Bilbao, Arauzo - Scale up of downdraft moving bed gasifiers 25-30 kghr.pdf

8/11/2019 Bilbao, Arauzo - Scale up of downdraft moving bed gasifiers 25-30 kghr.pdf

1/7

ioresource Techno logy 8

( 1 9 9 4 ) 2 2 9 - 2 3 5

1994 E l s e v i e r S c i e nc e L i m i t e d

P r i n t e d i n G r e a t B r i ta i n . A l l r i gh t s r e s e r ve d

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

E L S E V I E R

S C A L E -U P O F D O W N D R A F T M O V I N G B E D G A SIF IE R S

2 5 - 3 0 0 k g / h ) - D E S IG N , E X P E R I M E N T A L A S P E CT S A N D

R E S U L T S

P edro Ga rc ia -Baca i coa , Rafae l B i lbao , * Jest is Ar au zo M . Lui sa Sa lvad or

Department of Chem ical and E nvironm ental Engineering, Universi ty of Zaragoza, 50009 Zaragoza, Spain

(Received 20 Decem ber 1993 ; rev i sed vers ion rece ived 4 February 1994 ; accep ted 15 February 1994)

bstract i n s o m e s p e c i f i c i n d u s t r i a l s i t u a t i o n s ( u s i n g t h e s i t e

T w o i n s t a l l a t i o n s w i t h d i f f e r e n t b i o ma s s p r o c e s s i n g w a s t e ) . G a s i f i e r / e n g i n e s y s t e m s f u e l l e d w i t h u n p r o -

c a p a c it ie s ( 2 5 - 5 0 a n d 2 0 0 - 3 0 0 k g / h ) w e r e d e s i g n e d a n d c e s s e d b i o m a s s t e n d t o b e o f t h e m o v i n g - b e d d o w n -

c o n s t r u c t e d f o r a i r g a s if i c at i o n o f l i g n o c e l lu l o s i c b i o m a s s , d r a f t t y p e b e c a u s e o f t h e a b i l i t y o f d o w n d r a f t g a s i f i e r s

T h i s p a p e r d e s c r i b e s b o t h i n s t a l la t i o n s a s w e l l a s th e t o p r o d u c e l o w - t a r g a s ( M e n d i s , 1 9 8 9 ) . M o r e o v e r , t h e

e x p e r i m e n t a l p r o c ed u r e . T h e i n fl u e n c e o f o p e r a ti n g d o w n d r a f t g a s i f i e r p r e s e n t s s e v e r a l s u p p l e m e n t a r y

c o n d i t i o n s o n t h e a m o u n t a n d q u a l i t y o f p r o d u c t s w a s a d v a n t a g e s ( B i lb a o F e r n a n d e z , 1 9 8 8 ) w h i c h i n d i c a te

d e t e rm i n e d . T h e r e s u lt s o b t a i n e d f r o m p r o c e s s i n g t h a t i t i s a p p r o p r i a t e f o r a v e r a g e p r o c e s s i n g c a p a c i ti e s .

f o r e s t r y w a s t e a r e a n a l y s e d . V a l u e s a b o v e 9 0 f o r ma s s I n t h e 1 9 8 0 s a p r o g r a m m e w a s i n it i a te d t o d e v e l o p a

c o n v e r s i o n e f f i c i e nc y a n d o v e r 7 0 f o r c o M g a s e ff i- g a s if ie r s y s t e m t o u s e b i o m a s s g e n e r a t e d i n S p a in . T h e

c i e n c y w e r e r e a c h e d , o p t i o n c h o s e n w a s a i r g a s i f i c a t i o n i n a d o w n d r a f t

m o v i n g - b e d g a s if ie r. T h e s t u d y o f t h e i n f l u e n c e o f b o t h

K e y w o r d s: b i o m a s s g a s i f ic a t i o n , a i r g a s i f ic a t i o n , d o w n - o p e r a t i n g c o n d i t i o n s a n d s c a l e - u p i n v o l v e d t h e c o n -

d r a f t m o v i n g b e d , g a s i f ie r d e s ig n , m a s s e f f ic i e n c y , s t r n c t i o n a n d o p e r a t i o n o f s e v e r a l g a s i f ie r s ( G r o e n e -

e n e r g y e f f ic i e n cy , v e l d V a n S w a a i j, 1 9 7 9 ; L ' E c u y e r H u f f m a n , 1 9 8 1 ;

W a l a w e n d e r et aL, 1 9 8 5 ). I n o r d e r t o s t u d y t h e s c a l e - up

p r o b l e m s i n t h e d e v e l o p m e n t s ta g e o f o u r g a s i f ic a t io n

I N T R O D U C T I O N o p t io n , t w o d i ff e re n t p l an t s w e r e d e s ig n e d , b u il t a n d

o p e r a t e d . I n s t a l l a t i o n A , w i t h a p r o c e s s i n g c a p a c i t y

A i r g a s if i c a ti o n i s a t h e r m o c h e m i c a l p r o c e s s w h i c h b e t w e e n 2 5 a n d 5 0 k g b i o m a s s / h a n d i n s ta l l a ti o n B

u t il is e s l i g n o ce l l ul o s ic w a s t e s w i t h o u t a n y e x t e r n a l w i t h a c a p a c i t y b e t w e e n 2 0 0 a n d 3 0 0 k g b i o m a s s / h .

e n e r g y c o n t r i b u t i o n . T h e m a i n a i m o f t h e p r o c e s s i s t o R e s u l t s o b t a i n e d i n c o n v e n t i o n a l d o w n d r a f t r e a c t o r s

o b t a i n g a s o f t h e h i g h e s t p o s s i b l e h e a t i n g v a l ue . I n ( F o r i n te k C a n a d a C o r p o r a t i o n , 1 9 8 1 ; T w e n t e U n i -

s o m e c a s e s o n e fa c t w h i c h i m p r o v e s t h e e c o n o m i c v e rs it y , 1 9 8 1 ; H o i B r i d g w a t e r , 1 9 8 9 ; L a r s o n , 1 9 8 9 ;

v ia b il it y o f t h e p r o c e s s i s t h e s i m u l t a n e o u s p r o d u c t i o n M e n d i s et aL, 1 9 8 9 ; S h e n g , 1 9 8 9 ; T a l i b et aL, 1 9 8 9 )

o f c h a r c o a l w h i c h h a s a n a d d i ti o n a l m a r k e t v a lu e a n d in s t ra t if i ed o p e n - c o r e g a si fi e rs ( W a l te r et aL,

( F e r r e r o , 1 9 9 0 ) . 1 9 8 5 ; E a r p B r i d g w a t e r , 1 9 8 7 ; T a v a n g a r , 1 9 8 8 ;

T h e r e a r e e s s e n ti a ll y t h r e e ty p e s o f r e a c t o r f o r T i a n g c o , 1 9 9 0 ) h a v e b e e n r e p o r t e d . M o s t o f t h e s e

b i o m a s s g a s if ic a t io n : m o v i n g b e d ( o r f i x ed b e d ) , f l ui d - g a s if ie r s h a v e a b i o m a s s c o n s u m p t i o n l o w e r t h a n

i se d b e d a n d e n t r a in e d f lo w ( G r o e n e v e l d V a n 1 0 0 k g / h. S e v e ra l d i f f i c u l t i e s a p p e a r w h e n t h e s e r e s u l t s

S w a a ij , 1 9 7 9 ). B o t h t h e f u n d a m e n t a l p r i n c i p le s a n d th e a r e c o m p a r e d . T h e f i rs t i s t h a t e a c h i n st a l la t i on h a d i ts

r a n g e o f p r o d u c t s o f e a c h t y p e o f g a s if ie r a r e w e l l o w n i d e n ti t y a n d t h e r e s u l ts w e r e o b t a i n e d u n d e r

e s t a b li s h e d ( R e e d et aL, 1 9 8 0 ) . T h e c h o i c e o f g a s i f ie r s i m i la r , b u t n o t i d e n t i c a l, o p e r a t i n g c o n d i t i o n s . T h e

t y p e d e p e n d s o n t h e t y p e o f f u e l t o b e g a s if i ed a n d th e s e c o n d i s t h e n a r r o w r a n g e o f o p e r a t i n g c o n d i t i o n s i n

e n d - u s e o f t h e g a s p r o d u c e d . A g a s if i er c o u p l e d t o a n w h i c h e a c h w o r k w a s d o n e . F i n a ll y , a u t h o r s h a v e p r e -

i n t e r n a l c o m b u s t i o n e n g i n e is c u r r e n t l y a n a t t r a c t iv e s e n t e d t h e i r r e s u l t s i n d i f f e r e n t w a y s .

w a y o f g e n e r a t i n g s h a f t p o w e r o r e l e c tr i ci ty f r o m b i o - I n t h is p a p e r t h e r e s u lt s o b t a i n e d i n t w o d if f e r e n t

m a s s in t h e p o w e r r a n g e o f a f e w k i l o w a t t s t o s e v e r a l i n s t a ll a t i o n s o f d i f f e r e n t s i ze , b u t u s i n g t h e s a m e b i o -

m e g a w a t t s ( B e e n a c k e r s B r i d g w a t e r , 1 9 8 9 ) . T h i s m a s s , a r e p r e s e n t e d . T h e a i m o f t h e w o r k w a s t o s o l ve

s y s t e m c o u l d b e at t ra c t iv e i n d e v e l o p i n g c o u n t r i e s a n d t h e s c a l e - up p r o b l e m s a n d t o r e a c h i n a s e m i - c o m m e r -

c i a l i n s t a l la t i o n y i e l d s a t l ea s t s i m i l a r t o t h o s e o b t a i n e d

* T o wh o m t h e c o r r e s p o n d e n c e s h o u l d b e a d d re s s e d , i n a s m a l l e r p l a n t .

2 2 9


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2 3 0

P . G a r c ia - B a c a i c o a

et al.

M E T H O D S s 0 0

~

Bo th ins ta l la t ions ha d a s imi la r s t ruc tu re , a l tho ugh I Ain i

t h e r e w e r e s o m e d i ff e re n c e s b e t w e e n t h e m d u e m a i n ly v a m ~ s ,

t o t he i r d i f f e r e n t s iz es . T h e y ba s i c a l ly c ons i s t e d o f 'i - g ~ - -

ga s i f i e r a nd sys t e m s f o r b iom a ss a nd a i r f e e d ing , a sh

rem ov al sys tem and gas con di t io ning (cyc lone and he a t ~'R~ ~ ~11

e x c h a n g e r ) s y s te m s . T h e p r o c e s s e s o c c u r r i n g i n t h e ~ ~ i ~

g a s i fi e r a r e a l r e a d y k n o w n B a c o n e t a l . , 1 9 8 4 ; I ~ i

B u e k e n s & S c h o e t e r s, 1 9 8 5 ) a n d o n l y s o m e s p e c if ic

a spe c t s o f t he sys t e m de s ign w il l be shown. , ' /t

An im por t a n t a spe c t o f t h i s ga s i f i e r t ype i s t he

r

d e s ig n o f i t s o x i d a t io n z o n e i n o r d e r t o c r a c k t h e t a r s

a n d o il s f o r m e d i n t h e p y r o l y s is z o n e . S e v e r a l m e t h o d s i

h a v e b e e n p r o p o s e d ( G r o en e v e ld & V a n S waaij, 1 98 0 ; ~ ~ ~ ~ ,/,,

Ka upp & Goss , 1 981 ; Va n Swa a i j, 1981 ; E sp l in e t a l . ,

1 9 8 6 ). F r o m t h e s e m e t h o d s a r e d u c t i o n o f t h e g a s if ie r ~ 0

c r o s s - s e c ti o n b y m e a n s o f a s o - c a ll e d t h r o a t w a s ~

s e l e c t e d . T h e a i r w a s i n t r o d u c e d f r o m t h e t o p o f t h e

ga s i f i e r us ing a c e n t r a l a i r i n l e t . T he t h r oa t s i z e

d e p e n d s o n t h e v a l ue o f t h e b i o m a ss c o n s u m p t i o n - _ Ga~

a r e a r e l a t i o n s h i p a n d f o r a g o o d o p e r a t i o n s h o u l d b e

b e t w e e n 0 0 5 a n d 1 .0 k g b i o m a s s / s m 2 t h r o a t ( G r o e n e -

ve ld , 1980 ; Gr oe n e ve ld & Va n Swa a ij , 1980 ; Ka upp & ('AS

Goss , 1981) .

S REW ONVEYOR

G a s e s a n d c h a r co a l f r o m t h e c o m b u s t i o n z o n e r e a c t ~ 1 ~ 4 A O k '

i n t h e r e d u c t i o n z o n e . T h e g a s y i e ld i s a fu n c t i o n o f t h e

t . /

r e s i d e n c e t i m e i n th i s z o n e . A v o l u m e o f t h e r e d u c t i o n

z o n e g r e a t e r t h a n 0 5 m 3 / m 2 th ro at is wi de ly ac ce pt ed Fig. 1. Main dimensions ( in mm) of the gasif ier in instal la-

as suf f ic ient (Tw ente Un ivers i ty , 1981) . t ion A (25-50 kg/h) .

C o n c e r n i n g t h e b i o m a s s f e e d i n g a n d s o l i d r e m o v a l

sys t e m s , d i f f e r e n t de s igns f o r e a c h i ns t a l l a t i on we r e

use d .

w a s i n t r o d u c e d i n t o t h e g a s if ie r b y m e a n s o f a n e l e c -

D e s c r i p t i o n

o f i n s t a l l a t io n A 2 5 - 5 0 k g /h )

t r i c a l l y d r ive n p i s ton wor k ing i n r e gu l a r s t r oke s . I n

F i g u r e 1 s h o w s a p l a n o f t h e g a s if ie r w h e r e t h e m a i n e a c h s tr o k e , a b a t c h o f 5 - 6 k g o f m a t e r i a l w a s i n t ro -

d i m e n s i o n s a r e i n d i c at e d . T h e g a s if ie r w a l l c o n s i s t e d o f d u c e d .

two c onc e n t r i c , 110- r a m - th i c k , b r i c k l a ye r s. T h e i nne r A t t he ga s i f ie r e x it , t he ga s p r o du c t pa s se d t h r ou gh a

l a y e r w a s b u i lt o f r e f r a c t o r y m a t e ri a l ( h ig h a l u m i n a s t a in l e ss - s te e l c y c l o n e 2 5 0 c m i n d i a m e t e r a n d t h r o u g h

c on te n t ) , wh e r e a s t he ou t e r l a ye r wa s bu i l t o f a t he r - a he a t - e xc ha n ge r .

m a l l y i n s u la t in g m a t e r ia l . T h e t h r o a t c r o s s - s e ct i o n o f T e m p e r a t u r e w a s m e a s u r e d a t s e v e r al p o i n t s i n t h e

the ox ida t i on z on e wa s de s igne d us ing a nom ina l i ns t a l la t i on ( in t he ga s i f ie r a nd i n t he a i r a nd ga s p ipe s )

b i o m a s s p r o c e s s i n g c a p a c i t y o f 5 0 k g / h a n d a v a l u e o f a n d t h e g a s c o m p o s i t i o n (N 2 , H 2 , C O , C O 2 , C H 4 ) w a s

0 2 8 3 k g / s m 2 t h r o a t, d e t e r m i n e d b y c h r o m a t o g r a p h y .

T h e b e d r e s t e d o n a g r id i n t h e b o t t o m o f th e g a si -

t i e r . T h i s g r id wa s a l so use d t o r e gu l a t e t he b iom a ss D e s c r i p ti o n o f i n s ta l la t io n B 2 0 0 - 3 0 0 k g / h )

r e s i d e n c e t i m e i n t h e g a s if ie r b y re m o v i n g t h e a s h i n t h e F i g u r e 2 s h o w s t h e g a s if ie r p l a n w h e r e t h e m a i n d i m e n -

l o w e r z o n e . T h e g r i d w a s c o v e r e d w i t h 1 0 m m d i a - s io n s a r e i n d i c a te d . I n t e rn a l l y it w a s h e x a g o n a l i n

m e t e r h o l e s a n d i t w a s c o n n e c t e d t o a v i b r a t o r w h i c h s h a p e . F o r a n o m i n a l b i o m a s s c o n s u m p t i o n o f

o p e r a t e d a t c o n s t a n t t i m e i n te r va l s. 2 0 0 k g / h t h e t h r o a t d e s i g n p a r a m e t e r h a d a v a l u e o f

A r o o t e s b l o w e r p r o v i d e d a n u n c h a n g i n g ai r f l o w 0 3 4 2 k g / s m 2 t h r o a t.

r a t e o f 1 0 0 N m 3 / h . A b y p a s s s y s te m a l l o w e d a i r t o b e A c e r a m i c m a t e r i a l w i t h a d e n s i t y o f 3 5 0 k g / m 3 w a s

f e d t o t he ga s if i e r a t l ow e r r a t e s a s r e qu i r e d . A i r wa s use d t o bu i ld t he ga s i f ie r body . T h i s m a te r i a l ha d good

p r e h e a t e d b y b e i n g p a s s e d t h r o u g h a h e a t - e x c h a n g e r , i n su l a ti n g p r o p e r t ie s . T h e e x t e rn a l w a l l w a s a c a r b o n -

T h e a ir f l o w r a t e w a s m e a s u r e d b y m e a n s o f a r o t a - s t ee l s h el l.

m e t e r w i t h a n a l u m i n i u m f lo a t . T h e b e d r e s t e d o n a n e c c e n t r ic r o t a t in g g r a t e i n t h e

T h e b i o m a s s f e e d i n g w a s c o n n e c t e d d i r e c t ly t o t h e b o t t o m o f t h e g as if ie r. I t w a s c o n n e c t e d t o a m o t o r

top o f t he ga s i f ie r i n o r d e r t o a vo id l e a ks . I t c ons i s t e d wh ic h op e r a t e d a t c on s t a n t t im e in t e r va l s whic h

o f a 7 0 0 l it r e h o p p e r i n w h i c h t h e b i o m a s s a m o u n t a l lo w e d r e g u l a ti o n o f t h e r e s i d e n c e t i m e o f t h e

r e q u i r e d f o r a r u n w a s l o a d e d i n o n e b a t c h . T h e f e e d b i o m a s s .


3/7

Do w n d ra f t m o v in g b e d b io m a ss g a si fi er s

2 3 1

:_ 10ao . j c o m p a r t m e n t ( 3 5 0 m m x 7 3 0 m m ) c l o s e d a t b o t h e n d s

~ i . ._ - , b y t w o g a t e v a l v e s ( 3 5 0 m m d i a m e t e r ) w h i c h e n s u r e d

t h a t t h e g a s w a s s e a l e d o f f . B i o m a s s w a s t r a n s p o r t e d t o

t h e t o p o f t h e s y s t e m f r o m t h e f l o o r l e v e l u s i n g a b e l t

c o n v e y o r . T h i s s y s t e m f e d b i o m a s s i n a q u a s i - c o n -

t i n u o u s w a y .

At the gas i f i e r ex i t , gas passed th rough a s t a in l es s

s t e e l c y c l o n e 0 - 5 4 7 m i n d i a me t e r . A h e a t e x c h a n g e r

w a s f i t t e d i n t h e g a s s tr e a m. T h e g a s l in e w a s i n s u l a t e d

b y c e r a mi c w o o l a s f a r a s t h e c y c l o n e e x i t . T h e o f f - g a s

w a s b u r n t i n a t o r c h .

T e m p e r a t u r e m e a s u r e m e n t s i n t h e g a s i f i e r a n d a t

s e v e r a l p o i n t s o n t h e a i r a n d g a s p i p e s w e r e c a r r i e d o u t

b y m e a n s o f se v e r a l t h e r m o c o u p l e s . T h e p r e s s u r e w a s

a l s o me a s u r e d a t s e v e r a l p o i n t s .

G a s c o m p o s i t i o n ( N 2 , H 2 , C O , C O 2 ,

C H 4 , C 2 H 6 ,

C 2 H4 , C 2 H2 ) wa s

d e t e r m i n e d i n q u a s i - c o n t i n u o u s

m o d e . A p u m p t r a n s f e r r e d a s m a ll g a s- f lo w to t h e

c h r o m a t o g r a p h a n d t h i s w a s a n a l y s e d c o n t in u o u s l y .

T h e e x p e r i m e n t a l p r o c e d u r e w a s v e r y s i m i l a r i n

b o t h i n s t a l l a t i o n s . E a c h r u n w a s s t a r t e d w i t h t h e

i g n it i o n o f t h e c h a r c o a l b e d r e m a i n i n g , u p t o t h e c o m-

b u s t i o n z o n e , f r o m a p r e v i o u s e x p e r i m e n t . A r o o t e s

b l o w e r p r o v i d e d 7 5 % o f th e a i r f lo w r a t e s e l e c te d f o r

t h e e x p e r i m e n t . A f t e r 5 - 1 0 m i n i g n it io n w a s a c h i e v e d ,

t h e b i o ma s s f e e d i n g s y s t e m s t a r t e d a n d t h e a i r f l o w -

r a t e w a s i n c r e a s e d u p t o t h e s e l e c t e d v a l u e . W h e n t h e

g a s i f i e r w a s f u l l , t h e r e s i d e n c e t i me c o n t r o l d e v i c e s

( v i b r a ti n g g r i d - e c c e n t r i c r o t a t i n g g r a t e ) w e r e s t a r t e d . I t

w a s c o n s i d e r e d t h a t s t e a d y - s t a t e h a d b e e n r e a c h e d i n

a n e x p e r i m e n t w h e n t h e m e a s u r e d t e m p e r a t u r e s h a d

Fig. 2 . M ain dime nsio ns in m m ) of the gasifier in instal la-

c o n s t a n t v a l u e s . T h i s s i t u a t i o n w a s r e a c h e d i n

t io n B ( 2 0 0 - 3 0 0 k g/ h) . 2 0 - 3 0 mi n i n i n s ta l l a ti o n A a n d i n 4 0 - 6 0 mi n i n i n s ta l -

l a t io n B . E x p e r i me n t s l a s t e d a t l e a s t 2 .5 h i n s t e a d y -

s t a t e .

T w o d i f fe r e n t g r a t e d e s i g ns w e r e a n a ly s e d : A s t h e b i o m a s s c o n s u m p t i o n d e p e n d s o n t h e a i r

f l o w - r a te i n t ro d u c e d ( J e n k i n s & G o s s , 1 9 8 0 ) a n d o n

( a) O p e n - g r a t e d e s ig n . T h e e c c e n t r i c r o t a ti n g g r a t e t h e d e si g n o f t h e a s h - r e m o v a l s y s t e m ( R e e d et al.

c o n s i s t e d o f t h r e e c i r c u la r r i n gs p l a c e d o n e o n

t o p o f t h e o t h e r ( ma d e o f 8 m m s t a i n le s s st e el ). 1 9 8 9 ) t h e i n f l u e n c e s o f b o t h v a r i a b l e s w e r e a n a l y s e d i n

T h e l o w e r o n e w a s c e n t r e d w i t h t h e a x is o f t h e a n i n d e p e n d e n t w a y . F o r e a c h a s h r e m o v a l d e s i gn ,

e x p e r i m e n t s f o r d i f f e r e n t a i r f l o w - r a t e s w e r e p e r -

g a s i fi e r a n d t h e o t h e r t w o o u t o f l in e w i t h t h e f o r m e d . I n t h e s e e x p e r i me n t s t h e s o l i d h e i g h t w a s k e p t

a xis . A f t e r s e v e r a l t e s t s a d i s t a n c e o f 6 5 c m

b e t w e e n t h e r in g s w a s u s e d . c o n s t a n t i n t h e g a s if ie r i n o r d e r t o a v o i d o t h e r a d d i -

t i o n a l v a r i a b l e s b e i n g i n t r o d u c e d i n t h e p r o c e s s .

( b ) C l o s e d - g r a t e d e s ig n . T h e b a s i c s t r u c t u re o f t h r e e I n e a c h e x p e r i m e n t th e b i o m a s s c o n s u m p t i o n w a s

c i r cu l a r t in g s w a s m a i n t a in e d . T h e l a te r a l f a c e s n o t p r e v i o u s l y k n o w n , s o t h e b i o m a s s f e d w a s th e

o f t h e g r a t e c o n s i st e d o f a m e t a l s h e e t (5 m m a m o u n t n e c e s s a r y t o k e e p t h e s o l id - h e ig h t c o n s t a n t i n

t h ic k s ta i nl e ss s t e e l ) w i t h 7 2 0 h o l e s o f 1 5 r a m t h e g a s if ie r ( 1 0 5 0 m m i n t h e i n st a ll a ti o n A a n d

d i a me t e r . W i t h t h i s d e s i g n t h e a m o u n t o f r e s i d - 1 8 0 0 m m i n t h e B o n e ) . I n i n s t a ll a t io n A t h e b i o m a s s

u a l s o l i d o b t a i n e d w a s l e s s t h a n t h a t c o r r e -

c o n s u m p t i o n w a s c a l c u l a t e d f r o m t h e q u a n t i t y o f

s p o n d i n g t o t h e o p e n - g r a t e d e s ig n , b i o m a s s r e m a i n i n g i n t h e h o p p e r a f t e r t h e e x p e r i m e n t

T h e r o o t e s b l o w e r p r o v i d e d a n u n c h a n g i n g a i r - fl o w - i n r e l a t i o n t o t h e f e e d i n g ti me . I n in s t a l la t i o n B th e

r a t e o f 4 0 0 N m 3 / h , b u t a b y p a s s s y s t e m a l l o w e d a i r t o b i o m a s s c o n s u m p t i o n w a s c a l c u l a te d f r o m a n a s h

b e f e d t o t h e g a s i fi e r a t l o w e r r a t e s . T h e a i r f l o w - r a t e b a l a n c e , s i n c e t h e p r o x i m a t e a n d u l t i ma t e c h a r c o a l

w a s m e a s u r e d b y m e a n s o f a n a n n u b a r a n d t h e a i r w a s a n a l y se s w e r e c a r ri e d o u t f o r a ll t h e e x p e r i m e n t s. M a s s

p r e h e a t e d b y b e i n g p a s s e d t h r o u g h a n a i r - g a s h e a t - b a l a n c e s w e r e c o n d u c t e d o n a ll t h e o t h e r p r o d u c t s .

e x c h a ng e r . W h e n t h e e x p e r i m e n t f i n is h e d t h e a i r f l o w w a s

A n e w b i o m a s s f e e d i n g s y s t e m w a s d e si g n e d in s t o p p e d a n d a ll o t h e r s y s t e m s w e r e t u r n e d of f. T h e

o r d e r t o e n s u r e t h e p l a n t a u t o n o m y ( f o r a n y p r o c e s s i n g i n st a ll a ti o n w a s k e p t c l o s e d u n t il i t b e c a m e e x t in c t

c a p a c i t y o f t h e g a si fi e r) . T h i s c o n s i s t e d o f a c y li n d r i c a l ( a p p r o x i ma t e l y 1 -5 d a y s f o r i n s ta l la t io n A a n d 3 d a y s f o r


4/7

232 P . G arc ia - B ac a ic oa et al.

T a b le 1 . M a in ch a ra cter i s t i c s o f g a s i f i ed fo res try w a s te T a b le 3 . C o m p o s i t io n ( v o l . ) a n d lo w h ea t in g v a lu e o f th e

g a s p r o d u c e d in in s t a l l a ti o n A ( 2 5 - 5 0 k g / h )

Proxim ate analysis ( dry basis)

Fixed carbon 19.65 Experi- N 2 CO CO 2 CH4 H2 LHV

Volatiles 77.70 ment (kcal/Nm 3)

Ash 2.66

Elem entalana lysis ( dry basis) A-5 55 0 16.3 13.0 0-6 15.1 1007

A-4 53.4 16.1 13.6 0.7 16.2 961

Carbon 45.80 A-2 54.1 13.7 15.6 1.3 15.3 1006

Hydrogen 6-00

Nitrogen 0.30 A-6 54.0 16-4 13-2 1.2 15-2 1011

A-1 55'7 14.9 10.9 1.3 17.2 940

Oxygen 47.90

A-11 48.3 24.1 10.0 1.9 15-7 1292

Moisture level (wet basis) 12.10 A-2 52.7 14.1 16.0 1.6 15.6 1006

Low heating value (kcal/kg wet) 3590 A-7 49-8 19.3 11-7 1-2 18.0 1147

Particle size 84% between 0.5 and 16 nun A-9 46 .8 15.7 16.1 2.2 19.2 1129

T a b l e 2 . O p e r a t i n g c o n d i t i o n s a n d m a i n va l u e s o f th e

r e s u l t s o b t a i n e d i n i n s t a l la t i o n A ( 2 5 - 5 0 k g / h ) T a b l e 4 . O p e r a t i n g c o n d i t i o n s an d m a i n v a l u e s o f t h e

resu l t s o f th e ex p er im en ts p er fo rm ed in in s ta l la t io n B

Experi- Air Grid Biomass Gas Solid ( 2 0 0 - 3 0 0 k g / h )

ment (Nm3/h) vibration processed produced produced

(% time) (k g/ h) (Nm3/ h) (kg/h) Experi- Air Biomass Gas Solid

ment (N m3 /h ) processed produced produced

A-5 50 16 0 25.4 75 0 25 (k g/h ) (Nm3/h) (kg/h)

A-4 50 22 0 28.1 75 0'31

A-2 50 29-0 34.0 79 0 . 5 8 O p e n - g r a t eesign

A-6 50 38 0 37.8 72 1.02 P-3 250 220.4 318 7 31.8

A-1 50 50 0 46.1 73 3-04 P-4 250 214.7 340.5 25-6

A-11 40 29 0 31.7 65 1.43 P-22 250 251.4 283.2 23.5

A-2 50 29 0 34.0 79 0 58 P-30 250 262.8 325.2 23.7

A-7 60 29-0 39-3 95 0 79 P-5 300 231.6 375.4 26.6

A-9 70 29 0 48.9 117 0 73 P-13 300 291.7 416.4 39 5

P-20 300 259-0 365 3 42.3

P-32 300 315 3 371-1 31 1

P-12 350 334 5 500.3 59.8

P-25 350 316 6 503'7 31'1

installation B). Once the installation was cold, it was P-31 350 338-3 483.2 32.7

cleaned and the ash was removed from the cyclone and Closed -grate e s ign

the hopper. G-1 250 208.8 372.1 18.0

G-2 250 220.0 379.5 16.7

G-8 250 191.3 372-6 10.8

RESULTS AND DISCUSSION G-6 300 264.4 492.5 12.1

G-7 300 265.0 518.0 15.8

Wood chips from forestry wastes were processed in G-9 300 246.9 481.6 12.6

both instal lations. Table 1 shows the main character- G-10 350 283.1 521.6 14-5

istics of this biomass. Several kinds of experiments G-11 350 299.0 553-5 15.3

were carried out. The main variables analysed were G-12 350 275.0 526.4 10.8

inlet air-flow, and design and operat ion o f the grate.

In installation A, runs (A-i experiments) were per-

on the air introduced. Both values increased with

formed for different air flows (40-70 Nm3/h) and

different on/off times (16-50%) of the vibrator grid. the amount of air introduced.

For a gasifier and a given amount of air intro-

Tables 2 and 3 show the main results obtained.

In installation B two different experimental series duced, the biomass processed was influenced by

were done according to the design of the eccentric the design and opera tion of the ash-removal

rotating grate. Both grate models were described system. It can be observed in Table 2 that the

previously. For the open-grate design P-i experiments biomass consump tion increased with the grid

were performed, and for the closed-grate design G-i operation time. In installation B, Table 4, a

ones. Table 4 shows the operating conditions and the greater biomass consumption was obtained (for

main values of the results obtained. Tables 5 and 6 the same air-flow rate) in the P-i experiments than

show the main characteristics of the gas and the solid in the G-i ones. The different designs of the grate

generated, also influenced the amount of gas and solid pro-

The main features of these results are listed below, duced. In the G-i experiments more gas and less

solid were produced than in the P-i experiments.

For a gasifier and a given design and operation of The low heating values of the gas obtained with

the ash-removal system, the amounts of biomass the closed-grate design (G-i experiments) were

processed and of gas produ ced depen ded mainly higher than those corresponding to the open-


5/7

D o w n d r a f t m o v i n g b e d b i o m a s s g a si fie rs 2 3 3

Table 5. Com position ( vol.) and low heating value of the gas produced in the experiments perform ed in installation B

(2 0 0 -3 0 0 k g / h )

Experi- N z CO

CO CH 4 H C H4 C H6

C2H2 LHV

ment (kcal/N m3)

Open grate design

P-3 54.7 26.5 9-4 2 0 7-0 0.26 0.10 0 12 1209

P-4 54.4 19.1 14.5 3.2 8 0 0.58 0-15 0 10 1166

P-22 70.0 15.2 9-5 0.6 4-6 0.07 0.04 0-01 636

P-30 60-7 14.4 7.0 2.9 13 3 0.40 0-18 1 11 1259

P-5 63 1 17.0 12.9 3 0 2.9 0.65 0.18 0'30 1000

P-13 56'8 21.6 9 6 2.2 9.1 0.20 0.09 0 43 1119

P-20 53.4 25-6 12.4 2 3 5-8 0.32 0.12 0.08 1189

P-32 63-9 13.2 6 4 3.0 13 0 0.32 0.18 0.04 1069

P-12 55.2 15.2 15-7 3 9 9-0 0 70 0.22 0 13 1162

P-25 55 4 9.2 19.1 1.7 14 3 0.23 0.11 0.01 838

P-31 57.2 8.4 19 4 1-6 13 0 0.25 0.11 0.07 788

Closed grate design

G-1 53 1 16-6 17 3 2.9 9-5 0.26 0.15 0.17 1079

G-2 47-8 19.8 16 0 3.4 12.4 0 33 0.18 0.13 1296

G-8 47.8 26.3 10-1 2 1 13-2 0.31 0.11 0.04 1394

G-6 47.3 22.1 13 8 2-9 13 4 0 38 0.11 0.05 1336

G-7 43.9 22.1 12 2 2.6 18.6 0.37 0.11 0.04 1445

G-9 48.6 19.8 14 0 2 5 14.6 0 33 0.10 0 08 1265

G-10 43.0 25-0 11-1 3 6 16-7 0.47 0.15 0-05 1588

G-11 45'6 23.5 12 3 3 0 15 1 0 33 0 13 0.00 1420

G-12 44-4 21-5 14 4 3 3 16-0 0 33 0.13 0.00 1436

Table 6. Main characteristics of the solid generated in the Different mass and energy perfo rmance values

experiments performed in instal lation B ( 20 0- 30 0 kg/b) defined by Walawender et al. (1988) were evaluated.

Experi- Ash Vo la ti le s Fixed C. LHV The mass performance values used were: (i) the mass

ment (% wt.) (% wt.) (% wt . ) (kc al /k g) air/biomass (dry basis) relationship (A/F); (ii) the mass

gas/air relationship (G/A); (iii) the mass gas/biomass

Open grate design (dry basis) ratio (G/F); and (iv) the mass conversion

P-3 16.26 10.65 73.09 6195 efficiency (MCE) defined as the mass ratio of the dry

P-4 19-67 9-86 70-47 5885 gas output rate to the combined input rates of both wet

P-22 26.08 9.96 63 96 5285

P-30 26.89 21-30 51.81 4765 feed and air. To quantify the energetic yield, the cold

P-5 20.65 9.35 70.00 5876 gas efficiency (CGE) was used, defined as the ratio of

P- 13 17.85 11.05 71.10 6129 the energy content of the dry gas to the energy content

P-20 14.48 11.13 74.39 6513 of the dry feed. Table 7 shows the values of ER and of

P-32 23-95 24.85 51.20 4846 the per formances evaluated.

P-12 13.19 10-70 76.11 6495

P-25 23.26 16.43 60.31 5257 An important parameter in the gasifier yields is the

P-31 25.46 19-75 54.79 4994 A/F relationship (Desrosiers, 1979; Chen, 1986). For

Closed grate design each experimental series similar results of the influence

G-1 27.38 15.41 57.21 4825 of the air flow on the A/F ratio were obta ined and the

G-2 31-08 17.70 51.22 4424 affirmation tha t the A/ F relationship tends to regulate

G-8 43.76 14.12 42.12 3592 itself to a given value (Jenkins & Goss, 1980) was

G-6 51.75 14.24 34.01 2743 confi rmed. In our case, in the A-i series (29% vibration

G-7 40.68 15.12 44.20 3801

G-9 47.78 13.88 38.34 3215 time of the grid), an average A/ F value of 2 082 kg air/

G-10 47.39 11'34 41.27 3471 kg feed (dry basis) was obtained. For series P-i and G-i,

G-11 46.76 9.11 44.13 3578 values of 1.578 and 1.756 were respect ively deter-

G-12 61.45 8.04 30.51 2572 mined. Similar values are reported in the bibliography.

Thus, Chee (1990) showed values between 1-62 and

grate design (P-i experiments). This was mainly 1 84, Groeneveld et al. (1983) obtained a value of 1.81

due to the higher hydroca rbon concentrations and Walawender

et al.

(1985) reported values between

0 99 and 2.08.

obtained in the gas in the G-i experiments. With respect to the gas product obtained, the

The influencing variables (amount of air introduced average values of G/ A and G/F obtained in each

and design and operat ion of the grate) have been experimental series are shown in Table 8. The G/A

grouped in the equivalence ratio (ER), defined as the values corresponding to the A-i and G-i experiments

percentage between the real and the stoichiometric were similar to those reported by Chee (1990)

oxygen/biomass relationship. (between 1.47 and 1-52 kg gas/kg air). The G/ F values


6/7

234

P . G a r c i a B a c a i c o a

et al.

T a b l e 7 . T h r o u g h p u t a n d p e r f o r m a n c e i n d i c a to r s o f t h e 1 , 0 ~ , o

ex p er im en ts p er fo rm ed in b o th in s ta l la t io n s [ ] t~i'~Atx o o o

] o

Experi- ER A/F G/A G/F MCE CGE 0,8 O

ment (%) (m as s (m as s (mass o

units) units) units) 0,6 lID

ne

Open grate design in installation B 0

P-3 2 2 . 2 1. 66 0 1. 27 6 2.117 0.757 0.487 X 0,4

P-4 22 .8 1. 704 1.38 3 2. 355 0.829 0.515

P-22 19 .5 1. 45 5 1. 15 3 1. 67 7 0.647 0.200

P-30 18 .7 1. 39 2 1. 18 9 1.6 54 0.654 0.434

0 , 2

P-5 2 5 . 4 1. 89 5 1. 31 1 2.484 0.819 0.452

P-13 20 .2 1 .5 05 1.34 9 2.029 0.768 0.445

P-20 22 .7 1 .695 1 .247 2.113 0.746 0.467 0,0 . . . .

P-32 18. 7 1. 39 2 1. 14 3 1.5 91 0.629 0.350 15

2 0 2 5 3 0 3 5 4 0

P-12 20 .5 1. 53 1 1. 44 5 2. 21 2 0.829 0.484 Ell (%)

P-25 21 .7 1. 61 7 1. 42 2 2.300 0.835 0.371

P-31 20 .3 1 .514 1 .363 2 .063 0.778 0.314 Fig. 3. Mass conversion efficiencies for different equiva-

lence ratios.

Closed grate design in installation B

G-1 2 3 . 4 1.7 52 1. 51 3 2.650 0.917 0.563

G-2 22 . 2 1. 66 3 1. 48 7 2. 47 3 0.883 0.623 1,0

G-8 25 . 6 1. 91 2 1. 37 2 2. 62 3 0.860 0.756

G-6 22. 2 1. 660 1. 577 2.61 9 0.936 0.693

G-7 2 2. 2 1. 65 6 1. 54 2 2.554 0.914 0.787 0,8 A A o

G-9 23 . 8 1. 77 8 1. 50 4 2. 67 3 0.917 0.687 AA ~ o o

o

G-10 24 .2 1. 80 9 1. 33 9 2. 42 2 0.822 0.815 A o

G-11 22 .9 1. 71 3 1. 46 6 2. 51 1 0. 88 1 0.732 0,6 o

G-12 24 .9 1. 86 2 1. 39 3 2. 59 5 0. 865 0.766 O [] ~ []

Fo r different airflo ws in installation A 0 0,4 o

A-11 24 .7 1. 84 5 1. 42 3 2. 62 4 0.880 0.734 [] [] o

I : : : , t

-2 2 8 . 8 2. 15 2 1. 43 6 3.089 0.939 0.652

A-7 3 1. 1 2. 23 5 1. 38 8 3. 10 3 0.920 0.775 0,2 []

A-9 32 .1 2 .09 4 1. 52 8 3.199 0.990 0.750

0 0

. . . .

1 5 2 2 5 3 3 5 4

T a b le 8 . A v era g e v a lu es o f g a s /a i r a n d g a s / f eed ( in m a ss

u n i t s ) o b t a i n e d i n e a c h e x p e r i m e n t a l s e r i e s

Ell (%)

Fig. 4. Cold gas efficiencies for different equivalence

Experimental G/A G/F ratios.

series (kg gas/kg air) (kg gas/kg biomass)

A-i 1-44 3.00 throughput. Biomass consumption can be increased by

P-i 1.30 2.05

G-i 1.47 2.57 (i) increasing the operat ion of the grate, or (ii) increas-

ing the flow area of the grate.

Air flow is an influential variable and it determines

of G-i experiments were similar to those of Chee the biomass consumption and the gas and solid pro-

(between 2-47 and 2.70). ductions. The air/biomass ratio self-regulates at a given

The influence of ER on the MCE is shown in Fig. 3. value. Also the gas/air ratio and the solid yield remain

It can be observed that MC E increases with ER. In the virtually unchanged for each design and operation of

A-i and G-i experiments values above 0 9 have been the solid-removal system.

reached, whereas in the P-i experiments lower values Mass conversion efficiency (MCE) and cold gas effi-

were obtained. Other values repor ted in the literature iency (CGE) values increase with the equivalence ratio

were 0 91 (Chee, 1990) and 0 90 (Forintek Cana da values. Both values of MCE above 0.9 and of CGE

Corporat ion, 1981; Twente University, 1981). over 0-7 have been reached in the gasifiers. It can be

The influence of ER on the CGE values is shown in concluded that in a semi-commercial installation yields

Fig. 4. In the A-i and G-i experiments values of 0 7 similar to those in corresponding smaller plants were

were obtained. In the P-i experiments the CGE ranged obtained.

between 0 35 and 0-48. Chee (1990) reported values

between 0 66 and 0.71, which are similar to those

obtained in the A-i and G-i series. ACKNOWLEDGEMENTS

The authors express their gratitude to DGICY T (Pro-

CONCL USIONS ject PB91-0284) and to Consejer/a de Economia y

Hacienda de la Junta de Castilla-Le6n, IDAE and

The design and operation of the solid-removal system CIEMAT (PIEPMA Programme) for providing finan-

of the gasifier allows one to modify the biomass cial support for this work.


7/7

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Beena ckers , A . A . C. M. Br idgwate r , A . V . (1989) . gas i f ica t ion sys t em for e l ec t r ic i ty u t i li t y bo i l e r app l i ca -

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A . G . Bue kens A . V . Br idgwate r . E l sev ie r Appl . bed dow ndra f t gas i fi e r on a low qua l i ty re s idue fue ls .

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