Influence of Coal Nature and Structure on Ash Size Formation Characteristic and related Pollutant Emissions During CFB Combustion

8/7/2019 Influence of Coal Nature and Structure on Ash Size Formation Characteristic and related Pollutant Emissions During

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J. of Therm al Science, Vol.9, No.3

I n f l u e n c e o f C o a l N a t u r e a n d S t r u c t u re o n A s h S i z e F o r m a t i o n C h a r a c t e r i s ti ca n d R e l a t e d P o l lu t a n t E m i s s i o n s D u r i n g C F B C o m b u s t io n

M i n Q I A N A r n a u d B O E L L E P h il ip p e J A U DE l e c t ri c i t6 d e F r a n c e D i v i s i o n R & D , 6 q u a i W a f t e r B . P . 4 9 7 8 4 0 1 C h a t o u , F r a n c e

Y o n g ji e N A Q i n g g a n g L U S h a o li n B A O P i n g C U I W e i h on g J I A O H u a n m i n g Z H A OI n s ti tu t e o f E n g i n e e r i n g T h e r m o p h y s i c s , C h i n e s e A c a d e m y o f S c i e n ce s 1 0 0 0 8 0 B e i j in g , C h i n a

The size distribution of coal particles in a Circulating Fluidized Bed (CFB) boiler plays a crucial role in thecomplicated combustion, heat exchange and pollutant emissions in such a plant. Therefore, it is fundamental tostudy the different factors having influence on the size distribution of coal particles. Above all, the coal itself and inparticular, the coal comminution phenomenon is a ve ry influent factor. In the frame of this work, the coal nature(elementary compo sition) and coal internal structure (m ineral componen ts) are studied in detail. A t thisintermediary stage, experiments on three typical Chinese coals on a 1.5 MWt CFBC pilot plant have been made.Som e primary fragmentation tests have also been m ade in a small lab scale fluidized bed reactor. T he results f romthe hot pilot test show i) the variation of coal ash distributions and other CFB performance data due to the cycloneand the coal characteristics and ii) the variation of desulfurization efficiency with limestone. Whereas the benchscale primary fragmentation test, likely linked to the caking propriety of a coal, does not seem to changeconsiderably the char size distribution.

Keywords : circulating fluidized bed, coal characterization, ash form ation, size distribution, pollutan t emissions.Introduct ion

O n e o f t h e a d v a n t a g e s o f C F B b o i l e r i s it s a b il i ty t ous e d i f fe ren t k inds o f fue l s . T heore t i c a l ly , a l l t ypes o fc o a l s m a y b e u s e d i n a C F B b o i l e r . N e v e r t h e l e s s , a l lc o a l s d o n o t h a v e t h e s a m e b e h a v i o r i n a C F B b o i l e r .F u r t h e r m o r e , w e k n o w n o w t h a t t h e s i z e d i s t r i b u t i o n o fcoa l pa r t i c l e s c i rcu la t ing in a CFB bo i l e r p l ays a c ruc ia lr o l e i n t h e c o m p l i c a t e d c o m b u s t i o n , h e a t e x c h a n g e a n dp o l l u t a n t f o r m a t i o n m e c h a n i s m s . T h e r e f o r e , i t is o f p r i m ei n t e re s t t o k n o w b e t t e r t h e l in k b e t w e e n t h e n a t u r e o f t h ecoa l and the re s u l t ing pa r t i c l e s i z e d i s t r ibu t ion in s ide aC F B f u r n a c e w h i c h i n f l u e n c e s th e g l o b a l b e h a v i o r o f t h ebo i l e r .

T h i s e x p e r i m e n t a l p r o g r a m , l a u n c h e d b y E l e c tr i ci t 6d e F r a n c e / D i v i s i o n R & D i n c o ll a b o r a t i o n w i t h I n s ti t u t eo f E n g i n e e r i n g T h e r m o p h y s i c s ( I E T ) , h a s b e e n d e s i g n e dt o s t u d y t h e i n f l u e n c e o f t h e c o a l n a t u re ( e l e m e n t a r yc o m p o s i t i o n ) a n d c o al i n te r n a l s t r u c t u r e ( m i n e r a lc o m p o n e n t s ) o n t h e a s h f o r m a t i o n a n d r e l a t ed p o l l u t a n te m i s s i o n s . I n p r a c t i c e , t h e fi r s t a s p e c t o f t h e w o r kc o n s i s t s i n t es t i n g 6 C h i n e s e c o a l s o f w h i c h t h e

i m m e d i a t e a n d u l t i m a t e a n a l y s e s r e s u l t s a r e d i f f e re n t f o rthe 6 coa l s one f rom the o the r . Dur ing the t e s t s fo r thef i r st t w o c o a l s , t h e r o l e o f t h e c y c l o n e a n d t h e i n f l u e n c eo f l i m e s t o n e t y p e o n t h e S O 2 e m i s s i o n h a v e a l s o b e e ns tud ied . I f t he f i r s t a s pec t i s we l l kn ow n in the f i e ld o fc o a l c h a r a c t e r i z a t i o n f o r C F B u s e , t h e s e c o n d a s p e c t i sr a t h e r a n e w e x p e r i e n c e b a s e d o n t h e h y p o t h e s i s t h a t t h ef ina l a s h s i ze d i s t r ibu t ion i s s omehow a re f l ec t ion o f thecoa l mine ra l i nc lus ions s i ze d i s t r ibu t ion . S ince thep r i m a r y f r a g m e n t a t i o n c o u l d c a u s e s o m e v i o l e n t i n t e r n a lc h o c k , i n e a r l y ti m e s w e t h i n k i t is p r e f e r a b l e to c o m p a r et h e m i n e r a l i n c l u s i o n s i n t h e c h a r p a r t i c le s a f t e r p r i m a r yf r a g m e n t a t i o n w i t h t h a t a f t e r C F B c o m b u s t i o n .

Exp erim ental Faci l it iesT w o e x p e r i m e n t a l f a c i l i t i e s a r e u s e d t o c h a r a c t e r i z e

a coa l in th i s p rog ram .O n e i s a 1 . 5 M W t C F B C p i l o t pl a n t , o f w h i c h t h e

m a i n p a r t i s s h o w n i n F i g u r e 1 . S o l i d p a r t i c l e s a m p l i n g sa r e c a r r i e d o u t a t f i v e d i f f e r e n t l o c a t i o n s a m o n g w h i c hReceived 2000


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Min Qian et al. Influence of Coal Nature on Ash Size Formation and Pollutant Emissions During CFB Combustion 277

the f i r s t fou r ho le s a re s hown on the d iag ram be low: onein the bo t tom bed , one in the f reeboa rd zone , one ju s tbe fo re the cyc lone and one in the re tu rn l eg . T he f i f thone , no t s hown on the d iag ram, i s l oca ted in the bag -h o u s e t o g e t f l y a s h s a m p l e s . A g a s s a m p l i n g p r o b e i sin s t a l l ed in the ga s duc t . NOx, SO2 , 02 , CO and C O2 ing a s a r e a n a l y z e d o n l i n e a n d r e c o r d e d i n a c o m p u t e r . T h et i p s o f t h e t w o v a c u u m a s h p r o b e s i n t h e f u r n a c e a r e a l lloca ted a t t he cen te r o f the ho r i zon ta l c ros s s ec t ion o f thef u r n a c e , w i t h t h e t i p s d o w n w a r d .

e 4

b e d t e m p e r a t u r e : = 8 5 0 d e g r e e s Cf lu id iza t ion ve loc i ty : be tw een 0 . 15 and 0 . 5 rn / sh e a t i n g t i m e : b e t w e e n 3 a n d 1 0 m i n u t e sT he cha rac te r i s t i c s o f the d i f fe ren t t e s t ed coa l s a re

s how n in the t ab le he re a f t e r:

Table 1 Immediate and Ultimate analyses of the tested coals

A B C D EM oistu re ar 7.72 4.70 15.2 8.10

Ashad 12.66 29.26 28.58 15 .55 28.90Vol. M at. ad 27.44 8.96 21.28 30.19 44.50

Ca d 71 .48 61 . 15 52 .58 52 . 73 49 .60H ad 4.08 2.74 2.45 4.28 3.35O ad 7.39 0.86 6.72 7.06 12 .50

S total,ad 1.14 3.63 1. 62 0.38 4.31N ad 0.77 0.95 0.62 1.32 1.35

Qnet ,ar (MJ/kg) 26.22 22 .5 7 17.34

Fig. 1 Main part of the 1.5 MW t CFBC pilotConce rn ing the s econd a s pec t , a l ab s ca le f lu id ized

b e d i s u s e d t o m a k e e x p e r i m e n t s o n p r i m a r yf r a g m e n t a t i o n o f c o a l s . T h e f l u i d i z e d b e d i s m a d e o fs t a i n l e s s s t e e l w i t h 1 2 2 m m i n d i a m e t e r a n d 3 0 0 m m i nhe igh t . T h i s l ab s ca le bubb l ing f lu id ized bed reac to r i si n s e r t e d i n t o a n e l e c t r i c o v e n f r o m t h e b o t t o m t o b eh e a t e d d u r i n g e x p e r i m e n t . F l u i d i z i n g m e d i u m i s h i g hp u r e N i t r o g e n . W h i t e A 1 2 0 3 s a n d w i t h d i a m e t e r b e t w e e n0 . 3 5 m m a n d 0 . 5 m m i s u s e d a s b e d m a t e r i a l . B e dm a t e r i a l i s a b o u t 1 3 0 0 g i n w e i g h t a n d a b o u t 8 0 m m i nhe igh t .

E x p e r i m e n t s

T h r e e t y p i c a l C h i n e s e c o a l s : A , B a n d C , h a v e b e e nt e s t e d i n t h e C F B C p i l o t o f 1 . 5 M W t w i t h t h e s t a n d a r dope ra t ing cond i t ions :

c o a l f e e d r a t e = 2 0 0 k g / h ,b e d t e m p e r a t u r e : - 8 5 0 d e g r e e s C ( + 1 0 d e g r e e s C ) ,e x c e s s a i r : 2 0 % ,p r i m a r y a i r / s e c o n d a r y a i r = 5 5 / 4 5 ,Ca /S = 1 , 2 and 3 s ucces s ive ly .

Seve ra l Ch ines e coa l s : A , B , D and a F rench coa l : Eh a v e b e e n t e s t e d i n t h e l a b s c a l e f l u i d i z e d b e d u n d e rf o l l o w i n g o p e r a t i n g c o n d i t i o n s:

Cyclone ModificationsI t i s w o r t h n o t i n g t h a t s o m e m o d i f i c a t i o n s o n t h e

r e f r a c t o r y - l i n e d c y c l o n e s e p a r a t o r h a v e b e e n m a d ed u r i n g t h e p r o g r a m t o e v a l u a t e t h e i n f l u e n c e o f it se f f i c i en cy on the a s h s i ze d i s t r ibu t ion , t he de s u l fu r i za t ione f f i c i e n c y a n d t h e u n b u r n e d c a r b o n c o n t e n t i n t h e f l ya s h .

O n t h e o n e h a n d , t h e v o r t e x t u b e d i a m e t e r h a s b e e nr e d u c e d c o n s i d e r a b l y ( f r o m 4 0 0 r a m t o 2 6 5 m m ) . O n t h eo t h e r h a n d , t h e s e c t i o n o f t h e p i p e c o n n e c t i n g t h e e x i t o ft h e f u r n a c e a n d t h e e n t r a n c e o f t h e c y c l o n e h a s b e e nn a r r o w e d f r o m 0 . 1 1 5 m 2 t o 0 . 0 7 2 m 2 i n o r d e r t o i n c r e a s et h e g a s v e l o c i t y a t th e e n t r a n c e o f t h e c y c l o n e f r o m a b o u t15 m/s to 24 n t i s.

I n f a c t , o n l y c o a l A h a s b e e n t e s t e d b e f o r e t h ec y c l o n e m o d i f i c a t io n s . W h e r e a s c o a l B h a s b e e n t e s te dt w i c e b e f o r e a n d a f t e r t h e m o d i f i c a t i o n s , a n d c o a l C h a sb e e n t e s t e d w i t h t h e im p r o v e d c y c l o n e .

R e s u l t s a n d D i s c u s s i o nI n f l u en ce o f Cy c l on e E f f i d en cyA f t e r h a v i n g m o d i f i e d t h e c y c l o n e e f f i c i e n c y

b e t w e e n t h e p i lo t te s t s o f c o a l A a n d c o a l B , t h ec o m p a r i s o n o f d i f f e r e n t p a r a m e t e r s s h o w s t h e i n f l u e n c eo f t h e c y c l o n e e f f i c i e n c y i m p r o v e m e n t o n t h e o p e r a t i o no f t h e C F B C p i lo t .

F i g . 2 s h o w s t h a t t h e f u r n a c e t e m p e r a t u r e p r o f i l e o ft h e s a m e c o a l t e s te d a f t e r t h e m o d i f i c a t i o n o f t h e c y c l o n ei s m o r e e v e n t h a n t h a t b e f o r e t h e m o d i f i c a t i o n .


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278 Journal of Thermal Science, Vol. 9. No.3o 2000

9000

8000

7000

6000~E 5000

4 0 0 0

3000

2000

1000

075 0 800 850 900 950T (Degree C el s i u s)

Fig.2 Influence of cyclone efficiency on thefumace temperature profile

Fig.3 shows that for the same coal the f ly ash af tercyclone modi f ica t ions i s f iner than before . Moreover ,F igure 4 and Figure 5 con f i rm that bo th bo t tom ash andci r cu la t ing ash are f iner owing to the improvement o fcyclone eff iciency.

Besides, the solids circulat ion character is t ic isdif ferent for the two coals . According to themeasurement of gas pressure drop at dif ferent levels , inpar t icular the total drop between the heights of 120 mmand 7730 mm and the par t ial drop between the heights of940-7730mm, the ash weight in the 2 dif ferent par t canbe rough ly es t imated . The per fo rmance o f a CFB un i tdepends more o r less on the r a t io o f ash weigh t above thedense bed (940-7730 mm) to total (120-7730 mm) ashweight present in the furnace. In our case, af ter thecyclone modif icat ions, this rat io is increased f rom 23%to 42%. I t means that there are more solids in the di lutedpar t , therefore useful for the heat t ransfer af ter thecyclone modi f ica tions .

10 09 08 07 06 0504 03O2 010

0

II IIIIIIII 111111I II IIIIIII IIIIIIII IIIIIII I I I I I I ] .~/1[]1111 .~rI I I [ I I L ~I I . J~ r--,,~1"1 I[11

] 0

~ l l l lIIIlllI I I I I I = co~uo~

mo

. - . A - - C o ~aft~II mo

1 0 0D (micron)

B

B

1 0 0 0

Fig. 3 Influence o f cyclone efficiency on the sizedistribution o f fly ash

10090

|~ IoO.Ol

............S ................... ~"~""i'~'''~.................. F-7 "i r' z ~ l l 'T ................~'~'7i~

; ' ; i : i . .. .. . [ i , l c l i' : i ' = . . . . / ", ~1 I i i

i , I , , , i , = co ,Bi' : ! ]i ~i "~1/ i I] before: , ~ J a f t e r

0.1 D (mm) 10 100

1o o90807060

~ 504 03 02 0

Fig. 4 Influence of cyclo ne efficiency on the sizedistribution o f botto m ash

0.1

80706O

~5o" ~40

3 02 010

00.01 D (ram) 1 10

Fig.5 Influence of cyclo ne efficiency on the sizedistribution of circulating ash

I n f l u e nc e o f C o a l N a tu r eAs shown in Table 1, the three tested coals A, B and

C are dif ferent f rom each other by their volat i le matter ,carbon and ash contents etc. Logically , these dif ferencesshould lead to some var iat ions of the ash s izedistr ibutions. Howeve r , for coals A and B, both testedbefore the cyclone modif icat ions, the ash s izedistr ibutions do not vary a lot f rom one to the otherexcep t tha t the bo t tom ash o f coal B is much coar serthan that of the coal A. According to the exper imentalobservation, the last point ar ises probably f rom thecoarse gangue par t icles included in the raw coal B.

Never theless , w i th the improved cyclone , somedifferences for coals B and C are noted through severa lparameters which are worth thinking about.

Before al l , i t turns out that the furnace temperatureprof i le is more even for coal C than for coal B as shownin Fig.6.

Th is var ia t ion can p robab ly be exp la ined by theimportant increase (1.5 t imes) of the gas pressure drop(940-7730mm) ob ta ined wi th coal C compared~to theone got f rom coal B. Actually , the gas pressure dropref lects the mean solids concentrat ion above the densebed in the furnace. The more there are solids along thefurnace , the more homogen ous the tempera tu res are


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Min Qian et al. Influence of Coal Nature on Ash Size Formation and Pollutant Emissions During CFB Combustion 279

J0OO

8 0 0 O

7OOO

6 0 0 O

~ 5 o o ogE

3OO0

2 0 0 O

1000

07 5 0

1

8OO 85O

T ( D e g r e e C e l s i u s )

.. .. .. ~ ..............Coal C

- - - e - - - C o a l Bal term o d i f .,=

900 950

Fig. 6 Influence of coal nature on the furnacetemperature profile

at different heights.As shown by Fig.7, the s ize dis tr ibution of bottom

ash result ing f rom coal C is f iner than that f rom coal B. I tis suggested that this dif ference ar ises probably f rom thedif ferent s ize of gangue par t icles contained in the twodif ferent kinds of raw coals .

10090807060

~ 40302 010

00.01

IIIIIlitiid ,I IIIIILk:T

IIIIIII

. "rIIIIII0.1 1D ( r a m )

IIIIIIIIIIIIIII

- -0 . - - - Coal Baftermodi--- A--- C oal C

10 100

Fig.7 Influence of coal nature on the sizedistribution o f bottom ashOn the contrary, the circulat ing ash obtained with

coal C is coarser than the one result ing f rom coal B asindicated by Fig. 8 .

Whereas the compar ison made b y Fig . 9 o f the f lyash size dis tr ibution gives the opposite tendency for thecoals B and C.

1 0 09 08 07 06 0

,'e4030201000.01

I : 4 - ~ ~ - li i" 1 : ' : : : ] ] ,.r ! ~ r i ~

i r /13 [ /r I [ I i" ' ~ ' ] I i S - d 5 0 c - r - 2 7 1 m i c r o n s - ~ - ~ ld 5% =2 24m ic ron s 11,7 , , ~-~ . . . . . . . ,I~I I i I i i

' i " : ~ I t . . . . mo d i f .

0.1 D (ram) 1 10

Fig. 8 Influence of coal nature on the sizedistribution of circulating ash

1 0 09 08 07 0

, .~60~5 o~ 40

302010

0

d 5 0 c = 2 5 m i c r o n s ~ t " z d 5 % = 3 0 m i c r o n s _l i ; ~ @) ~ i i I " CatB I

L : , g : i i M t e r ij ,~ + i . . . . a . . .. . c oc c i. i i i{

1 1 0 D ( m i c r o n s ) 1 0 0 1 0 0 0

Fig. 9 Influence of coal nature on the sizedistribution of fly ash

Therefore, we can note the coal C gives an ash s izedistr ibution more dispersed than that of coal B. As f inerash par t icles (circulat ing ash and f ly ash par t icles) comefrom the iner t par t , more precisely the mineral par t incoal , i t is supposed that this dispersion of f inal ash s izedistr ibution could be a consequence of the coal 's mineralinclusions s ize dis tr ibution witho ut gangue.

Another important result l inked to the f ly ash isworth under l ining. I t is about the unburned carboncontent in this par t of ash, which is about 1% for the coalC and >20% for the coal B even af ter the cyclonemodif icat ions. This dif ference of 5 microns is l ikely notenough to explain the dif ference of 20% in terms ofunburned carbon in f ly ash. I t seems more to be aquestion of combustion reactivi ty .

In f lu en ce o f L imes ton e on th e Desu l fu r izat ionEff ic ien cy

During the program, several different types oflimestone have been used for different tests, it turns outto be interesting to use in the same test several of thesetypes of limestone of which the main characteristics areindicated in Table 2 :


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280 Journai of Thermal Science, Vol, 9, No.3, 2000Table 2 mai n characteristics o f the limestones

Limestone I LimestonelI Limestone l]ICaC 03 91.53 96.70M8CO3 1.50 1.62

CaO 80.3 92.08SiOz 4.58 1.42A1203 2.20 0.8

Actual ly , the l imes tone I and l imes tone I I comefrom the sam e or igin. Only the s ize dis tr ibution changesas shown in Fig.10.

10 09 0-80 -7 0-6 0-

~ 5o~ 4 0

302010

0 1

0 Limestone I_- L imestone I I

- - -X--- L imestone 11IIIIIIIIIIIIIIIIIIIIIIIII

10

!c I I l g lI IIIII_ 2 )

100 1000D (micron)

-I IIllllI)11111lIJrIII

IIIIII]I[tllll10000

Fig.10 Size distribution of limestones

Acco rding to the analysis , l imestone 11I contains mo reCaCO3 than the other two. Never theless , f rom Figure11, we can observe with the same rat io Ca/S the l imestoneHI catches less SO2 than the other two.

Whe reas the limestone s I and I I are dif ferent f rom eachother by the dispersion of their s ize dis tr ibution with thesame mean d iameter (d50) . I t seems l imes tone I I has abetter performa nce than l imestone I as shown on Fig. 11.

Primary F r a g m e n t a t i o n T e s t ResultsIn th i s tes t , a common exper imenta l p rocedure i s

used. How ever we meet the phenome nonwhich has no t been ment ioned by the o ther sc ien t i s t shav ing per fo rmed the same type o f test . Apparen t ly ,some coals ' f r agments can fo rm agg lomerates amongthemselves or with the sand par t icles under the testcondit ions. Fur thermore, this propr iety does not seem tobe l inked with operat ion condit ions (Table 3) . Accordingto the Chinese s tandard analyses, character is t ic of charresidue (CRC) , we can establish a l ink betw een thisindex wi th the propr ie ty o f a coal under thepr imary f ragmentation test condit ions as descr ibedbefore . The main r esul t s concern ing th i s phenome non areshown in Tab le 3.

Concern ing the p roper r esu lt s o f the p r imaryfragmenta tion test , the s ize dis tr ibution in mas s ofthe f r agments seems close to tha t o f the cor respondingraw coal . Conseque ntly, i t ' s worth thinking aboutthe n ecessi ty of carrying out this test for the coalmineral inclusions s tudy.

Conclusion

The crucia l ro le o f the cyclone separa to r ef f ic iencyin a CFB un i t is once more conf i rmed in our exper ience .

The l imestone nature and i ts s ize dis tr ibution have agreat inf luence on the desulfur izat ion eff iciency.However , the detai led s tudy on the l imestonecomminut ion does no t fo rm par t o f the p resen t work .The f inal ash s ize dis tr ibution depends on the coalnature. Never theless , i t tunas out that only theexper iment on a hot CFB pilot is not enough for us tof ind some c lear l ink between the coal na tu re and theformat ion o f i t s ash even i f th i s tes t can g ive somequal ita t ive ideas . The second aspect o f th is p ro gram :study of internal smacture of coal mineral inclusion, inprogress a t p resen t t ime, g ives more in fo rmat ion abou t

40003500

3000

2500E~2000

15001000

5000

~ L i m e s to ne II~ Ca/S =0.92 | l L imestone I II~ - S t o p o f l ~ e s t o n e - ~ . ] ~ - C a t S ~ 1 . 7 - - -

\ ~ \ . . . . . . . . . . . [ ~ r ~ ~ e S t 6 h e l l 1~t '~ L imestone I / ~ Ca/S =1.7 |~ t "~ . . . . CalS - ' [ 3 4 - - " T - t, ,2

.... i i i 1 2 1 1. o . . - . . ~ . . q . .m . . q o .o - . . ~ . . q . . m . . o . . o . o - . . ~ . . ~ . . m . . o . ~ ~ ~ . . . . . .

Fig. 11 Influence of limestone type on SO2 emissions


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Min Qian et al. Influence of C~al Nature on Ash Size Formation and Pollutant Emissions During CFB Combustion 281

th i s pos s ib le l ink , may exp la in the d i f fe ren t s i zed i s t r ibu t ions o f the f ine r a s h pa r t i c l e s (c i rcu la t ing a s hand f ly a s h ) . Whereas the coa rs e a s h pa r t i c l e s (bo t tom

a s h ) r e s u l t l ik e l y f r o m t h e c o a l g a n g u e . T h e u s e l e s sn e s so f t h e p r i m a r y f r a g m e n t a t i o n t e st r e m a i n s t o b e p r o v e d .

Table 3 Comparison of main results concem ing the phenomenonqhel~ gest ~ Ou: i l~a ,ea in~ Cal~gin~xC oa l B e d ~ a l B ed tr ot er ia l B e d rt n er ia l l qu id in ai on B e d ~ ( b a l s~ r ~ l e ~ c ak es iz e ~ e h a r ~

m i n e ~ g h t ( g ) s ~ s ( n m v ~ o ci ty ( ra s ) ( Q ~ g a ( g ) f i ne ( r an ) ( ra m) r e s et ( o ~ ~ ( c ~ ( c~ 0F l~ t l a J lS

D A1203 sand 1300 0.18-0,25 0.26 850 63 3 30-40 aggl~a-lt 'ale& 6 5 79mosl szmdwa sd ~ d b ~D si l icon sand 2000 0-2 0.17 850 74 10 30 Fragn-er ls 6 5 79

N oA silicon sand 2000 0-2 0.26 850 1G0 3 I / / /N oE A!20 3 sand 1269 J.3554).5 0.26 850 45.3 3 / / / /a~iamaion

A A1203 sa nd 1 68 2 0 ,355 -0 .5 0 .20 850 52 ,5 3 40 Som e f r a ~ t t a ~ 4 / 0~glorra~S a t e s m Jadhetedto

A AI203 sand 1 2 2 8 0355-0.5 0.28 850 49.0 5 / f iagn 'm ts& 4 / 0som e s,Tmdwa sd ~ b ~

A AI203 sand 1000 0.5-0.71 0.44 850 43,9 3 30 Some f i 'agl rmts 4 / 0a~c,re r~San'e sanda d h a ~ t o

A Silicons ar d 1 10 0 0 -2 0 .1 8 8 50 1 7 2 3 / ~ & 4 / 0som e sa rd w~d~dUac~

N oB AI203 sand 1 1 7 5 0.355-0,5 0.18 850 56.3 3 / 1 0 0agglam~on

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Influence of Coal Nature and Structure on Ash Size Formation Characteristic and related Pollutant Emissions During CFB Combustion