Chapter 4: Coal gasification for SNG production

C H A P T E R 4: COAL GASIFICATION FOR SNG PRODUCTION %

4.1.

Introduction

4. I - I .

The G r e a t P l a i n s Coal G a s i f i c a t i o n P l a n t (GPCGP)

In t h e e a r l y 1970s, w h e n " P r o j e c t I n d e p e n d e n c e " w a s b e i n g d e f i n e d b y t h e F e d e r a l Gove r n m e n t and s e r i o u s c o n c e r n s w e r e b e i n g r a i s e d about t h e NO r e s e r v e s and l o n g - t e r m s u p p l y of NG, t h e r e w e r e m o r e t h a n 100 m a j o r p r o j e c t s u n d e r c o n s i d e r a t i o n t h a t i n v o l v e d t h e p r o d u c t i o n o£ s u b s t i t u t e n a t u r a l gas (SNG) f r o m c o a l . T h e s e p r o j e c t s g e n e r a l l y i n v o l v e d p l a n t s t h a t would p r o d u c e t h e e q u i v a l e n t o f Z50 m i l l i o n s t a n d a r d cubic f e e t of g a s p e r day ( S C F / d ) w i t h a h e a t i n g v a l u e o f 950-1000 B t u / S C F o S o m e of t h e s e p l a n t s w e r e on a s c h e d u l e t h a t would h a v e p l a c e d t h e m o n s t r e a m in t h e m i d - to l a t e - 1 9 8 0 s . H o w e v e r , t h e w o r l d e n e r g y p i c t u r e c h a n g e d d r a m a t i c a l l y and t h e r e q u i r e m e n t f o r p r o d u c i n g p i p l i n e - q u a l i t y gas f r o m c o a l m o v e d f u r t h e r into t h e f u t u r e . Now, SNG f r o m c o a l i s b e i n g c o n s i d e r e d a s a p o t e n t i a l p i p e l i n e - q u a l l t y g a s s u p p l y o p t i o n f o r t h e p o s t Z000 t i m e f r a m e . As a r e s u l t of c h a n g e s in t h e e n e r g y m a r k e t , only t h e G P C G P w a s c o n s t r u c t e d . T h i s p l a n t is l o c a t e d in B e u l a h , N o r t h Dakota, and w a s d e v e l o p e d t h r o u g h t h e c o m b i n e d e f f o r t s of a c o n s o r t i u m of n a t u r a l g a s c o m p a n i e s and t h e F e d e r a l G o v e r n m e n t . S t a r t - u p o p e r a t i o n s b e g a n in 1984, w i t h a n o m i n a l output of 125 m i l l i o n S C F / d (at a 90% s t r e a m f a c t o r ) of p i p e l l n e - q u a l i t y g a s . T h i s p l a n t u s e s N o r t h Dakota l i g n i t e a s t h e f e e d s t o c k and i t s o p e r a t i o n is b a s e d on d r y b o t t o m L u r g l g a s i f i c a t i o n t e c h n o l o g y t o g e t h e r w i t h c o m m e r c i a l l y a v a i l a b l e m e t h a n a t i o n , gas c o n d i t i o n i n g and c l e a n - u p t e c h n o l o g y . To d a t e , t h e G P C G P i s c l e a r l y a t e c h n i c a l s u c c e s s . 1 It w a s c o n s t r u c t e d w i t h i n c o s t , c o m p l e t e d on s c h e d u l e a n d h a s i n v o l v e d o n l y m i n i m a l p r o b l e m s d u r i n g its i n i t i a l p e r i o d o f o p e r a t i o n . The p l a n t w a s d e s i g n e d to p r o d u c e 137.5 × 106 S C F / d , but h a s o p e r a t e d c o n s i s t e n t l y at l e v e l s e x c e e d i n g t h e o r i g i n a l d e s i g n c a p a c i t y . In M a r c h 1986, t h e p l a n t p r o d u c t i o n w a s a s f o l l o w s : h i g h e s t d a i l y r a t e = 154. 7 × 106 S C F (112.5% o£ d e s i g n ) , h i g h e s t w e e k l y r a t e = 1. 0463 109 S C F (109% of d e s i g n ) , h i g h e s t m o n t h l y r a t e = 4. 536 × 109 S C F (106.4% o f d e s i g n ) . in t h e c u r r e n t e c o n o m i c c l i m a t e r e s u l t i n g f r o m low w o r l d o i l p r i c e s , t h e G P C G P is not economically competitive with other g a s - s u p p l y options. However, the experience gained through t h e c o n s t r u c t i o n and o p e r a t i o n o f t h i s p l a n t is p r o v i d i n g t h e g a s i f i c a t i o n c o m m u n i t y w i t h a b e n c h m a r k of t h e r e a l c o s t s of SNG b a s e d on c o m m e r c i a l l y a v a i l a b l e t e c h n o l o g y . In a d d i t i o n , it is h e l p i n g to i d e n t i f y w h e r e p r o c e s s i m p r o v e m e n t s c a n b e e f f e c t e d t h r o u g h e n g i n e e r i n g c h a n g e s o r p r o c e s s s e l e c t i o n and w h e r e s u p p o r t i n g r e s e a r c h and d e v e l o p m e n t e f f o r t s c o u l d have a n i m p a c t . 4.1-2.

General Thermodynamic Considerations

The a t o m i c r a t i o of H to C in c o a l s is l e s s t h a n one. As a r e s u l t , i n o r d e r to c o n v e r t c o a l to p i p e l i n e - q u a l i t y g a s e f f i c i e n t l y a t a n H / C r a t i o of 4, it is n e c e s s a r y to p r o v i d e a s o u r c e of H Z. T h i s i s u s u a l l y a c c o m p l i s h e d b y the a d d i t i o n of s t e a m . The o v e r a l l r e a c t i o n s c h e m e for p r o d u c i n g p i p e l l n e - q u a l i t y g a s f r o m coal, with w a t e r a s s o u r c e of the n e c e s s a r y h y d r o g e n , r e p r e s e n t e d by coal + H20--~

CH 4 + CO 2.

(4.1-1)

In m o s t g a s i f i c a t i o n p r o c e s s e s , h o w e v e r , t h i s o v e r a l l r e a c t i o n is not r e a l i z e d in a s i n g l e s t e p b u t i s a c c o m p l i s h e d t h r o u g h a s e r i e s o f s t e p s to p r o v i d e r e a c t i o n e n v i r o n m e n t s f o r w h i c h c o n v e r s i o n s p r o c e e d at a c c e p t a b l e r a t e s . T h e s e s t e p s a r e t h e unit o p e r a t i o n s of c o a l - g a s i f l c a t i o n p l a n t s . As r e a c t i o n t e m p e r a t u r e s a r e r a i s e d to h i g h e r v a l u e s ( w h e r e g a s i f i c a t i o n r e a c t i o n s p r o c e e d at a d e q u a t e r a t e s ) , t h e s t a b i l i t y of CH 4 i s r e d u c e d and, at t h e h i g h e r t e m p e r a t u r e s s u c h a s t h o s e a s s o c i a t e d w i t h e n t r a i n e d - f l o w g a s i f i e r s (i. e. lZ50-1370 ° C), t h e r e i s no m e t h a n e p r o d u c t i o n in t h e g a s l f l e r . T y p i c a l o f f - g a s c o m p o s i t i o n s f r o m f l x e d - b e d , f i n i d i z e d - b e d and e n t r a l n e d - f l o w g a s i f i e f s a r e p r e s e n t e d i n T a b l e 4. 1-1, w h i c h s h o w s t h e r a n g e s of m e t h a n e p r o d u c t i o n t h a t c a n b e e x p e c t e d . T h e s e d a t a a l s o p r o v i d e an i n d i c a t i o n of t h e a d d i t i o n a l c o n v e r s i o n to m e t h a n e t h a t m u s t b e a c c o m p l i s h e d in o r d e r to a p p r o a c h t h e o v e r a l l r e a c t i o n s c h e m e r e p r e s e n t e d b y Eq. (4. i-1)o As t h e r e a c t i o n t e m p e r a t u r e i s r a i s e d , t h e r e a c t i o n s t h a t d o m i n a t e t h e g a s i f i c a t i o n p r o c ess include

t T h i s c h a p t e r h a s b e e n w r i t t e n b y K e r m i t E . W o o d c o c k and V e r n o n L. Hill of GRI. 663

664

Energy,

coal

The I n t e r n a t i o n a l J o u r n a l

> CH 4 + char + tars,

oils,

(4.1-2)

char + ~zo

>

char + 0 2

• C O + H2,

(4.1-4)

_ CO z+Hz,

(4.1-5)

cH 4 + H z o "

_co+3~z,

(4.16)

ZCH4 + o z "

. CO+4HZ,

(4.1-7)

" CO? + C .

(4. 1-8)

CO+HzO

"

2CO

_

co + ~z,

~4. l - 3 )

In a d d i t i o n to t h e p r i n c i p a l r e a c t i o n s , w h i c h c o n t r o l t h e c o n c e n t r a t i o n of t h e m a j o r p r o d u c t s of g a s i f i c a t i o n , t h e r e o c c u r a l s o a s e r i e s of r e a c t i o n s i n v o l v i n g t r a c e c o n s t i t u e n t s i n t h e c o a l s , s u c h a s t h e n i t r o g e n , s u l f u r a n d m i n e r a l m a t t e r , w h i c h r e s u l t in t h e f o r m a t i o n of a d d i t i o n a l g a s e o u s s p e c i e s (H2S , NH3, COS, m e r c a p t a n s , s u l f i d e s , e t c . ). T h e n a t u r e of t h e s e a d d i t i o n a l g a s eous s p e c i e s depends on the g a s i f i e r conditions and coal type and m u s t also be dealt with as p a r t of a coal-to-SNG process. W h e n the gasification process is controlled b y the types of reactions represented by F_qs. (4. I-Z) through (4. i-8) and w h e n S N G is the desired end product, additional processing steps are required to convert the C O and H z produced in the gaslfler to methane. T h e principal reactions to accompllsh this conversion are (a) the water gas shift reaction (~VGSI~) of F_q. (4° i-5), which provides the desired initial H 2 / C O ratio and ~) a methanatlon reaction w h i c h m a y proceed according to the following steps: T a b l e 4. 1 - 1 .

Commercial and developmental gasification processes, blown reactant consumption and gas production.

Movlng-bed Gasifiers Parameter

Fluidiz ed -bed Gaslfier

Lurgi BGC slagging dry-ash Lurgi Winkler (commercial) (pilot plant a) (commercial)

oxygen-

Entralned-flow Gasiflers HYGAS (pilot plant a)

KoppersTotzek Texaco (commercial) (pilot planta)

Gas exit T, °C

580

440

700

p, psi

430

290

14.7

Gas analysis, volt CO 2 CO

29.7

2.5

20.0

24.7

7.1

10.6

18.9

60.6

34.0

24.0

58.7

51.6

H2

39.1

27.8

41,0

30.5

32.8

35.1

cH 4

11.3

7.6

3.0

19.4

Other s b

1.0

1.5

2.0

1.4

1.4

2.6

H2/CO volume ratio

2.1

0.46

1.21

1.27

0.56

0.68

Product utilization Equivalent SNG, c nM3/lO00 kg of coal Equivalent CH4, d nM3/1000 kg of coal

340

1290

1290

i000

14.7

580

O. 1

1884

1939

1596

1850

1845

1988

529

517

413

542

462

470

laPilotplants are of various sizes: BGC/Lurgi, 1200 kg/h; HYGAS, 2500 kg/h; Texaco, 6500 kg/h. hThis value includes nitrogen and various impurities (H2S , COS, NHj, etc.). CThe SNG is assumed to be equal to the sun% of the concentrations of H2, CO, and 3 X C H 4 . dTl~e methane potentialis assumed to he equal to the methane (CH4) concentration plus (I/4) of the (H2+ CO) concentration.

Coal G a s i f i c a t i o n for SNG P r o d u c t i o n

co

+ 3H 2

,. C H 4

2CO + 2H 2

coz+4~ z

+

665

HzO,

(4. 1-9)

• CH 4 + CO 2 ,

{4.1-10)

cH 4 + z ~ z o .

(4.1-11)

•

These reactions depend on the overall initial gas composition and the methauatiou catalyst used. Workers at Exxon, through the use of al~ali metal or alkallue earth salts as gasification catalysts and an innovative process concept, were able to provide a reaction environment in the gasifler such that all of the methane was formed in the gasifler itsel~ and additional methanatlon steps were not required (compare Sec. 7.2). However, the methane was stillonly one constltuent of a multl-component gas mixture, and separation and gas clean-up steps were required to develop a final product stream of plpeHne-quallty gas. 4, i-3. General Flow Sheets Because of the heterogeneity of coal, the presence of heteroatoms and interactions of chemical kinetics and thermodynamics, the production of plpeHne-quallty gas from coal requires integration of m a n y process steps, regardless of the type of gasifler employed. Typical block diagrams showing the n u m b e r and sequence of major process steps needed for processes in which methanatlon is required downstream of the gasifler and where all methane formation is achieved in the gasifier, as iu the I~RW and Exxon catalytic processes, are shown in Figs. 4. I-I and 4. i-2; the Exxon process is described in detail iu Sec. 7.2. These diagrams emphasize the importance of effective process integration and indicate that there are m a n y opportunities where process improvements, achieved through continued research and development, can have a positive impact on process conflgurat{ons, capital costs, operating costs and, ultimately, the end-product cost of plpellue-quaHty gas. While all process elements contribute to the final end-product cost of S N G from coal, the gaslfler, methanatlon process and clean-up systems represent major determinants in other process requirements and overall process integration,

coa,,

i Compression .ocOas I'q

ROM

Shift Conversion

Coal Crushing Coal Sizing Coal

Drying Coal Feeding Steam

Convective Heat Recovery

COS Hydrolysis

Fines I / Recy

Quench Scrubbing

Removal

Gasification I . . ~ . ~ . -

Recycle Gas Compression

Removal

Particulate Removal

,~

|

H=S

CO=

Methanation

;

Drying

Air

Separation

CO,

Ash Removal

Compression

I Sour Water Stripping

I

Ammonia Recovery

[

> SNG

Ash Wa

To Re-Use I

I Fig. 4.1-1.

~

1 Ammonia

Sulfur

Recovery

r

I

Sulfur

Tail Gas

C o a l - t o - S N G in the K e l l o g g - R u s t - W e s t i n g h o u s e (KRW) g a s i f i c a t i o n p r o c e s s .

666

Energy,

The I n t e r n a t i o n a l J o u r n a l

ROM Coal I

Coal

Crushing

•p•

Steam

Coal Sizing

Recycle Gas

Compression

I,~ H2S Removal

Coal Drying

Char

CO2

Catalyst Addition

Recovery

Waste Heat Recovery

Catalyzed Coal Drying

Gasification

Raw Gas Scrubbing

' Pre°xidati°n1' I

Catalyst Recovery

Methane Recovery

Ash

Compression

Catalyst Makeup

I

CO2

Removal

ProcessGas Drying

_.~

I

Coal Feeding

Removal

SNG

Sour Water Stripping

Ash

Water To Re-Use

Ammonia Recovery

' D.~

Sulfur

Recovery

/

~

Tail Gas

~ R e q u l r e d for c a k i n g c o a l s .

I Fig. 4 . 1 - Z .

,~ Ammonia

I

~ Sulfur

C o a l - t o - S N G in t h e E x x o n g a s i f i c a t i o n p r o c e s s .

4. Z. A d v a n c e d G a s i f i c a t i o n T e c h n o l o g y f o r SNG T h e d e v e l o p m e n t of g a s i f i c a t i o n t e c h n o l o g y to c o n v e r t c o a l to SNG h a s b e e n t h e s u b j e c t of e x t e n s i v e r e s e a r c h , d e v e l o p m e n t a n d d e m o n s t r a t i o n p r o g r a m s f o r a t l e a s t t h r e e d e c a d e s . In t h e US a n d i n t h e m l d - 1 9 7 0 s , o v e r Z0 c o n v e r s i o n p r o c e s s e s w e r e in v a r i o u s s t a g e s of d e v e l o p m e n t and other approaches were being evaluated in Europe. These efforts encompassed exploratory p r o j e c t s , b e n c h - s c a l e s t u d i e s , e v a l u a t i o n s a t t h e e n g i n e e r i n g - t e s t u n i t (ETU) a n d p r o c e s s d e v e l o p m e n t u n i t (PDU) s c a l e s , p i l o t - p l a n t s t u d i e s , a n d d e t a i l e d d e s i g n s t u d i e s f o r d e m o n s t r a t i o n p l a n t s and p o s s i b l e c o m m e r c i a l o p e r a t i o n s . P r o c e s s c o n c e p t s t h a t h a v e b e e n o r a r e b e i n g e v a l u a t e d i n c l u d e t h e f o l l o w i n g : L u r g i d r y - b o t t o m ( L u r g i GmbPI), B i - G a s ( B i t u m i n o u s Coal R e s e a r c h , I n c . ) , C O z - A c c e p t o r (Conoco Coal D e v e l o p m e n t C o . ) , S y n t h a n e (U.S. B u r e a u of M i n e s ) , HYGAS ( I n s t i t u t e of G a s T e c h n o l o g y ) , COGAS (FMC C o r p o r a t i o n ) , High M a s s F l u x ( B e l l A e r o s p a c e ) , F l a s h H y d r o p y r o l y s i s ( R o c k w e l l I n t e r n a t i o n a l ) , Exxon C a t a l y t i c (Exxon R e s e a r c h and E n g i n e e r i n g ) , W i n k l e r ( K h e i n i s c h e B r a u n k o h l e n w e r k e AGR), U - G a s ( I n s t i t u t e of G a s T e c h n o l o g y ) , KKW A s h A g g l o m e r a t i o n ( W e s t i n g h o u s e / K K W E n e r g y ) , H y d r a n e (U. So B u r e a u of M i n e s ) , S l a g ging F i x e d - B e d ( B r i t i s h Gas C o r p o r a t l o n / L u r g i G m b H ) , F l u l d - b e d H y d r o g a s i f i c a t i o n ( l ~ h e i n i s c h e B r a u n k o h l e n w e r k e AGK), R u h r - 1 0 0 ( R u h r g a s / L u r g l GmbH). E a c h of t h e s e p r o c e s s e s w a s c o n c e i v e d i n a n e f f o r t to i m p r o v e t h e c o m m e r c i a l l y a v a i l a b l e t e c h n o l o g y w i t h r e s p e c t to p r o c e s s efficlency~ f e e d s t o c k u t i l i z a t i o n a n d f l e x i b i l i t y o r to r e duce the potential for unfavorable environmental interactions with the recognition that improved t e c h n o l o g y would t r a n s l a t e into l o w e r e n d - p r o d u c t g a s c o s t s . As t h e R ~ D p r o g r a m s p r o g r e s s e d a n d d a t a b e c a m e a v a i l a b l e for u s e in c o m p a r a t i v e e c o n o m i c e v a l u a t i o n s , w o r k w a s d i s c o n t i n u e d o n m o s t of t h e s e a p p r o a c h e s w h e n i t w a s s h o w n t h a t s u f f i c i e n t e c o n o m i c i n c e n t i v e s c o u l d not b e i d e n t i f i e d to j u s t i f y c o n t i n u e d R&D e x p e n d i t u r e s . Today, a s a r e s u l t of t h e a v a i l a b l e d a t a b a s e s and the supporting economic studies, development work is still proceeding on the ash-agglomera t i n g , f l u l d - b e d t e c h n o l o g y ( U - G a s , KKW a s h - a g g l o m e r a t i n g p r o c e s s ) , t h e B r i t i s h G a s / L u r g i s l a g g i n g g a s i f l e r , a n d t h e K h e l n b r a u n d i r e c t , f l u i d - b e d h y d r o g a s i f l c a t i o n p r o c e s s for SNG p r o d u c t i o n b e c a u s e of t h e u n i q u e c h a r a c t e r i s t i c s of t h e a v a i l a b l e c o s t r e s o u r c e b a s e a n d t h e a d v a n c e d s t a g e of t h e K&D p r o g r a m . Other than the fluid-bed hydrogaslflcation teclmology, continued gasifier development w o r k i s b e i n g j u s t i f i e d p r i m a r i l y b e c a u s e of p r o c e s s f l e x i b i l i t y a n d t h e p o t e n t i a l for a p p l i c a t i o n s in a r e a s o t h e r t h a n SNG p r o d u c t i o n (e. g . , IGCC f o r e l e c t r i c p o w e r g e n e r a t i o n ) . A b r i e f s u m m a r y of t h e t e c h n o l o g i e s s t i l l u n d e r d e v e l o p m e n t , w h i c h c a n b e a p p l i e d to c o a l - t o - S N G p r o c e s s e s , is g i v e n i n the following s u b s e c t i o n s , e x c e p t for the U - G a s p r o c e s s w h i c h is d e s c r i b e d i n d e t a i l i n S e c t i o n 3 . 3 - 3 .

Coal G a s i f i c a t i o n f o r SNG P r o d u c t i o n

4o 2 - 1 .

667

B G C / L u r g l Slagging G a s i f i e r

The B G C / L u r g l s l a g g i n g g a s l f l e r is a f l x e d - b e d g a s i f i e r (Fig. 4 . 2 - 1 ) and c o n s i s t s of a v e r t i c a l c y l i n d r i c a l r e a c t o r into w h i c h c o a l is i n j e c t e d t h r o u g h a l o c k h o p p e r and a r o t a t i n g c o a l d i s t r i b u t o r . The c o a l m o v e s s l o w l y down t h e r e a c t o r in c o n t a c t w i t h g a s e s p a s s i n g c o u n t e r c u r r e n t l y t h r o u g h t h e b e d . A m i x t u r e of s t e a m and o x y g e n is i n j e c t e d at t h e b o t t o m of t h e b e d t h r o u g h n o z z l e s (tuy~res)o The b a s e of the c o a l b e d is c a l l e d t h e r a c e w a y and is t h e l o c a t i o n w h e r e h i g h t e m p e r a t u r e s c a u s e the a s h to m e l t , y i e l d i n g a fluid s l a g w h i c h d r a i n s f r o m t h e h e a r t h t h r o u g h a c e n t r a l l y - p l a c e d s l a g t a p . The s l a g i s q u e n c h e d in a c h a m b e r f i l l e d w i t h w a t e r to f o r m a g l a s s y f r i t and is s u b s e q u e n t l y r e m o v e d via a s l a g lock h o p p e r . The p r e d o m i n a n t r e a c t i o n in t h e r a c e w a y is c o m b u s t i o n of d e v o l a t i l l z e d c o a l , y i e l d i n g a p r o d u c t s t r e a m of hot g a s e s t h a t c o n t a i n s t e a m and c a r b o n o x i d e s . As t h i s gas m o v e s up t h r o u g h t h e f i x e d b e d , c a r b o n is r a p i d l y g a s i f i e d b y s t e a m and c a r b o n d i o x i d e . Since t h e s e r e a c t i o n s a r e highly e n d o t h e r m l c , t h e t e m p e r a t u r e d r o p s r a p i d l y , e f f e c t i v e l y l i m i t i n g the v e r y h i g h t e m p e r a t u r e s l a g l i b e r a t i o n z o n e to a s m a l l a r e a . The s m a l l s l a g l i b e r a t i o n z o n e i s b e n e f i c i a l in r e d u c i n g t h e h e a t l o s s e s and p o t e n t i a l r e f r a c t o r y p r o b l e m s . As t h e g a s e s m o v e u p w a r d in t h e b e d , d i r e c t h e a t t r a n s f e r to t h e c o a l r e s u l t s in p r o g r e s s i v e l y l o w e r t e m p e r a t u r e s , e v e n t u a l l y r e d u c i n g r e a c t i o n r a t e s to t h e p o i n t w h e r e g a s i f i c a t i o n r e a c t i o n s e f f e c t i v e l y s t o p . Above t h i s z o n e , r a p i d h e a t i n g of t h e f r e s h c o a l r e s u l t s only in d r y i n g and d e v o l a t i l i z a t l o n r e a c t i o n s . T h e s e r e a c t i o n s y i e l d t a r s and o i l s , s i g n i f i c a n t a m o u n t s of m e t h a n e , s u l f u r c o m p o u n d s , s t e a m , and o t h e r m i n o r p r o d u c t s , w h i c h a r e c a r r i e d out of t h e g a s l f i e r b y t h e p r o d u c t g a s . The B G C / L u r g i s l a g ging g a s l f l e r o f f e r s p o t e n t i a l a d v a n t a g e s o v e r t h e d r y - b o t t o m L u r g i t e c h n o l o g y s i n c e it c a n a c c o m m o d a t e caking c o a l s m o r e e f f e c t i v e l y , u t i l i z e s c o a l f i n e s , and h a s l o w e r o x y g e n and s t e a m r equir ements. 4.2-Z.

KI~W ( I ~ e l l o g g - t ~ u s t - W e s t i n g h o u s e ) A s h - A g g l o m e r a t i n g , F l u i d i z e d - B e d G a s l f l e r

The I~I%W ( K e l l o g g - R u s t - W e s t i n g h o u s e ) p r o c e s s is a f l u i d - b e d g a s i f i e r (Fig. 4 . 2 - 2 ) in w h i c h coal a n d r e c y c l e d f i n e s a r e r e a c t e d with s t e a m and o x y g e n to f o r m a s y n t h e s i s gas c o n s i s t i u g m a i n l y of CO, CO 2, H 2, CH 4, and s t e a m . The p r o c e s s d e v e l o p m e n t unit (PDU) g a s i f i e r is a v e r t i c a l , r e f r a c t o r y - l l n e d v e s s e l o p e r a b l e up to 230 psig and 1000°C a n d c o n s i s t i n g of f o u r s e c t i o n s : the f r e e b o a r d , g a s i f i e r b e d , c o m b u s t i o n z o n e , and c h a r - a s h s e p a r a t o r . Raw c o a l , g r o u n d to S / 1 6 " × 0 " (and d r i e d to 5% s u r f a c e m o i s t u r e w h e n n e c e s s a r y ) , i s fed p n e u m a t i c a l l y to t h e g a s i f l e r t h r o u g h a l o c k h o p p e r s y s t e m , along w i t h t h e c h a r f i n e s f r o m

Feed Coal Coat =^ ^ " Hop1

Dri Gas Quench

Coal Distributor/ Stirrer actory lg

.~r Jacket Gas (

;team/Oxygen "eed

Press Shell Slag

Tuy~re

Circulati, Quench Water

Slag Quench Chamber

Slag Hopl:

Fig. 4.2-1.

The B G C / L u r g l s l a g g i n g g a s i f i e r .

668

Energy, The International Journal

~ R a w Fuel Gas Product and Fines

T

Freeboard

t 1

Gasifier Bed Auxiliary Steam

]z

Combustor Steam Recycle Gas

-

-

t Char-ash Separator

Oxygen Ash Agglomerates Coal and Transport Gas F i g . 4. 2-Z.

F u n c t i o n a l s c h e m a t i c of t h e W e s t i n g h o u s e g a s l f i e r .

c y c l o n e s d o w n s t r e a m of t h e g a s i f i e r . F e e d i n g i s a c c o m p l i s h e d b y m e a n s of s t a r w h e e l f e e d e r s a n d r e c y c l e g a s . T h e c o a l a n d c h a r a r e fed to t h e g a s i f i e r a l o n g i t s c e n t e r l l n e a n d c o m b u s t e d i n a s t r e a m of o x i d a n t ( o x y g e n o r a i r ) fed t h r o u g h a c o a x i a l f e e d t u b e . W h e n o x y g e n i s e m p l o y e d , steam is used together with the oxidant as the gasifying medium. T h e r e a r e s e v e r a l o t h e r k e y f l o w s into t h e g a s l f l e r , a s s h o w n in F i g . 4. Z - 2 . A flow of s t e a m i s p r o v i d e d b y a n n u l a r flow a r o u n d t h e n o z z l e tip to p r e v e n t c a r b o n d e p o s i t i o n at t h e b a s e of the jet. Additional r e c y c l e gas or s t e a m is injected r a d i a l l y at a location n e a r the rnlddle s e c t i o n of t h e i n j e c t i o n n o z z l e . T h i s flow m i l d l y f l u i d i z e s a n d c o o l s t h e a s h f o r w i t h d r a w a l ; t h e s h a r p t e m p e r a t u r e g r a d i e n t a t t h e c h a r / a s h i n t e r f a c e i s u t i l i z e d to c o n t r o l w i t h d r a w a l r a t e . 1%ec y c l e g a s i s a l s o i n j e c t e d t h r o u g h a s p a r g e r r i n g a t t h e b a s e of t h e a s h b e d to a i d i n a s h w i t h drawal. The coal, char and s t e a m r e a c t i o n s in the g a s l f i e r ~orm hydrogen, c a r b o n oxides and r e s i d u a l s t e a m as the p r o d u c t g a s . The c a r b o n in the char is c o n s u m e d by c o m b u s t i o n and g a s i f i c a t i o n a s t h e b e d of c h a r c i r c u l a t e s t h r o u g h t h e j e t . T h e t e m p e r a t u r e n e a r t h e b o t t o m of t h e b e d i s m a i n t a i n e d h i g h e n o u g h to e n s u r e t h a t t h e a s h - r l c h p a r t i c l e s r e s u l t i n g f r o m r e a c t i o n s s o f t e n , a g g l o m e r a t e a n d d e f l u i d i z e . T h e a g g l o m e r a t e s m i g r a t e to t h e a n n u l u s a r o u n d t h e f e e d t u b e a n d a r e c o n t i n u o u s l y r e m o v e d b y a r o t a r y f e e d e r to l o c k h o p p e r s . T h e m a j o r p o r t i o n of t h e g a s l f l e r o p e r a t e s in a n e s s e n t i a l l y i s o t h e r m a l c o n d i t i o n up to 1 , 0 0 0 °C. T h e l o w e r p o r t i o n of t h e a n n u l u s o p e r a t e s a t a b o u t 2 5 0 ° C ° C a r b o n c o n v e r s i o n i s t y p i c a l l y 90-95% on a n o v e r a l l b a s i s , w h i l e t h e a s h i s c o n c e n t r a t e d to 85% in t h e a g g l o m e r a t e s . T h e r a w p r o d u c t g a s c o n t a i n i n g no t a r s o r o i l s p a s s e s f r o m t h e g a s l f l e r to two r e f r a c t o r y l i n e d c y c l o n e s in s e r i e s , w h e r e t h e c h a r p a r t i c l e s a r e r e m o v e d . T h e f i n e s c o l l e c t e d i n t h e c y c l o n e s a r e c o o l e d , i n s e r t e d into a r e c y c l e g a s s t r e a m a n d r e i n j e c t e d into t h e g a s l f i e r , e i t h e r w i t h t h e c o a l f e e d o r s e p a r a t e l y into t h e l o w e r s e c t i o n of t h e b e d . T h e p r o d u c t g a s i s t h e n q u e n c h e d , c o o l e d a n d s c r u b b e d of a n y r e m a i n i n g f i n e s ( u s u a l l y 190) b e f o r e f u r t h e r p r o c e s s i n g a n d recycling. Experiments at the P D U scale have demonstrated that high conversion efflc~encles can be achieved with a wide variety of feedstocks, including both caking and non-caking coals, and that coal fines can be effectively c o n s u m e d in the gasifler.

Coal G a s i f i c a t i o n f o r SNG P r o d u c t i o n

4. Z-3.

669

l%heinbraun AG, H y d r o ~ a s i f i c a t i o n

l%heinbraun AG h a s b e e n p r o c e e d i n g z with the d e v e l o p m e n t and e v a l u a t i o n of a p r o c e s s to p r o d u c e s u b s t i t u t e NG t h r o u g h the d i r e c t r e a c t i o n of h y d r o g e n and c o a l via the o v e r a l l r e a c t i o n

(4. z-i)

coal + H z -----)CH 4 + char .

T h e o v e r a l l p r o c e s s u n d e r c o n s i d e r a t i o n will u t i l i z e two f l u l d - b e d r e a c t o r s . In the u p p e r b e d , h y d r o g e n is u s e d a s the f l u i d i z i u g a g e n t for the p r i m a r y coal f e e d s t o c k . The r e s u l t i n g p r o d u c t g a s is a m i x t u r e of CH 4 , H Z , CO, and CO 2 , along with HzS and NH 3 , t h a t m u s t s u b s e q u e n t l y u n d e r g o c l e a n - u p , s e p a r a t i o n and u p g r a d i n g s t e p s to a c h i e v e the final SNG p r o d u c t s t r e a m . The r e s i d u a l h y d r o g e n f r a c t i o n of the s t r e a m is s e p a r a t e d c r y o g e n i c a l l y and r e c y c l e d to the r e a c t o r . A s c h e m a t i c d i a g r a m of the pilot plant u s e d to d e v e l o p data for the h y d r o g a s i f i c a t i o n r e a c t o r is s h o w n in F i g . 4. Z-3. Table 4. Z-1 p r e s e n t s o p e r a t i n g data f r o m the h y d r o g a s i f i c a t i o n pilot plant for the r e l a t i v e l y r e a c t i v e l ~ h e n i s h b r o w n c o a l and a l s o f o r W e s t G e r m a n a n t h r a c i t e . The h y d r o g e n r e q u i r e d for h y d r o g a s i f i c a t i o n is p r o d u c e d in the l o w e r f l u i d - b e d , l~esidual c h a r f r o m the h y d r o g a s i f l c a t i o n s t a g e is r e a c t e d with s t e a m and o x y g e n to g e n e r a t e SNG t h a t c a n b e s h i f t e d to p r o v i d e the n e c e s s a r y c o n c e n t r a t i o n s of h y d r o g e n , The b a s i s for the c h a r g a s i f i e r is the h i g h - t e m p e r a t u r e W i n k l e r p r o c e s s , a p r e s s u r i z e d , f l u i d - b e d g a s l f i e r t h a t is a l s o b e i n g d e v e l o p e d b y K h e i n b r a u n . The h i g h - t e m p e r a t u r e W i n k l e r is a n e x t e n s i o n of e a r l i e r , a t m o s p h e r i c p r e s s u r e , f l u l d - b e d g a s i f i e r t e c h n o l o g y and is d e s i g n e d to p r o v i d e for h i g h e r t e m p e r a t u r e and h i g h e r p r e s s u r e o p e r a t i o n . The h i g h e r t e m p e r a t u r e l o w e r s the m a k e of liquid b y p r o d u c t and i n c r e a s e s c a r b o n u t i l i z a t i o n , H i g h e r p r e s s u r e s i n c r e a s e the g a s i f i e r t h r o u g h p u t . The h l g h - t e m p e r a ~ r e W i n k l e r t e c h n o l o g y h a s b e e n d e m o n s t r a t e d in a n o m i n a l 45 T P D pilot plant at p r e s s u r e s to a p p r o x i m a t e l y 130 psi a n d t e m p e r a t u r e s to a p p r o x i m a t e l y l l 0 0 ° C ° All t y p e s of c o a l s h a v e b e e n p r o c e s s e d and it h a s b e e n d e m o n s k r a t e d t h a t the a d d i t i o n of l i m e s t o n e to the fluld-bed can significantly reduce the H z S content of the r a w gas.

Methane (SNG) Pneumatic Conveying Drier

I II

Coal Sluice

H2

oo,0.ox

H~S,C02

Cyclone H20 Steam

,I, ~

Scrubber

I--J,/

Steam A'~soi

Plant Residual Gasometer 02

P i g . 4 . 2 - 3.

I i

H=

Raw Gas Condensate

P i l o t plant for h y d r o g a s i f i c a t i o n of coal (l%heinbraun AG); g a s i f i c a t i o n p r e s s u r e : up to 1750 psi; c o a l t h r o u g h p u t : up to 9.6 d r i e d t o n s / h r ; g a s i f i c a t i o n t e m p e r a t u r e : up to 950°C; gas p r o d u c t i o n : up to 7800 m 3 (i. N. ) C H 4 / h r .

670

Energy, The International Journal

Table 4.2-1.

O p e r a t i n g d a t a of the s e m i - t e c h n i c a l pilot p l a n t for h y d r o g a s i f i c a t i o n of c o a l a t R h e i n b r a u n A G . 1976-1982 Parameter R h e n i s h B r o w n Coal

Coal throughput, maf

1782 t o n s

13.6 tons

Special coal throughput, m a f

m a x . 700 l b / h r

m a x . 350 l b / h r

M e t h a n e c o n t e n t of c r u d e g a s

u p to 48 vol%

u p to 25 vol%

D e g r e e of C - g a s l f i c a t i o n

up to 82%

u p to 47%

Operating temperature

800-1000°C

9 4 0 - 9 6 0 °C

Operating pressure

800-1375 psi

1150-1250 psi

Solids r e s i d e n c e time

9-80 rain

28 - 38 r a i n

Plant in o p e r a t i o n with coal throughput

4. Z - 4 .

Anthracite

Z6987 hr 12253 hr

C a t a l y t i c Coal G a s i f i c a t i o n

E x x o n R e s e a r c h and D e v e l o p m e n t has conducted an engineering development p r o g r a m through the P D U stage (1-ton/day) to evaluate the potential for using coal gasification catalysts and a unique process flow sheet to produce S N G f r o m coal in a fluid-bed reactor, without the use of an oxygen plant or a separate methanatlon step. The catalyst, together with the process concept, led to the direct formation of m e t h a n e in the gasifler according to the overall reaction coal + H20

~ CH 4 + CO 2 .

(4.2-2)

T h i s t e c h n o l o g y , w h i c h i s s p e c i f i c a l l y f o c u s e d o n t h e p r o d u c t i o n of SNG f r o m c o a l , is d i s c u s s e d i n S e c . 7.Z. 4.3.

Catalytic Methanation

C a t a l y t i c m e t h a n a t i o u h a s b e e n s t u d i e d e x t e n s i v e l y s i n c e 1902, w h e n S a b a t i e r a n d S e n d e r e n s p u b l i s h e d t h e i r c l a s s i c a l p a p e r on Ni c a t a l y s t s . 3 M a n y c a t a l y s t s w e r e s u b s e q u e n t l y tried. B y 19Z5, m a n y e f f e c t i v e m e t a l c a t a l y s t s h a d b e e n i d e n t i f i e d . 4 A n o v e r v i e w of t h e s e c a t a l y s t s , t h e i r k i n e t i c s , r e a c t i o n m e c h a n i s m s , a n d s o m e c o m m e r c i a l e x a m p l e s m a y be found i n a 1973 r e v i e w p a p e r b y M i l l s a n d S t e f f g e n . 4 A n e x c e l l e n t d e s c r i p t i o n of c o m m e r c i a l p r o c e s s e s i s g i v e n i n R e f . 5. A l t h o u g h t h i s s u b j e c t i s c o n s i d e r e d i n C h a p t e r 7, we s h a l l d i s c u s s it h e r e f r o m a s o m e w h a t d i f f e r e n t p e r s p e c t i v e b e c a u s e of i t s p o t e n t i a l i m p o r t a n c e f o r SNG p r o duction. 4.3.1.

Chemistry and Thermodynamics

C a t a l y t i c m e t h a n a t i o n i n v o l v e s t h e e x o t h e r m i c f o r m a t i o n of CH 4 , u s u a l l y s t a r t i n g w i t h a m i x t u r e of H 2 a n d CO, a l t h o u g h m e t h a n a t i o n c a n a l s o be a c h i e v e d w i t h m i x t u r e s of H 2 a n d CO 2 . M e t h a n e i s f o r m e d in m a n y c o a l g a s i f i e r s , w i t h the l o w e r t e m p e r a t u r e g a s i f i e r s p r o d u c i n g r e l a t i v e l y m o r e CH 4 . T h u s , s o m e a m o u n t of CH 4 m a y be p r e s e n t i n t h e f e e d g a s to the c a t a l y t i c reactor. S t e a m i s u s u a l l y p r e s e n t or is a d d e d to the f e e d to a v o i d c a r b o n d e p o s i t i o n . The heat r e l e a s e d e p e n d s on t h e a m o u n t of CO p r e s e n t i n the f e e d g a s : f o r e a c h 1% of CO, a n a d i a b a t i c reaction will experience a 60°C temperature rise.

Coal G a s i f i c a t i o n for S N G P r o d u c t i o n

671

The p e r t i n e n t r e a c t i o n s a r e 4' 5 3H z + CO

T

~ CH 4 + H z O ,

(4.3-1)

ZH Z + Z C O

-

" CH 4 + CO z ,

(4.3-Z)

4H z + COp

-

~. C H 4 + Z H z O ,

(4° 3-3)

ZCO

-

• C + CO 2 ,

(4.3-4)

.

" C O z + H z.

(4.3-5)

CO +HzO

If m e t h a n a t i o n b e g i n s w i t h a m i x t u r e of H z and CO and n i c k e l - b a s e d c a t a l y s t s a r e u s e d , t h e d e s i r e d H 2 / C O r a t i o of the f e e d gas is 3:1 [ r e a c t i o n (4. 3 - 1 ) ] . When c a t a l y s t s s u c h a s G R I ' s s u l f u r - t o l e r a n t , d i r e c t m e t h a n a t i o n c a t a l y s t a r e u s e d , the d e s i r e d i n i t i a l H z / C O r a t i o is 1 and E q . (4. 3-Z) f o r m s the b a s i s for the m e t h a u a t l o n r e a c t i o n . O t h e r m e t h a n e - p r o d u c l n g p r o c e s s e s i n c l u d e the h y d r o c r a c k l n g of h i g h e r h y d r o c a r b o n s , typified by CzH 6 + H z

)ZCH 4 .

(4.3-6)

o o V a l u e s of AH[% and Z~G~ f o r r e a c t i o n s (4. 3-1) t h r o u g h (4. 3-5) a r e g i v e n in T a b l e 4° 3 - | f o r t e m p e r a t u r e s b e t w e e n Z7 and 7Z7 °C. T h e s e data s h o w t h a t all r e a c t i o n s a r e e x o t h e r m i c , w i t h a l l but the s h i f t r e a c t i o n (4. 3-5) b e i n g s t r o n g l y e x o t h e r m i c . F u r t h e r m o r e , the f l e e - e n e r g y v a l u e s in T a b l e 4. 3-1 show t h a t l o w e r t e m p e r a t u r e s f a v o r m e t h a n e p r o d u c t i o n ; t h u s , t h e r e m u s t be e f f e c t i v e h e a t - r e m o v a l m e t h o d s . At t e m p e r a t u r e s b e l o w ~ 4 Z b ° C , the m e t h a n e y i e l d is not n o t a b l y a f f e c t e d by p r e s s u r e ° C a r b o n d e p o s i t i o n , w h i c h l e a d s to c a t a l y s t fouling, c a n be e n c o u n t e r e d u n d e r c e r t a i n o p e r a t i n g c o n d i t i o n s . T h e s e c o n d i t l o u s a r e h i g h l y d e p e n d e n t on i n i t i a l g a s c o m p o s i t i o n , c a t a l y s t p r o p e r t i e s , t e m p e r a t u r e , and p r e s s u r e ° E x p e r i e n c e w i t h s u l f u r - t o l e r a n t , d i r e c t m e t h a n a t i o n c a t a l y s t s h a s s h o w n t h a t H p / C O r a t i o s a s low a s 0.1 can be p r o c e s s e d w i t h o u t c a r b o n d e p o s i t i o n . With c a t a l y s t s t h a t a c c o m p l i s h m e t h a n a t l o n t h r o u g h the o v e r a l l r e a c t i o n r e p r e s e n t e d b y E q . (4° 3-1) and for w h i c h f e e d gas H z / C O r a t i o s of 3 a r e d e s i r e d , c a r b o n d e p o s i t i o n o c c u r s m o r e r e a d i l y and m u c h l a r g e r r e g i o n s of t e m p e r a t u r e and H z / C O r a t i o s m u s t b e a v o i d e d , a s is s h o w n in F i g . 4. 3-1. 4. 3-Zo

Catalysts

In order of activity, the most important metal catalysts are: l~u > Ni > Co > Fe > M o . 4 Nickel is the m o s t c o m m o n l y used catalyst in cornrnerelal processes because of its relatively low cost. Despite the excellent catalytic performance of Ru, its high cost has precluded its widespread use. The activity of Ni is generally second to that l~u, but it is far cheaper and has therefore b e c o m e the most-used catalyst in commercial methanation processes. 4, 5 Nearly all cornrnerclally available methanation catalysts are rapidly poisoned by S-containing compounds and it is necessary to reduce the concentration of sulfur species in the inlet gas to less than 0.5 pprn in order to maintain adequate catalyst activity for long periods of time. The sulfurtolerant methanatlon catalysts currently under development do not have a similar requirement for low concentrations of sulfur species in the feed streams and thus afford the opportunity to m a k e major changes in the process elements and their integration in downstream processing trains. The catalyst base used and the composition of the Ni-based alloy are important. Investigators developing Ni-based catalysts have tried to find materials that yield o p t i m u m performance in terms of high CO-conversion, low C deposition, high methane selectivity, and yield. Other d e s i r a b l e p r o p e r t i e s a r e long, s t a b l e c a t a l y s t l i f e , a b i l i t y to a c c e p t f e e d s with low H z / C O r a t i o s , and h i g h s p a c e v e l o c i t i e s o v e r a r a n g e of t e m p e r a t u r e s a n d / o r p r e s s u r e s . A s u m m a r y of the m a n y d i f f e r e n t N i - b a s e d c a t a l y s t s i s g i v e n in T a b l e 5 of l l e f . 4. C o b a l t h a s a l s o b e e n found to b e q u i t e a c t i v e a s a m e t h a u a t i o n c a t a l y s t . 6, 7 H o w e v e r , c o m p a r e d to Ni, Co s u f f e r s m o r e s e v e r e c a r b o n d e p o s i t i o n , 6 r e q u i r e s h i g h e r t e m p e r a t u r e s f o r s i m i l a r CO c o n v e r s i o n s , 7 a n d i s l e s s m e t h a n e - s e l e c t i v e . 6, 7

672

Energy, The International Journal

Table 4.3-1.

Heats of r e a c t i o n and free energies of r e a c t i o n for reactions (4. 3-1) through (4. 3-5); reproduced from Ref. 4.

T e m p e r a t u r e , I.... °C

l

Reaction (4.3_i)

I (4.3_2)

l

(4.3_3)

I (4.3_4)

I (4.3_5)

Heat of Reaction, AHI~, kcal/mole 27

-49. 298

-59. 136

-39. 460

-41. 227

-9.838

127

-50.360

-60. 070

-40.650

-41,434

-9.710

227

-51, 297

-60.815

-41,779

-41. 499

-9.518

327

-52.084

-61. 376

-42.792

-41,460

-9. Z92

427

-52.730

-61.780

-43.680

-41. 350

-9. 050

527

-53.248

-62. 047

-44.449

-41. 190

-8,799

627

-53.654

-62. 2O3

-45.105

-40. 996

-8.549

727

-53.957

-62. 261

-45.653

-4O.729

-8.304

F r e e E n e r g y of Reaction, AG~, kcal/rnole Z7

-33. 904

-40.731

-27. 077

-28. 621

-6.827

127

-28. 610

-34. 451

-22.769

- 24. 385

-5o841

227

-23. 062

-27.956

-18. 168

-20. III

-4.894

327

-

17. 338

- 21. 329

-13. 347

-15.836

-3. 991

427

-II. 493

-14. 620

-8. 366

-II. 574

-3. 127

527

-5. 567

-7. 865

-3. 269

-7. 332

627

+0. 594

-I. 07 9

+I. 921

727

+6. 444

+5.715

+7. 173

-3. 108 +I. 090

-

-

2. 298 1. 500

-0.729

_ 1 Atmosphere 4 10 Atmospheres ."

u~

" ~ ~

.~

._.-___--~_ ...... ~C-.~ .... \ 25 Atmospheres

2

_

0

Carbon Deposition May Occur in Area Beneath Curve

I 500

~1~

600

I 700

I

I

800

900

I 1000

I

I

1 1 0 0 1200

I 1300

I 1400

Temperature, °K Fig. 4. 3-1.

The effects of synthesis gas ratio and pressure on carbon deposition. Carbon deposition m a y occur for conditions below the curves.

Coal G a s i f i c a t i o n f o r S N G

Production

673

I r o n - c a t a l y z e d m e t h a n a t i o n h a s b e e n d e s c r i b e d in two p a p e r s . 8, 9 The l o n g - t e r m e f f e c t i v e n e s s of t h i s c a t a l y s t w a s l i m i t e d b y C d e p o s i t i o n . B e c a u s e F e h a s v e r y poor m e t h a n e s e l e c t i v i t y , e v e n a t h i g h H 2 / C O r a t i o s , 8 it is c o n s i d e r e d to be m o r e s u i t a b l e for F i s c h e r - T r o p s c h s y n t h e s e s t h a n for m e t h a u a t l o n c a t a l y s i s . T y p i c a l y i e l d s c o n s i s t of 20% m e t h a n e and 8090 F i s c h e r - T r o p s c h p r o d u c t s w h e n 1 : 1 s y n t h e s i s gas w a s u s e d . 8 M o l y b d e n u m and W h a v e only m o d e r a t e a c t i v i t y and r e q u i r e h i g h t e m p e r a t u r e s for m e t h a u a t l o n . 10, 11 The m o t i v a t i o n f o r e x a m i n i n g t h e s e c a t a l y s t s is t h e i r h i g h r e s i s t a n c e to s u l f u r p o i s o n i n g . 10, 12 Noble m e t a l s h a v e a l s o b e e n s t u d i e d for a p p l i c a t i o n s i n c a t a l y t i c m e t h a n a t i o n . 10 T h e i r a c t i v i t i e s a r e g e n e r a l l y quite low, but P d , Kh, Os, and lZe h a v e the a d v a n t a g e of b e i n g h i g h l y methane -selective. 4. 3-3. C o m m e r c i a l P r o c e s s e s

M e t h a n a t i o n s y s t e m s a r e u s e d c o m m e r c i a l l y to r e m o v e s m a l l a m o u n t s of CO and COp b e c a u s e t h e s e o x i d e s a r e c a t a l y s t - p o i s o n s f o r m a n y c h e m i c a l manufacb~,ring s y s t e m s . A n e x a m p l e of a c o m m e r c i a l s y s t e m f o r w h i c h t h i s r e m o v a l is n e c e s s a r y i s found in a m m o n i a p l a n t s w h e r e the m e t h a u a t i o n s y s t e m s s e r v e a s gas p u r i f i e r s . As a r e s u l t , input CO and CO 2 c o n c e n t r a t i o n s to the a m m o n i a s y n t h e s i s r e a c t o r s a r e u s u a l l y l e s s t h a n ~ 1 % . 5 W h e n s c a l i n g up t h i s t e c h n o l o g y to the m e t h a n a t l o n s y s t e m s r e q u i r e d in a c o a l - g a s i f l c a t l o n plant p r o d u c i n g SNG, c o n s i d e r a t i o n m u s t b e g i v e n to a n u m b e r of p o t e n t i a l p r o b l e m a r e a s . The SNG s y s t e m s w i l l b e m u c h l a r g e r and w i l l be r e q u i r e d to h a n d l e input g a s e s w i t h m u c h h i g h e r CO c o n c e n t r a t i o n s . B e c a u s e of the h i g h h e a t r e l e a s e a s s o c i a t e d w i t h h i g h CO i n p u t - g a s c o n c e n t r a t i o n s , a d e q u a t e h e a t r e m o v a l m u s t be i n c o r p o r a t e d into the r e a c t o r d e s i g n . Sulfur p o i s o n i n g , c a t a l y s t d e a c t i v a t i o n b y h i g h t e m p e r a t u r e s i n t e r l n g of Ni c a t a l y s t s or b y C d e p o s i t i o n m u s t a l s o be a d d r e s s e d . N i c k e l - b a s e d c a t a l y s t s a r e c u r r e n t l y u s e d in the f i x e d - b e d m e t h a n a t o r s at the G P C G P . The f e e d g a s e s a r e p r e p r o c e s s e d b y a c l d - g a s r e m o v a l - s y s t e m s to r e d u c e the s u l f u r c o n t e n t to a c c e p t a b l e l e v e l s ( l e s s t h a n 1 ppm) b e f o r e t h e y e n t e r the m e t h a n a t l o n u n i t s . The s t a t u s of r e c e n t a d v a n c e d m e L h a n a t l o n t e c h n o l o g y d e v e l o p m e n t a c t i v i t i e s is s u m m a r i z e d i n the following s e c t i o n s . 4. 3-4.

Direct Methauatlon

Since 1978, GI~I h a s f u n d e d the d e v e l o p m e n t of the d i r e c t m e t h a n a t i o n p r o c e s s b e c a u s e of t h e p o t e n t i a l f o r i m p r o v i n g the c o a l - t o - S N G e c o n o m i c s . 13 P r o c e s s d e v e l o p m e n t h a s i n c l u d e d c a t a l y s t d e v e l o p m e n t , c a t a l y s t e v a l u a t i o n , e v a l u a t i o n of m a t e r i a l s of c o n s t r u c t i o n , and p r e l i m i n a r y a s s e s s m e n t of p r o c e s s e c o n o m i c s . D i r e c t m e t h a n a t i o n is a p r o c e s s b a s e d on a c a t a l y s t t h a t m e t h a u a t e s e q u l - m o l a r c o n c e n t r a t i o n s of H 2 and CO, p r o d u c i n g CO 2 r a t h e r t h a n s t e a m a s a p r o d u c t via the r e a c t i o n ZH 2 + 2CO

~

• CH 4+CO

2 .

(4. 3-7)

A c c o r d i n g l y , the p r o c e s s h a s no r e q u i r e m e n t for s t e a m , e i t h e r to s h i f t the gas to a n H 2 / C O r a t i o of 3 o r to p r e v e n t coking, a s is r e q u i r e d for N i - b a s e d c a t a l y s t s . Sulfur r e m o v a l is not r e q u i r e d p r i o r to m e t h a u a t i o n s i n c e the c a t a l y s t is not p o i s o n e d b y a n y sulfur c o m p o u n d s p r e s e n t in c o a l d e r i v e d g a s . As a r e s u l t , the p r o c e s s c a n be u s e d to t r e a t the r a w , q u e n c h e d gas f r o m a c o a l gasLfler w i t h l i t t l e o r no p r e t r e a ~ - n e n t , T h i s p r o c e d u r e a l l o w s u s e of the a c i d - g a s r e m o v a l s y s t e m to t r e a t a r e d u c e d v o l u m e of the a c i d - g a s s t r e a m to r e m o v e H2S and CO 2 . P o l i s h i n g m e t h a n a t l o n m a y b e r e q u i r e d to b r i n g the gas to US p i p e l i n e s t a n d a r d s . To d a t e , m o r e t h a n 800 c a t a l y s t f o r m u l a t i o n s h a v e b e e n t e s t e d , r e s u l t i n g in s e v e r a l c o m p o s i t i o n s t h a t h a v e p r o m i s e for a p p l i c a t i o n in the d i r e c t m e t h a n a t i o n p r o c e s s . C a r b o n f o r m a t i o n s h a v e not b e e n o b s e r v e d , e v e n w i t h H 2 / C O r a t i o s a s low a s 0.1 in a d r y gas s t r e a m . The GRI c a t a l y s t s p r o m o t e the m e t h a n a t i o n r e a c t i o n a t t e m p e r a t u r e s f r o m 260 to 650°C, p r e s s u r e s f r o m a t m o s p h e r i c to 1000 p s l g , f e e d gas H2]CO m o l a r r a t i o s f r o m 3 to l e s s t h a n 0. 4, s t e a m c o n c e n t r a t i o n s f r o m 0 to 15 m o l t , and in the p r e s e n c e of up to 1 m o l t of s u l f u r . C a r b o n f o r m a t i o n w a s not d e t e c t e d u n d e r any of t h e s e c o n d i t i o n s . HC a d d i t i o n s of up to 2 m o l t C6H 6 , 0 . 0 5 m o l t C6H~OH, a n d 0 . 3 m o l t NH 3 a l s o did not p o i s o n or foul the c a t a l y s t , L i m i t e d r e f o r m ing t e s t s h a v e i ~ d i c a t e d t h a t the c a t a l y s t s c a n y i e l d a s l n g l e - p a s s c o n v e r s i o n of a l m o s t 2590 of 22 p p m H z S - c o n t a i u i n g NG a t 8 7 0 ° C . C a t a l y s t s a m p l e s h a v e b e e n e x p o s e d to 2300 h r (Fig. 4. 3-2) u n d e r c o n t r o l l e d c o n d i t i o n s w i t h m a i n t e n a n c e of a c t i v i t y , a s w e l l a s 10,000 h r u n d e r a v a r i e t y of t e s t c o n d i t i o n s . B a s e d on t h e s e t e s t s , a m i n i m u m of a 1 - y r c a t a l y s t life h a s b e e n p r o j e c t e d f o r c o m m e r c i a l a p p l i c a t i o n . T a b l e 4. 3 - 2 l i s t s the r a n g e s of o p e r a t i n g c o n d i t i o n s o v e r w h i c h the c a t a l y s t h a s b e e n t e s t e d . The p r e s s u r e r a n g e is ~rpical of a n t i c i p a t e d o p e r a t i n g c o n d i t i o n s d o w n s t r e a m of a coal= g a s l f l c a t l o n plant. The c a t a l y s t c a n be o p e r a t e d up to 660 °C, w h i c h i s i n d i c a t e d b y t h e u p p e r l i m i t of the t e m p e r a t u r e r a n g e s~udled. The e x p e r i m e n t s w e r e c o n d u c t e d u s i n g g a s e s w h i c h

674

E n e r g y , The I n t e r n a t i o n a l J o u r n a l

Luzgi Peed Species

80

CO CO 2 H2 CH4 CZH 6 C 2H4 C3H6 C4H10 HzS COS CSz CH3SH C4H4S

d

A

ff 70

o

g 6o

0

-

~

0

a

o

"~ 50

-

o

o.,.o-

00

A GRI'C'600

4O 0

I 200

I 400

0

I 800

I 800

I 1000

I 1200

~

I 1400

0

I 1600

~

OI 1800

I 2000

N2

H20

Total

Time, hr Fig. 4. 3- 2. Life-test d a t a of the GRI-C-500 and GRI-C-600 catalysts using a clry-bottom Lurgl-type raw gas (450 psig, 6000 SCF/hr-ft 3 , 930 to 980°F, I0 g of -12 to +20 m e s h catalyst).

Table 4.3-Z.

G R I tests on direct methanation-catalysts.

Reactor conditions: p = 50-1000 psig, outlet T = 400-680°C. Types of feed gases simulated (gasification process/coal type): B G C / I L No. 6, I~RW/Pittsburgh No. 8, E R W / W y o d a k , Lurgi/ North Dakota Lignite, Lurgi/Kosebud, She ll{Wyodak, UCG/Rosebud. Feed-gas compositions Species

Volt

CO

4-4Z

CO z

0-42

Hz

8-44

CH 4

6-30

CzH 6

0-0.7

CzH 4

0-0.7

C 3H8

0-0. Z

C4H10

0-90 p p m

HzS

0.05-3

COS

0-0.14

N2

0.3-1.5

H20

0-38

C6H6

0-2.5

C6H5OH

0-0. O6

NH B

0-I

Total S

I00 p p m - 3

H z / C O ratio

0.6to 3

Space velocity = 500-Z5000 SCF/ft3-hr. Results: 18-86% C O conversion (defined as percentage of C O in the feed converted), Zl to 100% C H 4 selectivity (defined as the amount of CH 4 p r o d u c e d a s a p e r c e n t a g e of the a m o u n t of CO c o n v e r t e d ) .

tool%

16.73 28.35 39.70 lZ. 20 0.47 0. Z8 29 ppm 4 ppm

0.51 ?,49 ppm 1 ppm 1 ppm 2 ppm

I. 49 O. Z2

100.00

Coal Gasification for S N G Production

675

r e f l e c t (a) a n t i c i p a t e d r a w g a s c o m p o s i t i o n s a n d H z / C O r a t i o s f o r a v a r l e t y of c o a l - g a s i f l c a t i o n p r o c e s s e s a n d (b) g a s c o m p o s i t i o n s a n t i c i p a t e d a t the o u t l e t of a n u m b e r of d l r e c t - m e t h a n a t l o u r e a c t o r s o p e r a t i n g in s e r i e s . T h e c a t a l y s t h a s b e e n t e s t e d f o r h e a v y HC a n d s u l f u r c o n c e n t r a t i o n s i n t h e r a n g e of 50 to 1350 p p m . T h e c a t a l y s t h a s a l s o b e e n o p e r a t e d o v e r a w i d e r a n g e of s p a c e v e l o c i t i e s a n d f e e d - g a s w a t e r c o n c e n t r a t i o n s to o b t a i n a r a n g e of CO c o n v e r s i o n s a n d CH 4 s e l e c t i v i t i e s. T h e r e s u l t s of l a b o r a t o r y e x p e r i m e n t s to d e t e r m i n e the c o n v e r s i o n c h a r a c t e r i s t i c s of a GI%I direct-methanation catalyst, under conditions simulating the first stage of a methanation process, are presented in Fig. 4. 3-3. These data show the effect of temperature and space velocity on C O conversion and provide a basis for developing process-flow sheets that can be integrated into conceptual designs of coal-to-SNG plants. Workers at Haldor Topsoe, Inc., have been evaluating S-tolerant catalysts for converting C O / H 2 mixtures to methane. 14 They have demonstrated that the catalyst can also be an effective shift catalyst and, under s o m e conditions, leads to the formation of other low molecular weight, saturated, H C s in addition to methane. The general physical characteristics of the catalysts are shown in Table 4.3-3 and the range of test conditions investigated using simulated raw gas is shown in Table 4. 3-4. In addition to laboratory experiments, a methauatlon P D U was constructed and operated on a sllp-stream from an entrained-flow coal gaslfleatlou P D U being evaluated by Mountain Fuel Resources. The entrained-flow gasification experiments involved five different coal feedstocks and provided different r a w gas feed streams to the methautor. The results of these experiments are shown in Fig. 4. 3-4 as relative catalyst activity vs time. The activity was calculated as the space velocity for 90% conversion based on the rate-llmiting component (i.e. , the minor component which is H 2 for C O / H 2 > 1 and C O for C O / H 2 < I). Data are also included from the laboratory experiments carried out with the catalyst prior to performing the integrated P D U tests. A total of 1080 hr of testing was completed with catalyst activity levels remaining high throughout the test. The type of coal appeared to have no effect on the activity of the catalyst and the effects of variations in HzS concentration were also small. There appeared to be no effect of H2S on actlvlty below a 0.07 volt concentration. The catalyst activity remained constant during a 100-hr test with the H z S partial pressure as low as 1 ppm.

4. 3-5. Conaflux Process (Fluld-Bed Methauatlon) The Cornflux process is an Ni-catalyzed, pressurized, fluid-bed process to convert C O rich gasification gases into S N G in a single step. 15 This process performs both shift and methanation reactions simultaneously in a single reactor with complete C O conversion. The water formed in the methanatlon reaction is available for water-gas shift reaction. Thus, a gas with H z / C O < 3 can be methauated without adding steam. A simplified process flow diagram for the Cornflux process is shown in Fig. 4. 3-5. The desulfurized feed gas is preheated by heat exchange with the product gas to the reactlon-inltlation temperature and then fed into the reactor. The g a s flu~dizes the catalyst, and both methanation and water-gas shift reactions take place simultaneously in the fluldlzed bed. The axial temperature gradient in the fluidized bed is extremely small, and the reactor is operated under high loads almost isothermally. Heated catalyst particles are cooled sufficiently fast by mixing with colder particles and by contact wlth integrated heat exchangers so that the high heat of the methanatlon reaction does not cause superheating of the bed. The reaction heat is utilized to generate high-pressure superheated steam in a heat exchanger in the bed. The product gas wlth less than 0.1 volt of C O is cooled and process water condensed. If the feed gas has H z / C O < 3.0, the C O 2 formed with the reaction must be r e m o v e d to meet plpellne-quallty gas specifications. The resulting product gas is S N G with a heating value of 9Z6-I016 B T U / S C F and chemical properties i d e n t i c a l to NG. The C o m f l u x p r o c e s s was e v a l u a t e d initially in a 1 . 3 - i t d i a m e t e r E T U and l a t e r at the pilot plant scale with a 3.3-it diameter reactor and S N G production up to II 2, 000 SCF/hr. Performance data from these development programs are s u m m a r i z e d in Table 4, 3-5. 4. 3-6. H I C O M H I C O M methauatlon is a fixed-bed process and is being developed by the British Gas Corporation to a c c o m m o d a t e the relatively low Hz/CO-ratlo product-gases produced by gasiflers such as the B G C / L u r g i slagging gasifier, KI~V (Westinghouse), U-Gas, Shell (entrained-flow), and Texaco (entrained-flow). 16 Typical off-gas compositions for these gasiflers and the drybottom Lurgi gasifier are shown in Table 4. 3-6. The gases will also contain compounds of sulfur (HzS, COS, etc. ) at levels dependent on the sulfur contents of the coals. The HICO~v[ process employs a series of methanation stages, each of which involves a fixed bed of catalyst; each is connected as shown in the simplified process flow diagram of Fig. 4. 3-6. The principal method used to control the temperature rise in each stage is recycle of cooled, equilibrated product gas to dilute the feed gas. The amount of recycle gas is minimized by passing it through at least two stages, with fresh gas added to each stage (spllt-stream EGY 12:8/9-E

Energy, The InternationalJournal

676

C~

0

a

8 '13

--

u~

o

~o

o

o 0 0 o

u*J

o f~"

I~

.o %lOUJ ' u o ! l e J l u a 0 u o o

O0

•~ ,..:,

),onpoJd

¢) m u .~ m o o

o o o

e~ 0,1 ~00

o

I eU. U U)

o

~.~

~

04i

~o

U 0

U O. U) ~D

o

4 o o o o

% IOtU ' u o ! l e J l , u e o u o o

O0

|onpoJcl

o

~

% 'uo!sJe^uoo

o

lelO/

Coal Gasification

Table 4.3-3,

f o r SNG P r o d u c t i o n

677

Physical characteristics of the catalyst tested by Haldor Topsol, Inc.

Name

S M C 324

Size, L X D

4.5 turn ×4.5

Density

1 . 7 5 grnn/crn 3 (109 l b / C F )

Bulk density

1 . 2 7 5 k g / ~ (80 l b / C F )

Surface area

100 r n 2 / g r

Crushing strength

600 kg/crn 2 (8700 Ib/in2)

Table 4.3-4.

rnrn (0.18" x0.18")

S u m m a r y of direct rnethanation test conditions a n d results; concentrations are given in molt.

Parameters

90 - 300

Pressure, psia Volumetric flowrate, S C F / h r Inlet conditions

R a n g e of T e s t Conditions

Typical Test Data 300

3

1 - 8

( a d j u s t e d w l t h H 2)

CO/H 2 volume ratio

1.5

0 . 7 -

1.0

H2

30 - 45

35

CO

30 - 45

40

CO 2

10

15

40

-

1 pprn-

3.5

0.1

cH 4

0-13

1

N2

2-11

5

Outlet conditions

H2

0-

15

8

CO

Z - 15

8

40 - 55

50

CO 2 HzS

cH 4 CzH 6

2 pprn - 4.5

16 - 39

0.1 25 Z.5

1-4

0.5

C3H 8

0.2-0.7

N2

Balance

Balance

Fractional conversions CO

70 - 100

90

H2

70

9O

-

100

678

Energy, The International Journal

O

1.0

1.o ¢1 U

~

•

qlh

•• " S

k." •

O.O Ill -

• _~_ " •" • - O

087

•

"

0.5 I 0

440-I~ test at HTAS

Fig. 4 . 3 - 4 .

I 500

co

I 1000

Operating time, hr

d North Dakota lignite

Petroleum coke

Price River Utah bituminous coal

SUFCO Utah bitumiuous coal

Test completed

Relative catalyst activity vs time in the methauatiou P D U at Mountain Fuel Resources.

Reactor

Steam Drum

Filter

Cooler

Steam BFW

EII

¢

Feed

,©

Steam Desulfurization

Heat Exchanger

Preheater

Fig. 4. 3-5.

SNG

Compression

Simplified process-lqow diagram for the Cornlqux process.

Coal Gasification

T a b l e 4. 3 - 5 .

A.

Operating

Comflux methanation performance semi-technlcal test plant,

Conditions:

T = 400 - 500°C,

679

data for a

o u t p u t c a p a c i t y = 3500 - 1 2 3 0 0 f t 3 / h r ,

p = 290 - 8 7 0 p s i ,

H 2 / C O v o l u m e r a t i o = 1 . 8 - 3, r e c y c l e

feed ratio = 0 - 0.5,

B.

f o r SNG P r o d u c t i o n

volume-

gas velocity = 0.16 - 0.82 ft/sec.

SNGproductloninvol%:

methane

= 86 - 96, H 2 = Z - 8, C O

= Z - 6; gross

heating value = 926 - 1016 B T U / S C F .

C.

Operational

Data for the Pilot Plant:

reactor

450 - 550°C, Z.0-

3.0,

diameter

feed gas = 112,000 - 400,000 SCF/hr,

recycle-gas

I. 0 ft/sec,

volume ratio = 0 - 0.3,

SNG production

t i o n = 1o 0 - 5 . 2 t / h r ,

= 3 . 2 8 ft ( i n t e r n a l ) ,

steam temperature

size distribution

Table 4.3-6.

charge

gas veloclty=

0.16 -

steam produc-

= 370 - 4 8 0 ° C ,

= 0.8 - 1.6,

=

H2/CO volume ratio =

= 45,000 - 112,000 SCF/hr,

height = 6.4 - 12.9 ft, catalyst

Species

reactor

h e i g h t = 3 6 . 0 ft, p = 190 - 870 p s l , f l u i d i z e d b e d t e m p e r a t u r e

finidized-bed

catalyst-particle

= 10 - 400 ~ m .

Typical gasifier-product g a s e s (in m o l t ) f o r a n u m b e r g a s i f i e r s a n d c o r r e s p o n d i n g s t e a m to d r y - g a s r a t i o s .

Lurgl Dry- Ash

B GC / L u r gi Slagging

Shell

Texaco

of

KRW (Westinghouse)

40

29

29

35

27

CO

17

60

65

43

55

CO 2

32

3

Z

20

6

cH 4

I0

6

0.1

0.3

9

N2

1

1

4

Steam/dry gas ratio

1.4

0o 13

0.03

2

0.23

3

1.0

operation). Product gas from upstream stages (split-stream operation) also helps control the temperature rise in each subsequent reactor and hlgh-grade heat is recovered immediately downstream of each reactor. The effect of using spilt-stream o p e r a t i o n i n o r d e r to r e d u c e t h e amount of recycle gas needed for control of the temperature r i s e in t h e r e a c t o r b e d s i s s h o w n i n Fig. 4. 3 - 7 . The HtCOM process employs nickel-based catalysts and uses excess steam in the feed g a s to p r e v e n t c a r b o n d e p o s i t i o n . The process was initlally evaluated in small-scale laboratory experiments and subsequently tested at the semi-commercial scale on a slip stream from the B O C / L u r g l s l a g g i n g g a s i f l e r a t W e s t f i e l d , S c o t l a n d . In t h e i n t e g r a t e d t e s t s a t W e s t f i e l d , p u r i fied gases from the gaslfier were successfully processed at a nominal rate of approximately 4.5 x 106 S C F / d a y .

4. 3-7.

Liquid-Phase

Methanatlon

Workers at Chem Systemj Inc., have developed a liquld-phase methanation system in w h i c h a g r a n u l a r N i - c a t a l ~ s t i s i m m e r s e d i n a m i n e r a l - o l l c o o l a n t b a t h , w h i c h s e r v e s to c o n t r o l t h e r e a c t o r t e m p e r a t u r e . 17, 18 F i n i d i z a t l o n o f t h e c a t a l y s t o c c u r s b y c i r c u l a t i n g t h e o l l a n d f r e s h SG u p w a r d t h r o u g h t h e r e a c t o r . In a l a r g e - s c a l e p r o c e s s , h e a t i s r e c o v e r e d f r o m t h e o l l

Energy, The International Journal

680

Saturator

Purified Synthesis 4,Gas

H.R Steam Boiler Second Final Methanator Methanator Gas Cooling First Methanator H.R Steamboiler Train 4

!ii;I L b,,/I I [',,-'

'iT I Make Up Water

Purge Liquor

Coolers in Slagger Make Gas Cooling Train

HCM C02 --- SNG Cooling and Removal Train

(a) T y p i c a l g a s c o m p o s i t i o n s f r o m a HICOM ,ilot t e s t F e e d to t h e HICOM Reactor, molt

Component

Product from the HICOM R e a c t o r , m o l t

CO

lZ. 6

CO z

43,0

53.1

Hz

11.7

5.5

31.7

39.3

1.0

I°I

4

Nz

I.I

(b) R a n g e of o p e r a t i n g c o n d i t i o n s Inlet T

Z30 - 3 Z 0 ° C Z5 - 70 b a r

P Maximum T

46O - 640° C

Total test time Fig. 4 . 3 - 6 .

15,000

hr

T h e HICOM p r o c e s s d l a g r a m ~ g a s c o m p o s i t i o n s (a) a n d r a n g e of o p e r a t i n g c o n d i t i o n s (b),

.2 10

u

One Reactor

,,r 5

React°rs ~ 0

I 100

Fig, 4o 3 - 7 .

~ I

L |

200 300 Temperature Rise, °C

400

500

E f f e c t of t h e t e m p e r a t u r e r i s e on t h e r e q u i r e d r e c y c l e r a t i o (= r e c y c l e f l o w / p r o d u c t flow).

Coal G a s i f i c a t i o n f o r SNG P r o d u c t i o n

681

a n d f r o m t h e hot p r o d u c t g a s e s . F e e d s t r e a m s w i t h HP./CO < 3 a r e a c c o m m o d a t e d b y a d d i n g s t e a m to the f e e d , t h u s f o r c i n g t h e s h i f t r e a c t i o n . M u l t i p l e r e a c t o r s a r e r e q u i r e d to o b t a i n a C O - c o n c e n t r a t i o n b e l o w 0.1%° O p e r a t i n g t e m p e r a t u r e s a r e b e t w e e n 300 and 380°C and p r e s s u r e s b e t w e e n 300 and 1000 p s i . V e r y good CO c o n v e r s i o n s h a v e b e e n d e m o n s t r a t e d , but c a r b o n d e p o s i t i o n and c a t a l y s t d i s i n t e g r a t i o n h a v e b e e n p r o b l e m s f o r s o m e o p e r a t i n g r e g i m e s . 4.4.

Acid-Gas l~emoval

4.4-1. C o m m e r c i a l Processes An e s s e n t i a l e l e m e n t of a c o a l - t o - S N G p r o c e s s i s t h e r e m o v a l of g a s e s s u c h a s COp., HP.S, COS, m e r c a p t a n s , and o r g a n i c s u l f i d e s f r o m t h e p r o d u c t s t r e a m in o r d e r to s a t i s f y p r o c e s s c o n s t r a i n t s (such as catalyst poisoning), e n v i r o n m e n t a l c o n s t r a i n t s or product r e q u i r e m e n t s ( s u c h a s h e a t i n g v a l u e and t r a c e - c o n s t i t u e n t l e v e l s ) . B e c a u s e r e q u i r e m e n t s h a v e e x i s t e d f o r t h e r e m o v a l of t h e s e t y p e s o f g a s e s f r o m a w i d e v a r i e t y of p r o c e s s s t r e a m s t h a t a r e e n c o u n t e r e d in t h e c h e m i c a l i n d u s t r y , in p e t r o l e u m r e f i n i n g and NG p r o d u c t i o n , a l a r g e n u m b e r o f unlt p r o c e s s e s h a v e b e e n d e v e l o p e d and c a n b e u s e d in t h e d o w n s t r e a m p r o c e s s i n g t r a i n s o f c o a l - g a s l f i c a tion plants. T a b l e 4 . 4 - 1 c o n t a i n s a l l s t of t e c h n o l o g i e s t h a t have b e e n e x a m i n e d a n d / o r d e v e l o p e d f o r s p e c i f i c a p p l i c a t i o n s . C u r r e n t l y , t h e r e a r e m o r e t h a n 90 l%ectisol u n i t s in o p e r a t i o n o r u n d e r c o n s t r u c t i o n in v a r i o u s p a r t s of t h e world@ The 1%ectlsol t e c h n o l o g y , w h i c h u s e s m e t h a n o l a s t h e p h y s i c a l s o l v e n t , is in u s e a t t h e SASOL p l a n t s and i s a l s o e m p l o y e d in t h e d o w n s t r e a m p r o c e s s ing t r a i n in t h e G P C G P . The B e n f l e l d P r o c e s s , w h i c h u s e s a hot Kp.CO S s o l u t i o n f o r t h e c h e m i c a l a b s o r p t i o n of COP., H2S and COS, is in u s e o r b e i n g c o n s i d e r e d in o v e r 6P'0 a p p l i c a t i o n s throughout the world. The S e l e x o l p r o c e s s , a p h y s i c a l a b s o r p t i o n p r o c e s s w h i c h u s e s the d l m e t h y l e t h e r o f p o l y e t h y l e n e g l y c o l a s t h e s o l v e n t , h a s b e e n i n s t a l l e d at a p p r o x i m a t e l y 30 c o m m e r c i a l a n d / o r p i l o t - p l a n t f a c i l i t i e s . T h i s t e c h n o l o g y is c u r r e n t l y b e i n g u s e d at t h e Cool W a t e r IGCC p r o j e c t . 4. 4 - 2 .

Advanced Technolo$ies

B e c a u s e of t h e e x t e n s i v e c a t a l o g of c o m m e r c i a l l y a v a i l a b l e t e c h n o l o g i e s f o r a c i d - g a s r e m o v a l and t h e l a r g e d a t a b a s e t h a t e x i s t s on t h e p r o p e r t i e s of p o t e n t i a l s o r b e n t s f o r t h e g a s e s o f i n t e r e s t , t h e r e i s o n l y a l i m i t e d e f f o r t d e v o t e d to the d e v e l o p m e n t of n e w p r o c e s s e s t h a t c o u l d i m p r o v e t h e e c o n o m i c s of p r o d u c i n g SNG f r o m c o a l . GKI, t o g e t h e r w i t h DoE and C o n s o l i d a t e d I q a t u r a l Gas (CNG), h a s b e e n e v a l u a t i n g a n a d v a n c e d a c l d - g a s r e m o v a l p r o c e s s s p e c i f i c a l l y for c o a l c o n v e r s i o n . T h i s p r o c e s s r e l i e s on t h e u n i q u e g a s - s o l l d - l l q u i d e q u i l i b r i n m p h a s e r e l a t i o n s h l p s t h a t e x i s t f o r CO2-H2S m i x t u r e s . H y d r o g e n s u l f i d e and c a r b o n y l s u l f i d e a r e s o l u b l e in liquid CO 2 . H o w e v e r , w h e n t h e t e m p e r a t u r e of a CO2/H2S s o l u t l o n i s r e d u c e d to t h e p o i n t w h e r e c r y s t a l l i z a t i o n o c c u r s s t h e s o l i d p h a s e t h a t r e s u l t s i s a l m o s t 100% CO 2 and c o n t a i n s e s s e n t i a l l y no s u l f i d e s . T h i s p h a s e b e h a v i o r p r o v i d e s an e f f e c t i v e m e a n s for r e m o v i n g a c i d g a s e s s u c h a s CO2, H2S and COS f r o m a c o a l - g a s i f i c a t i o n p r o c e s s s t r e a m and s u b s e q u e n t l y i n c r e a s i n g t h e c o n c e n t r a t i o n of H?S in a s t r e a m w h e r e it c a n b e e f f e c t i v e l y c o n v e r t e d to e l e m e n t a l s u l f u r . A c o n c e p t u a l flow d i a g r a m for t h e CNG a c l d - g a s r e m o v a l p r o c e s s is s h o w n in F i g . 4 . 4 - 1 o The r a w f e e d gas is c o o l e d and r e s i d u a l w a t e r v a p o r i s r e m o v e d in a d e h y d r a t i o n s y s t e m to p r e v e n t s u b s e q u e n t i c i n g . The w a t e r - f r e e c r u d e gas i s f u r t h e r c o o l e d to i t s CO 2 dew p o i n t ( - 5 6 ° C ) b y c o u n t e r c u r r e n t h e a t e x c h a n g e w i t h r e t u r n c l e a n gas and COP. o D e p e n d i n g o n t h e COP. dew p o i n t , a f r a c t i o n of t h e COP. in t h e c r u d e g a s s t r e a m is c o n d e n s e d t o g e t h e r w i t h t h e s u l f u r c o m p o u n d s . The g a s at -55 ° C i s t h e n s c r u b b e d b y liquid COP. to r e m o v e HP.S, COS and o t h e r t r a c e i m p u r i t i e s f r o m t h e f e e d g a s . T h i s a b s o r p t i o n is e s s e n t i a l l y i s o t h e r m a l s i n c e t h e h e a t of a b s o r p t i o n is d i s s i p a t e d a s h e a t of v a p o r i z a t i o n of a s m a l l p o r t i o n of t h e liquid CO 2. The liquid COP., t o g e t h e r w l t h a l l of t h e s u l f u r c o m p o u n d s , e t h e r t r a c e c o n t a m i n a n t s and s o m e c o - a b s o r b e d light HCs i s c o m b i n e d w i t h the c o n t a m i n a t e d l i q u i d COp. t h a t w a s c o n d e n s e d in p r e c o o l l n g t h e r a w g a s . The light HCs a r e s t r i p p e d f r o m t h i s c o m b i n e d liquid CO 2 s t r e a m and r e c y c l e d and m i x e d w i t h t h e f e e d g a s . Any h i g h e r I-tCs (C4-C6) in t h e f e e d g a s w i l l r e m a i n w i t h t h e c o n d e n s e d COP.. The c o n t a m i n a t e d liquid COP. s t r e a m l e a v i n g t h e light e n d s s t r i p p i n g t o w e r is p r o c e s s e d in a d i r e c t - c o n t a c t , t r l p l e - p o l n t c r y s t a l l i z e r w i t h v a p o r c o m p r e s s i o n . Solid COP. i s f o r m e d b y a d i a b a t i c f l a s h i n g of t h e liquid COP. s ~ r e a m n e a r t h e top of t h e c r y s t a l l i z e r . An Hp.S-rich g a s s t r e a m is p r o d u c e d and i s c o n t i n u o u s l y w i t h d r a w n f r o m the top. A l l CP.-C 6 HHCs e n t e r i n g t h e c r y s t a l l i z e r a r e r e m o v e d w i t h t h e Hp.S-rleh s t r e a m . The s o l i d COP. c r y s t a l s f a l l to t h e b o t t o m of the c r y s t a l l i z e r , w h e r e t h e y a r e m e l t e d b y d i r e c t c o n t a c t w i t h c o n d e n s i n g COP. v a p o r . P u r e CO Z liquid thus p r o d u c e d i s s p l i t into two s t r e a m s : one i s r e c y c l e d to the HP.S a b s o r b e r and t h e o t h e r i s s e n t b a c k t h r o u g h t h e p r o c e s s f o r r e f r i g e r a t i o n and p o w e r r e c o v e r y and is s u b s e q u e n t l y d e l i v e r e d a s a p r o d u c t s t r e a m o r v e n t e d to the a t m o s p h e r e . C a r b o n d i o x i d e r e m a i n i n g in t h e gas a f t e r r e m o v a l of s u l f u r c o m p o u n d s i s a b s o r b e d a t t e m p e r a t u r e s b e l o w t h e CO 2 t r i p l e p o i n t w i t h a s l u r r y a b s o r b e n t . The s l u r r y a b s o r b e n t i s a

682

Energy,

The International Journal

Table 4. 4- I. S u m m a r y of commercial a n d developmental a c i d - g a s removal p r o c e s s e s ; a b b r e v i a t i o n s , f o r t h e p r o c e s s t y p e , AD = a d s o r p t i o n , AB = a b s o r p t i o n , CD = c r y o g e n i c d l s t i l l a t l o u ; f o r t h e s o l v e n t , C = c h e m i c a l s o l v e n t , P =

physical solvent; for the clean-up mode, S = selective, NS =non-selective. N a m e of Process

Type

Solvent

Mode

Major Contaminants Removed

Activated carbon

AD

C

NS

H2S, oil

ADIP

AB

C

NS

H2S, C O 2

Alkazid

AB

C

S, NS

H2S, C O 2

Amlsol

AB

C/P

S, NS

H2S, C O 2

Benfield

AB

C

NS

H2S, C O 2

Catacarb

AB

C

NS

H2S, C O 2

Chemsweet

AD

C

S

-2s

CNG

AB

P

S

H2S, C O 2

Estasolvan

AB

P

S, NS

H2S, CO2,o i l

Flexsorb SE

AB

C

S

H2S, C O 2

Fluor Econamine

AB

C

NS

H2S, C O 2

Fluor Solvent

AB

P

NS

H2S, CO2,o i l

Giammarco-Vetrocoke

AB

C

S

HzS, CO2

MEA

AB

C

NS

H2S, CO 2

MDEA

AB

C

S, NS

H2S , C O 2

Molecular sieves

AD

P

S

H2S

Purisol

AB

P

S, NS

H2S , C O 2

Rectlsol

AB

P

S, NS

H2S , C O 2

Ryan Holmes

CD

CD

S

H2S , CO2, C ;

Seaboard

AB

C

s

HzS

Selexol

AB

P

S, NS

H2S , COz, oil

Sepasolv MPE

AB

P

S, NS

H2S , CO2, oll

SNPA-

AB

C

NS

H2S, C O Z

Stretford

AB

C

s

HzS

Sulfiban

AB

C

NS

H2S, C O 2

Sulflnol

AB

C/P

NS

H2S, C O 2

Trlpotas sium phosphate

AB

C

S

H2S

V a c u u m carbonate

AB

C

S

H2S

Zinc oxide

AD

C

S

HzS

DEA

C o a t G a s i f i c a t i o n f o r SING P r o d u c t i o n

683

o Z

l

°®

~1

I)~

0

0

~o

~

!

u.I .~.

~(I

--(t o

=~"

!

0

~

_A

.1 4

o

o

684

Energy,

The International

Journal

s a t u r a t e d s o l u t i o n o f a n o r g a n i c s o l v e n t a n d CO 2 c o n t a i n i n g s u s p e n d e d p a r t i c l e s o f s o l i d CO 2 . A s CO 2 i s a b s o r b e d ( c o n d e n s e d ) , t h e l a t e n t h e a t r e l e a s e d m e l t s t h e s o l i d CO 2 c o n t a i n e d i n t h e slurry absorbent. T h e d i r e c t r e f r i g e r a t i o n p r o v i d e d b y t h e m e l t i n g o f s o l i d CO 2 e n a b l e s a s m a l l a b s o r b e n t f l o w to a c c o m m o d a t e t h e c o n s i d e r a b l e h e a t o f c o n d e n s a t i o n a n d a b s o r p t i o n o f t h e CO 2 vapor. The cold, purified gas stream then leaves the acld-gas removal process after heat exchange with the raw gas stream. T h e C O 2 - r l c h s o l v e n t l e a v i n g t h e CO 2 a b s o r b e r n e a r t h e t r l p l e - p o i n t t e m p e r a t u r e cont a l n s n o s o l i d CO 2. T h i s s t r e a m i s f l a s h e d in a d r u m to v a p o r i z e m e t h a n e o r o t h e r l i g h t c o m p o nents. T h e C O 2 - r i c h a b s o r b e n t i s n e x t c o o l e d b y e x t e r n a l r e f r i g e r a t i o n a n d t h e n f l a s h e d to l o w e r t h e p r e s s u r e in a n u m b e r o f s t a g e s , in o r d e r to g e n e r a t e a c o l d s l u r r y o f l i q u l d s o l v e n t a n d s o l i d CO 2. N i t r o g e n s t r i p p i n g o f t h e s o l v e n t m a y s o m e t i m e s b e r e q u i r e d to p r o d u c e a v e r y l e a n s o l v e n t . T h e r e g e n e r a t e d s l u r r y a b s o r b e n t i s r e c i r c u l a t e d to t h e CO 2 a b s o r b e r w h i l e t h e CO 2f l a s h e d g a s i s v e n t e d to t h e a t m o s p h e r e a f t e r r e c o v e r y o f r e f r i g e r a t i o n a n d p o w e r . 4o 5.

SNG E c o n o m i c s

The economics associated with producing natural gas from coal are a function of coal type and cost, the technologies used in the overall conversion processes, as well as slte-speciflc considerations. Figure 4o5-1 shows a comparison of calculated end-product gas costs (in 1982 dollars) for an ash-agglomerating, fluid-bed gasification technology and also for dry-bottom L u r g i t e c h n o l o g y w i t h b o t h US W e s t e r n a n d E a s t e r n c o a l s a s t h e f e e d s t o c k . These results are presented as a levelized constant dollar (LCD) cost, where the levellzed price represents the a v e r a g e g a s s e l l i n g p r i c e r e q u i r e d o v e r t h e l i f e o f t h e p l a n t i n d o l l a r s f o r a g i v e n y e a r to r e a l i z e a r a t e o f r e t u r n o n e q u i t y o f 14~5%= The LCD price also requires that all costs, except that of coal, escalate at the average rate of inflatlon. F i g u r e 4 . 5 - 1 s h o w s t h e r e l a t i v e d i s t r i b u t i o n o f t h e m a j o r c o s t e l e m e n t s (i. e . , f e e d s t o c k , operation and maintenance, and capital investment) for each of the four cases considered. A Western coal was used as the feedstock. T h e c o n t r i b u t i o n s o f t h e m a j o r e l e m e n t s to t h e o v e r a l l e n d - p r o d u c t g a s c o s t s a r e : f e e d s t o c k , 25 to 29%; o p e r a t i o n a n d m a i n t e n a n c e , 45 to 49%;

Western Coal (@ $.701MMBtu Delivered) 1982110e Btu

I

Eastern Coal (@ $1.751MMBtu Delivered) Dry Bottom Lurgi

9.00 -~

Dry Bottom Lurgi

7.00 --

Westinghouse ~ ~] Site Specific Factor (SSF) Process Development Allowance

I~i!i~!I

~-- ~ Westinghouse

~

5.00 --

3.00 -~ ]

1.00 0 -1.00 -

Fig.

LCDPrice L. m - - I W/O PDA 5.83 & SSF W PDA 6.14 & SSF

4.5-1.

~.-----J 4.93 5.84

(PDA) Coal

I ~

Variable Operation & Maintenance

~ I~1

Project Contingency & Working Capital Known Capital Investment

L_..J L__.J 8.86

6.43

9.38

7.06

IO,M)

C o m p a r i s o n of L C D costs of S N G for selected gasifiers. All estimates are based on a 30-yr plant life, 8 5 % debt financing, beginning operation i n 1990. D e l i v e r e d c o a l p r i c e s a r e a s s u m e d t o e s c a l a t e a t 2% p e r y e a r in real terms. Additional primary capital costs were estimated for u n k n o w n f a c t o r s r e l a t e d to p o t e n t i a l s i t e r e q u i r e m e n t s (SSF) a n d s t a t e of technology development (I°DA).

Coal G a s i f i c a t i o n for SNG P r o d u c t i o n

685

capital, 25 to 26%). With an Eastern coal, the relative contributions are as follows: feedstock, 42 to 5090; o p e r a t i o n and m a i n t e n a n c e , 31 to 39%1 c a p i t a l , 19 to 2090. F i g u r e 4 . 5 - 2 s h o w s a c o m p a r i s o n of b o t h t h e l e v e l l z e d c o n s t a n t d o l l a r e n d - p r o d u c t g a s c o s t s and t h e a n n u a l c o s t o f s e r v i c e for c o a l - t o - S N G c o n v e r s i o n f o r a p r o c e s s b a s e d on d r y B o t t o m L u r g l g a s i f i c a t i o n and c o m m e r c i a l l y a v a i l a b l e d o w n s t r e a m p r o c e s s e s , w h e n u s i n g a s y s t e m b a s e d o n a d v a n c e d g a s i f i c a t i o n ( a s h - a g g l o m e r a t i n g , f l u l d - b e d ) and d o w n s t r e a m p r o c e s s i n g ( d i r e c t m e t h a n a t i o n and a n a d v a n c e d a c i d - g a s c l e a n - u p s y s t e m ) t e c h n o l o g i e s . B o t h p l a n t s w e r e s i z e d to p r o d u c e 250 X 106 S C F / d a y of p l p e l i n e - q u a l i t 7 g a s u s i n g l i g n i t e a s t h e f e e d s t o c k . The a v a i l a b i l i t y o f a d v a n c e d t e c h n o l o g l e s w o u l d r e d u c e t h e a v e r a g e g a s c o s t f r o m a p p r o x irnately $6.20/106 B T U to approximately $4.80/106 B T U on a cost-of-service basis. The advanced technology would also lead to a first year gas cost that is approximately $2.00/106 B T U less than that estimated for the process based on dry-bottom Lurgl technology. This reduction in average and first year gas costs will permit coal-to-SNG processes to b e c o m e economically competitive with other energy- and gas-supply options in an earlier time frame than would o t h e r w i s e be the case. 4° 6. Research and Development Needs The r e s e a r c h and d e v e l o p m e n t n e e d s a s s o c i a t e d w i t h t h e l o n g - r a n g e o b j e c t i v e of p r o d u c ing SNG f r o m c o a l c o v e r a s p e c t r u m of a c t i v i t i e s , r a n g i n g f r o m e n g i n e e r i n g s t u d i e s to b a s i c research. T h e s e n e e d s i n c l u d e : (i) o p e r a t l o n a l / e c o n o r n l c data on l a r g e , i n t e g r a t e d c o a l g a s i f i c a t i o n p l a n t s , (ii) e x p a n d e d e n g i n e e r i n g data b a s e s , and (ill) t h e d e v e l o p m e n t of m o r e f u n d a m e n t a l l y - o r i e n t e d i n f o r m a t i o n on t h e r a t e - c o n t r o l l i n g s t e p s of t h e v a r i o u s p r o c e s s e l e m e n t s . W h i l e t h e s e n e e d s a r e f o c u s e d on c o a l g a s i f i c a t i o n a s r e l a t e d to t h e p r o d u c t i o n of h i g h - B T U SNC, m a n y o f t h e n e e d s a r e g e n e r i c in n a t u r e and w i l l b e u s e f u l in a v a r i e t y of c o a l - g a s l f l c a t i o n a p p l i c a t i o n s ° S p e c i f i c r e s e a r c h n e e d s a r e l i s t e d h e r e f o r t h r e e c a t e g o r i e s of R&D. 4.6-1.

E n g i n e e r i n g D e v e l o p m e n t and T e s t i n g

(1) L a r g e - s c a l e o p e r a t i o n a l and p e r f o r m a n c e d a t a a r e n e e d e d on IGCC p l a n t s s u c h a s Cool Water and also for the G P C G P converting coal-to-SNG. (il) Expanded engineering data bases should be developed for oxygen-blown, ash-agglomerating, fluldlzed-bed gasiflers to optimize designs for specific applications (pressure, fines collection and recycle, coal types, in-bed desu1~urizatlon).

12 11 10 9 -D O

% ~

8

Cost of s e r v i c e for dry-bottom Lurgl technology

°'-.. "..

-- 7

%% / ~.

. . . . . . .

~6

Levelized constant-dollar cost for dry-bottom Lurgi technology

~.~ . . . .

~.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

"°°°

O

~,

5 U

°°.

4 .

......

~

.

"-.... Levehzed constant cost for advanced ....... ""~.-...~... technology

/

°'"°°.°O..o..

~ - -.i ..~ ~ . ~

Cost of service for advanced technology ..................

I

1

I

3

I

I

5

I

I

7

I

I

9

I

!

I

11

!

13

I

I

15

~

----"-'--.

I

I

17

I

I

1

19

Y e a r of o p e r a t i o n

F i g . 4. 5- 2.

Estimated cost of S N G for dry-bottom Lurgl technology and advanced gasification and downstream-processing technologies (250 m m SCF/ day, lignite); c o n s t a n t 1985 d o l l a r s a r e u s e d .

686

Energy,

The I n t e r n a t i o n a l J o u r n a l

(ill) S c a l e - u p d a t a for e m e r g i n g t e c h n o l o g i e s a r e r e q u i r e d for s u c h p r o c e s s e s a s t h e d i r e c t m e t h a n a t l o n c o n c e p t a n d the CNG a d v a n c e d a c l d - g a s r e m o v a l c o n c e p t . (iv) I n t e g r a t e d p e r f o r m a n c e e v a l u a t i o n s of a d v a n c e d g a s i f i c a t i o n t e c h n o l o g i e s a r e n e e d e d for t e c h n o l o g i e s s u c h a s the B G C / L u r g i s l a g g i n g g a s i f l e r a n d the a s h - a g g l o m e r a t i n g , f l u l d l z e d b e d p r o c e s s w i t h a d v a n c e d d o w n s t r e a m p r o c e s s i n g , a s w e l l a s for c o n c e p t s s u c h a s the d i r e c t m e t h a n a t i o n p r o c e s s a n d t h e CNG a c i d - g a s r e m o v a l s y s t e m . (v) D e v e l o p m e n t a n d v a l i d a t i o n a r e r e q u i r e d of s c a l e - u p m o d e l s , w i t h p a r t i c u l a r e m p h a s i s on coal gasifiers. (vi) E x p l o r a t o r y s t u d i e s s h o u l d b e c a r r i e d out to d e v e l o p i n i t i a l d a t a b a s e s f o r new, a d v a n c e d p r o c e s s c o n c e p t s for g a s i f i c a t i o n a n d d o w n s t r e a m p r o c e s s i n g . (vii) I m p r o v e d , h l g h - t e m p e r a t u r e h e a t r e c o v e r y s y s t e m s a r e n e e d e d . (viii) E x p a n d e d e n v i r o n m e n t a l d a t a b a s e s s h o u l d b e e s t a b l i s h e d for a d v a n c e d t e c h n o l o g i e s i n the a r e a s of p r o d u c t i o n , f a t e , c o n t r o l , a n d d i s p o s a l or t r e a t m e n t of t r a c e c o n s t i t u e n t s . 4.6-Z.

T e c h n o l o g y B a s e Data f o r D e s i g n

(i) T h e d e v e l o p m e n t of m e t a l a l l o y s for h i g h - t e m p e r a t u r e , h e a t r e c o v e r y a p p l i c a t i o n s should be supported. (ii) The d e v e l o p m e n t of i m p r o v e d c e r a m i c s f o r h l g h - t e m p e r a t u r e a p p l i c a t i o n s (i. e . , particulate filters, valves) should be encouraged. (iii) E x p a n d e d d a t a b a s e s a r e n e e d e d on the e r o s i o n - c o r r o s l o n b e h a v i o r a n d r e s i s t a n c e of metals and ceramics in coal-gaslflcatlon environments. (iv) L o n g - t e r m c o r r o s i o n d a t a (for m o r e t h a n 1 0 , 0 0 0 h r ) s h o u l d b e o b t a i n e d i n c o a l g a s i f i c a t i o n e n v l r o r ~ n e n t s , w i t h p r o p e r c o n s i d e r a t i o n of a l k a l i m e t a l s , s u l f l d a t l o n , a n d c h l o r i d e s . (v) V a p o r - l i q u l d e q u i l i b r i u m d a t a a r e n e e d e d a t e l e v a t e d p r e s s u r e s a n d t e m p e r a t u r e s for s e l e c t e d m u l t l c o m p o n e n t s y s t e m s i n v o l v i n g s y n t h e s i s gas, s t e a m , h e a v y o i l s ( t a r s ) , l i g h t a r o m a t i c s , p h e n o l l c s , f a t t y a c i d s , CH4, HzS, CSz, COS, m e r c a p t a n s , NHB, HC1, HCN, A s H 3 , Sell 2, Hgo (vl) T r a n s p o r t d a t a ( t h e r m a l c o n d u c t i v i t y , v i s c o s i t y , d l f f n s l v i t y ) s h o u l d b e m e a s u r e d for tars and slurries (oil/solids, tar/sollds, water/solids). (vii) T h e r m o d y n a m i c d a t a a r e r e q u i r e d , i n c l u d i n g i m p r o v e d e s t i m a t e s f o r f r e e e n e r g y of f o r m a t i o n , h e a t s of f o r m a t i o n , e n t r o p i e s , s p e c i f i c h e a t s . (viii) S o u r - w a t e r s t r i p p e r v a p o r - l l q u l d e q u i l i b r i a s h o u l d be m e a s u r e d for H z O / N H j / C O z / HzS s y s t e m s a t 0 to 100 psig a n d Z0 to Z00°Fo (ix) I m p r o v e d c o r r e l a t i o n s a r e n e e d e d for p r e d i c t i o n s of m a s s - t r a n s f e r c o e f f i c i e n t s a n d other engineering design parameters whenever multicomponent systems are involved. 4. 6-3. Basic l~esearch Needs for Advanced Systems (i) controlling (il) component

I m p r o v e d u n d e r s t a n d i n g i s n e e d e d of the c h e m i c a l p r o c e s s e s a s s o c i a t e d w i t h a n d the f r a g m e n t a t i o n / g a s i f i c a t i o n of c o a l . I m p r o v e d m o d e l s a r e r e q u i r e d f o r p r e d i c t i o n s of v a p o r - l i q u i d e q u i l i b r i a i n m u l t i systems.

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