A Comparison of Coal Beneficiation Methods - ACS Symposium

7 A Comparison of Coal Beneficiation Methods 1

Downloaded by UNIV LAVAL on June 28, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch007

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

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

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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



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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


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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




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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

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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

C O A L DESULFURIZATION

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.


A Comparison of Coal Beneficiation Methods - ACS Symposium

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