coal ash deposit

7/23/2019 Coal Ash Deposit

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OVERVI EW OF COAL ASH DEPOSI TI ON I N BOI LERS

R. W Bor i o and A. A. Levasseur

COMBUSTI ON ENGI NEERI NG, I NC.

1000

P r o s pec t Hi l l Road, W nds or , CT 06095

I NTRODUCTI ON

T he ma nagement o f c oal as h i n ut i l i t y bo i l er s c o nt i nu es t o be on e o f t h e mo s t

i mpor t ant f uel p r ope r t y cons i der a t i ons i n t he des i gn and ope r a t i on o f commer c i a l

bo i l er s . T he behav i or o f m ner a l mat t er i n c oal c an s i gni f i c ant l y i nf l ue nc e f ur nac e

s i z i ng , heat t r a ns f er s u r f a c e pl ac eme nt , and c o nv ec t i o n pas s t u be s pa ci ng. I r o ni -

c al l y , ma ny o f t h e mo r e r e ac t i v e, l o w r ank U . S. coa l s mus t have l a r ge r f ur naces

t han t he l es s r e ac t i v e hi gher r a nk c oal s . T hi s i s s t r i c t l y a r e qui r e me nt bas ed

o n t he m ner a l ma t t er b ehav i o r ; F i g ur e i l l us t r a t e s t h i s poi nt . Gi v en t h e s a me

m ner a l

mat t er beha vi o r t he mo r e r e ac t i v e, l o wer r ank c o a l s woul d r e qu i r e l e s s

r e s i de nc e t i me and t h er e f o r e s mal l er f u r n ac e vo l umes t han t he l es s r e ac t i v e, hi gher

r a nk c oal s .

Al t hough pul ver i zed coal has been f i r ed f o r mor e t han 50 year s and much i s known

about combus t i on behavi o r t he r e ar e s t i l l a number

of

bo i l er s e x pe r i e nc i ng o pe r a t -

i onal pr o bl ems f r o m c oa l a s h ef f ec t s . As h- r e l at ed p r o bl e ms a r e o n e o f t h e p r i ma r y

c a us e s o f uns c hedul e d o ut a ge s , uni t de r a t i ng and unav ai l abi l i t y . Be c au s e o f v ar i a -

b i l i t y i n a gi ven coal seam and s i nce many boi l e r oper a t or s may expe r i ence changes

i n t hei r c oal s u pp l y dur i ng t h e l i f e of a bo i l e r , o per at i o nal p r o bl e ms c aus e d by

changes i n coal

as h pr o per t i e s can s i gni f i c ant l y af f ec t boi l er per f or manc e. Not

o nl y mus t t he i ni t i al boi l er des i gn be c or r ec t l y det er m ned bas ed o n t he s pec i f i -

c a t i o n c oal but r e l i a bl e j u dg eme nt s mus t be ma de r e ga r di ng t he s ui t a bi l i t y of o t h er

c andi da t e c oal s and t hei r ef f ec t o n oper a t i o n dur i ng t he l i f et i me o f t he bo i l er .

T he i nc r e as ed emp ha s i s on c oa l us age i n t h i s c o un t r y and, i nde ed, t h e s i gni f i c ant

e f f o r t under way t o c o ns i der c oal wa t e r m x t u r e s as pos s i bl e oi l s ubs t i t ut e s i n

o i l - des i gne d bo i l er s u nde r s c o r e s t h e need t o i mpr o ve t h e pr e di c t i o n o f m ner al

ma t t e r behav i o r i n a bo i l er env i r onment .

Coal i s a ver y het erogeneous, compl ex mat er i a l wh i ch pr oduces het er ogeneous, com-

pl ex p r oduc t s du r i ng combus t i on. S i nce, dur i ng pul ver i zed coal combus t i on, coal

pa r t i c l e s o f v ar i o us o r ga ni c and m ner al ma t t e r c o mp os i t i o ns c an be ha ve

i n

com-

pl e te l y d i f f e r ent manner s , p r edi c t i on based upon t he over al l o r aver age compos i t i on

may be m sl eadi ng. L i ke many of t he cur r ent l y - used ASTM coal ana l yses , t he met hod

f o r det e r m ni ng as h f us i bi l i t y t e mper at ur es wa s de vel o pe d when s t o ke r f i r i ng wa s

a pr edom nant coal f i r i ng t echn i que ; t he met hodol ogi es and cond i t i ons empl oyed

dur i ng many o f t he AST M t e s t s r e f l e ct t hi s . I t i s no t s ur p r i s i ng t h a t t he us ef ul -

ness o f some ASTM t es t r e su l t s may be l i m t ed when used f o r a pul ver i zed coal

f i r i ng appl i c at i on. I n r e c ent y e ar s r e s ea r c h er s ha ve dev el o ped me t h o do l o gi e s f o r

cha r ac t e r i z i ng coal ash behavi o r t hat be t t e r r e f l e c t t he f undament a l mechani sms

c ont r o l l i ng beha vi o r a nd mo r e c l o s el y s i mu l a t e t h e c ondi t i o ns t h at e xi s t i n

a

pul -

ver i z ed c oal f i r ed boi l er .

Cl ear l y t he r e i s a nee d f o r i mpr o ved m ne r a l mat t er beha vi o r p r e di c t i v e t e chni ques .

T hi s p aper wi l l pr o vi de a s t a t e me nt o f t h e a s h depo s i t i o n pr o bl em i n pul v er i z e d

c oal f i r e d boi l er s , i t wi l l pr e s ent an as s es s ment o f t he o l der , t r adi t i o nal met ho ds

f or pr e di c t i ng m ne r a l ma t t e r beha vi o r and i t wi l l addr e s s s o me o f t h e newe r t e c h-

n i ques t ha t have been sugges t ed as bet t e r ways o f char ac te r i z i ng coal ash behavi o r .

Addi t i o nal l y s ome a r e as of unc er t ai nt y wi l l be i dent i f i ed a s r e qu i r i ng t h e dev el o p-

ment of bet t er p r edi c t i ve t echn i ques .

193



STATEMENT OF

THE

PROBLEM

The presence o f a sh d e p o s i t s and f l y a s h c a n c r e a t e t h e f o l l o w i n g pr ob l em s i n a

b o i l e r :

1.

R e d u c e d h e a t t r a n s f e r

2.

Impedance o f ga s f l ow

3.

P h y s i c a l damage t o p r e s s u r e p a r t s

4. C o r ro s i on o f p r e s su r e p a r t s

5. E ro s io n o f p r e s su r e p a r t s

T h e s e p r o b l e m s c a n r e s u l t i n r e d u c e d g e n e r a t i n g c a p a c i t y , u n s ch e d u le d o u t ag e s ,

r ed uc ed a v a i l a b i l i t y , a nd c o s t l y m o d i f ic a t io n s .

Ash wh ich d e p o s it s on b o i l e r w a l l s i n t h e r a d i a n t s e c t i o n o f

a

f u rn a ce i s g e n e r a l ly

r e f e r r e d t o as s l a g g i n g . Ash d e p o s i t i o n o n c o n v e c t i o n t u b e s e c t i o n s d ow ns tr ea m

o f t he f ur n ac e ra d i an t z o ne i s t y p i c a l l y r e f e r r e d t o as f o u l i n g . Ash s l a g g i n g a nd

f o u l i n g ca n r e s u l t i n p r ob le ms l i s t e d i n i t em s 1 t h r o u g h

4;

i t e m 5, e ro s io n , i s

t h e r e s u l t o f i m p in g em e nt o f a b r a s i v e as h on p r e s s u re p a r t s . O f t e n c o a l a s h d e p o s i t

e f f e c t s a r e i n t e r - r e l a t e d . F o r e xa mp le , s l a g g i n g

w i l l

r e s t r i c t wa t er w al l h e a t

a b s o rp t i on c h a n gi n g t h e t e m p e ra t u re d i s t r i b u t i o n

i n

t h e b o i l e r w hich i n t u r n

i n f l u e n c e s t h e n a t u r e a n d

q u a n t i t y o f a s h d e p o s i t i o n i n do wn stre am c o n v e c t i v e

s ec t i ons . A sh dep os i t s ac c umu l a ted on c onv ec t i o n t ubes c an r educ e t he c r os s -

s e c t i o n a l f l o w a r e a i n c r e a s i n g f a n r e q u ir e me n ts a nd a l s o c r e a t i n g h i g h e r l o c a l

g as v e l o c i t i e s w h i ch a c c e l e r a t e s f l y a s h e r o si o n .

I n s i t u d ep o si t r e a c t i o n s can

p ro d uc e l i q u i d p ha s e c om po ne nt s w h i c h a r e i n s t r u m e n t a l i n t u b e c o r r o s io n .

One o f t h e m ost common m a n i f e s t a t i o n s o f a d e p o s i t i o n p r o bl e m i s r e d u c e d h e a t t r a n -

s f e r i n t h e r a d i a n t z on e o f a fu r n a ce . D ec re as ed h e a t t r a n s f e r due t o a r e d u c t i o n

i n s ur fa ce a b s o r p t i v i t y i s

a

r e s u l t o f t h e c o mb in at io n o f r a d i a t i v e p r o p e r t i e s

o f t h e d e p os i t

( e m i s s i v i t y l a b s o r p t i v i t y )

and t h er m a l r e s i s t a n c e ( c o n d u c t i v i t y ) o f

a d e p o s i t . T he rm al r e s i s t a n c e ( t h e rm a l c o n d u c t i v i t y and d e p o s i t o v e r a l l t h i c k n e s s )

i s u s u a l l y more s i g n i f i c a n t be ca use o f

i t s

e f f e c t o n a b s o r b i n g s u r f a c e t e m pe r a tu r e .

P r e vi o u s w or k has i n d i c a t e d t h a t t h e p h y s i c a l s t a t e o f t h e d e p o s i t can h av e a s ig n -

i f i c a n t e f f e c t o n t h e r a d i a t i v e p r o p e rt i e s , s p e c i f i c a l l y m ol te n d e p o s i t s show

h i g h e r

e m i s s i v i t i e s / a b s o r p t i v i t i e s

t h a n s i n t e r e d o r p o w d er y d e p o s i t s ( R e f. 1 ) .

A l t ho u g h t h i n , m o l t e n d e p o s i t s a r e l e s s t r o u b l es o m e f r o m a h e at t r a n s f e r a s p e ct

t h a n t h i c k , s i n t e r e d d e p o s i t s, m o l t en d e p o s i t s a r e u s u a l l y more d i f f i c u l t t o remove

a nd ca use f r o ze n d e p o s i t s t o c o l l e c t i n t h e l o w e r r ea c he s of t h e f ur n a c e; p h y s i c a l

removal then becomes

a

p r o bl e m f o r t h e w a l l b l ow e rs .

Impedance t o gas f l o w i s t h e r e s u l t o f h e av y f o u l i n g on t u b es i n t h e c o n v e c t i v e

s e c t io n . Pro blem s o f t h i s t y p e a r e most l i k e l y t o o cc ur w i t h c o a l s h a vi ng h i g h

s od iu m c o n t e n t s , u s u a l l y f o u n d i n l o w ra n k c o a l d e p o s i t s i n We st er n U.S. seams.

H ar d, b on de d d e p o s i t s c a n o cc u r w h i ch a r e r e s i s t a n t t o r em ov al b y t h e r e t r a c t s o o t-

b l o w e r s .

P h y s i c a l d amage t o p r e s s u r e p a r t s c an o c c u r i f l a r g e d e p o s i t s h a ve a cc um u la te d

i n t h e u p pe r f u r n a c e a nd p r o c e e d t o b ecome d i s l o d g e d o r b l o w n o f f a nd d r o p o n t o

t h e s lo p es o f t h e l o w e r fu r n a ce . Such d e p o s i t s a r e u s u a l l y c h a r a c t e ri z e d b y t h e i r

r e l a t i v e l y h ig h b on di ng s t re n g t h s a nd t h e i r h e a v i l y s i n t e r e d s t r u c t u r e .

1

I 9 4



F i r e s i de cor r os i on can occur on both wa te r wa l l and super hea t e r t ube sur f aces . Nor ma l

s ul f at e s and py r o s ul f at es a r e f r e que nt l y t he c a us e o f wa t e r wal l c o r r o s i o n, a l t h ou gh

r educ i ng c ondi t i o ns c a n al s o c au s e de pl e t i o n of p r o t e c t i v e o x i d e c o at i n gs on t u be

sur f aces . On hi ghe r t emper a t u r e meta l su r f aces ,

superheaters/reheaters)

a1 kal -

i r o n- t r i s ul f at es a r e of t en t h e c aus e o f c or r o s i on. Chl o r i ne c an al s o be a c o nt r i -

but i ng f act or t oward s uperheat er meta l cor r os i on. Whi l e exact mechan i sms can be

ar gued t her e have been exampl es

of

bot h l i qui d phase and gas phase cor r os i on when

chl o r i des have been pr esent ( Ref . 2 ) .

Er o s i on o f c onv ec t i v e pas s t ubes , whi l e no t a f u nc t i o n o f de po s i t s ,

i s

caused by

t he abr as i v e c ompo ne nt s i n f l y as h. F l y as h s i z e and s ha pe , a s h pa r t i c l e c o mp os i t i o n

and c onc ent r a t i o n, and l oc al gas v el o ci t i e s pl ay i mpo r t ant r o l e s c o nc e r n i n g e r o s i o n

phenomenon. Recent wor k has shown t hat qua r t z pa r t i c l e s above a ce r t a i n par t i c l e

s i z e ar e v er y i nf l uent i al i n t h e er o s i o n pr o ce s s and t ha t f u r n ac e t e mp er a t ur e

hi s t or y pl ay s an i mpor t ant r o l e i n det er m ni ng er o s i v e c ha r a c t e r i s t i c s o f t h e

par t i c l es ( Ref . 3 4 .

FUNDAMENTAL CONSI DERATI ONS I N ASH DEPOSI TI ON

The coal ash depos i t i on pr ocess i s ext r emel y compl ex and i nvol ves numerous aspect s

o f coal combus t i on and m ner a l t r a n s f o r m a t i o n / r e a c t i o n . T he f o l l o wi ng al l pl ay a

r o l e i n t he f o r ma t i on o f ash and t he depos i t on pr ocess .

Coal Or gani c Pr ope r t i e s

Coal Mi ner a l Ma t t e r P r o pe r t i e s

Combus t i on K i net i c s

Mi nera l Tr ansf or mat i on and Decompos i t i on

F l ui d Dy nam c s

Ash Tr anspor t Phenomena

Vapor i za t i on and Condensat i on of Ash Spec i es

De po s i t Chem s t r y - Spec i e Mi gr a t i on and Reac t i on

Heat T r ans f e r o and F r o m t he De po s i t

Despi t e cons i der abl e r e sear ch i n t hese ar eas , t her e a r e many gaps i n our f undament a l

under s t andi ng o f t he mechani sms r espons i b l e f o r m ner a l ma t t e r behavi o r . Al t hough

s ubs t ant i al k no wl edge ex i s t s c o nc er ni ng t h e de po s i t i o n pr o ces s , t h e c o mp l e xi t y of

t h e s ubj e ct do es n ot a l l o w det ai l ed d i s c us s i o n her e . Ho we ve r , t h e i mp or t a nc e o f

f u r nace ope r a t i ng cond i t i ons on t he combi ned r esu l t s o f each of t he above a r eas

must be s t r essed. For a gi ven coa l compos i t i on, f u r nace temper a tu r es and r es i dence

t i mes gene r a l l y di c t a t e t h e phy si c al and c hem c al t r a ns f o r ma t i o ns whi c h oc cur . The

ash f o r mat i on pr ocess i s pr i ma r i l y dependent on t he t i me / t emper a tu r e hi s t o r y o f

t he c oal par t i c l e. T h e r e s ul t ant phys i c al pr o pe r t i es o f

a

gi v en as h p ar t i c l e g en er -

al l y det er m ne whe t h er i t wi l l adher e t o heat t r a ns f e r s ur f ac es . L oc al s t o i c hi o -

met r i e s can al so i n f l uence t he t r ans f o r mat i on pr ocess and t her eby t he phys i cal

c har a c t e r i s t i c s of as h par t i c l es ; i r o n- be ar i ng par t i c l e s ar e a pr i me ex ampl e o f

t h i s .

Aer o dy nam c s c a n pl a y a r o l e i n t he as h depo s i t i o n pr o ces s i n al l f u r n ac e s r e ga r d -

l es s o f t he t y pe of f i r i ng; r e cent i nt er e st i n m c r o f i ne gr i ndi ng o f coal i s t es t i -

mony t o t h i s f a ct . I t has been po st ul at ed t hat s mal l er as h par t i c l es wi l l f o l l o w

gas s t r e am i nes and be l es s l i k el y t o st r i k e heat t r ans f e r s ur f ac es . T hi s i s a

l ogi c al hy po t h es i s f o r t ho s e as h pa r t i c l e s t h at c a us e depo s i t i o n due t o an i mpac t

mec hani s m I n addi t i on t o par t i c l e s i z e,

par t i c l e de ns i t y and s ha pe a l s o af f e ct

aer o dy na m c behav i or . Mo l t e n, s pher i c al pa r t i c l e s wi l l be l es s l i kel y t o f ol l ow

gas s t r ea m i nes t han a ngul ar or i r r egul a r par t i c l es o f t he s a me ma s s d u e t o t h e

di f f er e nc e i n dr a g f or c e s.

I 9 5



Most coa l ash w i l l r e s u l t i n d e p o si t s o f i n c r e a s i n g s e v e r i t y w i t h i n c re a s in g gas

t em pe ra tu re . T h i s i s n o t a l i n e a r r e l a t i o n s h i p , as i l l u s t r a t e d i n F i g ur e

2,

b u t

r a the r s hows

a

p r o g r e s s i v e l y m o re s ev er e a sh d e p o s i t c o n d i t i o n w i t h i n c r e a si n g

gas tempera ture (Ref . 5). B o i l e r s a r e n o r m a l l y d e s i g n e d so t h a t c l ea n a bl e , s i n t e r e d

d e p o s i t s

w i l l

be fo rmed. Th i s i s a reasona b le compromise between a very l a rg e,

e c o n o m i ca l l y u n c o m p e t i t i v e b o i l e r t h a t may p ro d uc e v e ry d r y , d u s t y d e p o s i t s a nd

a v e r y s m a l l , h i g h l y l o a d e d b o i l e r t h a t w ou ld p ro d uc e m o l te n , r u n n i n g a sh d e p o s i t s .

Th e k ey g o v e r n i n g f a c t o r , t he n , i s d e t e r m i n i n g how sm a l l a f u r n a c e c an b e, f o r

a g i v en MW output , and s t i l l r e s u l t i n d e p o s i ts t h a t a re c l e a n a bl e w i t h c onven-

t i o n a l s o o t b l o w i n g e q u i p m e n t .

Beca use o f t h e c o m p l e x i t y o f t h e a sh f o r m a t i o n a nd a sh d e p o s i t i o n p r o c e s s, it seems

l o g i c a l t o d ea l

f i r s t

w i t h t h o s e k ey c o a l

c o n s t i t u e n t s m o st r e s p o n s i b l e f o r a sh

d e p o s i t i o n . The i r o n a nd s od iu m c o n t e n t s o f an as h ha ve t y p i c a l l y be en c o n s i d e r e d

k ey c on s t i t ue n t s . T ec hn i ques hav e been dev e l oped t o de te r m i ne how thes e k ey c on-

s t i t u e n t s a re c o n t a i n e d i n t h e c o a l , i .e ., t h e p a r t i c u l a r m i n e r a l f or ms t h a t a re

p r e s e n t or t h e g r a i n s i z e o f t h e c o n s t i t u e n t i n qu e s ti o n . O b v io u s ly th e r e ma in de r

o f t h e m i n e r a l m a t t e r h a s an e f f e c t , b u t d e p en d in g on t h e c o n c e n t r a t i o n a nd f o r m

i n wh ic h i r o n a n d/ o r s od iu m c o n s t i t u e n t s a r e p r e s e n t , t h e r e m a i n i n g m i n e r a l m a t t e r

o f t e n has s econ d o r d e r e f f e c t s .

As p r e v i o u s l y d i s cu s s ed , a s h f o r m a t i o n

and th e r e s u l t i n g ash s i z e d i s t r i b u t i o n

i s ex t r eme l y c omp lex and i s d ep en de nt on s e v e r a l f a c t o r s i n c l u d i n g i n i t i a l c o a l

s i z e , c o al b u r n i n g c h a r a c t e r i s t i c s , m i n e r a l c o nt e n t, m i n e r a l g r a i n s iz e, v o l a t i l e

a sh s pe ci es , m e l t i n g b e h a v io r o f t h e m i n e r a l m a tt e r , and t em p e ra t ur e h i s t o r y o f

t h e p a r t i c l e . G e n er a ll y , c o a l c o n t a i n i n g l o w er m e l t i n g m i n e r a l m a t t e r h as a g r e a t e r

p o t e n t i a l f o r a sh a g g l o m e r at i o n as t h e p a r t i c l e b u r n s and y i e l d s f e we r a sh p a r -

t i c l e s p e r co a l p a r t i c l e w hi ch r e s u l t s i n c oa rs er ash

p a r t i c l e s t h a n th os e o f c o al

w i t h h i g h e r m e l t i n g ash. O b v i o u s l y th i n g s l i k e ash q u a n t i t y , and m i n e r a l

g r a i n

s i z e s c o u l d i n f l u e n c e t h i s h y p o t h e s i s. The way a c o a l

p a r t i c l e b u rn s may a l s o

i n f l u e n c e t h e number o f a s h p a r t i c l e s g e ne r at e d, i . e . , a s h r i n k i n g s ph e re b u r n i n g

mode may p r o d uc e a d i f f e r e n t r e s u l t fr o m a c o n s t a n t d i am e t e r, d e c r e a s i n g d e n s i t y

mode of b u r n i n g; s w e l l i n g c o a l s may be have d i f f e r e n t l y t h a n n o n - s w e l l i n g c o a l s.

I n r e f l e c t i n g o n t h e a bo ve d i sc u ss i on , t becomes apparent that one cannot com-

p l e t e l y d i v o r c e t h e p r e d i c t i v e t ec h n iq u e s em ployed, f ro m t h e p a r t i c u l a r c o a l

b u rn i ng a p p l i c a t i o n . P u l v er i ze d c o a l f i r i n g w l l r e q u i r e a s e n s i t i v i t y t o d i f f e r e n t

c o n d i t i o ns th an s t o k e r f i r i n g , o r a s la g g i n g c om bu st or . F a i l u r e t o a dd re ss t h e

s p e c i f i c c o n d i t i o n s i n h e r e n t i n each ty p e o f f i r i n g system

w i l l

l e a d t o l ow er

r e s o l u t i o n i n on e ' s p r e d i c t i v e a b i l i t i e s th an d es ir ed .

ASSESSMENT

O F

TRADITIONAL PREDICTIVE

METHODS

ASTM measurements such as ash f u s i b i l i t y

(D1857)

have fo r me d t h e b a s i s f o r t r a d i -

t i o n a l ash b e h av i or p r e d i c t i v e t ec h n iq u e s. These b e n ch -s ca le t e s t s p r o v i d e r e l a t i v e

i n f o r m a t i o n on a f u e l ; t h i s i s u sed i n a co m pa ra t i ve f a s h i o n w i t h s i m i l a r d at a

on f ue l s o f known be ha v i o r . Un fo r t un a te l y , t h e common ly us ed t e s t s do no t a l way s

p r o v i d e s u f f i c i e n t i n f o r m a t i o n t o p e r m i t a c c u ra t e c om p ar is on .

The f u s i b i l i t y t e m p e r a tu r e m ea su re me nt t e c h ni q u e a t t e m p t s t o r e c o g n i z e t h e f a c t

t h a t m i n e r a l m a t t e r i s made up o f a m i x t u r e o f c om pou nds ea ch h a v i n g t h e i r own

m e l t i n g p o i n t .

A s

a cone o f ash i s hea ted some o f t he compounds me l t b e fo r e o th e r s

and a m i x t u r e of m e l t e d a nd un m e l te d m a t e r i a l r e s u l t s . The s t r u c t u r a l

i n t e g r i t y

o r d e f o r m at i o n o f t h e t r a d i t i o n a l a sh c on e cha nge s w i t h i n c r e a s i n g t e m p er a tu r e as more

196



o f t he m ner al s mel t . Ho we ve r , mo r e r e c ent r e s ul t s i ndi c at e t hat s i g ni f i c ant

mel t i ng/ s i nt er i ng c a n o c c ur be f o r e i ni t i al de f o r ma t i o n i s o bse r v ed ( Ref . 6 .

The

f ac t t ha t t h e t i me/ t emper a t ur e h i s t o r y o f l abor at or y as h i s qui t e di f f er e nt f r om

c ondi t i ons exper i enc ed i n t h e boi l er c an r e s ul t

i n d i f f e r e nc e i n me l t i n g behavi or .

I n a ddi t i o n, t h e ash used i n t h i s t e c hn i q ue ma y no t r e pr e sen t t h e c o mp os i t i o n o f

as h depos i t s t h at a ct ual l y s t i c k t o t h e t u be s ur f ac es . Of t e n t h er e i s a ma j o r d i s -

cr epancy bet ween t he composi t i on of as- f i r ed ash and t hat whi ch

i s

f o un d a s d epo s i t s

( See Tabl e I . Thi s i s a maj or c r i t i c i s m of t h e as h f u s i bi l i t y t emper at ur es . T he

di s c r e panc i es be t we en f u s i b i l i t y t e mpe r a t u r e p r e di c t i o ns a nd ac t u al s l a gg i n g pe r -

f ormance i s usua l l y great er on ashes t hat may l ook r easonabl y good based on

f us i bi l i t y t empe r a t u r e r e sul t s . On e c a n usu al l y as su me , wi t h r e aso na bl e c onf i de nc e,

t ha t t h e me l t i ng t e mp er a t u r e o f t h e wa t e r wa l l

depos i t s wi l l be no hi gher t han ASTM

f us i b i l i t y t emper a tur es ; but depos i t me l t i ng t emper a t ures can be and a r e o f t en l ower

t han ASTM me l t i ng t emper a tur es . Th i s i s because se l ec t i ve depos i t i on of l ower

me l t i ng const i t uent s can and does occur ; hence t her e i s an enr i chment o f l ower

me l t i ng mat er i al i n t h e de po s i t .

As h vi s c os i t y meas ur e ment s s uf f e r s i m l ar c r i t i c i s m t o t h e f us i bi l i t y meas ur e ment s .

These test s ar e conduct ed on

l abora t o ry ash and on a compos i t e ash sampl e . Vi scos i t y

me asu r e me nt s a r e l es s s u bj e c t i v e and mo r e d ef i n i t i v e t ha n f l ui d t e mp er a t u r e det e r -

m na t i on f o r t h e as se ssme nt o f a sh f l o w c ha r a c t e r i s t i c s . Ho we ve r , t h ese me asur e ment s

r ef l ec t t h e pr oper t i es of a t o t a l l y di s s ol ved s ol ut i o n o f as h c ons t i t uent s and ma y

not b e r epr e s ent at i ve o f s l a g de po s i t pr oper t i es i n pul v er i z ed c oal - f i r ed boi l er s .

Dur i ng pul ver i zed coal

f i r i n g, a s e ve r e pr obl em ma y al r e ady e xi s t bef or e s l ag

depos i t s r e ac h t h e f l ui d/ r u nni ng s t at e. Ge ne r a l l y , onl y a s mal l qua nt i t y o f l i qui d

phase mat er i al e xi s t s i n d ep os i t s and i t i s t he par t i c l e- t o- par t i c l e s ur f ac e bondi ng

whi ch i s most i mpor t ant .

Much use

i s made o f t he ash compos i t i on wh i ch i s

no r mal l y a c omp i l a t i o n o f t h e maj o r

e l e ment s i n c oal ash e xpr esse d a s t h e o x i d e f or m F r o m t h i s c o mp i l a t i o n o f e l eme nt s ,

expressed as ox i des , j udgement s a r e of t en made based on t he quant i t y o f ce r t a i n

key const i t ut ent s l i ke i r on and sodi um Base/ ac i d r a t i os a r e comput ed and used as

i ndi c at o r s of ash be hav i o r ; n or ma l l y l o we r mel t i ng ash es f al l i n t h e 0. 4 t o 0 6

r a nge. I t h as b een sh own t h at base/ ac i d r a t i o s ge ne r a l l y c o r r e l a t e wi t h ash

so f t eni ng t emper a tur es , so a l t hough base/ aci d r a t i os have hel ped exp l a i n

why

ash

s of t eni ng t emper at ur e s v ar i ed, i t has not i mpr oved pr edi c t i v e c apa bi l i t i e s i n t h e

aut ho r s ' o pi ni o n. Ot h er r a t i o s su ch a s F e/ Ca and Si / Al h av e bee n used a s i ndi c at o r s

o f a sh de pos i t be ha vi o r . Ra t i o s

l i k e t he se ha ve hel pe d t o e xpl ai n de po s i t c ha r a c t e r -

i s t i c s , but t hei r us e as a pr i me pr e di c t i ve t ool i s ques t i onabl e es pec i al l y s i nc e

t he se r at i o s do not t ak e

i nt o ac c ount se l e c t i v e depo s i t i o n no r d o t h ey c ons i de r

t h e t o t al quant i t i es o f t h e c ons t i t uent s pr e s ent .

An Fe/ Ca r a t i o o f

2

c oul d r es ul t

f r o m 6/3 or 30/15; t h e l at t er n umbe r s woul d g ene r a l l y i ndi c at e a f a r wo r s e s i t uat i on

t han t h e f o r me r , but r a t i o s don' t sh o w t hi s .

Many s l a ggi ng and f o ul i n g i ndi c es a r e based u po n c e r t a i n a sh c o ns t i t u en t r a t i o s

and c or r ec t e d us i ng suc h f a c t o r s as ge ogr a phi c al a r e a , su l f u r c on t e n t , s o di um c o n -

t e n t ,

e t c . One commonl y used s l agg i ng i ndex uses Base/ Ac i d r a t i o and su l f u r cont ent .

F ac t o r i ng i n s ul f ur c o nt ent i s l i k el y t o i mpr o ve t he s ens i t i v i t y of t hi s i ndex t o

t he i nf l uenc e of pyr i t e on s l aggi ng. ( As pr e vi ous l y di s c us s ed, i r o n- r i c h m ner a l s

of t en pl ay an i mpor t ant r o l e i n s l aggi ng. ) However , t he use o f s uch co r r ec t i on

f ac t o r s i s o f t e n a c r u de sub s t i t u t e f o r mo r e d et a i l ed k n owl e dg e o f t h e f undame nt al

f uel pr o per t i es . Ano t h er e xa mp l e o f t hi s i s t h e use o f c h l o r i n e c o nt e nt i n a c oal

as a f oul i ng i ndex . T hi s c a n be t r u e i f t h e c h l o r i n e i s p r e sent as NaCl t he r e by

i ndi c at i ng t h e c o nc e nt r a t i o n o f so di um wh i c h i s i n an ac t i v e f o r m and t h at wi l l ,

i n f ac t , c aus e t he f oul i ng. Chl or i ne

adver s e l y af f ec t f oul i ng.

pr esent i n ot her f or ms may or may not

197



S i n t e r i n g s t r e n g t h t e s t s h a ve been u se d as an i n d i c a t i o n o f f o u l i n g p o t e n t i a l .

A ss um in g t h a t c o r r e c t a s h co m p o s i ti o n s h av e b ee n r e pr e s e n t e d ( w h i ch i s l e s s o f

a pr ob le m i n t h e c o n v e ct i o n s e c t i o n t h a n i n t h e r a d i a n t s e c t i o n ) w or th w h il e i n f o r -

m a t i o n may be o b ta i n e d r e l a t i v e t o a t i m e / te m p e r a tu r e v s. b o n d i ng s t r e n g t h

r e l a t i on s h i p . I n o rd er f o r s i n t e r i n g t e s t s t o a c c ur a te l y p r e d i c t a c t u a l

b e h a v i o r

i t

i s n e ce s sa r y t h a t t e s t s b e c o n d u ct e d w i t h a sh p r od u ce d u n de r r e p r e s e n t a t i v e

f u r na c e c o n d i t i o n s ( t i m e -t e m p er a t ur e h i s t o r y ) . F o u l i n g b e h a vi o r i s o f t e n g r e a t l y

i n f l u e n c e d by s o di u m r e a c t i o n s . S od iu m w h i c h v a p o r i z e s i n t h e f u r n a c e c an co nd en se

i n do wn stre am c o n v e ct i o n s e c t i o n s t h e r e b y c o n c e n t r a t i n g o n f l y a s h s u r f a c e s . P a r-

t i c l e s u rf ac e r e a c t i on s a r e p r i m a r i l y r e s p o n s ib l e f o r c o n ve c ti o n d e p o s i t b on di ng .

I n summary, t r a d i t i o n a l m et ho ds f o r p r e d i c t i o n a sh d e p o s i t c h a r a c t e r i s t i c s a r e

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

T he se c o n v e c t i o n a l a n a l y se s d o n o t p r o v i d e d e f i n -

i t i v e i n f o rm a t i o n c o nc e rn i ng t h e m i n e r a l fo rm s p re s en t i n t he c o a l s a nd t h e d i s t r i -

b u t i o n

of

i n o r g a n i c s p e c i e s w i t h i n t h e c o a l m a t r i x . Such i n f o r m a t i o n ca n b e e x t r e -

m e ly i m p o r ta n t i n e x t r a p o l a t i n g p re v i o u s ex p er i en c e, s i n c e t h e n a t u r e i n w hi ch

t h e i n o r g a n ic c o n s t i t u e n t s a r e co n t a in e d i n t h e c oa l c an be t h e d e t e rm i n i ng f a c t o r

i n t h e i r b e ha v io r d u r i n g t h e ash d e p o s i t i o n p r oc es s.

ASSESSMENT

OF

NEW PREDICTIVE TECHNIQUES

G e n e r a l l y s p e a ki n g t h e n ew er b en ch s c a l e p r e d i c t i v e t e c h n i q u e s a r e f a r m ore s e n s i -

t i v e t o t h e c o n d i t i o n s t h a t e x i s t i n co mm ercia l f u rn a ce s t ha n t h e o l d e r p r e d i c t i v e

me thods. S e l e c t i v e de po s i t i on , f o r exampl e, has been r ec o gn i z ed as a phenomenon

which cannot b e i g no r ed . M ore a t t e n t i o n i s b e i n g p a i d t o f u n d a me n ta l s o f t h e a sh

fo r m a t i o n and de po s i t i o n p r oc es s es . New to o l s , s uc h as S c ann i ng E l e c t r on M i c r os copy

(SEM), a r e b e i n g c o n s i d e r e d as ways t o i m p ro v e p r e d i c t i v e c a p a b i l i t i e s . O t h e r,

m ore s p e c i a l i z e d b en ch s c a l e a p p a r at u s e s a r e b e i n g d e ve l op e d t o s i m u l a t e i m p o r t a n t

aspec ts

o f

c om m er ci al c o n d i t i o n s and p r o v i d e q u a n t i t a t i v e i n f o r m a t i o n o n p a ra m e te rs

t h a t i n f l u e n c e b on d in g s t r e n g t h .

Rec en t wor k has shown th a t p u l v e r i z e d c oa l , i f s e pa r at e d b y g r a v i t y f r a c t i o n a t i o n ,

can y i e l d i m po r t an t i n f o r m a t i o n r e l a t i v e t o s l a gg i ng p o t e n t i a l due t o t h e i r o n

c o n t e n t . ( R e f .

6,

7 ) . R e s u l t s o f t h i s work h av e shown t h a t t h e p e r c e n t a g e o f i r o n

i n t h e hea vy f r a c t i o n s c o r r e l a t e s v e r y w e l l t o t h e s l a g gi n g b e ha v io r

i n

c ommer c i a l

b o i l e r s . (S ee F i g u r e 3 ) . T h i s t ec h ni q ue a pp ea rs t o i d e n t i f y t h e p r o p o r t io n o f

r e l a t i v e l y p ur e p y r i t e s p a r t i c l e s t h a t a r e g en er at ed i n t he p u l v e r i z e d co a l f e e d

a n d t h a t a r e c a p a b l e o f m e l t i n g a t r e l a t i v e l y l o w t e m pe r at u re s and t h a t w o ul d a c-

c ou n t f o r e n ri ch m en t o f i r o n

i n

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

A m et ho d f o r m e a s u r i n g a c t i v e a l k a l i e s h a s be en d e ve l o pe d a s a means f o r i m p ro v e d

p r e d i c t i o n

of

f o u l i n g p o t e n t i a l ( R e f. 8 ) . P r e v i o u s w isd om h e l d t h a t f o u l i n g p o t e n -

t i a l

was d i r e c t l y r e l a t e d t o t h e t o t a l sod iu m c o nt e nt . Much o f t h i s e a r l y work

was done on l ow rank co a l s i n w h i c h c a s e i t was n o t u ncommon f o r a l l o f t h e a l k a -

l i e s t o be p r e s e n t a s an a c t i v e s o di u m f o r m ( R e f . 9 ) . However, th e re were many

o cc as io ns wh ere t h e f o u l i n g p o t e n t i a l was n o t a d e q u a te l y p r e d i c t e d b y th e t o t a l

s od i um c on ten t .

( T a b l e

I 1

p r o v i d e s some e x am p le s o f a no ma lo us f o u l i n g b e h a v i o r . )

The m ech an ism p o s t u l a t e d f o r s o d i u m - r e l a t e d f o u l i n g w as o ne o f a v a p o r i z a t i o n / c o n -

den sat i on mechanism. S im ple fo rms o f sod ium compounds re su l t e d

i n t h e v a p o r i z a t io n

of sodium

i n

t h e r a d i a n t z on e o f t h e f u r n a c e w h er e pe ak t e m p e r a t u r e s a r e g en e r a te d .

Su bse qu en t c o n d e n sa t i o n o f t h e s od iu m o n t h e r e l a t i v e l y c o o l t u b e s u r f a c e s e f f e c t e d

a p r o ce s s f o r d e p o s i t i o n

o f

s od iu m. S od iu m i s a known, e f f e c t i v e f l u x i n g a g e nt

t h a t c a n c r e a t e h ar d,

b o nd e d d e p o s i t s . The r e f e r e n c e d m e th od r e l i e d on t h e u s e

O f weak a c i d t o p r e f e r e n t i a l l y l e a c h o u t s o di um f r o m s i m p l e com pounds l i k e NaCl

a n d /o r o r g a n i c a l l y - b o u n d a l k a l i a s w o u l d be p r e s e n t i n many o f t h e l o w e r r a n k

c o al s. T h is m ethod g i v e s r e s u l t s t h a t c o r r e l a t e w e l l w i t h f i e l d p er fo rm a nc e on

c o a l s h a v i n g s i g n i f i c a n t s od iu m c o n t e n t s (S ee T a b l e 11).

I98



I

T he us e of ne w anal y t i c al t e chni que s pr o m s es t o gi v e r es u l t s t ha t a l l o w m ner al

mat t er t o be i dent i f i ed ac cor d i ng t o co mpos i t i o b m ner a l f or m di s t r i but i on wi t hi n

t h e c oal mat r i x , and gr a i n si z e.

Techn i ques such a s comput e r - cont r o l l ed scann i ng e l ec t r on m cr oscopy ( CCSCM) t r ans -

m s s i on el ec t r on m c r o s c opy

( S T E M ) ,

X- r a y di f f r a ct o n c an be us ed t o c h ar a c t e r i z e

t h es e pr oper t i es on i ndi v i dual par t i c l e by par t i c l e bas i s . Ne w s p ec t r o s c opi e s s u ch

a s ex t ende d X- r a y a bs o r p t i o n o f f i n e s t r u c t u r e s p ec t r o s c o py ( EXAFS) , a nd el e c t r o n

e ne r g y l o s s s p ec t r o s co pe , ( E E L S ) a r e c a pa bl e o f d et e r m ni ng el ec t r o ni c b ondi ng

s t r uc t ur e and l oc al at om c env i r onment f o r o r g ani c al l y as s oc i at ed i no r g ani c s l i k e

c al c i um s odi um and s ul f ur . Ot he r ne w t e chni ques s uc h as F our i er t r a ns f or m i nf r ar ed

s pe ct r o s c opy ( F TI R) , e l ec t r o n m c r o pr o be , e l e ct r o n s p ec t r o s c opy f o r c hem c al

ana l ys i s ( ESCA) , et c . al l p r ov i de met hods of i mpr o vi ng pr e s ent c a pabi l i t i es . By

deve l opment and appl i ca t i on of t hese t echn i ques a much bet t er f undament a l ass essment

of c oal m ner a l ma t t e r b ehav i o r

i s

pos s i bl e. T he aut hor s bel i ev e t he s e r e s ul t s ,

coup l ed wi t h t hose of ot her exi s t i ng met hods , can mak e a s i gn i f i cant i mpr ovement

t o pr e di c t i ve capabi l i t i es .

AREAS OF UNCERTAI NTY

Pr e di c t i on of as h depo si t c ha r a c t e r i s t i c s bas ed s o l e l y o n benc h- s c al e f uel pr o-

per t i es al way s r e qui r e s subs t ant i al j udge me nt and a l l ows o nl y a ce r t a i n l ev el o f

c onf i denc e. As di s c us s e d, t h e as h de po s i t i o n pr o ce s s i s so comp l ex t hat det a i l ed

mode l l i ng of commerc i a l

sys t ems based on f undament a l dat a i s pr esen t l y un r eal i s t i c .

Howeve r , cu r r ent t echn i ques can pr ovi de r e l a t i ve dat a wh i ch i n mos t cases i s s u f -

f i c i e nt t o ma ke ac c ur a t e as s e s s ment o f s l a ggi ng and f o ul i n g po t e nt i al s r e l a t i v e

t o ot her f uel s .

The r e r ema i ns many a r eas o f unce r t a i n ty whe r e expe r i enced j udgement s mus t f i l l t he

gap be tween good l abor a t or y r e su l t s / p r edi c t i ons and bo i l e r des i gn dec i s i ons . One

o f t he s e ar e as c o nc er ns t he ex t e nt o f de po s i t c ov er a ge i n a boi l er . T ho ugh t he f u el s

r e s ea r c h er ma y ad eq ua t e l y c h ar a c t e r i z e a gi v en c oal a s h i n t e r ms o f i t s po t e nt i a l

depo si t ef f ec t s , he i s of t en at a l o s s t o a dequa t e l y des c r i be t h e e xt e nt o f c o ve r a ge

o f depos i t s i n t he boi l er . I t

i s

ne ce s s ar y t o ac c ur a t e l y de s c r i be f ur nac e c ondi t i o ns

i n o r d er t o as s es s r e s ul t i ng de po s i t s i n par t i c ul ar bo i l er r egi ons . T ho ugh s o me

good wor k

i s u nder wa y i n t h i s a r e a, t h e ques t i o n o f bo ndi ng s t r engt h and c l e an -

abi l i t y r e ma i ns a pr obl em a s f a r a s i t s pr edi c t i o n f r o m benc h s c al e t es t s . T ho ugh

some good cor r e l a t i ons have been deve l oped bet ween i r on cont ent of heavy gr av i t y

f r a c t i o ns and s l aggi ng, t h er e d oe s no t e xi s t a benc h s c al e t e c hn i q ue t h at c a n

s i mul a t e what t he ash depos i t compos i t i on shal l be when bur ned i n a commerc i a l

boi l er .

I t

i s

po ss i bl e t o i nc r e as e t h e l evel

o f c onf i denc e f o r p r edi c t i on o f depos i t ef f ec t s

by c o nduc t i ng pi l o t - s c al e c ombus t i o n s t udi e s i n t es t r i gs whi c h mo r e c l o s e l y

s i mu l a t e t h e c ondi t i o ns p r e s ent i n c omme r c i al boi l er s . Co mb us t i o n t e s t i n g a l l o ws

ev al ua t i o n o f t h e as h f o r ma t i o n and de po s i t i o n pr o ces s and pe r m t s d et a i l ed c h ar -

ac t e r i z at i o n of de po s i t s gener a t e d. Res u l t s c an al l o w det er m nat i on o f depo si t

cha r ac t e r i s t i c s a s a f unct i on o f f undament a l boi l e r des i gn par amete r s ( such as gas

t e mp er a t u r e ,

v el o ci t y , et c . ) . Co mbus t i o n t e s t r i g s al s o s e r v e as v al uabl e t o ol s

f or a s s es s ment o f f ue l s wi t h v er y unus ual pr o pe r t i e s a nd c a n s i g ni f i c a nt l y r e duc e

unc er t ai nt i es i n ex t r apo l at i o n of t he i r behav i o r f r o m pas t ex per i enc e.

Whenever t e s t r e su l t s a r e assessed and used t o e s t abl i sh boi l e r des i gn par amet e r s ,

t he r e pr e s ent at i v ene s s o f t h e t e s t s a mp l e mus t be c a r e f u l l y co ns i de r e d. T h e d eg r e e

of v ar i abi l i t y i n t h e c oal de po s i t a nd i t s i mpac t o n t he da y- t o - day f uel pr o pe r t i e s

199



a r e v e r y i m p o r t a n t f a c t o r s w h i c h m u st be e v a l u a t e d . J ud ge me nt s a r e a l s o r e q u i r e d

o n l on g t e r m c o a l s u p p l y p r o p e r t i e s .

I n summary, i t ca n be s t a t e d t h a t t h e a sh f o r m a t i o n and d e p o s i t i o n p r o c e s s i s n o t

f u l l y u n d er st o od . T r a d i t i o n a l ASTM a n a l y s e s d o n o t a l wa ys p r o v i d e i n f o r m a t i o n t h a t

c a n be u se d t o make p r e d i c t i v e j ud g em e n ts a t t h e c o n f i d e n c e l e v e l s d e s i r e d . Newer

tec hn i ques hav e been dev e l o ped and a r e be i n g dev e l oped

t h a t a r e mo re s e n s i t i v e

t o t h e c o n d i t io n s t h a t e x i s t i n t h e b o i l e r e nv ir on me nt , and t h a t re c og n iz e t h e

h e t e ro g e n e i ty o f t h e i n o r g a n i c c o n s t i t u e n t s i n t h e c o a l m a t r i x . T h er e a pp ea rs t o

b e a r e c o g n i t i o n t h a t n o one t e s t ca n a d e q u a te l y d e s c r i b e c o a l a sh b e h a v i o r; a

c o m b in a t io n o f t e s t s , e ac h d es i gn e d t o f o c us o n a p a r t i c u l a r a s p e ct o f ash b e h av i o r

seems t o be a l o g i c a l app r oac h . B as ed on t he r e s u l t s f r om many o f t he s e newer

t e s t s , on c o a l s t h a t a r e p r e s e n t l y b ei n g b u rn e d i n e x i s t i n g u n i t s , t h e a u th o rs

f e e l c e r t a i n t h a t s i g n i f i c a n t im pr ov em en ts ha ve be en made i n p r e d i c t i n g ash

b e h a v i o r .

p eo p le , t o t h e i d e a

o f

s t a n d a r d i z i n g some o f t h e n ew er p r e d i c t i v e t e c h n i q u e s a nd

i n c o r p o r a t i n g t hem a s su pp le m en ts t o e x i s t i n g

ASTM

t e s t s .

REFERENCES

F i n a l l y t h e a u t h o r s s ug ge st t h a t a t t e n t i o n b e g i ve n , b y c o g ni z an t

1.

G.

J.

G oetz ,

N .

Y .

Nsakala, and

R .W .

B o r i o , D e ve lo p m en t o f M et ho d f o r D e t e r -

m i n in g E m i s s i v i t i e s and A b s o r p t i v i t i e s o f C oa l Ash D e p os i ts , p a p er p r e s e n te d

a t t h e 1978 W i n te r A nnua l

ASME

Meet ing, Dec. 1978, TIS-5890.

R. W B o r i o , e t . a l . , The C o n t r o l o f H i g h T em p er at ur e F i r e s i d e C o r r o s io n i n

U t i l i t y

C o a l - F i r e d B o i l e r s ,

ORC

R&D Report

No.

41 (1969) .

F. Raask, F la me I m p r i n t e d C h a r a c t e r i s t i c s o f Ash R e l e v a n t t o B o i l e r S l a g g i n g

C o r r o s i o n and E r o s i o n , p r e s e n t e d a t t h e 1 98 1 J o i n t Power G e n e r a t i o n C o n f e r -

ence, ASME Paper No. 81-JPGC-Fu-1.

i z a t i o n o f E r o s i o n o f He a t T r a n s f e r Tu be s i n C o a l - F i r e d Power P l a n t s , p ap er

to be pr es en te d a t 1984 J o i n t Power Ge ner a t i o n Conference, Tor ont o , Cabnada,

September 1984.

R.

W.

B o r i o , G . J. Goetz, and A . A . L e v a s se u r , S l a g g i n g a nd F o u l i n g P r o p e r -

t i e s o f Co al A sh D e p o s i t s as D e te r m in e d i n a L a b o r a t o r y T e s t F a c i l i t y , p ap er

presen ted a t t h e ASME Win te r Annua l Mee t in g , December 1977, Combus t ion Eng ine-

e r i n g p u b l i c a t i o n T IS -5 15 5.

J .

P.Huffman and F.E . H i gg i ns , I n v e s t i g a t i o ns o f P a r t i a l Ash M e l t i ng by Phase

A na l y s i s o f Q uenc hed S ampl es , p r es e n ted a t 1981 E ng i ne e r i n g F oun da t i o n Con-

f e r e n c e - F o u l i n g a nd S l a g g i n g R e s u l t i n g F ro m I m p u r i t i e s i n C o mb u st io n G ase s,

Ju ly 1981, He nn ik er , NH.

R.

W. B o r i o ,

R . R

N a r c i s o , J r . , Th e Use o f G r a v i t y F r a c t i o n a t i o n T ec hn iq ue s

f o r A s s es s in g S l a g g i n g a nd F o u l i n g P o t e n t i a l o f Coal Ash, paper pre sen ted

a t t h e

ASM E

W in te r Annu al Meeting , December 10-15, 1978, San Fr an ci sc o, CA;

a v a i l a b l e a s Co m b us t io n E n g i n e e r i n g p u b l i c a t i o n s T IS -5 82 3.

I n f l u e n c e o n F i r e s i d e P ro bl em s i n Ste am G e ne r at o rs ,

ASME Paper

N o .

75-WA/CD-2,

1976.

2.

3.

4 -

W.

P . Bauver , J . D. Bianca, J .

D.

F i s hb u r n , and J.

G.

McGowan, Character-

5.

7 *

8. R .

W

B r y e r s , T he P h y s i c a l a nd C he mi ca l C h a r a c t e r i s t i c s o f P y r i t e s a nd T h e i r

200



9. G. L. Hale, A. A. Levasseur , A.

L.

T y l e r a n d R P.Hense1, T he A l k a l i Me ta l s

i n C oa l: A S t u dy o f T h e i r N a t u r e a nd T h e i r I m p a c t o n Ash F o u l i n g , p a p e r p r e -

s e n te d a t C o a l T e c h no l o g y '80, November 1980, TIS-6645.

G. H . Gronhovd,

W .

Becker ing , and

P .

H. T l u f t e , S tu dy o f F a c t o r s A f f e c t i n g

Ash Dep os i t i on f r om L i g n i t e and O the r Coa ls , an ASME p u b l i c a t i o n p re s en t ed

a t t h e ASME Wi nt er Annual Meet in g, November 16-20, 1969, Los Angeles, C A .

10.

FIGURE 1

EFFECT OF COAL PROPERTIES ON FURNACE SIZE

w x o

1.08Wx1.060

o n

. 1 6 Wx1 . 0 8 0 1 . 2 6 W4 . 2 4 0

r

~~

TEXAS LIGNITE

.29Wx1.260

EASTERN MIDWESTERN WILCOX SEAM YEGUA JACKSON SEAM NORTHERN

BITUMINOUS BITUMINOUS

SUB BITUMINOUS

PLAINS

LIGNITE

201



FIGURE 2

7

NmD

0 2

8

f;

g 3 w -

P

0

s

so0

P

t

loo

CML

A

-

PHYSZAL STATE OF DEPOSITS

..../

/Mu B

c

.

-- WYOER

S I I T E R E D F R I A B L E

WLTEI-FUSE0

..

i

.......

.... .......

........ .......

...... . . . . . .

... ............

+<,-....- __..

FIGURE 3

EFFECT

OF

SEGREGATED IRON ON M A L ASH SLAGGING

SLAGGINO POTENTIAL

VERSUS

PERCENT IRON IN 2.BGRAVlTV FRACTION

1

I

a m e n 7 0 8 0 eo

% F Q O ~ NASH OF 2.BW. OR. SINK FRACTION

202



TABLE

I

ENRICHMENT OF IRON I N BOILER WALL DEPOSITS

COMPARISON.OF COMPOSITION OF ASH

DEPOSITS AND AS-FIRED COAL ASHES

U N I T

SAMPLE

1

AS-FIRED WATERWALL

COAL ASH DEPOSIT

-

A sh Co m p o s i t i o n

S i02

A1203

Fe203

CaO

MgO

Na20

TiOp

K2°

so

3

47.0 33.3

26.7

18.0

14.6 43.5

2.2

1.2

0.7 0.5

0.4

0.2

2.3 1.6

1.3 0.8

1.1

0.5

2

AS-FIRED WATERWALL

COAL

ASH

DEPOSIT

50.2 55.1

16.9 14.6

5.9 18.3

12.8

7.2

3.5 2 .o

0.6 0.5

0.8

0.6

0.9 0.8

12

o

0.1

TABLE 2

ANALYTICAL DATAON us. COALS

b n h

L*nitW

R* N. Dakota

(Dry

Basis)

Volatile

......................

44.4

Fixed

C .....................

46.0

Ash

.........................

9.6

HHV (6tu/lb)

(Dry

Basis) ....

10640

Ash

Fusibility

1.0.

( F)

. . . . . . . . . . . . . . . . . . . 2130

S.T. ....................... 2180

H T ....................... 2190

F.T.

.......................

2200

SiO (%) .

. . . . . . . . . . . . . . . . . . 200

A1,03 ..................... 9.1

Fe,O,

..................... 10.3

CaO

.......................

22.4

I

MgO

......................

6.4

N a @ ...................... 5.0

1 K,O 0.5

Tr0

....................... 0.4

so3 ............ .

.

21.9

Ash Composition

.......................

Total alkali.

6. ash

basis

N a

fl

.................... 5 0

K @ ....................... 0.5

N a p

.....................

5.58

K @

.......................

Na@ ...................... 112%

K @ .......................

Soluble

Alkali.

96.

ash basis

Relative Soluble Alkali. %

Sub B

Montmu

42 2

52

0

5 6

12130

1980

2020

2060

2170

33 9

11 4

108

210

2 7

5 8

1 6

0 7

120

5 8

1 6

6 45

111%

nm

39.6 41.0

26.9 39.5

33.5 19.5

7750 9710

1940 2150

2200 2250

2430 2240

2610 2530

62.1 52 3

15.1 17 4

3.5 5.3

6.2 9.4

0.7

3.2

3.6 0.9

2.1 1.2

0.9 1.2

6.1

9.6

3.6 0.9

1.9 1.2

3.88 0.71

0.44

0 00

108

79%

3%

nm Modantw

3

AS-FIRED WATERWALL

COAL ASH DEPOSIT

49.7 41.8

16.5 15.8

12 o 28.5

6.5 9.0

0.9 0.9

1.1 0.6

1.5

0.9

1.1 0.7

2.0

0.2

h B b

Utah

41.5

48.3

10.2

12870

2190

2270

2390

2620

52.5

18.9

1.1

13.2

1.3

3.8

0.9

1.2

6.2

3.8

0.9

1.49

0.08

39%

9%

hvAb

h n n

32.5

54.0

13.5

13200

2370

2510

2560

2660

51.1

30.7

10.0

1.6

0.9

0.4

1.7

2.0

1.4

0.4

1.7

0.15

38

Limns

T s u r

(Witox)

38.1

33.0

28.9

8420

2210

2300

2420

2620

57.9

21.8

3.9

7.1

2.1

0.9

0.8

1.1

4.4

0.7

0.8

0.16

0.05

23%

6%

a

t

203

coal ash deposit

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