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ELSEVIER PII: $0016-2361(97)00112-9Fuel Vol. 76, No. 11, pp. 106 7-107 3, 1997 1997 E lsev ier Science L td . A l l r igh ts r eservedPrinted in Great Britain0016-2361/97 $17.00+0.00

Coal gas i f ica t ion character is t ics inan in te rna l l y c i rcu la t ing f lu id i zedb e d w i t h d r a u g h t t u b eYong Jeon K im , Jong Min Lee and Sang Done K imDepartm ent of Chemical Engineer ing and Energy & Env ironme nt Research Center, KoreaAdvan ced Ins t i tute of S cience and Technology, Taejon 305-701, Korea(Received 18 A pri l 1996; revised 17 March 1997)Australian coal was gasified at atmospheric pressure in an internally circulating fiuidized bed (0.3 m i.d . x 2.7 mhigh) with a draught tube (0.1 m i.d. X 0.9 m high) and a gas separator over the draught tube. The effects ofreaction temperature (780-900C), oxygen/coal m ass ratio (0.30-0.53), coal feed rate (5.3-12.1 kg h -z) andsteam/coal mass ratio (0.30-0.81) on composition o f product gas, carbon conversion, cold gas efficiency and gasyield and calorific value were determined. Low-CV gas in the draught tube region and medium-CV gas in theannulus region can be obtained. In the annulus region, the composition o f the product gas (vol.%) is H2 31.8- 46.2,CO 18.8-25.6, CO2 13.2-20.4 and C H 4 5.3-10.4, with a CV of 8.6-13.2 MJ m - 3 . In the draught tube region, thecomposition is H2 8.3-19.7, CO 6.7-13.1, CO2 18.9-35.3 and C H 4 1.9-4.4, with a CV of 3.3-5.9 MJ m - 3 . 1997 Elsevier Science Ltd.(Keyw ords: coal gasif ication; draught-tube; internally circulating fluidized bed ; product gas q u a l i t y )

G a s i f i c a t i o n i n a f l u i d i z e d b e d c a n b e u s e d t o c o n v e r tcoa l 1 -6, b iom ass 7 and w as te m a te r ia l s 7 '8 to fue l o r syn thes i sg a s . T h e i n t r i n s i c p r o b l e m s o f c o a l c o n v e r s i o n i n f l u i d i z e db e d s a r e k n o w n t o b e h i g h c a r b o n l o s s e s d u e t o c o a ls h a t t e ri n g a n d s u b s e q u e n t e l u t r ia t i o n o f f in e s , a n d l o wc o n v e r s i o n o f r e a c t a n t g a s e s d u e t o g a s b y p a s s i n g 4'6'9"1. T os o l v e t h e s e p r o b l e m s , a d r a u g h t t u b e h a s b e e n i n s e r t e d i n af l u i d iz e d b e d t o d i v i d e i t i n t o t w o r e a c t i o n z o n e s 9 -1 3. T w or e a c t i o n z o n e s c a n b e a c h i e v e d : c o m b u s t i o n i n t h e d r a u g h tt u b e w i t h a i r , a n d g a s i f i c a t i o n w i t h s t e a m i n t h e a n n u l u szone 9-12 , o r v ice ve rs a 13. By f lu id iz ing so l ids in a d rau ghtt u b e a t a v e l o c i t y o f s e v e n t o t e n t i m e s t h e m i n i m u mflu id iz ing v e loc i ty (Um f) and in the ann ulus a t 0 . 7 -1 . 5 Um f, i ti s p o s s i b l e t o i n d u c e g r o s s c i r c u l a t i o n o f t h e b e d m a t e r i a l u pt h e d r a u g h t t u b e a n d d o w n t h e a n n u l u s. C i r c u l a t i o n o f th es o l i d m a t e r i a l w i t h i n t h e r e a c t o r p r o v i d e s e n e r g y t r a n s f e rf r o m t h e c o m b u s t i o n z o n e t o t h e g a s i f i c a t i o n z o n e . B yi n s t a ll i n g a g a s s e p a r a t o r o v e r t h e d r a u g h t t u b e , g a s o f h i g hc a l o r if i c v a l u e c a n b e p r o d u c e d i n t h e a n n u l u s ( g a s i f i c a t io n )z o n e .T o i n c r e a s e t h e c a l o r i f i c v a l u e o f t h e p r o d u c t g a s i n t h ea n n u l u s z o n e , g a s b y p a s s i n g f r o m t h e d r a u g h t t u b e t o t h ea n n u l u s r e g i o n s h o u l d b e m i n i m i z e d , s i n c e t h is w o u l d c a u s ed i l u ti o n a n d b u r n i n g o f th e p r o d u c t g a s f r o m g a s i f i c a t io na n d c o n s e q u e n t d e g r a d a t i o n o f i t s q u a l i t y . T o r e d u c e t h i sb y p a s s i n g , a d r a u g h t tube h a v i n g o r i f ic e s in t h e b o t t o m p a r th a s b e e n d e v i s e d r4 . B y c h a n g i n g t h e t y p e o f d r a u g h t t u b e ,d i f f e r e n t f l o w c h a r a c t e r i s t i c s c a n b e o b s e r v e d . T h e d r a u g h tt u b e w i t h o r i f ic e s (Figure lb) p r o v i d e s l e s s b y p a s s i n g f r o mt h e d r a u g h t t u b e t o t h e a n n u l u s r e g i o n t h a n t h a t o f g a p h e i g h tt y p e (Figure la) w i t h a b o u t t h e s a m e s o l i d s c i r c u l a t i o n14 14r a t e . I n c o l d b e d e x p e r i m e n t s , b y p a s s i n g f r o m d r a u g h t

t u b e t o a n n u lu s w a s r e d u c e d f r o m 6 - 1 1 % t o - 1 % , w h i l eb y p a s s i n g f r o m a n n u l u s t o d r a u g h t t u b e w a s i n c r e a s e d f r o m7 . 7 - 1 7 . 3 % t o 2 9 . 4 - 3 8 . 9 % b y c h a n g in g t h e t y p e o f d r a u g h tt u b e . D u e t o t h e h i g h r a t e o f b y p a s s i n g f r o m t h e a n n u l u s t ot h e d r a u g h t t u b e , t h e d r a u g h t t u b e r e g i o n a c t s a s ac o n v e n t i o n a l f l u id i z e d b e d g a s i f i e r r a t h e r t h a n a c o m b u s t o r .

T h e o b j e c t i v e o f th i s s t u d y w a s t o d e v e l o p a n e w t y p e o fc o a l g a s i f ie r , n a m e l y a n i n t e r n a l l y c i r c u l a t in g t t u i d iz e d b e dg a s i f ie r w i t h a n o r i f i c e - t y p e d r a u g h t t u b e a n d a g a s s e p a r a t o ro v e r t h e d r a u g h t t u b e t o i m p r o v e p r o d u c t g a s q u a l i t y . T h eg a s i f i e r w a s o p e r a t e d a t a t m o s p h e r i c p r e s s u r e t o d e t e r m i n et h e e f f e c t s o f r e a c t i o n t e m p e r a t u r e ( 7 8 0 - 9 0 0 C ) , o x y g e n /c o a l m a s s r a t i o ( 0 . 3 0 - 0 . 5 3 ) , c o a l f e e d r a t e ( 5 . 3 -1 2 .1 k g h - 1 ) a n d s t e a m / c o a l m a s s r a t i o ( 0 . 3 0 - 0 . 8 1 ) o n t h ep r o d u c t g a s c o m p o s i t i o n , c a r b o n c o n v e r s i o n , c o l d g a se f f i c i e n c y a n d g a s y i e l d a n d c a l o r i f ic v a l u e .

E X P E R I M E N T A LE x p e r i m e n t s w e r e c a r r i e d o u t i n a s t a i n l e s s s t e e l c o l u m n(0 . 3 m i . d . x 2 . 7 m h igh) w i th a cen t ra l ly loca ted d raug httube (0 . 1 m i . d . X 0 . 9 m h igh) a s shown in Figure 2 .

T h e a i r c h a m b e r c o m p r i s e d t w o p l e n u m s t o s u p p l y g a s ess e p a r a t e l y i n t o t h e d r a u g h t t u b e a n d t h e a n n u l u s z o n e . F o rdraug ht tube a i r supp ly , a d i s t r ibu tor (0 .1 m i . d . ) wi th s e venb u b b l e c a p s ( f o u r h o l e s x 2 .5 m m i .d . ) w a s u s e d . A 6 0 c o n i c a l b a s e h a v i n g 1 8 b u b b l e c a p s ( f o u r h o l e s X 2 .5 m mi . d . ) w a s u s e d f o r s t e a m s u p p l y t o t h e a n n u l u s r e g i o n . T od e t e r m i n e t h e e f f e c t o f o x y g e n / c o a l r a t i o , o x y g e n w a sa d d e d t o t h e a i r s t r e a m . S t e a m w a s i n t r o d u c e d i n t o t h ep l e n u m c h a m b e r a n d i t s f l o w r a t e w a s m e a s u r e d b y a nor i f i ce m e te r . To prehea t a i r and s team , an e lec t r i c

Fuel 1997 Volume 76 Number 11 1067


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A n i n te rn a l l y c i r c u l a t i n g f l u i d i z e d b e d w i t h d ra u g h t t u b e : Yo J . K im e t a l .

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Fig ure 1 Fluidized bed with a draught tube: (a) gap height type;(b) orifice type

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Fig ure 2 Schematic diagram of the internally circulatingfluidized bed gasifier. 1, flow meter; 2, steam generator; 3, orificemeter; 4, air plenum; 5, distributor; 6, overflow drain; 7, viewport;8, draught tube; 9, main body; 10, separator; 11, freeboard; 12,screw feeder; 13, coal hopper; 14, cyclone; 15, condenser; 16,collector; 17, dust filter; 18, conden ser; 19, gas sampling b ottle; 20,ID fan

h e a t e r ( 3 k W ) w a s i n s t a l le d o n t h e o u t e r w a l l o f th e p l e n u mc h a m b e r .F o u r e q u a l l y s p a c e d 3 0 m m d i a m e t e r h o l e s w e r e d r i l l e di n t h e w a l l o f t h e d r a u g h t t u b e 4 0 m m a b o v e i t s b a s e . A g a ss e p a r a t o r w a s i n s t a l l e d t o s e p a r a t e t h e g a s s t r e a m se m a n a t i n g f r o m t h e a n n u l u s a n d d r a u g h t t u b e z o n e s . T o

m e a s u r e p r e s s u r e d r o p i n t h e a n n u l u s , s e v e n p r e s s u r e t a p sw e r e m o u n t e d f l u s h w i t h t h e w a l l o f t h e c o l u m n a t 0 . 2 mh e i g h t i n t e r v a l s f r o m t h e d i s t ri b u t o r . T w o p r e s s u r e t a p s w e r ea l s o m o u n t e d a t t h e b o t t o m a n d t h e t o p o f d r a u g h t t u b e t om e a s u r e p r e s s u r e d r o p a c r o s s t h e t u b e . T o m e a s u r e a x i a lt e m p e r a t u r e i n t h e a n n u l u s , s i x K - t y p e t h e r m o c o u p l e s w e r em o u n t e d a l o n g t h e b e d h e i g h t f r o m t h e d i s t r i b u t o r . A ne l e c t r i c h e a t e r ( 1 6 k W ) w a s i n s t a l le d a t t h e m a i n r e a c t o rw a l l t o h e a t t h e r e a c t o r t o t h e i g n i t i o n t e m p e r a t u r e o f c o a l( - 5 0 0 C ) . T h e r e a c t o r w a s i n s u l a t e d w i t h K a o w o o l t op r e v e n t h e a t l o s s t h r o u g h t h e w a l l . A s i g h t - g l a s s w a sm o u n t e d 1 .0 m a b o v e t h e d i s t ri b u t o r . A n a s h d r a i n p o r t w a sl o c a t e d a t th e b o t t o m o f th e r e a c t o r a n d a n o v e r f l o w d r a i np o r t w a s m o u n t e d 1 .1 m a b o v e t h e d i s t r i b u to r . T h ef r e e b o a r d ( 0 .4 5 m i .d . ) s e c t i o n w a s e x p a n d e d t o r e d u c ep a r t i c l e e n t r a i n m e n t f r o m t h e r e a c t o r .

T h e c o a l w a s f e d f r o m t h e t o p o f t h e r e a c t o r t h r o u g h as c r e w f e e d e r c o n n e c t e d t o a c o a l h o p p e r a n d t h e f e e d r a t e( 5 . 3 - 1 2 . 1 k g h - 1 ) w a s r e g u l a t e d b y a D C m o t o r c o n t r o l l e r.S i n c e c o a l g a s i f i c a t i o n t a k e s p l a c e i n t h e a n n u l u s r e g i o n( m o v i n g b e d ) , t h e c o a l s h o u l d b e f e d f r o m t h e t o p o f th er e a c t o r t o p r o v i d e a l o n g e r r e a c t i o n t i m e i n th e m o v i n g b e d .T w o c y c l o n e s ( 0 . 0 8 m i .d . 0 . 3 2 m h i g h ) w e r e i n s t a ll e d a tthe ou t l e t o f the gas i f i e r . P roduc t gas was coo led th rough acondense r and f ines were co l l ec ted by a bag f i l t e r . Gass a m p l i n g p r o b e s w e r e i n s ta l le d a t t h e o u t l e t o f t h e c o n d e n s e r.

A t t h e b e g i n n i n g o f a n e x p e r i m e n t , o n l y a i r w a s f e d i n t ot h e r e a c t o r u nt il t h e b e d t e m p e r a t u r e r e a c h e d 4 5 0 - 5 0 0 C .T h e r e a f t e r , t h e e l e c t r ic h e a t e r w a s t u r n e d o f f a n d c o a l w a sf e d i n t o t h e g a s if i e r. W h e n t h e d e s i r e d r e a c t i o n t e m p e r a t u r ew a s r e a c h e d , s t e a m w a s i n t r o d u c e d i n t o t h e g a s i fi e r . W h e nthe gas i f i e r ope ra t ion reached a s t eady s ta te , the gasc o m p o s i t i o n a n d t h e a m o u n t o f p a r t i c l e s c o l l e c t e d i n t h ec y c l o n e w e r e m e a s u r e d . T h e s a m p l e d g a s w a s a n a l y s e d b yg a s c h r o m a t o g r a p h y w i t h a t h e r m a l c o n d u c t i v i t y d e t e c t o ra n d c o l u m n s o f m o l e c u l a r s i e v e 5A a n d P o r a p a k Q . T oc a l c u l a t e th e a m o u n t o f p r o d u c t g a s a n d g a s c o m p o s i t i o n i nt h e a n n u l u s r e g i o n , h e l i u m g a s a s a t r a c e r w a s i n j e c t e db e t w e e n t h e a n n u l u s g a s o u t l e t a n d t h e c y c l o n e . A l o c a lm a s s b a l a n c e o f n i t r o g e n g a s w a s m a d e t o d e t e r m i n e t h ea m o u n t o f p r o d u c t g a s e s f r o m t h e d r a u g h t t u b e b y i n j e c t i n gn i t r o g e n a s a t r a c e r i n t o t h e d r a u g h t t u b e . T h e p a r t i c l e s i z e o ft h e b e d m a t e r i a l ( s an d ) w a s 3 9 0 # m a n d t h e s t at ic b e d h e i g h tw a s 0 . 8 m f r o m t h e d i s t r i b u t o r p l a t e . T h e g a s i f i e r r e a c h e ds t e a d y s t a te i n a r e a c t i o n t i m e o f 1 h a f t e r s t e a m w a s i n j e c t e din to the gas i f i e r .

T h e p a r t i c l e s i z e o f th e c o a l w a s 1 - 5 m m ; i t s p r o p e r t ie sa r e g i v e n i n Table 1.R E S U L T S A N D D I S C U S S I O NEffect of reaction temperature

T h e r e a c t i o n t e m p e r a t u r e i s e x p e c t e d t o b e o n e o f t h em o s t i m p o r t a n t o p e r a t i n g v a r i a b l e s a f f e c t i n g t h e p e r f o r -m a n c e o f t h e g a s i f ie r , s in c e t h e m a i n g a s i f ic a t i o n r e a c ti o n s( C + H 2 0 - -'* C O + H 2 and C + CO2 - --* 2CO ) a ree n d o t h e r m i c . H e n c e t h e r e a c t i o n t e m p e r a t u r e s h o u l d b e a tt h e h i g h e s t t o l e r a b l e l e v e l , l i m i t e d b y m a t e r i a l s o fc o n s t r u c t io n , a s h f u s i o n a n d p r o d u c t i o n o f u n d e s i r a b l egases su ch a s N Ox ~5. In the p re sen t s tudy , the con s t ruc -t i o n a l m a t e r i a l o f t h e g a s i fi e r r e s t r ic t e d t h e m a x i m u mo p e r a t i n g t e m p e r a t u r e t o 9 0 0 C .T h e e f f e c t o f r e a c ti o n t e m p e r a t u r e o n c o m p o s i t i o n o f t h eprod uc t gas in the annulus reg ion i s show n in Figure 3. A s c a nb e s e e n , th e c o m p o s i t i o n r an g e ( v o l . % ) i s H 2 3 6 . 7 - 4 5 . 1 , C O1 9 . 3 - 2 5 . 5 , C O 2 1 5 . 4 - 1 3 . 4 a n d C H 4 1 0 . 3 - 6 . 6 . T h e y i e l d s o f

1 0 68 F u e l 1 9 97 V o l u m e 7 6 N u m b e r 1 1


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An i n t e r n a l l y c ir c u l a t in g f l u id i z e d b e d w i t h d r a u g h t t u b e : Y . J . K i m et al.

Tab le 1 Typical analysis of Australian coalP r o x i m a t e a n a l y s i s ( w t % d b )

V o l a t i l e m a t t e r 2 6 . 4F i x e d c a r b o n 6 3 . 9A s h 9 . 7

U l t i m a t e a n a l y s i s ( w t % d a f )C 6 8 . 1H 4 . 5 8O 2 5 . 4N 1 .6S 0 .3

H e a t i n g v a l u e ( M J k g - J ) 2 6 . 2 7

6 0

5 0

"d 40

"~ 30

o 2 0

10

U d = 1 0 U m r H 2 0 / C = 0 . 7 5U a = 1.4 Umf O 2 / C = 0 . 2 5U , . r = 0 . 0 8 m / s

. .___-v CO

~ ~ - - - - ~ - - ~ t . co2C H 4

I I I07 5 0 8 0 0 8 5 0 9 0 0 9 5 0Temperature (C)

Figure 3 Effect of reaction temperature on composition ofproduct gas in annulus region

the chemica l reac t ion ra t e cont ro l under the presen texper imenta l condi t ions , so tha t y i e lds of H2 and COincrease s ign i f i can t ly wi th reac t ion t empera ture s ince thereac t ion ra t e inc reases about t enfo ld . In cha r combus t ion ,t h e a c t i v a ti o n e n e r g y c h a n g e s w i t h r e a c t io n t e m p e r a t u r e d u eto an inc rease in d i f fus iona l re s is t ance , and the k ine t i c s a recont ro l l ed by the gas f i lm d i f fus ion ra t e a t t empera turesa b o v e - 7 0 0 C . T h e r e f o r e t h e y i e l d o f C O 2 in c r e a se ss l igh t ly , s ince the reac t ion ra t e inc reases about 1 .14 t imesw i t h i n c r e a s i n g r e a c t i o n t e m p e r a t u r e b e t w e e n 7 8 0 a n d900C. The concent ra t ions of H2 and CO inc rease wi thr e a c t io n t e m p e r a t u r e5 '15 ']7, wh ereas those o f CO2, CH 4 andN2 dec rease s l igh t ly . These re su l t s a re comparab le w i tht h o s e o f J u d d 9 f o r a b e d w i t h a g a p h e i g h t t y p e o f d r a u g h ttube a t h ighe r reac t ion t empera tures than in the presen ts tudy . There fo re it can be c l a imed tha t t he draught tube w i thor i f i ces i s supe r ior to the gap he igh t type for p roduc ingmedium-CV gas in the annulus reg ion .T h e e f f e c t o f r e a c t io n t e m p e r a t u r e o n t h e c o m p o s i t i o n o fthe produc t gas in the draught tube reg ion i s shown inFigure 4 . The co mp os i t ion exhib i t s t he s ame t rend as in thea n n u l us r e g i o n . T h e i n c r e a s e in y i e l d o f H 2 a n d C O m a y b edue to vo la t i l e ma t t e r re l eased dur ing pyro lys i s and thec a r b o n - s t e a m r e a c t i o n , s i n c e s t e a m b y p a s s e d f r o mthe annulus to the draught tube s ec t ion . However , t hec o n c e n t r a t i o n o f c o m b u s t i b l e g a s e s i s r e d u c e d d u e t othe d i lu t ion of the produc t gas w i th n i t rogen and ca rbo ndioxide .A de ta i l ed ma te r i a l ba lance cann ot be cons t ruc ted , due tothe d i f f i cu l ty in e s t ima t ing t a r y i e ld accura te ly , whereas ac a r b o n b a l a n c e c a n e a s i l y b e d e t e r m i n e d a s s h o w n i nTable 3 . T h e c a r b o n c o n t e n t o f t h e s o li d s w a s d e t e r m i n e d b yc h e m i c a l a n a l y s i s a n d c a r b o n i n t h e p r o d u c t g a s w a sc a l c u l at e d c u m u l a t iv e l y f r o m t h e v o l u m e o f t h e g a s a n d i t sc h e m i c a l c o m p o s i t i o n . T h e u n a c c o u n t e d - f o r c a r b o n m a y b edue to the los s o f ca rbon in the form of t a r , li qu ids and som e

Ta ble 2 Kinetic parameters for the reactionsR e a c t i o n T e m p e r a t u r e r a n g e ko E( C) ( s - l a tm - i ) (kJ too l - i ) R D S ~ k780oc kg~ooc(s -I) (s -I)G a s i f i c a t i o n 7 0 0 - 8 5 0 6 . 4 7 1 03 1 6 7C o m b u s t i o n 5 0 0 - 5 7 5 7 . 5 8 1 04 1 1 3

5 7 5 - 7 0 0 0 . 4 4 2 7 . 67 0 0 - 8 0 0 0 . 0 4 5 9 . 6

c h e m i c a l r e a c t i o n 3 . 9 3 1 0 - 5 3 . 7 6 1 0 . 4c h e m i c a l r e a c ti o n - - - -

p o r e d i f f u s io n - - - -g a s f i l m d i f f u s i o n 1 . 4 7 x 1 0 - 2 1 . 6 8 1 0 - 2

a R a t e - d e t e rm i n i n g s t e p

H2 and CO inc rease wi th inc reas ing reac t ion t empera tures ince the gas i f i ca tion reac t ions a re en dothe rmic .In a p rev iou s s tudy 16, t he ra t e equa t ions for c ha rc o m b u s t i o n a n d s t ea m g a s i fi c a ti o n w e r e d e t e r m i n e d o n t h ebas i s o f the shr ink ing-core mo de l a s :dX n X)2/3= Kp02 o r . 2 0 ( 1 - -

E X)2/3= koexp ( - R-~)p 02 or H20(1 -- (1)where X , K , P02 o r PH20, ko , E , R and T a re ca rbon conv er -s ion , reac t ion ra t e cons tan t , pa r t i a l p res sure of 02 or H20,p r e - e x p o n e n t i a l f a c t o r , a c t i v a t i o n e n e r g y o f c o a l c o m b u s -t ion or s t eam gas i f i ca t ion , mola r gas cons tan t and reac t iontempera ture , re spec t ive ly . The va lues of ko and E ob ta ineda re shown in Table 2 .T h e k i n e t i c s o f s t e a m - c h a r g a s i f i c at i o n a re g o v e r n e d b y

ent ra ined p a r t i c le s . I t i s c l ea r ly ind ica ted tha t t he inc rease ingas y i e ld wi th reac t ion t emp era ture i s pa r t ly ach ieved a t t heexpense of t a r and l iqu ids . Dur ing gas i f i ca t ion , t he ave ragec a r b o n c o n t e n t i n t h e b e d w a s i n t h e r a n g e 6 - 1 0 w t % a t ac o a l f e e d r a t e o f 5 . 3 - 1 2 . 1 k g h - 1.Ca lor i f i c va lues of the produc t gas f rom the presen t andprev ious s tud ies ve rsus reac t ion t empera ture a re shown inF i g u r e 5 . T h e C V o f t h e p r o d u c t g a s o b t a i n e d in t h e a n n u l u sreg ion i s 1 1-1 2 M J m -3 , which i s mu ch h ig he r than tha t i nthe annulus reg ion (gas i f ica t ion) o f an in t e rna l ly c i rcu la t ing1of lu id ized bed wi th a gap he igh t type of d raught tube . Th eCV of the ~product gas in the drau ght tube reg ion i s 3 .3 -4 . 7 M J m - e , w h i c h i s c o m p a r a b l e w i t h t h a t f o r a c o n v e n -t ional f luidized bed 6 or spou ted bed gas i f ier 15'18. As the

reac t ion t empera ture i s i nc reased , t he H2 and CO concen-t r a t i o n s i n c r e a s e w h e r e a s h i g h - C V h y d r o c a r b o n s d e c r e a s es l igh t ly due to the inc rease in decompos i t ion reac t ions , a s

Fuel 1997 Volume 76 Number 11 1 0 6 9


4/7

An i n t e r n a l ly c i r c u l a ti n g f l u id i z e d b e d w i t h d r a u g h t t u b e : Y . J . K i m et al.

70 20

6 0. ~ 50,.,..i0&= 4 00

3 00o~ 2 0

100750

H 2 0 / C = 0.75O2/C = 0.25

M A - # CO2

COt t cH,

800 850 900Temperature (C)

950

Fig ure 4 Effect of reaction temperature on composition ofproduct gas in draught tube region

E

O"d

16

12

8

4

: T h i s s t u d y ( o r i f i c e t y p e ; a n n u l u s )[ ] : J e o n ( g a p h e i g h t t y p e ; a n n u l u s , 1 9 9 5 ) : T h i s s t u d y ( o r i f i c e t y p e ; d r a f t t u b e ) : L e e ( f l u i d i z e d b e d , 1 9 9 5 ) : F o o n g e t a l . ( s p o u t b e d , 1 9 8 1 )

tq F1LI u

0 I I I I700 750 800 850 900

Temperature (C)Figure 5 Calorific value of product gas versustemperature, and comparison with previous studies

950

reaction

Tab le 3 Carbon m ass balance in an internally circulating fluidized bed gasifierT G a s i f i ca t i o n p r o d u c t ( g m i n - I )( C) C i n c oa l C i n c yc l on e " C i n c yc l on e b C i n ove r f l ow C in gas

( C i n p r o d u c t) X1 0 0 % / ( C i n c o a l )

780 98 . 4 2 . 0 2 . 8 44 . 3 30 . 5 80 . 9800 93 . 9 2 . 2 1 .7 41 . 8 28 . 2 78 . 7850 89 . 7 0 . 9 4 . 8 38 . 7 30 . 5 83 . 5900 85 . 8 2 . 0 2 . 8 36 . 3 38 . 6 92 . 9a C y c l o n e l o c a t ed i n d r a u g h t t u b e g a s o u t l e tb C y c l o n e l o c at e d i n a n n u l u s g a s o u t l e t

can be s een in Table 43 '19 . Th ere fo re the ca lor i f i c va lue ofthe produc t gas in the annulus reg ion dec reases s l igh t lywhereas tha t i n the draught tube inc reases w i th inc reas ingreac t ion t empera ture . T h e e f f e c t s o f r e a c t i o n t e m p e r a t u r e o n g a s y i e l d , c a r b o nc o n v e r s i o n a n d c o l d g a s e f f i c i e n c y o f th e p r o d u c t g a s a r es h o w n i n Figure 6 . G a s y i e l d , c a r b o n c o n v e r s i o n a n d c o l dgas e f f i c i en cy a re de f ined a s :

Gas y ie ld- - - gas produc t ion ra t ecoa l feed ra t e (2)

C c o n t e n t o f p r o d u c t g a sC c o n v e r s i o n = ( 3 )C c o n t e n t o f f e e d c o a lC o l d g a s e f f i c i e n c y

= (CV ofgas ) ( to t a l gas prod uc t ion ra t e ) (4 )(coa l feed ra t e ) (CV of coa l )

The gas y i e ld inc reases f rom 0 .22 to 0 .35 m3k g - l coa l i n theannulus reg ion and f rom 0 .86 to 1 .09 m3kg - l coa l i n thed r a u g h t t u b e r e g io n . T h e g a s y i e l d m a y r e s u l t f r o m p y r o l y -s is , cha r ~as i f i ca t ion and s t eam re fo rmin g of t a r and l iqu ids(Table 3) . C a r b o n c o n v e r s i o n i n t h e t w o r e g i o n s i n c r ea s e s ,s i n ce th e ra t e s o f th e c a r b o n - s t e a m a n d c a r b o n - o x y g e n

reac t ions inc rease wi th reac t ion t empera ture , and the co ldgas e f f i c i ency inc reases due to an inc rease in gas y i e ld inboth reg ions .Effect of oxygen/coal ratio

T h e e f f e c t o f o x y g e n / c o a l m a s s r a t i o s u p p l i e d t o t h ed r a u g h t t u b e o n p r o d u c t g a s c o m p o s i t i o n in b o t h r e g i o n s a t ag iven s t eam/coa l ra t io i s shown in Figures 7 and 8 . In theannulus reg ion , t he concent ra t ions of H2, CO and CH4decrease s l igh t ly bu t the CO: conten t inc reases w i thinc reas ing oxygen/coa l ra t io f rom 0 .30 to 0 .53 . In th i scase , the dec rea se in H2, CO and CH4 con cent ra t ions may b ec a u s e d b y a n i n c r e a s e i n r e c o m b u s t i o n o f H 2 a n d C H 4 o w i n gt o t h e i n c r e a s e d a m o u n t o f o x y g e n b y p a s s i n g i n t o t h eannulus reg ion . Th e inc rease in CO2 conten t a r i s e s f rom thel o ss o f H 2 a n d C H 4 a s w e l l a s f r o m c o m b u s t i o n o f c a r b o n1 2 2 0a n d C O ' ' . T h u s , o w i n g t o th e r e d u c t io n o f c o m b u s t i b legas by recombus t ion of the produc t gas , t he ca lor i f i c va lueof the produc t gas in the annulus reg ion dec reases f rom 11 .9to 9 .9 MJ m-3 . In the draugh t tube reg ion , concent ra t ion s ofH2 and C H 4 decrease bu t the CO2 concent ra t ion inc reasesw i t h i n c r e a s in g o x y g e n / c o a l r a ti o . T h e C O c o n c e n t r a t io nt e n d s t o d e c r e a s e d u e t o r e c o m b u s t i o n a n d t o i n c r e a se d u e t oi n c o m p l e t e c o m b u s t io n , b u t t h e l a t t e r e f f e c t p re d o m i n a t e sso tha t t he ne t CO concent ra t ion inc reases s l igh t ly . Theca lor i f ic va lue of the produc t gas in the draught tube reg ionr e m a i n s i n t h e r a n g e 3 . 3 - 3 . 6 M J m -3 .

1 0 7 0 Fuel 1997 Volume 76 Number 11


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A n i n t e r n a l l y c i r c u la t i n g f l u i d i z e d b e d w i t h d r a u g h t t u b e : Y . J . K i m et al.

F i g u r e 6

?

"7"E._o;>

oL )

1.81.51.20.90.60.30.60.50 .4 i

I

0 . 3 -0.2 -0 . 1 -0,075 0

H 2 0 / C = 0 .75O / C = 0 . 2 5

D r a f t _ _ ~

A n n u l u s ~ _ ~I I I

"_.------1--- /M i x e d ( d r a f t + a n n u l u s )

I I I800 850 900

0.6- 0.5

0.4t 0.30.~

0.10.095 0

Temperature (C)

7"o

-6"6[,.)

Effect of reaction temperature on gas yield, carbon conversion and cold gas efficiency of product gas

60

50

.= 4 0Q

30

o 20

10

T = 8 5 0 - 8 6 0 C U d = I 0 U m fH 2 0 / c o a l = 0 . 6 3 U , = 1 . 4 U m f

H2

L ~ C O

C O2N~

CH4

o>o:5Eoo

7O

f

30L

2 0 ;1000.25

T = 8 5 0 - 8 6 0 Coal = 0 .63

N 2

t C O 2

f f - - _ _ _ ~ H 2v - - - - - - C O_~ _A _A & C H 40 I I I I I I I I I I I I0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.30 0.35 0.40 0.45 0.50 0.55 0.60

O2/coal (kg kg~) O2/coal (kg kg~)Figu re 7 Effect of O 2 / c o a l m a s s ratio on composition of productgas in annulus region Figure 8 Effect of O2/coal mass ratio on composition of productgas in draught tube region

Tab le 4 Hydrocarbon concentrations (vol.%) at different reaction temperaturesRegion T (C) C :H4 C2H 6 C3H 6 C 3H C4 compoundsDraught tube 780 0.503 0.164 0.153 0.037 0.02

8 0 0 0 . 5 6 5 0 . 1 7 8 0 . 1 3 4 0 . 0 2 2 0 . 0 48 5 0 0 . 4 9 4 0 . 1 2 0 0 . 0 5 7 0 . 0 1 2 n . d . "9 0 0 0 . 5 8 8 0 . 1 1 9 0 . 0 6 9 0 . 0 1 2 n . d .

A n n u l u s 7 8 0 1 . 6 06 0 . 4 6 0 0 . 3 1 9 0 . 0 4 4 0 . 0 3 78 0 0 1 . 6 7 4 0 . 4 3 6 0 . 2 9 4 0 . 0 3 2 0 . 0 7 7850 1 .123 0 .215 0 .07 n .d . n .d .900 1 .058 0 .150 0 .041 n .d . n .d .

F u e l 1 9 97 V o l u m e 76 N u m b e r 11 1 07 1


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An i n t e r n a l ly c i r c u l a ti n g f l u id i z e d b e d w i t h d r a u g h t t u b e : Y . J . K i m e t a l .

1.4 60

1. 2

"-" 1.0-~o?

"7 0 .s~E-~ 0 .6

0 .4

0 .2

0 .00.2~

D r a f t t u b e

A n n u l u s

T = 8 6 0 CH 2 0 / c o a l = 0 . 6 3

I I I I I I0 . 3 0 0 . 3 5 0 . 4 0 0 . 4 5 0 . 5 0 0 . 5 5 0 . 6 0O2/coal (kg kg 1)

50

.~ 40o

:~ 30

o~ 2 0

10

3 15

T = 8 7 0 C U a = 1 0 U m fH 2 0 / O z = 2 . 5 U a = 1 . 4 U m f

D

:C O 2C t t 4

N 2I I I

6 9 12Coal feeding rate (kg h"l)

Figu re 9 Effect of OJ coa l m ass ratio on yield of product gas inboth regionsT h e e f f e c t o f o x y g e n / c o a l r a t i o o n g a s y i e l d i n b o t hreg ions i s shown in Figure 9. A s t h e o x y g e n / c o a lra t io inc reases , t he fo l lowing two proces ses occurs i m u l ta n e o u s ly : H 2 , C O a n d C H 4 p r o d u c t i o n d e c r e a s e sd u e t o r e c o m b u s t i o n a n d C O 2 p r o d u c t i o n i n c r e a s e s d u e t oc o m b u s t i o n . T h e s e t w o o p p o s i n g r e a c ti o n s c o m p e n s a t e e a c hothe r to ma in ta in an a lmos t cons tan t gas y i e ld . Carbonconv ers ion inc reases w i th inc reasing oxy gen /coa l ra t io ,whereas co ld gas e f f i c i ency dec reases s l igh t ly due to adec rease in ca lor i f i c va lue of the produ c t gas .

Effect of coal fee d rateT h e e f f e c t o f c o a l f e e d r a te o n c o m p o s i t io n o f t h e p r o d u c tgas in the annulus reg ion a t a cons tan t s t ea m/o xyg en ra t io i ss h o w n i n Figure 10. As can b e s een , t he pe rcen tages of H2,CO, and CH4 inc rease wi th inc reas ing coa l feed ra t e f rom5,3 to 12 .1 kg h -1 due to an inc rease in supply of vo la t i l em a t t e r , w h e r e a s t h e C O 2 c o n c e n t r a t i o n r e m a i n s a l m o s tcon stant 1 '2 '15'17'18. Th us the calori f ic valu e of the pro du ct

gas in the annulus reg ion inc reases f rom 8 .56 to1 3 . 2 2 M J m - 3 s i n c e c o m b u s t i b l e g a s e s i n c r e a s e w i t hi n c r e a s i n g c o a l f e e d r a t e . T h e c o m p o s i t i o n o f t h e p r o d u c tgas in the draugh t tube fo l lows the s am e t rend as tha t i n thea n n u l us r e g i o n . T h e r a n g e o f p r o d u c t g a s c o m p o s i t i o n(vol .% db) in the draught tube reg ion i s : H2 10 .1-19 .7 , CO6 . 7 - 1 3 . 1 , C O 2 1 8 . 9 - 2 9 . 0 a n d C H 4 1 . 9 - 4 . 4 % , a n d t h eca lor i fi c va lue i s 3 .3 -5 . 9 M J m -3 .T h e e f f e c t o f c o a l f e e d r a t e o n g a s y i e l d , c a r b o nc o n v e r s i o n a n d c o l d g a s e f f i c i e n c y o f t h e p r o d u c t g a s i ss h o w n i n Figure 11. A l t h o u g h t h e a m o u n t o f p r o d u c t g a sinc reases s l igh t ly wi th coa l feed ra t e due to an inc rease inpyro lys i s p roduc t s , t he gas y i e ld dec reases . S ince theoxy gen/c oa l ra t io dec reases w i th inc reas ing coa l feed ra t e ,ca rbon conv ers ion dec reases 17. Th e co ld gas e f f i c i encytends to inc rease wi th inc reas ing ca lor i f i c va lue of theprod uc t gas bu t to dec rease due to the dec rease in gas y i e ldi n t h e a n n u l u s r e g i o n . T h e s e t w o e f f e c t s c o m p e n s a t e e a c hothe r and the co ld gas e f f i c i ency does no t exhib i t anynot i ceab le va r i a t ion .

Fig ure 10 Effect of coal feed rate on composition of product gasin annulus region

Effect of steam/coal ratioThe e f fec t o f s team/coa l mass ra t io suppl i ed to thea n n u l u s r e g i o n o n t h e c o m p o s i t i o n o f t h e p r o d u c t g a s a t ac o a l f e e d r a t e o f 7 . 5 6 k g h - ' a n d a O 2 /C m a s s r a t i o o f 0 . 3 0 i ss h o w n i n Figure 12. S i n c e t h e r e a c t i o n t e m p e r a t u r edec reases w i th inc reas ing s t eam/coa l ra t io 1 , i t was ma in-t a ined by an e l ec t r i c hea te r . As can be s een , t he prod uc t gas

compos i t ion in the annulus reg ion i s i nsens i t ive to changesin s t eam/coa l ra t io z5'17, s ince equi l ib r ium of the wa te r -gassh i f t r eac t ion favours H2 produc t ion and the re s idence t imeof s t eam in the annulus reg ion dec reases w i th inc reas ings team/co a l ra tio . The ca lor i f ic va lue of the prod uc t gas in thea n n u l u s re g i o n r e m a i n s in t h e ra n g e 1 1 . 0 - 1 1 . 5 M J m - 3 a n dt h e g a s y i e l d , c a r b o n c o n v e r s i o n a n d c o l d g a s e f f i c i e n c y o ft h e p r o d u c t g a s i n t h e a n n u l u s r e g i o n r e m a i n r o u g h l ycons tan t .

C O N C L U S I O N SCoa l gas i f i ca t ion in an in t e rna l ly c i rcu la t ing f lu id ized bedwi th an or i f i ce - type draught tube an d a gas s epa ra tor ove rthe draught tube a l lows low-CV gas in the draught tuber e g i o n a n d m e d i u m - C V g a s i n t h e a n n u l u s r e g i o n t o b eobta ined . In the annulus zone , t he comp os i t ion (vo l .% db) oft h e p r o d u c t g a s is i n t h e ra n g e 3 1 . 8 - 4 6 . 2 H z , 1 8 . 8 - 2 5 . 6 C O ,1 3 . 2 - 2 0 . 4 C O 2 a n d 5 . 3 - 1 0 . 4 C H 4 , a n d th e c a l o ri f ic v a lu e i s8 . 6 - 1 3 . 2 M J m - 3, w h i c h i s h i g h e r t h a n i s o b t a i n e d f r o mc o n v e n t i o n a l f l u i d i z e d b e d , s p o u t e d b e d o r o t h e r t y p e s o fin t e rna l ly c i rcu la t ing f lu id ized bed gas i f i e rs . In the drau ghtt u b e z o n e , t h e c o m p o s i t io n ( v o l . % d b ) o f t h e p r o d u c t g a s i s8 . 3 - 1 9 . 7 H 2, 6 . 7 - 1 3 . 1 C O , 1 8 . 9 - 3 5 . 3 C O z a n d 1 . 9 - 4 . 4C H 4 , and the ca lor i f ic va lue i s 3 .3 -5 .9 M J m -3 , which i sc o m p a r a b l e w i t h t h a t f r o m c o n v e n t i o n a l f l u i d i z e d b e d o rspouted b ed gas i fi e r s.

A C K N O W L E D G E M E N T ST h e a u t h o rs a c k n o w l e d g e a g r a n t - in - a i d f o r r e s e a rc h f r o mt h e M i n i s t ry o f T r a d e , C o m m e r c e a n d E n e r g y , K o r e a .

1 0 7 2 F u e l 1 9 97 V o l u m e 7 6 N u m b e r 11


7/7

An i n t e r n a l l y c i rc u l a t in g f l u id i z e d b e d w i t h d r a u g h t t u b e : Y . J . K i m et a l .

F i g u r e 1 1

1 .4o 1.2o, 1.0

~E 0.8~ 0 . 6 , 0 . 4

0.2(3 0 .0~ - 0 .5=" 0.4

0 .3o 0.2)=o 0.1,. 0

0.0 3

T = 870 CDraf t tube H20/O2 = 2.5

AnnulusI I I

o o s >

i i i6 9 12

0 . 5 " ~0 4 .o0.3 %)0 .2 r~o

- 0 . 1O0.015

Coal feed ing ra te ( kg h " l)Effec t o f coa l feed ra te on gas y ie ld , ca rbon con vers ion and co ld gas e ff ic iency of p roduc t gas

6 0

0

0o

0

50

4 0

30

20

10

T = 880 C Ua= 10 UmfO2/C = 0.30 Umf = 0.08 rrl/s

H 2

C Ov

-~ - ~ C O2D D o N2D&- - A A .o. CH4

0 I J I0.2 0.4 0.6 0.8 1.0S te a m /c o a l (k g k g )

F ig u re 1 2 E f fe c t o f s te a m /c o a l m a s s r a t io o n c o m p o s i t io n o fproduc t gas in annulus reg ion

R E F E R E N C E S1 Gutie rrez , L . A. and W atk inson , A. P . , Fuel, 1982, 61, 133.2 W atk inson , A. P . , Cheng , G. and Prakash , C. B. , CanadianJournal of Chemical Engineering, 1983, 61, 468.3 Neogi , D. , Chang , C. C. , W alawe nder , W . P . and Fan , L . T . ,AIChEJournal, 1986, 32, 17.4 Saffe r , M. , Ocam po, A. and Laguerie , C . , International Che-

mical Engineering, 1988, 28, 46.

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20 Sue-A -Quan , T . A. , Wa tk inson , A. P . , Ga ikw ard , R. P . , L im ,C. J . and Ferris , B. R. , Fuel Processing Technology, 1991,27, 67.

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coal gasification characteristics in

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