Fluid-Bed-Augmented CkES Systems

Albert J. Giramonti

CSITED TECHNOLOGIES RESEARCH CEXTER East Hartford, Connecticut USA 06108

For Presentation At

Tnternational Assembly on Energy Storage May 27 to June 1, 1979 Dubrovnik, Yugoslavia

This document has not yet been approved for publication by the Y.S. 9e~artzent of E n e r ~ y , It is only to be used f c r the normal snd neces- sary pre-conference review until this a?proval has been obtained. In addition, this document does not necessarily represent the views of the U.S. Department of Energy.

Work Supported by t h e U.S. D e ~ a r t m e n t o f Energy under Cont rac t DE-AC06-76RLO 1830

. P a c i f i c Northwest Laboratory Richland, Washington 99352

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UNITED TECblNObOGlES RESEARCH CENTER

East Hartford, Connecticut 06108

F l u i d Bed Augmented CAES Systems

A . J. Gi ramont i

Uni ted T e c h n o l o g i e s Resea rch C e n t e r

ABSTRACT

.Compressed A i r Energy S t o r a g e (CAES) s y s t e m s a r e p o t e n t i a l l y a t t r a c t i v e f o r f u t u r e e l e c t r i c u t i l i t y l o a d l e v e l i n g a p p l i c a t i o n s . A p o t e n t i a l long- term

. weakness o f t h e c o n v e n t i o n a l CAES c o n c e p t i s i t s r e l i a n c e on c l e a n p e t r o l e u m f u e l s d u r i n g t h e power g e n e r a t i o n p e r i o d . T h i s consumption o f p e t r o l e u m c o u l d

. b e c o m p l e t e l y e l i m i n a t e d by t h e u s e of c o a l - f i r e d f l u i d bed combus to r s i n second g e n e r a t i o n CAES p l a n t s . A l a r g e number of CAES power sys tem c o n f i g u r - a t i o n s a r e p o s s i b l e u s i n g a t m o s p h e r i c f l u i d bed combust ion (AFBC) and - p r e s s u r i z e d f l u i d bed combustion (PFBC). The . f u e l consumption r a t e s f o r t h e s e

. . s y s t e m s a r e g e n e r a l l y comparable t o t h o s e f o r o i l - f i r e d CAES s y s t e m s . The f u t u r e p r o g n o s i s f o r u s i n g PFBC i n CAES sys tems ' l o o k s good. Recent c o r r o s i o n and e r o s i o n e x p e r i m e n t s i n f l u i d bed s y s t e m s s u g g e s t t h a t g a s t u r b i n e s . w i t h a c c e p t a b l e l i f e t i m e s a r e a d i s t i n c t p o s s i b i l i t y . The commercial s t a t u s of t h e s e s y s t e m s depends on t h e outcome o f , e x t e n s i v e c o r r o s i o n / e r o s i o n t e s t i n g i n s t a t i c and r o t a t i n g t e s t r i g s . CAES s y s t e m s u s i n g AFBC may b e an a t t r a c t i v e alternative t o u s i n g PFBC, a l t h o u g h t h e m a t e r i a l s problem would t h e n b e t r a n s f e r r e d from t h e ' t u r b i n e t o t h e h i g h t e m p e r a t u r e h e a t s x c h a n g e r s u r f a c e .

A reasonable e x p e c t a t i o n f o r t h e d a t e o f c o m i i e r c i a l i z a t i o n o f f l u i d bed ,

a ~ g ~ e n r e d CAES sys tem r a n g e s from 1 0 t o 1 5 y e a r s .

: .

UNITED TECHNOLOGIES

INTRODUCTION

An e n e r g y s t o r a g e s y s t e m which cou ld b e a t t r a c t i v e f o r f u t u r e e l e c t r i c u t i l i t y p2ak power a p p l i c a t i o n s i s a modi f i ed g a s t u r b i n e power sys tem u t i l i z i n g underground s t o r a g e of compressed a i r . I n c o n v e n t i o n a l compressed a i r ene rgy s t o r a g e (CAES) schemes ( s e e R e f . / l ) , synchronous g e a r q l u t c h e s

. would be used t o .uncouple t h e compressor and t u r b i n e s o t h a t t h e y would o p e r a t e d u r i n g d i f f e r e n t t i m e i n t e r v a l s - ( s e e F i g . 1 ) . D u r i n g . 1 0 ~ - l o a d , o f f - peak p e r i o d s t h e main e l e c t r i c g e n e r a t o r would b e used a s a motor t o d r i v e t h e compressor . The compressed a i r would t h e n be s t o r e d underground. During - s u b s e q u e n t peak l o a d p e r i o d s t h e compressed a i r would b e withdrawn from s t o r a g e , mixed k i t h p e t r o l e u m f u e l , b u r n e d , and expanded t h r o u g h t h e t u r b i n e

. t o ge r i e ra te power. T h i s c o n v e n t i o n a l pe t ro ' l eum-f i red scheme r e p r e s e n t s a p r a c t i c a l compromise between low equipment c o s t , r e l a t i v e l y s m a l l s t o r a g e volume, and low f u e l consumpt ion. One such sys tem i s c u r r e n t l y i n o p e r a t i o n i n Vest Germany, and o t h e r s of t h i s t y p e a r e deemed l i k e l y i n t h e f o r e s e e a b l e f u t u r e .

A p o t e n t i a l long- te rm weakness of t h e c o n v e n t i o n a l CAES c o n c e p t i s i t s r e l i a n c e on c l e a n p e t r o l e u m f u e l s d u r i n g t h e power g e n e r a t i o n p e r i o d . It seems a p p r o p r i a t e , t h e r e f o r e , t o i n v e s t i g a t e advanced CAES c o n c e p t s d e s i g n e d

* t o s u b s t i t u t e c o a l f o r pe t ro leum. D i r e c t comb.ustion of p u l v e r i z e d c o a l i n g a s t u r b i n e s was a t t e m p t e d i n t h e 1 9 5 0 ' s b u t p,roved v e r y u n s u c c e s s f u l because o f

. . prob lems w i t h a s h s l a g g i n g , e r o s i o n , and c o r r o s i o n . F l u i d bed combust ion (FBC) i s an improved method of c o a l combust ion which o f f e r s a p r o m i s i n g s o l u t i o n t o t h e s e e a r l i e r problems.

A p p l i c a t i o n o f FBC t o t h e CAES c o n c e p t p r o v i d e s f o r a l a r g e number of p o s s i b l e FBCICAES power p l a n t sys tem c o n f i g u r a t i o n s i n c o r p o r a t i n g a t m o s p h e r i c f l u i d bed combust ion (AFBC) o r p r e s s u r i z e d f l u i d bed combust5on (PFBC). I n p r i n r i p l e , a l l of t h e s e c o n f i g u r a t i o n s would u s e a c o a l - f i r e d FBC t o r e p l a c e t h e p e t r o l e u m - f i r e d b u r n e r of t h e c o n v e n t i o n a l CAES a r rangement .

The p u r p o s e o f t h i s p a p e r i s t o p r e s e n t t h e h i g h l i g h t s of an ongoing t e c h n i c a l and economic a s s e s s m e n t of t h e f e a s i b i l i t y o f c o a l - f i r e d FBC augmented

. . CAES sys tem c o n c e p t s . T h i s s t u d y i s b e i n g s u p p o r t e d by B a t t e l l e P a c j f i c Northwest L a b o r a t o r y (PNL) under S u b c o n t r a c t No. B-51299-A-P a s p a r t o f a PNL c o n t r a c t ( C o n t r a c t No. EY-76-C-06-1830) w i t h t h e Department of Energy. I t i s b a i n g performed by a s t u d y team managed by t h e Uni ted Tech- n o l o g i e s Resea rch C e n t e r (UTRC) which i n c l u d e s Coal P r o c e s s i n g C o n s u l t a n t s , L t d . of t h e Uni ted Kingdom and Acres American, I n c , ,

T h i s p a p e r s.ummarizes t h e t e c h n i c a l work completed d u r i h g t h e f i r s t q u a r t e r of t h e s t u d y p e r i o d . The s u b j e c t s a d d r e s s e d i n c l u d e t h e f l u i d bed combus t i o n t e c h n o l o g y rev iew and a s s e s s m e n t , t h e turbomachinel-!: t echnd logy r e v i e w and Assessment., component a v a i l a b i l i t y and R&D r e q u i r e m e n t s , a l t e r n a t i v e s y s t e m c o n f i g u r a t i o n s , a n d . p r e l i m i n a r y performance e s t i m a t e s .

FLUID BED CObIBUSTION TECHNOLOGY

A f l u i d bed i s p r o d u c t e d by t u r b u l e n t f l o a t a t i o n of c r u s h e d i n e r t m a t e r i a l i n a r i s i n g a i r s t r e a m . The p r i n c i p l e of bed f l u i d i z a t i o n i s q u i t e s i m p l e ( s e e F'ig. 2 ) . When a s t a t i ' c bed of r e l a t i v e l y d e n s e p a r t i c l e s i s s u b j e c t e d t o an upward, low-ve loc i ty f low of g a s , t h e g a s p a s s e s th rough t h e bed w i t h o u t d i s t u r b i n g t h e p a r t i c l e s . I f t h e v e l o c i t y of t h e g a s i s con- t i n u a l l y i n c r e a s e d , however, a p o i n t w i l l e v e n t u a l l y b e . r e a c h e d a t which t h e i n d i v i d u a l p a r t i c l e s w i l l b e f o r c e d upwards by t h e aerodynamic d r a g f o r c e and i n c i p i e n t f l u i d i z a t i o n w i l l b e g i n . I f t h e g a s v e l o c i t y i s f u r t h e r i n c r e a s e d , expans ion o f t h e bed o c c u r s p e r m i t t i n g an i n c r e a s e i n t h e g a s f low r a t e .

. The bed becomes h i g h l y t u r b u l e n t and r a p i d mix ing of t h e p a r t i c l e s o c c u r s . The s u r f a c e i s no l o n g e r w e l l d e f i n e d b u t a p p e a r s d i f f u s e , and b u b b l e s of ' g a s ' s i m i l a r t o t h o s e formed i n a b o i l i n g l i q u i d r i s e th rough t h e bed. A

. ,bed i n t h i s s t a t e i s s a i d t o be f l u i d i z e d . S t i l l f u r t h e r i n c r e a s e s i n gas v e l o c i t y cause p r o g r e s s i v e l y l a r g e r p a r t i c l e s t o become e n t r a i n e d i n and .

c a r r i e d o f f ( e l u t r i a t e d ) by t h e g a s s t r e a m . Consequen t ly , f o r a p a r t i c u l a r bed w i t h a g i v e n p a r t i c l e s i z e range t h e r e w i l l be a n upper and lower l i m i t of v e l o c i t y ( f l u i d i z i n g v e l o c i t y ) between which s a t i s f a c t o r y f l u i d i z a t i o n w i l l be e s t a b l i s h e d .

. . I n FBC, t h e , p a r t i c l e s forming t h e bed a r e composed of s u i t a b l e i n e r t m i n e r a l m a t t e r . For c o a l b u r n i n g , t h e s e would p r o b a b l y be t h e r e s i d u a l ash from p r e v i o u s l y burned c o a l and g raded l i m e s t o n e o r d o l o m i t e t o a b s o r b s u l f u r d i o x i d e d u r i n g combustion. The f l u i d i z i n g g a s i s t h e combust ion a i r . Coal i s f e d c o n t i n u o u s l y i n t o t h e bed i n t h e q u a n t i t y r e q u i r e d t o m a i n t a i n t h e d e s i r e d

' bed t e m p e r a t u r e .

The d e s i g n of a c o a l - f i r e d FBC i s s i g n i f i c a n t l y i n f l u e n c e d by t h e o p e r a t i n g c o n d i t i o n s . The most i m p o r t a n t o f t h e s e a r e bed t e m p e r a t u r e , f l u i d i z i n g v e l o c i t y , o p e r a t i n g p r e s s u r e , and p a r t i c l e s i z e . The FBC bed t e m p e r a t u r e muSt be c o n t r o l l e d w i t h i n f a i r l y narrow limits, i . e . , ,1425 t o 1650 F (775 L U

. , 900 C). T h i s c o n t r o l i s n e c e s s a r y t o achieve. h i g h c o n b u s t i o n e f f i c i e n c y , ' . o b t a i n h i g h h e a t t r a n s f e r r a t e s t o in-bed t u b e s , maximize s u l f u r r e t e n t i o n ,

a v o i d a s h s i n t e r i n g , l i m i t t h e m e t a l t e m p e r a t u r e of h e a t t r a n s f e r s u r f a c e s ' i n

. . t h e b e d , and reduce e m i s s i o n s of n i t r o g e n o x i d e s and a l k a l i metal sa l t s . The f l u i d i z i n g velocity must a l s o be c o n t r o l l e d w i t h i n f a i r l y narrow l ' i m i t s , i. e . , 2 .5 t o 4 .5 f t / s e c (0 .75 t o 1 . 4 m / s ] f o r . a PFBC and 2 . 5 t o 8 f t l s e c (0 .75 t o 2.5 m/s) f o r a n AFBC. O p e r a t i o n w i t h i n t h i s r ange w i l l e s t a b l i s h bed f l u i d i z a t i o n , p r o v i d e oxygen f o r combust ion, and l i m i t e l u t r i a t i o n of bed p a r t i c l e s . The s e l e c t i o n o f o p e r a t i n g p r e s s u r e w i l l i n f l u e n c e combustion e f f i c i e n c y , s u l f u r r e t e n t ' i o n , n i t r o g e n o x i d e s emiss ion l e v e l s , and c a p i t a l c .os t s . O p e r a t i o n . . a t e l e v a t e d p r e s s u r e (PFBC) w i l l p roduce b e n e f i c i a l r e s u l t s f o r a l l o f t h e s e p a r a m e t e r s a s opposed t o o p e r a t i o n a t a t m o s p h e r i c p r e s s u r e (KFBC). The c h o i c e ' o f p a r t i c l e s i z e i s r e l a t e d t o t h e c h o i c e of f l u i d i z i n g v e l o c i t y . The lower l i m i t of p a r t i c l e s i z e i s de te rmined by t h e requirement t o a v o i d e x c e s s i v e c a r r y o v e r of combus t ib le m a t e r i a l , u n r e a c t e d s o r b e n t , and bed m a t e r i a l . The upper l i m i t i s de te rmined by t h e d e s i r e t o a c h i e v e h igh

h e a t t r a n s f e r r a t e s t o in-bed t u b e s and e f f e c t i v e s o l i d s mix ing w i t h o u t l o c a l i z e d s e g r e g a t i o n . The d e s i g n o f a PFBC f o r CAES a p p l i c a t i o n s i s a l s o i n f l u e n c e d by f a c t o r s un ique t o t h e a p p l i c a t i o n . These i n c l u d e l o a d f o l l o w i n g , h o t gas p a r t i c u l a t e c l e a n u p and a l k a l i e m i s s i o n r e d u c t i o n .

TURBOPIACHINERY TECHNOLOGY

The d e s i g n of t1.1rbomachinery i s a l s o s i g n i f i c a n t l y i n f l u e n c e d by t h e o p e r a t i n g c o n d i t i o n s . The o p e r a t i n g c o n d i t i o n s f o r t h e tu rbomachinery i n a - FBCICAES power p l a n t sys tem w i l l depend on whether an AFBC o r PFBC i s used . In' e i t h e r c a s e , however, t h e , o p e r a t i n g t e m p e r a t u r e w i l l be c h a r a c t e r i s t i c . o f c o n d i t i o n s which were a t t a i n a b l e twenty y e a r s ago.

The a p p l i c a t i o n o f an AFBC would r e q u i r e r e l a t i v e l y minor m o d i f i c a t i o n s o f c l e a n f u e l - f i r e d tu rbomachinery d e s i g n s . The AFBC would be used a s an a i r h e a t e r , and t h i s h e a t e d a i r would b'e expanded i n t h e t u r b i n e , . Although t h e t u r b i n e would be r e l a t i v e l y s i m p l e t o d e s i g n , a n A F B C ~ C A E S sys tem would s t i l l be f a c e d w i t h a m a t e r i a l s problem. I n p a r t i c u l a r , t h e e x t e n s i v e h e a t t r a n s f e r s u r f a c e s immersed i n t h e bed and i n t h e h o t c o n v e c t i v e zone f o l l o w i n g t h e bed must c o n t a i n t h e h i g h p r e s s u r e compressed a i r w h i l e b e i n g s u b j e c t e d t o h i g h t e m p e r a t u r e .

The u s e of a PFBC would p r e s e n t more of a d e s i g n c h a l l e n g e t o e n s u r e h i g h r e l i a b i l i t y and low main tenance f o r t h e t u r b i n e . The s i z e and amount of p a r t i c l e s e n t e r i n g t h e t u r b i n e would have t o be c o n t r o l l e d w i t h i n narrow l i m i t s by e f f e c t i v e h o t ' g a s c l e a n u p t o minimize t u r b i n e e r o s i o n and p a r t i c l e d e p o s i t i c n . A l i m i t e d amount o f p a r t i c l e s between 2 and 1 0 microns cou ld be t o l e r a t e d ; however, e s s e n t i a l l y a l l p a r t i c l e s g r e a t e r t h a n 1 0 microns would have t o , b e removed from t h e PFBC e f f l u e n t g a s s t r e a m b e f o r e ' the t u r b i n e . Smal l p a r t i c l e s ( 2 micronsand less i n s i z e ) have an a f f i n i t y t o a d h e r e on ,

impac t : t h e r e f o r e , c o n c e n t r a t i o n s s u f f i c i e n t t o c a u s e f o u l i n g of t h e a i r f o i l s must be avoidmed. The l e v e l o f v o l a t i l i z e d a l k a l i m e t a l s a l t s i n t h e PFBC e f f l u e n t g a s must be k e p t t o a minimum, and c o r r o s i o n r e s i s t a n t m a t e r i a l s o r c o a t i n g s must be u s e d . t o reduce t h e p o t e n t i a l f o r e x c e s s i v e c o r r o s i o n .

O f f - t h e - s h e l f F B C 2nd tu rbomachinery equipment does ' no t presrr lLly e x i s t f o r FBC/CAES a p p l i c a t i o n s .

S n a l l s c a l e , commercial f l u i d bed b o i l e r sys tems can be e n g i n e e r e d now. However, t h e l a r g e r , h i g h e r t e m p e r a t u r e FBC equipment . a s s o c i a t e d w i t h CAES s y s t e m s require c o n t i n u e d development , The major areas i n which R&D' on FBC i s r e q u i r e d . i n c l u d e f e e d e r s gor t h e c o a l and s o r b e n t , d e v i c e s f o r e n s u r i n g e f f i c i e n t l a t e r a l d i s t r i b u t i o n of f u e l i n t h e b e d , con ta inment f o r t h e combustor , d i s t r i b u t o r s f o r t h e f l u i d i z i n g and combustion a i r , h e a t t r a n s f e r

s u r f a c e s f o r b o t h in-bed and 'above-bed t u b e s , d e p r e s s u r i z a t i o n sys tems f o r s p e n t s o r b k n t and f u e l a s h , t u b e b u n d l e s f o r min imiz ing bed d e p t h and c o n t r o l sys tems f o r . l o a d f o l l o w i n g .

I f an AFBC were used i n a CAES power p l a n t sys tem a p p l i c a t i o n , t h e modi- f i c a t i o n of e x i s f i n g p e t r o l e u m - f i r e d tu rbomachinery shou ld n o t produce any s i g n i f i c a n t problems. However, t h e t u r b i n e s f o r expans ion of g a s e s from a PFBC r e p r e s e n t a major d e s i g n u n c e r t a i n t y a t t h i s t ime . The major a r e a s o f tu rbomachinery R&D would be d i r e c t e d toward c o m p a t i b i l i t y between t h e PFBC and t u r b i n e . The e f f e c t of e r o s i o n on g a s t u r b i n e s must be b e t t e r documented, and e f f e c t i v e h o t gas c leanup sys tems must b e developed t o c o n t r o l p a r t i c u l a t e s . Methods must b e developed which w i l l l i m i t d e p o s i t i o n . The c o r r o s i o n mechaiiism must be b e t t e r u n d e r s t o o d , and m a t e r i a l s must be developed t h a t w i l l w i t h s t a n d c o r r o s i o n p l u s t h e combined e f f e c t s o f c o r r o s i o n and e r o s i o n .

S u c c e s s f u l comple t ion of t h e development a c t i v i t i e s mentioned above cou ld l e a d t o c o m m e r c i a l i z a t i o n by t h e mid-1980's of an AFBCICAES sys tem

' . w i t h in-bed a i r h e a t e r t u b e m e t a l t e m p e r a t u r e l i m i t e d t o 1200 F (650 C). T h i s c o u l d be fo l lowed by t h e e a r l y 1 9 9 0 ' s w i t h a PFBCICAES sys tem w i t h t h e same t u b e m e t a l t e m p e r a t u r e l i m i t a t i o n . It i s e n v i s i o n e d t h a t a i r h e a t e r t u b e s i n t h e bed c o u l d o p e r a t e up t o t h e bed t e m p e r a t u r e f o r b o t h t h e A F B C ~ C A E S

- . and PFBCICAES sys tems by t h e mid 1 9 9 0 ' s .

A number of p o t e n t i a l CAES c y c l e c o n f i g u r a t i o n s have been c o n s i d e r e d u s i n g PFBC and AFBC, w i t h o r w i t h o u t h e a t ' recovery s team c y c l e s . Some of t h e s e c o n f i g u r a t i o n s would r e q u i r e t h e c o a l combustors t o c y c l e o r o p e r a t e o n l y d u r i n g t h e peak l o a d p e r i o d w i t h t h e e n e r g y f o r o f f -peak compress ion p r o v i d e d from t h e u t i l i t y g r i d . O t h e r s would a l l o w t h e f l u i d beds t o ' oprrzLe c o n t i n u a u s l y and p r o v i d e some or a l l of t h e . n f f - p e a k energy f o r a i r c o ~ ! ~ r e s s i o n ( s e e . ~ e f . 2 ) . Th i s paper i s r e s t r i c t e d t o t h e former t y p e of c o n f i g u r a t i o n .

One p romis ing c o a l - f i r e d P F B C ~ C A E S c o n f i g u r a t i o n i s d e p i c t e d i n F i g . 3 . T h i s a r rangement i s based on t h e p r e l i m i n a r y o i l - f i r e d CAES sys tem p r e s e n t e d i n Ref. 1. The major change i n v o l v e s s u b s t i t u t i o n of a c o a l - f i r e d PFBC f o r e a c h o f t h e two o i l - f i r e d b u r n e r s o r i g i n a l l y p laced .be fore t h e h i g h p r e s s u r e expans ion t u r b i n e (ET) and t h e r e h e a t low p r e s s u r e t u r b i n e (LT) . T h i s ar rangement h a s t h e advan tage o f e l i m i n a t i n g a l l h e a t t r a n s f e r t u b i n g from t h e b e d s . A l s o , t h e gas, t e m p e r a t u r e e n t e r i n g t h e ET and LT t u r b i n e s would b e a t t h e maximum p o s s i b l e t e m p e r a t u r e f o r f l u i d bed combustors , s o t h e performance shou ld be good.

An a l t e r n a t e c o n f i g u r a t i o n i n F i g . 4 would i n c o ' r p o r a t e a s i n g l e PFBC. Ins , t ead o f u s i n g a s e p a r a t e h i g h p r e s s u r e PFBC b e f o r e t h e expans ion t u r b i n e ,

a i r go ing t o t h e e x p a n s i o n t u r b i n e would b e h e a t e d i n tubes ' immersed i n t h e main PFBC. T h i s concep t would e l i m i n a t e t h e c o m p l e x i t i e s of o p e r a t i n g two combustors a t d i f f e r e n t p r e s s u r e s w i t h s e p a r a t e c o a l f e e d and c o n t r o l sys tems . A l s o , t h e problems of op .e ra t ing a PFBC a t t h e v e r y h i g h p r e s s u r e s a s s o c i a t e d w i t h a i r s t o r a g e (where no PFBC o p e r a t i n g d a t a e x i s t ) would be a v o i d e d , and t h e e x p a n s i o n t u r b i n e would n o t b e exposed t o p a r t i c l e - l a d e n a i r from t h e PFBC.

A v a r i a t i o n o f t h e p r e c e d i n g PFBC scheme ( n o t i l l u s t r a t e d ) would e l i m i n a t e t h e in-bed t u b e s by p a s s i n g t h e h e a t e d a i r from t h e r e c u p e r a t o r d i r e c t l y t o t h e e x p a n s i o n t u r b i n e . T h i s c o n f i g u r a t i o n shou ld r e s u l t i n lower t e c h n i c a l r i s k t h a n t h e two p r e c e d i n g o n e s , b u t i t would s u f f e r a s l i g h t performance l o s s due t o t h e reduced g a s t e m p e r a t u r e e n t e r i n g t h e ex- pans ion t u r b i n e .

A l t e r n a t i v e sys tem c o n f i g u r a t i o n s a r e p o s s i b l e u s i n g AFBC i n s t e a d o f ' PFBC. A s d e p i c t e d i n F i g . 5 a i r from s t o r a g e would be p r e h e a t e d i n t h e re- c u p e r a t o r , f u r t h e r h e a t e d t o i n t e r m e d i a t e t e m p e r a t u r e i n t h e AFBC, and h e a t e d t o l t s f i n a l t e m p e r a t u r e i n c o n v e c t i v e h e a t exchangers u s i n g h o t gas e f f l u e n t from t h e bed. The t h r e e c o n v e c t i v e h e a t exchangers d e p i c t e d cou ld be used i n c r o s s f l o w , c o u n t e r f low, o r p a r a l l e l f low a r rangements . V a r i a t i o n s of t h i s

. . scheme a r e p o s s i ' b l e i n which t h e c o n v e c t i v e h e a t exchanger b e f o r e t h e ex- pans ion t u r b i n e c o u l d be e l i m i n a t e d . I n s t i l l a n o t h e r v a r i a t i o n , t h e a i r i n t h e LT t u r b i n e c o u l d be e x t r a c t e d mid-way t h r o u g h t h e e x p a n s i o n , r e h e a t e d i n a d d i t i o n a l t u b e s p l a c e d i n t h e AFBC and i n an a d d i t i o n a l c o n v e c t i v e h e a t . exchanger , and r e a d m i t t e d - t o t h e LT t u r b i n e f o r c o n t i n u a t i o n of t h e expans ion p r o c e s s . These.AFBC schemes a r e of i n t e r e s t b e c a u s e t h e y comple te ly e l i m i n a t e p o t e n t i a l t u r b i n e e r o s i o n problems a s s o c i a t e d w i t h p a r t i c u l a t e e l u t r i a t i o n from t h e bed by p a s s i n g on ly h e a t e d a i r t h r o u g h t h e t u r b i n e s .

FEC /CAES SY STEP1 PERFOR?IANCE

P r e l i m i n a r y performance e s t i m a t e s f o r s e v e r a l of t h e AFBC and PFBC con- f i g u r a t i o n s i d e n t i f i e d above a r e summarized i n T a b l e I . I n a l l c a s e s , t h e FBC e x i t t e m p e r a t u r e s and t u r b i n e i n l e t t e m p e r a t u r e s were s e l e c t e d to , be

. c o n s i s t e n t with'maximum a l l o w a b l e m e t a l t e m p e r a t u r e s a n t i c i p a t e d f o r each con- f i g u r a t i o n . The g a s t e m p e r a t u r e a t t h e e i i t of t h e AFBC i s t a k e n t o b e h ighe r t h a n t h a t from t h e PFBC t o account f o r t h e a d d i t i o n a l combustion and temper- a t u r e r i s e e x p e c t e d i n t h e AFBC f r e e b o a r d .

I n g e n e r a l , t h e PFBC schemes have power o u t p u t s and h e a t r a t e s which a r e comparable t o t h d s e ' r e p o r t e d (Ref . 1 ) f o r o i l - f i r e d schemes.. The PFBC scheme w i t h two s e p a r a t e beds h a s t h e b e s t pe r fo rmance , b u t t h i s a l s o c l e a r l y r e q u i r e s a v e r y h i g h p r e s s u r e PFBC which i s beyond t h e c u r r e n t s t a t e of t ech- no logy . I n g e n e r a l , t h e performance of t h e PFBC schemes i s about 1 0 p e r c e n t b e t t e r t h a n f o r t h e AFBC schemes. A l l of t h e AFBC scheme. v a r i a t i o n s

i n v e s t i g a t e d t o d a t e seem t o y i e l d about t h e same l e v e l of performance.

PRELIPIINARY COMCLU SIONS

Seve ra l advanced c o a l - f i r e d CAES system concepts appear f e a s i b l e based on t h e use of p re s su r i zed and atmospheric f l u i d bed combustors. The p red ic t ed o v e r a l l l e v e l of performance of t h e s e system c,oncepts i s roughly comparable t o t h a t prev ious ly es t imated f o r o i l - f i r e d CAES systems. The p r i n c i p a l advantages of t hese systems a r e t h e use of indigenous c o a l r e sou rces and t h e lower c o s t of c o a l r e l a t i v e t o o i l .

The f u t u r e prognos is f a r using pres su r i zed f l u i d bed combustors i n C-4ES systems looks good. Recent cor ros io .n /e ros ion experiments i n f l u i d bed systems sugges t t h a t gas t u r b i n e s wi th accep tab le l i f e t i m e s a r e a d i s t i n c t p o s s i b i l i t y . Add i t i ona l component and f u l l s i z e t u r b i n e t e s t i n g i n . r e a 1 f l u i d bed environ- ments a r e r e q u i r e d , however, t o v e r i f y t h e s e pre l iminary l i f e t i m e f o r e c a s t s .

Atmospheric f l u i d bed combustion systems may be an a t t r a c t i v e a l t e r n a t i v e o r backup t o p re s su r i zed f l u i d bed combustion systems. The use of atmospheric f l u i d bed combustion systems would e l i m i n a t e t h e u n c e r t a i n t i e s a s soc i a t ed w i t h e r o s i o n and c o r r o s i o n i n t h e gas t u r b i n e s . However, t h e m a t e r i a l s problem would be s h i f t e d t o t h e ex t ens ive hea t t r a n s f e r s u r f a c e which must be immersed i n t h e bed o r l oca t ed i n t h e hot convec t ive zone fo l lowing t h e bed.

The s t a t u s of commercial development of coa l - f i r ed f l u i d i z e d bed aug- mented compressed a i r energy s t o r a g e systems i s . u n c e r t a i n and depends on t h e outcone of ex t ens ive e r o s i o n / c o r r o s i o n t e s t i n g i n s t a t i c and r o t a t i n g t e s t r i g s . A reasonable expec ta t ion f o r t h e d a t e of commercial izat ion ( fo l lowing t e s t i n g , p i l o t , and demonstrat ion phases) f o r t h i s type of system ranges from 10 t o 15 y e a r s .

CONCLUDING RPlA.F.KS

I n c l o s i n g , i t i s recognized t h a t t h e f l u i d bed CAES c y c l e s descr ibed h e r e i n r ep re sen t only a f r a c t i o n of t h e t o t a l number of c o n f i g u r a t i o n op t ions a v a i l a b l e . Other c o n f i g u r a t i o n s no t y e t examined might prove h igh ly a t t r a c - t i v e . Also, c a p i t a l and ope ra t ing cos t d i f f e r e n c e s between systems have n o t been eva lua t ed . Fu tu re work i s planned t o yrovide a meaningful t e c h n i c a l and economic f e a s i b i l i t y e v a l u a t i o n of c o a l - f i r e d f l u i d bed CbES power s y s t e m .

REFERENCES

1. Gi ramont i , A . 3.: P r e l i m i n a r y F e a s i b i l i t y E v a l u a t i o n of Compressed A i r S t o r a g e Power Systems, UTRC Repor t R76-952161-5,NTIS PB 259 281/4GI, s u p p o r t e d by N a t i o n a l S c i e n c e Founda t ion Grant AER74-00242, Te'chnical O v e r s i g h t by Energy Research and Development A d m i n i s t r a t i o n , December 1976.

2 . G i r a m o n t i , A . J . and R . L . S a d a l a : P r e l i n i n a r y E v a l u a t i o n of Coal-Fired F l u i d Bed Compressed A i r Energy S t o r a g e Power P l a n t s , p r e s e n t e d a t CAES Technology S)mposiurn, P a c i f i c Grove, CA, ?lay 1978.

TABLE I

F B C ~ C A E S SYSTEM PERFORMANCE SUMMARY

Heat Rate Turbine I n l e t Temp

System FBC P r e s s , .FBC E x i t Temp, ET, LT, Power, Compression, Generation; Round T r i p , No. a t m . F F . .F M"(l) ~ t u / k ~ h ( 2 ) ~ t u / l c w h ( ~ ) B t u l k ~ h . . - .

1. Based on cons t an t system a i r flow r a t e 2 . Based o n , u t i l i t y g r i d . hea t r a t e a t 10,000 BtuIkWh 3 . Based on co 31 h ighe r h e a t i n g va lue 4 . Counter f low hea t exchangers 5.. P a r a l l e l f I > w hea t exchangers 6.. I nc ludes t e x p e r a t u r e r ise i n FBC f reeboard

FIG. . . 1

Simplified CAE$ System , Air intake, Exhaust

. . Motorlgenerator I I I

@ I Turbine

Bed Fluidization

I t 4 I

0000 000 OOOOC ~ o o o + o o ~ 00000 000 0000

00000 00000000 nan+nap

\I t Static bed

t t t t t t

lncipien t fluidization

Fluidized bed

Increasing +

gas flow

FIG. 3 . .

Coal-Fired PFBC/CAES System With Very High Pressure Bed

UNITED TECMNOLQGIES _ \I%. '

RESEARCH CENTER b-.

FIG. 4 .

-Fired P&BC/CAES System

3tal;n WHITED TECWFdQLOGIES PIESEARCH CENTER Gw,,,

1 ,.

To Storage ,&,,l, 4

.

FIG. 5 .

-Fired AFBC/CAES System

Coal l089iTEQ TIECldHOUDGIES 'B. - RESEARCH CENTER b-.