Coal Desulfurization: Chemical and Physical Methods

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.fw001 Coal Desulfurization Chemical and Physical Methods In...

Author: Thomas D. Wheelock

42 downloads 796 Views 5MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form

DOWNLOAD PDF

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.fw001

Coal Desulfurization Chemical and Physical Methods

In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.



Coal Desulfurization Chemical and Physical Methods Thomas D . Wheelock, EDITOR


Iowa State University

Based on a symposium sponsored by the Division of Fuel Chemistry at the 173rd Meeting of the American Chemical Society, New Orleans, La., March 23,

1977

64

ACS SYMPOSIUM SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C.

1977



Library of Congress

Data

Coal desulfurization. (ACS symposium series; 64 ISSN 0097-6156) Includes bibliographic references and index. 1. Coal—Desulphurization—Congresses. I. Wheelock, Thomas D . , 1925II. American Chemical Society. Division of Fuel Chemistry. III. Series: American Chemical Society. ACS symposium series; 64. TP325.C516 662'.623 77-17216 ISBN 0-8412-0400-4 ACSMC8 64 1-332 1977

Copyright © 1977 American Chemical Society All Rights Reserved. N o part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN T H E UNITED STATES O F AMERICA


ACS Symposium Series


Robert F. G o u l d , Editor

Advisory Board Donald G . Crosby Jeremiah P. Freeman E. Desmond Goddard Robert A . Hofstader John L. Margrave Nina I. McClelland John B. Pfeiffer Joseph V . Rodricks Alan C. Sartorelli Raymond B. Seymour Roy L. Whistler Aaron Wold



FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishing symposia quickly in book form. The format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.


PREFACE mong the various impurities in coal, sulfur is one of the most prevalent and pervasive, and it has long been a serious problem since it interferes in one way or another with most major uses of coal. In metallurgical coal, sulfur adds to the difficulty and cost of making steel because it must be kept out of the final product. In steam coal, sulfur compounds contribute significantly to the wear of pulverizing mills and conveying equipment and, furthermore, upon combustion produce sulfur oxides which corrode boilers and create an environmental problem. Since the rate of coal use for heat and power generation is projected to increase greatly during the next few years, the problems caused by the sulfur are also projected to increase. Among various methods which have been proposed to solve these problems, precombustion desulfurization of steam coal offers several potential advantages over flue gas desulfurization, fluidized bed combustion, and conversion of coal into liquid and gaseous fuels. Precombustion desulfurization involves physical or chemical operations which span an entire range of complexity and sophistication. The simpler physical methods are the most cost effective, and even some of the proposed chemical desulfurization methods are likely to be more cost effective than processes which convert coal into liquid and gaseous fuels. Also precombustion desulfurization addresses not only the problem of environmental pollution but also the other problems of equipment wear and corrosion. In addition, desulfurized coal can be utilized in existing plants without extensive modification or retrofitting, and for non-base load power plants, the use of desulfurized coal can avoid tieing up investment capital in flue gas desulfurization systems which are not fully utilized. Furthermore in comparison with gaseous fuels, desulfurized coal is stored readily for future use. In spite of these foreseen advantages and years of research and development, only a few desulfurization methods are highly perfected and used commercially. These methods in commercial use generally depend on making a simple physical separation of coarse sulfur-bearing mineral particles from coal. Unfortunately many coal deposits contain finely disseminated minerals and organically combined sulfur which cannot be removed by these methods. However, because of the impetus of government pollution control regulations, increasing demand for coal,

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.pr001

1

ix



and greater influx of both government and private sector research funds, the development of new and more effective methods for desulfurizing coal is accelerating. The new methods include a wide gamut of physical and chemical processes with many different workers and organizations involved in their development. As a result of this effort and an attractive cost-benefit ratio, it is anticipated that coal desulfurization will be increasingly important in the future, not only in preparing coal for direct combustion but also for coking and for conversion into liquid and gaseous fuels. Because of the rising interest in coal desulfurization processes, a symposium on this subject was held which attracted a series of papers describing the results of recent research on a number of promising proc esses. These papers form the nucleus of the present volume. However, since not all areas of the field were equally well represented, additional material was added to produce a volume which provides a broad coverage of recent research. Included are reports of basic and applied research and development on physical separation methods ( such as froth flotation, selective oil agglomeration, high-gradient magnetic separation, and dynamic segregation ) and on chemical processes ( such as leaching, chlorinolysis, pyrolysis, hydrodesulfurization, and gas-phase oxidation). There is also a review of both current and developing industrial coal preparation practices. Although these methods may alter the physical and/or chemical properties of coal and may produce liquid or gaseous by-products, the principal product is still a solid carbonaceous material. Hence, methods designed primarily to produce desulfurized liquid or gaesous fuels are not included. Since progress in the field of desulfurization depends on knowing and understanding the nature and amount of sulfur in coal, several reports of work on characterizing the size distribution and physical form of the principal sulfur-bearing minerals (iron pyrite and marcasite) in coal and on developing new methods for determining the various chemi cal forms of sulfur in coal are also included. This related work is impor tant because the total amount of sulfur in coal and its distribution be tween various physical and chemical forms vary greatly. Among the new developments discussed is a method for the direct determination of organically bound sulfur. Because of its broad coverage and in-depth review of much of the current research on coal desulfurization, this volume provides both an introduction to the subject as well as a fairly comprehensive treatment and status report. Thus it should be of value to both the neophyte and the experienced worker not only because it describes possible solutions to the problem of sulfur in coal but also because it indicates where science χ


and technology stand in achieving these solutions and where there is need for more research and development. Many individuals contributed to the preparation of this volume. A number of researchers contributed the results of their efforts, the officers of the Fuel Chemistry Division of the American Chemical Society provided encouragement, and the editor and staff of the Symposium Series produced the volume. All of these individuals deserve our appreciation. THOMAS D. WHEELOCK


Iowa State University Ames, Iowa October 3, 1977

xi


1 Coal Microstructure and Pyrite Distribution

Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch001

RAYMOND T. GREER Department of Engineering Science and Mechanics, Engineering Research Institute, Ames Laboratory, U.S. ERDA, Iowa State University, Ames, IA 50011

The microstructure of coal is of interest in understanding coal properties. Microstructural features may affect the selection of coal beneficiation methods for removing impurities. For example, in planning sulfur removal schemes it is useful to understand the proportionment of inorganic sulfur compared with that of organic sulfur. Details of size, shape, orientation, and distribution factors for pyrite, certain pyrite and maceral groupings or fields, or other coal constituents(maceralsand other inorganic components) are of importance in supporting rational designs of sulfur removal processes. Recent scanning electron microscope (SEM) investigations help to show the interrelations between macerals and inorganic phases such as pyrite (FeS , the primary inorganic source of sulfur in coal) (1,2,3,4). This form of characterization complements optical microscope studies (5,6,7,8) and conventional transmission electron microscope (TEM) studies (9-15) which have been used to classify and to study coal constituents. SEM offers a way to visualize features hundreds and thousands of Angstroms in diameter by direct observation in three dimensions which is not available by any other technique. Many significant coal features (such as cellular components) and impurity crystals occur in this size range. Important features of coal constitution discovered by SEM are discussed below. 2

Experimental

Investigation

A p p a r a t u s . A JSM-U3 SEM w i t h a n EDAX e n e r g y d i s p e r s i v e x - r a y a n a l y s i s system i s used f o r t h e m i c r o s c a l e s t r u c t u r a l and c h e m i c a l studies. The r e s o l u t i o n c a p a b i l i t i e s o f t h e i n s t r u m e n t o n a d a y t o - d a y b a s i s a r e somewhat b e t t e r t h a n 200 Â f o r m i c r o s t r u c t u r a l i n f o r m a t i o n and s u b m i c r o m e t e r i n a c h e m i c a l a n a l y s i s mode f o r l o c a l i z e d c r y s t a l d e s c r i p t i o n . The s y s t e m p r o v i d e s s i z e , s h a p e , o r i e n t a t i o n , and d i s t r i b u t i o n i n f o r m a t i o n f o r i n o r g a n i c phases and coal constituents.

3


4

COAL DESULFURIZATION

Procedure. Samples f o r SEM s t u d i e s a r e mounted i n an o r i e n t a t i o n where t h e f a c e and v e r t i c a l p o s i t i o n i n t h e c o a l seam a r e maintained. The e l e c t r o n beam a c c e l e r a t i n g p o t e n t i a l u s u a l l y u s e d i n v i e w i n g t h e s p e c i m e n s i s 25 kV. S a m p l e s r e c e i v e a vacuumd e p o s i t e d c o a t i n g o f a p p r o x i m a t e l y 200 Â g o l d ( f o r m i c r o s t r u c t u r a l s t u d i e s ; to m i n i m i z e c h a r g i n g problems) or a vacuum-deposited g r a p h i t e c o a t i n g of 20-100 Â ( f o r m i c r o c h e m i c a l s t u d i e s ; to a v o i d p o s s i b l e i n t e r p r e t a t i o n d i f f i c u l t i e s o f t h e s u l f u r and t h e g o l d x-ray fluorescence l i n e s ) . A d d i t i o n a l i n f o r m a t i o n about e x p e r i m e n t a l t e c h n i q u e a p p e a r s i n R e f . 4_.


Materials. Samples o f h i g h - v o l a t i l e C b i t u m i n o u s c o a l f r o m b o t h s t r i p and s h a f t m i n e s i n Iowa f o r m t h e p r i m a r y m a t e r i a l s o f i n t e r e s t i n t h i s work. Results

and

Discussion

Microstructural Features. To see t h e i n t e r r e l a t i o n o f i n o r g a n i c p h a s e s s u c h as p y r i t e t o t h e c o a l c o n s t i t u e n t s (macérais), m i c r o g r a p h s have been chosen f i r s t to p r e s e n t the r e l a t i v e o r g a n i z a t i o n o f t h e m i c r o s t r u c t u r a l components. T h e s e w i l l be f o l l o w e d by a d d i t i o n a l m i c r o g r a p h s r e p r e s e n t a t i v e o f t h e common ways w h i c h p y r i t e c r y s t a l s occur i n c o a l . F i g u r e 1 p r o v i d e s d e t a i l s of c e l l u l a r compression. The c o a l s p e c i m e n f r o m t h e L o v i l i a ( s h a f t ) m i n e i s e x a m i n e d i n two o r i e n t a t i o n s : t h e top o f a f r e s h f r a c t u r e s u r f a c e c o r r e s p o n d i n g t o v a r i o u s m a g n i f i c a t i o n v i e w s o f the top o f t h e c o a l seam ( F i g u r e s l a - c ) ; and t h e s i d e , end-on v i e w o f t h e s t r a t i f i e d material (Figures l d - f ) . F r a g m e n t a t i o n and c o m p r e s s i o n f e a t u r e s of c e l l u l a r m a t e r i a l are seen f o r other c o a l s i n F i g u r e s 2, 3 , and 4 and i n R e f s . 1^ and 4_. I n F i g u r e s l a - c , the c o a l i f i e d p l a n t f i b e r s run from l e f t to r i g h t i n t h e i m a g e s . M o s t o f t h e f i b e r s a r e a p p r o x i m a t e l y 25 ym t h i c k , as s e e n f o r e x a m p l e i n a h i g h m a g n i f i c a t i o n v i e w i n F i g u r e le. M i c r o s t r u c t u r a l d e t a i l o f p i t s and o t h e r i n d i v i d u a l c e l l u l a r f i b e r d e t a i l s can be d i s c r i m i n a t e d i n t h i s v i e w as w e l l . The o p e n i n g s and r e g i o n s f o r m i n g p a t h w a y s o f i n t e r c o m m u n i c a t i o n f o r f l u i d s and gas b e t w e e n and w i t h i n c e l l s can be s e e n i n s i d e v i e w s ( F i g u r e s l d - f ) of the stacked f i b e r s . As t h e r e s o l u t i o n o f t h e s c a n n i n g e l e c t r o n m i c r o s c o p e i s o f t h e o r d e r o f 150 t o 200 A n g s t r o m s , m i c r o p o r e s o c c u r r i n g b e l o w t h i s s i z e w i l l n o t be o b s e r v e d , even a t the h i g h e s t m a g n i f i c a t i o n s . F i g u r e I f shows t h e c o a l o p e n i n g s i n t h i s c a s e t o be o f t h e o r d e r o f 20 ym o r l e s s , as i n f l u e n c e d by t h e d e g r e e o f c o m p r e s s i o n o f t h e f i b e r s s e e n i n t h e p a r t i c u l a r f i e l d o f view.* C o n s i d e r a b l e c o m p r e s s i o n o f t h e p l a n t s o u r c e m a t e r i a l i n t h e c o a l can o c c u r , and i n c e r t a i n e x a m p l e s t h e c e l l u l a r d e t a i l may be c o m p l e t e l y a b s e n t down t o t h e r e s o l u t i o n l i m i t of t h i s e l e c t r o n m i c r o s c o p y t e c h n i q u e . The c e l l w a l l s a r e o f t h e o r d e r o f 2 ym t h i c k i n t h e s e s i d e v i e w s ( F i g u r e I f , f o r e x ample) . F i g u r e 2 r e p r e s e n t s an e x a m p l e o f b o t h c o m p r e s s i o n and d i s -


GRÉER

Coal Microstructure and Pyrite Distribution

5


1.

Figure 1. Coal from the Lovilia mine (Iowa) showing detailed cellular features of the coalified plant material (a) (top left) Top view; scale bar, 200 \xm. (b) (top right) Top view; scale bar, 100 pm. (c) (middle left) Top view; scale bar, 20 ^m. (d) (middle right) Side view; scale bar, 200 fxm. (e) (bottom left) Side view; scale bar, 100 \xm. (f) (bottom right) Side view; scale bar, 20 pm.



6


t o r t i o n of the c o a l i f i e d p l a n t c e l l u l a r f e a t u r e s . The s p e c i m e n was t i l t e d so t h a t b o t h t h e t o p and s i d e o f t h e s p e c i m e n c o u l d be seen i n t h i s v i e w . Across the c e n t r a l r e g i o n of the micrograph this i s particularly clear. An a n a l o g y w o u l d be t o t a k e a s t a c k of s o l i d r e c t a n g u l a r b o x e s ( e a c h open a t t h e e n d s ) , e a c h a p p r o x i m a t e l y 25 ym χ 25 ym on t h e end by s e v e r a l h u n d r e d ym i n l e n g t h , to r e p r e s e n t a f i b e r , and c r u s h and bend t h e s t a c k by c o m p r e s s i o n p e r p e n d i c u l a r to the long dimension of the boxes. A r e s u l t some what s i m i l a r i n a p p e a r a n c e t o F i g u r e 2 c o u l d be o b t a i n e d . V a r i a t i o n s o f c e l l u l a r f o r m s and f r a g m e n t s a r e s e e n i n F i g u r e s 3 and 4. These r e p r e s e n t f r e s h f r a c t u r e s u r f a c e s of the c o a l t h a t r e v e a l t h e m a t e r i a l was a l r e a d y f r a g m e n t e d and c r u s h e d p r i o r to t h e s c a n n i n g m i c r o s c o p e i n v e s t i g a t i o n . T h i s i s a way t h e c o a l c o n s t i t u e n t s c a n o c c u r and s t a c k w i t h i n t h e seam i t s e l f , e x c l u s i v e of s a m p l i n g and p r e p a r a t i o n f o r e x a m i n a t i o n on a m i c r o s c a l e . T h u s , a w i d e r a n g e o f d e t a i l may be p r e s e n t , f r o m e x a c t s u b c e l l u l a r f e a t u r e s w h e r e l i t t l e o r no p e r t u r b a t i o n c a n be d e t e c t e d by m i c r o s t r u c t u r a l e x a m i n a t i o n , t o t h a t where t h e r e i s a complete absence of d e t a i l o f t h e s o u r c e m a t e r i a l . T h e s e c e l l u l a r o p e n i n g s c a n be f i l l e d w i t h p y r i t e , gypsum, c a l c i t e o r o t h e r m i n e r a l i n c l u s i o n s which were d e p o s i t e d e i t h e r a t t h e t i m e o f e a r l y s t a g e s o f c o a l i f i c a t i o n o r a f t e r t h e c o a l had formed. I n c e r t a i n p r o c e s s i n g schemes t o remove c r y s t a l l i n e p y r i t e , t h e p r e s e n c e o f t h i s t y p e o f open m i c r o m e t e r s i z e n e t w o r k m i g h t be u s e d t o a d v a n t a g e d e p e n d i n g i n p a r t on t h e o c c u r r e n c e , d i s t r i b u t i o n and s u r f a c e c h a r a c t e r i s t i c s o f t h e t y p e o f c o a l c o n stituent. M i c r o c h e m i c a l F e a t u r e s . M i n e r a l i n c l u s i o n s s u c h as p y r i t e a r e r e v e a l e d o v e r a v a r i e t y o f s c a l e s o f m i c r o s c o p i c and m a c r o scopic investigations. The s u l f u r - b e a r i n g p h a s e s a r e o f p a r t i c u l a r i n t e r e s t i n v i e w o f a t t e m p t s t o remove s u l f u r p r i o r t o combus tion. The p r i m a r y f o r m s o f s u l f u r i n c o a l i n c l u d e : (1) P y r i t i c s u l f u r : FeS (2) Sulfate sulfur: CaSOi *2H 0 (3) O r g a n i c s u l f u r : a. m e r c a p t a n o r t h i o l RSH (R and R b e i n g a l k y l b. s u l f i d e or thio-ether RSR or a r y l groups) c. disulfide RSSR d. a r o m a t i c s y s t e m s c o n t a i n i n g HC — CH the thiophene r i n g || || HC CH 2

+

2

f

1

1

V A s i g n i f i c a n t p o r t i o n o f t h e s u l f u r i n c o a l may o c c u r as p y r i t e i n t h e f o r m o f i n d i v i d u a l c r y s t a l s , o r as a s s e m b l i e s o f c r y s t a l s f o r m i n g f r a m b o i d s (a w o r d c o i n e d by R u s t (16) i n 1935 m e a n i n g b e r r y - l i k e ) , o r a s a s s e m b l i e s o f f r a m b o i d s i n t e r c o n n e c t e d by a d d i t i o n a l p y r i t e o c c u r r i n g o v e r a l a r g e - s i z e r a n g e up t o c e n t i m e t e r s i n w i d t h o r g r e a t e r . P y r i t e ( F e S , c u b i c ) and m a r c a s i t e ( F e S , 2


2

1.

GRÉER

Coal Microstructure and Pyrite Distribution


Figure 2. Compressed coalified plant cellular material showing both the top and the side of the fibers. Number 6, Midland, III. coal. Scale bar, 15 μm.

Figure 3. Phnt debris. Mich mine (Iowa). Scale bar, 10 μm.

Figure 4. Plant debris. Both fragmenta tion and distortion are seen. Horton, KY. Scale bar, 10 μm.



8


orthorhombic) are observed i n c o a l samples, the c u b i c form b e i n g t h e most a b u n d a n t o f t h e s u l f i d e m i n e r a l s . O t h e r i n o r g a n i c f o r m s o f s u l f u r s u c h a s gypsum a r e r e l a t i v e l y l o w i n abundance ( 14 mesh t o p s i z e m e c h a n i c a l l y c r u s h e d . The same o r d e r i s f o u n d f o r t h e a s h v s . r e c o v e r y c u r v e s i n F i g u r e 2. I n c o n t r a s t , t h e t o t a l s u l f u r v s . r e c o v e r y c u r v e s ( F i g u r e 3) d e m o n s t r a t e t h a t c h e m i c a l f r a c t u r e ( o n l y 4.53% i s < 100 mesh) l i b e r a t e s c o n s i d e r a b l y more p y r i t i c s u l f u r t h a n m e c h a n i c a l c r u s h i n g e v e n t o -14 mesh ( 2 1 . 9 % i s < 100 mesh). S i m i l a r r e s u l t s have been f o u n d w i t h R e d s t o n e , P i t t s b u r g h , and Upper F r e e p o r t seam c o a l s (1,2,3) a n d w i t h some Iowa c o a l s ( 4 ) . K e l l e r and S m i t h (_5) h a v e r e p o r t e d t h a t g r e a t e r s u l f u r l i b e r a t i o n does n o t o c c u r

58



Figure 1.

Size consist of Illinois No. 6 coal samples (Franklin County, IL)

Figure 2. Ash vs. recovery curves comparing the 3-hr chemical comminution to the mechanical crushing of the Illinois No. 6 seam coal sample (Franklin County, IL)



60

COAL

DESULFURIZATION

w i t h c h e m i c a l f r a c t u r i n g but they d i d not c o n s i d e r y i e l d s i n t h e i r comparisons ( 6 ) . The f a c t t h a t c h e m i c a l c o m m i n u t i o n c a n l i b e r a t e more o f t h e p y r i t i c s u l f u r w i t h o u t g r i n d i n g t o s m a l l s i z e s has c o n s i d e r a b l e economic b e n e f i t s . Although, a t t h i s stage i n the development, i t i s d i f f i c u l t to estimate the exact c o s t s of a c o a l p r e p a r a t i o n f l o w s h e e t u s i n g c h e m i c a l c o m m u n i t i o n as t h e s i z e r e d u c t i o n m e t h o d , some p r e l i m i n a r y e s t i m a t e s h a v e b e e n d e v e l o p e d ( 3 ) . The t o t a l c a p i t a l and o p e r a t i n g c o s t s f o r t h e c h e m i c a l t r e a t m e n t a l o n e u s i n g ammonia v a p o r , u n d e r c o n d i t i o n s shown t o be t e c h n i c a l l y f e a s i b l e i n t h e l a b o r a t o r y , v a r y f r o m $1.00 t o $1.50 per ton of c o a l product. Using r e l a t i v e l y inexpensive density s e p a r a t i o n t e c h n i q u e s , f e a s i b l e b e c a u s e o f t h e s m a l l amount o f f i n e s produced i n the c h e m i c a l f r a g m e n t a t i o n s t e p , would b r i n g t h e t o t a l c o s t f o r p r o d u c i n g c l e a n c o a l t o b e t w e e n $2.50 - $3.00 per ton of product. This i s very competitive with other processes c u r r e n t l y being considered f o r producing clean c o a l . I t i s e n v i s a g e d t h a t t h e c h e m i c a l l y comminuted p r o d u c t a f t e r c l e a n i n g w i l l c o n t a i n 80-90% l e s s p y r i t i c s u l f u r and 50-60% l e s s a s h , a n d , i n a p p r o x i m a t e l y 30-40% o f t h e N o r t h e r n A p p a l a c h i a n seam c o a l s , w i l l meet EPA new s o u r c e e m i s s i o n s t a n d a r d s . Because of the commercial s i g n i f i c a n c e of c h e m i c a l comminution, the e f f e c t s of d i f f e r e n t r e a c t i o n c o n d i t i o n s have b e e n s t u d i e d p r e l i m i n a r i l y t o p r o v i d e some i n s i g h t i n t o t h e mechanism o f t h e phenomena. The a v a i l a b l e i n f o r m a t i o n i s p r e s e n t e d i n t h e f o l l o w i n g s e c t i o n s , and f u r t h e r i n f o r m a t i o n i s being developed. E q u i p m e n t and

Procedures

The p r o c e d u r e s u s e d t o c h e m i c a l l y comminute 100 l b s . s a m p l e s ( F i g u r e s 1, 2, and 3) a r e d e s c r i b e d e l s e w h e r e ( 3 ) . S m a l l e r s a m p l e s were comminuted i n t h e a p p a r a t u s d e p i c t e d i n F i g u r e 4. U n l e s s i n d i c a t e d , t h e s m a l l e r c o a l s a m p l e s were f l o a t e d a t 1.6 s p e c i f i c g r a v i t y t o remove l a r g e p i e c e s o f m i n e r a l m a t t e r and t h e n c l o s e l y s i z e d ( e . g . , 3/4" χ 1/4") so t h a t t h e f r a g m e n t a t i o n r a t e s c o u l d be compared. The o p e r a t i o n of s m a l l bomb a p p a r a t u s i s o u t l i n e d i n P r o c e d u r e A. The f r a g m e n t a t i o n r a t e s u n d e r d i f f e r e n t c o n d i t i o n s o r w i t h d i f f e r e n t c o a l s w e r e compared i n two ways. One way was t o compare t h e w e i g h t p e r c e n t o f t h e v a r i o u s c o a l s a m p l e s t h a t p a s s e d 5 mesh. The o t h e r method c o n s i s t e d o f p l o t t i n g t h e s c r e e n a n a l y s i s o f t h e c o a l s a m p l e s on a R o s i n Rammler g r a p h and c o m p a r i n g t h e a b s o l u t e s i z e c o n s t a n t ( x j . The a b s o l u t e s i z e c o n s t a n t i s t h e s i z e where 36.79% o f t h e c o a l p a r t i c l e s a r e r e t a i n e d on t h e s c r e e n . U s i n g t h e a b s o l u t e s i z e c o n s t a n t f o r comparison r e q u i r e s t h a t the s l o p e of the s i z e d i s t r i b u t i o n r e m a i n a p p r o x i m a t e l y c o n s t a n t . W i t h c h e m i c a l l y comminuted s a m p l e s , a c o n s t a n t s l o p e has b e e n o b s e r v e d .


5.

HOWARD

Mineral

AND

DATTA

Chemical Comminution

61

Liberation


M i c r o s c o p i c e x a m i n a t i o n o f c h e m i c a l l y comminuted c o a l has b e e n c o n d u c t e d by G r e e r (7) o f Iowa S t a t e U n i v e r s i t y u s i n g a s c a n n i n g e l e c t r o n m i c r o s c o p e . The r e s u l t s d e m o n s t r a t e d t h a t f r a g m e n t a t i o n f r o m c h e m i c a l t r e a t m e n t was s t r o n g l y c o n t r o l l e d by m a c e r a l b o u n d a r i e s and o t h e r d e p o s i t s w i t h i n t h e m a t e r i a l s u c h as p y r i t e b a n d s . The a b o v e r e s u l t d e m o n s t r a t e s t h e s e l e c t i v e b r e a k a g e t h a t o c c u r s w i t h c h e m i c a l c o m m i n u t i o n and e x p l a i n s why p y r i t e i s l i b e r a t e d d u r i n g chemical treatment without excessive s i z e r e d u c t i o n . However, t h e d i f f e r e n c e b e t w e e n s u l f u r and a s h l i b e r a t i o n ( F i g u r e s 2 and 3) has n o t b e e n d e t e r m i n e d . Further pétrographie s t u d i e s o f t h i s e f f e c t a r e a n t i c i p a t e d . Effective

Chemicals

A l t h o u g h a number o f c h e m i c a l s h a v e some c o m m i n u t i o n a b i l i t y ( 8 ) , the c h e m i c a l s t h a t appear to have the g r e a t e s t e f f e c t a r e ammonia (gas and a n h y d r o u s and h y d r o u s l i q u i d ) and methanol. T h e s e compounds f a l l i n a c l a s s o f c h e m i c a l s c o n t a i n i n g a n o n b o n d i n g p a i r o f e l e c t r o n s ( o x y g e n and n i t r o g e n compounds) w h i c h s w e l l (9,10) and d i s s o l v e (10) c o a l a t a m b i e n t t e m p e r a t u r e s . A l t h o u g h s w e l l i n g s t u d i e s have not been conducted by u s , v e r y l i t t l e c o a l (< 0.1%) was d i s s o l v e d by e i t h e r m e t h a n o l o r l i q u i d a n h y d r o u s ammonia. The s w e l l i n g e f f e c t , w h i c h has b e e n o b s e r v e d w i t h m e t h a n o l - t r e a t e d c o a l by Bangham and Maggs ( 9 ) , may c a u s e t h e f r a g m e n t a t i o n w h i c h o c c u r s d u r i n g chemical treatment. K e l l e r and S m i t h (5) h a v e s u g g e s t e d t h a t s o l v e n t s w e l l i n g i s t h e mechanism c a u s i n g t h e b r e a k a g e . However, t h e i r o n l y s u p p o r t o f t h i s c o n t e n t i o n was a t h e o r e t i c a l discussion. The f a c t t h a t c o a l does comminute w i t h g a s e o u s ammonia i s n o t e x p l a i n e d by t h i s t h e o r y ( 6 ) . A n o t h e r a n a l o g y b e t w e e n c o a l s o l v e n t s and c o a l c o m m i n u t a n t s i s a r e d u c t i o n i n e f f e c t as the s o l v e n t i s d i l u t e d w i t h water. Other s p e c i f i c s o l v e n t s m e n t i o n e d as good c o a l s o l v e n t s ( 1 0 ) , s u c h as n - p r o p y l a m i n e and p y r i d i n e , h a v e b e e n b r i e f l y e x a m i n e d . These c h e m i c a l s do c a u s e f r a g m e n t a t i o n b u t a r e n o t a s e f f e c t i v e as ammonia. S i n c e t h e s e c h e m i c a l s a r e l a r g e r i n m o l e c u l a r s i z e , i t i s p o s s i b l e t h a t m o l e c u l a r s i z e i s an i m p o r t a n t p a r a m e t e r f o r chemical comminution, e s p e c i a l l y i f p e n e t r a t i o n of the c o a l i s a rate-determining factor. E f f e c t of R e a c t i o n C o n d i t i o n s The f r a g m e n t a t i o n c a u s e d by c h e m i c a l t r e a t m e n t i s a f f e c t e d by s u c h p a r a m e t e r s as m o i s t u r e , p r e s s u r e , w a t e r c o n c e n t r a t i o n i n t h e c h e m i c a l , s t a r t i n g s i z e o f t h e c o a l , and p r e c o n d i t i o n i n g o f the c o a l before treatment. T h e s e e f f e c t s , u s i n g I l l i n o i s No. 6 seam c o a l a s an e x a m p l e , a r e i l l u s t r a t e d i n F i g u r e s 5, 6, 7, and



COAL

DESULFURIZATION

Igure 3. Sulfur vs. recovery curves comparing the 3-hr chemical comminution to the mechanical crushing of the Illinois No. 6 coal sample (Franklin County, IL)

Figure 4.

Small bomb apparatus.

Procedure given on

following page.


5.

HOWARD

AND DATTA

Chemical Comminution Procedure A

P r o c e d u r e f o l l o w e d when p e r f o r m i n g t e s t s i n s m a l l p r e s s u r e v e s s e l s d e p i c t e d i n F i g u r e 4. At S t a r t :

C o v e r s removed f r o m Bombs © a n d © . P i p i n g on c o v e r s i n p l a c e up t o u n i o n s © a n d © .

D i p tube(Din p l a c e .


S t e p No. 1 2 3 4 5 6 7

W e i g h 300 gms. c o a l i n t o ® . C l o s e © w i t h c o v e r and a t t a c h p i p i n g t o © . E v a c u a t e (A) v i a c o n n e c t i o n a t © . Close valve© . C o o l down © w i t h d r y i c e a r o u n d i t . Add h y d r o u s o r a n h y d r o u s NH3 t o n e a r 1/2 f u l l . Close cover w i t h attached p i p i n g , v a l v e © o p e n , and t i g h t e n n u t s . Close valve© . I n s t a l l c o n n e c t i n g t u b i n g between © a n d © . Evacuate tubing through v a l v e © . Remove d r y i c e f r o m r o u n d © a n d add warm w a t e r t o c o n t a i n e r s © s o a s t o m a i n t a i n t e m p e r a t u r e a t 75°F. A l l o w p r e s s u r e t o b u i l d up i n © t o a c o n s t a n t amount, m a i n t a i n i n g w a t e r j a c k e t t e m p e r a t u r e a t 75°F. Open v a l v e s © a n d © , f o r c i n g c o n t e n t s f r o m ® t o © u n t i l p r e s s u r e i n © and © e q u i l i z e s . S t a r t t i m e r ( r e c o r d i n g t e m p e r a t u r e and p r e s s u r e ) , m a i n t a i n t e m p e r a t u r e o f w a t e r j a c k e t a t 75°F. Close valveffi). Disconnect © f r o m tubing a t © . 60 s e c . b e f o r e t h e d u r a t i o n o f t h e e x p e r i m e n t , remove w a t e r j a c k e t f r o m r o u n d © a n d c o o l © d o w n with dry ice. Vent © t o 0 p . s . i . g . through v a l v e s © a n d © . Remove c o v e r and s e p a r a t e l i q u i d f r o m s o l i d . Remove t h e r e s i d u a l NH i n c o a l by e l l u t r i a t i n g t h e sample w i t h b o i l i n g water i n an e l l u t r i a t i n g column. C o l l e c t s a m p l e , d r y , and p e r f o r m a p p r o p r i a t e analyses.

8 9 10 11 12

13 14

15 16

17 18 19

20 Note:

1. 2.

I n c a s e o f NH^ g a s t r e a t m e n t , t h e d i p t u b e © h a s t o be removed. F o r making hydrous known v o l u m e o f a n h y d r o u s NH^ i s added t o a known w e i g h t o f i c e . a



64

COAL

DESULFURIZATION

8. I l l i n o i s No. 6 seam c o a l i s v e r y s u s c e p t i b l e t o c h e m i c a l comminution, and, t h e r e f o r e , the r e s u l t s w i t h t h i s c o a l a r e not necessarily representative of other coals. F i g u r e 5 demonstrates the importance of evacuating the r e a c t o r before chemical treatment. The c o n t r a s t i n t h e e f f e c t o f e v a c u a t i o n b e t w e e n l i q u i d and g a s e o u s c o n d i t i o n s i s q u i t e a p p a r e n t . This effect has a l s o b e e n n o t i c e d w i t h o t h e r c o a l s , a l t h o u g h t h e y h a v e n o t been as d e m o n s t r a t i v e . F o r example, a l l t h e c o n d i t i o n s used i n F i g u r e 5 w o u l d h a v e no f r a c t u r i n g e f f e c t o n a P i t t s b u r g h seam c o a l t h a t was e x a m i n e d . F i g u r e 6 i l l u s t r a t e s t h e e f f e c t o f p r e s s u r e and w a t e r c o n t e n t and d e m o n s t r a t e s t h a t m e t h a n o l i s n o t a s e f f e c t i v e a c o m m i n u t i n g a g e n t a s even a d i l u t e ammonia-water s o l u t i o n . With gas t r e a t m e n t , i t a p p e a r s t h a t a l i t t l e m o i s t u r e i n t h e c o a l aids fracture. A l s o , when u s i n g g a s , a change o f p r e s s u r e f r o m 90 p s i g t o 120 p s i g h a s c o n s i d e r a b l e i m p a c t o n t h e amount o f breakage. D e t e r m i n a t i o n o f any t r e n d s w i t h t h e l i q u i d systems i s d i f f i c u l t b e c a u s e t h e p r e s s u r e was n o t h e l d c o n s t a n t . As m i g h t be e x p e c t e d , t h e i n i t i a l s i z e o f t h e c o a l b e f o r e t r e a t m e n t can e f f e c t t h e s i z e o f t h e t r e a t e d p r o d u c t . This effect i s i l l u s t r a t e d i n F i g u r e 7. As n o t e d p r e v i o u s l y ( F i g u r e 5 ) , e v a c u a t i o n b e f o r e t r e a t m e n t appears t o have a c o n s i d e r a b l e e f f e c t , e s p e c i a l l y w i t h gaseous treatment. E v a c u a t i o n a f t e r t r e a t m e n t a l s o appears t o have an e f f e c t ( F i g u r e 8) w h i c h may be c a u s e d by j u s t a d i f f e r e n c e i n r e a c t i o n t i m e , s i n c e r e a c t i o n i n t h e evacuated sample s h o u l d s t o p r a p i d l y w h i l e t h e u n e v a c u a t e d s a m p l e may c o n t i n u e t o r e a c t e v e n a f t e r t h e p r e s s u r e i s removed. E f f e c t o f C o a l Type The r e a c t i o n c o n d i t i o n s h a v e a c o n s i d e r a b l e i m p a c t on t h e amount o f b r e a k a g e t h a t o c c u r s w i t h d i f f e r e n t c o a l r a n k s ( F i g u r e 9 ) . G a s e o u s ammonia i s l e a s t a f f e c t e d by r a n k w h i l e l i q u i d ammonia e i t h e r a t e l e v a t e d o r a t a t m o s p h e r i c p r e s s u r e is strongly affected. The l i q u i d ammonia c o r r e l a t i o n b e t w e e n r a n k and c o m m i n u t i o n may be f o r t u i t o u s and c a u s e d i n s t e a d by d i f f e r e n c e s i n m i c r o o r macro p o r o s i t y , m a c e r a l c o n t e n t , c l e a t system, s w e l l i n g a b i l i t y ( 1 1 ) , m i n e r a l matter d i s t r i b u t i o n , o r perhaps other f a c t o r s . Chemical

Reactions

C h e m i c a l r e a c t i o n s b e t w e e n t h e ammonia and c o a l c o u l d h a v e an a d v e r s e e f f e c t on t h e r e c o v e r y o f t h e ammonia and o n t h e amount o f n i t r o g e n o x i d e s e m i t t e d when t h e c o a l i s c o m b u s t e d . T h e r e f o r e , t h e n i t r o g e n c o n t e n t o f c o a l b e f o r e and a f t e r ammonia t r e a t m e n t was d e t e r m i n e d f o r a v a r i e t y o f c o a l seams. The r e s u l t s presented i n Table I vary s l i g h t l y f o r d i f f e r e n t c o a l s , and t h e i n c r e a s e i n n i t r o g e n a p p e a r s t o be i n c o r r e l a t i o n w i t h a


5.

HOWARD

65


AND DATTA

Comminution Conditions / \

30% N H O H . 3 Hours. 7 5 ° F . Atmospheric Pressure. Without Evacuation

A

30% N H O H . 3 Hours. 75° F. Atmospheric Pressure . With Evacuation

4

4

Original Sample Chemically Comminuted in Gaseous N H . 3 Hours. 7 5 ° F . Atmospheric Pressure. With Evacuation


3

Chemically Comminuted in Gaseous N H . 3 Hours. 7 5 ° F . Atmospheric Pressure. Without Evacuation 3

1000

10000 Size (Microns)

Figure 5.

Effect of preevacuation on chemical comminution of Illinois No. 6 coal

Ο

Coal Contained 5% Moisture. Treated with NH3 Gas. 120 psig. Alter Evacuation

φ

Coal Contained 5% Moisture. Treated with NH3 Gas. 90 psig. After Evacuation

X

Coal Oven (100°C) Dried.

A

50% N H and 50% H 0 Solution. 55 psig. 75° F

^

75% N H and 25% H 0 Solution. 105 ps.g. 75° F

Q

Methanol. Atmospheric Pressure. 75° F

Treated with NH3 Gas. 120 psig. After Evacuation 3

3

2

2

T i m e (Minutes)

Figure 6. Effect of reaction pressure and water content in the coal or comminuting agent on fragmentation of A in. X V4 in. samples of Illinois No. 6 coal. 3

Illinois Number 6, Liquid N H , - 3 0 ° C . Atmospheric Pressure 3

Ο 3/4" χ 1/4" X

T i m e (Minutes)

1 1/2" χ

3/4"

Figure 7. Effect of start ing size on chemical com minution of Illinois No. 6 seam coal


C O A L DESULFURIZATION

Ο

N H Gas. 120 ps.g. 7 5 ° F, No Evacuation After Treatment 3

X

-)

N H Gas. 120 ps.g. 7 5 ° F. Evacuation After Treatment 3

T i m e (Minutes)

Effect of evacuation after chemical treatment of Illinois No. 6 seam coal


Figure 8.

Δ

N H Liquid, 120 psig. 75° F

ο

N H Gas, 120 psig. 75° F

•

100% Liquid N H , - 3 3 ° F

3

3

3

Exposure Time 3hrs. Starting Size 1/2" χ 0

ANTH S. ANTH

LV

MV

H VA

HVB

SubC

RANK

Figure 9.

Effect of coal rank on the amount of breakage at various reaction conditions



Numbers i n percent t o t a l

3

1.94 1.74

1.74

1,58

1.62

1.80

1.72

e l u t r i a t e d w i t h water at 100°C f o r 2 1/2 hr

1.71

1.69

1.96

1.75

1.94

1.58

e l u t r i a t e d w i t h water at 100°C f o r 1/2 h r

dried

air

1.39

1.21

0.98

1.25

e l u t r i a t e d w i t h water 100°C f o r 2 1/2 hr

1.37

1.15

1.21

0.97

1.44

20xl00M

1.20

8x20M

1,08

+8M

1.43

1.70

1.68

1.91

1.64 1.59

1.24

1.24

1.21

A i r Dried a t 100°C f o r 4 hr

1.16

1.22

1,21

-100M

A i r D r i e d a t 60°C and S i z e d

e l u t r i a t e d w i t h water 100°C f o r 1/2 h r

nitrogen.

240 min, 100% NH l i q u i d , atm. p r e s s . , -30°F

111inois No. 6, Franklin County, I L

1.12

1.21

air

dried

1.50

e l u t r i a t e d w i t h water a t 100°C, a i r d r i e d

240 min, 100% NH3 l i q u i d , atm. p r e s s . , -30°F

1.53

1.51

r i n s e d with d i l u t e HCl at 20°C, a i r d r i e d

1.43

30 rain, 100% NH liquid, 120 p s i g , 75°F

d r i e d , 60°C

Original ROM Sample

air

Treatment t o Remove Ammonia

Air Dried at 60°C Overnight

Nitrogen Content of Chemically Comminuted Coal

180 min, NH3 g a s , 120 p s i g , 75°F

Ammonia Treatment

Upper F r e e p o r t , Westmoreland County, PA

Pittsburgh, Green County, PA

Coal

Table I.


1.69

1.69

1.94

1.26

1.37

1.20

A i r Dried a t 200°C f o r 2 hr

1.96

1.82

2.00

1.11

1.38

1.24

A i r Dried at 300°C f o r 1 hr


68


d e c r e a s e i n r a n k . No i n c r e a s e a p p e a r s t o t a k e p l a c e w i t h Upper F r e e p o r t seam c o a l , a s l i g h t i n c r e a s e ( 6 % ) w i t h P i t t s b u r g h seam c o a l , and a p p r o x i m a t e l y a 20% i n c r e a s e w i t h I l l i n o i s No. 6 seam c o a l when t h e s a m p l e i s a i r d r i e d . However, some o f t h e n i t r o g e n c a n be removed b y h o t w a t e r w a s h i n g . I n g e n e r a l , t h e +8 mesh p a r t i c l e s show a l o w e r i n c r e a s e i n n i t r o g e n t h a n t h e o t h e r sizes. The n a t u r e o f t h e c h e m i c a l r e a c t i o n t h a t may be t a k i n g p l a c e i s unknown, b u t t h e r e a r e f u n c t i o n a l g r o u p s ( e . g . , e s t e r s ) i n c o a l t h a t c o u l d f o r m n i t r o g e n compounds. W i t h I l l i n o i s No. 6 seam c o a l , t h e l o s s o f ammonia w o u l d s t i l l be s m a l l (4.4 l b s . ammonia p e r t o n o f t r e a t e d c o a l when a h o t w a t e r wash i s u s e d ) , and i t i s unknown w h e t h e r n i t r o g e n o x i d e s e m i s s i o n s w o u l d change. From t h e a b o v e r e s u l t s , i t c a n be s e e n t h a t c o n s i d e r a b l y more i n f o r m a t i o n i s n e c e s s a r y b e f o r e t h e mechanism o f c h e m i c a l comminution i s understood. Studies directed at a better u n d e r s t a n d i n g o f t h e phenomena and t h e e f f e c t i t h a s o n t h e c h e m i c a l l y t r e a t e d c o a l a r e p r e s e n t l y underway. Acknowledgements T h i s w o r k was p a r t i a l l y s u p p o r t e d 14-32-0001-1777.

by ERDA

Contract

Literature Cited

1. Datta, R.S., Howard, P.H., Hanchett, A., "Pre-Combustion Coal Cleaning Using Chemical Comminution," NCA/BCR Coal Conference and Expo III. Coal: Energy for Independence, Louisville, October 19-21, 1976. 2. Howard, P.H., Hanchett, Α., Aldrich, R.G., "Chemical Comminution for Cleaning Bituminous Coal," Clean Fuels from Coal Symposium II Papers, Institute of Gas Technology, Chicago, Ill., June 23-27, 1975. 3. Datta, R.S., Howard, P.H., Hanchett, Α., "Feasibility Study of Pre-combustion Coal Cleaning Using Chemical Comminution," FE-1777-4, Final Report ERDA Contract 14-32-0001-1777, Syracuse Research Corp., November 1976. 4. Min, S., Wheelock, T.D., "Cleaning High Sulfur Coal," NCA/BCR Coal Conference and Expo III. Coal: Energy for Independence, Louisville, October 19-21, 1976. 5. Keller, D.V., Jr., Smith, C.D., "Spontaneous Fracture of Coal," Fuel (1976), 55, 273-280. 6. Howard, P.H., Datta, R.S., Hanchett, Α., "Chemical Fracture of Coal for Sulfur Liberation," Fuel (1977), 56, 346. 7. Greer, R.T., "Coal Microstructure and the Significance of Pyrite Inclusions," Scanning Electr. Microscopy, Vol. I, Proceedings of the Workshop on Materials and Component Characterization/Quality Control with the SEM/STEM, IIT Research Institute, Chicago, Ill., March 1977.


5. HOWARD AND DATTA


69


8. Aldrich, R.G., Keller, D.V., Jr., Sawyer, R.G., "Chemical Comminution and Mining of Coal," U.S. Patent 3,815,826 (June 11, 1974) and 3,850,477 (November 26, 1974). 9. Francis, W., "Physical Considerations," Chapter XI in "Coal, Its Formation and Composition," 2nd ed., Edward Arnold, London, 1961. 10. Dryden, I.G.C., "Solvent Power for Coals at Room Temperature," Chem. Ind. (June 2, 1952), 502. 11. van Krevelen, D.W., "Chemical Structure and Properties of Coal. XVIII-Coal Constitution and Solvent Extraction," Fuel (1965), 44, 229.


6 Use of the Flotation Process for Desulfurization of Coal


F. F. APLAN Mineral Processing Section, Pennsylvania State University, University Park, PA 16802

The flotation process is a method for desulfurizing fine coal whose time has come. The process has proven to be a great success in the beneficiation of a wide variety of metalliferous ores and industrial minerals, and currently, the United States has an installed capacity to treat about 1.7 million tons of ore per day. Unfortunately, coal processing has not participated in this growth in any major way. In the U.S. in 1973 only 14 million tons of clean coal were produced by the flotation process (1) . By comparison, in the same year approximately 400 million tons of coal were treated in preparation plants to produce 300 million tons of clean coal. This amount of coal produced by washing techniques was about half of the 600 million tons of the marketable coal produced in the U.S. that year. There are many reasons why coal flotation has not made a greater impact on the coal industry, but chief among them are the effectiveness of coarse cleaning processes (which treat particles of 1-5 in. top size), the low value of a ton of coal until recent years, the lack of an adequate research and development program to evaluate the process thoroughly, and, to some extent, inertia. To these reasons should be added the following shortcomings of the coal flotation process enumerated by Mitchell (2) in 1948: (1) (2) (3) (4) (5)

M a r k e t i n g problems w i t h t h e f i n e s , Cost of dewatering, I n d i f f e r e n t t e s t r e s u l t s i n removing s u l f u r , I n a b i l i t y t o make c l e a n s e p a r a t i o n s w i t h t h e f i n e r s i z e s , I n a b i l i t y t o clean s l u r r i e s containing a high percentage of c l a y . Two new f a c t o r s , w h i c h have come t o t h e f o r e w i t h i n t h e p a s t d e c a d e , have c a u s e d a s e r i o u s r e - e v a l u a t i o n o f t h e p r o c e s s i n c o a l preparation: t h e s h a r p l y i n c r e a s e d market value o f a t o n o f c o a l and e n v i r o n m e n t a l c o n s i d e r a t i o n s . The i n c r e a s e d c o a l p r i c e h a s l e d t o a g r e a t l y i n c r e a s e d e m p h a s i s on f i n e c o a l c l e a n i n g i n o r d e r to achieve a g r e a t e r y i e l d of combustible m a t e r i a l from a t o n o f raw c o a l . On t h e e n v i r o n m e n t a l f r o n t c o a l f l o t a t i o n h e l p s t o c l a r i f y t h e l a r g e q u a n t i t i e s o f w a t e r u s e d and r e c y c l e d i n t h e

70



6.

APLAN

Flotation Process for Coal Desulfurization

71

p r e p a r a t i o n p r o c e s s and i n t h e r e m o v a l o f p y r i t i c s u l f u r f r o m t h e coal. While f o r coarse c o a l , g r a v i t y concentration processes are very e f f i c i e n t , t h e i r f i n e c l e a n i n g counterparts are not n e a r l y as e f f e c t i v e i n e i t h e r c o a l r e c o v e r y o r i n p y r i t e r e m o v a l . The c o a l f l o t a t i o n process o f f e r s the p o t e n t i a l of overcoming both of t h e s e d e f e c t s f o r t h e t r e a t m e n t o f t h e f i n e , -28 mesh c o a l . In t h i s r e s p e c t i t c a n r e d u c e t h e s u l f u r c o n t e n t o f some c o a l s t o EPAa c c e p t a b l e l e v e l s o r , f o r h i g h e r s u l f u r c o a l s , can reduce the o v e r a l l s u l f u r c o n t e n t o f t h e c o a l s u c h t h a t t h e n e e d f o r f l u e gas d e s u l f u r i z a t i o n a t t h e power p l a n t c a n be m i n i m i z e d . Where a p p l i c a b l e , c o a l p r e p a r a t i o n t e c h n i q u e s c a n remove p y r i t i c s u l f u r f o r a f r a c t i o n o f t h e c o s t o f s u l f u r r e m o v a l by a f l u e gas s c r u b b i n g system. I n a r e c e n t a r t i c l e H o f f m a n e t a l . C3), have shown t h e e c o n o m i c p o t e n t i a l o f s u c h c o m b i n a t i o n c o a l p r e p a r a t i o n and f l u e gas d e s u l f u r i z a t i o n t e c h n i q u e s . The c o a l f l o t a t i o n p r o c e s s has b e e n d e t a i l e d i n t h e l i t e r a t u r e i n r e v i e w a r t i c l e s by A p l a n ( 4 ) , Brown ( 5 ) , and Zimmerman ( 6 ) . U n f o r t u n a t e l y , s i n c e the h i s t o r i c a l purpose of c o a l p r e p a r a t i o n has b e e n t o remove t h e h i g h - a s h c o n s t i t u e n t s , t h e l i t e r a t u r e does n o t c o n t a i n a g r e a t d e a l o f i n f o r m a t i o n on s u l f u r r e d u c t i o n by flotation. F o r t h i s r e a s o n , t h e M i n e r a l P r o c e s s i n g S e c t i o n a t The P e n n s y l v a n i a S t a t e U n i v e r s i t y s e v e r a l y e a r s ago embarked on a c o m p r e h e n s i v e p r o g r a m aimed a t u n d e r s t a n d i n g t h e f u n d a m e n t a l s o f the process, d e l i n e a t i n g the best c o n d i t i o n s f o r r e j e c t i n g p y r i t i c s u l f u r d u r i n g c o a l f l o t a t i o n , and e s t a b l i s h i n g a d a t a b a s e . T h i s c h a p t e r w i l l e m p h a s i z e t h a t work. G e n e r a l Methods of P y r i t e Removal T h e r e a r e t h r e e g e n e r a l methods t h a t may be u s e d t o r e j e c t p y r i t i c s u l f u r during coal f l o t a t i o n : (1) m u l t i p l e c l e a n i n g , (2) p y r i t e d e p r e s s i o n , and (3) c o a l d e p r e s s i o n w i t h c o n c u r r e n t f l o t a t i o n of the p y r i t e . The f i r s t p r o c e s s i s b a s e d on t h e a s s u m p t i o n t h a t c o a l i s e a s i l y f l o a t a b l e whereas p y r i t e i s not. I n t h i s c a s e any p y r i t e w h i c h f l o a t s w o u l d be c a u s e d by m e c h a n i c a l e n t r a p m e n t w i t h t h e floating coal. I t c o u l d t h u s be removed by r e p u l p i n g t h e f l o a t e d c o a l and r e p e a t i n g t h e f r o t h f l o t a t i o n p r o c e s s s e v e r a l t i m e s ; e a c h t i m e r e j e c t i n g some of t h e m e c h a n i c a l l y e n t r a p p e d p y r i t e p a r t i c l e s . The a s s u m p t i o n t h a t p y r i t e i s n o t f l o a t a b l e i s t r u e o n l y as a gross g e n e r a l i z a t i o n , s i n c e , i n p r a c t i c e , f i n e p y r i t i c s u l f u r o f t e n f l o a t s w i t h the c o a l . The f l o t a t i o n o f p y r i t e o c c u r s n o t o n l y by i t s e l f , b u t i t s f l o t a t i o n i s o f t e n e n c o u r a g e d by t h e e x i s t a n c e o f l o c k e d p y r i t e - c o a l p a r t i c l e s o r by t h e u s e o f an o i l y c o l l e c t o r f o r the f l o t a t i o n of the c o a l . Early-day ore f l o t a t i o n p r o c e s s e s , c i r c a 1905, u s e d f u e l o i l i n t h e f l o t a t i o n o f s u l f i d e minerals including pyrite. S t u d i e s by M i l l e r e t a l . (7) and more r e c e n t l y by Im (8) show t h a t t h e m u l t i p l e c l e a n i n g method i s n o t o n l y l a b o r i o u s but o f t e n not p a r t i c u l a r l y e f f e c t i v e . The f r o t h s p r i n k l i n g method, a l s o e v a l u a t e d by M i l l e r (9) i s a m u t a t i o n o f



72


the m u l t i p l e c l e a n i n g p r o c e s s . P y r i t e d e p r e s s i o n d u r i n g c o a l f l o t a t i o n w o u l d a p p e a r t o be t h e most l o g i c a l a p p r o a c h t o t h e p r o b l e m e s p e c i a l l y i n v i e w o f t h e f a c t t h a t p y r i t e d e p r e s s i o n t e c h n i q u e s d u r i n g the f l o t a t i o n of c o p p e r , l e a d , n i c k e l , and z i n c s u l f i d e s a r e w e l l known ( 1 0 ) . In c o a l f l o t a t i o n use has been made of pH c o n t r o l , l i m e , s o d i u m c y a n i d e , s o d i u m s u l f i d e , h y d r o s u l f i d e and s u l f i t e , p o t a s s i u m d i c h r o m a t e , p o t a s s i u m p e r m a n g a n a t e , and f e r r o u s and f e r r i c s u l f a t e t o r e j e c t p y r i t e ( 4 ) . The c l a s s i c w o r k i n t h i s a r e a i s t h a t o f Y a n c e y and T a y l o r ( 1 1 ) , and more r e c e n t w o r k has b e e n done by M i l l e r (12). Zimmerman (13) d e m o n s t r a t e d t h a t t h e s u l f u r c o n t e n t o f c l e a n c o a l p r o d u c e d by f l o t a t i o n o f P i t t s b u r g h Seam c o a l d e c r e a s e s as t h e pH i s r a i s e d f r o m 4 t o 11. U n f o r t u n a t e l y , the r e c o v e r y o f c l e a n c o a l d e c r e a s e s as t h e pH i s i n c r e a s e d above pH 7. The p r a c t i c a l i t y o f t h e s i t u a t i o n i s t h a t none o f t h e s e t e c h n i q u e s a r e u s e d i n d u s t r i a l l y , and l a b o r a t o r y t e s t i n g o f t e n shows m e d i o c r e r e s u l t s a t b e s t . T r u l y , t h i s i s an a r e a where an expanded r e s e a r c h and d e v e l o p m e n t e f f o r t i s c l e a r l y n e e d e d . The t h i r d method o f p y r i t e r e j e c t i o n i s t h a t o f c o a l d e p r e s s i o n and has r e c e n t l y been t e s t e d by t h e U.S. B u r e a u o f M i n e s (14) i n a process c a l l e d the two-stage or reverse f l o t a t i o n process. I t i n v o l v e s a f i r s t - s t a g e (rougher) f l o t a t i o n of the c o a l to r e j e c t t h e b u l k o f t h e a s h - c o n t a i n i n g c o n s t i t u e n t s i n c l u d i n g much o f t h e pyrite. The r o u g h e r f r o t h i s t h e n s e n t t o a c l e a n e r c i r c u i t where a p r o p r i e t a r y d e p r e s s a n t ( A m e r i c a n Cyanamid R e a g e n t 633) i s added t o d e p r e s s t h e c o a l w h i l e a x a n t h a t e c o l l e c t o r and a f r o t h e r a r e added t o f l o a t p y r i t e f r o m t h e c o a l . The p r o c e s s has r a t h e r s t r i k i n g l y reduced the s u l f u r l e v e l of the c l e a n c o a l a l t h o u g h the p r o b l e m s o f e x c e s s i v e r e a g e n t u s e and c o s t and i n a d e q u a t e r e c o v e r y of c l e a n c o a l w i l l r e q u i r e a d d i t i o n a l study. T h e r e i s a need t o e v a l u a t e c o a l d e p r e s s i n g a g e n t s , and t h e s e s t u d i e s a r e p r e s e n t l y in progress (8). Response of P y r i t e i n C o a l F l o t a t i o n Systems Because of the d e a r t h of d a t a c o n c e r n i n g the response of p y r i t e i n a c o a l f l o t a t i o n c i r c u i t , t h e c u r r e n t p r o g r a m a t Penn S t a t e has f o c u s e d on e s t a b l i s h i n g a p r o p e r d a t a b a s e . F a c t o r s t o be c o n s i d e r e d i n a d d i t i o n t o t h e n a t u r e o f t h e c o a l a r e t h e amount and k i n d o f f r o t h e r , q u a n t i t y and t y p e o f c o l l e c t o r ( i f a n y ) , t y p e o f f l o t a t i o n c e l l , and o p e r a t i n g c o n d i t i o n s . The f o l l o w i n g r e p o r t on t h e e x p e r i m e n t a l p r o g r a m i n p r o g r e s s e v a l u a t e s many o f t h e s e factors. E x p e r i m e n t a l Methods. A l l of the work r e p o r t e d h e r e , e x c e p t t h a t i n t h e f i r s t f i g u r e , has b e e n done w i t h c l e a n c o a l f r o m t h e Lower K i t t a n n i n g o r P i t t s b u r g h Seam t o w h i c h 5% p u r i f i e d p y r i t e has b e e n added. R e c e n t w o r k has shown (15) t h a t p y r i t e s a m p l e s from d i f f e r e n t c o a l sources possess d i f f e r e n t f l o a t a b i l i t i e s (which, i n t u r n , are d i f f e r e n t from the f l o a t a b i l i t y of ore p y r i t e ) .



6.

APLAN


73

T h e r e f o r e , t h e p y r i t e u s e d i n e a c h t e s t came f r o m t h e same seam as d i d t h e c o a l . T h i s p r o c e d u r e e l i m i n a t e s l o c k e d p a r t i c l e s so t h a t t h e p a t h o f t h e p y r i t e d u r i n g f l o t a t i o n c a n be a c c u r a t e l y t r a c e d , u n c o m p l i c a t e d by t h e i n t e r m e d i a t e r e s p o n s e o f p a r t i c l e s t h a t a r e p a r t c o a l and p a r t p y r i t e . O t h e r s t u d i e s a r e underway t o e v a l u a t e the response of l o c k e d p a r t i c l e s i n c o a l f l o t a t i o n systems. C o a l f r o m t h e Lower K i t t a n n i n g seam ( C a m b r i a C o u n t y , PA.) o r t h e P i t t s b u r g h seam ( F a y e t t e C o u n t y , PA.) was p u l v e r i z e d t o 100% -14 mesh, 90% -28 mesh, t o w h i c h -28 mesh p u r i f i e d p y r i t e f r o m e a c h r e s p e c t i v e seam was added. C o a r s e r p y r i t e was n o t added s i n c e R a s t o g i and A p l a n (16) have d e m o n s t r a t e d t h a t +28 mesh p y r i t e w i l l not f l o a t under the c o n d i t i o n s n o r m a l l y encountered i n f r o t h flotation. To i n s u r e t h a t s u r f a c e o x i d a t i o n d i d n o t i n f l u e n c e t h e r e s u l t s , t h e c o a l and p y r i t e s a m p l e s w e r e g r o u n d s h o r t l y b e f o r e flotation. The o l d e r s t y l e F a g e r g r e n l a b o r a t o r y f l o t a t i o n c e l l was u s e d , and t h e p u l p c o n c e n t r a t i o n was a b o u t 17% s o l i d s . The s p e c i f i c d a t a g i v e n i n t h i s r e p o r t w e r e drawn f r o m s t u d i e s on two d i f f e r e n t c o a l seams and t h u s a r e i n t e n d e d t o i l l u s t r a t e g e n e r a l p r i n c i p l e s r a t h e r t h a n t o s e r v e as a b a s i s f o r a f l o t a t i o n scheme f o r a g i v e n c o a l sample. I n u s i n g t h e d a t a , one c a u t i o n s h o u l d be n o t e d : s i n c e 95% c l e a n c o a l and 5% p y r i t e were u s e d , t h e maximum y i e l d o f c o m b u s t i b l e m a t e r i a l i s 95%. Y i e l d s a p p r o a c h i n g and e x c e e d i n g t h i s v a l u e a r e most c e r t a i n l y a c c o m p a n i e d by t h e f l o t a t i o n o f much l i b e r a t e d p y r i t i c s u l f u r (SLP). Coal F l o t a t i o n K i n e t i c s . H i s t o r i c a l l y , the r e s u l t s of s o f t c o a l p r e p a r a t i o n h a v e been most o f t e n a n a l y z e d i n t e r m s o f y i e l d and o f p r o d u c t a s h and, more r e c e n t l y , s u l f u r . As a r e s u l t o f o u r e x t e n s i v e s t u d i e s on t h e n a t u r e o f c o a l f l o t a t i o n , h o w e v e r , we b e l i e v e t h a t t h e r a t e o f c o a l f l o t a t i o n s h o u l d be added t o t h e l i s t of e v a l u a t i o n c r i t e r i a used f o r l a b o r a t o r y s t u d i e s . I t has b e e n amply d e m o n s t r a t e d (16) t h a t d i f f e r e n t f r a c t i o n s i n t h e raw c o a l f l o a t a t d i f f e r e n t r a t e s , and t h u s t h e c o a l f l o t a t i o n r a t e i s a v a r i a b l e t h a t c a n be u s e d t o a c h i e v e b e t t e r s e p a r a t i o n s , most p a r t i c u l a r l y b e t w e e n c o a l and p y r i t e . Coal f l o t a t i o n f o l l o w s a f i r s t - o r d e r r a t e equation (16): - £ = k C at

(1)

where C = c o n c e n t r a t i o n o f f l o a t a b l e m a t e r i a l ; t = t i m e , s e c ; k = r a t e constant, sec""l. This agrees w i t h the f i n d i n g s of B u s h e l l f o r the f l o t a t i o n of q u a r t z w i t h an amine (17) and t h e f i n d i n g s o f numerous o t h e r i n v e s t i g a t i o n s f o r ores (18). The e x p e r i m e n t a l a p p r o a c h was t o use a b a t c h f l o t a t i o n method and t o a p p l y t h e a n a l y s i s p r o p o s e d by B u s h e l l (17). F i g u r e 1 f o r t h e f l o t a t i o n o f P i t t s b u r g h Seam c o a l w i t h MIBC, shows t h a t c o a l f l o t a t i o n f o l l o w s t h e c u r v e AB3C3, and t h i s c u r v e i s a s t r a i g h t l i n e , and h e n c e f o l l o w s E q u a t i o n 1, o v e r t h e segment A-B3. T h i s c o r r e s p o n d s t o t h e f l o t a t i o n o f 80% o f t h e


COAL

DESULFURIZATION


100

TIME, MINUTES American Institute of Mining, Metallurgical and Petroleum Engineers

Figure 1. The rate of flotation of Pittsburgh seam coal using 0.84 lb/ton pine oil. Percentage remaining in the flotation cell as a function of time (16).


6.

75


APLAN

c o a l , and, i n f a c t , there i s o n l y s l i g h t d e v i a t i o n from l i n e a r i t y f o r t h e f l o t a t i o n o f 90% o f t h e c o a l . The f i r s t - o r d e r r a t e c o n s t a n t , i n s e c ~ l , may be d e t e r m i n e d g r a p h i c a l l y f r o m p l o t s s u c h a s t h o s e g i v e n i n F i g u r e 1 o r may be c a l c u l a t e d o v e r t h e s t r a i g h t l i n e p o r t i o n o f t h e c u r v e by t h e f o l l o w i n g equation: log k = 2.303

C

- log C Ν — ~

(2)

where = concentration of material at t ^ ; C = concentration of material at t . From F i g u r e 1 i t may be s e e n t h a t t h e f l o t a t i o n o f t h e a s h b e a r i n g c o n s t i t u e n t s and t h e l i b e r a t e d p y r i t i c s u l f u r (SLP) a l s o f o l l o w s the f i r s t - o r d e r r a t e law over the f i r s t minute t o minute and o n e - h a l f o f f l o t a t i o n . This period corresponds to the f l o t a t i o n o f n e a r l y a l l o f t h e c o a l p r e s e n t . Numerous o t h e r f l o t a t i o n t e s t s w i t h a v a r i e t y of c o a l samples, f r o t h e r s , c o l l e c t o r s , p a r t i c l e s i z e s , and o p e r a t i n g c o n d i t i o n s c o n f i r m t h e a c c u r a c y o f t h i s i n t e r p r e t a t i o n ( 1 5 , 1 6 , 1 9 , 2 0 ) . The s l o w f l o a t i n g f r a c t i o n t h a t f l o a t i n g a f t e r ^ 90 s e c - i s composed o f c o a r s e r p a r t i c l e s , t h o s e whose s u r f a c e i s s l i g h t l y o x i d i z e d , l o w e r r a n k and h i g h a s h f r a c t i o n s s u c h a s f u s i n i t e , a n d , i n raw c o a l s y s t e m s , l o c k e d particles. As w i l l be d e m o n s t r a t e d l a t e r , k i n e t i c a n a l y s i s i s a v a l u a b l e a i d i n e v a l u a t i n g t h e c o m p l i c a t e d i n t e r a c t i o n s between c o a l t y p e , f r o t h e r s y s t e m , and f l o t a t i o n o p e r a t i n g c o n d i t i o n s . 2


2

E f f e c t o f F r o t h e r Systems. A comparison o f f r o t h e r s i s g i v e n i n T a b l e I (15) s h o w i n g t h e y i e l d ( a f t e r 7.75 m i n o f f l o t a t i o n t i m e ) , p e r c e n t a g e o f l i b e r a t e d p y r i t i c s u l f u r (% S L P ) , and t h e amount o f c o a r s e , 14 χ 28 mesh, c o a l f l o a t e d . An e q u i m o l a r c o n c e n t r a t i o n o f e a c h f r o t h e r was c h o s e n a s t h e b a s i s o f c o m p a r i s o n . TABLE I .

F r o t h e r C o m p a r i s o n f o r t h e F l o t a t i o n o f Lower K i t t a n n i n g and P i t t s b u r g h Seam C o a l s ( 1 5 ) .

C o a l Type

Lower Kittanning Pittsburgh Seam

Frother

MIBC^ Pine O i l Cresol C

MIBC Pine O i l Cresol

Concentration mol lb. L. ton

Floated mat'l. Yield, %

h

SLP

+28 mesh

-4 2.4x10" 2.4x10"-4 2.4x10"-4

0.28 0.44 0.29

94 96 69

—

92 91 24

-4 2.4x10" 2.4x10"-4 2.4x10"-4

0.28 0.44 0.29

84 89 19

16 21 2

29 48 2

20 33

C o a l y i e l d a f t e r 7.75 m i n o f f l o t a t i o n . b SLP = L i b e r a t e d p y r i t i c s u l f u r . ° MIBC = M e t h y l i s o b u t y l c a r b i n o l , 4 - m e t h y l - 2 - p e n t a n o l .


%


76


From t h i s t a b l e s e v e r a l c o n c l u s i o n s emerge: (1) MIBC and p i n e o i l a r e r o u g h l y e q u i v a l e n t f r o t h e r s on an e q u i m o l a r b a s i s , b u t MIBC i s s u p e r i o r on a pounds p e r t o n b a s i s (2) C r e s o l i s a much i n f e r i o r f r o t h e r t o e i t h e r MIBC o r p i n e oil (3) P i n e o i l t e n d s t o f l o a t s l i g h t l y more p y r i t e t h a n does MIBC (4) P i n e o i l i s a s u p e r i o r f r o t h e r f o r the f l o t a t i o n of c o a r s e r c o a l p a r t i c l e s , e s p e c i a l l y f o r an i n t e r m e d i a t e f l o a t i n g c o a l s u c h as t h e P i t t s b u r g h seam (5) The Lower K i t t a n n i n g c o a l i s a f a s t e r f l o a t i n g c o a l t h a n i s t h a t f r o m t h e P i t t s b u r g h seam T h e s e a r e o n l y g e n e r a l c o n c l u s i o n s , and t h e n a t u r e o f t h e c o a l and t h e n a t u r e and c o n c e n t r a t i o n o f t h e f r o t h e r may w e l l change t h e o r d e r o f t h i n g s . Most c r i t i c a l i s the problem of i m p u r i t i e s w h i c h t e n d t o f l o a t p y r i t e . The p r o b l e m o f i m p u r e c r e s o l s i s p a r t i c u l a r l y c r i t i c a l ; t h e o i l y i m p u r i t i e s a c t as c o l l e c t o r s and, h e n c e , f a v o r t h e f l o t a t i o n o f c o a r s e and o t h e r d i f f i c u l t - t o - f l o a t p a r t i c l e s — b u t a t the expense of encouraging the f l o t a t i o n of u n d e s i r a b l e p y r i t e . O i l has l o n g b e e n u s e d t o enhance t h e f l o t a t i o n o f c o a l p a r t i c l e s otherwise d i f f i c u l t to f l o a t w i t h a f r o t h e r only. The i n t r o d u c t i o n o f an o i l y c o l l e c t o r i s , h o w e v e r , a c c o m p a n i e d by t h e f l o t a t i o n o f much u n d e s i r a b l e p y r i t e . T h i s i s c l e a r l y i l l u s t r a t e d i n T a b l e I I (21) w h e r e t h e i n t r o d u c t i o n o f 0.46 l b . / t o n o f f u e l TABLE I I .

E f f e c t o f F u e l O i l on I n c r e a s i n g t h e F l o t a t i o n o f P y r i t i c S u l f u r D u r i n g t h e F l o t a t i o n o f Lower K i t t a n n i n g Coal (21). 3 Flotation

MIBC lb./ton 0.17 0.17

Fuel O i l lb./ton 0 0.46

r a t e χ 10

,sec

-1 Yield,

k

C

37.5 55

k

SLP 2.3 12.4

a

SLP

floated,

%

kc/^SLP

90 97

16 4

% 13 56

C o a l y i e l d a f t e r 7.75 min o f f l o t a t i o n . k£ = F l o t a t i o n r a t e c o n s t a n t f o r c o a l . o i l t o a c o a l f l o t a t i o n s y s t e m u s i n g MIBC as f r o t h e r i n c r e a s e d the amount o f t h e l i b e r a t e d p y r i t i c s u l f u r (SLP) w h i c h f l o a t e d f r o m 13 t o 5 6 % ! ! ! I n t h i s c a s e t h e k i n e t i c a n a l y s i s i s h e l p f u l . Numerous o t h e r d a t a (15,16,19) have e s t a b l i s h e d t h a t c o a l g e n e r a l l y f l o a t s a b o u t 10-30 t i m e s f a s t e r t h a n d o e s p y r i t e ; t h e e x a c t v a l u e o f t h e r a t i o depends on t h e s p e c i f i c c o a l and p y r i t e and on t h e f r o t h e r s y s t e m and f l o t a t i o n o p e r a t i n g c o n d i t i o n s . An i m p o r t a n t e v a l u a t i o n c r i t e r i o n i s thus to l o o k at the r a t i o of the f l o t a t i o n r a t e c o n s t a n t of c o a l to t h a t of p y r i t e , k / k . As t h e v a l u e o f p

q T p


6.


APLAN

77

t h i s r a t i o d i f f e r s f r o m an a v e r a g e v a l u e o f , s a y , 16, t h o s e f l o t a t i o n c o n d i t i o n s e i t h e r f a v o r a b l e or unfavorable f o r p y r i t e r e j e c t i o n may be r e a d i l y d i s c e r n e d . I t c a n be s e e n f r o m T a b l e I I t h a t w i t h the a d d i t i o n of f u e l o i l , the c o a l f l o t a t i o n r a t e i n c r e a s e d somewhat b u t t h a t t h e p y r i t e f l o t a t i o n r a t e i n c r e a s e d f i v e - f o l d ; t h e k ç / k s p r a t i o d r o p p e d t o 4. O i l encourages the f l o t a t i o n o f p y r i t e much more t h a n i t d o e s t h a t o f c o a l i n t h i s instance.


L

E f f e c t of F r o t h e r Concentration. F i g u r e s 2 and 3 show t h e e f f e c t o f an i n c r e a s i n g amount o f t h e f r o t h e r , p i n e o i l , on c o a l y i e l d and t h e amount of l i b e r a t e d p y r i t i c s u l f u r (SLP) f l o a t e d as a f u n c t i o n of f l o t a t i o n time (22). With respect to y i e l d (Figure 2 ) , t h e r e i s a t h r e s h o l d amount o f f r o t h e r needed t o o b t a i n good coal yields. Beyond t h i s i n c i p i e n t amount o f f r o t h e r , h o w e v e r , a d d i t i o n a l f r o t h e r does n o t f u r t h e r i n c r e a s e y i e l d w i t h t h i s c o a l . The same p a t t e r n h o l d s f o r a f l o t a t i o n t i m e o f 0.25 o r o f 7.75 min. A 1-min f l o t a t i o n t i m e i s s u f f i c i e n t t o a c h i e v e n e a r l y c o m p l e t e y i e l d f o r f r o t h e r c o n c e n t r a t i o n s o f 0.5 l b . / t o n o r more. However, w i t h the f l o t a t i o n of p y r i t e (Figure 3 ) , a d i f f e r e n t p a t t e r n emerges: b o t h an e x c e s s f r o t h e r d o s a g e and e x t e n d e d f l o t a t i o n t i m e s l e a d t o t h e f l o t a t i o n o f an e v e r - i n c r e a s i n g amount o f p y r i t e . The a d v a n t a g e o f u s i n g s h o r t f l o t a t i o n t i m e s and a low f r o t h e r concentration i s obvious.

three

E f f e c t of F l o t a t i o n Operating Conditions. T a b l e I I I compares l e v e l s o f a i r r a t e and f l o t a t i o n c e l l i m p e l l e r s p e e d ( 1 6 ) .

TABLE I I I .

E f f e c t o f A i r F l o w R a t e and I m p e l l e r Speed on F l o t a t i o n o f P i t t s b u r g h Seam C o a l ( 1 6 ) .

C e l l Operating Conditions air rate speed (cfm) (rpm)

3 -1 F l o t . r a t e χ 10 , sec

Flotation

the

Data^

a

0.535 0.233 0.136

2540 1660 1380

.

h k

73 25.5 15.3

SLP

4.5

15.9

0.2

76

Yield

% SLP floated

92.4 79.1 67.8

27.9 17.7 1.4

C

% + 28M floated 70.3 29.8 15.0

MIBC 0.57 l b . / t o n . b kç = F l o t a t i o n r a t e c o n s t a n t f o r c o a l . ° SLP = L i b e r a t e d p y r i t i c s u l f u r ^ One m i n u t e f l o t a t i o n t i m e . I n t e n s e f l o t a t i o n c o n d i t i o n s ( h i g h a e r a t i o n r a t e s and h i g h i m p e l l e r speed) f a v o r t h e f a s t f l o t a t i o n o f c o a l , t h e f l o t a t i o n o f c o a r s e p a r t i c l e s , and t h e f l o t a t i o n o f p y r i t e . A g a i n , u s i n g t h e r a t i o o f t h e f l o t a t i o n r a t e c o n s t a n t s f o r c o a l and p y r i t e , k ç / k g L p , t h e maximum r e j e c t i o n o f p y r i t e o c c u r s u n d e r g e n t l e o p e r a t i n g


DESULFURIZATION


COAL

American Institute of Mining, Metallurgical and Petroleum Engineers

Figure 2. (top) Flotation yield of Lower Kittanning coal as a function of pine oil concentration and time (22) American Institute of Mining, Metallurgical and Petroleum Engineers

Figure 3. (bottom) Effect of pine oil dosage on the amount of liberated pyritic sulfur floated. Lower Kittanning coal (22).


6.

APLAN


79


conditions. Long f l o t a t i o n r e s i d e n c e t i m e s f a v o r t h e f l o t a t i o n o f b o t h c o a r s e p a r t i c l e s and p y r i t e . R a s t o g i and A p l a n (4,16) have d e m o n s t r a t e d t h a t t h e a i r r a t e alone i s r e s p o n s i b l e f o r the bulk of the increase i n c o a l f l o t a tion. The c o n t r i b u t i o n o f i m p e l l e r speed i s modest. T e s t E v a l u a t i o n . A s t u d y o f numerous f l o t a t i o n t e s t s shows t h a t t h e r e i s a r e l a t i o n s h i p b e t w e e n y i e l d and t h e amount o f p y r i t e w h i c h f l o a t s ( F i g u r e 4) ( 4 , 2 3 ) . This curve i s s i m i l a r to t h e g r a d e - r e c o v e r y c u r v e s o f t e n u s e d i n o r e d r e s s i n g s t u d i e s (24) and t o c o a l - s u l f u r d a t a r e p o r t e d by M i l l e r ( 1 2 ) . E a c h p a r t i c u l a r f l o t a t i o n s y s t e m shows a s i m i l a r f a m i l y o f c u r v e s . A s h , t o t a l s u l f u r , o r f l o t a t i o n r a t e may a l s o be u s e d as t h e a b s c i s s a and s i m i l a r l y shaped c u r v e s r e s u l t ( 4 , 2 3 ) . T h i s method may be u s e d to save c o n s i d e r a b l e time i n f l o t a t i o n t e s t i n g s i n c e s u l f u r v a l u e s a t i n t e r m e d i a t e y i e l d s may be r e a d i l y e s t i m a t e d w i t h o u t t h e need t o r e s o r t to s t i l l another t e s t . The b u l k o f t h e f r e e p y r i t e t h a t f l o a t s a c c o m p a n i e s t h e l a s t 20% o r so o f y i e l d . T h i s f a c t has b e e n u s e d t o d e v e l o p a c o a l f l o t a t i o n p r o c e d u r e c a l l e d t h e " g r a b and run" technique. The "Grab and Run" P r o c e s s . I n t h i s method a p p r o x i m a t e l y one-half to t w o - t h i r d s of the u l t i m a t e c o a l y i e l d i s f l o a t e d i n the rougher c e l l under g e n t l e o p e r a t i n g c o n d i t i o n s ( s t a r v a t i o n q u a n t i t i e s o f a g e n t l e f r o t h e r s u c h as MIBC, l o w a i r r a t e , l o w i m p e l l e r s p e e d , s h o r t f l o t a t i o n r e s i d e n c e t i m e , e t c . ) t o remove a f r a c t i o n low i n p y r i t e . U n d e r most c o n d i t i o n s s t u d i e d so f a r , t h i s f a s t - f l o a t i n g f r a c t i o n c a n go d i r e c t l y t o t h e c l e a n c o a l p r o d u c t ; hence t h e name " g r a b and r u n . " The b a l a n c e o f t h e r e c o v e r a b l e c o a l i s removed i n a s c a v e n g e r c i r c u i t u n d e r more i n t e n s e o p e r a t i n g c o n d i t i o n s . As t h e u l t i m a t e y i e l d i s a p p r o a c h e d , t h e amount o f p y r i t i c s u l f u r t h a t f l o a t s i n c r e a s e s g r e a t l y . The scavenger c o n c e n t r a t e , which i s h i g h e r i n p y r i t i c s u l f u r than the rougher c o n c e n t r a t e , i s sent to c l e a n e r f l o t a t i o n . H e r e two options are a v a i l a b l e : d e p r e s s p y r i t e and f l o a t c o a l o r v i c e versa. In the l a t t e r o p t i o n the scavenger c l e a n e r c i r c u i t r e s e m b l e s t h e U.S. B u r e a u o f M i n e s r e v e r s e f l o t a t i o n p r o c e s s e x c e p t t h a t o n l y a f r a c t i o n o f t h e t o t a l t o n n a g e n e e d be t r e a t e d . D e t a i l s o f t h i s p r o c e s s w i l l be r e p o r t e d s o o n ( 2 5 ) . Summary. P y r i t e i s b e s t r e j e c t e d u n d e r g e n t l e f r o t h i n g and o p e r a t i n g c o n d i t i o n s u s i n g short residence times i n the f l o t a t i o n cell. The u s e o f e x c e s s f r o t h e r and, e s p e c i a l l y an o i l y f r o t h e r and/or c o l l e c t o r , i s p a r t i c u l a r l y c o u n t e r - p r o d u c t i v e t o p y r i t i c sulfur rejection. The l a s t i n c r e m e n t f o r t h e r e c o v e r y o f c o a r s e o r o t h e r h a r d - t o - f l o a t p a r t i c l e s i s i n v a r i a b l y a c c o m p a n i e d by t h e f l o t a t i o n o f much p y r i t i c s u l f u r .


80



100

70h ι

0

•

10

20

30

ι

I

40

50

PERCENT SLP FLOATED American Institute of Mining, Metallurgical and Petroleum Engineers

Figure 4. Coal yield vs. liberated pyritic sul fur (SLP) recovery for Lower Kittanning coal

(4, 23j


6.

APLAN


81

Acknowledgements The a u t h o r w i s h e s t o t h a n k t h e A m e r i c a n I r o n a n d S t e e l I n s t i t u t e , The P e n n s y l v a n i a S c i e n c e and E n g i n e e r i n g F o u n d a t i o n , and t h e A p p a l a c h i a n R e g i o n a l C o m m i s s i o n f o r f i n a n c i a l s u p p o r t i n conducting these s t u d i e s . Acknowledgement i s made t o t h e f o l l o w i n g f o r m e r a n d p r e s e n t g r a d u a t e s t u d e n t s i n The M i n e r a l P r o c e s s i n g S e c t i o n , The P e n n s y l v a n i a S t a t e U n i v e r s i t y , who have c o n t r i b u t e d d a t a f r o m w h i c h t h i s r e p o r t was drawn: C. M. B o n n e r , V. C h o u d h r y , W. C. H i r t , C. J . Im, T. J . O l s o n and R. C. R a s t o g i .


Literature Cited

1. Miner. Yearbk., 1973 (1975). 2. Mitchell, D. R., Trans. AIME (1948), 177, 315. 3. Hoffman, L., Aresco, S. J., Holt, E. C , Deurbrouck, A. W., "Engineering/Economic Analysis of Coal Preparation with SO2 Clean-up Process for Keeping Higher Sulfur Coals in the Energy Market," in Second Symposium on Coal Preparation, J. F. Boyer, Jr., Ed., Bituminous Coal Research Inc., Monroeville, Pa. (1976). 4. Aplan, F. F., "Coal Flotation," in A. M. Gaudin Memorial International Flotation Symposium, M. C. Fuerstenau, Ed., AIME, New York (1976). 5. Brown, D. J., "Coal Flotation," in Froth Flotation - 50th Anniversary Volume, D. W. Fuerstenau, Ed., AIME, New York (1962). 6. Zimmerman, R. E., "Flotation," in Coal Preparation, J. W. Leonard and D. R. Mitchell, Eds., 3rd ed., AIME, New York (1968). 7. Miller, F. G., Podgursky, J. M., Aikman, R. P., "Study of the Mechanism of Coal Flotation and its Role in a System for Processing Fine Coal," Trans. AIME (1967), 238, 276. 8. Im, Chang J., unpublished data (1977). 9. Miller, F. G., "The Effect of Froth Sprinkling on Coal Flota tion Efficiency," Trans. AIME (1969), 244, 158. 10. Gaudin, Α. Μ., Flotation, 2nd ed., McGraw-Hill, New York (1957) 11. Yancey, H. F., Taylor, J. Α., "Froth Flotation of Coal; Sulfur and Ash Reduction," U.S. Bur. Mines Rep. Invest. (1935), 3263. 12. Miller, F. G., "Reduction of Sulfur in Minus 28 Mesh Bitumin ous Coal," Trans. AIME (1964), 228, 7. 13. Zimmerman, R. Ε., "Flotation of Bituminous Coal," Trans. AIME (1948), 117, 338. 14. Miller, K. J., "Coal - Pyrite Flotation," Trans. AIME (1975), 258, 30. 15. Hirt, W. C., Aplan, F. F., unpublished data (1977). 16. Rastogi, R. C., Aplan, F. F., "Coal Flotation as a Rate Process," accepted for publication in Trans. AIME.



82


17. Bushell, C. H. G., "Kinetics of Flotation," Trans. AIME (1962), 223, 266-278. 18. Arbiter, Ν., Harris, C. C., "Flotation Kinetics," in Froth Flotation - 50th Anniversary Volume, D. W. Fuerstenau, Ed., AIME, New York (1962). 19. Rastogi, R. C., Hirt, W. C., Aplan, F. F., "An Evaluation of Several Variables Influencing the Rate of Coal Flotation," submitted to Trans. AIME. 20. Rastogi, R. C., Hirt, W. C., Aplan, F. F., unpublished data (1977). 21. Bonner, C. Μ., Im, C. J., Choudhry, V., Aplan, F. F., "The Influence of Oil on Pyritic Sulfur Rejection During Coal Flotation," submitted to Trans. AIME. 22. Bonner, C. Μ., Aplan, F. F., "Frother Comparisons in the Flotation of Coal," accepted for publication in Trans. AIME. 23. Bonner, C. Μ., Hirt, W. C., Aplan, F. F., unpublished data (1977). 24. Aplan, F. F., "Mineral Processing - Evaluation to Indicate Processing Approach," Section 27.3 in SME Mining Engineering Handbook, A. B. Cummins and I. A. Given, Eds., pp. 27, 15-28, 86-88, New York (1973). 25. Bonner, C. Μ., Hirt, W. C., Im, C. J., Aplan, F. F., unpublished data (1977).


7 A Comparison of Coal Beneficiation Methods 1


SEONGWOO MIN and T. D. WHEELOCK Iowa State University, Department of Chemical Engineering and Nuclear Engineering, Energy and Mineral Resources Research Institute, Ames, IA 50011

Although iron pyrites and other minerals are removed from coal on an industrial scale almost exclusively by gravity separation methods at the present time, other beneficiation methods are coming into use. Among the developing methods, froth flotation (1,2,3) is the foremost, although the oil agglomeration method (4,5,6) is also promising. Both of these methods take advantage of the difference in surface properties of coal and inorganic mineral particles suspended in water to effect a separation. In the first method the hydrophobic coal particles are removed from the hydrophilic mineral particles by selective attachment to a mass of air bubbles, while in the second method the coal particles are selectively coated and agglomerated by fuel oil and then recovered by screening. While gravity separation methods are well suited for removing coarse mineral particles from coal, they are generally ineffective for removing microscopic particles. On the other hand, both the froth flotation and oil agglomeration methods offer the potential for recovering and separating coal fines from microscopic impurit i e s , t h u s c o m p l e m e n t i n g t h e gravity separation methods. However, none o f t h e s e p h y s i c a l s e p a r a t i o n methods a r e e f f e c t i v e u n l e s s the m i n e r a l i m p u r i t i e s a r e f i r s t l i b e r a t e d o r f r e e d f r o m t h e c o a l . A l t h o u g h m e c h a n i c a l c r u s h i n g a n d / o r g r i n d i n g have a l w a y s been used i n d u s t r i a l l y t o u n l o c k i m p u r i t i e s , t h e r e s u l t s have n o t a l w a y s been s a t i s f a c t o r y . C h e m i c a l c o m m i n u t i o n h a s been p r o p o s e d a s a means t o u n l o c k t h e i m p u r i t i e s (7,8,9) and t o s o l v e t h i s p r o b l e m . T h i s method o f c o m m i n u t i o n u s e s s p e c i f i c c h e m i c a l a g e n t s s u c h a s a n h y d r o u s ammonia t o f r a g m e n t c o a l . Since fragmentation occurs a l o n g b e d d i n g p l a n e s a n d b o u n d a r i e s between c o a l and m i n e r a l m a t t e r , t h e m i n e r a l i m p u r i t i e s t e n d t o be f r e e d more c o m p l e t e l y f o r a g i v e n s i z e r e d u c t i o n than would r e s u l t from m e c h a n i c a l comminution ( 7 ) .

P r e s e n t a d d r e s s : B a t t e l l e Columbus L a b o r a t o r i e s , Ohio 43201

Columbus,

83


84

COAL

DESULFURIZATION

In the work d e s c r i b e d h e r e , h i g h - s u l f u r b i t u m i n o u s c o a l s f r o m two Iowa s t r i p m i n e s were s u b j e c t e d t o a s e r i e s o f 16 d i f f e r e n t t r e a t m e n t s t o compare t h e e f f e c t i v e n e s s o f v a r i o u s b e n e f i c i a t i o n methods. These t r e a t m e n t s i n v o l v e d d i f f e r e n t com b i n a t i o n s o f s i z e r e d u c t i o n methods ( c r u s h i n g , p u l v e r i z i n g , g r i n d i n g , and c h e m i c a l c o m m i n u t i o n ) and o f p h y s i c a l s e p a r a t i o n methods ( g r a v i t y s e p a r a t i o n , f r o t h f l o t a t i o n , and o i l a g g l o m e r a t i o n ) . The r e s u l t s a r e compared b e l o w on t h e b a s i s o f p r o d u c t y i e l d and on t h e p e r c e n t a g e r e d u c t i o n i n s u l f u r and a s h b r o u g h t a b o u t by t h e treatments.


Experimental The f o l l o w i n g m e t h o d s , e q u i p m e n t , and m a t e r i a l s were u s e d the e x p e r i m e n t a l i n v e s t i g a t i o n : R o l l C r u s h i n g . Lump c o a l (4 cm χ 0) was c r u s h e d t o 6 mm t o p s i z e by p a s s i n g i t t h r o u g h a b e n c h - s c a l e d o u b l e r o l l c r u s h e r m a n u f a c t u r e d by S m i t h E n g i n e e r i n g W o r k s , M i l w a u k e e , WI. Pulverizing. P r e v i o u s l y c r u s h e d c o a l was p u l v e r i z e d t o -35 mesh by a M i k r o - S a m p l m i l l m a n u f a c t u r e d by P u l v e r i z i n g M a c h i n e r y D i v i s i o n , A m e r i c a n - M a r i e t t a Co., Summit, N J . Ball Milling. P r e v i o u s l y p u l v e r i z e d c o a l was ground t o -400 mesh s i z e i n a c e r a m i c j a r m i l l . F o r t h i s o p e r a t i o n 200 g c o a l , 1000 g w a t e r , and 1900 g f l i n t p e b b l e s were p l a c e d i n a 5.7-L j a r m i l l , and t h e m i l l was t h e n r u n f o r 20 h r . C h e m i c a l C o m m i n u t i o n . F o r t h i s o p e r a t i o n 500 g lump c o a l (4 cm χ 0) were p l a c e d i n a 2000-ml E r l e n m e y e r f l a s k w h i c h was t h e n p l a c e d i n a c o l d b a t h o f d r y i c e and m e t h a n o l and c o o l e d t o -70°C. L i q u i d a n h y d r o u s ammonia was t h e n added t o t h e f l a s k u n t i l t h e c o a l was immersed i n t h e l i q u i d . A f t e r t h e c o a l had s o a k e d f o r 1.0 h r , t h e f l a s k was removed f r o m t h e c o l d b a t h and was p l a c e d i n a w e l l v e n t i l a t e d hood where t h e ammonia e v a p o r a t e d . When t h e o d o r o f ammonia c o u l d no l o n g e r be d e t e c t e d , t h e comminu t i o n s t e p was c o m p l e t e d . G r a v i t y S e p a r a t i o n . To e f f e c t t h e g r a v i t y s e p a r a t i o n o f c o a l and m i n e r a l m a t t e r , 500 g c r u s h e d c o a l (6 mm χ 0) were added t o 2000 ml t e t r a c h l o r o e t h y l e n e ( s p e c i f i c g r a v i t y = 1.613) i n a l a r g e b e a k e r p l a c e d i n a w e l l v e n t i l a t e d hood. The m i x t u r e was s t i r r e d by hand t o i n s u r e w e t t i n g o f a l l p a r t i c l e s , and t h e n i t was a l l o w ed t o s t a n d f o r 30 m i n . The f l o a t p r o d u c t was s u b s e q u e n t l y skimmed o f f and p l a c e d on a 100-mesh s i e v e t o a l l o w any a d h e r i n g l i q u i d t o d r a i n away. The f l o a t p r o d u c t was t h e n p l a c e d i n a d r y i n g o v e n a t 100°C f o r 4 h r . Froth Flotation. To c o n d u c t a f r o t h f l o t a t i o n t e s t , 200 g p u l v e r i z e d c o a l (-35 mesh) were added t o 2000 ml t a p w a t e r i n a b o w l o f a l a b o r a t o r y model Wemco F a g e r g r e n f l o t a t i o n c e l l . With t h e a g i t a t o r r u n n i n g , t h e pH o f t h e s l u r r y was l o w e r e d b e l o w 5 by a d d i n g 10 ml a c i d s o l u t i o n c o n t a i n i n g 10 v o l % c o n c e n t r a t e d hydrochloric acid. B o t h k e r o s e n e (1.0 ml) and m e t h y l i s o b u t y l c a r b i n o l (0.5 ml) were added t o t h e a g i t a t e d s l u r r y , and t h e a i r for



7.

MIN

AND

WHEELOCK

Coal Bénéficiât ion Methods

85

f l o w t o t h e c e l l was s e t a t 9.3 L/min. The r e s u l t i n g f r o t h was c o l l e c t e d u n t i l i t a p p e a r e d t h a t no more c o a l was b e i n g r e c o v e r e d . The m a t e r i a l r e m a i n i n g i n t h e b o w l was p o u r e d o u t , t h e f r o t h p r o d u c t was p u t b a c k i n t h e b o w l , and f r e s h t a p w a t e r was added t o b r i n g t h e s l u r r y volume t o 2000 m l . W i t h t h e a g i t a t o r r u n n i n g , t h e pH o f t h e s l u r r y was r a i s e d above 9 by a d d i n g 40 ml b a s e c o n t a i n i n g 5 wt % p o t a s s i u m h y d r o x i d e . The c o a l was t h e n r e f l o a t ed w i t h o u t a d d i n g f u r t h e r r e a g e n t s and u s i n g t h e same a i r f l o w r a t e a s b e f o r e . A t w o - s t a g e s e p a r a t i o n was made b e c a u s e a l o w pH seemed t o f a v o r t h e r e m o v a l o f a s h w h e r e a s a h i g h pH seemd t o f a v o r the removal of p y r i t e . O i l Agglomeration. O i l a g g l o m e r a t i o n t e s t s were c a r r i e d o u t w i t h a 1 4 - s p e e d k i t c h e n b l e n d e r ( S e a r s I n s t a - B l e n d M o d e l 400) w h i c h h e l d up t o 1200 ml f l u i d . F o r an a g g l o m e r a t i o n t e s t , 200 ml o f an aqueous s l u r r y c o n t a i n i n g 10 wt % c o a l was p l a c e d i n t h e b l e n d e r t o g e t h e r w i t h 10 ml o f s o l u t i o n c o n t a i n i n g 0.2 wt % s o d i u m c a r b o n a t e . The s o d i u m c a r b o n a t e n o t o n l y i n c r e a s e d t h e pH o f t h e s l u r r y but a l s o s e r v e d as a d i s p e r s i n g agent f o r the c l a y p a r t i cles. The s l u r r y was a g i t a t e d f o r 5 min a t t h e l o w e s t s p e e d . An e m u l s i o n o f f u e l o i l and w a t e r was t h e n added t o t h e c o a l s l u r r y , and t h e a g i t a t i o n c o n t i n u e d f o r a n o t h e r 5 min a t t h e same speed to form agglomerates. The e m u l s i o n was p r e p a r e d by c o m b i n i n g 2.0 ml o f a m i x t u r e o f No. 1 f u e l o i l (86 v o l %) and No. 5 f u e l o i l (14 v o l % ) , t h e m i x t u r e h a v i n g a s p e c i f i c g r a v i t y o f 0.83, w i t h 200 ml t a p w a t e r and e m u l s i f y i n g t h e m i x t u r e w i t h an u l t r a sonic vibrator. The a g g l o m e r a t e d c o a l s l u r r y was p o u r e d i n t o a 1000-ml s e p a r a t o r y f u n n e l whereupon t h e c o a l f l o a t e d t o t h e s u r f a c e , and t h e r e f u s e p a r t i c l e s s e t t l e d t o t h e b o t t o m . The w a t e r and r e f u s e were d r a i n e d o u t t h r o u g h t h e b o t t o m o p e n i n g , and t h e a g g l o m e r a t e d c o a l was p u t b a c k i n t h e b l e n d e r and m i x e d w i t h 200 ml f r e s h t a p w a t e r . A f t e r a g i t a t i n g t h e m i x t u r e f o r 2 min a t t h e l o w e s t s p e e d , t h e c o a l s l u r r y was p o u r e d b a c k i n t o t h e s e p a r a t o r y f u n n e l where t h e a g g l o m e r a t e d c o a l was r e c o v e r e d a g a i n . T h i s w a s h i n g o p e r a t i n g was r e p e a t e d once more t o r e d u c e e n t r a p p e d impurities. C h e m i c a l A n a l y s i s M e t h o d s . C o a l s a m p l e s were a n a l y z e d f o r s u l f u r and a s h by t h e s t a n d a r d ASTM p r o c e d u r e s ( 1 0 ) . Materials. C o a l f r o m two Iowa s t r i p m i n e s was u s e d f o r t h i s investigation. A c h a n n e l sample f r o m t h e ICO mine and a r u n - o f mine sample f r o m t h e J u d e mine were t h e s o u r c e o f t h e m a t e r i a l s used. The p r o x i m a t e a n a l y s i s and s u l f u r d i s t r i b u t i o n o f e a c h o f t h e s e s a m p l e s a r e shown i n T a b l e I . A l t h o u g h t h e s u l f u r and a s h c o n t e n t s o f t h e s e s a m p l e s were w i d e l y d i f f e r e n t , t h e s a m p l e s r e p r e s e n t e d c o a l o f t h e same r a n k ( h i g h v o l a t i l e C ) . Investigation of the c o a l m i c r o s t r u c t u r e w i t h a s c a n n i n g e l e c t r o n microscope r e v e a l e d s u b s t a n t i a l amounts o f f i n e l y d i s s e m i n a t e d m i c r o c r y s t a l s of i r o n p y r i t e s (11,12). E a c h c o a l sample was c r u s h e d t o 4 cm t o p s i z e and t h e n was d i v i d e d i n t o t h r e e s i z e f r a c t i o n s (4 cm χ 1 cm, 1 cm χ 48 mesh, and 48 mesh χ 0 ) . E a c h s i z e f r a c t i o n was t h e n f l o a t - s i n k t e s t e d


86


Table I.

Composition

o f C o a l f r o m ICO and

Jude S t r i p M i n e s

P e r c e n t by Type o f A n a l y s i s Proximate


ICO

Jude

44.0 43.2 4.5 8.3

39.4 37.6 8.8 14.2

100.0

100.0

analysis

v o l a t i l e matter f i x e d carbon moisture ash total Sulfur

Weight

distribution

pyritic sulfate organic

2.41 0.05 0.99

2.97 0.44 3.53

total

3.45

6.94

a t v a r i o u s s p e c i f i c g r a v i t i e s u s i n g o r g a n i c l i q u i d s o f known specific gravity. The s t a n d a r d B u r e a u o f M i n e s p r o c e d u r e was used f o r t h i s t e s t ( 1 3 ) . The d a t a f o r t h e d i f f e r e n t s i z e f r a c t i o n s were combined t o p r o v i d e t h e c o m p o s i t e w a s h a b i l i t y a n a l y s i s f o r 4 cm χ 0 c o a l shown i n T a b l e I I . Treatment R e s u l t s The s e q u e n c e o f s t e p s i n v o l v e d i n e a c h o f t h e 16 t r e a t m e n t s w h i c h were a p p l i e d t o e a c h o f t h e two c o a l s a m p l e s i s shown i n F i g u r e 1. The f i r s t t r e a t m e n t was t h e s i m p l e s t and i n v o l v e d c r u s h i n g w i t h the r o l l c r u s h e r , p u l v e r i z i n g w i t h the M i k r o S a m p l m i l l , and o i l a g g l o m e r a t i o n . The s e c o n d t r e a t m e n t i n c l u d e d a b a l l m i l l i n g s t e p i n a d d i t i o n t o the o t h e r s t e p s . The t h i r d and f o u r t h t r e a t m e n t s i n c l u d e d a f r o t h f l o t a t i o n s t e p . I n t h e f i f t h t h r o u g h e i g h t h t r e a t m e n t s the c r u s h e d c o a l was s u b j e c t e d to g r a v i t y s e p a r a t i o n b e f o r e b e i n g p u l v e r i z e d and o t h e r w i s e t r e a t e d as i n t h e f i r s t f o u r t r e a t m e n t s . I n the l a s t e i g h t t r e a t ments t h e c o a l was c h e m i c a l l y comminuted b e f o r e b e i n g c o n d u c t e d through the r o l l c r u s h e r . F o l l o w i n g the c h e m i c a l comminution s t e p , the p a t t e r n o f t r e a t m e n t s was t h e same as f o r t h e f i r s t eight treatments. The f i n a l s t e p o f e a c h t r e a t m e n t was an o i l agglomeration step. A f t e r e a c h s e p a r a t i o n s t e p w i t h i n any g i v e n t r e a t m e n t , t h e w e i g h t o f c o a l r e c o v e r e d was measured a f t e r d r y i n g t h e m a t e r i a l




88

COAL

Table

II.

Composite W a s h a b i l i t y A n a l y s i s o f Coal ICO and J u d e S t r i p M i n e s

D i r e c t D a t a (%) Product Fraction


ICO

Weight

DESULFURIZATION

(4 cm χ 0) f r o m

Cumulative

Data

(%)

Sulfur Total

Weight

Ash

5.36 11.98 15.63 16.84 20.47 22.50 25.39 42.05

1. 80 2. 74 3. 66 4. 18 4. 83 4. 01 6. 46 17. 57

78 .7 85 .0 87 .8 90 .7 92 .7 94 .2 94 .7 100 .0

5 .36 5 .85 6 .16 6 .50 6 .80 7 .05 7 .15 9 .00

1.80 1.87 1.93 2.00 2.06 2.09 2.11 2.93

5.67 12.03 15.84 19.94 23.80 28.30 31.51 48.92

5. 07 4. 83 5. 24 6. 41 7. 91 7. 53 6. 79 12. 84

46.5 65.5 73.1 80.2 84.1 87.1 88.8 100.0

5.67 7.51 8.38 9.40 10.07 10.70 11.10 15.33

5 .07 5 .00 5 .03 5 .15 5 .28 5 .36 5 .38 6 .22

Ash

Sulfur Total

Coal

F l o a t 1.30 1.30 - 1.35 1.35 - 1.40 1.40 - 1.45 1.45 - 1.50 1.50 - 1.55 1.55 - 1.60 S i n k 1.60

78.7 6.3 2.8 2.9 2.0 1.5 0.5 5.3

Jude C o a l F l o a t 1.30 1.30 - 1.35 1.35 - 1.40 1.40 - 1.45 1.45 - 1.50 1.50 - 1.55 1.55 - 1.60 S i n k 1.60

46.5 19.0 7.6 7.1 3.9 3.0 1.7 11.2

o v e r n i g h t i n an oven a t 80°-100°C. A s m a l l sample o f t h e d r i e d c o a l was s u b s e q u e n t l y a n a l y z e d f o r a s h and p y r i t i c s u l f u r . The p e r c e n t a g e r e d u c t i o n i n e i t h e r a s h o r s u l f u r c o n t e n t was f o u n d f o r e a c h s e p a r a t i o n s t e p and f o r t h e o v e r a l l t r e a t m e n t by u s i n g the r e l a t i o n : π j . . Reduction

/ α , χ content of feed - content of product , (/ ) = —— ^ χ 100 content of feed The y i e l d o f c o a l f o r e a c h s e p a r a t i o n s t e p and t h e t o t a l y i e l d f o r t h e o v e r a l l t r e a t m e n t were d e t e r m i n e d a s f o l l o w s : Yield

n r k

0

(%) = d r y w e i g h t o f p r o d u c t dry weight of feed

In the case of o i l - a g g l o m e r a t e d c o a l ,

the y i e l d determined


i n this

7.

M I N A N D WHEELOCK

Coal Beneficiation

Methods

89


manner i n c l u d e d t h e s m a l l amount o f o i l w h i c h was n o t v a p o r i z e d d u r i n g oven d r y i n g . T h e r e f o r e , t o e x p r e s s t h e y i e l d on an o i l f r e e as w e l l as on a m o i s t u r e - f r e e b a s i s , the c a l c u l a t e d y i e l d was r e d u c e d b y 2%. I t was assumed t h a t l o s s e s o f m a t e r i a l s i n t h e c r u s h i n g and p u l v e r i z i n g s t e p s was n e g l i g i b l e . F i g u r e s 2, 3, a n d 4 show t h e c u m u l a t i v e e f f e c t s o f t h e d i f f e r e n t s e p a r a t i o n s t e p s w i t h i n each treatment as w e l l as the o v e r a l l r e s u l t s o f e a c h t r e a t m e n t . I n g e n e r a l t h e r e s u l t s were q u i t e v a r i e d between t r e a t m e n t s a n d b e t w e e n c o a l s . Thus i n t h e c a s e o f ICO c o a l , t h e o v e r a l l y i e l d v a r i e d among t h e d i f f e r e n t t r e a t m e n t s between 74 a n d 96%, t h e o v e r a l l r e d u c t i o n i n p y r i t i c s u l f u r c o n t e n t b e t w e e n 12 and 87%, a n d t h e o v e r a l l r e d u c t i o n i n a s h c o n t e n t between 22 and 72%. S i m i l a r l y i n the case o f Jude c o a l , t h e o v e r a l l y i e l d v a r i e d among t h e d i f f e r e n t t r e a t m e n t s b e t w e e n 75 and 92%, t h e o v e r a l l r e d u c t i o n i n p y r i t i c s u l f u r c o n t e n t b e t w e e n 31 and 88%, a n d o v e r a l l r e d u c t i o n i n a s h c o n t e n t b e t w e e n 34 and 8 4 % . Although the f i r s t s e p a r a t i o n step o f a m u l t i s t e p treatment produced t h e g r e a t e s t r e d u c t i o n i n l e v e l o f i m p u r i t i e s , subs e q u e n t s e p a r a t i o n s t e p s a l s o removed s i g n i f i c a n t amounts o f s u l f u r and a s h ( F i g u r e s 3 a n d 4 ) . Hence, t h e s e p a r a t i o n methods a p p e a r e d t o be c o m p l e m e n t a r y , p a r t i c u l a r l y when u s e d i n c o n j u n c tion with particle size reduction. Among t h e v a r i o u s t r e a t m e n t s , t r e a t m e n t 1 6 , w h i c h i n c l u d e d a l l o f t h e c o m m i n u t i o n and s e p a r a t i o n s t e p s , p r o d u c e d t h e c l e a n e s t p r o d u c t f r o m ICO c o a l . T h i s p r o d u c t , r e c o v e r e d w i t h an o v e r a l l y i e l d o f 7 8 % , c o n t a i n e d o n l y 2.3% a s h and 0.3% p y r i t i c s u l f u r w h i c h r e p r e s e n t e d a n o v e r a l l r e d u c t i o n o f 7 2 % i n a s h c o n t e n t and 8 7 % i n p y r i t i c s u l f u r c o n t e n t . T r e a t m e n t s 8, 1 2 , and 14 were n e a r l y a s e f f e c t i v e i n r e m o v i n g s u l f u r a n d a s h f r o m ICO c o a l a n d p r o v i d ed h i g h e r y i e l d s t h a n t r e a t m e n t 16. T r e a t m e n t s 8, 1 4 , a n d 16 were a b o u t e q u a l l y e f f e c t i v e i n r e m o v i n g s u l f u r a n d a s h f r o m Jude c o a l . The p r o d u c t o f t h e s e t r e a t m e n t s c o n t a i n e d a b o u t 0.4% p y r i t i c s u l f u r a n d 2.2-2.7% a s h w h i c h r e p r e s e n t e d a n o v e r a l l r e d u c t i o n o f 86-88% i n p y r i t i c s u l f u r c o n t e n t and 81-84% i n a s h c o n t e n t . However, t r e a t m e n t s 14 and 16 p r o v i d e d a l a r g e r o v e r a l l y i e l d (84%) t h a n t r e a t m e n t 8 (75%). The r e l a t i v e e f f i c i e n c y o f t h e v a r i o u s t r e a t m e n t s i s i l l u s t r a t e d by F i g u r e s 5 and 6 i n w h i c h t h e o v e r a l l y i e l d o f p r o d u c t i s p l o t t e d a g a i n s t the c o r r e s p o n d i n g p y r i t i c s u l f u r o r a s h c o n t e n t . The upper c u r v e i n e a c h d i a g r a m i s drawn t h r o u g h t h e p o i n t s r e p r e s e n t i n g t h e treatments which p r o v i d e d the h i g h e s t y i e l d s f o r t h e corresponding l e v e l s of impurities. Thus f o r ICO c o a l t r e a t m e n t s 2, 1 0 , 1 2 , 1 4 , and 16 were t h e most e f f i c i e n t f r o m t h e s t a n d p o i n t o f s u l f u r r e m o v a l and t r e a t m e n t s 2, 6, 8, 1 4 , and 16 f r o m t h e standpoint o f ash removal. S i m i l a r l y f o r Jude c o a l t r e a t m e n t s 10, 1 1 , 1 2 , and 14 were t h e most e f f i c i e n t f r o m t h e s t a n d p o i n t o f s u l f u l r r e m o v a l a n d t r e a t m e n t s 1 0 , 1 2 , 1 4 , a n d 16 f r o m t h e s t a n d p o i n t of ash removal. F o r t h e most p a r t , t h e s e t r e a t m e n t s had two t h i n g s i n common. Thus, e x c e p t f o r t r e a t m e n t 11 a p p l i e d t o Jude


COAL

TREATMENT 3 8 10 12

DESULFURIZATION

14 16


MM

• OIL AGGLOM. E) FROTH FLOT. • GRAVITY SEP. ICO COAL

100"

2

4

TREATMENT 6 8 10

m

12

14 16

95 90 Q _J

80 75

i

Figure 2.

JUDE COAL

Weight yield of product from the different treatments



7.

M I N AND WHEELOCK

Coal Beneficiation Methods

6

8 10 TREATMENT

100

• OIL AGGLOM. Θ FROTH FLOT. : 80U Ξ GRAVITY SEP.

60

JUDE COAL

m pi

40

:

1

2 0

ο 6

8 10 TREATMENT

12

14

16

Figure 3. Reduction in pyritic sulfur content provided by the different treatments


91


92

COAL

DESULFURIZATION

TREATMENT

100 80

OIL AGGLOM. FROTH FLOT. GRAVITY SEP.

JUDE COAL

il

§60 Ο

m

Ω 40 LU

3 20 0 6

Figure 4.

8 Ί0 TREATMENT

12

14

16

Reduction in ash content provided by the different treatments


M I N AND

WHEELOCK



7.

Figure 5.

Overall yield vs. final pyritic sulfur content of the product from the different treatments


93

DESULFURIZATION


COAL

\ure 6.

Overall yield vs. the ash content of the final product from the different treatments



7.

MIN

AND

WHEELOCK


95

c o a l , a l l of the treatments i n v o l v e d f i n e g r i n d i n g b e f o r e the o i l a g g l o m e r a t i o n s t e p . I n a d d i t i o n , e x c e p t f o r t r e a t m e n t s 2 and 6 a p p l i e d t o ICO c o a l , a l l o f the t r e a t m e n t s i n v o l v e d c h e m i c a l comminution. The u p p e r c u r v e i n e a c h d i a g r a m o f F i g u r e s 5 and 6 i l l u s t r a t e s t h e t r a d e o f f b e t w e e n o v e r a l l y i e l d and l e v e l o f i m p u r i t i e s i n the p r o d u c t . The y i e l d f e l l o f f as t h e l e v e l o f i m p u r i t i e s was r e d u c e d t h r o u g h a p p l i c a t i o n o f t r e a t m e n t s o f g r e a t e r and g r e a t e r c o m p l e x i t y . W i t h ICO c o a l t h e d r o p i n y i e l d was q u i t e p r e c i p i t o u s when t h e p y r i t i c s u l f u r c o n t e n t was r e d u c e d b e l o w 0.5% o r t h e a s h c o n t e n t b e l o w 2.5% ( F i g u r e s 5 and 6 ) . Therefore f o r t h i s c o a l , t r e a t m e n t s 14 and 16, w h i c h p r o v i d e d t h e c l e a n e s t c o a l b u t a t c o n s i d e r a b l e s a c r i f i c e i n y i e l d , w o u l d be e s p e c i a l l y hard to j u s t i f y . N e a r l y a l l o f t h e t r e a t m e n t s d e s c r i b e d by F i g u r e 1 were more e f f i c i e n t t h a n s i n g l e - s t a g e g r a v i t y s e p a r a t i o n o f 4 cm χ 0 c o a l . The y i e l d and c o r r e s p o n d i n g a s h c o n t e n t p r o v i d e d by g r a v i t y s e p a r a t i o n of the coarse m a t e r i a l s i n l i q u i d s of d i f f e r e n t s p e c i f i c g r a v i t y a r e r e p r e s e n t e d by the w a s h a b i l i t y c u r v e s i n F i g u r e 6. F o r e i t h e r k i n d o f c o a l t h e y i e l d f e l l o f f s h a r p l y as t h e a s h c o n t e n t was r e d u c e d t o l o w e r l e v e l s by s e p a r a t i o n i n l i g h t e r liquids. A comparison o f the r e s u l t s o f the f i r s t s e p a r a t i o n s t e p o f e a c h o f the v a r i o u s t r e a t m e n t s i n d i c a t e s t h e r e l a t i v e e f f i c i e n c y o f t h e d i f f e r e n t s e p a r a t i o n methods w h i c h were u s e d . Thus i n t h e c a s e o f ICO c o a l , the f r o t h f l o t a t i o n s t e p o f t r e a t m e n t s 11 o r 12 r e d u c e d t h e p y r i t i c s u l f u r c o n t e n t more t h a n t h e f i r s t s e p a r a t i o n s t e p o f any o t h e r t r e a t m e n t , and t h e f r o t h f l o t a t i o n s t e p o f t r e a t m e n t s 3 o r 4 r e d u c e d the a s h c o n t e n t more t h a n t h e f i r s t s e p a r a t i o n s t e p o f any o t h e r t r e a t m e n t . A l s o the r e s p e c t i v e f r o t h f l o t a t i o n s t e p s p r o v i d e d the h i g h e s t y i e l d s f o r the l e v e l o f i m p u r i t i e s a t t a i n e d . The g r a v i t y s e p a r a t i o n s t e p o f t r e a t m e n t s 5-8 was n e a r l y as e f f i c i e n t i n r e d u c i n g t h e a s h c o n t e n t o f ICO c o a l as t h e f r o t h f l o t a t i o n s t e p o f t r e a t m e n t s 3 o r 4, b u t i t was n o t as e f f i c i e n t i n r e d u c i n g t h e s u l f u r c o n t e n t . However, g r a v i t y s e p a r a t i o n was a p p l i e d t o c o a r s e r m a t e r i a l t h a n f r o t h f l o t a t i o n . In the case of Jude c o a l , the g r a v i t y s e p a r a t i o n s t e p o f t r e a t ments 13-16 p r o v i d e d t h e g r e a t e s t r e d u c t i o n i n p y r i t i c s u l f u r and a s h c o n t e n t s o f any o f t h e f i r s t - s t e p s e p a r a t i o n s as w e l l as t h e h i g h e s t y i e l d f o r t h e l e v e l o f i m p u r i t i e s a t t a i n e d . The n e x t most e f f e c t i v e f i r s t - s t e p s e p a r a t i o n was t h a t p r o v i d e d by o i l a g g l o m e r a t i o n o f b a l l - m i l l e d Jude c o a l i n t r e a t m e n t 10. This s t e p r e d u c e d t h e a s h c o n t e n t o f J u d e c o a l a l m o s t as much as t h e g r a v i t y s e p a r a t i o n s t e p and a l s o p r o d u c e d a h i g h e r y i e l d . On t h e o t h e r h a n d , i t was n o t n e a r l y as e f f e c t i v e i n r e d u c i n g t h e p y r i t i c s u l f u r c o n t e n t as t h e g r a v i t y s e p a r a t i o n s t e p o f t r e a t ments 13-16. I t has a l r e a d y been n o t e d t h a t g e n e r a l l y t h e most e f f i c i e n t t r e a t m e n t s i n v o l v e d f i n e g r i n d i n g and c h e m i c a l c o m m i n u t i o n . To e x a m i n e t h e e f f e c t o f f i n e g r i n d i n g f u r t h e r , the o v e r a l l r e s u l t s


96


T a b l e I I I . E f f e c t o f G r i n d i n g on O v e r a l l R e s u l t s

Excluded (Odd T r t . )

Included (Even T r t . )

ICO c o a l ash r e d u c t i o n pyritic sulfur reduction yield

47 58 83

55 67 87

65 61 82

71 71 84


Jude c o a l ash r e d u c t i o n pyritic sulfur reduction yield

o f t h e even-numbered t r e a t m e n t s w h i c h i n c l u d e d f i n e g r i n d i n g and the o v e r a l l r e s u l t s o f t h e odd-numbered t r e a t m e n t s w h i c h e x c l u d e d t h i s s t e p were a v e r a g e d s e p a r a t e l y . The two s e t s o f v a l u e s w h i c h a r e p r e s e n t e d i n T a b l e I I I i n d i c a t e t h a t on t h e a v e r a g e t h e t r e a t ments w h i c h i n c l u d e d f i n e g r i n d i n g p r o d u c e d a c l e a n e r p r o d u c t i n g r e a t e r y i e l d than the treatments which d i d n o t i n c l u d e i t . T h e r e f o r e i t a p p e a r s t h a t f i n e g r i n d i n g i s a v e r y e f f e c t i v e means f o r i m p r o v i n g t h e s e p a r a t i o n o f p y r i t e and o t h e r a s h - f o r m i n g m i n e r a l s f r o m b o t h ICO and J u d e c o a l s . S i m i l a r l y t o study the e f f e c t o f chemical comminution f u r t h e r , the o v e r a l l r e s u l t s o f the l a s t e i g h t treatments which i n c l u d e d t h i s s t e p and t h e r e s u l t s o f t h e f i r s t e i g h t t r e a t m e n t s w h i c h e x c l u d e d t h i s s t e p were a v e r a g e d s e p a r a t e l y . The two s e t s o f v a l u e s ( T a b l e I V ) i n d i c a t e t h a t on t h e a v e r a g e t h e t r e a t m e n t s wich i n c l u d e d c h e m i c a l comminution p r o v i d e d a c l e a n e r product than t h e t r e a t m e n t s which d i d n o t . A l s o w i t h Jude c o a l , b u t n o t w i t h ICO c o a l , a l a r g e r y i e l d was p r o v i d e d on t h e a v e r a g e by t h e t r e a t m e n t s which i n c l u d e d t h i s s t e p . T h e r e f o r e , a t l e a s t f o r Jude c o a l , c h e m i c a l c o m m i n u t i o n i s an e f f e c t i v e method o f i m p r o v i n g the s e p a r a t i o n o f m i n e r a l i m p u r i t i e s . The e f f e c t i v e n e s s o f t h e g r a v i t y s e p a r a t i o n s t e p was a l s o e v a l u a t e d f u r t h e r by a v e r a g i n g t h e o v e r a l l r e s u l t s o f t h e t r e a t ments w h i c h i n c l u d e d i t and t h e r e s u l t s o f t h e t r e a t m e n t s w h i c h e x c l u d e d i t s e p a r a t e l y . The a v e r a e e r e d u c t i o n i n b o t h D v r i t i c s u l f u r and a s h was much g r e a t e r f o r t h o s e t r e a t m e n t s w h i c h i n c l u d e d t h i s step than f o r those which excluded i t (Table V ) . A l t h o u g h t h e a v e r a g e p r o d u c t y i e l d was l o w e r f o r t h e t r e a t m e n t s w h i c h i n c l u d e d g r a v i t y s e p a r a t i o n , t h e p e n a l t y i n y i e l d was r a t h e r modest f o r t h e l a r g e r e d u c t i o n i n l e v e l o f i m p u r i t i e s w h i c h was a c h i e v e d .


7.

MIN

AND

WHEELOCK

Table IV.

97


E f f e c t o f C h e m i c a l C o m m i n u t i o n on O v e r a l l R e s u l t s

Excluded ( T r t . 1-8)

Included ( T r t . 9-16)

ICO c o a l ash r e d u c t i o n p y r i t i c sulfur reduction yield

50 55 88

52 70 82

63 63 80

73 68 86


Jude c o a l ash r e d u c t i o n p y r i t i c sulfur reduction yield

T a b l e V.

E f f e c t o f G r a v i t y S e p a r a t i o n on O v e r a l l R e s u l t s

Excluded ( T r t . 1-4,9-12)

Included ( T r t . 5-8,13-16)

ICO c o a l ash r e d u c t i o n pyritic sulfur reduction yield

41% 51% 88%

62% 74% 82%

60% 54% 86%

76% 77% 80%

Jude c o a l ash r e d u c t i o n p y r i t i c sulfur reduction yield


COAL

98

Table V I .

DESULFURIZATION

E f f e c t o f F r o t h F l o t a t i o n on O v e r a l l R e s u l t s

Excluded ( T r t . 1,2,5,6, 9,10,13,14)

Included ( T r t . 3,4,7, 8,11,12,15,16)

ICO c o a l ash r e d u c t i o n pyritic sulfur yield

reduction

40% 50% 87%

62% 75% 83%

reduction

61% 56% 84%

74% 75% 82%


Jude c o a l ash r e d u c t i o n pyritic sulfur yield

The e f f e c t i v e n e s s o f t h e f r o t h f l o t a t i o n s t e p was a l s o e v a l u a t e d by c o m p a r i n g t h e a v e r a g e o v e r a l l r e s u l t s o f t h e t r e a t ments w h i c h i n c l u d e d t h i s s t e p w i t h t h e a v e r a g e r e s u l t s o f t h e o t h e r t r e a t m e n t s T a b l e V I ) . Here a g a i n t h e t r e a t m e n t s w h i c h i n c l u d e d t h i s method o f s e p a r a t i o n p r o v i d e d a much c l e a n e r p r o d u c t than those which d i d not i n c l u d e i t w h i l e e x p e r i e n c i n g o n l y a modest r e d u c t i o n i n y i e l d . The e f f e c t i v e n e s s o f f r o t h f l o t a t i o n was v e r y s i m i l a r t o t h a t o f g r a v i t y s e p a r a t i o n , a l t h o u g h t h e two methods were a p p l i e d t o d i f f e r e n t s i z e s o f c o a l . The r e s u l t s o f t h e i n d i v i d u a l s t e p s o f o i l a g g l o m e r a t i o n and f r o t h f l o t a t i o n were a v e r a g e d t o compare t h e e f f e c t i v e n e s s o f one method a g a i n s t t h e o t h e r . A l s o i n the case o f o i l agglomeration, the r e s u l t s o f a g g l o m e r a t i n g -35 mesh c o a l were a v e r a g e d s e p a r a t e l y f r o m t h e r e s u l t s o f a g g l o m e r a t i n g -400 mesh c o a l t o d e t e r m i n e t h e e f f e c t o f p a r t i c l e s i z e on t h i s method o f s e p a r a t i o n . From the d a t a p r e s e n t e d i n T a b l e V I I i t c a n be s e e n t h a t t h e o i l a g g l o m e r a t i o n s t e p was much more e f f e c t i v e when i t was a p p l i e d t o -400 mesh c o a l t h a n when i t was a p p l i e d t o -35 mesh c o a l ; n o t o n l y d i d a c l e a n e r p r o d u c t r e s u l t , i t was r e c o v e r e d i n a l a r g e r yield. I n a d d i t i o n t h e o i l a g g l o m e r a t i o n s t e p a p p l i e d t o -400 mesh Jude c o a l was more e f f e c t i v e on t h e a v e r a g e t h a n t h e f r o t h f l o t a t i o n s t e p a p p l i e d t o -35 mesh m a t e r i a l . However, i n t h e c a s e o f ICO c o a l t h e r e s u l t s were m i x e d w i t h f r o t h f l o t a t i o n a p p e a r i n g t o have t h e edge w i t h r e g a r d t o s u l f u r r e m o v a l b u t n o t w i t h regard to ash removal. Conclusions The l a b o r a t o r y a p p l i c a t i o n o f 16 d i f f e r e n t

treatments i n -


7.

MIN

AND WHEELOCK

Table V I I .


99

O i l A g g l o m e r a t i o n Step v s . F r o t h F l o t a t i o n

O i l Aggl. -35 mesh ( T r t . 1,5, 9,13)

O i l Aggl. -400 mesh ( T r t . 2,6, 10,14)

Step

Froth Flot. -35 mesh ( T r t . 3,7, 11,15)

ICO c o a l


ash r e d u c t i o n pyritic sulfur yield

reduction

20 16 89

34 40 95

30 51 93

reduction

36 23 88

47 44 93

31 35 94

Jude c o a l ash r e d u c t i o n pyritic sulfur yield

v o l v i n g s i z e r e d u c t i o n and p h y s i c a l s e p a r a t i o n t o h i g h - s u l f u r c o a l c o n t a i n i n g s u b s t a n t i a l amounts o f f i n e l y d i s s e m i n a t e d microc r y s t a l s o f i r o n p y r i t e s p r o v i d e d s e v e r a l i n t e r e s t i n g and i m portant r e s u l t s . Comparison o f these r e s u l t s w i t h a standard w a s h a b i l i t y a n a l y s i s showed t h a t most o f t h e t r e a t m e n t s p r o d u c e d a c l e a n e r c o a l f o r a g i v e n y i e l d t h a n c o u l d be o b t a i n e d by g r a v i t y s e p a r a t i o n a l o n e o f 4 cm χ 0 s i z e c o a l . In t h i s regard the t r e a t m e n t s w h i c h f a i l e d t o p r o d u c e c o a l w i t h a l o w e r s u l f u r c o n t e n t were g e n e r a l l y t h o s e w h i c h i n v o l v e d o n l y s i z e r e d u c t i o n and o i l a g g l o m e r a t i o n . T r e a t m e n t s i n v o l v i n g two and sometimes t h r e e methods o f s e p a r a t i o n i n sequence proved p a r t i c u l a r l y e f f e c t i v e . Thus t h e p y r i t i c s u l f u r c o n t e n t o f two Iowa c o a l s was r e d u c e d 85-86% w i t h an o v e r a l l y i e l d o f 82-84% by t r e a t m e n t 14 w h i c h i n c l u d e d c h e m i c a l comminution, r o l l c r u s h i n g , g r a v i t y s e p a r a t i o n , f i n e g r i n d i n g , and o i l a g g l o m e r a t i o n . T h i s s u l f u r r e d u c t i o n was c o n s i d e r a b l y h i g h e r t h a n t h a t p r o v i d e d by s i n g l e - s t a g e s e p a r a t i o n . Thus a maximum r e d u c t i o n o f 6 6 % i n t h e p y r i t i c s u l f u r c o n t e n t o f ICO c o a l was r e a l i z e d d u r i n g t h e f r o t h f l o t a t i o n s t e p o f t r e a t m e n t s 11-12 and o f 64% i n t h e p y r i t i c s u l f u r c o n t e n t o f J u d e c o a l d u r i n g the g r a v i t y s e p a r a t i o n s t e p o f t r e a t m e n t s 13-16. E a c h o f t h e s e p a r a t i o n methods u s e d i n t h e s e treatments proved e f f e c t i v e i n i t s e l f . M o r e o v e r t h e methods seemed t o com p l e m e n t e a c h o t h e r , p a r t i c u l a r l y when used i n c o n j u n c t i o n w i t h particle size reduction. Chemical comminution g e n e r a l l y improved the s e p a r a t i o n e f f i c i e n c y o f t h e v a r i o u s t r e a t m e n t s and f i n e g r i n d i n g t h e s e p a r a t i o n e f f i c i e n c y o f t h e o i l a g g l o m e r a t i o n method o f sépara-


100

COAL

DESULFURIZATION

tion i n particular. Acknowledgement T h i s r e p o r t i s b a s e d on a p a p e r w h i c h was p r e s e n t e d a t t h e NCA/BCR CoaJ C o n f e r e n c e and Expo I I I , L o u i s v i l l e , KY, O c t . 1 9 - 2 1 , 1976. The work was s p o n s o r e d by t h e Iowa C o a l P r o j e c t and c o n d u c t e d i n t h e E n e r g y and M i n e r a l R e s o u r c e s R e s e a r c h I n s t i t u t e a t Iowa S t a t e U n i v e r s i t y .


Literature Cited

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Aplan, F. F., this volume, in press. Cavallaro, J. Α., Deurbrouck, A. W., this volume, in press. Zimmerman, R. Ε., Min. Cong. J. (1964) 50 (5), 26. Capes, C. E., Smith, A. E., Puddington, I. Ε., CIM Bull. (1974) 67, 115. Capes, C. E.,McIlhinney,A. E., Coleman, R. D., Trans. Soc. Min. Eng., AIME (1970) 247, 233. Brisse, A. H., McMorris, W. L., Jr., Trans. Soc. Min. Eng., AIME (1958) 211, 258. Howard, P. Η., Datta, R. S., this volume, in press. Datta, R. S., Howard, P. Η., Hanchett, Α., NCA/BCR Coal Conference and Expo III (Oct. 19-21, 1976), Louisville, KY. Howard P. Η., Hanchett, Α., Aldrich, R. G., Symposium II Clean Fuels from Coal, (June 23-27, 1975), Institute of Gas Technology, Chicago, IL. Book ASTM Stan., (1976) Part 26, "Gaseous Fuels; Coal and Coke; Atmospheric Analysis," Methods D2015-66, D2492-68, D3174-73, D3177-75. Greer, R. T., this volume, in press. Greer, R. T., "Nature and Distribution of Pyrite in Iowa Coal," Joint Meeting of the Electron Microscopy Society of America and Microbeam Analysis Society, (August 9-13, 1976), Miami, FL. Methods of Analyzing and Testing Coal and Coke, U.S. Bur. Min. Bull. (1967) 638.


8 Dry Table—Pyrite Removal from Coal D. C. WILSON


FMC Corp., Santa Clara, CA 95052

Particle segregation within a flowing granular bed during passage through material handling equipment or during transfer from one piece of equipment to another is commonplace. The most readily observable of these is size segregation. Usually such segregations are undesirable in a system because of the potential of unstable processing and an interruption of product continuity. Three factors determine the extent of particle segregation in a moving particle bed: the physical configuration of the material handling equipment, the forces which convey the particles through that equipment, and the differences between the particles in one or more of their physical properties (size, shape, bulk density, resiliency and surface roughness). The equipment described below, specifically designed as a separator for dry particulates, combines these factors to exploit the inherent segregation within moving particle beds. The equipment can be used to remove pyrite and other ash-forming minerals from coal; experimental results of cleaning bituminous and subbituminous coals with it are reported. Equipment D e s c r i p t i o n Figure 1 contains a p e r s p e c t i v e drawing o f the d r y t a b l e , being developed by FMC Corporation, and a c r o s s s e c t i o n through the u n i t i l l u s t r a t i n g the p a r t i c l e bed. The d r i v e u n i t f o r the t a b l e shown i s an electromechanical e x c i t e r o f the type used f o r v i b r a t i n g feeders. In f a c t , t h i s r e c e n t l y developed c o a l c l e a n ing u n i t i s a feeder, but with the f o l l o w i n g design d i f f e r e n c e s : (1) The deck surface i s short but very wide. (2) The c o a l i s i n s e r t e d a t one side o f the feeder's deck. (3) The conveying f o r c e i s reversed; i t feeds the m a t e r i a l i n t o the t a b l e ' s backwall. (4) The p a r t i c l e bed's net flow i s from one side o f the feeder t o the other s i d e . (5) The deck i s nonsymmetrical about the v e r t i c a l plane passing through i t s center o f g r a v i t y and the e x c i t e r ' s l i n e o f 101


102

DESULFURIZATION


COAL

Figure 1.

Dry table principle; schematic view


8.

WILSON

Dry Table—Pyrite Removal from Coal

drive. C o a l i s f e d o n t o t h e l o n g e s t s i d e o f t h e u n i t , and t h e c o n v e y i n g f o r c e f r o m t h e d r i v e moves t h e p a r t i c l e s t o w a r d s t h e backwall. A l a r g e p i l e of p a r t i c l e s forms a g a i n s t the b a c k w a l l , f i l l i n g the e n t i r e trough. G r a v i t y moves t h e p a r t i c l e s on t h e p i l e s s u r f a c e down t h e open s l o p e as t h e c o n v e y i n g f o r c e c o n t i n u e s to d r i v e the u n d e r l y i n g m a t e r i a l a g a i n s t the b a c k w a l l . The r e s u l t i s t h e c o n t i n u o u s o v e r t u r n i n g o f t h e bed. The p r e s s u r e o f t h e i n c o m i n g f e e d f o r c e s t h e o v e r t u r n i n g bed t o f l o w a c r o s s t h e d e c k away f r o m t h e f e e d s i d e i n a h e l i c a l m o t i o n , and b e c a u s e t h e deck's l e n g t h d i m i n i s h e s (tapers) i n t h i s d i r e c t i o n , the toe of the p i l e i s being c o n t i n u o u s l y d i s c h a r g e d . S i m u l t a n e o u s l y , s i z e and b u l k d e n s i t y s e p a r a t i o n s a r e o c c u r r i n g i n t h e o v e r t u r n i n g bed. The l a r g e o r l o w - d e n s i t y p a r t i c l e s move i n t o a s p i r a l l i n g p a t h t h a t m i g r a t e s t o w a r d t h e t o e o f t h e p i l e ( S e c t i o n Α-A, F i g u r e 1) w h e r e a s t h e s m a l l o r h i g h - d e n s i t y p a r t i c l e s move i n t o a s m a l l e r s p i r a l and c o n c e n t r a t e t o w a r d s t h e backwall. Those p a r t i c l e s t h a t a r e b o t h l a r g e and o f low d e n s i t y ( c o a l ) a d v a n c e p a s t t h e l a r g e and h i g h - d e n s i t y p a r t i c l e s ( r o c k and p y r i t e ) and p r e v a i l i n o b t a i n i n g p o s i t i o n s a t t h e t o e o f t h e pile. A l s o s m a l l p a r t i c l e s of p y r i t e w i l l c o n c e n t r a t e a t the b a c k w a l l i n preference to s m a l l p a r t i c l e s of c o a l . The o v e r a l l r e s u l t i n g d i s c h a r g e f r o m t h e h o r i z o n t a l d e c k p o r t i o n of the u n i t i s a s e r i e s of staggered p a r t i c l e s i z e g r a d a t i o n s o f d i f f e r e n t d e n s i t i e s (when b u l k d e n s i t i e s a r e d i r e c t l y r e l a t e d to apparent d e n s i t i e s ) . To a v o i d t h i s o v e r l a p p i n g o f t h e s i z e g r a d a t i o n s o f t h e r o c k and p y r i t e w i t h t h e c o a l , t h e f e e d t o t h e u n i t i s p r e s i z e d t o d e f i n i t e s i z e r a n g e s . F o r t h e c o a l , r o c k , and p y r i t e s e p a r a t i o n , the g e n e r a l i z e d top s i z e t o bottom s i z e of the f e e d p a r t i c l e s i n any one p a s s i s a 4 - t o - l r a t i o (8 χ 2 i n . , 2 χ 1/2 i n . , e t c . ) . The optimum ratio» however, i s a f u n c t i o n o f b u l k d e n s i t y , s h a p e , r e s i l i e n c y , and s u r f a c e r o u g h n e s s d i f f e r e n c e s b e t w e e n t h e c o a l and r o c k - p y r i t e f o r a p a r t i c u l a r c o a l seam and mining c o n d i t i o n s . The p a r t i c l e s d i s c h a r g e f r o m t h e n e a r l y h o r i z o n t a l d e c k o n t o an a t t a c h e d downward s l o p i n g s u r f a c e r e f e r r e d t o as t h e " d i s c h a r g e lip". T h i s l i p c a n make f u r t h e r s e p a r a t i o n s b a s e d on p a r t i c l e s h a p e , r e s i l i e n c y , and s u r f a c e r o u g h n e s s i f d e s i r e d . The shape s e p a r a t i o n i s b a s e d on t h e c u b i c a l c o a l p a r t i c l e s b e i n g u n s t a b l e on t h e d i s c h a r g e l i p and t h e n e a r t a b u l a r r o c k and p y r i t e p a r t i c l e s b e i n g s t a b l e when t h e u n i t i s v i b r a t i n g . The u n s t a b l e c o a l w i l l t h u s be d i s c h a r g e d by r o l l i n g o f f t h e l i p w h i l e t h e t a b u l a r r o c k and p y r i t e a r e c o n v e y e d b a c k up t h e l i p i n t o t h e p i l e . The s u r f a c e roughness of the h i g h l y m i n e r a l i z e d p a r t i c l e s i s g r e a t e r than that f o r the c l e a n c o a l p a r t i c l e s . T h i s a d d i t i o n a l roughness h e l p s t o c o n v e y t h e r o c k and p y r i t e b a c k i n t o t h e deep p a r t i c l e bed w h e r e a s t h e s l i c k c o a l t e n d s t o s l i p o f f t h e l i p . Generally, the r e s i l i e n c y of the c o a l i s g r e a t e r than t h a t of the r o c k particles. The c o n v e y i n g v i b r a t i o n s c a u s e s t h e more r e s i l i e n t c o a l p a r t i c l e s t o bounce and a s s u r e t h e i r u n s t a b i l i t y on t h e 1


103



104

COAL

DESULFURIZATION

discharge l i p . The above d e s c r i b e s t h e m a j o r s e p a r a t i o n s o c c u r r i n g a t s p e c i f i e d l o c a t i o n s on t h e d r y t a b l e . Even t h o u g h p a r t i c l e s h a p e , r e s i l i e n c y , and s u r f a c e r o u g h n e s s d i f f e r e n c e s a r e n o t i n c l u d e d i n t h e d e s c r i p t i o n o f t h e o v e r t u r n i n g p a r t i c l e p i l e , t h e y do c o n t r i bute t o minor s e p a r a t i o n s w i t h i n the p i l e . Likewise, particle b u l k d e n s i t y and s i z e d i f f e r e n c e s a r e i n v o l v e d i n t h e s e p a r a t i o n on t h e l i p , b u t t h e s e a r e o f m i n o r i m p o r t a n c e when compared t o t h e d i f f e r e n c e s i n p a r t i c l e s h a p e , r e s i l i e n c y and s u r f a c e - r o u g h n e s s . W i t h t h e s e p a r a t i o n d r i v i n g f o r c e s o f t h e f i v e known p h y s i c a l property differences operating simultaneously, i t i s highly u n l i k e l y that a l l f i v e are working together to a r r i v e a t the d e s i r e d c o a l c l e a n i n g . T h e r e f o r e , most c o a l c l e a n i n g s e p a r a t i o n s a r e a compromise i n w h i c h t h e d r y t a b l e ' s o p e r a t i n g p a r a m e t e r s a r e a d j u s t e d t o enhance t h e d e s i r e d p h y s i c a l p r o p e r t y s e p a r a t i o n s and depress the undesirable separations. The f o l l o w i n g p h y s i c a l p r o p e r t y d i f f e r e n c e s l i s t d e s c r i b e s how t h e d r y t a b l e p a r a m e t e r c o n t r o l s i n f l u e n c e t h e d e g r e e o f t h e individual separations. Size. For c o a l c l e a n i n g , the feed t o the d r y t a b l e i s pre-screened i n t o s i z e ranges t o minimize the n a t u r a l l y strong s i z e s e g r e g a t i o n e f f e c t s i n a m o v i n g p a r t i c l e b e d . The n a r r o w e r t h e s i z e r a n g e , t h e l e s s s i z e s e g r e g a t i o n e f f e c t on t h e o v e r a l l separation. Systems c a n be d e v i s e d f o r p o s t - s c r e e n i n g b u t a t a s a c r i f i c e of the d r y t a b l e ' s throughput r a t e . Bulk Density. F o r c o a l c l e a n i n g a m o d e r a t e l y deep p i l e i s b e s t , as d e s c r i b e d below. I f t h e f r e q u e n c y and/or a m p l i t u d e i s i n c r e a s e d above a n o r m a l l e v e l , t h e n t h e p a r t i c l e bed becomes q u i t e p o r o u s and a l l p a r t i c l e s w i l l e x h i b i t a l i g h t e r b u l k d e n s i t y , thus reducing the e f f e c t i v e bulk d e n s i t y d i f f e r e n c e s . Shape. F o r w a r d o r b a c k w a r d t i l t i n g o f t h e d r y t a b l e c a u s e s t h e d i s c h a r g e l i p t o be a t d i f f e r e n t a n g l e s r e l a t i v e t o t h e h o r i z o n t a l w h i c h d e t e r m i n e s what s h a p e s a r e r e j e c t e d o r r e t a i n e d o n the t a b l e . A d i s c h a r g e l i p a n g l e o f -12° i s g e n e r a l l y u s e d f o r the s e p a r a t i o n o f c u b i c c o a l from t a b u l a r r o c k - p y r i t e . I f t h e r o c k - p y r i t e i s present as round p a r t i c l e s , then a l e s s steep d i s charge l i p i s used. Resiliency. By i n c r e a s i n g t h e u n i t ' s f r e q u e n c y a n d / o r s t r o k e above t h e n o r m a l l e v e l , t h e more r e s i l i e n t p a r t i c l e s i n t h e bed w i l l e x h i b i t a l o w e r b u l k d e n s i t y i n t h e p i l e s e c t i o n and s i m u l t a n e o u s l y become more u n s t a b l e on t h e l i p s e c t i o n . S u r f a c e R o u g h n e s s . The t y p e o f s u r f a c e f i n i s h on t h e d i s c h a r g e l i p combined w i t h t h e p a r t i c l e ' s own s u r f a c e r o u g h n e s s w i l l d e t e r m i n e i f i t i s d i s c h a r g e d o r r e t a i n e d on t h e t a b l e . A very hard s l i c k s u r f a c e w i l l discharge n e a r l y a l l p a r t i c l e types w h i l e



8.

WILSON

Dry

Table—Pyrite Removal from Coal

105

a very hard rough s u r f a c e w i l l r e t a i n n e a r l y a l l p a r t i c l e types. The t h r o u g h p u t r a t e and bed r e t e n s i o n t i m e a r e c o n t r o l l e d by a l t e r i n g the c r o s s - s l o p e ( s i d e t o s i d e of u n i t ) . I n c r e a s i n g the c r o s s - s l o p e , by l o w e r i n g t h e f e e d s i d e o f t h e u n i t w i t h r e s p e c t t o i t s o p p o s i t e s i d e , w i l l c a u s e l o w e r t h r o u g h p u t r a t e s and l a r g e bed r e t e n s i o n times. There i s a c l o s e r e l a t i o n s h i p between the d r y t a b l e ' s v e r t i c a l s t r o k e component and f r e q u e n c y , w i t h some l i m i t a t i o n s d i c t a t e d by t h e p a r t i c l e s i z e s b e i n g s e p a r a t e d and t h e o p t i m i z a t i o n o f throughput r a t e s . Of o b v i o u s i m p o r t a n c e i s t h e h o r i z o n t a l c o n v e y ance of p a r t i c l e s t o form the o v e r t u r n i n g p i l e . The d e p t h o f t h a t p i l e i s t h e n , t o a l a r g e e x t e n t , d e t e r m i n e d by t h e v e r t i c a l c o n v e y a n c e . And t h e p i l e d e p t h i s i m p o r t a n t b e c a u s e v e r y deep p i l e s favor s i z e s e g r e g a t i o n w h i l e p i l e s of moderate depth favor b u l k density segregations. For c o a l c l e a n i n g , t h e r e f o r e , a f i x e d d r i v e a n g l e o f 30° was s e l e c t e d as t h e b e s t c o m b i n a t i o n o f h o r i z o n t a l and v e r t i c a l c o n v e y a n c e s i n f o r m i n g t h e d e s i r e d p i l e s o f m o d e r a t e d e p t h . The f r e q u e n c y i s r e l a t e d t o t h e s t r o k e ; w i t h i n c r e a s i n g s t r o k e l e n g t h , t h e f r e q u e n c y must be r e d u c e d t o m a i n t a i n t h e d e s i r e d t a b l i n g a c t i v i t y a t the s e l e c t e d d r i v e angle: 2 Stroke

(Frequency)

= Constant

The s t r o k e s h o u l d n o t be l a r g e r t h a n t h e s m a l l e s t p a r t i c l e d i a m e t e r t o be s e p a r a t e d o r p a r t i c l e m i x i n g becomes a f a c t o r i n t h e separation. However, u s i n g t h e l a r g e s t s i z e s t r o k e p o s s i b l e i s d e s i r a b l e because the throughput r a t e i n c r e a s e s w i t h i n c r e a s i n g stroke: 2 Stroke

<x ( T h r o u g h p u t R a t e )

S i n c e most o f t h e bed p a r t i c l e s a r e i n c o n t a c t w i t h e a c h o t h e r r a t h e r than w i t h the dry t a b l e s u r f a c e s , the c h a r a c t e r of the p a r t i c l e d i s c h a r g e i s a f u n c t i o n o f t h e bed c o m p o s i t i o n i t s e l f as w e l l as t h e a b o v e d e s c r i b e d p a r a m e t e r s . I f the r o c k - p y r i t e cont e n t of the feed i n c r e a s e s , a p r o p o r t i o n a l i n c r e a s e i n r o c k - p y r i t e w o u l d be e x p e c t e d t h r o u g h o u t a l l t h e d i s c h a r g e p r o d u c t s , i n c l u d i n g the c l e a n e s t c o a l product. T h i s phenomenon has been d e m o n s t r a t e d many t i m e s f o r a w i d e c o m p o s i t i o n o f f e e d w h i c h i n d i c a t e s t h a t t h e d r y t a b l e ' s s e p a r a t i o n p r i n c i p l e i s b a s e d on a p r o b a b i l i t y function. The d r y t a b l e has a d i s c h a r g e s i m i l a r i n c h a r a c t e r t o t h a t o f a wet c o n c e n t r a t i o n t a b l e i n t h a t i t i s a g r a d a t i o n f r o m a c l e a n c o a l product through m i n e r a l i z e d p a r t i c l e s to p y r i t e along the d i s c h a r g e edge. T h i s d r y method o f s e p a r a t i o n i s f u n c t i o n a l o v e r a b r o a d s p a n o f p a r t i c l e s i z e s . The l i m i t i n g f a c t o r f o r t h e minimum s i z e p a r t i c l e i s t h e f o r m a t i o n o f p a r t i c l e a g g l o m e r a t i o n s because of e l e c t r o s t a t i c charges or s u r f a c e moisture. No l i m i t i n g f a c t o r has b e e n e n c o u n t e r e d f o r t h e maximum s i z e p a r t i c l e s . The p r e s e n t p r a c t i c a l r a n g e i n c o a l p r e p a r a t i o n i s 1/8 - 8 i n . , t h e



106

COAL

DESULFURIZATION

l o w e r l i m i t b e i n g d i c t a t e d b y s c r e e n i n g p r a c t i c e s and t h e u p p e r l i m i t b y t h e s i z e o f t h e p r e s e n t 15 f t p r o t o t y p e d r y t a b l e . A small 12 i n . l a b u n i t c a n p r e d i c t t h e p e r f o r m a n c e o f t h e l a r g e r 8- and 1 5 - f t u n i t s o n a p a r t i c u l a r r a w c o a l w i t h a f e e d o f p r o p o r t i o n a l l y s i z e d p a r t i c l e s because o f t h e p r o b a b i l i t y base o f the d r y t a b l e ' s s e p a r a t i o n p r i n c i p l e . Therefore, small-scale coal c l e a n i n g t e s t s a r e made f i r s t w i t h t h e l a b u n i t t o d e t e r m i n e t h e p a r a m e t e r s e t t i n g s and t o r e d u c e f i e l d t e s t t i m e r e q u i r e m e n t s . S t a n d a r d w a s h a b i l i t y d a t a o f raw c o a l i s o f l i t t l e v a l u e i n p r e d i c t i n g what t h e p e r f o r m a n c e o f t h e d r y t a b l e w o u l d be b e c a u s e t h i s d a t a i s based on apparent d e n s i t i e s a l o n e . Most o f t h e d r y t a b l e e x p e r i e n c e i s i n t h e r e d u c t i o n o f t h e ash c o n t e n t o f c o a l s . However, t h e r e h a s b e e n a r e c e n t i n c r e a s e of i n t e r e s t i n t h e u s e o f t h e d r y t a b l e a s a method f o r s u l f u r reduction. Experimental Runs w e r e made w i t h t h e f o l l o w i n g - d e s c r i b e d s a m p l e s by p a s s i n g them t h r o u g h one o f t h e d r y t a b l e u n i t s i n one p a s s and c o l l e c t i n g the discharge as m u l t i p l e products. I n F i g u r e 1, a n 1 1 - p r o d u c t d i s c h a r g e i s shown, A t h r o u g h K, where t h e d i s c h a r g e s a r e o f e q u a l increments spaced a l o n g t h e d i s c h a r g e l i p . Each d i s c h a r g e p r o d u c t was a n a l y z e d f o r a s h , p y r i t i c s u l f u r , and BTU c o n t e n t , f o l l o w i n g t h e a c c e p t e d ASTM methods D-271 and D-2492. The two c o a l s a m p l e s u s e d a r e d e s c r i b e d i n T a b l e I . Table I .

Sample D e s c r i p t i o n s and T e s t P a r a m e t e r s Bituminous Subbituminous

Source location condition mine Analysis BTU/lb Ash (%) P y r i t i c s u l f e r (%) Sample r u n p a r t i c l e s i z e (range) surface moisture Dry t a b l e p a r a m e t e r s location unit size throughput r a t e d r i v e type f r e q u e n c y (Hz) stroke (in.) d r i v e angle

R a t o n , NM wet p r o c e s s e d (heavy m e d i a ) underground

F r u i t l a n d , NM raw ( d i r e c t f r o m p i t )

13,460 10.1 0.44

8,060 25.8 0.19

1/4 i n . χ 8 mesh ~ 0 % , as r e c e i v e d S a n t a C l a r a , CA (FMC) 12-in (labunit) 0.01 t o n s / h r . electromagnetic 60 0.03 30°

surface

2 χ 1/2 i n . ~ 0 % , as r e c e i v e d Navajo Mine 8-ft ( p i l o t only) 3 tons/hr. electromechanical 18 0.25 30°


8.

WILSON


107


Results The a n a l y t i c a l r e s u l t s o f t h e r u n s w i t h t h e b i t u m i n o u s and subbituminous samples were used t o c o n s t r u c t t h e d i s t r i b u t i o n c u r v e s shown i n F i g u r e 2. The h o r i z o n t a l a x i s f o r b o t h t h e u p p e r and l o w e r p o r t i o n o f t h e g r a p h r e p r e s e n t s t h e d i s c h a r g e f r o m t h e dry t a b l e as the 11-discharge products. I n t h e upper p o r t i o n , t h e v e r t i c a l a x i s g i v e s the r e c o v e r y as a percentage of the o r i g i n a l f e e d f o r h e a t i n g c o n t e n t (BTU), a s h , and p y r i t e . The c l e a n c o a l product i s the accumulation of discharge products s t a r t i n g at the f a r l e f t ( p e r c e n t a g e on l e f t v e r t i c a l a x i s ) , and t h e r e j e c t s t a r t s on t h e f a r r i g h t ( r i g h t v e r t i c a l a x i s ) . The d a t a p o i n t s p l o t t e d on t h e g r a p h a r e f o r r u n s w h i c h had a n e i g h t - p r o d u c t discharge. In t h e lower p o r t i o n of the graph, separate curves a r e p l o t t e d f o r p r o d u c t and r e j e c t w h i c h show t h e d i s t r i b u t i o n o f t h e p y r i t i c s u l f u r a s l b p e r m i l l i o n BTUs. Discussion As w i t h a l l c o a l c l e a n i n g e q u i p m e n t , t h e p e r f o r m a n c e i s a f u n c t i o n of the c o a l being cleaned. The d r y t a b l e i s no e x c e p t i o n t o t h i s and c a n be c o n s i d e r e d more s e n s i t i v e b e c a u s e i t u s e s a s many a s f i v e o f t h e p a r t i c l e s ' p h y s i c a l p r o p e r t y d i f f e r e n c e s f o r separation r a t h e r than j u s t the d e n s i t y d i f f e r e n c e alone. Also a f f e c t i n g t h e s e p a r a t i o n i s the degree t o which t h e major cons t i t u e n t s o f t h e r a w c o a l ( c l e a n c o a l , r o c k , and p y r i t e ) a r e l i b e r a t e d from each other. Therefore, a gradation of property differences f o r a l l the p a r t i c l e s p r o p e r t i e s , as w e l l as f o r s i z e , c a n e x i s t i n t h e g r a n u l a r f e e d t o be s e g r e g a t e d . Then t o t h i s add t h e d r y t a b l e ' s p r o b a b i l i t y b a s e f o r p a r t i c l e s e g r e g a t i o n , and t h e c o m p l e x i t y o f i n d e p t h i n t e r p r e t a t i o n o f t h e d r y t a b l e ' s r e s u l t s c a n be i n v i s i o n e d . The p y r i t e i n t h e two e x a m p l e s s e l e c t e d f o r t h i s d i s c u s s i o n i s u n l i b e r a t e d and o f r e l a t i v e l y l o w c o n c e n t r a t i o n . The l e t t e r e d discharge products A through D are d i v i s i o n s of the d r y t a b l e ' s d i s c h a r g e a r b i t r a r i l y s e l e c t e d f o r a n a l y t i c a l and d i s c u s s i o n p u r p o s e s , and t h e l a r g e number o f p r o d u c t d i v i s i o n s o r t h e i r s p e c i f i c b o u n d a r i e s , need n o t be u s e d i n a c t u a l c o a l c l e a n i n g applications. Subbituminous Coal. The o n l y p r e p a r a t i o n t h i s c o a l r e c e i v e d p r i o r t o b e i n g f e d t o t h e d r y t a b l e was p r e s i z i n g i n t o 4:1 s i z e r a n g e s . The s e q u e n c e o f t h e d i s t r i b u t i o n c u r v e s , ( F i g u r e 2, t o p ) show t h a t i n t h i s t h r e e component s y s t e m , c l e a n c o a l (BTU) r o c k (ash) - p y r i t e , t h e major s e p a r a t i o n i s between t h e c l e a n c o a l and t h e r o c k . The p y r i t e - a s h s e p a r a t i o n i s r e v e r s e d t o what w o u l d be e x p e c t e d f o r t h e more d e n s e p y r i t e , w h i c h f u r t h e r demons t r a t e s that t h e p y r i t e i s not l i b e r a t e d . There a r e three z o n a l types o f d i s c h a r g e from t h e d r y t a b l e w i t h t h i s c o a l . In the f i r s t z o n e , p r o d u c t d i s c h a r g e s A and B, t h e c o a l c o n t a i n s l o w a s h and h a s t h e p y r i t e m a i n l y a s s o c i a t e d w i t h t h e c o a l . I n t h e second 1


108

DESULFURIZATION


COAL

Figure 2.

Dry table discharge distribution


8.

WILSON

109


z o n e , p r o d u c t d i s c h a r g e s C t h r o u g h G, t h e c o a l c o n t a i n s l o w p y r i t e and a s h , b u t t h e p y r i t e i s a s s o c i a t e d w i t h t h e a s h . In the t h i r d z o n e , p r o d u c t d i s c h a r g e s H t h r o u g h K, t h e d i s c h a r g e c o n t a i n s a c o a l and r o c k m i x t u r e where t h e p y r i t e i s a s s o c i a t e d w i t h b o t h c o a l and r o c k a t h i g h e r c o n c e n t r a t i o n s . S e l e c t i n g d i s c h a r g e s A t h r o u g h I as a c l e a n c o a l p r o d u c t and J and Κ as r e j e c t g i v e s a 90% r e c o v e r y o f t h e c o a l ' s p o t e n t i a l h e a t i n g c o n t e n t and r e m o v a l s o f 75% o f t h e a s h and 50% o f t h e pyrite. The c o m p o s i t i o n s o f t h e p r o d u c t and r e j e c t a r e g i v e n i n Table I I .


Table I I .

S e l e c t e d Subbituminous Product

Yield (%) BTU/lb Ash (%) Pyritic sulfur

(%)

Coal

72 10,360 10.8 0.13

Product Rej e c t 28 2,160 64.1 0.32

W i t h t h e d i s c h a r g e s p l i t i n t o j u s t a c l e a n c o a l p r o d u c t and r e j e c t , t h e w e l l known compromise must be made b e t w e e n r e c o v e r i n g as much c l e a n c o a l as p o s s i b l e w h i l e r e j e c t i n g most o f t h e r o c k and p y r i t e . W i t h the d r y t a b l e , however, i t i s p o s s i b l e t o have a s many p r o d u c t s a s a r e r e a s o n a b l e . T h e r e f o r e , one c o u l d s e l e c t t h e zone o f l o w a s h c o n t e n t A t h r o u g h G as t h e c l e a n c o a l p r o d u c t and H t h r o u g h J f o r r e t r e a t m e n t , where t h e r e i s a m i x t u r e o f b o t h r o c k and c o a l , and Κ as t h e r e j e c t w h i c h e s s e n t i a l l y c o n t a i n s no usuable heat (Table I I I ) . Table I I I .

S e l e c t e d Subbituminous Product

Y i e l d (%) BTU/lb A s h (%) Pyritic sulfer

(%)

47 11,260 4. 7 0. 08

C o a l P r o d u c t and R e c y c l e Retreatment Reject 37 7,390 30.0 0.27

16 0 78 0.29

B o t h t h e c l e a n c o a l p r o d u c t and t h e r e j e c t a r e d e s i r a b l e : t h i s a r r a n g e m e n t , and i t s s u c c e s s depends upon t h e c h a r a c t e r o f the retreatment d i s c h a r g e . In t h i s p a r t i c u l a r case, the r e t r e a t ment i s a m i x t u r e o f c l e a n c o a l and l i b e r a t e d r o c k w i t h a s m a l l amount o f m i d d l i n g s ( t h i s w o u l d be e x p e c t e d b e c a u s e t h e d r y t a b l e ' s p a r t i c l e s e g r e g a t i o n has a p r o b a b i l i t y b a s e ) . The r e t r e a t m e n t c a n be r e c y c l e d t h r o u g h t h e same u n i t o r s e n t t o a n o t h e r u n i t f o r a second p a s s . Bituminous C o a l . T h i s c o a l i s the product from a p r e p a r a t i o n p l a n t , and t h e r e f o r e t h e r e i s e s s e n t i a l l y no l i b e r a t e d p y r i t e o r r o c k p r e s e n t . The s e q u e n c e o f t h e c u r v e s shows t h a t t h e u n l i b e r a t e d p y r i t e i s u n e v e n l y d i s t r i b u t e d among t h e c o a l p a r t i c l e s and t h a t t h e m a j o r s e p a r a t i o n i s b e t w e e n t h e c l e a n c o a l and p y r i t e . The a s h and BTU c u r v e s a r e v e r y s i m i l a r , e x c e p t f o r a s l i g h t



110

COAL

DESULFURIZATION

d i f f e r e n c e i n s l o p e s , showing t h a t t h e r e i s a n e a r - c o n s t a n t i n h e r e n t a s h i n t h e c o a l f o r t h e d i s c h a r g e p r o d u c t s A t h r o u g h H. The p y r i t e c u r v e i s q u i t e d i f f e r e n t i n shape and shows s m a l l amounts o f p y r i t e i n d i s c h a r g e p r o d u c t s A t h r o u g h D, i n c r e a s i n g amounts i n Ε t o J , and s u b s t a n t i a l q u a n t i t i e s i n K. There are f o u r z o n a l types of d i s c h a r g e f o r t h i s p a r t i c u l a r s e p a r a t i o n . In t h e f i r s t z o n e , d i s c h a r g e p r o d u c t s A t h r o u g h D, t h e c o a l has a minimum a s h and p y r i t e c o n t e n t . In the second zone, d i s c h a r g e p r o d u c t s D t o H, t h e c o a l c o n t a i n s a minimum o f a s h b u t has an increasing p y r i t e content. In the t h i r d zone, d i s c h a r g e p r o d u c t s I t h r o u g h J , t h e ash, and p y r i t e c o n t e n t p r o g r e s s i v e l y i n c r e a s e i n the c o a l . I n t h e f o u r t h z o n e , d i s c h a r g e p r o d u c t K, t h e c o a l i s h i g h e s t i n b o t h a s h and p y r i t e and c o n t a i n s a l l t h e m i s p l a c e d s i n k m a t e r i a l f r o m t h e wet w a s h i n g p r o c e s s . The s p e c i f i c g r a v i t y d i f f e r e n c e b e t w e e n t h e f i r s t and s e c o n d z o n e s i s q u i t e s m a l l , so t h e s e p a r a t i o n i s most l i k e l y c a u s e d by the o t h e r p h y s i c a l p r o p e r t i e s of the p a r t i c l e s . S i n c e the ash d i f f e r e n c e i s a l s o s m a l l , i t i s assumed t h a t t h e p r e s e n c e o f t h e p y r i t e i s r e l a t e d to the p h y s i c a l p r o p e r t y d i f f e r e n c e s which the d r y t a b l e c a n d i s t i n g u i s h f o r s e p a r a t i o n p u r p o s e s . The s u g g e s t e d method o f p r o c e s s i n g i s t o c o l l e c t t h e d i s c h a r g e f r o m d i s c h a r g e p r o d u c t s A t o H as a c l e a n c o a l p r o d u c t and I t o Κ f o r r e t r e a t m e n t (Table I V ) . T a b l e IV.

Selected

Yield (%) BTU/lb Ash (%) Pyritic sulfur

(%)

B i t u m i n o u s C o a l P r o d u c t and R e c y c l e Product Retreatment 75 13,750 7.5 0.22

25 12,600 17. ,5 1. ,08

F o r t h i s c o a l s a m p l e t h e r e t r e a t m e n t d i s c h a r g e s h o u l d not be p r o c e s s e d as a s e c o n d p a s s on t h e d r y t a b l e b e c a u s e l i t t l e b e n e f i t w o u l d be r e a l i z e d i n a s h and p y r i t e r e d u c t i o n . The b e s t a p p r o a c h w o u l d be t o r e c y c l e t h i s m a t e r i a l t o t h e wet p r e p a r a t i o n p l a n t after crushing. Conclusion The d r y t a b l e c a n r e d u c e t h e s u l f u r c o n t e n t o f a c o a l t h r o u g h p y r i t e r e m o v a l . The e x t e n t o f t h e c o a l - p y r i t e s e p a r a t i o n w i l l be a f u n c t i o n o f p y r i t e l i b e r a t i o n and t h e p h y s i c a l p r o p e r t y d i f f e r e n c e s b e t w e e n t h e f r e e f l o w i n g c o a l and p y r i t e p a r t i c l e s . How e v e r , t h e r e a r e c a s e s where e v e n c o a l c o n t a i n i n g u n l i b e r a t e d p y r i t e c a n be s e p a r a t e d i n t o c o a l p r o d u c t s o f l o w and h i g h p y r i t i c s u l f u r contents. The d r y t a b l e i s b e s t u s e d a s a r o u g h e r , s i n c e i t has a s e p a r a t i o n s i m i l a r t o t h a t o f a Baum J i g . I t c a n be u s e d a l o n e o r i n c o n j u n c t i o n w i t h e x i s t i n g c o a l c l e a n i n g e q u i p m e n t . And i t i s


8.

WILSON


111


e s p e c i a l l y a p p l i c a b l e where t h e u s e o f w a t e r i s r e s t r i c t e d b e c a u s e of l i m i t e d s u p p l y , f r e e z i n g , o r c o s t l y treatment p r i o r t o d i s charge or reuse.


9 Magnetic Desulfurization of Some Illinois Basin Coals H A Y D N H. M U R R A Y


Dept. of Geology, Indiana Univ., Bloomington, I N 47401

High extraction magnetic filtration (HEMF) is used successfully to process kaolin (1). This is the first successful commercial application of a new level of magnetic separation equipment and processing technology which resulted from the joining of four major concepts (2). 1. Discovery of the importance of retention time in mineral separation. 2. Development of very high gradient matrix collectors. 3. High intensity fields in wet magnetic separator (up to 20 kG). 4. Modern design of large high field magnets. Use of longer retention time permits finely divided particles to migrate and be captured by a magnetized collection surface. The canister in the magnet is filled with a matrix of steel wool, screens made of sharp thin ribbons, or other filamentary material which provides very high gradients. Modern electronic and magnet technology led to the design of a magnet with a high field throughout a large cavity. A diagrammatic sketch of a large high intensity magnet is shown on Figure 1. The diameter of the canister can be up to 84 in. with a height of 20 in. Up to 120 tons of kaolin per hour can be processed through the 84-in. unit. Fabrication of equipment larger than 84 in. is feasible, but the problems involved in shipping and for on site fabrication are such that it is probably more efficient to consider multiple installations of 84-in. machines. High e x t r a c t i o n magnetic f i l t r a t i o n i s very s u c c e s s f u l i n r e m o v i n g i r o n and t i t a n i u m i m p u r i t i e s f r o m k a o l i n . Potential a p p l i c a t i o n s f o r i t s use f o r b e n e f i c i a t i o n o f o t h e r i n d u s t r i a l m i n e r a l s and c o a l have been demonstrated by Murray ( 3 , 4 , 5 ) . P r e s e n t HEMF e q u i p m e n t u s e s e l e c t r o m a g n e t s t o g e n e r a t e f i e l d s

112


9.

MURRAY

Magnetic Desulfurization of Illinois Coals

113

o f 20 kG. Power c o n s u m p t i o n o f t h i s e q u i p m e n t i s i n t h e r a n g e o f 400-500 kW. The p r e s e n t HEMF e q u i p m e n t i s o p t i m i z e d f o r s e p a r a t i o n o f s l u r r y c o n t a i n i n g f i n e s b e l o w 200 mesh and p r e f e r a b l y b e l o w 20 microns. O t h e r m a t r i x t y p e s can be s u b s t i t u t e d f o r s t a i n l e s s s t e e l w o o l t o a c c o m o d a t e c o a r s e r f e e d m a t e r i a l s (up t o 20 mesh) i n c l u d i n g F r a n t z s c r e e n s , l o o s e l y packed coarse s t e e l w o o l , s t e e l s h o t , s t e e l f i l i n g s , and o t h e r f i l a m e n t a r y m a t e r i a l . New d e v e l opments a r e underway i n m a t r i x d e s i g n and c o m p o s i t i o n w h i c h can g r e a t l y enhance HEMF t e c h n o l o g y .


Magnetic D e s u l f u r i z a t i o n of

Coal

The e a r l i e s t w o r k c o n c e r n i n g t h e r e d u c t i o n o f s u l f u r i n c o a l by m a g n e t i c s e p a r a t i o n was d e s c r i b e d i n a German p a t e n t by S i d d i q u i i n 1957 ( 6 ) . Y u r o v s k y and R e m e s n i k o v (7) p u b l i s h e d a p a p e r i n 1958 r e p o r t i n g t h a t c o a l p u l v e r i z e d f i n e r t h a n 16-mesh s i z e s u b j e c t e d t o a t h e r m a l s t e a m - a i r t r e a t m e n t made t h e p y r i t e more m a g n e t i c , w h i c h e n h a n c e d b e n e f i c i a t i o n when p r o c e s s e d i n a s p e c i a l l y b u i l t magnetic separator. S u l f u r r e d u c t i o n s o f 85, 74.9, and 70% w e r e r e p o r t e d . P e r r y (8) r e p o r t e d t h a t f i n e p y r i t e (65 - 70 mesh) t r e a t e d i n s t e a m - a i r a t m o s p h e r e a t t e m p e r a t u r e s o f 570° - 750°F f o r v a r y i n g t i m e s up t o 10 m i n . i n c r e a s e d t h e q u a n t i t y o f p y r i t e amenable t o m a g n e t i c s e p a r a t i o n w i t h i n c r e a s ing i n t e n s i t y of treatment. K e s t e r ( 9 , 10,) d e m o n s t r a t e d t h a t s u l f u r c o u l d be r e d u c e d t o a g r e a t e r e x t e n t by m a k i n g a h i g h i n t e n s i t y m a g n e t i c s e p a r a t i o n d i r e c t l y on raw u n t r e a t e d c o a l without u s i n g the thermal pretreatment s t e p . T h u s , by p u l v e r i z i n g t h e c o a l t o a t y p i c a l power p l a n t s i z e and by m a g n e t i c a l l y s e p a r a t i n g t h e c o a r s e 48 by 200-mesh s i z e f r a c t i o n , s i g n i f i c a n t s u l f u r r e d u c t i o n was achieved. K e s t e r r e p o r t e d t h a t p y r i t i c s u l f u r a c c o u n t s f o r 40 t o as much as 80% o f t h e s u l f u r c o n t e n t o f most c o a l s ( 9 ) . Gluskoter and Simon (11) r e p o r t e d t h a t t h e mean t o t a l s u l f u r c o n t e n t i n 474 a n a l y s e s was 3.57% i n c o a l s f r o m I l l i n o i s , and t h e mean v a l u e o f p y r i t i c s u l f u r i n t h e s e same c o a l s was 2.06%. They f o u n d t h a t t h e r e i s on an a v e r a g e a p p r o x i m a t e l y 150% more p y r i t i c s u l f u r i n a s a m p l e as t h e r e i s o r g a n i c s u l f u r . Macroscopic p y r i t e occurs i n c o a l i n : v e i n s , u s u a l l y t h i c k and f i l m l i k e a l o n g v e r t i c a l j o i n t s ; i n l e n s e s t h a t a r e e x t r e m e l y v a r i a b l e i n shape and s i z e ; i n n o d u l e s o r b a l l s ; and i n d i s s e m i n a t e d c r y s t a l s and i r r e g u l a r a g g r e g a t e s . Microscopic pyrite o c c u r s as s m a l l g l o b u l e s and b l e b s , f i n e v e i n l e t s , d e n d r i t e s , s m a l l e u h e d r a l c r y s t a l s , c e l l f i l l i n g s , and r e p l a c e m e n t p l a n t material. K e s t e r , L e o n a r d , and W i l s o n (12) r e p o r t e d t h a t t h e mass s u s c e p t i b i l i t y o f powdered p y r i t e was 4.53 χ 10^ cgs u n i t s . A n o t h e r v a l u e commonly u s e d f o r t h e m a g n e t i c s u s c e p t i b i l i t y o f p y r i t e i s 25 χ ΙΟ ** e l e c t r o m a g n e t i c u n i t s p e r cm. The s t r e n g t h o f m a g n e t i s m , w h i c h c a n be i n d u c e d i n t o a m i n e r a l depends upon -


114

COAL

DESULFURIZATION

the p e r m e a b i l i t y o f the m i n e r a l a c c o r d i n g t o the e q u a t i o n : Β = uH W h e r e — = m a g n e t i c i n d u c t i o n i n g a u s s i n t h e m i n e r a l , _u = perme a b i l i t y o f t h e m i n e r a l , and Η = m a g n e t i c f i e l d i n t e n s i t y i n g a u s s . Therefore the s u s c e p t i b i l i t y i s :


B/H = 1 + 4 πΚ Where—Κ = magnetic s u s c e p t i b i l i t y expressed i n e l e c t r o m a g n e t i c u n i t s cm/gm/sec. I f t h e v a l u e o f Κ i s p o s i t i v e , t h e m i n e r a l i s termed p a r a m a g n e t i c and e x p e r i e n c e s a f o r c e w h i c h t e n d s t o a t t r a c t i t i n the d i r e c t i o n o f i n c r e a s i n g magnetic g r a d i e n t . I f Κ i s n e g a t i v e , t h e m i n e r a l i s d i a m a g n e t i c and e x p e r i e n c e s a repulsive force. Ferromagnetic m i n e r a l s , such as i r o n , e x p e r i ence s t r o n g m a g n e t i c f o r c e s i n t h e d i r e c t i o n o f i n c r e a s i n g mag n e t i c g r a d i e n t and t h u s have v e r y l a r g e p o s i t i v e v a l u e s o f K. C o a l i s d i a m a g n e t i c ( 1 3 ) , and p y r i t e i s p a r a m a g n e t i c . Thus, i f t h e c o a l i s c r u s h e d and p u l v e r i z e d f i n e enough t o l i b e r a t e t h e p y r i t e , a good m a g n e t i c s e p a r a t i o n i s p o s s i b l e . A r e c e n t s t u d y by K i n d i g and T u r n e r ( 1 4 ) r e p o r t e d on a new p r o c e s s f o r r e m o v i n g p y r i t i c s u l f u r and a s h f r o m c o a l . The p u l v e r i z e d c o a l i s t r e a t e d w i t h i r o n c a r b o n y l vapor which puts a t h i n s k i n o f m a g n e t i c m a t e r i a l on t h e p y r i t e and a s h b u t does not a f f e c t the c o a l . Thus m a g n e t i c s e p a r a t o r s y i e l d a n o n m a g n e t i c c o a l l o w i n s u l f u r and a s h and a m a g n e t i c f r a c t i o n h i g h i n s u l f u r and a s h . Experimental The c o a l s a m p l e s used f o r t h i s r e p o r t were p u l v e r i z e d so t h a t 90% p a s s e d t h r o u g h a 200-mesh s i e v e . The s a m p l e s were s l u r r i e d a t 30% s o l i d s f o r t h e wet m a g n e t i c t e s t s . F r a n t z s c r e e n s made f r o m t h i n s h a r p r i b b o n s o f 430 m a g n e t i c s t a i n l e s s s t e e l were u s e d a s the m a t r i x i n t h e c a n i s t e r . F o r the wet magnetic t e s t s r e t e n t i o n t i m e s o f 30, 6 0 , and 120 sec. were u s e d f o r one s e r i e s , and m u l t i p l e p a s s e s w i t h a r e t e n t i o n t i m e o f 30 sec. e a c h were used f o r a second s e r i e s . F o r t h e d r y t e s t s t h e s e r i e s were r u n u s i n g g r a v i t y feed w i t h m u l t i p l e passes. The m a g n e t i c s e p a r a t o r used i n t h i s s t u d y was a p i l o t p l a n t model m a n u f a c t u r e d by P a c i f i c E l e c t r i c M o t o r Co. o f O a k l a n d , California. The HEMF e q u i p m e n t i n c l u d e s a f i l t e r c a n i s t e r w h i c h can be p a c k e d w i t h a f i l a m e n t a r y m a g n e t i c m a t e r i a l . The m a t r i x m a t e r i a l c a n e a s i l y be changed d e p e n d i n g o n t h e p a r t i c l e s i z e o f the feed s l u r r y . The c a n i s t e r i s s u r r o u n d e d by h o l l o w c o n d u c t o r c o p p e r c o i l s w h i c h e n e r g i z e t h e e n t i r e c a n i s t e r volume t o a f i e l d up t o 20 kG. The c o p p e r c o i l s a r e s u r r o u n d e d by a b o x - l i k e enclosure of s t e e l p l a t e which completes the magnetic c i r c u i t . The u n i t e o p e r a t e s a t power l e v e l s o f 200 kW.


9.

MURRAY


The c o a l s a m p l e s were p u l v e r i z e d i n a l a b o r a t o r y hammer m i l l and a s m a l l r i n g m i l l . A f t e r t h e p u l v e r i z e d c o a l was s l u r r i e d w i t h t h e a i d o f a d i s p e r s a n t ( s o d i u m h e x a m e t a p h o s p h a t e ) , i t was a g i t a t e d w i t h a L i g h t n i n m i x e r and pumped up t h r o u g h t h e c a n i s t e r w i t h a p e r i s t a l t i c pump a t c o n t r o l l e d r a t e s . A p p r o x i m a t e l y 1 l b o f c o a l was r u n t h r o u g h t h e c a n i s t e r f o r e a c h t e s t . Samples o f -100 mesh were r u n and compared w i t h t h e -200 mesh s a m p l e s and much b e t t e r r e s u l t s were o b t a i n e d w i t h t h e f i n e r s a m p l e s . The c o a l s used f o r t h i s r e p o r t were c o m m e r c i a l l y mined c o a l s from the I l l i n o i s B a s i n . These a r e C o a l s V and V I f r o m I l l i n o i s and I n d i a n a . T a b l e I shows t h e s u l f u r c o n t e n t o f t h e v a r i o u s samples.


Table I . S u l f u r Content

Coal

(%)

Total Sulfur

Inorganic Sulfur

4.63 4.17 3.59 1.98

2.44 2.20 2.39 1.02

I n d i a n a V ( W a r r i c k Co.) I n d i a n a V I ( W a r r i c k Co.) I l l i n o i s V (Wabash Co.) I l l i n o i s V I ( W i l l i a m s o n Co.)

Organic Sulfur

% Ash 12.8 11.4 10.3 7.1

2.19 1.97 1.20 0.96

F i g u r e s 2 and 3 i n d i c a t e t h e s u l f u r r e d u c t i o n o b t a i n e d w i t h i n c r e a s i n g r e t e n t i o n t i m e and up t o t h r e e p a s s e s t h r o u g h t h e magnet u s i n g wet s e p a r a t i o n methods. F i g u r e 4 shows t h e s u l f u r reduction obtained using a dry separation technique. The d a t a show t h a t t h e b e s t r e s u l t s a s f a r a s s u l f u r r e d u c t i o n i s c o n c e r n e d were a t t a i n e d u s i n g a s l u r r y and t h r e e p a s s e s t h r o u g h t h e magnet, e a c h w i t h a r e t e n t i o n t i m e o f 30 s e c . T a b l e I I i s a summary o f t h e s u l f u r r e d u c t i o n o b t a i n e d u s i n g b o t h wet and d r y s e p a r a t i o n methods w i t h -200 mesh s a m p l e s . Table I I . S u l f u r Reduction

Coal Indiana Indiana Indiana Indiana Indiana Indiana Illinois Illinois Illinois Illinois Illinois Illinois a

Total S i n Product

Total S V V V VI VI VI V V V VI VI VI

3.00 3.30 3.78 2.30 2.45 3.31 1.96 2.18 2.87 1.15 1.29 1.57

4.63 4.63 4.63 4.17 4.17 4.17 3.59 3.59 3.59 1.98 1.98 1.98

Wet-three passes ;

a

b

c

a

b

e

D

a

b

e

a

b

e

(%)

Inorganic S i n Product 0.81 1.11 1.59 0.10 0.25 1.01 0.83 0.99 1.67 0.21 0.32 0.61

120-sec r e t e n t i o n ;

e

/'ζ I n o r g a n i c S Removed

dry- - t h r e e

)I A s h 6.4 7.9 9.2 6.2 7.1 8.8 5.8 6.3 8.6 4.1 4.9 5.6

67 55 25 85 78 39 65 59 30 79 69 40 passes


116



T O P VIEW

SLURRY OUT MAGNET

STEEL

ΙI

v

~

" *

ELECTRIC POWER

SLURRY

IN

SIDE V I E W SECTION THRU MAGNET

Figure 1.

Diagrammatic side and top view of HEMF

5.0

unit

I-

4.0

Figure 2. Sulfur content after I, 2, and 3 passes at 30 sec retention each (wet)

Control

ι 2 Number of Passes


9.

MURRAY


EXPLANATION • Coal V , Warrick C o . , Ind. A Coal V I , Warrick C o . , Ind. Ο


Coal V , Wabash C o . , III.

Δ Control

30

60

90

120

Coal V I , Williamson C o . , III.

Retention T i m e (seconds)

Figure 3.

Sulfur content wtih increasing retention time (wet)


117

118


One sample o f C o a l V f r o m I n d i a n a was p u l v e r i z e d so t h a t 90% o f i t s p a r t i c l e s p a s s e d 325 mesh and u s i n g 3 p a s s e s w i t h 3 0 - s e c r e t e n t i o n e a c h , 93% o f t h e p y r i t i c s u l f u r was removed. Further t e s t s on f i n e g r i n d i n g and o p t i m i z a t i o n o f the t e s t c o n d i t i o n s a r e now b e i n g c a r r i e d o u t i n t h e a u t h o r ' s l a b o r a t o r i e s . I n a d d i t i o n to the s u l f u r r e d u c t i o n , ash r e d u c t i o n i s b e i n g measured. The l o s s o f c o a l i n t h e m a g n e t i c f r a c t i o n s v a r i e d f r o m 6 t o 14% and i s r e l a t e d t o t h e s i z e and d i s t r i b u t i o n o f t h e p y r i t e i n t h e coal.


Economics Q u i n l a n and V e n k a t e s a n (15) r e c e n t l y d i s c u s s e d t h e e c o n o m i c s of c o a l p r e p a r a t i o n c o a l c l e a n i n g processes comparing j i g versus heavy media p l a n t c i r c u i t s . The o p e r a t i n g c o s t o f the j i g p l a n t was $0.85 p e r c l e a n t o n and f o r t h e h e a v y m e d i a c i r c u i t $1.25 per c l e a n ton. The c a p a c i t y o f e a c h was 500 TPH, and t h e c a p i t a l c o s t o f t h e j i g c i r c u i t was $6,000,000 and f o r t h e h e a v y m e d i a c i r c u i t $8,500,000. To d e s i g n a c l e a n i n g c i r c u i t t o p r o d u c t 500 TPH o f c o a l w o u l d r e q u i r e f i v e 8 4 - i n . magnets. The c a p i t a l c o s t ( i n s t a l l e d ) w o u l d be a p p r o x i m a t e l y $8,000,000. Table I I I . Operating

Costs

o f HEMF F o r 500 C o s t p e r Hour

A m o r t i z a t i o n of i n s t a l l e d s e p a r a t o r s o v e r 10 y e a r s , 80,000 h r . Magnet power (2000 kW @2c kW-h) Pumping and f l u s h i n g power (1000 kW @2ç kW-h) Labor Maintenance Total

Tons/hr.

Capacity

Cost per

$100. .00

$0. 20

40. ,00

0. 08

20. .00

0. 04

15. .00 10. .00

0. 03 0. 02

185, .00

0. 37

Ton

The c o s t p e r t o n o f m a g n e t i c c l e a n i n g i s r e l a t i v e l y l o w compared w i t h t h e o t h e r two methods c i t e d . In a d d i t i o n to the p o t e n t i a l r e m o v a l o f 70 - 90% o f the i n o r g a n i c s u l f u r , t h e a s h c o n t e n t o f t h e c o a l w o u l d be s u b s t a n t i a l l y r e d u c e d . A h i g h p e r c e n t a g e of the f o l l o w i n g i m p u r i t i e s , i f p r e s e n t , i n a d d i t i o n t o p y r i t e , w o u l d be removed m a g n e t i c a l l y b e c a u s e a l l o f t h e s e m i n e r a l s and r o c k s have a mass s u s c e p t i b i l i t y h i g h e r t h a n p y r i t e except f o r limestone: s i d e r i t e , l i m o n i t e , f e r r o u s and f e r r i c s u l f a t e , l i m e s t o n e , c l a y and s h a l e , and s a n d . Much a d d i t i o n a l r e s e a r c h and d e v e l o p m e n t work must be done to s u b s t a n t i a t e the p r e l i m i n a r y r e s u l t s r e p o r t e d i n t h i s paper. S e v e r a l s t u d i e s a r e underway i n t h e a u t h o r ' s l a b o r a t o r i e s a t


9.

MURRAY


119

Indiana University. S i n c e c o a l i s t o become t h e m a j o r e n e r g y s o u r c e i n t h e U.S. i n t h e f o r e s e e a b l e f u t u r e , m a g n e t i c c l e a n i n g o f c o a l l o o k s a s i f i t w i l l be a v i a b l e method o f p r o c e s s i n g which can provide a l o w - s u l f u r , low-ash c o a l .


Conclusions H i g h e x t r a c t i o n m a g n e t i c f i l t r a t i o n (HEMF) i s a p r o v e n comm e r c i a l p r o c e s s used e x t e n s i v e l y i n t h e p r o c e s s i n g o f k a o l i n . F i n e p u l v e r i z a t i o n t o -200 mesh o r p r e f e r a b l y t o -325 mesh t o l i b e r a t e t h e p y r i t e f r o m t h e c o a l i s n e c e s s a r y t o a c h i e v e optimum separation. From 65 - 9 0 % o f t h e i n o r g a n i c s u l f u r c a n b e s e p a r a t e d from a c o a l s l u r r y b y HEMF p r o c e s s i n g . The e s t i m a t e d c o s t p e r t o n i s l o w and compares f a v o r a b l y w i t h o t h e r methods o f p y r i t e removal. The r e s u l t a n t c o a l p r o d u c t f r o m t h e HEMF p r o c e s s i s r e l a t i v e l y c l e a n o f i n o r g a n i c s u l f u r and a s h c o n t e n t .

Abstract High extraction magnetic filtration (HEMF) has potential application to remove a high percentage of inorganic pyritic sulfur from coal. Newly developed high intensity separators with high intensity (20 kG) and high gradient collectors can remove up to 90% of the pyritic sulfur under optimum conditions. A canister filled with a filamentary matrix of sharp stainless steel screens provides high gradients and pyrite in pulverized coal (-200 mesh) will be attracted and held. Coal is diamagnetic, and pyrite is paramagnetic, and if the pyrite can be liberated from the coal, it can be magnetically filtered out in commercial practice. Coals V and VI from Indiana and Illinois were used for this study. These coals have a total sulfur content of between 1.98 and 4.63% of which approximately 60% is pyritic sulfur. Both dry and wet magnetic separation methods were used. Wet methods were more successful in that up to 90% of the pyrite was removed whereas the best results from the dry separation was 40% removal. The cost per ton of a 500 ton/hr installation would be of the order of $0.50 per ton and would produce a relatively low-sulfur, low-ash product. Literature Cited 1. 2. 3.

Iannicelli, J., "High Extraction Magnetic Filtration of Kaolin Clay," Clays Clay Miner., (1976) 24, 64-68. Iannicelli, J., "Assessment of High Extraction Magnetic Filtration," Special Report-RANN-National Science Foundation (1974). Murray, H.H., "Beneficiation of Selected Industrial Minerals and Coal by High Intensity Magnetic Separation," IEEE Trans. Magn., (1976) MAG-12, 498-502.


120 4. 5. 6. 7.


8. 9. 10. 11. 12. 13. 14. 15.

COAL DESULFURIZATION Murray, H.H., "High Intensity Magnetic Beneficiation of Industrial Minerals-Α Survey," Preprint 76-H-93 Amer. Inst. Min. Engrs. (1976). Murray, H.H., "High Intensity Magnetic Cleaning of Bituminous Coal," Proc. National Coal Research Symposium - Louisville, Ky., pp 74-81, Oct. 1976. Siddiqui, S., "Desulfurization and Concentration of Coal," German Patent 1,005,012, 1957. Yurovsky, A.Z., Remesnikov, I.D., "Thermomagnetic Method of Concentrating and Desulfurizing Coal," Coke Chem. (1958) 12, 8-13. Perry, Η., "Potential for Reduction of Sulfur in Coal by Other Than Conventional Cleaning Methods," SymposiumEconomics of Air Pollution Control, AICHE 59th Nat. Meeting 1966. Kester, W.M., Jr., "Magnetic Demineralization of Pulverized Coal," Mining Eng. (1965) 17. Kester, W.M., Jr., "The Effect of High Intensity Magnetic Cleaning on Pulverized High Sulfur, Bituminous Coals," Thesis, School of Mines, West Virginia Univ., 1966. Gluskoter, H.J., Simon, J.A., "Sulfur in Illinois Coals," Ill. State Geol. Surv., Circ. (1968) 432. Kester, W.M., Jr., Leonard, J.W., Wilson, E.B., "Reduction of Sulfur from Steam Coal by Magnetic Methods," Tech. Report 31, Coal Research Bureau, West Virginia Univ. (1967). Wooster, W.A., Wooster, Ν., "The Magnetic Properties of Coal," Bull. British Coal Utilization Research Assoc. (1944). Kindig, J.K., Turner, R.L., "Dry Chemical Process to Magnetize Pyrite and Ash for Removal from Coal," AIME Preprint 76-F-306 (1976). Quinlan, R.M., Venkatesan, S., "Economics of Coal Prepara tion" AIME Preprint 76-F-108 (1976).

This study was supported by a grant from the Electric Power Research Institute. The chemical analyses were done by Nily Sofer in the chemistry lab, Geology Department at Indiana University.


10 Desulfurization of Coals by High-Intensity High-Gradient Magnetic Separation: Conceptual Process Design and Cost


Estimation

C. J. LIN and Y. A. LIU Magnetochemical Engineering Laboratory, Department of Chemical Engineering, Auburn University, Auburn, AL 36830 It is well known that the main difficulty in increasing the utilization of coal in the United States lies in the pollution problem, and emission levels of sulfur oxides and ash particles from coal burning facilities must be reduced to meet stringent environmental standards. Although the particulate emission standards can generally be met by using electrostatic precipitators, there apparently exists no accepted technology for controlling sulfur oxide emissions in flue gases (1). Thus, there has been a growing effort recently to develop effective and economical alternatives to flue gas desulfurization. One of the most attractive alternatives is the precombustion cleaning of coal. Several new physical and chemical methods for removing sulfur and ash from coal prior to its combustion have already been proposed and are currently under intensive further development (2). An important physical method for cleaning coal that appears to hold much promise is the well established magnetic separation technique. Previous experimental investigations have indicated clearly that most of the mineral impurities in coal which contribute to the pyritic sulfur, the sulfate sulfur, and the ash content are paramagnetic. These sulfur-bearing and ash-forming minerals, if sufficiently liberated as discrete particles, can be separated from the pulverized diamagnetic coal by magnetic means (3-8). Indeed, the technical feasibility of the magnetic cleaning of coal has been demonstrated in a number of previous studies, with substantial amounts of sulfur and ash removal reported (9,10). D u r i n g t h e past few y e a r s , the magnetic c l e a n i n g o f c o a l has b e e n g i v e n new i m p e t u s w i t h t h e i n t r o d u c t i o n o f a new l e v e l o f magnetic separation technology, t h e h i g h - i n t e n s i t y h i g h - g r a d i e n t m a g n e t i c s e p a r a t i o n (HGMS). The HGMS t e c h n o l o g y was d e v e l o p e d a r o u n d 1969 f o r t h e wet s e p a r a t i o n o f f e e b l y m a g n e t i c c o n t a m i n a n t s f r o m k a o l i n c l a y ( 1 1 - 1 7 ) . A t y p i c a l HGMS u n i t f o r t h i s wet a p p l i c a t i o n i s shown s c h e m a t i c a l l y a s F i g u r e l a . The e l e c t r o m a g n e t s t r u c t u r e c o n s i s t s o f e n e r g i z i n g c o i l s and a s u r r o u n d i n g i r o n enclosure. The c o i l s i n t u r n e n c l o s e a c y l i n d r i c a l , h i g h l y magn e t i z a b l e w o r k i n g volume p a c k e d w i t h f i n e s t r a n d s o f s t r o n g l y

121



122

COAL

DESULFURIZATION

f e r r o m a g n e t i c p a c k i n g m a t e r i a l such a s f e r r i t i c s t a i n l e s s s t e e l wool. W i t h t h i s d e s i g n , a s t r o n g f i e l d i n t e n s i t y o f 20 kOe c a n be g e n e r a t e d and d i s t r i b u t e d u n i f o r m l y t h r o u g h o u t t h e w o r k i n g v o l u m e . F u r t h e r m o r e , by p l a c i n g i n t h e u n i f o r m m a g n e t i c f i e l d t h e f e r r o m a g n e t i c p a c k i n g m a t e r i a l s w h i c h i n c r e a s e and d i s tort the f i e l d i nt h e i r v i c i n i t y , large f i e l d gradients of the o r d e r o f 1-10 kOe/pmcan be p r o d u c e d . I n t h e wet b e n e f i c i a t i o n o f k a o l i n c l a y , t h e HGMS u n i t i s u s e d i n a b a t c h o r c y c l i c a l l y o p e r a ted p r o c e s s l i k e a f i l t e r . The k a o l i n f e e d c o n t a i n i n g t h e f e e b l y m a g n e t i c c o n t a m i n a n t s i n l o w c o n c e n t r a t i o n s i s pumped t h r o u g h t h e s t a i n l e s s s t e e l wool p a c k i n g o r m a t r i x o f t h e s e p a r a t o r from t h e b o t t o m w h i l e t h e magnet i s on. The m a g n e t i c m a t e r i a l s (mags) a r e c a p t u r e d and r e t a i n e d i n s i d e t h e s e p a r a t o r m a t r i x , and t h e n o n m a g n e t i c components ( t a i l s ) p a s s t h r o u g h t h e s e p a r a t o r m a t r i x and a r e c o l l e c t e d a s t h e b e n e f i c i a t e d p r o d u c t s f r o m t h e t o p o f t h e magnet. A f t e r some t i m e o f o p e r a t i o n , t h e s e p a r a t o r m a t r i x i s f i l l e d t o i t s l o a d i n g c a p a c i t y . The f e e d i s t h e n s t o p p e d , and the s e p a r a t o r m a t r i x i s r i n s e d w i t h water. F i n a l l y , t h e magnet i s t u r n e d o f f , and t h e mags r e t a i n e d i n s i d e t h e s e p a r a t o r m a t r i x a r e backwashed w i t h w a t e r and c o l l e c t e d . The w h o l e p r o c e d u r e i s repeated i n a c y c l i c f a s h i o n . I n general, i f t h i s batch process i s u s e d i n o t h e r wet a p p l i c a t i o n s where t h e m a g n e t i c m a t e r i a l s o c c u p y a l a r g e f r a c t i o n o f t h e f e e d s t r e a m , t h e down t i m e f o r b a c k w a s h i n g w i l l be c o n s i d e r a b l e , p o s s i b l y n e c e s s i t a t i n g t h e u s e o f one o r more b a c k - u p s e p a r a t o r s . To overcome t h i s p r o b l e m w h i c h i s inherent i n batch operations, a continuous process using a m o v i n g m a t r i x HGMS u n i t , c a l l e d t h e C a r o u s e l s e p a r a t o r , h a s been p r o p o s e d ( 1 2 , 15-17) a s shown s c h e m a t i c a l l y i n F i g u r e l b . A numb e r o f p i l o t - s c a l e s t u d i e s o f t h e wet b e n e f i c i a t i o n o f k a o l i n c l a y and i r o n o r e s u s i n g t h e C a r o u s e l s e p a r a t o r have b e e n r e p o r t e d (17). B e c a u s e o f t h e v e r y l o w c o s t s and t h e o u t s t a n d i n g t e c h n i c a l p e r f o r m a n c e o f HGMS d e m o n s t r a t e d i n t h e k a o l i n a p p l i c a t i o n , HGMS was r e c e n t l y a d a p t e d i n a b e n c h - s c a l e e x p l o r a t o r y s t u d y (8) t o remove s u l f u r and a s h f r o m a f i n e l y p u l v e r i z e d B r a z i l i a n c o a l suspended i n w a t e r . S i n c e t h e n , o t h e r i n v e s t i g a t o r s have u t i l i zed p i l o t - s c a l e HGMS u n i t s t o d e s u l f u r i z e and d e a s h w a t e r s l u r r i e s o f some E a s t e r n U.S. c o a l s . F o r i n s t a n c e , r e s u l t s o f p i l o t - s c a l e s t u d i e s that demonstrated t h e t e c h n i c a l f e a s i b i l i t y o f t h e m a g n e t i c s e p a r a t i o n o f s u l f u r and a s h f r o m w a t e r s l u r r i e s o f p u l v e r i z e d I l l i n o i s No. 6, I n d i a n a No. 5 and No. 6, K e n t u c k y No. 9/14, P e n n s y l v a n i a Upper F r e e p o r t and Lower K i t t a n n i n g c o a l s h a v e been r e p o r t e d ( 4 - 7 , 1 8 , 1 9 ) . I n p a r t i c u l a r , the q u a n t i t a t i v e e f f e c t s o f major s e p a r a t i o n v a r i a b l e s such as f i e l d i n t e n s i t y , r e s i d e n c e t i m e , e t c . , o n t h e g r a d e , r e c o v e r y and c o n c e n t r a t i o n breakthrough f o r the magnetic s e p a r a t i o n o f s u l f u r and a s h f r o m a w a t e r s l u r r y o f p u l v e r i z e d I l l i n o i s No. 6 c o a l have been e s t a b l i s h e d e x p e r i m e n t a l l y , and c a n be p r e d i c t e d s a t i s f a c t o r i l y by a n e w l y d e v e l o p e d m a t h e m a t i c a l m o d e l f o r HGMS ( 4 , 5 , 7 , 1 3 , 1 8 ) . D e p e n d i n g upon t h e t y p e s o f c o a l and t h e s e p a r a t i o n


L I N A N D Liu

High-Intensity and -Gradient Magnetic Separation


CLEANED

TAILINGS OUT

Figure 1.

(a) (above) Cyclic high-gradient magnetic separator; (b) (below) carousel high-gradient magnetic separator



124


c o n d i t i o n s u s e d , t h e e x i s t i n g b e n c h - a n d p i l o t - s c a l e r e s u l t s have shown t h a t t h e u s e o f s i n g l e - p a s s HGMS was e f f e c t i v e i n r e d u c i n g t h e t o t a l s u l f u r by 4 0 - 5 5 % , t h e a s h by 35-45%, and t h e p y r i t i c s u l f u r b y 80-90%, w h i l e a c h i e v i n g a maximum r e c o v e r y o f a b o u t 95% ( 1 0 , 1 8 ) . These a v a i l a b l e r e s u l t s have i n d i c a t e d a l s o t h a t b o t h t h e g r a d e and r e c o v e r y o f t h e s e p a r a t i o n c a n be enhanced g e n e r a l l y w i t h the u s e o f a l a r g e r s e p a r a t o r m a t r i x o r by t h e recycle of thet a i l products. Further detailed review of the r e p o r t e d r e s u l t s on t h e m a g n e t i c c l e a n i n g o f p u l v e r i z e d c o a l s i n w a t e r s l u r r i e s c a n be found i n t h e l i t e r a t u r e ( 9 , 1 0 , 1 8 ) . These p u b l i s h e d d a t a and o t h e r r e c e n t a n a l y s e s (2,10,18,20^24) have i n d i c a t e d t h a t a s i g n i f i c a n t p o r t i o n o f t h e U.S. c o a l r e s e r v e s , l o w enough i n o r g a n i c s u l f u r , c a n be m a g n e t i c a l l y c l e a n e d f o r u s e as a n e n v i r o n m e n t a l l y a c c e p t a b l e , l o w s u l f u r f u e l . i t has been e s t i m a t e d t h a t 100 m i l l i o n s h o r t t o n s o f U.S. c o a l s p e r y e a r may be m a g n e t i c a l l y c l e a n e d . T h i s amounts t o o v e r 1 7 % o f t h e t o t a l U.S. p r o d u c t i o n p e r y e a r ( 1 0 ) . A l t h o u g h t h e e x i s t i n g d a t a have n o t y e t e s t a b l i s h e d t o t a l d e a s h i n g b y m a g n e t i c means, t h e r e i s some i n d i c a t i o n t h a t b y o p t i m i z i n g t h e s e p a r a t i o n c o n d i t i o n s , and e n h a n c i n g t h e m a g n e t i s m o f a s h - f o r m i n g m i n e r a l s , e t c . , t h e e f f e c t i v e n e s s o f m a g n e t i c s e p a r a t i o n o f a s h f r o m c o a l c a n be i m p r o v e d (10) . R e c e n t s t u d i e s (4,5,9,10,25-27) have a l s o s u g g e s t e d t h a t c o a l c l e a n i n g b y HGMS c o u l d s e r v e a s a s i g n i f i c a n t a d j u n c t t o coal l i q u e f a c t i o n processes. In particular, thetechnical feasib i l i t y o f a d a p t i n g HGMS a s a n e f f e c t i v e a l t e r n a t i v e t o convent i o n a l p r e c o a t f i l t r a t i o n i n t h e s o l v e n t r e f i n e d c o a l (SRC) p r o c e s s h a s a l r e a d y b e e n d e m o n s t r a t e d by a b e n c h - s c a l e , e x p l o r a t o r y s t u d y done a t H y d r o c a r b o n R e s e a r c h , I n c . ( H R I ) . HGMS e f f e c t i v e l y removed up t o 9 0 % o f t h e i n o r g a n i c s u l f u r f r o m t h e l i q u e f i e d SRC f i l t e r f e e d s l u r r y o f I l l i n o i s No. 6 c o a l , and a b o u t h a l f o f t h e e x p e r i m e n t a l r u n s c o n d u c t e d by HRI i n d i c a t e d o v e r 8 7 % i n o r g a n i c s u l f u r removal (6,15,26). I n g e n e r a l , t h e work done by HRI showed t h a t HGMS was l e s s e f f e c t i v e i n a s h r e m o v a l b u t d i d remove 25-35% o f t h e a s h . Q u i t e r e c e n t l y , a p i l o t - s c a l e HGMS s y s t e m t o remove m i n e r a l r e s i d u e f r o m l i q u e f i e d c o a l h a s b e e n d e s i g n e d and c o n s t r u c t e d by t h e a u t h o r s ( 5 , 2 5 ) . Typical results f r o m e x p e r i m e n t s c o n d u c t e d w i t h t h e l i q u e f i e d SRC f i l t e r f e e d s l u r r y o f K e n t u c k y No. 9/14 and I l l i n o i s M o n t e r e y c o a l s have been q u i t e e n c o u r a g i n g , i n d i c a t i n g t h a t HGMS c o u l d r e d u c e t h e t o t a l s u l f u r , a s h and p y r i t i c s u l f u r c o n t e n t s by a s much a s 7 0 , 76, and 95%, r e s p e c t i v e l y . A v a i l a b l e d a t a from the above benchand p i l o t - s c a l e i n v e s t i g a t i o n have showed a l s o t h a t a n even g r e a t e r d e a s h i n g o f t h e l i q u e f i e d SRC f i l t e r f e e d c a n be a c h i e ved b y i m p r o v e d s e p a r a t i o n c o n d i t i o n s . A d e t a i l e d d i s c u s s i o n o f t h e s e r e s u l t s a l o n g w i t h t h e i r t e c h n i c a l i m p l i c a t i o n s c a n be found i n the l i t e r a t u r e (10,25,27). Furthermore, c l o s e examinat i o n o f t h e i n h e r e n t p h y s i c a l and c h e m i c a l c h a r a c t e r i s t i c s o f the hydrogenated products p r i o r t o t h e f i l t r a t i o n step i n the SRC and o t h e r r e l a t e d l i q u e f a c t i o n p r o c e s s e s i n d i c a t e s t h a t HGMS



10.

L I N A N D Liu


may be d e v e l o p e d a s a p r a c t i c a l m i n e r a l r e s i d u e s e p a r a t i o n method. Hydrogénation w i l l g e n e r a l l y r e d u c e a m a j o r p o r t i o n o f t h e p y r i t i c s u l f u r t o t h e h i g h l y m a g n e t i c p y r r h o t i t e ; and t h e s u l f u r b e a r i n g and a s h - f o r m i n g m i n e r a l s t e n d t o be l i b e r a t e d more e a s i l y f r o m t h e d i s s o l v e d o r g a n i c components i n t h e f i l t e r f e e d s l u r r y t h a n f r o m p u l v e r i z e d c o a l suspended i n w a t e r . A l s o , t h e t y p i c a l mean p a r t i c l e s i z e o f t h e f i l t e r f e e d sample i s o f t e n l e s s t h a n 5 m i c r o n s , w h i c h d i c t a t e s t h e u s e o f s e p a r a t i o n methods l i k e HGMS c a p a b l e o f h a n d l i n g m i c r o n - s i z e m a t e r i a l s . A l l o f these f a c t o r s seem t o s u g g e s t a v e r y s i g n i f i c a n t p o t e n t i a l f o r u t i l i z i n g HGMS t o remove m i n e r a l r e s i d u e s f r o m l i q u e f i e d c o a l . F o r c e r t a i n t y p e s o f c o a l , e v e n w i t h o u t f u r t h e r improvement i n t h e m a g n e t i c r e m o v a l o f a s h , m a g n e t i c a l l y c l e a n e d SRC w o u l d be a c c e p t a b l e f o r u s e a s a f e e d t o b o i l e r s w h i c h a l r e a d y have e l e c t r o s t a t i c p r e c i p i t a t o r s (28). T h i s f o l l o w s because t h e c o s t o f s o l i d - l i q u i d s e p a r a t i o n i n c o a l l i q u e f a c t i o n i s g e n e r a l l y subs t a n t i a l , and m o d e r a t e l y l o w - a s h SRC s h o u l d be l e s s e x p e n s i v e (27-29). Indeed, a p r e l i m i n a r y c o s t e s t i m a t e f o r the magnetic d e s u l f u r i z a t i o n o f l i q u e f i e d c o a l b a s e d on t h e l a b o r a t o r y d a t a o b t a i n e d by HRI seems t o s u p p o r t t h i s o b s e r v a t i o n ( 2 7 ) . The p r e c e d i n g d i s c u s s i o n h a s i n d i c a t e d t h a t t h e s c i e n t i f i c and t e c h n i c a l f e a s i b i l i t y o f m a g n e t i c d e s u l f u r i z a t i o n o f b o t h c o a l / w a t e r s l u r r y and l i q u e f i e d c o a l h a s b e e n w e l l established. R e c e n t l y , s e v e r a l e s t i m a t e s o f the c o s t o f m a g n e t i c d e s u l f u r i z a t i o n have b e e n r e p o r t e d i n t h e l i t e r a t u r e ( 8 , 1 4 , 1 9 , 2 2 , 2 7 ) . B e c a u s e o f t h e s i m p l i f y i n g a s s u m p t i o n s i n v o l v e d , as w e l l a s t h e t e c h n i c a l p e r f o r m a n c e s p e c i f i e d and t h e e s t i m a t i o n methods u s e d , t h e r e s u l t s seem t o be somewhat a p p r o x i m a t e i n n a t u r e . In this p a p e r , t h e l a t e s t d a t a f r o m p i l o t - s c a l e s t u d i e s o f s u l f u r and a s h r e m o v a l f r o m b o t h l i q u e f i e d c o a l and c o a l / w a t e r s l u r r y by HGMS a r e used t o d e s i g n c o n c e p t u a l p r o c e s s e s f o r m a g n e t i c d e s u l furization of coal. Estimates o f magnetic d e s u l f u r i z a t i o n chara c t e r i s t i c s and c o n c e p t u a l p r o c e s s r e q u i r e m e n t s a s w e l l a s i n s t a l l a t i o n and p r o c e s s i n g c o s t s a r e p r e s e n t e d . In particular, t h e e x t e n t t o w h i c h t h e p r o c e s s i n g c o n d i t i o n s c a n a f f e c t magnet i c d e s u l f u r i z a t i o n c o s t s i s examined. F i n a l l y , t h e r e s u l t s a r e compared w i t h o t h e r a p p r o a c h e s f o r the d e s u l f u r i z a t i o n o f coal. Magnetic D e s u l f u r i z a t i o n

o f Coal/Water S l u r r y :

P r o c e s s and C o s t s

A c o n c e p t u a l p r o c e s s f o r the magnetic d e s u l f u r i z a t i o n o f p u l v e r i z e d c o a l suspended i n w a t e r by HGMS i s shown s c h e m a t i c a l l y i n F i g u r e 2. A c o a l s l u r r y o f a f i x e d c o n c e n t r a t i o n i s p r e p a r e d f i r s t by m i x i n g known amounts o f p u l v e r i z e d c o a l , w a t e r , and a dispersant (wetting agent) l i k e Alconox. The HGMS u n i t used h e r e i s t h e l a r g e s t c o m m e r c i a l u n i t now i n u s e f o r p r o d u c i n g h i g h q u a l i t y paper c o a t i n g c l a y s . I t i s operated at a f i x e d f i e l d i n t e n s i t y o f 20 kOe g e n e r a t e d i n a n open volume 7 f t i n d i a m e t e r and 20 i n . l o n g . A s t a i n l e s s s t e e l w o o l s e p a r a t o r m a t r i x h a v i n g


125


126


94% v o i d s i s p l a c e d i n t h e open v o l u m e . The c o a l s l u r r y i s pumped t h r o u g h t h e e n e r g i z e d s e p a r a t o r m a t r i x a t a f i x e d r e s i dence time ( f l o w v e l o c i t y ) u n t i l the m a t r i x reaches i t s l o a d i n g capacity. A f t e r r i n s i n g w i t h w a t e r , t h e mags a r e s e n t t o a s e t t l i n g pond o r a c l a r i f i e r t o r e c o v e r w a t e r f o r r e - u s e . The t a i l s a r e c o l l e c t e d , d e w a t e r e d , and d r i e d . The s p e c i f i c a t i o n s o f p r o c e s s s t r e a m s f o r a t y p i c a l c a s e (Case Β i n T a b l e I ) a r e a l s o i n c l u d e d i n F i g u r e 2, and t h e d e t a i l e d o p e r a t i n g c o n d i t i o n s for such a case are g i v e n i n the Appendix. By r e m o v i n g 80-90% o f t h e p y r i t i c s u l f u r m a g n e t i c a l l y and a c h i e v i n g 85-90% r e c o v e r y as was d e m o n s t r a t e d by t h e r e s u l t s o f r e p o r t e d s t u d i e s of magnetic d e s u l f u r i z a t i o n of p u l v e r i z e d c o a l s i n w a t e r s l u r r i e s ( 4 - 1 0 , 1 3 , 1 8 , 1 9 ) , t h e p r o c e s s c a n be u s e d to c l e a n a b o u t o n e - f i f t h o f t h e r e c o v e r a b l e U.S, c o a l s w i t h a low o r g a n i c s u l f u r c o n t e n t o f 0.7-0.9 wt % t o p r o d u c e a n e n v i r o n mentally acceptable f u e l . A d e t a i l e d documentation of the r e s e r v e s and p r o d u c t i o n o f U.S. c o a l s w h i c h may be m a g n e t i c a l l y c l e a n a b l e t o 1 wt% t o t a l s u l f u r a c c o r d i n g t o t h e seam, d i s t r i c t and c o u n t y i n e a c h s t a t e , a l o n g w i t h t h e t o t a l and o r g a n i c s u l f u r c o n t e n t s c a n be f o u n d i n t h e l i t e r a t u r e ( 2 1 ) . H e r e , a r e a s o n a b l e r a n g e o f add-on c o s t s ( e x c l u d i n g t h o s e f o r g r i n d i n g , d e w a t e r i n g and d r y i n g and r e f u s e d i s p o s a l ) i s e s t i mated f o r t h e wet m a g n e t i c c l e a n i n g o f c o a l s l u r r i e s w h i c h have d e s u l f u r i z a t i o n c h a r a c t e r i s t i c s s i m i l a r to those r e p o r t e d i n the r e c e n t s t u d i e s ( 4 - 1 0 , 1 3 , 1 8 , 1 9 ) . The method used t o e s t i m a t e t h e c o s t s o f m a g n e t i c d e s u l f u r i z a t i o n i s b a s e d on t h e t e c h n i q u e u s e d by t h e F e d e r a l Power C o m m i s s i o n S y n t h e t i c G a s - C o a l F o r c e t o e s t i m a t e t h e c o s t o f s y n t h e s i s gas (29, 3 4 ) . The i n v e s t o r c a p i t a l i z a t i o n method u s e d i n t h i s a p p r o a c h i s t h e d i s c o u n t c a s h f l o w (DCF) f i n a n c i n g method w i t h assumed DCF r a t e s o f r e t u r n s u c h as 15% a f t e r t a x e s . T h i s method e s s e n t i a l l y d e t e r m i n e s t h e a n n u a l r e v e n u e d u r i n g t h e p l a n t l i f e w h i c h w i l l g e n e r a t e a DCF equal t o the t o t a l c a p i t a l i n v e s t m e n t f o r the p l a n t . Several m a j o r a s s u m p t i o n s a r e i n c l u d e d i n t h e method ( 2 9 , 3 4 ) : (1) The p l a n t l i f e i s assumed t o be 20 y e a r s w i t h no c a s h v a l u e a t t h e end o f l i f e . (2) A s t r a i g h t - l i n e method i s u s e d t o c a l c u l a t e t h e a n n u a l d e p r e ciation. (3) O p e r a t i n g c o s t s and w o r k i n g c a p i t a l r e q u i r e m e n t s a r e assumed to be c o n s t a n t d u r i n g t h e c o n s t r u c t i o n p e r i o d , and 100% e q u i t y c a p i t a l i s assumed. (4) T o t a l p l a n t i n v e s t m e n t , r e t u r n on i n v e s t m e n t d u r i n g t h e p l a n t l i f e , and w o r k i n g c a p i t a l a r e t r e a t e d as c a p i t a l c o s t s i n year zero (the year ending w i t h the c o m p l e t i o n of s t a r t - u p operations). (5) S t a r t - u p c o s t s a r e t r e a t e d as an e x p e n s e i n y e a r z e r o . (6) 48% f e d e r a l income t a x i s assumed. Based on t h e s e a s s u m p t i o n s , e q u a t i o n s f o r c a l c u l a t i n g t h e u n i t c o s t s ($ p e r t o n o f c o a l p r o c e s s e d ) a r e s u g g e s t e d by t h e p u b l i s h e d documents ( 2 9 , 3 4 ) . They a r e summarized i n t h e A p p e n d i x , i n w h i c h



10.

L I N A N D Liu


t h e d e t a i l e d o p e r a t i n g c o n d i t i o n s and e s t i m a t e d c o s t s f o r a t y p i c a l example shown i n F i g u r e 2 a r e a l s o g i v e n . The c o s t s o f m a j o r i n s t a l l e d equipment and t h e u n i t c o s t s l i s t e d i n t h e A p p e n d i x a r e based o n v a l u e s a s o f June 1976. For instance, the costs of pump and t a n k u s e d were e s t i m a t e d f i r s t a c c o r d i n g t o R e f . 3^5 and t h e n b r o u g h t up t o d a t e by m u l t i p l y i n g by t h e CE p l a n t c o s t index r a t i o o f (205/113.6), w h i l e the c o s t o f t h e i n s t a l l e d HGMS u n i t w i t h a s e p a r a t o r m a t r i x 7 f t i n d i a m e t e r and 20 i n . l o n g was e s t i m a t e d t o be $1.936 m i l l i o n ( 2 6 ) . The e s t i m a t e d c a p i t a l i n v e s t m e n t and u n i t c o s t s f o r f o u r t y p i c a l c a s e s , d e s i g n a t e d a s A-D, a r e summarized i n T a b l e I . S l u r r y v e l o c i t i e s o f 2.61 and 4.0 cm/sec, s l u r r y c o n c e n t r a t i o n s o f 15,25 and 35 wt%, a s w e l l a s s e p a r a t i o n d u t y c y c l e s o f 59,077.9% a r e c o n s i d e r e d . These s e p a r a t i o n c o n d i t i o n s i l l u s t r a t e c l e a r l y t h e e f f e c t s o f s l u r r y v e l o c i t y and c o n c e n t r a t i o n a s w e l l as s e p a r a t i o n d u t y c y c l e . F o r i n s t a n c e , c o m p a r i s o n o f c a s e s A t o C shows t h a t a t t h e same s l u r r y v e l o c i t y and s i m i l a r magnet i c d e s u l f u r i z a t i o n c h a r a c t e r i s t i c s the h i g h e r t h e s l u r r y conc e n t r a t i o n , t h e c h e a p e r w i l l be t h e i n v e s t m e n t and u n i t c o s t s . W h i l e t h i s o b s e r v a t i o n i s t o be e x p e c t e d , t h e r e h a v e been p i l o t s c a l e t e s t s which i n d i c a t e that i n c r e a s i n g the s l u r r y concent r a t i o n o f p u l v e r i z e d I l l i n o i s No. 6 c o a l f r o m 2.57 t o 28.4 w t % d i d n o t a p p r e c i a b l y change t h e g r a d e and r e c o v e r y o f t h e s e p a r a tion. F u r t h e r e f f e c t s o f p r o c e s s i n g c o n d i t i o n s , and o t h e r c o s t f a c t o r s on the u n i t c o s t s a r e i l l u s t r a t e d i n T a b l e I I . I t i s s e e n f r o m t h e t a b l e t h a t b y d o u b l i n g t h e amount o f c o a l p r o c e s s e d p e r c y c l e r e l a t i v e t o a f i x e d amount o f s t a i n l e s s s t e e l w o o l p a c k e d i n t h e s e p a r a t o r m a t r i x , t h e u n i t c o s t c a n be r e d u c e d by a b o u t 15%. T h i s r e s u l t shows t h e i m p o r t a n c e o f t h e s e p a r a t o r m a t r i x l o a d i n g c h a r a c t e r i s t i c s on t h e c o s t s o f m a g n e t i c d e s u l furization. Another f a c t o r w h i c h a f f e c t s the u n i t c o s t s cons i d e r a b l y i s the washing time r e q u i r e d i n a complete s e p a r a t i o n cycle. T h i s i s s e e n by c o m p a r i n g i t e m s 4 and 6 i n T a b l e I I . I n p a r t i c u l a r , t h e computed r e s u l t s i n d i c a t e t h a t d o u b l i n g t h e amount o f wash w a t e r r e q u i r e d o n l y l e a d s t o n e g l i g i b l e i n c r e a s e ( 0 . 2 7 0.60%) i n u n i t c o s t s . However, i f b o t h t h e amount o f wash w a t e r and t h e w a s h i n g t i m e a r e d o u b l e d , t h e u n i t c o s t s a r e i n c r e a s e d by a b o u t 15%. The above o b s e r v a t i o n s c l e a r l y s u g g e s t a n i m p o r t a n t economic i n c e n t i v e f o r f u r t h e r p i l o t - s c a l e i n v e s t i g a t i o n o f t h e s e p a r a t o r m a t r i x l o a d i n g and w a s h i n g c h a r a c t e r i s t i c s i n the magnetic d e s u l f u r i z a t i o n o f coal/water s l u r r y . F i n a l l y , item 7 o f T a b l e I I shows t h a t l a b o r c o s t seems t o be a s i g n i f i c a n t f r a c t i o n o f the u n i t c o s t . F o r t u n a t e l y , i t i s not expected that t h e l a b o r r e q u i r e m e n t w i l l be d o u b l e d i n a c t u a l c o m m e r c i a l p r a c t i c e from the nominal case i n Table I . T h i s f o l l o w s because e x i s t i n g experience i n the commercial c l e a n i n g o f k a o l i n c l a y s by HGMS i n d i c a t e s t h a t t h e l a b o r r e q u i r e m e n t s f o r b o t h o p e r a t i o n and m a i n t e n a n c e a r e m i n i m a l ( 1 1 , 2 2 ) . In Table I I I , the r e p o r t e d c o s t s o f magnetic d e s u l f u r i z a t i o n e x p r e s s e d i n t e r m s o f t h e c a p i t a l and u n i t c o s t s ($ p e r t o n o f


127

128

COAL

Table

1. 2. 3. 4. 5. 6.


7.

I.

Cost o f D e s u l f u r i z a t i o n o f Coal/Water S l u r r y by HGMS U s i n g S e p a r a t o r M a t r i x o f 7 - F t D i a m e t e r and 2 0 - I n L e n g t h

S l u r r y v e l o c i t y (cm/sec) S l u r r y c o n c e n t r a t i o n (wt %) Coal feed rate (ton/hr) C y c l e t i m e (min) D u t y c y c l e (%) Tons o f c o a l p r o c e s s e d per c y c l e U n i t c o s t s ($ p e r t o n coal processed) U

8.

Hi 5 C a p i t a l investment per ton c o a l p r o c e s s e d p e r y e a r ($)

Table I I .

DESULFURIZATION

Case A

Case Β

Case C

Case D

2.61 15 44.77 9.00 77.9

2.61 25 66.13 6.10 67.4

2.61 35 83.07 4.85 59.0

4.0 25 89.61 4.50 59.6

6.7

6.7

6.7

6.7

2.083

2.369

1.109

1.067

1.802

1.063

0.858

0.829

3.676

2.412

1.967

1.880

6.93

4.69

3.73

3.53

S e n s i t i v i t y A n a l y s i s o f U n i t C o s t s ($ P e r Ton C o a l P r o c e s s e d ) o f D e s u l f u r i z a t i o n o f C o a l / W a t e r S l u r r y by HGMS U $

1. B a s i s : 2.61 cm/sec, 25 wt % s l u r r y , and o t h e r c o n d i t i o n s i n t h e A p p e n d i x and T a b l e I 2. Amount o f c o a l p r o c e s s e d p e r c y c l e doubled 3. 25% r e d u c t i o n i n c a p i t a l investment 4. Amount o f wash w a t e r r e q u i r e d doubled (washing time un changed) 5. C o s t o f w a t e r i n c r e a s e d 5/3 t i m e s (5C/1000 g a l ) 6. B o t h amounts o f wash w a t e r and w a s h i n g t i m e d o u b l e d 7. L a b o r r e q u i r e m e n t d o u b l e d

—ο

% Change

$

% Change

1. 0628

0.00

2.4117

0.00

0. 9004

-15.28

2.0341

-15.66

0. 9389

-11.66

1.9506

-19.12

1. 0691

+0.60

2.4181

+0.27

1. 0835

+1.95

2.4324

+0.86

1. 2256 1. 3587

+15.32 +27.82

2.7883 2.7077

+15.62 +19.12



10.

L I N A N D Liu

High-Intensity

and -Gradient

Magnetic

Separation

129

c o a l p r o c e s s e d ) a r e compared w i t h t h e r e s u l t s o f t h i s s t u d y . The c o s t s g i v e n by M u r r a y (19) were b a s e d o n t h e e x i s t i n g c o s t e s t i mate f o r k a o l i n b e n e f i c i a t i o n by HGMS g i v e n i n R e f . 1 1 . F o r a r e s i d e n c e t i m e o f 0.5 m i n , t h e c o a l f e e d r a t e t o a c o m m e r c i a l HGMS u n i t w i t h a s e p a r a t o r m a t r i x 7 f t i n d i a m e t e r and 20 i n . l o n g was s e t a t 100 t o n s p e r h r by M u r r a y . T h i s r a t e a p p e a r s t o be h i g h e r t h a n t h a t e x p e c t e d i n c o m m e r c i a l p r a c t i c e . I n a d d i t i o n , t h e c o s t s o f l a b o r and m a i n t e n a n c e p e r HGMS u n i t were e s t i m a t e d by M u r r a y t o be $1 and $2 p e r h r , r e s p e c t i v e l y . These c o s t s a l s o a p p e a r t o be l o w e r t h a n t h o s e r e p o r t e d i n R e f . _11. C o n s e q u e n t l y , t h e c o s t s e s t i m a t e d by M u r r a y shown i n T a b l e I I I e s p e c i a l l y t h e u n i t c o s t U^, ($0.37 p e r t o n p r o c e s s e d ) , a r e b e l i e v e d t o be l o w e r t h a n t h e a c t u a l c o s t s . N e x t , w h i l e t h e c o s t s e s t i m a t e d by Oder (22) seem t o be r e l a t i v e l y c o m p a r a b l e to those obtained i n t h i s study, i t i s d i f f i c u l t t o i d e n t i f y c l e a r l y t h e d i f f e r e n c e s between the two e s t i m a t e s . T h i s f o l l o w s because s p e c i f i c d e t a i l s r e g a r d i n g the c o s t s o f major i n s t a l l e d e q u i p m e n t , c y c l e t i m e , a n d w a s h i n g t i m e , e t c . , were n o t r e p o r t e d i n R e f . _22. F i n a l l y , t h e c o s t s e s t i m a t e d by T r i n d a d e (8) a r e a l s o b e l i e v e d t o be l o w e r t h a n t h e a c t u a l c o s t s . I n t h e c o s t e s t i m a t e b y T r i n d a d e , a C a r o u s e l s e p a r a t o r was u s e d a s a b a s i s f o r t h e e s t i m a t i o n , a l t h o u g h t h e r e h a v e n o t y e t been a n y t e s t data r e p o r t e d on the magnetic d e s u l f u r i z a t i o n o f c o a l / w a t e r s l u r r y u s i n g a C a r o u s e l s e p a r a t o r . O n l y t h e s e p a r a t o r c o s t was i n c l u d e d i n t h e c a p i t a l c o s t i n t h e a n a l y s i s b y T r i n d a d e , and i t was a b o u t o n e - h a l f o f t h e c o s t o f i n s t a l l i n g a n e q u i v a l e n t c y c l i c HGMS u n i t . This l e d t o the r e l a t i v e l y low c a p i t a l investment p e r t o n o f c o a l p r o c e s s e d ( $ 0 . 8 2 - $ l . 6 4 ) e s t i m a t e d by T r i n d a d e as shown i n T a b l e I I I . The c o s t e s t i m a t i o n method u s e d by T r i n dade g e n e r a l l y l e a d s t o l o w e r u n i t c o s t s . F o r i n s t a n c e , b y u s i n g T r i n d a d e s method, t h e u n i t c o s t Up o b t a i n e d i n t h i s work f o r a s l u r r y v e l o c i t y o f 2.61 cm/sec shown i n T a b l e I I I w i l l be r e d u c e d f r o m $1.06 t o $0.85 p e r t o n o f c o a l p r o c e s s e d . 1

A c o m p a r i s o n o f a p p r o x i m a t e e s t i m a t e d c a p i t a l and u n i t c o s t s of d i f f e r e n t p y r i t i c s u l f u r removal p r o c e s s e s c u r r e n t l y under a c t i v e d e v e l o p m e n t (2,30,31,33) i s g i v e n i n T a b l e IV. With t h e e x c e p t i o n o f t h e MAGNEX p r o c e s s ( 3 1 ) , a l l t h e methods l i s t e d i n T a b l e I V a r e wet p r o c e s s e s and r e q u i r e g r i n d i n g o f f e e d c o a l , thus r e q u i r i n g r e l a t i v e l y comparable g r i n d i n g , dewatering, and d r y i n g c o s t s . T h i s t a b l e i n d i c a t e s t h a t t h e c o s t s o f wet m a g n e t i c d e s u l f u r i z a t i o n by HGMS a r e a t t r a c t i v e when compared w i t h those o f o t h e r approaches, even a f t e r adding the n e c e s s a r y c o s t s o f g r i n d i n g , d e w a t e r i n g and d r y i n g . However, t h e above c o m p a r i s o n i s o n l y a n a p p r o x i m a t e one, b e c a u s e o f t h e d i f f e r e n c e i n t h e methods u s e d t o e s t i m a t e t h e c o s t s and i n t h e d e s u l f u r i z a t i o n c h a r a c t e r i s t i c s r e p o r t e d , e t c . Based on t h e a v a i l a b l e c o s t i n f o r m a t i o n f o r these p y r i t i c s u l f u r removal p r o c e s s e s (3,30,31, 33), i t i s n o t y e t p o s s i b l e t o c a r r y out a r i g o r o u s comparison. Magnetic

Desulfurization of Liquefied Coal:

P r o c e s s and C o s t s


130

COAL

Table I I I .

Comparison

of Estimated Costs of D e s u l f u r i z a t i o n of Coal/Water

Murray(l_9)

1. 2. 3.

Slurry velocity (cm/sec) Slurry concentration (wt %) U n i t c o s t s , $ per ton c o a l processed


4.

C a p i t a l investment per ton c o a l processed per year ($)

T a b l e IV.

Oder(_22)

Trindade(8)

]1.7-3.4

2

2. .02

2. 3. A.

5.

25

1 .06 .

0..83

2..47-0.93

2,.41

1..88

4,.69

3..53

5..95-2.28

Comparison of U n i t Costs of

MAGNEX-Hazen Research, Inc.(31) Froth f l o t a t i o n Bureau of Mines(31) Meyers-TRW Systems and Energy Ledgeraont oxygen leaching-Kennecott Copper Corp.(30) HGMS-This work, see T a b l e I

4..0

2,.61

0..70-0.25. 0.39-0.84 0.22-0.45

1.64

0.82

E s t i m a t e d Approximate C a p i t a l and D i f f e r e n t P y r i t e Removal P r o c e s s e s

Process

1.

4

S l u r r y by HGMS

T h i s Work

30

0..37

i!o

DESULFURIZATION

hi

Capital

Investment^

5.83

7.05

4.17

2.77

4.47

5.71 13.80 (leaching 11.30 (leaching

6.0-14.0 comparable to Meyers 0.83-1.06

only)

3.53-A.69

1.88-2.41

U n i t c o s t s expressed i n $ per ton c o a l p r o c e s s e d . C a p i t a l investment expressed i n $ per ton c o a l p r o c e s s e d

only)

per

year.



10.

L I N A N D Liu

High-Intensity

and -Gradient

Magnetic

Separation

131

A f l o w d i a g r a m o f t h e c o n c e p t u a l p r o c e s s t o remove t h e m i n e r a l r e s i d u e f r o m l i q u e f i e d SRC by HGMS i s shown i n F i g u r e 3. The HGMS u n i t u s e d h e r e i s t h e same c o m m e r c i a l s e p a r a t o r used t o d e s u l f u r i z e the coal/water s l u r r y . The m a g n e t i c d e s u l f u r i z a t i o n o f l i q u e f i e d SRC i s t o be c o n d u c t e d a t e l e v a t e d t e m p e r a t u r e t o reduce the v i s c o s i t y o f the c o a l s l u r r y . Furthermore, the packed s t a i n l e s s s t e e l w o o l m a t r i x i s a l s o t o be h e a t e d t o t h e d e s i r e d s e p a r a t i o n t e m p e r a t u r e d u r i n g o p e r a t i o n . The e l e v a t e d t e m p e r a t u r e o f the m a t r i x w i l l prevent the c o a l s l u r r y from c o n g e a l i n g and p l u g g i n g t h e m a t r i x . I t i s a l s o necessary t o i n s u l a t e the h e a t e d p o r t i o n o f t h e m a t r i x f r o m t h e magnet w i n d i n g s . The i n s u l a t e d m a t r i x i s f u r t h e r s u r r o u n d e d by a w a t e r j a c k e t . These p r o v i s i o n s f o r h e a t i n g , i n s u l a t i n g , and c o o l i n g t h e s e p a r a t o r m a t r i x s l i g h t l y reduce the a c t u a l working volume o f t h e s e p a r a t o r m a t r i x and i t s d i a m e t e r f r o m 7.0 t o 6.83 f t . I n a c t u a l s e p a r a t i o n r u n s , t h e u n f i l t e r e d l i q u e f i e d SRC i s pumped t h r o u g h t h e energized separator a t a constant flow rate u n t i l the separator matrix reaches i t s l o a d i n g l i m i t . A f t e r r i n s i n g w i t h a process g e n e r a t e d s o l v e n t , t h e m a t r i x i s backwashed w i t h t h e same s o l v e n t w i t h t h e magnet d e - e n e r g i z e d . The mags a r e s e n t t o a h y d r o c l o n e separator. The o v e r f l o w f r o m t h e h y d r o c l o n e i s r e c y c l e d b a c k t o t h e wash s o l v e n t t a n k f o r r e - u s e ; w h i l e the u n d e r f l o w i s s e n t t o an e v a p o r a t o r t o r e c o v e r t h e s o l v e n t , and t h e r e s i d u a l s o l i d s a r e packed f o r o t h e r u s e s . The t a i l s f r o m t h e s e p a r a t o r a r e s e n t t o a vacuum c o l u m n t o r e c o v e r t h e s o l v e n t f o r p r o c e s s r e c y c l e and t h e vacuum b o t t o m i s s e n t t o a p r o d u c t c o o l e r t o p r o d u c e t h e s o l i d i f i e d SRC. The c o n c e p t u a l p r o c e s s i s d e s i g n e d t o a c h i e v e t h e same e x t e n t o f i n o r g a n i c s u l f u r r e m o v a l and m a t r i x l o a d i n g o b s e r v e d by HRI f o r s l u r r y v e l o c i t i e s o f 0.25-14.0 cm/sec ( 2 6 ) . The s p e c i f i c magnetic d e s u l f u r i z a t i o n c h a r a c t e r i s t i c s Corresponding t o t h e s e s l u r r y v e l o c i t i e s a r e summarized a s t h e f i r s t t h r e e rows o f T a b l e V. A c c o r d i n g t o a s u r v e y o f 455 U.S. c o a l s a m p l e s c o n d u c t e d by t h e B u r e a u o f M i n e s , t h e a v e r a g e t o t a l and i n o r g a n i c s u l f u r c o n t e n t s o f t h e s e s a m p l e s were 3.02 and 1.91 wt%, r e s p e c t i v e l y ( 2 0 ) . T h u s , i f t h e hydrogénation s t e p i n t h e SRC a n d o t h e r r e l a t e d l i q u e f a c t i o n p r o c e s s e s c a n remove 7 0 % o f t h e o r g a n i c s u l f u r , a r e d u c t i o n i n t h e i n o r g a n i c s u l f u r c o n t e n t by a b o u t 6 7 % a f t e r hydrogénation w i l l be s u f f i c i e n t t o p r o d u c e SRC w i t h a n e m i s s i o n l e v e l s m a l l e r t h a n 1.20 l b S 0 2 / m i l l i o n B t u , a s s u m i n g t h a t t h e SRC h a s a h e a t i n g v a l u e o f 16,000 B t u / l b . The same method o f c o s t e s t i m a t i o n summarized i n t h e Append i x e x c e p t f o r r e p l a c i n g t h e d i s p e r s a n t by steam w i t h a n o m i n a l c o s t o f $2/1000 l b was u s e d t o e s t i m a t e c a p i t a l i n v e s t m e n t and u n i t c o s t s o f the c o n c e p t u a l p r o c e s s . The r e s u l t s a r e p r e s e n t e d i n T a b l e V. H e r e , t h e c o s t o f m a j o r i n s t a l l e d equipment s u c h a s t h e HGMS u n i t , wash s o l v e n t t a n k , f e e d s u r g e t a n k , f e e d pump, f l u s h pump and e v a p o r a t o r , e t c . , h a s b e e n i n c l u d e d . I n T a b l e V I , t h e e f f e c t o f steam p r i c e on t h e u n i t c o s t U o f m a g n e t i c desulfurization of liquefied coal i s i l l u s t r a t e d . Doubling the Q


132


Water Supply 1.653 million gal/day Dispersant 5.3 Lb/Hr

Feed Ball Coal — 66.13 TPH Mill

Rinse Water 720 gal/cycle

794 6PM 25 Mixing Wt%j Tank Slurry 10,000 gal

Wash Water 1440 gal/cycle

HGMS 7'D, 20" L. 1480 2.61 cm/sec Velocity 6PM 480 gal. Canister Pump Volume 096 Tons S S. Wool 94% Void Volume 3846 GPM/Ft

Water Tails Vacuum Filter


2

Cycle Time 6.1 min. Duty Cycle 674%

Mags

Refute 9.92 TPH -

Figure 2.

Thermal Dryer

Clarifier or Settling Pond

Clean Dry Coal 56.21 TPH

Desulfurization of coal/water slurry by HGMS

Wash Oil Wash Oil Tank 2300 Gallons Rinse Oil 686 gal/cycle

Wash Oil 1372 gal/cycle Recycle Solvent

HGMS 7'D, 20" L. 2928 5.42 cm/sec Velocity GPM 457.23 gal. Canister Volume Pump 0.915 Tons S.S. Wool 94% Void Volume

Surge SRC Tank Filter Fee0.25% w/w). Three of the mines sampled were below t h i s l i m i t and, t h e r e f o r e , do n o t a p p e a r i n t h e t a b l e . A c t u a l t o t a l s u l f u r v a l u e s b e f o r e and a f t e r c h e m i c a l r e m o v a l a r e shown i n columnsΟ and 4. These may be compared w i t h c o l u m n 5, w h i c h shows s u l f u r v a l u e s w h i c h c a n be o b t a i n e d w i t h f u l l p r o c e s s o p t i m i z a t i o n . T h i s l a t t e r v a l u e was c a l c u l a t e d by a d d i n g t h e a c t u a l r e s i d u a l p y r i t i c s u l f u r and s u l f a t e c o n t e n t s of the c o a l to the i n i t i a l o r g a n i c s u l f u r v a l u e a f t e r c o r r e c t i o n f o r any c o n c e n t r a t i o n e f f e c t s r e s u l t i n g f r o m a s h r e moval. I n the survey program, complete removal of r e s i d u a l e l e m e n t a l s u l f u r and s u l f a t e was n o t a l w a y s o b t a i n e d s i n c e c o n d i t i o n s were s t a n d a r d i z e d but not o p t i m i z e d f o r each i n d i v i d u a l c o a l . T h u s , f o r e x a m p l e , a l t h o u g h 96% p y r i t e c o n v e r s i o n was o b t a i n e d f o r t h e B i r d No. 3 c o a l , t h e t o t a l s u l f u r was r e d u c e d t o 0.80%, n o t t h e t h e o r e t i c a l 0.45% c a u s e d by t h e s e e f f e c t s . These p r o c e s s i n g p r o b l e m s h a v e now b e e n r e s o l v e d as p a r t o f o t h e r p r o j e c t s ( 3 , 9 ) , and t h e v a l u e s shown i n c o l u m n 5 can be c o n s i d e r e d t o r e p r e s e n t the t r u e p o t e n t i a l of the p r o c e s s . Because of the widespread a p p l i c a t i o n of p h y s i c a l c l e a n i n g t e c h n i q u e s f o r removal of nonc o m b u s t i b l e r o c k ( w h i c h i n c l u d e s v a r y i n g amounts o f p y r i t e a l o n g w i t h some c a r b o n ) f r o m c o a l , f l o a t - s i n k f r a c t i o n a t i o n was p e r f o r m e d i n o r d e r t o d e f i n e t h e r e l a t i v e u t i l i t y o f w a s h i n g and chemical d e s u l f u r i z a t i o n f o r each c o a l . The r e s u l t s a r e shown i n c o l u m n 8 and a l s o i n F i g u r e 2. The s u l f u r r e d u c t i o n p o t e n t i a l o f t h e M e y e r s p r o c e s s i s h i g h l y a t t r a c t i v e and i n p a r t i c u l a r i t was found t h a t : (1) The M e y e r s p r o c e s s , a t i t s c u r r e n t s t a t e o f d e v e l o p m e n t , removed 83-99% o f t h e p y r i t i c s u l f u r c o n t e n t o f t h e 32 coals s t u d i e d , r e s u l t i n g i n t o t a l s u l f u r content r e d u c t i o n s o f 25-80%


11.

HAMERSMA

Meyers Process for Desulfurization

E T A L .

APPALACHIAN INTERIOR BASINS WESTERN

Ο Δ •

Ν 24 Ν- 7 Ν -• 4

TOTAL SULPHUR,

% w/w \

\

\ \

Δ


ο

\

Ρ

\

Ο

Δ

\ \

\

\

N

v

ο

° n

Ο Ο

\

v

\ ό

Ο

V , \

^o

OOO

\

S

\ \

co\ L_2 l l _ 0.5

1.0

\

\

_J 1.5

\

\

M . 2.0

2.5

ORGANIC SULPHUR, % W/W

ι

5

6

7

8

Figure 1.

Sulfur forms of sampled U.S. coals

Figure 2. Sulfur content of survey run-ofmine coals (curve a), the same coals physically cleaned (curve c), and chemically de sulfurized (curve b)



Navajo Kopperston No. 2 H a r r i s Nos. 1 & 2 Colstrip Warwick Marion Mathies Isabella Orient No. 6 Lucas Jane Martinka North River Humphrey No. 7 No. 1 Bird No. 3 Williams Shoemaker Meigs Fox Dean Powhattan No. 4 Eagle No. 2 Star Robinson Run

Mine 0..8 0.,9 1.,0 1.,0 1.,4 1.,4 1.,5 1.,6 1.,7 1.,8 1.,8 2.,0 2. ,1 2,,6 3..1 3.,1 3..5 3..5 3,.7 3,.8 4,.1 4..1 4,.3 4,.3 4,.4 0,.6 0,.6 0..8 0,.6 0,,6 0,,7 0,,9 0,,1 0..9 0..6 0,,7 0,.6 0..9 1..5 1..6 0,.8 1..7 1,.7 1,.9 1,.6 2,.1 1,.9 2,.0 2..5 2,.2

0.,5 0..5 0.,6 0.,7 0.,4 0.,6 0.,5 0.,5 0.,8 0.,5 0.,6 0.,8 0.,8 1.,2 1.,4 0.,4 1.,4 1.,5 1,.7 1..2 1,.6 1,.9 1,.9 1,.8 1,.6

% T o t a l S u l f u r w/w i n Coal2 A f t e r Meyers Process Current Revised Initial Results Processing^ 90 92 94 83 92 96 95 96 96 94 91 92 91 91 90 96 96 96 93 89 94 85 94 91 97

25 33 23 30 54 50 36 54 44 64 63 70 55 42 48 75 50 51 48 57 49 53 54 43 50

Meyers P r o c e s s " Pyrite Total S Conv. Decrease (% w/w) (% w/w)

Summary of P y r i t i c S u l f u r Removal Results^(100-150 u t o p - s i z e coal)

Nos. 6,7,8 Campbell Creek Eagle & No. 2 Gas Rosebud Sewickley Upper Freeport Pittsburgh Pittsburgh H e r r i n No. 6 Middle K i t t a n n i n g Lower Freeport Lower K i t t a n n i n g Corona Pittsburgh Mason Lower K i t t a n n i n g Pittsburgh Pittsburgh C l a r i o n 4A Lower K i t t a n n i n g Dean P i t t s b u r g h No. 8 I l l i n o i s No. 5 No. 9 Pittsburgh

Seam

Table I.


1.0 1.2 1.7 1.5 1.4 0.7 0.8 0.8 2.2 1.9 2.3 1.5 2.3 3.6 2.8 2.0 3.0 3.3 2.9 3.0 3.0

0.8 0.9

% Sulfur i n Coal^ After FloatSink


No. 11 No. 9 (W. Ky.) No. 9 Upper F r e e p o r t Meigs Creek Des M o i n e s No. 1 P i t t s b u r g h No. 8

Seam 4.5 4.5 4.8 4.9 6.1 6.4 6.6

Initial

% Total

1.7 2.0 2.8 0.8 3.2 2.2 2.7

1..6 2. ,1 2. ,2 0..5 2. ,7 1. ,7 2. ,1

S u l f u r w/w i n C o a l 2 ~ A f t e r Meyers Process Current Revised Results Processing^ 93 89 91 965 94 92 89

47 55 42 80 47 65 59

Meyers P r o c e s s " Pyrite Total S Conv. Decrease (% w/w) (% w/w) 3,.2 2,.9 3..5 2,.1 4,Λ 3.,9 4.,6

% Sulfur i n Coal^ After FloatSink

moisture-free

Run

using

a t 200 m χ 0.

Calculated

l a t e s t process

improvement.

14 mesh χ 0, i s d e f i n e d

basis.

1.90 f l o a t m a t e r i a l ,

Dry,

here as the l i m i t o f c o n v e n t i o n a l

coal

cleaning.

A 100 g s a m p l e o f c o a l was r e f l u x e d w i t h 2 L o f I N F e 2 ( S 0 4 ) 3 s o l u t i o n . A f t e r 4-6 h r s , t h e r e d u c e d s o l u t i o n was f i l t e r e d f r o m t h e c o a l a n d t h e c o a l was r e f l u x e d w i t h 2 L o f f r e s h I N F e 2 ( S 0 4 ) 3 . A f t e r a t o t a l e x t r a c t i o n t i m e o f 10-24 h r , t h e s l u r r y was f i l t e r e d and t h e c o a l c a k e was washed w i t h 0.2N H2SO4, t h e n w i t h w a t e r t o remove r e s i d u a l s u l f a t e . T o l u e n e (400 m l ) e x t r a c t i o n o f t h e c o a l removed e l e m e n t a l s u l f u r . The c o a l c a k e was t h e n d r i e d i n a vacuum oven a t 100-120°C.

Homestead Camp Nos. 1 & 2 Ken Delmont Muskingum Weldon No. 11 Egypt V a l l e y No. 21

Mine

Table I continued.


148


(2)

T w e l v e (38%) o f t h e c o a l s w e r e r e d u c e d i n s u l f u r c o n t e n t to t h e 0.6-0.8% s u l f u r l e v e l s g e n e r a l l y c o n s i s t e n t w i t h t h e F e d e r a l New S o u r c e P e r f o r m a n c e S t a n d a r d s ar»H many s t a t e standards I n a l l c a s e s , t h e M e y e r s p r o c e s s removed s i g n i f i c a n t - t o v e r y l a r g e i n c r e m e n t s o f s u l f u r o v e r t h a t s e p a r a b l e by physical cleaning I n two c a s e s , t h e C o r o n a and M a t h i e s m i n e s , c o a l c l e a n ing a c t u a l l y r e s u l t e d i n a s u l f u r content i n c r e a s e i n the f l o a t product.

(3)

(4)


Rate of P y r i t i c

S u l f u r Removal

The r e m o v a l o f p y r i t i c s u l f u r was measured as a f u n c t i o n o f t i m e a t 100°C f o r 18 A p p a l a c h i a n and 3 e a s t e r n i n t e r i o r r e g i o n coals. The r e s u l t s a r e d i s p l a y e d i n T a b l e I I , w h i c h shows t h e range of r a t e s observed. I t was assumed t h a t t h e e m p i r i c a l k i n e t i c r a t e e x p r e s s i o n (3) w h i c h was d e v e l o p e d p r e v i o u s l y f o r t h i s process i s a p p l i c a b l e to a l l c o a l s i n the survey. The k i n e t i c e q u a t i o n c a n be s i m p l i f i e d by h o l d i n g t h e r e a g e n t c o n c e n t r a t i o n r e l a t i v e l y c o n s t a n t , as was t h e c a s e i n t h i s s t u d y , t o y i e l d E q u a t i o n 2: -d[W ] p

, °τ» 2 _ . = k W = r a t e of p y r i t e D

removal

(2)

dt w h e r e : W = w e i g h t p e r c e n t p y r i t e i n t h e c o a l , and k° = f u n c t i o n of tempeTâture, c o a l t y p e and p a r t i c a l s i z e . By i n t e g r a t i n g E q u a t i o n 2, t h e f r a c t i o n o f p y r i t e removed as a f u n c t i o n o f t i m e i s shown i n E q u a t i o n 3: p

1-F where: F centration, The i n i t i a l f o r WWp ° and n

Ρ

_

(3)

F

f r a c t i o n o f p y r i t e removed, W = i n i t i a l p y r i t e con and t p = t i m e t o r e m o v a l a t T r a c t i o n F. w e i g h t p e r c e n t o f p y r i t i c s u l f u r Sp° may be s u b s t i t u e d E q u a t i o n 3 be r e a r r a n g e d t o E q u a t i o n 4 p

ο k = a c t u a l r a t e constant

(A)

T h u s , a s s u m i n g 80% r e m o v a l as a p o i n t o f c o m p a r i s o n , t h e v a l u e s o f 1/Sp_°_t80% shown i n c o l u m n 6 o f T a b l e I I i n d i c a t e t h e r e a c t i v i t i e s of t h e p y r i t e c o n t a i n e d i n t h e c o a l s t h a t w e r e s t u d i e d . A l a r g e amount o f e x p e r i m e n t a t i o n and e n g i n e e r i n g has b e e n p e r f o r m e d u s i n g r a t e d a t a o b t a i n e d f o r M a r t i n k a (3) c o a l ; t h e r e f o r e , t h e M a r t i n k a c o a l Sp°tftQ% has b e e n s e t e q u a l t o 1 as a b a s i s o f c o m p a r i s o n (as shown i n c o l u m n 7 ) .



Campbell Creek E a g l e & No. 2 Gas Upper F r e e p o r t Middle Kittanning Pittsburgh Pittsburgh No. 9 Corona No. 9 Pittsburgh P i t t s b u r g h No. 8 No. 11 Lower K i t t a n n i n g Pittsburgh Lower K i t t a n n i n g C l a r i o n 4A Lower K i t t a n n i n g Dean M e i g s C r e e k No. 9

Seam 149 149 149 100 149 100 149 149 100 100 75 149 75 149 149 149 100 100 149 0.47 0.49 0.90 1.42 2.19 2.23 2.85 1.42 2.66 1.05 2.75 3.11 3.09 1.07 1.42 2.19 2.87 2.62 3.65

Sp°

forPyritic

Top Size (Microns)

R e l a t i v e Rate Constants

2.0 2.3 3.0 3.25 2.9 3.0 2.5 5.0 3.0 9.0 4.0 3.5 4.5 13.0 10.0 8.5 8.0 10.2 8.0

80% (hrs)

u

Sulfur

1.1 0.89 0.37 0.22 0.16 0.15 0.14 0.14 0.13 0.11 0.091 0.092 0.072 0.072 0.070 0.054 0.044 0.037 0.034

^ % 0 %

1

R e a l t i v e Rate

Removal

16 13 5.3 3.1 2.3 2.1 2.0 2.0 1.9 1.6 1.3 1.3 1.0 1.0 1.0 0.77 0.62 0.53 0.49

Relative Rate

2

Constants

l/S>p_tgQ0£ r e l a t i v e t o v a l u e f o r M a r t i n k a m i n e .

o

As i n f o o t n o t e 1 o f T a b l e I , e x c e p t t o l u e n e e x t r a c t i o n was o m i t t e d . P y r i t e removal r a t e data was o b t a i n e d by p y r i t e a n a l y s i s o f c o a l s a m p l e s o b t a i n e d f r o m s l u r r y a l i q u o t s by c e n t r i f u g a t i o n .

K o p p e r s t o n No. 2 H a r r i s Nos. 1 & 2 Marion Lucas Shoemaker Williams Ken North River Star Mathies P o w h a t t a n No. 4 Homestead Fox Isabella Martinka Meigs B i r d No. 3 Dean Muskingum

Coal Mine

Table I I .


150

DESULFURIZATION


COAL

FLOAT - SINK SEPARATION (FLOAT FRACTION) MEYERS PROCESS

Figure 3.

Trace element removal data


11.

HAMERSMA

E T

AL.

Meyers Process for Desulfurization

151

I t c a n be e a s i l y s e e n f r o m T a b l e I I t h a t t h e r e i s a w i d e band o f r a t e c o n s t a n t s r a t h e r e v e n l y s p r e a d o v e r a f a c t o r o f a p p r o x i m a t e l y 30. The K o p p e r s t o n No. 2 a n d H a r r i s N o s . 1 and 2 c o a l s r e a c t more r a p i d l y t h a n t h e s l o w e s t c o a l s (Dean a n d Muskingum) b y a f a c t o r o f a b o u t 30. T h u s , i t i s a p p a r e n t t h a t r e a l a n d s i g n i f i c a n t r a t e d i f f e r e n c e s do e x i s t b e t w e e n p y r i t e i n various coals. C h a r a c t e r i s t i c s o f c o a l such as pore s t r u c t u r e , s i z e a n d s h a p e d i s t r i b u t i o n o f p y r i t e , e t c . may be t h e p r i m a r y f a c t o r s a f f e c t i n g t h e r a t e c o n s t a n t as r e f l e c t e d i n t h e observed band o f v a l u e s f o u n d f o r t h e r a t e s g i v e n i n T a b l e I I .


T r a c e Element Removals B e c a u s e b o t h c h e m i c a l l e a c h i n g and p h y s i c a l c l e a n i n g p r o c e s s e s c a n remove p o t e n t i a l l y h a r m f u l t r a c e e l e m e n t s f r o m c o a l e i t h e r by l e a c h i n g o r by p h y s i c a l p a r t i t i o n i n g , 50 c o a l s a m p l e s have been a n a l y z e d i n d u p l i c a t e o r t r i p l i c a t e t o determine t h e e x t e n t o f t h e r e m o v a l , i f a n y , o f 18 e l e m e n t s o f i n t e r e s t t o t h e E n v i r o n m e n t a l P r o t e c t i o n A g e n c y . The s a m p l e s i n c l u d e d 20 a s r e c e i v e d , 20 c h e m i c a l l y l e a c h e d , and 10 f l o a t - s i n k t r e a t e d c o a l s a m p l e s . The r e s u l t s a r e shown f o r 12 e l e m e n t s i n F i g u r e 3 i n cumulative fashion. The e x t r a c t i o n p r o c e d u r e was a s i n T a b l e I . S i x e l e m e n t s , B, B e , Hg, Sb, Se, and Sn y i e l d e d n e g a t i v e o r i n c o n c l u s i v e r e s u l t s because of low l e v e l s o r a n a l y s i s d i f f i c u l t i e s and t h u s a r e n o t p l o t t e d . A l t h o u g h t h e r e s u l t s v a r i e d g r e a t l y f r o m c o a l t o c o a l w i t h r e s p e c t t o t h e e l e m e n t s e x t r a c t e d and t h e d e g r e e o f e x t r a c t i o n , some g e n e r a l c o n c l u s i o n s c a n be r e a c h e d . (1) A s , C d , Mn, N i , P b , and Zn a r e removed t o a s i g n i f i c a n t l y g r e a t e r e x t e n t by t h e Meyers p r o c e s s (2) F and L i a r e p a r t i t i o n e d t o a g r e a t e r e x t e n t by p h y s i c a l separation procedures. (3) Ag a n d Cu a r e removed w i t h a s l i g h t p r e f e r e n c e f o r f l o a t - s i n k separation (4) C r a n d V a r e removed by b o t h p r o c e s s e s w i t h e q u a l success. The e f f e c t i v e r e m o v a l o f A s , C d , C r , N i , P b , and Zn f r o m t h e c o a l b y t h e M e y e r s p r o c e s s i s e s p e c i a l l y n o t e w o r t h y a s t h e s e compounds a r e c o n c e n t r a t e d ( a l o n g w i t h Se) i n t h e f i n e p a r t i c u l a t e s e m i t t e d f r o m c o a l - f i r e d power p l a n t s . This f i n e p a r t i c u l a t e matter passes through conventional f l y - a s h c o n t r o l devices.

Literature Cited

1. Meyers, R.A., Hamersma, J.W., Land, J.S., Kraft, M.L., Science, (1972),177,1187. 2. Meyers, R.A., "Removal of Pyritic Sulfur from Coal Using Solutions Containing Ferric Ions," U.S. Patent 3768988, 1973. 3. Koutsoukos, E.P., Kraft, M.L., Orsini, R.A., Meyers, R.A., Santy, M.J., Van Nice, L.J., "Final Report Program for BenchScale Development of Processes for the Chemical Extraction of


152 4. 5. 6.


7. 8.

9. 10.


Sulfur from Coal," Environ. Prot. Technol. Ser., (May 1976), EPA-600/2-76-143a. Hamersma, J.W., Koutsoukos, E.P., Kraft, M.L., Meyers, R.A., Ogle, G.J., Van Nice, L.J., "Chemical Desulfurization of Coal: Report of Bench-Scale Developments, Volumes 1 and 2," Environ. Prot. Technol. Ser., (February 1973),EPA-R2-173a. Magee, E.M., "Evaluation of Pollution Control in Fossil Fuel Conversion Processes, Coal Treatment: Section 1. Meyers Process," Environ. Prot. Technol. Ser., (September 1975), EPA-650/2-74-009k. Nekervis, W.F., Hensley, E.F., "Conceptual Design of a Commercial Scale Plant for Chemical Desulfurization of Coal," Environ. Prot. Technol. Ser. (September 1975), EPA-600/2-75-051. Tek, M. Rasin, "Coal Beneficiation," in Evaluation of Coal Conversion Processes, (1974) PB-234202. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC, "Applicability of the Meyers Process for Chemical Desulfurization of Coal: Initial Survey of Fifteen Coals," by J.W. Hamersma et al, Systems Group of TRW, Inc., Redondo Beach, CA. (April 1974), EPA-650/2-74-025, Contract No. 68-02-0647. Hamersma, J.W., Kraft, M.L., "Applicability of the Meyers Process for Chemical Desulfurization of Coal: Survey of Thirty-Five Coals," Environ. Prot. Technol. Ser., (September 1975), EPA-650/2-74-025a. Deurbrouck, A.W., "Sulfur Reduction Potential of Coals of the United States," U.S. Bur. Mines Rep. Invest. (1972), 7633.


12 Coal Desulfurization Test Plant Status—July 1977 L. J. VAN NICE, M. J. SANTY, E. P. KOUTSOUKOS, R. A. ORSINI, and R. A. MEYERS


TRW

Systems and Energy, Redondo Beach, CA 90278

An 8-metric ton/day process test plant for chemical desulfurization of coal utilizing ferric sulfate leach solution, has just been built atTRW'sCapistrano Test Site in California. The plant, shown in Figures 1 and 2, was constructed under an Environmental Protection Agency sponsored project for the development of the Meyers process. Current plans call for plant shakedown followed by processing of 100-200 tons of American Electric Power Service Corporation's Martinka mine coal. The Meyers process and its applicability for directly desulfurizing raw run-of-mine coal were presented in the previous chapter and the process is described in connection with the broad field of chemical desulfurization in a newly issued book (1). We have very recently verified that the ferric sulfate leach solution, which has a specific gravity of 1.2-1.4, can be used to gravity separate coal into float and sink fractions in a manner very advantageous to the Meyers process. This float-sink approach was tested many years ago by A. Z. Yurovskii in the U.S.S.R but only published in the open literature very recently (2). Yurovskii subsequently treated the sink coal with a mixture of nitric acid and ferric sulfate to remove pyritic sulfur, not realizing, that the separation medium itself was sufficiently active to accomplish near total pyritic sulfur removal. I n f a c t , a p r a c t i c a l method f o r a c t u a l f l o a t - s i n k c l e a n i n g of c o a l i n a dense l i q u i d has l o n g been sought as an a l t e r n a t i v e to mechanical c l e a n i n g . Heavy l i q u i d s , s u c h a s z i n c c h l o r i d e water, o r c h l o r i n a t e d , brominated, o r f l u o r i n a t e d hydrocarbons a r e u s e f u l f o r p r e d i c t i o n o f y i e l d s w h i c h c a n t h e o r e t i c a l l y be obtained i n mechanical washing p l a n t s , but a r e i m p r a c t i c a l f o r a c t u a l p r o d u c t i o n b e c a u s e t h e y a r e e x p e n s i v e and a d d p o l l u t a n t s t o t h e c o a l , a t m o s p h e r e o r w a t e r t a b l e . We f i n d t h a t t h e d e n s i t y o f aqueous f e r r i c s u l f a t e l e a c h s o l u t i o n , a s u t i l i z e d i n t h e M e y e r s process, i s i d e a l for accomplishing a p r a c t i c a l gravity separation o f c o a l f o r s p e c i f i c g r a v i t i e s b e t w e e n 1.2 a n d 1.4. F o r a b o u t 4 0 % o f A p p a l a c h i a n c o a l , t h e f l o a t c o a l ( w h i c h i s o f t e n 40-60% b y w e i g h t o f t h e t o t a l ) a v e r a g e s 0.8-1.2 l b s S O / 1 0 b t u a n d n e e d s 6

2

153


DESULFURIZATION


COAL

a.


In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Figure 2.

Test plant—view through tank farm


αχ

CO

3

«5

ο

Η

ο w

2

156


no f u r t h e r p r o c e s s i n g t o meet s t a n d a r d s , w h i l e t h e s i n k c o a l s l u r r y c o n t a i n s most o f t h e c o a l p y r i t e . T h i s c o a l s l u r r y can be p r o c e s s e d t h r o u g h t h e M e y e r s p r o c e s s t o g i v e c o a l c o n t a i n i n g 1.21.5 l b s b t u . This approach a l l o w s p r o d u c t i o n o f c o a l which w i l l meet a i r p o l l u t i o n c o n t r o l s t a n d a r d s f o r b o t h New a n d E x i s t ing S t a t i o n a r y S o u r c e s , and reduces t h e c o s t o f t h e Meyers p r o c e s s t h r o u g h a l l o w i n g 40-60% o f t h e c o a l t o b y p a s s r e a c t o r , e l e m e n t a l s u l f u r e x t r a c t i o n and d r y e r u n i t s . We t e r m t h i s a p p r o a c h , G r a v i c h e m C l e a n i n g . Where e s t i m a t e d processing costs using u t i l i t y financed depreciation of c a p i t a l and i n c l u d i n g c o a l g r i n d i n g a n d c o m p a c t i o n w e r e f o r e c a s t s f o r t h e new G r a v i c h e m C l e a n i n g a p p r o a c h a r e $8.50/ton

SO2/IO6

$10-12/ton (1),

6


($0.35/10 b t u ) . Process

Chemistry,

K i n e t i c s a n d Scheme

The p r o c e s s i s b a s e d o n t h e o x i d a t i o n o f c o a l p y r i t e w i t h f e r r i c s u l f a t e ( E q u a t i o n 1). The l e a c h i n g r e a c t i o n i s h i g h l y s e l e c t i v e t o p y r i t e w i t h 60% o f the p y r i t i c s u l f u r converted t o s u l f a t e s u l f u r and 40% t o e l e m e n t a l s u l f u r . The r e d u c e d f e r r i c i o n i s r e g e n e r a t e d b y o x y g e n o r a i r a c c o r d i n g t o E q u a t i o n s 2 o r 3. FeS

2

+

4.6 Fe (S0 ) + 4.8 H 0 -* 10.2 FeS0 + 4.8 H S0 + 0.8 S (1) 2

4

3

4

2

2

4

2.4 0 + 9.6 FeS0 + 4.8 H S0 + 4.8 Fe (S0 ) + 4.8 H 0

(2)

2.3 0 + 9.2 FeS0 +4.6 H S0 +4.6 Fe (S0 ) + 4.6 H 0

(3)

2

4

2

2

4

4

2

2

4

4

2

3

4

2

3

2

R e g e n e r a t i o n c a n be p e r f o r m e d e i t h e r c o n c u r r e n t l y w i t h c o a l p y r i t e l e a c h i n g i n a s i n g l e o p e r a t i o n o r s e p a r a t e l y . The n e t e f f e c t o f t h e p r o c e s s i s t h e o x i d a t i o n o f p y r i t e w i t h oxygen to y i e l d r e c o v e r a b l e i r o n , s u l f a t e s u l f u r , a n d e l e m e n t a l s u l f u r . The f o r m o f p r o c e s s p r o d u c t s v a r i e s t o some e x t e n t w i t h t h e d e g r e e of r e g e n e r a t i o n . Thus, E q u a t i o n s 1 and 2 l e a d t o t h e o v e r a l l p r o cess c h e m i s t r y i n d i c a t e d by E q u a t i o n 4 p r o d u c i n g a m i x t u r e o f i r o n s u l f a t e s and e l e m e n t a l s u l f u r . E q u a t i o n s 1 and 3 y i e l d f e r r o u s s u l f a t e , s u l f u r i c a c i d , and e l e m e n t a l s u l f u r as i n d i c a t e d by E q u a t i o n 5. FeS

2

+

2.4

0 + 0.6 FeS0 + 0.2 Fe (S0 ) + 0.8 S

(4)

FeS

2

+

2.3

0 + 0.2 H 0 -> FeS0 + 0.2 H S0 + 0.8 S

(5)

2

2

4

2

2

4

4

3

2

4

Several options e x i s t i n product recovery. I r o n s u l f a t e s may be r e c o v e r e d a s p u r e s o l i d s b y s t e p w i s e e v a p o r a t i o n o f a s p e n t r e agent s l i p s t r e a m w i t h f e r r o u s s u l f a t e b e i n g recovered f i r s t b e cause o f i t s lower s o l u b i l i t y . A l t e r n a t e l y , f e r r o u s s u l f a t e may be r e c o v e r e d b y c r y s t a l l i z a t i o n a n d f e r r i c s u l f a t e o r s u l f u r i c



12.

V A N NICE

E T A L .

Desulfurization

Test Phnt

Status

157

a c i d removed b y l i m i n g s p e n t r e a g e n t o r s p e n t wash w a t e r s l i p streams. I r o n s u l f a t e s may b e s t o r e d a s s o l i d s f o r s a l e o r may be c o n v e r t e d e a s i l y t o h i g h l y i n s o l u b l e b a s i c i r o n s u l f a t e s (by a i r o x i d a t i o n ) o r c a l c i u m s u l f a t e (by low-temperature s o l i d phase r e a c t i o n ) f o r d i s p o s a l . E l e m e n t a l s u l f u r may b e r e c o v e r e d f r o m c o a l b y v a p o r i z a t i o n w i t h s t e a m o r b y vacuum, o r i t c a n b e l e a c h e d out w i t h o r g a n i c s o l v e n t s such as acetone depending on product m a r k e t a b i l i t y and p r o d u c t r e c o v e r y economics. Recovery economics may b e i n f l u e n c e d b y q u a n t i t y a n d c o n c e n t r a t i o n o f p r o d u c t i n t h e process e f f l u e n t streams which i n t u r n a r e i n f l u e n c e d by t h e p y r i t e c o n c e n t r a t i o n i n t h e c o a l and t h e d e s i r e d e x t e n t o f d e s u l f u r i z a tion. The p r o c e s s h a s b e e n e x t e n s i v e l y s t u d i e d a t b e n c h - s c a l e . Parameters i n v e s t i g a t e d include c o a l t o p - s i z e , reagent composition, s l u r r y c o n c e n t r a t i o n , r e a c t i o n t e m p e r a t u r e and p r e s s u r e , and r e a c t i o n time. A d d i t i o n a l i n v e s t i g a t i o n s c o m p l e t e d o r underway i n c l u d e c o n current coal leaching-reagent regeneration, product recovery, product s t a b i l i t y , and t h e e f f e c t o f c o a l p h y s i c a l c l e a n i n g on p r o c e s s p e r f o r m a n c e a n d e c o n o m i c s . The p r o c e s s scheme d e p i c t e d i n F i g u r e 3 i s based on t h e b e n c h - s c a l e t e s t i n g . Coal i s (1) Crushed t o t h e d e s i r e d s i z e f o r p r o c e s s i n g (2) Contacted w i t h h o t r e c y c l e d reagent i n the mixer (90°-100°C) (3) Leached o f p y r i t e i n t h e r e a c t o r ( s ) w i t h simultaneous or separate reagent regeneration (4) Washed w i t h h o t w a t e r (5) S t r i p p e d o f e l e m e n t a l s u l f u r , d r i e d and f i n a l l y cooled. The i r o n a n d s u l f a t e s u l f u r a r e r e c o v e r e d f r o m s p e n t r e a g e n t s l i p s t r e a m s p r i o r t o r e a g e n t r e c y c l e . F i g u r e 4 shows t y p i c a l d a t a o n p y r i t e r e m o v a l r a t e s f r o m A p p a l a c h i a n c o a l a s a f u n c t i o n o f temperature. D u r i n g s l u r r y m i x i n g a n d h e a t - u p , 10-20% o f t h e p y r i t e i s removed. Bench-scale data i n d i c a t e d that t h e p y r i t e l e a c h i n g r a t e from c o a l c a n be a d e q u a t e l y r e p r e s e n t e d by t h e e m p i r i c a l r a t e e x p r e s s i o n (Equation 6 ) . r. = -

=h

W

2

Y

2

(6)

where: = A^ exp (-E^/RT), W = w t % p y r i t e i n c o a l , Y = f e r r i c i o n - t o - t o t a l i r o n r a t i o i n t h e r e a c t o r r e a g e n t , a n d A^ and E^ a r e c o n s t a n t s f o r e a c h c o a l a n d p a r t i c l e s i z e a t l e a s t o v e r most o f the r e a c t i o n range. The l e a c h r a t e i s a f u n c t i o n o f c o a l t y p e . Pyrite extraction r a t e s vary c o n s i d e r a b l y , as d e t a i l e d i n a study o f the Meyers p r o c e s s a s a p p l i e d t o U.S. c o a l ( 3 ) , e.g., t h e r e was more t h a n one o r d e r o f magnitude d i f f e r e n c e between t h e f a s t e s t and s l o w e s t r e a c t i n g c o a l . The r e a g e n t r e g e n e r a t i o n r a t e i s g o v e r n e d b y t h e rate expression (Equation 7 ) .




Figure 3.

Process flow schematic

REACTION TIME, HOURS

Figure 4.

Temperature effect on processing of 14 mesh top-size Lower Kittanning coal (33% w/w slurries)


12.

VAN

NICE

ET

Desulfurization

AL.

£

R

= "

= Κ* Pô Qt


Test Phnt

Status

2N0

+

0

->

2NX>

2

+

-S0 2

2

(3) (4)

We f o u n d t h a t we c o u l d i n d e e d o x i d i z e DBT t o i t s s u l f o n e u s i n g NO^ and a i r . When t h e r e a c t i o n was e x t e n d e d t o c o a l , h o w e v e r , a s i g n i f i c a n t amount o f c o n c u r r e n t r e a c t i o n t o o k p l a c e , i n c l u d i n g n i t r a t i o n o f t h e c o a l , w h i c h consumed t h e n i t r o g e n o x i d e s and t h u s w o u l d have n e c e s s i t a t e d a c o n t i n u o u s a d d i t i o n o f NO^ r a t h e r t h a n t h e r e c y c l i n g shown i n E q u a t i o n s 3 and 4. I n t h e meantime, o u r e x p e r i m e n t s on a i r o x i d a t i o n o f o r g a n o s u l f u r u s i n g h y d r o p e r o x i d e p r e c u r s o r s l e d us t o t h e u l t i m a t e e x p e r i m e n t , t h e one i n w h i c h H«0 was u s e d i n p l a c e o f an o r g a n i c l i q u i d p h a s e . T h i s r e a c t i o n o f c o a l w i t h w a t e r and c o m p r e s s e d a i r almost q u a n t i t a t i v e l y c o n v e r t e d the p y r i t i c s u l f u r i n c o a l



13.

FRIEDMAN

E T

AL.

Oxidative

Desulfurization

of

167

Coal

t o H^SO^. I n a d d i t i o n , we a l s o removed 2 5 % o f t h e o r g a n i c sulfur. H e r e was e v i d e n c e t h a t t h e r e was some o r g a n o s u l f u r i n c o a l w h i c h was n o t D B T - l i k e , s i n c e DBT f a i l e d t o r e a c t w i t h a i r and w a t e r u n d e r t h e s e c o n d i t i o n s . I n i t i a l experiments on t h e a i r - w a t e r o x y d e s u l f u r i z a t i o n o f c o a l were c a r r i e d o u t u s i n g a b a t c h , s t i r r e d a u t o c l a v e s y s t e m . In t h i s a p p a r a t u s , i n o r d e r t o r e p l a c e o x y g e n a s i t was u s e d , i t was n e c e s s a r y t o c o o l t h e a u t o c l a v e t o n e a r room t e m p e r a t u r e , v e n t t h e s p e n t a i r , r e p r e s s u r e , a n d r e h e a t . A l t h o u g h t h i s gave s a t i s f a c t o r y d e s u l f u r i z a t i o n , i t was a n i m p r a c t i c a l a p p r o a c h f o r s t u d y i n g r e a c t i o n parameters. The r e s u l t s c i t e d i n T a b l e s I , I I , and I I I a r e f r o m 1-hr b a t c h s t u d i e s w i t h o u t r e p r e s s u r i z a t i o n a n d t h u s r e p r e s e n t l e s s t h a n maximum d e s u l f u r i z a t i o n i n some c a s e s . A l l c o a l s , except those noted, a r e bituminous. The a p p a r a t u s h a s b e e n m o d i f i e d t o a l l o w a i r t o f l o w through t h e s t i r r e d r e a c t o r w h i l e the coal-water s l u r r y remains as a b a t c h r e a c t a n t . T h i s i s o u r c u r r e n t s y s t e m . I n t h i s way, we a r e s t u d y i n g many o f t h e v a r i a b l e s a s t h e y w i l l a f f e c t t h e r e a c t i o n i n a continuous system. Our newest a p p a r a t u s , now b e g i n n i n g o p e r a t i o n , i s a f u l l y c o n t i n u o u s u n i t , f e e d i n g b o t h a i r and c o a l - w a t e r s l u r r y i n t o a r e a c t o r tube. T h i s sytera i s d e s i g n e d t o o b t a i n d a t a on r e a c t i o n r a t e s , d e v e l o p i n f o r m a t i o n f o r e c o n o m i c e v a l u a t i o n , a n d answer those q u e s t i o n s which a r i s e concerning e n g i n e e r i n g aspects o f the p r o c e s s . H e a t i n g h i g h - p y r i t e c o a l s i n aqueous s l u r r y w i t h c o m p r e s s e d a i r a t 1000-1200 p s i and a t 150°-160°C d e c r e a s e s p y r i t i c s u l f u r to n e a r t h e l o w e r l i m i t o f d e t e c t i o n b y s t a n d a r d a n a l y t i c a l procedure. Some r e s u l t s o f 1 h r b a t c h e x p e r i m e n t s a r e shown i n T a b l e I . The s u l f u r w h i c h i s removed i s c o n v e r t e d p r i m a r i l y t o aqueous s u l f u r i c a c i d , w i t h s m a l l amounts o f f e r r i c a n d f e r r o u s sulfates i nsolution. A t i n i t i a l p r e s s u r e s o f 800 p s i a n d above and a t t e m p e r a t u r e s above 160°C, 8 0 % o r more o f t h e p y r i t i c s u l f u r i n t h e M i n s h a l l Seam ( I n d i a n a ) c o a l i s removed i n 5 m i n at temperature. S i m i l a r p y r i t i c s u l f u r r e m o v a l was o b s e r v e d i n a s e r i e s o f 10 m i n e x p e r i m e n t s a t 1000 p s i i n t h e c o n t i n u o u s unit. TABLE I . P y r i t e Removal f r o m R e p r e s e n t a t i v e C o a l s by Oxydesulfurization

Seam

State

Temp (°C)

I l l i n o i s No. 5 Minshall L o v i l i a No. 4 Pittsburgh Lower F r e e p o r t Brookville

Illinois Indiana Iowa Ohio Pennsylvania Pennsylvania

150 150 150 160 160 180

P y r i t i c S u l f u r (wt %) Treated Untreated 0.9 4.2 4.0 2.8 2.4 3.1

0.1 0.2 0.3 0.2 0.1 0.1



168


A t 200 p s i , t h e r e a c t i o n i s much s l o w e r , r e q u i r i n g s e v e r a l h o u r s t o a c h i e v e even 6 0 % p y r i t i c s u l f u r r e m o v a l . F o r some c o a l s , a t l e a s t , t h e d e s u l f u r i z a t i o n i s a l m o s t a s r a p i d a t 500 p s i a s a t 1000 p s i . The o x i d a t i o n o f p y r i t i c s u l f u r i s temp e r a t u r e dependent, but a t the c o n d i t i o n s of our experiments, r e a c t i o n i s s u f f i c i e n t l y f a s t t h a t above 150°C l i t t l e i m p r o v e ment i s n o t e d . I n a few c a s e s , where a c o a l a p p e a r s t o h a v e some r e s i d u a l p y r i t e w h i c h i s n o t o x i d i z e d r e a d i l y a t 150°C, i t may be removed a t 180°C. As t h e t e m p e r a t u r e a t w h i c h t h e o x i d a t i o n i s c o n d u c t e d i s i n c r e a s e d a b o v e 150°C, a n i n c r e a s i n g amount o f o r g a n i c s u l f u r i s removed f r o m t h e c o a l . A l t h o u g h t h e p e r c e n t a g e o f o r g a n i c s u l f u r removed p a r a l l e l s t h e t e m p e r a t u r e r i s e , so does t h e amount o f c o a l w h i c h i s o x i d i z e d . To p r e v e n t e x c e s s i v e l o s s o f c o a l , a p r a c t i c a l l i m i t o f 200°C h a s been c h o s e n f o r c a r r y i n g o u t t h e r e a c t i o n on most c o a l s . Removal o f o r g a n i c s u l f u r f r o m a s e r i e s o f c o a l s , shown i n T a b l e I I , v a r i e s f r o m 20 t o o v e r 40%. Further reduction of organic s u l f u r content i s probably p o s s i b l e w i t h some o f t h e s e c o a l s w i t h o u t s a c r i f i c i n g c o a l recoverability. An upper l i m i t on o r g a n i c s u l f u r r e m o v a l a p p e a r s t o be b e t w e e n 40 and 5 0 % , and v a r i e s f r o m c o a l t o c o a l . We b e l i e v e t h i s i s c a u s e d by t h e f u n c t i o n a l i t y o f t h e o r g a n i c s u l f u r , and g i v e s some r o u g h measure o f o x i d a t i o n r e s i s t a n t o r DBT t y p e o f sulfur. O b v i o u s l y , t h a t s u l f u r w h i c h i s removed by o x y d e s u l f u r i z a t i o n must be i n some o t h e r s t r u c t u r e w h i c h i s r e a d i l y o x i d i z e d , such as t h i o l , s u l f i d e , and/or d i s u l f i d e . A s i m i l a r amount o f o r g a n i c s u l f u r i s removed f r o m c o a l when i t i s h e a t e d a t 300°C w i t h aqueous a l k a l i , a r e a g e n t w h i c h does n o t a t t a c k DBT (_5,6) . TABLE I I .

O r g a n i c S u l f u r Removal f r o m R e p r e s e n t a t i v e C o a l s by O x y d e s u l f u r i z a t i o n

Seam

State

Temp (°C)

Bevier Mammoth Wyoming No. 9 Pittsburgh Lower F r e e p o r t I l l i n o i s No. 6 Minshall

Kansas Montana Wyoming Ohio Pennsylvania Illinois Indiana

150 150 150 180 180 200 200

O r g a n i c S u l f u r (wt %) Untreated Treated 2.0 0.5 1.1 1.5 1.0 2.3 1.5

1.6 0.4 0.8 0.8 0.8 1.3 1.2

Subbituminous. Even a t 150°-160°C many c o a l s , i n c l u d i n g some w i t h r a t h e r h i g h s u l f u r c o n t e n t s , c a n be d r a m a t i c a l l y d e s u l f u r i z e d a s shown i n Table I I I .



Indiana Illinois Iowa Montana Pennsylvania Wyoming Ohio Pennsylvania

Minshall I l l i n o i s No. 5 L o v i l i a No. 4 Mammoth Pittsburgh Wyoming No. 9 Pittsburgh Upper F r e e p o r t

Subbituminous.

State 150 150 150 150 150 150 160 160

Temp (°C) 5.7 3.3 5.9 1.1 1.3 1.8 3.0 2.1

2.0 2.0 1.4 0.6 0.8 0.9 1.4 0.9

T o t a l S u l f u r (wt %) Untreated Treated

Oxydesulfurization of Representative

Seam

TABLE I I I . 6

4.99 2.64 5.38 0.91 0.92 1.41 2.34 1.89

1.81 1.75 1.42 0.52 0.60 0.78 1.15 0.80

Sulfur ( l b / 1 0 Btu) Treated Untreated

Coals



170

COAL

DESULFURIZATION

The r e a c t i o n c o n d i t i o n s w h i c h we have f o u n d t o be s u i t a b l e for o x y d e s u l f u r i z a t i o nare: t e m p e r a t u r e b e t w e e n 150° and 220°C, o p e r a t i n g p r e s s u r e b e t w e e n 220 and 1500 p s i , and r e s i d e n c e t i m e of 1 h r or l e s s . Most o f o u r e x p e r i m e n t s h a v e b e e n c a r r i e d o u t b e l o w 220°C a n d a t a p p r o x i m a t e l y 1000 p s i . R e c o v e r i e s o f f u e l v a l u e s a r e e x c e l l e n t , g e n e r a l l y 9 0 % o r b e t t e r . The o n l y b y p r o d u c t o f t h e r e a c t i o n i s d i l u t e H«S0^ c o n t a i n i n g i r o n sulfates. T h i s c a n be r e c y c l e d w i t h no o b s e r v a b l e e f f e c t on desulfurization for at least five cycles. When t h e H^SO^ becomes t o o c o n c e n t r a t e d f o r f u r t h e r u s e , i t c a n be c o n v e r t e d to a commercial grade o f s u l f u r i c a c i d i f a s u i t a b l e , economic m a r k e t e x i s t s , o r i t c a n be d i s p o s e d o f by l i m e s t o n e n e u t r a l i z a t i o n a s a r e a d i l y f i l t e r a b l e CaSO,. The p r o c e s s , o u t l i n e d i n F i g u r e 1, n e e d s no n o v e l technology t o produce c o a l having over 95% o f i t s p y r i t i c s u l f u r and a s much a s 4 0 % o f i t s o r g a n i c s u l f u r removed. O t h e r t h a n t h e c o a l , a i r , and w a t e r , t h e o n l y o t h e r m a t e r i a l needed f o r t h e p r o c e s s i s t h e l i m e s t o n e u s e d t o n e u t r a l i z e t h e H^SO^. No s l u d g e i s f o r m e d , much o f t h e w a t e r c a n be r e c y c l e d , and t h e o n l y w a s t e p r o d u c t i s s o l i d CaSO^. S i m i l a r o x i d a t i v e d e s u l f u r i z a t i o n s u s i n g a i r and w a t e r (7) and o x y g e n and w a t e r (8) have been r e p o r t e d . A p r e l i m i n a r y estimate f o r t h i s process i n d i c a t e s a cost o f $8.00-$10.00 p e r t o n . A t t h i s p r i c e , t h e p r o c e s s w o u l d s t i l l be c o n s i d e r a b l y l e s s e x p e n s i v e t h a n c o a l c o n v e r s i o n t o gas o r l i q u i d f u e l . A s s u m i n g r e m o v a l o f 9 5 % p y r i t i c s u l f u r and 40% o r g a n i c s u l f u r , an e s t i m a t e d 4 0 % o f t h e c o a l mined i n t h e e a s t e r n U.S. c o u l d be made e n v i r o n m e n t a l l y a c c e p t a b l e a s b o i l e r f u e l a c c o r d i n g t o EPA s t a n d a r d s f o r new i n s t a l l a t i o n s . And t h e s u l f u r c o n t e n t o f t h e r e m a i n d e r o f t h e e a s t e r n c o a l c o u l d be d r a s t i c a l l y r e d u c e d , m a k i n g i t e n v i r o n m e n t a l l y acceptable f o r e x i s t i n g b o i l e r s . Conclusions T r e a t m e n t w i t h c o m p r e s s e d a i r a n d w a t e r a t 150°-200°C r e p r e s e n t s a p r a c t i c a l method t o d e s u l f u r i z e t o a c c e p t a b l e l e v e l s a s i z a b l e percentage of the a v a i l a b l e c o a l i n the e a s t e r n U n i t e d S t a t e s a t a c o s t i n money and f u e l v a l u e w h i c h i s l e s s t h a n c o a l c o n v e r s i o n and t o an e x t e n t w h i c h i s g r e a t e r t h a n c a n be a c h i e v e d b y p h y s i c a l d e p y r i t i n g methods. Abstract

Both pyritic and organic sulfur in coal can be removed by a variety of oxidation techniques, including treatment with NO , peroxygen compounds, air in the presence of specific organic media, or air and water at elevated temperature and pressure. The most promising method involves contacting an aqueous slurry of coal with air at pressures up to 1000 psi x


FRIEDMAN

Oxidative Desulfurization of Coal

E T A L .

COMPRESSOR


AIR

-CPGRINDING DESULFURIZED COAL FOR POWER PLANTS AND INDUSTRIAL BOILERS

HIGH-SULFUR COAL

MIXING TANK

DRYER

γ

HEAVY MINERALS WAT^R]

FILTER

+ LIMESTONE

CtS0

Figure 1.

4

Air-water oxydesulfurization process



172

COAL

DESULFURIZATION

and temperatures of 140°-200°C. Coals from different geo graphic areas of the U.S. have been treated with air and water in this way, resulting in removal of more than 90% of pyritic sulfur and up to 40% of organic sulfur as sulfuric acid, which is separated from the desulfurized coal by filtration. Fuel value losses are usually less than 10%. Costs for processing coal by this procedure will be somewhere between the less efficient, less thorough and less costly physical coal cleaning methods and the more thorough but much more costly coal conversion techniques. Oxidative desulfurization potentially can upgrade up to 40% of the bituminous coal in the U.S. to environmentally acceptable boiler fuel and can bring most of the rest of the bituminous coals at least close to acceptability with relatively little loss in total fuel value. Literature Cited 1. Reggel, L., Raymond, R., Wender, I., Blaustein, B. D., Am. Chem. Soc., Div. Fuel Chem. Preprints, (1972) 17 (2), 44. 2. Wallace, T. J., Heimlich, Β. Ν., Tetrahedron (1968), 24, 1311. 3. Reed, Ε., "Organic Chemistry of Bivalent Sulfur," Vol. II, p. 64, Chemical Publishing Co., Inc., New York, 1968. 4. LaCount, R. Β., Friedman, Sidney, J. Org. Chem (1977), 42, 2751. 5. Worthy, W., Chem. Eng. News, (July 7, 1975), pp. 24-25. 6. Friedman, Sidney, Warzinski, R. P., Trans. ASME, J. Eng. Power, (1977) 99A, 361. 7. Thomas, J., Warshaw, Α., U.S. Pat. 3,824,084 (Assigned to Chemical Construction Corp.) July 16, 1974. 8. Agarwal, J. C., Giberti, R. Α., Irminger, P. F., Petrovic, L. F., Sareen, S. S., Min. Congr. J., (1975) 61 (3), 40.


14 Sulfur Removal from Coals: Ammonia/Oxygen System S. S.

SAREEN

1


Ledgemont Laboratory, Kennecott Copper Corp., 128 Spring Street, Lexington, MA 02172

The emergence of chemical desulfurization of coal as a viable alternative to stack gas scrubbing (1) has prompted researchers in this field to consider a variety of chemical systems which remove pyritic sulfur or both the pyritic and part of the organic sulfur (2,3,4,5,6). A review of the more prominent chemical desulfurization schemes is presented in a recent article (6). Because chemical desulfurization is cost competitive with stack gas scrubbing (1), utilities are beginning to show an interest in the development of this technology which could provide them with a source of clean fuel to meet the rigorous EPA standards for sulfur emissions. This chapter discusses the sulfur removal from coals using an ammonia/oxygen/water system which removes almost all of the pyritic sulfur and up to 25% of the organic sulfur in about 2 hr. Because organic sulfur removal necessarily implies coal carbon losses, a balance must be struck between the amount of organic sulfur removed and the thermal losses that can be economically tolerated from the coals being cleaned. A l t h o u g h no e f f o r t h a s b e e n made t o o p t i m i z e t h e s y s t e m r e p o r t e d h e r e , t h e r e s u l t s o f B t u l o s s , oxygen consumption, r e t e n t i o n t i m e , e t c . , a r e f a i r l y c o n s i s t e n t w i t h t h e oxygen/water s y s tem f o r p y r i t e r e m o v a l f r o m c o a l s ( 2 ) . The c a r b o n l o s s e s , a s m i g h t b e e x p e c t e d , a r e somewhat h i g h e r . Furthermore, the data p r e s e n t e d h e r e c a n b e u s e d t o c o n s t r u c t a n o p t i m i z a t i o n scheme f o r f u t u r e d e v e l o p m e n t work. Process Description I n t h i s d e s u l f u r i z a t i o n scheme, r u n - o f - m i n e c o a l i s t r e a t e d i n a c o n v e n t i o n a l p r e p a r a t i o n p l a n t , where t h e c o a l i s c r u s h e d and washed t o remove r o c k a n d c l a y m a t e r i a l . The c o a r s e l y c r u s h e d c o a l i s t h e n f e d i n t o c l o s e d - c i r c u i t w e t b a l l m i l l s where i t i s f u r t h e r g r o u n d t o -100 mesh. The g r o u n d s l u r r y i s pumped i n t o TRW E n e r g y S y s t e m s , 7600 C o l s h i r e D r i v e , M c L e a n , V a . 22101 173


174


o x y g e n - s p a r g e d l e a c h r e a c t o r s w h i c h o p e r a t e a t a b o u t 130°C a n d 300 p s i o x y g e n p r e s s u r e . A l l o f t h e p y r i t i c s u l f u r and up t o 2 5 % o f t h e o r g a n i c s u l f u r i s removed i n a b o u t 2 h r . The d e s u l f u r i z e d s l u r r y now goes t h r o u g h a s o l i d / l i q u i d s e p a r a t i o n o p e r a t i o n where t h e c o a l and l i q u i d a r e s e p a r a t e d . Because o f t h e f o r m a t i o n o f s u l f a t e s a n d t h e a b s o r p t i o n o f some o f t h e CO2 ( f r o m c o a l o x i d a t i o n ) i n t o t h e ammonia s o l u t i o n , t h i s m i x e d s u l f a t e / c a r b o n a t e s t r e a m must be r e g e n e r a t e d t o r e c y c l e t h e ammonia b a c k i n t o t h e process. The ammonia r e g e n e r a t i o n may be a c c o m p l i s h e d b y c a l c i n i n g and/or steam s t r i p p i n g . S u l f u r removal from c o a l s as a f u n c t i o n o f ammonia c o n c e n t r a t i o n and r e t e n t i o n t i m e i s d i s c u s s e d below.


Experimental

Conditions

A l l o f t h e e x p e r i m e n t s r e p o r t e d h e r e were c a r r i e d o u t i n a b a t c h mode i n h i g h - p r e s s u r e s t i r r e d a u t o c l a v e s . The a u t o c l a v e s w e r e e q u i p p e d w i t h b a f f l e s , a n d t h e s p e e d o f a g i t a t i o n was c o n t r o l l e d w i t h t h e h e l p o f a t a c h o m e t e r and was v e r i f i e d a t f r e quent i n t e r v a l s w i t h a s t r o b o s c o p e . The s y s t e m was h e a t e d w i t h a j a c k e t e d e l e c t r i c h e a t e r e x t e r i o r t o t h e chamber, a n d t h e t e m p e r a t u r e was c o n t r o l l e d t o w i t h i n a c o u p l e o f d e g r e e s w i t h a t e m p e r ature c o n t r o l l e r . The r e a c t i o n m i x t u r e was c o o l e d r a p i d l y a t t h e end o f t h e e x p e r i m e n t w i t h a c o o l i n g s y s t e m f i t t e d i n s i d e t h e h i g h - p r e s s u r e r e a c t o r s . The mode o f o p e r a t i o n was a s f o l l o w s : 120 gms ( d r y b a s i s ) o f I l l i n o i s No. 6 c o a l was s l u r r i e d i n ammon i a c a l s o l u t i o n s t o g i v e a s o l i d s p u l p d e n s i t y o f 20 w/o. The a u t o c l a v e s w e r e s e a l e d and t h e a i r p u r g e d w i t h i n e r t g a s . This i n s u r e d no r e a c t i o n w i t h t h e c o a l s u l f u r d u r i n g t h e h e a t u p p e r i o d . The h e a t e r a n d s t i r r e r s w e r e t u r n e d o n , and t h e t e m p e r a t u r e was a l l o w e d t o s t a b i l i z e a t 130°C. The s y s t e m was t h e n p r e s s u r i z e d t o y i e l d a n o x y g e n p a r t i a l p r e s s u r e o f 300 p s i , and t h e r e a c t i o n was p e r m i t t e d t o p r o c e e d . The o x y g e n was a s p i r a t e d f r o m t h e v a por space o f t h e a u t o c l a v e , through t h e h o l l o w a g i t a t o r s h a f t , t o t h e i m p e l l e r . The r o t a t i n g i m p e l l e r a c t i o n r e s u l t e d i n t h e g a s being f i n e l y dispersed i n t o the s l u r r y . The v a p o r s p a c e o f t h e r e a c t o r was c o n n e c t e d t o a g a s c h r o m a t o g r a p h f o r measurement o f the gas phase f o r p r o d u c t s o f r e a c t i o n . Except f o r s m a l l q u a n t i t i e s o f g a s removed f o r a n a l y t i c a l p u r p o s e s , t h e r e was no g a s b l e d f r o m t h e s y s t e m o r any o x y g e n s u p p l i e d d u r i n g a n e x p e r i m e n t a l run. M i n u s 100 mesh c o a l was u s e d , a n d t h e d e g r e e o f a g i t a t i o n was f i x e d t o m a i n t a i n t h e system i n a k i n e t i c a l l y c o n t r o l l e d r e gime ( 2 ) . Ammonia c o n c e n t r a t i o n s b e t w e e n 0.5M a n d 5M were s t u d ied. An a n a l y s i s o f t h e s t a r t i n g I l l i n o i s No. 6 c o a l i s l i s t e d i n Table I .


14.

175

Ammonia/Oxygen System for Sulfur Removal

SAREEN

Table I.

Starting Coal

Analysis

ash 19.27% v o l . matter 35.6% f i x e d carbon 45.13% ΒTU (maf) 13477

Total sulfur 4.99% Pyritic sulfur 2.06% Sulfate sulfur 0.65% Organic s u l f u r 2.28% Experimental Results

The c h e m i c a l r e a c t i o n f o r t h e o x i d a t i o n n i a c a l s y s t e m i s g i v e n by E q u a t i o n 1 :


FeS

2

+

4NH + 7/2 H 0 3

2

+

15/4

o f p y r i t e i n an ammo

0 + 4NH* + 2S0^ 2

+

Fe(0H>

3

where a l l of the s u l f i d e s u l f u r i s o x i d i z e d to s o l u b l e s u l f a t e s . C a r e was t a k e n t o i n s u r e t h a t t h e molar r a t i o f o r the e x p e r i m e n t a l s t u d y was a l w a y s i n e x c e s s o f t h e 4 r e q u i r e d s t o i c h iometrically: a r a n g e b e t w e e n 6.5 and 65 was c o n s i d e r e d . The e f f e c t o f r e t e n t i o n t i m e and ammonia c o n c e n t r a t i o n on s u l f u r r e m o v a l f r o m I l l i n o i s No. 6 c o a l s i s g r a p h i c a l l y d i s p l a y e d i n F i g u r e 1. A p p r o x i m a t e l y 90% o f t h e p y r i t i c s u l f u r can be r e moved, and t h e r e a p p e a r s t o be no a p p a r e n t e f f e c t o f NH3 concen t r a t i o n on p y r i t e r e m o v a l . T h e r e seems t o be a d e f i n i t e t r e n d , h o w e v e r , i n t h e o r g a n i c s u l f u r r e m o v a l as a f u n c t i o n o f NH3 con centration. Measurements o f t o t a l change i n s u l f u r c o n t e n t o f t h e c o a l , e x p r e s s e d as l b s . SU2/MMBtu, shows a 50% change b e tween t h e s t a r t i n g c o a l and t h e d e s u l f u r i z e d c o a l . T h i s compares a g a i n s t a 25% change a f t e r d e s u l f u r i z a t i o n o f I l l i n o i s No. 6 c o a l s when u s i n g t h e system where o n l y p y r i t i c s u l f u r i s removed. The d e s u l f u r i z e d c o a l s , a f t e r an treatment, a l s o show no r e s i d u a l s u l f a t e s u l f u r . An i m p o r t a n t c o n s i d e r a t i o n i n any c h e m i c a l d e s u l f u r i z a t i o n p r o c e s s i n which the c o a l s u l f u r i s o x i d i x e d i s the o x i d a n t con sumption. For t h i s p r o c e s s the oxygen consumption to o x i d i z e the c o a l s u l f u r s p e c i e s and t h e c o a l i t s e l f may be l i s t e d as f o l l o w s :

NH3/FeS2

O2/H2O

(2)

(1)

Reaction with

(2)

O x i d a t i o n of o r g a n i c

sulfur

(3)

Oxygen u p t a k e by

coal

(4)

O x i d a t i o n o f c o a l t o f o r m CO phase

(5)

Formation of carbonates i n

NH3/O2

pyrite

the

and

CO2

i n the

gaseous

solution

The s t o i c h i o m e t r i c o x y g e n c o n s u m p t i o n f o r t h e p y r i t e r e a c t i o n , g i v e n by E q u a t i o n c a l c u l a t e s t o be l b . 02/lb.

FeS2.

1,

1.0


(1)

COAL


176

DESULFURIZATION

REACTION TIME, MINS.

Figure 1.

Sulfur removal as a function of ammonia concentration and time



14.

SAREEN


177

In the o x i d a t i o n of p y r i t e w i t h oxygen, i t i s inescapable t h a t oxygen w i l l a l s o r e a c t w i t h the c o a l c a r b o n . T h i s o x i d a t i o n o f t h e c o a l u s u a l l y r e s u l t s i n t h e f o r m a t i o n o f CO and CO2, together with soluble coal a c i d s . There i s a g r e a t e r p r o p e n s i t y f o r the f o r m a t i o n of c o a l a c i d s i n b a s i c systems than i n a c i d systems. F u r t h e r m o r e , t h e r e i s some p i c k u p o f o x y g e n by t h e c o a l t o f o r m an i n t e r m e d i a t e oxygen-coal complex. The g a s e s , as a n a l y z e d i n t h e v a p o r s p a c e o f t h e a u t o c l a v e s , u s i n g a gas c h r o m a t o g r a p h , show t h a t CO f o r m a t i o n i s n e g l i g i b l e and t h a t CO2 i s t h e m a j o r p r o d u c t o f r e a c t i o n . Some o f t h e CO2 formed from carbon o x i d a t i o n tends t o d i s s o l v e i n the ammoniacal l i q u o r and r e p o r t as c a r b o n a t e s i n s o l u t i o n . To d e t e r m i n e a c c u r a t e l y the e x a c t oxygen consumption f o r c o a l o x i d a t i o n , s o l u t i o n a n a l y s e s w e r e c o n d u c t e d t o measure t h i s amount o f c a r b o n a t e f o r m e d . T h e s e a n a l y s e s showed t h a t t h e amount o f c a r b o n a t e m e a s u r e d i n s o l u t i o n i n c r e a s e d w i t h i n c r e a s i n g ammonia c o n c e n t r a t i o n . The t o t a l o x y g e n consumed by c o a l o x i d a t i o n t o f o r m b o t h CO2 i n t h e v a p o r s p a c e and c a r b o n a t e i n s o l u t i o n , as a f u n c t i o n o f r e t e n t i o n t i m e and ammonia c o n c e n t r a t i o n , i s shown i n F i g u r e 2. These r e s u l t s show t h a t c o a l o x i d a t i o n i s f a i r l y i n s e n s i t i v e t o t h e ammonia concentration. B e c a u s e o f t h e f o r m a t i o n o f an o x y g e n - c o a l c o m p l e x , t h e r e i s some o x y g e n t i e d up w i t h t h e c o a l . T h i s c o n s u m p t i o n i s g r a p h i c a l l y d i s p l a y e d i n F i g u r e 3, w h i c h a g a i n shows no dependence on ammonia c o n c e n t r a t i o n . These oxygen v a l u e s r e f l e c t the t o t a l oxygen c o n t e n t o f t h e c o a l , f o r b o t h t h e s t a r t i n g c o a l s and a f t e r dep y r i t i z a t i o n , as m e a s u r e d by n e u t r o n a c t i v a t i o n t e c h n i q u e s . A minimum o x y g e n c o n s u m p t i o n f o r t h i s p r o c e s s i s t a b u l a t e d i n T a b l e II. Table I I .

Minimum Oxygen C o n s u m p t i o n LBS.

0 / L B . COAL 2

O2

for pyrite reaction

0.0375

a

O2

u p t a k e by

coal

0.0340

b

O2

f o r C0

C0 =

0.0350

b

2

+

3

0.1065 a

B a s e d on 2% p y r i t i c s u l f u r c o a l . A f t e r 2 hr. of s u l f u r removal.

T h i s t a b l e does n o t t a k e i n t o a c c o u n t any o x y g e n c o n s u m p t i o n f o r o r g a n i c s u l f u r o x i d a t i o n , w h i c h i s d i f f i c u l t t o measure. For a p l a n t p r o c e s s i n g 8000 t o n s / d a y o f 2% p y r i t i c s u l f u r c o a l ( w i t h a p y r i t i c s u l f u r / o r g a n i c s u l f u r r a t i o o f 1 ) , t h e o x y g e n demand b a s e d on T a b l e I I c a l c u l a t e s t o be 850 t o n s / d a y . W i t h a 20% c o n t i n g e n c y


178

COAL

•

0.5MNH

Ô

1.04MNH

Ο

1.94MNH-,

3

3

Ο


DESULFURIZATION

Ο Δ

•· t ? 20

J 40

-L

L

60

80

100

120 140

160 180

REACTION TIME, MINS. Figure 2.

Oxygen consumption for coal oxidation

Figure 3.

Oxygen uptake by coal


14.

Ammonia/Oxygen

SAREEN

System for

Sulfur

179

Removal

f a c t o r t o a l l o w f o r o r g a n i c s u l f u r o x i d a t i o n , a 1000 t o n s / d a y o x y gen p l a n t w o u l d be n e e d e d . T h i s t o t a l o x y g e n d u t y i s t h e same as that required f o r coal d e s u l f u r i z a t i o n using the system (2). An i m p o r t a n t c o n s i d e r a t i o n f o r t h e v i a b i l i t y o f any d e s u l f u r i z a t i o n process i s the o v e r a l l thermal e f f i c i e n c y o f the system. The B t u l o s s , on a m o i s t u r e - a s h - f r e e b a s i s , as a f u n c t i o n o f r e a c t i o n t i m e and ammonia c o n c e n t r a t i o n i s p r e s e n t e d i n F i g u r e 4. T h i s g r a p h shows t h a t b e t w e e n 8% and 1 3 % l o s s may be e x p e c t e d a f t e r 2 h r . o f s u l f u r r e m o v a l . The p a i r i n g o f t h e B t u l o s s a s a f u n c t i o n o f ammonia c o n c e n t r a t i o n shown i n F i g u r e 4 i s n o t immed i a t e l y o b v i o u s . The l o s s o f c a r b o n d u r i n g t h e d e s u l f u r i z a t i o n p r o c e s s i s g r a p h i c a l l y d i s p l a y e d i n F i g u r e 5. I n a l l c a s e s t h e c a r b o n l o s s i s much g r e a t e r t h a n c a n be a c c o u n t e d f o r by CO2 and carbonate formation. This suggests that the d i f f e r e n c e reports i n s o l u t i o n as c o a l a c i d s . The f o r m a t i o n o f t h e s e a c i d s i s n o t s u r p r i s i n g s i n c e t h e r e a c t i o n o f a l k a l i s w i t h c o a l t o form humic a c i d s i s w e l l known. A c o m p a r i s o n between t h e k e y parameters o f t h e systems ( o n l y p y r i t i c s u l f u r r e m o v a l ) and t h e system ( p y r i t i c s u l f u r and some o r g a n i c s u l f u r r e m o v a l ) i s p r e s e n t e d i n T a b l e I I I .


O2/H0O

H2O/O2

NH3/O2

Table I I I .

Comparison between H 0 / 0 ?

9

and mj0

Systems

o

H 0/0 2

2

N H

3

/ 0

3

2

S u l f u r removal pyritic

+

90 %

+

90 %

organic

0 %

25

%

Oxygen c o n s u m p t i o n (lbs. 0 / l b . coal) 2

Btu

0

2

f o rpyrite reaction

0.035

0.0375

0

2

uptake by c o a l

0.054

0.0340

0

2

t o form C 0

0.032

0.0350

loss

2

(MAF)

Carbon l o s s

(MAF)

8 %

13

%

10%

6.5%

I l l i n o i s No. 6 c o a l s , 20% s l u r r y d e n s i t y , 2% p y r i t i c s u l f u r . The h i g h e r B t u and c a r b o n l o s s e s f o r t h e N H / 0 s y s t e m a r e t o be e x p e c t e d b e c a u s e o r g a n i c s u l f u r r e m o v a l n e c e s s a r i l y i m p l i e s some c o a l (and t h e r e f o r e B t u ) l o s s e s . 3

2



180

COAL

DESULFURIZATION

2h 0

20

40

60

80

100 120 140

160 180 200

REACTION TIME, MINS. Figure 4.

Figure 5.

Btu loss from coals

Carbon loss from coals


14.


SAREEN

181

Summary and C o n c l u s i o n s 1. I n c r e a s i n g r e a c t i o n t i m e a n d ammonia c o n c e n t r a t i o n i m proved t h e extent o f o r g a n i c s u l f u r removal. F o r example, a f t e r 2 h r . u s i n g a 5M NH^ s o l u t i o n , 2 5 % o f t h e o r g a n i c s u l f u r c a n be removed. 2. C h a n g i n g t h e NH^ c o n c e n t r a t i o n h a d no a p p a r e n t a f f e c t on p y r i t i c s u l f u r removal. 3. The o x y g e n consumed t o o x i d i z e t h e c o a l c a r b o n ( r e p o r t i n g a s C 0 i n t h e gas p h a s e and c a r b o n a t e i n s o l u t i o n ) i s f a i r l y i n s e n s i t i v e t o t h e NH^ c o n c e n t r a t i o n . Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch014

2

4. Ammonia c o n c e n t r a t i o n h a s no a p p a r e n t a f f e c t on o x y g e n uptake by t h e c o a l . 5. B o t h t h e ammonia c o n c e n t r a t i o n and r e a c t i o n t i m e h a v e a n e f f e c t on t h e B t u a n d c a r b o n v a l u e s o f c o a l . Increasing either one d e c r e a s e s t h e B t u and c a r b o n v a l u e . A s much a s a 1 3 % B t u a n d 10% c a r b o n l o s s may be r e a l i z e d w i t h u s i n g a 3M NH^ s o l u t i o n and r e a c t i n g t h e c o a l f o r 2 h r . The l a r g e c a r b o n l o s s e s a r e f r o m t h e formation of coal acids.

Literature Cited

1. Agarwal, J. C., Giberti, R. Α., Irminger, P. F., Petrovic, L. J., Sareen, S. S., Min. Congr. J., (1975), 61 (3), 40-43. 2. Sareen, S. S., Giberti, R. Α., Irminger, P. F., Petrovic, L. J., AIChE Symp. Ser., (1977), 73 (165), 183-189. 3. Lorenzi, L. Jr., Land, J. S., VanNice, L. J., Koutsoukas, E. P., Meyers, R. Α., Coal Age, (Nov. 1972), 77 (11), 70-76. 4. Diaz, A. F., Guth, E. D., U.S. Patent No. 3,909,211 (1975). 5. Smith, E. G., Am. Chem. Soc., Div. of Fuel Chemistry, 169th National Meeting, Philadelphia, Pa., April 6-11, 1975. 6. "Coal Cleaning Readies for Wider Sulfur-Removal Role," Chem. Eng., (March 1, 1976), 83 (6), 70-74.


15 Desulfurizing Coal with Alkaline Solutions Containing Dissolved Oxygen


C. Y. TAI,* G. V. GRAVES, and T. D. WHEELOCK Iowa State University, Department of Chemical Engineering and Nuclear Engineering, Energy and Mineral Resources Research Institute, Ames, IA 50011 The extraction of pyritic sulfur from coal by leaching the comminuted material with hot aqueous solutions containing dissolved oxygen has been demonstrated in numerous laboratory experiments (1-6). Although acidic solutions have generally been used for such experiments, basic solutions appear to offer several important advantages. Thus Majima and Peters (7) showed that the rate of extraction of sulfur from relatively pure pyrite is much greater in basic solutions containing dissolved oxygen than in neutral solutions. Moreover it has been shown recently that basic solutions containing ammonium hydroxide and oxygen can extract a significant portion of the organic sulfur as well as most of the inorganic sulfur from coal at relatively moderate temperatures (e.g., 130°C) (4,5) whereas higher temperatures (150°-200°C) seem to be required with acidic solutions to remove organic sulfur (6). Furthermore some types of basic solutions are much less corrosive towards the common materials of construction than acidic solutions. A l t h o u g h the chemical kinetics and mechanism o f pyrite r e a c tion with an o x y g e n - b e a r i n g caustic solution have been studied, t h e y a r e n o t c o m p l e t e l y d e f i n e d . S t e n h o u s e and A r m s t r o n g ( 8 ) f o u n d s u l f a t e i o n s and i r o n o x i d e s t o be t h e f i n a l p r o d u c t s o f reaction. B o t h Fe2Û3 and Fe3Û4 were i d e n t i f i e d i n t h e r e s i d u e . I t a p p e a r e d t o t h e s e i n v e s t i g a t o r s t h a t t h e i r o n o x i d e s formed a s t a b l e l a y e r around t h e u n r e a c t e d p y r i t e . As a r e s u l t o f a l a t e r i n v e s t i g a t i o n , B u r k i n and Edward ( 9 ) c o n c l u d e d t h a t t h e f i n a l o x i d a t i o n p r o d u c t o f i r o n i s maghemite (yFe203) w h i c h i s formed t h r o u g h a s e r i e s o f t o p o t a c t i c t r a n s f o r m a t i o n s . These i n v e s t i g a t o r s o b s e r v e d t h a t t h e r a t e o f a t t a c k was more r a p i d a l o n g g r a i n b o u n d a r i e s and c r a c k s i n impure and i m p e r f e c t p y r i t e c r y s t a l s , w i t h t h e r e s u l t t h a t t h e s e p a r t i c l e s were l e a c h e d more r a p i d l y t h a n p a r t i c l e s c o n t a i n i n g few i m p e r f e c t i o n s and i m p u r i t i e s ,

*Present address: T a i w a n , R.O.C.

Chung-Shen I n s t i t u t e o f S c i e n c e and T e c h n o l o g y ,

182



15.

TAi E T A L .

Alkaline

Solutions

with Dissolved

Oxygen

183

even though t h e i n s o l u b l e o x i d a t i o n p r o d u c t adhered t o t h e imper f e c t c r y s t a l s b u t n o t t o t h e p e r f e c t o n e s . As a r e s u l t o f t h e i n t e r g r a n u l a r a t t a c k by t h e l e a c h s o l u t i o n , t h e s m a l l e r c r y s t a l s w i t h i n p a r t i c l e s composed o f d i f f e r e n t - s i z e d c r y s t a l s were d e s u l f u r i z e d b e f o r e t h e l a r g e r c r y s t a l s . The r e a c t i o n r a t e i n c r e a s e d w i t h temperature a c c o r d i n g t o the A r r h e n i u s e q u a t i o n w i t h an a c t i v a t i o n energy o f 9 k c a l / m o l . A l s o t h e r e a c t i o n r a t e was c o n t o l l e d by t h e o x y g e n c o n c e n t r a t i o n a t t h e m i n e r a l - s o l u t i o n i n t e r face so t h e r a t e i n c r e a s e d w i t h the oxygen p a r t i a l p r e s s u r e . In a d d i t i o n , the r a t e increased with i n c r e a s i n g concentration o f s o d i u m h y d r o x i d e up t o 2 wt %. H i g h e r c o n c e n t r a t i o n s r e d u c e d t h e rate s l i g h t l y . I n a s o l u t i o n o f some b a s e s u c h a s s o d i u m h y d r o x i d e , t h e s t o i c h i o m e t r y o f t h e r e a c t i o n o f p y r i t e w i t h o x y g e n and t h e s u b s e q u e n t n e u t r a l i z a t i o n o f t h e a c i d p r o d u c e d c a n p r o b a b l y be r e p r e s e n t e d by t h e f o l l o w i n g e q u a t i o n s : FeS

2

+ ^| 0

2

+ 2 H 0 = y F e ^ + 2 H SC> 2

2

4

2 H S 0 . + 4 NaOH = 2 N a S 0 , + 4 H 0 2 4 2 4 2 o

o

o

(1) (2)

A l t h o u g h these e q u a t i o n s s u g g e s t t h a t the main purpose o f t h e a l k a l i i s t o n e u t r a l i z e t h e a c i d and t o d r i v e t h e f i r s t r e a c t i o n t o c o m p l e t i o n , t h e a c t u a l r e a c t i o n mechanism i s p r o b a b l y more c o m p l e x w i t h t h e a l k a l i p l a y i n g a more s u b t l e r o l e a s w e l l a s t h e o b v i o u s one. An i n v e s t i g a t i o n by McKay a n d H a l p e r n ( 1 0 ) o f t h e r e a c t i o n o f p y r i t e w i t h o x y g e n i n a c i d i c s o l u t i o n s showed t h a t t h e p r o d u c t d i s t r i b u t i o n , and t h e r e f o r e t h e r e a c t i o n mechanism, i s q u i t e d i f f e r e n t f r o m t h a t n o t e d above f o r b a s i c s o l u t i o n s . Thus p y r i t e was c o n v e r t e d t o s o l u b l e f e r r o u s and f e r r i c s u l f a t e , s u l f u r i c a c i d , and e l e m e n t a l s u l f u r when l e a c h e d w i t h o x y g e n - b e a r i n g a c i d i c s o l u t i o n s a t 100°-130°C. The p r o d u c t d i s t r i b u t i o n depended on t e m p e r a t u r e a n d a c i d i t y , w i t h a l o w e r t e m p e r a t u r e and h i g h e r a c i d i t y f a v o r i n g t h e p r o d u c t i o n o f e l e m e n t a l s u l f u r a n d a h i g h e r tem p e r a t u r e and l o w e r a c i d i t y f a v o r i n g t h e p r o d u c t i o n o f s u l f u r i c a c i d and s o l u b l e s u l f a t e s . A l s o a t m o d e r a t e pH ( b u t n o t a t l o w ρΗ), t h e f e r r i c h y d r o x i d e h y d r o l y z e d , and f e r r i c o x i d e p r e c i p i tated. The A r r h e n i u s a c t i v a t i o n e n e r g y was d e t e r m i n e d t o be 13 k c a l / m o l , w h i c h , b e i n g s i g n i f i c a n t l y l a r g e r t h a n t h a t n o t e d above for the reaction of p y r i t e i na caustic s o l u t i o n , indicates a g r e a t e r e n e r g y b a r r i e r f o r t h e r e a c t i o n i n a n a c i d i c medium. The p r e s e n t i n v e s t i g a t i o n was u n d e r t a k e n t o e v a l u a t e t h e t e c h n i c a l f e a s i b i l i t y o f e x t r a c t i n g s u l f u r from c o a l w i t h h o t oxygen-bearing s o l u t i o n s . S i n c e i t was s o o n c o n f i r m e d t h a t a l k a l i n e o r b a s i c s o l u t i o n s r e s u l t e d i n a much g r e a t e r r a t e o f e x t r a c t i o n t h a n a c i d i c s o l u t i o n s , c o n s i d e r a b l e e m p h a s i s was p l a c e d on d e t e r m i n i n g t h e e f f e c t i v e n e s s o f d i f f e r e n t a l k a l i s a n d a l k a l i concentrations. Several h i g h - s u l f u r bituminous c o a l s , as w e l l as


184

COAL

DESULFURIZATION

p y r i t e w h i c h had been i s o l a t e d f r o m one o f t h e s e c o a l s , were l e a c h e d i n a s m a l l s t i r r e d r e a c t o r under a v a r i e t y of e x p e r i mental c o n d i t i o n s . In a d d i t i o n the o v e r - a l l e f f e c t i v e n e s s of c h e m i c a l l e a c h i n g i n c o m b i n a t i o n w i t h p h y s i c a l b e n e f i c i a t i o n was investigated.


Experimental L e a c h i n g e x p e r i m e n t s were c a r r i e d o u t i n a 1-L, s t a i n l e s s s t e e l a u t o c l a v e e q u i p p e d w i t h a r e m o v a b l e n i c k e l l i n e r and an a g i t a t o r c o n s i s t i n g o f two p i t c h e d b l a d e t u r b i n e i m p e l l e r s (7.3 cm d i a m e t e r ) mounted on a s h a f t d r i v e n by a c o m p r e s s e d a i r m o t o r . The a u t o c l a v e was a l s o e q u i p p e d w i t h a p r e s s u r e gauge, t e m p e r a t u r e i n d i c a t o r , and e l e c t r i c h e a t i n g j a c k e t . A s u s p e n s i o n o f c o a l o r p y r i t e p a r t i c l e s i n an a l k a l i n e s o l u t i o n o f a s p e c i f i c c o n c e n t r a t i o n was p l a c e d i n t h e r e a c t o r w h i c h was t h e n s e a l e d and h e a t e d t o a s p e c i f i c o p e r a t i n g t e m p e r a ture. A f t e r t h e s y s t e m a t t a i n e d t h i s t e m p e r a t u r e , o x y g e n was introduced f r o m a h i g h - p r e s s u r e c y l i n d e r e q u i p p e d w i t h a comb i n a t i o n p r e s s u r e - r e d u c i n g v a l v e and r e g u l a t o r . D u r i n g t h e s u c c e e d i n g o p e r a t i o n , t h e s y s t e m p r e s s u r e was k e p t c o n s t a n t by s u p p l y i n g o x y g e n on demand. A l s o a s m a l l amount o f gas was b l e d c o n t i n u o u s l y f r o m t h e r e a c t o r t o a v o i d any b u i l d - u p o f g a s e o u s r e a c t i o n p r o d u c t s i n the s y s t e m . R e a c t i o n c o n d i t i o n s were k e p t c o n s t a n t f o r a s p e c i f i c t i m e w h i l e t h e m a t e r i a l was l e a c h e d . At t h e end o f t h e r e a c t i o n p e r i o d , the f l o w o f o x y g e n i n t o t h e s y s t e m was s t o p p e d , and t h e s y s t e m was c o o l e d . Throughout the o p e r a t i o n t h e a g i t a t o r was k e p t r u n n i n g a t a c o n s t a n t speed w h i c h was u s u a l l y i n the r a n g e o f 250-350 rpm. A f t e r a run the l e a c h e d s o l i d s were r e c o v e r e d , d r i e d , and w e i g h e d . C o a l s a m p l e s w e r e a n a l y z e d by t h e s t a n d a r d ASTM methods o f a n a l y s i s ( 1 1 ) . When p y r i t e a l o n e was l e a c h e d , t h e amount o f s u l f u r e x t r a c t e d was d e t e r m i n e d by m e a s u r i n g t h e s u l f a t e c o n t e n t o f t h e s p e n t l e a c h a n t u s i n g t h e s u l f a t e t i t r a t i o n method o f F r i t z and Yamaraura ( 1 2 ) . C o a l s a m p l e s f r o m t h e B i g Ben, ICO, and ISU Demonstration M i n e No. 1, a l l l o c a t e d i n S o u t h e a s t e r n Iowa, were l e a c h e d . The rank of the c o a l from these mines i s h i g h v o l a t i l e C b i t u m i n o u s c o a l ; t y p i c a l c o m p o s i t i o n s a r e shown i n T a b l e I . S i n c e t h e c o a l from these mines i s v e r y heterogeneous, v a r i o u s batches used f o r s p e c i f i c s e t s o f e x p e r i m e n t s were r e - a n a l y z e d and the c o m p o s i t i o n reported along with other experimental r e s u l t s . A h a n d p i c k e d sample o f i r o n p y r i t e s was o b t a i n e d f r o m t h e c o a l d e p o s i t a t ISU D e m o n s t r a t i o n M i n e No. 1. T h i s m a t e r i a l was v e r y i m p u r e and seemed t o c o n t a i n a b o u t 74% FeS2» Nevertheless, i t was g r o u n d and s c r e e n e d i n t o v a r i o u s s i z e d f r a c t i o n s w h i c h were u s e d s u b s e q u e n t l y f o r v a r i o u s l e a c h i n g e x p e r i m e n t s . The s u l f u r c o n t e n t o f t h e d i f f e r e n t s i z e f r a c t i o n s i s shown i n T a b l e II. I n a d d i t i o n t o p y r i t i c s u l f u r , t h e m a t e r i a l c o n t a i n e d some s u l f u r i n t h e f o r m o f s u l f a t e s and some i n a f o r m w h i c h was n e i t h e r p y r i t i c nor s u l f a t e .


15.

TAi E T A L .

Alkaline

Solutions

with Dissolved

185

Oxygen

T a b l e I . P r o x i m a t e A n a l y s i s o f Iowa C o a l s

Proximate A n a l y s i s

Source o f C o a l


Big

Ben mine

Volatile Matter

Fixed Carbon

(wt %)

Ash

Moisture

37.5

48.8

1.2

12.5

ICO mine

44.0

42.0

4.5

9.5

ISU mine

38.1

44.2

2.2

15.5

Table I I .

Composition of Iron

Pyrites

Composition Size Fraction (U.S. S e r i e s Mesh)

Iron

Pyritic Sulfur

Sulfate Sulfur

(wt %) Total Sulfur

41.7

-60/+80 39.,2

0.,5

40.9

-200/+230

36.,4

0.,7

40.3

-230/+270

36.,3

0..7

39.4

-120/+140

Other

42.5

16.6

P y r i t e Leaching Experiments A s e r i e s o f l e a c h i n g e x p e r i m e n t s was c a r r i e d o u t t o d e t e r mine t h e e f f e c t o f v a r i o u s s y s t e m p a r a m e t e r s on t h e e x t r a c t i o n o f s u l f u r f r o m impure p y r i t e . F o r each experiment a s u s p e n s i o n cons i s t i n g o f 2.0 g o f p y r i t e p a r t i c l e s and 500 m l o f a n aqueous s o l u t i o n was t r e a t e d i n t h e s t i r r e d a u t o c l a v e a t 150°C w i t h o x y g e n d i s s o l v e d under a p a r t i a l p r e s s u r e o f 3.27 atm. S i n c e t h e v a p o r p r e s s u r e o f w a t e r a t t h i s t e m p e r a t u r e i s 4.56 atm, t h e t o t a l s y s t e m p r e s s u r e was 7.8 atm. U n l e s s i n d i c a t e d o t h e r w i s e , t h e l e a c h i n g o p e r a t i o n under o x y g e n p r e s s u r e a t t h e s p e c i f i e d t e m p e r a t u r e was c o n d u c t e d f o r 1 h r . The c o n v e r s i o n o f a l l forms o f s u l f u r i n t h e p a r t i c l e s t o s o l u b l e s u l f a t e was d e t e r m i n e d by a n a l y z ing the spent l e a c h a n t . The r e s u l t s p r e s e n t e d i n F i g u r e 1 i n d i c a t e t h a t among t h e v a r i o u s a l k a l i s t e s t e d , s o d i u m c a r b o n a t e was t h e most e f f e c t i v e . E s s e n t i a l l y a l l o f t h e s u l f u r was e x t r a c t e d f r o m -200/+230 mesh



186


p y r i t e p a r t i c l e s i n 1.0 h r by an o x y g e n a t e d s o l u t i o n c o n t a i n i n g 1.5 wt % s o d i u m c a r b o n a t e . The b e s t r e s u l t s o b t a i n e d w i t h e i t h e r s o d i u m h y d r o x i d e o r s o d i u m p h o s p h a t e were s l i g h t l y l e s s f a v o r a b l e and w i t h ammonium c a r b o n a t e much l e s s f a v o r a b l e . The ammonium c a r b o n a t e s o l u t i o n s were n o t i c e a b l y l e s s b a s i c t h a n t h e o t h e r s o l u t i o n s and t h i s f a c t o r p r o b a b l y a c c o u n t e d f o r t h e p o o r e r r e s u l t s o b t a i n e d w i t h them. However, t h e ammonium c a r b o n a t e s o l u t i o n s , as w e l l as t h e o t h e r a l k a l i n e s o l u t i o n s , a l l gave b e t t e r r e s u l t s t h a n w a t e r and o x y g e n a l o n e . Thus o n l y 27% o f the s u l f u r was e x t r a c t e d f r o m t h e p y r i t e d u r i n g a r u n made w i t h o u t any alkali. The e f f e c t i v e n e s s o f a l l o f the a l k a l i s i n c r e a s e d w i t h i n i t i a l c o n c e n t r a t i o n up t o some optimum v a l u e and t h e n d e c r e a s e d . F o r s o d i u m h y d r o x i d e t h e optimum i n i t i a l c o n c e n t r a t i o n was a b o u t 1 wt %, f o r s o d i u m c a r b o n a t e 1.5 wt %, f o r s o d i u m p h o s p h a t e 3 wt %, and f o r ammonium c a r b o n a t e 4 wt %. The s h a r p i n c r e a s e i n c o n v e r s i o n f o r i n i t i a l c o n c e n t r a t i o n s a t the low end o f the c o n c e n t r a t i o n s c a l e seems t o be r e l a t e d t o t h e amount o f a l k a l i r e q u i r e d to n e u t r a l i z e a l l of the a c i d produced i n o x i d i z i n g the pyrite. Thus i f i t i s assumed t h a t a l l o f the s u l f u r i n t h e s o l i d s was c o n v e r t e d i n t o s u l f u r i c a c i d d u r i n g t h e l e a c h i n g o p e r a t i o n , i t w o u l d have r e q u i r e d an i n i t i a l s o d i u m h y d r o x i d e c o n c e n t r a t i o n o f 0.40 wt % t o n e u t r a l i z e a l l o f t h e a c i d p r o duced. I n t e r e s t i n g l y enough, t h e d a t a p r e s e n t e d i n F i g u r e 1 show t h a t t h e c o n v e r s i o n f e l l o f f s h a r p l y when l e s s t h a n 0.40 wt % c a u s t i c was u s e d . The amount o f s o d i u m c a r b o n a t e r e q u i r e d t o n e u t r a l i z e t h e a c i d depends on t h e f i n a l p r o d u c t s o f n e u t r a l i z a t i o n . Two p o s s i b i l i t i e s a r e shown b e l o w . H S0. + N a C 0 2 4 2 3 o

o

o

= Na S0. + C0 + H 0 2 4 2 2 o

o

(3)

o

H S 0 . + 2 N a C 0 = N a S 0 . + 2 NaHC0 2 4 2 3 2 4 3 o

o

o

o

o

(4)

The f i r s t r e a c t i o n w o u l d have r e q u i r e d an i n i t i a l s o d i u m c a r b o n a t e c o n c e n t r a t i o n o f 0.53 wt % t o n e u t r a l i z e a l l o f t h e s u l f u r i c a c i d w h e r e a s t h e s e c o n d r e a c t i o n w o u l d have r e q u i r e d an i n i t i a l c o n c e n t r a t i o n o f 1.1 wt %. The e x p e r i m e n t a l r e s u l t s ( F i g u r e 1) i n d i c a t e t h a t t h e c o n v e r s i o n f e l l o f f s h a r p l y when l e s s t h a n a b o u t 1 wt % s o d i u m c a r b o n a t e was u s e d . I n t h e c a s e o f s o d i u m p h o s p h a t e an i n i t i a l c o n c e n t r a t i o n o f 1.65 wt % w o u l d have been r e q u i r e d t o n e u t r a l i z e a l l o f the p o s s i b l e s u l f u r i c a c i d a c c o r d i n g to the f o l l o w i n g r e a c t i o n : H S 0 . + 2 N a P 0 . = N a S 0 . + 2 Na HP0. 2 4 3 4 2 4 2 4 o

o

o

o

(5)

A l t h o u g h the e x p e r i m e n t a l r e s u l t s shown i n F i g u r e 1 i n d i c a t e t h a t the c o n v e r s i o n f e l l o f f s h a r p l y between 2 and 3 wt %, the s p a r s i t y o f t h e d a t a l e a v e c o n s i d e r a b l e d o u b t as t o the e x a c t c r i t i c a l



15.

TAI E T A L .

Alkaline

Solutions

with Dissolved

Oxygen

187

concentration. Why t h e c o n v e r s i o n d e c l i n e d a t h i g h e r a l k a l i c o n c e n t r a t i o n s w h i c h e x c e e d e d t h e optimum l e v e l s c a n n o t be e x p l a i n e d w i t h c e r tainty. A s i m i l a r d e c l i n e was o b s e r v e d by B u r k i n and Edwards ( 9 ) when p y r i t e was l e a c h e d w i t h c a u s t i c s o l u t i o n s , a n d t h e y a t t r i b u t ed t h e d e c l i n e t o the r e d u c e d s o l u b i l i t y o f o x y g e n i n t h e s e s o l u tions. A l s o s i m i l a r b e h a v i o r was o b s e r v e d i n l e a c h i n g b o t h g a l e n a and m o l y b d e n i t e w i t h c a u s t i c s o l u t i o n s c o n t a i n i n g d i s s o l v e d o x y g e n (13,14). I n the case o f both m i n e r a l s , a d e c l i n e i n r e a c t i o n r a t e w i t h i n c r e a s i n g a l k a l i c o n c e n t r a t i o n was a t t r i b u t e d t o t h e d e c r e a s i n g s o l u b i l i t y o f oxygen. The r e s u l t s o f l e a c h i n g d i f f e r e n t s i z e d f r a c t i o n s o f p y r i t e w i t h sodium carbonate s o l u t i o n s o f d i f f e r e n t c o n c e n t r a t i o n s a r e p r e s e n t e d i n F i g u r e 2. C l e a r l y t h e e f f e c t o f p a r t i c l e s i z e o n c o n v e r s i o n was v e r y p r o n o u n c e d w i t h t h e c o n v e r s i o n i n c r e a s i n g i n an a l m o s t e x p o n e n t i a l manner a s t h e s i z e was r e d u c e d ( F i g u r e 2 ) . P a r t i c l e s s m a l l e r t h a n 60 ym i n d i a m e t e r were c o m p l e t e l y d e s u l f u r i z e d i n 1.0 h r by s o l u t i o n s c o n t a i n i n g 2-5 wt % s o d i u m c a r b o n a t e f o r t h e c o n d i t i o n s shown i n F i g u r e 2. On t h e o t h e r h a n d , p a r t i c l e s l a r g e r t h a n 210 ym i n d i a m e t e r were o n l y a b o u t h a l f d e s u l f u r i z e d u n d e r t h e s e c o n d i t i o n s . F i g u r e 2 a l s o shows t h e advantage o f u s i n g an a l k a l i n e s o l u t i o n . The l o w e r c u r v e i n t h i s d i a g r a m r e p r e s e n t e d t h e c o n v e r s i o n o b t a i n e d when no a l k a l i was added t o t h e s y s t e m . Even w i t h t h e s m a l l e s t p a r t i c l e s o f p y r i t e , o n l y 3 5 % o f t h e s u l f u r was e x t r a c t e d i n the a b s e n c e o f a n a l k a l i . S e v e r a l r u n s were made u s i n g l o n g e r r e a c t i o n t i m e s t o s e e how the c o n v e r s i o n w o u l d change w i t h t i m e ( F i g u r e 3 ) . The r e s u l t s i n d i c a t e t h a t t h e r e a c t i o n r a t e d e c r e a s e d a s the b a t c h l e a c h i n g o p e r a t i o n p r o c e e d e d . The d e c l i n i n g r a t e c o u l d have been c a u s e d by t h e d e c r e a s i n g a v a i l a b i l i t y o f u n r e a c t e d p y r i t e , i n c r e a s i n g resistance to diffusion of reactants within p a r t i c l e s , increasing c o n c e n t r a t i o n o f some r a t e - i n h i b i t i n g r e a c t i o n p r o d u c t i n t h e l e a c h s o l u t i o n , o r a combination o f these f a c t o r s . Coal Leaching

Experiments

A s e r i e s o f l e a c h i n g e x p e r i m e n t s was c a r r i e d o u t t o d e t e r mine t h e e f f e c t s o f v a r i o u s a l k a l i s and a l k a l i c o n c e n t r a t i o n s on t h e d e s u l f u r i z a t i o n o f c o a l f r o m t h e I S U D e m o n s t r a t i o n M i n e No. 1. The raw c o a l was p u l v e r i z e d s o t h a t 9 0 % was f i n e r t h a n 200 mesh. F o r e a c h e x p e r i m e n t 50 g o f c o a l and 500 ml o f w a t e r o r a l k a l i n e s o l u t i o n were p l a c e d i n t h e s t i r r e d a u t o c l a v e . The c h e m i c a l t r e a t m e n t was c a r r i e d o u t f o r 2 h r a t 150°C w i t h o x y g e n d i s s o l v e d u n d e r a p a r t i a l p r e s s u r e o f 3.27 atm and u s i n g a t o t a l s y s t e m p r e s s u r e o f 7.8 atm. The t r e a t e d c o a l was r e c o v e r e d , d r i e d , w e i g h e d , and a n a l y z e d t o d e t e r m i n e t h e e f f e c t i v e n e s s o f t h e t r e a t ment . The b e s t o v e r a l l r e s u l t s were o b t a i n e d w i t h s o d i u m c a r b o n a t e among t h e f o l l o w i n g a l k a l i s w h i c h were t e s t e d i n v a r i o u s c o n c e n trations: sodium carbonate, sodium h y d r o x i d e , sodium phosphate,



188


PYRITE -200/+23O MESH 7.8 atm. TOTAL PRESS. 150 °C 1.0 h r .

Figure 1. The effect of different alkalis and alkali concentrations on the extraction of sulfur from pyrite

Figure 2. The effect of particle size on the extraction of sulfur from pyrite

J 2

4

L

6

8

10

INITIAL CONCENTRATION, wt. %

100

150

200

PYRITE PARTICLE SIZE, microns


250


15.

TAI E T A L .

Alkaline

Solutions

with Dissolved

Oxygen

189

c a l c i u m c a r b o n a t e , c a l c i u m h y d r o x i d e , and ammonium c a r b o n a t e . The o n l y a l k a l i w h i c h a p p r o a c h e d s o d i u m c a r b o n a t e i n e f f e c t i v e n e s s was s o d i u m p h o s p h a t e . However, i t r e q u i r e d a 7 wt % i n i t i a l c o n c e n t r a t i o n o f sodium phosphate t o produce c o a l w i t h a s u l f u r c o n t e n t c o m p a r a b l e t o t h a t o b t a i n e d w i t h a 1.4 wt % i n i t i a l c o n c e n t r a t i o n of sodium carbonate. M o r e o v e r , t h e B t u r e c o v e r y was l o w e r and t h e a s h c o n t e n t o f t h e p r o d u c t h i g h e r when s o d i u m p h o s p h a t e was used to o b t a i n c o m p a r a b l e d e s u l f u r i z a t i o n . The i n i t i a l c o n c e n t r a t i o n o f s o d i u m c a r b o n a t e had a v e r y p r o nounced e f f e c t on t h e e x t e n t o f d e s u l f u r i z a t i o n and t h e r e s u l t i n g s u l f u r c o n t e n t o f t h e t r e a t e d c o a l ( T a b l e I I I , F i g u r e 4 ) . The b e s t r e s u l t s were o b t a i n e d w i t h an i n i t i a l c o n c e n t r a t i o n o f 1.4 wt % and u s i n g e i t h e r l o w e r o r h i g h e r c o n c e n t r a t i o n s r e s u l t e d i n l e s s desulfurization. The t r e a t m e n t w i t h t h e optimum c o n c e n t r a t i o n r e duced t h e p y r i t i c s u l f u r c o n t e n t o f t h e c o a l by t w o - t h i r d s . A s i m i l a r e f f e c t o f c o n c e n t r a t i o n was o b s e r v e d when s o d i u m h y d r o x i d e was u s e d w i t h the optimum i n i t i a l c o n c e n t r a t i o n b e i n g a b o u t 1 wt %. Hence, t h e e f f e c t o f a l k a l i c o n c e n t r a t i o n was l i k e t h a t e x p e r i e n c e d in leaching pyrite (Figure 1 ) . Under t h e m i l d l e a c h i n g c o n d i t i o n s used i n t h i s w o r k , m a i n l y i n o r g a n i c s u l f u r was e x t r a c t e d f r o m t h e c o a l . Essentially a l l o f t h e s u l f a t e f o r m o f s u l f u r was e x t r a c t e d a n d a good s h a r e o f the p y r i t i c s u l f u r . Unfortunately the r e s u l t s reported i n Table I I I f o r o r g a n i c s u l f u r a r e so e r r a t i c t h a t i t i s n o t p o s s i b l e t o d i s c e r n w h e t h e r o r g a n i c s u l f u r was removed o r n o t . For the e x p e r i m e n t s i n v o l v i n g sodium c a r b o n a t e , the y i e l d o f d r y c o a l was 93-94%, and t h e B t u r e c o v e r y was 88-92%. These v a l u e s c o u l d have been h i g h e r w i t h t h e e x e r c i s e o f g r e a t e r c a r e in conducting the experiments. Since the heating value o f the t r e a t e d c o a l on a m o i s t u r e and a s h f r e e (maf) b a s i s was n e a r l y t h e same as t h a t o f t h e u n t r e a t e d c o a l , i t does n o t a p p e a r t h a t t h e c o a l was s i g n i f i c a n t l y d e g r a d e d by t h e t r e a t m e n t . A l s o the oxygen c o n t e n t o f t h e c o a l , a s d e t e r m i n e d by u l t i m a t e c h e m i c a l a n a l y s i s , d i d n o t a p p e a r t o be s i g n i f i c a n t l y d i f f e r e n t f r o m t h a t o f t h e untreated coal. These r e s u l t s c o n t r a s t m a r k e d l y w i t h t h o s e r e p o r t e d b y S a r e e n e t a l . ( 3 , 4 ) f o r t r e a t m e n t s u s i n g much h i g h e r oxygen p a r t i a l p r e s s u r e s which r e s u l t e d i n n o t i c e a b l e oxygen upt a k e by I l l i n o i s No. 6 c o a l . As a r e s u l t o f t h e a l k a l i t r e a t m e n t , t h e s o d i u m and a s h c o n t e n t o f t h e c o a l i n c r e a s e d m e a s u r a b l y ( T a b l e I I I , F i g u r e 5 ) . The i n c r e a s e i n a s h c o n t e n t was d i r e c t l y p r o p o r t i o n a l t o t h e i n c r e a s e i n s o d i u m c o n t e n t and seemed c a u s e d a l m o s t e n t i r e l y by t h e a d s o r p t i o n o f s o d i u m . Most o f t h e i n c r e a s e i n s o d i u m o r a s h c o n t e n t t o o k p l a c e a t l o w e r a l k a l i c o n c e n t r a t i o n s , and more t h a n 2 wt % sodium carbonate i n t h e l e a c h a n t g e n e r a l l y produced l i t t l e a d d i tional increase. I n o t h e r w o r d s , t h e c o a l seemed t o become s a t u r a t e d when t h e l e a c h s o l u t i o n c o n t a i n e d 2 wt % s o d i u m c a r b o n a t e o r more. On t h e o t h e r hand, t h e c o a l r e t a i n e d v e r y l i t t l e s o d i u m when t h e l e a c h s o l u t i o n i n i t i a l l y c o n t a i n e d 0.8 wt % s o d ium c a r b o n a t e o r l e s s b e c a u s e t h e s o l u t i o n became a c i d i c b y t h e



92

91

93

93

94

94

94

2.0

5.0

8.0

10.0

15.0

chemical

chemical

chemical

chemical

89

90

88

11,010

10,940

10,950

10,590

10,880

10,580

10,780

18.5 19.4 19.7 18.2

— — —

17.8

17.7

13,800

13,520

13,520

16.4

chemical

91

89

—

93

1.4

93

1.0

chemical

10,740

16.3

chemical

90

—

94

0.8

16.2

13,430

chemical

10,950

94

0.8

chemical

92

17.5

—

10,440

88

0

chemical

95

15.3

15.5

13,970

13,660

maf

1.52

1.90

—

1.29

1.14

0.80

0.33

0.10

0.10

—

0.03

0.05

Ash Na ( w t . % ) (wt %)

11,577

as r e e v d .

Heat Value ( B t u / l b )

wash

Btu Recov. (%) 11,240

Wt Yield (%)

none

Treatment

Na2CC>3 Cone. (wt %)

0.17

3.,21

2.,34

1.,63

1.,76

1.,75

1.,23

1.,11

1.,46

1.,89

1.,62

0.18

0.11

0.09

0.11

0.07

0.06

0.05

0.03

0.05

0.11

0.60

2.,28

(lb/10

6

Btu)

3.66 1.80

2.65

2.28

5.17

4.02

4.24

3.15

1.85

2.39

2.99

3.90 1.81

2.39

4.23

3.47

1.80 2.32

5.29

5.63

5.63

2.89

2.25

1.81

S u l f a t e Organic Total

3.,22

Pyritic

Sulfur Distrib.

T a b l e I I I . R e s u l t s o f L e a c h i n g ISU C o a l w i t h D i f f e r e n t C o n c e n t r a t i o n s o f A l k a l i



AL.

Alkaline Solutions tvith Dissolved Oxygen

191

PYRITE -120/+Ί40

7.8

MESH

atm.

150 °C

2

3

Figure 3. The effect of reaction time on the extraction of sulfur from pyrite

REACTION T I M E , h r .

-200 7.8

4 INITIAL

Figure 4.

6

8

SODIUM CARBONATE

10

MESH I S U COAL a t m . TOTAL P R E S S .

150° C 2.0 h r . I 12

CONCENTRATION,

I

WT. %

Sulfur content of IS U coal after leaching



192

COAL

DESULFURIZATION

end o f a r u n . W a s h i n g w i t h w a t e r d i d n o t remove s o d i u m f r o m the t r e a t e d c o a l , b u t w a s h i n g w i t h d i l u t e a c i d (0.1N hydrochloric a c i d ) d i d remove i t . A n o t h e r s e r i e s o f e x p e r i m e n t s was c o n d u c t e d t o see what e f f e c t r e d u c i n g the s i z e o f t h e c o a l w o u l d have on d e s u l f u r i z a t i o n by c h e m i c a l l e a c h i n g . ISU c o a l was f i r s t p u l v e r i z e d to -35 mesh ( a b o u t 50% b e l o w 200 mesh) w i t h a M i k r o - S a m p l m i l l ( P u l v e r i z i n g Machinery D i v i s i o n , A m e r i c a n - M a r i e t t a Co.). The c o a l was t h e n wet-ground i n a ceramic j a r m i l l f o r d i f f e r e n t time p e r i o d s . The p a r t i c l e s i z e d i s t r i b u t i o n o f the c o a l a f t e r g r i n d i n g f o r 2, 4, 8, and 20 h r i s shown i n F i g u r e 6. A f t e r g r i n d i n g f o r 2 h r , 97% o f t h e c o a l was f i n e r t h a n 400 mesh (38 ym) s i z e . The p u l v e r i z e d o r g r o u n d c o a l was t h e n l e a c h e d i n t h e s t i r r e d a u t o c l a v e f o r 2 h r a t 140°C w i t h a 2.0 wt % s o l u t i o n o f s o d i u m c a r b o n a t e c o n t a i n i n g o x y g e n d i s s o l v e d u n d e r a p a r t i a l p r e s s u r e o f 2.4 atm and w i t h a t o t a l s y s t e m p r e s s u r e o f 5.8 atm. F o r e a c h l e a c h i n g r u n 25 g o f c o a l was m i x e d w i t h 500 ml o f s o l u t i o n . The r e s u l t s p r e s e n t e d i n T a b l e IV show t h a t more s u l f u r was e x t r a c t e d f r o m c o a l w h i c h had been ground i n t h e b a l l m i l l t h a n f r o m c o a l w h i c h had o n l y been p u l v e r i z e d w i t h the M i k r o - S a m p l m i l l . Thus t h e p y r i t i c s u l f u r c o n t e n t o f t h e b a l l - m i l l e d c o a l was r e d u c e d 87% w h e r e a s t h e p y r i t i c s u l f u r c o n t e n t o f t h e p u l v e r i z e d c o a l was r e d u c e d o n l y 71%. However, g r i n d i n g t h e c o a l f o r more t h a n 2 h r d i d n o t p r o duce any a d d i t i o n a l b e n e f i t . Combined P h y s i c a l and

Chemical

Cleaning

A f i n a l s e t o f e x p e r i m e n t s i n v o l v e d combined p h y s i c a l and c h e m i c a l c l e a n i n g o f s e v e r a l Iowa c o a l s . Each c o a l was c r u s h e d t o 6 mm χ 0 s i z e w i t h a d o u b l e r o l l c r u s h e r and t h e n c l e a n e d by g r a v i t y s e p a r a t i o n i n an o r g a n i c l i q u i d h a v i n g a s p e c i f i c g r a v i t y o f 1.60. The c l e a n e d f l o a t f r a c t i o n was r e c o v e r e d , d r i e d , and p u l v e r i z e d w i t h the M i k r o - S a m p l m i l l . The p u l v e r i z e d c o a l was wetg r o u n d n e x t i n t h e c e r a m i c j a r m i l l f o r 20 h r and f i n a l l y l e a c h e d i n the s t i r r e d a u t o c l a v e f o r 2.0 h r w i t h a 2.0 wt % s o d i u m c a r b o n a t e s o l u t i o n . The e f f e c t s o f d i f f e r e n t l e a c h i n g t e m p e r a t u r e s and o x y g e n p a r t i a l p r e s s u r e s were s t u d i e d . The r e s u l t s p r e s e n t e d i n T a b l e V show t h a t g r a v i t y s e p a r a t i o n removed a s u b s t a n t i a l p a r t o f the p y r i t i c s u l f u r f r o m e a c h c o a l and t h a t c h e m i c a l l e a c h i n g removed most o f the r e m a i n i n g i n o r g a n i c s u l f u r , b o t h p y r i t i c and s u l f a t e . Thus t h r o u g h t h e combined t r e a t m e n t , the i n o r g a n i c s u l f u r c o n t e n t of each of the t h r e e c o a l s was r e d u c e d 93-95%. The t r e a t e d ICO c o a l came c l o s e to m e e t i n g the f e d e r a l new s o u r c e p e r f o r m a n c e s t a n d a r d o f 0.6 l b S/10 Btu. F o r the p h y s i c a l l y c l e a n e d and f i n e l y g r o u n d c o a l , i t d i d n o t seem to make any d i f f e r e n c e what l e a c h i n g t e m p e r a t u r e i n t h e r a n g e o f 120°-150°C o r what o x y g e n p a r t i a l p r e s s u r e i n t h e r a n g e o f 2.4-5.2 atm was u s e d b e c a u s e e s s e n t i a l l y a l l o f the i n o r g a n i c s u l f u r was removed even u n d e r the m i l d e s t t r e a t m e n t c o n d i t i o n s . 6


ET

AL.

Alkaline Solutions with Dissolved Oxygen


TAI


193


chemical

3-•108-8 b.mill (8hr) 11,237

11,070

b.mill

chemical

3-•108-6

(4 h r )

11,500

b.mill (2hr)

chemical

3-•108-7

11,360

11,040

H.V. (Btu/lb)

pulverized

pulverized

Grind

chemical

none

Treatment

16.2

16.6

14.7

15.8

12.0

Ash (wt %)

0.34

0.30

0.29

0.67

2.31

Pyritic

0.05

0.05

0.04

2.06

2.17

2.10

2.32

2.19

0.54 0.05

Organic

Sulfate

Sulfur Distribution (lb/10

R e s u l t s o f T r e a t i n g D i f f e r e n t G r i n d s o f ISU C o a l

3-•108-5

Run No.

Table IV.


b

2.46

2.51

2.43

3.05

5.04

Total

Btu


B i g Ben B i g Ben B i g Ben B i g Ben

ICO ICO ICO ICO ICO ICO ICO

ISU ISU ISU ISU ISU

Source

25 25

—

40 40 40 25 25

—

40 40 20

—

Amt.(g)

Coal

none float/sink chemical chemical

none float/sink chemical chemical chemical chemical chemical

none float/sink chemical chemical chemical

Treatment

T a b l e V.

— 2.9 3.2

132 150

2.7 3.7 5.2 3.2 3.2

120 120 120 150 150

—

—

5.8 7.8

—

4.7 5.8 7.3 7.8 7.8

—

4.4 5.8 6.9

2.4 2.7 2.4

Total

—

2

(atm.)

—

0

Pressure

—

120 135 150

—

iemp. (°C)

11,800 12,790 10,950 11,680

12,040 12,690 11,630 11,480 11,640 11,220 11,740

10,990 12,390 11,650 11,490 10,770

η. ν . (Btu/lb)

10.6 10.0

— —

11.6 11.6 10.8 14.1 13.2

— —

Ι.37 Ο,.42 0,.09 0.16

0.,37 0.,28 0..03 0.,04

0.,25 0.,20 0.,02 0.,02 0.,02 0.,03 0.,04

0.,33 0.,23 0.,06 0.,07 0.,04

3.,96 1,,38 0,,13 0.,18 0..21 1,,66 0.,70 0,.10 0,.15 0,.09 0,.14 0.11

Sulfate

%) P y r i t i c

12.2 12.1 24.0

—

(wt

Sulfur Distrib.

R e s u l t s o f Combined P h y s i c a l and C h e m i c a l T r e a t m e n t


,53 ,41 ,34 ,32 ,04

0..61 0,.81 0,.89 0.81

0.,62 0.,64 0.,58 0.,64 0.,60 0.,56

0. ,61

2. 2. 2. 2. 2.

2.36 1.47 1.00 1.01

2.52 1.53 0.76 0.75 0.74 0.77 0.71

6.81 4.02 2.53 2.57 2.29

Organic Total

(lb/10° B t u )

196


T h e r e f o r e , i t s h o u l d have b e e n p o s s i b l e t o o b t a i n a s good r e s u l t s even w i t h m i l d e r treatment c o n d i t i o n s o r a s h o r t e r r e a c t i o n time.


Conclusions D i l u t e a l k a l i n e s o l u t i o n s c o n t a i n i n g oxygen d i s s o l v e d u n d e r p r e s s u r e were v e r y e f f e c t i v e a t e l e v a t e d t e m p e r a t u r e s f o r e x t r a c t i n g t h e i n o r g a n i c s u l f u r f r o m c o a l . Of v a r i o u s a l k a l i s t e s t e d , s o d i u m c a r b o n a t e gave t h e b e s t r e s u l t s . T h i s m a t e r i a l a l s o has the advantages o f b e i n g r e a d i l y a v a i l a b l e , low i n c o s t , and r e l a t i v e l y n o n c o r r o s i v e i n aqueous s o l u t i o n t o w a r d s s t e e l and o t h e r common m a t e r i a l s o f c o n s t r u c t i o n . Although s u f f i c i e n t a l k a l i s h o u l d be u s e d t o n e u t r a l i z e a l l o f t h e a c i d w h i c h i s p r o d u c e d t h r o u g h o x i d a t i o n o f t h e c o a l s u l f u r , an e x c e s s i v e c o n c e n t r a t i o n o f a l k a l i seems t o s l o w t h e r a t e o f d e s u l f u r i z a t i o n . On t h e o t h e r h e a d , t h e r a t e o f d e s u l f u r i z a t i o n c a n be i n c r e a s e d by r e d u c i n g t h e s i z e o f t h e c o a l a n d / o r p y r i t e p a r t i c l e s . Leach i n g c o a l f i n e s w i t h d i l u t e sodium carbonate s o l u t i o n s a t tempera t u r e s up t o 150°C and w i t h o x y g e n p a r t i a l p r e s s u r e s up t o 5 atm f o r up t o 2 h r does n o t seem t o d e g r a d e h i g h v o l a t i l e b i t u m i n o u s coal. However, t h e c o a l does a d s o r b s o d i u m f r o m t h e l e a c h s o l u t i o n w h i c h c a n be removed s u b s e q u e n t l y by w a s h i n g w i t h d i l u t e acid. C h e m i c a l l e a c h i n g c a n be combined a d v a n t a g e o u s l y w i t h p h y s i c a l c l e a n i n g s i n c e t h e l a t t e r i s more a d e p t a t r e m o v i n g c o a r s e r p a r t i c l e s o f p y r i t e w h i l e t h e f o r m e r i s more a d e p t a t removing the microscopic p a r t i c l e s . Ac k n o w l e d gemen t T h i s work was s p o n s o r e d by t h e Iowa C o a l P r o j e c t and c o n d u c t e d i n t h e E n e r g y and M i n e r a l R e s o u r c e s R e s e a r c h I n s t i t u t e a t Iowa S t a t e U n i v e r s i t y .

Literature Cited

1. Nelson, H. W., Snow, R. D., Keyes, D. B., Ind. Eng. Chem. (1933) 25, 1355. 2. Agarwal, J. C., Giberti, R. Α., Irminger, P. F., Petrovic, L. J., Sareen, S. S., Min. Congr. J. (1975) 61 (3), 40. 3. Sareen, S. S., Giberti, R. Α., Irminger, P. F., Petrovic, L. J., Preprint 50c, 80th National Meeting AIChE, (Sep. 7-10, 1975), Boston. 4. Agarwal, J. C., Giberti, R. Α., Petrovic, L. J., U.S. Patent No. 3,960,513, 1976. 5. Sareen, S. S., This volume, in press. 6. Friedman, S., LaCount, R. B., Warzinski, R. P., This volume, in press. 7. Majima, Η., Peters, Ε., Trans. Metall. Soc. AIME (1966) 1409. 8. Stenhouse, J. E., Armstrong, W. M., Can. Min. Metall. Bull. (1952) 45, 49.


15.

TAI

ET

AL.

Alkaline

Solutions

with

Dissolved

Oxygen

197


9. Burkin, A. R., Edwards, Α. Μ., in "Mineral Processing," (A. Roberts, Ed.), pp. 159-169, Pergamon, Oxford, 1965. (Procedding of the Sixth International Congress held at Cannes, May 26-June 2, 1963.) 10. McKay, D. R., Halpern, J., Trans. Metall. Soc. AIME (1958) 301. 11. Book ASTM Stand., Part 26, "Gaseous Fuels; Coal and Coke; Atmospheric Analysis," Methods D2015-66, D2492-68, D3174-73, D3177-75, 1976. 12. Fritz, J. S., Yamamura, S. S., Anal. Chem. (1955) 27, 1461. 13. Anderson, J. E., Halpern, J., Samis, C. S., J. Met. (1953) 5, 554. 14. Dresher, W. H., Wadsworth, M. E., Fassell, W., Jr., J. Met. (1956) 8, 794.


16 Hydrothermal Coal Process E D G E L P. S T A M B A U G H


Battelle, Columbus Laboratories, 505 King Avenue, Columbus, O H 43201

Coal is the major source of energy for the U.S. and will continue to be so for many years. However, coal is dirty, containing high concentrations of contaminants such as sulfur, nitrogen, and mineral matter. These contaminants, if not removed from the coal before or during combustion, will find their way into the environment and thus constitute a serious health hazard. An alternative to insure a healthier environment, as the consumption of coal as the major source of energy increases, is to remove these contaminants by chemical coal cleaning before combustion. One such method based on hydrothermal technology is the hydrothermal coal process in which certain coals can be chemically cleaned to produce solid fuels which meet Federal sulfur emission standards for new sources. Process Description The basic process, as shown schematically in Figure 1, comprises five major processing operations: coal preparation, hydrothermal (desulfurization) treatment, liquid/solid separation, fuel drying, and leachant regeneration. Coal preparation may entail a simple grinding operation to reduce the raw coal to the desired particle size of 70% -200 mesh or 100% -28 mesh. On the other hand, this operation may involve two operations—grinding of the coal to the desired particle size followed by physical beneficiation to remove a portion of the mineral matter including a portion of the pyritic sulfur. Hydrothermal treatment e n t a i l s b a s i c a l l y three p r o c e s s i n g steps : (1) The g r o u n d c o a l i s m i x e d w i t h a n aqueous a l k a l i n e l e a c h a n t , f o r e x a m p l e , an aqueous s o l u t i o n / s l u r r y o f s o d i u m h y d r o x i d e and l i m e , t o produce a raw c o a l s l u r r y . (2) T h i s r a w s l u r r y i s h e a t e d i n an a u t o c l a v e a t a b o u t 250°-350°C ( s t e a m p r e s s u r e o f 600-2500 p s i g ) t o e x t r a c t a s i g n i f i c a n t p o r t i o n o f t h e s u l f u r and t h e m i n e r a l m a t t e r , d e p e n d i n g on t h e l e a c h a n t and p r o c e s s i n g c o n d i t i o n s .

198



16.

STAMBAUGH

Hydrothermal

Coal

Process

199

(3) The c o a l p r o d u c t s l u r r y i s c o o l e d and pumped i n t o a r e c e i v i n g tank. The d e s u l f u r i z e d c o a l i s t h e n s e p a r a t e d f r o m t h e s p e n t l e a c h a n t and washed w i t h w a t e r . The f i n a l p r o d u c t i s a s o l i d f u e l c o n t a i n i n g r e d u c e d c o n c e n t r a t i o n s o f s u l f u r a n d , d e p e n d i n g on t h e leaching c o n d i t i o n s , mineral matter. D r y i n g t h e f u e l t o remove t h e r e s i d u a l m o i s t u r e i s o p t i o n a l . F o r some u s e s , i t may be d e s i r a b l e t o b u r n t h e f u e l wet; i n o t h e r s , r e m o v a l o f a p a r t o r a l l o f t h e r e s i d u a l m o i s t u r e may be desirable. I n a n y e v e n t , t h e c o a l c a n be d r i e d i n c o m m e r c i a l l y available dryers. The s p e n t l e a c h a n t c o n t a i n i n g t h e e x t r a c t e d s u l f u r a s s o d i u m s u l f i d e (Na2S) c a n be r e g e n e r a t e d f o r r e c y c l e i n s e v e r a l ways; one a p p r o a c h i n v o l v e s t r e a t m e n t o f t h e s p e n t l e a c h a n t w i t h c a r b o n d i o x i d e t o remove t h e s u l f u r a s H2S w h i c h i s s u b s e q u e n t l y c o n v e r t e d t o e l e m e n t a l s u l f u r by t h e C l a u s o r S t r e t f o r d p r o c e s s . The r e s u l t i n g l i q u o r c o n t a i n i n g s o d i u m c a r b o n a t e s i s t r e a t e d w i t h l i m e t o c o n v e r t t h e c a r b o n a t e s back t o sodium h y d r o x i d e which i s r e c y c l e d t o t h e d e s u l f u r i z a t i o n segment a f t e r a d j u s t i n g t h e concentration. The c a l c i u m c a r b o n a t e i s t h e r m a l l y decomposed t o l i m e and c a r b o n d i o x i d e f o r r e c y c l e t o t h e l e a c h a n t r e g e n e r a t i o n segment. C a p a b i l i t y o f Process Sulfur Extraction. The p r o c e s s i s c a p a b l e o f c o n v e r t i n g , on a l a b o r a t o r y ( b a t c h ) and m i n i p l a n t (1/4 t o n p e r day) s c a l e , a v a r i e t y o f m a j o r seam c o a l s o f d i f f e r e n t r a n k s and l i g n i t e t o clean s o l i d f u e l s having a t o t a l s u l f u r content equivalent t o o r l e s s t h a n 1.2 l b S0 /10° B t u a s shown i n T a b l e I . T h i s i s a c h i e v e d by e x t r a c t i n g g r e a t e r t h a n 90% o f t h e p y r i t i c s u l f u r f r o m a l a r g e number o f c o a l s and e x t r a c t i n g up t o 50% o f t h e o r g a n i c s u l f u r from c e r t a i n c o a l s . Btu recovery as s o l i d c l e a n f u e l i s i n t h e r a n g e o f 90-95%, d e p e n d i n g on t h e c o a l and p r o c e s s i n g c o n d i t i o n s . The r e m a i n d e r , s o l u b i l i z e d b y t h e l e a c h a n t i s recovered during leachant regeneration. This m a t e r i a l could be u s e d a s p r o c e s s h e a t . T h u s , a w i d e v a r i e t y o f m a j o r seam, h i g h - s u l f u r b i t u m i n o u s c o a l s and s u b b i t u m i n o u s c o a l s i n a d d i t i o n t o l i g n i t e c a n be c o n v e r t e d t o e n v i r o n m e n t a l l y a c c e p t a b l e s o l i d fuels. These c o a l s c a n be u s e d d i r e c t l y a s a s o u r c e o f e n e r g y w i t h o u t f u r t h e r c l e a n i n g d u r i n g t h e combustion p r o c e s s , assuming a l l o f t h e s u l f u r i s e m i t t e d t o t h e atmosphere. With a l k a l i hydrothermally t r e a t e d c o a l s , a l l o f the s u l f u r i s n o t e m i t t e d t o the atmosphere. D u r i n g the d e s u l f u r i z a t i o n o p e r a t i o n , t h e c o a l s t r u c t u r e i s opened up t o g i v e a p r o d u c t h a v i n g a s p o n g e - l i k e m o r p h o l o g y ( s e e F i g u r e 2 ) . The p o r o u s s t r u c t u r e a l l o w s t h e a l k a l i t o p e n e t r a t e t h e c o a l p a r t i c l e s and subsequently t o r e a c t w i t h t h e f u n c t i o n a l groups, f o r example, c a r b o x y l i c a c i d groups, o f t h e c o a l molecules. A l s o , the a l k a l i 2


9

200

COAL

HEAT

DESULFURIZATION

EXCHANGER

GRINDING MIXING H I G H - SSUULLFFUURR COAL

^

^

j

REGENERATED LEACHANT

TANK

FILTER

S U L F U R REMOVAL AUTOCLAVE

HZ

J]H** DRYER

CLEAN

SPENT LEACHANT

SULFUR


SULFUR RECOVERY PLANT

Figure 1.

COAL

FOR POWER P L A N T S AND INDUSTRIAL BOILERS

LEACHANT REGENERATION

Schematic of hydrothermal coal process

Figure 2. Comparison of morphology of untreated (top) and HTT coal (bottom)


16.

STAMBAUGH

Hydrothermal Coal Process

Table I .

S u l f u r Emissions of Low-Sulfur Coals from Hydrothermal Coal Process

C o a l Source Seam


201

S0 Raw

o

Equivalent (lb/10 HTT Coal

6

Btu) Coal

Laboratory scale Lower K i t t a n n i n g Upper F r e e p o r t Ohio 6 Pittsburgh 8 . Pittsburgh Lignite Western

2.2 2.4 3.9 4.6 3.4 1.5 1.0

0.9 0.9 1.2 0.9 0.7 1.2 0.3

Prepilot plant Lower K i t t a n n i n g Upper F r e e p o r t

4.0 2.4

1.1 0.8

i s p h y s i c a l l y d e p o s i t e d w i t h i n and on t h e c o a l p a r t i c l e s . Conseq u e n t l y , i n a d d i t i o n to h a v i n g a reduced s u l f u r c o n t e n t , the h y d r o t h e r m a l l y t r e a t e d c o a l i s impregnated w i t h a l k a l i which a c t s as a s u l f u r s c a v e n g e r d u r i n g t h e c o m b u s t i o n p r o c e s s . I n some r e c e n t c o m b u s t i o n s t u d i e s s u p p o r t e d by EPA ( 1 ) , 41.4-75.7% o f t h e s u l f u r r e m a i n i n g i n t h e t r e a t e d c o a l was c a p t u r e d by t h e a l k a l i i n t h e t r e a t e d c o a l s , as shown i n T a b l e I I . ( T h i s c o m b u s t i o n s t u d y was c o n d u c t e d i n a 1 - l b / h r l a b o r a t o r y c o m b u s t i o n f a c i l i t y . ) S t a c k g a s e s c o n t a i n e d 120-290 ppm SO2 e q u i v a l e n t t o a b o u t 0.3-0.6 l b S 0 / 1 0 6 B t u . T h e o r e t i c a l l y , a s s u m i n g no s u l f u r c a p t u r e , t h e s t a c k g a s e s w o u l d have c o n t a i n e d 490-650 ppm SO2, e q u i v a l e n t t o a b o u t 1.0-1.5 l b S 0 / 1 0 B t u . T h i s added f e a t u r e o f t h e h y d r o t h e r m a l p r o c e s s g r e a t l y i n c r e a s e s t h e number o f c o a l s w h i c h can be u s e d as a s o u r c e o f c l e a n e n e r g y , e s p e c i a l l y t h o s e c o a l s c o n t a i n i n g r e l a t i v e l y h i g h c o n c e n t r a t i o n s of o r g a n i c s u l f u r not s u b j e c t t o r e m o v a l by m e c h a n i c a l c l e a n i n g . 2

6

2

Metal Extraction. Hydrothermal treatment r e s u l t s i n the e x t r a c t i o n o f a number o f t h e t r a c e m e t a l s . Examples of these a r e shown i n T a b l e I I I . T h e r e f o r e , t r a c e m e t a l e m i s s i o n s f r o m t h e c o m b u s t i o n o f h y d r o t h e r m a l l y t r e a t e d c o a l s h o u l d be l o w e r t h a n t h o s e f r o m t h e c o m b u s t i o n o f t h e c o r r e s p o n d i n g raw c o a l s . F u r t h e r m e t a l e x t r a c t i o n i s a c h i e v e d by c h e m i c a l l y d e a s h i n g the h y d r o t h e r m a l l y t r e a t e d c o a l w i t h d i l u t e a c i d , f o r example, sulfuric acid. As an i l l u s t r a t i o n , t h e a s h c o n t e n t o f u n t r e a t e d c o a l s f r o m O h i o , K e n t u c k y , West V i r g i n i a , and P e n n s y l v a n i a r a n g e d f r o m 4.6-13.2%; a s h c o n t e n t o f c h e m i c a l l y d e a s h e d h y d r o t h e r m a l l y t r e a t e d c o a l s r a n g e d f r o m 0.7-5.3%. Improved C o m b u s t i o n B e h a v i o r . C e r t a i n general combustion c h a r a c t e r i s t i c s o f b o t h t h e raw and t r e a t e d c o a l s , s u c h as



S0

2

(ppm)

(%)

30.7

41.4

120 75.7

1910 —

1115

290

493

1610

Westland Raw C o a l

1877

495

Martinka Coal Mixed Leachant

Coals

220

250

66.2

651

580

56.9

Westland Coal Mixed Leachant

Westland Coal Caustic

M a r t i n k a c o a l r e p r e s e n t s t h e Lower K i t t a n i n g Seam; W e s t l a n d c o a l r e p r e s e n t s t h e P i t t s b u r g h Seam.

Sulfur capture

SO^ i n s t a c k gas (ppm)

Theoretical

Martinka Coal Caustic

S u l f u r C a p t u r e by A l k a l i i n HTT

Martinka Raw C o a l

Table I I .


16.

STAMBAUGH


Table I I I .

203

T o x i c M e t a l s E x t r a c t e d by H y d r o t h e r m a l Treatment o f C o a l


Concentration Metal

Raw C o a l

Arsenic Beryllium Boron Lead Thorium Vanadium

25 10 75 20 3 40

Average v a l u e s from 3 Ohio

a

(ppm)

Treated

Coai

a

2 3 4 5 0.5 2 coals.

i g n i t i o n t e m p e r a t u r e and r e a c t i v i t y , were d e t e r m i n e d q u a n t i t a t i v e l y f r o m t h e d e r i v a t i v e t h e r m o g r a v i m e t r i c (dTGA) and t h e d i f f e r e n t i a l t h e r m a l (DTA) f u e l a n a l y s e s . The r e s u l t s o f t h e dTGA a n d DTA a r e summarized i n T a b l e s I V and V, r e s p e c t i v e l y . From t h e s e a n a l y s e s , t h e c o m b u s t i o n c h a r a c t e r i s t i c s o f t h e s e c o a l s i n terms o f i g n i t i o n , r e a c t i v i t y , and p o s s i b l y f l a m m a b i l i t y may have b e e n i m p r o v e d by t h e h y d r o t h e r m a l t r e a t m e n t . F o r e x a m p l e , t h e i g n i t i o n t e m p e r a t u r e o f W e s t l a n d c o a l was r e d u c e d f r o m 426°-344°C ( T a b l e I V ) , a r e d u c t i o n o f 82°C, by t r e a t i n g t h e c o a l w i t h s o d i u m h y d r o x i d e and t h e m i x e d l e a c h a n t s y s t e m s . A s i m i l a r e f f e c t was n o t e d by h y d r o t h e r m a l t r e a t m e n t o f t h e M a r t i n k a c o a l w i t h these leachant systems. T h i s was e x p e c t e d i n v i e w o f o t h e r h y d r o t h e r m a l work w h i c h has been c o n d u c t e d a t B a t t e l l e - C o l u m b u s . I n t h i s w o r k , h y d r o t h e r m a l t r e a t m e n t o f c o a l s r e s u l t e d i n a l t e r a t i o n and m o d i f i c a t i o n o f t h e c o a l s t r u c t u r e t o a more s i m p l i f i e d s t r u c t u r e . This i s e v i d e n c e d by t h e f a c t t h a t t h e l i q u i d p r o d u c t s f r o m t h e p y r o l y s i s o f HTT c o a l s c o n t a i n e d l e s s a s p h a l t e n e s t h a n t h e l i q u i d p r o d u c t s f r o m t h e c o r r e s p o n d i n g r a w c o a l s ( 2 ) . The l o w e r m o l e c u l a r w e i g h t o r g a n i c l i q u i d s f r o m t h e HTT c o a l s s h o u l d have a l o w e r i g n i t i o n t e m p e r a t u r e and a h i g h e r d e g r e e o f f l a m m a b i l i t y t h a n t h e h i g h e r m o l e c u l a r w e i g h t l i q u i d s from t h e raw c o a l s . The i n c r e a s e d r e a c t i v i t y i s r e f l e c t e d i n T a b l e V. F o r e x a m p l e , t r e a t m e n t o f t h e M a r t i n k a and W e s t l a n d c o a l s w i t h t h e m i x e d l e a c h a n t s y s t e m r e s u l t e d i n HTT c o a l s w h i c h b u r n e d o u t a t a maximum o f a b o u t 470°C w h e r e a s t h e r a w c o a l s b u r n e d o u t a t a b o u t 585°-600°C. A s i m i l a r e f f e c t , b u t n o t t o t h i s d e g r e e , was observed w i t h t h e sodium h y d r o x i d e - t r e a t e d c o a l s . W h i l e t h e r e may n o t be a d i r e c t c o r r e l a t i o n between c o m b u s t i o n and g a s i f i c a t i o n , h y d r o t h e r m a l t r e a t m e n t o f c o a l w i t h t h e m i x e d l e a c h a n t s y s t e m i n c r e a s e s s t e a m g a s i f i c a t i o n and h y d r o g a s i f i c a t i o n r a t e s by a s much as 40-50 f o l d ( 3 ) . T h i s h a s been a t t r i b u t e d t o a l t e r a t i o n and m o d i f i c a t i o n o f t h e c o a l s t r u c t u r e and t o i m p r e g n a t i o n o f t h e c o a l p a r t i c l e w i t h a c a t a l y s t , i n t h i s case c a l c i u m and/or sodium. T h i s work h a s a l s o



range^

622

-

243 432

615

233 426

252 344 488 564 263 360 508 578

Martinka Coal Sodium Treated

275

19.0

250-600


305

21.5

230-570

275

27.5

240-510

Martinka Coal NaOH Leachant

285

23.0

240-465

310

27.0

270-470


252 376 493 553



Coals

268 344 494 555


TGA p e r f o r m e d w i t h Cahn E l e c t r o b a l a n c e a t 15°C/min and a i r f l o w o f 800 m l / m i n . T e m p e r a t u r e r a n g e o v e r w h i c h most o f t h e sample i s l o s t .

320

17.5

220-585

Westland Raw C o a l

Westland Coal NaOH Leachant

T h e r m o g r a v i m e t i c A n a l y s e s o f Raw and HTT

T e m p e r a t u r e a t maximum r a t e o f w e i g h t l o s s (°C)

Maximum r a t e o f w e i g h t l o s s (mg/min)

Temperature

TABLE V.

S t a r t i n g e x o t h e r m (°C) I g n i t i o n p o i n t (°C) S e c o n d a r y e x o t h e r m (°C) End o f e x o t h e r m (°C)


Westland Coal Sodium Treated

D i f f e r e n t i a l Thermal A n a l y s e s o f C o a l Samples i n an A t m o s p h e r e o f A i r

We s t l a n d Raw C o a l Low A s h

Table IV.


>

16.

STAMBAUGH


shown t h a t t h e m i x e d l e a c h a n t - t r e a t e d c o a l i s more r e a c t i v e the sodium h y d r o x i d e - t r e a t e d c o a l .

205 than


Summary Hydrothermal p r o c e s s i n g i s a p o t e n t i a l technology f o r c o n v e r t i n g a v a r i e t y o f m a j o r seam, h i g h - s u l f u r c o a l s and l i g n i t e to c l e a n s o l i d f u e l s having a t o t a l s u l f u r content e q u i v a l e n t t o o r l e s s t h a n 1.2 l b SO2/IO" B t u . D u r i n g t h e t r e a t m e n t , t h e c o a l s are impregnated w i t h a l k a l i which a c t s as a s u l f u r scavenger, thereby reducing s u l f u r emissions s t i l l f u r t h e r d u r i n g combustion. The p r o c e s s i s a l s o e f f e c t i v e i n r e m o v i n g t r a c e m e t a l s s u c h a s b e r y l l i u m , b o r o n , v a n a d i u m , and a r s e n i c ; t h e r e f o r e , t h e g a s e o u s e m i s s i o n s f r o m c o m b u s t i o n o f HTT c o a l s s h o u l d be l e s s p o l l u t i n g i n terms o f s u l f u r and t r a c e m e t a l e m i s s i o n s t h a n f r o m r a w c o a l s . Hydrothermal treatment a l s o appears t o improve t h e combustion c h a r a c t e r i s t i c s o f c o a l i n terms o f i g n i t i o n , r e a c t i v i t y , and possibly flammability. Thus, h y d r o t h e r m a l treatment c o n v e r t s a t l e a s t c e r t a i n h i g h sulfur coals to environmentally acceptable s o l i d fuels with p o t e n t i a l l y improved combustion c h a r a c t e r i s t i c s . These c o a l s a r e p o t e n t i a l s o u r c e s o f e n e r g y f o r p u l v e r i z e d , s t o k e r , and c o a l s l u r r y combustion. Acknowledgement R e s u l t s a s r e p o r t e d were s u p p o r t e d i n p a r t by t h e B a t t e l l e E n e r g y P r o g r a m and i n p a r t by t h e U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y , R e s e a r c h - T r i a n g l e P a r k , NC, u n d e r C o n t r a c t No. 68-02-2119.

Literature Cited

1. Stambaugh, E. P., Levy, Α., Giammar, R. D., Sekhar, K. C., "Hydrothermal Coal Desulfurization with Combustion Results," Proceedings of the Fourth National Conference (October 3-7, 1976) 386-394. 2. Stambaugh, E. P., Feldmann, H. F. , Liu, K. T., Sekhar, K. C., "Novel Concept for Improved Pyrolysis Feedstock Production," 173rd National Meeting American Chemical Society, New Orleans, Louisiana (March 21-25, 1977). 3. Stambaugh E. P., Miller, J. F., Tam, S. S., Chauhan, S. P., Feldmann, H. F., Carlton, H. E., Nack, H., Oxley, J. H., "Battelle Hydrothermal Coal Process," 12th Air Pollution and Industrial Hygiene Conference on Air Quality Management in EPI, University of Austin, Austin, Texas (January 1976).


17 Coal Desulfurization by Low-Temperature Chlorinolysis


GEORGE C. HSU, JOHN J. KALVINSKAS, PARTHA S. GANGULI, and GEORGE R. GAVALAS* Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91103 Since most of the coals in this country, particularly the eastern and mid-western coals, have a high sulfur content (>2%), there is a need for an economical process of converting high-sulfur coals to clean fuel (


224

COAL

DESULFURIZATION

char prepared a t 600°C are presented here. The r e s u l t s o b t a i n e d f o r t h e c h a r p r e p a r e d a t 8 0 0 ° C a r e s i m i l a r and w i l l n o t be presented i n d e t a i l . The e f f e c t o f p r e s s u r e and c o m p o s i t i o n o f t h e I ^ - C H ^ m i x t u r e and t e m p e r a t u r e on t h e d e s u l f u r i z a t i o n r a t e o f c h a r p r e p a r e d a t 6 0 0 ° C i s shown i n F i g u r e s 4, 5 and 6. Lower s u l f u r c o n t e n t s and h i g h e r d e s u l f u r i z a t i o n r a t e s a r e f a v o r e d by a n i n c r e a s e i n P h and t e m p e r a t u r e . The p r e s e n c e o f CH^ i n h i b i t s d e s u l f u r i z a t i o n .


2

I n gas m i x t u r e s c o n t a i n i n g more t h a n 2 5 % CH^, g a s i f i c a t i o n ceased a f t e r about 30 min o f r e a c t i o n time t o a p l a t e a u ( F i g u r e 5). The g a s i f i c a t i o n c o r r e s p o n d i n g t o t h i s p l a t e a u i s shown as a f u n c t i o n o f t h e p e r c e n t a g e o f CH^ i n t h e gas i n F i g u r e 7. For the char prepared a t 600°C, g a s i f i c a t i o n d u r i n g d e s u l f u r i z a t i o n a t 8 0 0 ° C ( T S ) d e c r e a s e d c o n s i d e r a b l y w i t h i n c r e a s i n g CH percentage i n t h e g a s . G a s i f i c a t i o n f o r the c h a r prepared a t 800°C o n l y s l i g h t l y depended on t h e amount o f CH, i n t h e g a s , i r r e s p e c t i v e of the temperature of d e s u l f u r i z a t i o n . As s e e n f r o m t h e s e r e s u l t s , d e s u l f u r i z a t i o n o f c o a l c h a r t a k e s p l a c e i n two d i s t i n c t s t a g e s . The f i r s t s t a g e shows a s i m u l t a n e o u s r a p i d d e s u l f u r i z a t i o n and g a s i f i c a t i o n . D u r i n g t h e s e c o n d s t a g e s u l f u r i s removed more s l o w l y , p r a c t i c a l l y i n d e p e n d e n t o f t h e e x t e n t o f any f u r t h e r g a s i f i c a t i o n . The observed i n i t i a l r a p i d l o s s of s u l f u r together w i t h the i n i t i a l r a p i d g a s i f i c a t i o n s u g g e s t s t h a t a r e l a t i o n s h i p may e x i s t b e t w e e n t h e i n i t i a l f r a c t i o n a l r e m o v a l o f s u l f u r , (hS/S )^ and t h a t o f Q

9

c a r b o n , (àC/C )^. Q

The d a t a i n F i g u r e 8 show t h e r e l a t i v e s u l f u r r e m o v a l a f t e r a b o u t 1 5 min r e a c t i o n t i m e as a f u n c t i o n o f t h e r e l a t i v e c a r b o n l o s s i n c u r r e d d u r i n g t h i s t i m e . A s i m i l a r r e l a t i o n s h i p was observed f o r the char p r e p a r e d a t 800°C. I t i s seen from F i g u r e 8 t h a t f o r each d e s u l f u r i z a t i o n temperature (TS) the d a t a p o i n t s corresponding to various experimental conditions (e.g., t o t a l p r e s s u r e , CH* c o n t e n t ) f o r m a c u r v e , i n d i c a t i n g a r e l a t i o n s h i p b e t w e e n (Δ5/5 0 ) ± and (àC/CQ)±. F u r t h e r e x a m i n a t i o n o f t h e d a t a i n F i g u r e 8 shows t h a t t h e same f u n c t i o n a l r e l a t i o n s h i p b e t w e e n (LS/S )^ and (hC/CQ)^ e x i s t s , i r r e s p e c t i v e of the temperature a t which d e s u l f u r i z a t i o n t o o k p l a c e . T h i s i s shown i n F i g u r e 9 where t h e o p e n c i r c l e s r e p r e s e n t a l l t h e d a t a p o i n t s i n F i g u r e 8. A l s o i n F i g u r e 9 are the r e s u l t s o b t a i n e d f o r t h e char p r e p a r e d a t 800°C, which show a s i m i l a r r e l a t i o n s h i p b e t w e e n (hS/SQ)^ and ( A C / C q ) ^ ; however, the s l o p e i s s t e e p e r than observed f o r the char p r e p a r e d at 600°C. The h i g h e r t h e c h a r p r e p a r a t i o n t e m p e r a t u r e , t h e more g a s i f i c a t i o n and d e s u l f u r i z a t i o n t a k e s p l a c e d u r i n g c h a r r i n g . Q


KOR

Desulfurization

and Sulfidation

of Coal and Coal


18.

Char

225

Figure 3. Micrographs and electron probe analysis for coal and char, (top) Original dry coal; (middle) coal, treated in He at 600°C for 10 min; (bottom) char (3 hr in H at 600°C). 2

υ •

1

2

3

-

ce < * 2

-

0.6

OC

5

0.4

Q 1 atm

Z>

(Λ 0.2

^

5 atm

Figure 4. Desulfurization and gasi fication of Illinois char (prepared at 600°C) in H at indicated pres sures at800°C 2


COAL

DESULFURIZATION


226


18.

KOR

Desulfurization

and

0

50 CH


Sulfidation

4

of Coal and Coal

0

100

50

IN G A S , %

CH

4

Char

100

IN G A S , %

Figure 7. Final level of gasification as a function of the amount of CH in H -CH mixtures for two types of char, during desulfurization at 600° and 800°C (Ύ ) Jf

2

i

8

0

4

8

12

16

20

uc/c)„ % 0

Figure 8. Relation between initial loss of sulfur and car bon (after 15 min reaction time) for a char prepared at 600°C and subsequently desulfurized under indicated conditions at Ύ — 600° or 800°C β


227


228

T h e r e f o r e , i t s h o u l d n o t b e c o n c l u d e d t h a t i t i s g e n e r a l l y more advantageous t o use a c h a r , prepared a t a h i g h e r temperature, f o r subsequent d e s u l f u r i z a t i o n . A l s o i n c l u d e d i n F i g u r e 9 a r e t h e data from Jones e t a l . ( 4 ) who d e s u l f u r i z e d a c h a r d e r i v e d f r o m I l l i n o i s No. 6 c o a l , p r e p a r e d a t 870°C. The d e s u l f u r i z a t i o n t e m p e r a t u r e v a r i e d b e t w e e n 704° a n d 1010°C, t h e p r e s s u r e b e t w e e n 1 a n d ~8 a t m , a n d t h e y u s e d Η a s w e l l a s e q u i m o l a r m i x t u r e s o f H a n d CH^. A l t h o u g h t h e i r d a t a show some s c a t t e r , i t i s c o n c l u d e d t h a t t h e r e i s a r e l a t i o n s h i p b e t w e e n (AS/S ) a n d (àC/C ) . The d a t a o f B a t c h e l o r e t a l . ( 5 ) , who u s e d a c h a r p r e p a r e d a t 500°C f r o m a P i t t s b u r g h seam c o a l , a r e a l s o shown i n F i g u r e 9. D e s u l f u r i z a t i o n t o o k p l a c e i n H - H S m i x t u r e s ( p b e t w e e n 1 a n d 11 atm) a t t e m p e r a t u r e s v a r y i n g b e t w e e n 650° a n d 880°C. A l s o f o r t h e s e d a t a , a r e l a t i o n s h i p b e t w e e n (hS/So)^ a n d (AC/C^)^ i s o b s e r v e d . Thus t h e f u n c t i o n a l r e l a t i o n s h i p b e t w e e n (AS/S )± a n d (kC/CQ). depends o n l y o n t h e t e m p e r a t u r e a t w h i c h t h e c n a r was p r e p a r e d . Subsequent d e s u l f u r i z a t i o n o f a g i v e n char can o n l y be a c h i e v e d a t t h e expense o f l o s s i n carbon, the e x t e n t o f which i s determined by t h e a p p r o p r i a t e f u n c t i o n a l r e l a t i o n s h i p d e p i c t e d i n F i g u r e 9. A f t e r t h e i n i t i a l r a p i d drop i n s u l f u r c o n t e n t o f t h e c h a r , a more g r a d u a l d e c r e a s e i s o b s e r v e d ( F i g u r e s 4, 5, and 6 ) . Assuming t h a t f o r t h i s stage o f the p r o c e s s , the d e s u l f u r i z a t i o n r e a c t i o n may b e d e s c r i b e d b y a f i r s t - o r d e r r e a c t i o n r e l a t i v e t o the s u l f u r content o f t h e c h a r , then 2

2


Q

2

i

Q

2

±

H

(1) where S i s t h e c o n c e n t r a t i o n o f s u l f u r a t t i m e £ and.fega r a t e constant. Integration o f Equation 1 gives:

l o g y - = - fc £ Q

(2)

where 5 i s t h e s u l f u r c o n c e n t r a t i o n a f t e r 15 m i n o f r e a c t i o n t i m e , aîter w h i c h d e s u l f u r i z a t i o n p r o c e e d s more g r a d u a l l y . B e c a u s e o f t h e s c a t t e r i n t h e e x p e r i m e n t a l r e s u l t s , i t was n o t n e c e s s a r y t o t r e a t t h e r e s u l t s o b t a i n e d f o r t h e two c h a r s separately. F i g u r e 10, d e p i c t i n g t h e f i r s t - o r d e r p l o t s , t h e r e f o r e r e p r e s e n t s t h e a v e r a g e s f o r b o t h t y p e s o f c h a r . L o g (S/S ) i s a l i n e a r f u n c t i o n o f time w i t h i n t h e s c a t t e r o f t h e d a t a . Q


KOR

Desulfurization


18.

0

and Sulfidation

4

of Coal and Coal

'2

8

Char

;6

!^C/C ),, % 0

Figure 9. General relationship between initial loss of sulfur and carbon for two types of char, showing that the data for various experimental conditions for a given char are represented by the same function

TIME,

hours

Figure 10. Desulfurization of char in mixtures of H and CH at 5 atm and indicated temperatures, as a first-order reaction 2

k


229

230

COAL

DESULFURIZATION


The r a t e c o n s t a n t fc^, o b t a i n e d f r o m t h e s l o p e s o f t h e l i n e s i n F i g u r e 1 0 , i s shown i n F i g u r e 11A a s a f u n c t i o n o f t h e c o n centration of H i n the l^-CH^ mixture f o r the d e s u l f u r i z a t i o n e x p e r i m e n t s a t 5 a t m a t 600° a n d 800°C. A l t h o u g h t h e e q u i l i b r i u m c o n c e n t r a t i o n s o f CH i n H^-CH m i x t u r e s a t 5 a t m a r e 5 6 % a n d 16% a t 600° a n d 8 0 0 ° C , r e s p e c t i v e l y ( 2 ) , no m e a s u r a b l e w e i g h t i n c r e a s e o f t h e c h a r was r e c o r d e d a f t e r t r e a t m e n t i n CH, a t 800°C. T h i s i n d i c a t e s t h a t CH^ d i d n o t d i s s o c i a t e t o a n y m e a s u r a b l e e x t e n t under t h e p r e s e n t e x p e r i m e n t a l c o n d i t i o n s . Therefore, i t may b e assumed t h a t t h e p a r t i a l p r e s s u r e o f H^ p r e v a i l i n g d u r i n g t h e d e s u l f u r i z a t i o n e x p e r i m e n t s i n H^-CH^ m i x t u r e s was t h e same as t h a t i n t h e i n g o i n g m i x t u r e . On t h i s b a s i s , F i g u r e 11B was p l o t t e d , s u p p l e m e n t e d w i t h some d a t a o b t a i n e d f r o m d e s u l f u r i z a t i o n e x p e r i m e n t s i n 1 0 0 % H^ a t 1 a n d 5 a t m . The r a t e c o n s t a n t p e r t a i n i n g t o t h e s e c o n d s t a g e o f d e s u l f u r i z a t i o n i n 1 0 0 % H i s t h e same a s t h a t i n " " 4 m i x t u r e s , although i n 100% H g a s i f i c a t i o n continues i n t h e s e c o n d s t a g e ( F i g u r e s 4, 5 a n d 6 ) . T h i s s u g g e s t s t h a t d e s u l f u r i z a t i o n and g a s i f i c a t i o n a r e i n t e r r e l a t e d i n t h e i n i t i a l stages o n l y ; i n t h e second stage t h e d e s u l f u r i z a t i o n i s independent o f gasification. H

C H

2

2

To e x p l a i n t h e s e o b s e r v a t i o n s , i t i s s u g g e s t e d t h a t t h e i n i t i a l l o s s o f c a r b o n — w h i c h i s accompanied by a simultaneous l o s s o f ( m a i n l y o r g a n i c a l l y b o u n d ) s u l f u r — c r e a t e s new p o r e s p r o v i d i n g b e t t e r a c c e s s f o r t h e r e d u c i n g gas t o t h e p y r r h o t i t e p a r t i c l e s embedded i n t h e c h a r . T h i s i s s u p p o r t e d by t h e observed change i n s u r f a c e a r e a o f t h e c h a r d u r i n g d e s u l f u r i z a t i o n . The i n i t i a l s u r f a c e a r e a o f c h a r p r e p a r e d a t 600°C i s a b o u t 2 m /g. The change i n s u r f a c e a r e a i s most p r o n o u n c e d d u r i n g t h e f i r s t h o u r o f d e s u l f u r i z a t i o n , p a r t i c u l a r l y a t 800°C ( F i g u r e 1 2 ) . The pore s u r f a c e a r e a i n c r e a s e s w i t h i n c r e a s i n g temperature and p r e s s u r e a n d , h e n c e , s o does t h e amount o f g a s i f i c a t i o n . 2

A c h a r , p r e p a r e d a t 600°C a n d s u b s e q u e n t l y d e s u l f u r i z e d f o r 2 h r i n 5-atm H^ a t 800°C, was a n a l y z e d f o r t h e v a r i o u s f o r m s o f s u l f u r present i n the product. The a n a l y s i s showed t h a t o f t h e t o t a l s u l f u r c o n t e n t o f 0.16%, a b o u t 0.11% was p y r r h o t i t e a n d a b o u t 0.05% was o r g a n i c s u l f u r . The m i c r o g r a p h i n F i g u r e 1 3 a f o r t h i s p a r t i a l l y d e s u l f u r i z e d p r o d u c t shows t h r e e t y p e s o f particles: b r i g h t , g r e y i s h c o l o r e d , a n d two-phase p a r t i c l e s p a r t l y b r i g h t and p a r t l y grey. The c o m p o s i t i o n o f t h e g r e y i s h p a r t i c l e s v a r i e s somewhat b u t n o m i n a l l y a p p r o a c h e s t h a t o f p y r r h o t i t e ( F i g u r e 13b a n d 1 3 c ) . The b r i g h t p a r t i c l e s a r e i r o n ( F i g u r e 13d) f o r m e d b y t h e c o m p l e t e r e d u c t i o n o f p y r r h o t i t e .


KOR

Desulfurization


H

2

and Sulfidation

IN INGOING H - C H 2

4

231

of Coal and Coal Char

MIXTURE, %

Figure 11. First-order rate constants for desulfurization at indicated temperatures shown as a function of (A) H2 content of gas mixture (5 atm) and (B) partial pressure of H (solid symbols represent data for 100% H) 2

PH '

a

t

m

2


2



232

Figure 13. Optical micrograph and electron analysis of char, treated in p „ = 5 atm, 800° C for 2 hr, showing the presence of pyrrhotite and reduced iron 2


18.

KOR

Desulfurization

and

Sulfidation

of Coal and Coal

Char

233


I t i s c o n c l u d e d f r o m t h e s e o b s e r v a t i o n s t h a t most o f t h e s u l f u r i s i n t h e form o f p y r r h o t i t e d u r i n g t h e l a t e r stages o f desulfurization. The o v e r a l l r a t e o f d e s u l f u r i z a t i o n d u r i n g t h i s stage i s thus expected t o be mainly governed by t h e slow r e d u c t i o n ( 6 ) o f p y r r h o t i t e i n Κ^· Conclusions. I t was f o u n d t h a t t h e d e s u l f u r i z a t i o n o f c o a l char i n mixtures o f a n d CH t a k e s p l a c e i n two d i s t i n c t s t a g e s . In t h e f i r s t stage r a p i d d e s u l f u r i z a t i o n i s accompanied by gasification. These two p r o c e s s e s w e r e shown t o b e i n t e r r e l a t e d , the r e l a t i o n s h i p depending on t h e char p r e p a r a t i o n temperature only. The s e c o n d s t a g e o f d e s u l f u r i z a t i o n p r o c e e d s a t a much slower r a t e and i s b e i n g c o n t r o l l e d by t h e slow r e d u c t i o n o f pyrrhotite to iron. S u l f i d a t i o n o f C o a l Char a n d S y n t h e t i c C h a r s D e s u l f u r i z a t i o n o f c o a l and c o a l char i n hydrogen r e s u l t s i n e v o l u t i o n o f H^S. D e p e n d i n g o n t h e p r o c e s s , t h e H S i s e i t h e r e n t i r e l y o r p a r t l y removed a n d r e c i r c u l a t e d . The w o r k , d e s c r i b e d i n P a r t I I , was u n d e r t a k e n t o o b t a i n a b e t t e r u n d e r s t a n d i n g o f t h e i n t e r a c t i o n b e t w e e n c h a r s and g a s m i x t u r e s c o n t a i n i n g H^S. A l i t e r a t u r e s u r v e y i n d i c a t e d t h a t no i n v e s t i g a t i o n s h a v e b e e n made o f t h e s u l f i d a t i o n o f c a r b o n a c e o u s m a t e r i a l s , i n c l u d i n g c h a r s , i n gas m i x t u r e s o f H^ a n d H S s u c h t h a t t h e s u l f u r p o t e n t i a l was s y s t e m a t i c a l l y v a r i e d . Experimental. C h a r f r o m two d i f f e r e n t s o u r c e s , p r e p a r e d u n d e r a v a r i e t y o f c o n d i t i o n s , was u s e d i n t h i s w o r k . The p r e p a r a t i o n c o n d i t i o n s a r e summarized i n T a b l e I I . The p r e p a r a t i o n o f c h a r f r o m I l l i n o i s No. 6 c o a l was d e s c r i b e d i n t h e f i r s t s e c t i o n o f t h i s chapter under 'Experimental". C h a r f r o m a s h - f r e e f i l t e r p a p e r ( 0 . 0 0 8 % a s h ) was p r e p a r e d b y c h a r r i n g t h e paper, contained i n a h i g h - p u r i t y alumina boat, i n an a t m o s p h e r e o f d r y He a t 600° o r 900°C f o r 3 h r . A f t e r t h e p a p e r was c h a r r e d , t h e b o a t was p u l l e d t o t h e c o o l e n d o f t h e r e a c t i o n tube where i t s l o w l y c o o l e d . S u b s e q u e n t l y , t h e c h a r was q u i c k l y t r a n s f e r r e d t o a d e s i c c a t o r w h e r e i t was s t o c k e d . The c h a r s t h a t w e r e f u r t h e r t r e a t e d i n He a t 1250° a n d 1500°c f o r 24 a n d 9 6 h r r e s p e c t i v e l y , w e r e t a k e n f r o m t h i s s t o c k . t

The s u l f i d a t i o n e x p e r i m e n t s w e r e done i n a v e r t i c a l f u r n a c e w i t h t h e H^H^S m i x t u r e e n t e r i n g a t t h e b o t t o m o f t h e r e a c t i o n tube. The H ^ h ^ S - r a t i o i n t h e gas was a d j u s t e d b y u s i n g t h e u s u a l arrangement o f c a p i l l a r y f l o w meters. I n most o f t h e e x p e r i m e n t s a g a s f l o w r a t e o f 30 cm3(STP)/min was u s e d .


234

COAL

DESULFURIZATION


F o r e a c h s u l f i d a t i o n e x p e r i m e n t a b o u t 100 mg o f c h a r was p l a c e d i n an alumina t r a y . I n most c a s e s t h e s u l f i d i z i n g t r e a t ment was 1 h r a f t e r w h i c h t h e s a m p l e was q u i c k l y p u l l e d up t o t h e c o o l t o p o f t h e r e a c t i o n t u b e w h i l e t h e He was k e p t f l o w i n g . The c o o l e d s a m p l e was t h e n t r a n s f e r r e d t o a d e s i c c a t o r . Sulfur i n t h e c h a r was a n a l y z e d by t h e c o m b u s t i o n method ( 1 ) . I n some s e l e c t e d c a s e s a b o u t 750 mg o f c h a r was s u l f i d i z e d , and a f t e r w a r d s a n a l y z e d f o r o x y g e n by t h e n e u t r o n - a c t i v a t i o n method. The s u r f a c e a r e a s o f t h e c h a r s u s e d w e r e d e t e r m i n e d by t h e BET method. R e s u l t s and D i s c u s s i o n . The p a r t i a l l y d e s u l f u r i z e d c o a l c h a r ( T a b l e I I ) was s u l f i d i z e d a t 600°, 800°, and 900°C i n H -H S c o n t a i n i n g 0-100% ^ S . The r e s u l t s a r e g i v e n i n F i g u r e 14, I n which the s u l f u r content of the char a f t e r l h r r e a c t i o n time i s p l o t t e d v s . t h e p e r c e n t a g e o f H^S i n t h e gas a t t h e e x p e r i m e n t a l t e m p e r a t u r e , d e n o t e d by ( % H ^ S ) . S i m i l a r r e s u l t s w e r e o b t a i n e d after sulfidation for 4 hr. T

I n c a l c u l a t i n g ^ H ^ S ) ^ f r o m t h e p e r c e n t a g e o f H^S i n t h e i n g o i n g gas ( a t room t e m p e r a t u r e ) , due a l l o w a n c e s h o u l d be made f o r t h e p a r t i a l d i s s o c i a t i o n o f H^S a t h i g h e r t e m p e r a t u r e s . The e q u i l i b r i u m H S p e r c e n t a g e o f t h e gas a t t h e r e a c t i o n t e m p e r a t u r e was c a l c u l a t e d f r o m t h e a v a i l a b l e t h e r m o d y n a m i c d a t a ( 2 ) . The p r e s e n t r e s u l t s may be compared w i t h t h o s e o b t a i n e d by P o l a n s k y e t a l . (_7) who t r e a t e d c o k e i n H^S-N^ m i x t u r e s c o n t a i n i n g 4.2 and 8.8% H^S. T h e i r r e s u l t s show no p r o n o u n c e d d i f f e r e n c e i n t h e e x t e n t o f s u l f u r a b s o r p t i o n a t 800° and a t 900°C. Of s p e c i a l i n t e r e s t i s t h e a b s o r p t i o n o f s u l f u r a t 900°C i n H -H^S m i x t u r e s , c o n t a i n i n g l e s s t h a n 2% H^S, by p r e v i o u s l y d e s u l f u r i z e d c o a l char (from I l l i n o i s c o a l ) . This c o a l char was p r o d u c e d b y d e s u l f u r i z a t i o n o f a c h a r t h a t o r i g i n a l l y c o n t a i n e d 0.13% s u l f u r as p y r r h o t i t e ; t h i s i s e q u i v a l e n t t o about 0.23% i r o n . Upon s u l f i d a t i o n o f t h i s d e s u l f u r i z e d c o a l c h a r , p y r r h o t i t e i s e x p e c t e d t o f o r m when t h e s u l f u r p o t e n t i a l i s s u f f i c i e n t l y h i g h . T h i s i s i l l u s t r a t e d i n F i g u r e 15, where a s u d d e n r i s e i n t h e amount o f s u l f u r a b s o r b e d i s o b s e r v e d when (^2 \ agreement w i t h t h e v a l u e c a l c u l a t e d from the thermodynamic d a t a f o r t h e i r o n / p y r r h o t i t e e q u i l i b r i u m ^ ) a t 900°C. S u l f u r c o n t e n t i n c r e a s e s a b o u t 0.20% a t t h e " b r e a k p o i n t " i n t h e a b s o r p t i o n c u r v e , i n good a g r e e m e n t w i t h t h e e s t i m a t e d amount o f i r o n p r e s e n t i n t h e c h a r . S

>

0 , 3 e

T

h

i

s

i s

i n

g

o

o

d

The s u l f u r a b s o r p t i o n c u r v e s , d e p i c t e d i n F i g u r e 14, h a v e t h e g e n e r a l c h a r a c t e r o f a b s o r p t i o n i s o t h e r m s . However, p r o p e r i n t e r p r e t a t i o n o f t h e s e r e s u l t s i s h i n d e r e d by t h e p r e s e n c e o f



18.

KOR

Desulfurization and Sulfidation of Coal and Coal Char

Figure 14. Sulfidation of previously desulfurized char from Illinois No. 6 coal at indicated temperatures

τ

)£L 0

,

0 4

,

0 8

,

1.2

(% H S ) . ?

T

balance

1.6

H

I 2

2

Figure 15. Sulfidation of previously desulfurized char at 900°C in H -H S mixtures for low percentages of HS t

2

2


235

236

COAL

DESULFURIZATION

i m p u r i t i e s i n t h e c o a l c h a r . I t was t h e r e f o r e d e c i d e d t o s t u d y t h e s u l f i d a t i o n o f e s s e n t i a l l y i m p u r i t y - f r e e c a r b o n s and s y n t h e t i c chars. S u l f i d a t i o n o f S y n t h e t i c C a r b o n s and C h a r s . Granulated s a m p l e s o f h i g h - p u r i t y e l e c t r o d e g r a p h i t e and p y r o l i t i c g r a p h i t e were e q u i l i b r a t e d w i t h a 50% 50% H S m i x t u r e a t 1000°C f o r 1.5 h r ; t h e r e was no d e t e c t a b l e s u l f u r a b s o r p t i o n i n e i t h e r f o r m of g r a p h i t e . I n a n o t h e r e x p e r i m e n t s a m p l e s o f e l e c t r o d e g r a p h i t e and p y r i t e w e r e p l a c e d i n s e p a r a t e p a r t s o f an e v a c u a t e d s i l i c a c a p s u l e and a n n e a l e d f o r 20 hr at 650°. This corresponds to a p a r t i a l p r e s s u r e o f s u l f u r v a p o r o f a b o u t 0.14 atm, as e s t i m a t e d f r o m t h e t h e r m o d y n a m i c d a t a f o r t h e p y r r h o t i t e / p y r i t e system(_2) . A f t e r t h i s t r e a t m e n t , no s u l f u r was d e t e c t e d i n t h e g r a p h i t e . The p r e s e n t o b s e r v a t i o n s g e n e r a l l y agree with those of W i b a u t and v a n d e r Kam(jS) who f o u n d t h a t e v e n a t s u l f u r p r e s s u r e s above a t m o s p h e r i c , no d e t e c t a b l e s u l f u r was a b s o r b e d by e i t h e r diamond powder o r C e y l o n g r a p h i t e . The r e s u l t s o b t a i n e d f o r t h e s y n t h e t i c c h a r s a r e g i v e n i n F i g u r e s 16 and 17 f o r 600° and 900°C, r e s p e c t i v e l y . I n most e x p e r i m e n t s t h e r e a c t i o n t i m e was l h r ; h o w e v e r , some s a m p l e s w e r e s u l f i d i z e d f o r up t o 3hr,„ These s a m p l e s a b s o r b e d e s s e n t i a l l y t h e same amount o f s u l f u r as t h o s e s u l f i d i z e d f o r l h r . M o r e o v e r , e q u i l i b r i u m c o u l d be r e a c h e d f r o m b o t h s i d e s . For example, f i l t e r - p a p e r c h a r ( p r e p a r e d a t 900°C) w h i c h was f i r s t s u l f i d i z e d i n a 5 0 % Η , 5 0 % fi^S m i x t u r e a t 600°C t o a f i n a l s u l f u r c o n t e n t of ~ 1 % c o u l d s u b s e q u e n t l y be p a r t i a l l y d e s u l f u r i z e d i n a 90% H^, 10% R^S m i x t u r e t o y i e l d a f i n a l s u l f u r c o n t e n t o f 0.4%. T h i s i s e s s e n t i a l l y t h e same as t h e s u l f u r c o n t e n t a f t e r d i r e c t s u l f i d a t i o n o f t h e c h a r i n t h e same gas m i x t u r e . Similar o b s e r v a t i o n s w e r e made a t 900°C, i n d i c a t i n g t h a t t h e a b s o r b e d s u l f u r i s i n e q u i l i b r i u m w i t h t h e gas and t h a t t h e p r o c e s s o f s u l f u r uptake i s r e v e r s i b l e .


2

The s u r f a c e areas of the c h a r s ( T a b l e I I ) are i n d i c a t e d i n F i g u r e s 16 and 17. A c h a r w i t h a l a r g e r s u r f a c e a r e a h a s , i n g e n e r a l , a l a r g e r c a p a c i t y f o r s u l f u r a b s o r p t i o n . The r e s u l t s o b t a i n e d f o r c o a l c h a r a r e a l s o shown i n F i g u r e s 16 and 17 f o r easy comparison. C o a l c h a r and f i l t e r - p a p e r c h a r ( p r e p a r e d a t 600° and 900°C) h a v e a b o u t t h e same s u r f a c e a r e a s and a b s o r b s i m i l a r amounts o f s u l f u r . The r e s u l t s o f x - r a y a n a l y s i s o f t h e v a r i o u s c h a r s u s e d i n t h i s i n v e s t i g a t i o n w e r e compared i n a q u a l i t a t i v e way w i t h t h e d a t a r e p o r t e d b y T u r k d o g a n e t a l . 0 9 ) a s shown i n T a b l e I I I t o g e t h e r w i t h e s t i m a t e d mean c r y s t a l l i t e s i z e s . I t was mentioned



KOR

237


18.

ι 8 •

ι

y

ι

2

S (m /g)

CHAR Fp (600"O

330

Δ Fp (900'C)

272

V COAL (800'C)

400

•ΤΗ

/δ.

0

20

40

60

(% H S ) , balance Η , 2

T

I 80

1 100

Figure 17. Sulfidation at 900°C in H H S mixtures of various chars, having in dicated pore surface area (S) 2

2



238 Table I .

Forms o f S u l f u r ( i n Wt.%) i n D r i e d C o a l and D e r i v e d C h a r ( 3 h r , 600°C)

Form o f S u l f u r Pyrite Sulfate Sulfide Organic Total


Coal

Dried Coal 53 12 005 27 93

Char

0.005 0.13 0.61 0.75

Table I I . Source, Conditions of P r e p a r a t i o n , I n i t i a l S u l f u r ( S ^ ) a n d Oxygen ( 0 ^ ) C o n t e n t s , and S u r f a c e A r e a (SA) of t h e V a r i o u s Chars S t u d i e d

Preparation Conditions

Source Illinois

Coal

5 a t m H , 800°C f o r 3 h r 2

A s h - f r e e F i l t e r 1 atm Paper (0.008% 1 atm 3h) 1 atm 1 atm 1 atm 1 atm

Table I I I .

paper paper paper paper

600°C, 3 h r 900°C, 3 h r 600°C, 3 h r + 1250°C, 24 h r 600°C, 3hr+ 1500°C, 96h

2

S

S A ( m / g ) i ( % ) °i(%) 400

0.05

—

330 272

0.00 0.00

4.0 1.4

30

0.00

0.34

3

0.00

0.14

Q u a l i t a t i v e Comparison o f t h e C r y s t a l l i n i t y o f F i l t e r - P a p e r C h a r s Used i n T h i s Work W i t h t h e C r y s t a l l i n i t y a n d Mean C r y s t a l l i t e S i z e o f Some Carbons I n v e s t i g a t e d by Turkdogan e t a l . ( 9 )

Type o f C h a r and P r e p a r a t i o n

Filter Filter Filter Filter

He, He, He, He, He, He,

P r o p e r t i e s o f t h e Char

(600)( (900)j (1250) (1500)

1

C r y s t a l l i n i t y f r o m T u r k d o g a n s Work Q u a l i t a t i v e Comparison Mean C r y s t a l l i t e Size From Xbetween coconut c h a r c o a l and " v i t r e o u s " carbon approaching v i t r e o u s carbon same a s v i t r e o u s c a r b o n

-10 - -16


-16 -16


18.

KOR

Desulfurization

and

Sulfidation

of Coal and Coal

Char

239

b e f o r e t h a t g r a p h i t i z e d e l e c t r o d e g r a p h i t e , w h i c h h a s a mean c r y s t a l l i t e s i z e o f 500 Â, d i d n o t a b s o r b s u l f u r w h e r e a s t h e n o n g r a p h i t i z e d c h a r s d i d . Thus, i t i s c o n c l u d e d from t h e s e r e s u l t s t h a t t h e a b i l i t y o f a g i v e n char o r carbon t o absorb s u l f u r i s determined f i r s t by i t s s t a t e o f c r y s t a l l i n i t y . I n p o o r l y g r a p h i t i z e d o r n o n g r a p h i t i z e d c a r b o n s , t h e amount o f absorbed s u l f u r i n c r e a s e s w i t h i n c r e a s i n g pore s u r f a c e a r e a . In view o f t h e s t r o n g a f f i n i t y between s u l f u r and oxygen, an a t t e m p t was made t o i n v e s t i g a t e t h e e f f e c t o f o x y g e n on t h e s u l f u r a b s o r p t i o n b y c h a r . The i n i t i a l o x y g e n c o n t e n t o f s y n t h e t i c c h a r s i s shown a s a f u n c t i o n o f t h e s u r f a c e a r e a i n F i g u r e 18. I t i s seen t h a t t h e i n i t i a l oxygen c o n c e n t r a t i o n i s a s t r o n g f u n c t i o n o f t h e s u r f a c e a r e a and hence t h e temperature a t w h i c h t h e c h a r was p r e p a r e d ( T a b l e I I ) . To s t u d y t h e change i n o x y g e n c o n c e n t r a t i o n a f t e r s u l f i d a t i o n o f t h e c h a r s , a s e r i e s o f s p e c i a l e x p e r i m e n t s was c o n d u c t e d ; t h e r e s u l t s a r e s u m m a r i z e d i n T a b l e I V . The o x y g e n c o n t e n t a f t e r · s u l f i d a t i o n was i n d e p e n d e n t , w i t h i n t h e a n a l y t i c a l e r r o r , o f t h e ratio ( p ^ s / P l ^ T S increase i nthe sulfidation temperature r e s u l t e d i n a lower oxygen c o n t e n t i n t h e c h a r , p a r t i c u l a r l y i f t h e char had a l a r g e r surface area (Figure 18). In a l l cases i n v e s t i g a t e d , t h e chars w i t h l a r g e s u r f a c e a r e a s c o n t a i n e d more o x y g e n . B e c a u s e o f t h e i n t e r d e p e n d e n c e of s u r f a c e area and oxygen c o n t e n t , i t i s d i f f i c u l t t o s e p a r a t e t h e i r e f f e c t s on t h e c a p a c i t y o f a g i v e n char f o r s u l f u r a b s o r p t i o n . However, some i n d i c a t i o n o f t h e i n f l u e n c e o f o x y g e n on t h e s u l f u r a b s o r p t i o n may b e o b t a i n e d f r o m t h e r e s u l t s shown i n Table IV. F o r i n s t a n c e , the s u r f a c e areas o f f i l t e r - p a p e r c h a r p r e p a r e d a t 600° a n d 900°C w e r e 330 a n d 272 m /g, r e s p e c t i v e l y , a d i f f e r e n c e o f a b o u t 20%. A f t e r s u l f i d a t i o n a t 600°C i n a g a s of h i g h s u l f u r p o t e n t i a l , t h e oxygen c o n t e n t s o f these c h a r s d i f f e r e d b y a b o u t a f a c t o r o f two, y e t t h e d i f f e r e n c e i n s u l f u r a b s o r b e d was n o t more t h a n a b o u t 10%. These f i n d i n g s i n d i c a t e t h a t t h e i n f l u e n c e o f o x y g e n on t h e s u l f u r a b s o r p t i o n i s p r o b a b l y secondary. I n t h i s c o n t e x t t h e w o r k o f Hofmann a n d O h l e r i c h ( l O ) s h o u l d be m e n t i o n e d . They t r e a t e d s u g a r c h a r c o a l i n d r y 0^ a t a b o u t 500°C t o o b t a i n a c h a r c o n t a i n i n g a b o u t 1 0 % o x y g e n a s s u r f a c e complexes. Upon s u l f i d a t i o n o f t h i s o x y g e n a t e d c h a r i n at 600°C, t h e y f o u n d t h a t t h e amount o f s u l f u r t a k e n up was e q u a l t o t h a t a b s o r b e d b y a c h a r w h i c h was n o t p r e v i o u s l y a c t i v a t e d i n o x y g e n . Hofmann a n d O h l e r i c h c o n c l u d e d , a s d i d Hofmann a n d N o b b e ( l l ) , t h a t t h e amount o f s u l f u r a b s o r b e d b y c h a r depends o n l y on i t s s u r f a c e a r e a . i

n

t

n

e

a s

A

n

2




240

Some o f t h e f i l t e r - p a p e r c h a r s u s e d i n t h i s w o r k w e r e a n a l y z e d f o r hydrogen and n i t r o g e n . The r e s u l t s a r e summarized i n T a b l e V, w h i c h shows t h a t t h e m a j o r i m p u r i t i e s i n f i l t e r - p a p e r c h a r a r e oxygen a n d h y d r o g e n . The o x y g e n and h y d r o g e n c o n t e n t s decrease w i t h i n c r e a s i n g temperature o f char p r e p a r a t i o n w h i l e the n i t r o g e n content remains e s s e n t i a l l y c o n s t a n t . The shape o f t h e c u r v e s i n F i g u r e 1 9 , i n w h i c h t h e amount o f s u l f u r i n some s y n t h e t i c c h a r s i s shown a s a f u n c t i o n o f (pjj^s/PHo^T' s t r o n g l y s u g g e s t s a b s o r p t i v e b e h a v i o r . Hayward a n d T r a p n e l l t l 2 ) g i v e examples o f t y p i c a l a b s o r p t i o n i s o t h e r m s a n d note that chemisorption normally gives r i s e to isotherms of t h i s g e n e r a l form. A l t h o u g h a t r e a t m e n t o f t h e p r e s e n t r e s u l t s i n terms o f i d e a l i z e d a b s o r p t i o n i s o t h e r m s i s open t o c r i t i c i s m , a n a t t e m p t w i l l n e v e r t h e l e s s b e made t o t r e a t t h e r e s u l t s a c c o r d i n g l y . I t w i l l b e shown t h a t s u c h a t r e a t m e n t l e a d s t o r e s u l t s w h i c h may b e considered reasonable. A s s u m i n g t h a t t h e c h e m i s o r b e d s u l f u r forms a n i d e a l monolayer and t h a t e a c h c h e m i s o r b e d s p e c i e s o c c u p i e s a s i n g l e s i t e , a p p l i c a t i o n o f t h e i d e a l Langmuir i s o t h e r m g i v e s ( 1 2 ) :

-

θ

8(1

- θ)

(1)

where α i s t h e a c t i v i t y o f t h e c h e m i s o r b e d s p e c i e s , θ t h e f r a c t i o n a l coverage, and Β a temperature-dependent parameter containing the heat of chemisorption of s u l f u r . The f r a c t i o n a l c o v e r a g e θ = ν/υ , w h e r e ν i s t h e v o l u m e o f c h e m i s o r b e d s u l f u r (STP) p e r gram o ? c h a r a n d ν t h e v o l u m e g i v i n g a c o m p l e t e m o n o l a y e r o f s u l f u r o n t h e s u r f a c e o f t h e c h a r . The s u r f a c e a r e a , S nrVg, i s r e l a t e d t o ν by t h e f o l l o w i n g e x p r e s s i o n : m

where Ν i s A v o g a d r o ' s number a n d A t h e c r o s s - s e c t i o n a l a r e a o f an a b s o r b e d s p e c i e s i n A^. The v o l u m e , v , o f t h e c h e m i s o r b e d s u l f u r i s o b t a i n e d f r o m t h e measured s u l f u r c o n c e n t r a t i o n a s follows: (3)


18.

KOR

Desulfurization


Table IV.

and

Sulfidation

of Coal and Coal

Char

241

Oxygen and S u l f u r C o n t e n t s o f F i l t e r - P a p e r C h a r s a f t e r S u l f i d a t i o n a t 600° a n d 900°C f o r 1 h r i n Gases o f V a r i o u s S u l f u r P o t e n t i a l

Sulfidation Temperature C O

Preparation Temperature

600

600

4.0

0.05 61.5

1.7 1.6

0.80 9.50

900

1.4

0.05 61.5

0.8 0.8

0.20 8.40

/ Pn H ~ S \ &

α

m

900

CO

Λ

V

ί ν Λ

% )

/ 2 \

P H

^

\

,

,

S u l f i d i z e d Char

2 /τ

%S

%0

1250

0.34

0.05

0.2

0.03

1500

0.14

0.05 61.5

0.1 0.1

0.02 0.05

600

4.0

0.05 7.6

0.7 0.6

0.90 7.50

900

1.4

0.05 7.6

0.9 0.6

0.40 5.80

0.14

0.05 7.6

0.1 0.1

0.01 0.25

1500

a,

0^ » i n i t i a l o x y g e n c o n t e n t o f t h e c h a r .

T a b l e V.

Char Preparation Temperature(°C) 600 900 1250

C h e m i c a l A n a l y s i s o f F i l t e r - P a p e r Char i n R e l a t i o n t o P r e p a r a t i o n Temperature

Carbon 93.9 97.0 99.6

Composition(wt.%) Hydrogen Oxygen 4.0 1.4 0.34

1.9 0.6 0.2

Nitrogen 0.02 0.06 0.04




242

Figure 18. Oxygen concentration in synthetic chars as a function of surface area: initial, and after sulfidation at 600° and 900°C

Figure 19. Sulfidation of various chars at 600° and 900°C, showing curves typical for chemisorption


18.

KOR


S u b s t i t u t i n g f o r t h e s u l f u r a c t i v i tyy θ = v/v , a n d m a k i n g u s e o f E q u a t i o n s 2 and e x p r e s s i o n i s o b t a i n e d f r o m E q u a t i o n 1: a


( p

H

S

/ P

H

1.87

I

Β

+

( P

=

243

2

3, t h e f o l loowwi!n g

/ P

H S H > 2 2 -

(4)

T

The e x p e r i m e n t a l r e s u l t s p l o t t e d i n a c c o r d a n c e w i t h E q u a t i o n 4 a r e g i v e n i n F i g u r e s 20 a n d 21 f o r 600° a n d 900°C, r e s p e c t i v e l y . The s l o p e o f e a c h l i n e s h o u l d b e p r o p o r t i o n a l t o 1/S; i n f a c t , t h i s i s shown t o b e t h e c a s e i n F i g u r e 22, i n w h i c h t h e l o g (slope) i s d e p i c t e d as a l i n e a r f u n c t i o n o f l o g S w i t h a t h e o r e t i c a l slope of -1. From t h e i n t e r c e p t o f t h i s l i n e w i t h t h e o r d i n a t e t h e v a l u e o f A, t h e c r o s s - s e c t i o n a l a r e a o f a c h e m i s o r b e d s p e c i e s , i s c a l c u l a t e d t o b e 17 A . T h i s v a l u e i s Ço b e compared w i t h c r o s s - s e c t i o n a l a r e a s r a n g i n g f r o m 10 t o 50 A as estimated from p h y s i c a l a b s o r p t i o n data f o r a v a r i e t y o f gases(12). A c c o r d i n g t o E q u a t i o n 4, t h e i n t e r c e p t s o f t h e l i n e s i n F i g u r e s 20 a n d 21 w i t h t h e o r d i n a t e s h o u l d b e p r o p o r t i o n a l t o 1/S. T h i s i s shown t o b e t h e c a s e i n F i g u r e 2 3 , i n w h i c h l o g ( i n t e r c e p t ) i s d e p i c t e d as a f u n c t i o n o f l o g S w i t h a t h e o r e t i c a l slope of -1. From t h e i n t e r c e p t s o f b o t h l i n e s w i t h t h e o r d i n a t e , t o g e t h e r w i t h t h e p r e v i o u s l y d e t e r m i n e d v a l u e o f A, t h e t e m p e r ature-dependent parameter Β i s obtained. This parameter i s p r o p o r t i o n a l t o e ^ / ^ , where q i s t h e h e a t o f c h e m i s o r p t i o n o f s u l f u r on char. From t h e t e m p e r a t u r e dependence o f 8, t h e v a l u e o f q i s e s t i m a t e d t o b e a b o u t -10 k c a l / m o l e , a r e a s o n a b l e v a l u e when compared w i t h t h e h e a t s o f c h e m i s o r p t i o n o f o t h e r g a s e s o n c a r b o n , a s l i s t e d b y Hayward a n d T r a p n e l l ( 1 2 ) . The f o r e g o i n g a n a l y s i s , a l t h o u g h o f n e c e s s i t y o v e r s i m p l i f i e d , shows t h a t t h e a b s o r p t i o n o f s u l f u r b y s y n t h e t i c c h a r s i s most l i k e l y mainly governed by c h e m i s o r p t i o n . I t i s thus expected that the s u r f a c e area i s an important parameter i n determining whether a given char o r carbon i s a b l e t o r e t a i n s i g n i f i c a n t quantities of sulfur. T h i s i s i n agreement w i t h e a r l i e r w o r k by Hofmann a n d N o b b e ( l l ) a n d b y P o l a n s k y e t a l . ( 7 ) . However, t h e s u r f a c e a r e a i s n o t t h e o n l y p a r a m e t e r t o b e considered. Forinstance, electrode graphite i nthe unoxidized s t a t e h a s a s u r f a c e a r e a o f 1 m 2 / g ( 9 ) , a p p r o x i m a t e l y t h e same as f i l t e r - p a p e r c h a r p r e p a r e d a t 1500°C ( T a b l e I I ) . Y e t , no t a k e - u p o f s u l f u r b y e l e c t r o d e g r a p h i t e was o b s e r v e d a f t e r s u l f i d a t i o n i n 5 0 % H - 5 0 % H_S a t 1000°C. The mean c r y s t a l l i t e 2

2



244


Figure 20. Langmuir isotherms show ing chemisorption at 600°C on chars having indicated surface areas

J20

10

I

L40

30

50

(pH S/p 2

1

1

s = 3 m /g

_

2

.

Ο _

°

s

-

—

-

S

30

> Figure 21. Langmuir isotherms show ing sulfur chemisorption at 900°C on chars having indicated surface areas

272

S

-o-o—S—°

1

1

(pH S/pH ) 2

^/c,

?

T


18.

KOR

Desulfurization

and Sulfidation

of Coal and Coal


τ

J

,

0

1

I

I

,M

0.8

ν

Char

r

I 6

1

1

i.O

14

1 25

LOG S

Figure 22. Slope of chemisorption isotherms at 600° and 900°C as a function of the surface area of the char

0

0.4

0.8

1./

i.6

2.0

LOG S

Figure 23. Intercept of chemisorption iso therms with ordinate as a function of surface area of the char, sulfidized at indicated tem peratures


245

246



s i z e , together w i t h t h e x-ray a n a l y s i s , o f e l e c t r o d e graphite(9) shows t h a t i t s n a t u r e i s g r a p h i t i c a n d t h e r e f o r e more o r d e r e d . B l a y d e n and P a t r i c k ( 1 3 ) concluded f r o m t h e i r work t h a t s o - c a l l e d d i s o r d e r e d c a r b o n s w i t h s m a l l c a r b o n l a y e r s ( e q u i v a l e n t t o mean c r y s t a l l i t e s i z e ) a n d many d e f e c t s a r e b e t t e r a b l e t o a b s o r b s u l f u r t h a n t h e more c r y s t a l l i n e and g r a p h i t i c c a r b o n s . The present f i n d i n g s are consistent with t h i s viewpoint. Conclusions. I n t h e absence o f i m p u r i t i e s such as i r o n , t h e a b i l i t y of c h a r s o r c a r b o n s t o a b s o r b s i g n i f i c a n t amounts o f s u l f u r i n a s u l f i d i z i n g gas s u c h a s a H^-H^S m i x t u r e depends on t h e s t a t e o f c r y s t a l l i n i t y o f t h e c a r b o n a c e o u s m a t e r i a l . The s u l f u r absorption decreases w i t h i n c r e a s i n g c r y s t a l l i t e s i z e . ο

I n g e n e r a l , c a r b o n s h a v i n g a mean c r y s t a l l i t e s i z e o f a b o u t 15 A o r l e s s a b s o r b s i g n i f i c a n t amounts o f s u l f u r when t r e a t e d i n Η -H^S m i x t u r e s . F o r carbons w i t h a given c r y s t a l l i t e s i z e , the h i g h e r t h e p o r e s u r f a c e a r e a t h e h i g h e r i s t h e amount o f s u l f u r absorbed. S u l f u r a b s o r p t i o n i n h i g h - p u r i t y chars, obtained from a s h f r e e f i l t e r paper, i n c r e a s e d w i t h i n c r e a s i n g s u l f u r a c t i v i t y and pore surface area o f t h e char. This i s i n accord with the L a n g m u i r r e l a t i o n f o r c h e m i s o r p t i o n on s i n g l e s i t e s i n an i d e a l monolayer. I t i s concluded from t h e present experimental r e s u l t s t h a t s u l f u r i s n o t accommodated i n t h e t h r e e - d i m e n s i o n a l l a t t i c e o f t h e c a r b o n b u t i s c h e m i s o r b e d on t h e s u r f a c e . However, s u c h c h e m i s o r p t i o n t a k e s p l a c e o n l y on t h e p o r e w a l l s o f n o n g r a p h i t i c ( p o o r l y c r y s t a l l i n e ) c a r b o n s , o f w h i c h c h a r s a r e good e x a m p l e s . Acknowledgment The a u t h o r w i s h e s t o t h a n k J . R. C a u l e y o f t h i s for h i s a s s i s t a n c e w i t h the experiments.

laboratory

Litreature Cited

1. "Sampling and Analysis of Coal, Coke, and By-Products," pp. 84-86, Carnegie Steel Corp., Pittsburgh, 1929. 2. Kubaschewski, O., Evans, E. L., Alcock, C. B., "Metallurgical Thermochemistry," 4th ed., Pergamon, London, 1967. 3. van Krevelen, D. W., "Coal," Elsevier, Amsterdam, 1961. 4. Jones, J. F., Schmidt, M.R., Sacks, M.E., Chen, Y.C., Gray, C.A., Office of Coal Research, R&D Rept. 11, Suppl. to Final Rept., Jan. 9, 1967.



18. KOR Desulfurization and Sulfidation of Coal and Coal Char

247

5. Batchelor, J. D., Gorin, E., Zielke, C. W., J. Ind. Eng. Chem., (1960) 52, 161-8. 6. Kor, G. J. W., Met. Trans. (1974) 5, 339-43. 7. Polansky, T. S., Knapp, E. C., Kinney, C. R., J. Inst. Fuel, (1961) 34, 245-6. 8. Wibaut, J. P., van der Kam, E. J., Rec. Trav. Chim. Pays-Bas, (1930) 49, 121-37. 9. Turkdogan, E. T., Olsson, R. G., Vinters, J. V., Carbon, (1970) 8, 545-64. 10. Hofmann, U., Ohlerich, G., Angew. Chem., (1950) 62, 16-21. 11. Hoffman, U., Nobbe, P., Ber. Dtsch. Chem. Ges., (1932) 65, 1821-30. 12. Hayward, D. O., Trapnell, B. M. W., "Chemisorption," 2nd ed., Butterworths, Washington, D. C., 1964. 13. Blayden, H. E., Patrick, J. W., Carbon, (1967) 5, 533-44.


19 Fluid-Bed Carbonization/Desulfurization of Illinois Coal by the Clean Coke Process: PDU Studies N. S. BOODMAN, T. F. JOHNSON, and K. C. KRUPINSKI


U.S. Steel Research Laboratory, Monroeville, PA 15146

The Clean Coke Process combines both fluid-bed carbonization andhydrogenation/liquefactionto convert high-sulfur coal to low-sulfur metallurgical coke, chemical feedstocks, and to a lesser extent, liquid and gaseous fuels. The overall processing scheme, which has previously been described in detail (1), is illustrated by the sketch in Figure 1. Briefly, run-of-mine coal is beneficiated and classified by conventional means and split into two feed portions: a sized fraction suited for fluid-bed processing and a fines fraction suited for high-pressurehydrogenation.The sized feed is dried and subjected to a mild surface oxidation in a nonpressurized bed fluidized with air-enriched flue gas. The dry, preoxidized feed is then carbonized in two stages, at 820°F (440°C) and 1400°F (760°C), in fluid-bed reactors operated at pressures up to 150 psig, to produce low-sulfur char, tar, and gas rich in methane and hydrogen. The fines fraction of the beneficiated coal, combined with run-of-mine coal, is dried, pulverized, and slurried with a process-derived oil. The slurry is then pumped to a pressure r e a c t o r and l i q u e f i e d a t 850°-900°F (455°-480°C) and 3000-4000 p s i g t o produce l i q u i d s and Ci-to-C4 hydrocarbon gases. L i q u i d s from both operations are d i s t i l l e d t o produce a l i g h t chemical o i l , a middle o i l f o r r e c y c l e t o the hydrogénation r e a c t i o n , and a heavy o i l . The heavy o i l , a s o f t p i t c h , i s combined with the c a r b o n i z a t i o n char and processed to make a low-sulfur m e t a l l u r g i c a l formcoke, c u r r e n t l y i n the form of p e l lets. S i m i l a r l y , product gases from a l l operations are combined and processed to produce hydrogen f o r the hydrogénation operat i o n , f u e l , ethylene and propylene, s u l f u r , and ammonia. A d e t a i l e d d e s c r i p t i o n of y i e l d of chemical products and process economics has been presented p r e v i o u s l y (_2) .

248



Figure 1.

CARBONIZATION

Clean coke process

COAL PREPARATION

HYDROGENATION

COKE PREPARATION

CHAR

GAS

LIQUID PRODUCTS

LIQUIDS PROCESSING

LIQUID PRODUCTS

GAS

ASH A N D UNREACTED COAL

H E A V Y OIL

CHEM;CALS AND F U E L FEEDSTOCK

RECYCLE SOLVENT

GAS PROCESSING

t


BASES

ACIDS

{

I

METALLURGICAL COKE

F U E L GAS

HYDROGEN

CARBON DIOXIDE

SULF UR

ETHYLENE

AMMONIA

LIGHT OILS

LIQUID F U E L

NAPHTHALENE

BENZE NE

TAR

TAR

COAL


250

DESULFURIZATION

T h i s chapter presents the r e s u l t s obtained from sustained o p e r a t i o n of the c a r b o n i z a t i o n PDU (process development u n i t ) . These r e s u l t s confirm and extend the data obtained p r e v i o u s l y i n bench s t u d i e s (_3) . A l l t e s t s were run with I l l i n o i s No. 6 seam c o a l c o n t a i n i n g 2-2.5% s u l f u r a f t e r p r e p a r a t i o n . From t h i s were produced chars c o n t a i n i n g , g e n e r a l l y , 0.6-0.7% s u l f u r ; char cont a i n i n g as l i t t l e as 0.2% s u l f u r was produced under the more severe r e a c t i o n c o n d i t i o n s . Reaction c o n d i t i o n s i n v e s t i g a t e d f o r t h e i r e f f e c t on char s u l f u r content included residence time, temperature, pressure, and H2S concentration i n the f l u i d i z i n g gas. Data are a l s o presented to show the weight d i s t r i b u t i o n of m a t e r i a l s i n t o and out of the PDU system. The s c a l e of the t e s t s d i s c u s s e d i n t h i s paper i s best i l l u s t r a t e d by a d e s c r i p t i o n of the design and operation of the c a r b o n i z a t i o n PDU. Carbonization

PDU

F i g u r e 2 i s a photograph of the c a r b o n i z a t i o n PDU, i n which the f l u i d - b e d r e a c t o r occupies the second l e v e l ; the feed v e s s e l s are on the top l e v e l , and the char r e c e i v e r s are a t f l o o r l e v e l . Two other v e s s e l s v i s i b l e a t f l o o r l e v e l are l i q u i d catchpots attached to the gas-to-gas heat exchanger (on the r i g h t ) and the water-cooled exchanger (on the l e f t ) . C o n s t r u c t i o n d e t a i l s of the f l u i d - b e d carbonizer are i l l u s t r a t e d i n F i g u r e 3. The v e s s e l , i n c l u d i n g top and bottom c l o s u r e s , i s 9 f t 3 i n . t a l l and i s f a b r i c a t e d from 1 - i n . - t h i c k Incoloy A l l o y 800 to permit operat i o n at 1500°F (815°C) and 150 p s i g . The lower 36-in. s e c t i o n of the r e a c t o r i s the 10-in.-ID f l u i d - b e d area; the expanded upper 3 6 - i n . s e c t i o n has a 2 0 - i n . ID to f a c i l i t a t e deentrainment of f i n e s o l i d s from the f l u i d i z i n g gas. Feed enters the f l u i d bed by g r a v i t y flow through the feed pipe, p o s i t i o n e d about 1 i n . above the g a s - d i s t r i b u t o r p l a t e ; char e x i t s the f l u i d bed through the overflow pipe at 30 i n . above the d i s t r i b u t o r p l a t e . The v e s s e l a l s o contains an i n t e r n a l cyclone, which removes char f i n e s from the e x i t i n g gas and r e t u r n s them to the f l u i d bed. The major components and stream flows of the complete PDU are i l l u s t r a t e d i n the s i m p l i f i e d diagram i n Figure 4. Feed i s metered by r o t a r y feeders from e i t h e r of two lock hoppers to the f l u i d - b e d carbonizer, from which product char overflows and f a l l s i n t o one of the two r e c e i v e r s , a l s o lock hoppers. Residence time i n the r e a c t o r i s c o n t r o l l e d by v a r y i n g the s o l i d s feed r a t e . Gas d e r i v e d from c a r b o n i z a t i o n of the feed i s r e c y c l e d through the system to f l u i d i z e the bed. Carbonization gases, along with r e c y c l e gas, leave the f l u i d bed, pass through the i n t e r n a l cyclone i n the expanded s e c t i o n , and leave the v e s s e l .



19.

BOODMAN

E T A L .

Fluid-Bed

Carbonization/Desulfurization

251

Figure 2. Carbonization PDU for clean coke process

Figure 3.

Fluid-bed carbonizer


COAL


252

DESULFURIZATION

The gas then passes through an e x t e r n a l cyclone and i n t o the gas-to-gas interchanger ( s h e l l and tube d e s i g n ) . Hot c a r b o n i z a t i o n e f f l u e n t gas passes i n downflow through the tube bundle, where i t i s p a r t i a l l y cooled by heat exchange with c l e a n r e c y c l e gas moving upflow on the s h e l l s i d e of the interchanger, and r e t u r n i n g to the main gas heater. In the interchanger, the c a r b o n i z a t i o n gas i s a l s o contacted with a spray of wash o i l to remove t a r mist and char dust which c o l l e c t i n the interchanger pot. The gas then passes to a water-cooled exchanger f o r f i n a l c o o l i n g to about 110°F (45°C), a f t e r which i t passes i n s e r i e s through a wash-oil scrubber and a c a u s t i c scrubber f o r f i n a l cleanup of t a r mist, char dust, and a c i d g a s e s — p a r t i c u l a r l y H2S. The c l e a n gas i s then r e c y c l e d by a compressor through the s h e l l s i d e of the interchanger to the main e l e c t r i c heater, where i t i s reheated to the temperature d e s i r e d to maintain the f l u i d bed at design temperature. A c t u a l temperature of gas from the heater v a r i e s with operating c o n d i t i o n s i n the r e a c t o r , but the temperature of gas e x i t i n g the heater i s on the order of 100°F (55°C) higher than bed temperature. Net product gas i s vented by a pressure r e g u l a t o r - c o n t r o l l e r through a wet-test meter and sampled f o r a n a l y s i s . The f u n c t i o n of the w a t e r - i n j e c t i o n system, F i g u r e 4, i s to maintain a concentration of about 8 v o l % water vapor i n the r e c y c l e gas while the gas i s i n contact with the hot a l l o y metal surfaces of the main gas heater during second-stage c a r b o n i z a t i o n . The presence of 8 v o l % water vapor along with 50 ppm H S prevents formation of carbon d e p o s i t s on the hot metal surfaces, which a t t a i n temperatures above about 1500°F during second-stage c a r b o n i z a t i o n . Previous experience has shown t h a t without the water vapor, carbon d e p o s i t s grew l a r g e enough to impede gas flow through the heater s i g n i f i c a n t l y . Moreover, the carbon r e s u l t e d i n c a t a s t r o p h i c c a r b u r i z a t i o n of the metal and destroyed the o r i g i n a l r e c y c l e - g a s heater. With water vapor and H S present, carbon formation i s c o n t r o l l e d , a t l e a s t up to metal w a l l temperatures of 1550°F (845°C). Water i s i n j e c t e d as a l i q u i d i n t o the interchanger s h e l l - s i d e gas i n l e t , where i t i s vaporized by e x t e r n a l e l e c t r i c heaters. Most of the i n j e c t e d water condenses i n the wash-oil quench i n the interchanger pot and i n the gas c o o l e r . The remainder of the water condenses i n t o the c a u s t i c - s c r u b b e r s o l u t i o n . 2

2

The wash-oil spray system i s operated i n d i f f e r e n t modes f o r the two stages of c a r b o n i z a t i o n . For f i r s t - s t a g e carbonizat i o n a t 820°F, wash-oil quench of the gas occurs a t the top of the interchanger to provide a washed-tube flow, which prevents plugging of the tubes by t a r / c h a r agglomerates. For second-



19.

BOODMAN ET A L .

Fluid-Bed

Carbonization/

Desulfurization

253

stage c a r b o n i z a t i o n a t 1300°-1400°F (705°-760°C), wash-oil quench of the gas occurs below the interchanger tube bundle. In t h i s mode, t u b e - e x i t gas temperature i s c o n t r o l l e d a t about 900°F (480°C) t o prevent condensation of t a r w i t h i n the tubes. Fresh wash o i l , a t about 2 g a l / h r , i s metered continuously i n t o the wash-oil scrubber to maintain a low c o n c e n t r a t i o n of t a r and char f i n e s i n the o i l system. Overflow from the l e v e l c o n t r o l l e d scrubber flows i n t o the gas-cooler pot, from which the wash o i l i s pumped t o the spray nozzle i n the gas/gas interchanger. Wash-oil blowdown, i n c l u d i n g d i s s o l v e d t a r and suspended water and char, i s removed from the interchanger p o t . Wash-oil blowdown i s screened t o remove p l u s 50-mesh s o l i d s , heated to b o i l o f f contained water, and f l a s h - d i s t i l l e d to separate heavy o i l b o i l i n g above 540°F (280°C), which i s used as p a r t of the binder f o r coke production. The f l a s h d i s t i l l a t e i s processed through a continuous d i s t i l l a t i o n column a t atmospheric pressure to separate a chemical o i l d i s t i l l i n g t o 445°F (230°C) as overhead and f r e s h wash o i l as bottoms. The wash o i l c o n s i s t s e s s e n t i a l l y of mono- and dimethylnaphthalenes, acenaphthene, and q u i n o l i n e bases. The f i n a l system i s c a u s t i c scrubbing, which c o n t r o l s H S c o n c e n t r a t i o n i n the r e c y c l e gas. Normally, H2S c o n c e n t r a t i o n i n the gas i s maintained i n the range 50-100 ppm, which a i d s i n c o n t r o l l i n g carbon d e p o s i t i o n from the c a t a l y t i c decomposition of the carbon components i n the gas. C o n t r o l of H2S concentrat i o n may be e f f e c t e d by means of p a r t i a l bypass of gas around the c a u s t i c scrubber and by v a r y i n g the r a t e of metering f r e s h c a u s t i c s o l u t i o n (about 7% NaOH) i n t o the scrubber. G e n e r a l l y , the PDU operators p r e f e r t o use the l a t t e r method. 2

Continuous Coal O x i d i z e r An important adjunct t o the c a r b o n i z a t i o n PDU, the continuous c o a l o x i d i z e ^ d r i e s and p r e o x i d i z e s the s i z e d c o a l feed. The need f o r p r e o x i d a t i o n of I l l i n o i s c o a l was d i s c u s s e d i n the previous paper (3) on bench-scale s t u d i e s , which showed that a m i l d surface o x i d a t i o n of the c o a l diminishes i t s caking tendency s u f f i c i e n t l y t o prevent i t s agglomeration when i t i s heated a t 800°F (425°C) i n f i r s t - s t a g e c a r b o n i z a t i o n . M i l d surface o x i d a t i o n i n t h i s use r e f e r s t o o x i d a t i o n so s l i g h t that pétrographie examination r e v e a l s v i r t u a l l y no change i n the surface of the t r e a t e d c o a l (_4) . Analyses of c o a l feed before and a f t e r m i l d o x i d a t i o n a t 350°F f o r 20 minutes i n d i c a t e no s i g n i f i c a n t change i n the o x i d i z e d c o a l .


COAL

254 TABLE I.

A n a l y s i s of Oxidized I l l i n o i s


Component Carbon Hydrogen Oxygen^ Sulfur: Total Inorganic Ash

DESULFURIZATION

Coal

α A n a l y s i s (wt %) Oxidized Unoxidized 75.5 75.1 5.21 5.52 12.0 11.6 1.74 1.69 0.83 0.78 6.1 6.0

Moisture-free basis. Determined by neutron a c t i v a t i o n a n a l y s i s . Includes oxygen i n the ash. In p r a c t i c e , s i z e d c o a l feed i s heated at 350°F (177°C) f o r a 20-min residence time i n a bed f l u i d i z e d with a i r a t atmospheric pressure. The continuous c o a l o x i d i z e r , shown i n F i g u r e 5, i s s i m i l a r i n design and operation to the carbonizer r e a c t o r . The u n i t c o n s i s t s of a 10-in.-ID c a r b o n - s t e e l f l u i d bed r e a c t o r with a c o a l - f e e d and product-overflow system and an e l e c t r i c a l l y heated a i r supply. As i n the PDU, the f l u i d bed of the c o a l o x i d i z e r i s heated to and maintained a t design temperature by the heated f l u i d i z i n g a i r . This u n i t i s capable of o x i d i z i n g up to 1 ton of c o a l per 24 hr of o p e r a t i o n , and i t i s normally operated a t a c o a l feed r a t e of about 60 l b / h r . Heated a i r i s used i n the e x i s t i n g c o a l o x i d i z e r f o r convenience only. In a l a r g e r operation, the o x i d i z e r can be operated with waste f l u e gas c o n t a i n i n g about 2% oxygen to achieve adequate p r e o x i d a t i o n of the feed c o a l . Because the e f f l u e n t gas from the c o a l o x i d i z e r contains only moisture and dust from the f l u i d bed, waste-gas cleanup i s accomplished by a small e x t e r n a l cyclone and dust f i l t e r s i n the vent system. The y i e l d of dry, o x i d i z e d c o a l i s e s s e n t i a l l y a f u n c t i o n of moisture content i n the c o a l charged, which i s g e n e r a l l y about 8% by weight. Experimental

Results From F i r s t - S t a g e Carbonization

C a r b o n i z a t i o n of the o x i d i z e d c o a l i n the PDU i s conducted i n two separate stages to avoid agglomeration of feed i n the f l u i d bed. I n i t i a l c a r b o n i z a t i o n i s e f f e c t e d a t temperatures i n the range 800°-840°F (425°-450°C) to d e v o l a t i l i z e the c o a l p a r t i a l l y and to produce a semichar, which can be fed subsequently


19.

BOODMAN E T A L .

FEED

GAS

VESSELS


FEED

Fluid-Bed

4

CARBONIZER

INTERCHANGER

255


GAS COOLER

WASH-OIL

CAUSTIC

SCRUBBER

SCRUBBER

_

Figure 4.

a_ "Ψ

CAUSTIC SOLUTION

- 4

SPENT CAUSTIC

4

LIQUID PRODUCT

4

SOLID PRODUCT

Schematic of clean coke process carbonization PDU

Figure 5.

Continuous 10-in. coal oxidizer


COAL

256

DESULFURIZATION

i n t o a f l u i d bed a t 1400°F without agglomeration. The operating l i m i t s on temperature f o r the f i r s t stage were determined by bench-scale s t u d i e s of the agglomeration problem. A nonagglomerating semichar was obtained a t 800°F, and i n c i p i e n t agglomeration was observed a t about 850°F.


Although the primary f u n c t i o n of f i r s t - s t a g e c a r b o n i z a t i o n i s to reduce the agglomerating property of the c o a l , about 70% of the c a r b o n i z a t i o n t a r i s produced i n t h i s stage. Gas product i o n i s low i n the f i r s t stage, amounting to about 15 wt % of the t o t a l gas produced. A n a l y s i s of the r e c y c l e gas shows i t s composition ( i n mole %) to be methane, 71; ethane, 13; carbon monoxide, 10; hydrogen, 2; and C2~to-C4 hydrocarbons, 4. Tests were made i n the PDU to study the e f f e c t upon v o l a t i l e matter and s u l f u r contents i n the semichar of bed temperature, residence time, system pressure, and H2S c o n c e n t r a t i o n i n the r e c y c l e gas. The v a r i a t i o n i n v o l a t i l e - m a t t e r content with temperature and r e s i d e n c e time i s i l l u s t r a t e d i n Figure 6, which shows that v o l a t i l e - m a t t e r content v a r i e s i n v e r s e l y with temperature and residence time and i s independent of pressure over the range 15-160 p s i a . In the f i g u r e , a few data p o i n t s from a 1-in. continuous bench-scale u n i t were included t o extend the pressure range to 15 p s i a . G e n e r a l l y , about h a l f the v o l a t i l e s were eliminated from the c o a l i n f i r s t - s t a g e c a r b o n i z a t i o n , and a l l the semichar products were processed through second-stage c a r b o n i z a t i o n without agglomeration. Response of s u l f u r content to r e s i d e n c e time and temperature of f i r s t - s t a g e c a r b o n i z a t i o n i s shown g r a p h i c a l l y i n Figure 7. S u l f u r content of the semichar product a l s o v a r i e s i n v e r s e l y with temperature and residence time and i s independent of pressure over the ranges studied; c o n d i t i o n s i n c l u d e d temperat u r e s of 800° and 840°F, r e s i d e n c e times of 20-80 min, and pressures of 80-160 p s i a . In these t e s t s , H S c o n c e n t r a t i o n was c o n t r o l l e d i n the range 50-100 ppm. However, a t e s t was run a t 800°F, 52 min r e s i d e n c e time, 120 p s i a , and H2S concentrat i o n s v a r y i n g from 300 to 2000 ppm. The semichar product from t h i s t e s t contained 1.77% s u l f u r , which i s i n the range normally a t t a i n e d with low concentration i n the r e c y c l e gas. Because 2

gas evolved from d e v o l a t i l i z a t i o n of the c o a l was r e c y c l e d i n the system to f l u i d i z e the bed, gas composition was not a c o n t r o l l a b l e parameter, except f o r concentration of a c i d gases. Temperature and r e s i d e n c e time thus appear to be the only v a r i a b l e s having an e f f e c t on v o l a t i l e s and s u l f u r remaining i n the semichar product. The data i n F i g u r e s 6 and 7 i n d i c a t e that, a t the temperatures deemed f e a s i b l e , f i r s t - s t a g e devolat i l i z a t i o n / d e s u l f u r i z a t i o n i s adequate i n about 20 min r e s i d e n c e



BOODMAN

Fluid-Bed

E T A L .

10

20

30

40 RESIDENCF

Figure 6.

50

60

"Γ

Τ

I

Τ"

1

1 H

-

1 5

Ο

— ° — 80 psiâ 120 psia 160 psia

ο -

l

840 F

•

800 F

_

80 psia ) )· 840 F

120 psia

J

10

1

20

1

30

1

40 RESIDENCE

Figure 7.

\

•

• •

!

•

ο

ο Δ

80

800 F

^ \

•

70

TIME, minutes

Effect of temperature and residence time on coal devolatilization

1

_

257


ι 50

60

ι 70

ι 80

TIME, minutes

Effect of temperature and residence time on semichar sulfur content


COAL

258

DESULFURIZATION

time to produce a s u i t a b l e feed f o r second-stage c a r b o n i z a t i o n . To provide a c o n s i s t e n t data base f o r process design, f i r s t stage c a r b o n i z a t i o n s i n the PDU are now r o u t i n e l y run a t 820°F, 25 min residence time, 165 p s i a , and 100 ppm H2S i n the r e c y c l e gas. Under these c o n d i t i o n s , c o a l c o n t a i n i n g 35% v o l a t i l e matter and about 2.2% s u l f u r i s converted to semichar c o n t a i n i n g 20% v o l a t i l e matter and 1.7% s u l f u r .


Experimental R e s u l t s From Second-Stage

Carbonization

Completion of d e v o l a t i z a t i o n and d e s u l f u r i z a t i o n r e q u i r e d the higher r e a c t i o n temperatures of the second-stage carbonizat i o n . Tests were made i n the PDU to study e f f e c t s of temperature and r e s i d e n c e time i n the f l u i d bed upon s u l f u r content of the char produced i n second-stage c a r b o n i z a t i o n . The ranges f o r these v a r i a b l e s were 1250°-1450°F (675°-790°C) and 40-200 min. System pressure was g e n e r a l l y 165 p s i a , although other t e s t s were run at 80, 120, and 150 p s i a . Concentration of H2S i n the r e c y c l e gas was c o n t r o l l e d i n the range 50-100 ppm, but concentrations as high as 1500 ppm H2S were studied i n s p e c i a l tests. Results from the s t u d i e s of temperature and residence-time e f f e c t s are shown g r a p h i c a l l y i n F i g u r e 8. For c l a r i t y only data obtained a t 1250°, 1325°, and 1400°F are used. Sulfur content of the semichar feed f o r the t e s t s e r i e s ranged from 1.65-1.80% and averaged about 1.70%. The q u a n t i t y of char produced a t a s i n g l e set of c o n d i t i o n s was u s u a l l y about 600 l b , and more than 1600 l b of char was produced during the longest t e s t . S u l f u r content of the char products ranged from 1.1% a t the m i l d e s t c o n d i t i o n to 0.2% at 1400°F and 190 min residence time. Temperature exerted the g r e a t e s t e f f e c t on d e s u l f u r i z a t i o n of the char, as i n d i c a t e d i n F i g u r e 8; a temperature increase of 75°F provided a lower char s u l f u r content than i n c r e a s i n g residence time t h r e e f o l d or even f o u r f o l d . For example, 40 min residence a t 1400°F was the e q u i v a l e n t of 157 min a t 1325°F i n producing char c o n t a i n i n g 0.6% s u l f u r . I t i s apparent from the data that d e s u l f u r i z a t i o n of the feed occurred r a p i d l y during the i n i t i a l p e r i o d of heating and d e v o l a t i l i z a t i o n . Chars having s u l f u r contents i n the range 0.7-0.8% were obtained i n 40-50 min r e s i d e n c e time at f l u i d - b e d temperatures g r e a t e r than about 1300°F. D e s u l f u r i z a t i o n below about 0.8% s u l f u r proceeded at a much slower r a t e , and the r a t e then appeared t o be almost completely l i n e a r with time.


19.

BOODMAN

ET

AL.

Fluid-Bed


259


A l l the data i n F i g u r e 8 were obtained a t a system pressure of 165 p s i a , except f o r the one p o i n t , i n d i c a t e d on the 1325°F l i n e , which was obtained a t 100 p s i a . This p o i n t shows that the e f f e c t of pressure over the range of 100-165 p s i a i s not d i s c e r n i b l e i n the s u l f u r content of the char from the continuous f l u i d - b e d r e a c t o r . Other t e s t s i n the PDU gave s i m i l a r r e s u l t s ; f o r example, a t 1370°F and about 90 min residence time, the s u l f u r contents of the char products were 0.67 and 0.66% a t 120 and 150 p s i a , r e s p e c t i v e l y . The i n a b i l i t y to demonstrate a pressure e f f e c t i n the continuous r e a c t o r of the PDU r e s u l t s from the interdependence of v a r i a b l e s i n the system. For example, i n t e n t i o n a l l y changing the pressure a u t o m a t i c a l l y changes the mole f r a c t i o n of hydrogen i n the gas, which changes the hydrogen-to-sulfur r a t i o i n the f l u i d bed. In a d d i t i o n , a smaller mass of lower-pressure (lower density) gas must be r e c i r c u l a t e d through the bed to maintain the same degree of f l u i d i z a t i o n , and lower-pressure gas must be h o t t e r to e f f e c t the d e s i r e d heat t r a n s f e r t o maintain bed temperature. Because of t h i s , char p a r t i c l e s near the bottom of the bed are c o n t a c t i n g h o t t e r gas and are moment a r i l y heated to temperatures greater than the average bed temperature. These competing f o r c e s combine to mask the pressure e f f e c t i n the continuous r e a c t o r . However, the e f f e c t of increased pressure helps to decrease the s u l f u r content of the product char. T h i s has been demonstrated by numerous i n v e s t i g a t i o n s and by our bench-scale t e s t s i n batch r e a c t o r s (_3) , which were s u i t e d f o r studying the pressure e f f e c t s e p a r a t e l y from the other v a r i a b l e s . An important dependent v a r i a b l e , f o r which a continuous r e a c t o r i s best s u i t e d , i s average s u l f u r content of the bed. In a batch u n i t , the s u l f u r content of the bed d e c l i n e s throughout the r e a c t i o n time, but i n a continuous u n i t , the average s u l f u r content of the f l u i d bed remains e s s e n t i a l l y constant, because of the continuous a d d i t i o n of s u l f u r with the feed and depends upon the s u l f u r content of the feed and upon the feed r a t e . T h i s f a c t o r c o n t r i b u t e s s i g n i f i c a n t l y to the observed b e n e f i t of very long residence times, which were achieved i n the PDU by g r e a t l y reduced feed r a t e s . The consequent r e d u c t i o n i n r a t e of s u l f u r a d d i t i o n to the bed r e s u l t e d merely i n a lower average s u l f u r content i n the bed. From these c o n s i d e r a t i o n s , i t may be concluded that the important v a r i a b l e s i n d e s u l f u r i z a t i o n of char i n the PDU are temperature and average s u l f u r content of the bed, provided there i s a s i g n i f i c a n t c o n c e n t r a t i o n of hydrogen i n the f l u i d i z i n g gas.


COAL


260

DESULFURIZATION

Composition of the f l u i d i z i n g gas was not a c o n t r o l l a b l e v a r i a b l e , except f o r H2S c o n c e n t r a t i o n , because process-derived gas was r e c y c l e d i n the system. The gas was composed almost e n t i r e l y of methane, hydrogen, and carbon monoxide. Carbon d i o x i d e was present only i n tenths of a percent because of c a u s t i c scrubbing to c o n t r o l H2S c o n c e n t r a t i o n . At 165 p s i a , hydrogen concentration i n mole percent v a r i e d from the low 20s at 1250°F to the low 40s a t 1400°F; methane c o n c e n t r a t i o n ranged from the low 70s to the mid 50s; carbon monoxide concent r a t i o n was n e a r l y independent of r e a c t i o n temperature but v a r i e d from a high of about 6% at the shorter residence times to about 2% at the longer times. Hydrogen c o n c e n t r a t i o n was a l s o s e n s i t i v e to residence time and increased 3-5 percentage p o i n t s between the s h o r t e s t and longest times. The e f f e c t of s e v e r a l H S concentrations i n the r e c y c l e gas was s t u d i e d i n t e s t s conducted a t 1400°F (Table I I ) . The semichar feed f o r these t e s t s contained about 1.75% s u l f u r . The t e s t s were run p r i m a r i l y to generate data r e l e v a n t to the design of l a r g e r f l u i d - b e d r e a c t o r s , i n which bed height would be s i g n i f i c a n t l y greater than the 30-in. bed height i n the e x i s t i n g PDU. Concentration of H S increases i n the f l u i d i z i n g gas as i t passes up through the bed, and a t bed depths envisioned f o r r e a c t o r s designed f o r 100 tons or more of feed per day, average H2S c o n c e n t r a t i o n w i t h i n the f l u i d bed might e a s i l y reach 1000 ppm. 2

2

TABLE I I .

E f f e c t of H2S Sulfur

i n F l u i d i z i n g Gas on Char

a

H2S

Concentration 50-100 500 1000

(ppm)

Char Product 0.21 0.71 0.69

1400°F, 165 p s i a , 190 min residence

(wt % S)

time.

The data i n Table I I show a s i g n i f i c a n t d e t e r i o r a t i o n i n char s u l f u r content, from 0.2% to 0.7%, when the H2S l e v e l i n the gas e n t e r i n g the f l u i d bed was increased from the normal 50-100 ppm to the 500-ppm l e v e l . I n t e r e s t i n g l y , i n c r e a s i n g the H2S l e v e l to 1000 ppm d i d not have any p e r c e p t i b l e a d d i t i o n a l e f f e c t . These t e s t s were l i m i t e d by the exposure of a l l f l u i d i z e d p a r t i c l e s to the high H2S c o n c e n t r a t i o n i n the incoming gas, whereas a l l p a r t i c l e s i n a deeper f l u i d bed would a l s o be



19.

BOODMAN

ET

AL.

Fluid-Bed


261

exposed about h a l f of the time to gas of much lower concen tration. In a more recent t e s t , a l o w - s u l f u r char was fed a t 1400°F to a bed f l u i d i z e d with gas c o n t a i n i n g 1200-1500 ppm H2S. In t h i s case, the s u l f u r content of the char increased from 0.4% to 0.6% during a 104-min residence time i n the f l u i d bed. T h i s r e s u l f i d a t i o n of the char was expected, but i t s modest impact on the product q u a l i t y was g r a t i f y i n g . About three fourths of the pickup was reported as i n o r g a n i c s u l f u r , and the balance was organic s u l f u r . The design of the PDU does not lend i t s e l f to more d e f i n i t i v e s t u d i e s of deep f l u i d beds; however, the r e s u l t s do suggest t h a t d e s u l f u r i z a t i o n w i l l be somewhat l e s s e f f i c i e n t i n com m e r c i a l - s i z e c a r b o n i z e r s . Nevertheless, commercial production of char having an acceptable s u l f u r content appears f e a s i b l e . To i n d i c a t e the r e p r o d u c i b i l i t y of data p o i n t s , Table I I I presents analyses of the consecutive r e c e i v e r s of char produced during 10-day runs a t 1400°F, 165 p s i a , and residence times of 46 and 190 min. The t o t a l q u a n t i t i e s of feed f o r the t e s t s were 2170 and 875 l b , r e s p e c t i v e l y . The data show e x c e l l e n t r e p r o d u c i b i l i t y , c o n s i d e r i n g t h a t observed v a r i a t i o n s i n the products are the cumulative e f f e c t s of v a r i a t i o n s i n the semichar feed and process c o n d i t i o n s , p l u s the r e p e a t a b i l i t y of sampling and a n a l y s i s . TABLE I I I .

Uniformity of Product Char from Carbonization PDU a

Receiver 1 2 3 4 5 6 7 8 Average

α

1400°F, 165

Char S u l f u r Content (wt %) 190 min 46 min 0.26 0.69 0.21 0.70 0.18 0.68 0.18 0.61 0.18 0.68 0.25 0.66 0.68 — 0.71 — 0.21 0.68

psia.

Of i n t e r e s t a l s o are the incremental changes i n concentra t i o n of the v a r i o u s forms of s u l f u r o r i g i n a l l y present i n the raw c o a l . These changes are i l l u s t r a t e d by the a n a l y t i c a l



262

r e s u l t s i n Table IV f o r the feed and products i n v o l v e d i n the Clean Coke Process. Forms of s u l f u r are shown simply as organic and i n o r g a n i c , because the i n o r g a n i c s u l f u r was n e a r l y a l l p y r i t i c and contained a t most 0.05% s u l f a t e s u l f u r . Coals from s e v e r a l mines i n c e n t r a l I l l i n o i s were evaluated, and a l l samples were q u i t e s i m i l a r . However, only c o a l from No. 24 mine of the Old Ben Coal Co. was processed i n the c a r b o n i z a t i o n PDU, and the data i n Table IV were obtained with t h i s c o a l .


TABLE IV.

Incremental Change i n Forms of

Processing Step As-mined c o a l

Sulfur

S u l f u r Forms (wt %) Inorganic Organic 2.50 1.00 a

Cleaned and s i z e d c a r b o n i z a t i o n feed

1.13

1.00

Semichar ( f i r s t - s t a g e product)

0.91

0.81

Char (second-stage product, 1400°F)

0.13

0.08

Inorganic s u l f u r i s p y r i t i c s u l f u r p l u s about 0.05% s u l f a t e s u l f u r i n the as-mined c o a l . T y p i c a l l y , the run-of-mine c o a l sample contained about 1% organic s u l f u r and 2% or so inorganic s u l f u r . Conventional wet c l e a n i n g of t h i s c o a l by g r a v i t y separation and t a b l i n g operat i o n s removed inorganic s u l f u r s e l e c t i v e l y and produced a c l e a n c o a l feed which contained about 1% inorganic and 1.1% organic s u l f u r . D e v o l a t i l i z a t i o n and d e s u l f u r i z a t i o n i n f i r s t - s t a g e c a r b o n i z a t i o n at 820°F removed about 33% of the s u l f u r i n each form, and the r a t i o of organic to i n o r g a n i c remained about the same i n the semichar product as i n the feed c o a l . (The c o a l d r y i n g and p r e o x i d a t i o n treatment d i d not a f f e c t e i t h e r the amount or the forms of s u l f u r . ) F i n a l d e v o l a t i l i z a t i o n and d e s u l f u r i z a t i o n i n second-stage c a r b o n i z a t i o n at 1400°F removed about 90% of each form of s u l f u r i n the semichar feed, and the lowest s u l f u r char contained only s l i g h t l y more organic than inorganic sulfur. Both forms of s u l f u r c o n t r i b u t e d s u b s t a n t i a l l y to the production of H S during c a r b o n i z a t i o n . This f a c t i s i l l u s t r a t e d by the data i n Table V, which show the q u a n t i t y of s u l f u r i n 2


19.

BOODMAN

E T

AL.

Fluid-Bed


263

each form that was converted and the q u a n t i t y recovered as i n the c a u s t i c scrubbing s o l u t i o n . Converted p y r i t i c s u l f u r c o n t r i b u t e d about two t h i r d s of the H S produced by f i r s t - s t a g e c a r b o n i z a t i o n a t 820°F and the i n o r g a n i c s u l f u r remaining i n the semichar c o n t r i b u t e d about h a l f of the H2S produced during second-stage c a r b o n i z a t i o n a t 1400°F. Assuming t h a t a l l the r e a c t i n g i n o r g a n i c s u l f u r i s converted t o H S, Table V data show that about 70% of the organic s u l f u r r e a c t i n g a t 820°F was converted to H S, and about 95% was converted t o H2S a t 1400°F. Thus, r e a c t i o n c o n d i t i o n s i n both stages are adequate to convert both types of s u l f u r compounds to e a s i l y recoverable H S. The remainder of the s u l f u r l i b e r a t e d from the c o a l during p y r o l y s i s i s recovered as organic compounds i n the l i q u i d products, which c o n t a i n 1.1-1.3% s u l f u r . 2

f

2

2


2

TABLE V.

Conversion of Forms of S u l f u r t o H2S

a

D i s t r i b u t i o n of S u l f u r (lb) Recovered Total as H2S Organic Inorganic 9.5 20.8 11.3 —

Coal feed Converted s u l f u r (at 820°F)

3.0

4.4

7.4

6.5

Semichar feed

6.5

6.9

13.4

—

Converted s u l f u r (at 1400°F)

4.6

4.4

9.0

8.5

Char product

1.9

2.5

4.4

—

Basis:

1000 l b c o a l feed.

M a t e r i a l Flows and Mass Balance M a t e r i a l flows and mass balance through the two stages o f c a r b o n i z a t i o n of I l l i n o i s c o a l are shown i n the s i m p l i f i e d flow diagram of F i g u r e 9. The products of f i r s t - s t a g e c a r b o n i z a t i o n of the c o a l are ( i n wt %) semichar, 83.0; t a r , 11.9; water, 2.5; f u e l gas, 1.1; and a c i d gases, 1.5. At 1400°F and 77 min residence time, the products of second-stage c a r b o n i z a t i o n of the semichar a r e ( i n wt % of the coal) l o w - s u l f u r char, 6 2 . 9 ; t a r , 5.0; water, 2.0; process gas, 6.3; and a c i d gases, 6.8.


COAL


264

30

60

90

120

RESIDENCE

Figure 8.

TIME,

DESULFURIZATION

IbO

180

m.mjtes

Effect of temperature and residence time on char sulfur content (165 psia)

OXIDIZED

COAL

1000

GAS FIRST

c,-c, 1-^4

STAGE

f 11

TAR

119

H 0

25

2

rt H , S2: CO, SEMICHAR

SECOND H .

C H . CO

2

4

11

C0

57

2

CHAR

Figure

STAGE

63

H S 2

830

PRODUCT

629

9. Material flow and weight distribution staged carbonization

during


19.

BOODMAN ET

Fluid-Bed

AL.


265

Weight balances from PDU t e s t s were i n the range 99-102% of the weights fed i n t o the PDU. S p e c i a l material-balance t e s t s were run to e s t a b l i s h elemental balances on carbon and s u l f u r , Table VI. O v e r a l l weight balance i n these t e s t s accounted f o r 99.3% of the weight input. The carbon-balance data show an o v e r a l l a c c o u n t a b i l i t y of 99.7%, and the s u l f u r - b a l a n c e data show an o v e r a l l a c c o u n t a b i l i t y of 98.5%.


TABLE VI.

Coal Wash O i l Total

"Basis:

Elemental Balance - O v e r a l l

Input C 724 1981

(lb) S 20.7 25.3

2705

46.0

1000

Output (lb) S C 2.8 521 Char 27.1 Wash O i l & Tar 2099 15.4 76 Gas 45.3 T o t a l 2696

l b Coal Feed.

Conclusions The c a r b o n i z a t i o n PDU of the Clean Coke Process has proved to be a v a l u a b l e research t o o l i n demonstrating, on a s u b s t a n t i a l s c a l e , the e f f i c i e n t d e s u l f u r i z a t i o n of I l l i n o i s c o a l i n a continuous, p r e s s u r i z e d f l u i d - b e d c a r b o n i z e r . A f t e r conventional c l e a n i n g and s i z i n g , c o a l was processed during sustained operat i o n of up to 10 days through two separate stages of carbonizat i o n , which together removed more than 90% of the c o a l s u l f u r and produced char c o n t a i n i n g as l i t t l e as 0.2% s u l f u r . Firststage c a r b o n i z a t i o n a t about 820°F served p r i m a r i l y to produce a nonagglomerating semichar feed f o r high-temperature carbonizat i o n , but the f i r s t - s t a g e c a r b o n i z a t i o n removed about 33% of the s u l f u r from the c o a l and produced about 66% of the t o t a l t a r . Second-stage c a r b o n i z a t i o n removed up to 90% of the remaining s u l f u r and produced low-sulfur char, hydrogen-rich f u e l gas, and t a r . Both organic and i n o r g a n i c s u l f u r were removed with equal f a c i l i t y by the c a r b o n i z a t i o n process. In a d d i t i o n to the data on d e s u l f u r i z a t i o n and process y i e l d s and chemistry, the PDU has provided much u s e f u l engineering information that was needed f o r the design of a 100-ton/day p i l o t p l a n t . The p i l o t - p l a n t process-design work i s c u r r e n t l y i n progress, and continued t e s t i n g i n the PDU w i l l generate data needed f o r the design. Concurrently, s t u d i e s are i n progress on c a r b o n i z a t i o n of h i g h - s u l f u r c o a l s from other major


COAL

266

DESULFURIZATION

seams of n a t i o n a l i n t e r e s t . Coal from the Kentucky No. 9 seam i s being processed a t present, and t h i s w i l l be followed by t e s t i n g of a P i t t s b u r g h seam c o a l . Acknowledgments


The information contained i n t h i s paper and generated i n the c a r b o n i z a t i o n PDU would not have been p o s s i b l e without the design m o d i f i c a t i o n s and engineering a s s i s t a n c e of George A. Ryder and John S t i p a n o v i c h of the Chemical Engineering Design group. T h e i r c o n t r i b u t i o n s to the success of the PDU program were i n v a l u a b l e and are s i n c e r e l y appreciated. Literature Cited

1. Schowalter, Κ. Α., Boodman, N. S., "Clean Coke Process," presented at the Symposium on Coal-Conversion Processes, Meeting of the American Institute of Chemical Engineers, Philadelphia, November 1973. 2. Schowalter, Κ. Α., Petras, E. F., "Aromatics From Coal," presented at the Symposium on Aromatics, Meeting of the American Institute of Chemical Engineers, Houston, March 1975. 3. Johnson, T.F., Krupinski, K. C., Osterholm, R. J., "Clean Coke Process: Fluid-Bed Carbonization of Illinois Coal," presented at the Symposium on New Cokemaking Processes Minimizing Pollution, American Chemical Society Meeting, Chicago, August 1975. 4. Gray, R. J., Krupinski, K. C., "Use of Microscopic Procedures to Determine the Extent of Destruction of Agglomerating Properties in Coal," presented at the Coal Agglomeration and Conversion Symposium, West Virginia University, Morgantown, May 1975.

Support received from the U.S. Energy Research and Development Administration under Contract No. E(49-18)-1220.


20 Hydrodesulfurization of Coals DONALD K. FLEMING, ROBERT D. SMITH, and MARIA ROSARIO Y. AQUINO


Institute of Gas Technology, 3424 South State St., IIT Center, Chicago, IL 60616

The Institute of Gas Technology (IGT) is engaged in a program to develop a patented process (1) to desulfurize coal to produce a clean, solid fossil fuel product. This process — called the IGT Flash Desulfurization Process — uses a combination of chemical and thermal treatment of the coal. The present effort, funded by the U.S. Environmental Protection Agency (EPA Contract No. 68-02-2126), aims to determine the operating parameters of the primary reactors of the system. The objective of the process is to be able to treat any coal so that the resulting solid fuel can be directly consumed in an environmentally satisfactory manner. Equipment scaled to laboratory, bench, and continuous process development unit (PDU) investigations is being used in the project. Each coal tested is subjected to preselected conditions of temperature, heating rates, and residence time in a reducing atmosphere. After treatment, the material is chemically analyzed to determine the degree of sulfur removal. Results from tests with four different high-sulfur coals (all from abundant Eastern U.S. seams) show good sulfur reduction; calculated sulfur dioxide emissions of the treated material are below the present Federal EPA standards of 1.2 lb/10 Btu for direct combustion of the solid fossil fuel product. 6

Coals

Tested

S e v e r a l c a n d i d a t e c o a l s were c h a r a c t e r i z e d f o r s u l f u r c o n t e n t , seam l o c a t i o n , and q u a n t i t y a v a i l a b l e . S u b b i t u m i n o u s and l i g n i t e c o a l s were e l i m i n a t e d b e c a u s e o f t h e i r l o w c o n t e n t o f naturally occurring sulfur. Four b i t u m i n o u s c o a l s s e l e c t e d f o r t e s t i n g were t h e f o l l o w i n g : 1. W e s t e r n K e n t u c k y No. 9, c o n t a i n i n g 3.74% s u l f u r (run-of-the-mine) 2. P i t t s b u r g h Seam ( f r o m a West V i r g i n i a m i n e ) , c o n t a i n i n g 2.77% s u l f u r ( h i g h l y c a k i n g ) 3. P i t t s b u r g h Seam ( f r o m a P e n n s y l v a n i a m i n e ) , c o n t a i n i n g 1.35% s u l f u r ( h i g h a s h c o n t e n t ) 267



268

4. I l l i n o i s No. 6, c o n t a i n i n g 2.43% s u l f u r (washed). These c o a l s were s e l e c t e d w i t h o u t r e g a r d f o r t h e i r r e l a t i v e c o n t e n t o f p y r i t i c and o r g a n i c s u l f u r , b e c a u s e a u n i v e r s a l c o a l d e s u l f u r i z a t i o n p r o c e s s s h o u l d be a b l e t o m i n i m i z e any t y p e o f s u l f u r i n the c o a l .


Pretreatment The c o a l s s e l e c t e d a r e a l l c a k i n g c o a l s ; an o x i d a t i v e p r e treatment, p r i o r to h y d r o d e s u l f u r i z a t i o n , i s i n c l u d e d i n the system t o e l i m i n a t e t h i s c a k i n g . S i m i l a r to the p r e t r e a t m e n t used i n g a s i f i c a t i o n p r o c e s s e s , t h i s system would o p e r a t e w i t h a i r f l u i d i z a t i o n at near-atmospheric pressure using coal feedstock at —14 mesh. P r e t r e a t m e n t t e s t s were c o n d u c t e d i n a b a t c h r e a c t o r t o determine the proper p r e t r e a t m e n t c o n d i t i o n s f o r each c o a l . Ranges o f t e m p e r a t u r e s , r e l a t i v e - a i r r a t e s , f l u i d i z a t i o n v e l o c i t i e s , and r e s i d e n c e t i m e s were t e s t e d . R e s u l t s of these t e s t s i n d i c a t e d t h a t a t e m p e r a t u r e o f 750°F and a gas v e l o c i t y o f 1 f t / s e c were n e c e s s a r y t o a c h i e v e s a t i s f a c t o r y p r e t r e a t m e n t . ("Satisf a c t o r y p r e t r e a t m e n t " i s d e f i n e d , f o r p u r p o s e s o f t h i s p r o g r a m , as p r e t r e a t m e n t t h a t c o n d i t i o n s t h e c o a l s u f f i c i e n t l y t o p a s s an e m p i r i c a l c a k i n g t e s t . ) F o r t h e W e s t e r n K e n t u c k y No. 9 c o a l , a r e s i d e n c e t i m e o f 30 min and an o x y g e n c o n s u m p t i o n o f 1 S C F / l b o f c o a l were a d e q u a t e c o n d i t i o n s i n s a t i s f y i n g p r e t r e a t m e n t ; o t h e r c o a l s r e q u i r e d d i f f e r e n t degrees of p r e t r e a t m e n t . Based on t e s t r e s u l t s , p a r a m e t e r s o f r e s i d e n c e t i m e and o x y g e n c o n s u m p t i o n were a d j u s t e d f o r each f e e d s t o c k to y i e l d a noncaking m a t e r i a l . A p p r o x i m a t e l y 8% - 12% o f t h e c o a l i s consumed d u r i n g p r e t r e a t m e n t , g e n e r a t i n g steam f o r t h e r e s t o f t h e s y s t e m and a l o w B t u o f f - g a s t h a t can be b u r n e d o n s i t e t o p r o v i d e p r o c e s s steam o r to g e n e r a t e power. A p p r o x i m a t e l y 25% - 30% o f t h e c o a l s u l f u r i s removed d u r i n g p r e t r e a t m e n t ; t h i s s u l f u r becomes p r i m a r i l y S 0 i n the low-Btu pretreatment o f f - g a s . Pretreatment not o n l y prevents c a k i n g , i t a l s o i n c r e a s e s the s u l f u r removal i n the subsequent h y d r o t r e a t i n g s t e p . F i g u r e 1 r e p r e s e n t s two s e r i e s o f t h e r m o b a l a n c e t e s t s made w i t h W e s t e r n K e n t u c k y No. 9 c o a l . One t e s t s e r i e s was made w i t h c r u s h e d and s c r e e n e d c o a l ; t h e o t h e r t e s t u s e d c r u s h e d , s c r e e n e d , and p r e t r e a t e d c o a l as f e e d f o r h y d r o d e s u l f u r i z a t i o n . The r e s u l t s show t h a t t h e 70% s u l f u r r e m o v a l (based on t h e i n i t i a l f e e d ) , as a c h i e v e d w i t h u n t r e a t e d c o a l f e e d , was i n c r e a s e d t o 95% by u s i n g a p r e t r e a t e d f e e d . S u l f u r removed i n i t i a l l y d u r i n g p r e t r e a t m e n t , p r i m a r i l y p y r i t i c s u l f u r , i s a l s o r e a d i l y a t t a c k e d i n lowtemperature h y d r o t r e a t m e n t ; the improved s u l f u r removal a f t e r p r e t r e a t m e n t i s o b t a i n e d by more c o m p l e t e r e m o v a l o f o r g a n i c - t y p e sulfur. The more c o m p l e t e r e m o v a l may be c a u s e d by t h e i n c r e a s e i n c o a l pore s i z e d u r i n g p r e t r e a t m e n t , r e s u l t i n g i n b e t t e r c o n t a c t of t h e h y d r o g e n w i t h t h e c o a l s u l f u r and l a r g e r p a s s a g e s f o r removal of the r e s u l t a n t hydrogen s u l f i d e . Also, oxidative treatment o f s u l f u r compounds i s e x p e c t e d t o a c t i v a t e t h e s u l f u r f o r 2


Hydrodesulfurization

FLEMING ET A L .

of Coals

269

Ο


ΙΟ Λ 20

REMOVAL DURING PRETREATMENT

\

30 40 .TESTS USING RAW WESTERN KENTUCKY NO. 9

50 \

60

Ν

70 TESTS USING PRETREATED WESTERN KENTUCKY NO. 9

80 90 100 750 800

900

1000

1100

1200

1300

1400

TEMPERATURE, °F

Figure 1.

Sulfur removal indicating effect of coal pretreatment


1500

COAL

270 further

reactions.



DESULFURIZATION

Results

T h e r m o b a l a n c e T e s t s . A p r e l i m i n a r y e v a l u a t i o n o f t h e des u l f u r i z a t i o n o f e a c h c o a l was p e r f o r m e d i n a t h e r m o b a l a n c e , a l a b o r a t o r y d e v i c e t h a t c a n w e i g h c o n t i n u o u s l y a sample e x p o s e d t o a c o n t r o l l e d e n v i r o n m e n t o f t e m p e r a t u r e , p r e s s u r e , and c o n t a c t i n g gas c o m p o s i t i o n . (A c o m p l e t e d i s c u s s i o n o f e x p e r i m e n t a l e q u i p ment, o p e r a t i n g p r o c e d u r e s , and l a b o r a t o r y a n a l y t i c a l t e c h n i q u e i s p r e s e n t e d i n t h e f i n a l r e p o r t (2) p r e p a r e d under p r e v i o u s EPA c o n t r a c t No. 68-02-1366.) R e s u l t s a r e u s e d t o d e t e r m i n e s u l f u r removal from the f e e d s t o c k under a wide range of c o n d i t i o n s . A t o t a l o f 122 t h e r m o b a l a n c e t e s t s have been p e r f o r m e d i n t h i s program. Samples f o r t h e r m o b a l a n c e t e s t s were p r e p a r e d w i t h +40 mesh pretreated coal. T h i s f e e d was p l a c e d i n t h e sample b a s k e t and lowered i n t o the heated zone. A t h i g h gas f l o w r a t e s , r e l a t i v e t o t h e amount o f c o a l , t h e t h e r m o b a l a n c e o p e r a t e s as a d i f f e r e n t i a l reactor. H e a t i n g r a t e s o f 5° - 20°F/min were u s e d , up t o t e r m i n a l t e m p e r a t u r e s o f 1000° - 1500°F. S o a k i n g t i m e s a t t h e t e r m i n a l t e m p e r a t u r e were v a r i e d f r o m 0 t o 5.5 h r . The l a b o r a t o r y a n a l y s e s o f t h e t r e a t e d c o a l p r o v i d e d s u l f u r c o n t e n t by t y p e s , i n c l u d i n g p y r i t i c , s u l f i d e , s u l f a t e , and o r g a n i c s u l f u r . Because s a m p l e s were s m a l l , more c o m p l e t e c h a r a c t e r i z a t i o n c o u l d n o t be achieved. Figures 2 - 5 show s u l f u r r e m o v a l a c h i e v e d r e l a t i v e t o t h e i n i t i a l c o a l , as o b t a i n e d f r o m t h e t h e r m o b a l a n c e t e s t s , f o r e a c h of the f o u r s p e c i f i e d c o a l s . F o r t h e s e t e s t s , t h e r e a c t a n t gas was p u r e h y d r o g e n . Heat-up r a t e s were 5° - 20°F/min, and s o a k i n g t i m e s were 30 t o 60 m i n . The p r e s s u r e was n e a r a t m o s p h e r i c . R e s u l t s o f t e s t s w i t h t h e W e s t e r n K e n t u c k y No. 9 c o a l a r e shown i n F i g u r e 2. An a p p a r e n t i n c r e a s e i n p y r i t i c s u l f u r c o n t e n t d u r i n g p r e t r e a t m e n t may be c a u s e d by e l u t r i a t i o n i n t h e f l u i d i z e d - b e d p r e t r e a t e r ; h e a v i e r p y r i t e s a r e r e t a i n e d i n the r e s i d u e from p r e t r e a t m e n t . Most o f t h e r e d u c t i o n i n o r g a n i c s u l f u r c o n t e n t i s a t t r i b u t a b l e to d e v o l a t i l i z a t i o n . The f i g u r e s show t h a t n e a r l y a l l o f t h e p y r i t i c s u l f u r was removed and t h a t 88% o f t h e o r g a n i c s u l f u r was removed a t 1500°F. S u f f i c i e n t t o t a l s u l f u r r e m o v a l has been a c h i e v e d i n a l l t h e t e s t s above 1400°F so t h a t SO2 e m i s s i o n s f r o m c o m b u s t i o n o f t h e t r e a t e d p r o d u c t w o u l d be b e l o w 1.2 l b / 1 0 ^ Btu. The s u l f u r r e d u c t i o n o b t a i n e d f o r t h e P i t t s b u r g h Seam c o a l ( f r o m a West V i r g i n i a m i n e ) i s shown i n F i g u r e 3. A t a l l t e m p e r a t u r e s above 1300°F, 97% o f t h e p y r i t i c s u l f u r was removed. O r g a n i c s u l f u r c o n t e n t was r e d u c e d by 85% a t 1500°F. The r e d u c t i o n i n t o t a l s u l f u r c o n t e n t e x c e e d e d 90% a t 1500°F. The c o a l t r e a t e d a t any t e m p e r a t u r e above 1400°F c o u l d be b u r n e d i n compliance with present S0 emission l i m i t a t i o n s . 9


20.

FLEMING

E T

AL.


of

271

Coals

A; PYRITIC S U L F U R REMOVAL 40 30 20

SULFUR SHIFT DURING P R E T R E A T MENT

10 Ο 10

• RAW .COAL

B = ORGANIC S U L F U R REMOVAL 0 10 I^RAW ) REMOVAL DURING COAL j P R E T R E A T M E N T 20


20 30

30

40

40

50

50

60

60

70

70

80

80

90

90

\

7

8

9

10 II

\

\

\

Ν

8

I

9

1

10 II

12 13 14 15

T E M P E R A T U R E , ° F X 100

T E M P E R A T U R E , ° F X 100

10

\

ι 7

12 13 14 15

C = TOTAL SULFUR

\

\

100

100

0

\

REMOVAL

>— RAW COAL

—

REMOVAL DURING P R E T R E A T M E N T

20

\

30

\

\

40

\ \

50

60

70

—

\

\

\

\

\

\

80

\

90

I 100

«

1

1

7

8

1 9

1 10

1

1

1

I

II

12

13

14

ι 15

T E M P E R A T U R E , ° F X 100 Figure 2.

Sulfur removal in pretreated western Kentucky No. 9 coal


272


A= PYRITIC S U L F U R REMOVAL

10

Β : ORGANIC S U L F U R REMOVAL

pRAW

10

v 1

20

1

C

0

A

L

20


30

40

50

50

I-


90


\

\

\

60

70 80

\

30

40

60

RAW COAL

70

\

I-

L-

80 90

M i l

100 I—Y> 7

8

100

LjyAl I I 1 I I 1 I I

9 10 II 12 13 14 15 16

7

T E M P E R A T U R E , ° F X 100

8

9

10 II

12 13 14 15 16

T E M P E R A T U R E , ° F X 100

C = TOTAL SULFUR REMOVAL \RAW COAL R E M O V A L DURING PRETREATMENT

J 8

9

I 10

L II

12

13

J

L

14

15

16

T E M P E R A T U R E , ° F X 100

Figure 3.

Sulfur removal in pretreated Pittsburgh seam, West Virginia mine, coal



20.

FLEMING

E T

AL.


of

Coals

273

R e s u l t s f o r t h e P i t t s b u r g h Seam c o a l ( f r o m a P e n n s y l v a n i a m i n e ) a r e shown i n F i g u r e 4. P y r i t i c s u l f u r c o n t e n t h a s been r e duced 9 5 % a t 1300°F and r e a c h e s 1 0 0 % a t 1500°F. O n l y 6 0 % - 8 0 % o f the o r g a n i c s u l f u r was removed i n t h i s t e m p e r a t u r e r a n g e ; however, t h i s c o a l has a lower i n i t i a l s u l f u r content. A l l t h e r e s u l t a n t t r e a t e d m a t e r i a l , t h e r e f o r e , y i e l d s l o w SO2 e m i s s i o n v a l u e s . The r e m o v a l o f s u l f u r f r o m I l l i n o i s No. 6 c o a l i s shown i n F i g u r e 5. P y r i t i c s u l f u r h a s been c o m p l e t e l y removed a t 1300 F and above. O r g a n i c s u l f u r c o n t e n t h a s been r e d u c e d by 8 0 % and t o t a l s u l f u r c o n t e n t b y more t h a n 9 0 % a t 1500°F. A g a i n , enough s u l f u r i s removed so t h a t a l l s a m p l e s meet e m i s s i o n r e q u i r e m e n t s . The r e s u l t s f o r a l l f o u r c o a l s a r e s u p e r i m p o s e d i n F i g u r e 6; t h i s d i r e c t c o m p a r i s o n i n d i c a t e s t h a t a l l o f t h e c o a l s behaved similarly. In t h e t e s t s d e s c r i b e d a b o v e , e a c h sample was h e a t e d i n t h e t h e r m o b a l a n c e s l o w l y (5° - 20°F/min) t o i t s t e r m i n a l t e m p e r a t u r e . A s e r i e s o f t h e r m o b a l a n c e t e s t s w i t h W e s t e r n K e n t u c k y No. 9 c o a l used r a p i d h e a t i n g . R a p i d h e a t i n g i s a c c o m p l i s h e d by f i r s t h e a t i n g t h e r e a c t i o n zone o f t h e t h e r m o b a l a n c e t o t h e d e s i r e d t e m p e r a t u r e , t h e n l o w e r i n g t h e sample b a s k e t i n t o t h e p r e h e a t e d z o n e . Most o f t h e t o t a l w e i g h t change o c c u r s i n t h e f i r s t f e w s e c o n d s t h a t t h e sample i s i n t h e h o t zone. A f t e r 15 m i n , t h e w e i g h t changes o n l y s l i g h t l y , r e g a r d l e s s o f t h e u l t i m a t e r e s i d e n c e t i m e . The t o t a l o f s u l f u r removed, however, i n c r e a s e s w i t h r e s i d e n c e t i m e when r a p i d h e a t i n g i s u s e d . R e d u c t i o n o f s u l f u r content by 95% h a s been a c h i e v e d i n 2 - h r r e s i d e n c e t i m e a t 1500 F; h o w e v e r , s a m p l e s s u b j e c t e d t o 60 m i n o r more met t h e EPA e m i s s i o n l i m i t s for S 0 . 2

Batch Reactor Tests. A b a t c h r e a c t o r h a s been u s e d w i t h t h e W e s t e r n K e n t u c k y No. 9 and I l l i n o i s No. 6 c o a l s t o s u b s t a n t i a t e the r e s u l t s o f t h e t h e r m o b a l a n c e t e s t s and t o e x t e n d t e s t i n g t o o t h e r development phases. The b a t c h r e a c t o r i s c o n s t r u c t e d f r o m 1-1/2 i n . p i p e w i t h a s i n t e r e d - m e t a l p l a t e f o r g a s d i s t r i b u t i o n . T h i s r e a c t o r o p e r a t e s i n a f l u i d i z e d - b e d mode, s i m i l a r t o t h e a n t i c i p a t e d o p e r a t i o n o f t h e f u l l - s c a l e p l a n t , and c a n be s u b j e c t e d to programmed h e a t i n g r a t e s w i t h e x t e r n a l h e a t e r s c o n t r o l l e d b y i n t e r n a l bed t h e r m o c o u p l e s . The b a t c h r e a c t o r can t r e a t l a r g e r samples, and the t r e a t e d p r o d u c t i s more c o m p l e t e l y c h a r a c t e r i z e d analytically. The b a t c h r e a c t o r h a s been o p e r a t e d w i t h hydrogen gas at n e a r - a t m o s p h e r i c pressure; coal (or pretreated coal) feedstock was screened at —204-80 mesh. A t o t a l of 128 batch reactor t e s t s ( i n c l u d i n g pretreatment evaluations) have now been p e r f o r m e d . B a t c h t e s t s , w i t h c o n d i t i o n s s i m i l a r t o t h o s e i n t h e thermob a l a n c e e x p e r i m e n t s , were made a t t e r m i n a l t e m p e r a t u r e s o f 1400° and 1500°F. R e s u l t s were e x c e l l e n t , w i t h a s much a s 98.6% o f t h e s u l f u r c o n t e n t removed a t 1500°F; t h e s e r e s u l t s a g r e e w e l l w i t h the t h e r m o b a l a n c e t e s t s . The t r e a t e d m a t e r i a l w o u l d p r o d u c e SO^ e m i s s i o n s w e l l b e l o w t h e EPA l i m i t a t i o n s , c o n f i r m i n g e a r l i e r t h e r mobalance r e s u l t s .


274


Δ

:

B= ORGANIC S U L F U R

PYRITIC S U L F U R REMOVAL

REMOVAL

Ο 10

^RAW COAL


20 30 40 50 60

\

70 80

\


90 100

1

—V7

I I I

ι

8

12 13 14 15 16

9

10 II

7

8

9

10 II

12 13 14 15 16

TEMPERATURE,°F X 100

TEMPERATURE,°F X 100 C : TOTAL SULFUR REMOVAL

100 8

9

10

II

12

13

T E M P E R A T U R E , ° F X 100 Figure 4.

Sulfur removal in pretreated Pittsburgh seam, Pennsylvania mine, coal


20.

H y dr ode suif urization

FLEMING ET A L .

A= PYRITIC S U L F U R

Ο ΙΟ

"RAW \ "COAL

20

of

275

Coals

B ORGANIC SULFUR REMOVAL

REMOVAL


30 40 50 60

\

70


80

\

90 100 7

8

9

Κ) II

TEMPERATURE, C

TOTAL SULFUR RAW COAL

10

r-

7

12 13 14 15 16

8

9

10 II

12 13 14 15 16

T E M P E R A T U R E , ° F X 100

°FXIOO

REMOVAL


20

5

30

Ο

I

\

40

or 3 ^

\

50

CO h-

60

Ζ UJ (Τ UJ CL

\

\

\

70

\

\

\

80

90

100

8

9

10

II

12

13

14

15

16

T E M P E R A T U R E , ° F X 100

Figure 5.

Sulfur removal in pretreated Illinois No. 6 coal



276

COAL

DESULFURIZATION

T a b l e I p r e s e n t s t y p i c a l r e s u l t s f r o m two b a t c h r e a c t o r t e s t s . ( D e t a i l e d d a t a w i l l be p r e s e n t e d i n t h e f i n a l r e p o r t u n d e r EPA C o n t r a c t No. 68-02-2126 (3)·) For t h e s e t e s t s , the p r o d u c t r e c o v e r y i s a b o u t 60%; t h e r e m a i n d e r o f t h e c o a l has been g a s i f i e d (and p r e t r e a t e d ) i n t o l o w - B t u gas t h a t can be u p g r a d e d t o p i p e l i n e q u a l i t y o r consumed o n s i t e . The h e a t i n g v a l u e o f t h e t r e a t e d p r o d u c t i s a b o u t 5% l e s s t h a n t h a t o f t h e f e e d s t o c k , p r i m a r i l y b e c a u s e of b o t h the l o s t heat c o n t e n t a s s o c i a t e d w i t h b u r n i n g the c o a l s u l f u r and t h e i n c r e a s e d a s h c o n t e n t o f t h e p r o d u c t . The q u a n t i t y o f v o l a t i l e m a t t e r c o n t a i n e d i n t h e t r e a t e d p r o d u c t has been r e duced s i g n i f i c a n t l y ; m o d i f i e d c o m b u s t i o n equipment may be r e q u i r e d t o consume t h e d e s u l f u r i z e d c o a l . A l t e r n a t i v e l y , as i n a n o t h e r IGT p a t e n t , t h e t r e a t e d p r o d u c t can be r e c o m b i n e d w i t h t h e h y d r o carbons produced d u r i n g the treatment ( a f t e r o i l h y d r o d e s u l f u r i z a t i o n ) to improve the combustion c h a r a c t e r i s t i c s . F i g u r e 7 p r e s e n t s t h e b a t c h r e a c t o r r e s u l t s f o r t e s t s on W e s t e r n K e n t u c k y No. 9 c o a l . A t any t r e a t m e n t t e m p e r a t u r e , t h e s u l f u r r e m o v a l f r o m t h e c o a l a p p r o a c h e s a maximum a s y m p t o t i c a l l y with soaking time. Based on t h e s e t e s t s , a r e a s o n a b l e d e s i g n c o n d i t i o n w o u l d be 90 min o f r e a c t i o n t i m e a t 1500°F. PDU-Scale T e s t s Work has now p r o g r e s s e d t o l a r g e r e q u i p m e n t , u s i n g a 1 0 - i n . f l u i d i z e d - b e d u n i t t h a t can be f e d c o n t i n u o u s l y a t r a t e s between 25 and 100 l b / h r . The 1 0 - i n . u n i t has been u s e d t o v e r i f y p r e t r e a t m e n t o p e r a t i n g c o n d i t i o n s on a c o n t i n u o u s b a s i s . Pretreated f e e d s t o c k has been p r e p a r e d on t h i s u n i t f o r h y d r o d e s u l f u r i z a t i o n r u n s t h a t a r e ( a t t h e t i m e o f p r e p a r a t i o n o f t h i s p a p e r ) now planned. T h i s u n i t w i l l be u s e d t o c o l l e c t d a t a f o r m a t e r i a l and e n e r g y b a l a n c e s , s t r e a m c h a r a c t e r i s t i c s , e c o n o m i c s , and d e s i g n s p e c i f i cations for a larger i n s t a l l a t i o n . P r e l i m i n a r y e n g i n e e r i n g e v a l u a t i o n o f t h e s y s t e m , b a s e d on t h e i n - h o u s e d a t a b a s e a t IGT, i n d i c a t e s t h a t t h e p r o c e s s s h o u l d have f a v o r a b l e economics. S u f f i c i e n t h y d r o g e n s h o u l d be e v o l v e d f r o m the c o a l d u r i n g d e v o l a t i l i z a t i o n t h a t a supplemental hydrogen s o u r c e w i l l n o t be r e q u i r e d ; r a t h e r , t h e h y d r o t r e a t m e n t gas may be r e c y c l e d , a f t e r hydrogen s u l f i d e removal. F u r t h e r , the q u a n t i t y of low-Btu o f f - g a s generated d u r i n g the h y d r o t r e a t m e n t w i l l r e s u l t i n a s u b s t a n t i a l b l e e d stream from the r e c y c l e d gas; the v a l u e of t h i s b l e e d s t r e a m i s s i g n i f i c a n t and w i l l be i n s t r u m e n t a l i n r e d u c i n g t h e c o s t o f t h e t r e a t e d s o l i d p r o d u c t t o be c o m p e t i t i v e w i t h o t h e r c l e a n f u e l s . C o n f i r m a t i o n of t h e s e p r e l i m i n a r y e v a l u a t i o n s , however, must a w a i t d a t a f r o m PDU and, e v e n t u a l l y , p i l o t p l a n t tests.



(wt % ) ( d r y b a s i s )

Heating value (Btu/lb) S o l i d s r e c o v e r y (%) T o t a l s u l f u r r e m o v a l (%) P y r i t i c and o r g a n i c s u l f u r r e m o v a l

Ultimate analysis ash carbon hydrogen sulfur sulfide sulfate pyritic organic total nitrogen oxygen total

(%)

0.02 0.64 1.13 1.95

12,454

3.74 1.53 8.95 100.00

11.24 70.00 4.54

5.8 36.3 10.6 47.3 100.0

0.15 0.00 0.02 0.46

11,967 62.62 89.45 91.96

0.63 0.78 0.51 100.00

18.43 78.70 0.95

0.8 3.3 18.3 77.6 100.0

BR-76-3 R u n - o f - M i n e W. Ky. No. 9 Feed Product 26498 31996 1500 5 30

T y p i c a l B a t c h R e a c t o r Runs w i t h S p e c i f i e d

P r o x i m a t e a n a l y s i s (wt % ) ( a s r e c e i v e d ) moisture v o l a t i l e matter ash f i x e d carbon total

Run no. Coal type Sample L a b o r a t o r y ID no. T e r m i n a l t e m p e r a t u r e (°F) Heat-up r a t e (°F/min) S o a k i n g t i m e (min)

Table I .

13,168

2.43 1.60 8.95 100.00

8.31 73.90 4.81

2.4 34.0 8.1 55.5 100.0

0.05 0.05 0.03 0.49

12,793 62.70 84.00 86.58

0.62 0.90 1.51 100.00

12.51 83.40 1.06

0.4 3.3 12.5 83.8 100.0

BR-76-34 Washed I l l i n o i s No. 6 Feed Product 34428 33293 1500 5 30

Feedstock

0.01 0.13 0.82 1.47


278

C O A L DESULFURIZATION 0

KRAW COAL

PRETREATED REMOVAL DURING PRETREATMENT

10 20

Ο

WESTERN KENTUCKY NO. 9

Δ •

PITTS. SEAM (W. Va.) PITTS. SEAM (Pa.)

V

ILL. NO. 6

30 Ν

40 50 60


70 80 90 100 7.5

8

9

_L

JL

10

II

JL 12

13

T E M P E R A T U R E , ° F X 100

Figure 6.

Percent sulfur removed vs. temperature

HEAT-UP

Of-RAW COAL

•

0

101

Δ

20 f - PRETREATED COAL

• •

SLOW RAPID SLOW RAPID SLOW RAPID

TERMINAL TEMP, °F 1300 1400 1500

30 [ 40 50 60 70 80 90 100

60

120

180

240

300

EFFECTIVE RUN TIME, min

Figure 7. Degree of sulfur removal in batch reactor tests as a function of effective run time (total time during heatup or soaking at temperature greater than 750°F)


20.

FLEMING

E T

A L .


of

279

Coals

Conclusions L a b o r a t o r y - and b e n c h - s c a l e d a t a i n d i c a t e t h a t a c c e p t a b l e h y d r o d e s u l f u r i z a t i o n o f c o a l s c a n be a c h i e v e d w i t h t h e IGT F l a s h D e s u l f u r i z a t i o n Process. P r e t r e a t m e n t o f t h e c o a l enhances t h e removal o f s u l f u r i n t h e subsequent h y d r o d e s u l f u r i z a t i o n step t o p r o d u c e a s o l i d f u e l t h a t c a n be b u r n e d i n c o n f o r m a n c e w i t h t h e p r e s e n t F e d e r a l EPA New S o u r c e P e r f o r m a n c e S t a n d a r d s o f 1.2 l b Btu. Work i s p r o g r e s s i n g t o p r o v e t h e c o n c e p t on l a r g e r c o n t i n u o u s , P D U - s i z e d e q u i p m e n t . The c o m p l e t e f l o w s h e e t f o r t h e p r o c e s s h a s n o t y e t been d e f i n e d ; t h e r e f o r e , e c o n o m i c f a c t o r s a r e unknown.

SO2/IO6


Acknowledgement The work i n t h i s c o a l d e s u l f u r i z a t i o n p r o g r a m h a s been p e r f o r m e d u n d e r c o n t r a c t t o t h e U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y , R e s e a r c h T r i a n g l e P a r k , N o r t h C a r o l i n a , and EPA p e r m i s s i o n t o p u b l i s h these r e s u l t s i s g r a t e f u l l y acknowledged. Abstract

The IGT process for producing low-sulfur, solid fossil fuel from coal is based upon chemical and thermal treatment. Sulfur is removed from the coal by hydrogen treatment at elevated temperature and near-atmospheric pressure. Several coals, from abundant Eastern U.S. seams, have been tested in both laboratory- and bench-scale hardware. An oxidative pretreatment of the coal both prevents coal from caking and improves the overall sulfur removal. The data indicate that enough sulfur, both pyritic and organic types, is removed so that the treated product can be burned directly in conformance with present Federal EPA NSPS for SO emissions. The program, sponsored by EPA, is now testing the concepts in a larger, continuous fluidized-bed unit to verify the bench-scale results. 2

Literature Cited 1. 2. 3.

Lee, B. S. and Schora, F. C., "Desulfurization of Coal," U.S. Patent 3,640,016 (1972) February 8. Institute of Gas Technology, "Development Program for Treatment of Coal to Produce Low Sulfur, Solid Fossil Fuel," IGT Project 8945, EPA Contract No. 68-02-1366, Chicago, 1977. (To be published.) Institute of Gas Technology, "Pilot Plant Study of Conversion of Coal to Low-Sulfur Fuel," IGT Project 8973, EPA Contract No. 68-02-2126, Chicago, 1977. (Program still in progress.)


21 Improved Hydrodesulfurization of Coal Char by Acid Leach ANN B. TIPTON


Occidental Research Corporation, La Verne, CA 91750

Occidental Research Corporation's (ORC) Flash Pyrolysis coal liquefaction process (1) is designed to handle caking coals in a single-stage reactor without pretreatment. The process produces a maximum liquid yield and char co-product. When high-sulfur, bituminous coals are used as feed for the process, the char, like the coal, is also high in sulfur. The value of this char as a feed for utility boilers would be increased greatly i f its sulfur content were lowered to meet the EPA sulfur emission standard (1.2 lb SO/MM Btu). Hence, concurrent with the development of the Flash Pyrolysis coal liquefaction process, char desulfurization research has been performed. From this research, a two-step acid leach/hydrodesulfurization (AL/HDS) process has been developed (2). Acid leach, the first step of the process, removes p r i marily iron and calcium sulfides from the char. The absence of these minerals improves significantly the hydrodesulfurization step by allowing operation at shorter residence times and at higher H S concentrations. 2

2

The original research f o rthe acid leach/hydrodesulfurization process, reported by R o b i n s o n (2), studied the effects of temperature, pressure, residence times, s u p e r f i c i a l v e l o c i t y , p a r t i c l e s i z e , char preparation method, c o a l c l a s s (bituminous and subbituminous), a c i d t y p e , a n d H2S c o n c e n t r a t i o n i n t h e treatment g a s (H2). I n most o f t h i s work, chars prepared by p y r o l y s i s o f c o a l s i n a s t a t i c bed u n d e r an inert gas b l a n k e t were used. However, Robinson established that acid-leached Flash Pyrolysis chars have faster h y d r o d e s u l f u r i z a t i o n rates than acidleached static bed chars. Therefore, t h e work r e p o r t e d h e r e was p e r f o r m e d t o e s t a b l i s h t h e d a t a base

280


21.


TIPTON

of Coal

Char

281

required f o rthe design o f a n AL/HDS p i l o t p l a n t f o r Flash P y r o l y s i s char from h i g h - s u l f u r , bituminous coal.


Experimental T h e c h a r u s e d i n t h i s s t u d y w a s made i n ORC's Flash Pyrolysis coal liquefaction pilot plant by a s i n g l e p a s s o f -200 m e s h W e s t e r n K e n t u c k y N o . 9 c o a l t h r o u g h t h e p y r o l y s i s r e a c t o r a t 1200°F f o r 2.5 s e c . The f o l l o w i n g a d d i t i o n a l p r o c e s s s t e p s were p e r f o r m e d in laboratory batch reactors. The s i n g l e - p a s s Flash P y r o l y s i s c h a r w a s o x i d i z e d a t 1600°F f o r 0.1 s e c a n d t h e n h e l d i n a f l u i d i z e d b e d u n d e r n i t r o g e n a t 1600°F for 1 hr. The o x i d a t i o n represents a char burning step i n the coal l i q u e f a c t i o n process and t h e a d d i tional heating simulates continuous char recycle. The F l a s h P y r o l y s i s c h a r was a c i d - l e a c h e d five times with 6N h y d r o c h l o r i c a c i d a t 8 0 ° C f o r 5 m i n with a 2:1 a c i d - t o - c h a r ratio. Residual a c i d was removed by water r i n s i n g . The h y d r o d e s u l f u r i z a t i o n reactor and chemical and physical property analyses were described i n detail by Robinson (2). The h y d r o d e s u l f u r i z a t i o n r e a c t o r w a s b u i l t a r o u n d a 1.2-m χ 19-mm i . d . q u a r t z c y l i n d e r i n w h i c h 10-g s a m p l e s w e r e t r e a t e d a t 1600°F, 65 p s i a a n d 0.15 f t / s e c s u p e r f i c i a l v e l o c i t y . Before the t r e a t m e n t g a s was i n t r o d u c e d , t h e reactor and s a m p l e w e r e h e a t e d t o t e m p e r a t u r e a n d h e l d f o r 15 m i n w i t h n i t r o g e n a s t h e f l u i d i z a t i o n medium. The system was also purged with nitrogen during cool down. f

Results

and

Discussion

The c o m p o s i t i o n s of the feed coal, the Flash P y r o l y s i s char and t h e acid-leached char a r e given i n Table I . A comparison o f t h e s u l f u r forms i n feed coal and Flash P y r o l y s i s c h a r shows that the total sulfur was a p p r o x i m a t e l y constant and t h a t pyritic sulfur a n d some organic s u l f u r were c o n v e r t e d t o sulfide sulfur. The conversion of the coal pyritic s u l f u r t o s u l f i d e s u l f u r i n the char i s b e n e f i c i a l t o the AL/HDS process because t h e s u l f i d e form w i l l readily dissolve i n theprocess acids. The absence o f iron s u l f i d e s i s necessary f o r t h e improved hydro desulfurization rate.


COAL

282 Table I. Coal and Char Compos i t i o n


Feed Coal

DESULFURIZATION

a

Flash Pyrolysis Char

Acid-Leached Char

Moisture Ash (dry) Volatile matter (dry) Fixed carbon (dry)

3.43 9.28 38.15 52.57

0.66 24.77 5.17 70.06

2.26 17.97 12.34 69.69

Carbon (dry) Hydrogen (dry) Sulfur (dry) Oxygen and nitrogen (dry)

72.35 4.70 2.96 10.71

72.98 0.83 2.33 0

76.03 1.19 1.06 0

Total sulfur (MAF) Sulfide sulfur (MAF) P y r i t i c sulfur (MAF) Sulfate sulfur (MAF) Organic sulfur (MAF)

3.26 0.13 1.44 0.09 1.60

3.09 1.98 0.17 0 0.95

1.30 0.19 0.07 0 1.04

Chloride (dry)

-

0.05

0.33

Iron (dry) Calcium (dry) Silicon (dry) Aluminum (dry) Potassium (dry) Sodium (dry) Magnesium (dry)

1.32 0.31 2.36 0.86 0.17 0.08

4.01 0.98 5.35 2.03 0.43 0.18 0.12

0.36 0.14 5.66 2.03 0.43 0.18 0.08

Heating value (BTU/lb, dry)

12,780

11,280

EPA standard in % sulfur (MAF)

a

11,540

0.90

Values are wt % except for heating value.


0.84


21.

TIPTON


of Coal

283

Char

A comparison of the compositions i n Table I of t h e F l a s h P y r o l y s i s (FP)char and t h e acid-leached (AL) c h a r shows t h a t t h e a c i d l e a c h removed a p p r o x i mately 90% each o f t h e s u l f i d e sulfur, iron, and c a l c i u m a l o n g w i t h 30% o f t h e a s h . More moles o f i r o n and c a l c i u m were removed than moles o f s u l f u r ; thus, p o t e n t i a l s u l f u r scavengers i n t h e mineral matter such as o x i d e s w e r e a l s o r e m o v e d . Limited h y d r o d e s u l f u r i z a t i o n experiments were p e r f o r m e d w i t h FP c h a r t o c o n f i r m t h e i m p r o v e m e n t s i n hydrodesulfurization after acid leach. The d a t a f o r hydrodesulfurization rates o f FP char with pure h y d r o g e n a t 1600°F a n d 65 p s i a a r e s h o w n i n F i g u r e 1 with curves given f o r total sulfur, sulfide sulfur, and organic sulfur. A l lthree curves gradually decrease at similar rates thus showing t h a t sulfide s u l f u r and o r g a n i c s u l f u r a r e removed s i m u l t a n e o u s l y . F o r t h i s F P c h a r , t h e E P A e m i s s i o n s t a n d a r d o f 1.2 l b S0 /MM B t u i s e q u i v a l e n t t o 0 . 9 0 % t o t a l s u l f u r (MAF) w h i c h was n o t a c h i e v e d a f t e r 150 m i n i n p u r e h y d r o g e n . Hence, f o r FP chars residence time g r e a t e r than 150 min i n p u r e h y d r o g e n w o u l d be r e q u i r e d t o meet t h e EPA s t a n d a r d by h y d r o d e s u l f u r i z a t i o n a l o n e . The data f o rh y d r o d e s u l f u r i z a t i o n r a t e s o f FP c h a r w i t h 0 . 5 % H2S i n h y d r o g e n a r e s h o w n i n F i g u r e 2 with curves given f o r total sulfur, sulfide sulfur, and organic sulfur. The t o t a l s u l f u r and s u l f i d e s u l f u r both i n c r e a s e d , and t h e o r g a n i c s u l f u r remained approximately constant. In these experiments the H S/H r a t i o was 5 χ 1 0 " . A t 1600°F t h e a c c e p t e d experimental e q u i l i b r i u m constant (H2S/H2 ratio) i s 3 χ 1 0 ~ (_3) f o r t h e r e a c t i o n o f F e S w i t h h y d r o g e n : 2

3

2

2

3

FeS

+ H

2

^

Fe +

H S 2

Therefore, t h e 0.5% H S i n H w i l l force the equili brium r e a c t i o n t o t h e l e f t and prevent t h e removal o f sulfide sulfur. The i n c r e a s e i n sulfide sulfur confirms the presence of sulfur scavengers i n the mineral matter. The r e a c t i o n mechanisms o f o r g a n i c s u l f u r removal a r e t o o complex t o p r e d i c t t h e l e v e l o f H S that inhibits hydrodesulfurization. I t c a n be seen i n Figure 2 that a t a 5 χ 1 0 " H S/H ratio, the lowest used i n this study, the removal of organic sulfur i s also inhibited i n FP c h a r . After 150-min residence time, i tappears, i naddition, that there i s a conversion of sulfide sulfur t o organic sulfur as has been observed i n the coking of coals (4,5,6). 2

2

2

3

2

2




284

Figure 1.


of flash pyrolysis char at 1600°F hydrogen

and 65 psia in



of Coal

Char


TIPTON

Ο-TOTAL SULFUR • - SULFIDE SULFUR Δ-ORGANIC SULFUR

_1_

ΙΟ

20

30

40

50

60

70

RESIDENCE Figure 2.

80

90

.Χ

100

110

120

130 140 150

TIME (MINUTES)

Hydrodesulfurization of flash pyrolysis char at 1600°F in 0.5% HjS/BAL H

and 65 psia

2


COAL

286

Since long residence times are usually required for the h y d r o d e s u l f u r i z a t i o n of coals and chars, the possibility of sulfide sulfur conversion to organic sulfur can i m p o s e a d d e d r e s t r i c t i o n s on allowable H S i n the gas i f operative at lower H S/H ratios. The data f o r h y d r o d e s u l f u r i z a t i o n r a t e s of AL c h a r a t 1600°F a n d 65 p s i a w i t h p u r e h y d r o g e n a n d five levels of hydrogen s u l f i d e i n hydrogen are given in Figure 3. Only the t o t a l s u l f u r curves are shown since they are essentially the same a s the organic s u l f u r c u r v e s f o r AL c h a r s . The s u l f u r l e v e l s reached a s t e a d y s t a t e a f t e r 10 m i n i n a l l c u r v e s e x c e p t pure h y d r o g e n w h i c h r e q u i r e d a b o u t 30 m i n . As the h y d r o g e n sulfide c o n c e n t r a t i o n i n the hydrogen i n c r e a s e s , the hydrogen s u l f i d e i n h i b i t i o n of o r g a n i c s u l f u r removal is e x h i b i t e d i n the g r a d u a l l y i n c r e a s i n g s t e a d y - s t a t e l e v e l of s u l f u r i n the char. From the steady-state levels drawn i n these curves, t h e EPA standard of 0.84% total sulfur (MAF) f o r A L c h a r c a n be met with H S c o n c e n t r a t i o n s as h i g h as 4%. In both the 4.0% and 8.5% H S curves, there i s the i n d i c a t i o n that sulfur i n c r e a s e d a t 150 min r e s i d e n c e time as was observed w i t h t h e FP c h a r and 0.5% H S. This again supports the h y p o t h e s i s that the char's r e a c t i v i t y to t h e a d d i t i o n o f s u l f u r i s i n c r e a s e d by l o n g residence times. The i n h i b i t i o n isotherms are shown i n F i g u r e 4 f o r t o t a l s u l f u r , o r g a n i c s u l f u r , and s u l f i d e sulfur in FP char and AL char. The organic sulfur and sulfide sulfur curves f o r FP c h a r readily show t h a t b o t h f o r m s i n c r e a s e d when t h e a c i d - l e a c h a b l e m i n e r a l s and hydrogen sulfide are present. However, the inhibition isotherms f o r AL char show that organic s u l f u r i s r e m o v e d a n d t h a t no s u l f i d e s u l f u r i s f o r m e d through back r e a c t i o n f o r any of the H S/H ratios (0.005 - 0.093) t e s t e d . Hence, removing the acidl e a c h a b l e m i n e r a l s not only e l i m i n a t e s the scavenging o f h y d r o g e n s u l f i d e by t h e m i n e r a l s b u t a l s o makes i t possible to achieve effective organic sulfur removal in the presence of high H S/H ratios. 2


DESULFURIZATION

2

2

2

2

2

2

2

2

2

Conclusions E f f e c t i v e h y d r o d e s u l f u r i z a t i o n of F l a s h Pyrolysis chars requires essentially H S-free hydrogen and g r e a t e r t h a n 150 m i n r e s i d e n c e t i m e a t 1600°F a n d 65 psia. Effective h y d r o d e s u l f u r i z a t i o n of acid-leached chars c a n be a c h i e v e d w i t h h y d r o g e n m i x t u r e s containing up 2


{3

poj

fo uoiiDzimJinsdpoipfiH

NOXdLL

'\z Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch021

xm

%

TOTAL

S U L F U * ( MAF )

%

TOTAL

SULFUW

(MAF)

%

TOTAL

SULm*


( MAf )


288

COAL

DESULFURIZATION

Figure 4. Inhibition isotherms for flash pyrolysis char and acid-leached char at 1600° F, 65 psia, and 150 min residence time.OB) flash pyrolysis char, (O) acid-leached char, ( · " , Q ) starting value.


289

21. TIPTON Hydrodesulfurization of Coal Char

t o 4% H2S i n r e s i d e n c e 1600°F a n d 65 p s i a .

times

o f 10 m i n o r l o n g e r

at


Literature Cited

1. Sass, Α., Chem. Eng. Prog. (1974) 70, 72. 2. Robinson, Leon, Fuel (1976) 55, 193. 3. McKinley, Joseph B . , "Catalysis", P.H. Emmett, Ed., Vol. V, p. 453, Reinhold, New York, 1957. 4. Powell, Alfred R., J. Ind. Eng. Chem. (1920) 12, 1069. 5. Eaton, S.E., Hyde, R.W., Old, B.S., Am. Inst. Mine Met. Eng., Iron Steel Div. Metal Tech. (1948) 19, 343. Tech. Bull. 2453. 6. Cernic-Simic, S., Fuel (1962) 41, 141.


22 Coal Desulfurization during Gaseous Treatment E D M U N D TAO KANG H U A N G * and A L L E N H. PULSIFER


Department of Chemical Engineering and Nuclear Engineering and Energy and Mineral Resources Research Institute, Iowa State University, Ames, IA 50011

Sulfur removal from coal during treatment with gaseous atmospheres at elevated temperatures is of interest both because such a treatment might serve as a basis for a coal desulfurization process (1,2,3) and because knowledge of the fate of sulfur when coal is heated has application during carbonization or gasification. Early interest in desulfurization under these conditions concentrated mainly on the production of metallurgical coke. The various approaches included pretreatment of the coal before carbonization, carbonization of the coal in various gases to remove sulfur compounds, or treatment of the coke to reduce its sulfur content. Only recently has interest turned to desulfurization of coal or char for use as a power plant fuel. Sulfur removal from coal during carbonization has been investigated both with and without the addition of reactive gases such as hydrogen and oxygen. During carbonization in the presence of only the gases derived from the coal, hydrogen sulfide is released along with small amounts of other volatile sulfur-containing compounds (4). The iron pyrite decomposes when heated and releases half its sulfur, while one-quarter to o n e - t h i r d o f the organic s u l f u r i s converted t o hydrogen s u l f i d e (_5,(>). The t o t a l amount o f s u l f u r removed f r o m c o a l d u r i n g c a r b o n i z a t i o n i s i n f l u e n c e d b y t h e c o a l r a n k and q u a n t i t y and composition of the mineral matter (7). Snow ( 8 ) h e a t e d c o a l i n v a r i o u s r e a c t i v e g a s e s and f o u n d h y d r o g e n t o be t h e most e f f e c t i v e d e s u l f u r i z i n g a g e n t o f t h e gases t e s t e d . A h i g h e r r a t e o f d e s u l f u r i z a t i o n and l o w e r c h a r s u l f u r c o n t e n t were r e p o r t e d when h y d r o g e n was u s e d as compared w i t h normal c a r b o n i z a t i o n , w i t h both q u a n t i t i e s being favored by i n c r e a s e d h y d r o g e n p r e s s u r e (9,_10). P y r i t e r e a c t s w i t h hydrogen i n two s t e p s , b e i n g f i r s t c o n v e r t e d t o f e r r o u s s u l f i d e and t h e n t o pure i r o n . Y e r g y e t a l . (Il) found t h a t t h e f i r s t r e a c t i o n b e g i n s a t 400°C w h i l e t h e s e c o n d r e a c t i o n o c c u r s a t a somewhat higher temperature. The c o n v e r s i o n o f t h e p y r i t e t o s u l f i d e a p p e a r s t o be f a i r l y r a p i d w h i l e t h e r e a c t i o n o f h y d r o g e n w i t h f e r r o u s s u l f i d e i s slow (12). The c o n v e r s i o n o f o r g a n i c s u l f u r 290


22.

HUANG

A N D PULSIFER

Desulfurization

during

Gaseous

Treatment

291

t o h y d r o g e n s u l f i d e was r e p o r t e d b y P o w e l l ( 1 3 ) n o t t o be s i g n i f i c a n t b e l o w 500°C b u t i n c r e a s e s g r e a t l y a s t h e t e m p e r a t u r e i s r a i s e d f r o m 500° t o 1000°C. H y d r o d e s u l f u r i z a t i o n o f c o a l i s s t r o n g l y i n h i b i t e d by t h e presence o f hydrogen s u l f i d e i n t h e gas phase (_12,14,15), a n d G r a y e t a l . ( 1 2 ) f o u n d t h a t s u l f u r removal i s r a p i d and l i m i t e d by t h e e q u i l i b r i u m between hydrogen s u l f i d e and t h e s u l f u r i n t h e c o a l . An a c i d l e a c h o f t h e c o a l removes i r o n a n d c a l c i u m s u l f i d e s , r e d u c i n g t h e b a c k r e a c t i o n o f c o a l w i t h h y d r o g e n s u l f i d e and s i g n i f i c a n t l y i m p r o v i n g t h e e f f e c t i v e n e s s o f h y d r o d e s u l f u r i z a t i o n (16,17). D e s u l f u r i z a t i o n o f coke and c o a l w i t h o x y g e n - c o n t a i n i n g gases has been t h e s u b j e c t o f s e v e r a l i n v e s t i g a t i o n s (18,19,20). M a i n l y p y r i t i c s u l f u r i s removed i n o x i d i z i n g a t m o s p h e r e s . S i n h a a n d W a l k e r (18) r e p o r t e d t h a t 907 o f t h e p y r i t i c s u l f u r was removed i n 10 m i n u t e s a t 450°C w i t h a 5-177 sample w e i g h t loss. However, B l o c k e t a l . (20) f o u n d i n e x p e r i m e n t s a t s i m i l a r c o n d i t i o n s t h a t l e s s p y r i t i c s u l f u r was removed w i t h a g r e a t e r weight loss. S e v e r a l i n v e s t i g a t o r s have r e p o r t e d t h a t some o f t h e i n o r g a n i c s u l f u r i n c o a l i s t r a n s f o r m e d i n t o o r g a n i c s u l f u r upon h e a t i n g (5,7,8,11). C e r n i c - S i m i c (7^) added r a d i o a c t i v e s u l f u r i n t h e f o r m o f i r o n p y r i t e s t o a c o a l sample a n d a f t e r c a r b o n i z a t i o n f o u n d t h a t p a r t o f t h e r a d i o a c t i v e s u l f u r was r e t a i n e d by t h e c o a l i n t h e f o r m o f o r g a n i c s u l f u r . The amount o f r a d i o a c t i v e s u l f u r r e t a i n e d as o r g a n i c s u l f u r i n c r e a s e d as c o a l rank decreased. I n t h e work r e p o r t e d h e r e , d e s u l f u r i z a t i o n o f b o t h a raw and d e a s h e d Iowa c o a l were i n v e s t i g a t e d i n t h r e e d i f f e r e n t g a s e s : n i t r o g e n , h y d r o g e n , and a 6% o x y g e n - 947 n i t r o g e n gas m i x t u r e . W i t h each g a s , b o t h t h e t e m p e r a t u r e and h o l d i n g time a t temperat u r e were v a r i e d . W i t h h y d r o g e n and n i t r o g e n , t h e t e m p e r a t u r e was v a r i e d b e t w e e n 300° a n d 700°C. The t e m p e r a t u r e r a n g e u s e d w i t h t h e o x y g e n - n i t r o g e n m i x t u r e was o n l y 350° - 455°C b e c a u s e o f t h e l a r g e w e i g h t l o s s a t h i g h e r t e m p e r a t u r e s c a u s e d b y comb u s t i o n o f t h e sample. H o l d i n g t i m e a t t e m p e r a t u r e was v a r i e d f r o m 0 t o 60 m i n u t e s , e x c e p t i n t h e o x i d i z i n g a t m o s p h e r e where t h e maximum h o l d i n g t i m e was 40 m i n u t e s .


o

0

e

Experimental The i n v e s t i g a t i o n was c a r r i e d o u t w i t h a R i g a k u CN8001 H type thermal a n a l y z e r which included a thermal g r a v i m e t r i c a n a l y z e r , a preprogrammed h e a t i n g u n i t a n d t e m p e r a t u r e c o n t r o l s y s t e m , and a d a t a r e c o r d i n g u n i t . The c o a l sample was c o n f i n e d i n a 10-mm d i a m e t e r p l a t i n u m p a n h a v i n g a d e p t h o f 5 mm. The pan was s u p p o r t e d on a b a l a n c e t h a t c o u l d d e t e c t a w e i g h t change o f l e s s t h a n 0. 1 mg. The sample h o l d e r was c o n t a i n e d i n a 20-mm d i a m e t e r q u a r t z t u b e w h i c h was c o n t i n u o u s l y p u r g e d w i t h g a s . To c a r r y o u t a r u n , about 300 mg o f c o a l (o> So =

S i n c e t h e i n o r g a n i c and o r g a n i c s u l f u r c o n t e n t s o f t h e c h a r s p r o d u c e d f r o m b o t h t h e r a w and d e a s h e d c o a l s were d e t e r m i n e d a t


COAL

300

Table I I I .


Temp. (°C)

C a l c u l a t e d Parameters f o r S u l f u r Holding Time (min)

f

DESULFURIZATION

Reactions

Si

fi

-0.05 -0.06 -0.06 -0.05 -0.07 -0.05 -0.08 0.02 0.02 0.22 0.12 0. 20 0.23 0. 12 0. 13 0.19 0. 15 0. 14 0. 09 0.09 0. 10 0.17 0. 15 0. 19 0.29

0. 15 0. 42 0.52 0. 55 0.57 0. 58 0.58 0. 58 0. 61 0.58 0. 62 0.57 0.59 0. 62 0. 68 0.71 0. 75 0.73 0.76 0. 74 0. 83 0. 84 0.87 0. 88 0.90

2

Hydrogen atmosphere 300 400 400 400 400 400 400 500 500 500 500 500 500 600 600 600 600 600 600 700 700 700 700 700 700

0 0 10 20 30 40 60 0 10 20 30 40 60 0 10 20 30 40 60 0 10 20 30 40 60

0.10 0. 29 0. 34 0.41 0. 38 0. 42 0.45 0.51 0.51 0.43 0. 39 0. 34 0. 34 0. 49 0. 48 0.52 0.57 0.49 0.49 0.49 0. 47 0. 43 0.32 0. 25 0. 23


22.

HUANG

A N D

puLSiFER

Table I I I .


Nitrogen

during

Gaseous

Treatment

301

Continued Holding Time (min)

Γ emp. 0

5

I

10

Γr-n

15

1

20

1

25

CONVERSION OF SULFUR TO H S AND S0 ,% 2


2


23.

HALDIPUR

A N D WHEELOCK

Desulfurization

in a Fluid-Bed

Reactor

317

s u l f u r s p e c i e s i n c o a l , w h i c h i s i n agreement w i t h Y e r g e y e t a l . (7)· On t h e o t h e r h a n d , t h e c o n v e r s i o n o f s u l f u r i n r u n - o f - m i n e c o a l t o h y d r o g e n s u l f i d e does n o t a p p e a r t o be a f i r s t - o r d e r p r o c e s s s i n c e t h e c u r v e s f o r t h i s m a t e r i a l i n F i g u r e s 3 and 4 a r e nonlinear. B e c a u s e t h e r u n - o f - m i n e c o a l c o n t a i n e d l a r g e amounts o f b o t h p y r i t i c and o r g a n i c s u l f u r , t h e n o n l i n e a r b e h a v i o r c o u l d have been c a u s e d by t h e s u p e r p o s i t i o n o f r e a c t i o n s i n v o l v i n g t h e two s u l f u r s p e c i e s . Although the curves r e p r e s e n t i n g the format i o n r a t e o f h y d r o g e n s u l f i d e were s i m i l a r f o r b o t h h y d r o g e n a n d n i t r o g e n , i t i s a p p a r e n t t h a t f o r t h e same t e m p e r a t u r e a n d t y p e o f c o a l , t h e r a t e was l a r g e r when h y d r o g e n was u s e d . T h i s i s o n l y n a t u r a l s i n c e t h e r a t e s h o u l d depend o n t h e h y d r o g e n c o n c e n t r a t i o n , and when p u r e n i t r o g e n was f e d , a n y h y d r o g e n had t o come from t h e decomposition o f the c o a l i t s e l f . When an o x y g e n - b e a r i n g g a s was used t o t r e a t c o a l , s u l f u r d i o x i d e was u s u a l l y t h e m a j o r n o n c o n d e n s i b l e s u l f u r compound i n the o f f - g a s , b u t s i g n i f i c a n t amounts o f h y d r o g e n s u l f i d e were also present. The f o r m a t i o n r a t e o f s u l f u r d i o x i d e d u r i n g s e v e r a l r u n s made w i t h a n o x i d i z i n g gas i s shown i n F i g u r e 5. F o r e a c h r u n two d i s t i n c t p e a k s i n t h e s u l f u r d i o x i d e f o r m a t i o n r a t e were observed. The f i r s t peak m i g h t have b e e n c a u s e d by d e v o l a t i l i z a t i o n and o x i d a t i o n o f v o l a t i l e s u l f u r compounds i n c l u d i n g h y d r o g e n sulfide. A f t e r t h e i n i t i a l d e g a s s i n g o f c o a l had s u b s i d e d , o x y g e n c o u l d p e n e t r a t e t h e c o a l more r e a d i l y and r e a c t w i t h embedded p y r i t e s l e a d i n g t o t h e s e c o n d peak. Then a s t h e o x i d a t i o n r a t e o f p y r i t e s became l i m i t e d b y t h e d i f f u s i o n o f o x y g e n t h r o u g h a n i n c r e a s i n g l a y e r o f r e a c t i o n products such as i r o n o x i d e , t h e r a t e subsided. The d i f f e r e n c e i n t h e b e h a v i o r o f t h e two t y p e s o f c o a l further supports t h i s theory. Thus f o r d e a s h e d c o a l w i t h a r e l a t i v e l y s m a l l p y r i t e c o n t e n t , t h e s e c o n d peak was much s m a l l e r than f o r run-of-mine c o a l . A n a l y s i s and C o n c l u s i o n s The r e s u l t s o f t h i s s t u d y c o n f i r m e d t h a t i t i s p o s s i b l e t o remove s u b s t a n t i a l amounts o f s u l f u r f r o m p u l v e r i z e d b i t u m i n o u s c o a l i n a f l u i d i z e d bed r e a c t o r o p e r a t e d a t e l e v a t e d t e m p e r a t u r e s . However, f o r t h e t y p e o f c o a l used i n t h i s s t u d y , t h e r e m o v a l o f s u l f u r i s accompanied by a s u b s t a n t i a l l o s s o f v o l a t i l e m a t t e r . Both t h e degree o f d e s u l f u r i z a t i o n and extent o f d e v o l a t i l i z a t i o n a r e s t r o n g l y i n f l u e n c e d b y t e m p e r a t u r e . The c o m p o s i t i o n o f t h e f l u i d i z i n g g a s a p p e a r s t o have more e f f e c t on t h e r e m o v a l o f p y r i t i c s u l f u r t h a n on t h e r e m o v a l o f o r g a n i c s u l f u r a n d v o l a t i l e m a t t e r i n t h e 240°-400°C r a n g e . Thus a n o x y g e n - b e a r i n g gas a p p e a r s more e f f e c t i v e f o r r e m o v i n g p y r i t i c s u l f u r t h a n a h y d r o g e n - b e a r i n g gas, and n i t r o g e n i s completely i n e f f e c t i v e . On t h e o t h e r h a n d , t h e r e m o v a l o f o r g a n i c s u l f u r a p p e a r s due m a i n l y t o p y r o l y s i s a n d d e v o l a t i l i z a t i o n and i s n o t a s t r o n g f u n c t i o n of t h e treatment gas c o m p o s i t i o n . Since a s i g n i f i c a n t part o f t h e c o a l i s v o l a t i l i z e d , t h e r e c o v e r y and u t i l i z a t i o n o f t h e



318

COAL

DESULFURIZATION

TIME, MIN.

Figure 5. Rate of S0 formation during treatment with gas containing 10% oxygen 2



23.

HALDiPUR

A N D WHEELOCK

Desulfurization

in a Fluid-Bed

Reactor

319

v o l a t i l e products i s important. A l t h o u g h a number o f i n d u s t r i a l p r o c e s s a l t e r n a t i v e s b a s e d on t h e f l u i d i z e d - b e d method o f d e s u l f u r i z a t i o n a r e c o n c e i v a b l e , o n l y two w i l l be c o n s i d e r e d h e r e . One a l t e r n a t i v e i n v o l v e s t r e a t i n g p u l v e r i z e d c o a l i n a continuous flow system w i t h a i r o r a i r d i l u t e d w i t h r e c y c l e d o f f - g a s t o remove p y r i t i c s u l f u r and o r g a n i c sulfur. This approach i s i n d i c a t e d f o r c o a l s c o n t a i n i n g f i n e l y d i s s e m i n a t e d p y r i t e s w h i c h c a n n o t be removed by p h y s i c a l s e p a r a tion. I t i s c o n c e i v a b l e t h a t s u f f i c i e n t h e a t w o u l d be g e n e r a t e d through o x i d a t i o n t o s u s t a i n the process. However, t h e o f f - g a s w o u l d be d i l u t e d w i t h n i t r o g e n and w o u l d have a l o w h e a t i n g v a l u e . A l s o t h e s u l f u r d i o x i d e p r e s e n t i n l o w c o n c e n t r a t i o n w o u l d be d i f f i c u l t t o e x t r a c t . On t h e o t h e r h a n d , t h e l i g h t o i l i n t h e o f f - g a s w o u l d be r e l a t i v e l y e a s y t o remove, and t h e r e w o u l d be no t a r t o contend w i t h . A second a l t e r n a t i v e i n v o l v e s t r e a t i n g c o a l i n a f l o w s y s t e m w i t h r e c y c l e d o f f - g a s w h i c h h a s been d e s u l f u r i z e d and h e a t e d . This approach i s i n d i c a t e d f o r c o a l s w i t h important amounts o f o r g a n i c s u l f u r b u t l i t t l e p y r i t i c s u l f u r . The o f f - g a s w o u l d be r i c h i n h y d r o g e n and methane and w o u l d have a r e l a t i v e l y high heating value. Hydrogen s u l f i d e i n t h e g a s w o u l d be r e l a t i v e l y e a s y t o remove, b u t t h e t a r a l s o p r e s e n t w o u l d c r e a t e more o f a p r o b l e m t h a n t h e l i g h t o i l p r o d u c e d u n d e r o x i d i z i n g conditions. I n t h e case o f e i t h e r a l t e r n a t i v e , t h e c l e a n f u e l gas w o u l d be u s e d t o g e t h e r w i t h a c h a r p r o d u c t . W h i l e t h e methods a p p l i e d i n t h i s s t u d y d i d n o t r e d u c e t h e s u l f u r c o n t e n t o f t h e s e l e c t e d c o a l t o t h e p o i n t where t h e p r o d u c t w o u l d meet p r e s e n t a i r p o l l u t i o n c o n t r o l s t a n d a r d s , f u r t h e r improvement i n m e t h o d o l o g y i s p o s s i b l e . From t h e p u b l i s h e d r e s u l t s o f other workers (1,2), i t i s l i k e l y that e i t h e r reducing t h e p a r t i c l e s i z e o r i n c r e a s i n g t h e t e m p e r a t u r e w o u l d be b e n e f i c i a l , a l t h o u g h i n c r e a s i n g t h e t e m p e r a t u r e w o u l d remove more v o l a t i l e m a t t e r a s w e l l a s more s u l f u r . Also coals which i n i t i a l l y c o n t a i n l e s s s u l f u r o r a r e o f a h i g h e r r a n k t h a n t h e one s e l e c t e d c o u l d p o s s i b l y b e n e f i t more f r o m t h i s t y p e o f t r e a t m e n t . Achnowledgement T h i s work was s p o n s o r e d by t h e Iowa C o a l P r o j e c t and c o n d u c t e d i n t h e E n e r g y and M i n e r a l R e s o u r c e s R e s e a r c h I n s t i t u t e a t Iowa S t a t e U n i v e r s i t y .

Literature Cited

1. Jacobs, J. K., Mirkus, J. D., Ind. Eng. Chem. (1958), 50:24-26. 2. Sinha, R. Κ., Walker, P. L., Fuel (1972), 51:125-129. 3. Block, S. S., Sharp, J. B., Darlage, L. J., Fuel (1975), 54:113-120. 4. Cernic-Simic, S., Fuel (1962), 41:141-151. 5. Maa, P. S., Lewis, C. R., Hamrin, C. E., Fuel (1975),


320



54:62-69. 6. Snow, R. D., Ind. Eng. Chem. (1932), 24:903-909. 7. Yergey, A. L., Lampe, F. W., Vestal, M. L., Day, A. G., Fergusson, G. J., Johnson, W. H., Snyderman, J. S., Essenhigh, R. H., Hudson, J. E., Ind. Eng. Chem., Proc. Des. Dev. (1974), 13:233-240. 8. Batchelor, J. D., Gorin, E., Zielke, C. W., Ind. Eng. Chem. (1960), 52:161-168. 9. Gray, C. Α., Sacks, M. E., Eddinger, R. T., Ind. Eng. Chem. Prod. Res. Dev. (1970), 9:357-361. 10. Zielke, C. W., Curran, G. P., Gorin, E., Goring, G. E., Ind. Eng. Chem. (1954), 46:53-56.


Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ix001

INDEX

A

Β

Absorption isotherms 234 Acetone 157 Acid /leach/hydrodesulfurization 280 -leached char, inhibition isotherms for 288 -leachedflashpyrolysis char, hydrodesulfuriaztion of 287 Air 305 flow rate onflotation,effect of 77 regeneration by 156 table 46 -water oxydesulf urization process .. 171 Alkali concentration on sulfur extraction from pyrite, effect of 188 in H T T coals, sulfur capture by 202 impregnation with 201 leaching ISU coal with 190 Alkaline solutions, desulfurizing coal with 182 American Electric Power Service Corp 153 Ammonia anhydrous 83 breakage 58 concentration, sulfur removal as a function of 176 /oxygen system, sulfur removal from coals by 173 Ammonium carbonate 186 Appalachian region coals 37,143 Arsenic 151 Ash 58 content 308 of ISU coal after leaching 193 overall yield vs 94 vs. recovery curves 59 reduction 92 Ashing for the direct determination of organic sufur, plasma 20 Ashing technique, low-temperature ... 19, 25 ASTM methods, standard 16 Atomic adsorption spectrometry, pyritic iron by 16 Autoclave 184 high-pressure stirred 174

Batac jig 44 Batch experiments 164 reactor runs with specified feedstock 277 reactor tests 273 sulfur removal in 278 Beneficiation on coal reserves 38 by a float/sink technique 308 kaolin 122,129 methods, coal 83 Benzene 166 BET method 222 Black water studies 53 Bomb apparatus, small 61 Btu loss from coals 180 Btu recovery 189 Bulk density 104 Bureau of Mines coal preparation program 48 C Cadmium 151 Calcium 12 carbonate 189 hydroxide 189 sulfate 157,170 Capistrano test site, TRW's 153 Carbon 12 from a char, initial loss of 227, 229 dioxide 313 impurity-free 236 loss from coals 180 monoxide 313 -sulfur bond cleavage 208 Carbonization 305 /desulfurization of Illinois coal, fluid-bed 248 first-stage 254 material flow and weight distribu tion during staged 264 PDU 250 for clean coke process 251 product char from 261 second-stage 258 Carbonizer, fluid-bed 251, 265 Carbonyl sulfide 313

323




324 Carousel separator 122,123 Cashflowfinancingmethod (DCF), discount 126 Cellular components 3 Cellular features of coalified plant material 5 Channel sample 14 Char 311 from carbonization PDU, product .. 261 composition 282 desulfurization 221,225, 235,280 electron probe analysis for 225 filter-paper 238,241 flash pyrolysis 281 forms of sulfur in derived 238 hydrodesulfurization 280 of flash pyrolysis 284,285,287 Illinois 225 inhibition isotherms for flash pyrolysis and acid-leached 288 initial loss of sulfur and carbon from 227,229 oxygen concentration in synthetic .. 242 pore surface area of 237 sulfidation of previously desulfurized 235 sulfidation of synthetic 233 sulfur chemisorption on 244 content, effect of temperature and residence time on 264 effect of H S in fluidizing gas on 260 after treatment, surface area of 231 Chemical 84 analysis methods 85 cleaning, combined physical and .. 192 comminution 58, 59, 61, 84 on overall results, effect of 97 desulfurization of coal 52,153,173 kinetics and mechanism of pyrite .... 182 leaching 192 treatment, combined physical and .. 195 treatments, innovative 52 Chemicals, effective 63 Chemisorbed sulfur 240 Chemisorption on chars, sulfur 244 Chemisorption isotherms 245 Chlorination 207 kinetic data for 213 sulfur and chlorine in coal during .. 214 Chlorine in coal during chlorination .. 214 Chlorinolysis, coal desulfurization by low-temperature 206 Chlorinolysis data for bituminous coal desulfurization 212,215 Clay, the wet beneficiation of kaolin .. 122 Clean coke process 248,249 carbonization PDU for 251 2

Cleaning bituminous coal and lignite, mechanical 36 chemical 192,198 circuit, novel fine-size 46 combined physical and chemical .... 192 economic evaluation of physical coal 51 float-sink 153 Gravichem 153 mechanical 36 multistream coal 42 physical 145,192 precombustion 121 Closed water circuits 46 Coal(s) with alkali, leaching ISU 190 analysis data of tested 210 analysis, starting 175 Appalachian 39,143 availability, effect of crushing and cleaning on sulfur 41 beneficiation methods 83 bituminous .4,36,109,110,212,215,305 Btu and carbon loss from 180 carbonization of 248 chlorination, kinetic data for 213 during chlorination, sulfur and chlorine in 214 cleaning, economic evaluation of physical 51 composition 282 contact vessel, coarse 162 dechlorination data for bituminous 212 desulfurization 221,280,290 with alkaline solutions containing dissolved oxygen 182 by ammonia/oxygen system 173 chemical 52,153,173 chlorinolysis data for bituminous 212,215 flotation process for 70 in afluidized-bedreactor 248,305 by HGMS 128,130,132,133 by high-intensity high-gradient magnetic separation 121 of Illinois 223,248 kinetic data for 213 laboratory 214 by low-temperature chlorinolysis 206 magnetic 112,125,129 Meyers process for 143 oxidative 164 rate constants for 231 test plant status 153 devolatilization, resident time on 227,257,258 dewatering 46,52,53


325


INDEX

Coal (continued) Coal (continued) the direct determination of organic processing, coarse 159 sulfur in raw 22 product and recycle, bituminous .... 110 product and recycle, subbituminous 109 dry table - pyrite removal from 101 pyrite drying unit operation 159 electron probe analysis for 225 with ferric sulfate, oxidation of .... 156 flotation 72-74 flotation, two-stage 50 framboid, pyrite in Iowa 9 removal by 167 gaseous treatment of 290 by a reaction of leaching, extraction gasification at 223 of sulfur from 141 H T T (see H T T coal) refluxed with cyclohexane 20 hydrodesulfurization 267,280 refuse, fine 53 from ICO mines 86 reserves, beneficiation on 38 Illinois No. 6 59,61,112,174, resources 38,39 223,248,254,275 run-of mine 318 Iowa 185,291 samples, composition of 292 ISU (see ISU coal) samples in thermal analyses of 204 Jude mine 86,297,309 size consist of Illinois No. 6 59 kinetic data for chlorination studies 27 and desulfurization 213 subbituminous 107,109 after leaching, ash and sodium sulfidation of 221,233 content of ISU 193 sulfur leaching experiments 187 capture by alkali in H T T 202 after leaching, sulfur content of ISU 191 direct determination of organic liberating the mineral matter from .. 58 forms in 16,37,145, 238 low-sulfur 40 removal of organic 168,297 Lower Kittanning 158 removal by reaction and leaching 141 magnetic desulfurization of 112,129 thermogravimetic analyses of Martinka mine 148,153 raw and H T T 204 mechanical cleaning and thermal toxic metals extracted by hydrodrying of bituminous 36 thermal treatment of 203 Meyers process for desulfurization trace elements in 54 of U.S 143 trace metal removal from 215 microstructure 3 type, effect of 63 morphology of untreated washability analysis of 88 and H T T 200 washing 144 nitration of the 166 /water slurry by HGMS, organic sulfur removal 168, 297 desulfurization of 125,130,132 oxidation oxygen consumption for .. 178 Western Kentucky No. 9 271 oxidation technique applied to 30 yield 88 oxidative desulfurization of 164 vs. liberated pyritic sulfur oxidizer, continous 253,255 recovery 80 oxydesulfurization 169 Coalified plant fibers 4 oxygen uptake by 178 Coalified plant material, cellular features of 5 physically cleaned 145 162 Pittsburgh seam 228 Coarse coal contact vessel 159 Pennsylvania mine 274 Coarse coal processing 248,249,251 West Virginia mine 272 Coke process, clean 24 precombustion cleaning of 121 Collection procedure 201 preparation 35,70 Combustion behavior Combustion, direct-fired 207 process development facility, central 55 Comminuted coal, nitrogen content of chemically 67 prep/FGD combination study 51 Comminution, chemical 58,59,61,84 pretreatment, sulfur removal 83 indicating effect of 269 Comminution, mechanical 135 process, hydrothermal 198,200 Conditions, operating Control circuit, dense-medium process, morphology of untreated specific gravity 45 and H T T 200




326 Control circuit, novel 44 Cost(s) of desulfurization of coal/water water slurry by HGMS, estimated 130 of desulfurization of coal/water slurry by HGMS sensitivity analysis unit 128 estimation 121 of H E M F operating 118 investment 136 of magnetic desulfurization of coal/water slurry 125 of magnetic desulfurization of liquefied coal 129 operating 136 processing 156 of pyrite removal processes, capital and unit 130 of solid-liquid separation methods, capital and unit 134 Cross-sectional areas 243 Crushing 84 mechanical 59,61, 83 roll 84 stage 39 on sulfur coal availability effect of .. 41 Crystals 13 Crystallite sizes 236, 246 Crystallinity of filter-paper chars .... 238 Cyclohexane 20,166 Cyclone, dense-medium 46

Drying of bituminous coal and lignite, thermal

36

Ε Economic evaluation of physical coal cleaning Economics Electrode graphite Electromagnet Electron microprobe x-ray analyzer .. Electron probe analysis for coal and char desulfurization and gasifi cation Electrostatic precipitators Elemental sulfur recovery Emissons controlling sulful oxide of low-sulfur coals, sulfur trace metal Energy dispersive x-ray analysis Enviro-clear thickener Equipment performance evaluations .. Errors Ethane Evacuation and coal rank, effect of ....

51 118 236 121 12 225 125 156 159 37 201 201 3 49 54 17 313 66

F

Feedstock, batch reactor runs with specified 277 Ferric oxide 183 D sulfate 183 DBT sulfone 166 leaching 143,153 Decalin 166 oxidation of coal pyrite with 156 Dechlorination 209 regeneration of 159 data for bituminous coal, Ferrous sulfate 156,183 preliminary 212 Ferrous sulfide 306 Decomposition products, volatile 310 Financing method, the discount Dense-medium specific gravity cash flow (DCF) 126 control circuit 45 Fine-size cleaning circuit, novel 46 Density, bulk 104 Filtration of leach solution 159 Desulfurization Filtration, precoat 135 coal ( see Coal desulfurization ) First-order process 317 char {see Char desulfurization) First-order reaction 288 flue gas 121 Five-stage pressure vessel 161 Devolatization, coal 227,257,258 Flammability 203 Dewatering coal 46,52, 53 Flash pyrolysis char 281 Dibenzothiophene 165 hydrodesulfurization of 284,285,287 Discharge distribution, dry table 108 inhibition isotherms for 288 Discount cashflow(DCF) Float/sink financing method 126 cleaning 153 Disposal, landfill-type 53 separation 143 Dry table technique, benefication by a 308 discharge distribution 108 Flotation principle 102 froth 50,84,98 pyrite removal from coal 101 kinetics, coal 73


327


INDEX

Flotation (continued) Hydrogen (continued) of Lower Kittanning and Pittsburgh peroxide 313 seam coals 75 sulfide 306 operating conditions, effect of 77 sulfur released in 294 process for desulfurization of coal .. 70 Hydrogénation 125 of pyritic sulfur, effect of fuel oil on 76 Hydrolysis 209 rate of Pittsburgh seam coal 74 Hydroperoxide 166 systems, pyrite in coal 72 Hydrothermal coal process 198 two-stage coal-pyrite 50 morphology of 200 Flue gas desulfurization 121 toxic metals extracted by 203 Fluid-bed carbonizer 251 Heating value 189,314 continuous pressurized 265 Heats of chemisorption 243 Fluid-bed carbonization/desulfurizaHEMF, operating costs of 118 tion of Illinois coal 248 H E M F unit 116 Fluidized-bed 273 HGMS ( high-gradient magnetic reactor, desulfurization of separation) 51,121,122 coal in a 248,305 estimated costs of desulfurization of Fluidizing gas on char sulfur, effect coal/water slurry by 130 ofH Sin 260 sensitivity analysis unit costs of Framboids 6 desulfurization of coal/water Froth flotation 50, 84,98 slurry by 128 Frother concentration, effect of 77 High-intensity high-gradient magnetic Frother systems, effect of 75 separation, desulfurization of Fuel oil 83 coals by 121 on flotation of pyritic sulfur, High-sulfur bituminous coals 84 effect of 76 Homer City preparation plant 42 Fuels, solid 199 H T T coal morphology of 200 G sulfur capture by alkali in 202 thermogravimetic analyses of 204 Gas Hydroclone, separator 131 on char sulfur, effect of H S in fluidizing 260 Hydrodesulfurization acid leach/ 280 containing hydrogen, H S formation of acid-leached flash pyrolysis char 287 during treatment with 312 of coal char, improved 280 /solid reactions, sulfur removal by .. 219 of coals 267,290,291 Gaseous treatment of coal 290 offlashpyrolysis char 284,285 Gases, oxygen-bearing 310 removal of sulfur by 219 Gasification of dried Illinois No. 6 coal 223,225 Gasification, secondary 232 I Graphite, electrode 236 Graphite, pyrolitic 236 ICO mines, coal from 86 Gravichem cleaning 156 Ignition temperature 203 Grab and run process 79 Illinois char, desulfurization and Gravity separation 84, 97,153,192 gasification of 225 Grinding, mechanical 83, 84 Illinois coal 59,61,112,174, Grinding on overall results, effects of 96 223,248,254,275 Grinds of ISU coal 194 Impeller speed on the flotation, Gypsum 8 effect of 77 crystals 11 Impurities, level of 95 Inhibition isotherms forflashpyrolysis H and acid-leached char 288 24 HS 260,263,312 Ion chromatograph 185,291 H S0 167,170 Iowa coals Hydrogen 270,293,305 Iron 12,156 formation rates of 314 by atomic adsorption spectrometry, H S formation during treatment pyritic 16 with gas containing 312 oxides 182 2

2

2

2

2

4

2


328

COAL


Iron (continued) pyrites 83,185 pyrrhotite equilibrium 234 reduced 232 sulfates 143,156 crystallization 159 washing of residual 159 Isotherm absorption 234 chemisorption 245 Langmuir 240 ISU coal 191 with alkali, leaching 190 grinds of 194 after leaching, ash and sodium content 193 after leaching, sulfur content of 191 J Jude strip mines, coal from

86,297,309

Κ Kaolin beneficiation lattice Kinetic(s) data for chlorination and desulfurization equation method, nonisothermal process chemistry

122,129 17

213 148 306 156

L Laboratory coal desulfurization Laboratory processing Lamella thickener Landfill-type disposal Langmuir isotherm Leach rate solution, ferric sulfate solution, filtration of Leaching chemical experiments, coal extraction of sulfur from coal by .... ferric sulfate ISU coal with alkali of pyritic sulfur, pressure -regeneration, simultaneous sulfur content of ISU coal after Lead Lignite deposits

214 210 49 53 240 157 153 159 192 187 141 143 190 159 159 191 151 53

DESULFURIZATION

Lignite (continued) mechanical cleaning and thermal drying of 36 sodium content of 53 Limestone 170 Lithium aluminum hydride 18 Low -sulfur char 248 -sulfur coals, sulfur emissions of 201 -temperature ashing technique 19 Lower Kittanning coal 75,158 M Macérai grouping 3 Magnetic desulfurization of coal/water slurry 125 of Illinois Basin coals 112 of liquefied coal 129 separation ( H G M S ) 51,121 Magnex process 129 Mags 122 Manganese 151 Marcasite 6 Martinka mine coal 148,153 Mass balance, material flows 263 Mass spectrometer 306 Material balances, sulfur 299 Material flows 263 during staged carbonization, 264 Metal extraction 201 Metals extracted by hydrothermal treatment of coal, toxic 203 Methane content on the rate of sulfur removal, effects of 221 Meyers process for desulfurization of U.S. coal 143 Microchemical features 6 Microchemical studies 4 Milling, ball 84 Mineral -free basis 18 inclusions 6 liberation 63 matter from coal, chemical comminution to liberate 58 residue separation method 125 Ν Nickel 151 Nitration of coal 166 Nitrogen 293,305 content of chemically comminuted coal 67 dioxide 166 H S formation during pyrolysis in .... 312 2


INDEX

329

Nitrogen (continued) mixture, oxygensulfur released in Nonisothermal kinetic method,

296 294 306


Ο

Oil agglomeration 85 concentration, pine 78 on flotation of pyritic sulfur, effect of fuel 76 fuel 83 light 310 Optical microscopy 222 Organic solvents 157 Organic sulfur 165,173,182,207,222, 262, 270,283,292,305 from oxidation, repeatability runs of the analyses of 28 plasma ashing for the direct determination of 20 in raw coals, the direct determination of 22 removal from coals by oxydesulfurization 165,168 removal vs. sample weight loss 297 Oxidants 166 Oxidation of coal pyrite with ferric sulfate 156 organic sulfur from 28 product 183 of pyritic sulfur, selective 305 study of FeS 27 technique, low temperature 23 technique to various coals, appli cation of the 30 Oxidative desulfurization of coal 164 Oxidized Illinois coal, analysis of 254 Oxidizer, continuous coal 253,255 Oxydesulfurization of coals 169 organic sulfur removal from coals by 168 process, air-water 171 pyrite removal from coals by 167 Oxygen -bearing gases 310 concentration in synthetic chars .... 242 consumption 175 for coal oxidation 178 minimum 177 content offilter-paperchars after sulfidation 241 content of chars, initial 238 desulfurizing coal with alkaline solutions containing dissolved .. 182 -nitrogen mixture 296 2

Oxygen (continued) regeneration by on the sulfur absorption, influence of system, sulfur removal from coals by ammoniauptake by coal

156 239 173 178

Ρ Particle size on sulfur extraction from pyrite, effect of 188 Particles, volume of 193 PDU carbonization 250,251 product char form 261 scale tests 276 studies 248 Phases, inorganic 3 Physical and chemical cleaning, combined 192,195 Physical methods for removing sulfur from coal 33,145 Pine oil concentration 78 Pittsburgh seam coal 74, 75,228 Plant debris 7 fibers, coalified 4 material, cellular features of coalified 5 Plasma ashing for the direct determi nation of organic sulfur 20 Pore surface area of char 237 Precipitators, electrostatic 125 Precision 28 Precoat filtration 135 Precombustion cleaning of coal 121 Pre-evacuation, effect 65 Preparation plant, Homer City 42 Preparation process development facility, central coal 55 Pressure leaching of pyritic sulfur 159 on the rate of sulfur removal, effects of 65, 221 vessel, five-stage 161 Pretreatment 268 Price for desulfurization of SRC feed coal by HGMS, steam 133 Process chemistry, kinetics and scheme of 156 Process, clean coke 248,251 Processing costs 153 Pulverizing 84 Pyrite(s) (FeS 0) 222,270,293 in coalflotationsystems 72 distribution 3,12,13 effect of alkali concentration on sulfur extraction from 188 2



330


Pyrite (continued) effect of particle size on sulfur extraction from 188 effect of reaction time on sulfur extraction from 191 extraction rates 157 finely dispersed 17 flotation, two-stage coal 50 in Iowa coal 10,11 iron 83,185 leaching experiments 185 proportion of 13 reactivities, of the 148 removal 71 from coal, dry table 101 from coals by oxydesulfurization 167 processes, capital and unit costs of 130 system, pyrrhotite/ 236 Pyritic sulfur 39,58,159,165, 173,182,208,222 overall yield vs 93 reduction 91 removal 129,146,147 rate constants for 148,149 selective oxidation of 305 Pyrolitic graphite 236 Pyrolysis 305 H S formation during 312 removal of sulfur by 219 Pyrrhotite (FES) 18,222,232 equilibrium, iron/ 234 highly magnetic 125 /pyrite system 236 2

R Rate constant 228 for desulfurization 231 for pyritic sulfur removal 148,149 Raw coals, thermogravimetic analyses of 204 Reactivity, increased 203 Reaction conditions, effect of 63 extraction of sulfur from coal by .... 141 first-order 228 procedure 24 Recovery curves, ash vs 59 Recovery curves, sulfur vs 61 Recycle, bituminous coal product and 110 Recycle, subbituminous coal product and 109 Reduction potential 39 Reduction, sulfur 144 Refuse, fine coal 53 Refuse pond stabilization study 53 Regeneration 156 of ferric sulfate 159

Regeneration ( continued ) by oxygen or air simultaneous leachingRepeatability runs of the analyses of of organic sulfur Resiliency Roll crushing

156 159 28 104 84

S Sample, representative and homogeneous 18 Sandwich screen concept 46 Scanning electron microscope 3 Semicontinuous experiments 165 Sensitivity analysis unit costs, desulfurization of coal/water slurry by HGMS 128 Separation float-sink 143 gravity 84,97,153,192 magnetic (HGMS) 121 method 135 capital and unit costs, solid-liquid 134 mineral residue 125 Separator Carousel 122 hydroclone 131 matrix loading characteristics 127 Shape 104 Silica sand 308 Size 104 consist of Illinois No. 6 coal 59 effect of starting 65 reduction methods 84 Sizing 46 Sodium carbonate 166,186 content of ISU coal after leaching .. 193 content of lignite 53 hydroxide 166,183,186 phosphate 186 Solid fuels 199 -liquid separation methods, costs of 134,135 removal of sulfur by gas/ 219 Solvents, organic 157 Species, ionic 17 Specific gravity control circuit, dense-medium 45 Stabilization study, refuse pond 53 Stage crushing 39 Steam 305 Sulfate 156 analyses 24 conversion to 208



INDEX

331

Sulfate (continued) ferrie and ferrous 167 sulfur 6,156 Sulfidation of coal 221 char and synthetic chars 221, 233 oxygen and sulfur contents of filter-paper chars after 241 of previously desulfurized char 235 Sulfide 270 fusinite, n o n c r y s t a l l i n e 10 inorganic 311 loss of 18 occurrence of 17 sulfur 283 Sulfone, DBT 165,166 Sulfur ( see also Pyritic sulfur, Organic sulfur ) absorption of 234 absorption, influence of oxygen on the 239 capture by alkali in H T T coals 202 change in forms of 262 for a char, initial loss of 227 chemisorbed 240 chemisorption on chars 244 in coal 37 during chlorination 214 coal availability, effect of crushing and cleaning on 41 from coal by a reaction and leach ing, extraction of 141 content 115 of chars, initial 238 effect of temperature and resi dence time on char 264 effect of temperature and resi dence time on semichar 257 offilter-paperchars after sulfidation, 241 of ISU coal after leaching 191 determination of forms 1,16 dioxide 313,314 distribution 311 in dried coal, forms of 238 effect of H S in fluidizing gas on char 260 elemental 156,183 direct determination of 20 emissions of low-sulfur coals 201 extraction 199 from pyrite, effect of alkali con centration and particle size on 188 from pyrite, effect of reaction time on 191 forms of U.S. coals 145 to H S, conversion of forms of 263

Sulfur (continued) inorganic 262,292 material balances 299 organic (see Organic sulfur) oxide emissions, controlling 37 pyritic (see Pyritic sulfur) reactions, parameters for 300,301 vs. recovery curves 61 recovery, elemental 159 reduction 91,115,144 potential 38,39 released in hydrogen 294 released in nitrogen 294 removal in batch reactor tests 278 from coals by ammonia/ oxygen system 173 effect of temperature on 295 effects of temperature, pressure, and methane content on the rate of 221 effect of holding time on 295 as a function of ammonia con centration and time 176 indicating effect of coal pre treatment 269 pyritic ( see Pyritic sulfur removal ) by pyrolysis, hydrodesulfuriza tion, and other gas/solid reactions 219 removed vs. temperature, percent .. 278 scavenger 201 sulfate 6,156 sulfide 283 -sulfur bond 208 transformation of 299 Sulfuric acid 156,167,183 Surface area 240 of char after treatment 231 of char, pore 237 phenomena in coal dewatering 53 roughness 104 Surfactant solution as dewatering aid, hot 52

2

2

Τ Tails 122 Tar, black 310 Technical feasibility 183 Temperature on char sulfur content, effect of 264 on coal devolatilization, effect of ... 257 ignition 203 percent sulfur removed vs 278 on the rate on sulfur removal, effects of 221



332


Temperature (continued) on semichar sulfur content, effect of 257 on sulfur removal, effect of 293 Test evaluation 79 plant design and operation 159 plant status, coal desulfurization .... 153 Tetralin 166 Thermal analyses of coal samples in .. 204 Thermal efficiency 179 Thermobalance tests 270 Thermogravimatic analyses of raw and H T T coals 204 Thickener, Enviro-clear 49 Thickener, Lamella 49 Time on char sulfur content, effect of 264 on coal devolatilization, effect of residence 257 on semichar sulfur content, effect of residence 257 on sulfur extraction from pyrite, effect of reaction 191 on sulfur removal, effect of holding 295 sulfur removal as a function of 176 Trace element in coal 54 content 143 removal 150,151 Trace metal emissions 201 Trace metal removal from coal 215 Transmission electron microscope 3 Treatment, combined physical and chemical 195 TWR's Capistrano test site 153 Toxic metals extracted by hydrothermal treatment of coal 203

V Volatile matter

309

W Washability analysis of coal characteristics comparisons Washing coal with dilute acid of residual iron sulfate with water Water content, effect of oxydesulfurization process, airslurry, coalstudies, black Wave-length dispersive analysis Weight distribution during staged carbonization loss for deashed Jude coal sample .. yield of product

88 38 58 144 192 159 192 65 171 125 53 12 264 297 90

X X-ray analysis, energy dispersive X-ray analyzer, electron microprobe ..

3 12

Y Yield vs. ash content, overall Yield vs. pyritic sulfur, overall

94 93

Ζ Zinc


151

Coal Desulfurization: Chemical and Physical Methods

Physical and Chemical Methods in Soil Analysis

The Desulfurization of Heavy Oils and Residua (Chemical Industries)

Drug Targeting Technology: Physical, Chemical and Biological Methods

Drug Targeting Technology: Physical, Chemical and Biological Methods

Bioluminescence: Chemical Principles And Methods

Thermodynamics: Principles characterizing physical and chemical processes

Physical Chemical Treatment of Water and Wastewater

Chemical and Physical Behavior of Human Hair

Encyclopedia of Chemical Physics and Physical Chemistry

Physical Properties of Chemical Compounds

Perry's Chemical Engineers' Handbook Section 2: Physical and Chemical Data

Invariant Manifolds for Physical and Chemical Kinetics

Physical-chemical treatment of water and wastewater

Thermodynamics: Principles Characterizing Physical and Chemical Processes

Invariant manifolds for physical and chemical kinetics

Thermodynamics: principles characterizing physical and chemical processes

Physical-Chemical Treatment of Water and Wastewater

Physical-chemical Treatment of Water and Wastewater

Invariant manifolds for physical and chemical kinetics

Coal Combustion and Gasification (The Plenum Chemical Engineering Series)

Mathematical Methods for Physical and Analytical Chemistry

Coal and Coal-Related Compounds: Structures, Reactivity and Catalytic Reactions

Chemical Degradation Methods for Wastes and Pollutants

Chemical Thermodynamics: Basic Concepts and Methods

Asymmetric Synthesis with Chemical and Biological Methods

Physical Inorganic Chemistry: Principles, Methods, and Reactions

Reverse Chemical Genetics. Methods and Protocols

Chemical Analysis: Modern Instrumentation Methods and Techniques

Chemical Thermodynamics. Basic Concepts and Methods

Asymmetric Synthesis with Chemical and Biological Methods

Coal Desulfurization: Chemical and Physical Methods

Physical and Chemical Methods in Soil Analysis

The Desulfurization of Heavy Oils and Residua (Chemical Industries)

Drug Targeting Technology: Physical, Chemical and Biological Methods

Drug Targeting Technology: Physical, Chemical and Biological Methods

Bioluminescence: Chemical Principles And Methods

Thermodynamics: Principles characterizing physical and chemical processes

Physical Chemical Treatment of Water and Wastewater

Chemical and Physical Behavior of Human Hair

Encyclopedia of Chemical Physics and Physical Chemistry

Physical Properties of Chemical Compounds

Perry's Chemical Engineers' Handbook Section 2: Physical and Chemical Data

Invariant Manifolds for Physical and Chemical Kinetics

Physical-chemical treatment of water and wastewater

Thermodynamics: Principles Characterizing Physical and Chemical Processes

Invariant manifolds for physical and chemical kinetics

Thermodynamics: principles characterizing physical and chemical processes

Physical-Chemical Treatment of Water and Wastewater

Physical-chemical Treatment of Water and Wastewater

Invariant manifolds for physical and chemical kinetics

Coal Combustion and Gasification (The Plenum Chemical Engineering Series)

Mathematical Methods for Physical and Analytical Chemistry

Coal and Coal-Related Compounds: Structures, Reactivity and Catalytic Reactions

Chemical Degradation Methods for Wastes and Pollutants

Chemical Thermodynamics: Basic Concepts and Methods

Asymmetric Synthesis with Chemical and Biological Methods

Physical Inorganic Chemistry: Principles, Methods, and Reactions

Reverse Chemical Genetics. Methods and Protocols

Chemical Analysis: Modern Instrumentation Methods and Techniques

Chemical Thermodynamics. Basic Concepts and Methods

Asymmetric Synthesis with Chemical and Biological Methods

Recommend Documents