3 Hydrocarbonization H. D. COCHRAN, JR.
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Oak Ridge National Laboratory, T N 37830
H y d r o c a r b o n i z a t i o n processes produce l i q u i d , gaseous, and s o l i d f u e l s from c o a l by low-temperature c a r b o n i z a t i o n under hydrogen pressure. H y d r o c a r b o n i z a t i o n i s a r e l a t i v e l y recent s c i o n of the venerable c l a s s of low-temperature c a r b o n i z a t i o n process, having been l a r g e l y developed s i n c e World War I I . This paper w i l l review, g e n e r i c a l l y , the e f f e c t s of process v a r i a b l e s on product y i e l d s , product q u a l i t y , and hydrogen consumption. I t w i l l then present a b r i e f h i s t o r i c a l overview of process development i n the broad area of h y d r o c a r b o n i z a t i o n technology. T h i s w i l l lead t o a g e n e r a l d i s c u s s i o n of major process a l t e r n a t i v e s w i t h r e f e r e n c e t o s p e c i f i c processes. T e c h n o l o g i c a l developments i n problem areas f o r h y d r o c a r b o n i z a t i o n processes w i l l then be d e s c r i b e d as background f o r an assessment of the present s t a t u s and f u t u r e prospects of t h i s technology.
EFFECTS OF PROCESS VARIABLES
Hydrocarbonization processes a r e c h a r a c t e r i z e d by three primary independent v a r i a b l e s - temperature, hydrogen p r e s s u r e , and c o a l type - and f i v e o t h e r , important independent v a r i a b l e s s o l i d residence time, gas residence time, r e a c t o r c o n f i g u r a t i o n , c o a l pretreatment, and c a t a l y s t impregnation. C o n t r o l of these v a r i a b l e s permits c o n t r o l , over a wide range, o f (1) the r e l a t i v e y i e l d s of l i q u i d , gaseous, and s o l i d products, (2) the q u a l i t y of one o r more of these products, (3) hydrogen consumption, and, u l t i m a t e l y (4) product c o s t .
0-8412-0516-7/79/47-110-037$05.00/0 © 1979 American Chemical Society
Pelofsky; Coal Conversion Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1979.
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COAL
E f f e c t s of Temperature, H
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CONVERSION
TECHNOLOGY
P r e s s u r e , and Coal Type on
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Yields Among a l l independent v a r i a b l e s , temperature has perhaps the most pronounced e f f e c t on y i e l d s from h y d r o c a r b o n i z a t i o n processes. Representative y i e l d s (1) from h y d r o c a r b o n i z a t i o n of Wyodak c o a l at a hydrogen pressure of 300 p s i are shown i n F i g u r e 1. T y p i c a l l y , the y i e l d of l i q u i d products ( o i l and t a r s ) shows a g e n t l e maximum at a temperature about 1050 F. At h i g h e r temperatures, the maximum i s reached when the l i q u i d products are degraded to char and gas; thus, the temperature of maximum l i q u i d y i e l d may be s h i f t e d upward by reducing the time d u r i n g which l i q u i d s are exposed to c r a c k i n g c o n d i t i o n s . Char y i e l d decreases monotonically w i t h i n c r e a s i n g temperature as a r e s u l t of i n c r e a s i n g d e v o l a t i l i z a t i o n and h y d r o g a s i f i c a t i o n of the char. Gas y i e l d i n c r e a s e s monotonically w i t h i n c r e a s i n g temperatures, w h i l e water y i e l d i s r e l a t i v e l y i n s e n s i t i v e to temperature. F i g u r e 2 i n d i c a t e s the manner i n which y i e l d s (2) from h y d r o c a r b o n i z a t i o n are i n f l u e n c e d by hydrogen pressure. As expected, i n c r e a s e d hydrogen pressure r e s u l t s i n increased y i e l d s of l i q u i d and gaseous products and, consequently, i n decreased char y i e l d s . G e n e r a l l y , i t i s b e l i e v e d that hydrogen pressure i n c r e a s e s l i q u i d y i e l d s by s t a b i l i z i n g the r a d i c a l fragments of i n i t i a l p y r o l y t i c decomposition i n c o m p e t i t i o n w i t h p a r a l l e l p o l y m e r i z a t i o n and c r a c k i n g r e a c t i o n s which lead to l o s s of l i q u i d products. Hydrogen pressure r e s u l t s i n a s m a l l i n c r e a s e i n water y i e l d s from ambient to moderate pressures (~300 p s i ) , but the i n c r e a s e from moderate to h i g h pressures (~1000 p s i ) i s essentially negligible. L i t t l e systematic, q u a n t i t a t i v e information i s available concerning the e f f e c t s of c o a l type on h y d r o c a r b o n i z a t i o n y i e l d s . In g e n e r a l , however, h y d r o c a r b o n i z a t i o n y i e l d s may be estimated by n o r m a l i z a t i o n of known r e s u l t s by the F i s h e r assay of the c o a l t e s t e d and thereby extended to other c o a l s . The pronounced e f f e c t s of c o a l type on o p e r a b i l i t y and product q u a l i t y are reviewd below. E f f e c t s of Other V a r i a b l e s on Hydrocarbonization Y i e l d s The primary d e v o l a t i l i z a t i o n of c o a l i s a very r a p i d , thermal process and t h e r e f o r e not s t r o n g l y s e n s i t i v e to s o l i d residence
Pelofsky; Coal Conversion Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1979.
Downloaded by AUBURN UNIV on September 26, 2017 | http://pubs.acs.org Publication Date: November 21, 1979 | doi: 10.1021/bk-1979-0110.ch003
3.
COCHRAN
Hydrocarbonization
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Figure 1. Hydrocarbonization yields for subbituminous coal at 300 psi H pressure 2
Pelofsky; Coal Conversion Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1979.
40
COAL CONVERSION TECHNOLOGY
Downloaded by AUBURN UNIV on September 26, 2017 | http://pubs.acs.org Publication Date: November 21, 1979 | doi: 10.1021/bk-1979-0110.ch003
120
100 WATER
σ
80
GAS
2
