Phase Equilibria and Fluid Properties in the ... - ACS Publications

20 Thermodynamic Data Needs in the Synthetic Fuels

Downloaded by NANYANG TECHNOLOGICAL UNIV on June 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0060.ch020

Industry HOWARD G. HIPKIN Research and Engineering, Bechtel Corp., San Francisco, CA 94119

The petroleum industry, which is responsible for producing most of the energy used in modern society, has produced, as a byproduct over the past 40 years, a broad base of thermodynamic data for the hydrocarbons it processes. Even though the petroleum industry is mature, the data development and correlation effort has not slacked off, and indeed has accelerated in the last two decades. A similar, but more proprietary, effort has been carried on by the chemical industry for nonhydrocarbons. In view of these long-lived programs, the question arises,--does the new synthetic fuels industry, which promises to become important in the last quarter of the century, need specific data programs or are the present data systems adequate for its needs? This paper looks at that question and attempts to outline areas where work is needed. As in the petroleum industry, the need is for thermodynamic properties of a small number of pure compounds, and for mathematical procedures to predict the properties of mixtures of those compounds. What are the S y n t h e t i c Fuels? The s y n t h e t i c f u e l s comprise a spectrum of gaseous, l i q u i d , and s o l i d f u e l s . Gaseous f u e l s i n c l u d e h i g h - , medium, and lowheating values gas from c o a l , s i m i l a r gases from f e r m e n t a t i o n or p y r o l y s i s of biomass, low-heating v a l u e gas from r e t o r t i n g shale o i l , and hydrogen. L i q u i f i e d n a t u r a l gas, w h i l e not a s y n t h e t i c , i s i n c l u d e d here because i t promises to be an important answer to the near-term energy shortage, and because the data needs f o r LNG are s p e c i f i c . High-Btu gas from c o a l i s methane, made by r e a c t i n g carbon monoxide and hydrogen. I t can r e p l a c e n a t u r a l gas i n a l l i t s a p p l i c a t i o n s without any equipment changes. I t s heat of combustion i s about 950 Btu per standard cubic f o o t . Medium-Btu gas i s the carbon monoxide and hydrogen from which high-Btu gas i s made. I t s heat of combustion i s about 300 Btu per standard cubic f o o t . Since methanation i s n o t r e q u i r e d , i t i s cheaper to produce than high-Btu 390

Storvick and Sandler; Phase Equilibria and Fluid Properties in the Chemical Industry ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


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gas; but i s not i n t e r c h a n g e a b l e w i t h n a t u r a l gas, and i t i s more expensive to t r a n s p o r t because of i t s l a r g e r volume. Low-Btu gas i s carbon monoxide and hydrogen d i l u t e d w i t h atmospheric n i t r o g e n . I t i s made by u s i n g a i r i n s t e a d of oxygen i n the c o a l g a s i f i e r . I t i s the cheapest gas to make from c o a l , but i t s heat of combustion i s only 150 Btu per standard cubic f o o t , and the v e r y l a r g e volume r e q u i r e d prevents i t s t r a n s p o r t a t i o n much away from the g a s i f i e r . The major use f o r low-Btu gas i s expected to be f o r combined c y c l e power g e n e r a t i o n (gas t u r b i n e f o l l o w e d by steam t u r b i n e ) . Gas made by p y r o l y s i s of biomass, or of m u n i c i p a l s o l i d waste, resembles c o a l s y n t e h s i s gas i n composition, and can be produced i n the same h e a t i n g v a l u e s . Gas made by anaerobic f e r m e n t a t i o n of biomass i s predominantly methane and carbon d i o x i d e . When the c a r bon d i o x i d e i s removed, i t i s a replacement f o r n a t u r a l gas. Depending on the method of r e t o r t i n g , a gas of v a r i a b l e compos i t i o n and q u a n t i t y i s made from o i l s h a l e . The gas i s u s u a l l y burned as i n - p l a n t f u e l , but i t could be processed f o r syngas. An i n t e r e s t i n g new development i s the p r o d u c t i o n of high-Btu gas by h y d r o t r e a t i n g o i l s h a l e . This p r o c e s s , under development by the I n s t i t u t e of Gas Technology, p r o v i d e s more complete u t i l i z a t i o n of the organic carbon content than simple r e t o r t i n g . Hydrogen, from decomposition of water, may become the dominant gaseous f u e l w e l l a f t e r the turn of the century. This concept i s the b a s i s f o r the s o - c a l l e d "hydrogen economy", which v i s u a l i z e s a v i r t u a l l y i n e x h a u s t i b l e supply of n o n - p o l l u t i n g gaseous energy from t h i s source. The hydrogen economy s u f f e r s from three problems; the high-energy, high-temperature heat source r e q u i r e d , the r e l a t i v e l y low c o n v e r s i o n e f f i c i e n c y of that energy, and the d i f f i c u l t y of s t o r i n g hydrogen. Since t h i s form of s y n t h e t i c f u e l i s u n l i k e l y to be important i n the next 20 or 30 y e a r s , i t w i l l not be c o n s i dered f u r t h e r i n t h i s paper. L i q u i f i e d n a t u r a l gas has been produced i n commercial quant i t i e s f o r a number of years i n the Middle East and A l a s k a . A number of p r o j e c t s f o r l i q u i f y i n g waste n a t u r a l gas i n the Middle East, Indonesia, and A l a s k a , s h i p p i n g the LNG to the U n i t e d S t a t e s , and r e g a s i f y i n g i t to augment our d i m i n i s h i n g s u p p l i e s a r e under a c t i v e development a t present. LNG appears to be the cheapest way to supply gaseous f u e l t o the American market. The energy r e q u i r e d to l i q u e f y and t r a n s p o r t the gas i s l e s s than 15% of the heating v a l u e of the i n i t i a l gas; as 'a r e s u l t , the energy e f f i c i e n c y of t h i s process i s h i g h e r than that of any of the other processes under consideration. L i q u i d s y n t h e t i c f u e l s i n c l u d e s h a l e o i l and i t s v a r i o u s f r a c t i o n s ; c o a l l i q u i d s by cooking, by hydrogenation, and by F i s c h e r tropsch s y n t h e s i s ; methyl f u e l from c o a l or from overseas n a t u r a l gas; and l i q u i d products from biomass, probably by g a s i f i c a t i o n and Fischer-Tropsch s y n t h e s i s . O i l shale i s one of the most p l e n t i f u l resources i n the U n i t e d S t a t e s . I t i s w e l l known that the r e s e r v e s of o i l shale i n the Piceance Creek B a s i n of Colorado and Utah exceed a l l the known



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petroleum reserves i n the world. I t i s l e s s w e l l known that the reserves of o i l shale i n the deeper and leaner d e p o s i t s of the eastern s t a t e s are even l a r g e r (1) . Shale o i l i s produced by r e t o r t i n g o i l s h a l e , e i t h e r i n - s i t u , or on the s u r f a c e a f t e r mini n g . The v i s c o u s shale o i l r e q u i r e s a l i g h t hydrogenation to remove s u l f u r , n i t r o g e n , and oxygen, and then can be r e f i n e d l i k e a crude o i l . Simple p r y o l y s i s of c o a l produces l i g h t o i l s and t a r s , both predominantly aromatic i n c h a r a c t e r , together w i t h some gas and a r e s i d u e of s o l i d coke ( u s u a l l y high i n s u l f u r ) . The l i q u i d y i e l d can be i n c r e a s e d by hydrogenating the c o a l under pressure. The hydrogenation a l s o reduces the s u l f u r content of the s o l i d r e s i due, and e l i m i n a t e s the n i t r o g e n content as ammonia. An a l t e r n a t e p r o c e s s i n g scheme i s to g a s i f y the c o a l w i t h steam and oxygen to make hydrogen and carbon monoxide, which can then be c a t a l y t i c a l l y reacted to a spectrum of hydrocarbons and oxygenated compounds. This mixture i s then r e f i n e d to make v a r i o u s grades of f u e l s and chemicals. At present, only the S a s o l p l a n t i n South A f r i c a uses t h i s Fischer-Tropsch process commercially. A s p e c i a l case of Fischer-Tropsch i s the p r o d u c t i o n of methanol, e i t h e r from g a s i f i e d c o a l or from reformed n a t u r a l gas (overseas). Crude methanol can be used as a f u e l i n gas t u r b i n e s , i n d u s t r i a l b o i l e r s , f u e l c e l l s , and i n t e r n a l combustion engines. I t represents a commercially a v a i l a b l e way to convert c o a l to a l i q u i d f u e l , and has the advantage (as compared to conventional c o a l l i q u i d s ) of e l i m i n a t i n g the r e f i n i n g s t e p . A number of p r o p r i e t a r y processes produce l i q u i d products by p y r o l y s i s of biomass. A l t e r n a t i v e l y , the biomass can be g a s i f i e d and reacted to l i q u i d products by F i s c h e r - T r o p s c h . S o l i d f u e l s are, i n most cases, the u n d e s i r a b l e residues from c o a l processes. Obviously, i f a s o l i d f u e l i s needed, c o a l i t s e l f would be the cheapest m a t e r i a l . The r e s i d u e from most g a s i f i c a t i o n and l i q u i f i c a t i o n processes i s high i n ash and u s u a l l y contains a h i g h e r percentage of s u l f u r than the o r i g i n a l c o a l . I f the combust i b l e content of the r e s i d u e i s low, i t i s d i s c a r d e d . I f , as i n coke, i t i s too l a r g e to be economically d i s c a r d e d , the s o l i d can be g a s i f i e d to produce the hydrogen r e q u i r e d f o r the process. An exception i s Solvent Refined C o a l , a process which produces a l o w - s u l f u r s o l i d f u e l w i t h a m e l t i n g p o i n t of about 350°F. The process a l s o produced a h i g h - s u l f u r , carbonaceous r e s i d u e . The s o l i d r e s i d u e l e f t from r e t o r t i n g o i l s h a l e c o n s i s t s of l a r g e amounts of rock w i t h enough carbon to support combustion. The carbon i s u s u a l l y burned to supply the heat r e q u i r e d f o r r e t o r t i n g . Under some circumstances, t h i s m a t e r i a l could be a s o l i d f u e l f o r other purposes. Most of these processes have a common c h a r a c t e r i s t i c — t h e y are i n c r e a s i n g the hydrogen content of a raw f u e l t h a t i s hydrogend e f i c i e n t compared to petroleum f u e l s . There are three ways i n which t h i s i s done:


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The hydrogenation processes add hydrogen d i r e c t l y C + 2H = CH, 2 4


The g a s i f i c a t i o n processes add hydrogen from water. The oxygen i n the water i s r e j e c t e d t o the atmosphere as carbon d i o x i d e . A s i m p l i f i e d r e p r e s e n t a t i o n o f the c o a l - t o - s y n t h e t i c n a t u r a l gas processes i s 2C + 2H 0 = CH, + C 0 . 2 4 2 o

o

I t can be seen that about h a l f the carbon i n the c o a l i s r e j e c t e d i n order t o upgrade the other h a l f . The simple p y r o l y s i s processes create a high-carbon residue and a high-hydrogen product from the o r i g i n a l low-hydrogen f u e l . The coking o f c o a l can be represented i n an o v e r s i m p l i f i e d way as 10.71

(CH

n

= C,H, + 4.71C.

The good y i e l d of benzene i n d i c a t e d by t h i s equation i s deceptive, because the c o a l a l s o contains oxygen, n i t r o gen, and s u l f u r , and these elements are d r i v e n o f f as water, ammonia, and hydrogen s u l f i d e , thus reducing the hydrogen a v a i l a b l e f o r forming hydrocarbons. I t i s not p o s s i b l e to f o l l o w the technology o f a l l the synt h e t i c f u e l processes i n a s i n g l e paper. Since c o a l g a s i f i c a t i o n f o r the production o f high-BTU gas i s the process on which most e f f o r t i s c u r r e n t l y concentrated, and s i n c e c o a l g a s i f i c a t i o n i s the f i r s t step i n s e v e r a l l i q u i f i c a t i o n processes, and s i n c e c o a l or char g a s i f i c a t i o n i s the most l i k e l y way o f producing hydrogen f o r a v a r i e t y o f other processes, the v a r i o u s c o a l g a s i f i c a t i o n processes w i l l be f o l l o w e d i n some d e t a i l . I n a d d i t i o n , t h i s paper takes a s h o r t e r look a t i n - s i t u shale r e t o r t i n g . How

are S y n t h e t i c Fuels Made?

This look a t s y n t h e t i c f u e l s i s r e s t r i c t e d t o c o a l g a s i f i c a t i o n , as mentioned above. The present generation of commercial g a s i f i c a t i o n processes i n c l u d e s three, a l l German, and a l l designed f o r chemical feedstock, r a t h e r than f o r f u e l . L u r g i . The L u r g i g a s i f i e r has had more i n s t a l l a t i o n s than any other, p o s s i b l y because i t has been the only pressure g a s i f i e r (up to 500 p s i ) . I t i s the g a s i f i e r used i n s e v e r a l of the c o a l g a s i f i c a t i o n f a c i l i t i e s proposed f o r American SNG p r o d u c t i o n . I t i s a f i x e d bed g a s i f i e r , i n which c o a l i s fed i n a t the top through l o c k hoppers, and ash i s removed a t the bottom, a l s o through l o c k hoppers. Steam and oxygen enter a t the bottom and pass up counter-


P H A S E EQUILIBRIA

A N D FLUID PROPERTIES

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394

Figure 1.

Lurgi reactor



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current t o the c o a l . The s y n t h e s i s gas formed a t the bottom o f the r e a c t o r hydrogenates the c o a l i n the middle s e c t i o n s , then cokes and preheats the incoming c o a l . Because o f the c o u n t e r c u r r e n t o p e r a t i o n , the gas i s cooled t o about 1000°F b e f o r e i t leaves the r e a c t o r . The L u r g i r e a c t o r i s shown s c h e m a t i c a l l y i n F i g u r e 1. Since the c o a l i s heated g r a d u a l l y as i t passes s l o w l y down through the bed, the L u r g i r e a c t o r produces l i g h t o i l s , t a r s , and phenols, as w e l l as the u s u a l i m p u r i t i e s of hydrogen s u l f i d e and ammonia. A t y p i c a l L u r g i gas from bituminous c o a l has the f o l l o w ing dry composition: C0

H S, 2

2

20

H

38

2

CH, 4 N , Ar, etc. 2

29 volume%

CO

11 2

P u r i f i c a t i o n o f the gas from any c o a l g a s i f i e r i s a major task f o r s e v e r a l reasons: The gas c o n t a i n s up t o 50% o f unreacted water which, when condensed, i s contaminated w i t h s o l i d f l y a s h and carbon, d i s s o l v e d hydrogen s u l f i d e , ammonia, and c a r bon d i o x i d e , p o s s i b l y w i t h phenols. The water must be t r e a t e d t o remove these contaminants. The f i n e l y d i v i d e d s o l i d s , some o f them sub-micron i n s i z e , are p a r t i c u l a r l y d i f f i c u l t t o remove and, when removed, a r e a d i s p o s a l problem. I t i s always necessary t o remove hydrogen s u l f i d e , and u s u a l l y necessary t o remove carbon d i o x i d e . Any c l e a n up process which removes both a c i d gases d e l i v e r s a stream which i s too d i l u t e i n H2S to be handled i n a Claus p l a n t f o r elemental s u l f u r p r o d u c t i o n . As a r e s u l t , the gas i s u s u a l l y processed t w i c e , once f o r hydrogen s u l f i d e and l a t e r f o r carbon d i o x i d e , a t increased cost. The v a r i o u s p u r i f i c a t i o n steps o f t e n r e q u i r e the gas to be heated and cooled s e v e r a l times i n s u c c e s s i o n . Good heat economy r e q u i r e s fancy heat exchange between these streams, a t i n c r e a s e d c a p i t a l c o s t . With the L u r g i g a s i f i e r , the problem i s f u r t h e r complicated by the n e c e s s i t y to remove o i l s ( l i g h t e r than w a t e r ) , t a r s (heavier than w a t e r ) , phenols and cyanides ( d i s s o l v e d i n w a t e r ) , and other s u l f u r compounds (mercaptans, carbonyl s u l f i d e , and carbon d i s u l f i d e ) As a r e s u l t , the L u r g i gas p u r i f i c a t i o n s e c t i o n i s complicated and correspondingly expensive. F i g u r e s 2 through 8 show the p u r i f i c a -



B.F. WATER

FILLING GAS

COAL

COMPRESSOR

Figure 2. Gasification

LOCK GAS


LOCK GAS

GAS LIQUOR

TARRY GAS LIQUOR

CRUDE GAS

CRUDE GAS


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t i o n scheme used by L u r g i f o r the proposed ANG Goal C a s i f i c a t i o n Company P l a n t ( 2 ) . The gas l e a v i n g the r e a c t o r i s quenched through a v e n t u r i n o z z l e w i t h a m i x t u r e of r e c i r c u l a t e d water, t a r , and l i g h t o i l t o about 800°F. The gas i s then cooled by p a s s i n g up through the tubes o f a v e r t i c a l heat exchanger which generates 100 p s i steam on the s h e l l s i d e . ( I t i s worth n o t i n g , i n p a s s i n g , that c o a l g a s i f i e r s consume l a r g e amounts o f steam,—something over two tons of steam f o r each ton of c o a l . ) The condensate from t h i s exchanger, a m i x t u r e o f t a r , o i l , and water, washes the tubes i n c o u n t e r c u r rent flow and keeps them from f o u l i n g . P a r t o f the condensate i s r e c y c l e d t o the v e n t u r i scrubber (Figure 2 ) . The gas from t h i s exchanger i s s p l i t i n t o two streams. One stream goes to a second c o u n t e r c u r r e n t , v e r t i c a l heat exchanger which generates 60 p s i steam, then t o the two s h i f t c o n v e r t e r s , where the carbon monoxide i n the stream i s almost e n t i r e l y conv e r t e d t o carbon d i o x i d e , i n order to a d j u s t the r a t i o of carbon oxides to hydrogen f o r subsequent methanation (Figure 3 ) . The second stream bypasses the s h i f t c o n v e r t e r s , and goes to a s e r i e s of four v e r t i c a l exchangers which generate 60 p s i steam and 20 p s i steam, preheat b o i l e r feedwater, and f i n a l l y c o o l the gas w i t h c o o l i n g tower water. The gas from the s h i f t c o n v e r t e r s i s cooled through two b o i l e r feedwater exchangers i n s e r i e s , i s cooled i n an a i r c o o l e r , and f i n a l l y , i s cooled a g a i n s t c o o l i n g tower water, and i s compressed t o j o i n the bypassed stream. I n t h i s p r o c e s s i n g scheme, the gas i s c o u n t e r c u r r e n t l y scrubbed w i t h mixed-phase condensate f i v e times a t s u c c e s s i v e l y lower temperatures. This repeated c o n t a c t i n g , together w i t h the v e n t u r i scrub a t the react o r o u t l e t , removes almost a l l the p a r t i c u l a t e s i n the raw gas from the g a s i f i e r , and does i t i n a way that keeps the exchanger tubes from f o u l i n g w i t h t a r . The condensates from the h i g h temp e r a t u r e exchangers go to " t a r r y gas l i q u o r " treatment, and the condensate from the low temperature exchangers go to " o i l y gas l i q u o r " treatment (Figure 4 ) . At t h i s p o i n t , the gas i s e s s e n t i a l l y a t ambient temperature, and the condensate contains a l l the t a r and p a r t i c u l a t e s , a l l the ammonia and phenol, most o f the water and o i l , and some o f the hydrogen s u l f i d e and carbon d i o x i d e . The gas i s r e f r i g e r a t e d and t r e a t e d i n a R e c t i s o l u n i t t o remove hydrogen s u l f i d e . Rectisol i s L u r g i s tradename f o r a p r o p r i e t a r y process u s i n g r e f r i g e r a t e d methanol as a s o l v e n t . Methanol i s an e x c e l l e n t s o l v e n t f o r hydrogen s u l f i d e , c a r b o n y l s u l f i d e , carbon d i s u l f i d e , carbon d i o x i d e , hydrocarbons, and water. I t d i s s o l v e s hydrogen s u l f i d e pref e r e n t i a l l y to carbon d i o x i d e , and i t i s p o s s i b l e to p r o v i d e a concentrated hydrogen s u l f i d e stream from a R e c t i s o l u n i t . I n the design shown i n F i g u r e 5, the hydrogen s u l f i d e , w i t h some carbon d i o x i d e , i s removed f i r s t , then the gas a f t e r methanation i s scrubbed to remove the remaining carbon d i o x i d e . L i g h t o i l , hydrogen cyanide, and water are a l l recovered i n the R e c t i s o l u n i t . 1



TARRY GAS LIQUOR

CRUDE GAS

BFW.

'

60 PSIG ^ STEAM

Shift conversion

J

I

FIRST SHIFT REACTOR

—>h—^—^

Figure 3.

WASTE HEAT EXCHANGER

SECOND SHIFT REACTOR


CONVERTED GAS


PSIG

H E A T

S T E A M

60

G A S

BFW

G A S

E X C H A N G E R

C O N V E R T E D

G A S

L I Q U O R

BFW

E X C H A N G E R

W A S T E

G A S

C O N V E R T E D

T A R R Y

C R U D E

T

1

G A S

E X C H A N G E R

C O N V E R T E D

BFW

{

H E A T J

E X C H A N G E R

W A S T E

BFW

60 PSIG S T E A M

T.

Zk

B F W

P R E H E A T

G A S

C O O L E R

Gas cooling

AIR

G A S

C O O L E R

C O N V E R T E D

E X C H A N G E R

Figure 4.

LP

AIR

C R U D E

i

G A S

G A S

CW

C O O L E R

F I N A L

CW

CW

C O O L E R

F I N A L

L O C K

G A S

G A S

G A S

A N D

G A S

G A S

L I Q U O R

O I L Y

C R U D E

C O N V E R T E D

F I L L I N G

C O M P R E S S O R

C O N V E R T E D B O O S T E R

y



OFF GAS TO

TREATED WATER

HCN LIQUOR

WASH WATER

CRUDE AND CONVERTED GAS

SYNGAS TO METHANATION

S RECOVERY

Figure 5.

Rectisol unit


IMPURE WATER

METHANATED GAS

SNG

TO S. RECOVERY

EXPANSION GAS

20.


HIPKIN

401

The condensates are combined, dropped i n p r e s s u r e to f l a s h o f f d i s s o l v e d gases, and separated by s e t t l i n g i n t o t a r (heavier than w a t e r ) , t a r o i l ( l i g h t e r than w a t e r ) , and contaminated water ( F i g ure 6 ) . The water i s t r e a t e d i n another L u r g i p r o p r i e t a r y p r o c e s s , the Phenosolvan process, to remove phenols and ammonia (Figure 7). The v a r i o u s s u l f u r streams are processed through a Claus p l a n t f o r treatment o f the more concentrated hydrogen s u l f i d e streams. In the Claus p l a n t , p a r t o f the H2S i s burned t o S 0 , which i s r e a c t e d w i t h the r e s i d u a l to make elemental s u l f u r a c c o r d i n g t o the r e a c t i o n


2

S

°2

+

2 H

2

S

=

3 S

+

2 H

2°

Since the t a i l gas from the Claus p l a n t s t i l l contains more s u l f u r than EPA r e g u l a t i o n s p e r m i t , the t a i l gas i s t r e a t e d through a prop r i e t a r y IFP process f o r cleanup. The low s u l f u r c o n c e n t r a t i o n s are processed i n a S t r e t f o r d u n i t , which a l s o produces elemental s u l f u r . A l l these s u l f u r removal f a c i l i t i e s are shown i n F i g u r e 8. I t can be seen that c l e a n i n g up the crude s y n t h e s i s gas from a L u r g i g a s i f i e r i s a complicated o p e r a t i o n . P a r t o r a l l o f the cost o f t h i s cleanup i s o f f s e t by the v a l u e o f the recovered byproducts,—ammonia, phenols, hydrogen cyanide, aroma t i c s , t a r o i l , t a r , and s u l f u r . The gas cleanup i n a W i n k l e r o r Koopers-Totzek g a s i f i e r i s considerably simpler. W i n k l e r . The Winkler r e a c t o r i s a f l u i d i z e d bed, as shown i n F i g u r e 9. The c o a l i s p u l v e r i z e d b e f o r e b e i n g fed to the bed, and the f l u i d i z i n g medium i s steam and oxygen, o r steam and a i r . The r e a c t o r has no i n t e r n a l moving p a r t s , i s q u i t e s i m p l e , and has a w e l l - e s t a b l i s h e d r e p u t a t i o n f o r r e l i a b i l i t y . The r e a c t o r must operate i n the non-slagging mode to keep the bed f l u i d i z e d , and so i s l i m i t e d to c o a l s w i t h reasonably h i g h ash f u s i o n temp e r a t u r e s . Since the o p e r a t i o n i s not c o u n t e r c u r r e n t , the gas would leave the r e a c t o r a t r e a c t i o n temperature, but an i n t e r n a l heat exchanger i n the gas space above the bed removes some heat and drops the gas temperature. The c h i e f disadvantage o f the Winkler r e a c t o r i s i t s atmospheric p r e s s u r e o p e r a t i o n , b u t the l i c e n s o r i s working on a pressure m o d i f i c a t i o n . Because the c o a l i s brought r a p i d l y to r e a c t i o n temperature and the p y r o l y s i s products are exposed to the f u l l temperature, the Winkler r e a c t o r produces no t a r s o r phenols, and very l i t t l e methane. A t y p i c a l gas composition from bituminous c o a l i s (dry and s u l f u r - f r e e ) : CO£

21 volume %

CO

33

H

41

2

CH

4

3

N , Ar, etc.

2

2



LIQUOR

LIQUOR

LIQUOR

GAS

TARRY

GAS

GAS

OILY

WASH WATER

LIQUOR

LIQUOR

DUST

UNIT

SEPARATOR

REMOVAL

TAR

GAS

VESSEL

EXPANSION

GAS

LIQUOR

GAS

Figure 6. Gas liquor separation

TANK

LIQUOR

STORAGE

LIQUOR

SEPARATOR

FINAL GAS

SEPARATOR

GAS

4j~LoiL

—,

NH-J S C R U B B E R


GAS

LIQUOR

• EXPANSION GAS

HIPKIN



20.


403


S T R E T F O R D UNIT


HiPKiN



20.

Figure 9. Winkler gasifier


405

406

P H A S E EQUILIBRIA A N D


CHEMICAL

INDUSTRY


Most of the ash leaves the r e a c t o r w i t h the gas, so that p a r t i c u l a t e removal i s a more d i f f i c u l t problem than w i t h the L u r g i reactor. Koppers-Totzek. In t h i s r e a c t o r , shown i n F i g u r e 10, f i n e l y powdered c o a l i s e n t r a i n e d w i t h the oxygen i n t o a burner s u r rounded by steam j e t s . The r e a c t i o n temperature i s about 2700°F, no t a r s , phenols, a r o m a t i c s , or ammonia are produced. The react i o n temperature i s above the f u s i o n p o i n t of the ash, and about h a l f the ash i s tapped o f f as a molten s l a g ; the r e s t i s c a r r i e d over w i t h the gas. A t y p i c a l dry and s u l f u r - f r e e gas composition from bituminous c o a l i s C0

2

12 volume %

CO

53

H

33

2

CH. 4 N , Ar, etc. 2

0.2 1.5

The h i g h e r r e a c t i o n temperature r e s u l t s i n more CO and l e s s C 0 and CH4, as compared to the L u r g i or Winker r e a c t o r s . The K-T i s an atmospheric pressure r e a c t o r , but S h e l l i s working w i t h Koppers to develop a p r e s s u r i z e d model. The gas from the r e a c t o r i s quenched enough to s o l i d i f y the molten ash d r o p l e t s b e f o r e they reach the waste-heat b o i l e r , mounted d i r e c t l y above the g a s i f i e r . A spray washer cools the gas from 500°F to about 95°F a f t e r the b o i l e r . At t h i s temperature, the gas goes through two Thiessen d i s i n t e g r a t o r s , which mechanic a l l y a g i t a t e the gas w i t h water to remove more p a r t i c u l a t e s . A demister f o l l o w s the d i s i n t e g r a t o r s and, i f the gas i s to be compressed, the demister i s f o l l o w e d by 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 . The gas i s then t r e a t e d to remove s u l f u r , u s i n g any of a number of d i f f e r e n t processes, i n c l u d i n g dry i r o n o x i d e , S u l f i n o l , or R e c t i s o l . I t i s then s h i f t converted and carbon d i o x i d e i s removed (Figure 11). Obviously, the gas p u r i f i c a t i o n r e q u i r e d f o r W i n k l e r or Koppers-Totzek i s s i m p l e r than that f o r L u r g i , although the problem of p a r t i c u l a t e removal i s worse. The condensates from these processes must s t i l l be t r e a t e d to remove contaminants. 2

New G a s i f i c a t i o n Processes There are about a dozen g a s i f i c a t i o n processes under development i n t h i s country and i n Europe. A number of them have reached the stage of l a r g e p i l o t p l a n t s . The one that i s probably c l o s e s t to c o m m e r c i a l i z a t i o n i s the Texaco p a r t i a l o x i d a t i o n process. Texaco and S h e l l have both l i c e n s e d p a r t i a l o x i d a t i o n processes f o r use w i t h a v a r i e t y of petroleum feeds s i n c e the l a t e 1940 s, and over 250 g a s i f i e r s have been i n s t a l l e d , l a r g e l y f o r making f


Storvick and Sandler; Phase Equilibria and Fluid Properties in the Chemical Industry ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Figure 10. Koppers-Totzek gasifier



A N D F L U I D PROPERTIES



408

Figure 11.

Koppers-Totzek gas cleanup system


20.


HIPKIN

409

hydrogen as ammonia p l a n t feed. The process has been p a r t i c u l a r l y u s e f u l f o r g a s i f y i n g h i g h s u l f u r , h i g h m e t a l l i c content r e s i d s . R e c e n t l y , Texaco has t e s t e d through the p i l o t p l a n t stage, and has announced the a v a i l a b i l i t y f o r l i c e n s i n g o f a m o d i f i c a t i o n to gasify coal (3). The other processes under development, the main ones being Hygas, C0 -Acceptor, Synthane, Bi-Gas, COED, COGAS, Atgas-Patgas, Molten S a l t , B&W, and Exxon C a t a l y t i c , are designed w i t h three main o b j e c t i v e s i n mind: Downloaded by NANYANG TECHNOLOGICAL UNIV on June 10, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0060.ch020

2

to operate under pressure to c r e a t e modules l a r g e enough to supply gas f o r s y n t h e t i c f u e l s p r o d u c t i o n (a moderate s i z e s y n t h e t i c gas p l a n t would r e q u i r e 20 L u r g i g a s i f i e r s , o r 10 K-T g a s i f i e r s ) to maximize p r o d u c t i o n o f methane, and to minimize p r o d u c t i o n of other byproducts, such as o i l s , t a r , phenols, hydrogen cyanide, e t c . The advantages of pressure o p e r a t i o n are that i t e l i m i n a t e s the need t o compress the gas as much, and that i t i n c r e a s e s the amount of methane i n the product from the g a s i f i e r , thus reducing the subsequent l o a d on the methanation f a c i l i t i e s . The advantages o f pressure o p e r a t i o n are most pronounced f o r p r o d u c t i o n o f high-BTU gas, but are a l s o c o n s i d e r a b l e f o r p r o d u c t i o n o f methanol, ammonia, and hydrogen f o r subsequent hydrogenation. The e q u i l i b r i u m o f the methane-forming r e a c t i o n s i s b e t t e r under p r e s s u r e , but o f more importance i s the f a c t that the heat l o a d (that i s , the amount o f oxygen required) i s reduced i f methane i s made d i r e c t l y r a t h e r than carbon monoxide and hydrogen. Shale O i l A r i c h o i l s h a l e from the Piceance Creek B a s i n runs 30 o r 35 g a l l o n s per ton ( F i s h e r a s s a y ) , and l i e s , g e n e r a l l y , deep i n the f o r m a t i o n , — f r o m 200 to 2000 f e e t deep. To supply a s m a l l r e f i n e r y of 100,000 b a r r e l s per day c a p a c i t y , 140,000 tons per day of t h i s r i c h s h a l e must be mined. This i s a l a r g e o p e r a t i o n , much b i g g e r than the l a r g e s t underground c o a l mines i n the country, and l a r g e r than any s i n g l e open-pit o p e r a t i o n i n the western s t a t e s . The only l a r g e r o p e r a t i o n on t h i s c o n t i n e n t i s the Syncrude t a r sands proj e c t i n northern A l b e r t a , a t 250,000 tons per day. Furthermore, the spent s h a l e from such a mine amounts t o about 125,000 tons per day, and i s a f i n e , dry dust occupying more volume than the o r i g i n a l o i l s h a l e . This dust has to be disposed of somehow, and t o keep i t from blowing a l l over the S t a t e o f Colorado, i t has to be soaked w i t h w a t e r , — i n an a r i d country. Since 90% o f the s h a l e i n the B a s i n l i e s below a reasonable l e v e l f o r s t r i p mining, and s i n c e shaft-and-tunnel mining i s c o n s i d e r a b l y more expensive than


410

P H A S E EQUILIBRIA A N D F L U I D PROPERTIES I N C H E M I C A L INDUSTRY

OIL RECOVERY


AIR MAKE-UP COMPRESSOR

OiL SHALE RUBBLE BARRIER

5.o.^iVvfo,

'^M 'g§o c

OIL SUMP AND PUMP

Figure 12.

Oxy oil shale process retort operation



20.

HIPKIN


411

open-pit mining, there i s a r e a l i n c e n t i v e f o r an i n - s i t u r e t o r t ing o p e r a t i o n which e l i m i n a t e s the n e c e s s i t y to mine the s h a l e a t all. A number o f concepts f o r i n - s i t u r e t o r t i n g have been proposed. The best developed concept i s shown i n F i g u r e 12. A chamber i s mined out, e i t h e r i n the rock above o r below the formation, o r i n the upper o r lower o i l s h a l e s t r a t a , o r both, and s h a f t s are bored i n t o the s h a l e . Large amounts of c o n v e n t i o n a l e x p l o s i v e s a r e detonated throughout the s h a l e to break i t up. The formation i s thus rendered porous enough to permit the flow o f gas through i t , w h i l e the i n t a c t surrounding s h a l e w a l l s c o n f i n e the gas and pyrol y s i s products. Each such r e t o r t i s , t y p i c a l l y , 300 x 300 x 500 feet. In one concept, a i r i s pumped down through the formation w h i l e the upper s u r f a c e i s heated to i g n i t i o n temperature w i t h gas o r propane burners. Once i g n i t i o n s t a r t s , the process i s s e l f - s u s t a i n i n g . The hot gases i n f r o n t of the flame heat the shale to r e t o r t i n g temperature and p y r o l y z e i t , l e a v i n g a carbonaceous r e s i d u e which supports combustion when the flame reaches i t . The hot spent s h a l e behind the flame f r o n t preheats the a i r , and the c o l d u n r e t o r t e d s h a l e i n f r o n t of the r e t o r t i n g zone cools the combustion gases and (at l e a s t i n i t i a l l y ) serves to condense the l i q u i d products, which are c o l l e c t e d a t the bottom of the r e t o r t and pumped to the s u r f a c e . An i d e a l i z e d temperature g r a d i e n t f o r an a c t i v e r e t o r t i s shown i n F i g u r e 13. To m a i n t a i n continuous prod u c t i o n , s e v e r a l r e t o r t s are i n d i f f e r e n t stages o f development a t any given time, w i t h one being mined, another being r u b b l i z e d , and a t h i r d i n o p e r a t i o n . I n p r a c t i c e , the hot gases from a r e t o r t i n which the flame f r o n t i s approaching the bottom would most l i k e l y be d i r e c t e d up through a second completed r e t o r t w a i t i n g to be f i r e d , so that the l i q u i d products can be condensed without u s i n g c o o l i n g water. The problem w i t h t h i s scheme i s that the gas from such a r e t o r t has a low h e a t i n g v a l u e , — p r o b a b l y around 50 BTU per c u b i c f o o t , and p o s s i b l y approaching the lower flammable l i m i t . There i s an enormous amount o f t h i s gas, and i t cannot be d i s c a r d e d because: i t i s contaminated w i t h hydrogen s u l f i d e and ammonia i t represents an a p p r e c i a b l e f r a c t i o n of the h e a t i n g value o f the o i l s h a l e . For example, i n a goods i z e d o p e r a t i o n , the f u e l o i l e q u i v a l e n t o f the r e t o r t gas could be 20,000 b a r r e l s per day. To i n c r e a s e the h e a t i n g value o f the gas, and to reduce i t s volume, the gas can be r e c i r c u l a t e d from the r e t o r t through a heater and back t o the r e t o r t . I n t h i s case, no a c t u a l combustion occurs i n the r e t o r t , and the carbon r e s i d u e i s l e f t behind. P a r t o f the gas make i s used to f i r e the heater; the remainder i s a v a i l a b l e f o r steam g e n e r a t i o n , o r f o r s a l e . Obviously, the a d d i t i o n of the heaters i n c r e a s e s the c a p i t a l c o s t , but the i n c r e a s e d cost may be o f f s e t by the i n c r e a s e d v a l u e o f the h i g h BTU gas. A l l of the gas


412


IN C H E M I C A L

INDUSTRY



RUBBLE P R E H E A T Z O N E

I

I

I

1

I

TEMPERATURE-

Figure 13.

Idealized temperature gradient for in-situ retorting



20.

HIPKIN


413

must be t r e a t e d f o r s u l f u r and ammonia removal; and the water produced from the r e t o r t must be t r e a t e d before discharge. The rock m a t r i x o f western o i l shale i s l a r g e l y carbonate, and during r e t o r t i n g i t i s p a r t l y decomposed. I n some cases, i t may be necessary t o scrub the carbon d i o x i d e from the gas to i n c r e a s e i t s h e a t i n g v a l u e . The base rock of eastern o i l shales is s i l i c a t e . The shale o i l produced i s a viscous m a t e r i a l that r e q u i r e d hydrogenation t o e l i m i n a t e s u l f u r , n i t r o g e n , and oxygen, to reduce i t s v i s c o s i t y , and t o improve i t s s t a b i l i t y . The hydrogenation w i l l be done a t the p r o d u c t i o n s i t e to improve the p r o p e r t i e s of the shale o i l before p i p e l i n i n g to a r e f i n e r y . Hydrogenated shale o i l i s a reasonable s u b s t i t u t e f o r crude o i l , and s t i l l r e q u i r e s refining. What are the Data Needs? Three areas where more thermodynamic data are needed are f r e e energies and e n t h a l p i e s of formation; h i g h temperature and high pressure r e g i o n , p a r t i c u l a r l y w i t h p o l a r mixtures; and the cryogenic r e g i o n f o r c e r t a i n mixtures. Free Energies and E n t h a l p i e s o f Formation. Coal i s the b a s i s f o r s e v e r a l of the s y n f u e l s , and probably w i l l be the most important one d o m e s t i c a l l y . Coals vary t r e m e n d o u s l y , — f r o m l i g n i t e to a n t h r a c i t e ; and i n a l l o f i t s forms c o a l i s more r e a c t i v e than g r a p h i t e , which i s the thermodynamic standard s t a t e f o r carbon. In view of the very l a r g e d i f f e r e n c e s i n r e a c t i v i t y , the i n d u s t r y w i l l need b e t t e r heats and f r e e energies o f formation, probably as d i f f e r e n c e s between g r a p h i t e and carbon i n the c o a l , to p r e d i c t r e l i a b l e chemical e q u i l i b r i a and heat requirements. A f i r s t step i s a t a b u l a t i o n o f such data f o r a representat i v e v a r i e t y o f c o a l s . A second step i s the c o r r e l a t i o n o f these data a g a i n s t some e a s i l y measured p r o p e r t i e s o f c o a l , so that the f r e e energy and enthalpy of formation can be p r e d i c t e d f o r a new c o a l from some simple l a b o r a t o r y measurements. The same type of formation i s needed f o r s h a l e s , s i n c e i t can be a n t i c i p a t e d that shales from v a r i o u s sources w i l l vary c o n s i derably. The problem here i s complicated by the need to d i s t i n guish between organic and i n o r g a n i c carbon i n s h a l e s . A f u r t h e r c o m p l i c a t i o n , f o r both coals and s h a l e s , i s that the r e a c t i v i t y of the carbon v a r i e s as g a s i f i c a t i o n proceeds and that f o r accurate work the p r e d i c t i o n of t h i s v a r i a t i o n i s necessary. High-Temperature, High-Pressure Region. The g a s i f i c a t i o n processes are d i s t i n g u i s h e d from the more f a m i l i a r petroleum r e f i n i n g processes by much higher temperatures, and by the f a c t that mixtures c o n t a i n i n g p o l a r compounds are i n v o l v e d . Processing pressures are no higher than many encountered i n petroleum work, but the d i f f e r e n t types o f compounds handled add an e x t r a complexi t y t o the high pressure o p e r a t i o n s .



414




Very few r e f i n e r y operations operate about 800°F. The c o a l g a s i f i c a t i o n processes, on the other hand, s t a r t a t about 1300°F and some operate up to n e a r l y 3000°F. Many o f the new processes operate a t pressures of about 1000 p s i a . R e l i a b l e zero pressure e n t h a l p i e s up to these temperatures a r e a v a i l a b l e f o r most of the m a t e r i a l s found i n g a s i f i e r s , but the mixing r u l e s and pressure c o r r e c t i o n s which the trade has been using f o r nonpolar mixtures are probably inadequate. Another c o m p l i c a t i o n i s that the systems found i n g a s i f i e r s are r e a c t i n g systems a t high temperatures. I n a d d i t i o n to the heterogeneous r e a c t i o n s , the homogeneous gas phase has many p o s s i b l e r e a c t i o n s such as: CO + H 0 = C 0 + H 2

2

2

CH + H 0 = CO + 3H 4

2

2NH = N 3

2

+ 3H

2

2

and these r e a c t i o n s a r e c a t a l y z e d by the ash components and a r e promoted by the l a r g e area s o l i d surfaces of the coke. For some designs, i t may be necessary to p r e d i c t the chemical e q u i l i b r i a i n these systems. V a p o r - l i q u i d e q u i l i b r i u m p r e d i c t i o n s i n these systems are p a r t i c u l a r l y i n t e r e s t i n g , and w i l l r e q u i r e some d i f f e r e n t techniques than the ones that the petroleum i n d u s t r y has used. At the high pressures of the second generation g a s i f i e r s , water s t a r t s to condense as the gas i s cooled to about 500°F, and continues to condense down to the lowest temperature, probably around 100 F. The condensate contains a p p r e c i a b l e q u a n t i t i e s of hydrogen s u l f i d e and carbon d i o x i d e , probably a l l of the ammonia, p o s s i b l y phenols and cyanides. Depending on the type of g a s i f i e r , a hydrocarbon phase may a l s o c o n d e n s e , — r a n g i n g from t a r to benzene. I n some u n l i k e l y circumstances, two hydrocarbon phases may separate, one l i g h t e r and one h e a v i e r than water. The mutual s o l u b i l i t y of the phases i s a f f e c t e d by the d i s s o l v e d components, a l l of which a r e s o l u b l e i n a l l the phases. And the e q u i l i b r i u m c a l c u l a t i o n s are f u r t h e r complicated by r e a c t i o n s i n the l i q u i d water phase, between the a c i d i c and b a s i c components. The L u r g i gas cleanup system, shown i n Figures 2, 3, and 4, i s a good example of the problems i n v o l v e d . Each of the f i v e counter-current exchangers represents a s e r i e s of complicated, simultaneous e q u i l i b r i u m and heat t r a n s f e r c a l c u l a t i o n s f o r a p o l a r mixture, w i t h a three- and p o s s i b l y four-phase system. ( I f the s o l i d f i n e s are considered, the system i s f o u r , p o s s i b l y f i v e phases; but the s o l i d phase, which most l i k e l y stays w i t h the t a r , i s g e n e r a l l y neglected.) N e i t h e r the a v a i l a b l e enthalpy data, nor the a v a i l a b l e e q u i l i b r i u m c o r r e l a t i o n s , a r e r e a l l y adequate f o r such m i x t u r e s , and the problems would be worse i f the pressures were h i g h e r , as they may be i n the f u t u r e . This i s not to say that


20.

HIPKIN


415


L u r g i cannot design such a system; o b v i o u s l y they have, the p l a n t s so designed do work. E i t h e r L u r g i uses p r o p r i e t a r y data, o r they design from past experience; i n e i t h e r case, t h e i r techniques a r e not a v a i l a b l e to the t e c h n i c a l p u b l i c . Nor i s i t known how much s a f e t y i s b u i l t i n t o t h e i r designs. Cryogenic Region. A t the low end of the temperature s c a l e , there are other data needs. Here, the designer needs r e l i a b l e data f o r a s m a l l number o f simple systems. And he needs data on s o l i d - l i q u i d phase r e l a t i o n s f o r a few m a t e r i a l s , notably carbon d i o x i d e , hydrogen s u l f i d e , and the higher hydrocarbons. The c h i e f area where these data (or c o r r e l a t i o n s ) are r e q u i r e d has been f o r l i q u i f i e d n a t u r a l gas p l a n t s . I t would appear t h a t the a v a i l a b l e data should be adequate, s i n c e there i s a l o t o f i n f o r m a t i o n on the l i g h t hydrocarbons; but, i f the reader has not done i t , he w i l l be u n p l e a s a n t l y s u r p r i s e d to f i n d how much the s p e c i f i c heat of methane gas a t low temperatures v a r i e s between v a r i o u s p r e d i c t i o n methods. He w i l l a l s o f i n d that i t i s d i f f i c u l t to p r e d i c t where carbon d i o x i d e c r y s t a l l i z e s out of the l i q u i d hydrocarbon phase as n a t u r a l gas i s cooled. Since deep r e f r i g e r a t i o n i s expensive, cryogenic p r o c e s s i n g r e q u i r e s accurate c o r r e l a t i o n s . Exxon has r e c e n t l y p u b l i s h e d a paper on t h e i r new c a t a l y t i c g a s i f i c a t i o n process, i n which c o a l impregnated w i t h potassium carbonate i s g a s i f i e d w i t h steam and oxygen a t a low temperature (1200-1300°F) and a pressure of about 500 p s i ( 4 ) . Under these c o n d i t i o n s , the p r o d u c t i o n o f methane i s maximized, and the overa l l r e a c t i o n i s almost i s e n t h a l p i c . The carbon d i o x i d e and methane are separated from the carbon monoxide and hydrogen, which are r e c y c l e d to the r e a c t o r . The s e p a r a t i o n of methane from carbon monoxide and hydrogen i s cryogenic and, f o r good economy, r e q u i r e s r e l i a b l e enthalpy and e q u i l i b r i u m data. Almost any cryogenic s e p a r a t i o n design becomes, a t some p o i n t , a balance between heat exchange costs and compression c o s t s . And the optimum (minimum t o t a l cost) u s u a l l y occurs a t exchanger temperature d i f f e r e n c e s of only a few degrees, sometimes only a f r a c t i o n o f a degree. To design exchangers to these c l o s e approaches r e q u i r e s very accurate e q u i l i b r i a data, and good e n t h a l py data. I f the p l a n t uses a mixed r e f r i g e r a n t , the need i s more pronounced. How

Good Do the Data Need to Be?

For the high temperature p o l a r mixtures a t h i g h p r e s s u r e s , the need i s p r i m a r i l y f o r p r e d i c t i o n methods that can be f a i r l y sloppy, but even more important i s some knowledge o f the degree of u n c e r t a i n t y i n the method. The design engineer faced w i t h c a l c u l a t i n g the enthalpy o f a mixture o f CO, CO2, H , and CH4 w i t h 50% steam a t 1000 p s i a and 1500°F w i l l probably take the four gases at zero pressure and 1500°F, use some g e n e r a l i z e d pressure c o r r e c t i o n to r a i s e the mixture to 500 p s i a , and add the enthalpy o f 2



416

P H A S E EQUILIBRIA AND


CHEMICAL

INDUSTRY

pure steam a t 500 p s i a and 1500°F. Or, he may take a l l f i v e components at zero pressure (1 p s i a f o r the steam because he i s u s i n g steam t a b l e s ) and 1500°F, and use the g e n e r a l i z e d pressure c o r r e c t i o n to r a i s e the mixture to 1000 p s i a . I f he does both, he w i l l have two d i f f e r e n t answers. I f he uses d i f f e r e n t pressure c o r r e c t i o n s , he w i l l have more d i f f e r e n t answers. I f he i s knowl e d g a b l e , he w i l l worry a l i t t l e about the f a c t that the pressure c o r r e c t i o n i s based on l i g h t hydrocarbons, or on a i r . I f he checks, he w i l l f i n d t h a t the e f f e c t of pressure on the enthalpy of steam, from h i s steam t a b l e s , i s badly p r e d i c t e d by the genera l i z e d c o r r e l a t i o n . What he needs i s some method which t e l l s him that h i s c a l c u l a t e d enthalpy has a reasonable p r o b a b i l i t y of being o f f by, say, + 10%. Given that u n c e r t a i n t y , he can design enough s a f e t y f a c t o r i n t o the u n i t to take care of i t . H i s problem occurs when he b e l i e v e s h i s c a l c u l a t e d enthalpy and i t i s r e a l l y o f f by 10%. L a t e r , as the s y n f u e l i n d u s t r y becomes more s o p h i s t i c a t e d , b e t t e r accuracy w i l l be needed. The heat flows around a l a r g e g a s i f i e r p l a n t are immense, and much of t h a t heat i s s u p p l i e d from expensive oxygen r e a c t i n g w i t h the c o a l . A high-BTU syngas p l a n t producing 250 m i l l i o n standard c u b i c f e e t per day of gas a l s o produces about 15,000 tons per day of carbon d i o x i d e , e q u i v a l e n t to a heat of combustion of 5 b i l l i o n BTU per hour. To a v o i d l a r g e and expensive s a f e t y f a c t o r s i n the design of such p l a n t s , a c c u r ate enthalpy methods w i l l be needed. For cryogenic s e p a r a t i o n s , i n d u s t r y already has the a p p r o x i mate methods. What i s needed now i s accurate data and methods to reduce the cost of unnecessary s a f e t y f a c t o r s on expensive deep r e f r i g e r a t i o n . The i n d u s t r y a l s o needs techniques to p r e d i c t s o l i d phase formation. When Are the Data Needed? The petroleum i n d u s t r y and the n a t u r a l gas p r o c e s s i n g indust r y operated f o r about 40 years b e f o r e any r e a l attempt to develop data and c o r r e l a t i o n s was made. They used crude approximations, such as Raoult's and Dalton's Laws, because they were good enough for the p r o c e s s i n g that the i n d u s t r y was doing a t t h a t time. As p r o c e s s i n g became more complex, b e t t e r data were needed and were d e v e l o p e d , — a trend that s t i l l continues. The s y n t h e t i c f u e l i n d u s t r y cannot undergo a comparable i n c u b a t i o n p e r i o d f o r i t s data requirements f o r two main reasons: 1. The s y n t h e t i c f u e l s are intended to augment petroleum f u e l s that are p r e s e n t l y produced by s o p h i s t i c a t e d proc e s s i n g techniques based on adequate thermodynamic data. 2. S y n t h e t i c f u e l p l a n t s w i l l be horrendously expensive, and there i s a l a r g e economic i n c e n t i v e to provide data good enough to e l i m i n a t e expensive s a f e t y f a c t o r s from the design.


20.

HIPKIN

Thermo dynamic Data Needs

417


Literature Cited 1. Musser, William N., and John H. Humphrey, "In-Situ Combustion of Michigan Oil Shale: Current Field Studies", Eleventh Intersociety Energy Conversion Engineering Conference, page 341 (1976). 2. "Joint Application of Michigan-Wisconsin Pipeline Company and ANG Coal Gasification Company for Certificates of Public Convenience and Necessity", Docket No. CP75-278 before the Federal Power Commission, Volume 1 (1975). 3. Crouch, W. G., and R. D. Klapatch, "Solids Gasification for Gas Turbine Fuel: 100 and 300 BTU Gas", Eleventh Intersociety Energy Conversion Engineering Conference, page 268 (1976). 4. Epperly, W. R., and Siegel, H. M., "Catalytic Coal Gasification for SNG Production", Eleventh Intersociety Energy Conversion Engineering Conference, page 249 (1976).


Discussion


C. A. ECKERT

Two papers given i n t h i s s e s s i o n assessed the severe problems encountered by s c i e n t i s t s and engineers i n d e a l i n g w i t h processing under unusual c o n d i t i o n s . Mike M o d e l l s paper s t r e s s e d the d i f f i c u l t i e s thermodynamicists have i n d e a l i n g w i t h multicomponent systems i n the c r i t i c a l r e g i o n . He reviewed the c r i t e r i a f o r c r i t i c a l i t y i n multicomponent systems and developed the use of Legendre transformations to f i n d a s t a b l e p o i n t on the s p i n o d a l s u r f a c e . Much of the d i s c u s s i o n f o l l o w i n g the paper centered about whether one could use the same type of approach to determine the b i n o d a l s u r f a c e — t h a t i s , i n a p r a c t i c a l sense, f i n d the compos i t i o n of c o e x i s t i n g phases. Some comments on t h i s problem were as follows: H. Ted Davis, U n i v e r s i t y of Minnesota, "The s p i n o d a l c o n d i t i o n s are u s e f u l i n c o n s t r u c t i n g the b i n a r y and ternary phase d i a grams. M e i j e r i n g (_1) has used the s p i n o d a l e x t e n s i v e l y to l o c a t e c r i t i c a l p o i n t s f o r r e g u l a r s o l u t i o n s . Once the c r i t i c a l p o i n t i s l o c a t e d , then a simple numerical technique can be used to march along a b i n o d a l to c o n s t r u c t the b i n o d a l curve. Overlapping b i n o d a l s can then be used to l o c a t e three phases i n e q u i l i b r i u m , where such e x i s t . Such a process i s being c a r r i e d out f o r l i q u i d phase diagrams by J e f f K o l s t a d working w i t h C. E. S c r i v e n and me at Minnesota." John S. Rowlinson, U n i v e r s i t y of Oxford, United Kingdom, " I would l i k e to make two p o i n t s : I. By c o n c e n t r a t i n g on the s p i n o d a l s u r f a c e , as Modell and Reid's elegant transformations do, one runs the r i s k of overl o o k i n g other kinds of behavior on c r i t i c a l s u r f a c e s . For example, the s p i n o d a l curve may be o u t s i d e one of the b i n o d a l curves. This does happen w i t h the ternary diagram f o r which G i s q u a d r a t i c i n composition, a system which was analyzed f u l l y by M e i j e r i n g (_1). Here, there a r e three t r i c r i t i c a l p o i n t s , and i t i s the presence of these, which a r e s i n g u l a r i t i e s not envisaged i n G i b b s treatment, which would i n v a l i d a t e the use of the s p i n o d a l alone as a s o l e c r i t e r i o n of c r i t i c a l behavior. 2. The Gibbs (and r e l a t e d ) treatments assume that the extenT

E

f

418


ECKERT

419

Discussion

s i v e thermodynamic f u n c t i o n s form an a n a l y t i c s u r f a c e U = f(V,S,N^) around the c r i t i c a l p o i n t . This assumption c o n f l i c t s w i t h the known e x i s t e n c e of "weak" s i n g u l a r i t i e s at t h i s p o i n t (e.g., Cy oo) . In a mixture these s i n g u l a r i t i e s can g i v e r i s e to complic a t i o n s not, I t h i n k , encompassed i n M o d e l l s treatment. Thus, R. B. G r i f f i t h s and Wheeler (_2) have suggested that there are "anomalies" on a g a s - l i q u i d c r i t i c a l curve f o r a b i n a r y mixture, not only at the c r i t i c a l azeotrope but a l s o at p o i n t s where the c r i t i c a l curve passes through the extremum w i t h respect to changes of pressure or temperature." The second paper of the evening given by Howard H i p k i n of B e c h t e l Corporation complimented the f i r s t i n that i t s t r e s s e d , from a much more p r a c t i c a l p o i n t of view, s p e c i f i c needs that w i l l be encountered i n the near f u t u r e by i n d u s t r i a l designers d e a l i n g w i t h methods f o r energy recovery from f o s s i l f u e l s . He discussed what s y n t h e t i c f u e l s might be, and how they might be made, and from what we know about such processes now p r e d i c t e d what they indeed might be. He s t r e s s e d the need f o r heats of formation and Gibbs energies of formations at higher temperatures, e s p e c i a l l y f o r c o a l and o i l s h a l e ; f o r high temperature and pressure data e s p e c i a l l y for p o l a r mixtures; and the need f o r c a l c u l a t i o n a l methods f o r handling such data. As one example he held f o r t h the spectre to an a n a l y s t of a five-phase system emerging from a L u r g i g a s i f i e r . Rather extensive d i s c u s s i o n i n v o l v i n g a number of i n d i v i d u a l s f o l l o w e d d e a l i n g w i t h the imminent needs f o r new energy sources w i t h s m a l l l i k e l i h o o d of i t being s a t i s f i e d by n u c l e a r , s o l a r , or geothermal power. However, severe problems e x i s t i n the u t i l i z a t i o n of c o a l or o i l shale i n terms of high c a p i t a l requirements coupled w i t h the environmental r e s t r i c t i o n s on emissions from such p l a n t s . One q u i t e c o n s i d e r a b l e dilemma that becomes apparent i s that the production of energy from s y n t e h t i c f u e l s w i t h our current technology would only be p r a c t i c a l at c u r r e n t c a p i t a l c o s t s i f the s e l l i n g p r i c e of energy went up. However, i t i s q u i t e evident that c a p i t a l costs are l i n k e d to energy c o s t s . Thus, the consensus of the d i s c u s s i o n was that b e t t e r data are needed at higher temperatures and pressures, and i n the i n i t i a l stages, even r a t h e r "sloppy" data would be more u s e f u l than what i s now a v a i l a b l e . This w i l l r e q u i r e b e t t e r m a t e r i a l s and may lead to new techniques such as, f o r example, s u p e r c r i t i c a l s e p a r a t i o n processes and higher temperature processes. C e r t a i n l y the methods we now have f o r e s t i m a t i n g such p r o p e r t i e s w i l l prove inadequate, and new and b e t t e r methods w i l l c e r t a i n l y be r e q u i r e d . As i l l u s t r a t e d so g r a p h i c a l l y by the f i r s t t a l k of the evening these w i l l undoubtedly be more d i f f i c u l t to develop and apply than current methods. However, the general concensus was that i t i s q u i t e c l e a r that the energy c r i s i s w i l l soon be upon us i n a much more s e r i o u s sense than the general p u b l i c a p p r e c i a t e s , and we as s c i e n t i s t s and engineers must begin now to seek s o l u t i o n s i n terms of new data at more extreme c o n d i t i o n s and the thermodynamic framework w i t h i n which to apply them.


f


420




References


1. Meijering, J. L., Phillips Res. Rep. (1950) 5, 333; (1951) 6, 183. 2. Griffiths, R. B. and Wheeler, J. C. Phys. Rev. (1970) 2, 1047.


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