Oil Shale, Tar Sands, and Related Materials - American Chemical

12 Shell Pellet Heat Exchange Retorting: The S P H E R Energy-Efficient Process for

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Retorting O i l Shale J. E. GWYN, S. C. ROBERTS, D. E. HARDESTY, G. L. JOHNSON, and G. P. HINDS, JR. Shell Development Company, P.O. Box 1380, Houston, TX 77001 Oil shales o f primary interest f o r surface processing occur mainly i n the Piceance Basin o f western Colorado. These shales c o n t a i n , t y p i c a l l y , 10 t o 20 p e r c e n t w e i g h t o f h y d r o c a r b o n s r e coverable by simple p y r o l y s i s . Process r e s e a r c h and development i n s h a l e o i l p r o d u c t i o n has gone o n f o r d e c a d e s , b u t t h e once p l e n t i f u l s u p p l y o f low c o s t p e t r o l e u m c r u d e s made t h e e c o n o m i c s o f s u c h p r o c e s s e s v e r y u n f a v o r a b l e . T h e r e c e n t s h o r t a g e s and c o s t e s c a l a t i o n o f p e t r o l e u m c r u d e s have renewed i n t e r e s t s i n " u n c o n v e n t i o n a l " raw m a t e r i a l s o u r c e s s u c h a s c o a l and o i l s h a l e . S e v e r a l p r o c e s s e s f o r above ground r e t o r t i n g o f o i l s h a l e , w h i c h have been under d e v e l o p m e n t f o r some t i m e , i n c l u d e t h e T 0 S C 0 - I I , PARAH0, and U n i o n t e c h n o l o g i e s . ' S h e l l had p a r t i c u l a r i n t e r e s t s i n t h e f i r s t two. The TOSCO (The O i l S h a l e Company) p r o c e s s u s e s h o t b a l l s t o h e a t p r e h e a t e d s h a l e i n a r o t a r y k i l n t o r e t o r t i n g temperat u r e s . The s h a l e i s preheated d u r i n g staged, pneumatic t r a n s p o r t u s i n g f l u e gas f r o m t h e r e t o r t b a l l h e a t e r . The PARAH0 r e t o r t i s a v e r t i c a l k i l n e m p l o y i n g a downward moving r o c k bed w i t h u p f l o w i n g r e c y c l e gas and c o m b u s t i o n p r o d u c t s w h i c h sweep r e t o r t e d h y d r o c a r b o n s f r o m t h e v e s s e l . The U n i o n p r o c e s s i s s i m i l a r b u t u t i l i z e s an upward f l o w o f c r u s h e d s h a l e . S h a l e i s i n t r o d u c e d a t t h e bottom o f t h e r e t o r t and pushed upward b y a m e c h a n i c a l " r o c k pump". F l u i d i z e d bed r e t o r t i n g o f o i l s h a l e was p r o p o s e d i n t h e e a r l y f i f t i e s but was n e v e r developed t o a commercial s t a t e . The T 0 S C 0 - I I p r o c e s s i s c a p i t a l i n t e n s i v e b e c a u s e i t r e q u i r e s a l a r g e volume o f h e a t i n g g a s e s and m e c h a n i c a l l y complex e q u i p m e n t ; t h e PARAH0 and Union p r o c e s s e s a r e a l s o c a p i t a l i n t e n s i v e b e c a u s e t h e y have l o n g r e s i d e n c e t i m e r e q u i r e m e n t s t h a t e n t a i l m a s s i v e h a r d w a r e . The PARAH0 and Union p r o c e s s e s a r e , however, h e a t e f f i c i e n t a s a r e s u l t o f c o u n t e r c u r r e n t s h a l e and gas f l o w . But t h e TOSCO p r o c e s s , a l t h o u g h h a v i n g some d e g r e e o f h e a t r e c o v e r y , uses h e a t r e l a t i v e l y inefficiently. The p u r p o s e o f t h i s work was t o d e v e l o p a new r e t o r t i n g p r o c e s s o f r e l a t i v e l y low c a p i t a l c o s t t h a t i s m e c h a n i c a l l y s i m p l e , h i g h l y r e l i a b l e , and u s e s h e a t e f f i c i e n t l y . The p r o c e s s , ' t e r m SPHER f o r 1

2

0097-6156/81/0163-0167$05.00/0 ©

1981 American Chemical Society

Stauffer; Oil Shale, Tar Sands, and Related Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

OIL SHALE, TAR SANDS, AND RELATED

168

MATERIALS

S h e l l P e l l e t Heat Exchange R e t o r t i n g , i s a f l u i d i z a t i o n bed p r o c e s s conceived f o r the r e t o r t i n g o f o i l shale. T h e f l u i d i z a t i o n mode r e f e r r e d t o i n t h i s d i s c u s s i o n a p p l i e s t o a range o f s u p e r f i c i a l gas v e l o c i t i e s between t h o s e used f o r r i s e r t r a n s p o r t and d e n s e b e d o p e r a t i o n i n p r o c e s s e s such a s c a t a l y t i c c r a c k i n g . By t h i s mode, s h a l e can be made t o f l o w upward, c o u n t e r c u r r e n t l y t o l a r g e r h e a t c a r r i e r p e l l e t s that f a l l through t h e f l u i d i z e d mixture. This c o u n t e r f l o w o f h e a t - c a r r i e r p e l l e t s and r e l a t i v e l y c o a r s e s h a l e p a r t i c l e s i s the b a s i c idea around which n o v e l , small s i z e d , t h e r m a l l y e f f i c i e n t and e c o n o m i c a l l y v i a b l e p r o c e s s e s have been c o n c e i v e d . O t h e r f e e d s t o c k s t o w h i c h SPHER may have p o t e n t i a l a p p l i c a b i l i t y i n c l u d e numerous c o a l s , l i g n i t e , wood and bark w a s t e , a g r i c u l t u r a l r e s i d u e s , b i o t r e a t e r s l u d g e s , and i n d u s t r i a l and m u n i c i p a l s o l i d w a s t e s . Some s p e c i f i c p r o c e s s d e s c r i p t i o n s , w i t h some v a r i a t i o n s , are d i s c u s s e d below. B r i e f D e s c r i p t i o n o f Process Applied t o O i l Shale The SPHER p r o c e s s as o r i g i n a l l y c o n c e i v e d 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. T h i s c o n c e p t u a l d e s i g n p r o d u c e s 55,000 b b l / d a y (7575 t / d ) * o f raw s h a l e o i l f r o m 66,000 t o n / d a y (60,000 t / d ) o f 35 g a l / t o n (13.6%w) o i l s h a l e . I t c a n be seen t h a t t h e r e a r e two l o o p s f o r c i r c u l a t i o n o f h e a t c a r r y i n g b a l l s . The c o o l b a l l l o o p c a r r i e s heat f r o m t h e heat r e c o v e r y column t o t h e p r e h e a t e r . T h e hot b a l l l o o p c a r r i e s heat from the b a l l heater t o the r e t o r t . Shale i s crushed o r ground t o a f l u i d i z a b l e s i z e ; p r e f e r a b l y as l a r g e as i s compatible with heat t r a n s f e r requirements and ready s e p a r a t i o n from h e a t - c a r r y i n g b a l l s . I n i t i a l work i n d i c a t e s t h a t 1 / 1 6 - i n c h (1.6 mm) minus s h a l e and 1/4 (6 mm) o r 5/16 (8 mm) i n c h b a l l s are d e s i r a b l e . The s h a l e i s p r e h e a t e d i n a f a s t - f l u i d i z e d ( e n t r a i n i n g ) b e d b y outer loop, h e a t - c a r r y i n g b a l l s t h a t r a i n through the bed i n count e r c u r r e n t f a s h i o n ( F i g u r e 2 ) . W i t h a i r a s t h e f l u i d i z i n g medium, p r e h e a t i n g i s l i m i t e d t o a b o u t 600°F ( 3 1 5 ° C ) b e c a u s e t h e r e i s d a n g e r from a u t o - i g n i t i o n , w h i c h i s t i m e , t e m p e r a t u r e , and o x y g e n d e p e n d e n t . ) With other n o n o x i d i z i n g gases, p r e h e a t i n g i s l i m i t e d t o about 650°F (343°C) b y t h e o n s e t o f k e r o g e n p y r o l y s i s . In a d e n s e - b e d f l u i d i z e d b e d t h e p r e h e a t e d s h a l e i s f u r t h e r h e a t e d t o and h e l d a t t h e r e t o r t i n g t e m p e r a t u r e f o r s u f f i c i e n t t i m e t o c o m p l e t e t h e p y r o l y s i s r e a c t i o n s ( F i g u r e 3 ) . The t o t a l i n v e n t o r y o f shale i n the r e t o r t i n g v e s s e l i s determined by the r e q u i r e d r e s i d e n c e t i m e f o r c o m p l e t e k e r o g e n c o n v e r s i o n and t h e s h a l e t h r o u g h p u t . T h e r e t o r t h e a t r e q u i r e m e n t s a r e s u p p l i e d by c e r a m i c b a l l s w h i c h c i r c u l a t e i n t h e i n n e r l o o p . T h e y are r e h e a t e d i n a s e p a r a t e v e s s e l w h i c h may o p e r a t e a s a moving bed, r a i n i n g p e l l e t bed, o r e n t r a i n e d flow heater. The s p e n t s h a l e i s c o o l e d i n a f a s t - f l u i d i z e d b e d b y t h e r e c i r c u l a t e d cool p e l l e t s from the p r e h e a t e r . In t h i s manner, c o u n t e r c u r r e n t f l o w o f heat c a r r i e r s and t h e s h a l e a s s u r e s efficient * t o n = 2000 pounds, t = m e t r i c t o n = 1000 k g . 3


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Figure 1. SPHER oil shale process

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170

OIL SHALE, TAR SANDS, AND RELATED MATERIALS

65°C Figure 2.

SPHER

preheater


12.

GWYN ET A L .

Shell

Pellet

Figure 3.

Heat

Exchange

SPHER

Retorting

retort


171

172

OIL SHALE, TAR SANDS, AND RELATED

MATERIALS

energy u t i l i z a t i o n . T h i s c h a r a c t e r i s t i c i s a prime advantage o f the process. Most c o n d i t i o n s a n d f e a t u r e s o f t h e c o n c e p t u a l p r o c e s s a r e c h o s e n t o a s s u r e h i g h t h r o u g h p u t s ( s m a l l e q u i p m e n t ) and hence r e l a t i v e l y low c a p i t a l and f i x e d c o s t s . T h e s e i n c l u d e t h e c h o i c e o f f l o w r e g i m e s , h e a t c a r r i e r s ( d e n s i t y and h e a t c a p a c i t y ) and t h e s o l i d s - t o gas w e i g h t r a t i o s . A t t e n d a n t f e a t u r e s o f t h e p r o c e s s , such a s b a f f l e d e s i g n and gas r o u t i n g , a r e c h o s e n t o a c h i e v e o p e r a b i l i t y and optimum operation. S e g r e g a t i o n o f t h e two b a l l l o o p s p e r m i t s t h e t a i l o r i n g o f t h e b a l l m a t e r i a l , shape and s i z e t o e a c h s p e c i f i c t a s k . C i r c u l a t i o n o f b a l l s i n t h e o u t e r l o o p i s a r e l a t i v e l y low t e m p e r a t u r e o p e r a t i o n and i s d e d i c a t e d t o heat t r a n s f e r . T h e r e f o r e , d e s i r e d b a l l p r o p e r t i e s i n c l u d e high heat c a p a c i t y , small s i z e o r l a r g e heat t r a n s f e r s u r f a c e , e r o s i o n r e s i s t a n c e , and low c o s t . Hence, a pea g r a v e l may be s u i t a b l e . C o r r o s i o n r e s i s t a n c e may n o t be needed u n l e s s c o n d e n s a t i o n o c c u r s i n t h e h e a t r e c o v e r y s e c t i o n . T h e use o f t h e s m a l l e s t b a l l s s e p a r a b l e f r o m t h e s h a l e i n c r e a s e s h e a t t r a n s f e r and r e d u c e s t h e s i z e o f the exchange v e s s e l r e q u i r e d . In c o n t r a s t , c i r c u l a t i o n o f b a l l s i n t h e i n n e r l o o p i n v o l v e s t h e b a l l h e a t e r and r e t o r t where h i g h t e m p e r a t u r e s a n d l o n g e r r e s i d e n c e times a r e r e q u i r e d . Reaction r a t e r a t h e r than heat t r a n s f e r i s e x p e c t e d t o be t h e c o n t r o l l i n g f a c t o r i n t h e r e t o r t d e s i g n . I n o r d e r t o a c h i e v e t h e r e s i d e n c e t i m e needed f o r h i g h c o n v e r s i o n a p s e u d o p l u g - f l o w d e v i c e such a s a r o t a r y k i l n o r a s t a g e d , d e n s e - p h a s e f l u i d i z e d b e d may be d e s i r a b l e . Since heat t r a n s f e r i s n o t c o n t r o l l i n g , t h e b a l l s can be l a r g e r f o r e a s i e r s e p a r a t i o n f r o m s h a l e but t h e y must s t i l l be s m a l l enough t o p e r m i t p n e u m a t i c t r a n s p o r t . T h e s e i n n e r l o o p b a l l s must a l s o be r e s i s t a n t t o t h e r m a l s h o c k , c h e m i c a l a t t a c k b y t h e hot g a s e s and s p e n t s h a l e and e x p o s u r e t o h i g h temperatures. Thus, the c h o i c e of the inner loop b a l l s i s l i m i t e d t o m a t e r i a l s such a s c e r a m i c s . Detailed Process D e s c r i p t i o n A more p r o c e s s o r i e n t e d s c h e m a t i c F i g u r e 4.

o f the process

i s shown i n

S h a l e Feed P r e p a r a t i o n . S h a l e p r e p a r a t i o n f o r SPHER r e q u i r e s more e n e r g y t h a n i t d o e s f o r p r o c e s s e s such a s T 0 S C 0 - I I i n t h a t t h e l a r g e r c r u s h e d s h a l e used i n T 0 S C 0 - I I , e.g., 1 / 2 - i n c h (13 mm) m i n u s , must be r e d u c e d t o a r e a d i l y f l u i d i z a b l e s i z e , e.g., 1 / 1 6 - i n c h (1.6 mm) m i n u s , f o r use i n SPHER. G r i n d i n g b y s e p a r a t i n g and r e c y c l i n g coarse shale i s expected t o produce a b e t t e r s i z e range with l e s s f i n e s t h a n o n c e - t h r o u g h g r i n d i n g i s f o r t h e same maximum p a r t i c l e size. S e p a r a t i o n o f s h a l e with t h e d e s i r e d s i z e from o v e r s i z e d m a t e r i a l may be a c c o m p l i s h e d b y e l u t r i a t i o n w i t h gas o r b y s c r e e n i n g . The r e c o v e r e d c o a r s e s h a l e i s c o n v e y e d back t o t h e g r i n d e r . Shale w i t h t h e d e s i r e d t o p s i z e may t h e n be p n e u m a t i c a l l y t r a n s p o r t e d t o a feed hopper o r standpipe.



Raw Shale

0

Air + Fuel Gas

Ball Mill

50F 10C

1000F 538C

100F 38C

Air

Preheat

550F 288C

-8

625F 329C

Figure 4.

Aii from Heat Recovery

-67

Superheater Flue Gas

Raining

Steam

900F 482C

• 0 -

—g

scheme

Xir

560F 293C

Air to fteheat

11 OOF 593C

ball oil shale pyrolysis

900F 482C

900 F 482C

Retort

Steam

Moisturizer

.— _ 50F 10C

500 F 260C

175F

79C

=^> Spent Shale

• Flue Gas

Water

Product Vapor

Oil Shale, Tar Sands, and Related Materials - American Chemical

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