7 A Comparison of Coal Beneficiation Methods 1
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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.
84
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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.
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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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
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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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
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
i n this
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Coal Beneficiation
Methods
89
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
COAL
TREATMENT 3 8 10 12
DESULFURIZATION
14 16
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
91
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
M I N AND
WHEELOCK
Coal Beneficiation Methods
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7.
Figure 5.
Overall yield vs. final pyritic sulfur content of the product from the different treatments
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
93
DESULFURIZATION
Downloaded by UNIV LAVAL on June 28, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch007
COAL
\ure 6.
Overall yield vs. the ash content of the final product from the different treatments
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
Downloaded by UNIV LAVAL on June 28, 2014 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0064.ch007
7.
MIN
AND
WHEELOCK
Coal Beneficiation Methods
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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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
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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 .
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
7.
MIN
AND
WHEELOCK
Table IV.
97
Coal Beneficiation Methods
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
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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
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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%
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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 -
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
7.
MIN
AND WHEELOCK
Table V I I .
Coal Beneficiation Methods
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
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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-
In Coal Desulfurization; Wheelock, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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 .
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