Energy and Sustainability 2 (Wit Transactions on Ecology and the Environment)

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Energy and Sustainability II

WIT Press publishes leading books in Science and Technology. Visit our website for new and current list of titles. www.witpress.com

WITeLibrary Home of the Transactions of the Wessex Institute. Papers presented at ENERGY 09 are archived in the WIT eLibrary in volume 121 of WIT Transactions on Ecology and the Environment (ISSN 1743-3541). The WIT eLibrary provides the international scientific community with immediate and permanent access to individual papers presented at WIT conferences. Visit the WIT eLibrary at www.witpress.com.

SECOND INTERNATIONAL CONFERENCE ON ENERGY AND SUSTAINABILITY

ENERGY 2009 CONFERENCE CHAIRMEN C.A. Brebbia Wessex Institute of Technology, UK A.A. Mammoli University of New Mexico, USA

INTERNATIONAL SCIENTIFIC ADVISORY COMMITTEE N. Abatzoglou S. Basbas B. Bieda M. Ektesabi M. El-Genk M.A. Haggag G. Passerini F. Patania F.M. Pulselli E. Tiezzi A. van Timmeren T. Zdankus

Organised by Wessex Institute of Technology, UK University of New Mexico, USA Sponsored by WIT Transactions on Ecology and the Environment

WIT Transactions Transactions Editor Carlos Brebbia Wessex Institute of Technology Ashurst Lodge, Ashurst Southampton SO40 7AA, UK Email: [email protected]

Editorial Board B Abersek University of Maribor, Slovenia Y N Abousleiman University of Oklahoma, USA P L Aguilar University of Extremadura, Spain K S Al Jabri Sultan Qaboos University, Oman E Alarcon Universidad Politecnica de Madrid, Spain A Aldama IMTA, Mexico C Alessandri Universita di Ferrara, Italy D Almorza Gomar University of Cadiz, Spain B Alzahabi Kettering University, USA J A C Ambrosio IDMEC, Portugal A M Amer Cairo University, Egypt S A Anagnostopoulos University of Patras, Greece M Andretta Montecatini, Italy E Angelino A.R.P.A. Lombardia, Italy H Antes Technische Universitat Braunschweig, Germany M A Atherton South Bank University, UK A G Atkins University of Reading, UK D Aubry Ecole Centrale de Paris, France H Azegami Toyohashi University of Technology, Japan A F M Azevedo University of Porto, Portugal J Baish Bucknell University, USA J M Baldasano Universitat Politecnica de Catalunya, Spain J G Bartzis Institute of Nuclear Technology, Greece A Bejan Duke University, USA

M P Bekakos Democritus University of Thrace, Greece G Belingardi Politecnico di Torino, Italy R Belmans Katholieke Universiteit Leuven, Belgium C D Bertram The University of New South Wales, Australia D E Beskos University of Patras, Greece S K Bhattacharyya Indian Institute of Technology, India E Blums Latvian Academy of Sciences, Latvia J Boarder Cartref Consulting Systems, UK B Bobee Institut National de la Recherche Scientifique, Canada H Boileau ESIGEC, France J J Bommer Imperial College London, UK M Bonnet Ecole Polytechnique, France C A Borrego University of Aveiro, Portugal A R Bretones University of Granada, Spain J A Bryant University of Exeter, UK F-G Buchholz Universitat Gesanthochschule Paderborn, Germany M B Bush The University of Western Australia, Australia F Butera Politecnico di Milano, Italy J Byrne University of Portsmouth, UK W Cantwell Liverpool University, UK D J Cartwright Bucknell University, USA P G Carydis National Technical University of Athens, Greece J J Casares Long Universidad de Santiago de Compostela, Spain, M A Celia Princeton University, USA A Chakrabarti Indian Institute of Science, India

A H-D Cheng University of Mississippi, USA J Chilton University of Lincoln, UK C-L Chiu University of Pittsburgh, USA H Choi Kangnung National University, Korea A Cieslak Technical University of Lodz, Poland S Clement Transport System Centre, Australia M W Collins Brunel University, UK J J Connor Massachusetts Institute of Technology, USA M C Constantinou State University of New York at Buffalo, USA D E Cormack University of Toronto, Canada M Costantino Royal Bank of Scotland, UK D F Cutler Royal Botanic Gardens, UK W Czyczula Krakow University of Technology, Poland M da Conceicao Cunha University of Coimbra, Portugal A Davies University of Hertfordshire, UK M Davis Temple University, USA A B de Almeida Instituto Superior Tecnico, Portugal E R de Arantes e Oliveira Instituto Superior Tecnico, Portugal L De Biase University of Milan, Italy R de Borst Delft University of Technology, Netherlands G De Mey University of Ghent, Belgium A De Montis Universita di Cagliari, Italy A De Naeyer Universiteit Ghent, Belgium W P De Wilde Vrije Universiteit Brussel, Belgium L Debnath University of Texas-Pan American, USA N J Dedios Mimbela Universidad de Cordoba, Spain G Degrande Katholieke Universiteit Leuven, Belgium S del Giudice University of Udine, Italy G Deplano Universita di Cagliari, Italy I Doltsinis University of Stuttgart, Germany M Domaszewski Universite de Technologie de Belfort-Montbeliard, France J Dominguez University of Seville, Spain

K Dorow Pacific Northwest National Laboratory, USA W Dover University College London, UK C Dowlen South Bank University, UK J P du Plessis University of Stellenbosch, South Africa R Duffell University of Hertfordshire, UK A Ebel University of Cologne, Germany E E Edoutos Democritus University of Thrace, Greece G K Egan Monash University, Australia K M Elawadly Alexandria University, Egypt K-H Elmer Universitat Hannover, Germany D Elms University of Canterbury, New Zealand M E M El-Sayed Kettering University, USA D M Elsom Oxford Brookes University, UK A El-Zafrany Cranfield University, UK F Erdogan Lehigh University, USA F P Escrig University of Seville, Spain D J Evans Nottingham Trent University, UK J W Everett Rowan University, USA M Faghri University of Rhode Island, USA R A Falconer Cardiff University, UK M N Fardis University of Patras, Greece P Fedelinski Silesian Technical University, Poland H J S Fernando Arizona State University, USA S Finger Carnegie Mellon University, USA J I Frankel University of Tennessee, USA D M Fraser University of Cape Town, South Africa M J Fritzler University of Calgary, Canada U Gabbert Otto-von-Guericke Universitat Magdeburg, Germany G Gambolati Universita di Padova, Italy C J Gantes National Technical University of Athens, Greece L Gaul Universitat Stuttgart, Germany A Genco University of Palermo, Italy N Georgantzis Universitat Jaume I, Spain P Giudici Universita di Pavia, Italy F Gomez Universidad Politecnica de Valencia, Spain R Gomez Martin University of Granada, Spain D Goulias University of Maryland, USA

K G Goulias Pennsylvania State University, USA F Grandori Politecnico di Milano, Italy W E Grant Texas A & M University, USA S Grilli University of Rhode Island, USA R H J Grimshaw, Loughborough University, UK D Gross Technische Hochschule Darmstadt, Germany R Grundmann Technische Universitat Dresden, Germany A Gualtierotti IDHEAP, Switzerland R C Gupta National University of Singapore, Singapore J M Hale University of Newcastle, UK K Hameyer Katholieke Universiteit Leuven, Belgium C Hanke Danish Technical University, Denmark K Hayami National Institute of Informatics, Japan Y Hayashi Nagoya University, Japan L Haydock Newage International Limited, UK A H Hendrickx Free University of Brussels, Belgium C Herman John Hopkins University, USA S Heslop University of Bristol, UK I Hideaki Nagoya University, Japan D A Hills University of Oxford, UK W F Huebner Southwest Research Institute, USA J A C Humphrey Bucknell University, USA M Y Hussaini Florida State University, USA W Hutchinson Edith Cowan University, Australia T H Hyde University of Nottingham, UK M Iguchi Science University of Tokyo, Japan D B Ingham University of Leeds, UK L Int Panis VITO Expertisecentrum IMS, Belgium N Ishikawa National Defence Academy, Japan J Jaafar UiTm, Malaysia W Jager Technical University of Dresden, Germany Y Jaluria Rutgers University, USA C M Jefferson University of the West of England, UK P R Johnston Griffith University, Australia

D R H Jones University of Cambridge, UK N Jones University of Liverpool, UK D Kaliampakos National Technical University of Athens, Greece N Kamiya Nagoya University, Japan D L Karabalis University of Patras, Greece M Karlsson Linkoping University, Sweden T Katayama Doshisha University, Japan K L Katsifarakis Aristotle University of Thessaloniki, Greece J T Katsikadelis National Technical University of Athens, Greece E Kausel Massachusetts Institute of Technology, USA H Kawashima The University of Tokyo, Japan B A Kazimee Washington State University, USA S Kim University of Wisconsin-Madison, USA D Kirkland Nicholas Grimshaw & Partners Ltd, UK E Kita Nagoya University, Japan A S Kobayashi University of Washington, USA T Kobayashi University of Tokyo, Japan D Koga Saga University, Japan A Konrad University of Toronto, Canada S Kotake University of Tokyo, Japan A N Kounadis National Technical University of Athens, Greece W B Kratzig Ruhr Universitat Bochum, Germany T Krauthammer Penn State University, USA C-H Lai University of Greenwich, UK M Langseth Norwegian University of Science and Technology, Norway B S Larsen Technical University of Denmark, Denmark F Lattarulo, Politecnico di Bari, Italy A Lebedev Moscow State University, Russia L J Leon University of Montreal, Canada D Lewis Mississippi State University, USA S lghobashi University of California Irvine, USA K-C Lin University of New Brunswick, Canada A A Liolios Democritus University of Thrace, Greece

S Lomov Katholieke Universiteit Leuven, Belgium J W S Longhurst University of the West of England, UK G Loo The University of Auckland, New Zealand J Lourenco Universidade do Minho, Portugal J E Luco University of California at San Diego, USA H Lui State Seismological Bureau Harbin, China C J Lumsden University of Toronto, Canada L Lundqvist Division of Transport and Location Analysis, Sweden T Lyons Murdoch University, Australia Y-W Mai University of Sydney, Australia M Majowiecki University of Bologna, Italy D Malerba Università degli Studi di Bari, Italy G Manara University of Pisa, Italy B N Mandal Indian Statistical Institute, India Ü Mander University of Tartu, Estonia H A Mang Technische Universitat Wien, Austria, G D, Manolis, Aristotle University of Thessaloniki, Greece W J Mansur COPPE/UFRJ, Brazil N Marchettini University of Siena, Italy J D M Marsh Griffith University, Australia J F Martin-Duque Universidad Complutense, Spain T Matsui Nagoya University, Japan G Mattrisch DaimlerChrysler AG, Germany F M Mazzolani University of Naples “Federico II”, Italy K McManis University of New Orleans, USA A C Mendes Universidade de Beira Interior, Portugal, R A Meric Research Institute for Basic Sciences, Turkey J Mikielewicz Polish Academy of Sciences, Poland N Milic-Frayling Microsoft Research Ltd, UK R A W Mines University of Liverpool, UK C A Mitchell University of Sydney, Australia

K Miura Kajima Corporation, Japan A Miyamoto Yamaguchi University, Japan T Miyoshi Kobe University, Japan G Molinari University of Genoa, Italy T B Moodie University of Alberta, Canada D B Murray Trinity College Dublin, Ireland G Nakhaeizadeh DaimlerChrysler AG, Germany M B Neace Mercer University, USA D Necsulescu University of Ottawa, Canada F Neumann University of Vienna, Austria S-I Nishida Saga University, Japan H Nisitani Kyushu Sangyo University, Japan B Notaros University of Massachusetts, USA P O’Donoghue University College Dublin, Ireland R O O’Neill Oak Ridge National Laboratory, USA M Ohkusu Kyushu University, Japan G Oliveto Universitá di Catania, Italy R Olsen Camp Dresser & McKee Inc., USA E Oñate Universitat Politecnica de Catalunya, Spain K Onishi Ibaraki University, Japan P H Oosthuizen Queens University, Canada E L Ortiz Imperial College London, UK E Outa Waseda University, Japan A S Papageorgiou Rensselaer Polytechnic Institute, USA J Park Seoul National University, Korea G Passerini Universita delle Marche, Italy B C Patten, University of Georgia, USA G Pelosi University of Florence, Italy G G Penelis, Aristotle University of Thessaloniki, Greece W Perrie Bedford Institute of Oceanography, Canada R Pietrabissa Politecnico di Milano, Italy H Pina Instituto Superior Tecnico, Portugal M F Platzer Naval Postgraduate School, USA D Poljak University of Split, Croatia V Popov Wessex Institute of Technology, UK H Power University of Nottingham, UK D Prandle Proudman Oceanographic Laboratory, UK

M Predeleanu University Paris VI, France M R I Purvis University of Portsmouth, UK I S Putra Institute of Technology Bandung, Indonesia Y A Pykh Russian Academy of Sciences, Russia F Rachidi EMC Group, Switzerland M Rahman Dalhousie University, Canada K R Rajagopal Texas A & M University, USA T Rang Tallinn Technical University, Estonia J Rao Case Western Reserve University, USA A M Reinhorn State University of New York at Buffalo, USA A D Rey McGill University, Canada D N Riahi University of Illinois at UrbanaChampaign, USA B Ribas Spanish National Centre for Environmental Health, Spain K Richter Graz University of Technology, Austria S Rinaldi Politecnico di Milano, Italy F Robuste Universitat Politecnica de Catalunya, Spain J Roddick Flinders University, Australia A C Rodrigues Universidade Nova de Lisboa, Portugal F Rodrigues Poly Institute of Porto, Portugal C W Roeder University of Washington, USA J M Roesset Texas A & M University, USA W Roetzel Universitaet der Bundeswehr Hamburg, Germany V Roje University of Split, Croatia R Rosset Laboratoire d’Aerologie, France J L Rubio Centro de Investigaciones sobre Desertificacion, Spain T J Rudolphi Iowa State University, USA S Russenchuck Magnet Group, Switzerland H Ryssel Fraunhofer Institut Integrierte Schaltungen, Germany S G Saad American University in Cairo, Egypt M Saiidi University of Nevada-Reno, USA R San Jose Technical University of Madrid, Spain F J Sanchez-Sesma Instituto Mexicano del Petroleo, Mexico

B Sarler Nova Gorica Polytechnic, Slovenia S A Savidis Technische Universitat Berlin, Germany A Savini Universita de Pavia, Italy G Schmid Ruhr-Universitat Bochum, Germany R Schmidt RWTH Aachen, Germany B Scholtes Universitaet of Kassel, Germany W Schreiber University of Alabama, USA A P S Selvadurai McGill University, Canada J J Sendra University of Seville, Spain J J Sharp Memorial University of Newfoundland, Canada Q Shen Massachusetts Institute of Technology, USA X Shixiong Fudan University, China G C Sih Lehigh University, USA L C Simoes University of Coimbra, Portugal A C Singhal Arizona State University, USA P Skerget University of Maribor, Slovenia J Sladek Slovak Academy of Sciences, Slovakia V Sladek Slovak Academy of Sciences, Slovakia A C M Sousa University of New Brunswick, Canada H Sozer Illinois Institute of Technology, USA D B Spalding CHAM, UK P D Spanos Rice University, USA T Speck Albert-Ludwigs-Universitaet Freiburg, Germany C C Spyrakos National Technical University of Athens, Greece I V Stangeeva St Petersburg University, Russia J Stasiek Technical University of Gdansk, Poland G E Swaters University of Alberta, Canada S Syngellakis University of Southampton, UK J Szmyd University of Mining and Metallurgy, Poland S T Tadano Hokkaido University, Japan H Takemiya Okayama University, Japan I Takewaki Kyoto University, Japan C-L Tan Carleton University, Canada M Tanaka Shinshu University, Japan E Taniguchi Kyoto University, Japan

S Tanimura Aichi University of Technology, Japan J L Tassoulas University of Texas at Austin, USA M A P Taylor University of South Australia, Australia A Terranova Politecnico di Milano, Italy E Tiezzi University of Siena, Italy A G Tijhuis Technische Universiteit Eindhoven, Netherlands T Tirabassi Institute FISBAT-CNR, Italy S Tkachenko Otto-von-GuerickeUniversity, Germany N Tosaka Nihon University, Japan T Tran-Cong University of Southern Queensland, Australia R Tremblay Ecole Polytechnique, Canada I Tsukrov University of New Hampshire, USA R Turra CINECA Interuniversity Computing Centre, Italy S G Tushinski Moscow State University, Russia J-L Uso Universitat Jaume I, Spain E Van den Bulck Katholieke Universiteit Leuven, Belgium D Van den Poel Ghent University, Belgium R van der Heijden Radboud University, Netherlands R van Duin Delft University of Technology, Netherlands P Vas University of Aberdeen, UK W S Venturini University of Sao Paulo, Brazil

R Verhoeven Ghent University, Belgium A Viguri Universitat Jaume I, Spain Y Villacampa Esteve Universidad de Alicante, Spain F F V Vincent University of Bath, UK S Walker Imperial College, UK G Walters University of Exeter, UK B Weiss University of Vienna, Austria H Westphal University of Magdeburg, Germany J R Whiteman Brunel University, UK Z-Y Yan Peking University, China S Yanniotis Agricultural University of Athens, Greece A Yeh University of Hong Kong, China J Yoon Old Dominion University, USA K Yoshizato Hiroshima University, Japan T X Yu Hong Kong University of Science & Technology, Hong Kong M Zador Technical University of Budapest, Hungary K Zakrzewski Politechnika Lodzka, Poland M Zamir University of Western Ontario, Canada R Zarnic University of Ljubljana, Slovenia G Zharkova Institute of Theoretical and Applied Mechanics, Russia N Zhong Maebashi Institute of Technology, Japan H G Zimmermann Siemens AG, Germany


Editors: C.A. Brebbia Wessex Institute of Technology, UK A.A. Mammoli Univeristy of New Mexico, USA

Editors: C.A. Brebbia Wessex Institute of Technology, UK A.A. Mammoli Univeristy of New Mexico, USA

Published by WIT Press Ashurst Lodge, Ashurst, Southampton, SO40 7AA, UK Tel: 44 (0) 238 029 3223; Fax: 44 (0) 238 029 2853 E-Mail: [email protected] http://www.witpress.com For USA, Canada and Mexico Computational Mechanics Inc 25 Bridge Street, Billerica, MA 01821, USA Tel: 978 667 5841; Fax: 978 667 7582 E-Mail: [email protected] http://www.witpress.com British Library Cataloguing-in-Publication Data A Catalogue record for this book is available from the British Library ISBN: 978-1-84564-191-7 ISSN: 1746-448X (print) ISSN: 1743-3541 (on-line) The texts of the papers in this volume were set individually by the authors or under their supervision. Only minor corrections to the text may have been carried out by the publisher. No responsibility is assumed by the Publisher, the Editors and Authors for any injury and/ or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. The Publisher does not necessarily endorse the ideas held, or views expressed by the Editors or Authors of the material contained in its publications. © WIT Press 2009 Printed in Great Britain by MPG Book Group. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the Publisher.

Preface

The world’s economic system is driven by easily available energy. Few of the advances made in the past two centuries would have been possible without the large-scale exploitation of fossil fuels. Resource depletion and predictions of severe environmental effects deriving from continued use of fossil fuels are spurring renewed interest in sustainable energy. The effort that will be required to shift from a fossil-based economy to one hinged on sustainability is massive, requiring advances in the basic sciences (materials, electrochemistry, heat transfer to name a few) through to systems engineering (buildings, electric grids, transportation) and all the way to international policymaking. The evolution of new energy technologies and systems cannot follow the compartmentalized model that has worked so well in the past, because of the time constraint imposed by oil and global warming. All parts of the new energy economy are strongly interlinked, and researchers in the field must be aware of the entire enterprise to maximize their own contribution. This second Conference on Energy and Sustainability, offers an opportunity for scientists, professionals, policymakers and other parties to review recent developments in this rapidly changing environment. The papers contained in this book span many of the critical aspects of the new energy economy, including renewable energy technology, energy management, policy, environmental impacts, systems analysis, and efficiency. The role of the International Scientific Advisory Committee was instrumental in promoting the meeting and attracting the many excellent contributions contained here, each of which represents years of dedicated efforts. The Editors would like to thank both the ISAC and the paper authors for their contribution. The Editors Bologna, 2009

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Contents Section 1: Renewable energy technologies Solar thermal heating and cooling: experience of a practical implementation A. Mammoli, P. Vorobieff, H. Barsun & M. Ortiz ............................................... 3 A multicriteria space model to locate grid-connected photovoltaic power plants in Granada (Spain), case study M. Zamorano, J. Arán, A. Ramos & M. L. Rodríguez........................................ 13 Numerical analysis of a minichannel solar collector for CO2-based Rankine cycle applications G. Diaz............................................................................................................... 23 Biomass refineries: relationships between feedstock and conversion approach J.-M. Lavoie, M. Chornet & E. Chornet ............................................................ 35 Elimination of siloxanes by adsorption process as a way of upgrading biogas D. Ricaurte Ortega & A. Subrenat..................................................................... 49 Gasified residual/waste biomass as solid oxide fuel cell feed for renewable electricity production J. Jurewicz & N. Abatzoglou ............................................................................. 59 Lighting the world with LEDs S. J. Riley & M. Telugu...................................................................................... 71 The optical and electrical properties of Eu3+-Y3+codoped ITO transparent conductive electrodes as luminescent solar concentrators C.-C. Ting & C.-H. Tsai..................................................................................... 79

Towards a Southern Africa Development Community (SADC) model to assess financing options of renewable energy technologies V. H. van Zyl-Bulitta, B. Amigun & A. C. Brent ................................................ 91 Hydrogen fuelled agricultural diesel engine with electronically controlled timed manifold induction: an experimental approach P. K. Bose, S. Mitra, R. Banerjee, D. Maji & P. Bardhan............................... 103 Selection of renewable energy technologies in Africa: the case of efficient stoves in Malawi M. L. Barry, H. Steyn & A. C. Brent ................................................................ 117 The sustainable energy service company (ESCO) experience at DIC Corporation Y. Ishida, M. Bannai, K. Ishimaru, R. Yokoyama, S. Nakazawa & H. Yunoue............................................................................... 129 Renewable energy from restored prairie plots in southeastern Minnesota, USA B. Borsari, I. Onwueme, E. Kreidermacher & T. Terril .................................. 137 Iron catalysts supported on carbon nanotubes for Fischer–Tropsch synthesis: effect of pore size R. M. Malek Abbaslou, J. Soltan, S. Sigurdson & A. K. Dalai ........................ 147 Pyrolysis of physic nut (Jatropha curcas L.) residue under isothermal and dynamic heating processes D. Atong, C. Pechyen, D. Aht-Ong & V. Sricharoenchaikul ........................... 157 Section 2: Energy management Energy and sustainability through integrated water network management M. Ektesabi, A. H. Moradi-Motlagh & A. H. Abdekhodaee............................. 175 Vanadium battery technology – integration in future renewable energy systems C. K. Ekman, H. Bindner, T. Cronin & O. Gehrke .......................................... 187 Short-term wind forecasting using artificial neural networks (ANNs) M. G. De Giorgi, A. Ficarella & M. G. Russo................................................. 197

Section 3: Energy policies A review of the Bioenergy potential of residual materials in Quebec S. David & N. Abatzoglou................................................................................ 211 Potential transport energy demand and oil dependency mitigation measures T. E. Lane & M. J. W. A. Vanderschuren......................................................... 225 Sustainable energy policy choice: an economic assessment of Japanese renewable energy public support programs A. Suwa, K. Noda, T. Oka & K. Watanabe ...................................................... 237 An energy and environmental meta-model for strategic sustainable planning D. S. Zachary, U. Leopold, L. Aleluia Reis, C. Braun, G. Kneip & O. O'Nagy..................................................................................... 247 The Italian gas retail market: a cluster analysis based on performance indexes G. Capece, L. Cricelli, F. Di Pillo & N. Levialdi ............................................ 257 Participatory assessment of sustainable end-user technology in Austria M. Ornetzeder, U. Bechtold & M. Nentwich.................................................... 269 Towards a SADC model to assess financing options of renewable energy technologies V. H. van Zyl-Bulitta, B. Amigun & A. C. Brent .............................................. 279 Energy from biomass: decision support system for integrating Sustainability into technology assessment P. Lacquaniti & S. Sala ................................................................................... 291 Recovering energy from liquid sanitary waste for Direct Alcohol Fuel Cell V. Pelillo & D. Laforgia .................................................................................. 303 An innovative concept leveraging mass volunteerism and the viral nature of the Web to substantially reduce global carbon emissions H. Gandhi & B. S. Thompson .......................................................................... 311

Section 4: Energy and the environment Integrating intelligent glass facades into sustainable buildings: cases from Abu Dhabi, UAE M. A. Haggag................................................................................................... 323 Case study ‘the Vela Roof – UNIPOL’, Bologna: use of on-site climate and energy resources A. van Timmeren & M. Turrin ......................................................................... 333 Gap analysis of current research in the area of IT for energy in buildings K. U. Gokce, A. Hryshchenko & K. Menzel ..................................................... 343 Development of a sustainability assessment framework for planning for sustainability for biofuel production at the policy, programme or project level L. K. Haywood, B. de Wet, G. P. von Maltitz & A. C. Brent............................ 355 Production of biodiesel from Jatropha curcas and performance along with emission characteristics of an agricultural diesel engine using biodiesel S. Mitra, P. K. Bose & S. Choudhury .............................................................. 367 Environmental and exergetic performance of electrolytic hydrogen using life cycle assessment J. L. Gálvez, L. Pazos, C. García, G. Martínez & A. González García-Conde...................................................... 377 Section 5: Energy analysis Heat transfer from in-line tube bundles to downward aqueous foam flow J. Gylys, S. Sinkunas, T. Zdankus, R. Jonynas & R. Maladauskas .................. 389 Mathematical models of air-cooled condensers for thermoelectric units S. Bracco, O. Caligaris & A. Trucco ............................................................... 399 Optimisation of cogeneration systems – combined production of methanol and electricity C. Werner & H. L. Estrada Hummelt .............................................................. 411

Section 6: Energy efficiency The promotion of energy efficiency of the building envelope in the rehabilitation process. Case study: a minor centre in Abruzzo P. De Berardinis & M. Rotilio ......................................................................... 425 Domestic appliances end-use efficiencies: the case of eleven suburbs in greater Johannesburg M. V. Shuma-Iwisi & G. J. Gibbon .................................................................. 437 Analysis of energy conversion in ship propulsion system in off-design operation conditions W. Shi, D. Stapersma & H. T. Grimmelius ...................................................... 449 Development of combustion efficiency tables for biofuels D. F. Dyer........................................................................................................ 461 Combustion of urban solid wastes in an experimental fluidized bed combustor C. A. Torres-Balcazar, G. Lopez-Ocaña, R. G. Bautista-Margulis, J. R. Hernandez-Barajas, H. O. Rubio-Arias & R. A. Saucedo-Teran ............ 469 Optimisation of ammonia injection for an efficient nitric oxide reduction S. Ogriseck & G. P. Galindo Vanegas............................................................. 481 Conversion of waste rubber as an alternative rout to renewable fuel production M. Stelmachowski & K. Słowiński ................................................................... 489 Energy efficiency development in the German and Colombian energy intensive sectors: a non-parametric analysis C. I. Pardo M. .................................................................................................. 499 Section 7: Energy storage and management Assessing European power grid reliability by means of topological measures M. Rosas-Casals & B. Corominas-Murtra ...................................................... 515 Application of energy storage systems for DC electric railways R. Takagi.......................................................................................................... 527 Author Index .................................................................................................. 537


Section 1 Renewable energy technologies



3

Solar thermal heating and cooling: experience of a practical implementation A. Mammoli1, P. Vorobieff1 , H. Barsun2 & M. Ortiz1 1 Department

of Mechanical Engineering, The University of New Mexico, USA 2 Physical Plant Department, The University of New Mexico, USA

Abstract The Mechanical Engineering building at the University of New Mexico was an example of the state of the art in environmentally conscious architecture in the early 1980s. Along with many passive energy-conserving features, it had an active solar thermal heating and energy storage system. In the first decade of the twentyfirst century, we were presented with an opportunity to radically modernize this solar thermal system, preserving many of the original features, but also implementing solar cooling and making this project a part of a bigger plan involving a smart energy grid. Here we describe our work, the results in terms of energy savings, and discuss future improvements.

1 Introduction The solar thermal system at the University of New Mexico Mechanical Engineering (UNM ME) building was a part of the original design of the building, dating back to the 1970s energy crisis. At the time of its inauguration, the UNM ME building was hailed as “a true step in the future of energy.” (From the inauguration address by US Senator Pete Domenici, R-N.M., October 11, 1980.) Components of the original system [1] included thermal storage (400 tons of water in eight concrete underground tanks), a 300 m2 solar collector array, and a Rankine cycle engine driving an electric generator. Thus solar heat could be used to heat the building or to produce electricity. The original system performed quite well for a while, but gradually fell into disrepair due to lack of maintenance. In 2006, a grant from the State of New Mexico, along with additional funding and support from the University of New Mexico and the US Department of Energy, made it possible WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090011

4 Energy and Sustainability II to re-implement the UNM ME solar thermal system using modern hardware and controls, as described in our earlier paper [2]. Since the system commissioning on October 15, 2008, we have operated the thermal solar / storage system at the UNM Mechanical Engineering building and measured its performance. As a consequence of the late onset of cold weather, we were able to test summer, shoulder season, and winter conditions, and are now able to estimate the potential energy cost savings that the system will provide. Here we will base the cost savings on the system installed in the building prior to project implementation, which consisted of a stand-alone, 100 ton, 30 year old electric chiller, with a nominal coefficient of performance (COP) of 3.8 and actual (based on meter readings and estimated building load) COP of approximately 2.0. We will also use the electricity rates provided by the PNM utility company [3] to calculate costs, although the real situation is complicated by the fact that the University of New Mexico generates part of its electricity using a co-generation gas turbine. In summer operation, the system will be able to provide cost savings through its ability to store chilled water during the night, taking advantage of lower electricity rates, through an extremely efficient electric district chiller (COP of over 6.5), and through the production of chilled water by the solar water-fired absorption chiller (which has an equivalent electric COP of approximately 10, when the solar circulation pump and the cooling tower pump are included). The principal cost saving is provided by the chilled water storage system. Chilled water production from the absorption chiller further reduces the cost of cooling, especially in comparison to the stand-alone electric chillers that were operating prior to the project implementation. In the shoulder seasons, the solar system is able to provide all of the heating and cooling required by the building. We devised a control strategy that allows us to heat the building in the morning, and cool it in the afternoon, in the proportions required by weather condition. In the winter, we have shown that during sunny conditions, the system can provide over 90% of the weekly heating requirement, and we estimate an average of 70% to account for a fraction of cloudy days.

2 Cooling In 2008, the cooling season extended well into October, so we were able to test the cooling capacity of the solar assisted chiller, and to devise optimal operating procedures. As shown in the plot of Fig. 1, the absorption chiller produces a temperature drop of about or 5.5◦ C. Chilled water flow through the chiller was measured at 3.15 l/s. This corresponds to a cooling capacity of 72.4 kWt (the rated capacity of the chiller is 20 tons of cooling, or 70 kWt ). On days with little cloud cover, such as October 9, 2008, the chiller operates for approximately 5 hours, producing a total cooling effect of 362 kWh. This value matches exactly with our model calculations (TRNSYS [4]) for high temperature operation. In peak summer operation, we expect to produce over 400 kWh of cooling. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Figure 1: Typical ‘summer’ operation: Measured radiation on a flat plate with South orientation and 30◦ tilt for October 9, 2008 (top), and absorption chiller operating parameters, showing temperatures for heating, cooling and chilled water loops (bottom).

The total solar energy available throughout a day in October with collectors tilted at 30◦ is approximately 6 kWh/m2 , corresponding to 1392 kWh for perfectly efficient collectors with an area of 232 m2 . However, collector efficiency decreases substantially with low solar radiation values (below 500 W/m2 ) and high heat medium temperatures, so that useful energy collection only occurs between WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

6 Energy and Sustainability II approximately 10AM and 4PM, as can be seen from Fig. 1. Thus, the total energy collected daily in this period in October is approximately 566 kWh. The corresponding chiller COP is 64%, well within specification. We did not operate the solar system continuously through the summer, so we do not have sufficient data to show the total fraction of cooling load that is met by the absorption chiller. However, our detailed TRNSYS model of the system predicts a yearly cooling fraction of approximately 35% at high operating temperatures [5]. We also note that, somewhat surprisingly, the cooling fraction may increase if we operate at lower heat medium temperatures, as shown in Fig. 2. We plan to investigate this option during the 2009 cooling season.

Figure 2: Yearly fraction of cooling, and average absorption chiller C.O.P., as a function of solar loop outlet temperature.

The seven chilled water storage tanks contain up to a total of 350,000 liters of water. They are equipped with linear diffusers which allow stratification, with ∆T between the cool and warm layers anywhere above 5◦ C. The design ∆T of 11◦ C results in a total capacity of 4470 kWh, sufficient to meet the peak building load (approximately 2000 kWh) for two days, accounting for losses. In general, we will use fewer than seven tanks, to reduce thermal losses. We were able to observe that stable tank stratification indeed takes place. However, we were not able to fully test the chilled water storage last summer due to the degraded performance of the chilled water coil in the primary air handling unit, which was only able to provide a 5◦ C temperature difference, thereby halving the stored chilled water capacity. The coil has now been replaced in preparation for the 2009 cooling season, so that we will be able to take full advantage of night-time chilled water storage. The cost savings due to operation of the chilled water storage are the most significant. During the months of June, July and August, the daytime (8AM to 8PM) electricity cost is USD 0.054/kWh, versus a night-time cost of USD 0.026/kWh [3]. For a typical load of 1600 kWh/day, assuming a chiller COP of 6.5 (this is a 2000-ton Trane chiller located at UNM’s Ford Utilities Center, which now provides chilled water to the ME building), the cost of night-time storage versus daytime ondemand operation is USD 6.45/day and USD 13.23/day respectively. In addition, a reduction in monthly peak demand of up to 16kW results in an additional daily WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


7

saving of USD 4.20/day. The cost of producing chilled water is therefore reduced from USD 17.42/day to USD 6.45/day (a 63% reduction) solely by off-peak operation of the chiller. Meter readings from the stand-alone chiller prior to project implementation show an average power consumption of 43kW for the summer of 2006. Since the chillers were used primarily during the day, directly to offset load, this corresponds to a daily electricity cost of USD 55.50 for the energy charge, plus a demand charge of USD 23.45. Compared with the original cost of chilled water production, the new system results in a saving of 91.8%. The cost of circulating air in the building was also reduced by the installation of VFDs (variable frequency drives) on all the air handler fan motors, so that air handlers no longer operate at full power all the time. Over the next year, we will program the air handlers so that they provide the required minimum amount of outside air, as a function of building occupancy, if the outside air temperature is warmer than the building return air. If the outside air temperature is lower that of the than building return air, then the fraction of outside air will be increased to reduce the cooling load.

3 Shoulder season The shoulder season, generally occurring mid-October to mid-November, and midMarch to mid-April, posed a particular problem. Operating in cooling mode would make the building too cold, while operating in heating mode would make it too hot. At the same time, the solar collectors produce a large amount of hot water, which must be cooled to prevent tank overheating the next day. The building air handler schedule is such that the fans begin moving air at 6:00AM, including a fraction of cold outside air, making the building relatively cold and uncomfortable in the morning. As the day progresses, the building becomes progressively warmer, sometimes exceeding comfort levels. For a period of approximately one week, we cooled the building by operating the absorption chiller in the early to late afternoon, until the heat storage tank high temperature dropped to 74◦ C. The following morning, we operated the heating system until the air handlers no longer required hot water. We took advantage of the fact that the air handlers can function with a wide range of temperatures - if the supply water is very hot, the control valves reduce the flow rate to maintain a set air temperature. Usually, heating water is no longer required by mid-morning. At this time, the solar collectors begin to produce hot water at the set temperature for absorption chiller operation, 87◦ C. However, because of the heating, the tank lower temperature is colder than usual, so that the rate of hot water production is also lower than usual. This results in a lower total amount of hot water which is usable for cooling, reducing the chiller run time. This operating strategy is self-balancing: cooler days will result in longer heating operation and shorter cooling operation, and vice-versa. The implementation of the strategy merely required allowing the hot air handlers to request hot water from the tank in the morning within the summer operating strategy. The winter WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

8 Energy and Sustainability II operating strategy was left unaltered, with no possibility of cooling owing to the shutdown of the cooling tower. In the shoulder season, the solar system was able to supply all of the heating water and cooling water needs for the building. The night-time chilled water tank recharging was turned off.

4 Heating In late October, we switched the system operation to heating. We were able to provide comfortable conditions throughout, with temperatures in the vicinity of 22◦ C. A typical scenario of a sunny, cold day is shown in Fig. 3. At 6:00AM on November 20, the heating pump begins drawing hot water from the hot tank and circulating it thought the air handlers. The hot water temperature trace shows that some hot water (at 54 to 49◦ C) remained in the tank from the previous day. This hot water, however, was used up within the first hour of operation. The corresponding steam heat exchanger valve position trend plot shows that the steam valve gradually opens to maintain the temperature of the water entering the heating coils above a set point (49◦ C). At around 9:00AM, the solar array begins producing hot water, and the steam valve closes until around 8:00PM, when it opens briefly, until the system shuts down for the night. The solar system is able to provide heating water for over 9 hours out of 14 hours of operation, with a small amount of steam assistance for the remaining 5 hours. On a mostly cloudy day (see the solar radiation measurement in Fig. 4 for December 9, 2008), virtually no hot water was produced. As shown in Fig. 4, the steam valve remained open at an average value of approximately 40% for the entire heating cycle, from 6:00AM to 8:00PM. Thus, under the current operating schedule (7 days a week), the solar system reduces steam usage by 64%. However, it is UNM procedure to shut down ventilation over the week-end. In this case, we could accumulate enough hot water over the week-end to supply the heating system for an additional 18 hours. The hot storage tank can easily accumulate this amount of heat, and distribute it through the remainder of the week. This would result in the ability to operate for approximately 63 hours out of 70 with solar hot water only, a saving of 90%. Given that some days will be cloudy, it is more likely that the average saving in steam will be closer to 70%.

5 Energy cost savings Based on the observed performance of the system, the cost savings in chilled water production cost for a typical summer day are summarized in Table 1. We note that these costs represent only electricity savings, not operation and maintenance. The total daily electricity cost of the new system, including stored chilled water and solar chilled water, is USD 10.3. The cost of operating the old electric chiller, assuming peak performance (C.O.P. of 3.8) directly against the load would be WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Figure 3: Typical ‘winter’ operation: feedwater temperature to the heating coils from the hot storage tank for November 20, 2008 (top) and steam 1/3 valve position for the same day. Note that steam is only required in the early morning (bottom).

USD 49.9. The predicted saving in energy cost for cooling is therefore at least 79%. Because of the limited size of hot storage, the absorption chiller must be operated during peak time for at least part of the time. However, it is possible to stop WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

10 Energy and Sustainability II

Figure 4: Typical cloudy winter operation: measured solar radiation (top) and steam 1/3 valve position (bottom).

operation when the residual storage tank capacity is larger than the estimated remaining solar energy that will be collected during the remainder of the day. During the next cooling season, we will operate the absorption chiller at night to further reduce electricity cost. The calculation of energy savings with heating is more straight-forward. For example, on December 9, 2008, virtually no solar hot water was produced due to WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Table 1: Parameters and costs of chilled water production, assuming 90% storage efficiency. Cooling C.O.P. kWht

Equiv.

Energy

elec.

price

Energy Demand cost

cost

Total

kWhe

$/kWh

$/day

$/day

$/day

Original

1600

2.0

800

0.05379

43.0

27.2

70.2

Original

1600

3.8

421

0.05379

22.7

27.2

49.9

∗

0.026210

5.4

0.0

5.4

0.053769

2.15

2.72

4.87

Storage

1200

6.5

205

Solar

400

10.0

40

cloud cover. From meter data, 1534 kg of steam were used for heating, corresponding to 887 kWh of thermal energy. With a cost of USD 0.0686/kWh for steam, the cost of heating the building for December 9 was USD 60.70. Using the assumed 70% reduction in steam consumption from our observations discussed in the previous section, we expect to save, on average, USD 42.50 per weekday during the heating season. Sadly, we do not have conclusive meter data to confirm the above calculations, since the system has not operated at full capacity for a long enough period.

6 Discussion The overall efficiency of the absorption cooling cycle is offset by the need to operate several pumps for fluid circulation. In our case, both solar water and cooling water operate on an open cycle. We will install a high efficiency heat exchanger between the solar loop and the heat storage tank. The solar loop would become closed, and the heat medium would be changed from water to water-glycol mix. A closed loop would allow us to operate the solar circulation pump on VFD, greatly reducing the part load electricity consumption. furthermore, circulation of water through the solar loop during winter nights would no longer be necessary, and the risk of freezing would be eliminated. A loss of thermal efficiency of approximately 5% is estimated during summer high-temperature operation. The cooling tower pump is the most significant source of pumping loss in the system. There are two options for reducing the cooling tower power consumption. Relocating the cooling tower from the roof to the Rankine room is feasible but expensive. The second alternative is to recover the potential energy of the cooling tower return water by installing a small Pelton turbine, which would produce approximately 3kW. This could be fed back into the grid with a small inverter. Thermal storage is an often overlooked component of energy-conscious buildings. Aside from the cost benefit deriving from the ability to store chilled water off-peak, thermal storage could play a significant role in ‘smart grids’ of the future, WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

12 Energy and Sustainability II where bidirectional information allows a much more efficient optimization of the electricity generation, transmission, distribution and end use. For example, wellorganized storage strategies could reduce demand peaks, allowing for reduced generation infrastructure cost, as well as increase the penetration of intermittent resources, such as wind and photovoltaic. Our current activities are now heavily focused on determining an appropriate architecture for decentralized optimization of electricity generation and end-use.

References [1] Maurice W. Wildin. Results from the use of thermally stratified water tanks to heat and cool the mechanical engineering building at the university of new mexico. Technical Report ORNL/Sub/80-7967/1, Oak Ridge National Laboratory, 1982. [2] A.A. Mammoli, P. Vorobieff, and D. Menicucci. Promoting solar thermal design: the Mechanical Engineering building at the University of New Mexico. In C.A. Brebbia, M.E. Conti, and E. Tiezzi, editors, Management of Natural Resources, Sustainable Development and Ecological Hazards, volume 1, pages 265–274. WIT Press, Southhampton, Boston, 2006. [3] Public Service Company of New Mexico. 5th revised rate no. 15B – large service for public universities greater than 8,000 kW minimum with customerowned generation facilities served at 115 kV, May 2008. c 2002, The Board of [4] TRansient SYstems Simulation program. Copyright Regents of the University of Wisconsin System. [5] Mario Leroy Ortiz. A TRNSYS model of a solar thermal system with thermal storage and absorption cooling. Master’s thesis, The University of New Mexico, 2008.

WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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A multicriteria space model to locate grid-connected photovoltaic power plants in Granada (Spain), case study M. Zamorano1, J. Arán1, A. Ramos1 & M. L. Rodríguez2 1

Department of Civil Engineering, Section of Environmental Technology, University of Granada, Spain 2 Department of Applied Mathematics, University of Granada, Spain

Abstract Energy consumption grows year on year but present reserves of fossil fuels can only cover consumption at current rates for the next 40 years, in the case of oil, and for the next 60 in the case of natural gas. The emissions generated by the use of fossil fuels are the source of serious environmental problems which in many cases are irreversible. The use of renewable energy technologies seems to be a viable solution for environmental problems produced by other energy sources so today environmental policies are largely promoted to foresting the implementation of renewable energy technologies. In this sense, some countries, for example Spain, have taken an important step to foment grid-connected photovoltaic solar energy but the efficiency of these installations depends on location characteristics. This paper describes the structure and the principal phases of an environmental decision-support system, which combines multicriteria analysis as well as the analytic hierarchy process with geographical information systems technology, to make easier site selection of grid-connected photovoltaic power plants; it combines. The developed model has considered climate features that directly influence the performance of solar energy installation, environmental aspects, legal aspects, orography and finally social and economic factors. This model has been applied in Granada (Spain) and results have been test through a validation process consisting in sensibility analysis. Results have shown applicability and consistence of the model. Keywords: decision-support systems, multi-criteria analysis, renewable energy, photovoltaic systems. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090021


1

Introduction

Energy demands are growing day by day, one consequence of the growing population of the world and of energy consumption tied to industrialization and development; current previsions estimate the energy demand for the year 2020 to be 50-80% greater than that of 1990. As a result of this level of consumption, millions of metric tons of greenhouse-effect gases are released into the atmosphere contributing to progressive global warming, air pollution and reduction of the ozone layer, more frequently severe meteorological effects, an impact on agricultural yields, the proliferation of diseases and on the rising sea level [1–3]; indeed, the mean temperature of our planet has increased by 0.7ºC and by the year 2050 we may expect to see an increase of 4 to 5ºC. Aside from these drawbacks, the fossil fuel reserves themselves are running out, so the scarcity will account for a hike in their price, affecting economic development worldwide [4, 5]. In response to the need to fight global warming, a number of measures have been put forth. At the international level, the Kyoto Protocol set the goal to reduce by 5%, by the year 2012, global emissions of six of the gases responsible for global warming [6]. To reach these goals, it is necessary to take action in the priority areas of energy generation and use, as well as with regard to emissions. Up until now, energy planning have been focused on foreseeing demands in a given time period, with the objective of covering the corresponding demand, under an approach that treated energy as a never-ending resource. Yet the effects of the current system of energy generation, distribution and use on the environment and its impact on the global warming of the planet urge the introduction of a new energy model. From this standpoint, renewable energy resources are destined to satisfy part of the future demands currently placed upon fossil fuels. For this reason, current policies focus on fomenting their development and used in Europe as stated in currently legislation. In this sense Photovoltaic is the field of technology and research related to the application of solar cells for energy by converting sunlight directly into electricity. Photovoltaic energy production has been doubling every two years, increasing by an average of 48 percent each year since 2002, making it the world’s fastest-growing energy technology. At the end of 2007, according to preliminary data, cumulative global production was 12,400 megawatts [7]; roughly 90% of this generating capacity consists of grid-tied electrical systems. However, the main effect of the increase in projected and built grid connected photovoltaic power plants is to spot numerous optimal location errors regarding output efficiency, law observing and costs reduction. In consequence it is imperative that project designers have access to local information on climate, soil characteristics and extensive power transmission grid to absorb the electricity generated, used of soil and legal measures; without such data, optimal site selection for solar power installations cannot be guaranteed [8]. The objective of this research is the definition of a model to choose optimal sites for grid-connected photovoltaic power plants, which fulfil the requirements established by a decision rule. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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15

Materials and methods

2.1 Area of study The area selected in this study is located in the far northeast of the province of Granada (southeast of Spain), in the district of Huéscar. This area has been selected because it is representative of all the uses considered in the model, allowing us to test the behaviour of each variable in the final result. The geographic location of Andalusia in the south of Spain signifies that it is in a key position to play an important strategic role in the implementation of renewable energy technology in Europe, as well as providing sufficient energy for its own needs and even exporting such projects to other countries [9]. 2.2 Geographical information systems Since grid-connected photovoltaic power plants location requires processing a lot of spatial data, we have used Geographical Information Systems and its spatial analysis tools to create the digital geodatabase. GIS are defined as an integrated collection of computer software used to analyze, create, acquire, store, edit, transform, view and distribute geographic data GIS. The combination of spatial data with quantitative, qualitative and descriptive information databases, capable of dealing with a wide range of spatial queries, has made GIS an indispensable tool for location studies [10]. Commercial GIS software packages ESRI ArcGIS 9.2, has been used in this research. It is an integrated system for the creation, management, integration, and analysis of geographic data. It consists of a geo-referenced spatial database, which includes the parameters required for photovoltaic power plants location. The GIS Desktop includes various integrated applications and extensions. One of them is ArcView; it is geographic information system (GIS) software for visualizing, managing, creating, and analyzing geographic data. 2.3 Multi-criteria evaluation When making decisions, decision makers (DMs) always try to choose the optimal solution. Unfortunately, a true optimal solution only exists if you are considering a single criterion. In most real decision situations, basing a decision solely on one criterion is insufficient. Probably several conflicting and often noncommensurable objectives should be considered. Because of this, it is impossible to find a genuine optimal solution, a solution that is optimal for all DMs under each of the criteria considered [11]. The term multiple-criteria decision analysis (MCDA) describes various methods developed for aiding decision makers in reaching better decisions. Using MCDA can be said to be a way of dealing with complex problems by breaking the problems into smaller pieces. After weighing some considerations and making judgments about smaller components, the pieces are reassembled to present an overall picture to the DMs [12]. These techniques have been applied


16 Energy and Sustainability II to solve energy planning problems, based on complex problems with multiple decision makers and multiple criteria [13, 14]. MCDA methods can be divided in three main groups, each of which differs in its respective characteristics, evaluation, data type and objectives: compensatory techniques, non-compensatory techniques and fuzzy techniques. The model described in this article is a system based on multi-criteria evaluation with one objective and several criteria and it have been used Analytical Hierarchy Process (AHP) developed by Saaty’s because it can handle decision-making problems which require a high degree of flexibility and reliability.

3

Decision-making model to optimally place grid-connected photovoltaic power plants

The phases of the elaboration of the decision-making model are: (i) specification of the criteria, (ii) establishment of the decision rule, (iii) determination of the suitability of the land area for grid-connected photovoltaic power plants, (iv) sensibility analysis. 3.1 Definition of criteria A criterion is a measurable aspect of a judgement which makes it possible to characterize and quantify alternatives in the decision-making process [15, 16]. Table 1:

Criteria and factors considered in the model.

Criteria

Factors Land use Visual Impact Slopes (%) Orientation Highway access (km) Distance to substations (km) Distance to urban areas > 5000 inhabitants (km) Distance to urban areas < 5000 inhabitants (km) Global irradiance (Wh/m2/day) Diffuse radiation (%) Equivalent sun hours (ESH) (Kwh/Kwp) Average temperature (ºC)

Environment Orography Location

Climate

3.2 Definition of decision rule A suitable decision rule which integrated the criteria established was created to assign a weight to each criterion. Climate criteria have been considered the most important for the decision rule, following in order of importance by orography, environment and finally location criteria. Saaty’s AHP [17] has been used to WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


17

assign weights to each criterion and determine their relative importance in the final decision adopted within the model establishing a comparison matrix between pairs of criteria and contrasting the importance of each pair with all the others. 18 alternative scales have been considered {1/9, 1/8, 1/7, 1/6, 1/5, 1/4, 1/3, 1/2, 1, 2, 3, 4, 5, 6, 7, 8, 9}. If we compare two criteria, for example 2 and 3, and consider the relative importance “Intermediate”, the relative weighting is a23=4/1; then the relative importance of this attribute is its reciprocal a32=1/3. Table 2:

Indicators of land use factor.

Factor

Indicators Area without vegetation Dryland herbaceous crops Irrigated herbaceous crops Herbaceous and woody crops Woody crops Other uses

Land use

Table 3: Criteria Environment Orography Location Climate Total

∑a j

ij

Comparison matrix of the criteria.

Environment a11=1.00 a12=3.00 a13=0.33 a14=5.00

Orography a21=0.33 a22=1.00 a23=0.20 a24=3.00

Location a31=3.00 a32=5.00 a33=1.00 a34=9.00

Climate a41=0.20 a42=0.33 a43=0.11 a44=1.00

9.33

4.53

18.00

1.64

For example Table 3 shows comparison matrix of the criteria and Table 4 shows normalized values obtained for each criteria considering expressions [1, 2]. The same process has been followed to each factor and indicator.

Aij =

aij

∑a

(1) ij

j

Wj =

∑A

ij

i

4

(2)

3.3 Validation of the model Although the method has shown to be an excellent model to locate gridconnected photovoltaic power plants, it is necessary to accomplish a sensibility analysis in order to guarantee that it offers a reliable representation of the systems represented [18]. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

18 Energy and Sustainability II Table 4: Criteria Environment Orography Location Climate Total

Comparison matrix of the normalized values of criteria. Environment

Orography

Location

Climate

A11= 0.11 A12= 0.32 A13= 0.04 A14= 0.54

A21= 0.07 A22= 0.22 A23= 0.04 A24= 0.66

A31= 0.17 A32= 0.28 A33= 0.06 A34= 0.50

A41= 0.12 A42= 0.20 A43= 0.07 A44= 0.61

Normalized priority vector (wj) 0.1172 0.2556 0.0507 0.5764

Final weights (%) 12 26 5 58 100

The aim of sensitivity analysis is to estimate the rate of change in the output of a model with respect to changes in model inputs. Such knowledge is important for evaluating the applicability of the model, determining parameters for which it is important to have more accurate values, and understanding the behaviour of the system being modelled. The choice of a sensitivity analysis method depends to a great extent on the sensitivity measure employed, the desired accuracy in the estimates of the sensitivity measure, and the computational cost involved. Based on the choice of a sensitivity metric and the variation in the model parameters, sensitivity analysis methods can be broadly classified into the following categories [19]: (i) Variation of parameters or model formulation; in this approach, the model is run at a set of sample points (different combinations of parameters of concern) or with straightforward changes in model structure (e.g., in model resolution); sensitivity measures that are appropriate for this type of analysis include the response from arbitrary parameter variation, normalized response and extrema; of these measures, the extreme values are often of critical importance in environmental applications; (ii) Domain-wide sensitivity analysis; here, the sensitivity involves the study of the system behaviour over the entire range of parameter variation, often taking the uncertainty in the parameter estimates into account; (iii) local sensitivity analysis; here, the focus is on estimates of model sensitivity to input and parameter variation in the vicinity of a sample point. This sensitivity is often characterized through gradients or partial derivatives at the sample point. In this research the second category has been applied. To validate the model, using sensibility analysis, all factors and criteria have been compared with their final values after the model has been generated, so it has been possible analyzed their changes.

4

Applying the model in Granada (Spain)

4.1 Site suitability for the location of grid-connected photovoltaic power plants Layer related to criteria, factors and positive and negative indicators have been generated using the database of the Department of the Environment and the Department of Public Works of the Andalusian Regional Government; some layers have been carried out by the authors of the research study. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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One the weights were obtained, the criteria, factors and indicators were ordered according to their degree of importance and they have been normalized on a scale for 0 to 10. The criteria, factors and indicators were entered into a GIS. Layers of indicators were established in a first step. Taking into account decision rules and weights assigned to each one and by means of arithmetic overlay, layer of factors were also obtained. Layers of criteria were calculated in the last step. Finally carrying capacity of a territory for grid-connected photovoltaic power plants was determined on a scale from 1 to 10, corresponding 1 to the lowest suitability and 10 to the highest.

a

c Figure 1:

b

d

a) Map of restrictions; b) Map of the factor Global Irradiance; c) Environmental criteria; d) Suitability for the location of gridconnected photovoltaic power plants.

Figure 1 shows maps of restrictions obtained (Figure 1a), as so as the “Global Irradiance” map, one of the factors of the “Climate” criteria map (Figure 1b), the map of “Environment” criterion (Figure 1c) and, finally, the final layer obtained (Figure 1d). The study area does not show the presence of the lower levels of the final layer and any land with the maximum value for each factor; this can be explained because a large sector of the study area is not suitable for gridconnected photovoltaic power plants, located in protected areas, near rivers, etc. (Figure 1a). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

20 Energy and Sustainability II Areas with values 7-9 signifies that they are many suitable sites for the location of grid-connected photovoltaic power plants because of their favourable characteristics related to favourable climate, with uncultivated dryland or with herbaceous vegetation and out of protected areas (Figure 1d). The validation process has concluded that uncertainty is higher in the case of models that consider priority factors orography and location. It has also shown that the most important factors are those related to climate and the environment; factors related to location, for example distance to populated areas and road, do not influence the result, so if it is necessary to simplify the model they could be removed.

5

Conclusions

The decision-making model summarized in this paper provides very valuable information to select optimal site for location of grid-connected photovoltaic power plants, due chiefly to the generation of a final suitability index. Analysis of results for the other layers may also facilitate the study of potential problems related to the different environmental and climatic components as so as restricted areas, contributing to the decision of whether or not to locate grid-connected photovoltaic power plants in a particular setting. On the basis of the results of the practical application of the model in Granada as well as the sensitivity analysis, we may conclude that Multiple Criteria Decision Analysis, supported by on Geographical Information Systems, may be usefully applied to the optimal siting of facilities with such exceptional characteristics as this type of installations. It seems reasonable, moreover, to predict that this instrument has the potential to assist planners, decision-makers and other agents involved in the process of selecting suitable sites for photovoltaic power plants, by extending their knowledge of the physical terrain and facilitating the analysis and execution of plans of action. Energetic efficiency and lower environmental impact have been the main objectives to choose best location, although more criteria have been also considered, for example accessibility and power substations proximity. Finally, the application of the model in Granada and the validation process has shown applicability and consistency of the model.

Acknowledgement This research has been partially funded by Parque Metropolitano Industrial y Tecnológico de Granada, S.L, with the R+D Project entitled “Análisis de rendimientos y optimización de producción de distintas soluciones fotovoltaicas conectadas a red” (Fundación Empresa Universidad de Granada 3158-00).

References [1] Karakosta, C., Doukas, H. & Psarras, J. 2009. Sustainable energy technologies in Israel under the CDM: Needs and prospects. Renewable Energy, 34, pp. 1399-1409 WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


21

[2] Randall et al., 2005, Energy and the World Summit on Sustainable Development: what next, Energy Policy, 33, pp. 99–112. [3] Omer, A.M. 2008. Energy, environment and sustainable development. Renewable Sustainable Energy Reviews, 12, pp. 1988-1996. [4] Ramachandra, T.V., Kamakshi, G. & Shruthi, B.V. 2004. Bioresource status in Karnataka. Renewable Sustainable Energy Reviews, 8, pp. 1–47. [5] BP. 2006. Statistical Review of World Energy 2006. BP p.l.c., London [6] UNFCCC. The Kyoto protocol to the United Nations framework convention on climate change. United Nations, http://unfccc.int/resource/docs/convkp/kpeng.pdf; 1998. [7] Earth Policy Institute, 2007. Solar Cell Production Jumps 50 Percent in 2007. http://www.earth-policy.org/Indicators/Solar/2007.htm [8] Aran, J. 2008. Space model of analysis for the evaluation of the capacity of welcome of the territory in the location of connected photovoltaic power stations to network. PhD Thesis. University of Granada (Spain). http://hera.ugr.es/tesisugr/1764625x.pdf [9] Ramos, A., Hontoria, E., Moreno, B. & Zamorano, M. 2007. solar energy in Andalusia (Spain): present state and prospects for the future. Renewable and sustainable Energy Reviews, 11, pp. 148-161. [10] Church, R. 2002. Geographical information systems and location science, Computers & Operations Research , 29(6), pp. 541-562. [11] Loken, E. 2007. Use of multicriteria decision analysis methods for energy planning problems. Renewable and Sustainable Energy Reviews, 11, pp. 1584–1595. [12] Dodgson, J., Spackman, M., Pearman, A., Phillips, L. 2001. DTLR multicriteria analysis manual. UK Department for Transport, Local Government and the Regions. [13] Chatzimouratidis, A.M.A. & Pilavachi, P. 2008. Sensitivity analysis of technological, economic and sustainability evaluation of power plant using the analytic hierarchy process. Energy Policy, 36, pp. 1074-1089. [14] Ben Salah, C., Chaabene, M. & Ben Ammar, M. 2008. Multi-criteria fuzzy algorithm for energy management of a domestic photovoltaic panel. Renewable Energy, 22, pp. 993-1001. [15] Eastman, J.R, Jiang, H & Toledano, J. 1993. Multi-criteria and multiobjective decision making for land allocation using GIS. Dordrecht: Kluwer Academic Publishers, pp. 227-251. [16] Voogd, S.H. 1983. Multi-criteria Evaluation for Urban and Regional Planning. London: Pion. [17] Saaty, T.A. 1997. Scaling method for priorities in hierarchical structures. Journal of Mathematical Psychology, 15, pp. 234-281. [18] Rai & Kewski. 1998. Uncertainty and variability analysis in multiplicative risk models. Risk Analysis, 18(1), pp. 37-45. [19] Saltelli, A., Chan, K. & Scout, E.M. 2000. Sensitivity Analysis. Chichester. John Willey & sons, LTD.




23

Numerical analysis of a minichannel solar collector for CO2-based Rankine cycle applications G. Diaz School of Engineering, University of California, USA

Abstract The combined effects of increasing energy consumption, higher fuel prices, and green-house-related climate change are challenging universities and industry to develop more efficient and sustainable ways to produce power, heating, and cooling for industrial, commercial, and residential applications. The utilization of renewable energy sources is receiving considerable attention as a non-resource-depleting approach that reduces the emissions of pollutants and green-house gases to the atmosphere. Solar thermal systems have the capacity to provide heat in a sustainable way for a variety of applications due to the relatively large range of temperatures that different collector configurations can attain. Non-imaging-optics based compound parabolic concentrating reflectors combined with evacuated-tube collectors can operate at 200oC at efficiencies near 50% without the need for tracking. In addition, a trend towards natural working fluids to reduce the effects of global warming and ozone-layer depletion has sparked the proposal of several refrigeration and combined cooling, heating and power cycles using CO2. This paper analyzes the performance of a minichannel-based evacuated-tube solar collector operating with supercritical CO2 suitable for solar-driven Rankine cycle applications. Keywords: minichannel, solar collector, Rankine cycle, cogeneration.

1

Introduction

The fluctuating costs of fuel prices, the increasing demand for energy, and the evident signs of climate change have fostered the development of technologies that utilize renewable energy sources, use more environmentally-friendly WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090031

24 Energy and Sustainability II working fluids, utilize low-grade heat sources, and/or have higher energy efficiencies than the more traditional thermal applications. At the legislative level, some states have taken strong action to increase energy efficiency and power generation from renewable energy sources, and to promote the utilization of combined heat and power (CHP) and combined cooling, heating, and power (CCHP) systems. For instance, the California Air Resources Board is planning to increase CHP electricity production by 30,000 GWh by 2020. An important part of a CHP system is the power-generating cycle. In this respect, power cycles that utilize low-grade heat sources such as waste heat or heat from evacuated-tube solar collectors, have been proposed by several researchers. Organic Rankine cycles [1–2] have been proposed but they tend to use working fluids such as isobutane, propane, benzene, or toluene that are either flammable or toxic. Kalina cycles [3] utilize an ammonia/water mixture and consist of extensive internal heat recovery to improve efficiency in thermal power cycles. Although ammonia is a natural working fluid with zero ozone depleting and global warming potentials, it is toxic. Thus, one alternative natural working fluid for power generating cycle or CHP applications corresponds to CO2 [4–7]. Minichannels have successfully been utilized in heat exchangers by the residential air conditioning industry due to their improved performance and compact size compared to round-tube and fin heat exchangers [8, 9]. Minichannel tubes are classified with respect to their hydraulic diameter which covers the range between 200m and 3mm [8]. This technology will allow a reduction of 4.2 quadrillion Btus of electric energy consumption, between 2006 and 2030, and a decrease of 33 million metric tons in carbon emissions [10]. Non-imaging-optics based compound parabolic concentrating (CPC) reflectors [11] combined with evacuated-tube collectors have been shown to operate at temperatures near 200oC with efficiencies of 50% without the need of tracking. Solar collectors vary in performance depending on their design. One key issue that remains a subject of intense research relates to effectively transferring the heat obtained from the sun to the working fluid. Minichannelbased evacuated tube solar collectors have been proposed to improve the efficiency of the collector [12]. This paper analyzes the performance of an evacuated-tube solar collector utilizing minichannel tubes for a solar-driven Rankine cycle producing electric power and hot water.

2

Transcritical cycle

In recent years there has been a trend towards utilizing more environmentally friendly working fluids in air conditioning and low-grade power generating cycles. Carbon dioxide, water, air, hydrocarbons, and ammonia constitute a set of the natural working fluids that provides an environmentally friendly option to reduce ozone depletion and green-house-gas emissions. Table 1 shows a comparison of properties of commonly used working fluids, where global warming potential (GWP) is an index that relates the potency of a greenhouse gas relative to the emission of CO2 over a 100-year period. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Table 1:

R-744 R-12 R-22 R-134 R-407C R-410A R-717 R-290

25

Working fluid property comparison [13]. ODP/ GWP

FLAMMABLE/ TOXIC

0/1 1/8500 0.05/1700 0/1300 0/1600 0/1900 0/0 0/3

N/N N/N N/N N/N N/N N/N Y/Y Y/N

REFRIG. CAPACITY

(kJ/m3) 22545 2734 4356 2868 4029 6763 4382 3907

Carbon dioxide, R-744, has a higher volumetric capacity, higher heat transfer coefficients, and it is readily available which makes it low cost. One drawback is that it requires higher operating pressures. Its ODP and GWP compare favourably with other commonly used working fluids.

3

Minichannel solar collector

A variety of solar collectors available in the market serve different purposes depending on their optimal operating temperature. Absorber surfaces, flat-plate collectors, evacuated-plate collectors, evacuated-tube collectors, and external or internal concentrator with evacuated-tube collector are some of the different options available today. The most common evacuated-tube collectors include a U-tube, a concentric-pipe, or a heat pipe attached to a metal absorber that has a selective coating applied on its external surface. In these designs, heat transfer from the metal absorber to the working fluid encounters several thermal resistances. Heat flows from the absorber to the working fluid by conduction through the absorber fin. Cost reduction results in the absorber thickness being very thin, usually less than a millimetre, creating a resistance to the flow of heat. Also, the absorber is usually wrapped around the pipe carrying the working fluid and ultrasonic-welding is utilized at discrete points to attach the absorber fin to the pipe. Poor contact is obtained at points where the fin is not welded to the pipe. Figure 1a shows a schematic of a counter-flow evacuated-tube solar collector. A minichannel tube can have a similar free flow area as a round-tube but a much larger wetted perimeter. The port dimensions, shown in fig. 1b, tend to be small so that pressure-drop needs to be considered in performance analyses [12]. In solar collectors, the path of the heat transfer involves less thermal resistances than in absorber/round-tube designs. Also, the large wetted perimeter combined with the excellent heat transfer properties of CO2 reduce the amount of working fluid needed inside the collector. Charge minimization is an important safety advantage of minichannel tubes that operate at the high pressures required by CO2. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

26 Energy and Sustainability II Evacuated glass tube

Absorber

Fluid

Mini-channels

Selective coating Evacuated glass tube

(a)

Figure 1:

4

(b)

Schematic of evacuated-tube solar collectors. (a) Absorber/roundtube counter-flow design. (b) Minichannel solar collector.

Model description

In the following subsections we derive the models for the minichannel-based solar collector and the Rankine cycle operating with CO2. 4.1 Solar collector The radiation heat transfer coefficient between the tube and the glass is given by

1 D 1  g  ( Ae ) A Dg g

hr Ag  , 1

To model the heat transfer to the fluid using minichannels, we need to consider the resistance from the external tube surface to the fluid.

RT 0 

t wall 1  kCu P0 L 0 Atot h f

where twall is the tube wall thickness, PO is the tube perimeter, and surface efficiency is given by

0  1 (

NA fin )(1  fin ) Atot



27

where N is the number of webs inside the tube, Afin is the cross sectional area of the fin, Atot is the total heat transfer area inside the tube, and the fin efficiency is given by

 fin 

tanh(m f L fin / 2) m f L fin / 2

1/2

where mf =(hf P/(kCuAfin)) , P is the perimeter of the fin, and Lfin corresponds to half of the length of the tube webs. The energy balance at the glass becomes

Age ( g Gs  hair (Tg  T )   (Tg  Tsky ))  AAehr , Ag (Tb  Tg )  0 4

4

4

4

(1) An energy balance at the external tube surface gives

 A g

AAe ( Gs  hr , Ag (Tb  Tg ))  Q 1  (1   A )  g 4

where

Q

4

(2)

Tb  T f

(3)

RT 0

where Tb and Tf are the tube and fluid temperatures, respectively. 4.2 Solar-powered Rankine cycle The solar-driven Rankine cycle for heat and electric power generation, shown if fig. 2, is modelled using thermodynamic relations.

Solar collectors

b

c Wt Turbine

Heat Exchanger

Condenser e

d

a Pump

Wp

T w out Tw HW

Figure 2:

Tw in

Solar-powered Rankine cycle.

The power generated by the expander and the power used by the pump are modelled as: 



W t  m(hc  hd ) WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

(4)

28 Energy and Sustainability II 

where



W p  m(hb  ha )

(5)

hd  hc   t ( hds  hc ) , hb  ha  (hbs  ha ) /  p

(6) (7)

The isentropic efficiencies of the expander and pump have been considered as ηt = 0.7 and ηp = 0.85, respectively. The heat added to the working fluid at the solar collectors is calculated as: 



Q  m(hc  hb )

(8)

The heating of water at the heat exchanger and condenser are modelled as:

m PH (hd  he )  m W c pw (TWHW  TWout )

(9)

m PH (he  ha )  m W c pw (TWout  TWin )

(10)

The efficiency () of the CHP system is obtained as: 





 CHP  (W t  W p ) / Q 5

(11)

Numerical simulations

Numerical simulations were obtained using the Engineering Equation Solver (EES) software [15] that includes the thermophysical properties of carbon dioxide. The parameters used for the simulations, including the specifications of the evacuated-tube solar collector, are described in table 2 [12]. 5.1 Evacuated-tube solar collector The evacuated-tube solar collector is subdivided in sections along the length and eqns. (1) to (3) are utilized to obtain the performance of a single collector. Figure 3 shows the outlet temperature of the CO2 (solid line) as well as the Table 2: Property Glass tube length Glass external diameter Glass internal diameter Tube major Tube minor Tube wall Web thickness Number of webs Free flow area

Parameters used for the simulations.

Value 1,640mm 65 mm

Dimension External tube perimeter Wetted tube perimeter

Value 183 mm 240 mm

56 mm

α selective coating

0.90

88 mm 3.58 mm 0.7 mm 0.7 mm 21 1.6x10-5 mm2

ε selective coating Solar irradiation ηt ηp Inlet water temperature

0.1 1000 W/m2 0.7 0.85 17oC


Energy and Sustainability II 225

29

0.57 0.56 0.55 0.54

135

0.53 90

0.52

efficiency

Tout [oC]

180

0.51

45

0.5 0 0

0.01

0.02

0.03

0.04

0.49 0.05

mass flow rate [kg/s]

Figure 3:

Tout and efficiency versus mass flow rate for a single solar collector at Tin = 160 (oC). 250

0.7 0.65

200

0.55 100 0.5 50

0 50

Figure 4:

efficiency

Tout [oC]

0.6 150

0.45

85

120

155

T in [oC]

190

0.4 225

Tout and efficiency versus mass flow rate for a single solar collector at mass flow rate of 0.01(kg/s).

efficiency (dashed line) of the minichannel solar collector as a function of mass flow rate for a fixed inlet CO2 temperature of 160 (oC). It is observed that there is no significant gain in efficiency of the collector with mass flow rates higher than 0.02 (kg/s). The outlet temperature of CO2, Tout, remains above 200 (oC) at very low flow rates but it levels off approximately at 164 (oC) as the mass flow rate is increased. Figure 4 shows the performance of a single collector in terms of outlet CO2 temperature and collector efficiency as a function of inlet temperature for a fixed mass flow rate of 0.01 kg/s. The outlet temperature of the working fluid increases linearly with respect to Tin while the efficiency displays a nonlinear behaviour. It is observed that the collector operates at nearly 50% of efficiency WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

30 Energy and Sustainability II at 190 (oC). This is assuming the use of a non-tracking external compound parabolic concentrator designed using non-imaging optics [16]. 5.2 Rankine cycle operation We combined the model of the minichannel evacuated-tube solar collector with eqns. (4) to (11) that describe the performance of the Rankine cycle. The heat obtained at the collectors in eqn. (3) corresponds to the heat added to the Rankine cycle in eqn. (8). Twenty squared meters of collector area are utilized for the simulations. In order to increase the outlet temperature of the CO2, the collectors are connected in a combination of series and parallel configuration. Figure 5 shows the performance of two collectors connected in series operating at a pressure at state (b) of 13 (MPa). No significant gain in collector efficiency is obtained with mass flow rates higher than 0.002 (kg/s). 225

0.7 0.69

190

0.67

155

0.66

120

0.65 0.64

85

collector efficiency

Tout [oC]

0.68

0.63 50 0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0.62 0.005


Figure 5:

Collector performance in Rankine cycle as a function of mass flow rate at Pb = 13(MPa). The figure shows the results for two collectors connected in series.

Figure 6 shows the outlet temperature of the hot water TwHW and the efficiency of the Rankine cycle as a function of mass flow rate. It is seen that the maximum efficiency of the Rankine cycle does not correspond to the maximum efficiency of the solar collector. The efficiency of the Rankine cycle decreases with higher mass flow rate mainly because the work of the pump increases at a higher rate than the work of the turbine. The change in the outlet water temperature is not significant, remaining near 30 (oC) for a water flow rate of 0.2 (kg/s). Figures 7 and 8 show the effect of changing the operating pressure of the solar collector in the Rankine cycle at a constant mass flow rate of CO2 of 0.002 (kg/s). The efficiency of the collector in the Rankine cycle decreases only WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


31

slightly with increasing operating pressure. On the other hand, outlet collector temperature of the CO2 increases significantly with pressure. Figure 8 shows an increase in Rankine-cycle efficiency with increasing solar-collector operating pressure and a small decrease in TwHW with increasing pressure at the collector. The results indicate that an optimization process needs to be performed to obtain the optimum operating point for efficiency of the solar collectors and overall Rankine cycle. 0.08 0.07

31

0.06

TwHW [oC]

30.5

0.05

30

0.04 0.03

29.5

0.02 29

0.01

28.5 0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

Efficiency (Rankine cycle)

31.5

0 0.005


Figure 6:

Rankine cycle efficiency P collector = 13 MPa. The figure shows the results for two collectors connected in series. 105

0.698 0.696 0.694

95

0.692 0.69

90 0.688 85

0.686

efficiency

Tout [oC]

100

0.684

80

0.682

75 0.68 9500 10000 10500 11000 11500 12000 12500 13000 13500 14000

PCO2 [kPa]

Figure 7:

Tout and efficiency versus pressure at the collector in Rankine cycle for a fixed mass flow rate of 0.002 (kg/s). The figure shows the results for two collectors connected in series.



30.9

0.065

30.8

0.06

TwHW [oC]

30.7

0.055

30.6 0.05 30.5 0.045

30.4

0.04

30.3

efficiency (Rankine cycle)

Figure 9 shows a schematic of the pressure-enthalpy diagram for an arbitrarily chosen solar collector pressure of 13 (MPa) and a mass flow rate of 0.0015 (kg/s). The solar collectors outlet CO2 temperature reaches 145 (oC) and TwHW reaches 30 (oC) with a water flow rate of 0.2 (kg/s). It is noted that the carbon dioxide temperature at the exit of the turbine corresponds to 86 (oC). Thus, for residential or small commercial applications that require less amount of water at higher temperature, there is still the potential to increase TwHW.

30.2 0.035 9500 10000 10500 11000 11500 12000 12500 13000 13500 14000

PCO2 [kPa]

TwHW and Rankine-cycle efficiency versus pressure at the collector for a fixed mass flow rate of 0.002 (kg/s). The figure shows the results for two collectors connected in series.

Figure 8:

16 80oC

14

120oC 160oC 200oC

b

c

Pressu re [MPa

12 10 8 a

e

6

20oC

4

10oC 0oC

d

2 0 0

100

200

300

400

500

600

700

800

Enthalpy [kJ/kg]

Figure 9:

Pressure-Enthalpy diagram of the solar powered Rankine cycle.



6

33

Conclusions

The thermal analysis of a minichannel-based evacuated-tube solar collector has been performed. The numerical model developed has been combined with the model of a Rankine cycle operating with carbon dioxide. The results show that parameters such as mass flow rate and operating pressure at the solar collector have a significant influence in the performance of the solar collector as well as the overall Rankine cycle.

References [1] Hung, T.C., Waste heat recovery from organic Rankine cycle using dry fluids. Energy Conversion and Management, 42, pp. 539-553, 2001. [2] Vijayaraghavan, S. & Goswami, D.Y., Organic working fluids for a combined power and cooling cycle, Journal of Energy Resources Technology. 127, pp. 125-130, 2005. [3] Kalina, A.I., Combined cycle and waste-heat recovery power systems based on a novel thermodynamic energy cycle utilizing low-temperature heat for power generation, ASME Paper; 83-JPGC-GT-3. 1983 [4] Zhang, X.R., Yamaguchi, H., Fujima, K., Enomoto, M. & Sawada, N., A feasibility study of CO2-based ranking cycle powered by solar energy. JSME International Journal; Series B, 48(3), pp. 540-547, 2005. [5] Yamaguchi, H., Zhang, X.R., Fujima, K., Enomoto, M. & Sawada, N. Solar energy powered Rankine cycle using supercritical CO2. Applied Thermal Engineering, 26, pp. 2345-2354, 2006. [6] Chen, Y., Pridasawas, W. & Lundqvist, P. Low-grade heat source utilization by carbon dioxide transcritical power cycle. Proceedings of ASME-JSME Thermal Engineering Summer Heat Transfer Conference, Vancouver, BC; HT2007-32774, pp. 1-7, 2007. [7] Diaz, G., Performance Improvement of a CO2 Combined Cooling, Heating, and Power Cycle Using Solar Thermal Collectors. Proceedings of SOLAR, San Diego, CA, Paper # 0238, pp. 1-6, 2008. [8] Steinke, M.E. & Kandlikar, S.G., Single-phase heat transfer enhancement techniques in microchannel and minichannel flows. Proceedings of Microchannels and Minichannels ASME Conference, ICMM2004-2328, pp. 141–148, 2004. [9] Yun, R., Kim, Y., and Park, C., Numerical analysis on a microchannel evaporator designed for CO2 air-conditioning systems. Applied Thermal Engineering, 27, pp. 1320-1326, 2007. [10] Air conditioning efficiency standards: seer 12 vs. seer 13. Environmental and energy study institute report, 2001. http://www.eesi.org/030602_ SEER_13 [11] Winston, R., Principles of solar concentrators of a novel design. Solar Energy, 20, pp. 59-67, 1974.


34 Energy and Sustainability II [12] Diaz, G., Performance Analysis and Design Optimization of a Minichannel Evacuated-tube Solar Collector. Proceedings of ASME IMECE, Paper # IMECE2008-67858, Boston, MA, Nov. 2008. [13] Kim, M-H, Pettersen, J., Bullard, C.W., Fundamental process and system design issues in CO2 vapour compression systems, Progress in Energy and Combustion Science; 30, pp. 119-174, 2004. [14] Rahman, F., Al-Zakri, A.S., Rahman, M.A.A., Two-dimensional mathematical model of evacuated tubular solar collector. ASME Journal of Solar Energy Engineering, 106, pp. 341-346, 1984. [15] Klein, S.A. Engineering Equation Solver. Madison, WI, F-Chart Software. [16] Winston, R., Minano, J.C., Benitez, P.G. Nonimaging optics. Elsevier Academic Press, 2005.



35

Biomass refineries: relationships between feedstock and conversion approach J.-M. Lavoie1,2, M. Chornet2,3 & E. Chornet1,2,3 1

Industrial Research Chair on Cellulosic Ethanol and 2nd Generation Biofuels, Department of Chemical Engineering, Université de Sherbrooke, Canada 2 CRB Innovations Inc., Canada 3 Enerkem Inc., Canada

Abstract For conversion purposes, biomass can be classified into three main categories: homogeneous biomass (ex.: corn grains), quasi-homogeneous biomass (ex.: forest residues, straws and plantations in marginal lands) and non-homogeneous biomass (ex.: mixed forest residues, MSW, etc.). In North America homogeneous biomass costs (FOB plant) are over 100 $US/tonne in 2009 (anhydrous basis; 1 tonne = 18 GJ), therefore its conversion to biofuels requires subsidies. As well, alternate and added value uses (food and fibre) compete for such category of feedstock. Quasi-homogeneous biomass, whose cost (FOB plant) 30 - 60 $US/tonne in 2009 (anhydrous basis) for forest residues and straws and estimated between 80 and 100 $US/tonne for plantation biomass (i.e. willows, switchgrass, etc.), is suitable for bio-refineries aiming at co-products biofuels, green chemicals and fibres. However, the availability of large quantities of quasi-homogeneous residual biomass is strongly linked to the existing biomass industrial sector since mills processing sugar cane, corn, wheat and wood also have access to such biomass category whose competing use is the generation of bioenergy (process heat and, in some cases, power). It is however possible to integrate a pre-treatment (a better term is “fractionation”) of the quasi-homogeneous biomass to produce useful fractions for biofuels, green chemicals and fibres while using the residual fractions for bioenergy. Nonhomogeneous biomass is available in all urban centers of the planet and constitutes a major opportunity for biofuels and green chemicals since its cost is negative (i.e. it is a disposal cost paid by municipalities to landfills or incineration facilities) and a sustainable society ought to aim at zero residues. Non-homogeneous biomass can be prepared and converted into a homogeneous and clean syngas intermediate. The latter contains typically two thirds of the carbon in the feedstock and technologies to convert it into biofuels and green chemicals are being developed. Keywords: biodiesel, biorefineries, cellulose, ethanol, extractible, gasification, hemicelluloses, homogeneous biomass, lignin, quasi-homogeneous biomass, non-homogeneous biomass. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090041


1

Introduction

The utilization of biomass as a source of energy products requires considering its nature, cost, availability and the potential conversion approaches. Biomass cost is directly influenced by the quality of the carbon structures. As an example, homogeneous biomass obtained from a selected tissue of a defined tree species will be logically more expensive than an ensemble of different tissues from mixed plant species as well as more heterogeneous carbon matrices (such as municipal solid waste). In North America, cost of biomass ranges (2009) from more than 100 $US per anhydrous tonne (ex.: debarked wood chips) to -50 $US per anhydrous tonne (ex.: MSW). Three distinctive categories of biomass can be considered ; homogeneous, quasi-homogeneous and non-homogeneous biomass. Plantations can also be considered for energy products, even though their biomass cost will likely be higher than forest or agricultural straws. Their eventual use is of interest since they may help to reduce the pressure on the forest, particularly when such plantation biomass is grown on marginal lands. 1.1 Homogeneous biomass Lignocellulosic homogeneous biomass has as key example the wood chips from debarked single species used in the pulp and paper mills. Such a biomass has a cost (FOB plant) higher than 100 $US per anhydrous tonne (> 6 $US/GJ), thus rendering it difficult to consider for energy products. Only with co-products from specific fractions of the biomass, can such high-grade biomass be considered for this purpose. 1.2 Quasi-homogeneous biomass Quasi-homogeneous biomass refers to mixed tissues of a single species or of a mixture of closely related species such as residual straws and forest residues. Non-limiting examples are: corn stover [1,2], bagasse and straw from sugar cane plantations [3,4], straw from wheat [5], residual grape biomass [6] and residues from olives processing [7]. Also included in this category is “whole biomass” planted in marginal land: Arundo donax, Cynara cardunculus, Miscanthus sinensis, Panicum virgatum, Sorghum bicolor [8], Eucalyptus gunnii, Populus trichocarpa, Salix viminalis [9,10] and Miscanthus x Giganteus [11] among others. The forest residues produced during forest operations are also included in this category. Such forest residues have been estimated to about 6,9 million tons (anhydrous) per year in the province of Quebec alone [12]. Degraded biomass forest such as the large quantities of pines killed by the mountain pine beetle [13] fall within the quasi-homogeneous biomass category as well. Quasi-homogeneous biomass is composed of chemical structures derived from several types of tissues, thus more complex than homogeneous biomass which comes from specific tissues. Cost for this quasi-homogeneous biomass varies, in North America (2009) from 30 to 60 $US per ton (anhydrous base)



37

when residues are considered. Such biomass is a readily available feedstock for conversion processes whether biological, thermo-chemical or in combination. 1.3 Non-homogeneous biomass Non-homogeneous biomass is a category for which the cost ranges from 30 $US/ton (anhydrous basis) to negative values (tipping fee) for “waste”. Such negative value is related to the avoided cost of landfills. The key example of such biomass is municipal solid wastes (MSW) which comprise (i) residential residues (the «garbage»); (ii) institutional, commercial and small industries (ICI) wastes; and (iii) construction and demolition wood (C&W). Included in the latter are contaminated woods such as spent poles and railroad ties and sludge from rendering operations and wastewater treatment plants. These residues are available in large volumes and could become a significant source of carbon for which the supply would be local and recurrent. It is estimated that in the western world each person “produces” close to 1,0 kg of residential MSW per day with an equal amount of ICIs also generated. Only a fraction of such residual materials can be effectively recycled and biocomposted, leaving about half available for conversion processes. Since such materials are highly heterogeneous (MSW contains food remnants, paper, cardboard, plastics, glass and metals), the production of a homogeneous intermediate that can be better used than the original material limits the conversion technologies to a few options. Among these options, biogasification (i.e. anaerobic digestion) of sludge often preceded by a pre-treatment to improve digestibility and thermal gasification of sorted, dried and shredded solid wastes are efficient techniques which allow the production of a homogeneous gas (biogas or syngas). Purification of this gas and neutralization of contaminants allows its utilisation for heat and power production or in catalytic synthesis.

2

Choice of conversion process

The choice of an appropriate conversion technique very much depends on the availability, category and composition of the biomass. With quasi-homogeneous biomass a co-products strategy is possible. Such strategy is related to chemical pulping which is, overall, the isolation of the cellulose fibre from a lignocellulosic matrix. Most of the pulping processes used in the industry coproduce fibres and energy from the residues. The approach implies further separation/isolation of the macromolecular compounds and their conversion to “green chemicals” and/or alternative fuels from the lignin, hemicelluloses and the short chain cellulosic fibres. On the other hand, non-homogeneous and often heterogeneous biomass can, via higher severity conversion processes (pyrolysis or gasification) be transformed to intermediate uniform feeds (char and bio-oil via pyrolysis or syngas via gasification) which are more suitable that the original material for additional conversion into final products.


38 Energy and Sustainability II 2.1 Biorefineries based on fractionation A general illustration is depicted in Figure 1.

Figure 1:

Illustration of the biorefinery concept (courtesy of CRB) that could be used for the conversion of forest and agricultural quasihomogeneous biomass into biofuels and added value products.

The key goal in fractionation is to isolate the constitutive chemical families present in the feedstock. Thermocatalytic processes of low severity such as solvolysis or steam treatments accomplish this. The fractions produced will subsequently be transformed into defined chemicals and fuels. Any residue is used as source of heat and/or power. 2.1.1 Removal of extractives The quasi-homogeneous biomass contains a certain amount of extractives. These molecules are not part of the structural macromolecules in lignocellulosic plants and are often categorized as secondary metabolites. Extractives are used by plants against insects, fungus and bacteria [14]. They range between 3 to 10 wt% of the dry weight of the biomass. Removal and recovery of the extractives is the first unit operation to consider. Liquid-solid extractions are generally used [15]. Extracts are usually a complex mixture of molecules. Isolation and purification of extractives has lured researchers and industrial groups given the potential applications from aroma chemicals to the pharmaceutical potentials. However the purity required in fine chemicals has limited the use of “bulk extractives” as raw material. The simplest utilization of the bulk extractives in a generic biorefinery would be as input to a cogeneration plant. 2.1.2 Aqueous/steam and organo-solvolytic treatments After removal of bulk extractives, the fractionation of lignocellulosics into constitutive macromolecular families is central to the biorefinery concept. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Aqueous/steam treatments, of which steam treatments are a well known variation dating back to the beginning of the 20th century [16] are, essentially, hydrolytic processes (with or without soluble catalysts) applied for a few minutes in the temperature range from 170 to 230oC and at a steam pressure equal or higher than the vapour pressure of water at the chosen temperature. In the simplest application, the heated biomass saturated with water is suddenly depressurized and flown at high speed through an appropriately designed nozzle. The downstream side of the nozzle is at lower pressure than the upstream side and thus sudden vaporization of water occurs. The force generated by the sudden vaporization separates the fibres inducing a partial hydrolysis of the hemicelluloses. This technique is actually used as pre-treatment for the production of low cost fermentable sugars [17] for the production of paper [18] and for the production of fiber for board (masonite board as an example). Organo-solvolysis is a process by means of which an organic solvent, mixed generally with water, is used to solubilise specific macromolecules (a large fraction of the hemicelluloses and lignin) liberating cellulose. This technique (also called organosolv pulping) has been demonstrated using acidic water/alcohols media but it has not gained commercial status. The “liquefaction” of cellulose in a mixture of water, acetone and HCl has also been proposed [19]. The utilization of acid ethylene glycol [20] and formic acid [21] has also been studied as organosolv approaches. In both steam treatment and organosolv approaches, the process can be tuned for optimal results on the production of cellulose or sugars depending on severity. Steam treatments allow separation of hemicelluloses and cellulose fractions. Solvolysis usually allows recuperation of native lignin with little modification of the original macromolecule. 2.1.3 Hemicelluloses The hemicelluloses are macromolecules that are produced following a branched polymerization of C5 and C6 carbohydrates. Usually, the hemicelluloses found in ligneous plants are composed of xylose and glucose but also, in lower concentrations, of arabinose and mannose. The constraint concerning this heterogeneous composition of sugars is that the pentoses (xylose and arabinose) are difficult to ferment when using classical micro-organisms. Nevertheless, it has been shown in the last few years that it is possible to ferment xylose using genetically modified organisms [22]. The latter are promising but they are difficult to be used given inhibitors present in the hydrolyzates at industrial level. An alternative is to ferment C6 sugars using known microorganisms (such as yeasts), then use the C5 for dehydration to furfural with simple acid catalysts. At high temperatures, the hexoses are converted to 5-hydroxymethyl-2-furfural while pentoses are converted to furfural (see Figure 2). Furfural could serve as an added value chemical for polymerisation or, through conversion (mainly selective hydrogenation), could yield furanic oxygenates which blend well with established hydrocarbon fuels. The 5-hydroxymethyl-2-furfural is a relatively unstable compound in presence of water and acid catalyst and tends to be converted to levulinic acid and formic acid (see Figure 2). While formic acid WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

40 Energy and Sustainability II could be used as a green chemical, esterification of levulinic acid could lead to the production of biodiesel grade esters. Most of the previously mentioned molecules will likely be significant as a forthcoming generation of ‘green’ chemicals and biofuels [23]. O H HO H H

OH

OH O

H OH

O

H H3C O

OH

O

A

OH

O H HO H

+

O OH H

O

OH

O

H OH

OH

H

B

OH

Figure 2:

Dehydration of glucose to 5-hydroxyméthyl-2-furfural and then to levulinic acid and formic acid (A) and dehydration of xylose to furfural (B).

2.1.4 Delignification In case of solvolysis, lignin is directly solubilised during the treatment. When using steam treatments, delignification of the cellulose-rich fibres obtained from the removal of the hemicelluloses can be performed using either an organosolv method or, as in the Kraft pulping process, with NaOH at concentrations varying in the range 5-20% (wt∞). Abundance of the hydroxide ions will produce partial hydrolysis (the extent of which depends upon severity) of the C-O-C bonds in the lignin macromolecule thus generating monomeric, dimeric and trimeric structures. The alkaline solution allows the solubilisation of the lignin fragments and of the residual lignin itself. The dissolved dimers, trimers and the lignin itself can then be recovered after neutralization of the basic solution using a common acid as H2SO4. The latter will provide a proton to the aromatic structures thus rendering them un-miscible with water. The recovered mix (dimers, trimers and residual lignin) could be used as a source of energy via cogeneration. However, its subsequent secondary hydrolysis (at higher severities than those used in the delignification) could provide (i) additional monomeric units to those initially produced in the delignification step: catechols or aldehydes (vanillin or syryngaldehyde) could thus be isolated; and (ii) dimeric and trimeric compounds which both posses carbon-carbon bonds between the aromatic rings which could be transformed in high octane fuels via hydrotreatment techniques available in petroleum refineries. 2.1.5 Cellulosic fibers and fines Cellulosic fibres are the product derived from biomass having the most important market as a non-food material. In general, steam treatments and organosolv processes provide fibres that have a quality comparable or even better than the classical chemical pulps. Along with the (long) fibres required for pulp, the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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accompanying short fines are of interest. They could readily be brought to their microcrystalline structure which contains cellulosic chains at polymerization levels not exceeding 220 units. Such chains are linked together with hydrogen bonds. Although the crystalline system is highly polar because of the numerous alcohol functions found on the macromolecules, it is also highly resistant to aqueous solvation because the functional groups are generally oriented toward the center of the crystal. It is therefore usually difficult to attack the bond linking the glucose units and force the depolymerization of cellulose into its monomeric units (glucose). Enzymes are prime candidates as biocatalysts for the depolymerization [24]. Alternatively cellulose can be swollen by water or organic solutions having sufficient ionic strength to break the H-bonded matrix. Once cellulose is swollen its depolymerization (i.e. hydrolysis) to glucose, fermentation to ethanol or other end products is possible. 2.2 Pyrolysis and Gasification Non-homogeneous biomass is a complex and often variable mixture of numerous carbon-based structures. The amount of different compounds renders this type of feedstock difficult to fractionate. The biorefinery approach needs to yield homogeneous intermediates that can be upgraded to defined and marketable end products. Pyrolysis and gasification accomplish such goal by forcing major changes in the carbon-based structures. Pyrolysis (also known as thermal decomposition or thermal cracking), produces three streams: gas (normally used to fuel the process itself), a “bio-oil” (a complex mixture of dehydration water, organic compounds derived from carbohydrates, lignin and their cracked carbon structures) and residual charcoal (char as it is commonly known). In rapid pyrolysis processes, bio-oil (50 -70 wt% of the biomass) and char (10 – 20 wt% of the biomass) are the two intermediates that can be conveniently transported (they have higher bulk energy densities than the original solid feedstock) and used directly for their energy content (case of bio-oil replacing petroleum-based products in furnaces) and char as a soil additive. The bio-oil can also be fractionated into an essentially waterfree oligomeric lignin-rich fraction and an aqueous fraction which contains carbohydrate-derived compounds (aldehydes to a large extent). The oligomeric lignin fraction can be used very much like a near-petroleum feedstock (oxygenated since it has a phenolic structure) in crackers and hydrocrackers located in petroleum refineries. Alternatively, the oligomeric lignin-rich fraction can be catalytically converted into oxyaromatics having value as green chemicals (for instance, catechols) and biofuels (for instance, alkoxyaromatics). The aqueous fraction containing carbohydrate-derived compounds can also be upgradable to simpler intermediates, such as hydrogen. It can also be concentrated, via membranes, and used directly as fuel. With heterogeneous feedstock (such as “urban biomass”: sorted municipal solid waste residues), the pyrolysis route is constrained because of possible contaminants in the bio-oil. With such feedstock, synthetic gas is by far the best alternative because independently of the nature of the biomass used, it is essentially a homogenous intermediate. When oxygen and steam are used as WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

42 Energy and Sustainability II partial oxidation agents, the synthetic gas becomes syngas, which can be used for chemical synthesis if its conditioning and purification reaches levels that make it compatible with catalysts. Gasification is thus attractive because of its flexibility regarding feedstock. Urban biomass is a preferred input material because of its negative cost (i.e., the avoided landfill cost). Gasification of bio-oil can also be carried out. Biomass can thus be pyrolyzed in regional plants, the bio-oil transported and converted in a larger gasification and synthesis plant. Economies of scale may thus offset the high cost of the quasi-homogeneous biomass. Gasification of biomass is usually performed at temperatures close to 800oC [25]. However, the choice of temperature as well as the process conditions leading to the formation of syngas are highly dependent on the nature of the feedstock given the presence of inorganic salts (recognized as ‘ash”) having lowsoftening points often at near or lower temperatures than 800oC. Chlorides are particularly low melting point salts. Temperatures in the thermal decomposition zone thus need to be adjusted to the nature of the inorganics present in the raw material. The chemistry of the reactions involves the following sequence: dehydration, thermal decomposition, partial oxidation and steamdriven and, to a lesser extent, CO2-driven reactions. The initial products of this complex process will be gas, intermediates and char. Such a mixture undergoes the reactions shown in Table 1. Table 1:

Identification of the major chemical reactions associated with the gasification of carbon-based compounds.

Reaction C + ½O2 = CO CO + ½O2 = CO2 H2 + ½O2 = H2O C + CO2 2CO C + H2O CO + H2 C + 2H2 CH4 CnHmOk + aO2 + bH2O = cCO + dCO2 + eH2

Identification 1 2 3 4 5 6 7

Among these reactions it is possible to identify oxidation reactions (1,2,3), the Boudouard reaction (4), the water-gas shift (5), the methanation reaction (6) and the autothermal reforming reaction of the oxygenated compounds produced by dehydration and by thermal decomposition (7). The latter reaction (7) includes CO2 + H2]. All these reactions permit to the shift reaction [CO + H2O understand the importance of an oxygen input when feedstock as coal or plastic is gasified. Reactions 4, 5, 6 and 7 shows that it should be possible to control the composition of the syngas by partial oxydation of the char produced during its thermal decomposition. This particularity is important when it is necessary to homogenize the composition of the syngas independently of the gasified feedstock. The reforming of the oxygenated compounds is also an important aspect allowing the generation of a syngas with a limited amount of chemical WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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compounds as output. Carbon monoxide and hydrogen are the key compounds for synthesis and will also allow the utilization of advanced concepts such as coupling gasification with fuel cells. In equation (7), the coefficients a-e will depend upon the temperature and the composition of the oxygenated intermediates. Yields of synthetic gas vary within a range of 1.8 – 2.2 Nm3/kg biomass (dry) for air gasification and 0.8 to 1.0 Nm3/kg biomass (dry basis) for O2/steam gasification. The dry synthetic gas contains about 75% of the energy in the biomass being gasified. In addition heat recovered from the hot synthetic gas adds about 10% for a total of 85% as recovered energy. Low grade heat accounts for 5% and the rest and the remaining energy balance is due to the endothermic reactions and losses. Gas composition varies somewhat with technology and operating conditions. Table 2 shows typical compositions from Enerkem’s gasifiers operated with air and O2 / steam. Note the beneficial effect of reforming in reducing the gas mix components. The gasification technologies are usually categorized in three families; the slowly moving (often named “fixed”) bed reactor (in either downdraft or updraft Table 2:

Typical syngas compositions from biomass.

Gas compound

Air Gasification (Low severity)

Air gasification (Low severity) + steam reforming

O2 / steam Gasification (Low Severity)

O2 / Steam Gasification (Low severity) + steam reforming

N2 Ar H2 CO CO2 CH4 C2H4 CxHy (C2C5) CxHy (C6 and higher)

55.8 0.8 9.5 10.3 14.1 4.2 2.2 2.1

35.5 0.5 35.2 17.9 10.9 0.5 0 0

0.5 0.3 11.8 20.4 41.1 10.0 8.6 6.6

0.3 0.1 47.0 23.2 29.4 traces 0 0

O2 / Steam Gasification (Low severity) + steam reforming + CO2 scrubbing (partial removal) 0.4 0.2 65.0 32.0 2.4 traces 0 0

1.0

0

0.7

0

0

*Composition can be varied by adjusting the reforming step with steam and CO2 for specific applications. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

44 Energy and Sustainability II mode), the fluidized bed reactor and the entrained flow gasifier with or without slag formation. The fixed bed gasification relies on establishing a “pile” of solid material that is reacting progressively, and thus slowly moving downwards due to gravity. Addition of oxidant and of steam is done at strategic zones of the “pile”. Such approach, with numerous geometrical variations and feeding systems is the most ancient configuration used for the formation of synthesis gas. Coke or anthracite which are relatively pure carbon structures were used early on readily producing “water gas”. Lignocellulosic biomass can also be used as a feedstock but due care is needed for the management of the intermediate tar. Downdraft gasifiers where the gas is flown through a hot incandescent char zone permits to reach low tar levels in the synthetic gas produced. Fluidized beds imply inert solids (sand, alumina or olivine) being fluidized by air or oxygen/steam. The carbonaceous material is inserted in or just on top of the bed where the heat and mass transfer coefficients are high (200 – 500 watts/m2). This technique was identified as the most suitable for the gasification of biomass [25]. It requires that the size of the biomass particles that are introduced in the reactor is not superior to a few centimetres. The fine carbon particles that exit the bed entrained by the gas undergo additional conversion in the upper part of the reactor. A cyclone permits to recycle unconverted solids. The entrained flow gasifier is well developed for the gasification of fine coal particles and could also be used for biomass. In this type of process, the grinded feedstock is converted co-currently with the oxiding agent and steam in essentially a flow reactor. If the temperature at which the conversion is done is sufficiently high, the biomass will not produce any char residues and the slag will be solidified by contacting it with a liquid phase from which the solids are recovered. Unwanted components of synthetic gas comprise tars (composed of polyphenolics and poly-aromatics compounds), chlorine-based compounds (as HCl), sulphur (as H2S and COS), un-converted carbon particles as well as metal salts (mainly oxides). For further use the synthetic gas (syngas), needs to be purified. The sequential treatment used for the purification of the syngas is directly related to the utilization that is intended for it. When the gas is produced for the synthesis of alcohols or alkanes, removal of particulates and tar, as well as reduction of chlorine-based and sulphur-based compounds must reach essentially zero levels. As well carbon dioxide levels need to be compatible with desired synthesis strategies. In the last few years, numerous papers have been published on the purification of syngas. Experimental data points to sequential hot gas conditioning and wet scrubbing techniques capable of producing a clean syngas ready to be used for catalytic synthesis. Neutralization of chlorine using CaO is an efficient technique that permits to get rid off residual HCl. But reducing sulphur to sub-ppm levels (ppm = mg/Nm3) is a difficult task and thus catalytic reforming of the tar and low molecular weight hydrocarbons has not, to our knowledge (2009) been successfully implemented for long period of times (in excess of 200 h). If thermal reforming (without catalyst) is used, the destruction of the tar is not complete yet its removal can be achieved via scrubbing techniques. The latter use either aqueous or oil-based systems or a combination. The H2/CO ratio is adjusted during the thermal reforming step by WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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conducting such step at appropriate severities and steam/carbon ratios. Particulate levels are lowered to ppm levels via a combination of cyclones and scrubbers. Alternatively metal and ceramic filters have been tested. Final purification of the syngas for catalytic synthesis uses CaO and ZnO filters as well as chilled methanol (other solvents can also achieve the same result) which permits, as well, to adjust the CO2 concentration in the syngas to the desired level. Nitrogen gases, namely NH3 and HCN are not an issue since during the thermal reforming and subsequent scrubbing they are removed. Cleaning and recirculating the scrubbing liquids is an inherent component of the gas conditioning strategy. It implies stripping the dissolved gases and vapours and, as well, precipitating out as sludge the fine particulates present in the liquid phase.

3

Conversion of syngas to biofuels

Production of methanol from syngas is industrially practiced. Copper/zinc oxidebased catalysts show high productivities up to 2 kg of MeOH per kg of catalyst per hour [26] with selectivities reaching near the 100% level. Production of ethanol and long chain alcohols is one of the most researched areas currently (2009) in this field. Conversion of syngas to ethanol can be done using two distinct pathways: the direct catalytic conversion (associated with drastically lower conversion yields if compared to the methanol synthesis) or via the separate homologation of methanol. The latter pathway allows one to take advantage of high production yields associated with methanol synthesis yet it has a higher complexity than the direct pathway because of the additional synthesis steps required. Production of alkanes from synthesis gas is known as the Fisher-Tropsch synthesis (FT). At the industrial level, cobalt and iron are used as catalysts at temperatures close to 340oC. Such conditions allow converting close to 40% of the syngas into gasoline and 20% in propene and butene which can be partially inserted in synthetic fuel to increase its octane level [27]. The yields of useful product that can be commercialized as gasoline or as diesel following a FT synthesis are lower than those observed in the methanol synthesis [28]. The latter can be converted to gasoline via catalytic oligomerization, which constitute an alternative to the FT synthesis.

4

Conclusions

For the conversion of lignocellulosics to biofuels a decision on the technological route to be followed very much depends on the type and cost of biomass and availability within a reasonable transportation distance that does not exceed 100 km, as the norm in North America. For this purpose biomass can be categorized as follows: homogeneous biomass (>100 $US/t), quasi-homogeneous biomass (30-60 $US/t) and non-homogeneous biomass (≤ 0 $US/t, dry basis). Among the biofuel production techniques that are actually entering the market, gasification is by far the most versatile because it can be applied to all the different types of WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

46 Energy and Sustainability II biomass previously mentioned. However, because of the biomass availability and cost, the feedstock targeted by gasification will be preferentially nonhomogeneous biomass which permits moderate capacity plants (100 000 t biomass input, dry basis, per day) and, as well, quasi-homogenous biomass, the latter requiring, via gasification, large economies of scale. The homogeneous and quasi-homogeneous biomass, because of their higher costs (about 100 $US for homogeneous to a range of 30-60 $US per anhydrous tonne for quasihomogeneous) could be adapted to a co-product strategy. The biorefinery concept, using fractionation approaches, will allow the isolation and the utilization of the constitutive fractions of the biomass. Such approaches should also be designed to be self-sufficient in terms of energy. The isolated constitutive fractions are the “secondary biomass feedstock” for upgrading to marketable end products” green chemicals, biofuels and fibres.

Acknowledgements The authors would like to show their appreciation to the companies that are funding the Industrial research chair on cellulosic ethanol and 2nd generation biofuels: Enerkem, CRB Innovations and Ethanol Greenfield. We would also like to acknowledge NSERC for the strategic grant provided for the conversion of hemicelluloses and to the ABIP grant for the conversion of lignin. We would also like to acknowledge our colleagues Prof. J. Lessard for his input on hemicellulosic sugars conversion and Prof. N. Abatzoglou for his pioneering work on gasification and gas conditioning technologies.

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[6] Lapuerta, M., Hernandez, J.J., Pazo, A. & Lopez, J. Gasification and cogasification of biomass waste: Effect of the biomass origin and the gasifier operating conditions. Fuel Processing Technology, 89(9), pp. 828-837, 2008. [7] Link, S., Arvelakis, S., Spliethoff, H., De Waard, P. & Samoson, A. Investigation of Biomasses and Chars Obtained from Pyrolysis of Different Biomasses with Solid-State 13C and 23Na Nuclear Magnetic Resonance Spectroscopy. Energy & Fuels, 22(5), pp. 3523-3530, 2008. [8] Monti, A., Di Virgilio, N. & Venturi, G. Mineral composition and ash content of six major energy crops. Biomass and Bioenergy, 32(3), 216-223, 2008. [9] Sugiura, A., Tyrrel, S.F., Seymour, I. & Burgess, P.J. Water renew systems: wastewater polishing using renewable energy crops. Water Science and Technology, 57(9), pp. 1421-1428, 2008. [10] Labrecque, M. & Teodorescu, T.I. The influence of site and wastewater sludge fertilizer on the growth of two willow species in southern Quebec. Biomass: A Growth Opportunity in Green Energy and Value-Added Products, 4th Proceedings of the Biomass Conference of the Americas, Oakland, pp. 31-37, 1999. [11] Cappelletto, P., Mongardini, F., Barberi, B., Sannibale, M., Brizzi, M. & Pignatelli, V. Papermaking pulps from the fibrous fraction of Miscanthus x Giganteus. Industrial Crops and Products, 11(2-3), pp. 205-210, 2000. [12] Goyette, J. & Boucher, S. Communication from the engineering firm Roche, november 2008 Établissement d’une chaufferie centrale à la biomasse forestière : Lignes directrices dans un contexte québécois. [13] Pan, X., Xie, D., Yu, R.W. & Saddler J.N. The bioconversion of mountain pine beetle-killed lodgepole pine to fuel ethanol using the organosolv process. Biotechnology and Bioengineering, 101(1), pp. 39-48, 2008. [14] Canales, M., Hernandez, T., Rodriguez-Monroy, M.A., Jimenez-Estrada, M., Flores, C.M., Hernandez, L.B., Gijon, I.C., Quiroz, S., Garcia, A.M. & Avila, G. Antimicrobial Activity of the Extracts and Essential Oil of Viguiera dentata. Pharmaceutical Biology, 46(10-11), pp. 719-723, 2008. [15] Lavoie J.-M. & Stevanovic T. Ultrasonic Extraction of Lipophilic Constituents of Yellow Birch (Betula alleghaniensis) and White Birch (Betula papyrifera) Wood, Phytochemical analysis, 18(4), p. 291-299, 2007. [16] Marshall, G.H. Preparing cellulose from pithy or woody stalks, US 982379 19110124 Patent, 1911. [17] Viola, E., Cardinale, M., Santarcangelo, R., Villone, A. & Zimbardi, F. Ethanol from eel grass via steam explosion and enzymatic hydrolysis, Biomass and Bioenergy, 32(7), pp. 613-618, 2008. [18] Westenbroek, A.P.H., van Kessel, L.P.M., Hooimeijer, A., Thuene, P.C., Nierstrasz, V.A., Koopal, L.K., Lamot, J.E., Waubert de Puisseau, M., van Willige, R.W.G., Adriaanse, M., Lund, H., Dorschu, M. & Theunissen J. Fibre raw material technology for sustainable paper and board production, Paper Technology, 46(7), pp. 17-24, 2005. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

48 Energy and Sustainability II [19] Paszner, H.L. & Chang P.-C. Separation of cellulose fibers from lignocellulose. BE 870112 19781218 Patent, 1978. [20] Rezzoug, S.-A. & Capart, R. Liquefaction of wood in two successive steps: solvolysis in ethylene glycol and catalytic hydro-treatment. Applied Energy, 72(3-4), pp. 631-644, 2002. [21] Kleinert, M. & Barth, T. Towards a Lignincellulosic Biorefinery: Direct One-Step Conversion of Lignin to Hydrogen-Enriched Biofuel. Energy & Fuels, 22(2), pp. 1371-1379, 2008. [22] Jeffries T.W. Engineering the Pichia stipitis genome for fermentation of hemicellulose hydrolysates, Bioenergy , pp. 37-47, 2008. [23] Qi, X., Watanabe, M., Aida, T.M. & Smith R.L. Catalytical conversion of fructose and glucose into 5-hydroxymethylfurfural in hot compressed water by microwave heating, Catalysis Communications, 9(13), pp. 2244-2249, 2008. [24] Mussatto, S.I., Dragone, G., Fernandes, M., Milagres, A.M.F. & Roberto, I.C. The effect of agitation speed, enzyme loading and substrate concentration on enzymatic hydrolysis of cellulose from brewer's spent grain, Cellulose, 15(5), pp. 711-721, 2008. [25] Higman, C. & van der Burgt, M. Gasification. Elsevier: New York. 391 pp., 2003. [26] Pass, G., Holzhauser, C., Akgerman, A. & Anthony, R.G. Methanol synthesis in a trickle-bed reactor. AIChE Journal, 36(7), pp. 1054-60, 1990. [27] Dry, M.E. The Fischer-Tropsch process: 1950-2000. Catalysis Today, 71(34), pp. 227-241, 2002. [28] Luo, M., O'Brien, R. & Davis, B.H. Effect of Palladium on Iron FischerTropsch Synthesis Catalysts. Catalysis Letters, 98(1), pp. 17-22, 2004.



49

Elimination of siloxanes by adsorption process as a way of upgrading biogas D. Ricaurte Ortega & A. Subrenat GEPEA - UMR CNRS 6144, Ecole des Mines de Nantes, France

Abstract Biogas is increasingly being investigated as a source of renewable energy, however its utilisation requires an improvement of its quality. Certain biogases contain compounds called siloxanes; these compounds are the origin of some problems when using biogas. At high temperatures siloxanes are transformed to silicate oxides which can damage equipment (i.e. engines corrosion, the clogging of fuel cell membranes.). This paper provides details of the research done in the treatment of siloxane by adsorption process of adsorption. Different porous materials were studied in order to evaluate adsorption capacities. Influences of humidity and temperature on the mass transfer were evaluated. Moreover, reactors were filled with a mixture of methane and carbon dioxide (principal compounds on the biogas) in order to evaluate the impact of the gas composition in the adsorption capacities. Finally the capacity of adsorption is also evaluated in the presence of an organic volatile compound (VOC). Activated carbon cloth was chosen to continue with the experiences realised for the adsorption – desorption process. This porous material has shown good adsorption capacities. Furthermore, desorption process can be performed in situ and their implementation in industrial process is more easy. Adsorption-desorption cycles were performed and the possibilities of the material regeneration evaluated. Joule effect was employed in the desorption process in order to reduce the duration of regeneration. First cycles have been accomplished. Results are promising, even if the operational conditions of the process must be optimised. Keywords: siloxanes, biogas, adsorption, desorption, activated carbon cloth, zeolite, Joule effect.

WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090051


1

Introduction

Research in alternative sources of energy and the commitment of industrial countries towards a reduction of fossil fuel dependency have resulted in a growing interest in the use of biogas. This gas is produced in most of the Europeans countries, from landfills and digesters. The composition is basically methane (50-60%), carbon dioxide (3040%), nitrogen (2-5%), oxygen (0.1-1%) and others different compounds (less than 0.2%) [1], though the composition varies according to its origin. Biogas can be used in many different applications, fuel for vehicle, CHP engines, fuel cells, and all applications designed for natural gas, among others. However, suppliers and manufacturers often hesitate to use it due to the presence of organometallic compounds such as siloxanes [2]. The term siloxane makes allusion to a subgroup of silicones containing Si-O bonds with organic radicals attached to the atom of silicon.. These compounds can be viewed as a hybrid of both organic and inorganic compounds. The organic side chains confer hydrophobic properties while the -Si-O-Si-Obackbone is purely inorganic. Siloxanes are widely used in different applications: health care, dry cleaning, household products, paints and coatings, paper, personal care and so on. Due to their volatile nature, they are usually dispersed into the atmosphere. Siloxanes can also be presents in slurry from landfills. Due to this physical structure they can be classified in two groups, linear and cyclical molecules. During anaerobic digestion, when the temperature goes up to 60°C siloxanes are volatilised, forming part of the biogas. The growing consumption of siloxanes and silicones in industry has increased its predominance n the environment, restricting the possibilities of biogas upgrading and its utilisation as a source « of green energy ». At high temperatures siloxanes are transformed to silicate oxides (SiO2 or/and SiO3). An atom of silicone is liberated and bonded to the free oxygen (present in the environment). The main problem with silicate is the damage sustained by the equipment, seriously reducing its efficiency. In engines, silicate may adhere to metal or catalytic substrate surfaces forming a thickness of several millimetres difficult to remove by chemical or mechanical means, Priebe et al. [3]. In fuel cells, siloxanes can generate clogging in the membrane, Peregrina and Audic [4]. Depending on the origin of biogas, the amount of siloxane in the biogas can vary from 0 to 140 mg.m-3, Huppmann et al. [5]. Engine manufacturers usually recommend not to exceeding a limit of 5 mg.m-3 siloxane in biogas. There are no exhaustive studies in the literature concerning the treatment of siloxanes in biogases. Some of these researches are enunciated. Absorption into tetradecane, Schweigkofler and Niessner [6], cryogenic condensation, Ajhar and Melin [7], gas permeation, Wheless and Pierce [8], etc. on this paper adsorption technology will be performed. Nevertheless, for different reasons (costs, generation of secondary products, recycling material and low adsorption capacities) these techniques are not well adapted to a procedure of siloxane’s elimination.



51

The main objective of this study is to evaluate de feasibility of an adsorption process. This process is developed as a treatment of siloxane to reduce its presence in biogas. Three different porous materials are studied, activated carbon cloths, granular activated carbon and zeolite. The influence in the adsorption capacities of siloxanes is studied under the presence of methane and carbon dioxide in excess (representative of a biogas), humidity, and other volatile organic compounds (VOC). Temperature is also another determinant factor on this study.

2

Adsorption in batch reactor

2.1 Experimental procedure The porous material sample is confining into a batch reactor in order to proceed with the adsorption process. The mass of the material remains constant in each reactors (0.5g approximately). All the reactors are maintained under the same operative conditions. A certain volume of siloxanes is injected into the reactors, this quantity changes in each reactor and so the initial concentration of the pollutant. Therefore the adsorption capacity can be measured. All the measurements are performed by a Gas Chromatograph (y) connected to a Flame Ionisation Detector (GC-FID). Isotherms can be modelled with the Freundlich model. This model is based on the adsorption on monolayer (isotherm type I). Equilibrium adsorption capacity (qe) can be calculated according to the equation:

qe = KC

1 n e

(1)

Where Ce is the concentration in the rector after adsorption, K and n are the parameters of the equation, which depend on the nature of the gas. The siloxane compounds used in this study were selected due to their presence in biogas, McBean [9] and because of their physical structure. Octaméthylcyclotetrasiloxane (D4) was chosen as a cyclical compound and Hexaméthyldisiloxane (L2) as a linear compound. Some of their properties are listed below: Table 1: Name (Symbol) Hexaméthyldisiloxane (L2) Octamethylcyclotetrasi loxane (D4)

Physicochemical properties of siloxanes. Molecular formula

Molecular weight (g.mol-1)

Density at 20°C (g.m-3)

Melting point (°C)

Boiling point (°C)

Vapour pressure at 25°C (kPa)

C6H18OSi2

162.4

0.764

-67

100

4.12

C8H24O4Si4

296.6

0.956

17.4

175

0.17

Three different porous materials are studied; zeolite (DAY 40), chosen by its hydrophobic character and the presence of silicon atoms as part of its composition. Activated carbon in grain (ACG - NC 60) commonly used in VOC WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

52 Energy and Sustainability II adsorption, Le Cloirec and Faur [10]. Activated carbon cloth (ACC - FM 30K) recently studied with very good adsorption capacities, Subrenat and Le Cloirec [11]. Physical characterisations of these adsorbents are assembled in table 2. Table 2: Material

Texture

ACC - FM 30K ACG - NC 60 Zeolite - DAY40

Cloths Grain Grain

Physical properties of the materials. BET Surface (m2.g-1) 1000 1220 607

Micro porous Volume (cm3. g-1)

Total porous Volume (cm3.g-1)

0.371 0.320 0.227

0.494 0.670 0.328

% Volume Micro porous 75 47 69

2.2 Results and discussions Classical isotherms were obtained after adsorption. Modelling can be developed from the Freundlich model, eqn (1). In this model the coefficient K represents the maximal adsorption capacity, bigger is the coefficient K bigger is the capacity of the material to adsorbed the pollutant. For the coefficient n, the adsorption capacity will increase rapidly when the coefficient approaches to zero. As mentioned before, influence in adsorption capacity is studied under different operative conditions. Freundlich coefficients are presented in table 3. Table 3: Compound

Coefficients of Freundlich model for the isotherms adsorption. RH (%) 0

L2 70

D4

0

VOC 0 Tol g.m-3 0 Tol g.m-3 1 g.m-3 10 g.m-3

RH (%) 0 70

Dry Air Adsorbent K FM 30K 293.97 25 NC 60 341.17 DAY 40 123.60 60 FM 30K 265.05 FM 30K 290.01 25 NC 60 294.61 DAY40 104.82 FM 30K 386.73 25 DAY 40 124.10 60 FM 30K 302.92 Methane and carbon dioxide mixture with L2 Temperature (°C) Adsorbent K 286.57 271.98 25 FM 30K 257.02 226.09

Temperature (°C)

1/n 0.048 0.115 0.133 0.057 0.061 0.068 0.179 0.041 0.047 0.055

R2 0.938 0.944 0.953 0.999 0.988 0.950 0.908 0.825 0.909 0.925

1/n 0.077 0.064 0.058 0.056

R2 0.922 0.894 0.977 0.945

2.2.1 Influence of the porous material To observe the influence of the porous material, isotherms were realised under the same operative conditions. In the following example, siloxane L2 was used at 25°C with 0% humidity. The results are showed in fig. 1. The highest adsorption capacity was observed with the ACG – NC 60 (350 mg.g-1), while the lowest was obtained with zeolite DAY 40 (less than 150 mg.g-1). As a matter of fact, the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 1:

53

Influence of the porous material.

B.E.T. surface is related to the adsorption capacity, the larger the surface, the larger the capacity (see table 2.). 2.2.2 Influence of temperature Two temperatures were tested, 25°C and 60°C. Temperature was found to be inversely proportional to the adsorption capacity. The capacity decreases over 40 mg.g-1. In fact, siloxanes at high temperature tend to remain suspended in the atmosphere and not absorbed into the material. These results are supported by previous studies, Le Cloirec [12]. 2.2.3 Influence of the gas composition The adsorption capacity of siloxanes is studied according to various compositions of the gases enclosed in the reactors. The principle of these experiences is to emulate to the composition of a real biogas. As mentioned before, mainly methane, carbon dioxide, water, and some organic volatile compounds (VOC) form biogas. - Influence of humidity Adsorption capacities were measured under a relative humidity of 70% in the reactors. Results depend on the material. For the activated carbon cloth, no difference was appreciated. However for the activated carbon in grain this WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

54 Energy and Sustainability II difference is more perceptible, the dissimilarity is due to their micro porosity, more open for activated carbon in grain (NC 60) (approximately 20 mg.g-1 of difference). In the case of zeolite, a reduction on the adsorption capacity is noticed. This small discrepancy (5 mg.g-1) can be explained because of the hydrophobic character of zeolite. It is important to remark upon the low solubility of siloxanes in water, which also explains the small difference obtained between the adsorption capacities in presence of humidity versus a dry atmosphere. - Influence of methane and carbon dioxide Biogas can be described as basically a mixture between methane (CH4) and carbon dioxide (CO2). It is important to analyse their influence on the adsorption. A mixture of CH4 (50%) and CO2 (50%) was made and introduced into the reactors. This resulted in an adsorption capacity decrease (over 20 mg.g-1), as there competition between the methane and the siloxanes for being absorbed into the material. The results are shown in fig 2.

Figure 2:

Influence of methane and carbon dioxide mixture.

- Influence of volatile organic compound (VOC) Finally, toluene is used to analyse the implication of a VOC in the mass transfer. Two different concentrations of toluene (1 g.m-3 and 10 g.m-3) were used. In order to continue with the “biogas simulation”, reactors were also filled with, a WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


55

CH4 – CO2 mixture and a humidity of 70%. The adsorption capacity decreases considerably. More than 50 mg.g-1 of difference between the capacities was observed. Compounds such as methane, toluene, water and siloxanes are in competition to get adsorbed into the material, reducing in this way the final capacity of the adsorption of siloxanes. Fig 3. shows these results.

Figure 3:

3

Influence of VOC – Toluene.

Adsorption in dynamic system

3.1 Experimental procedure Activated carbon cloth was chosen to perform adsorption – desorption cycles. This porous material has shown good adsorption capacities compared to the others porous materials used in this study. However, these capacities remain low. For that reason a growing interest to develop shorts cycles in time. Moreover different studies over the utilisation of activated carbon cloth and their advantages in desorption process has been analysed by Subrenat and Le Cloirec [13] and Subrenat et al. [14]. Capacity for recycling of the material is very important in the selection of a treatment technology for siloxane, reducing times and costs. Adsorption – desorption cycles are performed. Electrical heating of the material known as a Joule effect is used in the desorption process. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

56 Energy and Sustainability II The adsorbent material (approximately 10g) is placed into a tubular canalisation of stainless steel and a small diameter. A thermocouple is installed into the material for posterior control of its heating. A flow of air charged with siloxane (L2) passes through the filter (adsorption process). When the adsorption time finishes, the filter starts to be heated by an electrical current, fig. 4. Once the target temperature is reached, a new air current (without siloxane) pass through the filter to carry out the desorbed compounds (desorption process).

Figure 4:

Dynamic system.

A control panel installed on a computer is related to the adsorption – desorption system. The characteristics of the adsorption – desorption cycles experiences are listed below and they are easily modifiable on the operative system. Table 4:

Adsorption – desorption cycles characteristics.

Time (min) Temperature (°C) Flow ( m3.h-1) Siloxane (L2 – mg.m-3)

Adsorption

Desorption

20

90

25

100

2.5

2.5

250

0

The adsorption capacity on dynamic systems can be calculated from the mass balance transfer. 3.2 Results and discussions First cycles are accomplished. The experiments of adsorption - desorption cycles have shown the feasibility of a treatment process for siloxane removal. Nevertheless, adsorption capacities decrease considerably over time. The stabilisation of cycles is reached after the third cycle. Fig 5 shows the capacities obtained for the first six cycles. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 5:

4

57

Adsorption capacity on adsorption – desorption cycles.

Conclusion

The viability of siloxane elimination by an adsorption process into a porous material is demonstrated. Good adsorption capacities were found with the materials. The adsorption capacity decreases with the increase of the temperature. Mass transfer is reduced in the presence of water (humidity), VOC (Toluene), methane, and carbon dioxide (principal compounds on a typical biogas). Competition between these compounds results in the material lowering of the adsorption capacity of siloxanes into the material. Activated carbon cloth was chosen to continue with the study on adsorption – desorption cycles, not only because of its adsorption capacities, but also for the ease of implementation into industrial processes. Moreover, this material can be heated in situ by Joule’s effect. Parameters of the adsorption – desorption cycles were established from the experiences in batch reactors. First cycles are accomplished. The adsorption capacity shut down remarkably, the interest of realise rapid cycles is know more important. Electrical heating reduces the duration required for regeneration. In this way material can be regenerated quickly and so the size of the installation reduced. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

58 Energy and Sustainability II Results are promising, even if the operational conditions of the process must be optimised.

References [1] Le biogaz energie renouvelable, http://www.biogaz-energierenouvelable.info/biogaz_composition.html [2] Biogas upgrading and utilisation, http://www.iea-biogas.net/ Dokumente/Biogas%20upgrading.pdf [3] Priebe, C. Grooterhorst, A., Jansen, T., Los siloxanos pueden poner en peligro la viabilidad del aprovechamiento energetico del biogas. Residuos: Revista técnica, pp. 88, 2002. [4] Peregrina C, Audic J, De la boue de station d'épuration à l'hydrogène : Un grand défi technologique, Xèmes Journées Cathala-Letort de prospective scientifique et technique, SFGP,(2008). [5] Huppmann R., Lohoff H.W. and Schröder H.F., Cyclic siloxanes in the biological waste water treatment process—determination, quantification and possibilities of elimination, Fr J Anal Chem, pp. 66–7, 1996 [6] Schweigkofler M. and Niessner R., Determination of siloxanes and VOC in landfill gas and sewage gas by canister sampling and GC–MS/AES analysis, Environ Sci Technol, pp. 3680–3685, 1999 [7] Ajhar M., Melin T., Siloxane removal with gas permeation membranes. Elsevir desalination, 234-235, 2006. [8] Wheless, E., Pierce, J., Siloxanes in landfill and digester gas update Swana 27th LFG Conference, 2004. [9] McBean, E.A., Siloxanes in biogases from landfills and wastewater digesters. Canadian Journal of civil engineering. Canada, pp. 431–436, 2008. [10] Le Cloirec, P., Faur, C., Adsorption of organic compounds onto activated carbon – applications in water and air treatments (chapter 8). Interface science and technology. pp. 375–419, 2006. [11] Subrenat A., Le Cloirec P., Volatile organic compound (VOC) removal by adsorption onto activated carbon fiber cloth and electrothermal desorption: an industrial application, Chem. Eng. Comm., pp. 1–9, 2006. [12] Le Cloirec P., Les composés organiques volatils (COV) dans l'environnement, Tech.& Doc./Lavoisier .1997. [13] Subrenat, A., Le Cloirec, P., Thermal behaviour of activated carbon cloths heated by Joule effect, Journal of Environmental Engineering, pp. 1077– 1084, 2003 [14] Subrenat, A., Baléo, J. N., Le Cloirec, P., Electrical behaviour of activated carbon cloth heated by Joule effect. Carbon, pp. 707–716, 2001



59

Gasified residual/waste biomass as solid oxide

fuel cell feed for renewable electricity production J. Jurewicz & N. Abatzoglou Chemical and Biotechnological Engineering Department, Université de Sherbrooke, Sherbrooke Québec, Canada

Abstract Gasification of waste biomass, a renewable feedstock, is considered as a sustainable technology for producing environmentally friendly feed (biosyngas) for fuel cells. This work examines the contaminants contents (i.e. sulphur and halogens) of typical waste biomass sources and evaluates their nuisance to Solid Oxide Fuel Cells (SOFC) performance for the two most considered types of anodes: metal-ceramic composites (cermets) and composite oxides. The necessity and the extent of physico-chemical purification of the bio-syngas and its cost depend upon the chemical stability of the anode material. These needs as well as their associated costs are evaluated and a first assessment of the sustainability of such solutions is undertaken and commented. Keywords: waste, biomass, gasification, sulphur, halogens, SOFC, syngas, gas purification, anode, cermet, composite oxide ceramics.

1

Introduction

As world energy consumption increases (currently ≈ 2% per annum [1]), the analysis [2] of energy scenarios concluded that it is possible to address simultaneously various sustainable development objectives, using available resources and technical options. The foreseen solutions are based on some combination of better exploitation of renewable resources, higher energy conversion efficiencies, and advanced energy conversion technologies. The latter includes the development of a variety of fuel cells, now widely identified [2] as a long term solution for higher than conventional energy conversion to electricity, WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090061

60 Energy and Sustainability II co-generation (combined heat and power or CHP), motive power and transport. Some important characteristics of the studied fuel cell technologies are presented in Table 1. The high operating temperatures of molten carbonate (MCFC) and solid oxide fuel cells (SOFC) make them well suited for co-generation [4]. Moreover, SOFC technology offers considerably higher CHP efficiencies, potentially longer operating lifetimes [5], safer operation due to the absence of a molten solid phase and lower capital and operational costs than MCFC. The typical «sandwich» type SOFC assemblies are composed of three, functionally distinct, layers (anode – electrolyte – cathode) where the anode is designed for electrochemical oxidation of the fuel associated with the charge transfer to a conducting contact. The most critical characteristics of materials considered as potential candidates for SOFC anodes are: electronic conductivity; oxygen diffusivity (ionic conductivity); oxygen surface exchange (reactivity); chemical stability and compatibility; thermal expansion; mechanical strength and dimensional stability under redox cycling. The particular advantage of the SOFC concept over all other types of fuel cells, is its ability to operate with a variety of fuels, both gaseous – such as methane, biogas, biosyngas, and liquids – such as gasoline, jet fuel, diesel fuels and oxygenates, e.g. methanol, ethanol (and bio-ethanol) and “green diesel”. However such a variety of fuels with their inherent contaminants make more stringent the requirements of anode’s chemical stability and compatibility. This capacity of solid oxide fuel cells to work with fuels originating from renewable resources like biomass is of particular interest. Table 1: Fuel Cell Type Polymer Electrolyte Membrane (PEM) Alkaline (AFC) Phosphoric Acid (PAFC) Molten Carbonate (MCFC) Solid Oxide (SOFC)

Comparison of fuel cell technologies [3].

Operating Temperature [oC]

System Output [kW]

Electrical Efficiency [%] 53 – 58 (transportation) 25-35 (stationary)

50 – 100

< 1 – 250

90 – 100

10 – 100

60

< 80 (low grade waste heat)

150 – 200

50 – 1000

> 40

< 85

600 – 700

< 1 – 1000

45-47

< 80

600 – 1000

< 1 – 3000

35-43

< 90


CHP Efficiency [%] 70 – 90 (low grade waste heat)


61

The aim of this work is to detail the constraints imposed in order to render compatible the use of syngas originating from residual and waste biomass gasification with the SOFC anodes.

2

Residual biomass availability

While renewable, so called “Green Power”, resources (hydro, wind, solar thermal and photovoltaic, geothermal, marine and biomass) are geographically more evenly distributed than fossil and nuclear resources, and energy flows from renewable resources are several thousand times higher than current total global energy use, the statistics [2] indicate that only 13,7% of worldwide primary energy use comes from renewable resources. The observed [6] most recent increase of global trade of woody biomass, primarily for energy, from 5,6 million tons in 2003 to over 11 million tons in 2007, witnesses the interest in such source of green energy. The economic potential of renewable sources is affected by many constrains including competing land use, the amount and timing of solar irradiation and wind patterns, as well as some other environmental factors. The land use is to be given priority for both human and animal feeding and, in most cases where the soil allows it, even the residuals from crop and forest harvesting are preferably to be left to replenish land’s nutrients [7]. However it is proposed [6] to periodically harvest for long-lived wood products which results in substantially greater carbon storage than when forests are left in an unmanaged state. The US Energy Information Administration, which forecasts US energy production, considers four components to the biomass supply schedule: agricultural residues, energy crops, forestry residues and urban wood waste/mill residues. The analysis [8] of their price and availability reveals that the less costly (1,42 $/GJ) is almost exclusively post-consumer urban wood waste/mill residue. Next (at 1,90 $/GJ and higher) come the agricultural residues followed by energy crops and forestry residues (at 2,18 $/GJ or higher). Such results confirmed similar projections obtained earlier [9]. The post consumer urban wood waste/mill residues include: - wood materials (like slabs, edgings, trimmings, sawdust, veneer clippings and cores, and pulp screening) and bark generated at primary (lumber) manufacturing plant; - similar wood scraps and sawdust from woodworking shops, furniture factories, wood container and pallet mills; - wood residues from Municipal Solid Waste (wood chips and pallets), utility tree trimmings and construction and demolition sites. At the European market [10] the post consumer wood is classified as: - A - quality wood: clean wood; - B - quality wood: slightly contaminated, e.g. with paints, glues and coatings; - C - quality wood: hazardous wood waste contaminated with heavy metals, fire retardants and wood preservatives.


62 Energy and Sustainability II The analysis [11] of markets for recovered wood in Europe indicates, that in Germany only in year 2003 up to 6,531 million tonnes of post consumer wood were available for the price of 20-30 euro/ton air dry of A – quality wood and 717 euro/ton air dry for B – quality wood. Such variety of wood residue feedstock is usually mechanically homogenized and converted into commercially available product - wood pellets.

3

Wood pellets as a fuel

Wood pellets as heating fuel originated in the US during the 1970s in response to high energy prices [12] but became recently a significant form of biomass consumption for energetic purposes with world market trades exceeding 3 000 000 tonnes per year [13]. Quite thorough analyses of global wood pellets markets and industry including policy drivers, market status and raw materials have been published recently [14]. Sweden, Canada and USA are world leading pellets producers with an annual production capacity exceeding 3 500 000 tonnes [14]. The production of wood pellets is based on several mechanical operations of milling interlaced with drying. This sequence is ending up with pressing through a mould with simultaneous plasticizing (due to lignin and resin content) of the wood. The latter operation may require some additives (like starch) for sawdust originating from hardwood (less rich in lignin) feedstock for preservation of the final shape of the pellet. The chemical elemental composition of such biomass-derived fuels depends upon the biomass type [15], the origin of the residue and its pre-processing prior to its final destination (use). The fuel components, once consumed, will all end up transformed preferably to element’s oxides either in the gaseous (i.e. CO2) or in solid form (ashes) and will be released to environment. While carbon dioxide and water are neutral, the release of all other compounds to the environment is regulated by norms; namely by standardization of the biomass fuels initial composition. Table 2 presents the acceptable limits of sulphur and chlorine, both Table 2:

Tolerated limits of sulphur and chlorine according to prevailing worldwide legislation.

Austrian ÖNORME M7135

Element: Wood pellets: Bark pellets :

German DIN51731 / DIN plus Swedish SS 187120

Group 1 : Group 2 : Group 3 :

Sulphur ≤ 0,04%* ≤ 0,08%* ≤ 0,08% ≤ 0,08% ≤ 0,08%

Chlorine ≤ 0,02% ≤ 0,04% ≤ 0,03% ≤ 0,03% ≤ 0,03%

CEN (draft) ** ≤ 0,05% CEN/TS 14961: 2005 Annex A * Dry basis; ** Recommended to be stated in category: Cl 0,03 ; Cl 0,07 ; Cl 0,10 ; Cl 0,10+ (if Cl > 0,10% the actual value to be stated) WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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elements being considered as hindering the long term operation of SOFC devices. The comparison of the sulphur limits, as imposed by different legislations, with residual sulphur contents in a variety of clean (pristine – without any manmade additives) biomass [16] indicates, that pure bark pellets, as well as many herbaceous fuels, could not be accepted – their residual sulphur content being above the imposed limits. The combustion of contaminated (B - quality) wood pellets for heating purposes bears some environmental consequences like increase of particulate emissions [17] beyond the current EU emission limit for dust as well as formation of dioxins [18].

4

Wood pellets from Canadian sources and their life cycle analysis

Canada has substantial Green Power resources and the natural potential to generate about half of its current electricity needs (∼590 TWh) using Green Power [19]. While current installed, biomass based technologies, count for 1 935 MW (just above 1% of its total generation capacity) percentage substantial rise might be expected when co-generation technologies will be used [19]. The Canadian wood pellet industry is predominantly located in 3 provinces: British Columbia (33% of production), Quebec (28% of production) and Ontario (20% of production) [20]. Its production capacity, as well as different market sales, are presented in Fig. 1. The origins of the raw materials for wood pellets production are the following:

3500 3000 2500

[kT]

2000 1500 1000 500 0 1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Year Production Capacity

Figure 1:

Actual Production

Domestic Sales

US Sales

Overseas Sales

Evolution of Canadian wood pellet industry and different markets [21].


64 Energy and Sustainability II -

Saw mills; where harvested wood (pine, Douglas fir, spruce, birch and Western Red Cedar) is converted into lumber (construction wood) and remaining saw dust, bark and other residues like shavings, standing for about 15% [3] of the total volume of the harvested wood, are transformed into pellets. - Standing dead wood either after a forest fire or as a result of infestation (e.g. infestation of pine forest by Mountain Pine Beetle). Both reasons are making remaining wood unsuitable for usual application in timber or paper industries. Such raw material (whole tree trunk) requires more energy to convert it into the shavings size needed by pellet industry. Such sources might be extended significantly by harvesting forest thinning, which are considered not only unnecessary to replenish forest nutrients but also the main reason for rapid spreading of forest fires. According to Canadian Forest Service [22] between 2,5 to 3 million hectares of forests are lost to about 10 000 forest fires every year. Canada is the world’s most prominent exporter of wood pellets and its main partner is Europe. Such long haul transport, means an energy consumption (mainly fossil) estimated [23] at 2,40 $/GJ for a 35000 ton vessel travelling a distance of 18000 km [24]. Moreover, it represents a high environmental nuisance because of the Green-House-effect Gases (GHG) generated during the overseas transport [25]. The life-cycle assessments of Canadian wood pellets exported from province of British Columbia (Prince George) to Sweden (port of Stockholm) are presented in Table 3. Energy consumed for each stage of the wood pellet production and transport (adapted from [26]).

Natural Gas as fuel

2,60

Sawdust as fuel

Energy consumed [GJ/ton] 0,52 0,07 3,78 2,97 0,26 Energy consumed if 7 1 52 4 sawdust as fuel [%] Energy consumed if 8 1 46 4 Natural Gas as fuel [%] *Trucking of lumber to mill (110 km) and residues to pellet plant (27 km)

Parameter

Transport*

Transport by ocean vessel (15500 km)

Process stage Production Transport by train (750 km)

Harvesting of lumber

Table 3:

36 40

The analysis of above data suggests, that while half of the energy is consumed for actual pellets production, their post-production transport requires between 40 and 44% of total energy. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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65

Gasified biomass as a feed for SOFC devices

Gasification appears to be the dominant biomass conversion technology. The gaseous products (syngas or biosyngas) from gasification processes are considered as vectors of high-efficiency power production or of the synthesis of chemicals and fuels. Each application requires specific syngas composition and the existing gasification technologies offer this possibility because this composition depends upon the gasification process, the gasification agent (air, oxygen, oxygen-enriched air and their mixtures with steam) and the processing temperature. Generally [27], for gasification processes carried-out at high temperatures (above 1200oC) the biomass is completely converted into CO and H2 (besides H2O and CO2) with an absence of tars which makes this technology interesting for a variety of chemical synthesis routes leading to high-end products. For processing temperatures between 800-1000oC the as-produced gas composition is characterized by a larger variety of chemical species including (besides CO2 and H2O) CO, H2, CH4, aliphatic hydrocarbons, benzene, toluene, and heavier compounds under the generic name “tars”. A thorough review on tar is available in the literature [28]. The energy contained in typical syngas components (CO, H2) stands for about 50% of the total, the remaining 50% being carried by CH4 and higher (aliphatic and aromatic) hydrocarbons making such gas useful for power generation purposes or for production of synthetic natural gas (SNG) [27]. Such as-obtained gas requires important post-gasification treatment like thermal cracking or reforming to match the quality of the gas produced during gasification at higher temperatures. Among the variety of gasification technologies classified as direct (autothermal) and indirect (or allo-thermal) processes the latter group is of particular interest as it offers nitrogen-free product gas as no oxygen is required for the gasification as well as carbon-free ashes. Another advantage of this technology is the possibility of operating it at smaller scale (less then 5 MWth) making it interesting candidate for distributed generation devices where the produced gas is fed into solid oxide fuel cells unit. During the analysis of such an option it is important, among others, to compare the produced gas composition with that required by SOFC unit. The composition of the gas produced from wood by three different indirect gasification technologies is presented in Table 4. An analysis of the gas composition reveals that all combustibles contained in the produced gas are ¨consumable¨ at typical, Ni-based cermet type SOFC’s anode: • Both hydrogen and carbon monoxide are desired SOFC fuels; • Methane, C2+ hydrocarbons and benzene are being reformed to CO and H2 at high temperature over such anodes with catalytic reforming activity in the presence of steam originating from hydrogen consumption over anode’s surface; • Ammonia is considered [29–31] as very interesting SOFC fuel; • Carbon deposition over anode’s surface due to tar presence may be avoided under specific current density [32];


66 Energy and Sustainability II •

Solid particles are filtered [33] from the gaseous fuel prior to SOFC unit. The only component of biomass gasification product, which is undesired, is the hydrogen sulphide. At very low concentrations of 0,05; 0,5 and 2 ppm, tested at 1023, 1173 and 1273 K respectively, the anode activity losses are reported [34] to be reversible once the fuel no longer contains H2S. At temperatures below 1073 K the sulphur poisoning was found [35] to be irreversible. The cell voltage drop increases significantly with H2S concentration in the fuel from 1 to 3 ppm and saturates at 5 ppm [36]. The reforming of methane on catalytically active sites is affected [37] as well. Table 4:

Typical gas composition of three indirect gasification processes [27].

Process Gas component, dry basis 1 2 Hydrogen H2 [vol%] 30 – 45 20 – 22 Carbon monoxide CO [vol%] 20 – 30 41 – 44 Carbon dioxide CO2 [vol%] 15 – 25 11 – 14 Methane CH4 [vol%] 8 – 12 12 – 16 C2+ hydrocarbons [vol%] 1–3 4–6 Benzene C6H6 [vol%] 1 Nitrogen N2 [vol%] 1–3 2 – 10 Ammonia NH3 [ppmV] 500 – 1000 Hydrogen sulphide H2S [ppmV] 50 – 120 Tar [g/mn3] 0,5 – 1,5 40 Particles [g/mn3] 10 – 20 1 – Fast Internal Circulation Fluidised Bed (FCIB) process; 2 – SilvaGas process; 3 – MILENA process

3 15 – 20 40 – 43 10 – 12 15 – 17 5–6 1 1–4 500 – 1000 40 – 100 40 -

To prevent such decrease in Nickel cermet based SOFC performances the removal of sulphur bearing compounds from the feed gas to acceptable level is required. A recent thorough review on H2S removal technologies is available in the literature [38]. Although this review covers the biogas purification most of the reviewed technologies can be used as well in the case of the syngases. The extrapolation of the permissible sulphur concentration in the natural gas feed, considering a deactivation rate of Ni-based planar SOFC of 0.75% per 1000 h (6.4% per year) has indicated the value of 18 ppb [35]. Such ¨deep¨ cleaning is very difficult to reach; only zinc-based sorbents operating at 673-823 K are reported [39] to be effective in removing of H2S to 1 ppm levels at elevated temperatures but not high enough to match typical operating temperatures of gasifier/SOFC tandem. The known deep gas cleaning technologies offers the possibility to lower the residual sulphur content but with excessive cost making such operation much less profitable from the economic stand point. The reported [40] cost of fuel processing module (sulphur removal unit, catalyst, fuel preheater and ejector) accounts for 33% of the total (without stack) balance of power (BOP) investment for 5 kW unit for building applications. The model for WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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250 kW planar SOFC unit for CHP application specifies [41] the cost of fuel system as 8% where the stack counts for 31% of total cost. It is clear that high sensitivity of Ni-cermet based anodes to sulphur bearing compounds inherently present even in pristine biomass makes the gas conditioning circuit more complex and increase overall investment and operational costs of BOP. The possible Nickel-free, sulphur-tolerant replacement for SOFC anode materials like fluorite, rutile, tungsten bronze, pyrochlore, perovskite and spinel structures were identified [42] and reviewed [43–45]. The direct oxidation of methane [46, 47] or diesel fuel [48] over substituted perovskites anodes are reported as well. The all-perovskite (anode, electrolyte and cathode) SOFC may be of particular interest due to structural similarity of layers. Such fuel cell [49], based on the “sandwich” of the (La0,75Sr0,25)0,95Cr0,5Mn0,5O3-δ (LSCM) as the anode, La0,8Sr0,2Ga0,8Mg0,15Co0,05O3-δ (LSGMCo) as the electrolyte and Gd0,4Sr0,6CoO3-δ (GSC) as the cathode, can minimize the polarization losses between electrolyte and electrodes, where the slight inter-diffusion between the perovskite components observed results in better contact at the interface, allowing for smoother transfer of oxygen ions between the electrodes and electrolyte. However the actual performances of composite oxide anodes do not match these obtained for Ni-based cermet anodes. More research efforts have to be carried out for optimization of both their composition and performances. For such complex structures the application of the combinatorial chemistry approach in their synthesis is of particular interest. Another concern for more widespread SOFC usage is the cost of their fabrication. The thermal plasma spraying, which is industrially proven and widely accepted technology, offers both rapid prototyping through combinatorial chemistry method as well as less-costly industrial mass-production allowing integrated deposition of all subsequent layers (anode, electrolyte and cathode) in one operation.

6

Conclusion

The possibility of the significant increase of biomass energy conversion efficiency for SOFC based Combined Heat and Power generation cycle is of special interest especially for colder climate regions like northern Canada. The export of Canadian biomass as far as to Europe makes overall energy balance (energy contained in biomass vs. energy consumed for its transport) less favourable – up to 40% of energy is lost to transport. The gasification process, compared to simple combustion or incineration, offers a better control of the release to environment of undesired conversion products, like manmade impurities contained in lesser quality wood’s residues, while still allowing for the full usage of their energy content. The direct gasification of as-obtained biomass (without drying, size reduction and pelletizing stages) may preserve both energy spent for pellets formation and that contained in the volatiles (mainly terpenes) usually lost [50] during drying process. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

68 Energy and Sustainability II The sulphur content represents a technological challenge for the gas conditioning technologies because Nickel-based SOFCs are ultra sensitive to sulphur bearing compounds. Consequently, the cleaning is usually complex and costly. The SOFC based on composite oxide anodes are sulphur tolerant and are considered as a replacement to Ni cermet anodes; however their actual electrochemical performances are still inferior to the Nickel based ones. The variety of the possible structures of composite oxides (perovskite-related like titanates, chromites, vanadates, gallates, niobates and ferrites; cubic fluorite related like zirconia-based and ceria-based as well as pyrochlores and spinels) makes combinatorial chemistry useful promising tool towards optimizing SOFC anode’s elemental composition and structure. The thermal plasma deposition technology allows for rapid SOFC prototyping using combinatorial chemistry approach as well as further industrial mass production of entire multi-layered fuel cells.

References [1] Mason J.E., World energy analysis: H2 now or later, Energy Policy, 35, pp. 1315-1329 (2007) [2] Goldemberg J. et al, World Energy Assessment, Overview 2004 Update, United Nations Report, (2004) [3] U.S. Department of Energy [4] Williams R.H., Advanced energy supply technologies, in World energy assessment, United Nations Report, (1998) [5] Bakker W., Advances in Solid Oxide Fuel Cells’ EPRI Journal, 21, (5), pp. 42-45, (1996) [6] UNECE/FAO, Forest products annual market review, (2008) [7] Pimentel D., et al, Biomass Energy from Crop and Forest Residues, Science, 212, pp. 1110-1115, (1981) [8] Haq Z., et al, Agricultural Residue Availability in the United States, Applied Biochemistry and Biotechnology, 129-132, pp. 3-21, (2006) [9] Easterly J., et al, Overview of biomass and waste fuel resources for power production, Biomass and Bioenergy, 10, 2-3, pp. 79-92, (1996) [10] Leek N., Data collection for post consumer wood in the Netherlands, Probos [11] Van Benthem M., et al, Markets for recovered wood in Europe; Case studies for the Netherlands and Germany based on the BioXchange project, Proc. 3rd European COST E31 Conf., 2-4 May 2007, Klagenfurt, Austria [12] Kotrba R., Closing the Wood Pellet Gap, Biomass Magazine, February (2009) [13] Forest News WIRE, June (2008); PR press release at: http://www.pr.com/press-release/89107 [14] Peksa-Blanchard M., et al, Global Wood Pellets Markets and Industry : Policy drivers, Market Status and Raw Material Potential, IEA Bioenergy Task 40 report, November (2007) WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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[15] Nordin A., Chemical elemental characteristics of biomass fuels, Biomass and Bioenergy, 6, 5, pp. 339-347, (1994) [16] Obernberger I., et al., Chemical properties of solid biofuels – significance and impact, Biomass and Bioenergy, 30, pp. 973-982, (2006) [17] Khan A., et al., Scale-up study on combustibility and emission formation with two biomass fuels (B quality wood and pepper plant resudue) under BFB conditions, Biomass and Bioenergy, 32, pp. 1311-1321, (2008) [18] Lavric A.D., et al., Dioxin levels in wood combustion – a review, Biomass and Bioenergy, 26, pp. 115-145, (2004) [19] Canadian Renewable Energy Alliance, Green Power for Electricity Generation – Creating an Industry in Canada, August (2006) [20] EUBioNet2, No 10-2 [21] Adapted from Canadian Wood Pellet Industry web page [22] Canadian Forest Service, The nature of forest fires, (2004) (http://canadaforests.nrcan.gc.ca/articletopic/32) [23] Aruna P., et al., An analysis of wood pellets for export: a case study of Sweden as an importer, Forest Products Journal, 47, 6, pp. 49-52, (1997) [24] Duffy A., et al., Embodied transport energy analysis of imported wood pellets, Transactions of the Wessex Institute, [25] Svedberg U., et al., Hazardous Off-Gassing of Carbon Monoxide and Oxygen Depletion during Ocean Transportation of Wood Pellets, Annals of Occupational Hygiene, 52 (4), pp. 259-266 (2008) [26] Magelli F., et al., An environmental impact assessment of exported wood pellets from Canada to Europe, Biomass & Bioenergy, 33, pp. 434-441, (2009) [27] Boerrigter H., et al., Review of applications of gases from biomass gasification, Rapport ECN.RX-06-066, (2006) [28] Milne T., et al., Biomass Gasifier "Tars": their Nature, Formation, and Conversion, The Biomass Energy Foundation Press, ISBN 1-890607-14-2 (1998) [29] Fournier G.G.M., et al., High performance direct ammonia solid oxide fuel cell, J. Power Sources, 162, pp. 198-206, (2006) [30] Meng G., et al., Comparative study on the performance of an SDC-based SOFC fuelled by ammonia and hydrogen, J. Power Sources, 173, pp. 189193, (2007) [31] Fuerte A., et al., Ammonia as efficient fuel for SOFC, J. Power Sources, (2008), doi:10.1016/j.jpowsour.2008.11.037 [32] Singh D., et al., Carbon deposition in an SOFC fuelled by tar-laden biomass gas: a thermodynamic analysis, J. Power Sources, 142, pp. 194199, (2005) [33] Sharma S.D., et al., A critical review of syngas cleaning technologies – fundamental limitations and practical problems, Powder Technology, 180, pp. 115-121, (2008) [34] Matsuzaki Y., et al., The poisoning effect of sulphur-containing impurity gas on a SOFC anode: Part I. Dependence on temperature, time, and impurity concentration, Solid State Ionics, 132, pp. 261-269, (2000) WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

70 Energy and Sustainability II [35] Cunningham R.H., et al., Sulphur poisoning of the active materials used in SOFCs, Report to Rolls-Royce, F/01/00222/REP, URN 04/559, (2004) [36] Sasaki K., et al., H2S Poisoning of Solid Oxide Fuel Cells, J. Electrochem. Soc., 153 (11) A2023-A2029 (2006) [37] Ouweltjes J.P., et al., Biosyngas Utilization in Solid Oxide Fuel Cells with Ni/GDC Anodes, (EFC2005-86089), 1st European Fuel Cell Technology and Applications Conf., Rome (2005), [38] Abatzoglou N., et al., A Review of Biogas Purification Processes, Biofuels, Bioproducts & Biorefining, 3, pp. 42-71 (2009) [39] Aravind P.V., et al., Impact of biosyngas and its components on SOFC anodes, Electrochem. Soc. Proc., 2005-07, pp. 1459-1467, (2005) [40] Brown J.R., et al., Assessment of SOFC in Building Applications, Solar Energy Laboratory, University of Wisconsin Madison, prepared for: Energy Center of Wisconsin, Nov. (2001) [41] Fontell E., et al., Conceptual study of a 250 kW planar SOFC system for CHP application, J. Power Sources, 131, pp. 49-56 (2004) [42] Tao S., et al., Discovery and Characterization of Novel Oxide Anodes for Solid Oxide Fuel Cells, Chemical Record, 4, pp. 83-95 (2004) [43] Gong M., et al., Sulfur-tolerant anode materials for solid oxide fuel cell application, J. Power Sources, 168, pp. 289-298 (2007) [44] Sun C., et al., Recent anode advances in solid oxide fuel cells, J. Power Sources, 171, pp. 247-260 (2007) [45] Goodenough J.B., et al., Alternative anode materials for solid oxide fuel cells, J. Power Sources, 173, pp. 1-10 (2007) [46] Tu H., et al., Performance of Alternative Oxide Anodes for the Electrochemical Oxidation of Hydrogen and Methane in Solid Oxide Fuel Cells, Fuel Cells, No 3-4, pp. 303-306, (2006) [47] Tao S., et al., Methane oxidation at Redox Stable Fuel Cell Electrode La0,75Sr0,25Cr0,5Mn0,5O3 - δ, J. Phys. Chem B. 110, pp.21771-21776, (2006) [48] Liu D.J., et al., Activity and Structure of Perovskites as Diesel-Reforming Catalysts for Solid Oxide Fuel Cell, Int. J. Appl. Ceram. Technol., 2, No.4, pp. 301-317 (2005) [49] Tao S., et al., An Efficient Solid Oxide Fuel Cell Based upon Single-Phase Perovskites, Adv. Mater., 17, pp. 1734-1737 (2005). [50] Stahl M., et al., Industrial processes for biomass drying and their effect on the quality properties of wood pellets, Biomass & Bioenergy, 27, pp. 621628 (2004)



71

Lighting the world with LEDs S. J. Riley1 & M. Telugu2 1

Sustainable Technology and Engineering Research Group, University of Western Sydney, NSW, Australia 2 MIC Technologies (Australia) Pty Ltd, NSW, Australia

Abstract Light Emitting Diodes (LEDs) present an opportunity to improve public health and to provide low-cost lighting to villages while significantly reducing CO2 emissions, petroleum fuel consumption, and hazardous waste. Lighting accounts for approximately 19% of the world’s greenhouse gas emissions and widespread use of LED lighting would significantly reduce this. Aspects of LED technology, the use of LED in lighting the developing world, and means of rapidly deploying the technology in an affordable manner are discussed. Keywords: LED lighting, public health, appropriate technology, energy conservation.

1

Introduction

The world’s population of 6 billion is expected to expand to 9 billion in the next 40 years [1]. In the absence of apocalyptic population reduction or a political will to reduce population growth the additional 3 billion people will have to be fed, clothed, housed, educated and provided with gainful employment. The consequences of this increase in population will be significant increases in resource use, particularly energy, whose availability underlies the technological and life-style advances of the last 3 centuries [2]. However, an increase in energy, using existing technology, will result in increased greenhouse gas emissions, which may impact on already stressed populations through climate change. Predictions of the problems of resource availability for the future of humanity are not new. The predictions of Malthus [3] and the Club of Rome [4] were addressed by technology development [5], which increased the availability and WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090071

72 Energy and Sustainability II security of food supplies, accessed energy resources in previously unavailable situations, and housed people in ever increasing clusters of high population density. These developments have required increased per capita energy consumption. There are several sources of energy that do not significantly impact on the environment, but supply is only half of the solution of managing the impact of energy use. The other part of the solution is to provide increased efficiency in energy use. Significantly reducing the per-capita demand for energy may meet the energy demands of increased population growth without increasing energy production. There are many national energy efficiency programs [6, 7]. Yet it has to be noted that a 50% increase in population requires a 33% improvement in energy efficiency to maintain today’s level of energy consumption per capita, and this does not allow for improving life-styles in the majority of the world that has the lowest per capita energy consumption, i.e. the developing economies. Energy efficiency savings will not be similar across all sectors of the economy, or all nations of the world, but the hope is that there will be a net decrease in per capita energy use. The most likely positive scenario to meet the future energy needs will be a combination of energy efficiency and energy production that has low impact on the environment in order to obtain the necessary target of providing energy for all without sacrificing the planet. This paper addresses the issue of providing cheap low-cost lighting to communities while addressing the energy consumption issue at the same time. The technology based around Light Emitting Diodes (LEDs) provides the opportunity of improving energy efficiency (in this case watts per lumens) which, when combined with PhotoVoltaic power generation, also provides the opportunity for alternative energy sources to be implemented to provide the power. The issue of ensuring the rapid uptake of this technology in an environment of poverty, low-technology training, and lack of familiarity with the technology is also addressed.

2

LEDs and energy efficiency

An LED is a PN junction semi conductor diode that emits monochromatic light as electrons, which move from the anode (p-side) to cathode (n-side), fall into a lower energy state and release energy. The wavelength of the light depends on the gap energy of the p-n junction. Light emitting diodes are not a new technology, by the standards of the rapid development in technology of the last 50 years [8], but there have been significant improvements in the last 20 years that are now available in the market place. These developments are part of continuing technological improvement, and research in a number of places around the world is improving the cost of production, efficiency and capacity of LEDs [9, 10]. It is estimated that 19% of the world’s energy is used for lighting: equivalent to the energy required for all transport and in equivalent greenhouse gas emissions equal to that produced from domesticated animals [11]. So the potential for energy and greenhouse gas emission savings is significant [12, 13]. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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At this stage LEDs are the most efficient light production system in terms of lumens per watt, having overtaken CFLs, and are still improving at a significant rate [14, 15]. Compact Fluorescent Lights (CFLs) are now widely used in domestic, commercial and industrial circumstances. They are very efficient compared with the incandescent lights and have much longer design lives, but have an environmental issue of mercury contamination, which neither discarded incandescent lights nor LED lights have. This contamination issue is well recognised, but is being rationalised against savings in energy. The savings in energy compensate the release of mercury in coal-fired powered stations. A CFL light may have 5-15mg of mercury (Hg) while a tonne of coal can release 0.1g of Hg or more [16]. LEDs do not pose a significant environmental problem, and have longer design lives and energy efficiency than CFLs. Short-term costs may be higher, but long term savings are significant. Their reduced power consumption results in a reduction of Hg production at power stations. The price of LEDs is higher than CFLs and much higher than incandescent lights, but when maintenance and longevity are considered, are significantly cheaper. LEDs have design lives of 20 years, and can last much longer than this, though at a slowly decreasing level of luminosity per watt [17]. The significant decrease in the power demand (Watts) of LED-based lighting per lumen and their reducing cost now means that battery-LED lantern systems with inbuilt solar recharges are affordable. Such system are suited for the majority of people who are forced to use alternative lighting systems because they are in areas not connected to the national power grids or have unreliable power supplies (presently estimated at 25-50% of the world’s population [18]). An issue with PV-based rechargeable LED lanterns in terms of future breakthroughs lies in the area of battery technology. PV and LED systems have design lives of approximately 20 years, and are known to continue to work after this time, albeit with reduced efficiency. The cheapest battery systems are leadacid systems, which are recyclable, but have design lives of 3 to 5 years, depending on the power drain regime, recharge cycles and quality. Clearly there would be great advantage in having a battery system whose design life was the same as the LED and PV systems, as all could be recycled at the one time. Work on battery technology is progressing the design life and power of batteries [19], but is not yet in the range of the PV and LED systems. New battery systems will have to be price competitive with lead-acid batteries, which are also being improved all the time.

3 Examples of LED lighting systems and alternative power LED lighting systems are now widely used. LED-powered lights are used in camping lights, helmet lights, torches, industries of various types, and community lighting projects. Some of these will be briefly discussed in the following. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

74 Energy and Sustainability II Probably one of the most ambitious projects in the world is to provide LED lanterns to the communities of the developing world, as ably illustrated in India [20,21] and Africa [22]. For most villages in India the kerosene lantern has been the standard source of light for many years but they present serious health and risk hazards associated with kerosene fumes and fire. In addition the luminosity is relatively low (10-20 lumins [23]). In many countries the kerosene has to be imported, so there is a significant drain on national budgets, not only in foreign exchange but through the subsidy programs that often apply to support the poor [24–27]. It is estimated that families use approximately 100L of kerosene per year and the subsidy at Rs8-9 per L is estimated at Rs340billion in India The indirect costs of poor lighting on eyesight, education, business and community activity probably dwarfs the direct cost.

Figure 1:

LED lanterns without solar power attachments (photo courtesy MIC Electronics).

LED lanterns that can be solar powered are now cost-effective, can be demonstrated to recover purchase and maintenance costs in terms of savings on kerosene purchases over a period of 2 to 5 years (depending on national kerosene prices). Solar power recharging can be achieved by fixing a PV panel to a lantern unit or through village (community based) recharging stations, which provide the recharging service for very small cost. The later saves on the cost of the lanterns. Battery recycling systems are also needed at the village and district level, as are servicing facilities. Indian railways have commenced the process of converting to LED lighting across their stations and rolling stock. A variety of facilities are being provided, from LED reading lamps in carriages to LED lights for stations. LED street lighting is an exciting opportunity to reduce power consumption and provide communities with security. LED street lights, with and without solar WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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power, are being roll-out in several cities in India. Rather than abandon existing infrastructure LED lights are replacing existing street lights, thus achieving an increase in luminosity while reducing power costs. For green-field sites the opportunity to install solar powered lights, supplied with the poles, is obvious. The reduction in cost in installation is also associated with not having to provide external power to each light. Self-contained solar-recharging LED street lights are an obvious choice in areas subject to natural hazards that may suffer cuts to power supplies. While there is no guarantee that any particular pole and light might survive a hazard, it is likely that enough will survive to provide lighting at the critical times of relief and recovery.

Figure 2:

4

Examples of PV powered LED street lights in India (photo courtesy MIC Electronics).

Lighting the World

While the technology is available, distributing LED-lighting technology is another matter. The urgency for savings in the consumption of petroleum products, improved health, and reduced greenhouse gas emissions is obvious. The Indian government, and others, are committed to distributing the technology as soon as possible. Recent improvements in efficiency and reduction in costs have made distribution more financially feasible in developing economies, as well as developed economies. Distribution is part of the story. There needs to be mechanisms for maintenance, recycling and recharging when PV facilities are not sold with each lighting unit. In addition, rapid roll-out requires financial management to enable communities and individuals to access the technology. Finally, the need for the technology is so great that manufacturing and distribution networks are also required. For communities, as in the case of street lighting, BOOT schemes (BuildOwn-Operate-Transfer) are viable options, as long as financial backing is provided. It should be noted that LED-based street lighting using PV generating systems is ideally suited to areas where rapid roll-out of lighting is required. A refugee camp could have a kilometre of street lighting (one light every 20 metres, offset on opposite sites of the street = 500 lights) in a matter of a week WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

76 Energy and Sustainability II given access to the site and landing of equipment and work teams. A health compound could be provided with light in a day. Small scale PV generators could also provide light within the buildings and this could be installed in a day. The advantages in savings on fuel cartage for conventional diesel powered generators are obvious. For families and individuals the conversion from kerosene lanterns to PV recharged LED lanterns could take place rapidly provided funding for the technological transition is provided in the form of loans. Micro-financing systems [28] are ideally suited to this, as the loans could be repaid from the savings on kerosene purchases. PV recharge stations would provide employment at the village and district level, as would recycling and financial management systems based around the micro-finance. Capital for the micro-finance could be derived from several sources, including direct government support as well as donor support. The advantage of microfinancing is that the capital injection is repaid within a matter of years, and the small profit margin on the sale of the goods finances the microfinance structure and, if care is taken with maintenance contracts, the maintenance and recycling of systems.

5

Conclusions

The rollout of LED lighting, replacing both incandescent and CFL lighting, should bring about considerable savings in energy use per capita, provide improved lighting to people at the bottom of the pyramid, who comprise the majority of the world’s population, reduce per capita greenhouse gas emissions, and stimulate employment and training. The rollout will have to happen in a micro-finance environment in order to maximise benefits of transferring to the new technology and to bring about the transference in the minimum possible time. A number of countries are already aggressively pursing the transformation, and coupled with photovoltaic power generation, should bring significant commercial, health and educational benefits to their people.

Acknowledgements Thanks are due to the many people of MIC Electronics in Hyderabad and elsewhere, particularly Dr Rao who initiated this work.

References [1]

US Census Bureau (2008), World Population Trends: International Data Base (IDB),US Census Bureau, Population Division, viewed 23 June 2008, . [2] Byrne, J., Toly, N., Glover, L (eds) 2006. Transforming power. Energy, Environment and Society in conflict. Energy and Environment Policy 9, New Brunswick, NJ. Transaction Publishers. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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[3] Malthus, T. 1798. An essay on the principal of population. Johnson, London. http://www.ac. wwu.edul ~stephan/malthus/malthus. 0.html [4] Meadows, D.H., Meadows, D.L., Randers, J., Behrebs, W.W. 1972. The limits to growth. Club of Rome. [5] Trewavas, A. 2002. Mal!hus foiled again and again. Nature 418, 668-670 [6] Australian government. 2006. Energy Efficiency Opportunities Act 2006. Australian Government Publishing Service [7] World energy Council. 2008. Energy Efficiency Policies around the World – Review and Evaluation [8] Zheludev, N. 2007. The life and times of the LED – a 100 year history. Nature Photonics, 1,179-182. [9] Oikubo, S. 2006. Nichia unveils white LED with 150lm/W luminous efficiency. Tech-on. http://techon.nikkeibp.co.jp/english/NEWS_EN /20061221/125713/ [10] US Department of Energy. 2008. Solid-state lighting portfolio. http://www1.eere.energy.gov/buildings/ssl/\ [11] Mills, E. 2002. The $230-billion global lighting energy bill. [12] Mills, E. 2002 Global lighting energy savings potential. Light and Engineering, 10(4),5-10. [13] Mills, E. 2005. The spectre of fuel-based lighting. Science, 308(5726),1236-1264 [14] Mr Beams. 2009. Comparison chart LED lights vs Incandescent Light Bulbs vs CFLs. http://www.mrbeams.com/index.asp?PageAction= Custom&ID=2 [15] Murkerjee, A.K. 2007. Comparison of DFL-based and LED-based solar lanterns. Energy and Sustainable Development, 11(3),24-32. [16] Australian Government. 2008. Fact sheet – fluorescent lamps, mercury and end-of-life management. http://www.environment.gov.au/settlements /energyefficiency/lighting/publications/fs.html [17] Narendran, N., Gu, Y. 2005. Life of LED-based white light sources. J Display Technology, 1(1),167-171. [18] Thong, V.V. Driesen, J., Belmans, R. 2008. How to electrify one fourth of the world population. 16th International Congress of Electrical Applications in a Modern World. Opening session paper. 4pp. [19] Lambert, D.W.H., Holland, R., Crawley, K. 2000. Appropriate battery technology for a new rechargeable micro-solar lantern. J Power Sources, 88,108-114. [20] Government of India. Ministry of New and Renewable Energy. 2009 http://mnes.nic.in/ [21] Velayudan, G.K. 2003. Dissemination of solar photovoltaics: a study on the government program to promote solar lantern in India. Energy Policy, 31(14),1509-1518. [22] Lighting Africa. 2009. http://lightingafrica.org/ [23] Tavaranan, S. and Duffy, J. 2005. Solar lanterns for remote areas. http://energy.caeds.eng.uml.edu/peru-07/ises05-1700-saline-elantern-0205-jjd%5B1%5D.pdf WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

78 Energy and Sustainability II [24] Nieuenhout, F.D.J., van de Rijt, P.J.N.M., Wiggelinkuizen, E.J., van der Plas, R.J. 1998. Rural lighting sources: a comparison of lamps for domestic lighting in developing countries. Netherlands Energy Research Foundation Report. http://www.ecn.nl/docs/library/report/1998/rx98035.pdf [25] Rubab and Kandpal, T.C. 1996. Financial evaluation of SPV lanterns for rural lighting in India. Solar Energy Materials and Solar Cells, 44(3),261270 [26] Gangopadhyau, S., Ramaswami, B., Wadhwa, W. 2005. Reducing subsidies on household fuels: how will it affect the poor? Energy Policy, 33(18),2326-2336. [27] Morris, S., Pandey, A., Barua, S. 2006. A scheme for effective subsidisation of kerosene in India. India Institute of Management, Working Paper 2006-07-06 [28] Yunus, M. 2007, Creating a world without poverty. Social Business and the Future of Capitalism. Public Affair, NY 261pp



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The optical and electrical properties of Eu3+-Y3+codoped ITO transparent conductive electrodes as luminescent solar concentrators C.-C. Ting & C.-H. Tsai Graduate Institute of Opto-Mechatronics Engineering, National Chung Cheng University, Taiwan

Abstract Rare earth ions (Eu3+) and Y3+ ions were codoped into the tin-doped indium oxide (ITO) transparent conductive electrode to make it possess visible luminescent properties. The Eu3+-Y3+codoped transparent conductive thin films with the precise control on the desired stoichiometry of dopants were fabricated by sol-gel spin-coating technologies. We first report that the Eu3+-Y3+codoped ITO thin films show better visible luminescent properties than Eu3+-doped ITO thin films. The higher Y3+ concentration can increase the 611 nm PL intensity of Eu3+-Y3+ codoped ITO thin films. However, the Eu3+ and Y3+ codoping concentrations should be controlled within 0.1% and 0.5%, respectively, to avoid the deterioration of conductivity. We believe that the Eu3+-Y3+codoped ITO thin films can play dual roles as the luminescent solar concentrators and transparent conductive electrode to enhance the efficiency of solar cells. Keywords: ITO, europium, yttrium, pyrocholre, photoluminescence.

1

Introduction

The luminescent solar concentrators (LSC) have attracted lots of attention for the efficiency enhancement of solar cell these past years [1–3]. Most of the LSC is the organic or inorganic fluorescent materials which were coated on the surface of solar cell devices [4–6]. However, this kind of LSC will increase the manufacturing procedures and cost. There is only 5% ultraviolet (UV) and near blue light (300~400 nm) that can reach the Earth surface [7] and most of the solar cells do not have good operating efficiency in this section because of the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090081

80 Energy and Sustainability II absorption of transparent conductive electrode [8, 9]. Therefore we hope that the luminescent solar concentrators can convert this UV light to 500~700 nm visible light, which can be further absorbed by solar cell. In this study, we try to codope Eu3+ and Y3+ ions into the transparent conductive electrode, tin-doped indium oxide (ITO), to make them possess visible luminescent properties. These Eu3+-Y3+ codoped ITO thin films with the precise control on the desired stoichiometry of dopants were fabricated by solgel spin-coating technologies. In order to maintain the conductivity of Eu3+-Y3+ codoped ITO thin films, the doping concentrations of Eu3+ and Y3+ ions were kept at a low contents, i.e. Eu3+ (0.1 mol%) and Y3+ (0~4 mol%). Optical and electrical properties such as fluorescence and sheet resistance (ohms/square) of the resulting Eu3+-doped ITO system were systematically examined in terms of the codoping concentrations and structural evolution of the films at 600°C annealing for 1 h.

2

Experiments

2.1 Preparation of precursor solutions The precursor solutions for the fabrication of Eu3+-Y3+ codoped ITO thin films and powders were synthesized by following procedures. The starting materials is anhydrous indium trichloride (InCl3, 99.995%, Acros) which was dissolved in the mixture of acetic acid (HAc, CH3COOH, 99.5%, Acros) and 2methoxyethanol (2-MOE, C3H8O, 99.5%, Merck) with molar ratio of In/HAc/2MOE=1/20/12. Then the solution was refluxed at 80°C for 3 h. Anhydrous tin chloride (SnCl4, 99%, Acros) was dissolved in ethanol (C2H5OH, 99.9%, JTBaker), which was dropped into the refluxed indium solution at room temperature. Finally, the yttrium acetate [Y(CH3COO)3．4H2O, 99.9%, Alfa] and europium nitrate [Eu(NO3)3．6H2O, 99.9%, Alfa] were dissolved in the solution (a mixture of methanol (CH3OH, ≧99.5%, Merck) and ethylene glycol (HOCH2CH(OH)CH2OH, ≧99.5%, Alfa)], which was added into the abovementioned ITO solution and followed by stirring for 10 h at room temperature in order to process homogeneous hydrolysis and polymerization reaction. The molar ratio of Eu/In and Y/In varied from 0.05/100 to 0.2/100 and 0.5/100 to 4/100, respectively. 2.2 Preparation of thin-film coatings All of the thin films were prepared by sol-gel spin-coating method in a class 100 clean bench. The Eu3+-Y3+ codoped ITO precursor solutions were spin-coated on silica glass substrates of 25 mm×25 mm×0.6 mm dimension (Corning, Eagle 2000). The as-deposited sol-gel films were first dried at 100°C for 10 min, and pyrolyzed in air at 400°C for 10 min at a heating rate of 10°C/min. Finally, the as-formed films were annealed at different temperatures ranging from WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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600-1000°C for 1 h in air. Multiple spin-coating processes were employed to deposit ~300 nm thick films. 2.3 Characteristic measurements The crystal structure was determined by an X-ray diffractometer (Shimadzu, XRD 6000). Scanning electron microscopy (Hitachi, S4800-I) was used for microstructural examination. The thickness of Eu3+-doped ITO films was measured by the SEM cross-sectional image. A monochrometer (Horiba Jobinyvon, MicroHr) equipped with 300 W Xe lamp (Hamamatasu, L2479) and a 325 nm He-Cd laser with an output power of 4 mW were used as the excitation light source. The visible fluorescence was detected by spectrophotometer (Horiba Jobin-yvon, iHR 550) equipped with a PMT detector (Hamamatasu, 7732P-01) at room temperature. Resistivity of the films was measured by using the four-point probe method (Fluke, 8845A).

3 Results and discussions 3.1 Crystal structures and film morphologies Figure 1 shows the XRD patterns of ITO film and Eu3+ (0.1 mol%)-Y3+ (0, 0.5, 1, 2, and 4 mol%) codoped ITO thin films annealed at 600°C for 1 h. All of the samples possessed the well-crystallized bixbyite phase identified by the characteristic XRD peaks: (222), (400), (440), and (622) [10]. Compared to the diffraction intensity of (222) peak between all samples, the addition of 0.5 mol% Eu3+ and 0.5-4 mol% Y3+ ions did not obviously influence the peak intensity of Eu3+-Y3+ codoped ITO thin films, which implies that the slight addition of Eu3+ and Y3+ ions with a total concentration of up to 4.1 mol% into the ITO host did not significantly degrade the crystallinity of ITO thin films. The average crystal size was determined by the Scherrer’s equation depending on the full width at half maximum (FWHM) of XRD peak [11]. For ITO film and Eu3+ (0.1 mol%)Y3+ (1 mol%) codoped ITO thin films annealed at 600°C for 1 h, the FWHM of (222) peak increased from 0.336° to 0.466° and the average crystal sizes decreased from ~22 to ~19 nm. On the other hand, all XRD patterns indicate the formation of single bixbyitestructured phase for Eu3+-Y3+ codoped ITO thin films without any possible other phases such as Y2O3, Eu2O3, SnO2, In4Sn3O12, and Y2Sn2O7. ITO is a kind of solid solution which Sn4+ concentration of up to 10 mol% can dissolve in In2O3 lattice, resulting in the maximum conductivity [12]. Moreover, In2O3, Y2O3, and Eu2O3 possessed the same structures, i.e., bixbyite phase and similar lattice constants (a), as summarized in Table I. Although Eu3+ and Y3+ ions in In2O3 lattice to form the solid solution i.e., YxIn2-xO3 and EuxIn2-xO3. On the other hand, Eu2O3 and Y2O3 can react with SnO2 to form the cubic pyrochlore phase, Y2Sn2O7 and Eu2Sn2O7. A. Ambrosini et. al. investigated that by doping Y3+ ions into In2O3 lattice, the lattice constant can be enlarged because of Y3+ ions has larger radius than that of In3+ ions, which indicates the formation WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 1:

XRD patterns of ITO film and Eu3+ (0.1 mol%)-Y3+ (0, 0.5, 1, 2, and 4 mol%) codoped ITO thin films annealed at 600°C for 1 h.

Table 1:

Ionic radii and crystallographic data of possible metal oxides in Eu3+-Y3+ codoped ITO thin films.

of solid solution YyIn2--yO3. In addition, any available Y2O3 and SnO2 in the Y3+doped ITO system can react with each other to form Y2Sn2O7 until one of the starting materials is completely depleted. The formation of pyrochlore Y2Sn2O7 at 1400°C annealing was detected by XRD even though the content of Y3+ ions is as low as 2 mol% in a Sn3+-doped In2O3 pellet [13]. Fujihara et. al. [14] reported that sol-gel derived Y2Sn2O7 thin films were in amorphous state for 500~700°C WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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annealing; however, the well-defined pyrochlore Y2Sn2O7 thin films were obtained at 800°C or higher annealing temperatures. In our system, annealing temperature was 600°C and hence, the amorphous pyrochlore Y2Sn2O7 can not crystallize to be detected by XRD. Park et. al. [15] observed that the pyrochlore phase Eu2Sn2O7 was detected in the Eu3+-doped SnO2 thin films annealed at 1200°C for 1 h while the doping concentration reached to 3 mol% [15]. In our experiment even though the light codoping concentration of Eu3+ and 3+ Y ions is as low as ~4 mol%, the pyrochlore phase should be detected if it forms. However, there is no pyrochlore phase can be detected in Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h. Based on the abovementioned reported literatures, therefore, the Eu3+ (0.1 mol%)-Y3+ (0, 0.5, 1, 2, and 4 mol%) codoped ITO thin films annealed at 600°C for 1 h could be composed of the mixture of amorphous EuxYySn2-x-yO7 and crystallized In2zSnzO3-δ (δ: oxygen vacancies) phases. 3.2 Fluorescent properties Fluorescence intensity of the Eu3+-Y3+ codoped ITO thin films with thickness of ~300 nm were found to be extremely low by the excitation of monochrometer equipped with 300 W Xe lamp, which could not be detected due to the limitation of our existing spectrophotometer measurement set-up. However, when the film thickness was up to ~900 nm, the fluorescence intensity was stronger enough to be detected by monochrometer excitation. The ~900 nm thick film appeared to have some cracks, which can not be used for the measurement of sheet resistance but can be used for the measurement of excitation spectrum. Therefore, the fluorescent measurement of all samples with thickness of ~300 nm was executed by using a 325 nm He-Cd laser with an output power of 4 mW as the excitation light source. Figure 2 shows the emission fluorescence spectra of (a) Eu3+ (0.1 mol%)-Y3+ (0, 0.5, 1, 2, and 4 mol%) and (b) Eu3+ (0.05, 0.1, and 0.2 mol%)-Y3+ (1 mol%) codoped ITO thin films annealed at 600°C for 1 h. Obviously, the Eu3+ ions show only one characteristic visible emission, 611 nm red light, which is attributed to the 5D0→7F2 transition of Eu3+ ions. Interestingly, no 5D0→7F1 transition (~590 nm) of Eu3+ ions can be detected for all samples. It is well known that the probability of intra-4f-f transitions strongly depends on the site The electric-dipole 5D0→7F2 transition is allowed for the Eu3+ site without inversion symmetry. On the other hand, the Eu3+ ions can exhibit the magneticdipole 5D0→7F1 transition because of the Eu3+ site with inversion symmetry [16]. In general, both of the electric-dipole and magnetic-dipole transitions coexist in the fluorescent spectra of many Eu3+-doped inorganic materials but one is always much stronger than the other. Further, the intensity ratio of the electric-dipole and magnetic-dipole transitions can be used to investigate the asymmetry of Eu3+ ions in the host lattice site [16]. It is reasonable that only electric-dipole 5D0→7F2 transition was observed in our system because Eu3+ ions is located in the amorphous EuxYySn2-x-yO7 lattice site which results in reducing site symmetry of



Figure 2:

Emission fluorescence spectra of (a) Eu3+ (0.1 mol%)-Y3+ (0, 0.5, 1, 2, and 4 mol%) and (b) Eu3+ (0.05, 0.1, and 0.2 mol%)-Y3+ (1 mol%) codoped ITO thin films annealed at 600°C for 1 h.



85

Eu3+ ions, i.e., no inversion symmetry. Similar spectral structure is also observed in other Eu3+-doped amorphous materials. The more Eu3+ or Y3+ doping concentrations can increase the PL intensity, as shown in Fig. 2 (a) and (b). Because the Eu3+ (0.05, 0.1, and 0.2 mol%)-Y3+ (0, 0.5, 1, 2, and 4 mol%) codoped ITO thin films annealed at 600°C for 1 h could be composed of the mixture of amorphous EuxYySn2-x-yO7 and crystallized In23+ ions replace Y3+ ions and are located at the Y3+ site in zSnzO3-δ phases, Eu 3+ Y2Sn2O7. The more Y ions doped, the more Y2Sn2O7 formed, which results in the more Eu3+ ions can be dissolved in the Y2Sn2O7 lattice to reduce the concentration quenching effect and increase the PL intensity. The excitation spectrum corresponding to the 5D0→7F2 transition of Eu3+ ion in Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h is shown in Figure 3. The broad bands with wavelengths from 350 to 500 nm are ascribed to the f–f transitions of the Eu3+ ions [17]. Within this broad band, a sharp and strong band at 465 nm can be assigned to the 7F0→5D2 transition. Additionally, because the band gap energy of In2O3 nanocrystal is ~4 eV (~300 nm) which is larger than the bulk In2O3 (3.7 eV; ~335 nm), a very small excitation band at 300 nm could be attributed to the energy-transfer transition between Eu3+and In2zSnzO3-δ [18]. The existence of the excitation band corresponding to the band gap energy is the evidence of energy transfer from the In2-zSnzO3-δ nanocrystal to the Eu3+ ions but the very small In2-zSnzO3-δ host band in the excitation spectrum of Eu3+ indicates that there is a little energy transfer from the In2-zSnzO3-δ host to the doped Eu3+ ions.

Figure 3:

Excitation spectrum corresponding to the 5D0→7F2 transition of Eu3+ ion in Eu3+-Y3+ codoped ITO thin films annealed at 600°C/1 h.


86 Energy and Sustainability II On the other hand, the spectrum consists of two very strong broad peaks centered at 207 and 236 nm. It is well known that the charge-transfer transition between Eu3+ and O2- generally occur at 250~260 nm. L.R. Singh reported that because the covalency of Eu-O bonds in Y2O3 nanocrystals increases, the Eu-O charge transfer energy can be blue shifted in comparison with that of bulk Y2O3 [19]. In our system, the average crystal size of Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h was ~20 nm, which could result in the Eu-O charge transfer energy blue shifting to 236 nm. Moreover, band gap energy of bulk Y2Sn2O7 is 4.45 eV (~279 eV) but because of quantum confinement effect, the band gap energy of nanosized Y2Sn2O7 should be more than 1~2 eV of that value [20]. Therefore, the 207 nm excitation band could be related to the energytransfer transition between Eu3+ and Y2Sn2O7 because the EuxYySn2-x-yO7 is amorphous phase with nanosized crystals. The above-mentioned results reveal that Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h with bixbyite structure can transfer the UV~blue light (200-470 nm) to visible light (611 nm). We believe that Eu3+-Y3+ codoped ITO thin films should have good application in the single crystal or poly crystal Sibased solar cells which have less quantum efficiency in the wavelength range from 300 to 500 nm.

Figure 4:

Sheet resistance of Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h as a function of different doping concentrations.



87

3.3 Electrical properties The sheet resistance of Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h as a function of different Eu3+-Y3+ doping concentrations is illustrated in Fig. 4. The resistivity of ITO thin films increased up to ~5 % by light Y3+ or Eu3+ doping concentration (0.5 mol%). However, higher doping concentrations can significantly deteriorate the conductivity. For example, for only 1% Y3+ doping concentration the resistivity of ITO thin film was approximately doubled. The addition of Eu3+ and Y3+ ions into ITO lattice can induce the formation of amorphous pyrochlore phase EuxYySn2-x-yO7, an insulator with the energy gap of 4.46 eV, which results in the increase of resistivity. [20] Furthermore, because Y3+ and Eu3+ ions can react with Sn4+ ions to form the pyrochlore phase EuxYySn2-x-yO7, the Sn4+ content in In2-zSnzO3-δ should be reduced, which also results in the decrease of the carriers created by the dopant and the increase of resistivity. According to the above-mentioned investigations of luminescence and resistivity properties, the result reveals that there exists a kind of tradeoff between the luminescence and conductivity. It is hard to achieve a Eu3+-Y3+ codoped ITO transparent conductive electrode with both of the high luminescent and high conductivity properties. The Eu3+ and Y3+ codoping concentration should be less than ~0.5% in order to avoid the serious deterioration of conductivity.

4

Conclusions

Eu3+ and Y3+ ions were codoped into the tin-doped indium oxide transparent conductive electrode to make it possess visible luminescent and conductive properties. The Eu3+-Y3+codoped ITO transparent conductive thin films with the precise control on the desired stoichiometry of dopants were fabricated by solgel spin-coating technologies. The Eu3+-Y3+ codoped ITO thin films annealed at 600°C for 1 h could be composed of the mixture of amorphous EuxYySn2-x-yO7 and crystallized In2-zSnzO3-δ phases, which results in 611 nm visible luminescence. However, no PL can be detected in Eu3+-doped ITO thin films. The higher Y3+ concentration can increase the PL intensity because of the formation of more EuxYySn2-x-yO7. On the other hand, the Eu3+ and Y3+ codoping concentrations should be controlled within ~0.5% to avoid the deterioration of conductivity. The Eu3+-Y3+codoped ITO thin films should be a good solution as the luminescent solar concentrators to covert the 350~465 nm excited light to 611 nm for the enhancement of solar cell efficiency.

Acknowledgement The authors would like to thank the National Science Council of the Republic of China for financially supporting this research under Contract No. NSC 96-2221E-194-042-MY2.



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[18]

[19]

[20] [21]

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Dutta, D.P, Sudarsan, V., Srinivasu, P., Vinu, A. & Tyagi, A.K., Indium Oxide and Europium/Dysprosium Doped Indium Oxide Nanoparticles: Sonochemical Synthesis, Characterization, and Photoluminescence Studies. Journal of Physical Chemistry C, 112, pp. 6781-6785, 2008. Singh, L.R, Ningthoujam, R.S., Sudarsan, V., Srivastava, I., Singh, S.D., Dey, G.K. & Kulshreshtha, S.K., Luminescence study on Eu3+ doped Y2O3 nanoparticles: particle size, concentration and core–shell formation effects. Nanotechnology, 19, 055201, 2008. Subramanian, M.A., Aravamudan, G., & Rao, G.V.S., Oxide pyrochlores - A review. Progress in Solid State Chemistry, 15, pp. 55-143, 1983. Nadaud, N., Lequeux, N., Nanot, M., Jove, J., & Roisnel, T., Structural Studies of Tin-Doped Indium Oxide (ITO) and In4Sn3O12. Journal of Solid State Chemistry, 135, pp. 140-148, 1998.




91

Towards a Southern Africa Development Community (SADC) model to assess financing options of renewable energy technologies V. H. van Zyl-Bulitta1, B. Amigun1,2 & A. C. Brent1, 3 1

Sustainable Energy Futures, Resource Based Sustainable Development, Natural Resources and the Environment, Council for Scientific and Industrial Research, South Africa 2 Department of Process Engineering, Stellenbosch University, South Africa 3 Graduate School of Technology Management, University of Pretoria, South Africa

Abstract Access to energy in the form of electricity and fuels is a necessary requirement for sustainable development. Despite the resource abundance for Renewable Energy Technology (RET) in Africa, the potential of RETs is still underexploited. In light of the COP15 meeting, RET is a focal point in the response to global challenges, such as climate change and energy security, and the investment landscape in RET and energy efficiency has recently undergone considerable transformation. To realise its potential, investment in RET infrastructure is critical for Southern Africa. However, the development of sustainable energy is curbed in the region by the lack of adequate and secure finances. A plethora of generic technological and non-technological restrictions, such as scarce political support and poverty, impede RET (financial) support and adoption. A deeper understanding of the consequences of different energy policies could positively influence stakeholders, gain investor confidence, and subsequently contribute to the global community. The financial valuation of factors that are important for RET introduction, pertaining to the risks of RETs, are described through a systems dynamics approach. Specifically, issues in the social and environmental spheres are discussed by means of a Southern African case study. By applying such an approach, through a further research agenda, it is envisaged that RET implementation may be accelerated. Keywords: energy finance, system dynamics, renewable energy, Africa. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090091


1

Introduction

Energy plays a critical role in the development process, firstly as a domestic necessity, but also as a factor of production, where cost directly affects prices of other goods and services [1]. Although better energy supply does not automatically guarantee an acceleration of human development, it is a prerequisite for it. Energy affects all aspects of development - social, economic, and environmental - including livelihoods, access to water, agricultural productivity, health, population levels, education, and gender-related issues. Energy also places excessive strain on investment capital in developing countries. It is not uncommon for an African country to spend in excess of 30% of its development budget on the energy sector; limiting the need for capital expenditure in the energy sector could therefore free up resources for other pressing needs. Therefore, ensuring the provision of adequate, affordable, efficient and reliable high-quality energy services with minimum adverse effects on the environment for a sustained period is not only pivotal for development, but crucial for African countries, most of which are struggling to meet present energy demands. Furthermore, the continent needs such energy services to be in a position to improve its overall net productivity and become a major player in global technological and economic progress [2]. The UN Millennium Development Goals (MDGs), especially MDG 1, i.e. reducing the percentage by half of people living in poverty by 2015, cannot be met without major improvements in the quality and magnitude of energy services in developing countries. In addition, lack of access to such services often exacerbates poverty and leads to unacceptable health risks, for example through exposure to indoor air pollution resulting from cooking with traditional biomass fuels. Africa has a landmass of just over 30.3 million km2, an area equivalent to the US, Europe, Australia, Brazil, and Japan combined. As of 2004, Africa housed 885 million people in 53 countries of varied and diverse sizes, sociocultural entities, and resource endowments, including fossil and renewable energy (RE) resources [3]. Most of these energy resources are yet to be exploited, which is a contributing factor in making the continent the lowest consumer of energy. An African uses only one eleventh, one sixth, and one half of the energy used by a North American, a European, and a Latin American, respectively. There is an urgent need for substantial increases in energy consumption in Africa as a whole if Africa is to become competitive with other developing regions of the world [4]. The Southern African Development Community (SADC) is a treaty organisation comprising 15 member states in the Southern African region. The ultimate objective of SADC is to “build a region in which there will be a high degree of harmonisation and rationalisation to enable the pooling of resources to achieve collective self-reliance in order to improve the living standards of the people of the region” [5,6]. Southern Africa is rich in natural energy resources. With abundant hydropower potential in the north, vast coal fields in the south, oil reserves off the west coast, and fertile land, there is a definite potential to supply low cost energy in the region. However, the disparate distribution of natural, WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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human, and capital resources in the region, as observed in any other transitional country, necessitates regional coordination and cooperation to ensure the development of an efficient and reliable energy system. Trade can improve the security of supply though diversification of supply and sharing of reserve margins. This paper investigates the potential for RET in SADC countries, in particular South Africa, by emphasising the energy geography in Africa, financial aspects thereof, and limitations to RET adoption; future energy paths, with an increased share of RE in the African energy mix, are suggested. It is believed that the paper will assist energy policy makers and future players in the development of sustainable energy finance (SEF), not only in the Southern African context, but also in other transitional and developing countries.

2

International investment climate for RET

The concept of sustainable energy finance (SEF) combines RE and activities for energy efficiency. It is important to distinguish between energy investments for poverty reduction, and for industry and economic development purposes. Carbon Finance (CF) has evolved from the need to develop carbon markets. These entail tradable instruments, such as certificates from Emissions Trading, the Clean Development Mechanism (CDM) and Joint Implementation (JI), all established in the Kyoto Protocol, i.e. articles 17, 12, and 4, respectively. The history of the underlying concepts for carbon trading started in 1968. Flaws of these mechanisms are the insignificant role played by JI projects, the so-called ‘additionality’ requirement of the CDM, and challenges related to the need for projects to assist developing nations achieving sustainable development. [7]. The Global Environment Facility (GEF), the financial mechanism for the United Nations Framework on Climate Change (UNFCCC), currently represents the largest source of funds for RE to developing countries. $900 million have been assigned to 110 projects in 50 countries leveraging nearly $6 billion of added co-financing [8]. Its role is in need for redefinition. In particular, it would ease CF processes immensely if it took a more central, rather than peripheral role. The design of a future global carbon finance market is yet to be defined [9]. RE options are becoming economical in the marketplace, due to the simultaneous decrease in technology costs and rising fossil fuel prices. The design of an energy system incorporating renewables from an energy system that was built around fossil fuels is more than a challenge. Distribution networks and infrastructure are designed around carbon-intensive energy carriers. Funds currently in place are restricted in time until 2012, which more resembles a trial period rather than establishing a “long-term architecture of global environmental funding” [9]. To support the adoption of RETs, sources of investment are needed by developing countries to circumvent the unsustainable energy paths that other, more developed countries, in the world have taken. Funding could be raised from public or private sources, carbon finance, and multilateral funding. The Pew Centre on global climate change sketches a technology funding framework for WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

94 Energy and Sustainability II the period after 2012 [10]. The establishment of a clean energy fund in the African region, the African Biofuels & Renewable Energy Fund (ABREF), also addresses the uncertainty about the post-2012 carbon market setting. The fund aims to exploit Africa’s underexploited resources with a financing strategy between export credit agencies and commercial banks from the viewpoint of perceived risk and bankability. Building on the three pillars climate change, carbon market opportunities and energy security, ABREF manages project performance risk and failure to deliver carbon credits, and it mitigates the market risk that stems from uncertainty in the carbon market. It reports on the number of projects as of April 2008 in the pipeline, where biofuels (14) and solar energy (13) rank second and third after hydro (21) [11]. Many carbon funds (11) have been established under the supervision of the World Bank and another 60 carbon funds have come into being [12]. If the World Bank were to become the central agency for climate change finance, a bias may be introduced towards the interests of industrialised nations [8]. To ensure quality of CDM and JI projects, a gold standard has been proposed to make them comparable and effective. A similar function to ensure best project results is provided by environmental due diligence (EDD) procedures [13, 14]. Sustainable energy (SE) as an investment sector has been on the rise over recent years. Despite RE only serving 5% of global capacity and 3.4% of global power generation, 9.4% of global energy investing and 23% of new electricity generating capacity are based on renewables [15]. Investments have been projected to reach around $450 billion by 2012 and $600 billion by 2020 [16]. Recent increases in the RE investment sector showed that it is able to raise the $200-210 billion needed yearly to return global greenhouse gas (GHG) emissions to current levels, according to the UNFCCC Secretariat. The Copenhagen meeting of the climate convention is approaching, where “governments must reach agreement on a new and decisive climate agreement”; there is a need for carbon markets to evolve and be fostered to achieve their potential of cleaning up current energy infrastructures [16]. Africa strongly lags behind other regions such as India, China, and Brazil. Energy in Southern Africa is largely underexploited, though at the same time presents an unprecedented opportunity to choose “a cleaner development pathway via low-carbon energy alternatives that can reduce GHG emissions and, at the same time, meet current suppressed energy demand and future needs more efficiently and affordably” [12]. Sub-Saharan Africa can gain most from RE. Moreover, this region is stated to be the only one which is not likely to reach the MDGs by 2015 [16]. The role of energy in reaching the MDGs is highlighted in a study by the Forum of Energy Ministers of Africa (FEMA). However, despite the study’s important contribution by identifying links of achieving the MDGs and energy, no priority is assigned to RE [17, 18]. Policies and investment need to be shaped in accordance with the formulation of a coherent strategy to reach the targets set to enable climate change mitigation [19]. The current state of South Africa’s RE sector, for example, is marked by pilot projects, powered by the state-owned electricity utility Eskom. South Africa’s energy service provision structure is largely directed by Eskom. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Electricity prices, though currently on the rise, are inexpensive in South Africa; one reason being that the true cost of facilities is not accounted for. Feeding externally generated electricity into the grid is currently not possible. The pilot projects in South Africa in line with the South African Bulk Renewable Energy Generation Programme comprise different solar technologies, wind, and biomass [17]. Depending on the energy carriers and technology and equipment needed to convert the energy for consumption, REs differ in their cost structures. The cost of wind and solar energy from the nature of the source used could be accounted for in financial models as a zero fixed cost, while the cost for biofuels is mostly given by feedstock cost, e.g. up to 85% of biodiesel production cost. The dominance of feedstock contribution to total cost decreases orderly as agricultural feedstock, industrial by-products and waste materials are used [20]. While some renewables may incur higher capital costs, immense savings can be achieved in operating costs as compared to fossil fuels or nuclear energy. A comparison of cost, energy supply, and job creation for solar water heaters and the pebble bed nuclear power plant, the construction of which was considered in South Africa has been given and is depicted in Table 1 below [17]. Table 1:

Solar water heaters compared to pebble bed technology nuclear reactor, source: [17], Forex rates (24-02-2009): 1 EUR = 12.73 ZAR, 1 USD = 10.00 ZAR [http://www.xe.com/].

Energy saved/supplied Cost Creation of jobs

3

Solar water heaters

Pebble bed nuclear power plant

890 GWh/annum ZAR 2.6 billion 13 440 jobs

750 GWh/annum ZAR 10 billion 135 jobs

Barriers to RET adoption and a system dynamics-based approach in the southern African energy context

For developed countries, RE sources primarily serve as a means to diversify the national energy supply and a means by which the concept of sustainable development can be implemented, and GHG emissions reduced. However, for developing countries such as those in Africa, RET in general plays a very different role. There is a major difference in the background motives and a resulting performance gap between the South and the North in terms of harnessing RE. Therefore, it has become important to fill this gap with experiences gained in the developed world, but adapted to the needs of developing countries. The fundamental problems to commercialise RETs exist in both developed and developing countries. However, their magnitude and characteristics are more pronounced in developing countries. The multi-dimensional differences among regions and countries make the analysis of the magnitude of these hurdles more complex. Despite national differences, it is possible to generalise some barriers, which have been extensively discussed [2]. For example, various generic barriers WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

96 Energy and Sustainability II currently identified to hinder the adoption and commercialisation of biofuel technologies in Africa, apart from the high cost of raw materials and other economics related constrictions, may be categorised as technological and nontechnological (policy, legal, financial, institutional, cultural, social, etc.) constraints. Table 2 gives a schematic view of barriers to accelerated adoption and commercialisation of RETs in Africa. These barriers are common to RE:  Type A: Technologically advanced developing countries, with well diversified and fairly comprehensive industrial, energy and R&D infrastructures – only South Africa.  Type B: Technologically advancing developing countries, which are industrialising fairly fast, but are still quite limited in the diversification of their industrial, energy and R&D infrastructure, e.g. Egypt, Morocco, and Algeria.  Type C: Slowly industrialising developing countries, with still very limited infrastructure in industry, energy and R&D, such as Nigeria, Mauritius, and Libya.  Type D: Technologically least developed countries: Most sub-Saharan African countries, e.g. Ethiopia, Chad, Burundi, Mozambique, Ivory Coast, Niger, DR Congo, Somalia, Mali, and Sudan. Table 2:

Schematic barriers assessment on a classified country basis, source: [2] Low:*, Medium: **, High: ***.

Countrytype

Institutional/ policy hurdle

Technical hurdle

Economic hurdle

Financial hurdle

Information hurdle

Capacity hurdle

Type A

**

*

**

**

*

*

Type B

**

**

**

**

**

**

Type C

***

**

***

***

***

**

Type D

***

***

***

***

***

***

Threshold-21 (T21) models [21] that dynamically link economic, environmental, and societal aspects of a country, sector, or company, have been formulated by the Millennium Institute for Mali, Malawi, South Africa, and Mozambique. Other African countries have also been investigated and modelled to enhance an understanding of policies to support sustainable development and the achievement of the MDGs. The strength of system dynamics models lies in their ability to directly evaluate consequences of different policies [22]. The energy sector has been investigated exclusively in South Africa with a T21 approach, and is detailed elsewhere [23]. The T21 system dynamic model was developed for integrated policy planning to outline future energy paths for South Africa. The study draws on the current energy context in South Africa and WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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projects different energy mix policy scenarios until 2030, using the T21 framework [23]. Energy efficiency measures are considered as well as the influence of GDP, energy price, and demand and supply balances. In this paper the dynamic modelling of the energy sector of South Africa is used as an example with particular attention to biofuels development in the Eastern Cape Province of the country, and possible impacts of such developments on the country’s energy supply as well as consumption patterns. The Eastern Cape Department of Agriculture (ECDoA) is embarking on a large scale biofuels production project that includes the construction of a biodiesel plant in East London, a large city in the Eastern Cape Province, and the development of 500 hectares of land to grow, amongst others, canola and soybeans for biodiesel production. This project is to leverage the Mass Food Production Programme of the Province, which is already in place, and to bring numerous benefits to communities, such as the creation of approximately 350 jobs, Black Economic Empowerment (BEE), empowerment of local farmers, skills development, and food security, since biofuels are not to be produced from maize, which is the staple food for many South Africans. Many potential pitfalls of biofuels production are addressed by dry-land crop cultivation, off-take agreement contracts to prevent adverse effects of price volatility in raw materials, as well as stringent control in the choice of contractors. Exports to other SADC countries that currently import internationally would save transaction costs. The already existing oversupply of glycerine is to be addressed by the development of alternative uses for glycerine and the erection of a methane gas facility is planned to process surplus oilcake [24, 25]. The ECDoA case is used as basis to pave the way for incorporating financial valuation methods to dynamic modelling techniques. By considering, first, South Africa and one of its provinces, African-specific factors to consider would be identified that are also relevant for a future SADC model for RET introduction.

4

Representing the process of sustainable energy finance (SEF) for development

Dynamic modelling techniques have already been shown to contribute to energy modelling, and the evaluation of alternative energy paths. The financial assessment of different energy paths could be facilitated by two methodologies, i.e. the sustainable value (SV) and real options (RO) approach. 4.1 The sustainable value (SV) approach SV assesses the contribution of a company in terms of sustainability and the efficiency with which it uses its resources. It enables environmental performance to be measured in monetary terms, where not only capital, but also environmental and social resources, are considered. SV accounts for different economic actors using resources in different ways to create several possible outputs. The results of their respective activities are weighed in relation to the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

98 Energy and Sustainability II resources used in the course of such activities. Whenever the resource is used in a better way than possible alternative uses, value is created in financial terms [26]. SV has been applied on company level where a benchmark, such as a stock exchange index, is used to compare performance. If the SV of the company is larger than what could have been achieved with the same resources by the benchmark, value above the opportunity costs, (the equivalent performance of the benchmark had the resources been invested in the benchmark instead of the company) is created. SV enables a differentiation between individual resource uses, and their assessment in sustainable terms. In this way emissions, pollution and health hazards could be rated individually and one may determine which of these costs are incurred in the process of activities in a value-creating way. It “reflects how well companies have reconciled economic output and environmental and social stewardship” [26]. SV aids in decisions regarding the consequences in generating return by the allocation of resources to different possible uses by showing “how a limited and scarce amount of resources should best be used in order to generate highest returns” [26]. SV does not replace other approaches to sustainability assessment. An inherent assumption on the workings of financial markets is that opportunity cost thinking will positively affect the efficiency of resource use. Approaching the development of an emerging market with opportunity cost thinking involves identifying existing resources that would be consumed by RET and the consequences of taking different energy or RE paths. Profit potential, costs and impacts on society and economies of a country may be assessed in monetary terms besides qualitative factors involving quality of life and gender equity. In the SADC context of RET introduction, the SV methodology could be applied in the valuation of alternative uses of resources. The environmental effects of different energy paths as well as vulnerability to future emissions reduction targets can be evaluated [26]. 4.2 The real options (RO) approach The RO approach assesses economic performance by evaluating alternative uses, focusing only on financial measures. They may be incorporated in the analysis through the assessment of when to invest in one or more RETs in a specific country cluster, sector, or area. Furthermore, multiple stakeholders, their actual interactions, as well as believed interactions are important to integrate. Modelling techniques and learning tools to fully understand the consequences of decisions are valuable for investments that are not easily reversible. Modelling techniques that can deal with uncertainty in price fluctuations or changes of fossil fuels and the expected change in prices for renewables would be able to pinpoint the breakeven point of when a technology becomes competitive and under what circumstances it would stay competitive. The RO approach has been used to develop a dynamic programming model for RET diffusion, which features uncertainties in the energy sector and the flexibility to delay. They highlight the use of more sophisticated valuation techniques, the need for WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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financial incentives and the important role of targeted RET policies to achieve widespread adoption [27]. Combining sustainable efficiency using the SV and RE approaches with a model flexible enough to incorporate future changes in economy, politics, society, technology and environment in consideration of requirements and resources in the African context, will aid to pave a financially sound energy path. In view of the above, it is important to consider the risks associated with RET introduction. Risks and mitigation steps were identified for the biofuels project in South Africa. These include market related risks, operating model risks, risks of financial evaluation and funding, as well as project implementation and evaluation and regulatory risks [24]. In a study of climate change for the financial services industry the United Nations Environment Program (UNEP) proposed recommendations for different players in CF [28]. These include the industry as a whole, insurance and reinsurance companies, asset managers, pension funds and financial analysts, investment banks and consultants, political decision makers, and governments in industrialised countries. The recommendations follow the lines of progressive long-term orientated strategies for incorporating climate change and its consequences in the financial sector, as well as raising awareness of the linkages that have not yet been broadly accepted [28]. Approaches from Bayesian statistics have been applied to financial analysis and investment decision support to identify risk measures in valuation processes and future value drivers and cash flows [29].

5

Conclusion and future research agenda

Energy is a key factor in industrial development and the provision of vital services that improve the quality of life. However, its production, use, and byproducts have resulted in major pressures on the environment, both from a resource use (depletion) and pollution point of view. Limited access to energy is a serious constraint to development in the developing world, where the per capita use of energy is far less than in the industrialised world. RET could assist in achieving sustainable development in Africa and keep the UN MDGs on schedule. The decoupling of inefficient, polluting fossil energy use from development represents a major challenge of sustainable development. The long-term aim is for development and prosperity to continue through gains in energy efficiency rather than increased consumption, supported by a transition towards the environmentally responsible use of renewable resources. RETs offer developing countries some prospect of self-reliant energy supplies at national and local levels, with potential economic, ecological, social, and security benefits. Achieving the widespread implementation of RETs may be realised through proper understanding of policies, economics, and financial levers. NEPAD and the African Union (AU) both have roles to play in developing rational energy policy and encouraging biofuel investment across the continent. Information


100 Energy and Sustainability II exchange and experience sharing should be encouraged amongst institutions and practitioners that are engaged in RET development. Having sketched the landscape of RET investment internationally, as well as specific to the Southern African region, the paper proceeded to describe barriers to its adoption followed by examples of system dynamic modelling for RET embedded in the South African energy market. Tools combining system dynamic and other dynamic modelling approaches are needed for the development of a coherent framework for financing RET options in Southern Africa, time investments and to assess and address related risks. The future research aim is to develop and implement a dynamic model that would be able to capture the problems posed by RETs in the SADC context, and to propose solutions for policy guidance. The previous section has built on the scenario sketched in this study to address the challenges of the SADC region to open the door to a SE path. Learning from South Africa has shown the feasibility of RE projects to some extent, and simultaneously highlighted serious challenges impeding the effective development of RE markets in Southern Africa. Future research will entail a competitive analysis of RET opportunities in SADC countries using critical factors, such as government subsidies and willingness to invest, regional policies in place, the presence of a formal strategy plan for RE, the availability of risk capital, the RET industrial scale, local commercial sector commitment to participate in production and marketing, and availability of raw materials. These factors will be analysed as a composite of their relative ranking of a key attractiveness factor for RET and will be compared amongst several countries in the SADC region. The outcome is to be a matrix of summary measures, which may assist in attracting commercial activity.

References [1] New Partnership for African Development (NEPAD) conference report. Abuja, 2001. http://www.uneca.org/eca- conferencereport/NEPAD.htmlS. [2] Amigun B., Sigamoney, R. & von Blottnitz, H., Commercialisation of biofuel industry in Africa: A review. Renewable and Sustainable Energy Reviews, 12, pp. 690–711, 2008. [3] World Development Report. World Bank: Washington DC, 2005. [4] Davidson, O., Chenene, M., Kituyi, E., Nkomo, J., Turner, C. & Sebitosi, B., International Council for Science (ICSU). Regional Office for Africa Science Plan. Sustainable Energy in sub-Saharan Africa, 2007. http://www.icsu-africa.org/sustainable_energy_rep_2007.pdf [5] Transformation from Conference to Community, 2008. http://www. sadc.int/index/browse/page/53. [6] Alfstad, T., Development of a least cost energy supply model for the SADC region. M.Sc Thesis in Engineering, unpublished, 2005. [7] Bond, P. & Erion, G., South African carbon trading: A counterproductive climate change strategy. Electric Capitalism - Recolonising Africa in the Power Grid, ed. D.A. McDonald, HRSC Press and earthscan: Cape Town and London, 2009. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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[8] Fleming, C., The GEF and Renewable Energy, 2005. http://www.gefweb.org/Projects/focal_areas/climate/documents/GEF_and_ Renewable_Energy.pdf. [9] Porter, G., Bird, N., Kaur, N. & Peskett, L., New finance for climate change and the environment, 2008. http://www.odi.org.uk/fecc/ resources/reports/s0178 final report.pdf. [10] Technology Funding in a post-2012 Climate Framework. Pew Centre on Global Climate Change, 2008. http://www.pewclimate.org/ docUploads/BackgroundNoteTechFunding.pdf. [11] Memorandum of Information for African Biofuels & Renewable Energy Fund, 2008. http://www.faber-abref.org/fichiers/Note FABER. pdf. [12] Faurie, J., Low-carbon Energy Projects for Development in Sub-Saharan Africa - Unveiling the Potential, Addressing the Barriers, 2009. www.carbonfinance.org/docs/Main_Report_Low_Carbon_Energy_projects _for_Development_of_Sub_Saharan_Africa_8-18-08.pdf , http://www.envirovaluation.org/index.php/2008/09/21/low-carbon-energyprojects-for-developme [13] Kenber, M. & Salter, L., The Gold Standard: Quality Standards for CDM and JI Projects. WWF, 2002. http://www.energy-base.org/fileadmin/media/ base/downloads/toolsEDD/eddgeothermal.pdf, http://www.wwf.or.jp/ activity/climate/lib/kyotoprotocol/COP8standards.pdf. [14] Environmental Due Diligence (EDD) of Renewable Energy Projects Guidelines for Geothermal Energy Systems. UNEP, BASE, n.d. http://www.energybase.org/fileadmin/media/base/downloads/toolsEDD/edd geothermal.pdf. [15] Renewables 2007 Global Status Report. World Watch Institute, 2007. http://www.worldwatch.org/node/5633. [16] Boyle, R., Greenwood, C., Hohler, A., Liebreich, M., Sonntag-OBrien, V., Tyne, A. & Usher, E., United Nations Environment Programme, Global Trends in Sustainable Energy Investment 2008, Analysis of Trends and Issues in the Financing of Renewable Energy and Energy Efficiency, 2008. http://sefi.unep.org/fileadmin/media/sefi/docs/publications/GlobalTrends 2008.pdf. [17] McDaid, L., Renewable energy: Harnessing the power of Africa? Electric Capitalism - Recolonising Africa in the Power Grid, ed. D.A. McDonald, HRSC Press and earthscan: Cape Town and London, 2009. [18] Energy and the Millennium Development Goals in Africa. The Forum of Energy Ministers of Africa (FEMA), 2006. http://www.esmap.org/filez/ pubs/FEMAForPrintshop.pdf. [19] Flavin, C., Low-Carbon Energy: A Roadmap, 2008. http://www.worldwatch.org/ taxonomy/term/37. [20] Amigun, B., Processing cost analysis of the African Biofuels industry with Special Reference to Capital Cost Estimation Technique. PhD Thesis, unpublished: University of Cape Town, 2007.


102 Energy and Sustainability II [21] Bassi, A. M., Modelling U.S. Energy with Threshold 21 (T21), 2006. http://www.systemdynamics.org/conferences/2006/proceed/papers/BASSI2 05.pdf. [22] Africa region. Millennium Institute, 2009. http://www. millenniuminstitute.org/projects/region/africa/. [23] Musango, J. K., Brent, A. C. & Bassi, A. M., South African energy Model: A systems dynamics approach. Conference of the Systems Dynamics Society, Albuquerque, New Mexico, USA, 2009. [24] ECDoA, Business plan for an integrated dry-land cropping and processing plan for rural development in the Eastern Cape. Unpublished, 2007. [25] Jansen, W., ASGISA Eastern Cape integrated cropping and biofuel development programme. KPMG, 2008. www.sacities.net/members/pdfs/ 3.1.2_eastern-cape_case_study.pdf. [26] Figge, F. & Hahn, T., Sustainable Value of European Industry - a Valuebased Analysis of the Environmental Performance of European Manufacturing Companies, 2006. http://sefi.unep.org/fileadmin/media/sefi/ docs/industryreports/advancesurveyfullversion.pdf. [27] Kumbaroglu, G., Madlener, R. & Demirel, M., A real options evaluation model for the diffusion prospects of new renewable power generation technologies. Energy Economics, (30), pp. 1882–1908, 2008. [28] Das Klimarisiko für die Weltwirtschaft / Climate Change and the Financial Services Industry. UNEP Finance Initiative: Paris. http://www.gci. org.uk. [29] Bals, C., Mainstreaming of climate risks and opportunities in the financial sector. http://www.climate-mainstreaming.net/.



103

Hydrogen fuelled agricultural diesel engine with electronically controlled timed manifold induction: an experimental approach P. K. Bose1, S. Mitra2, R. Banerjee3, D. Maji3 & P. Bardhan4 1

National Institute of Technology, Silchar, India Jalpaiguri Engineering College, India 3 School Of Automotive Engineering, Jadavpur University, India 4 JIS College of Engineering, India 2

Abstract The important motivations for exploring alternative fuel resources are energy security, air pollution, and climate change; problems that are collectively calling into question the fundamental sustainability of the current energy system. Natural gas and bio fuels are seen as the most important short-term options for meeting these goals, whereas in the long run, a substantial contribution is expected to be delivered by hydrogen which would facilitate the transition from limited non-renewable stocks of fossil fuels to unlimited flows of renewable sources. Hydrogen-fuelled internal combustion engines with near-zero emissions and efficiencies exceeding today's port-fuel-injected (PFI) engines are a potential near-term option and a bridge to hydrogen fuel cell vehicles where fuel cell undergoes development to make it economically viable. The unique combustion properties of hydrogen make it an ideal choice for its use in compression ignition engines. The present work attempts to explore the performance and emission characteristics of an existing single cylinder four-stroke compression ignition engine operated in dual fuel mode with hydrogen as an alternative fuel. The hydrogen was premixed with the incoming air and inducted during the duration of intake valve opening by an indigenously developed electro-mechanical means of solenoid actuation The performance and emission characteristics with hydrogen–diesel blend and neat diesel are compared. In this experiment hydrogen flow rate was kept constant at 0.15 kg/hr. The brake thermal efficiency with hydrogen–diesel blend is about 15.7% greater than that of neat diesel operation at 40% rated load. CO, CO2, HC and smoke emissions were significantly less with hydrogen–diesel blend. Smoke level was 41.6% lower than that of neat diesel operation at 80% load, whereas emission of CO2, CO, and HC levels were lower by 40.5%, 44.3% and 53.2% respectively for hydrogen enrichment at 80% load. In our present work EGR technique was examined in reducing NOx concentration. The NOx level decreased from 1211 ppm to 710 for hydrogen enrichment (0.15kg/hr) at 80% of the rated load. Keywords: hydrogen, diesel, dual-fuel, timed manifold injection, electromechanical actuation, hot EGR, cold EGR. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090101


1

Introduction

With the uncertainty of today's petroleum market with its declining oil reserves, ongoing tensions in oil producing nations, and environmental regulatory activity soaring to new heights, the time has come for the world to embark on the road of independence from the ‘addiction’ of fossil fuel and to find sustainable alternative fuel resources of the future. According to the European Commission’s White Paper ‘European transport policy for 2010: time to decide’, natural gas and bio fuels are seen as the most important short-term options for meeting these goals, whereas in the long run, a substantial contribution is expected to be delivered by hydrogen which would facilitate the transition from limited nonrenewable stocks of fossil fuels to unlimited flows of renewable sources. According to the World Energy Assessment, released in 2000 by several UN agencies and the World Energy Council, which emphasizes “the strategic importance of hydrogen as an energy carrier”, the accelerated replacement of oil and other fossil fuels with hydrogen could help achieve “deep reductions” in carbon emissions and avoid a doubling of pre-industrial carbon dioxide (CO2) concentrations in the atmosphere – a level at which scientists expect major, and potentially irreversible, ecological and economic disruptions. Hydrogen-fuelled internal combustion engines with near-zero emissions and efficiencies exceeding today's port-fuel-injected (PFI) engines are a potential near-term option and a bridge to hydrogen fuel cell vehicles where fuel cell undergoes developments to make it economically viable (Is Hydrogen the Solution? [1]). Under the given circumstances, dual fuel operation with hydrogen within the framework of contemporary existing engine structure is a good alternative. The high flame speed of hydrogen makes engine operation approach the ideal Otto cycle with near constant volume heat addition thus enhancing thermal efficiency. In addition, the potential of hydrogen combustion in reducing green house hydrocarbon, smoke and PM emissions provide the motivation of study of a hydrogen fuelled diesel engine combining both the advantages of a spark ignition engine and a compression ignition engine at the same time. 1.1 Hydrogen as an alternative fuel in compression ignition engines The use of hydrogen as a clean fuel for premixed spark ignited engines is fairly well developed, (Yi et al. [2], Das et al. [3], Das [4], El-Emam and Desoky [5], Karim [6], Subba Rao et al. [7]) but the same is not true for use in diesel engines. However, the unique combustion properties of hydrogen make it an ideal choice for its use in compression ignition engine. The burning velocities of hydrogen air mixture range from 153 to 232 cm/sec for its stoichiometric mixture, (Isadore and Drell [8], Wallace and Ward [9]). This results in a more isochoric, thus thermodynamically more favourable combustion than conventional diesel engines which undergo a pressure and temperature rise spread over several degrees of crank travel. The flammable range is exceptionally wide for hydrogen in air-lower limit 4%, upper limit 75% by volume. (Isadore and Drell [8], Wallace and Ward [9]) This is an equivalence ratio of about 0.24, as compared with a lean flammability limit of about Φ=0.5 for most hydrocarbon fuels. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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A significant advantage is that the engine can work with very lean mixtures, thus omitting a throttle valve–this ideally suits a diesel engine operation. Hydrogen has a higher auto ignition temperature than conventional fossil fuels. This means that a higher compression ratio is allowed than in a gasoline engine and this makes it an ideal candidate for use in high compression ratio engines without any danger of knocking. 1.2 The hydrogen-diesel dual fuel concept The hydrogen-diesel dual fuel concept method combines the advantages of the high part load efficiency, lower specific fuel consumption, of a diesel engine and the clean combustion characteristics of hydrogen and oxygen. However hydrogen with its cetane number being very low, are not directly suited to compression-ignition (CI) engines. Hydrogen has an auto-ignition temperature of about 571°C and as such it is not possible to achieve ignition of hydrogen by compression alone at the compression ratio of 17.5 at the existing engine configuration in the present work. Some source of ignition has to be created inside the combustion chamber to ensure ignition. (Ikegami et al. [10], Lee et al. [11], Mansour et al. [12], Naber and Siebers [13]). A small amount of liquid Diesel fuel is injected by means of the existing fuel injection equipment near the end of the compression stroke to ignite the gaseous mixture. Diesel fuel auto ignites and creates ignition sources for the surrounding air–gaseous fuel mixture. The pilot liquid fuel, which is injected by the conventional diesel injection equipment, normally contributes only a small fraction of the engine power output. In dual-fuel engines both types of combustion coexist together –the primary gaseous fuel of high-octane index is premixed with air in the inlet manifold and compressed and then fired by a small liquid fuel injection which ignites spontaneously at the end of compression phase. The advantage of this type of engine resides in the fact that it is an attempt for the combination of the better of the two combustion processes using the difference of flammability of two fuels at different stages of the combustion process.

2

Hydrogen induction: some considerations

Hydrogen is a peculiar fuel and it has properties distinct from the conventional fossil fuels. (El-Emam and Desoky [5], Isadore and Drell [8], Wallace and Ward [9]) The necessary ignition energy of a hydrogen-air mixture is very low (0.02 mJ), especially at the stoichiometric condition. This enables the ignition of very lean mixtures and ensures immediate ignition. Contact with hot spots or residual gas, can cause the mixture to ignite spontaneously. (Liu and Karim [14]) This pre-ignition tendency results in backfire if the mixture ignites when the inlet valve is still open. The flame in the combustion chamber ignites the mixture in the inlet manifold through the inlet port, which causes a very loud bang and can result in severe engine damage. The backfire phenomenon is also called flashback or back flash and is one of the main issues of hydrogen fuelled internal combustion engines. Hydrogen has a small quenching distance, about three times as small as gasoline. This implies that it can burn slowly in small and narrow WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

106 Energy and Sustainability II clearances, like crevice regions. The burning in these small regions can continue up to and during the intake process. During the intake process, the hot burning gases can flow out of the crevice volumes and ignite the intake charge thus causing backfire. Thus if an existing IC engine without any modification were to be fuelled by hydrogen, some problems, such as small power output, abnormal combustion (e.g. backfire, pre-ignition, high pressure rise rate and even knock) would occur. So its fuel supply system and combustion system need suitable modification. The prevalent modes of hydrogen induction were examined and their merits and demerits were evaluated in the present context on the basis of literature survey (Yi et al. [2], Das et al. [3], Das [15], Lee et al. [11], Zhenzhong et al. [16], HariGanesh et al. [17], Varde and Frame [18]) Timed manifold injection (TMI) systems offer an alternative to load control method by throttling. It possesses the ability to initiate fuel delivery at a timing position sometimes after the beginning of intake stroke ensuring a pre-cooling effect and thus rendering the pre-ignition sources ineffective. Furthermore, it helps to quench and dilute any residual combustion products that could be present in the compression space near TDC. 2.1 Hydrogen induction circuit development The design of the solenoid actuation [Fig1], which formed the heart of the TMI system, was dictated by the necessity of ensuring simplicity in implementation and the reduction of possibility of undesirable effects of abnormal hydrogen combustion such as pre ignition and flashback at the operating loads. The triggering mechanism essentially consisted of a metal plate mounted on a damper spring held in place by an actuator mounting as shown in Fig 1. The metal plate was designed to ensure a positive contact with the free end of the rocker arm during the inlet valve opening. The design ensured a contact only during the maximum valve lift. The contact having made, the metal plate acting as the switch, closed the 12V DC circuit, thereby energizing the solenoid and allowing hydrogen gas to be injected at a predefined rate in the inlet manifold The metal plate lost contact with the rocker arm during the closing of the inlet valve ensuring that hydrogen being injected into the cylinder only during the maximum valve lift as dictated by the dwell period of the valve lift cam and also that hydrogen was inducted only after a definite time lag after the initiation of the opening of the inlet valve. The time lag arising out of mechanical inertia of the valve components ensured that hydrogen was injected only after a sufficient flow of cooler ambient air was inducted in the cylinder during the opening of the inlet valve, this being critical in quenching any residual hot spots remaining in the cylinder thereby removing any possibility of flash back .In the present study, the hydrogen gas was routed to the engine. According to the setup shown in Fig 2. The hydrogen induction inside the cylinder being actuated by a solenoid is periodic in nature rather than continuous. As a result, a surge tank is included in the circuit to dampen out any pressure fluctuations in the hydrogen supply line. A flow regulator in the hydrogen circuit was used to regulate the mass flow rate of hydrogen in the hydrogen circuit. A flame trap was incorporated in the setup keeping in mind the inherent explosive nature of a hydrogen air mixture and the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 1:

Figure 2:

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Solenoid actuated electro-mechanical TMI circuit.

Schematic diagram of experimental setup.

flashback and blow off nature of hydrogen flames. This acts a safety buffer against explosive mixtures formed in the intake manifold to travel back to the hydrogen cylinder by quenching any freak flame.

3 Methodology The diesel engine was fired on no load initially and it was run for a period of time until it reached steady state conditions, denoted by the constant cooling water outlet temperature. Then the engine running on diesel as the main fuel was taken on load in steps by means of the Eddy current dynamometer of SAJ TEST PLANTS make and after attaining the steady-state conditions all the pertinent readings were noted. This procedure was repeated for 20%, 40%, 60% and 80% loading. The engine exhaust was analysed by means of a AVL 437 smoke meter while common engine emissions (CO,HC,CO2,O2,NOX) were calculated via a WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

108 Energy and Sustainability II AVL DIGAS 444 -5 gas analyzer fitted with a DIGAS SAMPLER. The engine was again allowed to attain steady state conditions at no load. Then hydrogen was supplied at a pressure of 1 bar using hydrogen pressure regulator. By keeping the flow of hydrogen gas@ 0.15kg/hr, the performance and emissions of the hydrogen enriched engine without EGR were noted at 20%, 40%, 60% and 80% load. At the end of this process, hydrogen flow rate was reduced to zero and the engine was made to run at steady-state condition using diesel at no load condition. For EGR operation the quantity of exhaust gas was regulated by a control valve [Fig 3], installed in the EGR loop. An air box was provided in EGR loop to dampen the fluctuation of recirculated exhaust. An orifice was installed in the EGR loop after the air box in order to measure the flow rate of recirculated exhaust. There was an EGR cooler placed before the air box. The engine was run by using hydrogen enrichment (0.15kg/hr hydrogen flow) with 10% EGR and 20% EGR in hot and cold conditions. In both these cases above mentioned readings are taken on no load, 20% load, 40% load, 60% load and 80% load.

Figure 3:

EGR setup.

4 Results and discussions 4.1 Performance characteristics 4.1.1 Variation of brake thermal efficiency with brake power The variation of brake thermal efficiency with brake power is shown in Fig 4. The brake thermal efficiency for hydrogen with diesel as ignition source is 34.1% at 80% load with a flow rate of hydrogen 0.15kg/hr whereas that of baseline diesel fuel is 30.2% showing an appreciable increase of 12.9%. This increase in thermal efficiency is attributed to an enhanced combustion rate due to high flame velocity of hydrogen. Use of EGR has a negative effect on engine combustion due to fresh air dilution and addition of inert elements such that efficiency decreases for all cases of EGR operation as compared to hydrogen enrichment but is greater at all loads when compared with neat diesel operation. At 80% load with 10% cold EGR brake thermal efficiency is 32.3% and with 10% hot EGR it is 32.45% while that for 20% cold EGR is 30.8%, thus indicating that thermal efficiency under the present conditions was affected by the quantity and quality (hot or cold) of EGR operation. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 4:

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Variation of brake thermal efficiency with load.

4.1.2 Variation of brake specific fuel consumption with brake power Fig 5 shows the variation of brake specific fuel consumption with brake power Part load operation (20% load) shows a drastic reduction of 63.3% in bsfc readings during hydrogen enrichment as compared with neat diesel operation proving the excellent combustion properties of hydrogen which helps to achieve the desire brake power at a lower energy input. All EGR cases of operation showed a reduced trend of bsfc while 10% hot EGR showed the best characteristics when compared to pure diesel operation with a 61.71% and 43.3% reduction in bsfc readings at 20% and 80% load. 4.1.3 Variation of volumetric efficiency with brake power The air/fuel ratio (A/F ratio) of stoichiometric combustion of hydrogen in air based on mass is 34.33 kg air/kg and that based on volumetric analysis is 29.6% Volume percent of the combustion chamber occupied by hydrogen is then 29.6%. This means that a significant part of a given combustion chamber volume cannot be filled with air in contrast with conventional liquid fuel that only displaces 1.8% of the combustion chamber.

Figure 5:

Variation of BSFC with load.



Figure 6:

Variation of volumetric efficiency with load.

This decreases the volumetric efficiency of a given engine when compared to its operation with conventional liquid fossil fuel. Fig 6 shows the variation of volumetric efficiency with brake power. The volumetric efficiency obtained for 0.15kg/hr hydrogen enrichment without EGR is 78.9% compared to neat diesel fuel of 80.1% at 80% load. Volumetric efficiency decreases with all cases of EGR operation. Maximum penalty is suffered during 20% hot EGR operation with a 50.1% efficiency at 80% load .10% cool EGR provided the best volumetric efficiency characteristics among all EGR operations with 70.2% at no load and 63.9% at 80% load. 4.2 Emission characteristics 4.2.1 Carbon dioxide emissions The variation of CO2 emission with brake power for all cases under study is shown in Fig 7. CO2 emissions in case of hydrogen enrichment are lower compared to that of diesel. At 80% load CO2 emission for hydrogen enrichment without EGR is 4.7% by volume where as that of neat diesel is 7.9% by volume. The CO2 emission in case of hydrogen enrichment is lowered because of better combustion characteristics of hydrogen fuel and also due to the absence of carbon atom in hydrogen molecule. Due to the use of EGR, CO2 emissions increase and go on increasing with the increase in EGR percentage. At 80% load CO2 emission for 10% EGR is 4.8% by volume and that of 20% EGR is 5.6% by volume. The reason of this increase in CO2 emissions in case of EGR is the presence of CO2 in exhaust gas being recycled back to the fresh air intake. 4.2.2 Carbon monoxide emissions Fig 8 depicts the variation of carbon monoxide with brake power. Results indicate a drastic reduction of 86.6% as compared to neat diesel operation at no load for hydrogen enrichment while 45.8% reductions at 80% load for the same conditions. Hydrogen does not contain any carbon. This is the reason for low CO emission in case of hydrogen enrichment, and the registered amount being only due to pilot diesel and lube oil. Operation with EGR resulted in reduction of CO WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 7:

Figure 8:

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Variation of CO2 emissions with load.

Variation of carbon monoxide emissions with load.

emissions for all cases as compared to pure diesel operation but had a reduced gain as compared to hydrogen enrichment. Operation under 10% hot EGR produced the best gains in CO emissions among all EGR operations with a reduction of 42.3% at 80% load as compared to neat diesel operation. Further analysis showed that gains in CO emission reduction reduced with increasing load for all cases of dual fuel operation. 4.2.3 Hydro carbon emissions Fig 9 shows the variation of HC with brake power .It can be observed that HC emission for hydrogen enrichment without EGR scores an 83% reduction compared to neat diesel operation at no load and a 57% reduction at 80% load. The best HC reduction characteristics in EGR operations were provided by 10% hot EGR with a 57.6% reduction at 80% load. Diesel engines with their inherent lean combustion are prone to HC emissions due to inhomogeneous local air fuel ratios which are either over lean or fuel rich to support combustion. The interesting observation with dual fuel operation with hydrogen is that though the overall equivalence ratio of the combustible mixture is leaner than that of normal WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

112 Energy and Sustainability II diesel operation the HC emissions are still remarkably lower. This is attributed to a more homogenous air fuel mixture having wide ignitability limits due to hydrogen, which helps sustain combustion even under lean conditions. The gains in mixture quality are penalized with EGR operation where residual gases promote fresh air dilution and increases local equivalence ratios beyond ignitability limits.

Figure 9:

Variation of HC emissions with load.

4.2.4 Smoke emissions The operation range of diesel engines is mainly constrained by the smoke emissions at high loads. This limits the exploitation of the advantages of a compression ignition engine to its fullest potential. The variation of smoke level with brake power is shown in Fig 10. As the load increases, diesel engines tend to generate more smoke. Present analysis showed that gains in smoke reduction were maximum with hydrogen enrichment for all the load ranges but decreasing with increasing load, with a maximum of 64.28% at 40% load and a notable 41.6% at 80% load .EGR operation registered lesser gains in smoke reduction as

Figure 10:

Variation of smoke emissions with load.



113

compared to hydrogen enrichment, the 10% hot EGR case showing the best gain trend among all EGR operations. Hydrogen being devoid of any carbon atoms show obvious characteristics of reduction in smoke levels. This is why there is low smoke level in case of hydrogen enrichment. Smoke level increases with increasing EGR rate and increasing engine load. EGR reduces availability of oxygen for combustion of fuel which results is relatively incomplete combustion and increased formation of particulate matter. This results in higher smoke level in case of EGR. 4.3 NOx emissions Fig 11 shows the variation of NOx with brake power. NOx emission for hydrogen enrichment without EGR is 1211 ppm compared to neat diesel fuel of 810 ppm at 80% load. The reason for this higher concentration of NOx in case of hydrogen enrichment without EGR is peak combustion temperature and high residence time of the high temperature gases in the cylinder. Fig 11depicts that with 10% EGR, NOx formation is 760 ppm at 80% load and that of 20% EGR is 710ppm. So the NOx formation decreases with the use of EGR and goes on decreasing with increase in EGR percentage. The primary effect of the burned gas diluents in the unburned mixture on the NOx formation process is that it reduces peak temperatures by increasing the heat capacity of the cylinder charge, per unit mass of fuel. When recirculated to engine inlet, it reduces oxygen concentration and act as a heat sink. All the combustion process is delayed with diluted air consequently the whole combustion process is shifted further into the expansion stroke, leading to lower combustion temp. Lower combustion temp is the reason of decrease of NOx.

Figure 11:

5

Variation of NOx emissions with load.

Conclusion

The present study showed a persistent increase of the brake thermal efficiency over the entire range of operation under all cases of hydrogen enrichment with a maximum increase of 15.73% at 40% load .The bsfc decreased with all cases of WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

114 Energy and Sustainability II hydrogen enrichment (with and without EGR) showing a significant decrease of 63.3% at 20% load. The volumetric efficiency suffers a decrease for all cases of hydrogen enrichment with a decrease of 37.5% at 80% load. Smoke emissions displayed a decrease for all cases of hydrogen enrichment with a decrease of 64.28% and 61.5 at 20% and 40% load respectively for non EGR cases, thereby improving the part load operation characteristics. HC emissions decreased for the entire range of operation for hydrogen enrichment with a substantial decrease of 80.0% at 20% load and a 57.6% decrease at 80% load. CO emissions reduced remarkably by 69.5% and 64.5% at 20% and 40% loading with a trend of decrease for all hydrogen enrichment operations as compared with neat diesel combustion. Hydrogen enrichment as compared to pure diesel operation displayed a steady decrease of CO2 for all ranges of operation with a decrease of 71.05% and 40.05% at 20% and 80% loading. The ultra-lean combustion characteristics of hydrogen provide the perfect environment for NOx emissions which are compounded with the inherent tendency of neat diesel fuel combustion. It thus creates a challenge to solve the paradox of simultaneously reducing NOx emissions and simultaneously reap the benefits of using hydrogen in the context of reduced pollutant emissions of typical diesel engines. In our present work EGR technique was examined in reducing NOx concentration. The NOx level decreased from 1211 ppm to 710 for hydrogen enrichment (0.15kg/hr) at 80% of the rated load. NOx levels showed a decreasing tendency for all EGR induction under these conditions of hydrogen enrichment. The emergence of hydrogen as a sustainable fuel for the future is well established by now. Its pertinence to internal combustion engines which still must be considered the best driving units of the immediate future dictates the exploration of hydrogen as a strategic sustainable energy carrier for internal combustion engines. In view of this, the present study offers a pilot study to extend the operational benefits of using hydrogen in compression ignition engines which form the mainstay of the present industrial powerhouse.

References [1] Hydrogen the Solution? http://www.nrdc.org/air/transportation/ phydrofuel.asp [2] H.S. Yi, K. Min and E.S. Kim. “The Optimised Mixture Formation for Hydrogen Fuelled Engines.” International Journal of Hydrogen Energy 25(7) pp: 685-690. 2000. [3] L.M. Das, Rohit Gulati and P.K. Gupta (June 2000). “Performance Evaluation Of A Hydrogen-Fuelled Spark Ignition Engine Using Electronically Controlled Solenoid-Actuated Injection System.” International Journal of Hydrogen Energy 25(6) pp: 569-579; 2000 [4] Das, L. M. “Hydrogen engine: research and development (R&D) programmes in Indian Institute of Technology (IIT), Delhi” International Journal of Hydrogen Energy 27(9) pp: 953-965; 2002 [5] El-Emam, S. H. and A. A. Desoky (1985). “A study on the combustion of alternative fuels in spark-ignition engines.” International Journal of Hydrogen Energy 10(7-8): 497-504. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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[6] Karim, G. A. (2003). “Hydrogen as a spark ignition engine fuel.” International Journal of Hydrogen Energy 28(5): 569-577. [7] Subba Rao, K., V. Ganesan, et al. (1983). “Modelling of combustion process in a spark ignited hydrogen engine.” International Journal of Hydrogen Energy 8(11-12): 931-933 [8] Isadore L. and Drell, F. E. B. (1958). “Survey of hydrogen combustion properties. http://naca.central.cranfield.ac.uk/reports/1958/naca-report1383.pdf [9] Wallace, J. S. and C. A. Ward (1983). “Hydrogen as a fuel.” International Journal of Hydrogen Energy 8(4): 255-268. [10] Ikegami, M., K. Miwa, et al. (1982). “A study of hydrogen fuelled compression ignition engines.” International Journal of Hydrogen Energy 7(4): 341-353. [11] Lee, C. S., K. H. Lee, et al. (2003). “Experimental and numerical study on the combustion characteristics of partially premixed charge compression ignition engine with dual fuel [small star, filled].” Fuel 82(5): 553-560. [12] Mansour, C., A. Bounif, et al. (2001). “Gas-Diesel (dual-fuel) modelling in diesel engine environment.” International Journal of Thermal Sciences 40(4): 409-424. [13] Naber, J. D. and D. L. Siebers (1998). “Hydrogen combustion under diesel engine conditions.” International Journal of Hydrogen Energy 23(5): 363371. [14] Liu, Z. and G. A. Karim (1995). “Knock characteristics of dual-fuel engines fuelled with hydrogen fuel.” International Journal of Hydrogen Energy 20(11): 919-924. [15] Das, L. M. “Hydrogen engine: research and development (R&D) programmes in Indian Institute of Technology (IIT), Delhi” International Journal of Hydrogen Energy 27(9) pp: 953-965; 2002 [16] Yang Zhenzhong, W. J., Fang Zhuoyi, Li Jinding (February 2002). “An Investigation of Optimum Control of Ignition Timing and Injection System in an In-Cylinder Injection Type Hydrogen Fuelled Engine.” International Journal of Hydrogen Energy 27(2) pp: 213-217 [17] Hari Ganesh, R., V. Subramanian, et al. (2008). “Hydrogen fuelled spark ignition engine with electronically controlled manifold injection: An experimental study.” Renewable Energy 33(6): 1324-1333. [18] Varde, K. S. and G. A. Frame (1983). “Hydrogen aspiration in a direct injection type diesel engine-its effects on smoke and other engine performance parameters.” International Journal of Hydrogen Energy 8(7): 549-555.




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Selection of renewable energy technologies in Africa: the case of efficient stoves in Malawi M. L. Barry, H. Steyn & A. C. Brent Graduate School of Technology Management, University of Pretoria, South Africa

Abstract Malawi is one of the most densely populated and least developed countries in the world. Agriculture is the main source of external revenue and 90% of the population is employed in this sector. The population, 85% of whom live in rural areas, is mostly dependent on biomass in the form of firewood for their energy needs. One of the main challenges facing Malawi is deforestation and the use of efficient stoves provides an opportunity to reduce the dependency on firewood. The purpose of the case study presented in this paper was to validate factors for the selection of renewable energy technologies in Africa which were previously identified during a Delphi study. The focus of this case study was on the efficient stove program currently being undertaken in Malawi. Questionnaires were developed to structure discussions and interviews were conducted in Malawi with individuals from the Malawian Ministry of Energy, producers of efficient stoves and households that use efficient stove installations. Secondary data were also collected in the form of different reports on the project. The primary data obtained from the interviews and the secondary data in the reports were analyzed by comparing the information with the factors previously defined during the Delphi study. This paper discusses the results, which confirm that most of the factors identified during the Delphi study were indeed seen as important for project success during the selection of efficient stove technology in Malawi. Keywords: technology selection for developing countries, renewable energy, case study.



1

Introduction

1.1 Renewable energy in Africa Most African countries are faced with reaching maintainable levels of positive economic growth in the 21st century [1]. In order to achieve positive economic growth, industrialisation is needed and in order to industrialise, African countries need sustainable and affordable energy services even where the grid cannot reach [1]. Poverty reduction is linked to economic development and both require affordable and sustainable access to energy [2].

Figure 1:

Electricity deprivation (millions) [3].

According to the World Energy Outlook for 2004 [3], developing countries will contribute to two-thirds of the global energy demand by 2030 but on the other hand also predicts that the population without electricity in Africa will increase from 526 million in 2002 to 584 million in 2030 (see Figure 1). 1.2 Realities of Malawi The Republic of Malawi is a small country in southern Africa. It shares borders with Zambia, Tanzania and Mozambique (see Figure 2). Malawi is one of the least developed countries in the world, ranking 168 out of a total of 174 countries [4] and more than 90% of the export revenue of the country comes from agricultural products. The deforestation rate in Malawi is 2.8% per year and is the highest in Africa which is contributed to by the fact that 95% of Malawi’s primary energy supply and 90% of total energy is from biomass, mainly in the form of firewood and charcoal [4]. Other energy sources used in Malawi include electricity (mainly from hydro) petroleum products, coal and other renewable energy sources but these account for only 7% of the total supply with only 6% of the population of Malawi having access to electricity [4].



Figure 2:

119

Map of Malawi [5]. Literature survey Focus group

Delphi study

Case studies

Figure 3:

2

Overall research methodology.

Research methodology

2.1 The broader research programme The research described in this paper is the result of a larger study which involved a focus group; Delphi study and case study research (see Figure 3). Three countries in Africa were selected for the purpose of the case study research. This paper only reports on the case study for Malawi as indicated by the text in black in Figure 4. Yin [6] cites three general strategies that can be followed for case studies namely: use of theoretical propositions; generation of rival explanations and development of a case description. For the purpose of the case study reported in this paper, the theoretical propositions approach was followed. The theoretical proposition is that the factors identified during the Delphi study are important for the selection of renewable energy technologies in Africa. The factors identified as important during the Delphi study [7] are shown in Figure 5. These are the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

120 Energy and Sustainability II factors that were rated feasible, highly desirable and highly important in the Delphi study. The case study design, data collection and data analysis is discussed in detail in the paragraphs that follow. INPUT from Delphi study Case studies Design

Malawi

Tanzania

Rwanda

Data collection

Data collection

Data collection

Data analysis

Data analysis

Data analysis

Final Analysis and Reporting

OUTPUT Final factors

Figure 4:

Process followed of case studies.

Achievability by performing organisation Project management Technological capability Financial capacity

Site selection

Suitable sites for pilot studies Local champion Adoption by community Access to suitable sites can be secured

Figure 5:

Economic

Contribution to economic development Availability of finance

Technology

Ease of maintenance and support Ease of transfer of knowledge and skills

Factors identified in various categories during the Delphi study [7].



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2.2 Case study design The case study research methodology is a research strategy appropriate to test contemporary phenomenon in real-life scenarios and is especially helpful when the boundaries between the phenomenon and scenario are not clearly defined [6]. George and Bennett [8] propose the following six theory building research objectives for case studies namely: i) Theoretical/ configurative idiographic case studies. ii) Disciplined configurative case studies. iii) Heuristic case studies. iv) Theory testing case studies. v) Plausibility probes. vi) Building block studies. The case study research discussed in this paper is of a theory testing nature. Factors have been identified using the Delphi method and the purpose of the proposed case studies is to test these factors in a real-life environment. The research design process advocated by George and Bennet [8] and shown in Figure 6 was followed. The output of the process was the selection of the case study and two questionnaires. In order to gather the data for the case study, interviews were required with both the implementing organizations and the users. Implementing organizations and users have different levels of interaction with the project and for this reason a separate questionnaire was developed for each. The questionnaire for the implementing organizations is called the technical questionnaire and the one for domestic households is called the user questionnaire. Both of the questionnaires start out with demographic questions. Each factor identified during the Delphi study as important for the selection of renewable energy technology in Africa is then explored. Finally the interviewee is asked what other factors, which were not yet discussed, are important.

Data requirements and general questions

Problem specification and research objectives

Variance and variable description

Research strategy

Case selection

Figure 6:

Steps in case study design [8].


122 Energy and Sustainability II The technical questionnaire was piloted using a Zimbabwe biogas implementation project. The questionnaire was updated during the pilot phase to improve ease of use and comprehension. 2.3 Data collection The Malawi Department of Energy together with Programme for Biomass Energy Conservation (ProBEC) have several efficient energy intervention programmes under implementation. For the purposes of this paper however, the focus will be on the implementation of efficient stoves. Table 1: No i)

ii)

iii) iv)

v)

Document title Promotion of alternative energy sources project (PAESP) [16] Houses Baseline situation for Limbulit, Landerdello and Esparanza Tea Estates in Mulanje district for biomass energy conservation technologies [17] Assessment of durability of portable clay stoves [18] Impact assessment at local level: experiences from Malawi-Mulanje district [19] Impact assessment of Chitetezo Mbaula improved household firewood stove in rural Malawi [20]

Summary of secondary data. Issue date November 2006

Organization(s) Department of energy affairs

Author(s)

April 2007

SADC, ProBEC, GTZ

Vincent Gondwe

November 2006

ProBEC

Kondwani Nyengo

December 2004

ProBEC, GTZ

Verena Brinkmann

March - July 2008

GTZ

Britta Malinski

Data was collected in Malawi from 26 to 28 September 2008. In terms of implementing organisations, the acting director of the department of Energy Affairs [9] and personnel of ProBEC were interviewed [10, 11]. The group estate manager was interviewed at the Minimini tea estate in the Mulanje district regarding the fixed efficient stoves, a group of women who produce efficient stoves was interviewed on the Lujeri tea estate [13], a stove user was interviewed on the Glenorchy estate [14] and a newly trained stove producer was interviewed in the Chigwirizano township [15]. All interviews were captured with a digital WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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recorder and notes on each interview were made by two researchers. Several documents were given to the researchers to use as secondary data. A summary of these documents is shown in Table 1. 2.4 Data analysis Yin [3] advocates five methods for case study data analysis namely: pattern matching; explanation building; time-series analysis; logic models and crosscase synthesis. For purposes of analysis of the data for the Malawian case study, pattern matching was utilized. The proposition that each of the factors identified during the Delphi study (see Figure 5) is important is tested by determining whether the primary and secondary data support this proposition. This is done by studying the transcriptions of the interviews and also the supporting documentation to determine whether support can be found for each proposition. A summary of the data analysis for each of the propositions is discussed below. 2.4.1 Technology factors There was an emphasis on ease of maintenance and support over the life cycle of the technology during the programme design as the aim of the programme was to keep the technology as close as possible to the existing technology that the people know [9]. This ensures that stove maintenance is simple and the same was what the people are used to for their three stone hearths [11]. The quality of the stoves, especially the first ones that were not fired, caused a problem for the programme as some users did not want to replace the stoves when they broke [16, 18–20]. Ease of transfer of knowledge and skills to relevant people in Africa was taken into account from the start as no implementation was done without training and training was seen to be successful [9–20]. In this case, there is an emphasis on the fact that training was required not only in the production and use of the stove but also in peripheral skills such as kitchen management, cooking practices, and firewood management [10, 17–19]. 2.4.2 Site selection factors A strong emphasis is placed on local champions to continue after ProBEC withdraws. To this end local capacity is being built [16], there is a direct connection with the village level leaders and empowerment of local people [10, 12, 18], and partner organisations are sought to help with implementation [11]. Adoption by community is constantly being monitored with two studies on adoption having been conducted in 2004 [19] and 2008 [20] respectively. Adoption by the community was found to be dependent on the education level of the community as well as the availability of firewood whereas non-adoption was found to be influenced by lack of access to information and lack of interest in changing current cooking methods [19]. Adopters noted the following advantages to adoption the technology: less time and effort on wood gathering, improvement in health due to less smoke, less burnt food and less accidents [19]


124 Energy and Sustainability II and [20]. Petty jealousies in the village [11] and negative attitudes of traditional doctors [18] can also hamper adoption. The following two factors identified during the Delphi study namely suitable sites ready for pilot studies and access to suitable sites can be secured did not seem to be important in the implementation of efficient stoves in Malawi. This is most probably due to the strong emphasis on local champions.

Figure 7:

Images of an efficient stove and a kiln.

2.4.3 Economic/financial factors The main emphasis in terms of economic or financial factors for the implementation of efficient stoves in Malawi is economic development. Economic development is targeted on two levels namely commercialisation of stoves [9–13, 15, 16, 18, 19], which enables producers to be economically active, and saving money on firewood [17–19]. Availability of finance did not seem to affect this project as the cost of a stove is $1 in rural areas and $3 in the cities [10], an amount which is quickly recovered by savings in firewood [19] and in the case of the fixed stoves for tea estate employees, the stoves are supplied free of charge [12]. The payment method is also flexible as credit [13] or payment is kind is allowed [19]. 2.4.4 Achievability by performing organization A large emphasis has been placed on ensuring that the organizations implementing the efficient stoves have sufficient skills for long term sustainability. In the Delphi study project management skills of the performing organization were identified as important but during this case study, it has transpired that the skills required are more general than project management and should also include business development skills such as marketing and market development [10, 11, 16, 17, 19]. It is thus proposed that that the description of this factor be changed to business management skills which would then encompass all of these skills. Financial capacity of the stove producers is not that important for this case study as clay which is available in the area is used for stove manufacture [13] and the only capital outlay is the building of the kiln [10]. Technological capacity was found to be very important in this case study as quality of the stoves is of paramount importance [19, 20]. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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2.4.5 Other factors Governmental support was found to be important in this case study as the implementation is being done with strong support from the government [9, 19]. Environmental imperatives were the main drivers for the implementation of this programme [9, 16].

3

Conclusions and recommendations

The proposition that the factors identified during the Delphi study are important when selecting renewable energy technologies has been partly confirmed by this case study as three of the factors identified in the Delphi study were seen as not important and one factor was seen as not so important. The wording of the one achievability by performing organization factor, project management skills should also be updated to read business management skills. Two additional factors have also been identified namely government support and environmental benefits. The updated list of factors as determined by this case study is shown in Figure 8. Achievability by performing organisation Business management skills Technological capability Site selection

Economic Contribution to economic development Other

Government support Environmental benefits

Technology Ease of maintenance and support

Local champion Adoption by community

Ease of transfer of knowledge and skills

Figure 8:

Updated factors.

It is recommended that these factors be compared to the factors that are identified during the analysis of the other case studies performed (see Figure 4) before a final conclusion is made on which factors are applicable when selection renewable energy technologies in Africa.

Acknowledgements The authors wish to thank the Acting director of the Department of Energy Affairs for giving up so much of his precious time as well as the ProBEC WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

126 Energy and Sustainability II personnel who transported us to all the case study sites and also were very generous with their time. We further wish to thank Maxwell Mapako for his support in conducting the case study.

References [1] UNEA 2007 Energy for sustainable development: Policy options for Africa [online]. UN-Energy/Africa. Available from: http://www.uneca.org/ eca_resources/Publications/UNEA-Publication-toCSD15.pdf [Accessed 12 March 2008]. [2] Huba, E.M and Paul, E. 2007. National Domestic Biogas Program Rwanda Baseline Study Report. MINIFRA. Kigali, Rwanda. [3] IEA. 2004. World Energy Outlook 2004. International energy agency. Available from: http://www.iea.org/textbase/nppdf/free/2004/weo2004.pdf [Accessed 19 March 2008]. [4] GTZ. 2009. ProBEC [online]. Available from: http://www.probec.org/displaysection.php?czacc=&zSelectedSectionID=se c1192750452 [Accessed 6 February 2009] [5] CIA. 2008. The World Factbook – Malawi. [online]. Available from: https://www.cia.gov/library/publications/the-world-factbook/geos/rw.html [Accessed 11 September 2008]. [6] Yin, R.K., 2003. Case Study Research: Design and Methods. . Thousand Oaks, California: SAGE Publications, 3rd edition. Applied Social Research method series. Volume 5. [7] Barry, M-L, Steyn, H.S and Brent, A. 2008. Determining the Most Important Factors for Sustainable Energy Technology Selection in Africa: Application of the Delphi Technique. IAMOT 2008 Proceedings. [8] George, A.L. and Bennett, A., 2005. Case studies and theory development in social sciences. Belfer Centre for Science and International Affairs, Harvard University, Cambridge, Massachusetts. [9] Chitenje, H, Interview, 26 September 2008, Acting director of the department of Energy Affairs, Lilongwe, Malawi. [10] Gondwe, V, Khonje, T, Interview, 27 September 2009, ProBEC personnel, Blantyre, Malawi. [11] Sukasuka, T, Interview, 27 September 2009, ProBEC personnel, From Blantyre to Lilongwe, Malawi. [12] Vutuza, P, Interview, 27 September 2008, Group estate manager Minimini tea estate, Mulanje district, Malawi. [13] Mwalimu, E, Njwambo, L, Nchenga, E, Waisen, A, Nathenwe, T, Timu, E and Nazambe, J, Interview, 27 September 2008, Stove producers, Lujeri tea estate, Mulanje district, Malawi. [14] Chioyoza, K, Interview, 27 September 2008, Stove user, Glenorchy Estate, Mulanje district, Malawi. [15] Banda, W, Interview, 28 September 2008, Stove producer, Chigwirizano township, Malawi.



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[16] Anon. 2006. Promotion of alternative energy sources project (PAESP). Department of energy affairs. [17] Gondwe, V. 2007. Houses Baseline situation for Limbulit, Landerdello and Esparanza Tea Estates in Mulanje district for biomass energy conservation technologies. SADC, ProBEC, GTZ. [18] Nyengo, K. 2006. Assessment of durability of portable clay stoves. ProBEC. [19] Brinkmann, V. 2004. Impact assessment at local level: experiences from Malawi-Mulanje district. ProBEC, GTZ. [20] Malinski, B. 2008. Impact assessment of Chitetezo Mbaula - improved household firewood stove in rural Malawi. GTZ.




129

The sustainable energy service company (ESCO) experience at DIC Corporation Y. Ishida1, M. Bannai1, K. Ishimaru2, R. Yokoyama3, S. Nakazawa1 & H. Yunoue1 1

Urban Planning and Development Systems, Hitachi, Ltd., Japan DIC Corporation, Japan 3 Waseda University Graduate School of Environment and Energy Engineering, Japan 2

Abstract An ink manufacturing company in Japan is focused on reducing its energy consumption and CO2 emissions. This paper describes energy supply systems that have been applied to actual plants in recent years. We have planned and installed new sustainable systems that combine heat and power (CHP) facilities driven by biomass fuel with large-scale wind power facilities. In our biomass boiler and steam turbine system, the boiler produces high-pressure steam to drive the extraction and condensing steam turbine. The steam turbine generates power (electricity) and heat (process steam) simultaneously. The ratio of heat and power can be controlled according to factory energy demand. We have also built a wind power plant capable of generating total power of 4 MW. An ink factory consumes all the power internally generated by the wind power plant, except that exceeding factory demand. In this way, we plan to reduce the CO2 emission rate. These facilities will be able to reduce our previous use of fossil fuels by 65%, and consequently reduce CO2 emissions by 75%. This paper also introduces the content of our project, subsequent effects and evaluation results. Keywords: energy saving, CO2 emission, energy service company, biomass, wind turbine.

1

Introduction

Effective February 2005, the Kyoto Protocol dictates that measures designed to reduce greenhouse gas emissions will be implemented over a five-year period from 2008 to 2012. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090121

130 Energy and Sustainability II Since Japanese manufacturing industries have already devoted considerable efforts to practicing energy-saving measures designed to curtail their energy usage, an approach based on a new perspective is being sought to speed up the pace of energy savings. Toward achieving the goal of drastically reducing carbon dioxide (CO2) emissions, a conversion from fossil fuels to sources of carbon-free energy or those of lower CO2 emissions would prove useful in exhibiting the heightening effectiveness of such sustainable sources of energy as wind power, solar energy and biomass. This paper provides a summary insight into ongoing approaches to saving energy consumption at DIC Corporation and its Energy Service Company (ESCO) business through sustainable sources of energy.

2

Efforts made to date at the DIC Kashima Plant

DIC is a fine chemicals manufacturer extensively involved in four sectors of business including printing materials, based on printing inks and organic pigment inks. The manufacturer has publicly committed itself to a management policy of environmental preservation and operational safety in the form of a Responsible Care (RC) program, a voluntary management activity that implements measures related to the environment, safety and health in pursuit of further reducing environmental pollution, minimizing environmental impact and saving energy. With organic inks, base inks and other inks as its principal line of products, the Kashima Plant is the largest energy consumer among all the plants of DIC Corporation, consuming about 20,000 kL of energy a year in crude equivalents. The environmentally-conscious, energy-saving activities undertaken at the Kashima Plant to date include installing woodchip boilers fueled by waste materials in 1985 and setting up a gas turbine co-generation system in 1997, thereby enabling the plant to achieve about a 40% savings on its electric contract demand over a five-year period from 2001 to 2005, and cutting its annual energy operating cost by about 120 million yen [1].

3

Introduction of ESCO for the purpose of reconstructing energy supply systems

The Kashima Plant has explored various ways to achieve further cuts in energy usage and a drastic reduction in CO2 emissions. It has therefore decided to install a combined heat and power (CHP) system and wind turbine generators (run by the Hitachi Group as an ESCO operator) in an effort to proceed further with an eco-friendly energy reconstruction scheme. Installing such systems entails such a huge amount of investment that it will be implemented on an ESCO contract basis. Leveraging the ESCO business offers the following benefits: (1) Assuring a constant rate of energy savings at all times; WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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(2) Eliminating the need for capital investment on DIC’s part, with the ESCO operator providing the funding necessary to finance facility procurement; and (3) Off-balance sheet treatment of energy-saving facilities. Still another benefit is utilizing the operational experience accumulated by Kashima Plant operators for more than 20 years to operate and maintain biomass-fueled boilers.

4

Overview of the sustainable energy ESCO business

4.1 Overview of the ESCO business Table 1 summarizes the ESCO business under discussion [2]. Because the contract concluded between DIC and an ESCO operator is signed on a shared-saving ESCO basis, all facilities needed to achieve energy savings are procured and owned by the ESCO operator. The ESCO operator also operates and maintains these facilities, and assumes responsibility for the successful functionality of all equipment during the contract period. DIC, on the other hand, assumes responsibility for procuring biomass fuels. Since all sets of facilities are scheduled to be commissioned into service in April 2009, the ESCO contract package will be started from now on. Table 1:

Overview of ESCO business.

1. Contract method

Shared savings (investment costs borne by the ESCO operator)

2. Contract period

15 years

3. Installed facilities

(a) Woody biomass-fueled boiler: 30 t/h x 1 set (b) Extraction-condensing turbine generator: 4,000 kW x 1 set (c) Auxiliary boilers (for backup): 5.5 t/h x 6 sets, 2 t/h x 1 set (d) Wind turbine generator: 2,300 kW x 2 sets

4. Facility and contract startup times

(a) Biomass boiler and turbine generator facility: Commissioned into service in April 2008 (b) Wind turbine generator facility: To be commissioned into service in April 2009 (scheduled) (c) ESCO contract: At the beginning of 1st April 2009 (scheduled)

Figure 1 shows a general flowsheet of the ESCO facilities. The ESCO facilities are organized into the following two systems: (1) Facility which generates steam and electricity by biomass, in which a biomass fuel is combusted at high temperature to generate steam energy in a boiler, from which electricity is recovered in a turbine. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

132 Energy and Sustainability II (2) Wind turbine generator facility that recovers wind energy as electricity. Any lacking portion of energy supplied from these facilities is met by purchasing electricity from a power company or producing steam energy by running an auxiliary boilers. These ESCO facilities offer such significant energy-saving effects that Hitachi and DIC have been granted jointly the following two types of subsidies for operators: (1) Biomass generator facility: Energy Use Rationalization Subsidy (New Energy and Industrial Technology Development Organization) (2) Wind turbine generator facility: Supportive Measures applicable to the Promotion of ESCO Projects (Agency for Natural Resources and Energy)

Abbreviation CGS: Co-generation system

Figure 1:

General flowsheet of ESCO facilities.

Figure 2 shows the expected energy consumption rate, CO2 emission rate, and their reductions for a one-year period. Plans call for annual energy usage at the Kashima Plant to be cut from its year 2006 level of 20,000 kL by 11,220 kL(to 8,780 kL), and CO2 emissions from 39,300 tons by 30,500 tons (to 8,800 tons). 4.2 Woody biomass generator facility The plant requires large volumes of electricity and steam to operate its production equipments. These energy demands fluctuate widely on a seasonal, daily and hourly basis. The required steam pressure used at the plant is at a medium pressure (of 1.1 MPa (G)). This value must be maintained at all times. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 2:

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Expected energy consumption rate, CO2 emission rate, and their reductions (compared between existing and new ESCO facilities).

To enhance the efficiency with which energy is recovered from biomass fuels, the following design enhancements have been factored into the steam usage system: (1) Higher-enthalpy steam recovered from waste heat Steam requirements for the biomass-fueled boilers have been enhanced to a higher pressure (of 6.08 MPa (G)) and higher temperature (of 683 K) to increase the amount of power recovered by the steam turbine. Steam of higher enthalpy is able to efficiently produce heat and electricity. (2) Combined heat and power (CHP) generation by a steam turbine generator facility Electricity is recovered by a back-pressure turbine to enable the effective utilization of energy from high to medium pressures. Should the steam demand be lower than the amount of steam generated from the boiler, excess steam is generated. In such a case, a condensing steam turbine is used to recover electricity from excess steam energy as it generated. An extraction-condensing turbine generator facility is planned in order to meet both requirements. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

134 Energy and Sustainability II This system feeds steam to meet the heating demand, with any excess proportion of steam being dedicated to generating electric power (free from CO2 emissions) in order to make effective fuel derived from biomass. Woody biomass fuels that vary in terms of heating value and shape would require enhancing the reliable supply of fuel (woodchips) to ensure stable and consistent system operation. To achieve the projected increase in the volume of woody biomass fuel procurement from 40,000 tons to 60,000 tons a year, more procurement sources are needed, and entail a specifically designed fuel supply system. Based on past experience, the following two improvement measures have been incorporated into the fuel supply system: (1) The previously manual night-time fuel charging system has been automated through the use of a hoist crane. This method significantly lessens operator workload at night. (2) The sharp-angled (75-degree), chain-driven flight conveyor previously used in the fuel charging system often impeded successful travel as it developed problems, such as a cut chain or deformed flight. As a solution, loading over a belt conveyor gradually angled at 45 degrees has been introduced to alleviate such problems.

Figure 3:

Woody biomass-fueled steam and generator facility commissioned into service at the DIC Kashima Plant.

Figure 3 shows an overview of the newly installed woody biomass-fueled steam and generator facility commissioned into service in April 2008. The facility has since been successfully running as of March 2009. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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4.3 Wind turbine generator system Conveniently located along on the Pacific coast, the Kashima area is such an appropriate location in terms of wind conditions (e.g., wind intensity, occurrence probability) that wind turbine generator facilities have already been constructed in this area, mainly for the purpose of selling the electricity generated to power companies. Power producers who sell electricity generated by wind turbines to a power company are called “independent power producers (IPPs).” In contrast, all electricity generated by the generator facility at the DIC Kashima Plant is dedicated to its internal consumption in order to enhance energy saving effects, thereby marking the first time in Japan where the total amount of electricity generated by a total 4 MW-class large wind turbine generator facility is consumed in-house. It is generally known that the higher above ground level, the better the wind conditions. This wind turbine generator facility has an elevated hub height of 64 m to generate more wind power, and also features a diameter of 71 m to produce as much as 2,300 kW of generated power. Two sets of the wind turbine generator facility capable of generating 2,300 kW are currently planned. As of February 2009, both were in the final

Figure 4:

Overview of the wind turbine generator facility (2,300 kW class x 2 sets).


136 Energy and Sustainability II stage of construction. Figure 4 shows an overview of the wind turbine generator facility nearing completion.

5

Conclusions

This paper has introduced an example of an energy restructuring ESCO business that makes positive use of sustainable forms of energy free from carbon dioxide emissions. While the market for fossil fuels has fluctuated erratically in recent years amid the perceived peaking of crude oil supply and a rapidly developing world recession, sustainable forms of energy are predicted to gain accelerating popularity in response to these situations. Sustainable forms of energy are subject to certain uncertainties, however, such as wind conditions, heating value and shape, thereby demanding handling experience essentially and expertise to put them to positive use. We would like to take advantage of the experience gained from operating these and other systems, and also promote their ongoing popularity by releasing relevant information.

References [1] Ishimaru: Energy Saving Effort in Practice at a Fine Chemicals Plant, The Institute of Electrical Engineers of Japan, General Industry Workshop Literature (February 2008) (in Japanese). [2] Yunoue et al.: Carbon Dioxide Gas Reduction Using Renewable Energy, Hitachi Hyoron, 89, 3, pp. 294-297 (March 2007) (in Japanese).



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Renewable energy from restored prairie plots in southeastern Minnesota, USA B. Borsari1, I. Onwueme2, E. Kreidermacher3 & T. Terril4 1

Department of Biology, Winona State University, Winona, MN, USA College of Natural & Applied Sciences, Missouri State University, Springfield, MO, USA 3 Pork & Plants, Altura, MN, USA 4 Winona County Soil & Water Conservation District, Lewiston, MN, USA 2

Abstract Although prairies occupied most of North America prior to European settlement, an extirpation of these habitats has inevitably occurred since the expansion of intensive, agricultural systems. In recent years, however, a renewed interest in prairie restoration has spurred increasing efforts for looking at prairies as possible sources of renewable energy. The purpose of our work was to establish a prairie community on marginal farmland with the goal of producing pellets from its biomass to be burned on site for heating greenhouses, instead of relying on corn (Zea mays) as a biomass source. Plots of grass only and plots of mixtures of forbs and grass species were planted in 2007 on a farm in southeastern Minnesota. In its second year of growth, the biomass produced was compared to what was obtained from corn stover cultivated at the farm. The biomass yield data produced from the different plots of equal hectarage were analyzed through a one-way ANOVA and Scheffe’s test to verify significant differences among the three different cropping conditions (grass, grass and forbs, corn). Our data indicated that prairie plots with mixtures of grass species can be the most productive for biomass production. This preliminary work is of value in this part of the world and should inspire more farmers in the Midwest region of the U.S. to restore prairies on marginal lands. Keywords: biofuel, forb, grass, pellet production, prairie, renewable energy, sustainability.



1

Introduction

The extirpation of American prairies allowed for an expansion of gigantic agricultural systems, dominated by corn (Zea mays) monocultures cultivated in rotation with soy beans (Glycine max) to support a highly centralized, fossil fuel dependent food system. In more recent times however, a chronic agricultural crisis has been affecting US agriculture and the current fluctuation in oil prices upon which modern agriculture depends remains a chronic threat to large scale agriculture, both economically and environmentally [1]. The recent enthusiasm for producing ethanol from corn as a new source of renewable energy has not contributed to aid U.S. agriculture, nor to alleviate the compelling need for employing renewable fuels as alternatives to petroleum, although Mielenz [2] contends that there is great potential for corn and more plant species in the emerging world of bioenergy, through an application of biotechnological approaches and genetic engineering. Thus, U.S. economy remains heavily reliant on oil and other non renewable fuels while the effort to produce ethanol from corn remains challenged in its reductionist attempt to resolve the current energy crisis. This effort has contributed to amplify visions and ideas about the obsolescence of an agricultural paradigm, which demands instead a more careful consideration to be designed to fulfil the needs of 21st century society with more sustainability in mind and a higher level of commitment to stewardship.

2

A quest for developing more sustainable energy systems

The challenge of designing renewable and more sustainable energy systems is often hampered by several barriers, including the difficulty of evolving farming systems from large annual monocultures to perennial polycultures. To this end, Fargione et al. [3] have demonstrated that a conversion of natural ecosystems into agricultural monocultures for biofuel production like ethanol releases a much larger amount of CO2 in the atmosphere than the one that can be offset by biofuel use, and thus proving a major fallacy for making this and similar approaches feasible. On the other hand, recent studies [4, 5] have suggested that perennial, rhizomatous grasses like switchgrass (Panicum virgatum) and many other species possess great attributes to be grown for energy purposes [6]. Concurrently, opportunities wait to be further explored in the agro industry of North America when herbaceous feedstock is converted into pellets to be burned for heating purposes [7]. We remain critical however that the emerging biofuel model of production be constructed with the similar approaches that led to the design of annual monocultural systems but rather, we envision agroecosystems of perennial polycultures dominating the future landscape of our bioregion. As a matter of fact, at the opposite end of this epistemological spectrum, low-input polycultures of native grasses and forbs appear to possess even higher potential for renewable biofuels production [8] and for attenuating the gas emissions during the conversion process. Inspired by this approach, we decided in 2007 to verify the initial findings of Tilman and his collaborators by establishing prairie patches on a larger scale than the typical size of a few squared meter plots. The WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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intent of this endeavour consisted in developing an on-farm biomass production system, capable of weaning itself from propane and corn combustion for heating its greenhouses [9]. The purpose of this study focused on assessing the yields of prairie biomass from mixed perennial grasses, and grasses with forbs when these were compared to corn (Zea mays) stover for the production of pellets that were going to be used on site, thus attempting to achieve a greater level of sustainability for the farm. The need for this study was spurred by the increasing necessities of developing more sustainable and renewable energy systems, especially after the disappointing outcomes of ethanol production from corn in recent years. There may be significant opportunities for farmers interested in developing markets for agropellets as the estimated 500,000 pellet burning stoves and furnaces in North America [10] provide an indication for a viable market niche from biomass in most of the USA. In addition to this, there is an increasing need to restore the ecological equilibria and services that regulate food production systems and enterprises [11] as fast anthropogenic changes upon the landscape continue to obliterate the natural attributes of the same [12]. The Canadian experience in producing pellets from prairie biomass appears to have already made major steps forward in developing an efficient pellet production system, while identifying promising plant species, best management practices and while proposing viable solutions to technical challenges for employing native perennial plants as biofuels. A similarity of environmental conditions and resources to the above mentioned Canadian studies provided us with another significant stimulus to work towards the development of a renewable energy system feasible for our bioregion.

3


In the early summer of 2007, 7.9 hectares of a 16.2 hectare farm (Pork &Plants), located in south eastern Minnesota (Winona County), were planted with mixed grasses (4.7 Ha.) and mixtures of grass with forbs species (3.2 Ha.), fig. 1. This approach stemmed from the idea of reducing reliance on corn and propane gas, which are burned on-site for heating purposes [9]. The seed was drilled into the soil with equipment already available at the farm and no other inputs were used to establish the prairie plots. Adjacent fields were planted to corn and raised with the standard inputs for corn production in Minnesota. Toward the end of the first growing season (2007) an evaluation of prairie establishment was conducted to assess prairie establishment and species richness in the grass with forbs plots, when these were compared to the grass only plots [9]. For the three cropping conditions (corn, grass polyculture, grass with forbs polyculture) we considered 1-acre parcels (0.405ha) as our units of analysis. Thus, we collected 10 biomass weights from the corn field, 8 from the grass polyculture field (these plots were harvested twice). Twenty four sample weights were collected from 9.7ha of adjacent prairie of the Minnesota Department of Natural Resources (MNDNR), which has been restored for 15 years. The decision of harvesting the DNR prairie was made in order to collect more reliable data from the grass with forbs cropping system since the one WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

140 Energy and Sustainability II planted at Pork & Plants in 2007 was flooded in the summer of 2008 and thus, mostly inaccessible. In 2008 the prairie plots were harvested and biomass yield data were collected in order to verify which one of the three systems was most productive and thus substantiate or refute experimental data obtained in Minnesota a few years ago by Tilman and his collaborators [8]. The harvest took place in mid-November 2008. Plots planted with a mixture of prairie grasses (4.7 Ha) were harvested in August in addition to the autumn harvest. The biomass was mowed and subsequently baled with a rotobaler.

Figure 1:

Aereal photograph of Pork & Plant Farm, showing the five prairie plots that were established in the early summer of 2007. The grid in the lower left corner shows the location of the farm in Winona County (south eastern Minnesota).



4

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Results and data analysis

Biomass yields (Mg/ha) were measured as the fields were harvested in the summer and autumn of 2008. A summary of quantitative and qualitative data for the three different types of fields are reported in table 1. Table 1:

Summary statistics for yields, plot type and crop species.

Plot

Mean Yield (Mg/ha)

Crop type

Number of Harvests

polyculture

Land type (agricultural vs. marginal) Marginal

Grasses and forbs Prairie grasses Corn

1.14+0.78 2.17+0.87

polyculture

Marginal

3.15+0.68

Corn

Agricultural

Summer and autumn Autumn

Autumn

A description of biomass yield (Mg/ha) for the three different cropping systems is reported in figure 2. In addition to this, the data were analysed with a one-way ANOVA in order to identify any significant difference [10].

Figure 2:

Biomass yields for each plot (0.405ha) and for the three cropping systems (grass with forbs polyculture, corn, grass polyculture).

Although the mean biomass yield was the highest in the corn stover plots (fig. 3), the analysis of the variance (ANOVA) indicated that the type of vegetation composition (monoculture versus polyculture) had a significant effect on biomass yield, F (2, 39) = 149, p < 0.01. Furthermore, a post hoc test (Scheffe’s test) was also employed to identify differences among pairs of bioenergy cropping systems [13, 14]. This analysis WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

142 Energy and Sustainability II did not indicate any significant difference between the biomass yields of prairie grasses versus those of grasses and forbs, nor between those of prairie grasses with forbs and those from the corn stover crop. However, the data provided sufficient evidence to suggest that there was a difference between the grass mixture plots versus the corn fields. Our findings did not support entirely the data of Tilman and his collaborators [8]. However, these preliminary results indicate that there is a realistic match with those data (fig. 3) and that these will emerge with greater emphasis as more yield measurements will be taken in future growing seasons.

Figure 3:

5

Mean biomass yields for the three cultivation conditions (grass with forbs polyculture, corn, grass polyculture) and standard errors.

Discussion

The mean biomass yield from corn stover was higher than yields obtained from 0.405ha plots where mixed perennial grasses and grasses with forbs were grown. For this reason the skepticism for producing biofuels from low-input highdiversity (LIHD) grassland biomass remains consistent and in favour of corn cultivation rather than perennial polycultures. However, it must be pointed out that corn cultivation requires several off-farm inputs such as: 148 kg/ha of nitrogen, 23 kg/ha of phosphorus, 50 kg/ha of potassium on a yearly basis [15], in addition to water for irrigation and the inevitable loss of topsoil due to erosion and leaching of nutrients into underground aquifer and other water reservoirs [11]. In addition to this, corn must be grown on fertile soils whereas prairie plant communities can be productive on marginal land and be successful without the inputs necessary to grow corn and other annual agronomic crops. Thus, the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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lower the inputs and fertility conditions, the better the relative performance of the prairie grasses compared to corn. Finally, our experiment yielded data from one growing season only since establishment of native vegetation plots at the farm. An unusually rainy summer in 2008 affected harvesting operations and did not allow the first of the two planned harvests. Concurrently, a variety of grass species have been identified as possible crops for pellet production [4, 6, 7, 16, 17] and are studied to be genetically modified so that they may acquire the desirable traits to be grown on a large scale and to yield pellets of superior quality, that burn completely and leave minimum ash residue in the burner, after combustion [7, 10]. A long-term field study by Varvel et al [16] to compare the potential for ethanol production between corn (Zea mays) and switchgrass (Panicum virgatum) indicated that the potential of switchgrass was superior to the annual grass (corn) and did not require the costly inputs normally used to achieve successful yields. However, the challenge of cultivating native, perennial species consists in utilizing marginal soils and minimum inputs in order to achieve a positive carbon balance between productivity and crop growth. Prairie restoration requires normally a three to five year time frame for the plant community to become sufficiently established and diverse in its floral composition. At Pork & Plants we were in the second year since the restoration effort began in 2007 and thus, despite our ability to substantiate only partially the experimental outcomes obtained by Tilman and co-workers in 2006, we remain convinced that similar results will be achieved as the perennial polycultures at Pork & Plants will enter their fourth, or fifth year since restoration commenced. Ultimately, we remain optimistic that harvests in future years will favour the high diversity plots as supported by the literature. 5.1 Conclusion and implications for future research Wes Jackson envisions a new agricultural paradigm (Natural Systems Agriculture) that relies more and more on perennial species and on a model of food production that mimics the ecological processes and services of the prairie; he foresees this knowledge to become the framework for a 50-year Farm Bill in the U.S. [1]. The compelling need of conserving biodiversity and a more sustainable employment of resources demands an inevitable reconciliation between agriculture and resource use [18]. The prospects of a flourishing agropellet industry in the near future appear to be feasible for large agricultural regions of Canada and the Midwestern region of the U.S. [7]. However, several technical aspects remain to be resolved as prairie biomass contains a high amount of alkali and thus leaves a higher ash residue after combustion than the one left by other types of biomass. Although delaying harvest to late autumn or to the following spring seem to reduce the amount of unwanted elements (as these are translocated into the underground root system), more technical and management issues need to be resolved [2, 7]. A minimization of biomass loss during baling is of great importance also to possible pellet producers, in addition to a development of local market niches. It would be paradoxical to develop such a new agroindustry upon the similar tenets that rule the commercialization of present agricultural commodities, as a majority of the environmental benefits WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

144 Energy and Sustainability II of this enterprise would evaporate inevitably, because of transportation costs. Rather, we envision the feasibility of an agro-pellet production enterprise with prairie biomass for North American territories where a restoration of farmland to prairie is achievable with success, reduced off-farm inputs, and major environmental benefits for the agrarian landscape. This approach is also in tune with present conservation needs of the agricultural environment to limit soil erosion as a loss of topsoil continues to affect the sustainability of agriculture [19] even when the best agronomic practices are employed [20]. Therefore, a cultivation of perennial polycultures is to be encouraged instead of researching the benefits of annual, non-perennial, non-native species like Miscanthus [17] and others, regardless of their potential as bioenergy crops. The next 50 years of land management in the U.S. will require the greatest wisdom to achieve sustainability and to ensure that future generations may continue to enjoy a comparable quality of life and prosperity with a clearer understanding about the finiteness of our natural resource base [1]. To this end, we support the vision of prairie farming to be embraced by farmers in Minnesota and in several other states of the of the U.S. Midwest region.

Acknowledgements We are grateful to the Department of Natural Resources (DNR) of Minnesota for granting access to its land and for allowing us to harvest biomass from its prairie. Daryl Buck of the Soil and Water Conservation Service of Winona County, Minnesota was generous in donating seed and technical service for prairie establishment at Pork & Plants.

References [1] Jackson, W., The Prairie Meets the Farm: The Next 50 Years on the American Land-Perennializing Policy and the Landscape. Proc. of the 21st North Am. Pr. Conf., eds. B. Borsari, N. Mundahl, L. Reuter, E. Peters & P. Cochran, Winona State University: Winona, MN (in press). [2] Mielenz, J.R., Bioenergy for ethanol and beyond. Current Opinion in Biotechnology, 17(3), pp. 303-304, 2006. [3] Fargione, J., Hill, J., Tilman, D., Polasky, S. & Hawthorne, P., Land Clearing and Biofuel Carbon Debt. Science, 319(5867), pp. 1235-1238, 2008. [4] Lewandowski, I., Scurlock, J.M.O., Lindvall, E. & Christou, M., The development and current status of perennial rhizomatous grasses as energy crops in the US and Europe. Biomass and Bioenergy, 25(4), pp. 335-361, 2003. [5] McLaughlin, S.B. & Walsh, M.E., Evaluating environmental consequences of producing herbaceous crops for bioenergy. Biomass and Bioenergy, 14(4), pp. 317-324, 1998.



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[6] Schmer, M.R., Vogel, K.P., Mitchell, R.B., Moser, L.E., Eskridge, K.M. & Perrin, R.K., Establishment Stand Thresholds for Switchgrass Grown as a Bioenergy Crop. Crop Science, 46, pp. 157-161, 2006. [7] Samson, R., Mani, S., Boddery, R., Sokhansanj, S., Quesada, D., Urquiaga, S., Reis, V. & Ho Lem, C., The potential of C4 perennial grasses for developing a global BIO-HEAT industry. Critical Review in Plant Science, 24, pp. 461-495, 2005. [8] Tilman, D., Hill, J. & Lehman, C., Carbon-Negative Biofuels from LowInput High-Diversity Grassland Biomass. Science, 314(5805), pp. 15981600, 2006. [9] Borsari, B. & Onwueme, I., A New Lease on Life for Marginal Farmland: Convergence of Prairie Restoration with Biofuel Production. Proc. of the 16th IFOAM Organic World Congress, eds. D. Neuhoff, N. Halberg, T. Alföldi, W. Lockeretz, A. Thommen, I.A. Rasmussen, J. Hermansen, M. Vaarst, L. Lueck, F. Caporali, H.H. Jensen, P. Migliorini & H. Willer, ISOFAR: Bonn, vol.2, pp. 608-611, 2008. [10] PFI (Pellet Fuels Institute), http://www.pelletheat.org [11] Brown, L.R., Plan B 3.0-Mobilizing to Save Civilization. W.W.Norton & Company Inc., New York, NY, 2008. [12] Tilman, D. & Lehman, C., Human-caused environmental change: Impacts on plant diversity and evolution. PNAS, 98(10), pp. 5433-5440, 2001. [13] Huck, S.W. & Cormier, W.H., Reading Statistics and Research, HarperCollins Publishers Inc.: New York, 1996. [14] Patten, M.L., Understanding Research Methods. An Overview of the Essentials, Pyrczak Publishing: Glendale, CA, 2002. [15] Tilman, D., Hill, J. & Lehman, C., Response to Comment on “CarbonNegative Biofuels from Low-Input High Diversity Grassland Biomass. Science, 316(5831), pp.1567, 2007. [16] Varvel, G.E., Vogel, K.P., Mitchell, R.B., Follett, R.F. & Kimble, J.M., Comparison of corn and switchgrass on marginal soils for bioenergy. Biomassand bioenergy, 32(1), pp. 18-21, 2008. [17] Heaton, E.A., Dohleman, F.G. & Long, S.P., Meeting US biofuel goals with less land: the potential of Miscanthus. Global Change Biology, 14(9), pp. 2000-2014, 2008. [18] Ceroni, M., Liu, S. & Costanza, R., Ecological and Economic Roles of Biodiversity in Agroecosystems, pp. 446-472 In: Managing Biodiversity in Agricultural Ecosystems, eds. Jarvis, D.I., Padoch, C. & Cooper, H.D., Columbia University Press, 2007. [19] Kort, J., Collins, M. & Ditsch, D., A review of soil erosion potential associated with biomass crops. Biomass and Bioenergy, 14(4), pp. 351359, 1998. [20] Zentner, R.P., Lafond, G.P., Derksen, D.A., Nagy, C.N., Wall, D.D. & May, W.E., Effects of tillage method and crop rotation on non-renewable energy use efficiency for a thin Black Chernozem in the Canadian Prairies. Soil and Tillage Research, 77(2), pp. 125-136, 2004.




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Iron catalysts supported on carbon nanotubes for Fischer–Tropsch synthesis: effect of pore size R. M. Malek Abbaslou, J. Soltan, S. Sigurdson & A. K. Dalai Catalysis & Chemical Reaction Engineering Laboratories, Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Canada

Abstract In this report, the effects of pore diameter and structure of iron catalysts supported on carbon nanotubes (CNTs) on Fischer–Tropsch (FT) reaction rates and product selectivities are presented. Two types of CNTs with different average pore sizes (12 and 63 nm) were prepared. The CNTs were chosen in a way to have comparable surface areas so as to eliminate the effects of different surface areas. The iron catalysts (the narrow pore catalyst denoted Fe/np-CNT and wide pore catalyst denoted Fe/wp-CNT) were prepared using incipient wetness impregnation method and characterized by ICP, BET, XRD, TPR, SEM and TEM analyses. The TEM and XRD analysis showed that the iron oxide particles on the Fe/wp-CNT (17 nm) were larger than those on Fe/np-CNT sample (11 nm). TPR analyses of the catalysts showed that the degree of reduction of the Fe/np-CNT catalyst was 17% higher compared to that of the Fe/wp-CNT catalyst. For the FT reactions, it was found that the activity of the np-CNT catalyst (%CO conversion of 31) was much higher than that of the wpCNT catalyst (%CO conversion of 11). Also, the Fe/wp-CNT was more selective toward lighter hydrocarbons with a methane selectivity of 41% whereas, the methane selectivity of the np-CNT catalyst was 14%. It can be concluded that the deposition of the metal particles on the CNT with narrow pore size (in the range of larger than 10 nm) results in more active and selective catalyst due to higher degree of reduction and higher metal dispersion. Keywords: Fischer–Tropsch synthesis, iron, carbon nanotubes, pore size.



1

Introduction

Fischer–Tropsch (FT) synthesis is a potentially attractive technology for production of clean liquid fuels from syngas. The syngas can be supplied through gasification of coal or biomass and reforming of natural gas. FT synthesis proceeds on metal (Fe, Co and Ru) supported catalysts. The efficiency of the FT synthesis can be enhanced by design of new catalysts with higher syngas conversion, higher C5+ yield, and lower methane selectivity [1–2]. In the FT processes, the catalyst activity and selectivity are influenced by nature and structure of the support, nature of the active metal, catalyst dispersion, metal loading, and catalyst preparation method [3]. Most studies on FT catalysts have been carried out with the metals supported on silica, alumina or titania and their structural properties such as pore size have been studied [4]. Recently, carbon nanotubes (CNTs) as a new support have been investigated for FT reactions [5–11]. Carbon nanotubes with unique properties such as uniform pore size distribution, meso and macro pore structure, inert surface properties, and resistance to acid and base environment can play an important role in a large number of catalytic reactions [11]. CNTs are different than the other supports in that they have graphite layers with a tubular morphology [7–8]. Also, CNT structure such as inner and outer diameter and length of nanotubes can be manipulated using different synthesis processes and operating conditions. Literature review including our previous work on the application of CNTs as support for catalytic reactions especially FT reactions have shown that CNTs can be considered an alternative support which can improve performance of metal catalyst compared to the other supports [4–9,12]. However, the effects of pore size and diameter of carbon nanotubes on the catalytic performance of FT catalysts have not comprehensively been studied. In general, pore size of supported catalysts can influence particle size distribution, dispersion, extent of reduction, and mass transfer rates [4]. In this report, the effects of pore diameter of the support CNTs on FT reaction rates and selectivities over iron catalysts are presented. Two types of CNTs with different average pore sizes (10 and 63 nm) were prepared in a way to have comparable surface areas so as to remove the effects of different surface areas.

2

Experimental

In order to analysis solely the effects of inner pore of CNTs on the performance of the iron catalyst for the FT reactions, two CNT samples with considerable difference in the pore diameters were used. The narrow pore CNT sample (denoted as np-CNT) was purchased. The wide pore CNT sample (denoted as wp-CNT) was synthesized using anodic aluminum oxide (AAO) films and chemical vapor deposition method. The details of synthesis procedure were given in our previous paper [12]. Both CNT samples were treated in nitric acid (60 wt%) at 110oC for 16 hours. The catalysts were prepared according to the incipient wetness impregnation WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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method. For the preparation of the catalyst with iron particles inside the nanotube pores with 20 wt% Fe, an appropriate amount of Fe(NO3)3·9H2O was dissolved in deionised water. The volume of the salt solution was equal to total pore volume of the CNT samples. In this case, the metal solution filled the inner pores of the CNTs due to capillary effects [5]. After drying at 120oC and calcination at 400oC for 3 hours, the catalysts were characterized by nitrogen adsorption, ICP, TPR, XRD, SEM and TEM. The surface area, pore volume of the CNTs and catalysts were measured by an ASAP-2000 Micromeritics system. The samples were degassed at 200oC for 2 h under 50 mTorr vacuum and their BET surface area and pore volume were determined. XRD analysis was performed using a Philips PW1840 X-ray diffractometer with monochromatized Cu/Kα radiation. The crystallite diameter was estimated using Debye–Scherrer equation The reduction behavior of the catalyst precursors was studied by temperature programmed reduction (TPR) using a CHEMBET-3000 equipped with a thermal conductivity detector. 0.1 g of the catalyst was placed in U-shaped quartz tube. A 5% hydrogen/nitrogen mixture was introduced (flow rate = 36 cm3 (STP)/min) and the furnace was ramped from room temperature to 1173K at 10 K/min. Morphology of the samples was studied by transmission electron microscopy (TEM). Sample specimens for TEM studies were prepared by ultrasonic dispersion of the catalysts in ethanol, and the suspensions were dropped onto a copper grid. TEM investigations were carried out using a Hitachi H-7500 (120kV). Several TEM micrographs were recorded for each sample and analyzed to determine the particle size distribution. A Phillips SEM-505 scanning electron microscope operating at 300 kV in SE display mode was also used. For characterization prior to analysis, all the samples were gold coated in a sputter coating unit (Edwards Vacuum Components Ltd., Sussex, England). The Fischer–Tropsch synthesis was performed in a fixed-bed micro reactor. Prior to CO hydrogenation, in-situ reduction was conducted according to the following procedure. The catalyst (0.5 g) was placed in the reactor and diluted with 5 g silicon carbide. Then pure hydrogen flow was established at a rate of 45 ml/min. The reactor temperature was increased from room temperature to 380oC at a rate of 1oC/min and maintained at this activation condition for 14 h. After the activation period, the reactor temperature was decreased to 275oC under flowing hydrogen. Hydrogen and syngas flow rates were controlled by Brooks 5850 mass flow controllers. Argon was used as internal standard gas in the reactor feed. The mixed gases (30%CO, 60%H2, 10% Ar) entered the top of the fixed bed reactor. The temperature of the reactor was controlled via a PID temperature controller. Synthesis gas with a space velocity of 7200 cm3(STP)/(h g) was introduced and the reactor pressure was increased to 2 MPa. Products were continuously removed from the vapor and passed through two traps. The pressure of uncondensed vapor stream was reduced to atmospheric pressure. The composition of the outlet gas stream was determined using an on-line GC-2014 Shimadzu gas chromatograph. The contents of traps were removed every 24 h, the hydrocarbon and water fractions were separated, and then analyzed by Varian WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

150 Energy and Sustainability II 3400 GC. Catalytic activity and product selectivity were calculated after a time on stream of 50 hours.

3 Results and discussions 3.1 Supports and catalysts characterizations SEM images (Figure 1a and 1b) of the acid-treated and purified CNTs samples (np-CNT and wp-CNT) revealed that the samples contained solely CNTs and no other impurities such as amorphous carbon was observed. Figure 1a shows that the np-CNT sample contained woven nanotubes with high aspect ratios. For wpCNT sample, SEM image (Figure 1b) exhibited that nanotubes were well-aligned and the caps of nanotubes were open. TEM images of the acid-treated CNT samples are given in Figure 2a and 2b. Figure 2a shows that the np-CNT sample had uniform nanotubes diameter and their inner and outer diameters varied between 8-12 nm and 20-25 nm, respectively. TEM analysis also revealed that a vast majority (more than 70%) of the np-CNT sample possessed open caps nanotubes (Fig 2a). As seen in Figure 2b, the wp-CNT sample comprised of straight nanotubes with diameter of 50-70 nm along with several Y junctions with inner diameters of 30-50 nm. The thickness of the walls varied in 7-9 nm range.

a

Figure 1:

b

SEM micrograph of the CNT supports, a) np-CNT, b) wp-CNT.

The particle size distribution and position of the iron particles inside or outside of the CNTs were studied using several TEM images from each of the catalyst samples. Figure 3a and 3b show a representative TEM image of the iron catalyst supported on narrow pore CNT sample (Fe/np-CNT) and iron catalyst supported on wide pore CNT sample (Fe/wp-CNT). Dark spots represent the iron oxides which are attached inside or outside of the nanotubes. For both catalysts, a vast majority of the iron particles (80%) were distributed in the inner pores of CNTs (Fig. 3a and 3b). This can be attributed to carbon nanotubes’ tubular structure which can induce capillary forces during the impregnation process. In WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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the case of Fe/np-CNT, the size of iron oxide particles varied from 4 to 14 nm with most abundant particles with a diameter of 8-10 nm. Whereas in the case of Fe/wp-CNT catalyst, particle size covers a wide range varying form 5 to 65 nm with the most abundant particle size of 14-21 nm. The data suggest that inner pore of nanotubes physically restricted the particle size growth unless the particle was located on the exterior surface of the nanotubes.

a

b

Figure 2:

a

Figure 3:

TEM images of CNT supports a) np-CNT b) wp-CNT.

b

TEM images of the iron catalysts a) Fe/np-CNT b) Fe/wp-CNT. Dark spots represent the iron oxide particles inside and outside of the nanotubes.

Table 1 shows the metal content for the Fe/np-CNT and Fe/wp-CNT catalysts. ICP analyses of the catalysts revealed that the metal contents of the catalysts were fairly similar and close (±0.4%) to the target metal content of 20 wt% Fe. Table 1 also shows the results of surface area measurements of both CNT supports and corresponding iron catalyst. As discussed earlier, both CNT samples had a comparable surface areas (212 m2/g for np-CNT and 218 m2/g for WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

152 Energy and Sustainability II wp-CNT). As a result, both Fe/np-CNT and Fe/wp-CNT catalysts held similar metal loading per surface area of the supports. According to the N2 adsorption analysis, the loading of 20% Fe decreased the surface area of Fe/np-CNT and Fe/np-CNT catalysts to 155 and 186 m2/g, respectively. These data show that the BET surface area of the catalysts were lower than that of the supports indicating pore blockage due to iron loading on the supports. However, comparison between BET surface area of the Fe/np-CNT and Fe/wp-CNT catalysts showed that the extent of pore blockage in the Fe/np-CNT was higher than that in Fe/wpCNT.

Figure 4:

XRD spectra of Fe/np-CNT and Fe/wp-CNT. (1: Fe2O3, 2:Fe3O4, 3: CNT).

Table 1:

Metal content and surface properties of CNT samples, Fe/np-CNT and Fe/wp-CNT catalysts.

Catalyst Name np-CNT-support wp-CNT-support np-Fe/CNT wp-Fe/CNT

Metal Content%1 0 0 19.6 20.1

BET Surface Area (m2/g) 212 218 155 186

Total Pore Volume (cm3/g) 0.58 0.55 0.44 0.48

1-Determined by ICP analysis.

Figure 4 shows XRD patterns of the calcined Fe/np-CNT and Fe/np-CNT catalysts. For both catalysts, the peaks at about 26 and 44o correspond to the graphite layers of multi-walled nanotubes. Surprisingly, the Fe/np-CNT and Fe/wp-CNT catalyst did not show similar XRD patterns. According to the XRD spectra, the diffraction peaks for Fe/np-CNT catalyst matched very well with the standard Hematite (Fe2O3) phase. Whereas, for Fe/wp-CNT catalysts, the peaks at 2θ of 30 and 35.7o exhibited the standard Magnetite (Fe3O4) phase.



Figure 5:

153

H2-TPR profiles for Fe/np-CNT and Fe/np-CNT catalysts.

Table 2 shows the average iron oxides particle sizes on the catalysts calculated from XRD spectrum using Debye–Scherrer equation at the most intense peak of 36o. The data verified that the iron oxide on Fe/wp-CNT (17 nm) grew larger than that of on the Fe/np-CNT catalysts (11nm). To compare the particle size calculated based on XRD with TEM analysis, the size distribution of the particles is also shown in Table 2. There is a good agreement between the data for average particle size calculated based on XRD and the most abundant sizes from TEM analysis. TPR analyses were performed to evaluate the reducibility of the Fe/np-CNT and Fe/wp-CNT catalysts . TPR patterns of Fe/np-CNT and Fe/np-CNT catalysts are shown in Figure 5. Four peaks (A, B, C and D) can be observed on the TPR profile of the Fe/np-CNT catalyst. Whereas, two peaks appeared on the TPR profile of the Fe/wp-CNT catalysts. Generally, the reduction of iron oxides takes place as below [10]: Fe2O3 → Fe3O4→ FeO→ Fe In the case of Fe/np-CNT, the first peak (A) can be assigned to the reduction of Fe2O3 to Fe3O4. The second peak, B, can be assigned to the subsequent reduction of Fe3O4 to FeO. Peak C, observed at 500-700 °C, can be related to the reduction of FeO to metallic Fe. Peak D can be attributed to gasification of CNTs at a temperature higher than 600oC. For Fe/wp-CNT catalyst, since the iron oxide was in the form of Fe3O4, the first peak (A) corresponded to the reduction Table 2:

Particle sizes (iron oxide) based on XRD and TEM analysis. Catalyst

Fe/np-CNT Fe/wp-CNT

d (Fe2O3)a nm 11 17

a) Based on XRD analysis. b) Based on TEM analysis. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

d (Fe2O3)b nm 8-10 14-21

154 Energy and Sustainability II Table 3:

Reduction temperature (°C) and extent of reduction (from 25800oC) based on H2-TPR analysis.

Catalyst

Peak A

Peak B

Peak C

Peak D

Fe/np-CNT Fe/wp-CNT

401 459

438 574

667 -

747 -

Extent of reduction (25-700oC) 69 52

of Fe3O4 to FeO and the second peak, B, can be assigned to the subsequent reduction of FeO to Fe. There was a tailed peak for gasification of wp-CNT as seen in the TPR profile of the Fe/wp-CNT catalyst Table 3 shows reduction temperature for both catalysts. According to the reduction temperature, deposition of iron oxide particles inside the nanotubes with narrow pores results in a decrease in the temperature of the first TPR peak from 459 to 401oC and that of the second TPR peak from 574 to 438oC. The degree of reduction for the Fe/np-CNT and Fe/wp-CNT catalysts is also given in Table 3. The degree of reduction of the metal is the ratio of H2 consumed from ambient temperature to 700oC to the calculated amount of H2 for the complete reduction of metal oxides. According to Table 3, the degree of reduction for Fe/np-CNT (69%) was higher than that of Fe/wp-CNT (52%). This can result in partial reduction of metal sites in the case of the Fe/wp-CNT catalyst and lower FT activity. According to the literature, in the case of FT catalysts with average particle size of larger 10 nm, the particle size does not affect the extent of reduction [4]. Thus, this phenomenon may be attributed to a different interaction of iron oxide with interior surface of the Fe/np-CNT catalyst compared to that of the Fe/wp-CNT catalysts. As reported by other researchers [7, 8], the confinement of iron oxide inside in the CNT pores results in easier reduction at lower temperature. It has been postulated that the electron deficiency of the interior CNT surface is possibly responsible for this phenomenon and extent of this phenomenon decreases as inner diameter of nanotube increases.

4

Fischer–Tropsch synthesis

The performances of the Fe/np-CNT and Fe/wp-CNT catalysts for the FT synthesis were evaluated in a fixed bed reactor. All the reactions were performed under a set of similar conditions (275oC, 2MPa, H2:CO = 2). CO hydrogenation (blank runs with no iron) was performed on both acid treated CNT supports (npCNT and wp-CNT samples) under the same operating conditions as the metal loaded samples. For blank runs, the main product formed with a very low conversion (1%) was methane with almost no higher hydrocarbons. The activity and product selectivity (% CO conversion, CH4, C2-C5, C5+ and CO2) of the catalysts is given in Table 4. According to Table 4, the Fe/np-CNT catalyst showed a CO conversion of 30.7% whereas; this number for the Fe/wpCNT catalyst was only 12.2%. Also, CH4 selectivity of the Fe/np-CNT WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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(14.7 wt%) catalyst was much lower than that of the Fe/wp-CNT catalyst (41.1wt%). Accordingly, C5+ selectivity of the Fe/np-CNT (48.1 wt%) was considerably higher than that of Fe/wp-CNT (11.9 wt%). Table 4:

CO conversion and product selectivity of Fe/np-CNT and Fe/wpCNT.

Catalyst activity and product Fe/np-CNT selectivity CO% 30.7 CH4 14.7 C2-C4 37.3 C5+ 48.1 CO2 19.5 - Process conditions: 7.2 Nl/g-cat/h, 2MPa, H2/CO = 2. -All catalysts contain 20wt% Fe. -HC in wt%; CO2 in mol%.

Fe/wp-CNT 12.2 41.1 47.1 11.9 15.0

The result of FT analysis for both Fe/np-CNT and Fe/wp-CNT catalysts showed that the deposition of iron particles inside the nanotube pores with narrower pores within the range of studied pore diameters (higher than 10 nm) enhances FT activity and product selectivity of the catalyst. Several reasons can be associated with the improvement in activity and product selectivity. As discussed earlier, H2-TPR analysis revealed that the reducibility of the Fe/npCNT catalyst was remarkably better in comparison to the Fe/wp-CNT. This phenomenon can result in the formation of more catalytically active carbide species during FTS. Also, confinement of the reaction intermediates inside the pores can enhance their contact with iron catalysts, favoring the growth of longer chain hydrocarbons. As given in Table 4, CO2 selectivity of the Fe/wp-CNT was less than that of the Fe/np-CNT catalyst. This can be resulted from lower CO conversion for the Fe/wp-CNT catalyst. At a low CO conversion, the amount of the produced water was lower which provided a lower water concentration for water-gas-shift reaction during the FT reactions.

5

Conclusions

The results of this work revealed that the structure and pore diameter of CNTs as support for FT catalysts have significant influence on the catalytic performance of the catalysts. The deposition of metal particles inside the nanotube with narrow pore structure resulted in smaller metal particle sizes and better dispersion due to confinement effects inside CNT pores. Also iron catalyst supported on the narrow pore support improved the reduction behavior of the CNT catalyst most likely due to difference in electronic properties of the inner surface of the CNTs with different diameters. Higher metal dispersion and better extent of reduction resulted in more active and selective catalysts. In the case of WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

156 Energy and Sustainability II catalysts with metal particles inside the narrow pores, confinement of reaction intermediates inside the channels may also increase the contact time with active metal sites, resulting in production of heavier hydrocarbons.

References [1] Dry, M. E., Fischer–Tropsch reactions and the environment. Applied Catalysis A: General 189 pp. 185-190, 1999. [2] van der Laan, G. P. & Beenackers, A. A. C. M., Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review. Catalysis Reviews, 41(3&4), pp. 255-318, 1999. [3] Bukur, D. B., Lang, X., Mukesh, D., Zimmerman, W. H., Rosyenek, P. & LI, C., Binder/Support Effects on the Activity and Selectivity of Iron Catalysts in the Fischer–Tropsch Synthesis, Industrial Engineering Chemistry Research. 29, pp. 1588-1599, 1990. [4] Khodakov, A. Y., Griboval-Constant, A., Bechara R. & Zholobenko, V. L., Pore Size Effects in Fischer Tropsch Synthesis over Cobalt-Supported Mesoporous Silicas, Journal of Catalysis 206, pp. 230–241, 2002. [5] Malek Abbaslou, R. M., Tavasoli, A. & Dalai, A. K., Effect of pretreatment on physico-chemical properties and stability of carbon nanotubes supported iron Fischer–Tropsch catalysts, Applied Catalysis A: General 355, pp. 33–41, 2009. [6] Tavasoli A., Malek Abbaslou R. M., Trepanier M. & Dalai A. K., Fischer– Tropsch synthesis over cobalt catalyst supported on carbon nanotubes in a slurry reactor, Applied Catalysis A: General 345, pp. 134–142, 2008. [7] Chen, W., Pan, X. & Bao, X., Tuning of Redox Properties of Iron and Iron Oxides via Encapsulation within Carbon Nanotubes, Journal of American Chemical Society, 129, pp. 7421-7426, 2007. [8] Chen, W., Fan, Z,, Pan, X. & Bao, X., Effect of Confinement in Carbon Nanotubes on the Activity of Fischer–Tropsch Iron Catalyst, Journal of American Chemical Society, 130, pp. 9414-94192008 [9] Bahome, M. C., Jewell, L. L., Hildebrandt, D., Glasser, D. & Coville, N. J., Fischer–Tropsch synthesis over iron catalysts supported on carbon nanotubes, Applied Catalysis A: General 287, 60-67, 2005. [10] Ma, W., Kugler, E. L., Wright, J. & Dadyburjor, D. B., Mo-Fe Catalysts Supported on Activated Carbon for Synthesis of Liquid Fuels by the Fischer–Tropsch Process: Effect of Mo Addition on Reducibility, Activity, and Hydrocarbon Selectivity , Energy & Fuels 20, 2299-2307, 2006. [11] Serp P., Corrias M. & Kalck P., Review Carbon nanotubes and nanofibers in catalysis, Applied Catalysis A: General 253, 337-358, 2003. [12] Eswaramoorthi I., Sundaramurthy V.& Dalai A.K., Partial oxidation of methanol for hydrogen production over carbon nanotubes supported Cu-Zn catalysts, Applied Catalysis A: General 313, pp. 22-28, 2006.



157

Pyrolysis of physic nut (Jatropha curcas L.) residue under isothermal and dynamic heating processes D. Atong1, C. Pechyen2, D. Aht-Ong2,3 & V. Sricharoenchaikul4 1

National Metal and Materials Technology Center, Thailand Science Park, Thailand 2 Department of Materials Science, Faculty of Science, Chulalongkorn University, Thailand 3 National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Thailand 4 Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Thailand

Abstract Pyrolysis of physic nut residues was conducted under isothermal and dynamic heating conditions in a vertical fixed bed type reactor at final temperature of 500, 700 and 900°C under N2. The solid, liquid, and gas products were in the ranges of 26.94-29.04, 9.43-21.36, 51.70-61.54 wt% for slow pyrolysis, while those attained from rapid condition were 11.16-15.25, 15.00-23.43, and 61.3273.84 wt%, respectively. Results indicated that char decreased with increasing temperature and hold time. Char with highest fixed carbon of 85.32% with relatively low volatiles of 9.28% was obtained by pyrolysis at 900°C for 60 min. Release of volatile matter led to development of char porous structure. The maximum liquid product of 21.35% was observed at the pyrolysis temperature of 900°C for 60 min under dynamic heating and 61.54% under isothermal heating at 500°C. Decreasing hold time to 15 min caused 2 times decrease of liquid yields. The liquid product mainly consisted of several fatty acids such as oleic acid, palmitic acid and lignoleic acid in the range of 15-19%, 40-45%, and 2534%, respectively. Increase in temperature and hold time lead to greater production of hydrogen, carbon monoxide, and light hydrocarbons. Mode of heating displayed significant effect to the product distribution, LHV and H2/CO ratio. Higher LHV values were obtained at 900°C under rapid pyrolysis condition. Mole ratio of H2/CO close to unity was found in the case of pyrolysis at 900°C for both slow and rapid trials. The LHV obtained from slow processes were 7.8-15.0 MJ/Nm3 while those from rapid runs were 14.8-17.2 MJ/Nm3. Keywords: pyrolysis, physic nut residue, fixed bed. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090151


1

Introduction

Biomass as an energy source is now at the forefront of the renewable energy developments due to its renewable character and a net carbon neutral energy conversion. Biomass are abundant and can be supplied from various industries which produce organic plant materials as wastes, such as agricultural, sugar, wood processing, food industry, etc., or alternatively, they can be purposely grown for energy supply. The recovery of energy from biomass and residues has centered on biochemical and thermochemical processes. Of the later route, pyrolysis has recently received more interest. It is a thermal destruction of biomass in the absence of air/oxygen that starts at 350°C and goes up to 700°C [1,2]. Process conditions can be optimized to maximize the production of char, liquid or gas. Production of pyrolysis liquids has been investigated for use directly in fuel applications or by upgrading to refined fuels or chemical products. Char can be used as a fuel in the form of briquettes or upgraded to activated carbon. Gas has low to medium heating value and may contain sufficient energy to supply the energy requirements of a pyrolysis plant [3]. The proportion of gas, liquid and solid products depends on the pyrolysis technique used and reaction parameters. High heating rates of up to 100 K·s-1, to temperature less than 650°C with short retention time or rapid quenching, favor the formation of liquid products and minimize char and gas formation. High heating rates to temperatures higher than 650°C tend to favor the formation of gaseous products at the expense of liquids [3,4]. Slow heating processes over long periods of time lead to maximum yield of char with moderate amounts of tar by-products [5,6]. Thailand is an ideal country for abundant supply of various biomass sources. Physic nut (Jatropha curcas L.) is one of the principal sources of plant oil for biodiesel production in the country. Extraction of physic nut oil results in residue that is needed to be disposed. In general, collection and disposal of residues are becoming more difficult and expensive and may create environmental problems if not properly done. Pyrolysis could be a promising way for residue management to convent them to value added products that are easier to transport, storage, handling, and utilizing. Rapid and slow processes are both important for development of renewable energy source for the country. While rapid pyrolysis is generally suitable for large-scale industrial operations, slow pyrolysis may be easily adopted by majority of small operators in the countryside. In this study, the slow (dynamic) and rapid (isothermal) pyrolysis of physic nut waste were investigated in fixed-bed tubular reactor. Particularly, the influences of final pyrolysis temperature, retention time, and mode of heating on product yields were studied. In addition, an in-depth analysis of the properties of the solid and liquid products generated at different pyrolysis conditions was performed for a better understanding of the mechanism of physic nut waste pyrolysis and to determine its possibility of being a potential source of renewable fuel and chemical feedstock.



2

159

Experimental

2.1 Material The physic nut residues from oil-extraction process were obtained from local plant. Samples were grounded, sieved to size fraction of 0.43–0.50 mm, and dried overnight at 80°C. The average proximate and elemental analyses are show in Table 1. Weight fractions of carbon, hydrogen and nitrogen were determined by using elemental analyzer Perkin Elmer PE2400 series II. Large amount of oxygen is reported by difference, so this number is not conclusive since there may be other elements not analyzed by this method. The proximate analysis was performed following ASTM methods to determine moisture (ASTM E871), volatile matter (ASTM E872), fixed carbon (ASTM E872) and ash content (ASTM D1120). Additional chemical components of physic nut residue sample were also identified using Tappi T203 and T222 standard methods and shown in the same table, which are hemicellulose, cellulose and lignin. Bomb calorimeter (Leco model AC-350) was used to determine the higher (gross) heating value following ASTM D240. The heating value of 19.51 MJ/Kg for physic nut waste was comparable to that of palm shell (18.26 MJ/Kg), cane trash (16.80MJ/kg) and greater than some other biomass such as rice husk (14.75 (MJ/Kg), corncob (11.3 MJ/kg), bagasse (9.24 MJ/kg), or tapioca rhizome (7.45 MJ/kg) [7]. Table 1: Ultimate analysis (wt.%) Carbon 47.3 Hydrogen 8.1 Nitrogen 6.4 Oxygen* 38.2

Chemical analysis of physic nut waste. Proximate analysis (wt. %) Volatiles 51.7 Fixed carbon 39.1 Ash 7.5 Moisture 0.7

Component analysis (wt. %) Hemicellulose 20.8 Cellulose 54.6 Lignin 24.6

*By difference

2.2 Pyrolysis experiment Pyrolysis of physic nut residues was conducted under isothermal and dynamic heating conditions in a vertical fixed bed type reactor. The influences of final pyrolysis temperatures and hold time on the product yields were also studied. The experimental set up is shown in Figure 1. The system consisted of a quartz tube reactor (height = 300 mm., i.d. = 12 mm., and o.d. = 13 mm.) with a sample retainer made of quartz frit at the bottom end and a three stage condensers for the collection of water and condensable organics (tar) followed by gas-measurement devices. The reactor is heated by a tubular ceramic furnace equipped with a PID temperature control and K-type thermocouple placed at the center. In each run, approximately 10 grams of sample material was used and the system was purged with 2 L/min of N2 for 15 min to ensure inert conditions in the bed [8]. For dynamic cases, the physic nut waste was placed into the reactor prior to heating and the temperature was raised with 20°C·min-1 from ambient to final temperature of 500, 700 or 900°C. Experiments were carried out in three different hold times, namely, 15 min, 30 min and 60 min. For isothermal WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

160 Energy and Sustainability II g

exhaust

h CO CO2 H2 CH4

j a

b c d

N2 e

i f

a) Tube furnace b) Sample d) Quartz tubing e) Flow controller g) Thermocouple h) Temp. controller j) Online gas analyzer

Figure 1:

c) Retainer f) Condensers i) Bubble flowmeter

Schematic of the pyrolysis system setup.

pyrolysis trials, the reactor was preheated to a final temperature of 500, 700 or 900°C and instantaneous decomposition started as soon as waste sample was rapidly inserted into the reactor. The retention time was kept at 15 min. After each run, char left in sample retainer was carefully weighed, liquid product was collected in cold traps maintained at 0°C. Non-condensable gas was analyzed by online gas analyzer (MRU GmbH, SWG 200-1) which capable of continuous real time quantification of CO, CO2, CxHy (as CH4) and H2 by using thermal conductivity detector (TCD) and non-disperse infrared detector (NDIR). Solid and liquid yields were calculated on a dry basis from the measured weight of each fraction. Yields of identified gas were calculated based on conversion of measured mole (vol.) to mass of that particular gas species. 2.3 Characterization of products 2.3.1 Solid char analysis Major elemental components of the solid were analyzed using a CHNS/O analyzer (Perkin Elmer PE2400 series II). Fixed carbon, volatile, and ash analyses were carried out using a thermogravimetric analyzer. When the sample was heated under an inert atmosphere to 850°C, the weight loss during this step is a volatile component. The gas atmosphere is then switched to air to burn off fixed carbon, while the temperature is reduced to 800°C. Finally, any residue left after the system is cooled to room temperature is considered as ash. The surface property of solid char was examined using an accelerated surface area and porosimetry instrument (ASAP 2020: Micro Merities). It was detected WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


161

using adsorption of liquid N2 at -196 °C. The N2 adsorption–desorption isotherms were used to determine the following parameters: surface area using the Brunauer–Emmett–Teller (BET) equation, total pore volume, total micropore volume, and total mesopore volume. Scanning electron microscopy (SEM, model JSM 5410, JELO) was also used to characterized the microstructure and pore properties of solid char generated from physic nut waste pyrolysis. 2.3.2 Liquid product analysis The surface organic functional groups of collected liquid product were studied by Fourier transform infrared spectroscopy (Perkin Elmer System 2000 FT-IR). Oil was dissolved in 100 ml of acetone solution, and 1 ml of the solution was added on to a KBr pellet. The pellet was heated at 50°C for 10 min to allow acetone to be fully vaporized to minimize the interference of transparent caused by acetone. A thin film of organics was, thus, formed on the KBr pellet and absorbed IR spectra. The spectra were recorded from a wavenumber of 400-4000 cm-1 [8]. The liquid product was analyzed using gas chromatography coupled with a mass selective detector (SHIMADZU 2010). Only fatty acids components were investigated by conversion to their respective methyl esters. Fatty acid methyl esters were prepared by transesterification and purified by thin-layer chromatography using potassium hydroxide for saponification of glycerides in a reflux condenser attached to the flask and heated to about 200°C until the fat droplets disappeared. Methanol and heptane were added through the condenser and the boiling continued for few minutes. After addition of sodium chloride, the obtained heptane solution was prepared for direct injection into GC for analysis.

3

Results and discussion

3.1 Product yields and gas characterization Pyrolysis of biomass results in solid, liquid, and gas products of different fractions depending on operating condition. In this work, the effect of heating pattern and reaction temperature on product yields is shown in Figure 2. Generally, rapid pyrolysis resulted in greater changes on product yields at different temperature when compared with those of slow conversion processes. For slow heating, solid yields were much higher than those obtained from isothermal runs and decreased slowly with temperature within the range of less than 2.0 wt.%. The effect of hold time at final temperature was insignificant on solid yields from this process. Larger drop on solid yields with increased temperature was obtained by isothermal experiments but still accounted for less than 4.0 wt.% changes. It may be suggested from these results that pyrolysis processes on formation and decomposition of solid are mainly rapid primary reactions and this fraction plays minor role on subsequent secondary reactions during the overall conversion. This also explains small changes on solid yields with temperature for dynamic runs. During slow heating process, all samples were subjected to similar temperature history (identical heating rate) and not on final temperature. Since pyrolysis reactions start early at temperature around WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

162 Energy and Sustainability II 400-500°C, major rapid primary reactions related to solid yields should already take place and mostly finish by the time that reaction temperature increased to final set point for higher temperature experiments. Hence, small reduction on solid yields at higher temperature resulted from insignificant slower secondary decomposition reactions. On the other hand, historical temperature profile for rapid heating at different reaction temperature is different and pyrolysis reactions occur mainly at that particular set point results in larger difference on yields. 30

Solid yield (wt.%)

25 20

Liquid yield (wt. %)

30

Dynamic - 15 min Dynamic - 30 min Dynamic - 60 min Isothermal - 15 min

15 10 5 400

600 800 o Temperature ( C) 80

Gas yield (wt. %)

75

25 20 15 10 5 400

600 800 Temperature (oC)

1000


70 65 60 55 50 400

Figure 2:

1000


600 800 Temperature (oC)

1000

Product yields from dynamic and isothermal heating of physic nut wastes.

Gas and liquid yields from slow pyrolysis of physic nut displayed opposite trend from those of rapid experiments. For slow pyrolysis, liquid yields increased with temperature while continuous drop on liquid product was obtained from rapid runs. Obviously, decomposition reactions of liquid products resulted in higher gas yields for isothermal trials. During dynamic heating, higher temperature increased the formation of liquid products at the expense of lower gas yields. Generally, gas is major product from pyrolysis of physic nut with yields of more than 50 wt.% to as much as 73 wt.% at any operating conditions. More detail on gas production is exhibited in Figure 3 for isothermal experiment at 900°C. Measured gas concentrations are reported as percentages of carbon or hydrogen in feed material that are converted to carbon or hydrogen in specified gas species. Due to distance from reactor to gas analyzer, there is WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


163

around one minute lag time for response on gas measurement. As a result, it may be seen from this figure that gas production started immediately as soon as raw material was inserted into the reactor vessel. Most of gas was formed within 15 minutes with CO2, CO, CH4, and H2 as major gas species. However, from material balance, relatively large fraction of gas species is still unaccounted for which probably be those C2-C4 hydrocarbons. Comparisons between gas production profile of H2 and CH4 via isothermal and dynamic experiments are displayed in Figure 4 and 5, respectively. As expected, rapid heating resulted in large production of gas in short time while much slower gas release was typical pattern for dynamic runs due to gradual rise in reaction temperature. 7 CO2- instantaneous CO- instantaneous H2- instantaneous CH4- instantaneous CO2 - accumulated CO -accumulated H2 -accumulated CH4 -accumulated

% C or H input conversion

6 5 4 3 2 1 0 0

5

10

15

Time (min)

Figure 3:

Gas produced from isothermal heating of physic nut wastes at 900°C.

Ratio of H2 to CO and lower heating value (LHV) of gas product which are important parameters with respect to gas utilization viewpoint are shown in Figure 6. LHV of product gas is determined from heat content of each measured gas which is: LHV (MJ/Nm3) = 0.126×[CO] + 0.108×[H2] + 0.358×[CH4] where [CO], [H2], and [CH4] are volume (molar) percentage of these gas species, respectively. At lower temperature, H2/CO ratios of gas from dynamic runs were higher than isothermal experiment while these data were quite similar for runs at higher temperature. Since gas yields and LHVs were also higher at low temperature for dynamic runs, lower reaction temperature would be appropriate for slow heating operation to obtained enriched H2 gas. Since ratios were indifferent for isothermal trials while gas productions were much higher at high temperature, factors including LHV and other operational constraints have to be considered when selecting optimal process temperature in this case. Note that LHVs of gas WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

164 Energy and Sustainability II 0.6 isothermal - 900°C isothermal - 700°C isothermal - 500°C dynamic - 900°C dynamic - 700°C dynamic - 500°C

% H input converted to H2

0.5 0.4 0.3 0.2 0.1 0 0

5

10

15

20

25

Time (min)

Hydrogen gas produced from isothermal and dynamic heating of physic nut wastes. 2.0

1.0 isothermal - 900°C isothermal - 700°C isothermal - 500°C dynamic - 900°C dynamic - 700°C dynamic - 500°C

% H input converted to CH4

1.8 1.6 1.4

0.9 0.8 0.7

1.2

0.6

1.0

0.5

0.8

0.4

0.6

0.3

0.4

0.2

0.2

0.1

0.0

% C input converted to CH4

Figure 4:

0.0 0

5

10

15

20

25

Time (min)

Figure 5:

Methane produced from isothermal and dynamic heating of physic nut wastes.

from any runs were relatively high (more than 3.7 MJ/Nm3) indicating that these gases are at least suitable for power production without need for auxiliary fuels. Table 2 is a summary of overall product distribution as well as other important product gas characteristics obtained from this work. In the table, carbon and hydrogen conversions are determined from total amount of carbon or hydrogen in feed that end up as carbon containing gases (CO, CO2, and CH4) or WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

165


H2/CO ratio

3.6

20.0


2.8 2.0 1.2 0.4 400

Figure 6:


17.5 LHV (MJ/m3)

4.4

15.0 12.5 10.0 7.5

(a) 600 800 Temperature (oC)

5.0 400

1000

(b) 600 800 Temperature (oC)

1000

(a) H2/CO and (b) lower heating value (LHV) of product gas.

hydrogen containing gases (CH4, H2) as detectable by gas analyzer, respectively. Cold gas efficiency (ηgas) is a parameter that is defined as: η gas (%) =

LHVgas × Ygas LHVraw material

× 100%

where Ygas is yield of product gas per kilogram of fed raw material (Nm3/kg) and LHVraw material may be measured by bomb calorimeter. Table 2:

Effect of reaction temperature, hold time, and mode of heating on product distribution and gas characteristics.

Temperature (°C) Hold time (min) Solid (wt.%) Liquid (wt.%) Gas* (wt.%) LHV (MJ/m3) H2/CO C conversion to gas (wt. %) H conversion to gas (wt. %) Cold gas efficiency, ηgas (%) Gas yield, Ygas (Nm3/kg)

Dynamic heating Isothermal 500 700 900 500 700 900 15 30 60 15 30 60 15 30 60 15 15 15 29.0 9.5 61.5 13.4 2.0 10.4 9.7 8.0 0.12

28.9 11.9 59.2 14.4 2.2 14.2 15.3 12.4 0.17

28.4 13.6 58.0 15.0 4.2 20.8 25.0 19.4 0.25

28.9 13.8 57.3 8.1 1.4 10.8 5.6 4.8 0.12

28.3 14.3 57.4 7.8 0.9 18.1 7.7 7.5 0.19

28.2 16.0 55.8 8.3 1.0 20.3 9.8 9.0 0.21

28.0 17.2 54.8 9.4 1.1 14.3 7.8 7.0 0.15

27.5 20.4 52.1 9.1 1.1 18.9 10.0 8.9 0.19

26.9 21.4 51.7 10.1 1.0 25.6 15.2 13.5 0.26

15.3 23.4 61.3 14.8 0.8 12.6 11.2 10.5 0.14

12.3 18.2 69.5 15.5 0.7 16.9 15.4 14.6 0.18

11.2 15.0 73.8 17.2 1.1 22.7 25.5 22.6 0.26

*by difference

As seen from this table, carbon and hydrogen conversion increased with hold time and temperature. Up to around a quarter of carbon or hydrogen in feed might be transformed to product gases at some operating conditions. Since these experiments were pyrolysis, cold gas efficiencies were relatively low when compared with typical gasification process, ranging from 4.83% to 22.55% at most. Longer hold time and higher reaction temperature resulted in greater cold gas efficiency with maximum value occurred at 900°C for isothermal process WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

166 Energy and Sustainability II though the overall economic analysis of the process has to be carried out to suggest the optimal condition since pyrolysis is mainly endothermic and operation at high temperature is energy intensive process. 3.2 Influence of Pyrolysis conditions on solid-char In this work, “char” is used collectively to represent the solid residue that remained after pyrolysis. Appreciable amount of char with high fixed carbon left after pyrolysis is an important factor to determine optimum operating condition. Results of the proximate analyses of chars obtained from pyrolysis of physic nut waste at different conditions are given in Figure 7. As expected, an increase in temperature results in char with higher fixed carbon and decrease in volatile matter. As the pyrolysis temperature increased from 500 to 900°C, the volatile content of the chars correspondingly decreased from 76.50-81.10 to 9.80-14.40%. The fixed carbon content increased sharply from 16.34-20.28% at 500°C to 57.25-62.20% at 700°C and rose continually to 81.10-85.40% at 900°C. Elemental analysis of char shows similar trend of higher portion of carbon content and lower amount of other elements with temperature (Figure 8). The devolatilization during pyrolysis resulted in the char to be predominantly carbon. Losses in hydrogen and oxygen correspond to the scission of weaker bonds within char structure favored by the higher temperature [9]. Decreasing trends in the volatile content of chars were also observed when the hold time was increased for a particular final temperature. For the hold time increased, larger amount of volatile matters were released, hence the decreasing volatile content thus leaving char with high fixed carbon content. Mode of 100 Ash

Fixed carbon

Volatile

Weight (%dry)

80 60 40 20

50 0° C 50 15 0° C m 50 30 in 0° C m in 60 m in 70 0° C 70 15 0° C m 70 30 in 0° C m in 60 m in 90 0° C 90 15 0° C m 90 30 in 0° C m in 60 m in 50 0° C 70 15 0° C m 90 15 in 0° C m in 15 m in

0

Dynamic

Figure 7:

Isothermal

Proximate analysis of char from dynamic and isothermal heating of Physic nut wastes.


Energy and Sustainability II Nitrogen

Hydrogen

Oxygen

167

Carbon

Elemental analysis (wt%)

100 80 60 40 20

50 0° C 50 15 0° C mi 50 30 n 0° C min 60 m in 70 0° C 70 15 0° C mi 70 30 n 0° C min 60 m in 90 0° C 90 15 0° C mi 90 30 n 0° C min 60 m in 50 0° C 70 15 0° C mi 90 15 n 0° C min 15 m in

0

Dynamic

Figure 8:

Isothermal

Elemental analysis of char from dynamic and isothermal heating of Physic nut wastes.

Table 3: Temperature (°C)

Surface area and porosity characteristics of chars. Hold time (min)

BET (m2·g-1)

Total volume (cm3·g-1)

Mesopore area (m2·g-1)

Mesopore volume (cm3·g-1)

500 500 500

15 30 60

140.54 154.63 171.85

0.274 0.315 0.352

124.04 131.18 142.62

0.093 0.099 0.104

700 700 700

15 30 60

188.32 197.91 202.37

0.386 0.497 0.545

153.90 178.47 185.51

0.110 0.118 0.123

900 900 900

15 30 60

199.13 215.82 217.55

0.512 0.607 0.628

180.22 189.92 192.38

0.120 0.128 0.131

500 15 114.38 0.204 700 15 154.16 0.295 900 15 169.79 0.332 Pyrolysis conditions: nitrogen flow rate = 2 L·min-1.

100.23 129.76 134.45

0.074 0.096 0.102

Dynamic heating

Isothermal heating

However, char from rapid pyrolysis had higher carbon content and lower amount of oxygen and hydrogen compared to one produced from slow pyrolysis. It was thought that remaining of inorganic substance, e.g. carbonate, after isothermal heating in a short period of time might be the cause for higher amount of carbon. The effects of pyrolysis temperature, hold time and method of heating on the BET surface area, mesopore area and mesopore volume of chars are shown in Table 3. BET surface areas increased progressively with increased pyrolysis WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

168 Energy and Sustainability II temperature and exposure time which was explained with the burnout of carbon that led to the development of porosity [10]. Char obtained from rapid pyrolysis condition had lower surface area and pore volume than ones attained from slow pyrolysis approximately 15-19%. The highest surface area of char was achieved at pyrolysis temperature of 900°C for an exposure time of 60 min. (c)

(b)

(a)

(d)

Figure 9:

(e)

SEM of chars: dynamic heating at (a) 500°C–15 min, (b) 900°C– 15 min, and (c) 900°C–60 min; and isothermal heating at (d) 500°C–15 min, and (e) 900°C–15 min.

SEM was applied to characterize the shape and the size of the char particles, as well as their porous surface structure. Figure 9 shows SEM images of physic nut chars produced under different conditions. At a low temperature of 500°C under dynamic heating, surface of char showed cracked and pitted morphology (Figure 9(a)). At 700°C, the presence of small pores on the surface explained that char was starting to develop an elementary pore network (not shown). After 900°C, surface morphological change was evident. Porous structure and opening pores on the surface was developed, thus char possessed high surface area. Increasing exposure time at a particular pyrolysis temperature also increased the surface area. This trend was less pronounced at high temperature suggesting that decomposition reactions would have been rapid at such high temperature and mostly finished in short time. The SEM image of char pyrolyzed at 900°C for 60 min (Figure 9(c)) exhibited relatively smooth in some regions as well as open pores were being seal off indicating initial stage of sintering at high exposure time. The char particles obtained after isothermal heating were slightly different as seen in Figure 9(d)-(e). While a gradual release of volatile compounds occurred as the temperature increased during dynamic heating; the fast volatile release throughout isothermal condition produces relatively substantial internal overpressure and the coalescence a more open structure (Figure 9(d)). Partial smooth surface of char particles were also observed at a higher pyrolysis temperature of 900°C under isothermal heating.



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3.3 Influence of pyrolysis conditions on liquid product The liquid products from pyrolysis are mostly oxygenated complex mixtures of hundreds of individual substance that can be grouped into many various chemical classes [11]. FT-IR spectra of the liquid product obtained from either isothermal or kinetic pyrolysis of physic nut waste are quite similar as shown in Figure10. The O-H stretching vibrations between 3200 and 3450 cm-1 indicates the presence of phenols and alcohols. The band at the about 3100 cm-1 may indicate the presence of hydrocarbon groups bound to aromatic rings. The C-H stretching vibrations between 2800 and 3000 cm-1 and deformation vibrations between 1350 and 1475 cm-1 indicate the presence of alkane. The C=0 stretching vibrations with absorbance between 1680 and 1780 cm-1 represent the presence of ketone or aldehyde. The presence of both O-H and C=0 stretching vibrations also indicates the presence of carboxylic acids and derivatives. The absorbance peaks between 1575 and 1675 cm-1 represent C=C stretching vibrations which indicate the presence of alkenes and aromatics [12–15].

% Transmittance

Dynamic heating

Isothermal heating

4000

3600

3200

2800

2400

2000

1600

1200

800

400

-1

Wavenumber (cm )

Figure 10:

FT-IR spectra of liquid product: (a) dynamic heating at 700°C for 60 min and (b) isothermal heating at 700°C for 15 min.

Liquid products were further processed and analyzed for fatty acid methyl esters. The relative distribution of fatty acids was determined as percent of chromatographic peak area of following derivative acids: palmitic acid (C16:0:C16H32O2), oleic acid (C18:1:C18H34O2), and lignoleic acid (C18:2:C18H32O2). Example of the distribution of fatty acids in liquid product produced from both isothermal and dynamic heating was shown in Figure 11. It was found that the content of fatty acid was not influenced by hold time, mode of heating, or temperature (not shown). Overall, contents of these components were in the range of 19.05-19.82% for palmitic acid, 45.03-45.77% for oleic acid, and 34.24-35.94% for lignoleic acids. Nevertheless, the results indicated that carbon chain length of liquid product from pyrolysis of physic nut waste is greater than that of diesel fuel and within the range of gas oil. It may be use on slow speed, heavy machinery but further cracking and refining of this product are required in order to utilize it in place of gasoline or diesel. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

170 Energy and Sustainability II Oleic acid(C18:1) 50

Palm itic acid(C16:0)

Lignoleic acid(C18:2)

% Fatty acid

40 30 20 10

Dynamic

Figure 11:

4

70 0° C

15

m in

m in 70 0° C

60

30 70 0° C

70 0° C

15

m in

m in

0

Isothermal

Relative distribution of fatty acids in liquid product.

Conclusions

Pyrolysis of physic nut residue was performed to study the effect of several operating parameters on distribution and characteristic of obtained products. Rapid pyrolysis resulted in greater changes on product yields at different temperature. Char yields were much higher from slow pyrolysis. The effect of hold time was insignificant on char yields which suggested key rapid primary reactions started around 400-500°C on the overall thermal conversion operation. BET surface areas increased progressively with increased pyrolysis temperature and exposure time. Char obtained from rapid pyrolysis condition had lower surface area and pore volume than ones attained from slow pyrolysis. Liquid yields increased with temperature for slow pyrolysis while continuous drop on liquid product was obtained from rapid runs. Functional groups of liquids from any processes are quite similar. Carbon chain length of liquid product from pyrolysis of physic nut waste is within the range of gas oil. Gas is major product from pyrolysis of physic nut with yields greater than 50 wt.% at any operating conditions. Most of gas was formed within 15 minutes with CO2, CO, CH4, and H2 as major gas species. LHVs of gases from any runs were relatively high indicating their suitable for power production without need for additional fuels though cold gas efficiencies were relatively low which is typical for pyrolysis process.

Acknowledgements This research was carried out under the research program of the National Metal and Materials Technology Center (project number MT-B-52-CER-07-249-I). Authors also acknowledge The 90th Anniversary of Chulalongkorn University Fund (Ratchadaphiseksomphot Endowment Fund) for partial support of this work. C. Pechyen also appreciates the scholarship provided by the Thailand Graduate Institute of Science and Technology (TGIST, TG-33-09-49-030D). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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References [1] Reed, A.R. & William, P.T., Thermal processing of biomass natural fibre wastes by pyrolysis. International Journal of Energy Research, 28(2), pp. 131-145, 2004. [2] Kang, B.-S., Lee, K.H., Park, H.J., Park, Y.-K. & Kim, J.-S., Fast pyrolysis of radiata pine in a bench scale plant with a fluidized bed: Influence of a char separation system and reaction conditions on the production of bio-oil. Journal of Analytical and Applied Pyrolysis, 76(1-2), pp. 32-37, 2006. [3] Horne, P.A. & Williams, P.T., Influence of temperature on the products from the flash pyrolysis of biomass. Fuel, 75(9), pp. 1051-1059, 1996. [4] Bridgwater, A.V., Principles and practice of biomass fast pyrolysis processes for liquids. Journal of Analytical and Applied Pyrolysis, 51(1-2), pp. 3-22, 1999. [5] Maggi, R. & Delmon, B., Comparison between ‘slow’ and ‘flash’ pyrolysis oils from biomass. Fuel, 73(5), pp. 671-677, 1994. [6] Encinar, J.M., Beltrán, F.J., Ramiro, A. & González, J.F., Pyrolysis/gasification of agricultural residues by carbon dioxide in the presence of different additives: influence of variables. Fuel Processing Technology, 55(3), pp. 219-233, 1998. [7] Garivait, S., Chaiyo, U., Patumsawad, S. & Deakhuntod, J., Physical and chemical properties of Thai biomass fuels from agricultural residues. Proc. of the 2nd Joint Int. Conf. on Sustainable Energy and Environment, Bangkok, pp. 541, 2006. [8] Sricharoenchaikul,V., Pechyen, C., Aht-Ong, D. & and Atong, D., Preparation and characterization of activated carbon from the pyrolysis of physic nut (Jatropha curcas L.) waste. Energy and Fuels, 22(1), pp. 31-37, 2008. [9] Demirbas, A., Effect of temperature on pyrolysis products from four nut shells. Journal of Analytical and Applied Pyrolysis, 76(1-2), pp. 285-289, 2006. [10] Pechyen, C., Atong, D., Aht-Ong, D. & Sricharoenchaikul,V., Investigation of pyrolyzed chars from physic nut waste for the preparation of activated carbon. Journal of Solid Mechanics and Materials Engineering, 1(4), pp. 498-507, 2007. [11] Tsai, W.T., Lee, M.K. & Chang, Y.M., Fast pyrolysis of rice husk: Product yields and compositions. Bioresource Technology, 98(1), pp. 22-28, 2007. [12] Onay, O. & Koçkar, O.M., Slow, fast and flash pyrolysis of rapeseed. Renewable Energy, 28(15), pp. 2417-2433, 2003. [13] Onay, O. & Koçkar, O.M., Fixed-bed pyrolysis of rapeseed (Brassica napus L.). Biomass and Bioenergy, 26(3), pp. 289-299, 2004. [14] Ate, F., Pütün, E. & Pütün, A.E., Fast pyrolysis of sesame stalk: yields and structural analysis of bio-oil. Journal of Analytical and Applied Pyrolysis, 71(2), pp. 779-790, 2004. [15] Onay, O., Fast and catalytic pyrolysis of pistacia khinjuk seed in a wellswept fixed bed reactor. Fuel, 86(10-11), pp. 1452-1460, 2007. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Section 2 Energy management



175

Energy and sustainability through integrated water network management M. Ektesabi, A. H. Moradi-Motlagh & A. H. Abdekhodaee Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Australia

Abstract Sustainable cities of the future require effective urban water systems that can cope effectively with urban population growth and fluctuations on water resource levels. Existing urban water systems are often old, difficult and/or expensive to change for improvement. Despite literature on water network management being extensive with many interesting papers published, it seems there are still numerous opportunities to be explored in this area. The water distribution system is becoming increasingly a multi-dimensional problem. It is complex as it has many evolving subsystems and there is more competition for this finite resource. At the same time, there are new technologies that can be incorporated for effective and efficient water management. This paper attempts to provide an overview of different types of optimisation techniques available for the water management system and provide an integrated approach to Optimise Water Distribution Chain. The optimisation of each section and the total effect as the result of integration provides reliability improvement and significant energy saving for more sustainable system. Keywords: water management, integrated water distribution management, optimisation technique, sustainability.

1

Introduction

Water, as a basic necessity of human life, had always a special role in different societies. Access to fresh water was fundamental in selecting a land to live on from the very beginning of the human race. Demanding water was not particular to agricultural societies but was also seen increasing after industrial revolution. Many industries such as textile, paper industries, chemical plants, power plants WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090161

176 Energy and Sustainability II and almost all industries require substantial water resources to be able to operate. This ever-growing demand for water in urban areas, the agriculture sector as well as manufacturing industries may not be sustainable. The availability of water resource, its acquiring and its distribution, as well as its usage should be closely considered for sustainable cities. In this paper we highlight some of the complexities that are associated with water management and discuss some of the opportunities that seem to be available to improve on efficiency and effectiveness of water management systems. Though this is a major problem which has various perspectives to look at, in this paper we focus mainly on control engineering perspectives and technologies that might be used to convey and deliver water in urban areas. 1.1 Water demand Various reports on supply and demand for water, portray a worrying picture when considering the fact that access to clean water is essential for the health and economic development of communities. Cashman and Ashley [1] wrote that” The water sector is set to continue to face severe challenges in meeting the financial requirements for maintaining, extending and upgrading new and ageing water systems in the face of growing water scarcity, stricter regulatory requirements and competition for capital.” Based on their research, they argue that domestic water usage will rise from 10% of global demand in 1995 to 25% of global demand in 2025 in relative terms. In absolute terms, however, overall domestic consumption will increase by 70%. The World Bank has indicated that worldwide demand for water is doubling every 21 years and supply cannot cope with such demand in growth. The demand in growth can partially be attributed to population growth. It is predicted that world population will reach 9 billion by 2050 from the current 6 billion level. However, the pattern of consumption is also changing and with increasing standards of living, a higher consumption is expected, particularly in developing countries. The quality of water is another dimension to water scarcity. It seems because of human activities, the quality of water is deteriorating rapidly. 1.2 Water and energy Water and energy are closely related resources in many ways. One of the main methods of generating electricity is through hydroelectricity. Moreover, the water is also needed for power plants and water is used to release redundant heat energy to air. On the other hand, energy is required to source water, treat it and deliver it to consumers in urban areas, manufacturing plants and for agricultural purposes. Based on research by Cohen et al. [2], it is estimated that the use of water consumes approximately 8 percent of the nation’s energy for its treatment, conveyance, use (including heating), and disposal. The California Energy Commission estimates that over 20 percent of electricity and 30 percent of natural gas use in that state is associated with the use of water. This report details the energy requirements of a particular water supply at five stages of the water cycle: extraction, treatment, distribution, use, and disposal. It is highlighted that WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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a significant energy saving can be achieved if better water policy decisions are made. 1.3 Water and infrastructure As discussed earlier, the need for new facilities to provide water, electricity and other services to consumers and particularly in urban areas is growing rapidly. The water management and energy consumption are highly related. However, an aspect that should be noted is that water management systems in most countries have been developed over a long period of time. They are often very costly to replace or even maintain. Some of the researchers in the field of water distribution optimisation have considered only optimal design of new networks which are good solutions for future development. There are interesting opportunities in using new control systems with existing infrastructures for water distribution systems. Having online and accurate data from a system could naturally improve the intelligence of the system. And any feed back control parameter will result in improvement. This way, some researchers have tried to develop new techniques for the operational optimisation of existing infrastructures. The objective of the latter method is mainly to generate control strategies ahead of the present time, using predictive techniques to guarantee a competent network service, while simultaneously achieving certain quality objectives. In this method either minimisation of supply and pumping costs, or maximisation of water quality or leak prevention are among the main targets [3]. In many cases the objectives are interrelated and can be managed by an intelligent management technique which is the main objective of this paper.

2

Water supply and distribution network

We can name three main types of water supply and distribution network which are commonly related to the geographical specifications of available resources and location of users: Gravity based water distributing system – in this case source of water is usually surface water accumulated in a dam. After going through water treatment process, usually water is transferred to a reservoir that has been located high enough relative to the lowest point of consumption so that water can be provided with adequate pressure. Elevated reservoirs / Intermediate tank pump based water distribution system – in this system during off peak consumption period; water is pumped to high elevated tanks and during consumption this water is channeled to the water distribution network. Pump based water distribution without intermediate tanks – in this method pumps channel water directly to artillery pipes. This method is not very common as it is highly relied on continuous operations of pumps and might be interrupted by disruption in power etc.


178 Energy and Sustainability II 2.1 Importance of intermediate reservoir/tank For various reasons, we need to have intermediate reservoirs tanks in a water distribution process. Perhaps the main reason is to stabilise and to regulate water supply and demand. Generally, pumps work at a constant rate while demand for water fluctuates. With the use of intermediate storage, water can be stored in reservoirs to be provided for customers in constant rate. It is also helpful to make the quality of water consistent. Water might be obtained from various resources such as surface water, or through water wells, and in some cases through desalination plants. Use of intermediate reservoirs is helpful to mix different types of water and have acceptable quality levels. Intermediate reservoir/tank systems provide the possibility of off peak pumping which in turn is a part of load management and provides a better use of energy in an appropriate time slot. In this case the pumping system can be ONOFF control type for the required duration of pumping. 2.2 Importance of optimised control system for direct pump based water distribution without intermediate tanks In the case of pump based water distribution without intermediate tanks, pumps require a more advanced type of control. In conventional control system, the pumps run at maximum operating flow rates, whenever the consumer demand changes, the demand for control of flow in the pipes change and this change is normally achieved by throttle valves or by bypass valves. This type of control system results in wasting of energy in throttling or bypassing the water. In the following sections, it is shown that by use of Variable Speed Drives and replacing the conventional control systems with newer techniques, not only energy saving is achieved but it also helps in constant demand based flow in pipes without causing pressure impacts. Smooth flow and reduction of pressure impact in turn increases the useful life time of infrastructure which is one of the main objectives. 2.3 A simplified water distribution process Water distribution process, as illustrated in Figure 1, can be divided into various stages, mainly as follows: Stage 1: In the first stage, water from various sources such as dams, water wells, etc are conveyed to water treatment plants. In the treatment process, water is filtered and its content minerals are adjusted to required set values. It should be noted that if the water source is in a geographically lower level and gravity cannot be used to convey water to treatment plants, then use of pumps is required. This generally requires substantial energy. In plants too, we need energy to do treatment process such as filtration. Stage 2: In the second stage, water need to be conveyed from treatment plants to an echelon of water storage facilities, usually a main reservoir to smaller storage facilities. The main reservoir based on consumption would distribute water to the smaller storage facilities. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Stage 3: In the third stage, water from smaller storage facilities is distributed to the end users via a network of pipes. These storage facilities are either positioned in higher lands relative to end users or they are elevated from the surface level. In the latter case, energy is required to convey water to these facilities.

Figure 1: Table 1:

Water distribution process. North Tehran division.

North of Tehran Utilities Stage2 Stage3 1710 Km Water 47 Water Well 42 Reservoir Distribution Network 20 Pump Resident Population is about Latian Dam Station 1,450,000 Water Consumption per 30 Km Pipeline year is 140,000,000 m3 Water Treatment Plants 3 & 4* 14407 Valve Stage1

An example of the above three stages can be shown in the following Tehran water distribution system. Tehran is the capital and largest city of Iran, and perhaps it is the largest city in the region. It is the most populated city in South Western Asia with a population of approximately 15 million.


180 Energy and Sustainability II Water consumption in Tehran is almost three million cubic meter per day and it is sourced from three major dams and one thousands wells. In this case, water management has been divided into six divisions. The information of these divisions (North Tehran division) is presented in Tables 1 & 2 and the geographical relative location of one of the resources is presented in Figure2. One of the Water treatment plants has been operational since 1967 and the other one was added to the system in 1984. Their capacities are similar and they provide 4 cubic meters per second each. Untreated water is conveyed from Latian dam via a 28-kilometer long tunnel with a diameter of 2.7 meter. Table 2:

A section of water supply network.

Water supply network for Tehran North Division Channels

8 km

Dimension 64.1 m × 2.1m

Tunnel

28 km Diameter 2700mm

Steel pipes

73 km Diameter 1000mm

Concrete pipes 67km Diameter 2000mm

Figure 2:

3

Latian dam and its location relative to the capital city, Tehran.

Optimisation possibilities

Figure 3 illustrates six main areas in which optimisation of water and energy can be considered. This classification is helpful to categorize some of the contributions that will be discussed in this paper. Its main purpose is to highlight WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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that optimisation can be viewed in smaller scale and individual component of a system as well as in a larger scale when a control system needs to be integrated. Here a brief description of each area is provided. In Area 1, it can be considered to optimise the amount of water obtained from various sources to have an acceptable mineral content, minimize leakage and energy through transportation. Techniques such as linear programming can be applied. In the Area 2, water levels in intermediate storage are investigated. The level should be set to a value acceptable as level of service while minimising energy in the process, accurate prediction and rapid adjustment could be vital. In Area 3, processes at treatment plant are scrutinised.

Figure 3:

Optimisation areas for a water distribution process.

In Area 4, pump applications can be investigated. We discuss this further later in this paper, however, scheduling of pumping as well as pumping technology has a significant impact on energy consumption. Efficiencies of pumps vary greatly and depend on operational requirements. Fine-tuning the system could significantly reduce energy usage. In Area 5, valve operations can be investigated. ON-OFF control systems can be replaced with more accurate PID control systems. Finally, in Area 6, demand side management as well supply side management could improve the system performance. By active participation of consumers, it is possible to reduce pressure in the distribution network. This not only minimizes leakage but it also might prolong the operating life of a water distribution system. Usually, a water servicing network extends over a region covering a wide area and very long distance and conveys treated water to and from many storage reservoirs to the consumers within the Metropolitan Area. The water is distributed via tunnels/channels/pipes, which branches outwards from the storage WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

182 Energy and Sustainability II reservoirs. The reservoir volumes are measured on-line and sent to a central control system where all of the relevant data are stored. In one example [3], to deliver potable water with an adequate pressure, even in remote parts of the system, there are hundreds pump-stations. Until recently, the topic of optimisation in water systems in the literature has been mainly focused on the design of optimised configurations for pipe-interconnected reservoirs, whereas there are many more parameters which have to be considered for optimum solutions. In this section some of these parameters are presented. Switching between the resources and use of the reservoir with suitable level for optimum pumping is one of the popular techniques discussed in many of the available literatures [4–6]. Mixing of water from different resources requires another type of optimisation. In the case study of Tehran, it was shown that the water supply can be from more than one on-ground or underground resource, each with different treatment requirements. Use of an intelligent mixing system can reduce / optimise the treatment process. This approach is very similar to a chemical plant with dozing of water quantities from each of the resources based on their quality and usage. In most networks, this optimisation problem is equivalent to optimising the scheduling of pumps. Creasey [7] reviewed the appropriate mathematical techniques to solve the problem of operational optimisation for water distribution networks, insisting particularly on the pump-scheduling problem. He concludes that better pump scheduling could save £10 million (1988) a year to the UK water industry alone.

4

Challenges and opportunities

Pump applications account for a large per cent of motive power in the water industry [8]. In this case, the power consumed by pumps is proportional to the operating speed cubed. Efficiencies of pumps vary greatly and depend on operational requirements. Fine-tuning the system can have a big impact on energy consumption. Though pump operation and energy cumsumption are two separate entities, they are totally dependent on each other. Changing the patern of operation of pumps will have a significant impact on the total energy consumption or saving. There are many interrelated chalenges involved when handling the control systems in water industry. There are many places where the power is wasted and can be recovered. There are also places where there are oportunities of energy savings. If there is an excess head (pressure) that must be throttled or there are unnecessary flow paths or excessive frictional losses in the system there is wasted energy. In such places these control challenges surely result in opportunities for improvement. These opportunities may also be linked to the long operating hours which are unavoidable in the water industry, or high horsepower pumps which can cause the highest savings if they are properly controlled. It is also evident that variable applications that use throttling as a form of control and operate below full load for a significant length of time offer potential opportunities for higher efficiency through improved control WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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technologies. And finally, the regular maintanace and removal of blocked filters, cavitation or poorly maintained pipes can deliver huge savings in energy consumption. 4.1 Type of infrastructure Whether it is new requirement or existing infrastructure, proper utilisation of resources for minimum energy consumption and sustainable development is very important. Water levels of resources and the pumping operation of different pump stations remotely by telemetry from the central control room. The old/present infrastructures have been designed for a particular pressure (flow rate). Due to aging the safe operation of the system to service the end users is very important. The continuous monitoring of the pressure in these systems can ensure the safe operation as well as fault detection. This is easily achievable by use of the sensor networks of and adapting a suitable flow management control system as mentioned in section 3. Switching or conversion of old systems for optimization of all sections may be very difficult, but if a new design has to be considered, then the best solution may be applying all the optimization techniques of previous section for the entire system. 4.2 Energy saving opportunities The most basic form of control in the water industry is to manage flow by adding friction at the pump outlet. This is usually achieved by a throttle valve. It is effective, but inefficient. Most industrial systems have pumping requirements with several operating points or variable flow and pressure requirements. Picking the pump with the optimum efficiency for a specific delivery is only part of the story. The other part is controlling the flow rate to match the process requirements. The most efficient control option is by use of the VSD which most closely matches the ideal pump curve. Water industry consumes high share of electricity to operate motor-driven pump systems. With an improvement in energy saving systems, the potential savings are very large - over 100 billion KWh/year energy savings and billions of annual energy cost savings opportunity with new technology [8]. Fig.4 shows the Percentage of Power Consumption in Pumps with Different Control Options and obvious advantages replacing throttle valve or bypass valves in water industry. 4.3 Sensor network and new trends in control/sustainable approach In the report on Energy Using Product (EuP) [9], it was shown that the use of high efficient subsystems can improve the overall efficiency of the system. In a simple example in the same report, it is shown that a normal pumping system with subsections as; a standard motor, coupling system, pump, throttling valve control system and transmitting pipe can result to overall efficiency of 31%, where as by improvement of each subsection and replacement of the components with higher efficient ones the over all efficiency can increase to above 72%. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

184 Energy and Sustainability II To have a sustainable system, optimized management of resources is as important as of using new improved systems. A simple substitution of the conventional old systems with that of more efficient subsystems, such as motorpumps, pips, flow controllers and valves, can result in an increase in overall efficiency of the system. 120

80

Percentage of flow Throttle valve

60

Bypass valve

40

VSD replacing throttle valve VSD replacing bypass valve

100

20

Figure 4:

10

20

30

40

50

60

70

80

90

10 0

0

Percentage of power consumption vs. control options.

Creasey [7], in his studies by just considering optimal ON-OFF pump scheduling, claimed a huge saving in the UK water industry. Due to development of technology and improvements in semiconductors and their use in recent control systems caused advancement of flexible hardware systems. Now-a-days, everyone knows the advantages of variable speed drives in speed control of pumps for variable flow control, and their use in implementation of a more flexible feedback loop of controllers to supply the required flow rates based on demand that has made it an attractive technology in the water industry with much higher energy saving [8]. Use of sensors networking for accurate high response monitoring and control of parameters and transfer of data to the control stations eliminates the errors, breakdown and make easier predication of faults/leakage in water network system. The flow sensors placed in the line of flow senses the flow water and feed back signals to VSDs control the proportional speed of pumps. As speed of pumps are related to the flow rate, the speed sensors along with the pressure sensors in pips are part of the control systems determining the control commands/ algorithms for assuring the consumers demand fulfillment as well as fault monitoring system in case of leakages. In the previous section, it was explained that on line monitoring of the pressure in each line, is a measure of the consumer demand. On the other hand, regular monitoring of the flow-speed or pressure-speed characteristics of each section is an indication of regular operation of the system based on required water demand in that section. In this system any irregularity of operation is detected and compared with the regular signature of the system. Hence any deviation from the regular operation can be used as an early fault detection or alarm. System improvement opportunities in many cases may include: improved WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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sizing and proper matching to demand, use of more efficient drive trains, improved system layout, updated and well-maintained controls, improved operation and maintenance.

5

Conclusion

To select the appropriate control option, it is required to balance the capital cost of the control equipment against the savings which are achieveable. Although the more efficient control options generally have higher initial set up costs, they can result in large and reoccurring energy savings over the life cycle of the equipment. This paper suggested savings and optimisation of each section of water network while consdering the overall performance of system. It was shown that by improvement of each subsection and replacement of the components with higher efficient ones the over all efficiency can increase and an advancement in control of water flow to supply consumer demand can result on monitoring of the pressure in each line. In this case, flow-speed or pressure-speed characteristics of each section was an indication of regular operation of the system in that section and any irregularity of operation could be detected and compared with the regular signature of the system.

References [1] A. Cashman and R. Ashley (2008) Costing the long-term demand for water sector infrastructure, Foresight, V10, N3, pp9-26. [2] R. Cohen, B. Nelson, and G. Wolff, (2004), Energy Down the Drain: The Hidden Costs of California’s Water Supply. Natural Resources Defense Council, Oakland, CA. [3] G. Cembrano, G. Wells, J. Quevedo, R. Perez, R. Argelaguet (2000), Optimal control of a water distribution network in a supervisory control system, Control Engineering Practices, V8, pp. 1177-1188. [4] M. C. Cunha and J. Sousa (1999), Water distribution network design optimisation: Simulated annealing approach. J. Water Resour. Planning and Manage. 125 (4) 215-226. [5] J. Schaake and D. Lai (1969) Linear Programming Dynamic Programming Applications to Water Distribution Network Design. Dept. of Civil Eng., Massachusetts Inst. of Technol., Cambridge, Massachusetts. Report no 116. [6] E. Alperovits and U. Shamir (1977) Design of optimal water distribution systems. Water Resour. Res. 13 (6) 885-900. [7] J. G. Creasey, (1988), Pump Scheduling in Water Supply: More Than a Mathematical Problem.n in Coulbeck, B. and Orr, C.H. (eds), ”Computer Applications in Water Supply”, Vol. 2, Research Studies Press, Ltd, U.K, and John Wiley k Sons Inc, U.S. [8] M. Ektesabi and H. Felic, (2007) “Motor Management and Energy Saving by Integration of Motor Drive System”, World Congress on Engineering 2007, Conference Proceeding published by IAENG, Page 421-424


186 Energy and Sustainability II [9] Aníbal T. de Almeida, (2006), Energy Using Product (EuP) Directive Preparatory Study, Lot 11: Motors Analysis of existing technical and market information, DG TREN, Brussels, June 29 2006, ISR-University of Coimbra



187

Vanadium battery technology – integration in future renewable energy systems C. K. Ekman, H. Bindner, T. Cronin & O. Gehrke Risø National Laboratory for Renewable Energy, Denmark

Abstract Energy systems with high penetrations of intermittent renewable energy sources face great challenges when it comes to demand-supply balancing and power reserves. The vanadium battery technology may offer solutions to this by providing both energy storage and power system services. This paper presents the recent research activities on vanadium battery technology integration carried out at Risø National Laboratory. A vanadium battery has been installed in a research energy system SYSLAB. It has been characterized and its capabilities for the balancing of wind power have been demonstrated. A small simulation case study (based on the performance measurements of the real system) is presented and the results with respect to diesel fuel savings discussed. Keywords: vanadium battery, energy storage, load management, wind power integration.

1

Introduction

In future energy systems with an increased share of fluctuating renewable energy sources, the challenge of balancing of electrical load and power production will grow. The need for increased balancing capabilities will be present on both longer (energy management) and shorter (regulation and reserve) timescales. Different electricity storage technologies, that can provide balancing capability and thereby facilitate a higher share of renewable energy, are available today (for an overview see [1]). This paper presents a study of one such technology, namely the vanadium redox flow battery. A 15kW/120kWh vanadium battery was installed at the renewable energy research facility SYSLAB and its performance WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090171

188 Energy and Sustainability II characteristics as well as its integration in a renewable energy system have been studied during the last year [2]. This paper presents some of the test results obtained in this period. The results of the battery characterization have also been used as input to a modelling tool, which can provide insight to battery integration in energy systems. The remaining parts of the paper are organised as follows: Section 2 gives a brief overview of the technology. Section 3 describes the battery installed at SYSLAB. Section 4 presents the results of test runs where the battery has been used to balance a wind turbine. Section 5 describes how the results from the battery characterization have been used to model the performance of a power system with a vanadium battery. Finally, Section 6 summarizes the work.

2

Vanadium redox flow battery technology

The vanadium battery technology is based on electron/H+ transfer between different ionic forms of vanadium. The liquid electrolytes containing the vanadium ions flow from two separate containers through an electrochemical cell on each side of the membrane. The electrochemical potential across the cell is used to convert the chemical energy to electrical energy (in the discharge mode) or vice versa (in the charge mode). The chemical reactions are: Positive electrolyte:

Negative electrolyte:

The voltage across one cell is around 1.4V and cells are therefore stacked in order to reach higher voltages. Figure 1 shows a schematic drawing of the battery technology. Note, that the electrolyte does not flow between the electrolyte tanks – the electrolyte is pumped through each of the half cells back to the same tank, ensuring that there is, at all times, sufficient electrolyte in the two half cells available to undergo the chemical reactions. The concept is different from conventional batteries where the electrodes take part in the chemical reaction. The chemical reduction/oxidation and the flow of electrolyte (which facilitates the electron transfer and therefore the energy storage) give rise to the name: (vanadium) redox flow battery. More details on the technology can be found in ref. [1]. The technology has the advantage that the energy storage and power capacity can be sized independently (either by changing the amount of electrolyte in the system or the number of cell stacks). The fast response of the electrochemical reactions makes the technology suitable for primary reserves (real time balancing and frequency support). The lifetime of a vanadium battery system is expected to be long and there is in principle no self discharge since the electrolytes are physically separated. However, vanadium battery systems are still relatively expensive and the low energy density makes the footprint of the system considerable. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Figure 1:

Schematic drawing of a vanadium battery. The aqueous electrolyte is pumped into the fuel cells (here only one cell is depicted) on each side of the cell membrane. The concentration of the different vanadium ions in the two electrolytes leads to an electrochemical potential over the cells.

Figure 2:

Photo of the vanadium battery installation at SYSLAB. The three blue units in front are the cell stacks, each containing 40 cells. Behind the cell stacks and the pump/pipe system, the two 6500 liter electrolyte tanks are situated. The box to the right is the control unit.



3 Vanadium battery at SYSLAB SYSlab is a research facility at Risø-DTU that has been built to study integration of energy technologies. It includes two wind turbines (11 and 55kW), solar panels (9kW), office building (max. load of 20kW), hybrid vehicle-to-grid car (9kWh), a diesel generator (48kW), a dump load (75kW) and a vanadium battery (15kW/120kWh). The research activities focus on renewable energy integration, intelligent (distributed) control and communication. For more information on SYSlab see ref. [2]. In 2007 the 15kW/120kWh vanadium redox battery was connected to the system as part of the research project “Characterization of vanadium battery” funded by the PSO framework (ForskEl project 6555). Figure 2 shows a photo of the battery system. In order to understand the battery performance and be able to develop a realistic model, the losses in the different parts of the battery system have been analyzed independently. There are losses in the power converter, losses in the cell stack and parasitic losses (due to the auxiliary system and selfdischarge).

Figure 3:

Battery efficiency as function of power for the stacks only (upper yellow curve), stacks and power converter (middle green curve) and total (lower curve). The widths indicate the spread depending on state of charge. When the power is negative, the battery is being charged.

The losses in the cell stacks are primarily ohmic losses. The area specific resistance has been estimated to be around 0.16Ωcm2. The efficiency of the cell stack can be determined from the ratio of the actual voltage (at a certain current level) and the open circuit voltage (which depends slightly on the state of charge WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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of the battery). The cell stack efficiency lies in the range from 88% to 100% in the DC power range from -15kW to 15kW. The cell stack efficiency is lowest when the battery is close to being discharged and delivering full DC power (+15kW) and highest when the DC power is close to zero. The efficiency of the power converter is about 55% at 1kW, 80% at 2kW and 93% at full power (15kW). The power consumption of the auxiliaries (pumps and control) varies with the power as follows. The pumps have two operational speeds resulting in a power consumption of about 1.2kW at battery powers lower than 4kW and about 1.5kW above 4kW. This auxiliary power consumption could probably be optimized by installing pumps with higher efficiency and an energy saving control unit. The electrolyte level in the tanks may change slightly due to water diffusion through the membranes of the electrochemical cells (caused by the osmotic pressure). The levels are equalized every 24 hours by opening a valve for half an hour, allowing the electrolyte to flow between the two tanks. The losses during this equalization process depend on the state of charge, but on average it corresponds to a constant power loss of about 110W. Figure 3 shows the efficiency of the different parts of the system. It is expected that the energy consumption of the auxiliary system (pumps and control) and the losses in the equalization process can be reduced significantly in larger battery systems.

4 Test run VRB-WT balancing The vanadium battery at the SYSLAB facility at Risø-DTU has been operated in parallel with the 11kW Gaia wind turbine, balancing the combined output to a constant 4kW. The flexible configuration of SYSLAB has allowed for the connection of the two components to the same busbar, which was then connected to the national grid. Measurements of the power flow from the turbine, the battery and the total output to the grid is shown in Figure 4 (5 minute averages). The power from the wind turbine is balanced and the desired output of 4kW is sustained (when the battery state of charge is not zero or 100%). Due to the speed of the communication and control program, complete balance on the shorter timescale has not been achieved. Measurements taken every second show a mean variation of 0.8kW around the 4kW set point. Further studies will include operating the battery in droop mode in an island system together a wind turbine and a variable load. In such a system, the battery can be the grid-forming unit and at the same time provide energy management on the longer timescale.

5

Modelling of vanadium battery in power system

A vanadium battery model has been developed and implemented in the IPSYS modelling environment [3]. IPSYS offers the possibility of modelling energy systems with a special emphasis integration of renewable energy technologies. Detailed modelling of power systems is provided with a quasi-static description of the power flows, voltages, frequencies, as well as losses.



Figure 4:

Lower panel: Power as function of time for the wind turbine (positive, red line), the battery (blue line) and the sum (around 4kW, black). After a period with no wind (around hour 20 and hour 110), the turbine consumes power in a short period to start up – this can be seen as a small dip below zero in the wind turbine power output. Upper panel: Battery state of charge (SOC). When the battery is fully charged (around hour 260), the 4kW output cannot be sustained.

Based on the power set point (and the state of charge), the battery model recalculates the state of charge after each time step, taking into account the different losses in the system: • Stack losses: The efficiency of the electrochemical cells is simply the cell voltage relative to the electromotoric force (open cell voltage). The model includes the open cell voltage dependence on the state of charge and a linear change in the voltage depending on the current over the stack. • Power converter losses: The power converter efficiency (both AC to DC and DC to AC) and its dependence on power has been used to model the losses in this part of the system. • Parasitic losses: The auxiliary power consumption is modelled a linear function of the AC power of the battery (400W losses at zero power and 7% losses at full power). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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This parameterization of losses in the battery system is based on the measurements of losses in the vanadium battery installed at Risø-DTU (see section 3), which makes the model both detailed and realistic. 5.1 A small island system simulation case study The IPSYS model including the newly added battery component has been used to simulate a small imaginary island power system including a wind turbine, two diesel generators, a variable load (emulating a number of households), a dump load and a vanadium battery. The layout of the systems is shown in Figure 5.

Figure 5:

Layout of the small island system. The diesel generators, the vanadium battery (VRB) and the dump load are connected the same busbar (bus 2). The wind turbine and the load are connected to the two other busbars (bus 1 and bus 3).

The load has a weekday and a weekend load profile with an additional stochastic behaviour and it ranges from approximately 30 to 70 kW. The wind speed input is based on measurements from the Risø-DTU meteorological mast over a full year. The wind power is determined from the measured wind speed and a simple power curve. The turbine capacity is 75kW. The two diesels can supply 60kW each and they have a lower power limit of 6kW. The battery has a power capacity of 40kW. A quite simple battery load management control strategy has been applied. The battery power is set to balance the wind power plus the load, i.e. charging the battery when there is excess of wind power and discharge the battery when the load exceeds the wind power. When the battery is fully charged, absorbing the excess wind is not possible and the battery power is then set to the standby power. Likewise, when the battery is fully discharged and the load exceeds the wind power. In effect, the battery will save excess wind power and supply power to the system when the wind does not meet the load. One diesel is required to be on constantly in order to maintain frequency and voltage on the grid (being the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

194 Energy and Sustainability II grid forming unit). The other diesel is turned off when there is sufficient power in the system. The studied time period is one year and simulation has been carried out with 6 different battery capacity sizes: 0, 3, 5, 10, 15 and 20 hours (at full power, i.e. 0, 120, 200, 400, 600 and 800kWh).

Figure 6:

Upper panel: Battery state of charge (SOC) as function of time for an example week. Lower panel: power of the different components. This example is for battery storage capacity of 5 hours.

The lower panel of Figure 6 shows the power of the different system components during one week. The upper panel shows the battery state of charge as function of time. The lower panel shows the power of the different components. The battery power cycles are clearly seen in the figure: first a period of charging followed by a period of discharging that continues until the battery is fully discharged. The dump load is often used simultaneously with the battery – this undesirable behaviour comes from the fact that only the dump load and the diesels can actively react on the system frequency. When the wind exceeds the load, (downward) regulation of the frequency can only be provided by the dump load (the spinning diesel supplies the minimum power of 6kW and WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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cannot regulate downward). Using more intelligent control, where the battery provides a part of the frequency regulation at times with excess wind power, would result in even less power being dumped.

Figure 7:

Amount of energy dumped and lost in the battery as function of battery size. The corresponding diesel fuel consumption is shown as square markers (axis on right side of the plot).

Figure 7 shows the amount of dumped energy, the losses in the battery and the diesel fuel consumption as function of battery storage capacity. The figure illustrates that the energy dumped can be reduced by about 45% if a 20-hour battery storage capacity is used. When the losses in the battery are also taken into account, the reduction in lost energy is about 35%. In terms of diesel fuel savings the battery only saves about 2000 litres per year (with the present control strategy). This is only about 2% of the total fuel consumption and clearly not sufficient to cover the cost of installing and operating a vanadium battery. It is expected that larger saving on the diesel fuel consumption can be achieved by applying more intelligent control strategies. First, the diesels can be turned off during hours where the battery (and wind) can supply the load consumption, i.e. the battery can be the grid-forming unit during some periods. This would prevent the diesels from running close to minimum power, which results in high fuel consumption (per kWh). Secondly, the battery can be controlled so that the diesels primarily are operated at full power. This will also save diesel fuel, since diesels are more efficient at full power. Finally, wind power forecasts can be used to charge and discharge the battery depending on the expected wind power WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

196 Energy and Sustainability II in the coming hours. The potential fuel saving is to the first approximation limited by the total amount dumped energy times the heating value of diesel (about 10kWh/liter) divided by the electrical efficiency of the diesels. If the latter is 30%, the maximum diesel fuel savings is about 7100 litres. Future studies on island systems with wind, diesel and vanadium batteries will be focussed on more intelligent control strategies and the possibilities for diesel fuel saving.

6 Summary and outlook This paper has outlined the research activities on the vanadium battery technology integration carried out at the Risø National Laboratory. A 15kW/120kWh battery has been characterized and its capabilities to balance wind power has been demonstrated at the SYSLAB facility. The results from the battery characterization have been used to implement a realistic battery model in the IPSYS modelling environment. A simulation case study has been presented showing how a battery can be integrated and controlled in a small island system. The case study illustrates a simple strategy for control of the battery depending on the wind power and the load. With this strategy (in this island system) the savings of diesel fuel are very limited, even with a battery storage capacity of 20 hours. More intelligent control strategies are needed in order to decrease diesel fuel consumption further. Whether or not the saving on diesel fuel consumption can become sufficient to ensure economic viability of vanadium battery integration in island systems depends on many factors, like system design, system control, price of diesel fuel and the cost of a battery system. These issues will be treated in further studies.

Acknowledgement The work has been supported by Energinet.dk as part of the project “Characterisation of Vanadium Batteries” (ForskEl project 6555).

References [1] EPRI-DOE Handbook of Energy Storage for Transmission and Distribution Applications, EPRI, Palo Alto, CA, and the U.S. Department of Energy, Washington, DC: 2003. 1001834 [2] Bindner H., et al. Initial tests of vanadium flow battery at Risø-DTU, 4th European PV-Hybrid and Mini-Gird Conference, Glyfada, Greece, 2008 [3] Bindner, H. et al., IPSYS – A Simulation Tool for Performance Assessment and Controller Development of Integrated Power System Distributed Renewable Energy Generated and Storage, WREC VIII, Denver, Colorado, 2004



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Short-term wind forecasting using artificial neural networks (ANNs) M. G. De Giorgi, A. Ficarella & M. G. Russo Department of Engineering Innovation, Centro Ricerche Energia e Ambiente, University of Salento, Italy

Abstract The integration of wind farms in power networks has become an important problem. As electricity cannot be preserved because of the highest cost of storage, electricity production must following market demand, necessarily. Short-long term wind forecasting over different time steps is becoming an important process for the management of wind farms. Time series modelling of wind speeds is based on the valid assumption that all the causative factors are implicitly accounted for in the sequence of occurrence of the process itself. Hence, time series modelling is equivalent to physical modelling. Artificial neural networks (ANNs), which perform a non-linear mapping between inputs and outputs, provide a robust approach for wind prediction. In this work, these models are developed for simulating wind speed and energy production of a wind farm with three wind turbines, comparing different prediction temporal periods. We applied artificial neural networks for short and long term load forecasting using real load data. Keywords: neural artificial networks (ANNs), forecasting wind, turbine, CFD.

1

Introduction

Electricity markets throughout the world are changing to allow the integration of alternative energy sources, in particular wind energy. The major criticality in the use of renewable energy, particularly of wind energy, concerns the management of wind farms. As electricity cannot be preserved because of the highest cost of storage, electricity production must follow the market demand, necessarily. In the state of the art there are two types of approach in the prediction of wind energy [1]: those based on physical WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090181

198 Energy and Sustainability II modelling and those based on historical series analysis. The first is used in meteorology to reproduce the atmospheric state, but this is a very complex system since it requires big resources of hardware for the calculation. While, approaches based on historical series estimate the future values on the basis of past values after identification of a model that simulates the process analyzed. This methodology is based on the valid assumption that all the factors influence the process are taken into implicitly using the past values and so it is possible to make a probable prediction. A good prediction model in real time of wind energy must be able to guarantee reliability for the prediction as soon the time horizon is extended. In order to understand the different issues involved in wind energy forecasting it is useful to divide the problem into three difference time scales: very short-term (0-6 hrs), short-term (6-72 hours), and medium range (310 days). In the small terms, in particular when the time horizon swings from a few minutes to some hours, various studies, based on ARMA models [2,8] and ANNs model [3,5–7], obtained a good result in the prediction of wind energy. In [5] an ANN model is presented, based on a back-propagation method, it was evaluated with real data measured at two different locations and demonstrated a correct dynamic performance in all evaluation tests, so it can be concluded that the algorithm is valid for estimating average speed values. The initial point for the approach in [6] is mainly the fact that none of the forecasting approaches for hourly data, that can be found in the literature, based on time series analysis or meteorological models, gives significantly lower prediction error than the elementary persistent approach. This was combined with the characteristics of the wind speed data, which are determined by the power spectrum values, distinguished by the spectral gap in intervals between 20 minutes and 2 hours. The finally proposed methodology is based on the multi-step forecasting of 10 minutes averaged data and the subsequent averaging to generate mean hourly predictions. In [7] the ANNs models are found to perform better for the forecast length of one hour, as seen from the actual and simulated data. For the forecast length of one hour, artificial networks are found to perform better than other methods, but the study suggests that, for increased forecast lengths, modified methods need to be investigated. In [8] a linear, time-varying autoregressive (AR) process is used to model and forecast wind speed. This modelling approach takes into account the non-stationary nature of wind speed. The time-varying parameters of the AR model are modelled by smoothed, integrated random walk processes. A Kalman filter is used to estimate the time-varying parameters of the AR model. The algorithm is used to forecast wind speed from 1 h to a few hours ahead. Other studies, for example in [14], are focused on a real-world application, the long-term wind speed and power forecasting in a wind farm using locally recurrent multilayer networks as forecast models. To improve the performance of the models, considering the complexity of the process, a class of optimal on-line learning algorithms is employed for training the locally recurrent networks based on the recursive prediction error (RPE) algorithm. The experimental results demonstrate that the recurrent forecast models provide better multistep ahead forecasts compared to the persistent method, the atmospheric and time-series models. In [15] the wind speed prediction in wind WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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farms has been performed by using local recurrent neural networks with internal dynamics, as advanced forecast models. The efficiency of the proposed approach is tested on a real-world wind farm problem, where multistep ahead wind speed estimates from 15 min to 3 h are sought. In [16] results are presented of a number of advanced prediction systems performed in the frame of the European project Anemos. The European project Anemos is focused on several topics related to wind power forecasting such as physical and statistical modeling, uncertainty estimation, upscaling and others. From the very first stage of the project it was recognized by both end-users and modelers the necessity to map the existing wind power forecasting technology both in terms of research approaches and also in terms of performance. In [17] a statistical forecasting system is implemented for short-term prediction (up to 48 h ahead) of the wind energy production of a wind farm: for a given wind farm, the input variables are the meteorological predictions of wind (velocity and direction) for the next 48 h and past values of output power. The forecasting system has then to supply, on an hourly basis, the predicted output power up to 48 h ahead. In this work, artificial neural networks have been applied for the prediction of wind energy when the time horizon swings from 1 to 24 hours, using historical series data wind only, for a wind farm. Preliminarily, the statistical analysis of the historical series was processed and the probable distribution of wind speed and direction of the three turbines were represented. Application of a neural network for the prediction of wind energy able to an acceptable error on the observation when the prediction length is under 6 hours. So, with the extension of a prediction time horizon, the reliability of a prediction based only on statistical methods reducing considerably, but the need of planning on mediumlong terms of the wind productivity asks for approaches that are able to integrate knowledge from historical series with the outputs of numerical weather models.

2

Wind farm characteristics

There are a number of complex issues associated with the evaluation of wind energy forecasts. The most significant issue is which parameter(s) should be

Figure 1: Seasonal trend of wind speed in year I of the wind park.

Figure 2:

Wind speed and wind direction – Month of April (year I).


200 Energy and Sustainability II used as the metric(s) for forecast performance. One’s choice of metrics can have a significant impact on one’s impression of forecast performance. So the first step in the wind forecasting is the statistical analysis of the historical series data. Our data set contains wind speed observations for a period of four years (years I, II, III, IV). In fig. 1 the seasonal trend of average wind speed for the first year of dataset (year I) is represented: in general, the average daily wind speed is higher in the winter than the summer months. In Fig. 2, the peak of wind speed is at a consistent wind direction, this means that a consistent wind direction can be considered as a factor that explains the high wind speed.

3 ANNs models for wind speed and energy prediction 3.1 Artificial neural networks and architectures Neural networks are composed of simple elements operating in parallel. These elements are inspired by biological nervous systems. As in nature, the network function is determined largely by the connections between elements. You can train a neural network to perform a particular function by adjusting the values of the connections (weights) between elements. A typical neural network used in the present study is the Multi Layer Feed Forward (MLFFN) network. In the Feed-Forward networks the data flow from input to output units is strictly feed-forward [13]. The data processing can extend over multiple (layers of) units, but no feedback connections are present, that is, connections extending from outputs of units to inputs of units in the same layer or previous layers. Each layer consists of units which receive their input from units from a layer directly below and send their output to units in a layer directly above the unit. There are no connections within a layer. The ANN learns through the set of examples supplied to it during the training process. Once the network weights and biases are initialized, the network is ready for training. During training the weights and biases of the network are iteratively adjusted to minimize the network performance. The default performance function for feed-forward networks is mean square error – MSE – the average squared error between the network outputs a and the target outputs t. Several algorithms for training use the gradient of the performance function to determine how to adjust the weights to minimize performance. The gradient is determined using a technique called back-propagation, which involves performing computations backward through the network. The goal of the algorithm is to minimise the global error E defined below,

1 n E = ∑ (t (k ) − o( k )) 2 2 k =1

(1)

where o(k) and t(k) are the outputs and target network for any k output node. The summation is carried out over all output nodes for every training pattern. A pair of input and output values constitutes a training pattern. The back-propagation WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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algorithm calculates the error E as per Eq. (1) and distributes it backward from the output to hidden and input neurons. This is done using the steepest gradient descent principle where the change in weight is directed towards negative of the error gradient. The incremental change in the weight may be expressed as,

∆wn = α∆wn −1 − η

∂E ∂w

(2)

where w is the weight between any two nodes ∆wn and ∆wn-1 are the changes in the weight at nth and n-1th iterations; α the momentum factor and η the learning rate. The learning rate governs the size of the weight change during each iteration. The momentum factor prevents the weight oscillations during training iterations and also accelerates the training on flat error surfaces [11]. The activation function used for the hidden neurons of the networks are generally the sigmoid function (‘tansig’). The output neurons can have linear activation function (‘purelin’). In the present study, fast algorithms, developed as modified versions to the standard back propagation algorithm are used, known as the Levenberg-Marquardt algorithm (‘trainlm’). Also, the learning function used are the gradient descent weight/bias learning function (‘learngd’). 3.2 Models In the present work, ANN models are developed to obtain wind speed for forecast length of 1 hour and wind energy for forecast lengths of 3, 6, 12 and 24 hours. The available database concerns the wind farm is in the form of average wind speeds obtained through anemometric measurements and collected every 10 minutes. The wind speed data is divided into training dataset (years I, II, III) and test dataset (year IV). For each of the prediction lengths, results are obtained for Multi Layer Feed Forward Networks. The required functional relationship for the hourly average wind speeds observed for the site may be expressed as, (3) v = f (v , v , v , v ,...) t +1

t −1

t

t −2

t −3

where vti is the hourly average wind speed of periods before t. The required functional relationship for the hourly wind energy observed for the site may be expressed as, ∆t (4)

∑ P = f (v , v i =t

i

t

v

v ,...)

t −1, t − 2, t − 3

where ∆t is the forecast length for the wind energy prediction (3, 6, 12 and 24 hours), Pi is the hourly wind energy and vti is the hourly average wind speed of periods before t. Energy wind is calculated by the mean power curve of turbines of park. There is no systematic approach for selection of the input variables which could be followed, but certain statistical parameters can be used to determine the relevant inputs. In this work an autocorrelation coefficient (ρ) was WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Statistical properties of wind speed for the site.

Wind speed

Training set (years I,II,III)

Test set (year IV)

Minimum Maximum Mean Standard deviation

0 26.38 6.6 4.1805

0.34 24.837 6.77 4.3148

Table 2:

MSE for different number of inputs and prediction lengths (global training set).

Number of inputs

1 hour

3 hours

6 hours

7 16 24 36 48

0,0167 0,011 0,02 0,033 0,06

0,05 0,047 0,04539 0,1 0,15

0,05 0,039 0,01 0,028 0,03

Table 3:

12 hours 24 hours 0,183 0,1 0,0967 0,09 0,098

0,2 0,1 0,13 0,111 0,08

Architecture network: Multi-layer feed forward networks. (1): (vt, vt-1, vt-2, …vt-16), (2): (vt, vt-1, vt-2, …vt-24), (3): (vt, vt-1, vt-2, …vt-24), (4): (vt, vt-1, vt-2, …vt-36), (5): (vt, vt-1, vt-2, …vt-48).

Parameters Training function Adapt learning function Performance function Number layers Neurons (layer 1) –inputs Neurons (layer 2) Neurons (layer 3) –output Activation function hidden layer Activation function output layer Epochs

Parameters Training function Adapt learning function Performance function Number layers Neurons (layer 1) –inputs Neurons (layer 2) Neurons (layer 3) –output Activation function hidden layer Activation function output layer Epochs

1 hour TRAINLM LEARNGD MSE 3 16 (1) 8 1 (vt+1) Tansig Purelin 150

12 hours TRAINLM LEARNGD MSE 3 36 (4) 18 1(Pt:t+12) Tansig Purelin 200

3 hours

6 hours

TRAINLM LEARNGD MSE 3 24 (2) 12 1 (Pt:t+3) tansig Purelin 300

TRAINLM LEARNGD MSE 3 24 (3) 12 1(Pt:t+6) tansig purelin 100

24 hours TRAINLM LEARNGD MSE 3 48 (5) 24 1(Pt:t+24) tansig purelin 200



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used to obtain the required number of inputs for the models. The values of autocorrelation coefficient give an indication about the number of previous data values which are significant for forecasting the wind speed at a future time point. The database is partitioned into two disjoint subsets: training and test set. The motivation is to assess the network’s ability to generalize supplying a data set different from the one used for parameter estimation. Also, the target’s network for the prediction of 1 hour in advance is wind speed while for the prediction in the time horizon of 3-24 hours is the wind energy. The statistical properties of the wind speed data and for the various sets are given in table 1. Before training, inputs and targets are scaled so that they always fall within a specified range of [-1,1]. Post processing is done while simulating the network after the training process. For the selected network type and architecture, the parameters (weights and bias values) are assumed as random values. The parameters relevant in the training algorithm, error goal and number of epochs. Table 2 shows the observed MSE for different number of inputs and prediction lengths. Table 3 shows the principal parameters assumed for the networks.

4


ANNs models are developed, simulated and tested for forecast lengths of 1 hour, 3, 6, 12 and 24 hours. So, in the following, results of network simulations were shown. In order to show the model accuracy, the results using the ANNs models, are compared with the observations. The MSE function, expressed as:

MSE =

1 N

(5)

N

∑ (t (k ) − o(k ))2 k =1

measures the network’s performance according to the mean of squared errors. The correspondent values are shown in table 4. Results of network simulations are compared in terms of average percentage error on test data set. As shown in fig. 3, the approximation of the prediction of wind speed in the 1-hour ahead and for the two week of test set is good. During training of network the MSE stabilizes at value of 0.0115968 after 150 epoch. Table 4:

Values of performance function of ANNs – MSE.

ANNs

1 hour

3 hours

6 hours

12 hours

24 hours

MSE

0.0115968

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Forecast errors increase with increasing of prediction length. Fig. 4 shows the simulated of the network’s output for forecast energy for all time horizons in two weeks of test data. In the 3 hours ahead (a) the output of the network approximates the observed energy with an error greater than the error realized for forecasting the wind speed in the 1 hour ahead. The value of the MSE stabilizes at 0.05 after 300 epochs of learning. In the 6 hours ahead (b), the output of the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Adimensional Velocity

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network approximates the observed energy with an error greater than the error realized obtained for forecasting the wind energy in the 1 and 3 hours ahead. The value of the MSE stabilizes at 0.1 after 100 epochs of learning. (c) shows the simulated of the network’s output for forecast energy in the 12 hours ahead, the value of the MSE stabilizes at 0.09769 after 200 epochs of learning. (d) shows the simulated of the network’s output for forecast energy in the 24 hours ahead, the value of the MSE stabilizes at 0.08069 after 200 epochs of learning.

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ANN for prediction of wind velocity (adimensionalized with respect to the maximum observed velocity in the period) – Prediction length of 1 hour.

The 24-hour forecast is the longest horizon forecast included in this study, and is well outside the acknowledged boundaries for statistical estimation of wind speed, as described in literature. The ANN method for prediction shows signs of reduced accuracy at this range. Fig. 5 shows the fraction of average errors on wind energy observed for the test set and for all prediction lengths. For prediction length of 1 hour the average percentage error on the power observed changes from a minimum of 1% (April) to a maximum of 2.6% (November). From April to August these figures show a lower error than winter months. This is correlated with the result of the statistical analysis in fact the wind speeds in winter months were higher than summer months: the neural network has major difficult to prediction the high wind speeds, so prediction errors in these months are greater. For prediction length of 3 hours the average percentage error on energy observed changes from a minimum of 7% (July) to a maximum of 12% (January). For prediction length of 6 hours the average percentage error changes from a minimum of 10% (December) to a maximum of 16% (August). For prediction length of 12 hours the average percentage error changes from a WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


205

Adimensional Wind energy

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minimum of 13% (December) to a maximum of 18% (August-February). For prediction length of 24 hours the error on energy observed changes from a minimum of 16% (December) to a maximum of 25,5% (February). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

206 Energy and Sustainability II So, with the extension of prediction time horizon, the reliability of a prediction based only the statistical methods reducing considerably. The maximum error rate is 25% with time horizon of 12 and 24 hours so we cannot consider acceptable these forecasts. Fig. 6 shows the fraction of standard deviation of prediction errors for all prediction lengths.

Average error of prediction

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5

207

Conclusions and perspectives

The present paper has developed artificial neural networks (ANN) models to forecast the wind power prediction of a wind farm for different time horizons. We have shown how wind power density forecasts, for lead times from one to 24 hours ahead, can be generated from wind speed observations. There is a clear difference in the ability of ANN forecast models applied to different time horizons. The results show that for a forecast horizon under 6 hours this method can be considered a valid instrument to support control by the management of a wind park. The study shows lower errors compared to those found in literature to forecast one hour in advance [7]. The reliability of a prediction based only the statistical methods reducing considerably, with the extension of prediction time horizon. The error rate is 20% with time horizon of 12 and 24 hours so we cannot consider these forecasts to be acceptable. For prediction with time horizons of 12 and 24 hours other methods should be investigated because forecasts with neural networks are not reliable. We believe that the errors obtained could be reduced with a neural network able of taking different atmospheric variables as inputs, such as wind direction (useful particularly for prediction of higher speeds), pressure, temperature, etc. Also, we think that an application, in future work, of mixed methods such as neuro-fuzzy networks, will be useful to obtain reliable wind forecasts.

Nomenclature E= global error o(k)= network’s output t(k)= network’s target vti= average wind speed t i w= connection weight α = momentum factor η = learning rate ∆t =forecast length Pi=hourly wind energy MSE=mean square error

References [1] [2] [3]

Burton, N. J. & Bossanyi, Wind energy handbook, Wiley 2001. Bossanyi, E.A. Short-term stochastic wind prediction and possible control application, Proceedings of the Delphi Workshop on “Wind Energy Application” Greece (1985), pp. 137-142. Kariniotakis, N.E. & Stavrakakis, Advanced short-term forecasting of wind power production, Proceedings of the 1996 European Union Wind Energy Conference EUWEC’97 , Dublin, Ireland, 1997, pp. 751-754.


208 Energy and Sustainability II [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

Dibike, P.C, Temporal neural networks for downscaling climate variability and extremes, Proceedings of the 2005 International Joint Conference on Neural Networks, Montreal, Canada, 2005. Flores, A. T. & G. Tapia, Application of a control algorithm for wind speed prediction and active power generation, Renewable Energy 30,p. 523-536, 2005. A. Sfetsos, A novel approach for the forecasting of mean hourly wind speed time series, Renewable Energy, 27 (2), pp. 163-174 Jayaraj, K. P., E. S. & Arun, Wind speed and power prediction using artificial neural networks, European Wind Energy Conference 2004 (EWEC). Huang, Z.S., Chalabi, Use of time-series analysis to model and forecast wind speed, Journal of Wind Engineering and Industrial Aerodynamics, 56, pp. 311-322, 1995. Giebel, R. B, G. K., The state-of-the-art in short-term prediction of wind power. a literature overview. Wind Energy 6(3), pp.273-280, 2003. C. Mohrlen, Uncertainty in wind energy forecasting, 2004, PhD Thesis. More, D.MC, Forecasting wind with neural networks, Marine Structures 2003, 16: 35-49. Demuth, M. B., M.H, Neural network toolbox 5, User’s Guide, The mathworks. Krose & Van der Smagt, Mathematics, an introduction to neural networks. Eighth edition, November 1996 Barbounis, J.B. T, Locally recurrent neural networks for long-term wind speed and power prediction, Neurocomputing, 69 (4), pp. 466-496, 2006 Barbounis, J.B. T, Locally recurrent neural networks for wind speed prediction using spatial correlation, Information Sciences, 177 (24), pp. 5775-5797, 2007 Martí, G. K., Evaluation of advanced wind power forecasting models – results of the anemos project. http://anemos.cma.fr I. Sanchez, Short-term prediction of wind energy production. International Journal of Forecasting, 22 (1), pp.43-56, 2006.


Section 3 Energy policies



211

A review of the Bioenergy potential of residual materials in Quebec S. David1 & N. Abatzoglou2 1

Laboratoires Shermont Inc., Canada Université de Sherbrook, Department of Chemical Engineering, Canada

2

Abstract In Quebec more than 48% of residual materials produced in 2006 throughout all societal activities have been disposed of finally in landfills. Despite government policies on the 3Rs (Reduction, Reutilization, Recycling) and the total recovery objectives set-up, the total mass landfilled has increased by 120% over the last 10 years. Over the last 50 years, although the agricultural surface decreased by half, the number of pigs tripled. With an annual production of almost 8 million pigs, more than 400 out of a total of 1200 Quebec municipalities have a considerable surplus in liquid manure. The present work undertakes a review of these two growing problems-opportunities in Quebec and proposes alternative and sustainable solutions. Since the building and operation of experimental bioreactors (manure digesters) in some farms in Quebec, the anaerobic co-digestion of the rural and urban putrescible materials seems an interesting avenue. The development of a green energy vector by valorising the so-produced biogas would also contribute in decreasing the rejection of contaminants in the environment. In this work, only the biomass, resulting from the residential sector and the quantity of the liquid manure available in Quebec, is considered to calculate the Bioenergy potential. The Bioenergy output of the various methanisation processes are compared with that abroad, particularly in Europe. The available biomass in Quebec has been calculated based on available statistical data regarding the production of urban waste and manure. The review shows that this Bioenergy vector technology is sustainable and that its commercialization can be profitable at a cost no higher than that of disposal in landfills. Keywords: biomass, organic waste, anaerobic methanisation, bioreactor, codigestion, green energy, Bioenergy. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090191


1

Introduction

It is well established that the actual prices of the majority of the goods and services do not integrate the real social and environmental cost. This is ecologically unacceptable. This is mainly due to the fact that the markets, in their current structure, are unaware of the limits of the natural processes. In nature, all residual matter generated by a living organism is used as a resource by another; this insures the natural recycling of all used resources. The challenge of our society is to reproduce this process in its economy. Putrescible matter is one of the principal causes of contamination in the places of disposal. In landfills, the anaerobic fermentation generates GreenHouse Gases (GHG). The organic compounds released by this fermentation migrate with water of leaching (leachates) and can contaminate surface as well as subsoil waters and aquifers, thus rendering them unsuitable for human consumption and to the surrounding biotopes. The recovery of the putrescible matter at the end of valorisation reduces the polluting load and the GHG emissions while providing us with Bioenergy and valued products (i.e. compost). The reduction of residual materials that end up in landfills is a positive element on the economy and the environment for a variety of reasons, including the reduction of the transport of these residual materials. Hog farm activities and the resulting manure spreading for fertilizing purposes contribute considerably to the release of ammonia emissions, the increase of the phosphorous content in the soil and the pathogenic organisms in the environment. The emissions of ammonia contribute to the GHG emissions as well as to an imbalance of the nutritive elements in the ecosystems, including surface water. Long-term liquid manure spreading in Quebec, based on directives inspired by soil nitrogen enrichment, led to an excess of phosphorus. Moreover, spreading of the liquid manure also increases the water-soluble phosphorus concentrations, which causes direct eutrophication conditions in surface waters. Currently the farm-by-farm approach, stipulated in 2002 by the Law on agricultural production, led to a serious problem. Indeed, instead of calculating the rate of available phosphorus by catchment area, the quantity of phosphorus surplus is calculated based on the surface of the so-fertilized soil. This approach does not consider the type of soil, the zones easily flooded, the antibiotics present in the liquid manures and the initial quality of the surface waters (lakes and rivers) near the ground of spreading. These factors can have direct repercussions for certain rivers and more sensitive underground sheets of water. In an effort to minimize the harmful effects on the environment by the actual residual materials disposal and by the management of the liquid manure, this review tries to establish if methanisation of the organic residues and the liquid manure can be a sustainable solution.

2

Solid waste management in Quebec

In Quebec, based on data from 2006, only half of the materials that may undergo beneficiation were recovered. The landfill of the putrescible materials, the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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spreading of the animal manure and their storage are not sustainable solutions. These practices contribute to higher management costs, to increasing GHGs and other environmental nuisances, including the direct effect on the natural resources availability. 2.1 Waste recycling in Quebec Since 1989, the year of the publication of the Integrated Solid Waste Management Policy, Quebec made a significant step in the direction of sustainable development. However, 17 years later, according to a Recyc-Quebec [1] assessment in 2006, Quebec recovered hardly 52% of its residual materials. More specifically, inasmuch as organic matter is concerned, its collection is at present under development in Quebec. This collection comprises green residues, such as branches, grass and sheets, as well as waste from food. There are currently 44 composting installations in Quebec. Moreover, the cities or municipalities of Laval, Victoriaville, Lachute, Saint-Donat, Rawdon and the Island-of-the-Madeleine, have successful organic matter collection activities. However, the rate of recovery of all putrescible residual materials is as low as 8%. In 2006, the quantity of recovered organic matter rose to 0.36 million tons on a potential of approximately 4.5 million tons. It should be noted that the objectives of the Policy are expressed according to the potential that may undergo beneficiation. It is estimated that 85% to 90% of the residual materials of the various branches of activity have a potential of being valuably recovered. Recyc-Quebec announced in 2006 that nearly 13 million tons of residual materials are generated annually in Quebec. As Quebec’s population in 2006 was 7.651 million inhabitants, the total rate of production of residual matters per capita and year is estimated at 1.69 tons, including industries, trade activities and institutions. A noticeable fact is that, in 2006, the rate of final disposal of these materials through landfill and incineration was estimated at 880kg/year/inhabitant, whereas ten years earlier, this quantity was lower; 740kg/year/habitant in 1996. Thus, the average inhabitant of Quebec, including industrial, trade, construction, restoration/demolition and institutional activities, as well as the municipalities, in 2006 eliminated 875 kg/year/inhabitant and recovered 940 kg/year/inhabitant. 2.2 Compostable material coming from the municipal residential sector The municipal sector generates an average of 23%w/w of Quebec’s residual materials. Thus, in 2006, the municipal sector generated 3.015 million tons. This represents an average of 400 kg/year/inhabitant. Although 95% of these materials are theoretically recyclable, only 31% of them were recovered. Thus, 255 kg/year/inhabitant were disposed of finally in landfills or incinerated. The putrescible materials represent 44% of the total 3.015 million tons generated annually. This is 1.327 million tons of compostable organic material per year that may undergo beneficiation. The available statistical data give us the information that only 0,110 million organic tons of materials were recovered in 2006. Table 1 presents Quebec’s population by administrative areas, according WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

214 Energy and Sustainability II to the 2001 census, and an estimation of the quantity of putrescible materials available by areas. This estimation was done by assuming that the residual material generation is geographically uniform in Quebec. Globally it is easy to calculate that the remaining available compostable material is 183kg/year/inhabitant. Table 1:

Generation of organic compostable materials by the residential sector in the different administrative regions in Quebec.

Administrative regions Bas-Saint-Laurent Saguenay-Lac-Saint-Jean Capitale-Nationale Mauricie Estrie Montréal Outaouais Abitibi-Témiscamingue Côte-Nord Nord-du-Québec Gaspésie-îles-de-laMadeleine Chaudière-Appalaches Laval Lanaudière Laurentides Montérégie Centre-du-Québec Total :

200 630 278 279 638 917 255 268 285 613 1 812 723 315 546 146 097 97 766 38 575

Organic compostable materials (tons/year) 36 715 50 925 116 922 46 714 52 267 331 728 57 745 26 736 17 891 7 059

96 924

17 737

383 376 343 005 388 495 461 366 1 276 397 218 502 7 237 479

70 159 62 770 71 095 84 430 233 581 39 986 1 324 460

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2.3 Landfill sites The average maintenance costs of the landfill sites is approximately 65 cnd$/ton. The law “Règlement sur l’enfouissement et l’incinération de matières résiduelles” (c. Q-2, r.6.02) adds an additional fee (tax) of 10.22 cnd$/ton. On this basis, approximately 504 million cnd$ have been spent in Quebec only in 2006 for the landfill of the residual materials. These numbers do not include the transport cost. Moreover, these costs do not contain the management of the animal manure, mining, paper mills and sawmills residues, the contaminated soils as well as all materials characterized as dangerous and biomedical. According to the “Règlement sur l’enfouissement et l’incinération de matières résiduelles” (c. Q-2, r.6.02), a soil of minimal thickness of 30cm must cover each WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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day the landfilled residual materials in order to prevent from vermin and biogas spreading. 2.4 The porcine industry In June 2002, Quebec adopted the law “Règlement sur les exploitations agricoles” (REA); this law is aimed at agricultural activities within the context of the sustainable development. Its main objective is to have the farmers being more concerned about the management of the animal manure and other fertilizing matters, more particularly phosphorus. The phosphorus assessment, required by the REA, is one of the main tools of this law. The farms having a surplus of fertilizing potential will be in the obligation, according to REA, to reach a balance between the capacity of the soil to receive phosphorus and the quantities of manure to be spread out in these lands. For some of them, the only solution enabling them to reach this balance will be the treatment of the liquid manure. In Quebec, the number of farms passed from 135 000 in 1951 to 35 000 in 1996. Moreover, the agricultural surfaces decreased by about 50% since 1951; from 3.4 to 1.9 million hectares. However, during the same period the number of pigs has tripled. The annual volume of production should not be confused with the number of pigs in inventory on the porcine exploitations during the year. Quebec counted approximately 3.9 million pigs in inventory in 2004 and 4.2 million in 2006. There were 4097 producers of pigs in 2004 and 4309 in 2003, a fall of 212 in one year. Such a geographically uniform space reduction, in one year only, accompanied by a production increase, can be explained by the increase of the activities of the existing integrators. Indeed, since the total annual volume of animal manure appears constant in Quebec (at approximately 32 million m3 of animal manure, of which approximately 10 million m3 of liquid manure), the farms have to manage an increasingly larger volume of manure. The quantity of liquid manure was multiplied by a factor of 90 between 1951 and 2001! Approximately 60% of the hog farms must have to establish local agreements for manure land spreading, because they do not possess enough arable land to respect the law. According to the Quebec Ministry of the Environment, more than 400 municipalities out of 1200 are in theoretical surplus of manure and/or liquid manure. Table 2 presents the quantity of liquid manures produced in Quebec. In March 2006, a refundable temporary tax credit was founded for the acquisition of installations for the treatment of pig liquid manure. This credit accounts for 30% of the acquisition and the installation costs of such a system of manure treatment; a maximum of 200 000 cnd$ is allocated by agricultural establishment. Only porcine companies, which do not qualify or make use of the provisions of chapter 6 of the program Premium-Green, qualify for this tax credit. All technologies of liquid manure treatment decrease the volume of the final disposal; this means that all fertilizing elements are concentrated in smaller volumes. They also contribute to reduce the odours associated with the management of liquid manures. Denmark is a pioneer in the management of livestock wastes and the optimal use of the nutritive elements contained in them. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Manure production by region in Quebec.

Administrative regions Bas-Saint-Laurent Saguenay-Lac-Saint-Jean Capitale-Nationale Mauricie Estrie Montréal Outaouais Abitibi-Témiscamingue Côte-Nord Nord-du-Québec Gaspésie-îles-de-la-Madeleine Chaudière-Appalaches Laval Lanaudière Laurentides Montérégie Centre-du-Québec Total :

Number of pigs [2] (2006) 153 459 16 954 97 433 142 945 249 363 n.d. 365 n.d. n.d. n.d. n.d. 1 296 635 n.d. 274 458 31 178 1 420 141 519 365 4 202 296

Manure (tons / year) 475 723 52 557 302 042 443 130 773 025 n.d. 1 132 n.d. n.d. n.d. n.d. 4 019 569 n.d. 850 820 96 652 4 402 437 1 610 032 13 027 119

Several successful programs have directly risen from Denmark’s agricultural policy: for example, the installation of V and W shaped sludge pits leads to a reduction of the ammonia evaporation by as high as 25%, while the cooling of the sludge in the pits results in an additional reduction of 20%. 2.5 The methanisation industry The management of the organic residues is not only one a concern in Quebec. In Europe there are already biogas production facilities from the anaerobic fermentation of organic residues. In Quebec, the final disposal of the majority of organic compostable material is done systematically as follows:  Incineration for the municipal wastewater treatment sludge;  Landfill disposal for the residential (table) residues;  Composting for the green residues;  Land spreading for the animal manure. 2.5.1 Legal context for the energy in Quebec In Canada, energy is under provincial jurisdiction and the law provisions vary considerably from one province to another. The new strict regulations covering the management of waste and the high costs of energy seem to boost the interest in all provinces. In fact, the province of Ontario has recently put in application a regulation establishing the price of 0.11$/kWh (0.14$/kWh at the peak hours) for green electricity. This makes biogas more attractive to the Ontario’s farmers. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Ontario and Quebec are the only provinces to offer subsidies to those who install and operate biogas production systems. In fact, Quebec pays 70% of the costs incurred to install a manure handling system (maximum of 200 000$). The Ontarian producers can obtain a subsidy up to 60 000$ for a system of manure treatment and storage capacity in the farm. Currently in Quebec, no law exists covering specifically the production of biogas. However, some regulations like the one covering the Waste elimination activities (Landfill and Incineration) and the production of electricity contain some clauses on biogases. For example, the landfills must be appropriately sealed in order to avoid the migration of biogases through the air or the subsoil. Thus, biogases from these sites must be collected and, in the absence of energetic exploitation, this biogas must be burned safely and in accordance with the law for the atmospheric quality preservation. It is rather obvious that, without a specific regulation covering the production of biogas, and which defined clearly all constraints to be respected, it is difficult to establish a long-term biogas production system. However, according to the article 22 of Quebec’s Law on the Environmental Quality (LQE), a certificate of authorization is requested for the establishment of a residues management activity. To produce such a certificate, an Environmental Impact Assessment study must be deposited to the Ministry of the Sustainable Development, the Environment and Parks (MDDEP). In the case of the construction of a high capacity power station, the project team has to deposit the preliminary draft of such a study to the Office of the Public Hearings (Bureau d’audiences publiques sur l’environnement - BAPE), such as defined in article 31.1 of the LQE. In Canada, under the article 5 of the Canadian Law on the environment, an environmental assessment is requested also for having the project authorized. If the project contributes in establishing more sustainable management activities, the Ministry of the Natural Resources Canada could even provide financial assistance to the project in order to help respecting the Environmental Law provisions. Moreover, the Federal Government brought modifications to the rates of the deduction for goods amortization (DGA). The maximum rate of DGA for each type of redeemable good is fixed in the Law covering the field of income tax payment. The rate of DGA applicable to certain high efficiency cogeneration units and renewable energy production passes from 30% (rate of category 43.1) to 50% because of the inclusion of these goods in the new category 43.2. To qualify for this new increased rate, the material used in building such a unit must generally be new and be acquired after February 22, 2005 and before 2012. This new rate will also apply to any biogas production material and district energy distribution networks which use efficient cogeneration technology after February 22, 2005 and before 2012. 2.5.2 Biogas production Methanisation represents a possible sustainable solution for the recycling of organic matter. All organic materials can produce biogas: i.e. animal dejections, fruits, vegetables, remainders of slaughter-house, rejections of dairy, brewery, distilling. The organic matter rich in fibre like the grass, sheets and wood is WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

218 Energy and Sustainability II however difficult to digest and are not recommended to use as source of biogas. The biogas composition depends upon the nature of the treated waste and the treatment conditions which depend largely on the local climate. The average composition of biogas is 60% methane (CH4) and 40% carbon dioxide (CO2). The bioreactor is an anaerobic tank where organic matter is introduced and the temperature has to be maintained at an appropriate level depending upon the nature and the activity of the anaerobic digestion microorganisms. Under the selected conditions, anaerobic bacteria use the organic matter as feed to multiply and produce biogas as a result of their metabolism. The quantity of organic matter which exits the bioreactor is equal to that at the entrance minus the produced biogas. The digested organic matter is practically odourless, has a high fertilizing value, it is less polluting and reduced in organic load (DBO5). The exiting solid/liquid mixture can be separated; the solid muddy part (sludge) can be composted and the liquid part can be used directly as a fertilizer or treated and disposed of safely according to the existing regulations. The collection and energetic exploitation of the biogas produced during the anaerobic methanisation decreases the GES by a factor of just as 20. Since the digestion conditions are better controlled within a bioreactor, the total quantity of biogas per unit of organic matter extracted from a bioreactor is higher than that extracted from a landfill site. A bioreactor is 3 to 10 times more energy efficient than landfill. The quantity of biogas which can be extracted from the organic matter also depends on the type of organic residues and the performance of the bioreactor. Therefore, the production of biogas varies from 20 to 800 m3 per ton of organic material. Each m3 of biogas contains the equivalent of 6kWh of energy. However the conversion of biogas into electricity by an electric generator produces 2kWhe; the other 4 kWh is dissipated in the form of heat and at least 75% of this which can be recovered and used for thermal energy needs. The capital investment for a bioreactor is relatively high [3]. The payback period for such an investment is estimated [4] at 7-10 years and it is due to the value of the biogas and more precisely its value as an electrical and/or thermal energy vector. Regarding the biogas as an energy vector, three uses are tested industrially: (a) combustion in a boiler for heat generation; (b) fuel of internal combustion engines for the production of electricity or for car motors and (c) in cogeneration for the simultaneous production of heat and electricity. The treatment by methanisation of a tone of agricultural organic matter produces 500 m3 of methane at standard conditions. The Methanisation by anaerobic digestion utilizes the organic matter which most easily digestible, that is 30-80% of the oven dry organic material. Besides, this is the part which generates organic pollution, unpleasant odours and biogas. The part remaining after methanisation (20-70%) can be used as fertilizer in agriculture. The methanisation of wastewater treatment plants sludge as well as all putrescible domestic (residential) and industrial waste, reduced their quantity up to 35%. A ton of these organic residues generates up to 175 m3 of biogas. A landfill recovers an average of 100 m3 of methane per ton of treated waste, whereas in agriculture, a ton of manure produces in 90 days approximately 60 m3 of biogas containing 55% of methane. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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The oldest and more mature methanisation technology through anaerobic digestion is that of "the infinitely mixed" bioreactor in whom mixing is ensured hydraulically or more frequently by biogas recirculation. This type of bioreactor is generally operated with mesophilic organisms towards 35ºC. In the last years several technological novelties have been proposed and improved the efficiency of this type of bioreactor in such a way that streams like domestic organic materials, which are generally more complex than manure, could be received and methanised as well. Degrémont, for example, has proposed the upstream use of a "hydropulpor", a metal tank equipped with a central propeller which lyses the vegetable cells and puts the organic matter in full suspension in the recycle stream of the process (proceeded BTA). In this process the inorganic matters which could enter the unit (e.g. plastic, textile) float on the surface and are recovered by a hydraulic comb; the heavy mineral elements (e.g. glass, stones, bones) decant and are extracted by the bottom. The thus produced liquid pulp passes then in a hydrocyclone which removes the heavy fine and abrasive particles like sand. In Germany and Austria, appeared bioreactors in ovoid forms [5]. This form has a smaller footprint per volume, allows a more homogeneous and regular mixing thus reducing the dead zones or those of preferential fermentation and facilitates decantation. The second generation bioreactors use the technology of the fixed cells or "anaerobic filter". This technology allows a quasi continuous flow bioreactor operation because the bacteria are fixed in a preselected support and they are not entrained by the treated liquid flow. In France, the process suggested by Proserpol, comprises a support made up of plastic rings in bulk and the injection of the feed is carried out by the top of the bioreactor all over and through the bacterial stabilization rings. In the Netherlands introduced the process UASB (Upflow Anaerobic Sludge Blanket) [found in 5] in which the support is biological and flow is ascending. Compared to the old technique, this technology has the advantage of being much faster (a few hours or a few days instead of two weeks). It is possible to still speed up the process by adopting the thermophilic fermentation, which multiplies the productivity by a factor of 4-10 and produces a biogas richer in methane (up to about 80%v CH4). For the hog farms manure, the process must proceed in two stages, the preliminary acidification, then methanisation, which call upon families of different bacteria, which must, thus, be held in distinct tanks. The Tilburg bioreactors in the Netherlands (1994, 52 000 tons/year) and that of Engelskirchen in Germany (1998, 35 000 tons/year), are fed only with organic materials coming from domestic waste. The methane produced in Tilburg’s bioreactors is introduced into the gas network of the municipality for domestic use. The Engelskirchen’s biogas is used for the production of electricity. Thanks to a sorting at the source, both produce a compost of high quality. During its high output operation, the factory of Tilburg produces 4 million m3 of biogas per year. This biogas contains 56% CH4, very small amounts of hydrogen sulphide, and 31 000 tons/year of organic soil conditioner which may undergo beneficiation in agriculture. The idea of a selective and centralized co-digestion of agricultural biomasses was born in Denmark and was applied since 1988 thanks to the support of the government. It consists in collecting in the vicinity of the manures WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

220 Energy and Sustainability II production sites the existing domestic and/or industrial organic waste, sludge from wastewater treatment stations and methanise them together. The economic assessment of the operation is mitigated. With a starting investment of 8 million $ and operating costs of 600 000 $/an, the payback period has been 8-10 years thanks to the subsidy of 3 million $ granted by the Danish Ministry of Energy. The main part of the incomes comes from the sale of biogas (800 000 to 1 000 000 $/year) and from the waste management tipping fee which the industrialists pay to get rid of their waste (approximately 200 000 $/year).

3

Methanisation in Quebec?

Methanisation represents a complement of activity for the farmers, who can develop economically and energetically the liquid manure and even the organic part of the domestic residues. Methanisation is synonymous with energetic autonomy for the biogas producers. While bringing an energetic and ecological response to the problem of the treatment of the liquid manures and organic residues, methanisation is an activity of depollution and an alternative to landfill. The environmental cost of the deterioration of nature by hog farming must be taken into account in the market price of the pig. This cost can be attenuated by agreements between eco-energy the hog farms; thus, hog farms manure can be a feedstock for eco-energy farms producing compost and biogas as an energy vector. Only the cost of transport would be the responsibility of the producer, whereas the eco-energy farms would recover and market the green energy. Producers' cooperatives can also contribute financially in order to install common bigger bioreactors. As explained below, the establishment of a “two ways” selective waste sorting at the source and pick-up could be a sustainable solution. Our residues would be split in putrescible organic and non-putrescible materials. This strategy would allow recovering nearly 95% of all residual matters in the domestic sector. The codigestion of putrescible organic residues and liquid manure would be beneficial to both the agricultural and municipal sectors. The accessibility of this putrescible resource was established by administrative regions in Quebec. The density of the population is not an important factor, since in rural as well as in urban areas, the transport of the organic matter to an eco-energy farm is at least as easy as in any existing landfill site. The only element which differentiates the administrative regions between themselves is that certain among them do not have or have few hog farms, which would be favourable to install and operate bioreactors because of their characteristics as large urban Number of eco-energy farms required per administrative region and potential revenues. However, due to the proximity of the territories of Montérégie and Lanaudière, the administrative areas of Montreal and Laval, which are such urban centres, could easily transport their organic residues in bioreactors operated in these two other areas. Table 3 presents the energetic potential of the combined domestic putrescible organic material and the manure in Quebec. Each ton of organic matter was estimated as having a potential of production of 100 m3 of biogas. This is very conservative because it represents the equivalent of the production in a landfill WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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which is at least 3 times lower than that in a bioreactor. The energy, which can be recovered by a biogas, was evaluated to 2 kWh/m3. Thus, according to Table 3, an energy potential of 2 844 656 000 kWh is available in Quebec. Considering that in Quebec, a one-family residence consumes 17 000 kWh annually, the energy needs of about 167 000 houses can be covered. Since the cost of residential electricity in Quebec is approximately 0.05 cnd$/kWh, the green energy worth is roughly 142 millions of cnd$. The number of eco-energy farms was evaluated according to a self capacity of 50 000 tons of organic matter per year. The cost for the establishment of such a farm was estimated at 0.3 millions of cnd$. It should be noted that the actual cost of the management of the organic matter coming from the domestic (residential) sector is equal to 90% of the capital cost of the installation of the 285 bioreactors necessary for methanise annually the 14 million tons of the available putrescible materials (domestic + manure). Considering the contribution of income of the residential sector, only the areas of the Boiler-Appalachian Mountains and Centre-of-Quebec, do not offer an income higher than the cost of establishment of an eco-energy farm.

4

Conclusion

The establishment of a two ways (putrescible and non-putrescible) selective sorting and pick-up of the domestic residues in Quebec would increase the rate of recovery of all the residual matters. The non-putrescible matters can be recycled up to 95%, whereas the organic matter can be used as a renewable energy vector. The only problem comes from the green residues (grass, sheets, paper and paperboard) which contain a high percentage of non-easily digestible collection which is already established in some municipalities (i.e. Victoriaville, Sherbrooke). A good sorting of the putrescibles at the source (residential) is important because the efficiency of the methanisation bioreactors and the quality of the resulting compost are strong function of the feedstock quality. The existence of incentives and the appropriate enforcement of a regulation establishing an obligation to treat the manure of all hog farms in eco-energy farms using bioreactors would also contribute to the reduction of contaminants in the environment. All putrescible matters (domestic putrescible organic materials and liquid manure) can be treated (methanised) in eco-energy farms, equipped co-digestion bioreactors. As it is well established that the ideal operation conditions of the anaerobic digestion of these two distinct families of putrescible organic materials are not the same some additional fundamental and applied research is necessary to have a sustainable operation. The existence of two parallel bioreactors might be an appropriate solution since it is known that different bacterial populations are needed. By considering only the income received from the production of green energy, the payback period of a bioreactor at an average Quebec hog farm is approximately 10 years. As for the eco-energy farms, they could require higher initial investments because of the combined feed complexity. These additional costs can be set-off by the perception of the equivalent landfill disposal tipping fee which in Quebec is in average 65$/ton. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

Administrative regions

Montérégie (+Montréal) Chaudière-Appalaches Centre-du-Québec Lanaudière (+ Laval) Estrie Bas-Saint-Laurent Mauricie Capitale-Nationale Laurentides Saguenay/Lac-Saint Jean Total :

(a) (b) (c) (d) (e) (f) (g) (h)

Energetic potential of the domestic putrescible organic material and manure in Quebec. (a) Domestic organic residues (tons/yr) 565 309 70 159 39 986 133 865 52 267 36 715 46 714 116 922 84 430 50 925

(b) Revenue Residential Sector (M$cnd/yr) 36.7 4.6 2.6 8.7 3.4 2.4 3.0 7.6 5.5 3.3

1 197 292

77.8

(c) Manure (tons/yr) 4 402 437 4 019 569 1 610 032 850 820 773 025 475 723 443 130 302 042 96 652 52 557 13 025 987

(d) No

(e) Capital cost

(f) Power (MWh)

(g) Revenue from energy (M$cnd/yr)

(h) Mixed Revenue (M$cnd/farm/yr)

99 82 33 20 17 10 10 8 4 2

(M$cnd) 29.7 24.6 9.9 6.0 5.1 3.0 3.0 2.4 2.1 0.6

993 549 817 946 330 004 196 937 165 058 102 488 97 969 83 793 36 216 20 696

49.7 40.9 16.5 9.8 8.3 5.1 4.9 4.2 1.8 1.0

0.573 0.255 0.279 0.625 0.388 0.450 0.490 1.175 1.300 1.850

285

86.4

2 844 656

142.2

0.469

Tons of domestic organic materials = Table 1 Revenue residential sector = 65$cnd * tons of domestic organic materials Tons of manure = Table 2 Number of farms = (tons of domestic organic materials + tons of manure) / 50 000 tons Capital cost for bioreactor installation and operation = 0,300 M$cnd * number of eco-energy farms Power = (tons of domestic organic materials + tons of manure) * 100 m3 of biogas * 2 kWh Revenue from energy = Power * 0.05 $cnd/kWh Mixed Revenue = Revenue from energy + Revenue from domestic sector – Capital cost for bioreactor installation and operation



Table 3:


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If this scenario becomes a reality, nearly 13 million tons of liquid manure and 1 million tons of putrescible domestic organic materials produced annually in Quebec could become a source of green, renewable energy in a sustainable development context, without any economic or social sacrifice.

Acknowledgements The contributions of Steve Boivin, Eng. and Richard Royer, Eng. of Bio-Terre Systems Inc., (150, rue Vimy, Sherbrooke, Québec, Canada, J1J 3M7) are gratefully acknowledged.

References [1] Recyc-Québec, Bilan 2006 de la gestion des matières résiduelles au Québec, Bibliothèque et Archives nationales du Québec, 2007. [2] Institut de la statistique du Québec, Inventaire de fin de semestre de porcs, par région administrative, Québec 2005-2006, Gouvernement du Québec, 2007. [3] Électrigaz, Le biogaz est une énergie renouvelable issue de la décomposition naturelle de la matière organique par des bactéries anaérobiques. 2007. http://www.electrigaz.com [4] Électrigaz, Le biogaz est une énergie renouvelable issue de la décomposition naturelle de la matière organique par des bactéries anaérobiques. 2007.

http://www.electrigaz.com [5] Énergie Plus, Rapport, études France, 2007. http://www.energie-

plus.com




225

Potential transport energy demand and oil dependency mitigation measures T. E. Lane & M. J. W. A. Vanderschuren Centre for Transport Studies, University of Cape Town, South Africa

Abstract Transportation, including the movement of both people and freight, accounts for over 60% of all oil consumed globally, while the world’s transportation systems are over 90% dependent on oil and oil by-products. The predicted depletion of oil and subsequent rising fuel prices pose a significant threat to transportation systems worldwide. The choice of transportation system technologies and the use of transportation systems will influence a country’s vulnerability to ‘oil shocks’. Transport and energy planning policies must prepare for the likelihood of such shocks and ameliorate them via policy options. A precautionary approach needs to be adopted to reduce the dependency on oil, in order to improve the sustainability of transportation systems. This paper addresses the need for oil independence and describes potential ways in which Europe can progress towards this goal. Various mitigation measures for various transport modes are discussed. These measures are ultimately combined into strategies to bridge the gap between oil supply and demand. The objective of the paper is to alert the reader to energy demand management measures available, to the potential impacts of these measures and to the definite need for a move towards new transportation technologies if oil depletion is to be successfully traversed. Keywords: peak oil, oil dependence, transport energy, energy mitigation.

1

Introduction

Transportation, the platform for economic activity and personal mobility, is entirely dependent on the energy supply that powers it. The transport sector has been the fastest growing consumer of energy in the European Union (EU), accounting for a share of nearly 31% of total final energy demand in 2004 [1] WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090201

226 Energy and Sustainability II and 71% of all oil consumption in the EU [2]. The sustainability of the transport sector depends on both the quantity of energy consumed and the sources of energy used. Currently, European transport is powered by petrol, diesel, liquefied petroleum gas (LPG), electricity and jet fuel. Apart from electricity (that is not generated from oil-based resources), all of these energy sources are dependent on crude oil. In fact, 95% of European transport is dependent on oil and, therefore, exposed to oil supply risks. This is highly unsustainable. This paper addresses the EU’s need for oil independence (section 2) and potential mitigation measures and strategies (sections 3 and 4) to facilitate the achievement of reducing oil dependence.

2

The need for oil independence

Oil is a finite, non-renewable energy source. Although it has been abundant and cheap for the past century, at some stage oil production will start to taper off. Current oil fields are rapidly depleting, but there is little consensus about the rate of decline. The International Energy Agency (IEA) predicts the rate of decline to be 6.7% [3], whilst Colin Campbell, the chairman of the Association for the study of Peak Oil and Gas, expects it to be around 2.6% per annum [4]. Another item under dispute is the timing of the production peak. Geopolitical events (such as wars in oil producing countries), extreme weather conditions (like hurricanes in the Gulf of Mexico) and economic factors (e.g. an international recession) could all influence either supply or demand for oil [4]. The IEA does not expect peaking before 2030 [5], while Schoppers and Murphy are 97.5% certain that the peak will occur by 2015 ( 1.26 years) [6]. Many others believe that the peak might have occurred already. To reflect this uncertainty, three oil supply depletion possibilities are considered: firstly that nothing will change before 2030, secondly that a peak is reached in 2020 and, pessimistically third, that peaking occurs in 2012. Figure 1 showcases the resulting transport energy supply trajectories. Global demand for oil has been growing for decades, resulting from both population expansion and economic growth. In 2007, the IEA forecasted that global oil demand will grow from 85 million barrels of oil per day to 130 million barrels of oil per day by 2030 [7], corresponding to a growth rate of around 2.15% per annum. In 2008, the IEA made a significant downward revision to the 2007 forecast, lowering the expected growth rate to 1% per annum [5]. This revision reflects the impact of higher prices and slightly slower GDP growth, as well as new policies to promote more fuel-efficient vehicles and encourage biofuels. Both an optimistic and conservative growth trajectory is reflected in figure 1. If oil does peak in 2012, transport energy demand will exceed supply somewhere between 2018 and 2022 (see fig. 1). This leaves a preparatory window of opportunity of 9 to 13 years. Should the peak happen in 2020, problems will start somewhere between 2023 and 2029, leaving a 14 to 20 year period to prepare for it. Even if peaking does not occur before 2030, demand still outstrips supply (from 2029), if demand grows at the optimistic rate. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Transport energy supply and demand projections Index Base year value = 2006 Demand

170.0

165.6 163.3

160.0 150.0 140.0 130.0

127.9

120.0

120.0

110.0 100.0 91.5

90.0 80.0

Year Supply (No Peak)

Supply (Peak 2020)

Demand (Optimistic)

Demand (Conservative)

Supply (Peak 2012)

Source: Adapted from IEA [5, 7], Eurostat [8] and ASPO [3, 4]

Figure 1:

Transport energy supply and demand projections.

It is highly unlikely that demand continues along the slow growth trend for the entire period, because demand is linked to economic growth and economic growth is the main aim of most countries around the world. It can be concluded that, if oil remains the world’s primary transport energy resource, transportation systems will face serious obstacles from anywhere between 2018 and 2029. The maximum lead time to try and avoid this is thus 20 years.

3

Measures to mitigate oil and energy dependency

There are various ways and means of either reducing transport’s oil or total energy demand. The most important measures are those that reduce the demand for transport, thereby reducing both energy and oil demand. These measures aim to eliminate excessive travel, although this can only be done to a certain level – some travel will always be required. For the remaining travel demand, the highest priority measures are those that improve energy efficiency. Energy efficiency measures also reduce total energy demand, regardless of the energy source used or the effective modal split. These measures can assist the EU in achieving the target of increasing energy efficiency by 20% by 2020, set by the European Commission in 2007 [9]. The third type of measure is aimed at reducing the demand for oil-based transport fuels, by substituting conventional fuels with alternative energy sources. 3.1 Transport demand reduction measures Developments in information and communications technology allows for the possibility of telecommuting, online shopping and distance learning, where the WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

228 Energy and Sustainability II use of technology substitutes physical travel. The development of sophisticated logistics chains is also enabled. Although many jobs lean themselves towards telecommuting, a certain amount of travel will always be required to allow face to face meetings and facilitate the shared use of equipment. An estimated reduction of between 1% and 10% in car trips is plausible [10]. Route optimisation entails planning trips along a route with the lowest generalised energy cost, by taking congestion penalties and empty running into account. In aviation, the shortest available routes are underused due to a lack of real-time and precise information, as well as the unavailability of certain parts of airspace [9]. The potential reduction in aviation emissions through optimised routing is estimated at 6% to 12% [9]. Emissions are related to fuel consumption; hence, emissions savings indicate relative fuel savings. Efficient usage of passenger vehicles results in less vehicle-kilometres needed to transport the same amount of passengers [11]. A high occupancy rate in passenger cars and buses has relatively little impact on the overall vehicle weight and, therefore, on energy consumption. Measures to increase occupancy rates include ridesharing, carpooling and high-occupancy vehicle lanes. Increasing vehicle load factors is a way to reduce the growth in freight transport vehicle-kilometres. The fact that some freight transport companies achieve much higher load factors than others in the same sector, suggests that load factors can be improved in the EU [12]. Methods to improve load factors include abandoning just-in-time manufacturing practices, promoting cabotage, avoiding empty return trips and load consolidation (bundling of products via advanced information systems). Estimates are that bundling could reduce the expected future doubling of vehicle-kilometres by 20% to 30% [12]. Land-use planning can have a dramatic influence on the amount of transport required in a settlement. Mixed use developments negate the need for long commuter trips and promote the use of non-motorised transport. Although this measure can potentially have the largest impact, it is difficult to estimate the extent to which it can be applied in the EU region. 3.2 Energy efficiency improvement measures Improving vehicle design increases the distance covered per unit of fuel consumed, by: reducing air and rolling resistance, improving engine technology or using light weight materials. New cars consumed approximately 10% less fuel in 2002 than they did in 1990 [13] and this trend is expected to continue. Airlines are aiming for a 25% fuel efficiency improvement through vehicle design by 2020 [14]. Railways can realise large potential savings from light-weighting (up to 20%) and cutting drag and friction (up to 10%) [15]. Technology options for reducing energy use in the shipping industry include hydrodynamic improvements and machinery; these technologies could reduce energy use by 5% to 30% on new ships and 4% to 20% on retrofitted old ships [16]. Vehicle maintenance is very influential in terms of fuel efficiency. According to estimations, fitting appropriate tyres and maintaining proper tyre pressure can improve vehicle fuel efficiency by more than 5% [10]. Keeping engines properly tuned can save 4%, checking and replacing air filters regularly WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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up to 10% and using the recommended grade of motor oil can save up to 2% [10]. Flight Sciences International [17] indicates that improved maintenance reduces aviation energy consumption between 5% and 10% over the long term. Another key area to improving energy efficiency is vehicle renewal practice. This affects the average age of the vehicle fleet, as well as the average size and efficiency of vehicles. Old vehicles should only be replaced with newer, more efficient technology vehicles. To illustrate: new aircraft are typically 70% more fuel efficient than 40 year old aircraft and 20% better than 10 year old aircraft [14]. The majority of new heavy vehicle engines are electronically controlled, providing a 7% to 15% improvement in fuel economy [18]. The European Commission (EC) has launched initiatives to promote a market for greener vehicles (i.e. the Car Fuel Efficiency Labelling Directive (1999/94/EC)) [19]. Vehicles with smaller engines are more fuel efficient, especially in urban areas. It is estimated that the move towards smaller vehicles will reduce total fuel consumption by between 10% and 20% [10]. In freight transport, matching engine size to the required task will give the best fuel economy. Better driver education and public campaigns provide the possibility to reduce fuel consumption substantially. Aggressive driving (rapid acceleration and braking) wastes energy. In road-based transport, improved driving behaviour can reduce fuel consumption by up to 33% [10]. The ECODRIVEN project (2006 to 2008) is an example of such an education programme [9]. In rail transport, fuel usage can vary by 12% to 20% between crews [20]. Intelligent transport systems (ITS) can be utilised to manage traffic in a more efficient manner. This would entail reducing idle time (when fuel efficiency is at its lowest) through optimised signal settings and managing speed (with variable speed limits, for example) to improve traffic flows. Such measures have been demonstrated to save between 5% and 20% of fuel consumption [10]. Air traffic management enhancements could improve fuel efficiency and reduce CO2 emissions by up to 12% [14]. Information on actual traffic flows can help drivers to avoid routes that are heavily congested, thereby reducing idling time and fuel consumption, accordingly. Modelling studies estimate that, if between 20% and 40% of road users are fully informed, network efficiency improves with up to 10% [10]. Live information on a vehicle’s fuel demand can assist drivers in driving more economically. Fully automated driver assistance systems can save up to 23% [21]. Fleet vehicle tracking systems introduced by freight companies can result in a reduction in fuel consumption by between 15% and 25% [19, 22]. ITS initiatives underway in the EU include: the Intelligent Car Initiative, the SESAR programme, the ERTMS system and the River Information Services (RIS) system [2]. The Commission is currently involved in two global navigation satellite system projects: EGNOS and GALILEO [9]. Inter-modality (the efficient use of different modes on their own and in combination) results in the optimal utilisation of resources, including energy [19]. Inter-modal systems typically make use of the most efficient modes (i.e. rail or water) for long segments of a journey between hubs, combined with road transport for shorter segments (spokes). Trans-European Networks for Transport WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

230 Energy and Sustainability II (TEN-T) aims to promote the interconnection and interoperability of and access to national networks [9]. All modes of transport are not equally energy efficient. The most efficient modes should enjoy the highest priority in terms of planning and development. In passenger transport, air transport has the lowest energy efficiency, followed by private cars, motorcycles, buses, rail and non-motorised transport (NMT) respectively. For freight the order of increasing efficiency is: air, road, rail, water and pipeline transport. Presently, road transport accounts for the lion share of both passenger and freight transport (see figure 2). Public transport (excluding air) constitutes 16.1% of passenger transport. There appears to be quite some scope for a modal shift towards public transport in the EU. A shift between motorised transport and NMT (cycling or walking), results in a 100% transport energy reduction for the same amount of travel. The utilisation of rail, pipelines and inland waterways in freight transport can also be increased.

Figure 2:

European passenger and freight transport modal shares [1].

Economic instruments (taxes, charges or emission trading schemes) can encourage transport users to switch to cleaner vehicles or modes, to use less congested infrastructure or to travel at different times [23]. Price signals are the most effective when the market offers realistic alternatives (e.g. cleaner vehicles at an affordable price or appropriate levels of service in other modes). Fuel prices can influence consumer choice, both in terms of the quantities and the type of fuel purchased. Moreover, persistent price differences can influence decisions on the type of vehicle purchased, leading to changes in the vehicle stock and fuel mix over time [1]. The extent of potential savings needs to be assessed on a case by case basis, as many factors can influence the effectiveness of this measure. 3.3 Alternative fuels and propulsion systems In 2001 the European Commission (EC) set out a strategy to achieve a 20% substitution of conventional automotive fuel by 2020, identifying biofuels, WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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natural gas and hydrogen as the main replacement possibilities [9]. Subsequently, in 2008, the EC proposed a directive requiring each member state to have at least 10% of its petrol and diesel fuels for transport coming from alternative fuels by 2020 [9]. Biofuels (mainly biodiesel and bioethanol) are slowly, but steadily, increasing its market share in the EU, although it is still limited at present [24]. The main driving force behind the increase is government policies introduced in response to the EU Biofuels Directive (2003/30/EC), which sets the European biofuels market penetration target at 5.75% in 2010 [1, 13]. To increase volumes further, fuel standards need to be adapted, distribution needs improvement and the compatibility of the vehicles with biofuels needs to be improved. The maximum biofuels market penetration percentage is 5% [1, 13] with existing fuel standards. Though biofuels will lessen the reliance on crude oil, it cannot untie itself completely from oil at present. This places a question mark on the long term sustainability of the biofuels industry. However, in the 2006 review of the Biofuels Directive, respondents proposed market penetration targets of 8% by 2015 and between 15% and 20% by 2020 [25]. Alternative fossil fuels currently commercially available are Liquid Propane Gas (LPG) and Compressed Natural Gas (CNG), but their market shares are limited to specific niches [24]. Because these fuels are dependent on nonrenewable resources, they are not considered a viable alternative to oil. The IEA does not expect any major shift away from conventionally-fuelled vehicles before 2030, although the penetration of hybrid-electric cars is projected to rise, reducing oil demand growth [7]. The fuel efficiency improvement obtained from switching to a hybrid-electric car can be more than 100% [26]. These vehicles are already on the market. It is believed that this is a very viable option to reduce oil dependency, if combined with government incentives. However, the number of hybrid car models available on the European market has changed little between 2001 and 2006 [24]. It should be noted that the concept of hybrid propulsion can also be applied to other transport modes. Electricity is a budding contender in the alternative fuels industry. Some advantages of using electricity to power the transport sector include: the existence of the core infrastructure, the relatively high efficiency of electric propulsion and the possibility to generate electricity from renewable sources (increasing sustainability and mitigating environmental impacts). Electricity already powers rail lines and some public transport vehicles. Disadvantages are that transport will have to compete with other sectors of the economy for electricity in a system that is currently quite strained, the problem of centralised filling stations needs to be solved, exposure to the risk of power failures and the current state of technology development in terms of vehicle range, cost, availability and the need for expensive battery replacements [26]. Some alternative propulsion systems can be powered by electricity, for example magnetic levitation (maglev) and tubular freight systems. Maglev systems are incredibly energy efficient and have high performance levels. They consume approximately a tenth of the energy required by an average automobile per passenger-kilometre [27]. In low pressure tunnels the average energy WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

232 Energy and Sustainability II efficiency could potentially be increased to around 4000 km/l [27]. Even though the advantages of maglev seem to outweigh the disadvantages, the main obstacle to the wide-scale adoption of this technology is cost. There are six functioning maglev systems in the world at present and new systems are currently being considered in 12 countries. Many maglev research projects are underway [27]. Tubular freight transportation is a group of unmanned transportation systems in which close-fitting capsules or trains of capsules carry freight through tubes between terminals [10]. Although research and development around tubular freight (and passenger) systems has been emerging for several decades, no final conclusion regarding the feasibility and energy efficiency benefits have been reported. Hydrogen (fuel cell technology) is a clean alternative fuel that is not necessarily dependent on fossil fuels and causes very low to zero emissions when used in fuel cells (assuming good production and transportation practice). The future of hydrogen within the transport sector is uncertain, as there are still many issues that need to be resolved (such as the storage and transportation of hydrogen, safety concerns, infrastructure requirements, high costs involved, vehicle performance and low energy efficiency) [26]. Hydrogen is an energy carrier, not an energy source. Energy thus needs to be converted to hydrogen from another source and from hydrogen to electricity, incurring energy losses of between 57% and 80% [28]. So much energy is lost in the manufacture, distribution and final use of hydrogen in the fuel cell, that it is less energy efficient than a petrol-electric hybrid car [10]. Creating hydrogen through electrolysis is less efficient than using electricity directly in electric vehicles [10]. Developing the infrastructure required to convert to a hydrogen economy has very long lead times (10–15 years) [26]. Despite all the obstacles facing the wide-scale adoption of hydrogen as a transport fuel, a lot of research is currently being invested in. An example is the Zero Emissions Ships project (ZEMSHIPS), which demonstrated the functioning of the first hydrogen and fuel cell powered ship (with a capacity of more than 100 persons) [9]. In 2007, the EC proposed extending the scope of the EU's type approval system for cars, vans, trucks and buses to include hydrogen as a fuel, to facilitate the introduction of this technology into the EU market [9]. Prototype vehicles incorporating compressed air technology (CAT) have recently been introduced to the market by Moteur Development International [26]. CAT vehicles are claimed to have a driving range close to 2000 km, with zero pollution in cities and considerably reduced pollution outside urban areas. These vehicles are a very recent addition to the alternative propulsion arena and thus little verified information is available on them. 3.4 Summary of energy demand and oil dependency mitigation measures Based on the literature available, projections were made regarding the potential energy savings that could be achieved by 2030, through the implementation of measures. These projections take the modal split, as well as the split between passenger and freight transport per mode, into account. A modal shift (comprising a 15% road to rail freight shift and roughly a 25% shift from air and WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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private vehicles to public transport an NMT) proves to be the measure with the highest savings potential (26%). This is followed by the wide-scale adoption of hybrid cars (21%) and biofuels (17%). Measures are not mutually exclusive and, when they are combined into groups, the interaction between measures must be taken into account. For example: improved traffic signal settings will decrease the potential for savings from improved driver behaviour (which minimises stop and go driving). It is very unlikely that the full potential of any measure will be realised. All elements that could influence the success of a measure cannot be controlled or foreseen. Alternative fuels can reduce oil demand (but not necessarily energy demand) the most. If 55% of all road vehicles were replaced with alternative fuels (20% E-85 biofuels, 25% hybrids and 10% either electric or hydrogen), an estimated maximum of 34% of oil demand could be eliminated by 2030. A potential pitfall for alternative fuel technologies is described by the Khazzoom-Brookes postulate [29]. It states that, when a person acquires a vehicle that is more efficient, (s)he will simply drive it more, negating the potential benefits. Time constraints counteract this tendency [26]. Combining alternative fuel strategies are ultimately expected to realise an estimated 18% saving by 2030. Of all the efficiency improvement measures, the modal shift is the best, seconded by the roll-out of intelligent transport systems (13% saving). Combined, a saving of 17% can be expected from the implementation of efficiency improvement measures. Demand reduction measures can, similarly, account for a 15% saving by 2030. Vehicle load factor and passenger occupancy optimisation is the most effective demand reduction measure.

4

Bridging the oil supply and demand gap

Tables 1 and 2 indicate the shortfall (negative) or surplus (positive) oil supply by 2030 (expressed as a percentage of demand) in each of the three supply scenarios and for three mitigation strategies. If demand grows at a conservative rate (as explained in section 1), there is excess supply in the no peak scenario (see table 1). If a peak is expected, however, demand reduction strategies (strategy 1) will suffice to bridge the oil gap, if peaking happens during the latter half of the period. A combination of energy efficiency and demand reduction measures (strategy 2) are sufficient to close the gap in this scenario. Considering the optimistic demand growth scenario (as explained in section 1), if there is no oil peak before 2030, the supply of oil will not be enough to satisfy the projected demand. None of the three mitigation measure groups can alone traverse the oil gap successfully, regardless of when peaking occurs. The measure groups will, thus, have to be combined. It is prudent to remove unnecessary demand from the system before trying to improve the efficiency of the demand that cannot be removed; therefore, demand reduction measures are applied first (strategy 1). Only if there is no oil peak will this be enough to bridge the gap (see table 2). Combining demand reduction and efficiency improvement measures (strategy 2), results in a supply deficit in the 2012 oil peak scenario only, requiring a combination of all three measure groups (strategy 3). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

234 Energy and Sustainability II Reducing the demand for oil has additional benefits to avoiding a devastating supply shortfall. Every barrel of oil saved (dubbed nega-barrels) is worth just as much money as a regular barrel of oil to the EU, either due to reduced production or reduced import costs [15]. A 16% saving in oil imports converts to 696.65 million barrels saved. At a (low) crude oil rate of $35.30 per barrel, this equals a saving of €19.43 billion. Similarly, a 45% saving would be worth €54.64 billion. At a high oil price ($150 a barrel), the 16% saving is worth €80.88 billion. This analysis showcases the value of reducing oil dependency, regardless of the occurrence of an oil peak. Table 1:

Transport energy supply scenarios – conservative demand growth. Oil Supply Scenarios

CONSERVATIVE demand Demand Reduction (1) (1) + Efficiency improvement (2) (1) + (2) + Alternative fuels (3)

Table 2:

No Peak

2020 Peak

2012 Peak

29% 50% 88% 157%

-6% 10% 38% 89%

-28% -16% 5% 44%

Transport energy supply scenarios – optimistic demand growth. Oil Supply Scenarios

OPTIMISTIC demand Demand Reduction (1) (1) + Efficiency improvement (2) (1) + (2) + Alternative fuels (3)

5

No Peak

2020 Peak

2012 Peak

-1% 16% 45% 99%

-28% -15% 6% 46%

-45% -35% -19% 11%

Conclusions and recommendations

There is an important distinction between mitigation measures: those that save energy, regardless of the energy source, and those that only reduce oil dependency. Because the measures only focused at oil dependency (mostly alternative fuels and propulsion systems) will stimulate greater demand for other energy sources (such as electricity, natural gas, etc.) and resources (agricultural land for biofuels), it is important to evaluate the sustainability of switching energy sources. It is unwise to solve one problem by creating another; hence it is recommended that measures reducing total energy demand be given preference over measures simply aimed at reducing the demand for oil. Demand reduction and energy efficiency improvement measures are generally less expensive and have shorter lead times than that required for a switch to alternative fuels. For many viable mitigation options to have substantial impact, they must be initiated more than a decade in advance of peaking. An analysis of the European disposition regarding oil depletion (section 2) shows that the maximum lead time at the EU’s disposal is 20 years. The lead time required to implement mitigation measures (often in excess of 10 years) stresses need for governing bodies to start reducing oil dependency now. It can be concluded from section 4 that applying measures individually will not suffice to bridge the supply and demand gap that will follow peak oil. Depending on the timing and extent of the peak, different combinations of WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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measures are required. The most promising mitigation measures are the facilitation of modal shifts, increased market penetration of hybrid vehicles, the implementation of intelligent transport systems and increased average vehicle occupancies (load factors for freight). It should be kept in mind that demand will eventually overtake supply, albeit not before 2029. Regardless of whether there is an oil peak or not, it is worthwhile to reduce a country’s oil dependency, because every nega-barrel is worth as much as a regular barrel of oil. Likewise, reducing the demand for other forms of energy can also lead to monetary savings. At the time when this paper is written, the world is moving into an economic recession. This significantly impacts global oil demand, delaying the impending oil peak. In terms of transport readiness, this is somewhat of a blessing in disguise. The opportunity now exists to start planning for the oil peak in a timely fashion, because the lead time for preparation is extended. During recessionary periods, governments tend to increase their infrastructure spending, in order to stimulate the economy. This creates the opportunity to start investing in the infrastructure required to step away from oil. Budgets should not be allocated to projects that will foster the current transport status quo. Reduced global oil demand has resulted in low prices. It is relatively inexpensive to undertake infrastructure projects at present, compared to what it will cost after the oil peak has occurred. The authors would like to highlight the need for governments to start peak oil mitigation now, although it might seem like an unlikely time to do so. Carpe diem.

References [1] European Commission, Panorama of Transport, Eurostat Statistical Books: Belgium, 2007. [2] European Commission, Keep Europe Moving – Sustainable mobility for our continent, Communication from the commission to the council and the European parliament, Brussels, 2006. Online. http://ec.europa.eu/transport/ strategies/2006_keep_europe_moving_en.htm [3] Association for the study of Peak Oil and Gas, www.peakoil.net [4] Hendler, P., Lane, T., Ratcliffe, S., Vanderschuren, M. & Wakeford, J., Energy and Transport Status Quo: Demand and Vulnerabilities, Section 2 of report submitted to the National Department of Transport, 2008. [5] International Energy Agency, World Energy Outlook 2008, IEA Publications, France, 2008. [6] Schoppers, M. & Murphy, N., Uncertainty in Peak Oil Timing, Presentation, ASPO, 2005. [7] International Energy Agency, World Energy Outlook 2007, IEA Publications, France, 2007. [8] European Commission, Energy – Yearly Statistics 2006, Eurostat Statistical Books: Luxembourg, 2008. Online. http://ec.europa.eu/eurostat [9] European Commission, Greening transport inventory, Commission staff working document, Brussels, 2008. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

236 Energy and Sustainability II [10] Hendler, P., Lane, T., Ratcliffe, S., Vanderschuren, M. & Wakeford, J., Reducing oil dependency and alternatives to oil-based liquid fuel transport, Section 3 of report submitted to the National Department of Transport, 2008. [11] European Environment Agency, TERM 2005 29 – Occupancy rates in passenger transport, Indicator fact sheet, 2007. [12] European Environment Agency, TERM 2005 30 – Load factors in freight transport, Indicator fact sheet, 2007. [13] European Environment Agency, Transport and environment: on the way to a common transport policy, EEA Report, Copenhagen, 2007. [14] European Environment Agency, TERM 2005 27 – Overall energy efficiency and specific CO2 emissions for passenger and freight transport, Indicator fact sheet, 2005. [15] International Air Transport Association (IATA), www.iata.org [16] Lovins, A., Datta, K.E., Bustnes, O., Koomey, J.G. & Glasgow, N.J., Winning the oil endgame: innovation for profits, jobs and security, Rocky Mountain Institute, Colorado, 2005. [17] InterAcademy Council, Lighting the way: Toward a sustainable energy future, A’dam, 2007. [18] Flight Sciences International, www.flightsciences.com [19] Baas, P. & Latto, D., Heavy vehicle efficiency, Report prepared for the Energy Efficiency and Conservation Authority, New Zealand, 2005. [20] European Commission, Action plan for energy efficiency: Realising the potential, Communication from the commission, Brussels, 2006. [21] Stodolsky F. et al, Railroad and Locomotive Technology Roadmap, Centre for Transportation Research, Energy Systems Division, Argonne National Laboratory, 2002. [22] Van der Voort, M.C., Design and evaluation of a new fuel-efficiency support tool, University Twente (NL), PhD dissertation, 2001. [23] Vanderschuren, M.J.W.A., Intelligent Transport Systems in South Africa, Impact assessment through microscopic simulation in the South African context, TRAIL Thesis Series T2006/4, ISBN: 9055840777, August 2006. [24] European Commission, Greening transport, Communication from the Commission to the European Parliament and the Council, Brussels, 2008. [25] Londo, H.M., Deurwaarder, E.P. & van Thuijl, E., Review of EU Biofuels Directive Public consultation exercise, Amsterdam, 2006. [26] Vanderschuren, M., Jobanputra, R. & Lane, T., Potential transportation measures to reduce South Africa’s dependency on crude oil, Journal of Energy in Southern Africa, Volume 19, Issue 3, August 2008. [27] Lane, T., MAGLEV – Moving around by magnetic force, Mobility Magazine, June 2008. [28] Gilbert, R. & Perl, A., Transport revolutions: moving people and freight without oil, Earthscan, ISBN: 9781844072484, 2008. [29] Strahan, D., The Last Oil Shock, London: John Murray, 2007.



237

Sustainable energy policy choice: an economic assessment of Japanese renewable energy public support programs A. Suwa1, K. Noda1, T. Oka2 & K. Watanabe3 1

Environmental Division, Musashino University, Japan New Industries Promotion Division, City of Kitakyushu, Japan 3 Department of Sociology, Teikyo University, Japan 2

Abstract Given the associated environmental and economic benefits, electricity from renewable energy sources (RES-Es) is expected to play a significant role in shaping the human energy future. For the development of RES-E, the Japanese government introduced a national public support system based on a renewable portfolio standard (RPS) scheme. There is, however, a gap in the international and domestic literature about the Japanese renewable deployment policy. As a result, lessons to be learned from the Japanese experience have not been shared by the academic community. This paper fills this gap by paying a focused attention on the Japanese renewable portfolio standard (J-RPS) scheme, with an assessment on whether the scheme is promoting effective and efficient RES-E development. It reveals how certain types of RES-Es are marginalized from the market under the RPS equimarginality rule. Clear policy recommendations are made for a better design of the J-RPS, based on the exclusive empirical analysis. Keywords: renewable energy, feed-in tariff, renewable portfolio standard.

1

Introduction

With the scarce fossil fuel reserves, renewable energy deployment has been on the Japanese government energy policy agenda for decades. It had been especially so after the oil crisis, with a significant amount of government budget allocated to renewables research and development. Surprisingly little attention has been paid to public support for renewable energy deployment, where WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090211

238 Energy and Sustainability II government subsidy for specific renewable energy technologies had been the only explicit official mechanism for supporting renewables. Against this background, in 2003 the Japanese government enacted a legislation based on the renewable portfolio standard (RPS) scheme, which requires electricity retailers to supply a certain amount of renewable electricity to grid consumers. The RPS legislation was expected to ensure market efficiency, as well as bringing a steady increase of renewable capacity. There is, however, very little research conducted to evaluate the real effect of the Japanese RPS (J-RPS). This paper aims to establish the position of RPS in the environmental economics theory, and assess whether the Japanese RPS delivers the expected renewable capacity increase and efficiency gains. This paper is therefore structured as: 1) a general discussion on renewable public support schemes, 2) overviews on the Japanese RPS and an updated information on its effect on renewables development in Japan, and 3) discussion on market condition and RPS using the Japanese example, with concluding remarks.

2

Overviews on renewable public support schemes

2.1 Renewable energy sources: its barriers for common use Renewable energy sources are defined as those that are replenished by natural processes at rates exceeding their use for human purposes (Eblen and Eblen [1]). If natural replenishment is either non-existent or slower than the rate of usage, the energy resources (e.g. nuclear and fossil fuels) are non-renewable. Renewable energy sources have several advantages over the conventional energy sources, being not likely to be depleted, and having less impact on the environment. Although physically abundant as energy sources, there are several significant barriers upon transition to more common use of renewable energy technologies. Those barriers are generally identified as follows (Mendonca [2]): 1) Costs and pricing Renewable energy technologies are regarded as having less impact in terms of environmental externalities, but the market often has a problem to sufficiently evaluate the externalities resulting from the use of conventional energy fuels. In addition, renewable energy sources have not received subsidies to the extent that conventional energy sources had. This constitutes another reason for renewable technologies being perceived as “expensive”. 2) Legal and regulatory The development of renewable energy technology is frustrated by the lack of appropriate legal and regulatory frameworks. If restrictions are too strict, for example, on siting and construction for renewables, they often become major limitations on renewable development. The requirement of transmission access and utility interconnection could also be significant barriers for grid-connected renewable electricity. 3) Market performance Lack of credibility, resulted from unfamiliarity with renewable energy technology can increase the perceived uncertainty and risks associated with WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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them. Basic information and understanding on the installation and operation of renewables many not be sufficiently shared among members of the society. 2.2 Public support schemes for renewables Government intervention is theoretically justified as a means to correct the negative externalities relating to the use of conventional energy sources and technologies. Adding to that, government policy is highly important for the support of renewable energy technologies, especially to protect the technologies in their initial phases. Currently, there are broadly two major approaches for supporting renewable technologies (Menanteau et al. [3]). 2.2.1 Feed-in tariff Feed in tariff (FIT) consists of an obligation for electric utilities to allow electricity from renewable sources (RES-E) to be transmitted through the electricity grid (feed-in), and to purchase RES-E at a regulated price. It is generally known as a price-based approach that establishes a premium per generated kWh. Under FIT, the regulated price (tariff) determines the overall volume of RES-E production (Figure 1).

Figure 1:

Price-based approach (Source: Menanteau et al. [3]).

Since FIT normally contributes to the correction of price inequality between conventional and renewable energy technologies, it has been proved as a very powerful mechanism for RES-E deployment in many EU countries (e.g. Germany, Spain, etc). 2.2.2 Renewable portfolio standard (RPS) Renewable portfolio standard (RPS) requires electricity operators to supply a fixed quota of RES-E in the market. Tradable certificates (tradable green certificate, TGC) may be purchased for the fulfilment of the quota obligation. It is a quantity-based instrument, where regulators determine the RES-E sales volume and quotas are allocated among electricity operators (Figure 2). The prices of RES-E purchase are open to individual contracts, thus it is to follow the equi-marginality rule, where RES-E at lowest price would be deployed. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Figure 2:

Quantity-based approach (Source: ibid.).

The majority of the US states and some EU countries, together with Japan, have adopted the RPS scheme, though the target levels and details of policy designs vary.

3

The regulatory and other frameworks for RES-E in Japan

3.1 Historical overviews: net-metering and government subsidy Renewable energy first won public recognition in Japan in 1960-70s, when the oil crisis hit the country’s economy. The Japanese government initiated a series of projects to support renewable technologies. Its primary focus, however, was mainly on technology research and development, while less attention was paid to public policy to support and deploy the renewables. It was only after 1992, when “net-metering” was launched as a voluntary scheme by the electricity utilities, that the rate of deployment of, at least specific RES-Es (PV and Wind), gained the momentum. Net-metering enables customers to use their own electric generation to offset their consumption over a billing period. This offset means that customers receive retail prices for the excess electricity they generate. This has been a crucial mechanism in supporting RES-E generation. Its introduction was clearly the turning point in the history of Japanese RES-E development. The deployment rate of RES-E has picked up since the beginning of 1990s when the net-metering started (Figure 3). Apart from the voluntary net-metering scheme, a government subsidy program was in place from 1994 to 2005. Since there was a significant increase in renewable capacity and the average cost of a residential PV system dropped by more than half during 1990s, the effect of the subsidy program is often overemphasised (Haas et al. [4]). It is important to remember that the capacity increase and cost reduction were the combined results of net-metering and the subsidy program. It is, however, not clear whether the utilities will continue the voluntary netmetering scheme, because the costs associated with the power purchase are increasingly felt as a financial burden. This creates an uncertainty for future renewable development. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


250000

1000 net-metering Total cumulative PV subsidised PV

MWh

600

150000

500

Net-metering started 100000

National subsidy started 50000

Figure 3:

800 700

200000

0

900

400

cummulative M

300000

241

300 200 100

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 year

0

The Japanese residential PV growth, with an annual increase of net metering and subsidised PVs.

BOX 1 The main programs related to RES-E promotion in Japan before RPS introduction was summarised as follows: 1) Voluntary net-metering (Since 1992) The 10 main electric companies set the basic conditions for contracts with PV and wind power producers 2) Government subsidy program (1994-2005) Providing subsidies for initial investment for residential roof-top PVs 3.2 Adoption of RPS over FIT Apart from the private sector’s voluntary net-metering scheme, there has been awareness that there should be an official program to support renewables more effectively. With the recognition that FIT being a powerful mechanism for RESE development in several EU countries, a political initiative (the Parliamentary Initiative for Renewable Energy Promotion) was established by some members of the Parliament to address the introduction of FIT in Japan. The momentum for FIT was, however, lost when the government announced its intention to adapt a RPS-based system instead. The Japanese government launched a RPS legislation (J-RPS) in 2003, which requires 30 electricity retail companies to supply RES-E. The eligible RES-Es are “new energies”, a unique definition by the Japanese government, meaning PV, wind, geothermal, small hydro-power (less than 1MW) and biomass. It is WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

242 Energy and Sustainability II notable that power from municipal waste incineration can be counted as “biomass” on the basis of biomass content in waste, though critics disagree with allowing power from waste being included into the green basket. The national target was initially set as 3.3 TWh in 2003 (1.35% of the total electricity sales), which gradually increases to 12.2 TWh in 2010, then 16 TWh in 2014 (about 1.6% of total electricity sales). For the fulfilment of the quota, retail suppliers are either to 1) generate RES-E themselves, 2) purchase RES-E from RES-E generators or 3) purchase RPS certificates. The maximum certificate price is regulated as 11 JPY/kWh (approximately 9 US cents/kWh). The retail suppliers are allowed to carry out banking and borrowing. 3.3 Assessment of the Japanese RPS system The Japanese government is highly optimistic about the effect of J-RPS in stimulating RES-E development. Unfortunately, this government view is widely shared by the academic community so far. It is stated, for example, that RES-E generation has steadily increased since the J-RPS introduction, and the trend is expected to continue. It is argued that the RES-E costs have declined and the certificates are at a stable price range of approximately 5 JPY/kWh (about 6 US cents/kWh) during 2003-5. Also, they explain that the J-RPS national target level is lower than those of the US and some EU member countries, mostly because large hydro and geothermal powers are ineligible under the scheme (Haas et al. [4]). The level of the national J-RPS target and how that relates to RES-E price range requires a more detailed assessment. An integrated evaluation of the Japanese RPS, thus, will be given in this section. Empirical research will be carried out by data obtained from official and other sources. The assessment criteria will be on the following aspects: effectiveness, transaction cost and equimarginality. 3.3.1 Effectiveness The J-RPS target was established as 1.35% of the total electricity sales in 2010, and 1.6% by 2014. The low level of the J-RPS level is usually explained by the exclusion of hydropower (Haas et al. [4]). A detailed comparison without hydropower component, however, clearly reveals that renewable targets in many countries are significantly higher than that of Japan (Figure 4). The level of the J-RPS target, in fact, seems to be too low to reflect the physical potential for renewable development. Since 2003, the RPS initial year, a significant amount of banking has accumulated, to the extent that the banking amount reached to 6.8 TWh in 2007. This is sufficient to supply over 90% of 2008 target of 7.5 TWh (Figure 5). The extremely high level of banking is proof that the initially established J-RPS targets are too low to reflect the RES-E potential in Japan. 3.3.2 Cost and equi-marginality The low target level has resulted in many undesirable effects for the deployment of RES-E. One of the advantages of quota-TGC (tradable green certificate) WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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10.0 5.0 0.0 -5.0

2010 target JP

EU

DE

UK

FR hydropower contribution

-10.0 -15.0 -20.0 Figure 4:

Target level without hydropower contribution. Hydropower contribution level (taken from 1997 data) is deducted from 2010 target level for neck to neck comparison. The Japanese target is significantly lower than others.

140 120

100GWh

100 80 60 Banking

40

Banking+yearly supply Official target

20 Compulsory target

0 2003

Figure 5:

2004

2005

2006

2007

2008

2009

2010

The Japanese RPS targets and the level of banking. The official targets are nominal. The compulsory targets, as legally binding targets, can be satisfied by the banking from previous years.



30 25 W ind H ydro B iom ass P V(residential) P V(industrial)

100GWh

20 15 10 5 0 2003

Figure 6:

2004

2005 year

2006

2007

The price level for J-RPS eligible renewable technologies.

is to create a certificate market that could raise necessary funding for RES-E generation. The J-RPS target, however, is too low to create a TGC market, as there is little incentive for TGC purchase. The level of certificate price is virtually fixed at “stable range”, because of the absence of the TGC market (Figure 6).

80 70

100GWh

60

O thers B iom ass H ydro PV W i nd

50 40 30 20 10 0 2003

2004

2005

2006

2007

year

Figure 7:

Shares of power produced by J-RPS eligible renewable technologies.

The price inelasticity relates to another problem as to the kinds of RES-E being developed. The eligible J-RPS renewables includes power from municipal waste incineration as “biomass” (the biomass rate is calculated on the basis of its inclusion in municipal waste). Power from “biomass” including waste WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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incineration dominates more than half of the J-RPS contracts, reflecting its relatively inexpensive price range compared with the prices of other RES-E technologies (Figure 7). It is notable that power from incineration of waste are heavily subsidised by public funds, in terms of e.g. waste collection and construction of incineration facilities. This means the equi-marginality rule inherent to the RPS scheme, is applied in the selection of RES-E technologies, to the extent that RES-Es which are more environmentally desirable, but in their initial development stages, are forced into the competition with the subsidised energy technology. As a result, economically competitive (subsidised) RES-E wins market penetration, while economically less competitive RES-Es are marginalized from the market. Figure 8 demonstrates the marginalisation of environmentally desirable but economically less competitive RES-Es. Price

MCA

MCB

QD

Figure 8:

4

MCD

MCc

Quantity

The marginalisation of less competitive RES-Es.

Conclusion

Japan, as a country with high technological capacity, is a leader in solar and other renewable energy technologies. With the increasingly potent effects of climate change, and as a country that hosted one of the historic conferences of the United Nations Framework Convention on Climate Change (UNFCCC), Japan has sufficient reasons to deploy renewable energy technologies. The energy policy and regulation of the country, however, do not necessarily address the potential for the renewables. The great opportunity for RES-E development has been lost due to the lack of an ambitious renewable target being adopted in the J-RPS system. The absence of an ambitious target seems to have resulted in several negative effects. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

246 Energy and Sustainability II 1) The RES-E potential are overlooked and underdeveloped. The level of the J-RPS target is embarrassingly low, to the extent that majority of the target can be satisfied by the accumulated banking. 2) As the TGC market is underdeveloped, the generators are forced into a contract with the utilities, which fixes the price of the certificate at the minimum level. 3) With the equi-marginality rule in operation, only the currently most economically competitive energy technology is deployed, while less developed RES-E technologies being marginalised from the market. In order to boost RES-E development, the current J-RPS needs, at least, to address the following issues: 1) To establish a higher national target, with individual targets for each sources of RES-E at different stages of development; 2) To recognise the significance of fixed-price payment on RES-E deployment, as just demonstrated by the utilities' voluntary netmetering. Net-metering works as a mechanism to concentrate on prices and stabilises the long-term cost-benefit balance related to RES-E investment Currently, J-RPS targets have become more of a limitation than a stimulating objective. Having regard to the fact that many EU countries are actively promoting RES-E through a FIT system, there seem to be much for Japan to learn from their experiences, because FIT, without subscribing to a regulatory quota, will not operate as a limiting factor to renewable development.

References [1] Eblen, R.A. and Eblen, W.R., Encyclopaedia of the Environment, Houghton Mifflin, New York, 1994. [2] Mendonca, M., Feed-in Tariffs: Accelerating the Deployment of Renewable Energy, Earthscan, London, 2007. [3] Menanteau, P., Finon, D., Lamy, M., Prices versus quantities: choosing policies for promoting the development of renewable energy, Energy Policy, 31, pp799-812, 2003. [4] Haas, R., Meyer, N.I., Held, A., Finon, D., Lorenzoni, A., Wiser, R., Nishio, K., Promoting Electricity from Renewable Energy Sources – Lessons Learned from the EU, United States, and Japan, Competitive Electricity Markets, pp 419-468, 2008.



247

An energy and environmental meta-model for strategic sustainable planning D. S. Zachary, U. Leopold, L. Aleluia Reis, C. Braun, G. Kneip & O. O’Nagy Resources Centre for Environmental Technologies, Public Research Centre Henri Tudor, Luxembourg

Abstract This paper describes a geo-spatially distributed reference based energy model that is coupled to a reduced-order (efficient) photochemical air quality model. Project LEAQ, the Luxembourg Energy Air Quality Model, is built upon the large-scale systems analytic method, a meta-modelling approach that includes a full geospatial database of energy sources, devices, and their emissions for four broad sectors of the economy: transportation, industrial, residential, and commercial. The energy model is coupled to an air quality transport model, handling nitrous oxides, volatile organic compounds, ozone, particulate matter, carbon dioxides and carbon monoxides. The model assists in choosing lowest cost energy solutions given environmental (air quality) constraints in a spatially distributed map. The application is designed for the Luxembourg context and would later be applied to R other European cities and regions. We present the MATLAB beta-version of the model and describe first results and the development plan and implementation in a proposed European project. We also present the main user functionalities that would assist a researcher in the implementation of the model. We give a first view of the beta-version and its use in modelling Luxembourg’s national energy system. Keywords: meta-model, reference based energy models, convex optimization, air pollution, air quality, NOX , VOC, ozone, reduced-order photo-chemical models, geo-spatial.

1 Overview of sustainability meta-models in European projects The European community has, for some time, been one of the global leaders in the field of sustainable energy and environmental model building and project support [1]. The number of European supported sustainability projects is a clear WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090221

248 Energy and Sustainability II indication as to the importance of this research. As a result, the quality of life and the standards of living in Western Europe have benefited from such efforts [2]. Both energy use and environmental concerns are two forefront research agendas that are formulated in sustainable growth research (e.g. Adams [3]); it should be noted that these concerns are essentially ”competitive” in nature. The global importance of both disciplines has introduced the need for a coupled modelling approach that will simultaneously address these issues. We also note here that a ’third leg’ of the sustainability equation, the social aspect, is not discussed in this paper, but is addressed in many other sources (e.g. Adams [3], Ott [4], Söderström et al. [5]). From the modeler’s point-of-view, sustainability can be viewed in terms of a multi-systems analysis, also known as a meta-modelling approach. We define a meta-model as a model with several components that are interconnected forming a complete model that defines the components of a conceptual idea, process, or system and useful for modelling predefined classes of problems (e.g. Gigch [6], Söderström et al. [5]). Metamodel building has become an important activity in interdisciplinary problem solving, and in this paper, we use it to address the diverse modelling field associated with sustainable energy infrastructure growth and its environmental impact. There is an extensive history of European projects leading up to the present state of environmental and energy related meta-models. Our methodology builds on the past several years of European sustainable urban projects, beginning with the Fifth Framework Programme [7] and the Sixth Framework Programme [8] projects. To begin, several projects in the LUTR (Land use and Transportation Research) cluster addressed core issues and ancillary problems concerning urban sustainability. A planning, evaluation and consultancy strategy was formulated in the EcoCity project where seven model settlements provided a test-bed for techniques and tools in carrying out urban planning. CityFreight explored modifications of motorways and its effect on traffic in and around a major metropolitan centre. The project also performed cost modelling for future freight transportation in a European multimodal network using calibrated origin-destination (O-D) matrices in transportation models. Other FP5 projects have focused on setting up guidelines for optimal integrated transportation and land use strategies. The PROSPECTS project, for example, explored this guideline challenge for urban sustainability. The PROPOLIS project also explored issues of sustainability and urban spatial transportation analysis. Finally, the Sustainable Urban Transportation project (SUTRA) came closest to establishing a meta-model ”cascading” methodology where model based quantitative analysis tools were used to construct comprehensive approaches to urban transportation solutions in sustainable cities; overall, the SUTRA project integrated the socio-economic and environmental concepts pertinent to urban transportation planning (Fedra [9]). Several FP6 projects continued in the theme of urban sustainability. The project MATISSE proposed a general tool to study Integrated Sustainability Assessment (ISA). TRIAS explored ISA for transport technologies and transport energy supply together with economic, environmental and social impacts. The SENSOR program WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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added a slight twist to the traditional modelling focus; building, validating and implementing Sustainability Impact Assessment Tools (SIAT) using a spatially referenced framework. Finally, a cost assessment program, CASES, explored the external and internal costs of energy production for different energy sources for the EU-25 countries and for some non-EU countries. These costs are projected in energy scenarios to the year 2030. Sustainability is not limited to air quality management in FP6; Urban Water Management, UWM, was explored in the SWITCH project. What lacks in these previous models, whether it was a FP5 or FP6 project, is the ability to employ a ”feedback” mechanism, where the energy infrastructure expansion can be ’predicted’ or rather suggested, in accordance with the projected quality of air. Thus, a beckoning need for a coupled energy-environmental model has presented itself where future energy infrastructure planning periods will be guided by the determination of future air quality. The LEAQ model will be built within an overall optimization framework and will fulfill this ”feedback” mechanism void in sustainable energy modelling.

Figure 1: Overview of the LEAQ model, showing the connectivity of each submodel. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


2 The Luxembourg Energy Air Quality model – LEAQ 2.1 The model overview The two major models in the LEAQ project include an energy model - GEOECU (GEO-spatial Energy CalCulator) and the air quality model, AYLTP (AsYmptotic Level Transport Pollution Model). Both models are used in an optimization framework as characterized in Fig. 1. Spatial and temporal data are provided as inputs to the GEOECU model, which computes atmospheric emissions of primary pollutants, including spatially distributed VOC, NOX , CO, CO2 SO2 and particulate matter (PM2.5 and PM10). The LEAQ model searches for the lowest cost energy solution for a city or region using an economic model with constraints (e.g. demand, operational, technological, seasonal, . . . etc.). GEOECU is based on ETEM (Energy Technology Environment Model), a bottom-up energy reference model that provides a representation of the energy and technology choices that could best deliver the needed energy services in a city or region. The ETEM model and other models of this type (e.g. MARKAL models) aim to supply energy services at minimum global cost and simultaneously calculates optimal equipment investment, operation level and primary energy importation and exportation (Drouet and Thénié [10]). GEOECU’s emission outputs are subsequently passed to the AYLTP model. In addition to these emissions, AYLTP uses spatio-temporal information, such as meteorological, topographical, and land use information to predict the concentration for the primary pollutants and the secondary pollutant O3 . AYLTP calculates pollutant concentrations with variable space resolution (100 m × 100 m - 1 km × 1 km) and variable temporal resolution (10 min - 1 hr). An optimization routine called ACCPM, the Analytic Centre Cutting Point Method, (Gondzio et al. [11]) is embedded in an open source wrapper, OBOE, an Oracle Based Optimization Engine supported by the ORDECSYS Company [12]. ACCPM is used to efficiently guide an n-dimensional, discrete or continuous convex problem, or a set of problems to an optimal (either minimal or maximal) solution. In our application, ACCPM checks O3 concentration levels against upper limits. If the calculated O3 concentration levels are within bounds, then an update of the precursor maximum bounds, NOX and VOC, are also adjusted in the GEOECU model to reflect this change. If the calculated concentration values of O3 are not satisfied, a cut is made on the limit of the O3 precursors. The GEOECU is then rerun using readjusted upper limits of NOX and VOC. The process is repeated until an optimum energy solution satisfying O3 concentration bounds is obtained. We model the economic activity for each (hypothetical) economic planning period, i = 1, . . . NP where each economic period lasts for 5 years (e.g. 20092014, 2014 - 2019, . . .). Energy related economic activity vector, x and the associated constants c can be formulated in an objective/constraint problem in a compact slack form notation,



min c, x

251

(1)

x

s.t. Ax = a,

(2)

Ui x = Ui max , i = 0, 1, . . . Np − 1,

(3)

Ui ≥ 0, i = 0, 1, . . . Np − 1,

(4)

x ≥ 0,

(5)

Aj,i (Ui , s) ≤ Aj,i

max (s),

j ∈ J , i = 0, 1, . . . Np − 1,

Gi (Aj,i (Ui ), s)x ≤ Gi,max , i = 0, 1, . . . Np − 1,

(6) (7)

The first constraint Eq. 2 consists of all the technical, operational, seasonal, etc. constraints that are found in the technoeconomic model, the reader is referred to (Carlson et al. [13]) for more information. The conversion vectors Ui convert economic activity to emissions and are constrained against maximum levels, Umax . Spatially dependent air quality levels Ai,j (Ui , s), s ∈ (s1 , s2 , s3 ), the three dimensions of the air shed region, arise from primaries j ∈ J representing NOX and VOC and are also limited by maximum levels, Ai,j . The geo-spatial weight criteria Gi is constructed by factoring the spatial distribution of population density and air quality levels, so as to limit potential economic growth scenarios in poor air quality regions . Details of this development are given in (Zachary [16]). Subtleties of the above problem are numerous and too technical to address in this paper. We note one subtlety, the ‘=’ sign in Eq. 3 results from the fact that the technoeconomic model, GEOECU, allows activity to increase so that the optimal solution always results in activity driven emissions that will match the upper bounds. Eqs. 1–5 are described in GEOECU, while Eqs. 6–7 are described in the air quality model and in an auxiliary routine that combines spatially dependant air quality with population density. The entire objective constraint problem solved by the overseeing ACCPM (OBOE) methodology and tool. The LEAQ project builds on an earlier prototype [13] coupled model scheme, based on a ‘lite’ version of the full MARKAL model (Abilock et al. [14]) and a reduced-order photochemical air quality model (Zachary et al. [15]). The current project brings in several important technical developments, including geo-spatial modelling of both the AYLTP and GEOECU sub-models (detailed in Zachary [16]). The AYLTP simulation is improved using a more accurate meteorology package and spatial terrain package. The AYLTP model will also include an augmented species list as mentioned above and a fast turbulence calculator that will complement the topographical input. Likewise, improvements to the energy model and the development of a spatially distributed energy use database for Luxembourg will allow for a detailed technoeconomic analysis of the region. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

252 Energy and Sustainability II nox

voc

O3

Subgrad Values : mapped to [0 1] space 1

137.3491

C = Total Economic model cost

40.43373 80.06739

271.6995

last subgrad

101.6543101.6543

0.75 271.6995 137.3491

202.3124

137.3491 STN3

STN3 STN1 101.6543 202.3124 101.654

STN1 271.6995 271.6995 137.3491 406.0499 STN2

Air Quality Indexes peak O3 =159.3347 mean O3 =42.3922 AOT60 (avg)=87.4443 iPer/NPer =1/1 time =13:00 dfdy : i/Dim =0/4

(NOX & VPC/5 & O3*5 ppbv)

202.3124 302.9706 STN2

100

80.06739 40.43373 40.43373

STN1 119.7011 80.06739 80.06739 40.43373 119.7011 STN2

Daily variations in concentrations

80 60 40 20 0 12 12.2512.512.75 13

historical subgrads

STN3 40.4337

STN 1 − NOX STN 2 − NOX STN 3 − NOX STN 1 − VOC STN 2 − VOC STN 3 − VOC STN 1 − O3 STN 2 − O3 STN 3 − O3

0.5

0.25

0 dC/di_1

dC/di_2

dC/di_3

dC/di_4

V =−1.4581 and V 3.8448 E

N

Figure 2: The LEAQ active data windows and graphs (Part I): top – (a) in the table, the air quality output; bottom – (b) in the table, the optimization directional information. lux cantons

lux pop. density

LEAQ - β Version lux GEO weights (Period1 only) lux cadaster map

G1 G2 ... = 1.0074

0.99257

Figure 3: The LEAQ active data windows and graphs (Part II): left – (c) in the table, the average O3 levels per iteration; right – (d) in the table, the maps used in the problem.

Other new developments in the LEAQ project include a complete open-source version that will be accessible via the web. This version would first be tested in the Luxembourg context and then is expected to be exported for use in the greater Thessaloniki, Greece region. This project is now in review for development as a European LIFE+ project [17]. A spatial uncertainty analysis is also foreseen in the LEAQ project. Pollutant measurements, as with any measurements, and their simulations are never without uncertainty. A validation campaign posted at several sites in Luxembourg will be critical to test the model against several different weather and air quality episodes. As with all models, the uncertainties from input are propagated throughout the model. An added complexity is created as errors are passed from GEOECU to WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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Table 1: Description of Figs. 2 and 3. R MATLAB window

GUI sub-

Description

(a) The air quality output

The pollutants NOX , VOC, and O3 concentration levels (for Luxembourg). The air quality values and the evolution are shown. Measurement stations are also shown.

(b) Directional Info.

Sensitivity values for the tuning parameters of the problem. The (dot - •) lines are the past (historical) values, the (solid line - ♦) is the current values. This information is used in ACCPM (OBOE) to guide the problem to an optimal solution.

(c) The average O3 profile

The asymptotic ozone level profile is plotted as a function of NOX and VOC levels. The AOT60 cutoff (flat plane) is also shown. Precursor NOX and VOC levels are shown (sharp peaks); iterations 1 and 2 are shown in this example. The point where the peaks cross the O3 curve shows the air quality for that iteration. The iterative steps show the ’walk’ towards lower O3 values. The iterative steps continue until the precursor levels result in a solution that is off the O3 ’hill’. At this point, the sharp peaks will arrive in the flat regions of the figure representing the AOT60 threshold level, and the optimization search engine (ACCPM), will subsequently produce a feasible solution.

(d) Input/output maps

Maps showing the 12 Luxembourg cantons, the population density, the ’canton-weighted’ maps, and land use maps. The 12 cantons are grouped into two regions, the 5 most populous cantons in the south and the 7 less populous cantons in the north (G1 and G2 ). The ’cantonweighted’ maps show the two region weights (see Eq. 7), G1 and G2 . The higher weight (G1 ) calculated for the more populous south of Luxembourg and the smaller weight (G2 ) calculated for the less populous north. R command window (Input of meta-model commands) The MATLAB

(not shown)

and the output data file also used in the β version data analysis. The data file shows the iterative update of the type of cut (feasible, non-feasible), the iterative objective function, the sub-gradient (directionality information), the precursor (NOX and VOC) levels and the O3 concentration levels. A status window, including the air quality and energy models’ basic parameters, the size of the problem, and the current number of optimization iterations is also not shown in the figure.

AYLTP; errors are accumulated in the iterative optimization process as suggested in Fig. 1. The uncertainty analysis must also be considered in the constraint relations given in Eqs. 2–7. The analysis of spatial uncertainties and the treatment of meta-model error propagation will be explored in a Luxembourg national project (under review) (Zachary and Leopold [18]). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


3 The LEAQ β version The working test version or β-version of LEAQ is shown in Figs. 2 and 3 and described in Table 1. The different parts of the graphical user interface (GUI) are enumerated in the table. The plenary project foresees the entire model as an open-source, web-based decision tool. The tool will determine a lowest cost energy for the current (hypothetical) 5-year economic planning period (2009–2014) and for subsequent periods (2014–2019), (2019–2024), . . . etc., for a total of 5 × 6 = 30 years of planning. The user will be able to assess an easy-to-use GUI, and determine air quality for the current energy infrastructure (for various weather episodes) of the region in question and will be able to predict air quality for future energy infrastructures. The air quality assessment can be done for Business as Usual (BaU) scenarios and various energy expansion scenarios. Finally, the model will be employed as an environmental - energy management tool and will assist in searching for environmentally friendly energy scenarios and in the crafting of cost effective national and transnational action plans.

Acknowledgement This project is supported by the Ministère de la Culture, de l’Enseignement Supérieur et de la Recherche (MCESR) du Luxembourg under the project identifier CRTE-07-LEAQ.

References [1] UrbanEnvironment2007, Integrated Environmental Management, Guidance in relation to the Thematic Strategy on the Urban Environment, Technical Report – 2007-013, 2–7, 2007. [2] European Sustainable Energy Review (ESER), Russell Publishing media pack; quote from Prof. Arthouros Zervos, President of EWEA – EWEA - European Wind Energy Association, “It is crucial to acknowledge the numerous benefits of renewable energy sources. A renewable energy policy is much more than just a climate policy, promoting renewable energy is giving priority to economic growth, creation of jobs as well as, due to their mainly decentralised nature, rural development. Renewables contribute to securing the future welfare and prosperity of Europes citizens and, not to forget, they are extremely popular among the European population, www.internationalsustainableenergy.com, 2009. [3] Adams, W.M. The Future of Sustainability: Re-thinking Environment and Development in the Twenty-first Century. Report of the IUCN Renowned Thinkers Meeting, 29–31 January, 2006. [4] Ott, K., The Case for Strong Sustainability. In: K. Ott & P.P. Thapa (eds.). Greifswalds environmental ethics. Greifswald: Steinbecker Verlag Ulrich Rose. ISBN 3-931483-32-0. Retrieved on: 2009-02-16, 2003. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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[5] Söderström E., Andersson B., Johannesson P., Perjons E., Wangler B., Towards a Framework for Comparing Process Modelling Languages, in: Lecture Notes In Computer Science; Vol. 2348. Proceedings of the 14th International Conference on Advanced Information Systems Engineering. pp 600–611, 2001. [6] P. van Gigch, System Design Modeling and Metamodeling, Plenum Press, New York, 1991. [7] Fifth framework programme (FP5, 1998-2002), European Commission Community Research. Thematic program of the 5th Framework. Energy, Environment, and Sustainable Development http://cordis.europa.eu/fp5/ [8] Sixth framework programme (FP6, 2002–2006), http://cordis.europa.eu/ fp6/projects.htm [9] Fedra, K. Sustainable Urban Transportation: a model-based approach. Cybernetics and Systems, 35: 455–485, 2004. [10] Drouet L., Thénié J., ETEM An Energy/Technology/Environment Model to Assess Urban Sustainable Development Policies. Reference ManualVersion 1.0 July (2008). www.ORDECSYS.com [11] Gondzio J., O. du Merle, R. Sarkissian and J.-Ph. Vial, PROXIMAL-ACCPM - A Library for Convex Optimization Based on an Analytic Centre Cutting Plane Method, European Journal of Operational Research, 94, 206–211, 1996. [12] The ORDECSYS (Operations Research and DECision support SYSTEMS) consulting company, http://www.ordecsys.com/en [13] Carlson, D., Haurie, A., Vial, J.-P., Zachary, D., Large-scale convex optimization method for air quality policy assessment. Automatica 40 (3), 385–395, 2004. [14] Abilock, H., Bergstrom, C., Brady, J., Doernberg, A., Ek, A., Fishbone, L., Hill, D., Hirano, M., Karvanagh, R., Koyama, S., Larsson, K., Leman, G., Moy, M., Sailor, V., Sato, O., Shore, F., Sira, T., Teichman, T., Wene, C.O. (1980). MARKAL: A multi-period linear programming model for energy system analysis. In R. Kavanagh, (Ed.), Proceedings of the international conference on energy system analysis, Dublin, Ireland (p. 482). Dordrecht: Reidel, 1979. [15] Zachary D.S., Haurie A., Siverguina I., A Reduced-Order Photochemical Air Quality model. Cybernetics and Systems: An International Journal Vol 35, pp. 1–15, 2003. [16] Zachary D.S., An integrated geo-spatial energy - air quality impact assessment tool Draft for Environmental Research Letters, 2009. [17] Zachary D.S. and Leopold U., Urban Horizons, A LIFE+ Project,(LIFE08 ENVL000445, 2008. [18] Zachary D.S. and Leopold U., The unLEAQ project: UNcertainty analysis for the Luxembourg Energy Air Quality project, a Luxembourg national research (FNR) proposal, 2009.




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The Italian gas retail market: a cluster analysis based on performance indexes G. Capece1, L. Cricelli2, F. Di Pillo1 & N. Levialdi1 1

Department of Enterprise Engineering, University of Rome ‘Tor Vergata’, Italy 2 Department of Mechanics, Structures, the Environment and Land Management, University of Cassino, Italy

Abstract The liberalization of the European natural gas sector radically changed the structure of the competitive environment which in turn forced companies to make changes in order to stay in the market. In Italy the liberalization process also had a strong impact on the strategies adopted by the companies involved. This situation instigated various studies of the changing nature of performance through the analysis of company profits and financial positions throughout the first three years following the market liberalization. This paper focuses on the changes in performance in the natural gas retail market by analyzing the profit and financial position of the companies concerned over the first three years following the market liberalization. The balance sheets of 105 Italian companies in this sector are analysed, after which a cluster analysis is performed employing the most significant performance indexes. The companies are then analysed within each cluster with respect to age, size, geographical location. The analysis is further developed by studying the strategies in terms of business diversification adopted by the operators in response to the radically altered competitive environment. The results of our analysis show that the majority of companies attained a high level of performance, although this positive outcome was mitigated by the gradual decrease of the average values of performance indicators during the period concerned. There appear to be several reasons for this decline: the performance observed during the three-year period was strongly influenced by regulatory factors; increased competition resulted in reduced profit margins; and exceptionally mild climatic conditions over this period significantly decreased the volume of gas sales. Finally, it should be noted that the best performance was achieved by companies based in northern Italy which were members of longstanding groups and were single rather than multi-business companies. This result contrasts with the failure of the business diversification strategy, which was widely adopted by enterprises from the utility sectors following the liberalization process. Keywords: Italian gas market liberalization, performance indexes, cluster analysis. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090231


1

Introduction

The fact that natural gas is relatively environmentally compatible and that its use in the thermoelectric sector guarantees a high level of consumption resulted in the European Community deciding to regulate the natural gas market. It was in this regard that on June 22 1998 the European Parliament and the European Council, by means of Directive 98/30/CE [1], began the liberalization of the European natural gas market, which had previously been characterised by vertical integration and public monopoly [2]. This process ended in 2003 with the Gas Directive 2003/55/EC [3], which is the European gas legislation in force at present. The European Gas Directive was transposed into Italian law by Legislative Decree n.164/2000, known as the Letta Decree [4], which laid down important guidelines concerning the definition of the eligible customers, competition, and conditions of reciprocity. The most significant change brought about by this legislation was that the Letta Decree imposed the unbundling of the distribution companies from those in retail, and thus allowed the latter to operate in a more competitive market. Extensive research has previously been conducted in order to analyse one specific aspect of performance in the natural gas market, such as the efficiency or the productivity. Examples of such studies are: Aivazian et al. [5], Jamasb et al. [6], Herbert and Kreil [7], and Sickles and Streitwieser [8] who explore the natural gas industry in the USA; Price and Weyman-Jones [9] who study the United Kingdom's natural gas distribution sector; and Lee et al. [10] who estimate the total factor productivity based on an international comparison. To date, very little research regarding the natural gas market has been carried out in relation to the simultaneous effects of the various aspects of performance, such as financial, liquidity, and profitability indicators. An evaluation of the gas sector with regard to economic performance is carried out by Kim et al. [11], although their work concentrates on the transportation segment. In connection with the Italian natural gas market, a performance analysis is carried out by Erbetta and Fraquelli [12] who focus on the distribution segment. In contrast, the present paper concentrates on the retail segment which, having undergone major transformations in recent years, is the only sector to be opened to free market competition and is therefore deemed more suitable for a comparative analysis of competitiveness. In our study the performance of the gas retail companies are evaluated in relation to the companies’ age, size, geographical location and degree of business diversification. The methodology employed here is divided into two consecutive stages: 1. The evaluation of the main financial, liquidity and profitability indicators; 2. The performance of a cluster analysis utilising the indicators from stage 1. The latter allows the sample to be subdivided into homogeneous groups which are then analysed in relation to the main characteristics of the company. The aim of the analysis is to answer the following research questions: WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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•

Can the Italian natural gas retailers be grouped into clusters characterized by internal homogeneity and external heterogeneity? • Can the clusters be formed by simultaneously considering financial, profitability and liquidity indicators? • If so, do these clusters indicate some market features with respect to the following company characteristics: geographical position, age, size and business diversification? This research paper is organized as follows: Section 2 provides a description of the data set; Section 3 describes the cluster analysis; Section 4 presents an analysis of the results with respect to the following characteristics of the companies: size, geographical position, age and business diversification; Section 5 concludes.

2

Data set

The data set, supplied by the Unione Italiana delle Camere di Commercio (Italian Union of the Chambers of Commerce), is comprised of data relating to 105 companies operating in Italy, including the balance sheet for each company. The present analysis refers to the three year period from January 2004 to December 2006. Most of the retail companies in the sample were formed in 2003 and were consequently still in the start-up phase during the three year period considered here. Thus it was not possible to analyse historical data dating back prior to 2004. On the 1st January 2006 there was a total of 414 companies authorised by the ‘Ministero delle Attività Produttive’ (Ministry of Productive Activities) to practise in the retail market. However, according to research undertaken by the Italian Regulatory Authority for Electricity and Gas (AEEG), only 194 of these companies appeared to be active. Data regarding the three year period considered here were available for 105 of the active companies. Therefore, these 105 companies became our sample representing a significant proportion of the total number of retail companies operating in Italy (approximately 54%). As regards the geographical distribution, 63% of the companies are located in northern Italy, 24% in central Italy and the remaining 13% in southern Italy. In relation to company size, the companies analysed have been divided into three groups according to their revenue: small, medium and large sized companies. Our sample is comprised of 48 small companies (45.7%), 33 medium companies (31.4%) and 24 large companies (22.9%). Approximately 60.8% of the firms in the sample are members of longstanding business groups, while the remaining 39.2% is made up of newly-formed companies. Finally, with regard to the choice of strategy, whether to diversify or to specialise, 81 firms (77%) are single-business companies (specialised), while 24 (23%) are multi-business (diversified).



3

Cluster analysis

In order to analyse company performance, cluster analysis is applied [13–16]. This analysis is intended to create groups which have the maximum cohesion internally and the maximum separation externally. Among the various clusterisation methods, the technique employed by Ward [17] was chosen as it generates a classification hierarchy while minimising the variance within each of the groups. The cluster analysis is carried out using SPSS (Statistical Package for the Social Sciences): this allows subjects (the companies) to be grouped in relation to the probability of certain values being scored by a set of variables (grouping variables). The grouping variables used in this study are the following profitability indicators: Return on Equity (ROE), Return on Investment (ROI), Return on Sale (ROS), and the following liquidity and financial indicators: Liquid Asset index (LA) and Leverage Ratio (LR). The liquid asset index shows the short-term debtpaying ability and it is determined by subtracting from current assets the current liabilities. The Leverage Ratio provides a view of the company overall debt situation and it is calculated by dividing net debt to equity. The above indicators have been chosen since they have a low level of inter-correlation. Table 1 shows the value ranges chosen for the various performance indicators utilised in the cluster analysis. Table 1:

Performance indicator ranges.

Range

Performance

ROI

ROE

ROS

LA

LR

1

Poor

x1000). The results of the analysis are insentive to the value Wfuel so long as a large value is used. In this analysis Wfuel is assume to be 1000. Equations (3.1) and (3.2) can be solved for A and B so that the equivalent hydrocarbon fuel is now specified. The result is

B = Wfuel/(1 + MfC/MfH) A = (Wfuel – B)/12

(3.3) (3.4)

If we assume that 1 mole of fuel is reacting then

α = 1- α1 - α2 - α3 – α6 - α7

(3.5)

where αi represents the mole fraction of each species derived from the ultimate analysis using equation 2.3. The molecular weight of the complete fuel can be calculated by W F = ∑ α i • Wi

(3.6)

where the summation is over all species in the fuel. The enthalpy of formation of the complete fuel, h computed by D

h fF

1 = HHV WF

D

fF

, in BTU/1bm may be

169, 297 • (α • A + α 7 )   + 61, 485 (α • B + 2α 2 )   + 127, 744 • α6

    

(3.7)

where: HHV = the higher heating value of the fuel in BTU/1bm and it is obtained from a laboratory analysis.



4

Development of theory underlying efficiency charts

The problem considered in this section is to develop the underlying theory for a set of charts which gives the efficiency, theoretical Air Fuel ratio, and excess air for the complete combustion of a general fuel as described by equation (2.4). The amount of oxygen in the flue gas and the flue gas temperature are known in this situation. In addition, only CO2, H2O, N2, and SO2 will be present in the products. The amount of these constituents must be determined depending on the fuel type and oxygen level in the flue gas. For complete combustion of one mole of fuel with dry air, one obtains

α C A H B + α1 N 2 + α 2 H 2 0 + α 3 0 2 + α 6S 2 + α 7 CO 2

(4.1)

+ a0 2 + 3.76aN2 → dCO 2 + g0 2 + hN 2 + jH 2 0 + kS0 2 We will be given the percent O2 in the dry productions, i.e.,

Percent

O

2

= known value ≡ PO2 =

g x 100 (4.2) d+g+h+k

Marking mass balances on elements in the combustion reaction gives

Carbon Nitrogen

d = αA + α 7 h = 3.76α + α1

Oxygen

d+g+ j 2+k = a+

Hydrogen

j = α2 +

Sulfur

k = 2α 6

αB

(4.3) (4.4)

α2 2

+ α3 + α7

2

(4.5) (4.6) (4.7)

In Equations (4.2) through (4.7), we have the following unknowns:

a, d, g, h, j, k Thus, we have six independent equations and six unknowns. Equations (4.3), (4.6), and (4.7) can be used to determine values for d, j, and k respectively, leaving three unknowns and three equations. From Equation (4.2):

g = R(d + h + k) where

R = (PO2/100)/(1 – PO2/100) WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

(4.8)

465


Solving equation (4.4) for “a” gives:

a=

h − α1 3.76

(4.9)

Substituting equation (4.9) into equation (4.5) gives:

d + g + j/ 2 + k =

h − α1 α + α7 + α3 + 2 3.76 2

(4.10)

Substituting equation (4.8) into equation (4.10) gives:

d + R(d + h + k) + j / 2 + k =

α h −α1 + α 7 + α3 + 2 3.76 2

(4.11)

Grouping coefficients in equation (4.11) gives:

1   d (1 + R ) + h  R −  + k (R + 1) + j / 2 3.76   = α7 + α3 +

α2 2

α1

−

(4.12)

3.76

Substituting equations (4.3), (4.6), and (4.7) into equation (4.12) gives:

α αB α α1 (αA+α7 ) (1+ R) + k(1+ R) + 22 + 4 − α7 − α3 − 22 + 3.76 = −h( R − 13.76) (4.13)

Solving for h gives:

h= −

(1 + R) (αA + α7 + k ) + αB 4 − α7 − α3 + α1 (R − 1 3.76)

3.76

(4.14)

Using the value of h calculated from equation (4.14) in equation (4.9) yields a value for “a”. Finally, g can be calculated from equation (4.8). The combustion efficiency is a measure of the percent of available energy in the fuel and air which is released in the combustion process. It is easier to obtain the necessary measurements using the indirect method; however, the calculation is more involved. The combustion efficiency is defined as follows:

nC =

h3 −

h1 + h 2

HHV

100

(4.15)

The combustion efficiency can be calculated from this equation where the enthalpies h1, h2, and h3 are calculated from their definitions given in equations (4.16), (4.17), and (4.18). These enthalpy calculations are based on the fuel WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

466 Energy and Sustainability II temperature being the same as the combustion air supply temperature which is 77 F. The effect of different inlet temperatures can easily be incorporated into these enthalpy calculations. D h ≡ h fF (4.16) 1 h2 ≡ 0 (4.17) h3 ≡ +

jα

d+g+h+k

α W

H2

0

WF

WD WF

•

  D   ∑  hfi M fi  + .25    D

=  −5779 + .445

The actual air-fuel ratio

( T3A -

(

 T3A − 77   (4.18)

)

77 )

D D    AF ≡ M A M F  can be computed from the  

known moles of oxygen calculated by equation (4.8) since air contains 4.76 moles for every one mole of oxygen. Multiplying the ratio of moles of air per mole of fuel by the ratio of the molecular weight of air (28.93) to the molecular weight of the fuel gives AF = 4.76·a·28.93/WFuel (4.19) Table 2:

Combustion efficiency chart for biodiesel.

Temperature of flue gas less Temperature of combustion air, F % % Oxygen Excess air 0 0.0 1 4.8 2 9.9 3 15.7 4 22.1 5 29.3 6 37.4 7 46.7 8 57.5 9 70.0 10 84.8 11 102.6 12 124.3 13 151.5 14 186.4 15 232.9

AF Theo 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6 14.6

AF

14.6 15.3 16.1 16.9 17.8 18.9 20.1 21.4 23.0 24.9 27.0 29.6 32.8 36.8 41.9 48.7

% CO2 15.1 14.4 13.7 13.0 12.3 11.5 10.8 10.1 9.4 8.7 7.9 7.2 6.5 5.8 5.1 4.3

250

300

350

400

450

500

% Combustion Efficiency

88.3 88.1 87.8 87.5 87.1 86.8 86.3 85.8 85.3 84.6 83.8 82.8 81.7 80.2 78.3 75.8

87.1 86.8 86.5 86.1 85.7 85.2 84.7 84.1 83.4 82.6 81.7 80.5 79.1 77.4 75.1 72.1

85.9 85.5 85.1 84.7 84.2 83.7 83.1 82.4 81.6 80.6 79.5 78.2 76.6 74.5 71.9 68.4


84.7 84.3 83.8 83.3 82.8 82.2 81.5 80.7 79.7 78.7 77.4 75.9 74.0 71.7 68.7 64.7

83.4 83.0 82.5 81.9 81.3 80.6 79.8 78.9 77.9 76.7 75.3 73.6 71.5 68.8 65.5 61.0

82.2 81.7 81.2 80.6 79.9 79.1 78.2 77.2 76.1 74.7 73.1 71.2 68.9 66.0 62.3 57.3


467

The theoretical air fuel ratio is obtained assuming complete combustion with no excess air and balancing equation (4 .1) i.e., (4.20)

AFtheoretical =

 B 4.76 WA    α  A + 4  − α 3 + 2α 6  WF    

The excess air is the difference between the actual and theoretical air-fuel ratio expressed as a percentage of the theoretical air-fuel ratio, namely Table 3:

Combustion efficiency chart for yellow grease.

Temperature of flue gas less Temperature of combustion air, F % % Excess % AF theo AF Oxy air CO2 0 0.0 14.3 14.1 15.5

1

3.9

14.3

300

350

400

450

500

% Combustion Efficiency

90.1

88.9

87.7

86.4

85.2

84.0

14.8

14.7

89.8

88.6

87.3

86.0

84.8

83.5

2

9.0

14.3

15.5

14.0

89.6

88.2

86.9

85.6

84.3

83.0

3

14.7

14.3

16.4

13.2

89.2

87.9

86.5

85.1

83.7

82.4

4

21.1

14.3

17.3

12.5

88.9

87.5

86.0

84.6

83.1

81.7

5

28.2

14.3

18.3

11.8

88.5

87.0

85.5

84.0

82.4

80.9

6

36.4

14.3

19.4

11.0

88.1

86.5

84.9

83.3

81.6

80.0

7

45.6

14.3

20.8

10.3

87.6

85.9

84.2

82.5

80.7

79.0

8

56.3

14.3

22.3

9.6

87.0

85.2

83.4

81.5

79.7

77.9

9

68.8

14.3

24.1

8.8

86.3

84.4

82.4

80.5

78.5

76.5

10

83.5

14.3

26.2

8.1

85.5

83.4

81.3

79.2

77.1

75.0

11

101.2

14.3

28.7

7.4

84.6

82.3

80.0

77.7

75.4

73.1

12

122.8

14.3

31.8

6.6

83.4

80.9

78.4

75.8

73.3

70.7

13

149.8

14.3

35.6

5.9

82.0

79.1

76.3

73.5

70.7

67.8

14

184.6

14.3

40.6

5.2

80.1

76.9

73.7

70.5

67.3

64.1

15

230.8

14.3

47.2

4.4

77.6

73.9

70.2

66.5

62.8

59.1

Excess air ≡ EA =

5

250

AF-AF theoretical AF theoretical

x 100

(4.21)

Results

Combustion efficiency charts for the two bio-fuels whose values are listed in table 2.1 were developed using the equations and procedure described above. The charts are produced assuming complete combustion of the fuel and that the fuel and air enter at 77 F. These conditions can be changed but for most cases the results are sufficient. Table 2 is a combustion efficiency chart for yellow grease and Table 3 is for biodiesel. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

468 Energy and Sustainability II The charts show that one can easily obtain data from simple stack analysis for the efficiency of the device burning the fuel. The data can easily show what happens when the combustion is tuned or heat recovery is applied. Further value for these charts can be obtained when one wants to check flow instrumentation. For example, the fuel flow rate can be measured and the airflow determined from the efficiency charts knowing the Air Fuel ratio. This would allow an analysis of the combustion air fan performance. Many other useful results also can be obtained. Finally, the development in this paper allows one to easily develop combustion efficiency charts for any carbon, hydrogen, oxygen fuel. As biofuels become more prevalent, the need to develop such charts will only increase in importance.

References [1] Dyer, D.F. & Maples, G., Boiler Efficiency Improvement, Boiler Efficiency Institute: Auburn, Alabama 2001. [2] Adams, T.T., A Demonstration of Fat and Grease as an Industrial Boiler Fuel, University of Georgia Outreach Service, June 30, 2002. [3] Chien, Yi-Chi, Mingming, L., & Boreo, F.J. Characterization of Biodiesel and Biodiesel Particulate Matter by TG, TG-MS, and FTIR, Energy Fuels, 23(1), pp 202-206, December 5, 2008.



469

Combustion of urban solid wastes in an experimental fluidized bed combustor C. A. Torres-Balcazar1, G. Lopez-Ocaña1, R. G. Bautista-Margulis1, J. R. Hernandez-Barajas1, H. O. Rubio-Arias2 & R. A. Saucedo-Teran3 1

The Juarez Autonomous University of Tabasco, Mexico The Autonomous University of Chihuahua, Mexico 3 INIFAP, Mexico 2

Abstract Outdoor incineration of low-grade solid fuels is still an inadequate and common practice in developing countries worldwide. To date, advanced combustion systems, such as fluidized bed, have been successfully developed and implemented to deal with these environmental issues. However, optimum operating conditions have to be attained in order to reach the highest combustion efficiency of each particular system. The objective of this investigation was to study the combustion efficiency behaviour of urban solid wastes (USW) in an experimental fluidized bed combustor under various operating conditions. Five experimental tests were conducted by using USW collected in the city of Villahermosa-Tabasco, Mexico. The experimental tests were carried out under the following conditions: excess air of 281%, bed particle size of 0.8 mm and static bed height of 0.2 m. The combustion efficiency varied from 54 to 82% at a bed temperature between 770 and 914ºC, being significantly correlated to a minimum square regression model (R2 = 0.87, p < 0.01). At bed temperatures lower than 800ºC, the USW composition and heterogeneity affected the combustion efficiency (54-64%), giving rise to an increase in CO emissions (1,092 ppm). At bed temperatures greater than 870ºC, however, high combustion efficiencies (80-82%) were achieved with maximum SO2 (18 ppm) and NO (11 ppm) emission levels complying with the maximum permissible levels established in the Mexican environmental legislation (NOM-098-SEMARNAT). The proposed experimental prototype was demonstrated to be both technically and environmentally feasible for USW treatment via fluidized bed technology. Keywords: combustion, urban solid waste, fluidized bed.



1

Introduction

In developing countries, it is common for municipalities to spend 20-50% of their available recurrent budget on solid waste management. Yet, it is also common that 30-60% of all USW in developing countries is uncollected and less than 50% of the population is served. In some cases, as much as 80% of the collection and transport equipment is out of service, in need of repair or maintenance. In most developing countries, open dumping with open burning is the norm. To date, state of the art on incineration systems have demonstrated to achieve the highest levels of control and destruction of USW over traditional direct methods (e.g., landfill and underground injection). To reduce waste volume, local governments or private operators can implement a controlled burning process called combustion or incineration. In addition to reducing volume, combustors, when properly equipped, can convert water into steam to fuel heating systems or generate electricity. The United States has about 89 operational USW-fired power generation plants, generating approximately 2,500 megawatts, or about 0.3% of total national power generation [1]. Incineration facilities can also remove materials for recycling. Over one-fifth of the U.S. USW incinerators use refuse derived fuel (RDF). In contrast to mass burning—where the USW is introduced “as is” into the combustion chamber—RDF facilities are equipped to recover recyclables (e.g., metals, cans, glass) first, then shred the combustible fraction into fluff for incineration. Burning waste has been a common means of disposal throughout history. In 1995, The U.S. EPA estimated that 16% of solid waste had been disposed of by some form of combustion. Incinerators reduce the volume of waste by about 90% [2], a significant reduction of waste that would otherwise go into a landfill. Incineration at high temperatures also destroys many of the toxins and pathogens in medical waste and other hazardous wastes, in addition to reducing volume. However, the variation in the composition of USW affects the emissions impact. For example, if USW containing batteries and tires are burned, toxic materials can be released into the air. A variety of air pollution control technologies are used to reduce toxic air pollutants from USW power plants [3]. The incinerator provides a means to control the combustion process through the application of a proven technology. However, the incinerators must comply with a given regulation for performance and operation, such as: high combustion efficiency, removal and destruction of toxic gases, permissible limits for particulate emission, semi-continuous monitoring in the process, a specific minimum temperature, and acceptable levels of residence time in the exhaust gases [4–6]. In this context, various incineration technologies have been developed to deal with different types and physical forms of residues [7, 8]. Some of these technologies have been highlighted in the following categories: moving grate, fixed grate, liquid injection, rotary kilns and fluidized bed incinerators. The fluidized bed combustors represent one of the most promising technologies for incinerating organic and plastic residues, contaminated sludge, biomass and WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


471

other industrial wastes [9–13]. Also, control of the combustion process has been selected as the main strategy for reducing emissions into the atmosphere. Furthermore, a strong correlation has been found among temperature, residence time and emission rate [14, 15]. Fluidized bed combustion can be used for energy production or incineration for almost any material containing carbon, hydrogen and sulfur in a combustible form, whether it is in the form of a solid, liquid, slurry or gas. The technology’s fuel flexibility arises from the fact that the fuel is present in the combustor at a low level and is burnt in the mass of a thermally inert bed material (typically this is limestone if sulfur capture is required, otherwise sand). However, fuel flexibility must either be built into the design of the combustor or alternatively the FBC system must be tailored for a specific fuel or combination of fuels. In addition, the designer must consider issues like heat release patterns, ash characteristics (particularly if the ash has any potential for agglomeration or fouling of heat transfer surfaces or blockage of the return valve in the case of a circulating FBC) and any special requirements of the fuel such as the need for sulfur or hydrochloric acid capture [16]. The objective of the present investigation was to evaluate the combustion efficiency and gases products from a three-phase combustor in order to thermally treat specific USW generated in Villahermosa-Tabasco, Mexico. The experimental combustor was specifically designed and constructed to cope with the operating and fluidizing requirements in the current study. Also, the flue gas composition (CO, NO and SO2) was determined during the combustion process under various operating conditions, and compared with the NOM-098SEMARNAT-2002 in Mexico.

2


2.1 Characterization of USW The USW samples were taken according to the Mexican technical norm specifications [17]. The fieldwork was performed at the open municipal waste site located outskirts Villahermosa city in Tabasco, Mexico. Indirect methods were employed to quantify the USW, the loading count and the truck number [18]. To determine the USW generation, the samples were applied for a period of eight days and analyzed in seven days. Nevertheless, the first day of USW sampling was excluded for not being representative. In this study six sectors were considered throughout the sampling: central downtown (S1: 17º 59′ 04.95″ N, 92º 56′ 14.19″ W), northeast (S2: 18º 00′ 10.18″ N, 92º 56′ 59.98″ W), southwest (S3: 17º 58′ 10.94’’ N, 92º 58′ 09.94″ O), north-northeast (S4: 18º 01′ 17.31″ N, 92º 53′ 56.80″ W), east (S5: 17º 58′ 47.17″ N, 92º 54′ 51.88″ W) and peripheral area (S6: surroundings of the city). Samplings were carried out three times a week within each sector, allowing for a specific classification and quantification of the products and by-products.


472 Energy and Sustainability II 2.2 Design and operating characteristics of the experimental combustor The combustor was made up of mild steel and constructed in three cylindrical sections with an internal diameter of 0.1 m, as can be seen in Figure 1. The bed and plenum sections are 0.45 m and 0.25 m high, respectively; while the height (freeboard) of the two remaining sections is 0.50 m each. Two tubes in “V” shape were coupled to the combustor walls in a 45° angle. Such adjacent tubes were employed, on the one hand, for the pilot burner and, on the other hand, as an observation port. To feed the USW, an open area was made in the bed section. The bed material was made up of silica sand with a mean particle size of 0.8 mm. The plenum comprised the air and gas distributor and was constructed in stainless steel with a 0.1 m internal diameter and 0.01 thick. To distribute the air and gas inside the combustor, five standpipes were made of stainless steel with 9 mm diameter and 54 mm length. At the top of each standpipe, four orifices were perforated with 2 mm diameter. Exit Flue Gas Cyclone Fluidized Bed Combustor Hooper Feeding System

Perspex Window Vibrating Tray

Conveying System

Observation Port Cooling System

Fluidizing Air Figure 1:

Catchpot

Propane for Start-Up

Experimental setup for the combustion trials.

The feeding of USW into the experimental prototype was performed manually and discontinuously, working as a batch reactor. The USW was triturated to get an average size of 5 mm diameter [20, 21]. Thermocouples type “K” was used to monitor the temperature in the bed, the freeboard and the exit flue gas. The thermocouple material was stainless steel with a temperature interval between -129 to 1371°C, and ± 0.1% error. The temperature was recorded in a Pro TM 45 panel control (43/4 Digit Microprocessor Based Temperature/Process Indicator). The air for both the pilot burner and combustion system was supplied by a compressor with a capacity of 0.56 m3/min and 14 kg/cm2 pressure. The temperature and concentration of the combustion products were measured with a portable analyzer TESTO 300 M&XL. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


473

Five experiments were conducted as follows: test C1 was a preliminary trial to calibrate the prototype when operated at Tb= 770 – 914 °C; tests C2, C3 and C4 were carried out when the combustor operated at a Tb range between 850 and 900°C (typical operating conditions of commercial incinerators). The results were plotted by considering the efficiency as dependent variable and the temperature as independent variable in order to observe a particular trend, so that the appropriate regression model was adjusted. Finally, test C5 was conducted to run a broader Tb range, from 400 to 900°C, and using the same USW mixture. All the experiments were conducted under the following operating conditions: 13 h operating time; 66-90 g/min mass flowrate; 800-900°C bed temperature; 0.35-1.06 kg/cm2 air pressure; 12.0-16.9% excess oxygen; 0.8 mm mean particle bed size and 5 mm average residue size. 2.3 Combustion efficiency The combustion efficiency (η) was determined by monitoring carbon monoxide (CO) and carbon dioxide (CO2) in the exit flue gases. The CO and CO2 concentrations were measured with a portable combustion gas analyzer and used to calculate the combustion efficiency, as follows:



η = 100 −  K net 

(T

k1Q gr CCO  −Ta )  (210 + 2.1Tg − 4.2Ta )  + +X   Qnet CCO + CCO  CCO2 1000Q gr   2  g

Where Tg is the flue gas temperature, Ta is the room temperature, CCO2 is the CO2 concentration measured, CCO is the CO concentration measured, X is the moisture content plus the hydrogen content in the fuel, Knet = 0.390, k1 = 40, Qr= 53.42 y Qnet = 48.16. In addition, nitric oxide (NO) and sulfur dioxide (SO2) were measured in the exhaust gases. The combustion products were analyzed every 10-15 min period after reaching stable operating conditions, that is, 5 min of constant bed temperature. The desired bed temperature was obtained by adjusting the USW feeding flow.

3


From the USW estimated in six sectors of Villahermosa city, sector S1 was shown to be the highest generation with 210 tons/day and average density of 230.3 kg/m3. The other five sectors produced various quantities of volumetric weight and USW generation, as illustrated in Table 1. In average, the six sectors generated 747 tons/day throughout the sampling period. In some sectors, certain materials are recovered before its final disposal. In Mexico, this pre-selection of recycled material is known as “pepena”. Because of this activity, the information shown in Table 1 does not represent the USW generation but the USW composition at site. Given the highest generation, sector S1 was chosen to be the fuel supply for feeding the USW in the experimental fluidized-bed combustor. Such a sector represents approximately 28% of the total USW volume generated in the city and the “pepena” reduces the recyclable material (e.g., textiles, aluminum, cardboard, paper and cans). WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

474 Energy and Sustainability II Table 1: Volumetric weight (kg/m3) Generation (Tons/day)

USW generation (mean ± standard deviation) for each sector. Sector 1 230.3 ±

Sector 2 203.7 ±

49.7

11.3

210.0 ±

160.0 ±

50

40

Subproducts Rigid plastic

2.7 ± 3.1 10.0 ± 2.3

Paper

5.9 ± 6.3 17.3 ± 5.8

Polyetilene

Sector 5 180.3 ±

8.7 100.0 ± 70.0 ± 30 40

19.8

92.0 ±

115.0

18

Percentage (%) 26.7 ± 26.3 ± 7.2

3.4

15.8 ±

7.0 ± 3.4

9.7 ± 1.6

Sector 6 200.2 ±

29.7

±

35

12.7 ± 3.2 13.0 ± 3.3 29.0 ± 3.5

4.2

15.5 ± 1.2 Plastified cardboard Organic matter

Sector 3 Sector 4 216.3 ± .9 ± 14.1

11.2 ± 1.2

12.7 ±

11.9 ±

2.2

2.5

9.9 ± 1.4 8.9 ± 1.3

7.7 ± 1.0

6.3 ± 1.0 47.9 ± 5.6

43.6 ± 5.4

29.0 ±

29.0 ±

8.2

8.1

30.3 ± 3.9 47.7 ± 6.3

Glass

3.2 ± 4.0

10.3 ± 3.9

4.6 ±2.3

0.9 ± 2.7

Fine residues

2.7 ± 3.2

11.9 ± 2.3

1.7 ± 3.9

3.9 ± 3.8

Textiles

2.9 ± 0.2

1.0 ± 0.3

2.3 ± 0.1

Aluminum

2.2 ± 1.2

9.9 ± 3.2

Polystyrene

6.8 ± 2.8

0.9 ±0.3

Cardboard

8.3 ± 3.1

11.3 ± 3.6

Cans

7.5 ± 1.5

14.4 ± 2.8

5.8 ± 2.5

The following by-products were found in S1: rigid plastic (10%), paper (17.3%), polyetilene (15.5%), organic matter (43.6%), glass (3.2%) and fine residues (2.7%). Likewise, Table 2 shows the elemental analysis for the USW composition from S1 to S6. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Table 2:

475

Ultimate analysis (mean ± standard deviation) of USW collected.

Ultimate analysis of USW (% in weight) Ash C H O N S 32.7 4.6 20.6 1.4 2.0 ±0.2 20.1 ±7.9 ±4.3 ±0.2 ±1.4 ±0.4 2 41.5 5.9 30.0 3.4 0.3 ±0.1 5.2 ±4.1 ±0.5 ±0.1 ±1.0 ±0.1 3 26.3 5.5 28.0 0.3 0.2 ±0.1 7.0 ±3.8 ±3.7 ±0.5 ±3.0 ±0.2 4 34.4 4.3 32.2 1.8 0.5 ±0.05 4.0 ±0.2 ±3.6 ±0.7 ±4.8 ±0.1 5.5 29.3 1.6 0.3 ±0.1 2.2 ±0.8 5 42.2 ±0.8 ±0.5 ±2.3 ±0.3 6 34.2 5.0 30.6 0.4 2.3 ±0.1 3.6 ±0.1 ±3.8 ±1.0 ±3.3 ±0.2 Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Sulfur (S). N.B. obtained by difference [100% - Σ (C + H + N + S)]. Sector 1

Moisture 18.6 ±1.4 13.7 ±2.3 32.7 ±3.7 22.8 ±0.2 18.9 ±0.2 23.9 ±1.9 Oxygen was

Combustion efficiency [%]

85 80 75 70 65 60 55 50 750

800

850

900

Bed temperature [°C]

Figure 2:

Quadratic regression fitting for combustion efficiency with different temperature increases for C1, C2, C3 and C4 experimental tests. —x— Standard error; y Original data; ……… Polinomial approach.

In test C1 (Figure 2), the combustion efficiency varied from 54.4 to 82.3% at Tb ranging from 810 to 914°C, respectively. The CO concentration diminished from 810 to 278 ppm as the Tb increased from 820 to 900°C. This behavior may be explained by the oxidation of CO to form CO2 at high temperatures, since the reaction velocity at 900°C is six times higher than that at 820°C [22]. On the contrary, the CO2 and NO values increased as the temperature was raised above 820°C. The increase in NO concentration was presumably due to the kinetic reaction of NO, according to the extended Zeldovich mechanism, where the atomic oxygen reacts with the molecular nitrogen to form NO and atomic WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


2500

90

2000

80

1500

70

1000

60

500

50

0 400

Combustion efficiency [%]

Carbon monoxide [ppm]

nitrogen. At 900°C, the NO reaction velocity is 20 times higher than that at 800°C, which favors its formation [22]. Meanwhile, the SO2 concentration did not present a clear tendency. Also, it was observed that maximum SO2 values of 11 ppm were attained for Tb= 900°C. In the data obtained from tests C1, C2, C3 and C4, the combustion efficiency increased as increasing the bed temperature to some extent. The statistical data presented a R2 value of 0.87 (Figure 2) which resulted to be highly significant (p < 0.01) and well correlated with a = -0.0015; b = 2.7197; c = -1139.5247 en η = aT2 + bT + c (where T is expressed in ºC). For the computed model, the efficiency increased linearly 2.67 units per degree centigrade, particularly in the range of 770 and 817°C. However, the parabolic trend shows a decrease of 0.002 units of efficiency per degree centigrade for temperatures above 900°C. The results obtained in test C5 showed that the combustion efficiency increased when increasing the temperature of the fluidized bed combustor, having a decrease in CO concentration (Figure 3). At Tb= 400°C, the efficiency obtained was approximately 43% with CO concentrations of 1,973 ppm; while at Tb= 900°C, the efficiencies increased up to 80% and the CO levels diminished to 237 ppm.

40 500

600

700

800

900

Bed temperature [°C]

Figure 3:

Combustion efficiency (η) and CO concentration at different operating temperatures (Test C5). — — — Carbon monoxide; — + — Efficiency.

In the experimental combustor, it is desirable to favor the oxidation from CO to CO2 in order to assure complete combustion of the fuel and thus avoid any environmental damage. The high CO concentration in the flue gases was due to incomplete combustion of the elemental carbon within the fluidized bed combustor (low temperature and insufficient excess air) which, in turn, gave rise to an inefficient mixing of USW with the supplied air into the system. The NO and SO2 were below the maximum permissible levels (MPL) established by the Mexican Normativity [17]. The maximum values obtained for NO y SO2 were 18 and 10 ppm at the corresponding operating temperatures of 880 and 900°C, WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


477

respectively (Figures 4 and 5). On the contrary, the average values for CO were 220 ppm at the same high temperatures, exceeding the MPL of discharge to the atmosphere established by the above referred Normativity (Figure 6).

Nitrogen monoxide [ppm]

310 Temperatura vs CO

300

20 10 0 400

500

600

700

800

900

Bed temperature [ºC]

Figure 4:

NO concentration at different operating temperatures and its comparison with the maximum permissible level. —y— NO; ……… MPL NOM 098 SEMARNAT-2002.

Sulfur dioxide [ppm]

100 80 60 40 20 0 400

500

600

700

800

900


Figure 5:

SO2 concentration at different operating temperatures and its comparison with the maximum permissible level. —y— SO2; ……… MPL NOM 098 SEMARNAT-2002.

Although the current experimental combustor does not have any connection to other treatment system or gas recirculation by-pass, the combustion efficiencies achieved in the fluidized bed were reasonably high (82.3%) at high temperatures (900°C). The NO and SO2 concentrations were found to be below the maximum permissible levels established in the Mexican environmental legislation [17]. The proposed experimental prototype showed that high combustion efficiencies can be proportional to the increase in temperature within WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


Carbon monoxide [ppm]

2500 2000 1500 1000 500 0 400

500

600

700

800

900


Figure 6:

CO concentration at different operating temperatures and its comparison with the maximum permissible level. —y— CO; ……… MPL NOM 098 SEMARNAT-2002.

the fluidized bed combustor. In this case, the combustor could presumably reach higher efficiencies if heat losses to the surroundings were reduced and the excess air was appropriate [7]. In a fluidized-bed incinerator at pilot scale, Saxena and Jotshi [19] reported that oxygen concentrations in the flue gas should be ranging between 13.4 and 16.1%; Swithenbank et al. [20] determined an optimum oxygen concentration of 16.9% during the incineration of clinical waste. Previous works on this field have also found that commercial incinerators were operated under similar excess oxygen conditions. In agreement with these investigations, the proposed fluidized bed combustor presented similar oxygen concentrations varying from 12.0 to 16.9% throughout the experiments. On the other hand, companies like Energy Incorporated Co (EIC) and Energy Products of Idaho (EPI) reported CO2 values in the flue gas in the range of 5.2 and 6.6% [21]. For a clinical waste incinerator, the CO2 discharges were found to be in 3.1% [19]. While in the current experimental combustor, the CO2 concentrations were measured between 1.5 and 6.3%. In this context, Saxena and Jotshi [19] reported SOx and NOx values in the range of 20-35 ppm and 100-139 ppm, respectively. The EIC and EPI prototypes showed SOx concentrations of 350 ppm and NOx concentrations of 35 ppm. Likewise, Swithenbank et al. [20] found higher emission levels for NOx (51 mg/m3) than SO2 (17 mg/m3) from the incineration of clinical residues. In the current experiments, the SO2 and NO concentrations never exceeded 40 ppm in the exhaust gases under similar operating conditions (900°C). Regarding the combustion efficiency, the experimental works mentioned above reported higher values (93-99%) than those obtained in this investigation (80-82%) since they combined the fluidization process with pyrolysis. Those prototypes operated at temperatures between 850 and 950°C and excess air ranging from 35 to 60%.



4

479

Conclusions

The experimental combustor demonstrated to be technically and environmentally feasible for the thermal treatment of USW via fluidized bed combustion. The highest combustion efficiency (82.3%) was obtained at 914°C bed temperature and 14.5% excess oxygen. The experimental results suggest that higher combustion efficiencies may be achieved if: 1) the USW mixtures are homogenized; 2) a continuous feeding system is used; and 3) the combustor is well insulated as to avoid important energy losses to the surroundings. Also, the SO2 and NO emissions did not exceed the MPL established by the Mexican environmental legislation. Nevertheless, CO emission levels were over 200 ppm at Tb= 900°C, exceeding the MPL presumably due to a heterogeneity of the USW mixture in the fluidized bed combustor. It is recommended to run more experiments in order to better understand the heterogeneous combustion fundamentals of USW as well as its solid and gaseous emissions, under various fluidizing and operating conditions.

References [1] U.S. Environmental Protection Agency (2009) Combustion and incineration regulations, 40 CFR Part 60. [2] Knox, A. (2005) Overview of incineration, an overview of incineration and EFW technology as applied to the management of municipal solid waste (MSW), University of Western Ontario, Canada. [3] SEMARNAT (2002) Dirección general de manejo integral de contaminantes. Página web, http://www.semarnat.gob.mx. Correo: [email protected] [4] Scala F, Salatino P (2001) Modeling fluidized bed combustion of highvolatile solid fuels. Chemical Engineering Science. 57: 1175-1196. [5] Lin W, Johansen KD, Frandsen F (2003) Agglomeration in bio fuel fired fluidized bed combustors. Chemical Engineering Journal. 96: 171-185. [6] Oxley JH (1995) Combustion in fluidized beds. 1st International colloquium on pollution control and diagnosis. Instituto de Investigaciones Eléctricas. Cuernavaca, Morelos, Mexico. 10-12 July 1995. pp 1-24. [7] Kaynak B. Topal H. Atimtaya AT (2005) Peach and apricot stone combustion in a bubbling fluidized bed. Fuel Processing 86: 1175-1193. [8] Lin CL, Wey MY, Yu WJ (2005) Emission characteristics of organic and heavy metal pollutants in fluidized bed incineration during the agglomeration/defluidization process. Combustion and Flame. 143: 139149. [9] Oka SN ET (2004) Fluidized bed combustion. Marcel Dekker. [10] Kisuk CPE (1998) Solid waste incineration. U.S. Corps. of Engineers, Engineering Division, Report Tl 814-21, Washington D.C. [11] Hristov JY (2002) Fluidized Bed Combustion as a Risk-Related Technology: a Scope of Some Potential Problems. IFRF Combustion Journal. Article No. 200208, ISSN 1562-479X, 1-34 pp. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

480 Energy and Sustainability II [12] Scala F, Chirone R (2004) Fluidized bed combustion of alternative solid fuels. Experimental Thermal and Fluid Science. 28(7):691-699. [13] Scala F, Chirone R, Salatino P (2003) Fluidized bed combustion of tyre derived fuel. Experimental Thermal and Fluid Science. 27(4):465-471. [14] Fang M, Yang L., Chen G, Shi Z. Luo Z, Cen K (2004) Experimental study on rice husk combustion in a circulating fluidized bed. Fuel Processing Technology. 85: 1273-1282. [15] Yan R, Liang DT, Tsen L (2005) Case studies–problem solving in fluidized bed waste fuel incineration. Energy Conversion & Management. 46: 11651178. [16] Anthony, E.J. (1995) Fluidised bed combustion of alternative solid fuels; status, successes and problems of the technology. Progress in Energy and Combustion Science. 21(3):239-268. [17] Norma Oficial Mexicana NOM-098-SEMARNAT-2002, Protección ambiental-incineración de residuos, especificaciones de operación y límites de emisión de contaminantes. [18] Tchobanoglous G, Theisein H, Vigil SA (1994) Gestión Integral de Residuos Sólidos. Ed. McGraw-Hill. México, D.F. [19] Saxena SC, Jotshi CK (1994) Fluidized-Bed incineration of waste materials. Prog. Energy Combust. Sel. 20: 281-324. [20] Swithenbank J, Nasserzadh V, Ewan and Delay BCR, Lawrence D, Jones B (1997) Research investigations at the municipal and clinical waste incinerators in Sheffield, UK. Environmental Progress. 16(1): 65-81. [21] Wiley SK (1987). “Incinerate-bed your hazardous waste”. Hydrocarbon Processing. Tulsa, Oklahoma. [22] Borman GL, Ragland KW (1988) Combustion engineering. The McGrawHill Companies. USA. 613 pp



481

Optimisation of ammonia injection for an efficient nitric oxide reduction S. Ogriseck & G. P. Galindo Vanegas Infraserv GmbH & Co. Hoechst KG, Frankfurt am Main, Germany

Abstract Dry flue gas cleaning systems using activated coke as a catalyst reduce sulphur dioxide and nitric oxide emissions. The sulphur dioxide reduction in this system has an efficiency of over 98%. Therefore, the main purpose is the optimisation of the NOx reduction process by means of ammonia injection optimisation. Such a flue gas cleaning system is currently in operation at the Industriepark Hoechst site in Germany. This paper shows the analysis of the ammonia load on activated coke and denitrification experiments in laboratory scale under variation of different parameters. The results of the ammonia loading tests show a relation between temperature and loading capacity. The tests were driven for temperatures between 110 and 469°C. The denitrification tests pointed out that the highest efficiency is obtained with the activated coke loaded at the highest temperature at 469°C. Keywords: ammonia, activated coke, nitric oxides, denitrification, dry flue gas cleaning, adsorption.

1

Introduction

The maximum emission limits for nitric oxides (NOx) in Germany are set in the Ordinance on Large Combustion Plants and Gas Turbine Plants, 13th BImSchV. For power plants with a thermal input of more than 100 MW, the NOx emission limit value is of 200 mg/m³ (STP) dry basis measured as NO2. A new ordinance for the assurance of air quality requirements (37th BImSchV) has been proposed. One of the focus points of this regulation is to reduce the amount of emitted nitrogen oxides and for this reason sets up a new limit for new plants, starting operation on the 31st of December 2012, to 100 mg/m³ (STP). The decrease in the emission limit allowance for existing plants is very likely to happen due to WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090431

482 Energy and Sustainability II the everyday increasing efforts of the governments to protect and improve the environment. This work will expose the evaluation of the possibilities to optimise the existing flue gas cleaning system at the combined heat and power plant (CHP) at Infraserv Hoechst, Germany to ensure a more efficient NOx emissions reduction without a complete change in the process.

2

Description of the power plant

Infraserv Hoechst is the operator and service provider of the Industriepark Hoechst in Frankfurt am Main, Germany, one of Europe's largest production and research sites. As part of its wide range of services Infraserv Hoechst is in charged of the production, purchase, management and distribution of electrical energy, heat and process steam. In site, Infraserv Hoechst operates a combined heat and power plant fueled with hard coal and natural gas. Flue gas to the stack

Flue gas from the boilers

Classifier

to Firing

Desorber Fuel

Activated coke

Burner

3 SO 2 Rich gas

2

Water

to Rich gas cleaning

4

Air

5 Nitrogen

Injection cooler

Ammonia

1

Adsorber

Figure 1:

Sieve 1 – First Stage 2 – Second Stage 3 – Heating Zone 4 – Degassing Zone 5 – Cooling Zone

AC to by out

Modified BF/Uhde Process at Infraserv Hoechst.

The CHP plant has a thermal capacity of 750 MW and an electricity capacity of 160 MW. The plant consists of four boilers with a steam capacity of 830 t/h together. The control of the emissions of nitrogen oxides in the plant is specially achieved by the employment of primary measures. The secondary measures for the control of nitrogen oxides emissions are not a main use. The flue gas from the two coal boilers containing predominantly nitrogen and sulphur oxides is cleaned after combustion by means of a simultaneous desulphurisation/ WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


483

denitrification dry flue gas cleaning system based on the adsorption and catalytic reaction with adsorbed ammonia on activated coke (AC), operating under the principles of the Bergbau-Forschung-Uhde process [1], Figure 1. According to the mass balance of the plant, the losses of the ammonia that is injected on the activated coke for the catalytic reduction of NOx in the system are considerable. This is why the main focus on the efforts directed to increase the efficiency of the system were set on the optimisation of the ammonia injection. The flue gas cleaning system in the plant was designed for a simultaneous desulphurisation and denitrification of the flue gas produced during combustion of coal. In the past, the direct injection of ammonia was stopped due to the clogging of the system caused by the formation of ammonium chloride. Today, only primary measures are applied in the combustion to ensure the emission limits of 200 mg/m3 (STP), dry basis. The initial design of the BergbauForschung-Uhde process was modified in such a way that the ammonia is injected in the system to load the activated coke before entering the adsorber unit. NH3 loaded activated coke Flue gas from Boilers

Adsorber

Desorber

NH3 slip

NH3 slip

to stack

Rich Gas Cleaning Ammonia input

Figure 2:

3

Ammonia flow.

Current ammonia injection

The current situation of the ammonia mass balance, Figure 2, was analysed and also the losses as an ammonia slip with the flue gas or with the rich gas. The reduction of the ammonia losses should be executed by the optimisation of the ammonia injection. This optimisation should, on the other hand, ensure a better adsorption of the ammonia on activated coke with the aim to both increase the denitrification capacity and decrease the ammonia losses of the system. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

484 Energy and Sustainability II The total mass balance showed that 60% of the ammonia fed is being lost part as ammonia slip (27%) and part with the rich gas (33%). Only 40% of the ammonia is being used for the reduction of the nitric oxide. Longer residence times at the NH3 injection point increase the probability of the adsorption and reaction of the ammonia with the nitric oxide and could avoid the ammonia slip to the rich gas. This way the residence time can increase the efficiency for the nitric oxide reduction, as is the case of this system. The influence of the residence time has already been discussed by [2].

4

Experimental investigations of ammonia load and denitrification

4.1 General overview In order to evaluate possible process modifications for the above mentioned optimisation, the analysis of the system and the information obtained through the literature research were used to set a plan for laboratory scale tests. The experimental work done in a laboratory test plant was divided into two groups. The first group was the ammonia loading test, focused on the evaluation of the ways to optimise the ammonia loading. The optimisation of ammonia loading was tested using two variables: the activated coke type (different sulphur content) and the loading temperature. The second group was the denitrification test which aim was the determination of the nitric oxide reduction efficiency with some of the previously loaded activated cokes. Two samples of activated coke, one before and one after the desorber, were extracted from the plant. An additional activated coke mixture sample was produced. This sample was composed of 50% vol of activated carbon before desorber and 50% vol of activated coke after desorber and represents a point in between the points before and after desorber. A reference gas for the tests was set according to the real operating conditions of the flue gas cleaning system at Infraserv Hoechst. In the case of the denitrification tests, the flue gas composition entering the denitrification stage of the flue gas cleaning plant had to be measured. The mass of loaded ammonia was calculated by the breakthrough time. As a way to verify the results of the calculation of the mass of ammonia adsorbed on the activated coke, a test under the method for the determination of the KjedahlNitrogen was done on the samples. The Kjedahl-Nitrogen under the ISO 1126 [3] is a measurement of the total nitrogen content as: ammonium nitrogen, nitrate nitrogen, nitrite nitrogen and organical bounded nitrogen. The samples where tested under this method to determine the amount of nitrogen on them and its increase or decrease after treatment, as a reference to determine the amount of ammonia physisorbed or chemisorbed. A sample taken from each of the tests after the loading was finished (that means 10 minutes after breakthrough time) was analysed under this method and as a result the total Kjedahl-nitrogen contents were obtained.



485

4.2 Test results of ammonia load

1,6

1,6

1,4

1,4

1,2

Highest Quantity

1,0

1,2 1,0

0,8

0,8

Highest Efficiency

0,6

0,6

0,4

0,4

0,2

0,2

0,0 100

150

200

250

300

350

400

450

Kjedahl-Nitrogen (% ma)

Loading (% ma NH3)

The ammonia loading tests (see Figure 3) proposed that the highest ammonia loading was obtained for the activated coke before desorber, compared to all of the other samples, even those loaded at high temperatures. The results of the ammonia loading tests show a relation between temperature and loading capacity. The tests were driven for temperatures between 114 and 469°C. Calculated with the breakthrough time this relation shows a decrease in the ammonia loading capacity for the temperatures between 114 and 250°C and a posterior increase for temperatures between 250 and 469°C, Figure 3.

0,0 500

Loading Temperature (°C) AC after desorber (breakthrough) AC before desorber (Kjedahl-N) Polynomial (AC after desorber (Kjedahl-N))

Figure 3:

AC mixture (Kjedahl-N) AC after desorber (Kjedahl-N) Polynomial (AC after desorber)

Ammonia loading and Kjedahl-Nitrogen results.

The increase in the load capacity of ammonia on activated coke until 250°C (on line calculated with breakthrough time) can be explained with dominant physisorption which state that the increase in temperature decreases the capacity of the adsorbent (activated coke) to trap the adsorptive (ammonia), explained also in the fact that adsorption is an exothermic process. A similar result was obtained by Rodriguez [4] on studies done for the ammonia adsorption in a fixed bed of activated carbon for temperatures between 40 and 120°C. It was found that with increasing testing temperature the ammonia breakthrough time was smaller. According to the literature (e.g. [5]) the behaviour of increase at temperatures above 250°C is caused by the temperature-activated chemisorption of the ammonia on the activated coke. The Kjedahl-Nitrogen tests confirmed that the highest ammonia load is achieved at the highest temperatures, Figure 3. Regarding the activated coke type variable it was determined that the activated coke sample before desorber had a higher ammonia loading capacity WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

486 Energy and Sustainability II than the sample after desorber and this was explained with the existence of already adsorbed species that can react with the ammonia and delay the breakthrough time. The comparison of the two polynomials in the above figure results in the determination of a region of highest efficiency and a point of highest quantity. The highest efficiency region represents the temperature at which, the relation between the amount of nitrogen introduced to the amount of ammonia used is highest. The highest loading, referred as highest quantity, was in any case achieved at the highest temperatures. 4.3 Test results of denitrification The denitrification process works by the reaction of the nitric oxide with ammonia in the presence of oxygen, as expressed in Equation (1). 4 NO + 4 NH3 + O2 → 4 N2 + 6 H2O ∆HR = -1628,36 kJ/mol (1) This equation has been referred in the literature to represent the reaction happening on the surface of the activated coke when this last is used as catalyst. The comparison between the different denitrification tests will be focused on the tendency of its efficiency for the removal of NO from the flue gas. The efficiency was calculated as the relation between the exit concentration and the concentration after 300 minutes (c300), that is c/c300. The results of this analysis are shown in Figure 4. 1,0 0,9 0,8 0,7 c/c300

0,6 0,5 0,4 0,3 0,2 0,1 0,0 0

50

100

150

200

250

300

Time (min) AC after desorber withot NH3 loading AC mixture, NH3 load at 116 °C AC after desorber, NH3 load at 469 °C

Figure 4:

AC before desorber, NH3 load at 116 °C AC after desorber, NH3 load at 115 °C D-ABD-O2ausfall

Denitrification results.

The denitrification tests pointed out that the highest efficiency is obtained with the activated coke loaded at the highest temperature at 469°C. This result expresses a higher nitric oxide reduction efficiency than that of the activated coke test representing the current situation, ammonia loading at 110°C, Figure 3. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


487

For the test with AC mixture and NH3 load at 116°C the dotted section represents an oxygen stoppage, caused by a technical failure. The oxygen concentration is a factor affecting the reduction of NO with ammonia on carbonaceous adsorbents. It has been probed that the oxygen content in the gas stream affects the behaviour of this reduction. In literature it is found that in the absence of oxygen, the NO conversion through reduction with ammonia on activated carbon is only 15% [6]. These effects gain importance for contents of less that 3% of oxygen. The sudden increase in the c/c300 ratio in Figure 4 shows a reduction in the efficiency caused by the absence of the oxygen. Once the technical problem was corrected and the oxygen was normally flowing, the efficiency increased again and the gradient of the curve was decreased.

5

Summary

The combined loading and denitrification conclusions suggest that the injection of ammonia at temperatures over 350°C will result in the optimisation of the process. The increase in the efficiency of a flue gas cleaning system is in every case important to permanently reduce the influence of pollutants on the environment. The investigations at Infraserv Hoechst make a contribution to improve the dry flue gas cleaning process for desulphurisation and denitrification under the use of activated coke. The results of the work represent that the efficiency of ammonia adsorption on activated coke and subsequent denitrification can be enhanced with some process changes. It is planned, that with further investigations the founded results can be verified and a technical concept for the realisation can be finalised.

References [1] Richter, E., BF/Uhde/Mitsui-Active Coke Process for Simultaneous SO2and NOx-Removal, in Sulphur Dioxide and Nitrogen Oxides in Industrial Waste Gases: Emission, Legislation and Abatement, Springer, 1991. [2] Knoblauch, K., Richter, E., Jüntgen, H., Application of Active Coke in Processes of SO2- and NOx-removal from Flue Gases, Fuel, Vol. 60, pp. 832-838, 1981. [3] International Norm ISO 11261:1995. Soil Quality Determination of Total Nitrogen, Modified Kjedahl Method, 1995. [4] Rodrigues, C. C.; et al., Ammonia Adsorption in a Fixed Bed of Activated Carbon. Biore-source Technology, Vol. 98, pp. 886-891, 2007. [5] Guo, J., et al.: Adsorption of NH3 onto Activated Carbon Prepared from Palm Shells Impregnated with H2SO4, Journal of Colloid and Interface Science, Vol. 281, pp. 285-290, 2005. [6] Jüntgen, H., Kühl, H., Richter, E., Katalytische Reaktionen an Aktivkoks und Aktivkohle zur Entfernung von SO2 und NOx aus Rauchgasen, DECHEMACongress, Frankfurt am Main, February 1987.




489

Conversion of waste rubber as an alternative rout to renewable fuel production M. Stelmachowski & K. Słowiński Faculty of Process and Environmental Engineering, Technical University of Lodz, Poland

Abstract Waste rubber (particularly scrap tires) generated worldwide exerts a detrimental influence on the world economy and the environment. Their fraction in municipal wastes amounted to 2% by mass in 2000. By the end of the 20th century, rubber production was about 34 million tons in the world. It is estimated that 20% of tires have to be recycled every year. Dumping and land filling of used tires were the most popular methods of utilization of them not long ago. Other alternative methods that have been used for tire recycling such as retreating, reclaiming, incineration, grinding have also significant drawbacks and/or limitations but they influence the environment to a lesser extent than dumping. Pyrolysis or gasification of waste rubber may be the best way of its utilization. The results of the thermal degradation of waste rubber performed in a new type of the tubular reactor with molten metal are presented in the paper. The melting and degradation processes were carried out in one apparatus at the temperature 390-420°C. The problems encountered with: the disintegration of wastes, the heat transfer from the wall to the particles, cooking at the walls of the reactor, and mixing of the molten volume of wastes are significantly reduced. Two products: gaseous (below 15% weight %) and liquid (over 40 weight %) product were obtained during the degradation of waste rubber. Both streams of products were analyzed by gas chromatography. The gaseous stream contained hydrocarbons from C2 to C8 and the liquid product consisted of hydrocarbons C4 to C24. Over 80 mol % of liquid hydrocarbons mixture was the fraction C4-C10. The obtained liquid product may be used in petrochemical, refinery or may be recycled for tires manufacturing. Keywords: thermal decomposition, waste rubber, scrap tires, molten metal.



1

Introduction

Scrap tires cause an enormous environmental and economical problem. Dumping and land filling of used tires were the worst methods of their utilization but, simultaneously, the most popular [1–5] not long time ago. The statistical data about the amount of waste rubber and scrap tires and the methods of their utilization are sometimes incoherent. Selected, estimated and integrated data are presented in table 1. Table 1:

Recycling methods of scrap tires in 2004. Integrated and estimated data from different sources.

UE 106Mg

%

106Mg

%

Thermal (incineration)

0.75

30.7

1.10

43.4

Dumping, land filling Civil engineering Direct recycling

0.95 0.28 0.15

38.9 11.5 6.1

0.87 0.29 0.14

34.3 11.4 5.5

Other methods e.g. pyrolysis, cracking & chemical methods

0.31

12.7

0.14

5.3

Data not available

Method

JAPAN & CHINA

USA

106Mg

Total

2.44

100.0

2.54

100.0

2.2-2.6

At the end of the 20th century, rubber production was about 34 million tons in the world [1, 2, 4, 5]. A huge amount of produced rubber is used in tires production. It is estimated that 20% of tires have to be recycled every year [5]. A typical used automobile tire weighs 9-10 kg. Recoverable rubber (about 5.45.9 kg) consists of natural (about 35 weight %) rubber and synthetic rubber (about 65 weight %). A typical scrap truck tire weighs 18-20 kg and also contains 50-60% of recoverable rubber. The remaining part consists mainly of carbon black, zinc oxide and steel cord. These components may be also recovered. The rubber wastes recycling industry was almost as old as the rubber production industry and over 50% of used rubber products was reclaimed in the beginning of the 20th century. In the 1960s and 1970s only 20% of scrap rubber was recycled and in the end of the 20th Century about 40-70% of used tires were dumped in massive stockpiles in many countries, provide ideal breeding grounds for diseases and may also cause a fire hazard (e.g. in California 1999, in Poland 2003). The other alternative methods that have been used in tire recycling such as retreating, reclaiming, incineration, grinding have also significant drawbacks and/or limitations but they influence the environment to a lesser extent than



491

dumping [1–6]. Thermal methods have been applying for rubber utilisation as well. The thermodynamic analysis of different thermal processes points out that the best (from energy saving point of view) methods are: gasification, cracking (pyrolysis) and, finally, incineration [4]. Therefore, gasification, pyrolysis and cracking can be considered as viable recycling methods to treat the scrap tires to obtain valuable raw materials and/or energy. The scientific investigations are focused on the pyrolysis [1–3, 6, 7]. The pyrolysis gas can be used as a fuel in the pyrolysis process. A solid residue may be used for producing low-grade carbon black and the liquid product – a mixture of hydrocarbons may be used in petrochemical and refinery industry for producing fuel. Several types of the reactors were invented and patented. The laboratory scale apparatus, pilot and industrial plants are generally based on tubular reactors to perform thermal pyrolysis [1–7]. Fluidized-bed reactors (for pyrolysis of disintegrated tires) have been proposed as well due they have many advantages [8–10]. However, the industrial applications of the invented reactors are rare. It means that the patented solutions are probably technically imperfect and their profitability is weak. The main weakness that should be overcome concerns the heat transfer from a heating medium to the particle of disintegrated rubber, because rubber has very low value of thermal conductivity [9, 10]. Other obstacles are connected with the utilization methods of other components of tires: black carbon, sulphur, zinc oxide and steel cord because rubber content in a tire is only about 50% by mass. Thermal conversion of rubber will be profitable only if all components of tires are recycled and the gas product of pyrolysis is desulfurized. The methods of desulfurization of gases are well known and there are also methods of utilization of carbon black [11, 12]. The problem of bad conditions of the heat transfer from a heating medium to the particle of disintegrated scrap tire may be solved by a new technology based on the thermal decomposition of waste in the molten metal bed reactor [13]. Several patents are based on this process for the degradation of organic wastes [14–17] scrap plastics. The paper presents the results of the investigations of thermal rubber decomposition in the molten metal.

2

Experimental

2.1 Materials Disintegrated waste bicycle tires and flat rubber boards were the stock for the thermal decomposition. Thirteen kilograms of alloy of tin and lead was used to create the molten metal bed. The properties of the alloy are presented in Table 2. 2.2 Experimental set-up The degradation of rubber was carried out in a new type of a tubular reactor with molten metal called “the tube in the tube”. The construction of the reactor differs from the known basin reactors that have been patented until now [14–16]. It was WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

492 Energy and Sustainability II built from two tubes of different diameters [17]. The inner (input) tube was placed coaxially in the external (outflow) tube. A mobile piston was located inside the inner pipe for transporting wastes into the molten metal bed. The holdup time of waste rubber in volume of the liquid metal bed depends on the piston’s speed of shifting. The scheme of the reactor and the scheme of the experimental set-up are presented in Figure 1. Table 2:

The composition of the alloy used in the reactor.

Fraction of tin, % weight Fraction of lead, % weight Fraction of impurities, % weight Specific gravity, g/cm3 Melting temperature, °C

(1) the reactor with a molten metal layer, (2) the loading port, (3) the piston, (4) the outlet of vapors, (5) the basic cooler of the liquid product, (6) receivers of liquid products, (7) the final cooler, (8) thermostats, (9) the computer and acquisition system data, (10) thermocouples, (11) electrical heating. A – polymers, B, C – vapor products, D – noncondensable gases to bubble flow meter and to GC, E – cooling water, F – temperature signal to the acquisition system. Figure 1:

59 – 61 38 – 40 1 8.5 183 – 185

(1) the external (outflow) tube, (2) the inner (input) tube, (3) the loading port, (4) the piston for wastes transporting (5) the outlet of vapors, (6) the bed of molten metal, (7), (8) thermocouples (gas phase, molten metal), (9) electrical heating.

The scheme of the laboratory set-up and the vertical section of the tubular reactor.



493

2.3 The run description Disintegrated rubber particles were put through the loading port to the inner tube and then slowly transported by the piston into the liquid molten alloy to the end of the inner tube. Meanwhile, rubber was melted and decomposed. Products of degradation and un-decomposed components flowed out to the external tube and next to the surface of the bed. Further degradation was carried out in the molten metal bed in the external tube and on the surface to give final products – the mixture of hydrocarbons. The vapours flowed out from the reactor and were condensed in coolers. Liquid products were collected in the small receivers. Gaseous product, the mixture of un-condensable hydrocarbons, flowed out from the reactor to the bubble flow meter and next through sampling port to the ventilation system. Samples of liquid product and gaseous product were analyzed by gas chromatography. The temperatures: of the molten metal bed, the gas phase, and the liquid product in the coolers were measured and recorded by the acquisition data system. Table 3:

Run number 1 2A 2B 2C 2D 3A 3B 3C 3D

3

The profile and mass balance of all runs.

Mass of the stock g 299.5 156.97 (51.43+30.19 +39.33+36.02) 153.37 (38.02+38.38 +38.39+38.58)

Mass fraction of the products Temperature ºC 409-440 425-427 391-431 365-427 379-430 400-403 403 396-403 395-403

solid (residue)

gas

liquid

5.79

% mass. 41.04 53.17

14.74

41.28

44.4

14.73

43.62

41.64


Several experiments of thermal degradation of waste rubber have been performed in the reactor with molten metal. The results of nine of them carried out in three runs are presented in the paper. The general profile and mass balances of all of them are presented in Table 3. In the first run only flat rubber board was decomposed and it was performed in different way than two others. The rubber plate was cut to particles by size about (5-15)x(2-4)x3 mm. Total mass of the loaded stock was 229.5 and it was put into the reactor in three portions of 77.00, 100.01 and 120.72 g in very short intervals, one after one. The WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)

494 Energy and Sustainability II liquid product was received in the first cooler at the temperature 408°C of the molten metal bed after 8 minutes after the time of loading. The temperature in the first, basic cooler of hydrocarbons was 23°C. The liquid product was collected to several small receivers. It enabled to calculate the liquid stream product in time. The temperature of the gaseous phase in the reactor was between 228°C and 226°C during all the experiments. The gas product was cooled in two steps. In the first cooler heavy hydrocarbons were condensed and next the gas flowed to the second cooler, where light condensable components were received. Non-condensable hydrocarbons flowed through the sampling port and bubble flow meter to the vent system.

Figure 2:

The distribution of the temperature of the molten alloy in the reactor and flow rates of the gas and liquid products in the runs 1 and 3.



495

Runs 2 and 3 consisted of four experiments each. The stock consisted of scrap bicycle’s tires. They were cut to particles on size between 5 and 10 mm. The total stock was divided in four portions, in both runs. When the liquid metal obtained demanded temperature, the first small part of disintegrated rubber particles was input through loading port into the reactor and next transported into molten metal by the piston. The gaseous product was obtained in a few minutes after loading and in further few minutes the liquid product was collected to only one collector for each experiment (each decomposed portion of rubber). When the flow of product was decreased, the temperature of the molten metal bed was changed. When new conditions were achieved another part of rubber waste was loaded to the reactor for the next experiment. The profile of product flow rates, the temperature distribution of molten metal for the run 1 and 3 is presented in Figure 2, as a representative example.

Figure 3:

The carbon number gas product (a) and liquid product distribution for rubber decomposition in the run 3.


496 Energy and Sustainability II The runs 2 and 3 were very similar. The method of performing of the runs and the amount of the stock material were almost the same. The liquid and gas product distributions for the run 4 are presented in the Figure 3. It is also representative for all experiments. The compositions of the gas and liquid samples were similar and stable during all the run as it can bee seen in the Figure 3. The lines present the GC analysis results of different samples collected in the time. The run 1 was carried out in another way and in other conditions as in run 2 and 3 but liquid average products obtained in all experiments are very similar and stable for all runs that are shown in figure 4. The fraction compositions of liquid average samples collected in all runs are presented in table 4. The liquid products obtained from thermal decomposition of waste rubber in the molten metal contained above 95% mol most valuable, light fractions of hydrocarbons (called “gasoline” (C4-C10) and “diesel” (C11-C16) fraction. The composition of the liquid product makes it usable as a stock in petrochemical or rubber industry.

Figure 4:

The carbon number average liquid product distribution for rubber decomposition in the runs: 1, 2 and 3.

Table 4:

Fraction composition of the average liquid products.

Run number

1

Fraction

2 (A-D)

3 (A-D)

Fraction composition of the liquid product

C4-C10

% mol

68.8

75.3-75.8

73.6-77.7

C11-C16

% mol

24.2

21.2-22.0

19.6-24.2

C17-C24

%mol

7.0

2.6-2.9

2.0-3.0

paraffin

% mol

31.5

27.5-32.3

38.5-39.7

olefins

%mol

68.5

65.7-72.6

60.3-62.5



497

The received products are generally the mixture of paraffin and olefins. The ratio of paraffin to olefins is presented in table 4 too for liquid products. The amount of olefins is about 50% greater then paraffin. The liquid products are fluids in ambient conditions; however, black carbon is suspended in a liquid mixture. Therefore before further using it has to be clarified. The qualitative analysis of the liquid samples made by FTIR proofed that the content of aromatic hydrocarbons was below 5 mol.%. The content of heavy metals in liquid product was analyzed too and it was made by AAS. The concentration (in liquid) of lead (Pb) and tin (Sn) was between 20 and 30 mg/kg, zinc below 17 mg/kg, nickel (Ni) and chromium (Cr) below 1.5 mg/kg. The relative analytical errors of metals determination were: 0,8-1,0% (for Pb, Sn, Zn) and 4% (for Ni and Cr)

4

Conclusions

The thermal decomposition of rubber wastes performed in the reactor with molten metal may have many advantages. The process is fast. The problems with the heat transfer resistance between the particles of wastes and the heating medium is overcome due to direct contact between rubber and molten metal. Therefore, the cocking processes may be minimized. The ratio of the amount of gaseous product to amount of liquid product is less then resulted in other thermal decomposition processes. The liquid product contains mainly gasoline fraction of hydrocarbons. The hold-up time of wastes in the reactor and the reaction time are shorter than in classical reactors applied for rubber pyrolysis. Therefore the amount of the recombination reactions products is minimized and the fraction of aromatic hydrocarbons is smaller than in other processes based on pyrolysis in tubular or fluidized rectors. The content of heavy metals is small that means that the process temperature is proper and the metal particles and metal ions have not been transferred to the liquid products. However, thermal cracking processes of rubber in the reactor with molten metal bed (as other thermal processes) will be cost-effective if all of obtained products: not only hydrocarbons but for example carbon black as well may be recycled and used for producing fuel and other useful semi-products. About 10% of recovered energy has to be used (recycled) for the disintegration of waste rubber.

References [1] Galvagno S., Casu S., Casablanca A., Cornacchia G., Pyrolysis for treatment of scrap tyres: preliminary experimental results, Waste Management, 22(8), pp. 917-923, 2002. [2] Rodriguez del Marco I., Laresgoiti M.F., Cabrero M.A., Torres A., Chomon N.J., Caballero B., Pyrolysis of scrap tires, Fuel process Technology, 72, pp. 9-22, 2001. [3] Wiliams P.T. Brindle A.J. Catalytic pyrolysis of tyres: influence of catalyst temperature, Fuel, 81, pp. 2425-2434, 2002.


498 Energy and Sustainability II [4] Stelmachowski M., Termo-katalityczna degradacja polimerów, (Thermocatalytic degradation of polymers – monograph in polish), Monografie, PAN Oddział w Łodzi, Komisja Ochrony Środowiska, Łódź, 2003, ISBN – 83-86492-19-8. [5] Sharma V. K., Fortuna F., Mincarini M., Berillo M., Conacchia G., “Disposal of waste tires for energy recovery and safe environment”, Applied Energy, 65, pp. 381-394, 2000. [6] Lin I-P, Chang Ch-Y., Wu Ch-H., Shih S-M. Thermal degradation kinetics of polybutadiene rubber, Polymer Degradation and Stability 53, pp. 295300. 1996; [7] Darmstadt H., Roy Ch., Kallaguine S. Characterization of pyrolytic carbon blacks from commercial tire pyrolysis plants, Carbon; 33(10), pp. 14491455, 1995. [8] Dai X., Yin X., Wu Ch., Zhang W., Chen Y. Pyrolysis of waste tires in a circulating fluidized-bed reactor, Energy, 26, pp. 385-399, 2001. [9] Scheirs J. Kaminski W., (editors), Feedstock recycling and pyrolysis of waste plastics: converting waste plastics into diesel and other fuels, Chapter 17: Kaminski W., “The Hamburg Fluidized-bed Pyrolysis Process to Recycle Polymer Wastes and tires, pp. 475-490, Wiley Series in Polymer Sciences, John Wiley & Sons, Ltd, 2006. [10] Yang J., Tanguy, P.A. Roy C., Heat transfer, mass transfer and kinetics study of the vacuum pyrolysis of a large used tire particle, Chemical Engineering Science, 50(11), pp. 1909-1922, 1995. [11] Ko D.C.K, Mui E.L.K., Lau K.S.T. McKay. G. Production of activated carbons from waste tire – process design and economical analysis, Waste Management, 24, pp. 875-888, 2000. [12] Benallal B., Roy C., Pakdel H., Chabot S., Poirier M.A. Characterization of pyrolytic light naphta from vacuum pyrolysis of used tyres. Comparison with petroleum naphtha, Fuel, 74(11), pp. 1589-1594. 1995 [13] Newborough M., Highgate P., Vaughan P., Thermal depolymerisation of scrap polymers, Applied Thermal Engineering, 22(17), pp. 1875-1883, 2002. [14] Domingo J. Cabanero D., Process and device for regeneration of monomer from polymethyl methacylate, Spanish patent 192909, (1949). [15] Mausre, W.E., Donahue J.R., Larue G.W., Bonney L.H., Glanton G.W., Harris W.L., Method and Apparatus for thermal conversion of organic matter. US 342056 and European Patent Application 90401093.1, (1989). [16] Stelmachowski M., Tokarz Z. The method of continuous conversion of waste plastic, Patent application (polish) P358773, (2003). [17] Stelmachowski M. The reactor and method for thermal conversion of waste polymers Patent application (polish) P384806, (2008).



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Energy efficiency development in the German and Colombian energy intensive sectors: a non-parametric analysis C. I. Pardo M. University of Wuppertal, Wuppertal Institute, Germany University of La Salle, Colombia

Abstract This study approaches the measurement of energy efficiency development in the manufacturing sector at different aggregation levels from a production-theoretic structure, using the method of Data Envelopment Analysis (DEA). Using data from the German and Colombian Annual Surveys of Industries for the years 1998 to 2005, the analysis compares the energy efficiency performance in the German and Colombian energy intensive sectors (EISs) at three levels of aggregation, and then applies several alternative models. The results show considerable variation in energy efficiency performance in the EISs of both countries. Comparing the results across models, it was found that, in the German industrial sector, the three measures of energy efficiency were similar, indicating that an appropriate combination of technical efficiency and cost minimisation are necessary for energy efficiency improvement. In the Colombian industrial sector, the highest energy efficiency measured was from the cost minimisation model, suggesting that the relative energy prices have not generated the right incentives to improve energy efficiency. A second-stage regression and correlation analysis reveals that, in German EISs, energy costs and investments have played an important role in energy efficiency performance and decreasing CO2 emissions. In Colombian EISs, inter-fuel substitution was the most significant variable. Finally, the results of DEA models show a significant correlation with the traditional energy efficiency measure, indicating that the energy efficiency measured through DEA could be complementary to the energy intensity in analysing other key elements of energy efficiency performance in the industrial sector. In addition, energy efficiency is one of the quickest and the most efficient strategies for reducing energy demand and CO2 emissions. Keywords: DEA, Energy efficiency, energy intensive sectors. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) doi:10.2495/ESU090451


1

Introduction

Improving energy efficiency has become an important element of different perspectives that guarantee consumption and sustainability as key elements of economic development. The main objectives for improving energy efficiency on a macroeconomic level are to maintain reserves of fossil fuels, enhance energy security, prevent global warming, and improve environmental quality. On a microeconomic level, achieving energy efficiency’s main objectives are cost minimisation, reduction of energy use when prices increase, and seeking substitutes or clean energy. This analysis seeks to measure energy efficiency development from a production theoretic framework, and uses DEA to present several alternatives models for measuring energy efficiency performance in German and Colombian EISs at three aggregate levels between 1998 and 2005. Moreover, to explain variations in energy efficiency development across EISs, we use regression analysis involving several key factors that might have influenced the energy efficiency performance in EISs in both countries. Three alternative models were assessed in this study. The first model measures the potential reduction in energy use when maintaining output levels and without including additional amounts of other inputs (technical efficiency); a second model (cost efficiency) considers energy efficiency based on the objective of minimising the total input costs (these models were developed by [1] in the US manufacturing sector). The third model analyses the energy mix effects for energy efficiency and calculates Malmquist indices for the total factor of productivity (TFP), technological change (TC), and technical efficiency up to the output level (desirable output) and CO2 emissions (undesirable output). The rest of this paper is organised as follows: Section 2 provides a review of the literature on energy efficiency and DEA analysis in the industrial sector. Section 3 presents the methodology of DEA and the models used to measure energy efficiency development from different perspectives in the German and Colombian EISs. In section 4 and 5, we present the data, the empirical application in EISs, and the main findings from the analyses. Section 6 concludes.

2 A brief review of the literature on energy efficiency and DEA The most common definition of energy efficiency is energy intensity, defined as the quantity of energy required per unit of output or activity. According to the Directive 2006/32/EC of the European Council and the Parliament on energy end-use efficiency and energy services, energy efficiency is the ratio between an output of performance, service, goods, or energy and an energy input. These concepts show that when the relations between E/O (where E total energy is consumed and O total output is produced at the time) decrease over time, energy efficiency has improved. WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


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In the last few years, some researchers have analysed energy efficiency within a framework with inputs and outputs, where energy is an input in the productive process that can be analysed to determine the relation between energy intensity and the level of productivity [2].

3

Measuring energy efficiency development with DEA

DEA allows for the measurement of relative efficiency for a group of decisionmaking units (DMUs) that use resources (inputs) to produce products (outputs). This methodology involves the use of linear programming methods to build a non-parametric piecewise frontier over data, so as to be able to calculate efficiencies relative to this frontier. Furthermore, DEA allows for the identification and quantification of inefficient DMUs when it has several inputs and outputs. The definition of efficiency in DEA consists of three components: technical efficiency, which reflects the ability of a firm to obtain maximal output from a given set of inputs, allocative efficiency, which reflects the ability of a firm to use inputs in optimal proportions, given their respective prices, and scale efficiency, which, according to the features of performance scale, brings about the DMU. These three measures are then combined to provide a measure of total economic efficiency [3–5]. Following [1, 6] for models 1and 2 and [7, 8] for model 4, this study uses DEA to estimate energy efficiency as a normative measure rather than just a descriptive measure of energy intensity, and to analyse the effects of input and fuel substitution on energy efficiency performance in the EISs. Consider an industry producing a single output y from a vector of n inputs x = (x1, x2,…,xn). Let yi represent output and the vector xi represent the input package of the ith DMU. Suppose that input–output data are observed for m DMUs. Then, the technology set can be completely characterised by the production possibility set S = {(x, y):y can be produced from x} based on a few regularity assumptions of feasibility for all observed input–output combinations, free disposability with respect to inputs and outputs, and convexity. If, in addition, a constant return to scale is assumed, then this implies that all radial expansions, as well as (non-negative) contractions of the feasible input–output combinations, are also considered feasible. The purpose of model 1 is to know the maximum possible reduction in the energy input only (), and that this maintains or increases the output level without requiring any additional amounts of other inputs. Through the model 1, where the input vector x0 is divided explicitly into every input component – in this study, Capital (K), Labour (L), materials (M), and energy (E) – Moreover, inequalities (1b) and (1d) ensure that the other inputs not be increased at the optimal solution and inequality (1e) ensures that the output produced is no lower than what is actually being produced. Models 1 can be used to measure energy efficiency when the underlying objective is the conservation of energy and maintenance of environmental quality by reducing energy use and maintaining the level of output.


502 Energy and Sustainability II DEA Model (1): , (1a) Subject to



∑



∑



∑ ∑



(1b)

(1c)

ß

(1d)



∑

(1e)



(1f)

0,

1,2, … ,

1g

n: number of DMUs  : non negative multipliers that define the target operation point as a linear combination Another objective for achieving energy efficiency is based on the economic objective of minimising costs during periods of relatively high energy prices, under which achieving cost effectiveness would typically lead to substituting other inputs for energy. Suppose that the given input price vector for the DMU under evaluation is w’0. The DEA model for cost minimisation can be written as in the model (2) below, which comprises (2a)–(2d). DEA Model (2): 2a Subject to ∑



,



∑



0,

,

,

2b 2c

1,2, … ,

2d

: the amount of input i of DMU n In model 2, the objective is to minimise the total input cost. The inequalities (2b) and (2c) ensure that the optimal input bundle is chosen, so as to minimise the total cost, but such that it can still produce the output bundle y0. The ratio of minimum cost (C*) to the actual cost (C) obtained from this model gives a measure of cost efficiency for the DMU, i.e., CE = C*/C. Moreover, the model can compare energy use at the optimal solution to this problem to actual energy use in order to obtain a measure of energy use efficiency (*) based on cost minimisation. Since this model allows other inputs to be substituted for energy, it WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


503

can potentially generate greater reductions in energy beyond model (1). However, the objective of cost minimisation does not always lead to energy conservation. During periods when energy prices are relatively low compared to the prices of other inputs, cost minimisation may call for increased use of energy to substitute for those other inputs, in which case we would obtain *>1. A common feature of the above two models is that energy consumption is an input within a production framework where energy and other non-energy inputs are used to produce desirable outputs. Nevertheless, energy use also generates some undesirable outputs, e.g., CO2 emissions. Model 3 evaluates energy efficiency performance within a joint production framework, in which both desirable and undesirable outputs are considered simultaneously. Moreover, this model treats different energy sources as different inputs so that changes in energy mix can be accounted for in calculating indices of the total factor of productivity change (TFP), technological change (TC), and technical efficiency change (TEC) through the application of Malmquist DEA methods. DEA model 3: 

 3a

Subject to 

∑



∑ ∑





0



0,

1,2, … ,

: total outputs

3b 3c

3d (3e)

However, note that in this model the inputs and outputs are not specified in the traditional sense, because gross production and CO2 emissions are not outputs that are only due to energy consumption. This fact must be interpreted in this study as the representative outputs and inputs relevant for computing energy efficiency performance. Moreover, CO2 emissions are a difficult problem because it is an undesirable output and creating more is not desirable. In this study, undesirable outputs are introduced as their reciprocal values in the DEA model, and the objective of this model (3) is to study patterns of energy efficiency performance in terms of energy consumption by source (electricity, natural gas, petroleum products, and other), economic activity (output), and CO2 emissions (as well as the links between fuel substitutions, CO2 emissions, and TFP). When industrial sectors have TFP equal to or above one, they are efficient, whereas scores below one mean lower efficiency. This indicates that a higher TFP in the EISs produces more output and less CO2 given the energy sources and non-energy input consumed.



4

Data construction and model application

The data for the industrial sector in both countries come from each country’s respective static offices. It conceptualised a desirable output (measured by the gross value of manufacturing, deflated by the wholesale price index), and four input production technology factors: labour (measured by the total number of persons employed); energy (measured by energy consumed in every sector); capital (measured as a stock, deflated by the wholesale price index); and materials (measured by the expenditure on materials, deflated by the wholesale price index). In model 2, all inputs are measured by the appropriate quantity indices, with 1998 as the base year and price indices for individual inputs used as the relevant input prices. Model 3 considers four categories of energy consumption by source as inputs, namely electricity, petroleum products, gas, and other energy. It also considers as undesirable output the reciprocal of CO2 emissions (in million tons). In this study, EISs was selected taking into account German energy tax law and using cluster analysis (German energy tax law defines the EISs as the sectors where the cost of energy is above 3% of total costs. Moreover, to confirm this criterion applied cluster analysis using as criteria the energy intensity, the share of energy cost and energy consume.) to apply models (1) and (3). In the case of model (2), EISs was divided between higher-energy intensive sectors (HEISs) and lower-energy intensive sectors to achieve better comparisons, again applying cluster analysis with final criteria.

5

Results from the DEA analysis of EISs

Table 1 provides average results for energy consumption, energy intensity, and from the DEA models for German and Colombian EISs. First, the table shows that energy consumption in the German EISs has decreased 2.1% whereas in the Colombian EISs has increased 7.6% on average during the sample period. The average energy intensity of German and Colombian EISs during this period was 0.0151 and 0.0359, respectively, implying that in order to produce 1€ worth of output, the German and Colombian EISs used, on average, about 0.015 and 0.035 TJ of energy, respectively. The optimal solution of model (1) allows for a limited substitution of other inputs for energy without requiring any additional inputs other than the observed amounts. For German and Colombian EISs, the average efficiency during the sample period was 0.727 and 0.631, respectively. These results imply that, on average, the EISs in both countries could have produced the observed output levels by consuming 27% and 37% less of energy input, respectively. From an economic perspective, it is insufficient to simply achieve technical efficiency. To achieve cost efficiency, a firm needs also to be efficient in its allocation of inputs, given input prices. Model (2) allows for the measurement of cost efficiency for a DMU. In German and Colombian EISs, the results showed that when input prices were taken into consideration, the annual average energy efficiency across EISs WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


505

was higher than the measured cost efficiency, suggesting that, for cost minimising over a set of inputs, EISs should be conserving more of other inputs rather than energy. Furthermore, the overall average energy efficiency from this model was higher than that obtained from model (1). The measured energy efficiency from the model (2) should be higher than that from model (1) only if the optimal solution to the cost minimisation model (based on input prices) calls for more energy consumption than at the optimal solution for the model (1), where the model minimised energy input without increasing the amount of other inputs. In the German case, the two measures of energy efficiency were similar, indicating that energy efficiency improvement is necessarily an appropriate combination of technical efficiency and cost minimisation. On the other hand, in the Colombian case, we saw that the highest energy efficiency measured was from the cost minimisation model, suggesting that the relative price of energy in Colombian industry does not reflect the real cost of using energy. As such, energy is the relatively cheaper input. Table 1:

Average results of energy consumption, energy intensity and DEA models in German and Colombian EISs (3-digit level). 1998

Germany Colombia Germany Colombia Germany Colombia Germany Colombia Germany Colombia

Germany Colombia

1999 2000 2001 2002 2003 2004 2005 Average Energy Consumption (values have been indexed to 1998 ) 1.000 0.969 1.000 0.970 0.958 0.972 0.980 0.983 0.979 1.000 0.974 1.074 1.117 1.132 1.104 1.072 1.135 1.076 Energy intensity (E/Y = TJ/Tsd. €1998) 0.0147 0.0152 0.0144 0.0147 0.0149 0.0160 0.0152 0.0154 0.0151 0.0324 0.0354 0.0354 0.0380 0.0378 0.0407 0.0359 0.0318 0.0359 Energy efficiency based on energy input minimisation (model 1-) 0.680 0.723 0.720 0.711 0.763 0.729 0.756 0.735 0.727 0.554 0.660 0.656 0.609 0.617 0.626 0.633 0.693 0.631 Cost efficiency (model 2-CE) 0.831 0.813 0.666 0.645 0.648 0.648 0.639 0.635 0.691 0.643 0.601 0.608 0.671 0.634 0.589 0.562 0.571 0.610 Energy efficiency based on cost minimisation (model 2-) 1.03 0.80 0.85 0.84 0.83 0.82 0.90 0.89 0.87 0.88 1.07 1.07 1.09 1.03 1.01 0.84 0.87 0.98 Patterns of efficiency indexes based on model 3 () 98-99 04-05 Average TC TE TC TE TFP TFP TE TFP TFP 0.99 1.12 1.10 1 1.04 1.04 1 1.10 1.08 0.98 0.95 0.94 1.02 1.18 1.20 1.00 1.03 1.03

The efficiency index calculated using model (3) combines output, CO2 emissions, non-energy inputs, and energy consumption by sources. For German and Colombian EISs, the TFP improved, indicating that the output increased; alternately, CO2 emissions decreased during the sample period due to a positive contribution of technical progress, mainly by application of energy-efficient technologies or adoption of new technologies.


506 Energy and Sustainability II 5.1 Analysing inter-industrial variations in energy efficiency development To explain the observed variation in energy efficiency across EISs in both countries over sample period, regression analysis was used. The two alternative measures of energy efficiency (model 1- and model 2-) assessed in the previous section were defined as dependent variables in several regression models that included different evaluation parameters in order to determine the differences and factors that could have influenced the results for energy efficiency performance. The variables used in this study are as follows:  The manufacturing value added, VAGP, is a measurement of output. The variable VAGP was measured as the share of value added in the total gross production for each industrial sector. We would expect a higher value on this variable to be associated positively with energy efficiency.  The labour quality (in terms of labour productivity), is labelled LAPRO. For each industrial sector, the average annual labour productivity over the sample period was used. We hypothesise that a higher quality labour force has a direct relationship with improvement in energy efficiency.  The enterprise size variable, ENSI, has a direct relationship with capital and the potential investments in every manufacturing sector branch. The variable ENSI was measured as the share of gross production in medium and large enterprises for each industrial sector, by year. We expect a higher production in medium and large enterprises to be associated with greater energy efficiency.  The share of electricity, ELE, in total energy (fuel) consumed by the industrial sector during the study period is also analysed as a variable in evaluating differences in inter-fuel composition and the role of substitutions fuels in the development of energy efficiency performance.  The capital input, KL, is measured by the capital-labour ratio. The average ratio over the sample period is used.  The change in energy costs, EC, is measured as the energy cost index for each industrial sector over the sample period. This variable could determine the relationship between the energy efficiency measure and changes in energy prices. We expect that the higher the energy costs or prices, the higher the energy efficiency.  The investments, INV, are measured as the share of investments (The investments include machinery and equipments, property and buildings.) in gross production. Several investments in the industrial sector have relationships with energy efficiency improvement. When these investments are assessed and implemented properly, the returns can be high and the technical risks relatively low. Such investments can help reduce energy consumption and may also have other positive effects, such as improved product quality. Benefits can also be gained through environmental improvements and through a demonstration effect on the business community [9]. We expect a higher investment to be positively associated with energy efficiency. The regression for energy efficiency results (model 1-) are estimated using the Tobit procedure, which is the appropriate method when the dependent variable is censored (the energy efficiency results in this model is censored WIT Transactions on Ecology and the Environment, Vol 121, © 2009 WIT Press www.witpress.com, ISSN 1743-3541 (on-line)


507

because 1 is equal to the actual score whenever the actual score is

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