition tendency were discussed.
2. Experimental section 2. 1. Solvent treatment procedure An Australian brown coal, Loy Yang (abbreviated to LY), was used in this study. Its analyses are given in Table 1. Its moisture content and O content are respectively as high as 50.6 % (a. r.) and 27.7 % (d. a. f.). The coal was ground into fine particles of less than 53 μm in diameter. Figure 1 shows a schematic diagram of the apparatus used for the treatment of coal in 1-methylnaphthalene (1-MN). A stainless steel autoclave Table 1 Ultimate and proximate analyses of LY coal Ultimate analysis wt%, d. a. f. C H N O
LY
66.7
4.7
0.9
27.7
Atomic ratio ‐ H/C O/C
0.85
0.31
Proximate analysis wt%, d. b. Moisture VM FC Ash wt%, a. r.
51.7
47.8
0.6
50.6
HHV MJ/kg
25.4
Autoclave 350 mL TC
Pressure gauge
Raw Coal Residue
Impeller Furnace
Valve
N2
Stainless Steel Filter 0.5 mm
Gas Soluble
Deposit
Reservoir 350 mL Figure 1 Schematic diagram of the apparatus for solvent treatment
(350 cm3, 55 mm I. D.) was charged with 30 g of as-received LY coal (14 g on d. a. f. basis) and 300 cm3 of 1-MN. A stainless filter (65 mm O. D. and 0.5 μm opening) was equipped at the bottom of the autoclave. After sufficiently purging the autoclave with nitrogen, the sample in the autoclave was heated up to 350°C at which it was kept for 1 h under sufficient agitation. Then the coal was separated into extract, residue, and gaseous product at the treatment temperature by opening the valve connecting the autoclave and the reservoir. The extract was further separated into solvent-soluble fraction, Soluble, and solvent-insoluble fraction, Deposit, at room temperature by filtration. Solvent treated coal (abbreviated to STC) was also prepared under the same conditions but without separating the coal into fractions. For comparison purpose, LY char was prepared by pyrolyzing LY coal at 350°C for 1 h in a helium stream. Carbon type distribution of each sample was measured by 13C-NMR and pore surface area was measured by CO2 adsorption at 25°C.
1.2
600
1
Relative weight
0.8
22 % O2/He
He
0.6
400 200 0 0
50
Oxidation 65°C, 2 h
0.4
Temperature
0.2
100 150 Time min
200
Relative weight kg/kg – d. a. f.
Temperature °C
800
0 250
Figure 2 Typical experimental procedure; temperature profile and weight change 2. 2. Procedure to estimate self-ignition tendency Self-ignition tendency of the solvent treated samples was examined using a thermogravimetric analyzer (Shimadzu TGA-50) connected to a micro gas chromatograph (Varian micro GC, CP-4900). The product gas composition was analyzed in every 80 s using the micro-GC. Experimental procedure is shown in Figure 2. Residue, Deposit and STC were first heated up to 250°C in a helium stream to remove solvent remaining, and then cooled to 65°C. Soluble and char were heated up to 65°C in a helium stream. Then the gas stream was changed to a 22 % oxygen-containing helium stream to absorb oxygen onto samples. The amount of oxygen adsorbed onto the sample after 2 h of adsorption, nO, was estimated from the weight change and the amount of gases formed. The nO value thus estimated was employed as the index of self-ignition tendency. After the adsorption step, the sample was heated up to 700°C at the rate of 20 K/min to estimate its gasification rate.
3. Results and Discussion 3. 1. Yields and properties of solvent treated samples Figure 3 shows the yields, the elemental compositions and the heating values of the prepared samples. All of the products were almost completely free from water as expected. The yields of Soluble and Deposit were 0.13 kg/kg-coal (d. a. f.) and 0.22 kg/kg-coal (d. a. f.) respectively. These two fractions were almost free from ash. The oxygen contents were as small as 10.2 kg/100 kg-coal (d. a. f.) and 16.9 kg/100 kg-coal (d. a. f.) for Soluble and Deposit, respectively. The sum of the yields of Soluble, Deposit
Yield
HN
Sample
C
Raw coal
66.7
STC
66.6 38.5
Residue
4.7 4.4
O
—
25.4
174.1
0.85
26.6 / 31.3
66.0
0.50
29.2 / 14.5
151.8
0.13
30.8 / 4.0
30.3
0.1 2.2
0.22
36.7 / 8.1
18.7
18.5
0.84
23.0 / 27.4
206.2
0.9 27.7 0.7
13.1
2.0 0.5 8.7
Deposit
10.1 0.7 0.1 2.2
Soluble
18.0
Char
HHV Surface area on the raw/ treated Sp kg/kg‐coal coal basis d. a. f. MJ/kg‐d. a. f. m2/g‐sample
61.0
1.7
3.7
0.7
0 20 40 60 80 100 Elemental composition kg/100 kg‐coal, d. a. f.
Figure 3 Elemental compositions, yields and heating values of the treated coals and Residue corresponds to the yield of char, but the elemental compositions are significantly different between the two. The oxygen content of STC was much smaller than that of char. Figure 4 shows the 13C-NMR spectra of the samples prepared. Soluble was richer in aliphatic carbons than the original coal, while other treated coals were less rich in aliphatic carbons than the raw coal. It is also clearly shown that the solvent treated products are free from –COOH. Figure 3 also gives the higher heating values (HHVs) of the samples prepared on
Intensity a.u.
200
150
100
50
Chemical Shift ppm
0
‐40
O‐CH3 ‐CH2 ‐CH3
COOH Ar‐O Ar‐C Bridgehead Ar‐H
Raw coal Residue Deposit Soluble
Raw coal STC Char
Intensity a.u.
O‐CH3 ‐CH2 ‐CH3
COOH Ar‐O Ar‐C Bridgehead Ar‐H
both the sample basis and the raw coal basis. The HHVs on the sample basis,
200
150
100
50
Chemical Shift ppm
0
‐40
Figure 4 Carbon type distributions of the prepared samples measured by 13C-NMR
representing energy density, are 28.7 to 37.4 MJ/kg-d. a. f. for the solvent treated samples. These values are comparable to those of subbituminous or bituminous coal. The sum of the HHVs of the three solvent treated fractions on the raw coal basis is 26.6 MJ/kg-d. a. f. and is slightly larger than the HHV of the raw coal. The above results clearly show that the proposed solvent treatment is very effective for dewatering and upgrading of LY coal. In addition it was found that the treatment does not lose the heating value.
3. 2. Examination of self-ignition tendency of the solvent treated samples Figure 5 shows how oxygen is adsorbed on the samples when they are exposed to the 22 % oxygen-containing helium stream at 65°C. Oxygen was rapidly adsorbed on both char and Residue, and the nO values were 2.3 and 2.2 mg-O/g-sample (d. a. f.) for char and Residue respectively. Oxygen was rapidly adsorbed on the raw coal at only the initial stage, and the nO value was 1.1 mg-O/g-sample (d. a. f.) for the raw coal. Oxygen was steadily adsorbed on Soluble at relatively small adsorption rate, and the nO value was 1.0 mg-O/g-sample (d. a. f.) for Soluble. Oxygen uptake was saturated at around 30 min for Deposit, and its nO value was only 0.3 mg-O/g-sample (d. a. f.). The oxygen uptake behavior of STC could be explained by the oxygen uptake behaviors of Soluble, Deposit, and Residue. The nO values in Figure 5 show that the self-ignition tendency of Deposit and Soluble are respectively much lower and slightly lower than that of the raw coal, suggesting that the proposed solvent treatment is effective also to suppress the self-ignition tendency of the extract. nO
mg‐O/g‐sample d. a. f.
Oxygen adsorption mg‐O/g‐sample d. a. f.
2.5 2.0
65°C, 22 % O2/He
Residue STC
1.5
1.6 1.1 1.0
Raw coal
1.0
Soluble
0.5 0 0
2.3 2.2
Char
Deposit 30
60 Time min
90
0.3
120
Figure 5 The oxygen uptake profiles and nO values of the treated coals
The self-ignition tendency of low rank coal is believed to be governed by many factors [Ref. 3]. One of the largest chemical factors is the abundance of aliphatic carbons, and one of influential physical factors is the pore surface area. Soluble was richest and Residue was poorest in the aliphatic carbons, but the nO values in Figure 5 do not reflect the abundance of the aliphatic carbons. Then the pore surface areas of the treated samples, Sp, were measured by the CO2 adsorption method at 25°C, and the Sp values are listed in Figure 3. The Sp value of Soluble was 18.7 m2/g-sample and was the smallest of all of the samples. The Sp value of Deposit was also as small as 30.3 m2/g-sample, whereas the Sp values of the raw coal, char, and Residue were much larger than the Sp value of either Soluble or Deposit. These results show that the small nO value of Soluble is due mainly to its small Sp value and the smallest nO value of Deposit comes from the low content of aliphatic carbons and the small nO value. Summing up the above results, it was clarified that the proposed solvent treatment method is not only very efficient for both dewatering and upgrading but promising for the suppression of self-ignition tendency of low rank coal.
4. Conclusion The posibility of non-polar solvent treatment at 350°C, which realizes dewatering and upgrading, as self-ignition suppression method of low rank coals was examined. It was found that the solvent treated samples contained little amount of water and had the heating values corresponding to subbituminous or bituminous coal. The extracted fractions, Deposit and Soluble, showed significantly low self-ignition tendency because of their small pore surface areas even though Soluble is richer in aliphatic carbons. Thus, the validity of the proposed solvent treatment method as the dewatering and upgrading method of low rank coal was clarified.
References [1] K. Miura, et al., ACS Div. Fuel Chem. 2009; 54-2; 212 [2] X. Li, et al., ACS Div. Fuel Chem. 2010; 55-2; 870 [3] Wang H, Dlugogorski BZ, Kennedy EM. Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modeling. Prog. Energy Combust. Sci. 2003; 29; 487–513
Upgrading of Low-quality Coals by Thermal Extraction
T. Takanohashi1, N. Sakimoto1, K. Koyano1, Y. Harada2 and H. Fujimoto3 1 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, 16-1 Onogawa, Tsukuba 3058569, Japan 2 Sakaide Plant, Mitsubishi Chemical Co., 1 Bannosu-cho, Sakaide-shi, Kagawa 762-8510, Japan 3 Steel Research Lab., JFE Steel Co., 1 Kokan-cho, Fukuyama, Hiroshima 721-8510, Japan E-mail:
[email protected] Abstract “HyperCoal” (ash-free coal) is produced from low-quality coals, such as subbituminous coals and lignites, by thermal extraction using cost-effective industrial solvents below 400 °C in an inert atmosphere. It was found that some upgrading reactions took place during the thermal extraction at 380 – 420
o
C; degradation of oxygen functional groups and
aromatization of unit structure in coals. As a result, the chemical properties of HyperCoals became similar to those of bituminous coals.
1.
Introduction Coke making is becoming more expensive because of the sudden rise in the price of caking
coals due to the decreasing supply, and so a technology to manufacture good-quality coke from coal blends containing low-quality slightly caking or non-caking coals is strongly required. “HyperCoal” (ash-free coal, HPC) is produced by thermal extraction using cost-effective industrial solvents below 400 °C in an inert atmosphere. Thermal extraction using industrial solvents such as light cycle oil (LCO) and crude methyl naphthalene oil (CMNO) has been applied to produce ash-free coal called HyperCoal (HPC) [1-4]. It has originally a wider temperature range of thermoplasticity during heating [5]. When the HPC was mixed instead of a caking coal in coal blends, a significant improvement in the thermoplasticity of coal blends was observed [6]. HPC can be produced from various ranks of coals including lignite and subbituminous coal, however, the chemical property of HPC is different depending on the coal rank [7]. In addition, the chemical and physical properties of HPC are also dependent upon the manufacturing condition of HPCs. Especially, for low-quality coals such as low-rank and high-sulfur coals, some chemical reactions take place during the thermal
extraction. In the current work, upgrading of low-quality coals by changing the manufacturing conditions such as the extraction temperature and solvent type was investigated.
2. Experimental section Materials
One subbituminous coal (PA) and one lignite (MUL) were used. The coals
were ground and sieved less than 1.0 mm of particle size, and dried under vacuum at 80 °C for 12 h.
In dynamic shear rheometric test (DSR), the samples were ground less than 0.15
mm. The ultimate analysis of coals are shown in Table 1. Reagent grade 1-methyl-naphthalene (1-MN) was used as the thermal extraction solvent without further purification. In addition, 20% of reagent grade indole (IN) was added to 1-MN and the mixture was used as the polar extraction solvent [8].
Table 1 Coal
Ultimate analysis of coal samples used. C
H
N
PA
73.5
5.3
(wt%, daf) 1.9
MUL
65.5
5.0
0.9
Thermal extraction.
S
O(diff)
Ash
0.2
19.1
(wt%, db) 4.4
0.1
28.5
3.2
Thermal extraction of coal was carried out using a flowing solvent
extractor. Details of the extraction procedure are described elsewhere [6]. The coal sample was extracted for 60 min at 300 - 420 oC. After the extraction, the extract was precipitated by adding an excess of n-hexane (400 mL) to the extract solution, and collected as the solid extract (called HyperCoal, HPC). While, the extraction residue (RES) was washed with toluene and acetone. The extract and residue samples were dried at 80°C for 12 hr in a vacuum. The extraction yield of coal was defined as Extraction yield = (1 – Wr/Wc )/(1 – Ash/100) × 100
(1)
where Wc (g), Wr (g), and Ash (wt%, db) are the initial mass coal, the mass of the residue, and the ash content of the initial coal, respectively.
Nuclear magnetic resonance (NMR) measurement
Solid-state 13C nuclear magnetic
resonance (NMR) measurements were made using the CP (cross-polarisation)/MAS (magic angle spinning) method using a Chemagnetics CMX-300 NMR spectrometer. The peaks were assigned according to the chemical shifts of model compounds: the peak from 185 to 170 ppm was assigned to carbonyl carbon (COOH, C=O); the peak from 170 to 148 ppm to phenolic carbon; the peak from 148 to 129 ppm to nonprotonated aromatic carbon; the peak from 129 to 93 ppm to protonated aromatic carbon; the peak from 75 to 50 ppm to aliphatic carbon connected to oxygen; the peak from 50 to 25 ppm to methylene and methyne carbon; and the peak from 25 to 0 ppm to methyl carbon. The fraction of each carbon was obtained from the area intensity ratio of each carbon peak divided by the chemical shifts described above.
Dynamic shear rheometric test. Around 0.4 g of sample was pressed under 100 MPa to a pellet with a diameter of 13.1 mm and height of around 3 mm.
The dynamic shear
rheometer test was carried out usually at 40-550˚C at a heating rate of 3˚C/min under nitrogen flow of 80 L/min.
3.
The detail of procedures was described elsewhere [9].
Results and discussion Table 2 shows H/C and O/C atomic ratios, and the extraction yield of HPCs when the
extraction temperature was changed from 300 to 420 oC. The H/C ratio for both coals was gradually decreasing with an increase in the extraction temperature. The value of HPCs produced at lower temperatures; 300 – 340 oC for PA coal, and 300 oC for MUL coal, was higher than that of raw coals. While, at higher extraction temperatures; 380 – 420 oC for PA coal, and 320 – 420 oC for MUL coal, the value became lower. These results show that low-molecular-weight components were mainly extracted at low temperatures, and heavier components were extracted at higher temperatures. As the extraction temperature is increasing, demethanation and dehydrogenation (aromatization) reactions might have occurred. The O/C ratio was also decreasing with an increase in the temperature. Over around 350 oC, decarboxylation reaction would have occurred. While, the extraction yield gave the maximum at 400 oC for both coals, suggesting that the ratio of heavier components was increasing up to 400 oC. While, retrogressive reactions take place simultaneously over around 400 oC. As a result, at 420 oC the extraction yield might have decreased.
Table 2
H/C and O/C atomic ratios of HPCs and the extraction yield. Temperature [oC]
H/C [-]
O/C [-]
Extraction yiled [wt%, daf]
PA raw coal PAHPC
300 320 340 360 380 400 420
0.86 0.93 0.91 0.87 0.86 0.82 0.79 0.77
0.19 0.15 0.14 0.13 0.13 0.13 0.13 0.09
18.6 25.6 31.2 37.8 46.0 49.4 39.1
MUL raw coal MULHPC
300 320 340 360 380 400 420
0.91 0.93 0.9 0.85 0.82 0.8 0.76 0.77
0.33 0.18 0.17 0.17 0.16 0.15 0.14 0.14
18.0 22.5 27.3 35.8 40.3 46.7 39.8
Figure 1 shows the relationship between the H/C atomic ratio and O/C one of raw coals and their HPCs produced at different extraction temperatures. For reference, the plots for three bituminous coals and their HPCs produced at 360 oC are also shown. For both low-grade coals, the plot was moving obliquely left downward as the extraction temperature was increasing. Consequently, the plots at 380, 400 and 420 oC for the both low-grade coals are almost within those for bituminous coal samples. This result suggests that HPCs produced at 380 – 420 oC for low-grade coals may have similar chemical properties.
Figure 2 shows the carbon distribution for PA coal. At 360°C, the distribution of PAHPC was similar to that of the raw coal. As the extraction temperature was increased to 380 and 400°C, the ratios of methylene (CH2) and methyl (CH3) groups decreased and the ratio of protonated aromatic carbon (Ar-H) increased. These results suggest that with increasing extraction temperature, the aromaticity of the extract components obtained became higher, in agreement with the ultimate analysis.
0.95 bituminous raw PA raw MUL raw
bituminous HPC PA HPC MUL HPC
H/C atomic ratio [-]
0.9 360
0.85 380
0.8
400
420
0.75
0.7
0
0.05
360 380 400 420
0.1 0.15 0.2 0.25 O/C atomic ratio [-]
0.3
0.35
Figure 1 Relationship between H/C and O/C atomic ratio for various kinds of raw coals and their HPCs.
PA R aw C =O P henolic A r-C A r-H -C H 2-O CH2 CH3
P AR ES (360) P AH PC (360) P AH PC (380) P AH PC (400) 0
20
40
60
80
100
Ratio [%] Figure 2 Carbon distribution of PA raw coal, its extraction residue and HyperCoals obtained at different extraction temperatures.
Conclusions HyperCoal (HPC) was produced from two low-grade coals (PA subbituminous coal and MUL lignite) at different extraction temperatures. For both coals, the H/C and O/C atomic ratios of HPCs were gradually decreasing with an increase in the extraction temperature from 300 oC to 420 oC. Their H/C and O/C ratios of HPCs obtained at 380 – 420 oC are almost within those for bituminous coals, suggesting that some upgrading reactions such as aromatization and decarboxylation reactions, took place during the thermal extraction.
Acknowledgment This work has been done in Development of Cokemaking Technology from Low-grade coals and Nonconventional Carbon Resources, Division of High-Temperature Processes, Academic Society, the Iron and Steel Institute of Japan. The authors would like to acknowledge the research group members gratefully.
References [1] Yoshida T, Takanohashi T, Sakanishi K, Saito I, Fujita M, Mashimo K, Energy Fuels, 2002, 16: 1006 [2] Okuyama N, Komatsu N, Shigehisa T, Kaneko T, Tsuruya S, Fuel Proc. Tech., 2004, 85: 947 [3]Yoshida T, Li C, Takanohashi T, Matsumura A, Sato S, Saito I, Fuel Proc. Tech., 2004, 86: 61 [4] Kashimura N, Takanohashi T, Saito I, Energy Fuels, 2006, 20: 1605 [5] Takanohashi T, Shishido T, Kawashima H, Saito I, Fuel, 2008, 87: 592 [6] Takanohashi T, Shishido T, Saito I, Energy Fuels, 2008, 22: 1779 [7] Koyano K, Takanohashi T, Saito I, Energy Fuels, in press. [8] Kashimura N, Takanohashi T, Saito I, Energy Fuels, 2006, 20: 2063 [9] Yoshida T, Iino M, Takanohashi T, Kato K, Fuel, 2000, 79: 399.
Arsenic leachability and speciation in fly ashes from coal fired power plants S. Kambara*, M. Endo, S. Takata, K. Kumabe, H. Moritomi Gifu University, Environmental and Renewable Energy Systems Division, Graduate School of Engineering, 1-1 Yanagido, Gifu, 501-1193, Japan *Corresponding author:
[email protected] Abstract To determine dominant factors on arsenic leaching from the coal fly ash, arsenic leaching test under a constant pH was performed. Twelve fly ash samples were collected from two coal fired power plants (600 MWe) having different boiler types. Arsenic in the raw coal was almost all associated with the fly ash in both power plants; however arsenic leaching fraction was strongly differed in boiler types. It found that the dominant factors of arsenic leaching were calcium contents in fly ashes and ash contents in raw coals. 1. Introduction Major fractions of coal fly ash generated from pulverized coal combustion processes have been used as fill materials to reclaim land from the sea. Coal fly ash contains hazardous toxic elements such as arsenic, and often contains elevated concentrations of the toxic elements. An ash storage area is usually holding seawater and rainwater (called excess water), therefore some elements including arsenic in the fly ash are leach out the excess water. If arsenic concentration in the excess water exceeds the environmental limit (0.1 mg/L in Japan), the excess water can not be drained to the sea. This is a serious situation, because ash storage has to discontinue. In this concern, it is important to find leachability of arsenic from the fly ashes for various coal types. Another interest is effect of the boiler types on the leachability, because the ash properties and arsenic partitioning may be changed by types of coal fired boilers. Some researchers investigated As partitioning and its mechanisms during coal combustion [1, 2]. It concluded that As in raw coal was released as vapor at high temperature during combustion, and generated gaseous arsenic oxide reacted with calcium oxide on fly ash. Consequently, Ca 3 (AsO 4 ) 2 is formed on fly ash surface, which is the most thermodynamically stable calcium–arsenic compound under conditions of coal fired boilers [3]. Oxidation state of As (+3 and +5) is an important factor in controlling As leachability [4]: hence, As leachability may depend on combustion conditions. In this paper, As leachability was investigated for various coal fly ashes collected from two different power plants. Effects of Ca and boiler types on As leachability were discussed.
2. Experimental section 2.1. Fly ash samples Six fly ash samples were carefully collected from each coal fired power plants (Unit A and Unit B: 600 MWe). Fig. 1 depicts the process flow of the plants, ash collection locations, and typical gas temperatures between the boiler exit and the low temeprature electrostatic presipipator (ESP). The unit B has a DeNOx (SCR) system. To prevent contamination of samples, after enough time from coal switching, the ash sampling was began at each chamber (#1, #2, and #3). Table 1 lists coal properties and ash composition. Coal F and G, and coal H and I are same coal between unit A and B. 370℃
350℃
Boiler
145℃
A/H
GGH
ESP
FGD
DeNOx (Unit B only) #1
Eco-hopper Clinker
#2
#3
85% 10% 5% Multi Cyclone
(Ash partitioning)
Flue gas Ash collection
Fig. 1. Process flow of the coal fired power plants and ash collection points. Table 1. Properties of raw coals and fly ashes collected from #1 chamber of ESPs. Power station
Unit A
Unit B
Key E F H O P R G I K L M Q
Raw coal (on dry basis) C Ash As wt% wt% mg/kg 67.9 14.3 2.14 71.5 13.3 0.84 68.3 10.4 3.69 69.6 9.7 1.45 70.9 13.0 0.78 76.5 9.5 0.88 71.5 13.3 0.84 68.3 10.4 3.69 67.9 13.9 1.35 73.1 10.3 0.87 73.0 9.7 1.53 74.0 9.5 1.02
As mg/kg 12.16 3.16 26.46 15.65 4.96 8.23 4.53 39.22 8.85 9.46 10.41 7.48
SiO2 wt% 55.5 67.0 59.3 75.7 62.1 62.6 65.4 59.0 56.1 58.1 64.5 62.3
Fly ashes (on dry basis) Al2O3 Fe2O3 CaO Na2O wt% wt% wt% wt% 31.2 5.35 2.18 1.17 26.2 2.26 0.68 0.26 25.6 7.49 2.05 0.60 17.2 2.79 0.97 0.47 26.5 4.77 1.68 0.95 28.7 3.86 0.93 0.45 26.5 3.18 0.93 0.28 26.0 7.25 2.09 0.65 20.6 7.80 9.46 0.71 21.4 6.40 8.24 0.83 22.9 6.31 1.46 0.51 27.8 4.04 1.39 0.73
K2O wt% 1.18 0.60 1.56 0.94 0.98 0.69 0.56 1.50 2.04 1.86 1.74 0.89
SO3 wt% 0.29 0.24 0.42 0.00 0.15 0.00 0.64 0.51 0.80 0.84 0.34 0.04
2.2. Leaching tests To simulate pH of the excess water, a buffer solution adjusted pH = 10 was prepared as a leaching solvent. The ash sample (1.0 g) was added to the leaching solvent (10 mL), and it was shaken for 30 minute at 200 rpm. After shaking, the solid and the solvent were separated by filtration, and both arsenic concentration of the solid and the solvent was measured by ICP-AES.
3. Results and Discussion 3.1. Arsenic partitioning In pulverized coal combustion processes, arsenic has classified as Group II elements which are not incorporated into the bottom ash. It is believed that volatilized arsenic during combustion is chemically condensed on fly ash at low temperature processes [2]. For twelve fly ash samples, percentage of As partitioning was ranged from 95−157% as calculated from data listed in Table 1, which represented the behavior of Group II elements. To compare arsenic partitioning in the unit A and B, relation between modified arsenic concentration in the raw coals, [As 0 /Ash 0.65 ], and arsenic concentration in the fly ashes, As FA , for the unit A and B is shown in Fig. 2. As 0 and Ash are As concentration and ash content in the raw coals, respectively. It found that As FA can be accurately estimated by the parameter [As 0 /Ash 0.65 ], and arsenic partitioning was same behavior between the unit A and B.
Arsenic leaching fraction [%]
Arsenic conc. in FA [mg/kg]
40 Unit A Unit B
35 30 25 20 15 10 5 0 0
20
40 60 80 As0 /Ash0.65 ×100 [ - ]
100
Fig. 2. Relation between modified As concentration in the raw coals and As concentration in the fly ashes for the unit A and B.
2.5 2.0
Unit A
Unit B
1.5 1.0 0.5 0.0 E F H O P R G I K L M Q Fly ashes
Fig. 3. Variation in As leaching fraction for various fly ash samples and for the unit A and B. (pH of the leaching solvent was fixed on 10.)
3.2. Arsenic leaching Fig. 3 shows the arsenic leaching fraction, L As , for the fly ash samples of the unit A and B. With the unit A, L As was observed in the range of 0.3−3.0%, which was a wide range comparing that of the unit B. Particularly, L As of fly ash F and G, although the both raw coals were same, significantly differed. It clarify that arsenic leaching is affected by boiler types. 3.3. Dominant factors on arsenic leaching Ca 3 (AsO 4 ) 2 is a stable compound formed during combustion, which is an insoluble material: it seems that fly ash types having high CaO/Ash ratios generate much Ca 3 (AsO 4 ) 2 , and have low As leaching fraction. Fig. 4 shows variation in L As for all
fly ash samples as a function of CaO/Ash×100, where CaO is ash composition of the raw coal. L As increased suddenly below CaO/Ash = 50 in both units. CaO/Ash×100 of coal F and G is 6.3: it is reasonable that both fly ashes have high L As among the same unit. However, L As of coal F (unit A) is much higher than that of coal G (the unit B). The reason for the difference may be the difference in CaO content of the fly ash between unit A and B. Fig. 5 shows CaO% in the fly ashes of coal F and G. It found that the fly ash F from the unit A indicated low CaO% compared to the fly ash G. Therefore actual CaO/Ash ratio of the fly ash F was much lower than the appearance CaO/Ash ratio. It is supposed that high L As of the fly ash in unit A is owing to the loss of calcium during combustion.
1.4
Unit A Unit B
2.0
1.2
CaO % in FA
Arsenic leaching fraction [%]
2.5
1.5 1.0 0.5
1.0
Unit A, Coal F Unit B, Coal G
0.8 0.6 0.4 0.2
0.0
0.0
0
50
100 150 CaO/Ash×100 [-]
200
Fig. 4. Variation in LAs% as a function of CaO/Ash ratios for the unit A and B.
#1
#2 #3 Sampling location
Average
Fig. 5. Different in CaO% in the fly ashes between the unit A and B.
4. Conclusions Arsenic petitioning in the unit A and unit B represented the same behavior. Most arsenic in the raw coal associated with the fly ash for various coal types. However, arsenic leaching fraction of the fly ashes in the buffer solution (pH = 10) was strongly affected by coal types and boiler types. It was found that arsenic content, calcium content, and ash content were the dominant factors controlling As leachability. References [1] Seames WS, Wendt JOL, Regimes of association of arsenic and selenium during pulverized coal combustion, Proc. Combust. Inst., 2007;31:2839–2846. [2] Senior CL., Lignell DO., Sarofim AF., Mehta A., Modeling arsenic partitioning in coal-fired power plants, Combust. Flame, 2006;147:209–221. [3] Frandsen F., Dam-Johansen K., Rasmussen P., Trace elements from combustion and gasification of coal—An equilibrium approach, Prog. Energy Combust. Sci. 20 (1994) 115–138. [4] Jing C., Liu S., Meng X., Arsenic leachability and speciation in cement immobilized water treatment sludge, Chemosphere, 2005;59:1241–1247.
Low temperature SNCR by photochemical activation of ammonia
S. Kambara* 1 , M. Kondo 1 , N. Hishinuma 2 , M. Masui 3 , K. Kumabe 1 , H. Moritomi 1 1 Gifu University, Environmental and Renewable Energy Systems Division, Graduate School of Engineering, 1-1 Yanagido, Gifu, 501-1193, Japan 2 Ushio Inc., 1194 Sazuchi, Bessho-cho, Himeji, Hyogo 671-0224, Japan 3 Actree Co. Ltd., 375 Hakusan, Ishikawa, 924-0053, Japan *Corresponding author:
[email protected] Abstract To broaden and lower the temperature window of the selective non catalytic reduction (SNCR) of nitric oxide (NO), the use of activated ammonia was examined. A wavelength of 172 nm was employed as the excitation source for molecular ammonia. Activated ammonia was injected into a model flue gas (NO/O 2 /N 2 ) at room temperature. The effects of reaction temperatures, oxygen concentrations, and NH 3 /NO molar ratios on NO removal were investigated in a lab-scale plug flow reactor. Reaction temperatures ranged from 500 °C to 850 °C. A temperature window enlargement of 150 °C was achieved at the lower boundary of the temperature window. Above 600 °C, NO removal was effected by injection of activated ammonia, while around 750 °C, conventional SNCR by injection of molecular ammonia was effective. An approximate 80% NO removal was attained at 700 °C with an MR = 2.0 and 8.3% O 2 . The formation of nitrous oxide (N 2 O) using activated ammonia SNCR technology was also investigated and was found to be strongly affected by O 2 concentrations, while the concentration of N 2 O increased with an increase in NO removal. 1. Introduction Selective non catalytic reduction (SNCR) techniques are a conceptually simple process that involves injecting molecular ammonia into the furnace without using a catalyst [1]. SNCR systems seem to be a promising technology because of their cost-effectiveness, although critical issues regarding their application still exist. In SNCR systems, NO x reduction occur at temperatures between 850 °C and 1175 °C (temperature window), however, high enough NOx reduction was not obtain in large-scale combustors [2]. To improve NOx reduction efficiency, the expansion of the temperature window is desired. It has been reported that chemical additives together with molecular ammonia can lower and widen the temperature window. Various additives have been studied, including hydrogen, hydrogen peroxide, hydrocarbons, and carbon monoxide [3], all of which are effective. However, utilization of chemical additives increases the cost
of NO reduction. A recognized research goal is to expand the temperature window without the need for additives. The aim of the research presented in this study was to find an alternative method of producing effective chemical species for NO removal without the use of argon gas. 2. Experimental section The experimental setup is shown in Fig. 1. The apparatus consists of two gold furnaces with quartz tubes, the gas mixing and flow control systems, the photochemical reactor, and the gas analyzers. The quartz tubes were connected via the mixing chamber. An NO/O 2 /N 2 gas mixture was prepared as the model flue gas, and fed into the pre-heater quartz tube. Ammonia gas diluted with nitrogen was used as the NO removal agent, which was fed into the photochemical reactor at room temperature. Molecular ammonia is excited by photons emitted from the excimer lamp in the photochemical reactor. In this paper, the chemical species generated by VUV radiation will be termed “activated ammonia”. Activated ammonia was introduced into the mixing chamber. The reaction temperature was varied from 500 °C to 850 °C. The total gas flow rate of the NO/O 2 /NH 3 /N 2 gas mixture was fixed at 3.0 L/min for all experimental conditions. The gas composition of the output stream was continuously measured by gas analyzers for NO x , O 2 , and N 2 O. Fig. 2 depicts the configuration of the photochemical reactor. The excimer lamp (USHIO Inc.) was placed on top of the center of the power unit. An aluminum cylindrical chamber coaxial in configuration to the excimer lamp was fitted around the excimer lamp. An NH 3 /N 2 gas mixture was fed into the gap between the excimer lamp and the inside wall of the cylindrical chamber. The radiation power of the VUV ray was 26 mW/cm 2 on the quartz glass surface of the excimer lamp.
Fig. 1. Experimental setup.
Fig. 2. Configuration of the photochemical reactor.
3. Results and Discussion 3.1. Effect of reaction temperatures The relationship between reaction temperatures and NO removal in both SNCR systems is presented in Fig. 3. In conventional SNCR system, it can be observed that an NO removal of 3–4% was effected at 750 °C and increased significantly above 800 °C for both molar ratios of 1.0 and 1.5. In the activated ammonia SNCR, slight NO removal began at the reaction temperature of 600 °C and increased almost proportionally with a further increase in the
reaction
temperature.
It
clearly
indicates that the injection of activated ammonia
broadened
window
and
the
lowered
temperature its
starting
temperature. The temperature shift was 150 °C at an NO removal of 20%. This result suggests that effective chemical species for NO removal were formed from activated ammonia generated by VUV
radiation
at
the
reaction
temperature above 600 °C.
Fig. 3. NO removal performances of conventional SNCR (Thermal) and activated ammonia SNCR.
3.2. Effect of molar ratios and oxygen concentrations Fig. 4 shows the variation in NO removal with the variation of NH 3 /NO molar ratios in the range of 1.0–3.5 at 700 °C. With the activated ammonia SNCR, NO removal proportionally increased with increasing the molar ratios up to MR = 2.0, beyond which a gradual increase in NO removal was observed. With conventional SNCR, because the reaction temperature of 700 °C was outside the temperature window, slight NO removal was observed even at high molar ratios. Approximately 80% NO removal was obtained at MR = 2.0 at 700 °C using the activated ammonia SNCR technology. The effect of the oxygen concentration on NO removal in the MR range of 1.0 to 2.0 is also shown in Fig. 4. A slight increase of about 5% NO removal was observed at 8.3% O 2 compared to that at 2.1% O 2 for the activated ammonia technology. With the conventional SNCR, the O 2 concentration had a weak effect on NO removal, although NO removal increased monotonically with O 2 concentration. This suggested that the reaction mechanisms for NO removal in the activated ammonia SNCR was caused by similar elemental reaction pathways to the conventional SNCR, although the reaction temperatures differed for both SNCR systems. 3.3. N 2 O formation In conventional SNCR systems, N 2 O is usually generated as a byproduct during the
reactions that effect NO removal. Fig. 5 shows the N 2 O formation with the activated ammonia SNCR as a function of NO removal with the different oxygen concentrations and NH 3 /NO molar ratios. It can be seen that N 2 O concentrations increased with increasing NO removal for all experimental conditions. The increase in the O 2 concentration significantly promoted N 2 O formation, while the molar ratio did not have much effect on N 2 O formation. The maximum N 2 O concentration of 17 ppm was detected at 80% NO removal with 8.3% O 2 and MR = 1.5.
Fig. 4. Variation in NO removal with NH 3 /NO molar ratios in activated ammonia SNCR and conventional SNCR at temperature of 700 °C.
Fig. 5. N 2 O formation with activated ammonia SNCR as a function of NO removal with different O 2 levels and NH 3 /NO molar ratios.
4. Conclusions With the activated ammonia SNCR, NO removal began at a reaction temperature of 600 °C, and NO removal almost proportionally increased with a further increase in reaction temperature. Approximately 80% NO removal was obtained at a molar ratio of 2.0 at 700 °C. Oxygen concentrations had little influence on NO removal: an increase of about 5% NO removal was observed with an increase from 2.1% to 8.3% O 2 . However, an increase in the oxygen concentration caused the formation of N 2 O. The molar ratios had a large impact on NO removal. Acknowledgment The authors would like to acknowledge that funding for this study was provided by the Japan Science and Technology Agency through the Adaptable and Seamless Technology Transfer Program (A-STEP). References [1] Lyon RK. Method for the reduction of the concentration of NO in combustion effluents using NH 3 . US. Patent 3900554. 1975. [2] Jodal, M., Nielsen, C., Hulgaard, T., Dam-Johansen, K., Pilot-scale experiments with NH 3 and urea as reductants in selective non-catalytic reduction of nitric oxide. 23rd Symp. (Int.) on Combus. 1990; 237–243. [3] Javeda MT, Irfana N, Gibbs BM. Control of combustion-generated nitrogen oxides by selective non-catalytic reduction. J. Env. Manage. 2007;83:251–289.
Oviedo ICCS&T 2011. Extended Abstract
Optimum temperature for sulphur retention in fluidised beds working under oxy-fuel combustion conditions A. Rufas, M. de las Obras-Loscertales, L.F. de Diego, F. García-Labiano, A. Abad, P. Gayán, J. Adánez. Dept. Energy and Environment, Instituto de Carboquímica (ICB-CSIC) Miguel Luesma Castán 4, 50018 Zaragoza. Spain Corresponding author:
[email protected] Keywords: Oxy-fuel combustion, SO2 retention, limestone, fluidised bed. Abstract In the oxy-fuel combustion process the fuel is burned in pure oxygen gas diluted with recirculated flue gas, mainly composed of CO2, producing a gas stream leaving the combustor highly concentrated on CO2, up to 95%, which greatly facilitates the capture of CO2. The fluidised bed combustors are very appropriate for this process, allowing additionally the in situ desulphurisation by feeding calcium-based sorbents into the combustor. In this work, the effect of the temperature of the combustor on the retention of the SO2 generated in the combustion of two coals with very different sulphur content (a lignite and an anthracite) has been studied. The experimental facility used has been a bubbling fluidised bed (BFB) combustor operating under oxy-fuel combustion conditions. Several tests were also carried out under enriched air combustion conditions for comparison reasons. A Spanish limestone “Granicarb” was used as Ca-based sorbent for sulphur retention. The temperatures tested were between 800 and 950 ºC using Ca/S molar ratios of 2 and 3. It was found that under oxy-fuel combustion conditions in BFB the optimum temperature to achieve the highest sulphur retention was 900-925 ºC, whereas in enriched air combustion the optimum was 850 ºC. Working at the optimum temperature for each case, the SO2 retentions were higher in enriched air combustion than in oxyfuel combustion conditions.
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Oviedo ICCS&T 2011. Extended Abstract
1. Introduction Carbon dioxide (CO2) and sulphur dioxide (SO2) emissions are a major concern in combustion processes using fossil fuels, as for example coal; the former is implicated in global climate change and the latter produces acid rain. CO2 is one of the major contributors to the build-up of greenhouse gases in the atmosphere. At the same time, fuels containing sulphur produce SO2 emission during combustion. The capture and storage of CO2, emitted in large quantities from power plants, is considered an option to be explored in the medium term for reducing CO2 levels released to the atmosphere. Oxy-fuel combustion is one of the possibilities under investigation within the different options for CO2 capture [1-3]. This technology uses for combustion pure O2 mixed with recirculated flue gases, instead of air used in conventional combustion, and so, the flue gas stream finally produced is highly concentrated on CO2. It is believed that an oxy-fuel circulating fluidised bed (CFB) combustor will be an important candidate for new coal fired power plants [4-5] mainly because the circulation of solids in the combustor can help to an effective control of the temperature. Other of the best known advantage of fluidised bed (FB) combustion is the in-situ desulphurisation of the flue gas with the addition of Ca-based sorbents such as limestone or dolomite. Sulphur capture with these sorbents is a process highly dependent on the temperature and CO2 concentration according to the thermodynamic equilibrium curve of CaCO3 calcination, plotted in Figure 1. 100
P CO2 (kPa)
80 OXY-FUEL COMBUSTION
60
CaCO3
40
CaO
20 AIR COMBUSTION
0 700
750
800
850
900
950
1000
Temperature (ºC)
Figure 1. Thermodynamic equilibrium curve of CaCO3 calcination.
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Oviedo ICCS&T 2011. Extended Abstract
In conventional air-combustion in FB boilers, characterised by low CO2 concentrations (~15%) and temperatures about 850 ºC, the operating conditions lead to a previous sorbent calcination (R1) and to the sulphation of calcines (R2), i.e. indirect sulphation: CaCO3
CaO + CO2
CaO + SO2 + ½ O2
(R1) CaSO4
(R2)
However, in oxy-fuel combustion, CO2 concentration in the flue gas may be enriched between 60 and 90%. Under so high CO2 concentration, the sorbent can behave in two ways depending on the temperature. In oxy-fuel combustion conditions at 850 ºC, the sulphur retention will be produced under direct sulphation (R3), being necessary higher temperatures to operate under indirect sulphation. CaCO3 + SO2 + ½ O2
CaSO4 + CO2
(R3)
The objective of this work was to analyse the behaviour of a limestone in a continuous FB combustor working in typical oxy-fuel operating conditions to determine the optimum temperature for SO2 retention using this technology.
2. Experimental section Coal combustion experiments with limestone addition were carried out in a bubbling fluidised bed (BFB) combustor working in oxy-fuel combustion conditions and also with enriched aire. Figure 2 shows a photograph and a schematic diagram of the installation used. The experimental installation consisted mainly of a gas supply (air, CO2, O2) system using mass flow controllers; a fluidised bed reactor, 10 cm internal diameter, that could operate with two bed heights (25 cm and 40 cm); and a freeboard with an internal diameter of 15 cm and a height of 45 cm. The solids were fed to the reactor by means of two screw feeders located just above the distributor plate: One to feed coal and sorbent and the other to feed sand as inert solid. The flow rate of solids entering the reactor was controlled by regulating the velocity of the screw feeders. The facility was equipped with pressure sensors and thermocouples to measure solid inventory, temperature and to control the system. To ensure good temperature control, a heat exchanger was installed. An air pre-heater was used to heat the bed up to the ignition temperature of coal during the start-up of the plant. The flow of combustion gases passed through a high efficiency
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Oviedo ICCS&T 2011. Extended Abstract
cyclone for the retention of elutriated solids and then was sent to the stack. The composition of gases leaving the reactor was analysed continuously by on-line gas analysers.
Heat-exchanger
On-line analysers
Condenser
SO2, O2, CO2, CO, NOx To stack
T5 P3
Cyclone
Cyclone deposit T4 Bubling fluidised bed T3 Coal + Limestone
Drain deposits
T2 Sand P2
Distributor plate
Refrigerated Screw O2
T1 P1
CO2 Air
Preheater
Figure 2. Bubbling Oxy-fuel Fluidized Bed Combustor at ICB-CSIC.
The coals used were a Spanish lignite from Teruel basin with high sulphur content and a spanish anthracite from Bierzo with lower content of sulphur. The calcium sorbent used was the Granicarb limestone. Sand was used as inert solid in the fluidised bed. Tables 1 and 2 show both the composition of the coals and the particle size of the solid materials used.
Table 1. Composition of coals. Proximate analysis (wt%)
Ultimate analysis (wt%)
Lignite
Anthracite
Lignite
Moisture
12.55
1.00
C
45.43
60.66
Ash
25.17
31.55
H
3.90
2.05
Volatiles
28.65
7.55
N
0.65
0.87
Fixed C
33.63
59.90
S
5.17
1.33
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4
Oviedo ICCS&T 2011. Extended Abstract
Table 2. Particle size of the solids used in the experimental tests. Material
dp (mm)
Sand
0.2 - 0.6
Coal
0.2 - 1.2
Limestone
0.3 - 0.5
Experiments were carried out at different temperatures between 800 and 950 ºC under oxy-fuel combustion conditions, keeping constant the O2 concentrations (27% O2 -73% CO2 and 35% O2 - 65% CO2), and under enriched air combustion conditions (27% O2 73% N2). Limestone was fed to the reactor, for SO2 retention, using Ca/S molar ratios of 2 and 3. In all of the experiments, the operation conditions were held in a steady state for 2 hours while CO, CO2, SO2 and O2 were measured. Experimental SO2 retention (SR) was calculated, taking into account the feed rate of coal (F0,coal), its ultimate analysis (XSO2,coal), the gas flow rate (Q), and the SO2 concentration (CSO2) measured in the flue gas at the exit of the reactor, by the following equation: SR =
(F0 ,coal X SO 2 ,coal / M SO 2 ) − Q ⋅ CSO 2 F0 ,coal X SO 2 ,coal / M SO 2
being MSO2 the molecular weight of SO2.
3. Results The experiments with the two coals were performed in the BFB combustor at different temperatures between 800 and 950 ºC, with 27 and 35% O2 in the feed gas, and using Ca/S molar ratios of 2 and 3. Coal and limestone were added together to the combustor and the sand was fed continuously to control the residence time of sorbent in the combustor. Influence of temperature. When a Ca-based sorbent is added to a FB combustor, one of the most important parameters affecting the SO2 retention process is the temperature. Figure 3 shows the concentration of the SO2 measured at the exit of the combustor during typical tests
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Oviedo ICCS&T 2011. Extended Abstract
working with the lignite in oxy-fuel combustion conditions at the temperatures of 850, 875 and 900 ºC and with a Ca/S molar ratio of 3. An increase in the SO2 emissions was observed when the temperature decreased from 900 to 850 ºC.
SO2 Emissions (vppm)
7000
850 ºC
6000 5000
875 ºC 4000
900 ºC
3000 2000 1000 7
8
9
10
11
12
13
14
Time (h)
Figure 3. SO2 concentration in the outlet gas stream during oxy-fuel combustion of lignite. O2/CO2 : 35/65, Ca/S = 3. 100 90
No-calcining conditions
Calcining conditions
SO2 Retention (%)
80 70 60 50 40 30 20
Lignite Anthracite
10 0 825
850
875
900
925
950
975
Temperature (ºC)
Figure 4. Effect of temperature on the sulphur retention with Granicarb limestone. Ca/S=3; O2/CO2 : 35/65. Calcining and non-calcining conditions calculated with the gas inlet composition.
Figure 4 shows the effect of the temperature on the SO2 retention working with the two coals in oxy-fuel combustion conditions and using a Ca/S molar ratio of 3. For both coals, the sulphur retention initially increased with increasing temperature up to a maximum of 900-925 ºC and then, further increases in temperature caused a decrease in sulphur retention. These results are in good agreement with the results obtained in a TGA and in a batch FB reactor in previous works where the sulphur retention capacity of limestones was analysed [6-7]. In these works, it was found that the effect of the
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temperature was different for the direct and indirect sulphation reactions (see Figure 5). In direct sulphation or non-calcining conditions, the sulphation reaction rate rose with increasing the temperature. On the contrary, in conditions of indirect sulphation or calcining conditions, the sulphation reaction rate increased with increasing the temperature up to 900 ºC and then decreased due to the sinterization of the sorbent. As a consequence, the maximum sorbent conversion was reached at temperatures about 900 ºC.
Sulphation conversion
0.6 925
0.5
900 ºC 950 975
0.4
850 0.3
800
0.2 0.1 0.0 0
2
4
6
8
10
Time (h)
Figure 5. Effect of the temperature on the Granicarb sulphation conversion in TGA. dp= 0.1-0.2 mm; 60 vol.% CO2; 3000 vppm SO2. Indirect sulphation (____) and direct sulphation ( - - -).
It can be also observed in Figure 4 that the behaviour of the limestone with both coals was qualitatively similar but higher SO2 retentions, and so, higher limestone sulphation conversions, were achieved working with the lignite. Previous studies in a TGA [6] and and in a batch FB reactor [7] demonstrated that the sulphation conversion of the sorbent increased as the SO2 concentration increased. As the lignite has a higher sulphur content than the anthracite, the SO2 concentration generated in the combustor was higher with the lignite and therefore the limestone was larger sulphated.
Influence of the Ca/S molar ratio As it is well know, the utilisation of Ca-based sorbents for SO2 retention in FB boilers is not complete due to the relatively large particle sizes used and the pore blockage there produced by CaSO4 formation. In the typical operating conditions used in FB combustors, the sulphation reaction usually takes place at the external surface and
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around the pores of the sorbent particles. Since the molar volume of CaSO4 is higher than the molar volume of CaCO3 or CaO, the pores are blocked and the centre of the particles remains essentially unsulphated. Therefore, an important parameter in the SO2 retention process is the Ca/S molar ratio used in the plant. This Ca/S molar ratio has to be necessarily higher than 1 in order to achieve a significant retention. Figure 6 compares the sulphur retention achieved in oxy-fuel combustion working with the lignite with Ca/S molar ratios 2 and 3. Each data corresponds to 2 hours of steady-state operation in the oxy-fuel plant. Qualitatively the effect of the temperature was very similar for the two Ca/S molar ratios used. However, as expected, an increase in the Ca/S molar ratio produced higher sulphur retentions in all range of temperature studied.
100 90
SO2 Retention (%)
80 70 60 50 40 30 20
Ca/S=3 Ca/S=2
10 0 775
800
825
850
875
900
925
950
975
Temperature (ºC)
Figure 6. Effect of the Ca/S molar ratio on the SO2 retention working with the lignite in oxy-fuel combustion conditions at different temperatures. O2/CO2 : 35/65.
Oxy fuel combustion vs. air combustion In order to compare the oxy-fuel combustion and the conventional combustion with air technologies in fluidised beds, Figure 7 shows the results of the SO2 retention obtained with the Granicarb limestone in conditions of enriched air (O2/N2 : 27/73) and in oxyfuel combustion (O2/CO2 : 27/73) working with the lignite as fuel.
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Oviedo ICCS&T 2011. Extended Abstract
100 90
SO2 Retention (%)
80 70
AIR
60 50 40 30
OXY-FUEL
20 No-calcining conditions
10 0 775
800
825
850
Calcining conditions
875
900
925
950
975
Temperature (ºC)
Figure 7. Sulphur retention with Granicarb limestone in the BFB combustor. Coal: lignite; Ca/S=2. Calcining and non-calcining conditions calculated with the gas inlet composition.
As it can be observed in the Figure, the maximum SO2 retention under enriched air combustion was obtained at 850 °C, while under oxy-fuel combustion the maximum retention was obtained at 900-925 °C. In addition, considering the optimal temperature for each case, the SO2 retention obtained in oxy-fuel combustion are lower than that obtained in enriched air combustion conditions.
4. Conclusions - In oxy-fuel combustion with limestone addition in FB, the retention of SO2 were higher working at calcining (indirect sulphation) than at non-calcining (direct sulphation) operating conditions. - The optimum FB combustor temperature from of point of view of sulphur retention shifted from 850 ºC in combustion with air to 900-925 °C in oxy-fuel combustion conditions. - For Granicarb limestone, working at the optimum temperature of combustion for each technology, the SO2 retentions obtained in oxy-fuel combustion conditions were lower than those obtained under air combustion conditions.
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Acknowledgements This work has been supported by Spanish Ministry of Science and Innovation (MICINN, Project: CTQ2008-05399/PPQ) by FEDER and by Fundación CIUDEN. A. Rufas thanks CSIC for the JAE fellowship and M. de las Obras thanks MICINN for the F.P.I. fellowship.
References [1] Wall T, Liu Y, Spero C, Elliott L. An overview on oxyfuel coal combustion – State of the art research and technology development. Chem Eng Res Des 2009;87:10031016. [2] Kanniche M, Gros-Bonnivard R, Jaud P, Valle-Marcos J, Amann JM, Bouallou C. Pre-combustion, post-combustion and oxy-combustion in thermal power plant for CO2 capture. Appl Therm Eng 2010;30:53-62. [3] Toftegaard MB, Brix J, Jensen PA, Glarborg P, Jensen AD. Oxy-fuel combustion of solid fuels. Prog Energ Combust 2010;36:581-625. [4] Myöhänen K, Hyppänen T, Pikkarainen T, Eriksson T, Hotta A. Near Zero CO2 Emissions in Coal Firing with Oxy-Fuel Circulating Fluidized Bed Boiler. Chem Eng Technol 2009;32:355-363. [5] Czakiert T, Sztekler K, Karski S, Markiewicz D, Nowak W. Oxy-fuel circulating fluidized bed combustion in a small pilot-scale test rig. Fuel Process Technol 2010;91:1617-1623. [6] García-Labiano F, Rufas A, de Diego LF, de las Obras-Loscertales M, Gayán P, Abad A, Adánez J. Calcium-based sorbents behaviour during sulphation at oxy-fuel fluidised bed combustion conditions. Fuel (in press,doi:10.1016/j.fuel.2011.05.001). [7] de Diego LF, de las Obras-Loscertales M, García-Labiano F, Rufas A, Abad A, Gayán P, Adánez J. Characterization of a limestone in a batch fluidized bed reactor for sulfur retention under oxy-fuel operating conditions. Int J Greenh Gas Con (in press).
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Oviedo ICCS&T 2011. Extended Abstract
Carbon based catalytic briquettes for NOx removal in flue gases M.J. Lázaro, M.E. Gálvez, S. Ascaso, I. Suelves, R. Moliner Instituto de Carboquímica, CSIC, Miguel Luesma Castán, 4, 50018 Zaragoza (Spain) Corresponding author:
[email protected] Abstract Catalytic briquettes were prepared using a low-rank coal as carbon precursor and vanadium compounds, i.e. V2O5 and petroleum coke ash (PCA), as the source of the active phase. The catalytic briquettes presented herein offer a feasible low-cost possibility for flue gas cleaning in medium and small industrial facilities. For their preparation, coal was first pyrolysed, then blended with tar pitch and cold pressed to produce the cylindrical briquettes. Pressed briquettes were submitted then to pyrolysis and activation in the presence of steam or CO2, at different temperatures and residence times. Activated briquettes were functionalized by means of HNO3 and H2SO4-wet oxidation. Physical and chemical properties of the produced briquettes were evaluated using N2 adsorption, temperature programmed desorption (TPD) and NH3 chemisorption. Important mechanical properties such as Impact Resistance Index (IRI) and Water Resistance Index (WRI) were also determined for this series of briquettes. Briquettes showed considerable activity in the SCR of NO in a wide temperature range (75-350ºC) and high selectivity towards N2. The several steps involved in the preparation of the catalytic briquettes influence both their structural-chemical and mechanical properties, as well as their catalytic activity in the SCR of NO. 1. Introduction Increasingly stricter environmental regulations concerning the emission of nitrogen oxides (NOx), have forced the development of each time more efficient technologies to reduce the discharge of this pollutants from small and medium industrial facilities. In response, researchers and manufacturers are considering Selective Catalytic Reduction (SCR) as one of the most promising NOx reduction options. While SCR performance has been well established through power plants and evaluation under laboratory conditions, there exists little data characterizing SCR performance under small and medium industrial facilities operating conditions over time. The promulgation of more stringent European regulation of NOx coupled with considerable interest by government, industry,
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and other stakeholders to reduce NOx from the existing small and medium facilities, has prompted renewed interest in SCR [1,2]. The use of carbon materials presents unique advantages over other catalyst supports, such as the simplicity of their preparation process, their potentially low-cost, and the easy availability of carbon precursors [3]. Moreover, the carbon support can be shaped as low-pressure drop aggregates, like carbon briquettes and pellets, with good mechanical resistance to withstand abrasion phenomena. Carbon-based catalysts doped with various transition metal oxides. i.e. Cu [4,5], Fe [5], Mn [6-8] and V [9], have shown large potential for their application as SCR catalysts at low temperatures (100250ºC). In previous works we reported the preparation of powder carbon-based catalysts, using a low-rank coal that was subsequently pyrolysed, activated and loaded with different vanadium compounds [10,11]. These catalysts showed high activity and selectivity in the SCR of NO in the presence of NH3, at temperatures between 150 and 200°C [12,13]. Both the characteristics of the carbon support and the preparation method were found to be decisive for optimizing the catalytic activity of the materials prepared [12,14,15]. The present work considers the preparation of catalytic briquettes for their application in small or medium scale deNOx facilities. The several steps involved in their preparation and affecting the final properties of the briquettes, such as pyrolysis and activation, functionalization and calcination after active phase loading, are being considered. Carbon-based catalytic briquettes were prepared using either vanadium pentoxide or the ashes of a petroleum coke (PCA) as active phase precursors. The use of this petroleum residue for producing catalytic briquettes is supposed to be a totally innovative way of upgrading the value of this waste material. In addition, both the use of a low-rank coal and PCA could make the production cost of these catalytic briquettes considerable lower. This fact may involve a considerable reduction of the economic effort that medium and small industrial facilities will be forced to face in order to meet to the upcoming legislation in the near future. In addition, some other pollutants present in the flue gas stream, such as volatile metals or organic compounds, could be at the same time retained within the activated carbon matrix of these catalysts, due to its adsorptive properties. 2. Experimental section SAMCA coal from SAMCA mines in Teruel, Spain [16], was used as carbon support precursor. This coal was pyrolysed at 800°C in nitrogen in a fixed bed. The obtained Submit before January 15th to
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char was blended with ground commercial tar pitch, SP-110, used as binder agent. Coal and binder were blended and cold pressed at 125 MPa in a plug and mould press to produce cylindrical briquettes of approximately 10.5 mm diameter, 13.5 mm height and 1.2 g weight. Produced briquettes were subsequently cured in air for 2 hours in an electric oven, rising the temperature up to 200ºC at a heating rate of 2ºC/min. Pyrolysis was performed at 800°C and pressure of 0.1MPa under N2, in a bench-scale reactor described elsewhere [16]. Finally, the briquettes were activated either using 20% of water vapor in N2 at temperatures between 600 and 750°C, or in pure CO2 between 700 and 800°C. Functionalization of the carbon briquettes was performed by means of wet oxidation using sulphuric and nitric acid. Briquettes were immersed in a 2 N HNO3 or H2SO4 aqueous solutions and stirred for 3 hours, then rinsed with distilled water and finally dried at 108ºC for 24 hours. Vanadium pentoxide (V2O5, Aldrich, 99.99% pure) and a refinery waste, i.e. the ashes of a petroleum coke (PCA), were used as the active phase precursors. PCA were obtained from a petroleum coke from the Delayed Coke Unit in the REPSOL in Puertollano (Spain), by combustion under air at 650°C. The PCA contain 23% (w/w) of V, 3.5% (w/w) of Fe and 3% (w/w) of Ni, determined by atomic absorption spectroscopy. A more complex description of PCA can be found in [10]. The impregnation was carried out by equilibrium adsorption of vanadium. Briquettes were immersed into suspensions containing 3% (w/w) V, either of V2O5 or the PCAs, stirred for 3h and carefully washed up afterwards in distilled water. Finally, the catalysts were dried overnight in an oven at 108°C and subjected to a final thermal treatment in Ar for 4-6 hours and at temperatures ranging from 200 to 600 ºC. Carbon briquettes were physically and chemically characterized by means of N2 adsorption at -196ºC (Micromeritics ASAP-2000), temperature programmed desorption (TPD), scanning electron microscopy (SEM-EDX, Hitachi S-3400 coupled to Röntec XFlash analyzer) and NH3 chemisorption (Micromeritics Pulse Chemisorb 2700). Mechanical strength was tested by means of Impact Resistance Index (IRI) and Water Resistance Index (WRI). Catalytic briquettes were tested for NO reduction in a laboratory scale installation consisting of a tubular quartz reactor of 7 mm internal diameter, heated up with the help of an electric oven and connected to a mass spectrometer (Quadrapole Balzers 422) as online gas analysis system. Experiments were performed feeding 22,2 ml/min of a reactant mixture containing 1000 ppm of NO, 1500 ppm of NH3 and 3,5% O2 in Ar, at temperatures between 75 and 350°C and 1,4 s of residence time.
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3. Results and discussion Activation provided the adequate textural properties and modified the support’s surface chemistry leading to a proper dispersion of the active phase. Activation in the presence of steam led to the production of carbon briquettes with a more developed porous structure in comparison to CO2-activated ones. Maximal development of surface area, micropore and mesopore volumes was gained at 750ºC and 2 hours residence time in both cases. Surface chemistry was also modified upon activation. In general, activation in the presence of CO2 led to the formation of a higher amount of surface groups, particularly of thermally more stable functionalities, i.e. carbonyls and quinones, as determined by TPD analyses. Mechanical properties of the briquettes such as, Impact Resistance Index (IRI) and Water Resistance Index (WRI), were notably influenced as a consequence of activation. IRI decreased with increasing severity of the activation process, Figure 1 shows the surface area and IRI determined for both steam and CO2activated briquettes, as a function of burn-off. IRI decreases almost linearly with burnoff whereas for surface area, an optimal burn-off around 10% can be observed, resulting in an adequate development of porosity, SBET ≈ 250 m2/g, and IRI around 400. On the other hand, the presence of new surface functionalities introduced upon activation slightly improved briquette’s resistance. WRI decreased also with increasing activation temperature and residence time, due to the loss of hydrophobic structures which are thought to avoid water adsorption on surface and briquette disintegration. 400
2
SBET (m /g)
800
IRI
600
200
IRI (-)
400
2
SBET (m /g)
300
200
100
0
4
8
12
16
0 20
Burn-off (%)
Figure 1. Surface area (SBET) and Impact Resistance Index (IRI), as a function of burn-off Wet oxidation of the carbon briquettes, either with HNO3 or H2SO4, led to a partial
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collapse of the porous structure, with H2SO4-treatment causing even a more dramatic decrease of the textural parameters vis-à-vis HNO3-oxidation. Surface chemistry was substantially modified after acid treatment. New surface functionalities were introduced, especially carboxylic and lactones in the case of HNO3-treated briquettes, and carboxylic and phenolic, for the H2SO4-oxidized ones. Impact Resistance Index (IRI) was found to decrease considerably for the oxidized briquettes in comparison to the nonoxidized ones, most probably due to the enlargement of pore sizes as a consequence of the functionalization treatment. Lower values of Water Resistance Index (WRI) were found also for the acid-treated briquettes, suggesting the presence of carboxylates that might have enhanced briquette wetting, or just due to the generalized loss of textural properties, which resulted in an easier swelling of the compacted carbon particles. Briquettes either loaded with V2O5 or PCA showed similar activity, demonstrating the feasibility of using this petroleum residue as a source of the active phase. In fact, most of the catalytic briquettes prepared showed significant activity in the SCR of NO (40-90% conversion) at temperatures from 75 to 350ºC. NO reduction was found to be completely selective towards N2. As shown in Figure 2 a, activity increases with surface area. This is due to the fact that a considerable initial surface area of the support seems to be necessary, in order to avoid pore blockage and allow an adequate distribution of the active phase. Surface chemistry does play also a definitive role in activity, contributing to metal anchoring on surface, concretely on phenolic (-OH) groups, as can be observed in Figure 2 b. Thus, activity increased when using the HNO3 and H2SO4-treated briquettes as support. Moreover, ammonia adsorption was favored by the presence of the newly created oxygen functionalities. As shown in Figure 3, thermal treatments of the catalytic briquettes, in Ar at temperatures from 200 to 600ºC, substantially enhanced their catalytic activity. Vcompounds are oxidized by the radicals generated as a consequence of oxygen surface group evolution upon heating. Increasing calcination temperature results in the formation of acidic sites of different strength, which might explain the differences in activity observed for the catalytic briquettes treated at different temperatures and residence times.
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Oviedo ICCS&T 2011. Extended Abstract
1.4
1.4 a)
PCA-loaded briquettes
1.2
V2O5-loaded briquettes PCA-loaded briquettes
1.2 1.0
3
k (cm /s·g)
1.0
3
k (cm /s·g)
b)
V2O5-loaded briquettes
0.8 0.6
0.8 0.6
0.4 100
150
200
250
300
0.4 0.04
350
2
0.08
0.12
0.16
0.20 3
SBET (m /g)
0.24
2
Basic surface functionalities (cm /m )
Figure 2. Apparent kinetic constant as a function of a) surface area (SBET) and b) surface area normalized basic surface group concentration, for both steam and CO2-activated briquettes loaded either with V2O5 or PCA 100
100
b)
a) 80
NO conversion (%)
NO conversion (%)
80 60 40 20 0
60 40 20 0
not calcined 200ºC,4 h 200ºC,6 h 400ºC,4 h 500ºC,4 h 600ºC,4 h
not calcined 200ºC,4 h 200ºC,6 h 400ºC,4 h 500ºC,4 h 600ºC,4 h
Figure 3. NO conversion at 150ºC after 1 hour time-on-stream, for a) PCA-loaded steam activated (700ºC, 2 h) briquettes and b) PCA-loaded steam activated (700ºC, 2 h), HNO3-treated briquettes, after calcination at different temperatures and residence times 4. Conclusions The catalytic briquettes presented in this work represent a low-cost option for flue gas treatment in medium and small industrial facilities. They have shown significant activity in the SCR of NO (40-90% conversion) in a wide range of temperatures (75-350ºC). NO reduction was found to be completely selective towards N2. Both catalytic activity and mechanical properties (IRI and WRI) of the briquettes were strongly influenced by the several steps in their preparation procedure. Both an adequate surface area development and the presence of oxygen surface groups were found to be fundamental for achieving
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Oviedo ICCS&T 2011. Extended Abstract
an optimal active phase distribution, and minimizing pore blockage towards an adequate diffusion of both reactants and products. Functionalization by means of wet oxidation treatments led to the introduction of phenolic structures which are thought to contribute to active phase fixation, as well as more acidic surface functionalities which enhance NH3 chemisorption ability of the carbon surface, both facts resulting in increased catalytic activity. Thermal treatments upon the introduction of the active phase also resulted in a higher deNOx activity. Acknowledgement. Authors acknowledge AECI (A/18200/08, A/9858/07), Gobierno de Aragón-La Caixa (GA-LC-030/2008), M.E. Gálvez is indebted to the Spanish Ministry of Science and Innovation for her Juan de la Cierva post-doctoral fellowship. S. Ascaso acknowledges CSIC for her JAE pre-doctoral grant. References [1] Hjalmarsson AK. Report 24: NOx control technologies for coal combustion. London IEA Coal Research Publication, 1990, p. 40. [2] Wood SC. Chem Eng Prog 1994;90:32-38. [3] Rodriguez-Reinoso F. Carbon 1998;36:159-175. [4] Teng S, Tu YT, Lai YC, Li CC. Carbon 2001;39:575-582. [5] Zhu Z, Liu Z, Liu S, Niu H, Hu T, Liu T, Xie Y, Appl Catal B: Environ 2000;26:25-35. [6] Grzybek T, Pasel J, Papp H. Phys Chem Chem Phys 1999;1:341-348. [7] Marbán G, Fuertes AB. Appl Catal B: Environ 2001;34:43-53. [8] Marbán G, Fuertes AB. Appl Catal B: Environ 2001;34:55-71. [9] Zhu Z, Liu Z, Liu S, Niu H. Fuel 2000;79:651-658. [10] Vassilev SV, Braekman-Danheux C, Moliner R, Suelves I, Lázaro MJ, Thieman T. Fuel 2002;81:1281-1296. [11] Lázaro MJ, Suelves I, Moliner R, Vassilev SV, Braekman-Danheux C. Fuel 2003;82:771782. [12] Lázaro MJ, Gálvez ME, Suelves I, Moliner R, Vassilev SV, Braekman-Danheux C. Fuel 2004;83:875-884. [13] Gálvez ME, Lázaro MJ, Moliner R. Cat Today 2005;102-103:142-147. [14] Lázaro MJ, Gálvez ME, Artal S, Palacios JM, Moliner R. J Anal Appl Pyrolysis 2007;78:301-315. [15] Lázaro MJ, Gálvez ME, Ruiz C, Juan R, Moliner R. Appl Catal B: Environ 2006;68:130138. [16] Moliner R, Ibarra J, Lázaro MJ. Fuel 1994;73:1214-1220.
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Oviedo ICCS&T 2011. Extended Abstract
Identification of Operational Regions in the Chemical-Looping with Oxygen Uncoupling (CLOU) Process with a Cu-based Oxygen-Carrier I. Adánez-Rubio, A. Abad, P. Gayán, L. F. de Diego, F. García-Labiano, J. Adánez Instituto de Carboquímica (ICB-CSIC), Dept. of Energy & Environment, Miguel Luesma Castán, 4, Zaragoza, 50018, Spain Tel.: +34 976 733977; fax: +34 976 733318 Email address:
[email protected] Abstract Chemical-Looping with Oxygen Uncoupling (CLOU) is an alternative chemical-looping process for the combustion of solid fuels with inherent CO2 capture. The CLOU process demands a material as oxygen-carrier with the ability to decompose through O2 release at suitable temperatures for solid fuel combustion, e.g. copper oxide. In this work, the combustion of coal by using a promising Cu-based oxygen-carrier prepared by the spray drying method was tested. The oxygen-carrier (Cu60MgAl) was composed of 60 wt% CuO and MgAl2O4 was used as supporting material. The capability for oxygen generation in a CLOU process was evaluated in a batch fluidized-bed reactor at temperatures ranging from 900 to 980 ºC, as well as the oxygen generation rate was determined. Three different regions were identified depending on the oxygen-carrier to coal mass ratio. For oxygen-carrier to coal ratios higher than 50 (Region I), coal was fully converted to CO2 and H2O. In addition, an excess of oxygen was present in the flue gases, which was close to the equilibrium concentration. When this ratio was in the range 50-25 (Region II), the concentration of oxygen was decreasing whereas some CO was observed as the only unconverted gas. Further decrease in the oxygen-carrier to coal ratio below 25 (Region III) caused the depletion of oxygen in the exhaust gases but CO remained as the only unconverted gas. The rate of oxygen generation calculated in every case was related to the solid inventory in the fuel-reactor to get complete combustion of the fuel. The estimated solids inventory in the fuel-reactor was 39, 32 and 29 kg/MWth at Tmax of 930, 955 and 980 ºC, respectively. The results obtained in this work showed that the use of the Cu60MgAl oxygen-carrier is suitable for the coal combustion by CLOU process. 1. Introduction Chemical-Looping with Oxygen Uncoupling (CLOU) is one of the most promising technologies to carry out CO2 capture at low cost when solid fossil fuels are used in
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energy generation. In the CLOU process the oxygen required for combustion is supplied by a solid oxygen-carrier (OC) which is able to evolve gaseous oxygen. The OC is continuously circulated between two interconnected fluidized-bed reactors, namely the fuel-reactor and the air-reactor. Figure 1 shows a CLOU system schematic design. In the CLOU process several reactions take place in the fuel-reactor, as it is showed for coal: 2 MexOy ↔ 2 MexOy-1 + O2
(1)
Coal → Volatiles + Char + H2O
(2)
Char + O2 → CO2
(3)
Volatiles + O2 → CO2 + H2O
(4)
First the oxygen-carrier releases oxygen according to reaction (1) and the solid fuel begins devolatilization producing a porous solid (char) and a gas product (volatiles), reaction (2). Then, the char and volatiles are burnt as in usual combustion according to reactions (3) and (4). After that the oxygen-carrier is re-oxidized in the air-reactor: O2 + 2 MexOy-1 ↔ 2 MexOy
(5)
The overall heat release over the fuel- and air-reactors is the same as for conventional combustion. The advantage is that the CO2 and H2O are inherently separated from the nitrogen in the combustion air, and thus no energy is needed to obtain pure CO2. N2 (+O2)
CO2 + H2O
CO2
Condenser
MexOy
Fuel Reactor
Air Reactor
CO2
H2O(l)
Coal
MexOy-1
CO2 Air
Ash
Figure 1: CLOU system schematic design. Three metal oxide systems have been identified with CLOU properties: CuO/Cu2O, Mn2O3/Mn3O4, and Co3O4/CoO [1]. Focused in Cu-based materials, cyclic testing with solid fuels verified a high reactivity during oxidation and reduction, where very rapid release of oxygen was observed [2]. In addition, Cu-based materials have other advantages as its high oxygen transport capacity (RO = 10 wt%) and the global process in the fuel-reactor is exothermic.
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4 CuO + C → 2 Cu2O + CO2
D H r950ºC = - 134 kJ / mol O2
(6)
Previously to this work, a screening of different Cu-based materials was carried out [2, 3]. From this work, it was shown that particles prepared by mechanical mixing followed by pelletizing by pressure containing 60 wt% CuO and using MgAl2O4 as supporting material were adequate for its use as oxygen-carrier for the CLOU process. The aim of this work was to investigate the performance of a CuO/MgAl2O4 material as oxygen-carrier for the CLOU process. The rate of oxygen release was determined when batches of “El Cerrejon” coal particles were added to a fluidized-bed reactor containing the oxygen-carrier material. Different oxygen-carrier to fuel ratios, as well as several temperatures between 900 and 950 ºC were tested. The needed solids inventory in the fuel-reactor for complete fuel combustion was inferred from the results obtained. 2. Experimental section 2.1 Materials
The material used was a Cu-based oxygen-carrier prepared by spray drying manufactured by VITO. The CuO content was 60 wt% and MgAl2O4 was the supporting material. The oxygen transport capacity of the oxygen-carrier was ROC=6 wt% and the particle size was 100-200 μm. From now on the oxygen-carrier was named as Cu60MgAl. The fuel used was a bituminous Colombian coal “El Cerrejón”. Ultimate and proximate analysis are shown in Table 1. The coal particle size used for this study was +200-300 μm. The Low Heating Value was 21899 kJ/kg. Table 1. Properties of pre-treated “El Cerrejón” coal.
C
65.8 %
Moisture
2.3 %
H
3.3 %
Volatile matter
33.0 %
N
1.6 %
Fixed carbon
55.9 %
S
0.6 %
Ash
8.8 %
2.2 Experimental setup: batch fluidized-bed reactor
Reduction-oxidation multi-cycles were carried out in a fluidized-bed reactor to know the oxygen release behaviour of the oxygen-carrier in similar operating conditions to that existing in the CLOU process. A schematic layout of the laboratory set-up is presented in Figure 2. Solids are placed in the reactor (55 mm inner diameter and 700 mm height )
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above the distributor plate, assuring a bed height about 50 mm at static conditions. The total fluidizing flow was 200 LN/h, which corresponds to a gas velocity of 0.1 m/s at 900 ºC. The oxygen-carrier particles were exposed sequentially to reducing and oxidizing conditions. The reducing period consisted in loads of a certain amount of coal particles in N2, whereas oxidation was done by air.
N2
v1
v2
Solids feeding system
P
Filter v3 Gas analysis
Furnace H2O (l) Thermocouple
ΔP
Distributor plate N2
P Air
Figure 2. Schematic layout of the laboratory setup.
Three series of experiments were performed to increase the oxygen-carrier to coal ratio covered. The first tests were done with an amount of 240 g of oxygen-carrier material in the bed. Loads of coal between 0.2 and 2 g were added, corresponding to OC/coal = 1200-120. The second and third series were carried out diluting the oxygen-carrier in alumina particles. Thus, the mass fraction of the OC in the bed was 10 wt% and 2.5 wt%, respectively. Loads of coal between 0.4 and 1.2 g (OC/coal = 60-20) in the first case, and 0.03 and 0.5 g (OC/coal = 200-12) in the second case were used. The experimental work has been carried out at temperatures between 900 and 950 ºC. The temperature of the reactor was fixed before starting the reducing or oxidizing period, but during reaction the temperature could increase up to 50 ºC because the exothermic reaction when coal is burnt. Different gas analyzers measured continuously the gas composition (CO, CO2, CH4, H2, O2) at the reactor exit after water condensation. 2.3 Data Evaluation
During the reduction period, the rate of oxygen generation per amount of oxygen-carrier,
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Oviedo ICCS&T 2011. Extended Abstract
rO2 , was calculated from a mass balance to the oxygen in the reactor. rO2 (t ) =
(
M O2
)
⎡ FO + FCO + 0.5 FCO + FH O − 0.5 FO ,coal ⎤ 2 2 ⎦ mOC ⎣ 2
(7)
being Fi the gas flow of each component exiting the fuel-reactor. Possible gas i includes O2, CO2, CO and H2O. The water concentration was not measured, but the H2O flow was calculated as:
(
FH 2O = 0.5 f H / C FCO2 + FCO
)
(8)
fH/C being the hydrogen to carbon molar ratio in the coal (fH/C = 0.61). Equally, the flow of oxygen coming from coal, FO,coal, was calculated as:
(
FO ,coal = fO / C FCO2 + FCO
)
(9)
fO/C being the oxygen to carbon molar ratio in the coal (fO/C = 0.20). The oxidation conversion was calculated from the integration of rO2 (t ) with time: X o (t ) = 1 −
1 N O2
t
∫r 0
O2
(t )dt
(10)
being N O2 the molar amount of oxygen in the oxygen-carrier active for CLOU process, i.e. from reduction of CuO to Cu2O expressed as mol of molecular O2. 3. Results and Discussion
As example, Figure 3 shows the concentration of O2, CO2 and CO measured at the outlet of the reactor and the bed temperature during a typical reduction and oxidation cycle at initial temperature T0 = 925 ºC with an OC inventory in the reactor of 240 g. The time t = 0 corresponds to the initial time of the reduction period. At the beginning a rapid oxygen release occurred close to the oxygen concentration equilibrium for the measured bed temperature. After a short period, a batch of 2 g of coal particles were fed to the reactor, and only CO2 and O2 were observed in the outgoing gases, indicating full combustion of the volatiles and char. The CO2 concentration in this case was as high as 76 vol% which was maintained constant during ~8 s, and eventually decreased to zero when the complete coal combustion was reached. During coal combustion the bed temperature increased being the maximum temperature (Tmax) reached about 30 ºC higher than T0 due to the exothermic reaction of CuO with coal, see equation (6). The oxygen concentration was correspondingly increased, remaining close to the equilibrium condition when temperature varied. This result suggests a fast combustion of coal. In
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Oviedo ICCS&T 2011. Extended Abstract
addition, the oxygen release rate was high enough to supply an excess of gaseous oxygen in the combustion gases. In Figure 3, the variation of solids conversion, X0, with reacting time is also shown. It can be seen that the oxygen-carrier was slowly converted during the initial period before coal addition. A sharp decrease in the OC conversion occurred when coal was fed to the reactor because the fast oxygen release. The variation in the solids conversion during the reducing period was 41%. Then, oxidation period starts at t = 360 s and a quick increase in the temperature occurred due to the highly exothermic reaction. Equally to reduction period, oxygen concentration was close to the equilibrium condition until the OC was fully oxidized. reduction
1.0
100
0.8
80
oxidation
1000
0.4
0.2
0.0
980
T
60
960
40
20
940
Coal addition
CO2
O2
0 0
300
600
Temperature (ºC)
0.6
Concentration (vol%)
Solids conversion (-)
Xo
920
900 900
time (s)
Figure 3. Variation of solids conversion, bed temperature and concentration of O2 and
CO2 during redox cycle with Cu60MgAl. T0 = 925 ºC; mOC: 240 g; mcoal: 2 g. Similar behaviour was observed in redox cycles when different amount of coal was added to the bed in the range 0.2-2.0 g. From the CO2 and O2 evolution in the gas phase, it was possible to calculate the oxygen generation rate, rO2 , from equation (7). In every experiment the highest value of rO2 was reached when CO2 is maximum. Figure 4 shows the highest value of rO2 as a function of the OC/coal ratio. It can be observed a similar trend of the data obtained with different oxygen-carrier dilutions. When the OC/coal ratio decreased until a value of 25 the oxygen generation rate increased. However, at lower OC/coal values it seemed that the oxygen generation rate reached a maximum. Thus, for OC/coal < 25 the coal conversion was limited by the oxygen generation rate from the oxygen-carrier. The calculated average value for the oxygen generation rate
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was 2.6·10-3 kg O2/s per kg of OC when the temperature increased up to Tmax = 955 ºC. Analogous experiments were carried out at initial temperatures, T0, of 900 ºC and 950 ºC. In these cases, temperature increased until Tmax of 930 ºC and 980 ºC, respectively, when coal was added to the bed the reactor. Similar trend was found for the oxygen generation rate with the OC/coal ratio. Nevertheless, the maximum oxygen generation rate increased with the reacting temperature. The oxygen generation rate was 2.1·10-3 and 2.8·10-3 kg O2/s per kg of oxygen-carrier at Tmax of 930 and 980 ºC, respectively.
rO x103 (kg O2/s per kg OC) 2
10
1
0.1
0.01 1
10
100
1000
10000
OC/coal (kg/kg)
Figure 4. Maximum oxygen generation rate, rO2 , for the OC as a function of the
OC/coal ratio. T0 = 925 ºC. OC in the reactor: (□) 100 wt%; (▲) 10 wt%; (○) 2.5 wt%. The maximum rate of oxygen generation calculated by the procedure above described can be related to the solids inventory needed to fully convert the fuel. Assuming that there was an excess of oxygen in the circulating solids in a CLOU system the coal combustion was not limited by the availability of oxygen transported from the airreactor. Thus, the solids inventory, mFR, depends on the flow of coal which is able to process the oxygen-carrier at its maximum rate of oxygen generation, rO2 ,max , and taking as reference 1 MWth for the fuel feeding rate, it can be calculated as:
mFR = 103
mO rO2 ,max LHV
(11)
being mO the mass of oxygen required per kg of coal to fully convert it to CO2 and H2O, as for the case of the conventional combustion with air. LHV is the lower heating value of the solid fuel. From coal analysis showed in Table 1, a value for mO = 2.1 kg O2 per
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kg of coal was calculated. The solids inventory in the fuel-reactor was dependent on the reactor temperature because the increase of the reactivity with the temperature. Thus, 39 kg/MWth would be necessary in the fuel-reactor at a Tmax = 930 ºC, being decreased to 29 kg/MWth if Tmax was 980 ºC. Here, the temperature is the maximum temperature reached during the reduction period. Figure 5(a) shows the CO2 yield, yCO , defined as carbon fraction in the form of CO2 in 2
the outgoing gases, whereas the ratio between the oxygen concentration at the reactor exit and that present at equilibrium conditions, O2/O2,eq, was plotted in Figure 5(b). It can be seen as both the CO2 yield and the oxygen concentration decreases when the OC/coal mass ratio was lower than 50. The observed decrease in the CO2 yield was due to the presence of CO in the gases, but CH4 or H2 were not observed in any case, indicating that volatiles had enough contact time to be burnt in the bed. Moreover, the oxygen concentration becomes zero when the maximum rate of oxygen generation was reached. This fact determines a change in the limiting process during conversion of coal towards the rate of oxygen production by the oxygen-carrier. Thus, different region can be differentiated depending of the OC/coal ratio.
1.0
100
(b)
(a) 0.8
O2/O2,eq (-)
CO2 yield (%)
95
90
85
0.6
0.4
0.2
0.0
80 1
10
100
1000
10000
OC/coal (kg/kg)
1
10
100
1000
10000
OC/coal (kg/kg)
Figure 5. (a) CO2 yield and (b) ratio between the oxygen concentration at the reactor
exit and at equilibrium conditions, O2/O2,eq, as a function of the OC/coal mass ratio. T0 = 925 ºC. OC in the reactor: (□) 100 wt%; (▲) 10 wt%; (○) 2.5 wt%. Figure 6 shows the limiting conditions for these regions and the calculated solids inventory with different OC/coal ratios used in this work. The Region I was defined as
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the region where CO was not present in the exhaust gases, corresponding to OC/coal ratios higher than 50. The minimum solid inventory in this region was 58 kg/MWth. In the Region II, O2 and CO simultaneously appeared in the outgoing gases. At this condition, the minimum solid inventory was about 43 kg/MWth at Tmax = 955 ºC. Finally, in the Region III no oxygen was present in the exhaust gases. The maximum rate for oxygen generation of the OC is reached, and lowering the solids inventory does not permitted to fully convert the coal in the fuel-reactor. This region was observed for OC/coal ratios lower than 25.
1000
mFR (kg/MW th)
Regime III Regime II
Regime I
100
10 10
100
1000
OC/coal (kg/kg)
Figure 6. Calculated solids inventory in the fuel-reactor for the OC as a function of the
OC/Coal ratio. T0 = 925 ºC. OC in the reactor: (□) 100 wt%; (▲) 10 wt%; (○) 2.5 wt%. From the results showed in this work, to avoid the presence of CO and thus the necessity of an oxygen polishing step, a small oxygen amount is desirable in the flue gases coming from the fuel-reactor. Thus, it can be suggested that a CLOU system should be operated in the Region I, where complete combustion of coal can be obtained. However, the excess of oxygen could be problematic for the transport and storage of the CO2, and it must be removed from the exhaust gas stream. To address the excess of oxygen one option would be to separate the oxygen in the purification and compression process of the CO2 before being transported. This situation is similar to that present in coal oxycombustion units. 4. Conclusions
A Cu-based oxygen-carrier prepared by spray drying was tested for the CLOU process
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in a batch fluidized-bed reactor. The oxygen-carrier contained 60 wt% CuO and MgAl2O4 was used as inert material. A bituminous Colombian coal “El Cerrejón” was used as fuel. The capability of particles to evolve gaseous oxygen in the fuel-reactor was evaluated as a function of the oxygen-carrier to coal mass ratio and reactor temperature. A decrease in the oxygen-carrier to coal mass ratio caused a continuous increase in the oxygen generation rate of the Cu60MgAl material until the maximum rate of oxygen generation was reached. Three operating regions were identified depending on the solids inventory. Unburnt compounds were not present in the outgoing gases in Region I when the calculated solids inventory was higher than 58 kg/MWth at Tmax = 955 ºC. CO2 and H2O were the only products of coal combustion and an excess of O2 was observed, which was found to be close to the equilibrium concentration. At these conditions, the oxygen concentration from the reactor increased with the temperature. The Region II was confined between 32 and 58 kg/MWth, at Tmax = 955 ºC, where both CO and O2 were present in the exhaust gases together CO2 as majority compound. The maximum rate of oxygen generation was found in the so-called Region III. Oxygen was not present in the flue gases, and a certain concentration of CO was present as unburnt compound. To operate in Region III, the estimated solids inventory in the fuel-reactor was 39, 32 and 29 kg/MWth at Tmax of 930, 955 and 980 ºC, respectively. The results obtained in this work showed that the use of the Cu60MgAl oxygen-carrier is suitable for coal combustion by CLOU process. Acknowledgement
This work was partially supported by the European Commission, under the RFCS program (ECLAIR Project, Contract RFCP-CT-2008-0008), ALSTOM Power Boilers (France) and by the Spanish Ministry of Science and Innovation (ENE2010-19550). I. Adánez-Rubio thanks CSIC for the JAE fellowship. References
[1] Mattisson, T.; Lyngfelt, A.; Leion, H. Chemical-looping with oxygen uncoupling for combustion of solid fuels. Int. J. Greenhouse Gas Control, 2009, 3, 11-19. [2] Adánez-Rubio, I.; Gayán, P.; García-Labiano, F.; de Diego, L.F.; Adánez, J.; Abad, A. Development of CuO-based oxygen-carrier materials suitable for Chemical-Looping with Oxygen Uncoupling (CLOU) process. Proc 10th Int Conf Greenhouse Gas Technology (GHGT-10). Amsterdam, The Netherlands; 2010. [3] Adánez-Rubio, I.; Gayán, P. Abad, A; García-Labiano, F.; de Diego, L.F.; Adánez, J.CO2 Capture in Coal Combustion by Chemical-Looping with Oxygen Uncoupling (CLOU) with a Cu-based Oxygen-Carrier. Proc 5th Int Conf on Clean Coal Technology (CCT-11). Zaragoza, Spain; 2011.
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Influence of hydrogenation on the mercury capture by activated carbons Jorge Rodríguez-Pérez, M. Antonia López-Antón, Roberto García, Mercedes DíazSomoano and M. Rosa Martínez-Tarazona Instituto Nacional del Carbón (CSIC), Francisco Pintado Fe, 26, 33011, Oviedo, Spain. Abstract In this study, activated carbon (AC) sorbents have been used for elemental mercury retention experiments at a laboratory scale. A previous hydrogenation treatment of the parent AC resulted in improved performances, in terms of mercury retention capacity (RC) and efficiency. The surface functional groups of the untreated and hydrogenated AC have been investigated by temperature programmed desorption (TPD) experiments and by X-ray photoelectron spectroscopy (XPS) analysis. The presence of an increased concentration of protons in the carbon surface seems to have a greater influence on the enhanced Hg retention capacity than the variation in the proportion and types of oxygen functional groups.
1. Introduction Power generation by coal combustion is the largest anthropogenic source of mercury emissions in the world. Then, removing mercury from power plant flue gas streams is a priority environmental issue. Mercury can be emitted in oxidized or elemental forms, and the capture of elemental mercury is especially problematic, due to its volatility, chemical inertness, and insolubility in water. The typical air-pollution control systems are ineffective and it has to be addressed with retention devices ad hoc. A possible approach is the use of carbonaceous sorbents with and without supported catalysts. Activated carbons have been considered as sorbents for Hg0 in many studies [1-7]. However, the mechanism of the adsorption process is not well understood yet. The influence of the textural properties and of the presence of several types of surface functional groups has been studied and both physisorption and chemisorption effects have been proposed. It seems clear that, in addition to a good surface area, the surface chemistry turns out to be very relevant when choosing the appropriate carbon material, to the extent that the presence of a metallic catalyst could not be strictly necessary.
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In this contribution, an activated carbon has been tested for the capture of Hg0, both in its fresh state and after hydrogenation. The influence of hydrogenation in the surface distribution of oxygenated functional groups and the effect of such groups in Hg0 capture have been studied.
2. Experimental section A commercial activated carbon (RB3, from Norit), ground to a size of 0.2-0.5 mm, was used as Hg0 sorbent. The surface chemistry of the sorbent samples was analysed by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) to study the oxygenated surface functional groups. BET surface area was determined by means of volumetric adsorption of nitrogen at 77 K. Hydrogenation of RB3·was carried out in a stainless steel reactor, at 350 °C in 3 hourexperiments, using 0.6 g of activated carbon, ground to 0.2-0.5 mm, under 35 bar of H2. The experimental device used for the Hg retention experiments consists of a glass reactor heated by a furnace (Figure 1). Gas phase Hg0 was obtained from a permeation tube and passed through the sorbent bed in an air flow of 0.5 L min-1. The concentration of Hg in the air stream was 100 μg m-3 and the sorbent temperature was kept at 120 ºC. A continuous Hg emission monitor (VM 3000) was used to obtain the Hg adsorption curves. The concentration of Hg retained (retention capacity) was determined by a postretention analysis of the sorbents using an automatic mercury analyzer (AMA). VM 3000
R1 N2
Sorbent 120ºC
Permeation tube activated carbon
R2
R3 Air
Figure 1. Schematic diagram of the experimental device for mercury retention.
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3. Results and Discussion The continuous mercury analyzer employed in this study is only able to detect elemental mercury. Then, the fact that the sample curves do not reach the background line (Cout/Cin=1) could indicate that the samples have not reached their maximum retention capacity, but the same effect would be observed if the mercury in the gas phase leaving the sorbent bed was oxidised. To ensure that all the Hg leaving the sorbent was Hg0, a study of Hg speciation in the RB3 samples was carried out. For this purpose, the gas at the sorbent bed outlet was collected in an Ontario Hydro impinger train device, instead of the VM 3000 analyzer. This method is able to distinguish between Hg0 and Hg2+. The results obtained clearly show that no oxidation of Hg0 took place during the retention experiments.
1 0,9 0,8
Hg C out/C in
0,7 0,6 0,5 0,4 0,3
RB3
0,2
RB3 (red. H2)
0,1 0 0
500
1000
1500
2000
2500
t (min)
Figure 2. Hg0 adsorption curves of the activated carbon before (RB3) and after hydrogenation (RB3 (red. H2)). Figure 2 displays the Hg0 adsorption curves obtained with RB3 activated carbon before and after hydrogenation. The curves represent the outlet/inlet Hg concentration ratio (Cout/Cin) versus time. The Hg0 retention capacities are listed in Table 1. The results indicate that hydrogenation of the activated carbon promotes a significant improvement of its Hg0 retention capacity.
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Table 1. Retention capacity of the activated carbon-based sorbents. Sample RB3 RB3 (red. H2)
texp (min) 4320 2796
RCAMA (μg g-1) 10 934
The values of the BET surface area of the activated carbon and its hydrogenated counterpart are listed in Table 2. No significant differences can be noticed, indicating that under the conditions used for the Hg0 retention experiments physisorption does not play a significant role in the mercury uptake. At least, it cannot account for the differences observed between the two kinds of sorbents. Then, the retention of elemental mercury must be ruled by its interactions with the surface functional groups present in the activated carbons. Table 2. BET surface area of the sorbents. Sample RB3 RB3 (red. H2)
SBET (m2 g-1) 1183 1137
The TPD curves of the activated carbon undergo significant changes after hydrogenation (Figure 3). RB3 shows the presence of several kinds of oxygenated groups. The CO evolution curve indicates the presence of C=O groups with a wide band in the 700-900 °C zone. The shoulder at ~600 °C can arise from OH groups in phenols and anhydrides. The evolution of CO2 indicates the presence of anhydrides and lactones (two peaks at ~600 °C) and also carboxylic groups (wide band in the 100-400 °C area). In the case of RB3 (red H2), the evolution curves displays less features, and only C=O groups seem to be present.
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TPD - CO curves
TPD - CO2 curves
0,05
RB3 (red. H2) RB3
0,08
Concentration (%)
Concentration (%)
0,1
0,06
0,04
RB3 (red. H2) RB3
0,04
0,03
0,02
0,01
0,02
0
0 0
200
400
600
800
1000
0
200
Temperature (º C)
400
600
800
1000
Temperature (º C)
Figure 3. CO and CO2 TPD curves. XPS results are shown in Figure 4. C 1s peaks are very similar for both samples, but the as received RB3 displays a slightly higher intensity at high binding energy (~288 eV), next to the main peak centred at 284 eV, that arises from oxygenated carbon [6]. Accordingly, in the O 1s spectrum, the band of RB3 is wider than that of the hydrogenated sample, indicating the presence of more types of oxygen functional groups.
O1s
C1s RB3 RB3 (red. H2)
298
296
294
292
RB3 RB3 (red. H2)
290
288
286
284
282
280 540
538
Binding Energy (eV)
536
534
532
530
528
Binding Energy (eV)
Figure 4. C 1s and O 1s XPS spectra. It has been previously reported that carbonyl groups [5,7] can be activated sites for Hg0 capture. In our case, however, although such groups are the most abundant oxygenated groups in the reduced activated carbon, their concentrations are much lower than in the as received RB3 sample, and therefore they alone cannot account for the increased Hg0 adsorption. However, the same study [5,7] identifies OH and phenolic groups as inhibitors of Hg0 adsorption, indicating that the best adsorption capacities are observed
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Oviedo ICCS&T 2011. Extended Abstract
in activated carbons with the lowest CO/CO2 ratios released in TPD. In our case, this ratio is very similar for both samples (RB3, 2.51; RB3 (red H2), 2.66), and even higher in the hydrogenated activated carbon. Apparently, the beneficial effect of the loss of phenolic groups and the reduction of their inhibitory effects for mercury capture is more significant that the decrease in the concentration of C=O groups. It has been suggested that the mechanism of Hg0 adsorption involves an electron transfer process with the carbon acting as an electrode, accepting electrons from mercury, which oxidises to Hg2+ [5,8-9]. The equilibrium reaction proposed is as follows, involving quininoid complexes: C6H4O2 + 2 H+ + 2 e- ↔ C6H4(OH)2 In such a scenario, the presence of additional protons, such as those supplied by the previous hydrogenation of the activated carbon, would be beneficial. The potential (Eh) of the electrode can be calculated as [5,8-9]: Eh = E0 – (R T/2 F) ln(a[C6H4(OH)2]/(a[C6H4O2] a[H+]2) where E0 is the characteristic constant potential, R is the molar gas constant, T is the temperature, F is the Faraday constant, and a is the activity (concentration × activity coefficient). Higher H+ concentration as in the hydrogenated activated carbon could increase the potential of the electrode and also the potential difference (ΔE) required for the oxidation-reduction reaction.
4. Conclusions The low Hg0 retention observed in activated carbon RB3 increases significantly after hydrogenation. The modification of the concentration and types of oxygen functional groups in the surface of the carbon does not seem to explain this enhancement. However, the increased presence of protons in the surface can improve the potential difference required for the oxidation-reduction reaction that may be responsible for Hg0 capture.
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Oviedo ICCS&T 2011. Extended Abstract
Acknowledgement. The authors thank the CSIC (PIF-06-050) and the Spanish Ministerio de Ciencia e Innovación (CTQ2008-06860-C02-01) for financial support.
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Granite EJ, Pennline HW, Hargis RA. Novel sorbents for mercury removal from flue gas. Industrial & Engineering Chemistry Research 2000;39:1020-9. Li YH, Lee CW, Gullett BK. The effect of activated carbon surface moisture on low temperature mercury adsorption. Carbon 2002;40:65-72. Kwon S, Borguet E, Vidic RD. Impact of surface heterogeneity on mercury uptake by carbonaceous sorbents under uhv and atmospheric pressure. Environmental Science & Technology 2002;36:4162-9. Ghorishi SB, Keeney RM, Serre SD, Gullett BK, Jozewicz WS. Development of a cl-impregnated activated carbon for entrained-flow capture of elemental mercury. Environmental Science & Technology 2002;36:4454-9. Li YH, Lee CW, Gullett BK. Importance of activated carbon's oxygen surface functional groups on elemental mercury adsorption. Fuel 2003;82:451-7. Maroto-Valer MM, Zhang Y, Granite EJ, Tang Z, Pennline HW. Effect of porous structure and surface functionality on the mercury capacity of a fly ash carbon and its activated sample. Fuel 2005;84:105-8. Liu J, Cheney MA, Wu F, Li M. Effects of chemical functional groups on elemental mercury adsorption on carbonaceous surfaces. Journal of Hazardous Materials 2011;186:108-13. Leon Y, Leon CA, Radovic LR. Interfacial chemistry and electrochemistry of carbon surfaces. In: Thrower PA (editor). Chemistry and physics of carbons, New York: Marcel Dekker; 1994, p. 213-310. Puri BR. Surfaces complexes on carbons. In: P.L. Walker J (editor). Chemistry and physics of carbon, New York: Marcel Dekker; 1970, p. 191-282.
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Oviedo ICCS&T 2011. Extended Abstract
SUB-PRODUCTS OF GASIFICATION AS SORBENTS FOR MERCURY RETENTION A. Fuente-Cuesta, M. Diaz-Somoano, M.A. Lopez-Anton, M.R. Martinez-Tarazona Instituto Nacional del Carbón (CSIC). C/ Francisco Pintado Fe Nº26, 33011, Oviedo, Spain. Phone: +34 985119090. Fax: +34 985297662 E-mail:
[email protected] Abstract Different technologies can be used to limit the release of mercury during coal combustion, such as particulate control devices and flue gas desulphurization systems. Even so, it is very difficult to remove vapour elemental mercury because a large proportion of it eludes the typical air-pollution control devices. Activated carbon injection is currently considered as the most promising specific technology in terms of efficiency and reliability for mercury removal. However, it is still necessary to overcome the high operational costs of this technology. The aim of this work is to evaluate the mercury retention capacities of low cost biomass gasification chars. The tested solids were sub-products from the gasification of sunflower husks, chicken manure, wood and plastic-paper wastes. The capture of mercury was evaluated in a labscale device under inert and oxygen atmospheres. The mercury retention capacities of these chars were compared with those of a commercial activated carbon (impregnated with sulphur) considered as a reference material. The results showed that the highest mercury capture was attained by the chars obtained from plastic-paper wastes. The chars with a high chlorine content and low pH present high mercury retention capacities. For all the chars studied, retention was higher under oxygen than under nitrogen, which indicates that mercury adsorption capacity depends not only on the properties of the chars, but also on the composition of the flue gas.
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Oviedo ICCS&T 2011. Extended Abstract
1. Introduction Coal combustion in power stations releases different gaseous trace elements, such as mercury, which are harmful to the environment and to human health. Several technologies and policies have been developed over the last two decades for the control of mercury emissions from coal-fired power plants [1], the major source of anthropogenic mercury emissions. The leading technology is the injection of powdered activated carbon into the flue gas prior to the particulate control devices (PCD). Nevertheless cheaper sorbents need to be developed in order to reduce costs and make this technology economically competitive.
Nowadays biomass gasification is a viable alternative for energy production from renewable sources. Chars are the solid wastes left behind after the gasification process. They contain part of the carbonaceous material, nitrogen and sulphur of the original biomass, as well as almost all its mineral matter. These characteristics make gasification chars potential sorbents for mercury capture. Although some studies have used biomass chars after the activation process for mercury removal [2], there is a lack of knowledge about the behaviour of untreated biomass chars as mercury sorbents.
The final objective of this research is to develop low-cost sorbents for direct injection in power plants. For this purpose a study at lab-scale was carried out in nitrogen atmosphere using five different gasification chars to evaluate the influence of the physico-chemical properties of the char on mercury adsorption capacity. After that, an air atmosphere was used to determine whether the gaseous components have any influence on mercury capture. The mercury adsorption capacities of the chars were compared with those of a commercial sulphur-activated carbon (Filtracarb).
2. Experimental section The five biomass gasification chars used in this study were produced at the Energy Research Centre of the Netherlands (ECN) in a pilot plant of 500 kW of power with a circulated fluidized bed gasifier (BIVKIN). The samples were labelled as follows: SH is the gasification char obtained from sunflower husks, PL is the one from chicken manure, WW the one from wood wastes and PW1 and PW2 the ones from plastic-paper wastes. The only difference in the production method of samples PW1 and PW2 was the gasification temperature. The commercial activated carbon used as reference was Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
Filtracarb D47/7+S.
Before the retention experiments, the solids were characterised using different techniques. The sulphur content was determined by a LECO automatic analyzer, the chlorine content by ionic chromatography and the total organic carbon content (TOC) using a TOC V-CPH E200V equipment. The Brunauer-Emmett-Teller (BET) surface area was measured by volumetric adsorption of nitrogen at 77 K. The pH of the chars and activated carbon sample suspensions was determined after 48h of stirring in water, once the samples had reached equilibrium. Finally, the mercury content before and after the retention experiments was determined by means of an automatic mercury analyzer (AMA254).
The lab-scale device employed for the mercury retention experiments is shown in Figure 1. Four main parts can be distinguished in this device: i) a system to generate gaseous elemental mercury from a permeation tube, ii) a fix bed reactor, iii) a system to produce the atmospheres in which the materials were tested (N2 or O2 (12.6 % v/v) and iv) a continuous mercury emission analyzer to monitor Hg concentration at the reactor outlet (VM3000). The experiments were carried out at 150ºC and the flow rate through the reactor was 0.5 L min-1. The sorbent bed consisted of a mixture of the sample and fine sand at a weight ratio of 1:3. The mercury concentration in the gas phase was approximately 100 µg m-3.
Rotameter VM 3000 N2
Mercury analyzer
Permeation tube Clean flue gas Reactor
N2 / Air Dilution Air
Activated carbon
Figure 1. Schematic diagram of the lab-scale experimental device for mercury retention.
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Oviedo ICCS&T 2011. Extended Abstract
3. Results and discussion The total organic carbon (TOC), sulphur and chlorine contents, pH, surface area (SBET) and mercury content of the raw biomass gasification chars and the activated carbon are shown in Table 1, whereas the mercury retention capacities in the two atmospheres used in this study are presented in Table 2.
Table 1. Total organic carbon (TOC), sulphur and chlorine contents, pH, surface area (SBET) and mercury content in the biomass gasification chars and the activated carbon. SAMPLES
TOC (%)
S (%)
Cl (%)
pH
SBET (m2·g-1)
Hg (µg·g-1)
SH
55
0.5
0.8
9.9
5
0.01
PL
11.7
1.7
1.8
11.4
12
0.02
WW
37.8
0.7
2.6
10
2
0.02
PW1
32.7
0.09
4.7
7.9
65
0.01
PW2
24.6
0.08
5.2
8
42
0.01
FILTRACARB
68.3
2.5
0.07
5.8
560
0.34
The mercury content in the raw biomass chars was very low (PW2>WW>SH>PL in both atmospheres (Table 2). Although the highest mercury retention capacity was achieved by Filtracarb activated carbon, the PW chars, which have a much smaller surface area than that of the activated carbon (Table 1) and sulphur contents, can reach similar retention capacities.
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Oviedo ICCS&T 2011. Extended Abstract
Table 2. Mercury retention capacities of the materials studied in the nitrogen and oxygen atmospheres. SAMPLES
Hg retained N2 (µ µg·g-1)
Hg retained O2 (µ µg·g-1)
SH
1.1
4.1
PL
700°C); CFB: Circulating Fluidised Bed
It is important to evaluate the impact of implementing CO2 capture processes on the overall energy efficiency of coal fired power stations. Next Table 2 presents a comparison of expected energy efficiency % for different power station configuration with (w) and without (w/o) CO2 capture implementation, made by data evaluation of several reports [9, 10, 11, 12, 13].
Oxy SC PC Oxy USC PC
Oxy CFB
Oxy PC
SC PC (w) USC PC (w/o) USC PC (w)
SC PC (w/o)
IGCC (w/o) IGCC (w)
CFB (w)
CFB (w/o)
PC (w)
PC (w/o)
Table 2. Evaluation of %Efficiency for Coal Fired Power Stations
36– 26– 36– 25– 42 – 32– 38 – 28 – 43 - 33 - 26- 25 - 30- 3238 28 40 28 44 34 40 29 45 34 28 29 34 38 Notes: Number range in %; for abbreviations meaning please referred to Table 1
Oviedo ICCS&T 2011. Extended Abstract
CO2 Transport might not represent a big issue within the CCS deployment, apart from infrastructure investment costs, adequate monitoring during transport and availability of clear and efficient regulation. Transportation of carbon dioxide can be by tanks, onto ships or trains, and by pipe lines depending on the CCS strategy, integrated project definition and cost analysis. [11] Pipelines for transporting nearly 30 million tCO2/y for EOR are available in some regions of the United States. Storage of carbon dioxide is a crucial link of the chain to make CCS feasible. Many official studies have been carried out in order to evaluate necessary removal capacity of the total CO2 amount, which results from the potential application of CO2 capture technologies [14]. Due to the large amount of CO2 expected to be necessarily removed, only little portion would be used by industrial sector (food / beverage industry and fertiliser production). Storage appears the only option short term to reduce the huge amount of CO2 emitted. Three ways of CO2 storage are considered: geological storage, ocean storage and mineral carbonation [11]. Only geological storage would be applicable in the short term. The options for geological storage are sequestering into deep saline aquifers and EOR (Enhance Oil Recovery) or EGR (Enhance Gas Recovery), which consists in pumping CO2 at particular conditions into depleted oil or gas fields to improve fossil fuel extraction. World storage required in 2050 will be about 144.7 GtCO2 [14]. Potential viable capacity of 1,680 GtCO2. Only for OECD Europe this potential is 94 GtCO2.
3. Results and Discussion According to the vision provided by the IEA CCS Technology Roadmap 2009, some 100 commercial-scale CCS projects must be operational worldwide by 2020 and 3,400 by 2050 if global warming is to stay below 2°C [15]. The principal metric used to define commercial scale integrated projects are those with a storage capacity rate of 1 million tCO2/y or greater [16]. Achieving 0.4 GtCO2 abatement per year from CCS in Europe by 2030, would require the installation of between 80 and 120 commercial scale CCS projects [8]. It is likely to develop as a series of capture clusters, all connected into a common transport and storage network. To reach this range of power stations in operation would be necessary to evaluate and prove the technical and economical feasibility of integration projects comprising capture, transport and storage of carbon dioxide, hence in a previous demonstrations scale.
Oviedo ICCS&T 2011. Extended Abstract
For European market, studies shows that first demonstration projects will have a CO2 reduction cost between 60 – 90 €/tCO2, considering capture, transport and storage and assuming similar costs for capture process selected [8]. First commercial scale projects would have around 35 – 50 €/tCO2, forecast 30 – 45 €/tCO2 achievable by 2030. Distribution of the total will be 64 – 72% for capture, 11 – 12% in transport and 11 – 24% in storage. Construction of new built coal fired power stations implementing CO2 capture technologies will bring better results than retrofit existing ones [8], mainly because of high efficiencies reached by the implementation of new technology and units. In the year 2010 there are globally 238 active or planed CCS projects [16], with 151 projects integrated. From the total, up to 80 are large-scale integrated projects, presenting the following relation by technology implementing: 33 Pre-combustion, 22 Post-combustion, 13 Gas processing, 2 Oxyfuel combustion, 3 Pre-combustion and Post-combustion, 1 Pre-combustion and Gas processing, 1 Oxyfuel combustion and 5 not specified. On 9 December 2009, the European Commission announced details of the 6 CCS demonstration scale projects (around 300 MWe) which receive funding of 1 billion € under the EEPR [17]. The origin of EEPR (European Energy Program for Recovery) is the global 200 billion € European Economic Recovery Plan presented by the Commission at the end of 2008. The six projects selected are Belchatow (Postcombustion, Poland), Compostilla (Oxyfuel, Spain), Hatfield (Pre-combustion, UK, location/project to be confirmed), Jänschwalde (Oxy + Post-combustion, Germany), Porto
Tolle
(Post-combustion,
Italy)
and
Rotterdam
(Post-combustion,
The
Netherlands). Final Investment Decision for the construction of these projects is scheduled by middle 2012, bearing further funding under the NER300 (New Entrant Reserve), in principal only for selected ones. NER makes funding available for commercial-scale CCS projects, with the funds generated through the sale of 300 million EU ETS allowances for the New Entrant Reserve of Phase 3 of the EU ETS. The European Commission estimates that the sale of these allowances will raise between 15 – 30 €/tCO2, dependent on the carbon price. The UK Demonstration Programme, managed by the OCCS (Office Of Carbon Capture and Storage), part of the UK Government´s DECC (Department of Energy and Climate Change), will fund 4 CCS commercial-scale projects, involving coal and gas fuel, with up to £1b to support the capital cost of the first one ongoing [18]. Main features of the UK Demonstration Programme are: alignment with NER300 schedule and compatibility with other funding programme; projects will receive a fixed strike price per tCO2 abated, and therefore the fund received will be strike price minus EAUs (EU ETS);
Oviedo ICCS&T 2011. Extended Abstract
requirements and specification of CO2 transport will be proposed by the Project Proposer; no onshore storage projects will be funded; only will be funded offshore UK storage in compliance with storage terms of the Energy Act 2008, Storage Carbon Dioxide Regulation 2010 and the EU Directive 2009/31/CE. US Power generation sector produced more than 40% of total US anthropogenic CO2 emissions in 2008, and the majority result from the combustion of coal, about 1.9 billion tCO2 [11]. EPRI and other recent studies result that wide-scale deployment of CCS provides the largest share of potential CO2 reduction. The CCPI (Clean Coal Power Initiative) will begin to demonstrate, by 2015, commercial-scale capture and storage or beneficial reuse technologies that target to achieve 90% capture efficiency for CO2 to enable subsequent commercial deployment in the coal fired utility industry. Under the CPPI Programme [11], 7 CO2 capture demonstration projects in USA are planed and ongoing. 3 of them Pre-combustion technology related, another 3 of them Post-combustion related and only 1 will demonstrate Oxy-combustion deployment. Within the USA framework, the Recovery Act funding is being used for the following CCS related activities [11]: CCPI with a total of $800 million; Industrial Carbon Capture & Storage with a total of $1.5 billion; around $20 million for scale-up a current project; a total of $100 million is being used to characterize about 10 geological formations; a total of $20 million is being used in education related to CCS sector; FutreGen 2.0 with a total of $1 billion for the construction of Oxy-combustion power station to capture 1 million tCO2/y since 2015; Carbon Capture and Storage Simulation Initiative with a total of $40 million is being used to accelerate CCS technology development using advanced simulation and modeling techniques; and the National Risk Assessment Partnership to develop the tools and science base for ensuring longterm storage. In China, the GreenGen Project ongoing will demonstrate the feasibility of 250 MW IGCC in 2009, scale up to 400 MW and 25% CO2 captured by 2015. According to OECD/IEA currently exist more than 20.000 km of CO2 pipeline globally, and forecasts the total CO2 pipeline needs over 200.000 km for the period 2030 – 2050 contingent on the level of optimisation in building common carriage networks able to link multiple sources and storage sites. Currently, a pan-European project called GeoCapacity is underway in order to provide a comprehensive database of European CO2 storage availability.
4. Conclusions Coal reserves are widespread and the international coal market ensures that demand is largely met from the most economic suppliers. Coal will represent, at least, a steady
Oviedo ICCS&T 2011. Extended Abstract
share of the World Primary Energy demand over the next 20 years and the future contribution to power generation relies mostly on how coal's carbon intensity can be coupled with sustainable emission levels. CCS and clean coal technologies are paving the way to meet the most demanding greenhouse-gas emission targets and the design of the future coal power stations will be more capital intensive and more sustainable.
Acknowledgment Special thanks to Javier Pisa for his outstanding support.
References [1] IPCC – CO2 equivalent - IPCC data base [2] IPCC 4Assessment Report 2007 [3] U.S. Census Bureau [4] BP 2011, Energy Outlook 2030 [5] International Energy Outlook 2010 [6] The Role of Coal Power Generation 2008, EURACOAL statistics, official website [7] World Energy Outlook 2009 [8] McKinsey&Company 2008 – Carbon Capture & Storage: Assessing the Economics [9] Air Liquide Technical Papers 2010 – Air Separation Unit for Oxy-coal Combustion [10] Air Liquide / B&W Technical Presentations 2010 – Oxy-coal Combustion for Demonstration Plants [11] DOE/NETL Carbon Dioxide Capture and Storage RD&D Roadmap – December 2010 [12] International Energy Agency, Clean Coal Technologies, 2008 [13] MIT, The Future of Coal, 2007 [14] OECD/IEA, Carbon Capture & Storage Roadmap, 2010 [15] CO2 Capture Project, Annual Report 2010, April 2011 [16] Global CCS Institute, The Status of CCS Projects, Interim Report 2010 [17] CCS European Energy Program for Recovery (EEPR), Energy European Commission website 2010 [18] UK Department of Energy and Climate Change, UK CCS Commercial Scale Demonstration Programme, Delivering Projects 2-4, December 2010
Co-combustion of coals and biomass blends in an entrained flow reactor under oxy-fuel atmospheres J. Riaza, L. Álvarez, M.V. Gil, C. Pevida, F. Rubiera, J.J. Pis
Instituto Nacional del Carbón, INCAR-CSIC, Apartado 73, 33080 Oviedo, Spain
[email protected] Abstract Co-combustion of different coals and biomass blends were carried out in an entrained flow reactor under different O2/CO2 atmospheres (21%O2/79%CO2, 30%O2/70% O2 and 35%O2/65%CO2), and the results obtained were compared with those attained in air. Coal burnout for the 21%O2/79%CO2 atmosphere were lower than in air. However, for O2/CO2 conditions when the O2 concentration was increased to 30 and 35%, an improvement on coal burnout was observed. The effect of blending biomass with coals of different rank under oxy-fuel atmospheres resulted in higher burnout for all cases. A reduction of NO emissions was observed when biomass was mixed with coal.
1. Introduction Carbon dioxide capture and storage technologies are necessary to produce energy from fossil fuels in a friendly environmental way. Oxy-fuel combustion is one of the most promising CO2 capture technologies as it could be adapted to both new and existing pulverized coal-fired power stations, and a significant and simultaneous reduction on NOX and CO2 emissions can be achieved. During oxy-fuel combustion a mixture of O2 and recycled flue gas (mainly CO2 and H2O) is used for fuel combustion. Due to higher O2 concentration and differences in gas properties between N2 and CO2, oxy-fuel combustion differs greatly from air combustion in several ways, inclufing coal burnout and pollutant formation [1]. Another approach for reducing CO2 emissions is the use of renewable fuels such as biomass, that is considered a neutral carbon fuel because the CO2 released during its utilisation is an integral part of the carbon cycle. Co-firing coal with biomass offers other environmental advantages due to the reduction of sulphur oxides (SOX), and the potential reduction of nitric oxides (NOX) [2]. The combination of oxy-fuel combustion with biomass could be used as a sink for CO2 emissions. The aim of this work is to asses the effect of cofiring biomass with coal in both air and oxy-fuel conditions.
1
2. Experimental Two coals of different rank were used: a semi-anthracite (HVN) and a high-volatile bituminous coal (SAB). Also two different biomasses were used: olive waste (OR) and pine straw (PI). The samples were ground and sieved to obtain a particle size fraction of 75-150 μm. The results of the proximate and ultimate analyses, and high heating value of the samples are shown in Table 1 . Table1. Proximate and ultimate analyses and high heating values of the samples Sample HVN SAB OR PI
Rank sa hvb -
Proximate Analysis (wt%, db)
Ultimate Analysis wt%, daf)
HHV
Ash
V.M
F.C.a
C
H
N
S
Oa
(MJ/kg,db)
10.7 15,0 7.6 3,8
9.2 29.9 71.9 79,8
80.1 55.1 20.5 16,4
91.7 81,5 54,3 45,9
3.5 5,0 6,6 6,1
1.9 2,1 1,9 0,7
1.6 0,9 0,2 0,0
1.3 10,5 37,0 42,3
31.8 27.8 19.9 18,9
sa: semi-anthracite; hvb: high-volatile bituminous coal. db: dry basis; daf: dry and ash free bases. a Calculated by difference.
Combustion experiments were carried out in an entrained flow reactor (EFR). This reactor is electrically heated to a temperature of 1000 ºC, and it reproduces some of the characteristics found in pulverised coal combustion such as high heating rates and short residence times. The samples were fed in from a hopper and the mass flow was controlled using a mechanical feeding system. The samples were introduced through an air-cooled injector to ensure that their temperature did not exceed 100 ºC before entering the reaction zone. The gases were preheated before being introduced into the reactor through flow straighteners. The flow rates of N2, CO2 and O2 were set to ensure a particle residence time of 2.5 seconds. A water-cooled collecting probe was inserted into the reaction chamber from below. Nitrogen was introduced at the top of this probe to quench the reaction products. Particles were removed by a cyclone and coal burnout was calculated by the ash tracer method. The exhaust gases were monitored using a battery of analysers (O2, CO, CO2, NO, N2O, SO2). A schematic diagram of the entrained flow reactor (EFR) used in the experiments can be seen in Fig. 1.
2
Figure 1. Schematic diagram of the entrained flow reactor (EFR). Four binary mixtures of O2, N2 and CO2 were employed to study the behaviour of the coals and blends. Thus, for the combustion tests, air (21%O2/79%N2) was taken as reference and three binary mixtures of O2 and CO2 were compared: 21%O2/79%CO2, 30%O2/70% CO2 and 35%O2/65%CO2.
3. Results and Discussion Coals and biomass blends were burnt under different levels of oxygen excess for each atmosphere studied. The fuel ratio, defined as the ratio between the coal mass flow rate and the stoichiometric value, was used to asses the excess of oxygen during combustion. The burnout values attained for coals SAB and HVN at different fuel ratios are shown in Fig. 2. It can be seen that the coal burnout decreased as the fuel ratio increased, due to the lower availability of oxygen at higher fuel ratio values. For both coals, the burnout obtained under the 21%O2-79%CO2 atmosphere was lower than that reached under 21%O2-79%N2 conditions. CO2 has a higher specific molar heat than N2, which implies that when N2 is replaced by CO2 the heat capacity of the gases increases, leading to lower flame and gas temperatures. Therefore, the particle temperature during
3
the 21%O2-79%CO2 atmosphere can be expected to be lower, causing the combustion rate of the char and the coal burnout value to fall [3].
100
100
HVN
SAB
90 Burnout (%)
Burnout (%)
90
80 70 21%O2/79%N2 21%O2/79%CO2
60
80 70 21%O2-79%N2 21%O2-79%CO2 30%O2-70%CO2 35%O2-65%CO2
60
30%O2/70%CO2 35%O2/65%CO2
50
50 0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.2
0.4
Fuel ratio
0.6
0.8
1.0
1.2
1.4
Fuel Ratio
Figure 2. Burnout of coals HVN and SAB under different atmospheres at different fuel ratios. Under the 30%O2-70%CO2 and 35%O2-65%CO2 atmospheres, the burnout for both coals was higher than in air, since the higher oxygen concentration produced an increase in the char combustion rate. Increasing the O2 fraction in CO2 up to 30% is still insufficient to match the specific heat capacity of air. However, coal burnout in the 30%O2-70%CO2 atmosphere reached a higher value than in air, which means that another parameter must have changed to offset the negative effect of the specific heat capacity of the gas. Though the gas temperature increases only slightly when the O2 fraction in bulk gas is increased, it is likely that the increase in the mass flow rate of O2 from the bulk gas to the coal surface at higher O2 concentrations promotes the consumption rate of the volatiles, providing extra heat feedback to the coal particle to enhance its devolatilisation, ignition and combustion [4]. For the co-combustion tests, HVN-OR blends were used and their burnouts were also determined at different fuel ratios. Fig. 3 shows the burnout of the HVN-OR blends at a selected fuel ratio of 0.8. The burnout of the blends presents a behaviour similar to that of the individuals coals under the different atmospheres studied, that is, there is a decrease in burnout when N2 is replaced by CO2 for the same oxygen concentration, and an improvement in O2/CO2 atmospheres when the oxygen concentration increases.
4
100
HVN-OR
Burnout (%)
90
80
70
81.7 82.4
79.5
83.5 83.5 80.4 79.7
86.1 85.5 83.0
81.0
77.2
21%O2-79%N2 21%O2-79%CO2
60
30%O2-70%CO2 35%O2-65%CO2
50
HVN
90% HVN-10% OR 80% HVN-20% OR
Figure 3. Burnout of HVN-OR blends at a fuel ratio of 0.8. As shown in Fig. 3, blending biomass with coal has an impact on burnout. For all the atmospheres studied, an improvement on coal burnout was achieved with the increase in the percentage of biomass. The highest improvement on burnout was observed for the combustion of HVN-OR in 30%O2/70%CO2. When the oxygen concentration increased to 35%, no significant differences were observed in comparison with combustion under 30%O2. The concentrations of NO at a fuel ratio of 0.8 during HVN-OR combustion are shown in Fig. 3. The NO concentration (mg NO/ g burned coal) obtained under the 21%O2/79%CO2 atmosphere was lower than that achieved under 21%O2/79%N2. This reduction on NO emissions can be explained due to the higher CO concentrations in oxy-fuel environments [5]. In the 30%O2/70%CO2 and 35%O2/65%CO2 atmospheres, the NO concentration was slightly higher than that in the oxy-fuel atmosphere containing 21% of O2, since higher oxygen concentrations enhance coal nitrogen conversion to NO. However, the NO concentrations still remained lower than in air, and small differences between the three oxy-fuel atmospheres were observed. As seen in Fig. 4, a decrease in NO emissions was observed with biomass blending. This decrease is significantly marked for air-firing conditions.
5
12 HVN-OR mgNO/g burned fuel
10
9.7 8.8
8
6.7 6.9
7.4
7.1 6.5
6.5
6.6
6.1
6.6 6.5
6 4 2
79%N2-21%O2 79%CO2-21%O2 70%CO2-30%O2 65%CO2-35%O2
0
HVN
90% HVN-10% OR 80% HVN-20% OR
Figure 4. NO emissions of HVN-OR blends at a fuel ratio of 0.8.
4. Conclusions The burnout of individual coals and blends was determined under both air and oxyfiring conditions. The burnout of the samples in a 21%O2/79%CO2 atmosphere were lower than those obtained in air-firing conditions due to the higher specific molar heat of CO2 compared to N2, and the lower diffusivity of O2 in CO2 than in N2. However, when the O2 concentration was increased to 30 and 35%, the burnouts increased above those reached under air-firing, due to an increase in the mass flow of O2 to the coal particles. When blending biomass, an improvement on burnout was observed for both air and oxy-firing conditions. NO emissions were lower during oxy-fuel combustion than in air-firing due to a higher reduction of NO by reaction with CO. A slight increase in NO emissions was observed as the O2 concentration increased in O2/CO2 atmospheres. A decrease on NO emissions was observed for both air and oxy-firing conditions when the percentage of biomass in the blends was increased.
Acknowledgements Work carried out with financial support from the Spanish MICINN (Project PS120000-2005-2) co-financed by the European Regional Development Fund. L.A. and J.R. acknowledge funding from the CSIC JAE program, co-financed by the European
6
Social Fund, and the Asturias Regional Government (Severo Ochoa Program), respectively.
References [1] Wall TF, Liu Y, Spero C, Elliot L, Khare S, Rathman R et al. An overview on oxyfuel coal combustion-state of the art research and technology development. Chemical Engineering Research and Design 2009; 87: 1003-16. [2] Demirbas A. Potential applications of renewable energy sources, biomass combustion problems in boiler power systems and combustion related environmental issues. Progress in Energy Combustion Science 2005; 31: 171-92. [3] Berejano PA, Levendis Y. Single-coal particle combustion in O2/N2 and O2/CO2 environments. Combustion and Flame 2008; 153: 270-87. [4] Shaddix CR, Molina A. Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion. Proceedings of the Combustion Institute 2009; 32: 2091-8. [5] Hu YQ, Kobayashi N, Hasatani M. Effects of coal properties on recycled-NOX reduction in coal combustion with O2/recycled flue gas. Energy Conversion and Management 2003; 44: 2331-40.
7
Effect of the activation temperature and the burn-off degree on the CO2 capture capacity of microporous activated carbons M.V. Gil, M. Martínez, S. García, J.J. Pis, F. Rubiera, C. Pevida Instituto Nacional del Carbón, INCAR-CSIC. Apartado 73. 33080 Oviedo, Spain
[email protected] Abstract Phenol-formaldehyde resins and a low-cost biomass residue, olive stones (OS), were used to prepare two activated carbons for the separation of CO2 in post-combustion processes. Two phenol-formaldehyde resins were synthesized: Resol, obtained by using an alkaline environment, and Novolac, synthesized in the presence of an acid catalyst. Carbon precursors were prepared by mixing the Resol resin, R, with potassium chloride, K, and the Novolac resin, Cl, with olive stones, OS. The precursors were carbonized under an inert atmosphere of N2 at 1000 ºC, yielding the RKC10 and ClOSC10 materials. The last stage in the synthesis of the adsorbents involved physical activation with carbon dioxide. Response surface methodology (RSM) was used as a tool for rapidly optimizing the activation parameters in order to obtain the highest CO2 capture capacity of the activated carbons. By means of this methodology it was possible to obtain the optimum values of temperature and burn-off degree during the activation step to maximize CO2 uptake by the activated carbons, within the experimental region considered. The maximum value of CO2 capture capacity for ClOSC10 was obtained when the activation was carried out at 942 ºC, independently of the burn-off value. For RKC10, the maximum value of CO2 capture capacity was obtained with an activation temperature of 722 ºC and a burn-off of 50%. Values of CO2 adsorption capacity of 4.4 and 7.3 wt.% at 35 °C and atmospheric pressure were achieved for the RKC10 and ClOSC10 activated carbons, respectively.
1. Introduction Coal is the most abundant and widely geographically distributed fossil fuel. The stability of its supply and relatively low cost ensure its inclusion in the energy mix in the foreseeable future. The use of coal in power plants generates high amounts of CO2. It is widely accepted that climate change is a global phenomenon influenced by greenhouse gas emissions to the atmosphere, CO2 being the main greenhouse gas contributing to global warming. In the short-to-medium term, carbon capture and storage (CCS) will be
1
necessary in order to reduce CO2 emissions to the atmosphere, CO2 capture being the most costly component of the CCS process [1]. This has led to intensive research aimed at the production of CO2 capture materials with significant levels of CO2 uptake. Different types of adsorbents, such as zeolites and activated carbons, have been used for this purpose. Activated carbons have a high adsorption capacity at ambient pressures and present important advantages over zeolites, such as their hydrophobicity, their significant lower cost and the lower amount of energy needed to regenerate them. Adsorption with activated carbons at atmospheric pressure could be a useful technology for post-combustion CO2 capture. These materials can be obtained from almost any carbonaceous product by a process of carbonization followed by an activation step. However, the use of naturally occurring precursors to produce activated carbons limits the purity, strength and physical form of the end-product materials. This drawback can be overcome by using polymeric precursors, where the reproducibility and purity of the precursor is within the control of the manufacturer, and the physical forms and structures can be tailored by means of the polymer production process [2]. Phenolic resins constitute a family of low-cost polymers, one of the most common being those produced from phenol and formaldehyde [3]. Response surface methodology (RSM) is a multivariate statistical technique used to optimize processes, i.e., to establish the conditions in which to apply a procedure in order to obtain the best possible response in the experimental region studied. This methodology involves the design of experiments and multiple regression analysis as tools to assess the effects of two or more independent variables on dependent variables [4]. It is based on the fit of a polynomial equation to the experimental data to describe the behaviour of a set of data. In the present work, phenol-formaldehyde resins and olive stones were employed as precursor materials for the preparation of microporous activated carbons for use in post-combustion CO2 capture. The CO2 capture capacity of the different activated carbons was optimized in relation to temperature and burn-off degree during the activation stage by means of response surface methodology. The objective of this study was to determine the optimum values of activation temperature and burn-off degree for the activated carbons, which maximize the CO2 capture capacity within a given experimental region.
2
2. Experimental Phenol-formaldehyde resins and a low-cost biomass residue, olive stones (OS), were used as starting materials. Two types of phenol-formaldehyde resins were synthesized. The first one was obtained by basic catalysis using sodium hydroxide (NaOH) and is commonly referred to as Resol. In this case a 2.5:1 formaldehyde-tophenol ratio was used. The second type of resin was synthesized by acid catalysis with hydrochloric acid (HCl) and is known as Novolac. In this case a 1:1.22 formaldehyde-tophenol ratio was used. Then, the resins were cured in a rotary evaporator (40-70 ºC) and a forced-air convection oven (60-100 ºC) and, finally, the cured resins and the olive stones were ground and sieved to obtain a particle size fraction of 1.0-3.35 mm. Two carbon precursors were then prepared by incorporating potassium chloride to the Resol resin, and olives stones to the Novolac resin (80:20 wt. ratio of OS:resin). The precursors were then carbonized in a horizontal furnace under a nitrogen flow at 1000 ºC, which yielded the RKC10 and ClOSC10 carbonized samples. The carbonized materials were physically activated with CO2 in a thermobalance under a 10 mL min-1 flow rate of CO2 at different temperatures. The RSM was used to evaluate the effect of temperature and burn-off degree during the activation stage on the CO2 capture capacity of the activated carbons. The independent variables were activation temperature (T) and burn-off degree attained after the activation process (B), while the dependent variable was the CO2 capture capacity. For ClOSC10, the activation temperature was studied between 900 and 1000 ºC and the burn-off degree between 30 and 50%. For RKC10, the activation temperature was assessed between 600 and 800 ºC and the burn-off degree between 10 and 50%. A three-level full factorial experimental design was used and 13 experiments were carried out, which are shown in Table 1, together with the experimental values of CO2 capture capacity. The mathematical-statistical treatment of the experimental data consisted in fitting a polynomial function to the set of data: y = β0 + β1x1 + β2x2 + β12x1x2 + β11x1x1 + β22x2x2 + ε
(1)
where β0 is the constant term, β1 and β2 represent the coefficients of the linear parameters, β12 represents the coefficient of the interaction parameter, β11 and β22 represent the coefficients of the quadratic parameters and ε is the residual associated with the experiments. Multiple regression analysis was used to fit Eq. (1) to the
3
experimental data by means of the least-squares method, which makes it possible to determine the β coefficients that generate the lowest possible residual. Table 1. Levels of the independent variables (coded levels in parentheses), activation temperature (T) and burn-off degree (B) for the activated carbons, using a three-level full factorial design, and experimental values of CO2 capture capacity Run RKC10 ClOSC10 CO2 capture CO2 capture T (ºC) B (%) T (ºC) B (%) capacity (wt.%) capacity (wt.%) 1 600 (-1) 10 (-1) 0.8 900 (-1) 30 (-1) 6.8 2 600 (-1) 30 (0) 0.8 900 (-1) 40 (0) 7.0 3 600 (-1) 50 (+1) 0.7 900 (-1) 50 (+1) 7.0 4 700 (0) 10 (-1) 2.5 950 (0) 30 (-1) 7.1 5 700 (0) 30 (0) 3.8 950 (0) 40 (0) 7.5 6 700 (0) 50 (+1) 5.0 950 (0) 50 (+1) 7.5 7 800 (+1) 10 (-1) 1.1 1000 (+1) 30 (-1) 6.5 8 800 (+1) 30 (0) 3.2 1000 (+1) 40 (0) 6.7 9 800 (+1) 50 (+1) 3.1 1000 (+1) 50 (+1) 6.6 10 700 (0) 30 (0) 3.7 950 (0) 40 (0) 7.2 11 700 (0) 30 (0) 3.0 950 (0) 40 (0) 7.1 12 700 (0) 30 (0) 3.6 950 (0) 40 (0) 7.3 13 700 (0) 30 (0) 3.2 950 (0) 40 (0) 7.5
Evaluation of the fitness of the models was carried out by applying an analysis of variance (ANOVA) and a lack of fit test. The coefficient of determination adjusted by the number of variables (Adj-R2) and the absolute average deviation (AAD) were calculated in order to check the accuracy of the model. Adj-R2 represents the proportion of variability of the data that is accounted for by the model. The AAD is a direct parameter that describes the deviations between the experimental and calculated values and it is calculated by means of the following equation [5]: AAD (%) = 100 [Σi=1 n (|yi,exp – yi,cal|/yi,exp)]/n
(2)
where yi,exp and yi,cal are the experimental and calculated responses, respectively, and n is the number of experiments. The statistical analyses were carried out by SPSS Statistics 17.0 software. The model obtained can be three-dimensionally represented as a surface (response surface plot) and the best operational conditions inside the studied experimental region can be found by visual inspection. A two-dimensional display of the surface plot generates the contour plot, where the lines of constant response are drawn on the plane of the independent variables. Response surface and contour plots were generated using the software SigmaPlot 8.0. The CO2 capture capacity of the adsorbents at atmospheric pressure was assessed
4
in a Mettler Toledo TGA/DSC 1 thermogravimetric analyzer under a CO2 flow rate of 100 mL min-1 at 35 ºC up to constant weight. The maximum CO2 uptake at atmospheric pressure and 35 ºC was evaluated from the increase in mass experienced by the sample, and it was expressed in terms of mass of CO2 per mass of dry adsorbent (wt.%).
3. Results and Discussion Table 2 shows the results of fitting Eq. (1) to the experimental data by multiple regression analysis, and those obtained from evaluating the fitness of the model by means of ANOVA, together with the Adj-R2 and AAD values. The ANOVA tests showed that the models for CO2 capture capacity were statistically significant at a 95% confidence level (p-value0.05). Table 2. Results of multiple regression analysis and ANOVA used to to the CO2 capture capacity experimental data of the activated carbons RKC10 ClOSC10 Coded Sum of Coded DF p-value coefficient squares coefficient Intersection 3.579 74.306 1 0.000 7.334 T 0.850 4.335 1 0.007 -0.167 B 0.733 3.227 1 0.014 0.117 TB 0.525 1.103 1 0.100 -0.025 T2 -1.878 9.737 1 0.001 -0.521 B2 -0.128 0.045 1 0.714 -0.071 Model 20.696 5 0.002 Residual 2.156 7 Total 22.852 12 Lack-of-fit 1.684 3 0.083 Pure error 0.472 4 R2 0.906 0.887 Adj-R2 0.838 0.806 AAD (%) 8.12 1.39
fit the polynomial model Sum of squares 312.009 0.167 0.082 0.003 0.749 0.014 1.233 0.157 1.391 0.029 0.128
DF p-value 1 1 1 1 1 1 5 7 12 3 4
0.000 0.030 0.098 0.748 0.001 0.459 0.003 0.822
Table 2 also shows which of the terms in the models were statistically significant at a 95% confidence level (p-value10), because of high lime (CaO) content and is defined as Class F. Of course the high base content makes the fly ash feasible as a chemical scrubber for acidic wastes. The chemical composition of the South African and Columbian fly ash (SAFA, COFA) is given in Table 1. Table 1: the major components and Minor elements in the SAFA and COFA of the South African and Columbian fly ashes COFA*
SAFA*
54.4 20.8 1.05 6.18 4.65 2.05 0.12 0.05 0.75 0.13 9-7
40.9 31.4 1.75 3.05 8.35 2.45 0.05 0.02 1.95 0.35 5-4
Component %weight SiO2 Al2O3 TiO3 Fe2O3 CaO MgO K2O Na2O P2O5 SO3 C
Element ppm Ag As Ba Be Cd Co Cr Cu Mn Ni
COFA** SAFA** 9.5 1300 °C and p > 30 bar), putting much burden in economy and safety respect. The kinetics of the gas conversion can be significantly increased by introducing the catalyst. However, the catalytic activity is commonly deactivated by its irreversible interaction with mineral matters in coal. This work addresses how to achieve the coal gasification at the mild condition. Following the production of ash-free coal by thermal extraction using 1methylnaphthalene solvent, preliminary experiments on its pyrolysis and CO2/H2O gasification were carried out. The ash-free coal made of a low rank coal (Samhwa, lignite) was a little less susceptible to devolatilization during pyrolysis than its raw coal. In the absence of the catalysts and at T < 800 ˚C, no evident gasification of the ash-free coal was observed, showing very similar TGA profile to its pyrolysis run. With a further increase in temperature, the gasification reactions kicked in, and which produced CO by CO2 gasification (Boudouard reaction), and H2/CH4/CO/CO2 by steam gasification (coal-water and water-gas shift reaction). As a next step to achieve faster kinetics at the mild condition, a mixture of the gasification catalyst and the ash-free coal will be prepared and evaluated in terms of the advantage over its raw coal.
1. Introduction Coal is one of the most important energy sources, currently accounting for ~25% of energy consumption around the world1, 2. The use of coal is expected to increase as a result of its abundance and economic advantage, even though there are various problems coupled with the combustion of coal such as emission of greenhouse (GHG) and pollutant gases. Especially, a coal–fired power sector is responsible for ~35% GHG
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Oviedo ICCS&T 2011. Extended Abstract
emission and has been continuously blamed as a main culprit of global warming3. The Korean legislature enacted Low Carbon Green Growth Act in 2009, targeting 30% reduction of GHG emissions, compared to BAU, by 20204. A series of measures are required in order to meet the goal without damaging the energy security and the economy. In the way of this challenge, Korean government listed an integrated gasification combined cycle (IGCC) in the action plan, aiming at the development of the commercial scale plant. Many of IGCC demo plants (50 − 600 MW scale) have been operated successfully, mostly in USA, EU, and Japan5. The thermal efficiency was estimated to be above 48%, much improved from conventional coal-fired power plants (~28% for subcritical and ~43% for ultra supercritical class)6. IGCC is now outlooked as a realistic and energyefficient alternative and also as low carbon next generation technology. In the foreseeable future, IGCC is very likely to play a key role for coal utilization in Korea. Coal gasification is one of the most critical processes in highly efficient IGCC7. The majority of the gasification processes scaled up for commercialization adopted entrained-flow, slagging gasifiers, which are practically meaningful only at harsh operating condition (> 1400 °C and 20 − 70 atm)8. This severity puts much burden in economy and safety respect. At the lower temperature (T < 800 °C), the conversion kinetics is generally slow and therefore of no practical use, unless the catalyst-aided coal gasification is performed. The coal to gas conversion can be significantly increased by using alkali, alkali earth, and Ni/Fe based active catalyst 9 . However, the catalytic activity is commonly not repeatable due to deactivation by irreversible interaction of the catalyst with the mineral matters in coal9. The ash in coal is ill-natured, decreasing the power efficiency and also being discharged as an air pollutant10. A lot of works have concentrated on the development of efficient methods to prepare ash-free coal 11 . Among them, thermal extraction with organic solvents has produced ash-free coal, namely “Hypercoal,” most successfully, potentially solving the ash problem12. This work addresses how to realize the coal gasification at the mild condition. The ash in coal was removed by thermal extraction method and the resultant ash-free coal was gasified under H2O and CO2 flow. The pyrolysis and gasification behavior of the ash-free coal was discussed.
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Oviedo ICCS&T 2011. Extended Abstract
2. Experimental A soluble carbon component in Samhwa coal (brown coal) was extracted using 1methylnaphthalene (1-MN) solvent. The extraction was processed via extraction, filtration, and drying step. The raw coal was ground, meshed to < 74 μm, and dried in a vacuum oven at 100 °C. Coal slurry was prepared by adding 20 g coal into 200 g 1-MN. The slurry was added to an extractor (0.5 liter volume), which was then purged with N2 gas. While stirring, the mixture was heated to 370 °C and held for an hour under 30 bar. To separate the solvent extract from the residual matter, a filtering was done at the stainless steel filter unit. The solvent in the extract was removed by being kept in a vacuum oven (~300 °C) under N2 atmosphere for 3 − 4 hr. Finally, extracted coal (EC) was obtained. Properties of Samhwa coal and its solvent extract are tabulated in Table 1. Table 1. Proximate/ultimate analysis and calorific value of Samhwa coal (raw coal) and its solvent extract. Sample (wt%) Raw Extract
Moisture
Volatile matter*
Ash (dry)
6.7 0.9
52.3 46.5
2.2 0.2
Fixed carbon* 38.6 52.3
C
H
N
O
70.5 86.3
5.1 5.2
0.9 0.9
23.5 7.6
Heat value (kcal/kg) 4,554 8,066
*daf: dry & ash-free
Preliminary results on catalytic gasification reactions of ash-free coal were obtained using thermogravimetric analysis {TGA, SDT Q600 (TA Instrument) and Setsys (Setaram)}. In this work, no catalysts were introduced to the system. In the beginning, both the raw coal and its solvent extract were pyrolyzed under 100 cc/min N2 or Ar flow. Temperature increased from 20 to 950 ˚C at 10 ˚C/min ramp rate and then stayed at 950 ˚C for 30 or 60 min. The effluent gases were analyzed using either FT-IR (Nicolet 6700, Thermo Scientific) or quadrupole mass spectrometer {(QMS, E5CN (Omnistar)}. Then, the ash-free coal was gasified with 100 cc/min of CO2 and H2O supply. The analysis of the effluent gases was repeated using the same instruments.
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Oviedo ICCS&T 2011. Extended Abstract
3. Results and Discussion Pyrolysis profile of the ash-free coal was compared with that of the raw coal and shown in Fig. 1. No significant difference was found until 600 ˚C. The raw coal lost more weight than the extract at 600 − 800 ˚C, likely due to higher content of the volatile matter (Table 1). During a further increase of temperature (800 to 950 ˚C) and isothermal at 950 ˚C, the lines were parallel with each other, indicating that the labile nature of the extracted portion was similar to that of the raw coal. 120
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Fig. 1. Pyrolysis profile under N2 flow for Samhwa coal and its ash-free solvent extract. The CO2 gasification of the ash-free coal was performed and compared with its pyrolysis reaction (Fig. 2). A wt% profile of the CO2 gasification was about the same as that of the raw coal at T < 850 ˚C, which pointed out that CO2 behaved like an inert N2 gas and no CO2 gasification occurred in this region (Fig. 2(a)). In the analysis of the effluent gases using FT-IR, CH4 peaks were similarly positioned at 300 − 550 ˚C (Fig. 2(b)). Again, this indicated that CO2 was non-reactive with the coal at the lower temperature. A gap between the two lines was formed from ~850 ˚C and became bigger with increasing temperature. A continuous loss of the weight was shown for CO2 gasification at 950 ˚C isotherm, while there was negligible weight change with N2 flow at the same condition. As shown in Fig. 2(c), a Boudouard reaction (CO2 + Ccoal Æ CO) kicked in and produced CO gas under CO2 flow, but only after temperature reached above ~700 ˚C. A faster kinetics is expected with an introduction of the gasification catalysts, which will be investigated later on.
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Oviedo ICCS&T 2011. Extended Abstract
120
6x 10 -3
(b) CH4
(a) wt%
CO2
100
5x 10 -3
o
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200 C 80
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time (min)
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Intensity (arb.)
1.5 x1 0 -2
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1x 10 -2
5x 10
-3
N2 0
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Fig. 2. Comparison of pyrolysis under N2 and CO2 gasification reaction of the ash-free coal. (a) weight change profile, and evolved gas profile for (b) CH4 and (c) CO. The ash-free coal was gasified in the presence of 10% H2O in N2 and pyrolyzed under Ar gas (Fig. 3). The general trend of weight change for the steam reaction was very similar to that for the CO2 gasification, such that the reactions of coal with water at T < 850 ˚C were unnoticeable and mainly pyrolysis products were obtained (Fig. 3(a)). The evolved gases were analyzed as a function of temperature using QMS. The peaks listed below corresponded to the gas evolution by pyrolysis; a H2 peak (the maximum at ~750 ˚C, Fig. 3(b)), a CH4 peak (the maximum at ~520 ˚C, Fig. 3(c)), and a CO2 peak (the maximum at ~500 ˚C, Fig. 3(e)). A pyrolyzed CO peak was not identified due to strong m/e = 28 background. However, a significant increase of H2 and CO production was detected during the temperature ramp of 800 to 950 ˚C and the isotherm at 950 ˚C, as shown in Fig. 3(b) and (d), respectively. This increase happened as a consequence of coal-water (Carbon + H2O Æ CO + H2) reaction. In addition, a water-gas shift reaction (CO + H2O Æ CO2 + H2) resulted in an increase of a CO2 peak at T > 800 ˚C. As a next step, a mixture of up to Submit before May 15th to
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Oviedo ICCS&T 2011. Extended Abstract
20% catalyst (K, Na, Ca, Mg, Fe, and Ni) and the ash-free coal will be prepared and evaluated in terms of the advantage over its raw coal. 120
1x 1 0
-10
(a) wt%
(b) H2
Ar 10% H2O
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Intensity (arb.)
wt%
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Fig. 3. Comparison of pyrolysis under N2 and H2O gasification reaction of the ash-free coal. (a) weight change profile, and evolved gas profile for (b) H2, (c) CH4, (d) CO, and (e) CO2 profile.
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4. Conclusions Preliminary experiments were performed on the pyrolysis and CO2/H2O gasification of the ash-free coal at the mild condition using TGA, FT-IR, and QMS. The pyrolysis profile of the ash-free coal was similar to that of its raw coal, showing a little less devolatilization. In case of the CO2/H2O gasification without adding catalysts, the gases were evolved mainly from the pyrolysis at T < 800 ˚C. Production of CO by CO2 gasification (Boudouard reaction) and H2/CH4/CO/CO2 by steam gasification (coalwater and water-gas shift reaction) were enhanced by a further temperature increase (800 − 950 ˚C) and an isotherm at 950 ˚C. To obtain faster kinetics at mild condition, the gasification catalysts will be mixed with the ash-free coal and evaluated in terms of the advantage over its raw coal.
References 1. World Energy Outlook 2007 China and India Insights. Paris: IEA; 2007, p663. 2 . Kurose R, Ikeda M, Makino H, Kimoto M, Miyazaki T. Pulverized Coal Combustion Characteristics of High-Fuel-Ratio Coals. Fuel 2004;83:1777-85. 3. Climate analysis indicators tool (CAIT). version 2009. world resources institutel; 2009. 4. Overview of the Republic of Korea’s National Strategy for Green Growth. UNEP; 2010. 5. Liu H, Ni W, Li Z, Ma L. Strategic thinking on IGCC development in china. Energy Policy 2008;36:1-11. 6. Henderson C. Clean coal technologies. IEA clean coal centre report: CCC/74. London: Graham & Trotman; 2003. 7. Pérez-Fortes M, Bojarski A, Velo E, Nougués J, Puigjaner L. Conceptual model and evaluation of generated power and emissions in an IGCC plant. Energy 2009;34:1721-32. 8. Higman C, van der Burgt M. Gasification. 2nd ed. Amsterdam: Gulf professional publishing; 2008. 9. Corella J, Toledo JM, Molina G. Steam gasification of coal at low-medium (600 − 800 ˚C) temperature with simultaneous CO2 capture in fluidized bed at atmospheric pressure. Ind Eng Chem Res 2006;45:6137-6146. 10. Steel K, Patrick J. The Production of Ultra Clean Coal by Chemical Demineralization. Fuel 2001;80:2019-23. 11. Li C, Takanohashi T, Yoshida T. Effect of Acid Treatment on Thermal Extraction Yield in Ashless Coal Production. Fuel 2004;83:727-32. 12. Okuyama N, Komatsu N, Shigehisa T, Kaneko T, Tsuruya S. Hyper-coal Process to Produce the Ash-free Coal. Fuel Processing Technology 2004;85:947-67.
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Kinetic Study on the Lignite-CO2 Gasification in the Presence of K2CO3 V.C. Bungay1, B.H. Song1, S.D. Kim2, J.M. Sohn3, H.M. Shim4, Y.J. Kim4, G.T. Kim4, S.R. Park4, and Y.I. Lim5 1
Chemical Engineering Department, Kunsan National University, Gunsan, Jeonbuk 573-701, Korea:
[email protected] 2 Department of Chemical & Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea 3 Department of Mineral Resources & Energy Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Korea 4 SK energy Institute of Technology, Daejeon 305-712, Korea 5 Department of Chemical Engineering, Hankyong National University, Anseong, Gyonggi-do 456-749, Korea
Abstract The catalytic CO2 gasification of Mongolian lignite with K2CO3 has been performed in a thermogravimetric analyzer (TGA) and the kinetics of the reaction was studied. The gasification temperature was from 600°C to 900°C at ambient pressure. Catalyst was added to the lignite samples with 5-15 wt% loading by physical mixing or impregnation. The kinetic parameters like the rate enhancement factor and activation energy of the reaction have been evaluated using the gas-solid reaction models in the literature. It was observed at 600°C that the addition of K2CO3 increased the carbon conversion by 45% with respect to the uncatalyzed reaction. The enhancement in gasification rate at this temperature ranged between 10-25 times that of the uncatalyzed reaction. For coal gasification at higher temperatures, the enhancement in gasification rate was between 56 times that of the uncatalyzed reaction which implies that any further increase in the catalyst loading will not significantly affect the rate of the gasification reaction. On the other hand, the experimental results showed no significant difference in gasification rate whether catalyst was added by physical mixing or by impregnation. This study further confirms that K2CO3 exhibits good mobility which makes it an effective catalyst regardless of catalyst addition method. In addition, carbon conversion increases with increasing CO2 partial pressure as a result of the reduction of K2CO3 volatilization during gasification with N2-CO2 gas mixture. Most of gasification conversion behavior could be well predicted with the extended modified volumetric model.
1
1. Introduction Gasification of coal with CO2 and steam has been one of the main processes of producing inexpensive, clean and effective fuel. Specifically, gasification of low-rank coals draws much attention due to its higher reactivity relative to high-rank coals [1-2]. Alkali metal carbonates, either alone or in combination with other compounds, are known to enhance the reactivity of coal and other carbonaceous materials. The presence of these compounds greatly reduced the gasification temperature thus improving the process from the economic point of view. For coal gasification with CO2 [3,4] and steam [5-10], potassium carbonate (K2CO3) has been used and proven to improve the rate of coal conversion and significantly lower the gasification temperature. In most kinetic studies, thermogravimetric method is commonly employed being cost-effective, simple and provides rapid analysis of gasification reactions involving numerous parameters. Such method employs a thermogravimetric analyzer (TGA) which generates a curve that shows the variation of the sample weight with time and its derivative. This data is then converted to a rate-conversion curve and interpreted using various gas-solid reaction models. In this work, the kinetics of catalytic gasification of Mongolian lignite in the presence of K2CO3 was studied. The performance of the catalyst was reported at different temperatures, CO2 partial pressure, catalyst loading and catalyst addition method. Possibility of recycling the catalyst was also presented along with the evaluation of goodness of fit using various gas-solid reaction models. 2. Experimental section Mongolian lignite was used in this study with the proximate and ultimate analysis shown in Table 1. Coal samples were pulverized to particle sizes less than 0.250 mm. Potassium carbonate (99.5% purity) was used as catalyst and purchased from Samchun Pure Chemicals Co. Ltd. The catalyst was used as received and added to the coal sample by physical mixing and impregnation at 5%, 10% and 15% wt loading. Physical mixing was done by the addition of K2CO3 of particle size less than 0.250 mm to the coal sample and mechanically mixed in a sealed container. Impregnation was done by the addition of an aqueous solution containing the desired amount of K2CO3 to the coal sample and mixed thoroughly. Removal of the solvent was done in a rotary vacuum evaporator, air dried overnight and sieved to particle size less than 0.250 mm. Gasification experiments were carried out in a thermogravimetric apparatus (TGA Q50, TA Instruments) at temperatures ranging from 600°C to 900°C using CO2-N2 gas
2
mixtures. About 20 mg of the lignite sample was accurately weighed and filled in a platinum plan. Initially, the sample was heated isothermally at 110°C to remove the moisture and heated to the desired gasification temperature at ambient pressure to remove the volatile matter under N2 environment. The gas was then switched to CO2-N2 gas mixture at 0.60 atm CO2 partial pressure for the gasification of the fixed carbon. The residue was then treated with a mixture of air-N2 gas to obtain ash. This procedure was done to coal samples where temperature, catalyst loading and catalyst addition method were varied. To investigate the effect of CO2 partial pressure to the gasification reaction, CO2 partial pressure was varied from 0.20 atm to 0.80 atm from 600°C to 900°C with 5% wt loading of K2CO3. To evaluate the possibility of catalyst recycling, lignite with similar loading of K2CO3 was physically mixed and gasified at 700°C and 0.60 atm CO2 partial pressure. To maximize the use of the catalyst, recycling was done for the lignite-gasification with 0.60 atm CO2 partial pressure in the presence of 5% wt K2CO3 at 700°C. This gasification temperature was chosen due to the attainment of complete conversion for the given sample size at approximately 30 min of gasification time with CO2 and to investigate the catalytic effect rather than the thermal effect experienced at higher temperatures. In addition, the said temperature was far below the melting points of K2CO3 in N2 and CO2 environment which are 900°C and 905°C, respectively [11]. Ash and catalyst that remained from this process was weighed and lignite was added to obtain the same catalyst loading on the assumption that the amount of catalyst present was constant. Table 1. Proximate and ultimate analyses of Inner Mongolian lignite Proximate analysis (wt.% ar) Ultimate Analysis (wt.% daf) Moisture 23.34 C 65.33 Volatile matter 30.01 H 4.67 Fixed carbon 35.55 N 0.57 Ash 11.10 S 0.23 a O 18.10 a by difference Data of mass versus time from the gasification process was used to evaluate kinetic parameters using various gas-solid reaction models – homogeneous model (HM) [12], shrinking-core model (SCM) [1,13], random pore model (RPM) [14], modified volumetric model (MVM) [15] and the extended modified volumetric model (EMVM) [16]. From these parameters, the performance of the catalyst was evaluated based on its ability to lower the activation energy and to enhance the rate of the gasification process.
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3. Results and Discussion 3.1. Uncatalyzed lignite-CO2 gasification To serve as a baseline data, uncatalyzed gasification of the lignite sample was carried out from 600°C to 900°C using CO2-N2 mixture at 0.60 atm CO2 partial pressure. As shown in Fig. 1a, about 90% conversion was attained at about 10 min for the given sample weight at 900°C. This shows that gasification was mainly influenced by temperature and such runs will serve as a basis for comparison for the catalyzed reactions. Using various gas-solid reaction models, the reaction rate constant was determined and from the Arrhenius plot shown in Fig. 1b, the activation energy and frequency factor of the uncatalyzed reaction was found to be 159.3 kJ-mol–1 and 2.5×108 hr–1, respectively.
b
1
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ln k (-)
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Dimensionless gasification time, t/t10 min (-)
(4.0) 0.8
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1.2
1/T, (1000 K-1)
Figure 1. (a) Time-conversion and (b) Arrhenius plot for uncatalyzed lignite-CO2 gasification 3.2. Effect of temperature and catalyst loading The addition of K2CO3 dramatically increased carbon conversion as shown in Fig. 2. At 600°C, the presence of K2CO3 at 5% wt loading increased carbon conversion by 45% which signifies the positive effect of the catalyst. In addition, it is worth noting that at 800°C and 900°C, complete conversion was attained for the same gasification time and sample weight considered.
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a
b
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1 900°C
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Figure 2. Time-conversion plot for catalyzed lignite-CO2 gasification at various temperature and catalyst loading: (a) 5%, (b) 10% and (c) 15% wt loading K2CO3 To provide quantitative measure of the effect of the catalyst on the gasification reaction, Fig. 3 shows the gasification enhancement factor evaluated as the ratio of the reaction constant of the catalyzed reaction to that of the uncatalyzed reaction. From this plot, maximum enhancement in gasification rate was observed at 600°C which shows dominant catalytic effect rather than thermal effect. At temperatures higher than 600°C, enhancement in gasification rate was found to increase from 5-6 times that of the uncatalyzed reaction as catalyst loading was increased. As such, increase in the catalyst loading at these temperatures will not increase the rate of gasification reaction to a significant magnitude. One possible explanation for such saturation effect [3] in the reaction is the blocking of carbon pores by the catalyst therefore restricting the access of CO2.
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Rate enhancement factor, kcat/kuncat (-)
27 15% Loading 10% Loading 5% Loading
24 21 18 15 12 9 6 3 600
700
800
900
Gasification temperature, T (oC)
Figure 3. Rate enhancement factor at different temperature and catalyst loading In terms of the ability of the catalyst to lower the activation energy of the gasification reaction, Fig. 4 shows the Arrhenius plots of the gasification reaction with and without the catalyst. From this plot, the activation energies of the gasification reactions with 5%, 10% and 15% wt loading of K2CO3 was found to be 132.90 kJ-mol-1, 124.88 kJ-mol-1 and 120.04 kJ-mol-1, respectively. 5 4 3
ln k
2 1 0 15% Loading 10% Loading 5% Loading Uncatalyzed
(1) (2) (3) 0.8
0.9
1
1.1
1.2
1000/T (K-1)
Figure 4. Arrhenius plots of gasification reactions 3.3. Effect of catalyst addition method In the previous runs, physical mixing was used to load the lignite samples with the catalyst due to its simplicity. To evaluate the effect of catalyst addition method, impregnation method was used to load 5% wt K2CO3 to the lignite sample. As shown in Fig. 5, reaction constants obtained from physically mixed and impregnated samples showed no significant difference with a square value of correlation index of 0.9970. Such observation is consistent with previous studies [9,17-19] wherein K2CO3 exhibited good mobility and proven to be effective whether loaded to coal via physical mixing or impregnation.
6
90
-1
kphysical mixing (hr )
80
5% loading
70
10% loading
60
15% loading
900°C
50 40 30
800°C
20 10
700°C
0
600°C
-10 -10 0
10 20 30 40 50 60 70 80 90
kimpregnation (hr-1)
Figure 5. Comparison of reaction constants for lignite sample physically mixed and impregnated with 5% wt loading of K2CO3 3.4. Effect of varying CO2 partial pressure For the variation of partial pressure of CO2 in a mixture of N2-CO2, Fig. 6 shows timeconversion plots for lignite gasification with 5% wt loading of K2CO3 at various temperatures. As expected, the subsequent increase in the concentration of the gasifying agent increased carbon conversion and hence the rate of gasification reaction. This positive effect in the gasification rate can be explained by the reduction of the rate of volatilization of K2CO3 in a N2-CO2 environment. Such observation was observed from a thermal stability study of K2CO3 near its melting point [11]. In this study, it was observed that the rate of volatilization of K2CO3 in pure N2 was nearly four times greater than the rate under pure CO2 environment. Therefore, the presence of increasing concentration of CO2 favored the backward reaction of the reversible decomposition of K2CO3. The activation energy of the reactions with varying CO2 partial pressure was found to be in the range of 132.7 ± 4.3 kJ-mol–1. Values obtained have relatively small deviation since activation energy is mainly a function of temperature and not concentration dependent.
a
b 0.80 atm CO2-0.20 atm N2 0.60 atm CO2-0.40 atm N2 0.40 atm CO2 - 0.60 atm N2 0.20 atm CO2 - 0.80 atm N2
0.8
Carbon Conversion, X (-)
Carbon Conversion, X (-)
1
0.6 0.4 0.2 0
1 0.80 atm CO2-0.20 atm N2 0.60 atm CO2-0.40 atm N2 0.40 atm CO2 - 0.60 atm N2 0.20 atm CO2 - 0.80 atm N2
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1
Carbon Conversion, X (-)
c
0.8 0.6 0.4 0.80 atm CO2-0.20 atm N2 0.60 atm CO2-0.40 atm N2 0.40 atm CO2 - 0.60 atm N2 0.20 atm CO2 - 0.80 atm N2
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0
1
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Dimensional gasification time, t/t10 min (-)
Dimensionless gasification time, t/t10 min (-)
Figure 6. Time-conversion plots for lignite gasification at various CO2 partial pressures and gasification temperatures: (a) 600°C, (a) 700°C, (a) 800°C and (a) 900°C 3.5. Recycling of catalyst As shown in Fig. 7, the first re-use of the catalyst reduced the gasification rate by 60% and the succeeding recycle runs resulted to an average of 20% reduction in gasification rate. Decrease in rate may be attributed to the hindered diffusion of the catalyst to the coal surface as a result of the accumulation of ash particle and inefficient mixing of coal and catalyst. Another reason for deactivation of the catalyst is the possible reaction with compounds present in the ash [6,10,20]. Whether deactivation is physical or chemical in nature, recycle tests showed that K2CO3 present in the ash residue still possess some catalytic activity and can be used to some extent to enhance the rate of lignite-CO2 gasification. Catalyzed Reaction (5% K2CO3) 1st Recycle 2nd Recycle 3rd Recycle 4th Recycle 5th Recycle 6th Recycle Uncatalyzed
0.6
7 6
Catalyzed (5% K2CO3)
-1
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Carbon Conversion, X (-)
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1
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5 4 3 2
Uncatalyzed
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Dimensionless gasification time, t/t30 min (-)
1
0 1
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3
4
5
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Reuse number
Figure 7. Plots of (a) carbon conversion and (b) reaction rate constants for gasification reactions with catalyst recycling 3.6. Kinetic modeling of catalytic lignite-CO2 gasification In the evaluation of kinetic parameters, several gas-solid reaction models were used. To evaluate which model best simulates the catalytic gasification reactions, goodness of fit was determined based on the square values of correlation index, R2. The validity of the models based on this parameter is shown in Fig. 8. From this figure, the extended 8
(EMVM) and modified (MVM) volumetric model and the random pore model was proven to correlate the gasification reactions at all temperatures. However, the simple models – shrinking core and homogeneous model – were observed to show goodness of fit at low temperatures. 600°C
0.98 0.96 0.94 0.92 0.90
EMVM
MVM
RPM
SCM
700°C
1.00
Square value of correlation 2 index, R
Square value of correlation 2 index, R
1.00
0.98 0.96 0.94 0.92 0.90
HM
EMVM
Gas-solid reaction models
800°C
0.98 0.96 0.94 0.92 0.90
EMVM
MVM
RPM
SCM
Gas-solid reaction models
RPM
SCM
HM
HM
900°C
1.00
Square value of correlation 2 index, R
Square value of correlation 2 index, R
1.00
MVM
Gas-solid reaction models
0.98 0.96 0.94 0.92 0.90
EMVM
MVM
RPM
SCM
HM
Gas-solid reaction models
Figure 8. Square value of correlation index (R2) for modeling catalytic of lignite-CO2 gasification using various gas-solid reaction models at different temperatures 4. Conclusions The catalytic activity of K2CO3 was proven to enhance gasification rate and lowering the gasification temperature to 800°C for the same given gasification time and sample weight. Increase in catalyst loading above 5% wt and addition of catalyst by physical mixing or impregnation showed no significant effect on enhancing gasification rate. Enhancement in gasification rate was observed to range from 10-25 times at 600°C while between 5-6 times at higher temperature. Increasing CO2 partial pressure results to increase in gasification rate due to reduced volatilization of the catalyst in CO2 environment. The extended modified volumetric model showed goodness of fit in all gasification reactions.
Acknowledgement This work was supported by Energy Efficiency and Resources R&D program (2009T100100675) under the Ministry of Knowledge Economy, Republic of Korea and SK Energy Co. Ltd.
9
References [1] Ye DP, Agnew JB, Zhang DK. Gasification of a South Australian low-rank coal with CO2 and steam: kinetics and reactivity studies. Fuel 1998;77:1209-19. [2] Beamish BB, Shaw KJ, Rodgers KA, Newman J. Thermogravimetric determination of the carbon dioxide reactivity of char from some New Zealand coals and its association with the inorganic geochemistry of the parent coal. Fuel Process Technol. 1998;53:243-53. [3] Li S, Cheng Y. Catalytic gasification of gas-coal char in CO2. Fuel 1995;74:456-8. [4] Sun Q, Li W, Chen H, Li B. The CO2-gasification and kinetics of Shenmu maceral chars with and without catalyst. Fuel 2004;83:1787-93. [5] Yeboah YD, Xu Y, Sheth A, Godavarty A, Agrawal PK. Catalytic gasification of coal using eutectic salts: identification of eutectics. Carbon 2003;41:203-14. [6] Wang J, Sakanishi K, Saito I, Takarada T, Morishita K. High-Yield Hydrogen Production by Steam Gasification of HyperCoal (Ash-Free Coal Extract) with Potassium Carbonate: Comparison with Raw Coal. Energy Fuels 2005;19:2114-20. [7] Wang J, Jiang M, Yao Y, Zhang Y, Cao J. Steam gasification of coal char catalyzed by K2CO3 for enhanced production of hydrogen without formation of methane. Fuel 2009;88:1572-9. [8] Wang J, Yao Y, Cao J, Jiang M. Enhanced catalysis of K2CO3 for steam gasification of coal char by using Ca(OH)2 in char preparation. Fuel 2010;89:310-7. [9] Sharma A, Takanohashi T, Saito I. Effect of catalyst addition on gasification reactivity of HyperCoal and coal with steam at 775-700 °C. Fuel 2008;87:2686-90. [10] Sharma A, Takanohashi T, Morishita K, Takarada T, Saito I. Low temperature catalytic steam gasification of HyperCoal to produce H2 and synthesis gas. Fuel. 2008;87:491-7. [11] Lehman RL, Gentry JS, Glumac NG. Thermal stability of potassium carbonate near its melting point. Thermochim Acta 1998;316:1-9. [12] Jaffri GR, Zhang JY. Catalytic gasification of Fujian anthracite in CO2 with black liquor by thermogravimetry. J Fuel Chem Technol 2007;35:129-35. [13] Wen CY. Noncatalytic heterogeneous solid fluid reaction models. Ind End Chem 1968;60:34-54. [14] Bhatia SK, Perlmutter DD. A random pore model for fluid-solid reactions. I. Isothermal, kinetic control. AIChE J 1980;26:335–379. [15] Kasaoka S, Sakata Y, Tong C. Kinetic evaluation of the reactivity of various coal chars for gasification with carbon dioxide in comparison with steam. Int Chem Eng 1985;25:160-75. [16] Wu Y, Wu S, Gao J. A study on the applicability of kinetic models for Shenfu coal char gasification with CO2 at elevated temperatures. Energies 2009;2:545-55. [17] Wen WY. Mechanisms of alkali metal catalysis in the gasification of coal, char, or graphite. Catal Rev 1980;22:1-28. [18] Wigmans T, Elfring R, Moulijn JA. On the mechanism of the potassium carbonate catalysed gasification of activated carbon: the influence of the catalyst concentration on the reactivity and selectivity at low steam pressures. Carbon 1983;21:1-12. [19] Spiro CL, McKee DW, Kosky PG, Lamby EJ. Observation of alkali catalyst particles during gasification of carbonaceous materials in CO2 and steam. Fuel 1984;63:686-91. [20] Formella K, Leonhardt P, Sulimma A, van Heek KH, Jüntgen H. Interaction of mineral matter in coal with potassium during gasification. Fuel 1986;65:1470-2.
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Oviedo ICCS&T 2011. Extended Abstract
Prediction of Steam Reforming of the Simulated Coke Oven Gas with a Detailed Chemical Kinetic Model K. Norinaga1, R. Sato2, and J.-i. Hayashi1 1 Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan. 2 Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628, Japan *Corresponding author:
[email protected] (A/Prof. Norinaga) Abstract The detailed chemical kinetic modeling with a reaction mechanism consisting of thousands of elementary step like reactions has been successfully applied to predict combustion and pyrolysis characteristics of hydrocarbon fuels. This approach, however, has seldom been used for predicting steam reforming of aromatic hydrocarbons. In this study, the predictive capability of the existing detailed chemical kinetic model was critically evaluated for the thermal conversions of aromatic hydrocarbons in the presence of hydrogen and steam. Published experimental data of steam reforming of simulated coke oven gas (mixture of hydrogen, steam, and an aromatic hydrocarbon such as benzene, toluene, and naphthalene) in a tubular flow reactor (total pressure 160 kPa, 1073-1673 K, and residence time up to 2 s) were used for the kinetic model evaluations. Simulation using the kinetic model that consists of more than 200 chemical species and more than 2000 elementary step like reactions, and a plug flow reactor model precisely reproduced the experimental results for major products such as CO, CO2, CH4 as well as the conversions of source aromatic hydrocarbons. The coke yield is also fairly well predicted when assumed that computationally obtained total yields of polycyclic aromatic hydrocarbons and acetylene, both are the most potential coke precursors, correspond to the experimentally determined coke yields. Besides, influences of hydrogen partial pressure and residence time on the product distributions were also well predicted. 1. Introduction Volatile matter released at the primary stage of pyrolysis and gasification of solid fuels frequently contains tarry components, besides non-condensable gases such as H2, H2O, CO, CO2 and CH4. For using such product gases as synthesis gas for chemicals productions or fuel gas for gas engine or fuel cells, they should preferably be tar-free. This is commonly achieved by quenching to recover the condensable tar and further expensive gas treatment. An exhaustive reforming of tar into dry gas is thus highly desirable to reduce the cost for the separation. It can be found literatures dealing with thermal reforming of tar derived from pyrolysis of biomass1-4 and coal,5-7 as well as tar emitted from metallurgical coke ovens.8-15 Catalytic and non-catalytic approaches to reforming tar have been reported. Since deactivation of the catalyst by coking as well as sulfur/chlorine poisoning due to H2S/HCl contained in the product gas from solid fuels are likely to be unavoidable, catalytic reforming of the tar-containing gas from biomass and coal seems to be not at practical application phase still at fundamental study phase.16, 17 Non-catalytic methods are also being studied, aiming at a more robust reforming technology, and are already included some of the practically developing gasification processes such as the Carbo-V process developed by CHOHREN18 and a fluid bed gasifier coupled with high temperature thermal reformer developed by ENERKEM 19.
1
Oviedo ICCS&T 2011. Extended Abstract
An experimental study on the gas phase reforming characteristics of the model compounds of tar such as benzene, toluene, and naphthalene was reported.8 It should be important to interpret the observations in the reforming of the each aromatic hydrocarbons mechanistically toward deeper understanding of the chemistry and kinetics of the tar reforming. The detailed chemical kinetic approach to developing a reaction mechanism consisting of hundreds or thousands of elementary-like reaction steps is a promising method for elucidating an accurate description of the phenomena that occur in gas phase. To date, numerical simulations with detailed chemical kinetic models have been performed to predict the chemistry and kinetics of combustion,20 as well as the pyrolysis of hydrocarbons.21-25 However, few studies have reported on the steam reforming of aromatic hydrocarbons. In this study, numerical simulations for the steam reforming of aromatic hydrocarbons were conducted using a detailed chemical kinetic model. The kinetic model was evaluated critically by comparing the simulation results with the published experimental results by Jess 8 who made a systematic study on the kinetics of the thermal conversion of aromatic hydrocarbons, such as naphthalene, benzene, and toluene, in the presence of hydrogen and steam using a flow reactor. 2. Kinetic Model and Numerical Simulation A reaction mechanism for hydrocarbon combustion and polycyclic aromatic hydrocarbon growth developed by Richter and Howard26 was used as the primary basis for the kinetic model to simulate the steam reforming of aromatic hydrocarbons. The reaction mechanism consisted of 2216 reactions, including 257 chemical species from the smallest species of hydrogen radical to the largest molecule of coronene. This mechanism successfully predicted characteristics of the COG partial oxidation at a pilot scale test plant.15 The calculations were performed with the PLUG code in the DETCHEM program package (DETCHEMPLUG).27 Boundary conditions necessary for the calculations such as pressure, linear velocity, composition of the feed gas at the reactor inlet were determined from the experimental conditions reported.8 The reaction conditions used in the experiments are summarized in Table 1. Another required input such as a temperature profile along the reactor length was given as a polynomial function fit to the measured temperature profiles reported in the literature. Detailed description of the numerical simulation can also be found elsewhere.28 Table 1 Reaction Conditions for Thermal Conversions of Aromatic Hydrocarbons in a Tubular Flow Reactor a content, vol.% (rest nitrogen)
benzene toluene naphthale ne a
hydrocarbo n 0.6 0.6
hydrogen 40 40
steam 20 20
residence time at 1373 K, s 0.5 1
temperature at isothermal zone (TR), K 1073 - 1673 973 - 1673
0.5
0 – 48(48)
0-32(20)
0.3-2(0.5)
1073 - 1673
Standard conditions in brackets; total pressure 160 kPa
2
Oviedo ICCS&T 2011. Extended Abstract
3. Results and Discussion Figure 1 shows the wall temperature profile in which the quasi isothermal zone temperature (denoted as TR, reference temperature) is 1573 K used for the computations (upper) and computed mole fraction profiles of major components for the thermal conversion of naphthalene along the reactor length. Naphthalene starts to decompose and products such as CH4, CO, and CO2 start to form at the reactor length of 0.15 m at which temperature is around 1400 K. Naphthalene decomposes almost completely at around 0.3 m and little changes in any species’ concentrations occur beyond 0.4 m, most likely due to the temperature drop. Figure 2 compares the conversions of source aromatic hydrocarbons derived from the numerical simulation with those obtained by the experiments as a function of TR. The computationally predicted conversions were calculated based on the mole fraction of each feed hydrocarbon at the reactor outlet (length = 0.5 m). Excellent agreements are obtained for the conversions of these aromatic hydrocarbons. Benzene is a bit more refractory than naphthalene while toluene is most reactive. This trend is traced by the kinetic model perfectly. 1600
‐ , er 1200 u ta re 800 p 400 m et ‐, n o it ca rf el o m
0 0.6 H2
0.5 0.4 0.3 0.2
H2O
0.1 0.0 0.012
‐ 0.010 , n 0.008 o it ca 0.006 rf el 0.004 o 0.002 m 0.000 0.0
CH4
CO
naphthalene
CO2
0.1
0.2
0.3
0.4
0.5
distance from reactor inlet, m Figure 1. Temperature profile used for the numerical simulation (upper) and computationally obtained mole fraction profiles of major components (middle and lower) in thermal conversion of naphthalene in the presence of hydrogen and steam along the reactor flow direction. Velocity, temperature, and composition of the gas at reactor inlet are 0.086 m/s, 571 K, and naphthalene 0.5 vol%; H2 20 vol.%; H2O 48 vol% (rest nitrogen), respectively.
3
Oviedo ICCS&T 2011. Extended Abstract 100 80
toluene
, % 60 n io sr ev 40 n o c
naphthalene benzene
20 0 900
1100
1300
1500
1700
temperature (TR), K
Figure 2. Numerically (lines) and experimentally (symbols) derived conversions in thermal conversions of aromatic hydrocarbons (benzene, toluene, and naphthalene) in the presence of hydrogen and steam as a function of TR. Residence time 0.5 s (naphthalene and benzene) and 1.0 s (toluene) at TR = 1373 K; the experiments were conducted with a constant volume rate of the feed gas, therefore at higher and lower temperatures the residence time is slightly shorter and longer respectively.
The product distribution obtained at the steam reforming experiment of naphthalene, is shown in Figures 3. The computationally obtained product yields are also drawn for evaluating the kinetic model critically. For the naphthalene steam reforming, yields of CH4 and total yields of CO and CO2 are excellently reproduced by the present simulation. The yields of the other major products such as benzene and soot (plus condensed products) are also predicted well, although under-predictions are observed in benzene yields at around 1500 K and soot yields at temperature higher than 1500 K. Actually it is difficult to evaluate the soot yield based on the numerical simulation because the kinetic model considers chemical reactions and species in gas-phase. Here it is assumed that the total yield of thirty-three polycyclic aromatic hydrocarbons (PAHs), which are included in the kinetic model and are the most potential coke precursors, corresponds to the experimentally determined yields of coke. 100
‐% C , s ld iey t c u d o r p d n a e n el a h t h p a n la u id se r
50
80 60
40
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0 30
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5
0 80 60
0 40
soot and condensed products
30
40
20
20
10
0 900
1100
1300
1500
1700
0 900
C2 hydrocarbons
1100
1300
1500
1700
temperature (TR), K Figure 3. Numerically (lines) and experimentally (symbols) derived product distributions in thermal conversion of naphthalene in the presence of hydrogen and steam as a function of TR.
4
Oviedo ICCS&T 2011. Extended Abstract
To understand why the kinetic model under-predict the yields of C2 hydrocarbons and organic cracking products, the yield of each component involved in the organic cracking products was examined. Figure 4 compares the yields of CH4, C2H2, C2H4, and C2H6 determined experimentally with those determined numerically for the benzene conversion. The yields of CH4 and C2H4 are excellently predicted and the C2H6 yield is fairly predicted, whereas the C2H2 yield is significantly over-predicted. This indicates that the gaps found in the yields of C2 hydrocarbons in the experiment of naphthalene steam reforming (Figure 3), and the gaps found in the yield of organic cracking products in the benzene steam reforming are attributed to the over-predicted C2H2 yield. C2H2 is one of the most potential coke precursors and easily form solid carbon deposited on the reactor wall29 and soot.30 In the flow reactor experiments, C2H2 should be consumed by these gas-solid reactions extensively and does not survive as much as predicted by the present numerical simulation with the chemical kinetic model which includes only homogeneous gas phase reactions. This augment is supported by the results demonstrated in Figure 5 which shows soot yields in the steam reforming of naphthalene (left) and benzene (right). Two types of predicted yields are drawn; the dashed line is obtained by assuming that soot yields correspond to the total yields of the PAHs while the solid line is obtained by assuming that the soot yields correspond to the C2H2 yields plus the total PAHs yields. The soot yields are significantly under-predicted when the total yields of PAHs account for the soot yields. But once the C2H2 yield is added to the total PAHs yields, the resulted predicted values are very similar with the experimental yields of soot. This result implies that the prediction of the soot yield is possible with the present kinetic model, which involves no carbon deposition chemistry though, when we assumed that the PAHs as well as C2H2 forms soot quickly and their yields correspond to the experimentally determined soot yields.
50 ‐% CH4 C ,s 40 tc 30 u d 20 ro p g 10 in kc 0 ar 20 c ci 15 C2H4 n ag r 10 o f o s 5 d le iy 0 900 1100
50
C2H2
40 30 20 10 0 5 4
C2H6
3 2 1 0 1300
1500
1700
900
1100
1300
1500
1700
temperature (TR), K Figure 4. Numerically (lines) and experimentally (symbols) derived yields of organic cracking products in thermal conversion of benzene in the presence of hydrogen and steam as a function of TR.
5
Oviedo ICCS&T 2011. Extended Abstract
30
80
naphthalene
benzene
% 60 ‐ C , ld ei 40 y t o o s 20 0 900
20
10
1100
1300
1500
0 1700 900
1100
1300
1500
1700
temperature (TR), K temperature (T R), K Figure 5. Numerically (lines) and experimentally (symbols) derived yields of soot in thermal conversions of naphthalene (right) and benzene (left) in the presence of hydrogen and steam as a function of TR. Dashed lines are obtained by assuming polycyclic aromatic hydrocarbons to be soot and condensed products, while solid lines are obtained by assuming acetylene besides polycyclic aromatic hydrocarbons to be soot and condensed products.
Figure 6 shows conversion and soot yield in thermal conversion of naphthalene at TR = 1373 K, and at varying residence time and hydrogen volume percent in the feed gas. Influence of hydrogen in inhibiting naphthalene conversion and soot formation is obvious and is well reproduced by the numerical simulation. The predictions are better when more than 12 % of hydrogen is included in the feed gas, while the model underpredicts naphthalene conversion and soot yield at the lower hydrogen volume percent. Ignorance of direct conversion of naphthalene into soot which is very likely favored at lower hydrogen partial pressure, would lead to the under-predictions of the naphthalene conversion as well as the soot formation, and thus contribute to the gaps between the experiments and the computations. Effect of temperature on the soot formation kinetics is examined in Figure 7. Experimental values for the soot yield at TR = 1473 K exhibit maxima at residence time around 0.8 s, and those at 1573 K also exhibit a maximum value at around 0.4 s. The decrease in the soot yield at longer residence time is attributable to the soot gasification by steam. These trends are well captured by the numerical simulation. Experimental values at 1673 K show no maximum, but the computations suggest that soot yield has a peak at around 0.1 s. These results imply that soot formation is inevitable and soot is a primary product regardless of the temperature in thermal conversion of naphthalene.
6
Oviedo ICCS&T 2011. Extended Abstract 100
f o n o is re v n o c
80
0 vol.% H2
% , e n el 60 a h t 40 h p a n
6 12
20
48
0 100
% ‐ C , d le iy t o o s
80
0 vol.% H2
60
6 40
12 48
20
0 0.0
0.2
0.4
0.6
0.8
1.0
residence time, s Figure 6. Influences of hydrogen and residence time on the conversion of naphthalene and the yields of soot. Reaction temperature 1373 K. Lines are numerically obtained, whereas symbols are experimental values. 100
1473 K
80 60 40 20 0 100
% ‐ C , ld ei y t o o s
1573 K
80 60 40 20 0 100
1673 K
80 60 40 20 0 0.0
0.5
1.0
1.5
2.0
residence time, s Figure 7. Yield of soot as a function of residence time and TR in thermal conversion of naphthalene: numerically predicted curves and experimental values (symbols).
4. Conclusions A detailed chemical kinetic modeling approach was first applied to simulate the thermal conversions of aromatic hydrocarbons including naphthalene, benzene and toluene, in the presence of hydrogen and steam. The critical evaluation of the kinetic model
7
Oviedo ICCS&T 2011. Extended Abstract
proposed by Richer and Howard26 was conducted by comparing the computationally obtained values with published experimental data of steam reforming of simulated coke oven gas in a tubular flow reactor.8 It was found that the numerical simulation using the kinetic model that consists of more than 200 chemical species and more than 2000 elementary step like reactions, and a plug flow reactor model precisely reproduced the experimental results for major products such as CO, CO2, CH4 as well as the conversions of source aromatic hydrocarbons. The soot yield is also fairly well predicted when assumed that the computationally obtained total yields of polycyclic aromatic hydrocarbons and acetylene, both are the most potential soot precursors, correspond to the experimentally determined soot yields. Besides, influences of hydrogen partial pressure and residence time on the product distributions were also well predicted. Acknowledgement. The authors are grateful to New Energy and Industrial Technology Development Organization (NEDO) for their financial supports to this study. References 1. Caballero, M. A.; Aznar, M. P.; Gil, J.; Martin, J. A.; Frances, E.; Corella, J. Ind. Eng.Chem. Res. 1997, 36 (12), 5227-5239. 2. Corella, J.; Toledo, J. M.; Aznar, M. P. Ind. Eng. Chem. Res. 2002, 41 (14), 33513356. 3. Corella, J.; Caballero, M. A.; Aznar, M. P.; Brage, C. Ind. Eng. Chem. Res. 2003, 42 (13), 3001-3011. 4. Hosokai, S.; Kishimoto, K.; Norinaga, K.; Li, C. Z.; Hayashi, J. I. Energy Fuels 2010, 24 (5), 2900-2909. 5. Hayashi, J. I.; Takahashi, H.; Iwatsuki, M.; Essaki, K.; Tsutsumi, A.; Chiba, T. Fuel 2000, 79 (3-4), 439-447. 6. Hayashi, J. I.; Iwatsuki, M.; Morishita, K.; Tsutsumi, A.; Li, C. Z.; Chiba, T. Fuel 2002, 81 (15), 1977-1987. 7. Matsuhara, T.; Hosokai, S.; Norinaga, K.; Matsuoka, K.; Li, C. Z.; Hayashi, J. I. Energy Fuels 24 (1), 76-83. 8. Jess, A. Fuel 1996, 75 (12), 1441-1448. 9. Miura, K.; Kawase, M.; Nakagawa, H.; Ashida, R.; Nakai, T.; Ishikawa, T. J. Chem. Eng. Jpn. 2003, 36 (7), 735-741. 10. Hashimoto, T.; Onozaki, M. J. Jpn. Inst. Energy 2006, 85 (5), 364-370. 11. Hongwei, C.; Yuwen, Z.; Xionggang, L.; Weizhong, D.; Qian, L. Energy Fuels 2009, 23 (1), 414-421. 12. Cheng, H.; Lu, X.; Liu, X.; Zhang, Y.; Ding, W. J. Natural Gas Chem. 2009, 18 (4), 467-473. 13. Cheng, H.; Lu, X.; Zhang, Y.; Ding, W. Energy Fuels 2009, 23 (6), 3119-3125. 14. Norinaga, K.; Hayashi, J. Energy Fuels 2010, 24, 165-172. 15. Norinaga, K.; Yatabe, H.; Matsuoka, M.; Hayashi, J. I. Ind. Eng. Chem. Res. 2010, 49 (21), 10565-10571. 16. Hepola, J.; Simell, P. Applied Cat. B-Environmental 1997, 14 (3-4), 305-321. 17. Tomishige, K.; Miyazawa, T.; Kimura, T.; Kunimori, K.; Koizumi, N.; Yamada, M. Applied Cat. B: Environmental 2005, 60 (3-4), 299-307. 18. Blades, T. Industrial Bioprocessing 2007, 29 (5), 9-10. 19. Chornet, E. In Converting non-homogeneous blomass residues into alcohols, 8th
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Oviedo ICCS&T 2011. Extended Abstract
World Congress of Chemical Engineering: Incorporating the 59th Canadian Chemical Engineering Conference and the 24th Interamerican Congress of Chemical Engineering, Montreal, QC, 2009; Montreal, QC, 2009. 20. Warnatz, J.; Maas, U.; Dibble, R. W., Combustion; 3rd Edition. Springer-Verlag: Heidelberg, New York, 2000. 21. Dean, A. M. J. Phys. Chem. 1990, 94 (4), 1432-1439. 22. Dagaut, P.; Cathonnet, M.; Boettner, J.-C. Int. J. Chem. Kinet. 1992, 24 (9), 813837. 23. Sheng, C. Y.; Dean, A. M. J. Phys. Chem. A 2004, 108 (17), 3772-3783. 24. Ziegler, I.; Fournet, R.; Marquaire, P. M. J. Anal. Applied Pyro. 2005, 73 (2), 212230. 25. Norinaga, K.; Deutschmann, O. Ind. Eng. Chem. Res. 2007, 46 (11), 3547-3557. 26. Richter, H.; Howard, J. B. Phys. Chem.Chem.Phys. 2002, 4 (11), 2038-2055. 27. Deutschmann, O.; Tischer, S.; Kleditzsch, S.; Janardhanan, V.; Correa, C.; Chatterjee, D.; Warnatz, J. DETCHEM V2.0, http://www.detchem.com. 28. Norinaga, K.; Janardhanan, V. M.; Deutschmann, O. Int. J. Chem. Kinet. 2008, 40 (4), 199-208. 29. Norinaga, K.; Hüttinger, K. J. Carbon 2003, 41 (8), 1509-1514. 30. Richter, H.; Howard, J. B. Prog. Energy Combust. Sci. 2000, 26 (4), 565-608.
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Oviedo ICCS&T 2011. Extended Abstract
Invention of Quantitative Method of Char and Soot to Clarify Soot Production and Reaction Behavior in Coal Gasification S. Umemoto*, S. Kajitani and S. Hara Energy Engineering Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 2-6-1 Nagasaka Yokosuka, Kanagawa 240-0196, Japan *Corresponding author:
[email protected] Abstract Coal gasification is one of the key technologies for utilization of coal. Coal gasification mainly consists of coal pyrolysis, char gasification and gas phase (including volatile matters) reactions. “Soot” is a fine solid carbon particle produced from volatile matter decomposition. Soot has lower gasification reactivity than char. However, there is no proper quantitative method of soot because char and soot are mixed together in the solid products from coal gasification, and it is difficult to identify soot in the mixture by the conventional methods. In this study, a novel quantitative method of char and soot utilizing a laser diffraction particle size analyzer was developed. Moreover, coal gasification experiments were performed using a pressurized drop tube furnace (PDTF). The yield of soot with low gasification reactivity did not decrease, while char was promptly consumed by CO2 gasification. Hence, the carbon conversion ratio increased initially, but was kept around 0.8 even at 1673 K.
1. Introduction Integrated coal gasification combined cycle (IGCC) plants have been developed worldwide to use coal more efficiently and cleanly. There are many types of gasifiers in the world. Most of them are oxygen-blown entrained flow type. In Japan, an air-blown entrained flow gasifier has been developed by CRIEPI and Mitsubishi Heavy Industries, Ltd [1]. 250 MW IGCC power plant using the air-blown gasifier was constructed and is in operation [2]. Furthermore, CRIEPI has proposed an “oxy-fuel IGCC system with CO2 recirculation for CO2 capture”, which includes an O2/CO2 blown gasifier [3]. In any type of a gasifier, coal gasification consists of coal pyrolysis, char gasification and gas phase (including volatile matters) reactions. Char gasification is believed to control the overall conversion rate. Therefore, a great number of papers concerning to char gasification have been published [4–6]. On the other hand, another type of solid carbon,
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Oviedo ICCS&T 2011. Extended Abstract
“soot” (coke) is produced from the volatile matter decomposition at high temperature above 1200 K. Besides, soot prepared from coal pyrolysis in inert gas has lower gasification reactivity than char [7, 8]. However, the amount of soot produced in coal gasification has never been quantified in any experiment, because char and soot are mixed together in the solid products from coal gasification and it is difficult to identify soot in the mixture by the conventional methods. In this study, a novel char and soot quantitative method was proposed. Moreover, coal gasification tests with CO2 utilizing a pressurized drop tube furnace (PDTF) were conducted to clarify the production and the gasification behavior of soot.
2. Experimental section Table 1 shows the properties of coals (NL coal from Australia, DT coal from China, MN coal from Indonesia and TN coal from Indonesia). Table 1 Ultimate and proximate analyses of coals used Ultimate analysis (wt%, d.a.f.)
Proximate analysis (wt%, db
C
H
N
O(diff.)
FC
VM
Ash
NL
82.5
5.1
1.4
11.0
57.4
28.7
13.8
DT
83.2
4.3
0.3
12.2
61.5
27.3
11.2
MN
81.1
5.7
2.0
11.2
51.0
40.7
8.4
TN
71.3
5.7
1.6
21.4
43.2
47.8
9.0
Coal
A drop tube furnace (DTF) shown in Figure 1 was used for coal pyrolysis tests and gasification tests. Coal pyrolysis tests were conducted using DTF without the sampling probe at ambient pressure and 1673 K to examine the char and soot quantitative method. Residence time was set at about 3 s. Coarse particles were trapped in the ash pot at bottom of furnace. On the other hand, fine particles were carried by gas and caught in the trapping bottle and the cartridge filter. The ash pot samples are almost char particles because char particles are courser than soot particles. The trapping bottle samples include both of char particles and soot particles. And the cartridge filter caught almost only soot particles. The ash pot samples were used as the char samples and the cartridge filter samples were used as the soot samples for the examination of the char and soot quantitative method.
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Oviedo ICCS&T 2011. Extended Abstract
Coal gasification tests with CO2 were also
N2
conducted using pressurized DTF with the
Particle feeder
sampling probe to clarify the production and reaction behavior of soot. The residence time
Reaction tube (I.D. 50 mm)
was controlled by traversing the sampling probe. The temperature was 1473 to 1673 K; the furnace pressure was 0.5 MPa; the partial pressure of CO2 was 0.05 MPa (N2 balance);
H2O
Heater Cartridge filter
N2 Air Ash pot
and total oxygen to carbon ratio (O/C
Sampling probe
[mol/mol]) was 1.4.
Trapping bottle Sampling filter
Figure 1 Schematic of the Drop Tube Furnace (DTF) 3. Results and Discussion 3.1 Char and soot quantitative method using a laser diffraction particle size analyzer Figure 2 shows the particle size distribution of the samples prepared by NL coal pyrolysis. The char sample, the soot sample and their mixtures are measured by a laser
Laser diffraction intensity [–]
cummulative passing [vol%]
Summation = index I
100 Soot 80
Char 20%
60 40
50% 40% 60%
Char
20 0 –1 10
80% 0
1
2
10 10 10 Particle size [μ m]
0.016 Char 80% 0.012 0.008
50% 0% (Soot)
0.004 0 0
3
10
Figure 2 Particle size distribution of
36
0.02
10 20 30 40 50 60 70 Detection element number [–]
Figure 3 Laser diffraction intensity used for determination of index I (NL coal)
char, soot and their mixture (NL coal) diffraction particle size analyzer (SALD-2200, Shimadzu). The distribution of the soot sample was completely different from the distribution of the char sample. However, the
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Oviedo ICCS&T 2011. Extended Abstract
distribution did not change proportionately with changes in the char mixing ratio. For example, the percentage of cumulative distribution under 10 μm reached 90% for the sample with 20% of the char mixing ratio, whereas reached only 30% for the sample with 40% of the char mixing ratio. Therefore, the raw data of the laser diffraction measurements were proposed to utilize for the soot quantitative method. Figure 3 shows the laser diffraction intensity data used for calculation of the particle size distribution shown in Figure 2. The detection elements which have the number under 36 did not detect any intensity for the soot sample (the char mixing ratio = 0%). The numbers of the detection elements mean the location of the element and the smaller number elements are located nearer to the center. In the laser diffraction particle size analyzer, the first peak of the laser diffraction intensity corresponds to the particle size. The peak for smaller particle shifts to the side where the detection element number is larger. The detection elements which have the number under 36 were not able to detect any Soot mixing ratio[%]
diffraction intensity for pure soot sample because the intensity too low. 100 80 60was 40 20 Thus, 0 the 0.5
index I, which was defined as the summation of normalized intensity of the detection index I [–]
NL coal 0.4 DTthe coal elements from number 0 to 36, was proposed to evaluate char and soot mixing ratio. MN coal Figure 4 shows the relationship between the 0.3 index I and char mixing ratio for the calibration curve 0.2 0.1 0 0
20 40 60 80 Char mixing ratio [%]
100
Figure 4 Calibration curve of index I
1
Carbon conversion, Yield [–]
Carbon conversion, Yield [–]
v.s. Char mixing ratio (1) 1473 K
0.8
Carbon conversion
0.6 0.4
Char
0.2 Soot 0 0
1
2 3 4 5 Residence time [s]
6
1
(2) 1673 K
0.8 Carbon conversion
0.6 0.4
Char Soot
0.2 0 0
1
2 3 4 5 Residence time [s]
6
Figure 5 Carbon conversion, char yield and soot yield obtained from CO2 gasification using PDTF (TN coal, initial CO2 0.05 MPa) (1) 1473 K (2) 1673 K
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Oviedo ICCS&T 2011. Extended Abstract
from NL coal, DT coal and MN coal. The index I increased monotonously with the char mixing ratio for any coals. Using the calibration curve drawn in Figure 4, the char and the soot mixing ratio in solid products of coal gasification can be quantified.
3.2 Results of the coal gasification test using DTF Figure 5 shows the carbon conversion, the char yield and the soot yield in TN coal gasification with CO2 at 1473 K and 1673 K. The carbon conversion increased as the temperature increased. However, the carbon conversion did not reach 1.0 and was still kept around 0.8 even at 1673 K and 3 seconds of residence time. The soot yield which was quantified by the proposed method was about 0.2 at any temperature. Furthermore, the soot yield did not decrease very much as residence time advance, while the char yield decreased by CO2 gasification. Consequently, the carbon conversion increased initially because of the char gasification but did not reach 1.0 because of the soot remaining.
4. Conclusions A novel char and soot quantitative method utilizing a laser diffraction particle size analyzer was developed. Coal gasification tests were performed using a pressurized drop tube furnace. The yield of soot with low reactivity did not decrease while char was promptly consumed by CO2 gasification. Hence, the carbon conversion ratio increased initially, but was kept around 0.8 even at 1673 K.
Acknowledgement. A part of the presented work was supported by New Energy and Industrial Technology Development Organization (NEDO) program “Innovative zero-emission coal gasification power generation project”, P08020.
References [1] Inumaru, J. A 2T/D pressurized two-stage entrained bed coal gasifier and test resutls. Proceedings of International Conference on Coal Science. 1989; 2: 297–300 [2] Watanabe T. Results and estimations of the 5,000 hour durability test at the Nakoso air blown IGCC plant (including other activities). presented at Gasification Technologies Conference 2010, Washington, D.C., 2010 [3] Oki Y, Inumaru J, Hara S, Kobayashi M, Watanabe H, Umemoto S, et al. Development of
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Oviedo ICCS&T 2011. Extended Abstract oxy-fuel IGCC system with CO2 recirculation for CO2 capture. Proc. Clearwater Coal Conference, 2011; 4: 1066–1073 [4] Miura K, Hashimoto K, Silveston P. Factors affecting the reactivity of coal chars during gasification, and indices representing reactivity. Fuel, 1989; 68: 1461–1475 [5] Kajitani S, Suzuki N, Ashizawa M, Hara S. CO2 gasification rate analysis of coal char in entrained flow coal gasifier. Fuel, 2006; 85: 163–169 [6] Roberts D, Harris D. Char gasification in mixtures of CO2 and H2O: Competition and inhibition. Fuel, 2007; 86: 2672–2678 [7] Miura K, Nakagawa H, Nakai S, Kajitani S. Analysis of gasification reaction of coke formed using a miniature tubing-bomb reactor and a pressurized drop tube furnace at high pressure and high temperature. Chemical Engineering Science, 2004; 59: 5261–5268. [8] Kajitani S, Nakagawa H, Miura K, Hara S. Study on coal pyrolysis property in pressurized entrained flow coal gasifier - Rapid pyrolysis property with pressurized drop tube furnace -. Proceedings of International Conference on Coal Science, Okinawa. 2005: 3D10
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NEW CANDLE PROTOTYPE FOR HOT GAS FILTRATION INDUSTRIAL APPLICATIONS M. Rodríguez-Galán1, M. Lupión1*, B. Alonso-Fariñas1, J. Martínez-Fernández2. 1
Department of Chemical and Environmental Engineering, ETS Ingenieros-University of Seville (Spain) 2 Departamento de Física de la Materia Condensada, Physics Faculty-University of Seville (Spain)
Abstract The improvement of gas cleaning technologies is crucial for the establishment of advanced clean power generation coal-based technologies such as Integrated Gasification Combined Cycle (IGCC) or Pressurized Fluidized Bed Combustion (PFBC) which need high performance of the syngas clean-up process. New materials and advanced operating strategies at higher temperatures that could give lower energy penalty are required to be developed. A large scale high temperature filtration pilot is currently in operation at the ETSI University of Seville, with financial support from the European Commission and the Spanish Ministry of the Environment. This pilot plant allows testing different filters and pulses cleaning strategies using real coal ash under an extensive range of operating conditions such as temperature and pressure. The aim of the on-going research is the evaluation of the alternatives for hot gas filtration technologies and the optimization of the operation and performance of the filtering elements. A new experimental campaign has been carried out to test a new type of silicon carbide candle. The prototype is fabricated from pyrolyzed wood and other materials as result of a novel environment friendly patented process (BioSiC®). This process provides good thermo-mechanical, chemical and structural stability in an extensive range of temperatures. During the testing campaign, main parameters for the characterization of the prototype have been studied such as filtration velocity, permeability, porosity, pressure drop across the filter, cleaning pulse interval, baseline pressure drop, filtration efficiency and durability of the filter. Optimal operating conditions and optimal pulse cleaning strategies for filter elements have been also determined. Additionally, a model to predict the behaviour of the elements under diverse operating conditions has been determined.
1
In general, the experimental results showed that the prototypes are suitable for industrial applications under the operating conditions indicated in this study, typical of those needed for hot gas cleaning of coal combustion and gasification flue gases. However, the analysis of the results shows possible improvements in the performance of the elements that should be faced in the next experimental campaign. This paper describes the main characteristics of the new material developed, and the results obtained from experimentation, as well as major conclusions extracted from the analysis. 1.
Introduction
Commercial ceramic filters type candles made of silicon carbide (SiC) are commonly used in industrial facilities for power generation such as coal IGCC Power Plants. Silicon carbide is a relatively new material in technological and industrial applications although it was discovered and manufactured a century ago. Nowadays it is used as a structural material in applications which require hardness, high temperature strength, high thermal conductivity, a low coefficient of thermal expansion and good wear and abrasion resistance [1]. Biomorphic silicon carbide (BioSiC®) is a SiC-based advanced ceramic material, fabricated through a cost effective and environmental friendly process that uses cellulose as its starting point. This material shows excellent thermo-mechanical performance, chemical and structural stability, in a wide interval of temperatures. It is possible to tailor the thermal and electrical properties of these materials to a wide range of values to satisfy device requirements [2]. This paper describes the main characteristics of the new material developed, and the results obtained from an extensive experimental campaign with the goal of characterizing the performance and behaviour of the prototypes developed. Optimal operating conditions and optimal pulse cleaning strategies for filtration applications at high temperature and pressure have been also determined
2.
Experimental section
A large scale high temperature filtration pilot is currently in operation at the ETSI University of Seville. This pilot plant allows testing different filters and pulses cleaning strategies using real coal ash under an extensive range of operating conditions such as 2 * Corresponding author: Tel.: +34954481181; Fax: +34 954461775; E-mail address:
[email protected] tempperature and d pressure. The aim of o the on-gooing researrch is the evaluation e o the of alternnatives for hot gas filtrration techn nologies andd the optimization of thhe operationn and perfoormance of the filteringg elements. The diagram off the pilot is i illustrated in Figuree 1. The faacility is described in detail elsew where [3-6]..
Figure 1: Baasic diagram m of the testt facility The objective of o the testinng campaign n presentedd in this papper is the evaluation e o the of s carbbide candle fabricated from pyroolyzed perfoormance off a new proototype of silicon woodd and otherr materials as result of o a novel environmen e nt friendly patented p prrocess (BioS SiC®). BioS SiC® is a ceellular silicoon carbide material m wiith hierarchical porositty obtained from reacttive infiltrattion of carrbon templaates throughh wood py yrolisis. In this t approaach, a woodd precursor is selectedd among thee many woood species available a coommerciallyy and convverted to carrbon by expposition to high h temperaatures (10000ºC) in an inert atmospphere. The resulting carbon tempplate, whichh retains thhe wood prrecursor's microstructu m ure, is then machined to t near net--shape and melt infiltraated with liiquid Si in vacuum at hightempperatures. Reaction R of Si S and C prroceeds by a solution-rreprecipitaioon mechanism to produuce SiC. Th he final matterial consissts of a SiC skeleton with w a microostructure cllosely resem mbling that of the woood precursorr, with poroosity often filled f residuual Si that can be remooved by acid leaching. Final propperties of thhe material, such as po orosity, poree size and ddistribution, can be taillored by selection of thhe wood precursor. 3
An appropriate selection of physical-chemical properties and geometries suitable for use as a material constituent of BioSiC® ceramic filters has been carried out. Table 1 shows the main characteristics of the BioSiC® material [7]. Table 1: Main characteristics of the BioSiC® material Mechanical Properties at room Temperature Density (g/cm3)
1.1 -2.6
Young modulus (GPa)
25-250
Compressive strength (MPa)
1500
Bending Strength (MPa)
430
Toughness (MPa·m1/2)
3
Dilatation coefficient (1/K)
3.5 · 10-6
Thermal Properties Anisotropic Thermal Conductivity
Variation up to 30%
Tailorable values in a wide range (W/mK)
50 - 120
Electrical Properties Anisotropic Electrical Resistivity
Ratio over 10
Tailorable values in a wide range (cm)
0.02-20
Adjustable dependence with temperature BioSiC® ceramic candles prototypes were designed and manufactured to be tested in the hot filtration pilot facility at ETSI of the University of Seville. Structural and geometric characteristics of prototypes were defined, as well as the conditioning of the filtration facility in order to accommodate the characteristics of the new prototypes. The dimensions of the prototypes are 18 mm outer diameter, 14 mm internal diameter, 225 mm total length with 10 mm neck for the fixation to the supporting plate which holds the elements. The number of filtering elements simultaneously tested was 36 with a total effective area of filtration of 0.43 m2.
4
Fig gure2: BioS SiC® prototyype for testiing in the filtration faciility 2.1
Characteriization testss
characterissation Folloowing the methodolog m gy proposedd in previouus testing campaigns, c tests were done in first placce with the aim of defi fining the test matrix annd the base case, that is, i the deterrmination of o the param meters that ccould influeence on thee performannce of the prototypes p such as thee maximum m filtration velocity, th he minimum m pressure drop acrosss the protottypes, or cleeaning pulse intervals [5][8]. 2.2
Operationnal tests
The aim of thee operationnal tests is the estimaation of thhe influencee of the crritical meters on th he performaance of the prototypes.. Critical paarameters sttudied connnected param to shhort term tesst are: (1) thhe pressure drop acrosss the filterinng element, (2) the cleaning pulsee interval defined d as the t frequen ncy of the cleaning c op peration or the period time betw ween conseccutive cleanning operatiions, (3) thee baseline pressure p drop, which is i the presssure drop im mmediately after cleanning and (4) filtration efficiency e of the elemeent. In relatiion to long g term, thhe durabilityy or deterrioration off the filtering elemennts is invesstigated.
3. Reesults and discussion d 3.1. C Characterization tests 5
Relevant parameters such as the value of the maximum filtration velocity rate compatible with the operation and the residual pressure drop of the “virgin” element among others were determined by means of characterization tests. In Figure 3, the evolution of the pressure drop with filtration velocity for virgin elements and clean gas is shown. It is observed a linear increase of the pressure drop with filtration velocity, as Darcy´s Law indicates [9] [10]. BioSiC Candles. CLEAN FILTER. (7 bar(g), 370 ºC) 2500
2000
Pressure drop (mmwc)
y = 24.555x 2 + 319.12x R² = 0.9981
1500
1000
500
0 2.50
3.00
3.50
4.00
4.50
5.00
Filtration velocity(cm/s)
Figure 3: Virgin element. Pressure drop vs. filtration velocity at 370 ºC The effect of the temperature has been also investigated. Figure 4 shows the evolution of the pressure drop across the prototypes at two levels of temperature, 235 and 370 ºC. It is clear than higher temperatures imply higher values of pressure drop. 2500
Pressure Drop (mm wc)
2000
1500 235 370 1000
500
0 2.50
3.00
3.50 Filtration velocity(cm/s)
4.00
4.50
Figure 4: Virgin element. Pressure drop vs. filtration velocity at two levels of temperature When loaded gas is injected, the operation becomes non-viable at gas velocities above 3cm/s as it is illustrated in Figure 5. During unstable operating conditions there is a rapid increase in the maximum pressure drop as well as a reduction in time between 6
pulses. On the contrary, Figure 6 shows an example of stable operating conditions, where the pressure drop after a cleaning pulse remains at similar levels. 2000
Pressure Drop (mm wc)
1800
1600
1400 Particle concentration: 13 g/Nm3 Filtration velocity: 3.3 cm/s Gas cleaning pressure: 16±0.2 barg
1200
1000
0
500
1000
1500
2000
2500
Time (s)
Figure 5: Unstable operation with gas velocity >3 cm/s 2200
Pressure Drop (mm wc)
2000 1800 1600 1400 Particle concentration: Particle concentration:1313 g/Nm3 g/Nm3 Filtration velocity: Filtration velocity:3.3 2.8cm/s cm/s Gas cleaning Gas cleaningpressure: pressure:16±0.2 16±0.2barg barg
1200 1000 0
500
1000
1500
2000
2500
3000
3500
4000
Time(s)
Figure 6: Stable operation with gas velocity 98 %. Operational parameters and their influence on the performance of the filtering elements have been also identified and analyzed. In particular, the influence of filtration velocity, permeability, porosity, pressure drop across the filter, cleaning pulse interval, baseline pressure drop, filtration efficiency and durability of the filter has been investigated. Optimal operating conditions and optimal pulse cleaning strategies for filter elements have been determined. Figure 7 shows the effect of the cleaning pressure in the evolution of the pressure drop across the prototypes. The graphs show the evolution of the pressure drop for three different values of cleaning pressure: 14 barg, 16 barg and 19 barg.
8
Pressure Drop (mm wc)
2100
1900
1700
1500
Particle concentration: 16.7 g/Nm3 Filtration velocity: 2.7 cm/s Gas cleaning pressure: 14±0.2 barg
1300
1100 0
500
1000
1500
2000
2500
3000
Time (s)
Pressure Drop (mmwc)
2100
1900
1700
1500 Particle concentration: 16.7 g/Nm3 Filtration velocity: 2.7 cm/s Gas cleaning pressure: 16±0.2 barg
1300
1100 0
500
1000
1500
2000
2500
3000
3500
4000
Pressure Drop (mm wc)
Time(s)
Particle concentration: 16.7 g/Nm3 Filtration velocity: 2.7 cm/s Gas cleaning pressure: 19±0.2 barg
2100 1900 1700 1500 1300 1100 0
500
1000
1500
2000
2500
3000
3500
4000
4500
Time (s)
Figure 7: Effect of pressure pulse cleaning of the pressure drop across the prototypes. Cleaning pressure: 14, 16, 19 barg
It is shown that the pressure drop after cleaning is slightly lower at higher cleaning pressures, that is, the interval between cleaning cycles is higher at higher cleaning pressure. While the baseline pressure drop after 19 barg pulses is about 1300 mmwc, this value is around 1400 mmwc and 1500 mmwc when cleaning at 14 and 16 barg respectively. Therefore, it can be concluded that the cleaning pressure has a positive influence in the operation. It must be pointed out though that the cleaning operation at higher pressure results in a faster deterioration of the filtering elements, and higher
9
OPEX (increase of nitrogen consumption). In this sense, it s also noted that cleaning pressures above 19 barg showed no significant benefit. 3.3 Maximum Pressure Drop Tests at different values of maximum pressure drop were carried out. Figure 8 compares two values of maximum pressure drop, 1800 and 1950 mmwc; the rest of operational parameters remaining constant.
Pressure Drop (mm wc)
1900
1700
1500
Particle concentration: 13 g/Nm3 Filtration velocity: 2.9 cm/s Gas cleaning pressure: 19±0.2 barg Max. Pressure Drop: 1800/1730 mm wc
1300
1100 0
250
500
750
1000
1250
1500
1750
2000
2250
2500
2750
Time (s)
Pressure Drop (mm wc)
2500
2000
1500
1000 Particle concentration: 13 g/Nm3 Filtration velocity: 2.9 cm/s Gas cleaning pressure: 19±0.2 barg Max. Pressure Drop: 1950/1860 mm wc
500
0 0
500
1000
1500
2000
2500
3000
3500
4000
Time (s)
Figure 8: Effect of the cleaning by Maximum Pressure Drop
It is illustrated that an increase of the maximum pressure drop implies more separation between cleaning cycles, and therefore better performance of the filtering elements. In this regards, an increase of 15% in the maximum pressure drop resulted in 7 times less frequency cleaning cycles. Nevertheless, higher values of maximum pressure drop result in a faster deterioration of the filtering elements. 3.4 Baseline pressure drop The influence of the operation time was observed by analyzing the evolution of the baseline. In this regard, Figure 9 shows how the pressure drop increases with time. This
10
is due to the gradual saturation of the filters, and also affects to the cleaning parameters, since higher cleaning pressures are required. 1900 1800
Pressure Drop (mm wc)
1700 1600 1500 BASELINE 1400 1300
Particle concentration: 11.7 g/Nm3 Filtration velocity: 3.0 cm/s Gas cleaning pressure: 16±0.2 barg
1200 1100 0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000 11000 12000 13000 14000 15000
Time (s)
Figure 9: Evolution of the baseline pressure drop with time
3.5. Modelling Experimental data obtained during the testing have been used for the developing of a model based on the Darcy’s law in order to predict the behaviour of the filtering element during the filtration process. General approaches pursued by most researchers on the flow of fluids through porous medium started with the Darcy’s law. As the Reynolds numbers for flow through the filter and cake is very small, the differential pressure drop can be described by the well known Darcy’s law: dP KU dz
(1)
Following the methodology proposed in [11], the total pressure drop, ∆P, comprises the pressure drop across the cake and that across the filter medium. Hence the total pressure drop can be expressed as:
P Pm Pc
(2)
Therefore the following relationship can be established by integration of eq. (1) [10-12]:
P K m z mU K c z c U
(3)
The solid balance in one single element shows the increase of the cake as a measurement of the thickness, and it is shown in the expression: zc
gUC t p (1 )
(4)
11
The term of the thickness is replaced in the general expression of the pressure drop through the cake, as follows:
Pc k c
g p (1 )
CU 2 t
(5)
The general expression of pressure drop in the filtration process can be written in a more simplified form using a coefficient b:
PT k m U bCU 2 t
(6)
The model is now being processed and will be available to be presented at the ICCST Conference.
4. Conclussions The analysis of experimental results, and based on the described in the preceding paragraphs, it can be drawn the following conclusions: In relation to the performance of filtration, the prototypes have an average yield around 98% and an outlet particle concentration around 200 mg/Nm3. This value of particle matter concentration is relatively high, and may be due to the fact that the prototypes are operating at high values of filtration velocity. It is expected that scale commercial filters with improved design to present better efficiency. With respect to the filtration rate, it has been observed that the real capabilities of the prototypes are generally higher than those specified for commercial filter elements. It is noted that the pressure drop across the prototypes elements is an order of magnitude bigger than across commercial filters. The dependence of cleaning performance, the residual pressure drop and the separation of the cleaning cycles with the next variables have been determined: -
Cleaning pressure
-
Maximum pressure drop
-
Pulse cleaning duration
-
Filtration velocity
-
Time
In this sense, the values of effective cleaning pressure have been set around 16 barg. It has been reached maximum pressure drop values up to 1950 mmwc without having seen any deterioration in the prototypes.
12
The study of the pulse cleaning duration concludes that the influence of the parameter is not significant if the pulse is short (500 – 800 ms). The influence of the filtration velocity on cleaning parameters has been investigated. An increase in gas filtration rate implies a reduction in cleaning performance and an increase in the pressure drop and in the fouling velocity. The analysis of the baseline pressure drop indicates that cleaning requirements increase as the experiment progress which implies a decrease in the separation of cleaning cycles. It has been found that, at high temperature (550 ºC), expansion, contraction or significant deformation of the material have been not observed.
Acknowledges This work is carried out with the financial support of the Spanish Innovation and Science Ministry and the European Commission (former ECSC Research program). References [1] Presas M, Pastor JY., Llorca J, Arellano López AR, Martínez Fernández J, Sepúlveda R. Microstructure and fracture properties of biomorphic SiC. Refractory metals & Hard Materials, July 2005. [2] Lupion M, Rodriguez-Galan M, Barbosa V, Cruz JL. Operating experiences of new filtering materials for syngas filtration at high temperature and high pressure.4th International Freiberg Conference on IGCC & XtL Technologies. Dresden (Germany). 2010. [3] Navarrete B, Lupión M, Gutiérrez F J, Cortés V J, Coca P, García Peña F. Improving the ELCOGAS IGCC dedusting system: facility plant erection and testing. International Freiberg Conference on IGCC & XtL Technologies 2005. [4] Lupión M, Navarrete B, Gutiérrez FJ, Cortés VJ. Design and operation experiences of a hot gas filtration test facility for IGCC power generation. Advanced Gas Cleaning Technology. Proceedings of the 6th International Symposium on Gas Cleaning at High Temperatures 2005. ISBN4 915245-61-6. [5] ECSC Project 7220-PR-141 Technological Improvement of Hot Gas Filtration for Onstream IGCC Plants in the European Union (GASFIL). Final Report 2007. [6] Lupión M, Gutiérrez FJ, Navarrete B, Cortés VJ. Assessment performance of hightemperature filtering elements. Fuel, 2010. Volume 89, Issue 4, Pages 848-854 13
[7] Martínez-Fernández J, Qispe J, Barbosa JV. Biomorphic Ceramics Materials for High Temperature and pressure industrial filtration Processes. 4th International Freiberg Conference on IGCC & XtL Technologies. Dresden (Germany). 2010. [8] Lupion M, Navarrete B, Alonso-Fariñas B, Rodriguez-Galan M. Hot gas filters for coal-based power generation systems: Operating Experiences. International Symposium on Gas Cleaning at High temperature (GCHT-8). Taiyuan, Shanxi (China). August 2010. [9] Seville, J P K; Clift R; Withers, C J; Keidel, W. Rigid Ceramic Media for filtering hot gases. Filtration & Separation, 1989. Pages 265-271. [10] Seville, J P K; Clift, R. Gas cleaning in demanding applications. 1997. J P K Seville (Ed), Blackie Academic & Professional, London, UK Seville. [11] Lupión M., Alonso-Fariñas B., Rodríguez-Galán M, Navarrete B. Modelling of the performance of filtering elements at high temperature and high pressure. 4th International Congress on Energy and Environmental Engineering and Management. Mérida (SPAIN). May 2011. ISBN13: 978-84-9978-014-6. [12] Duo, W; Seville, J P K; Kirkby, N F; Büchele, H; Cheung, C K. Patchy cleaning of rigid gas filters-II. Experiments and model validation.1997.Chemical Engineering Science, Volume 52, Issue 1, Pages 53-164.
14
FLUID DYNAMIC SIMULATION OF DRY FILTER FOR REMOVAL OF PARTICULATES FROM COAL AND BIOMASS GASIFICATION C. B. da PORCIÚNCULA1, N. R. MARCILIO1, M. GODINHO2 e A.R.SECCHI3 1
Dequi - Federal University of Rio Grande do Sul - Brazil e-mail: {cleiton,nilson}@enq.ufrgs.br 2 University of Caxias do Sul - RS e-mail:
[email protected] 3 COPPE/PEQ – Federal University of Rio de Janeiro - RJ e-mail:
[email protected] ABSTRACT – The presence of particulates and other solid contaminants is very common in gasification and combustion processes. These by-products consist essentially of tar, fly ash and char, which may cause severe problems of corrosion and deposit in turbines, heat exchangers and other process equipments. The retention of such particulates in a bench filter comprised of a spheres glass bed has been studied in order to remove those particulates prior the process equipments cited above, as well as avoiding pollutant emissions to the atmosphere. In a first step, computation fluid dynamic simulations (CFD) were applied to this system in steady-state and transient conditions. The original filter design has two conical sections with the filtering bed between them, and its dimensions are to be adapted in a gasification and combustion pilot plant. Different modeling approaches were tested (Lagrangian, Eulerian, and Lagrangian-Eulerian), and the previous results show a pressure drop fourfold its initial value. The Darcy model for flow in porous media was employed in this modeling, and the permeability of the filter bed was estimated by semi-empirical correlations. Two different values of dimensions for the porous media were tested: 50 and 100 mm. Laboratory tests in a minor scale have been carried out in order to estimate the properties of the porous media and also evaluate the rise of pressure drop along the time. KEY WORDS: dry filter; particulate; fluid dynamic simulation, porous media.
1. Introduction One of the major drawbacks encountered in gasification and combustion processes is the presence of solid contaminants. Tar, ash, and other particulates cause severe problems in equipments upstream like turbines, combustion chambers, heat exchangers and boilers. The particulates greater than or equal to 5 μm diameter are most difficult to be removed, which can bring about problems concerning air pollution, incrustation and corrosion. The technology of dry filters is very promising in the sense of retaining such particulates. Yang and Zhou (2007), Hassler and Nussbaumer (1999) cite that sand filters might remove up to 99.9% of particulates of a process stream. Stanghelle et al. (2007) studied the granular filtration of biomass gasification by-products at temperatures around 550oC, and their results show high removal efficiencies combined with low pressure drop when the material to be filtered is fly ash, by utilizing a filter medium of aluminum oxide spheres. Neiva and Goldstein (2002) compared the pressure drop with classical literature models (Darcy, Karman-Kozeny and Happel laws) in a ceramic fiber bed, where the particulates have been arisen from char of a coal gasifier.
In terms of mathematical modeling and simulation of filtration processes, one may highlight the works of Deuschle et al. (2008), a computational fluid dynamics study of a diesel filter, Dittler and Kasper (1999), by simulation of a two-dimensional filter to prevent pressure drop among different regeneration efficiencies, Moghadasi e al. (2004) by means of a mixed filter media comprised of a compacted sand and glass sphere bed. The objective of this work is to provide a full CFD analysis of pressure drop in a pilot-plant filter still to be constructed. Initially, the simulations were carried out with estimated values of permeability from empirical correlations. Further on, other simulations were developed based on experimental values of permeability measured from a bench scale plant, and both results were compared. 2. Mathematical Modeling The governing equations are the Navier-Stokes (1) in a three-dimensional domain. The turbulence model k-ε was employed coupled with those equations (2 and 3) together with the continuity equation (4) as described below:
(
)
∂ ( ρu i ) ∂ ρu j u i ∂P ∂ + =− + ∂t ∂x j ∂xi ∂x j
⎛ ∂ui ⎜μ ⎜ ∂x j ⎝
⎡⎛ μ ∂ ( ρk ) + ∇ ⋅ (ρu i k ) = ∇ ⋅ ⎢⎜⎜ μ + T ∂t σk ⎢⎣⎝
⎞ ⎤ ⎟⎟∇k ⎥ + Pk − ρε ⎠ ⎥⎦
⎡⎛ μ ∂ (ρε ) + ∇ ⋅ (ρu i ε ) = ∇ ⋅ ⎢⎜⎜ μ + T σε ∂t ⎣⎢⎝
⎞ ⎟ + S ui ⎟ ⎠
⎞ ⎤ ε ⎟⎟∇ε ⎥ + (Cε 1 Pk − Cε 2 ρε ) ⎠ ⎦⎥ k
( )
∂ρ ∂ ρu j + =0 ∂t ∂x j
(1)
(2) (3)
(4)
Lagrangian transport particle implementation is written in terms of the second Newton law, as equation (5):
mp
dU p dt
=
(
CD ρ f Ap U f − U p U f − U p 2
)
+
πd p 2 (ρ p − ρ f )g 6
(5)
If considering an Eulerian-Lagrangian approach, one considers the diffusion term of the conservation equation per component:
(
)
∂Ci ∂ ρu j Ci ∂ = + ∂x j ∂x j ∂t
⎛ ∂Ci ⎜D ⎜ ∂x j ⎝
⎞ ⎟ ⎟ ⎠
(6)
Steady-state and transient simulations were performed for three cases: Lagrangiang track of particles, Eulerian-Lagrangian and Eulerian-Eulerian. The Darcy law was implemented in order to account the pressure drop along the filter bed:
U=
1 dV ΔP = μ Rt + R f A dt
(
)
(7)
Where the resistance of the cake, Rt , is a linear function of time:
Rt = αρUφt
(8)
3. Materials and Methods A bench scale filter was constructed in order to estimate resistance and permeability of the porous medium that could be applied to the pilot-plant filter. Simulations taking into account different bed widths (50 and 100 mm length) and also a mixed medium with properties of sands with different mean diameters (25 mm long each) were carried out by applying simulations in steady state and transient conditions to verify the behaviour of the pressure drop with time. The scheme of the filter is depicted in Figure 1 below:
Figure 1 - Scheme of the dry filter 4. Preliminary Results. The results of the steady-state simulations are shown in Table 1 below:
Table 1 - Results of steady state simulations Bed length (mm) 100 50 25 mm mixed – thicker sand 25 mm mixed – finer sand
Pressure drop (mmH2O) 93.2 83.1
Permeabilidade (m2) 4.4.10-9 4.4.10-9
0.4 0.4
Bed particle diameter (mm) 2 2
39.2
4.4.10-9
0.4
2
499.5
3.41.10-10
0.3
1
Porosity
From the Table 1 above, one can see that the larger values of pressure drop were obtained for the 100 mm bed and for the section of 25 mm of the mixed bed for finer sand. A similar test is described in the literature by Yang and Zhou (2007), where one might conclude that the finer are the particles, the larger is the pressure drop but the larger is the retention. Thus, there should be a trade-off between bed particle size and removal efficiency of the filter in order that the equipment may work out with reasonable pressure drops and high removal efficiency. For the transient regime, the results are illustrated in Figure 2 below:
Figure 2 - Pressure drop in transient simulation From Figure 2, one can see that there is no practical difference in any of the three mathematical approaches. All of them reproduce the same result for pressure drop in different times, so that we can conclude these three approaches are adequate. In Figure 3 it is possible to view an example of gas streamlines being distributed inside the filter chamber, for the geometry with 100 mm bed length.
Figure 3 - Gas streamlines in 100 mm bed The vortexes that are visualized in Figure 3 before the gas entering the bed is a picture of what might happen in practice: the deposit of particulates cake has a major probability to deposit on this areas. 5. Concluding remarks Based upon the results that were obtained by simulations, it is possible to predict a fourfold increase in pressure drop if considering a total cycle of operation about 10 hours. This result is the same one obtained for the three mathematical approaches that were tested.
Acknowledgments Authors are very grateful to RNC (Brazil Coal National http://www.ufrgs.br/rede_carvao) by the financial support for this research.
Network,
References
DEUSCHLE, T.; JANOSKE, U.; PIESCHE, M. A CFD model describing filtration, regeneration and deposit rearrangement effects in gas filter systems. Chemical Engineering Journal, v.135, p.49-55, 2008. DITTLER, A.; KASPER, G. Simulation of operational behaviour of patchily regenerated, rigid gas cleaning filter media. Chemical Engineering and Processing, v.38, p.321-327, 1999. HASLER P.; NUSSBAUMER TH. Gas Cleaning for IC Engine Applications from Fixed Bed Biomass Gasification. Biomass and Bioenergy, v.16, p.385-395, 1999. MOGHADASI, J.; STEINHAGEN, H.M.; JAMIALAHMADI M.; SHARIF, A. Theoretical and experimental study of particle movement and deposition in porous media during water injection. Journal of Petroleum Science & Engineering, v.43, p.163-181, 2004. NEIVA, A.C.B.; GOLDSTEIN, L. A procedure for calculating pressure drop during the build-up of dust filter cakes. Chemical Engineering and Processing, v.42, p.495-501, 2003. STANGHELLE, D.; SLUNGAARD, T.; SØNJU, O.K. Granular bed filtration of high temperature biomass gasification gas. Journal of Hazardous Materials, v.144, p.668-672, 2007. YANG G.; ZHOU J. Experimental Study on a New Dual-Layer Granular Bed Filter for Removing Particulates. Journal of China University of Mining and Technology, v.17, p. 201204, 2007.
Oviedo ICCS&T 2011. Extended Abstract
Capture of CO2 during low temperature biomass combustion in a fluidized bed using CaO. A new larger scale experimental facility J.R. Chamberlain, C. Perez Ros Gas Natural Fenosa, Avenida San Luis 77, 28033, Madrid, Spain Abstract
This paper outlines a new experimental test facility of 300kWt being commissioned in the grounds of Gas Natural Fenosa’s La Robla coal-fired power plant in the Leon region, Northwest of Spain, with the goal to advance the demonstration of the capture of CO2 with CaO in a circulating fluidized bed (CFB) combustor-carbonator reactor, where the combustion of biomass with air occurs simultaneously with the carbonation of CaO, thereby capturing the CO2 released from the combustion process. This process intends to exploit the high reactivity of most natural biomasses permitting the possibility of combustion at low temperatures (around 700ºC) and the capability of CaO to absorb CO2 at these temperatures. This is a niche application for the carbonate looping cycles, which is currently being developed for other post-combustion and pre-combustion processes. Previous results obtained in a 30kWt test facility made up of two interconnected CFB reactors (combustor-carbonator and combustor-calciner) located at the facilities of the Spanish Institute of Coal (INCAR-CSIC) in Oviedo, Spain, have demonstrated the experimental feasibility of in situ CO2 capture during a “lowtemperature” when operating at around 700ºC that maximizes both combustion and CO2 capture efficiencies in circulating fluidized beds fed with a continuous supply of CaO. CO2 capture efficiencies of over 80% have been obtained, remarkably close to those allowed by the equilibrium and the combustion mass balances, when an adequate stock of active CaO in the combustor-carbonator reactor, combined with an intense circulation of solids between this carbonator and calciner have been achieved. These positive results have justified the construction of the new larger scale test facility in La Robla, some 10 times larger, which is described in this abstract. Over the next year this facility should permit the validation of the smaller scale experimental work and provide crucial experimental results from longer duration experiments to further verify the process and provide data for models that need to be developed for the next scale up of the concept, both as a standalone process and as a possible co-combustion concept when integrated
1
Oviedo ICCS&T 2011. Extended Abstract
with an existing thermal power plant.
1. Introduction
In order to keep global warming below 2ºC, it is foreseen by the International Energy Agency (IEA) that Carbon Capture and Storage (CCS) must provide 20% of the global CO2 cuts required by 2050; the costs of doing so without CCS will be over 70% higher [1]. The integration of CCS with biomass will lead to CO2 “negative emissions” in the generation of electricity or in other energy products, which is a very attractive concept. This was initially recognized by Ishitani and Johansson [2] and the positive implication of negative emissions in energy technologies for long term climate change mitigation has been highlighted in many recent scenario exercises [3, 4].
The capture of CO2 in the niche application of the carbonate looping cycle of this work with CaO in a circulating fluidized bed (CFB) combustor-carbonator reactor, where the combustion of biomass with air and the carbonation of CaO takes place simultaneously has been presented before [5, 6]. Results were obtained in a small scale experimental 30kWt located at the facilities of the Spanish Institute of Coal (INCAR-CSIC) in Oviedo, Spain and many tests have been carried out at different carbonation reaction temperatures, solids inventories, superficial gas velocities, solids circulation flow rates and concentrations of CO2 generated by biomass combustion. Three different biomasses were tested: saw-dust, crushed olive pits and wood pellets and experiments up to 14 hours at steady state conditions were achieved. An example of previously published results [6] is shown in Figure 1.
2
Oviedo ICCS&T 2011. Extended Abstract
100
25
(a)
O2 analyzer
20
Capture Efficiency (%)
Concentration (% vol.)
CO2 O2 probe 15
10
5
80
60
40
20
(b)
Experimental Equilibrium
0 19:10
19:20
19:30
19:40
19:50
time (h:min)
20:00
20:10
0 19:10
19:20
19:30
19:40
19:50
20:00
20:10
time (h:min)
Figure 1. Example of experimental results in the combustor-carbonator reactor in a typical experiment. (a) Combustor-carbonator exit gas concentrations of CO2 and O2 measured by the on-line gas analyzer and O2 zirconia probe (b) Experimental capture efficiency and maximum capture efficiency allowed by equilibrium.
In this example, the average CO2 concentration at the exit of the combustor-carbonator reactor was 3.1 vol%. The average oxygen concentration at the exit of the combustorcarbonator was 7.6 vol.%. From a combustion mass balance, the CO2 produced by biomass combustion was estimated to be around 13.6 vol.% , therefore, the average CO2 capture efficiency was 77%. The average temperature in the combustor-carbonator was 690 ºC during the period, which according to the equilibrium of CO2 on CaO allows for a 2.4 vol% of CO2 (maximum efficiency allowed by the equilibrium of 81%, remarkably close to the experimental value).
These positive results have led to a decision by Gas Natural Fenosa to scale-up the process and design and construct a new larger test facility in La Robla.
2. Scale-Up of Test Facilities
As a result of these positive results from the 30kWt test facility, Gas Natural Fenosa took the decision to construct the new larger test facility, some 10 times larger at a nominal capacity of 300kWt, to advance and further demonstrate this niche concept.
3
Oviedo ICCS&T 2011. Extended Abstract
The smaller 30kWt test facility located in Oviedo consists of two interconnected CFB reactors: a 6.5m high carbonator and a 6m high air-fired calciner (it was assumed that the rate of sorbent reaction is similar that when operating the calciner in oxy-fired mode). Both reactors had an internal diameter of 0.1 m.
The new test facility located in the grounds of the Gas Natural Fenosa’s La Robla coal fired power plant also has a central part consisting of two interconnected CFB reactors. However, in this case the carbonator is a cylindrical reactor of some 12 metre high with a diameter of 600mm. In order to control the temperature of the biomass combustion in the range of 650-700ºC a heat exchanger has been installed in the carbonator that employs thermal oil as the cooling medium. The calciner has the same dimension as the carbonator, 12m high with a diameter of 600mm. This reactor is ceramic lined as it operates in the temperature range of 850-900ºC. As with the smaller experimental plant, the calciner is air fired. It is again assumed that the rate of sorbent reaction will be similar to that when operating the calciner in oxy-fired mode and the novelty of this concept that has to be demonstrated is the process of combustion and capture in the carbonator.
Figure 2. Images of the 300kWt experimental plant in La Robla power plant actually in the stages of commissioning.
As one of the objectives of this larger test facility is to undertake experiments of longer duration the power plant includes automated systems for biomass handling and injection via screw-feeds. Biomass storage for one week experimentation is contemplated, sufficient to provide both the nominal 1.7T/day of biomass to the carbonator and 2,5T/day of biomass to the calciner. Limestone storage and injection is also contemplated, capable of injecting over 0,5T/day for make-up if required so depending 4
Oviedo ICCS&T 2011. Extended Abstract
on sorbent deactivation and breakdown. There is obviously the capability to receive further supplies of biomass and limestone during plant operation for longer experimental runs. Air is preheated and supplied to independently to both the carbonator and calciner reactors in a controlled manner through variable speed forced draft fans. As biomass and air are injected at the bottom carbonator, which will contain a bed of predominantly CaO and if the temperature of combustion can be controlled to temperatures approaching 700ºC, via fuel supply and coolant flow control, combustion of the biomass and capture of CO2 through the reaction with the CaO to produce CaCO3 should occur simultaneously. The mixture of gases and solids that leave the top of the carbonator pass through two cyclones situated in series in order to separate the solids from the combustion gas without CO2. The solid separated in the first cyclone are then introduced into the calciner via a loop seal in order to permit the regeneration of CaO from CaCO3, thus separating the CO2. Biomass is added to the calciner as a fuel source to obtain the required temperature, above 850ºC. In a similar manner to the carbonator, in the calciner the solids, in this instance mainly CaO and a gas enriched in CO2, leave the top of the calciner and pass through two cyclones situated in series in order to separate the solids from the CO2 enriched gas. The solids separated in the first cyclone are returned to the carbonator via loop seal in order to close the loop of the process.
The experimental plant is fully automated and contemplates extensive monitoring equipment throughout the loops to permit the process to be followed at each step and thus characterised. Additionally, some of the energy input will be recovered from the hot gases leaving the reactors in heat exchangers that serve to preheat the air.
3. Summary
Carbonate looping is one of the emerging second generation CO2 capture technologies considered to be of promise as it employs a low cost and readily available sorbent and due to the process temperatures, it should be possible to recover and use much of the heat input required, reducing the final energy penalty. The niche concept being investigated in this work, where the combustion of biomass with air and the carbonation of CaO take place simultaneously is considered to be an attractive option for this technology, promoting a concept of negative emissions for the biomass consumed. However, to date much of the experimental work undertaken has been at a very small 5
Oviedo ICCS&T 2011. Extended Abstract
scale of various kWt. The new larger experimental plant being commissioned in the grounds of La Robla power plant of Gas Natural Fenosa is one of the required next steps to further develop and validate the concept. Over the next year, this larger experimental plant should deliver experimental results at a larger scale from experiments of longer durations to confirm and validate the previous smaller scale experimental work. Also, and more importantly, these results should determine the sorbent performance and make-up requirements, a key issue, contribute to both the technical and economical evaluation of the concept as well as generating data for the future scale up of this option to sizes in the order of several megawatts.
4. Acknowledgments
This work has been carried out thanks to the financial support from Spanish Centre for the Development of Industrial Technology (CDTI) under the auspices of the projects CENITCO2 and MENOSCO2. The participations of the Spanish Institute of Coal (INCAR-CSIC) in Oviedo and the Centre of Research for Energy Resources and Consumption (CIRCE) in Zaragoza in the project are also gratefully acknowledged.
5. References [1] International Energy Agency (IEA), World Energy Outlook, 2009 [2] Ishitani, H., Johansson, T. B. Energy supply mitigation options. In: R. T. Watson, M. C. Zinoyowera and R. H. Moss, editors. Climate Change 1995: Impacts, Adaptations, and Mitigation of Climate Change: Scientific-Technical Analyses, Cambridge, UK: Cambridge University Press; 1996, p. [3] Rhodes, J. S., Keith, D. W. Biomass with capture: negative emissions within social and environmental constraints: an editorial comment. Climatic Change 2008; 87: 321-8 [4] Obersteiner, M., Azar, C., Kauppi, P., Mollersten, K., Moreira, J., Nilsson, S., et al. Managing climate risk. Science 2001; 294: 786[5] Abanades Garcia, J. C., Alonso, M., Rodriguez, N. Experimental validation of in situ CO2 capture with CaO during the low temperature combustion of biomass in a fluidized bed reactor. Int. J. Green. Gas. Cont. 2010; d.o.i 10.1016/j.ijggc 2010.01.006: [6] Alonso, M., Rodriguez, N., Gonzalez, B., Arias, B., Abanades Garcia, J. C., Capture of CO2 during low temperature biomass combustion in a fluidized bed using CaO. Process description, experimental results and economics. GCGT-10, Energy Procedía 6
Oviedo ICCS&T 2011. Extended Abstract
2010;
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Oviedo ICCS&T 2011. Extended Abstract
Measurement of Gasification Rate of Coal Char under High Pressure and High Temperature using A Mini Directly-heated Reactor K. Miura*, M. Makino, E. Sasaoka, S. Imai, R. Ashida Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan
[email protected] Abstract A mini directly heated reactor (mini-DHR) was constructed to measure the gasification rate handily under high CO2 pressure of ~2 MPa in the presence of other gases, such as CO and H2, at T = ~ 1200°C. The mini-DHR was made of U-shaped SUS or Pt tubing of 3 mm I.D. The reactor itself was used as a heating element. An electric current of 75 – 150 A and a few volts were introduced to the reactor to heat up the reactor up to 900 to 1200°C. About 1 mg of char was placed in a platinum mesh basket of 1.0 mm I.D. and 10 mm high. The basket with the char sample was placed just above a thermocouple in the reactor. The conversion of char, X, was estimated by weighing the remaining char sample. The X vs. t relationships obtained under various conditions were analyzed to formulate a gasification rate equation in the presence of both CO2 and CCO for a char prepared from an Australian brown coal. 1. Introduction Enhancement of gasification reactivity of coal chars is very effective in increasing coal gasification efficiency.
Gasification reactivity of coal chars is believed to be
controlled mainly by catalytic effect of inherent minerals [1-4].
Then addition of
catalyst has been performed to further increase the gasification reactivity of coal char. A more cost-effective method, however, has been desired to enhance the gasification rate. We have recently proposed an upgrading method of low rank coal which consists of treatment of coal in non-polar solvent, such as 1-methylnaphthalene, at temperatures below 350°C [5]. The products obtained from the treatment are solvent-soluble fraction (extract) and insoluble fraction which we call “upgraded coal”. It was found that the gasification reactivity of the upgraded coal char was much larger than that of the raw coal for all the three coals tested. The CO2 gasification rate at 900°C of the upgraded coal char prepared from an Australian brown coal, Loy Yang coal, was surprisingly larger than the gasification rates of any other coal chars reported in the literature. Thus,
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Oviedo ICCS&T 2011. Extended Abstract
it was found that the proposed upgrading method of low rank coal can be one of the ways of enhancing the gasification reactivity of coal char without using catalyst. In Japan oxygen blown gasification with recycled CO2 has been proposed to facilitate the CO2 separation and hence to increase the gasification efficiency under the NEDO “Innovative Zero-emission Coal Gasification Power Generation Project”. To realize the gasification concept practically, it is essential to increase the CO2 gasification reactivity of coal chars under high CO2 pressure of ~2 MPa at T = ~ 1200°C. This requests the development of methods to increase the gasification rate and to measure the gasification rate under such extreme conditions. In this work a mini direct heating reactor was constructed to measure the gasification rate under the extreme conditions. Then the char conversion vs. time relationships obtained under various conditions were analyzed to formulate a gasification rate equation in the presence of both CO2 and CO for a char prepared from an Australian brown coal. 2. Experimental 2.1 Samples. An Australian brown coal, Loy Yang coal (LY), was used as a low rank coal in this study. The detailed upgrading procedure has been described in a previous paper [5]. The coal was treated in 1-methylnaphthalene (1-MN) at 350°C under 2.2 MPa for 3 h and then separated into 1-MN-soluble fraction (extract) and insoluble fraction (residue) which we call “upgraded coal (UC)”. The elemental compositions of the LY coal and the upgraded coal (LY/UC) are given in Table 1. LY and LY/UC were carbonized for 30 min at 900°C in an inert atmosphere to prepare their chars. The char particles ranging from 75 to 150 μm in diameter were served to the gasification experiment. Table 1. Analyses of Loy Yang brown coal (LY) and the upgraded coal prepared from LY (LY/UC). Sample
Ultimate analysis [wt%, d.a.f.]
Ash
C
[wt%, d.b.]
H
N
O+S(diff.)
LY
66.7
4.7
0.9
27.7
1.5
LY/UC
77.4
4.0
1.0
17.6
2.9
2.2 Gasification Experiment.
Figure 1 shows the set up used for the gasification
experiment. The detail of the custom made reactor, mini direct heating reactor (miniDHR), is shown in Figure 2. The reactor was made of U-shaped SUS or platinum tubing of 3 mm I.D. The reactor itself was used as a heating element. An electric current of 75
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Oviedo ICCS&T 2011. Extended Abstract V5
reactor V1
MFC1
V3
regulator
V6
V12 NV3
MFC3
V9
P
BV1
He
P NV1 regulator
MFC2 V4
He or CO2 Reaction gas CO
V10
V11
V13 BV2
NV2
V7 V8
Fig. 1. Experimental set up for gasification at high temperature and high pressure.
Quartz wool
35 mm
Char in mesh basket (1 mg)
90 mm
ID: 3 mm SUS or Pt tube
Thermo-couples
Gas flow 600 cm3/min(NTP)
Fig. 2. Detail of the custom made mini directly heated reactor (mini- DHR). – 150 A and a few volts was introduced to the reactor to heat up the reactor up to 900 to 1200 °C. About 1 mg of char was placed in a platinum mesh basket of 1.0 mm I.D. and 10 mm high. The basket with the char sample and wrapped by quarts wool was placed just above a thermocouple in the reactor. The sample was heated up to a desired temperature in a He stream. Figure 3 shows a typical heating profile. It is shown that the temperature can be controlled very accurately. After reaching the gasification temperature the gas stream was switched to the stream containing CO2 or CO2/CO mixture to start the gasification. After the elapse of a predetermined reaction time the gas stream was switched back to the He stream, and cooled down to room temperature in the He stream. The the weight of basket containing the remaining char was measured by a micro balance to estimate the conversion of char, X. By repeating this procedure the accurate relationships between X vs. reaction time,t, could be obtained.To examine
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1200
temperature [ºC]
1000 800
CO2 & He CO
600 400
He
30 s
200 0
3～5 V 60～130 A
0
30
60
90
120
150
180
210
time [s]
Fig. 3. A typical heating profile of the mini-DDHR. the validity of the mini-DHR, the X vs. t relationships obtained under an atmospheric pressure was compared with those obtained by a sensitive thermobalance (Shimadzu, TGH-50). The X vs. t relationships below atmospheric pressure were obtained by use of the thermobalance. 3. Results and Discussion 3.1 Examination of the validity of mini-DHR.
Figure 4 compares the X vs. t
relationships measured by using the mini-DHR (keys) and those obtained by the thermobalance (broken lines) at 900 °C under 0.1 MPa of CO2 pressure (pCO2) for the LY and LY/UC chars. Good agreements between the mini-DHR and TG experiments show the validity and accuracy of the gasification rate measurement using the mini-DHR. The gasification rates 1.0 LY LY/UC TG
X[-]
0.8 0.6 0.4 0.2
( = 900 ℃, pCO2 = 0.1 MPa 0 0
100
200
300
400 t [s]
500
600
700
Fig. 4. Comparison of the X vs. t relationships measured by using the mini-DHR (keys) and those obtained by the thermo-balance (broken lines). 3.2 Formulation of gasification rate in the presence of CO2 and CO.
The gasification
rate of char, -rc, was formulated by the by combining the Langumuir-Hinshelwood type equation representing the gasification of each active site and the Random-Pore model [6]
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Oviedo ICCS&T 2011. Extended Abstract
describing the active site number as a function of X as follows: − rC =
k1 pCO2 f 0 dX / dt = 1 − ψ ln ( 1 − X) 1− X 1 + (k1' k 2 ) pCO + (k1 k 2 ) pCO2
(1)
where ψ is the structural parameter of the char, f0 is the initial value of the number of active sites, and the rate constants, k1, k1’, k2, are the rate constants of the following elementary reactions: k1
CO2 + Cf → ← CO + C(O) k 1’
(2)
k
C(O) →2 Cf + CO
(3)
The structural parameter ψ was found to be set equal to 0 from the accurate X vs. t relationships obtained by use of the thermo-balance at atmospheric pressure of CO2. The X vs. t relationships measured under a wide a range of CO2 pressures and at four different temperatures are shown in Figures 5 and 6.
The -rc values at X = 0.3 were
estimated from these data and used to estimate the rate parameters k1f0 and k1/k2. 1
1
0.8
pCO2 = 2.0 MPa
1100℃
1.0 MPa
0.6
X[-]
X[-]
0.8
0.6 MPa
0.6 1000℃ 0.4
0.4 0.2 MPa
0.2 0
T = 1200℃
0
100
200
300
0.2
400
500
0
0
20
40
60
t [s]
t [s]
(mini-DHR T = 900ºC、pt = pCO2 + pHe = 2.0 MPa)
(mini-DHR pCO2 = 1.0 MPa, pHe = 1.0 MPa)
Fig. 5. X vs. T relationships in CO2 (1)
Fig. 6. X vs. T relationships in CO2 (2)
The X vs. T relationships in CO2/CO gas mixtures were measured systematically under several selected conditions.
Figure 7 shows
typical X vs. T relationships
obtained. Using all of the X vs. T relationships obtained, -rc values at X = 0.3 were estimated and plotted against pCO2 at several different values as shown in Figure 8. Figure 9 shows final Arrhenius plots for estimating k1f0, k1/k2, and k1’/k2. The Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
2.5
-rC (X = 0.3) ×103 [s-1]
pCO = 0
0.8
X[-]
T = 900℃ pCO2 = 0.8 MPa
0.1 MPa
0.6 0.4
1.0 MPa
0.5 MPa
X = 0.3 0.2
pCO = 0 0.1 MPa 0.5 MPa 1.0 MPa
2.0
PCO = 0
0.04 MPa
1.5 0.1 MPa
1.0 0.5
0.5 MPa 1.0 MPa
0
0 0
2000
4000
0
6000
0.5
1.0 pCO [MPa]
1.5
2.0
2
t [s]
(T = 900℃)
Fig. 7. X vs. T relationships in CO2 /CO.
Fig. 8. -rc values in CO2 /CO.
k1f0 [MPa-1 s-1], k1’/k2, k1/k2 [MPa-1]
1000
k1/k2
100
10
k1’/k2 1
k1f0
0.1
0.01 6
7
8
9
104/T [K-1]
Fig. 9. Arrhenius plots for estimating k1f0, k1/k2, and k1’/k2. Table 2. Estimated values for k1f0, k1/k2, and k1’/k2. Ai k1f0 k1’/k2 k1/k2
1.6×107 MPa-1 s-1 0.16
MPa-1
6.2×10-4 MPa-1
Ei [kJ mol-1] This work Kajitani7) 2.0×102
2.22×102
-39
-23
-91
-48.1
estimated values are shown in Table 2. The activation energies estimated by Kajitani [7] are also shown for comparison purpose. The activation energies of k1f0, are so close to each other. Finally the experimentally obtained X vs. T relationships were compared with the X vs. T relationships calculated by the estimated rate equation in Figure 10.
Good
agreement was obtained between the X vs. T relationships, showing the validity of the rate equation estimated.
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1 T = 900℃ ψ=0
calc
0.8
pCO = 0.6 MPa pCO = 0.1 MPa
pCO = 1.5 MPa
X[-]
2
2
0.6 0.4 0.2
pCO = 0.8 MPa pCO = 0.5 MPa 2
0 0
300
600
900
t [s]
1200
1500
Fig. 10. Comparison of experimentally obtained X vs. T relationships and calculated X vs. T relationships. 4. Conclusions A mini direct heating reactor (mini-DHR) was successfully constructed to measure the CO2 gasification rate of coal chars at high temperature of up to 1200°C and high pressure up to 2 MPa. The validity and accuracy of the gasification rate measurement by the mini-DHR were well clarified, indicating that the mini-DHR can be a handy apparatus for the gasification measurement under extreme gasification conditions. The gasification rate equation was successfully formulated by combining the Langmuir-Hinshelwood model and the Random-Pore mode. Acknowledgement. This work was commissioned by the Central Research Institute of Electric Power Industry (CRIEPI) under the NEDO “Innovative Zero-emission Coal Gasification Power Generation Project”. References [1] Walker, P. L.; Rusinko, F.; Austin, L.G. In Gas Reactions of Carbon, Advances in Catalysis, Vol.11, Academic Press, New York, 1959, p.133. [2] Essenhigh, R. H. In Chemistry of Coal Utilization 2nd Supplementary Volume, John Wiley & Sons, 1981, p.1153. [3] Van Heek, K. H.; Muehlen, H. J. Fuel 1985, 64; 1405-1414 [4] Miura, K.; Hashimoto, K.; Silveston, P. L. Fuel 1989; 68; 1461-1475. [5] Miura, K.; Ashida, R.; Umemoto, S.; Sakajo, A.; Saito, K.; Kato, K. Proceedings of the 25th Pittsburgh Coal Conference, Pittsburgh, 2008. [6] Bhatia, S.K; Perlmutter, D.D. AIChEJ 1980, 26,379-386. [7] Kajitani, S.; PhD thesis (Kyoto University, 2007).
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Oviedo ICCS&T 2011. Extended Abstract
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Oviedo ICCS&T 2011. Extended Abstract
IMPLEMENTATION OF COAL GASIFICATION IN A FLUIDIZED BED FIRING SYSTEM FOR BRICK TUNNEL KILN.
F. Chejne1, C. londono1, C. Gómez1, J. Espinosa1, F. Mondragon2, J.J Fernandez2, Erika Arenas3 L. C Cuartas4 1
2
Universidad Nacional de Colombia, Facultad de Minas. Grupo de Termodinámica Aplicada y Energías Alternativas, TAYEA. Medellín, Colombia.
[email protected] Universidad de Antioquia, Grupo Química de recursos Energéticos y medio Ambiente, Instituto de química y medio Ambiente, Medellín, Colombia.
[email protected] 3
Grupo de Energía y Termodinámica. Instituto de Materiales y Medio Ambiente. Escuela de ingeniería. Universidad Pontificia Bolivariana, Medellín- Colombia,
[email protected] 4
Ladrillera San Cristóbal - Las Playas, Medellín, Colombia. Conm. 427 01 45,ladrillera
[email protected] Abstract We present the results of the design, installation and commissioning of a fluidized bed gasifier coupled to a tunnel kiln for firing bricks. The main objective of the project was put gasification technology of coal in fluidized bed developed by the Universidad Nacional de Colombia-Medellín, Universidad Pontificia Bolivariana, Universidad de Antioquia and Ladrillera San Cristobal for firing brick in a tunnel kiln. The idea of burning the bricks in the tunnel kiln with coal gas by replacing the system that uses pulverized coal, is that significantly reduces specific fuel consumption and produces building blocks for a more cleanly, cheaply and with less waste, further emerges as a need to search for better alternatives to burning coal because it is an abundant resource in Colombia.
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1. Introduction. Coal is one of the non-renewable energy still available and disseminated worldwide. However, improper use can be one of the most dangerous pollutants to the environment.
As the century progresses, there is a growing need for energy due to global economic growth. It is projected that fossil fuels will remain the main energy sources in the world in this century, and the coal should increase its participation in power generation, using the large reserves, estimated at 987.066 billion tonnes in the world with an estimated availability of this fuel from 216 to 500 years at current consumption rates. However, environmental concerns have grown about the use of coal with respect to greenhouse gas emissions of pollutants and particulate material available, therefore, there is a clear global need to develop environmentally friendly technologies for the management coal.
The most appropriate system to make the coal more competitive with other fossil energy resources to meet environmental requirements, is the gasification, which is obtained with a combustible gas that can be cleaned of contaminants to be used then processes combined cycle generating electricity with high efficiencies and a significant reduction of pollutant gases such as CO2, SOx, NOx and particulate matter. Have identified several of them, such as Integrated Gasification Combined Cycle (IGCC), Pressurized Fluidized Bed Combustor (PFBC) and Combustion in Pulverized Coal Injection (PCI) as the most viable alternatives to the use of clean coal IGCC to be the most efficient. In the development of these technologies employ high operating pressures, for example, 15-25 atmospheres for IGCC, PFBC atmospheres for 10-15, and less than 5 atmospheres for PCI. One of the most efficient technologies for coal gasification are fluidized bed reactors.This type of equipment are widely used in the chemical industry, energy, environmental and oil, due to good mixing of solids and high transfer rates and reaction that provides the fluid-solid contact made. Coal gasification in a fluidized bed has advantages over other technologies to allow the use of coal rubble, which is lower cost granular carbon, there is a reduction of NOx by working at low temperatures, the order of 850 ° to 900oC and allows recovery of SO2 in-situ.
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For proper and optimal use of coal, leading to the award of new sub-products that maximize the use and greater value to this mineral, this project was developed as a major objective. Coal is an abundant resource in Colombia and as such should take advantage of the occasion, looking to get the best possible use. Should investigate ways to add value to this raw material displaying different aspects of traditional combustion, as demonstrated in the previous investigation DESIGN, INSTALLATION AND COMMISSIONING OF A fluidized bed gasifier For DRYING of BRICK , "held by the same research group, in which it was found that gasification is a more efficient alternative.
The idea of burning the bricks in the tunnel kiln with syngas by replacing the system that uses pulverized coal, significantly reduce the specific fuel consumption and produces a brick clean, cheaply and with less waste. The objetive industry is the brick firing clean, more efficient and environmentally friendly.
Currently the company Ladrillera San Cristobal has replaced a Hoffmann kiln for firing bricks by for tunnel kiln. Which allows significantly reducing specific fuel consumption and achieving better production quality, lower cost and less waste? The project aims to put the technology of coal gasification in fluidized bed developed by the Universidad Nacional de Colombia-Medellín, Universidad Pontificia Bolivariana, Universidad de Antioquia and San Cristobal Ladrillera in the process for firing brick in a tunnel kiln.
Some of the advantages that brings the implementation of this technology are: The brick comes out spotless avoiding a washing process and economy of the builders, fuel economy with the system currently used, facilitates the reuse of hot gases, the combustion gas produced by gasification is cleaner as there is no particulate matter (fly ash) in suspension, being a more efficient, reduce the emission of CO2, CO and other polluting gases in the atmosphere such as NOx and SOx, the fluidized bed gasifier can gasify particles, which is achieved use of energy from solid waste, increased business productivity and modernizing and simplifying the process of brick production.
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2. Experimental section
Based on the proposed initial system design, it had to make modifications in accordance with recommendations of the employees of the company. One change relates to the arrangement of the burners in the tunnel kiln, which was initially contemplated that were arranged laterally and eventually he settled in the oven roof. Figure 1 shows a diagram of the plant.
Figure 1. Schematic illustration of the plant with the gasifier. The Figure 1 shows a schematic of the final gasification plant designed for Ladrillera San Cristobal. It can detail the complete set of gasifier, hopper, cyclone and exchangers.
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Oviedo ICCS&T 2011. Extended Abstract
Figure 2. Scheme of the gasification plant
Figure 2 shows the reactor, the high efficiency cyclone and high flow heat exchanger to generate steam entered the cyclone. In Figure 3, on the other hand, presents the current pattern of distribution of gas in the oven where it has a dual system for the supply of gas or coal. Besides the main components, the coal gasification system to operate and carry to the kiln gases to be burned there, require additional peripheral equipment, which must be selected in accordance with the requirements of each, among them are : blower, water pump, coal feeder, etc.
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Figure 3. Displaying the gasification system with air lines and synthesis gas.
The minimum fluidization velocities for these two particle sizes and were to be 0.3 m / s for sample 1 and 0.21, for the other. According to this information was determined to work with a particle size of 0.8 to 1.3 mm to ensure a fluidized bed gasification tests. For tests initially hot burner was installed at the outlet of the heat exchanger as shown in Figure 4 in order to ensure the necessary conditions do not significantly affect the process of firing in the oven.
Figure 4. Preliminary tests burner installed.
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For the first hot test starts with a Wood bed as shown in Figure 5, was later introduced to diesel to start the fire. It was done to the first gasification tests subsequently given the problem of formation of tars from the start come on only with coal.
Figure 5. Wood bed on.
Once the system has a temperature above 300 ° C in the freeboard the door is closed, parallel turns on the air supply and start the process posteriori power supply gradually to 720 kg / h. Before starting the gas supply to furnace gases are lit in the fireplace as shown in Figure 6.
Figure 6. Turning on the fireplace. Submit before January 15th to
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Once it reaches a temperature in the freeboard of about 700 ° C starts the water supply to the cyclone, which in turn goes to the reactor as gasification agent, the time when the temperature is around 800 ° C starts gas supply to the furnace.
For the first tests it lit the flame at the outlet of heat exchanger as shown in Figure 7, later made a rough cut of gas supply to the furnace for testing without affecting production processes up and got a flame in furnace as shown in Figure 7
Figure 7. Flame obtained by burning the synthesis gas burner outlet provisional in the oven.
During the process of setting up interim assembly was required given the complexity of the cooking process and to not change the heating curve of the oven without having the certainty of producing synthesis gas with the necessary conditions for the process 3. Results and Discussion In order to evaluate the energy and environmental performance of tunnel kiln using the synthesis gas in burning, is scheduled measurement of variables such as flow coal in the gasifier and tunnel kiln, ceramic work flow, flow tunnel furnace and air gasifier, temperatures, flow of gases in the chimney of the furnace, gas concentrations and emissions of particulate matter and acid mists tunnel kiln, among others.
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Oviedo ICCS&T 2011. Extended Abstract
It was noted that the unburned carbon is deposited on trucks that carry loads of bricks in the tunnel kiln fell more than 80% from a pickup truck waste by 8.181 kg to 1.766 kg on average. This means that the quality of the bricks is improved by 80% for not having sulfur coal residue on the surface, which generates the yellow stains on the bricks called called "efluorecencia. " During the experimental trials were conducted sampling for gas composition analysis via gas chromatography. The results are presented in Table 1.
Tabla 1. Composition of gas generated
% MASS GAS
Experimental date
DRY BASIS Simulated data
Flow Coal, Kg/h ~700
720
Flow air kg/h Máx 1900
1525
Flow water kg/h NO3− with S being the most abundant and mobile constituent in the leachates. The order in which the alkalis were leached was in decreasing order: Na > K > Li > Rb > Cs with Na and K in concentrations of up to 200 mg/kg and the leachable concentrations of Li, Rb and Cs only up to 7 mg/kg. The alkaline earths leached in the following order: Ca > Mg > Sr > Ba > Be with Ca the main cationic species most easily released due to its high mobility and occurrence in various species. Leachable levels of Mg and Sr were 1 order of magnitude lower than those of Ca, while extractable Sr showed a wider range of variation with pH. Ba was highly insoluble, accounted for the B > As > Sb = Ge with the leachable contents of Si ≈ 35 mg/kg. B and As were leached in levels Mn > Zn > Cu > Co > Ni > V > Cd > Cr > Mo > Ti > W > Zr > Hf showed a well-defined pH-dependent leaching behaviour for most of these elements and the leachable contents were generally higher under acidic conditions, with very few exceptions. The leaching behaviour of Fe may be primarily linked to the occurrence of leachable Fe sulphates (e.g. jarosite), but in samples containing pyrite sludge, other phases also controlled Fe solubility [23]. Mn showed an order-of-magnitude variation in its total and leachable contents, suggesting a Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
considerable mobility with respect to the other transition metals and thus a persistent pollutant in neutralized AMD [24]. Besides Mn, Zn, Cu, Co and Ni were the main heavy metals released from the CCR, with a mean leachable contents of 14 mg/kg for Zn and 2 mg/kg for the remaining elements. The total contents of V and Cr were extracted to < 1%, revealing a low mobility whatever the pH. Zr and Hf were highly immobile in CCR and these elements were leached below the detection limit, regardless of the pH [7] The remaining metals leached according to the sequence: Al > Pb > Sn > Ga > Tl > Bi. Al leached at very low rates with respect to the high total contents with the only remarkable leachable contents measured at acidic pH. Pb is one of the most abundant toxic metals in coal [17] with a total content in the CCR reaching 100 mg/kg, but this metal was highly immobile with a leachable contents not exceeding 0.3 mg/kg regardless of pH and it can be assumed that the CCR will not result in Pb contamination. Sn, Ga and Tl were leached in very low levels in the most acidic samples (up to 0.4 mg/kg), while being immobile in the remaining samples and the total leachable contents of Bi in CCR was close to the detection limit [7]. Lastly the sequence for the Rare Earth elements (REE) and other metals was: Ce > Nd > U > Th > Y > La > Sc > Gd > Sm > Dy > Pr > Er = Yb > Eu > Ho > Tb > Tm = Lu. These elements were mostly associated with clay and detrital phosphate minerals and the acidity of the coal-forming environment exerted an influence on their concentration. In general, the total contents of these elements displayed a narrow variation among all the samples with Ce the REE most prominently leached (3 mg/kg), followed by Nd and La. The remaining REE’s were leached in concentrations 10μm-particles). This device allowed time-resolved collection of elutriated fines. The fluidizing gas flow, composed by a mixture of air and N2-SO2, was measured by means of two high precision mass flowmeters which were specifically calibrated for each gas used. Analysis of CO2 and SO2 concentrations in the flue gas was accomplished by means of two NDIR analyzers on line. Further details can be found in [9]. Procedures. The reactor was charged with a bed made of sand (150g), and then heated to
the temperature of 850°C prior to each experiment. The fluidizing gas superficial velocity was 0.75m/s. Experiments were carried out by feeding a 20g sorbent batch in the bed while keeping a flow of dry air containing sulfur dioxide (1800ppm) and 8.5% by volume of oxygen. Under these conditions calcination and sulfation occurred at the Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
same time. Calcium conversion degree during sulfation was calculated as a function of time by working out the SO2 concentration at the exhaust. SO2 oxidation to SO3 inside the reactor was accounted for following the procedure detailed by Scala et al. [9]. Rates of fines generation by attrition of bed material were determined by measuring the amount of fines carried over by the fluidizing gas and elutriated from the reactor. The assumption underlying this procedure was that the residence time of elutriable fines in the reactor could be neglected and that elutriation rate could be assumed equal to the rate of fines generation by attrition at any time during limestone conversion. Elutriated fines were collected by means of the two-exit head by letting the flue gas flow alternately through sequences of filters (one was in use while the previous one was replaced) for definite periods of time. In order to prevent hydration and/or recarbonation of the collected material, each filter was readily put in a drier after being used where it was cooled down before it was weighed. The difference between the weights of the filters before and after operation, divided by the time interval during which the filter was in operation, gave the average fines generation rate relative to that interval. Attrition of sand could be neglected [9]. Particle size distribution of bed sorbent at the end of the run was determined by retrieving the bed material from the reactor and subjecting it to particle size analysis. Retrieval of sorbent particles after sulfation could be easily accomplished by discharging the bed from the reactor and sieving the sorbent out of the sand. This operation was carried out gently in order to avoid further attrition of particles, but rapidly because of the propensity of calcined sorbent to absorb moisture when in contact with ambient air. The sorbent was eventually characterized from the standpoint of particle size distribution by sieving. Materials. The bed material consisted of mixtures of sorbent and sand. Sand belonged to
the nominal size range 900-1000µm. Minimum fluidizing velocity was 0.4m/s. The sorbent used in this work was a high-calcium Italian limestone (Boundstone in Dunham’s classification) quarried from Mesozoic carbonate succession (Est Sardinia) and commonly named “Biancone di Orosei”. Chemical analysis of the raw limestone was carried out by a Philips PW 1400 XRF spectrometer, operating with a Rh tube at 30kV and 60mA, and gave a CaCO3 content of 98,83% by weight.
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Oviedo ICCS&T 2011. Extended Abstract
A
B
Figure 1 A) Slaking kinetics of pre-treated CaO (62°C at 25’); B) SEM micrograph
(Secondary Electrons) of the surface of a pre-treated CaO particle.
The sorbent was used either as received or after a proprietary pre-treatment process. This pre-treatment process consisted in the slow calcination of limestone at mild temperature and under controlled gaseous environment. After this pre-treatment, the sorbent consisted mostly of CaO (95.0%). Batches of both as received and pre-treated sorbent were sieved in the two nominal size ranges: 200-300 and 400-600μm. Microstructural-morphological SEM investigation of the CaO manufactured by Calcidrata S.p.A. was performed, on conductive samples, by a Zeiss Leo 50 XP apparatus operating with 20kV of accelerating voltage and an electron source of LaB6. Pore size distribution and total porosity of CaO were obtained by means MIP (mercury intrusion porosimetry) techniques using
a Micromeritics Autopore IV porosimeter
operating at 2000bar. Slaking kinetics test of CaO was carried out in wet condition in a special dewar device (Fapa instrument) according to UNI EN 459-2:2002 standard.
3. Results and Discussion Pre-treated lime characterization. Quicklime manufactured by Calcidrata S.p.A. by
means of the slow calcination treatment is very reactive as results from the slaking kinetics test (Fig. 1A). In fact, after addition of water, the temperature of the lime sample rises up to 60°C in few tens of seconds. SEM investigations (Fig. 1B) indicate that the microstructure of the pre-treated lime is composed of equigranular CaO crystallites, of pseudocylindrical shape, with dimensions in the range 2÷3μm. MIP porosity is around 50%, with a unimodal dimensional distribution of pores. Pore size radius classes are mostly concentrated in the interval 0.4÷0.9μm. The calculated specific surface area is over 15m2/g.
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Oviedo ICCS&T 2011. Extended Abstract
0.5
0.5
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d = 400 - 600 μm d = 200 - 300 μm
0.4
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Figure 2 Calcium conversion vs. time for sorbent particles of different size sulfated
batchwise in FB at 850°C and 1800 ppm SO2. A) Raw limestone; B) Pre-treated CaO. Desulfurization performance. Figure 2 reports the degree of calcium conversion XCa as a
function of time during the FB sulfation of batches of either sorbent. Two particle sizes have been tested. For the raw limestone calcium conversion at the end of the test was relatively low, especially for the larger particle size. The pre-calcined sorbent performed better with a 34-43% calcium conversion after about 300-350min. The increase of calcium conversion was particularly evident for the 400-600μm particles. In order to better compare the performance of the two sorbents, the sulfur capture data have been worked out to obtain the SO2 capture capacity of the sorbents. This quantity represents the grams of SO2 captured per gram of sorbent, and is a more practical way to rank the sorbent performance. Figure 3 shows the SO2 capture capacity as a function of time for the same experiments reported in Fig. 2. Comparison of the results for the two sorbents highlights the much better performance of the pre-calcined lime. 0.5
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SO2 capture capacity, g(SO2)/g(sorbent)
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Figure 3 SO2 capture capacity vs. time for sorbent particles of different size sulfated
batchwise in FB at 850°C and 1800 ppm SO2. A) Raw limestone; B) Pre-treated CaO.
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1.0
d = 400 - 600 μm d = 200 - 300 μm 0.8
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Cumulative particle undersize distribution, -
Oviedo ICCS&T 2011. Extended Abstract
1.0
d = 400 - 600 μm d = 200 - 300 μm 0.8
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Figure 4 Cumulative particle size distribution of sorbent of different size sulfated
batchwise in FB at 850°C and 1800 ppm SO2. A) Raw limestone; B) Pre-treated CaO. Under similar operating conditions, 2-4 times less sorbent is needed to obtain the same SO2 capture performance. This result relies on the combination of two effects: the better calcium exploitation of the pre-calcined sorbent (Fig. 2), and the lower molecular weight of CaO with respect to CaCO3. This last effects determines a larger number of moles of Ca available for reaction with SO2 in the pre-calcined lime per unit mass of sorbent. Attrition behavior. Figure 4 reports the cumulative particle size distribution of the
sorbent samples discharged from the bed after FB sulfation, for both particle sizes tested. The raw limestone (Fig.4A) exhibits a moderate fragmentation for the 200-300μm particles, and a significant fragmentation for the 400-600μm particles. Limestone fragmentation is mostly caused by the rapid calcination of the particles upon feeding in the hot bed, which generates significant overpressures inside the particles during CO2 release [9]. Larger particles are related to higher internal overpressures, which determine a higher degree of fragmentation. The population of particles below the initial particle size range (fragments) accounts for 4 and 23% of the sample mass for the 200-300 and 400-600μm particles, respectively. The pre-calcined sorbent exhibits a different behaviour (Fig.4B). Very limited fragmentation is evident at the end of the run. For this sorbent the fragments account for less than 1% of the sample mass for both particle size ranges. This result is certainly caused by the absence of significant calcination in the fluidized bed for the pre-calcined lime, but also indicates that the slow calcination/treatment is effective in strengthening the sorbent structure. Figure 5 shows the fines elutriation rate measured during FB sulfation tests with the two sorbents. The elutriation rate shows an initial high peak due to particle rounding off. Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
0.30
0.30
A
B 0.25
Elutriation rate, g/min
Elutriation rate, g/min
0.25
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Figure 5 Fines elutriation rate vs. time during batchwise sulfation of sorbent of different
size in FB at 850°C and 1800 ppm SO2. A) Raw limestone; B) Pre-treated CaO. As sulfation proceeds, the fines elutriation rate decreases until a steady value is reached. This decay occurs over a time scale comparable to that over which calcium is sulfated, and should be related to the progress of reaction through the formation of a sulfate layer, harder than the oxide, on the particle surface [9,11]. A comparison between the two sorbents shows the raw limestone generates more fines especially during the first 20min. The total quantity of elutriated fines during the raw limestone experiments was 0.92 and 0.82g for the 200-300 and 400-600μm particles, respectively. For the pre-calcined lime the total quantity of elutriated fines was approximately halved, namely 0.49 and 0.34g for the 200-300 and 400-600μm particles, respectively. This result further confirms that the sorbent pre-treatment is able to give a large mechanical resistance to the particles.
4. Economic analysis
A simple case study was carried out on the basis of the typical operating conditions of an Italian full-scale FB unit burning international low-sulfur coals and using a limestone similar to that used in this work. The analysis of the solid residues coming out from the plant (coal ash + spent sorbent) gave an average content of unused CaCO3 and CaO of ∼7 and ∼20%, respectively. Taking into account that the total quantity of solid residues
is of the order of 160,000 tons per year, and that the raw limestone has an average cost of 30€ per ton, the following “penalties” associated with the inefficient use of traditional limestone in the plant can be estimated (yearly costs): a) the cost for unused CaCO3 (336,000€); b) the cost for unused CaO (1,714,560€); c) the cost associated to the consumption of coal that is burned to generate the necessary heat to produce unused Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
CaO by calcination (521,600€) – this cost was calculated assuming an average cost of 100 € per ton of coal; d) the cost for CO2 emissions deriving from limestone calcination in the FB and from the fraction of coal burning for unused CaO production (606,239€) – this cost was calculated assuming an average cost of 15 € per ton of produced CO2; e) the cost associated to landfilling of unused CaCO3 and CaO and of ash from the fraction of coal burning for unused CaO production (1,958,085€) – this cost was calculated assuming an average landfilling cost of 45 € per ton of residue. Summing up these costs, the total penalty associated to the inefficient use of limestone for this plant is 5,136,484€. From this simple estimation, it is clear that considerable economies can be obtained by the plant operator if these penalties can be minimized. With this respect, the use of the pre-treated sorbent developed by Calcidrata S.p.A. would be associated with a number of advantages. First, since the sorbent is precalcined, no unused CaCO3 would be present in the process, no coal would be necessary for CaO production, and no CO2 would be produced by sorbent calcination. This means that costs a), c) and d) would become zero. Second, the fraction of unused CaO would decrease because of the better calcium conversion and lower sorbent attrition in the FB. As a consequence, also the cost associated to landfilling of unused CaO would decrease. Thus, on the basis of these simple considerations the pre-treated sorbent appears to be promising for its use in FB coal-burning plants. It will be possible to carry out the detailed calculation of these economies once the cost per ton of the pre-treated sorbent will be available. Finally, a further advantage for the sorbent supplier should be mentioned. Since the FB operator requires a well defined particle size distribution of the sorbent, after milling a significant fraction of undersize particles are typically produced. While this residue has practically no market for limestone, it is highly valuable for lime and can be used to produce slaked lime for the building market. On the other side, it must be highlighted that since lime is hygroscopic and irritant, the storage and conveying devices should be sealed in order to avoid contact with moisture and with plant operators. This would of course add an initial cost to upgrade the storage and conveying devices of the plant.
Acknowledgement
The experimental support of G. Somma and A. Coppola is gratefully acknowledged.
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Oviedo ICCS&T 2011. Extended Abstract
References [1] Anthony EJ, Granatstein DL. Sulfation phenomena in fluidized bed combustion systems. Prog Energy Combust Sci 2001;27:215-36. [2] Dam-Johansen K, Østergaard K. High-temperature reaction between sulphur dioxide and limestone-I. Comparison of limestones in two laboratory reactors and a pilot plant. Chem Eng Sci 1991;46:827-37. [3] Dam-Johansen K, Østergaard K. High-temperature reaction between sulphur dioxide and limestone-II. An improved experimental basis for a mathematical model. Chem Eng Sci 1991;46:839-45. [4] Montagnaro F, Salatino P, Scala F. The influence of sorbent properties and reaction temperature on sorbent attrition, sulfur uptake, and particle sulfation pattern during fluidized-bed desulfurization. Combust Sci Technol 2002;174:151-69. [5] Duo W, Laursen K, Lim J, Grace JR. Crystallization and fracture: product layer diffusion in sulfation of calcined limestone. Ind Eng Chem Res 2004;43:5653-62. [6] Montagnaro F, Salatino P, Scala F. The influence of temperature on limestone sulfation and attrition under fluidized bed combustion conditions. Exp Therm Fluid Sci 2010;34:352-8. [7] Chandran RR, Duqum JN. Attrition characteristics relevant for fluidized bed combustion. In: Grace JR, Shemilt LW, Bergougnou MA, editors. Fluidization VI, New York: Engineering Foundation; 1989, pp 571–80. [8] Couturier MF, Karidio I, Steward FR. Study on the rate of breakage of various Canadian limestones in a circulating transport reactor. In: Avidan AA, editor. Circulating Fluidized Bed Technology IV, New York: AIChE; 1993, pp 672–8. [9] Scala F, Cammarota A, Chirone R, Salatino P. Comminution of limestone during batch fluidized-bed calcination and sulfation. AIChE J 1997;43:363–73. [10] Di Benedetto A, Salatino P. Modelling attrition of limestone during calcination and sulfation in a fluidized bed reactor. Powder Technol 1998;95:119–28. [11] Scala F, Salatino P, Boerefijn R, Ghadiri M. Attrition of sorbents during fluidized bed calcination and sulphation. Powder Technol 2000;107:153–67. [12] Chen Z, Lim CJ, Grace JR. Study of limestone particle impact attrition. Chem Eng Sci 2007;62:867–77. [13] Scala F, Montagnaro F, Salatino P. Attrition of limestone by impact loading in fluidized beds. Energy Fuels 2007;21:2566–72. [14] Scala F, Montagnaro F, Salatino P. Sulphation of limestones in a fluidized bed combustor: the relationship between particle attrition and microstructure. Can J Chem Eng 2008;86:347–55. [15] Yao X, Zhang H, Yang H, Liu Q, Wang J, Yue G. An experimental study on the primary fragmentation and attrition of limestones in a fluidized bed. Fuel Process Technol 2010;91:1119–24.
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Oviedo ICCS&T 2011. Extended Abstract
Synthetic gas bench study of CO2 capture from PCC power plants
E. Ruiz, J. M. Sánchez, M. Maroño, J. Otero CIEMAT, Avda. Complutense, 22, 28040, Madrid (SPAIN),
[email protected] Abstract
Much attention is currently paid to the global warming effect due to CO2 emissions. Physical adsorption of CO2 using regenerable sorbents is a promising approach for CO2 capture from flue gases. The Combustion and Gasification Division of CIEMAT recently participated, under the supervision of Tecnicas Reunidas, in the CENIT CO2 Project, funded by CDTI, and led by ENDESA Generación, with the relevant collaboration of UNIÓN FENOSA, 12 industrial partners and 16 research institutions. The role of CIEMAT was to study the potential for CO2 capture of different sorbents, at a representative scale and under realistic conditions resembling those of flue gases after the desulphurisation tower of conventional pulverized coal combustion (PCC) plants. Firstly, comparative adsorption-desorption studies for CO2/N2 mixtures were performed for different sorbents: one alumina-based, one zeolitic-type and one activated carbon. The zeolitic type sorbent was identified as most promising and was subjected to a subsequent in-depth study of its stability, tolerance to poisoning and durability over cycles. Short term tests were performed to assess the effect of competitive adsorption e.g. H2O, and deactivation due to SO2 and NOx. Long term tests were conducted to study the effect of the number of adsorption-desorption cycles. CO2 adsorption breakthrough curves (exit CO2 concentration about 1 %) of the fresh zeolitic material under different gas compositions were obtained. The addition of water had a detrimental effect on CO2 adsorption, shifting CO2 breakthrough curve to shorter times, probably due to competitive adsorption of H2O. The simultaneous presence of H2O and SO2 has a synergic negative effect on CO2 adsorption. However, when H2O, SO2 and NO coexist in the testing gas, the synergic negative effect on CO2 adsorption is slightly attenuated. The adsorbent was also studied on consecutive adsorption-desorption cycles under the different gas compositions. In all cases, there was a certain loss in CO2 adsorption capacity on passing from the first to the second cycle, being almost constant in successive cycles.
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1. Introduction
Recently, much attention is being paid to the global warming effect caused by excessive CO2 emissions. Carbon dioxide is contained, among others, in exhaust gas from combustion of fossil fuels. In post-combustion capture, the CO2 in the exhaust gas is captured using chemical or physical solvents (e.g. amine scrubbing). This is a fairly mature technology for CO2 separation at low temperature and in gases with low CO2 content. However, several drawbacks are often reported in literature such as large scale equipment, chemicals handling, and reduction of thermal efficiency [1-2]. Therefore, new approaches to capture CO2 are now being tackled, e.g. physical adsorption using regenerables adsorbents. Target materials should exhibit high adsorption capacity, selectivity and adsorption rate for CO2 capture. The process of capturing CO2 through physical adsorption methods consists of a first stage of CO2 separation, and a subsequent stage of regeneration in which CO2 is concentrated.
Commercially available devices based on physical adsorption processes operate in adsorption-regeneration cycles. At the adsorption stage, the gas passes through the adsorbent where CO2 is retained, ideally in a selective way. Once the bed of adsorbent reaches CO2 saturation, the gas to treat is forced to flow through another bed of adsorption while the saturated one is regenerated.
Adsorption-desorption cycle time is of the order of minutes and depends on the degree of purification required. The separation of the adsorbent and captured gas is a key stage in the process of adsorption. There are several methods to make the process of adsorption-desorption: -
Temperature Swing Adsorption (TSA): adsorption and desorption of CO2 occurs
at different temperatures. -
Pressure Swing Adsorption (PSA): adsorption and desorption of CO2 occurs at
different pressure. When vacuum is required for regeneration then it is called "Vacuum Swing Adsorption (VSA)".
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Oviedo ICCS&T 2011. Extended Abstract
The use of regenerable adsorbent solids could be a potentially valid alternative to absorbing liquids for capture of CO2 in combustion gases from power plants, although the separation process should be cost-effective, what happens when a highly efficient CO2 adsorbent material is used. It is necessary that the solid adsorbent has a high CO2 adsorption capacity, more than about 90 mg/g of adsorbent, high selectivity towards capturing this component in the gas mixture and the difference of temperatures between the process of adsorption and desorption of CO2 should be the smallest possible. In addition, since the exit of the exhaust gas temperature is around 120 - 150 ° C, the adsorbent material should be able to operate at temperatures relatively high to avoid the stages of cooling and condensation of corrosive compounds.
A number of solids capable of capturing CO2 are being studied, and, according to literature, they can be broadly divided into alumina-based materials, zeolite-type materials, mesoporous materials and carbon materials with different degrees of modifications to enhance CO2 adsorption features. Certain type of zeolite is used as adsorbent of CO2 in industrial applications [3] and it has been considered as a potential candidate for CO2 adsorption in postcombustion capture. However, it is necessary to evaluate its performance under realistic operating conditions and at a scale representative of the new process application.
2. Experimental section
Adsorption and desorption tests were performed in an existing bench-scale plant which was subsequently adapted for postcombustion capture of CO2 (Figure 1). The plant can treat up to 20 Nm3/h of both simulated and actual combustion off-gases. Process temperature can be up to 500ºC at about atmospheric pressure. The plant has been described in detail elsewhere [4].
The analytical monitoring of the adsorption-desorption processes was carried out by means of an FTIR analyzer.
Temperature and pressure drop along the bed and gas constituent flow rates were recorded during the adsorption/desorption tests.
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Oviedo ICCS&T 2011. Extended Abstract
Adsorption/desorption cycles were carried out in an atmospheric pressure fixed bed reactor.
The tested adsorbents were a commercial activated carbon and a synthetic activated alumina impregnated with Na2CO3 (10% weight), both of them in the form of cylindrical pellets, as well as a commercial zeolite-based material simulating one prepared from ashes of thermal power stations, in the form of spherical pellets.
Figure 1. Diagram of the bench-scale plant modified to study CO2 capture from combustion off-gases
Conditions of the adsorption-desorption comparative tests are listed in Table 1. Operating conditions utilized for the zeolite stability study are listed in Table 2. Desorption tests were carried out by flowing N2 at 110 º C and at atmospheric pressure. Table 1. Adsorption-desorption comparative tests. Operating conditions Adsorbent Adsorption gas (v/v) Adsorption T. (ºC) Desorption gas (v/v) Desorption T. (ºC) Space velocity (Nl h-1 g-1) Number of cycles
Activated alumina 15 % CO2 in N2 47 N2 47 0,88 3
Activated carbon 15 % CO2 in N2 47 N2 110 0,88 1
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Oviedo ICCS&T 2011. Extended Abstract
Table 2. Zeolitic adsorbent stability study. Operating conditions Adsorption composition (%) 15 CO2, N2 balance 15 CO2, 10.7 H2O, N2 balance 15 CO2, 10.7 H2O, 5 O2, 0.0174 SO2, N2 balance 15 CO2, 10.7 H2O, 5 O2, 0.0174 SO2, 0.0495 NO, N2 balance
Temperature (˚C) 47 47 47 47
3. Results and Discussion
In order to compare the performance of the different materials studied, the CO2 breakthrough adsorption curves of the fresh adsorbents were obtained.
The adsorption process was characterised in terms of net CO2 capture capacity and useful adsorption time. They are defined as:
- Net CO2 capture capacity: amount of CO2 adsorbed until the CO2 exit concentration reaches 1% v/v. - Useful adsorption time: time during which the CO2 exit concentration is less than 1% v/v.
The experimental results obtained in dry gas adsorption tests for activated alumina, activated carbon and zelolite are shown in Table 3, 4 and 5 respectively.
A comparison between CO2 breakthrough adsorption curves corresponding to activated alumina, activated carbon and zeolite is depicted in Figure 2.
Table 3. Experimental results. Activated Alumina Test Net CO2 capture capacity (mg CO2/gadsorbent) Useful adsorption time (sec) 1st cycle 22.4 330 rd 3 cycle 3.6 54 Table 4. Experimental results. Activated carbon Test Net CO2 capture capacity (mg CO2/gadsorbent) Useful adsorption time (sec) st 1 cycle 4.2 78
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Oviedo ICCS&T 2011. Extended Abstract
Table 5. Experimental results. Zeolite Test 1st cycle 2nd cycle 3rd cycle 4th cycle 5th cycle
Net CO2 capture capacity (mg CO2/gadsorbent) 134.2 85.9 82.4 80.3 77.5
Useful adsorption time (sec) 1716 1188 1140 1110 1068
1.0
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Figure 2. Comparative between CO2 breakthrough curves of the different adsorbents Analyzing the experimental results shown in Table 3 and Figure 2, respectively, it can be seen that there is a significant adsorption capacity loss in the case of activated alumina on passing from the first adsorption cycle to the following one. In fact, Table 3 shows a sharp decline in both the net CO2 capture capacity and the useful time of adsorption. Figure 2 shows a shift in the breakthrough curve to lower adsorption times, in line with the trend observed in the adsorption parameters.
The activated carbon exhibits a low adsorption capacity, even in the case of using fresh adsorbent, as seems to be evident from the experimental results shown in Table 4 and Figure 2 respectively. For this reason, only looking at performance in the first cycle of adsorption, it was ruled out both the subsequent regeneration run and to conduct successive cycles of adsorption-desorption.
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Oviedo ICCS&T 2011. Extended Abstract
For the zeolite adsorbent, there was a considerable reduction in CO2 adsorption capacity on passing from the first to the second cycle, remaining, however, almost constant in successive cycles. The capacity loss in the second adsorption cycle was probably due to an inefficient regeneration at the temperature level imposed by the postcombustion CO2 capture process, as it is clear from the experimental results shown in Table 5 and Figure 2, respectively. In fact, Table 5 shows a sharp decline in both the net CO2 capture capacity and the useful adsorption time on passing from the first cycle to the following one and a more gradual reduction in successive cycles. Figure 2 shows a shift in the breakthrough curve to lower adsorption times, in line with the trend observed in the adsorption parameters.
In the case of the zeolitic adsorbent the value of the regeneration temperature (47 ° C and 110 ° C) was alternated in the successive adsorption-desorption cycles in order to analyse the influence of the regeneration temperature in the subsequent behaviour of the adsorbent. The analysis of the adsorption parameters in Table 5, and the trend of the breakthrough curves in Figure 2, follows that regeneration at 110 ºC is slightly more effective than at 47 ° C. However, it is necessary to analyse if the energy penalty associated with this increase in the desorption temperature is compensated by the improvement in the effectiveness of regeneration.
On comparing the CO2 breakthrough curves of activated alumina, activated carbon, and zeolite in the presence of dry gas (Figure 2), it can be derived that the behaviour of the latter is far superior to those of the activated alumina and activated carbon. Therefore, this material was selected at the most promising at this point and was subsequently subjected to an in-depth stability study under more realistic conditions.
CO2 breakthrough (CO2 exit concentration about 1 %) adsorption curves of the fresh zeolitic material under the different gas composition are shown in Figure 3. Addition of water has a detrimental effect on CO2 adsorption, shifting CO2 breakthrough curve to shorter times, probably due to competitive adsorption of H2O. The simultaneous presence of H2O and SO2 has a synergic negative effect on CO2 adsorption. It seems that both H2O and SO2 compete with CO2 for adsorption sites on the zeolite surface. However, when H2O, SO2 and NO coexist in the testing gas, the synergic negative effect on CO2 adsorption is slightly attenuated. Submit before 31 May 2011 to
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Oviedo ICCS&T 2011. Extended Abstract
1.0 FRESH ZEOLITE
Exiting CO2 (%)
0.8
CO2+N2 CO2+H2O+N2
0.6
CO2+H2O+O2+SO2+N2
0.4
CO2+H2O+O2+SO2+NO+N2
0.2 27mg/g 54mg/g 70 mg/g
134 mg/g
0.0 0
250
500
750
1000
1250
1500
1750
Time (sec) Figure 3. CO2 breakthrough adsorption curves of the fresh zeolite adsorbent The adsorbent was also studied on consecutive adsorption-desorption cycles under the different gas compositions shown in Table 2. In all cases, there was a considerable reduction in CO2 adsorption capacity on passing from the first to the second cycle, being almost constant in successive cycles, probably due to an inefficient regeneration at the temperature level imposed by the postcombustion CO2 capture process. As an example, the long term performance of the zeolitic material in the presence of all typical constituents of the combustion flue gas is shown in Figure 4.
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Oviedo ICCS&T 2011. Extended Abstract
1.0
Exiting CO2 (%)
0.8
4º
ZEOLITA ENSAYO MULTI-CICLO MULTY-CYCLE TEST O+O CO2CO +H2 2+SO 2+NO+N 2 +H O+O +SO +NO+N 2
2
2
2
2
0.6 28 mg/g
6º
2º
0.4
1º 0.2 0.0 0
50 100 150 200 250 300 350 400 450 500 550
Time (sec) Figure 4. CO2 breakthrough adsorption curves of the zeolite adsorbent on consecutive adsorption-desorption cycle.
4. Conclusions
On the one hand, activated alumina rendered a poor behaviour of adsorption, with low adsorption capacities (including for the fresh sample) and low effectiveness of regeneration under the operating conditions imposed by the potential application of the process (at the exit of the desulfurization tower), because the temperatures are lower than the required for an effective regeneration of the adsorbent. For this reason, it was discarded as promising adsorbent.
The activated carbon was also discarded as promising adsorbent due to the observed low adsorption capacity even for the first cycle with fresh adsorbent.
The adsorption/desorption behaviour of the zeolite is far superior to those of the activated alumina and activated carbon. For this reason, the zeolite was selected as the most promising adsorbent for further deepen in the study of the CO2 adsorption/desorption processes under different operating conditions and over successive cycles. However, there are some limitations for the application of the tested
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Oviedo ICCS&T 2011. Extended Abstract
zeolite to postcombustion CO2 capture, due to a lack of selectivity and regenerability under conditions representative of flue gases from atmospheric pulverized coal boilers. Moreover, the tolerance and durability studies make evident that the CO2 adsorption capacity of the zeolite decreased on passing from the first to the second cycle, the presence of water diminished CO2 adsorption capacity by competitive adsorption and the simultaneous presence of H2O and SO2 has a synergic negative effect on CO2 adsorption capacity, although this synergic negative effect on CO2 adsorption is slightly attenuated under the coexistence of H2O, SO2, O2 and NO Acknowledgement.
Financial support from Centro para el Desarrollo Tecnológico Industrial of the Ministerio de Ciencia e Innovación of Spain (Project CENIT CO2) is acknowledged. The authors thank project partners for supplying the different adsorbents studied.
References [1] Bredesen R, Jordal K, Bolland O. High-temperature membranes in power generation with CO2 capture. Chem Eng Proc 2004;43:1129–58. [2] Simmonds M, Hurst P, Wilkinson MB, Watt C, Roberts CA. A study of very large scale post combustion CO2 capture at a refining & petrochemical complex. In: Gale J, Kaya Y, editors. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies, London: Elsevier; 2003, p. 39–44. [3] Zhao Z, Cui X, Ma J, Li R. Adsorption of carbon dioxide on alkali-modified zeolite 13X adsorbents. International Journal of Greenhouse Gas Control 2007;1:355–9. [4] Ruiz E, Sánchez JM, Maroño M, Otero J. CO2 capture from flue gases by physical adsorption. In: Abstracts of International Symposium about Capture and Storage of CO2, Seville, 2008.
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The influence of particle size on the steam gasification of coal G. Hennie Coetzee, Hein W.J.P Neomagus*, Raymond C. Everson School of Chemical and Minerals Engineering, Energy Systems, North-West University, Potchefstroom Campus, Private Bag X6001, Noordbrug 2520, South Africa *corresponding author: Tel. + 27 18 2991991, Fax: + 27 18 2991535, E-mail:
[email protected] Abstract The conversion of coal with steam into synthesis gas is an important intermediate reaction for e.g. the production of synthetic fuels. Due to the importance of this reaction, numerous reaction kinetic studies have been carried out on steam gasification, mainly on powdered coal samples. However, very few studies have addressed the steam gasification of large particles (> 1 mm) although several combustion and gasification technologies are based on the conversion of large particles. In this study, the effect of particle size (5 mm – 30 mm) on the steam gasification reaction rate is studied.
For this purpose, a medium rank, bituminous coal was investigated and particles with a density between 1400 and 1500 kg/m3 were selected using a mercury submersion technique. The results from this method were also compared with the results obtained from helium picnometry and mercury intrusion, so as to obtain more information about the porous structure of the coal.
The reactivity experiments were carried out in a large particle TGA, constructed in-house. The TGA is operated in such a way that the single coal particles are converted in the chemical reaction controlled regime. Steam and nitrogen were fed to the reactor, with a feed composition of 90 mol% steam. The data obtained from the reactivity experiments were modelled by several particle models, including (modifications of) the random pore and shrinking core model. Keywords: steam gasification; large coal particles; reaction kinetics; mercury submersion density analysis.
1. Introduction Coal is not only one of the most important sources of energy, but also the fastest growing energy source in the world[1]. According to WCI[1], South Africa is the fifth largest producer of coal and has the seventh largest coal reserve. South Africa’s abundant coal reserves allow it to meet the increasing energy demand. However, the coal reserves will eventually deplete, and therefore the efficient utilization of coal is crucial.
Comentario [A1]: Capacity increase?
South Africa’s unique synfuels and petrochemical industry is largely driven by SASOL, where coal is used as a feedstock to the gasification process. The coal is converted to synthesis gas, which is then converted to fuel using the Fisher-Tropsch process. The global demand for syngas is increasing at a rate of around 10% per year, which results in intensive research regarding the optimization and improvement of the gasification process[2].
Comentario [A2]: No problems here with quoting Sasol?
Due to the large size distribution of coal particles fed to the gasifier, it is important to extend the knowledge of particle size influence on the steam gasification reaction rate. Previous studies conducted on the steam gasification of coal were done on small particles or pulverised coal (-1 mm) [3-6]. Therefore, this study investigates the influence of large coal particles (5-30 mm) on steam gasification reactivity.
2. Experimental The coal used for this study originates from a Highveld coalfield, number 4 seam, and is mostly used for synthetic fuel production[7]. The reactivity experiments were done on single large coal particles, which were hand selected on a dimension basis. The length, width and height of the particles are used to categorise the size of the coal particle. The hand selected coal particles are then further sorted according to bulk density using the mercury submersion analysis. 2.1 Mercury submersion The mercury submersion analysis determines the bulk density of a coal particle using mercury as the submersion fluid. The coal particle is submerged and the buoyancy force of the coal particle is measured using a laboratory scale. The experimental setup is shown in Figure 1.
Comentario [A3]: Not always, inform that you use single particles for 20 and 40 and multiple (how many?) for 5 and 10
Figure 1: Mercury submersion experimental setup.
Single coal particles are used when determining the bulk density of the 20 and 30mm particles, while an average bulk density is calculated for the 5 and 10 mm particles.
2.2 Reactivity experiments The reactivity experiments were carried out in a large particle TGA, constructed in-house. The TGA consists of a vertical tube furnace which has an inner pipe diameter of 53mm. The reactants, steam and nitrogen, are fed from the top of the furnace as shown in Figure 2. Steam is generated using heating coils and water is fed to the heating coils using a variable speed peristaltic pump. The sample is situated inside a sample basket, which is located on top of a laboratory mass balance. The reactivity experimental setup is shown in Figure 2.
Figure 2: Reactivity experimental setup.
The samples were charred at the reactivity temperature in an inert nitrogen atmosphere. The reactivity experiments were carried out isothermally at 775 ˚C, 800 ˚C, 825 ˚C, 850 ˚C and 900 ˚C, in a 90 mol% steam concentration atmosphere. Single coal particles were used for the reactivity experiments of the 20 mm and 30 mm particles, while coal samples with several particles were used for the reactivity experiments of the 5 mm and 10 mm.
3. Results and discussion 3.1 Mercury submersion The mercury submersion method, which is a non-destructive method, was developed to accurately determine the bulk density of a single large coal particle. Since this method is non-destructive, the density of a single large particle can be measured, after which the same particle can be used for reactivity experiments. 20 mm (70 particles) and 30 mm (80 particles) single coal particles were hand selected and the bulk density of each coal particle was determined using the mercury submersion method. The results are shown in Figure 3 and 4.
Figure 3: Density analysis of 20 mm particles.
Figure 4: Density analysis of 30 mm particles.
From Figure 3 and 4 it is seen that the mean bulk density is between 1400-1500 kg/m3 and for this reason a density cut between 1400-1500 kg/m3 was used for the reactivity experiments. A density cut is used to reduce the deviation in ash percentage[8,9] and maceral composition[8,10,11] for the single coal particle which will increase the homogeneity of coal samples used. This will result in smaller deviations obtained in the reactivity experiments. 3.2 Coal characterisation
The Proximate, Ultimate, Calorific value and XRF analysis were done on a representative coal sample. The analyses were outsourced to Advanced Coal Technology Laboratories (Pty) Ltd. The summarised results for these analyses are shown in Table 1: Table 1: Coal characterisation results and comparison with literature.
Procedure Proximate analysis Moisture content (%) Ash content (%) Volatile matter content (%) Fixed carbon content (%) Fuel ratio (%) Ultimate anlysis H/C ratio O/C ratio Other Calorific value (MJ/kg) Alkali index
Result
Hoffman (2009)
Pinheiro (1999)
7.0 18.4 23.4 51.2 2.2
6.5 20.5 22.3 50.7 2.3
5.6 28.3 22.0 44.1 2.0
0.062 0.267
0.071 0.308
0.053 0.175
22.59 5.9
22.28 5.8
19.69 3.3
The results obtained for the coal characterisation was compared to Hoffman[12] and Pinheiro[13], which studied coal from the same region and seam (Highveld seam 4). It was found that the characterisation results compares well to what was found by Oberholzer[12]. However, the results obtained by Pinheiro do not compare well and the difference may be as a result of the different areas of the coal field mined over the past 10 years.
The mercury intrusion and CO2-BET analysis were done on a density cut (1400 – 1500 kg/m3) of the 5, 10, 20 and 30 mm particles. The analysis was done to determine the effect of particle size on the physical structure of the chars. The different coal samples was charred at 900 ˚C for 1h and prepared for mercury intrusion and CO2-BET. The short coal method was used for CO2-BET analysis at 273.15 K (which includes BET, Langmuir, DubininRadushkevich and Horvart-Kawazoe models). The results obtained for mercury intrusion and CO2-BET (BET model results) are shown in Table 2. Table 2: Mercury intrusion and CO2-BET results.
CO2-BET Particle size mm 30 20 10 5
Surface area (m2/g) 185 188 183 168
Mercury intrusion Particle size mm 30 20 10 5
Porosity (%) 16 16 16 23
From the results presented in Table 2, it is seen that there is no considerable physical structural change between the 10, 20 and 30 mm particles. However, the results obtained suggest that there are structural changes between the 5 mm particles and the other three particle sizes.
The deviation can be attributed to the sample selection method used to
determine the bulk density of the 5 mm coal particles.
3.3 Reactivity experiments
The reactivity experiments were done in order to determine the influence of coal particle size on the reactivity of steam gasification of coal. 5, 10, 20 and 30 mm coal particles were gasified at 775, 800, 825, 850 and 900 ˚C, using a steam concentration of 80 mol%. The coal samples for the 5 mm and 10 mm particles were weighed to ensure sufficient sample weight, in order to overcome large particle TGA limitations. Adequate repeatability of the 5 mm and 10 mm TGA runs were obtained after 2 to 3 runs. However, up to 4 runs were required for the 20 mm and 30 mm particles to obtain repeatable results. Repeatability tests for the steam gasification of the 30 mm single coal particles, at 900 ˚C, are shown in Figure 5.
Figure 5: Results to determine the repeatability of reactivity experiments at 900 ˚C.
From Figure 5 it is seen that 3 runs were used to validate repeatability of the results. The average conversion (up to 90%) for the 3 runs where determined and is also shown in Figure 5. The same was done for all the particle sizes at the various gasification temperatures, and the average conversion is used from this point on to compare results. Figure 6 shows the results for the average conversion of 30 mm coal particles for 775, 800, 850 and 900 ˚C.
Figure 6: Average conversion for the 30 mm coal particles.
The average conversion results are shown in Figure 6 for the 30 mm particles at the various gasification temperatures. The 95% confidence errors obtained from the multiple runs are also included in Figure 6 and range from 0.01 for the 850 ˚C runs to 0.1 for the 825 ˚C runs. From Figure 6 it can be seen that an increase in temperature results in an increase in reaction rate. For the increase in temperature (from 775 to 800 ˚C and 800 to 825 ˚C) a large decrease in reaction time is seen. However, the decrease in reaction time for an increase in reaction temperature (from 825 to 850 ˚C and 850 to 900 ˚C) is much smaller than what is observed for the lower temperatures. The same trend is observed for the 5, 10 and 20 mm reactivity experiments.
To determine the influence of particle size on the reactivity of steam gasification of coal, the average conversion of four particle sizes at a set temperature is compared. Figure 7 illustrates the average conversion (up to 90%) of the 5, 10, 20, and 30mm particles at 900 ˚C.
Figure 7: Comparison of average conversion of all the particle sizes at 900 ˚C.
From Figure 7 it is seen that the particle size does have an influence on the reactivity of steam gasification of coal at 900 ˚C. There is no distinct difference in the average conversion (up to 90%) of the 20 and 30 mm particle size, which can be attributed to the fracturing of large coal particles at high temperatures. A study conducted by Bunt & Waanders14on the thermal breakage of coal, concluded that particles larger than 25 mm fracture to form multiple smaller particles. However, thermal breakage of coal particles larger than 25 mm is not observed at lower gasification temperatures (
