COM8USTION/PVROPI(OCESSING ... When to enrich the kiln1

by Larry Farmer & Frank Romano, Air Prod ucts and Chemicals Inc, USA

Thi~ ,Irt icl" ;I rlnro>sso>s the f'{OI1Cll'!lic~

tor three con UlIon cement pl,lo'It

operating (onnlhcns that would

warrdnt COtlSldtoldbo<\ of oxygen·

enh;Jncoo tombu~ l ion_

Fan limited Wh.lt l i.st (jrov!' the USI' 01 oKyg~n IfI

the 1"lc ·l990s wa, the ~ uddcn Up~Uf'gl'

on the USA demand fa. cenwnt following

yN' S of lottie or 110 growth if' capacIty. As (ement planh uiecl to squeeze exlr.1

cI :nket out 01 theu kl)n~, IN.-y Dilen

Wl'fe hmited bV their inritl(f' d d.aft (ID)

f,l!l~. Incremental plO(luchofl ,C1:!ulfcd

.lddit,on.,1 fuel ;\IId tombu~tion air At

most plant;, the It) f.m reached its hmit

before other N ltHpmenl or ~y5tems

lK'd 10 Ihe kiln. In thelot· CJ5e'i, oxygen

f'nr;chment prOVIded thl' ne.::es!o.1ry additlOn.ll o~ygen fa. tcmbu~\1on WI thout

AIR..!.: "ooucrs .....:

Sincc 1!J97, cC'ment plants h.1VC rootinely appliC'd oxygen f"nrichmClJt to

enhance kiln performalJce and ((t.'alc economic bt.'lIclil. The technical

advantages of oxygen-enhanced combustion have been well documented.

but there arc .. ttll .mme quest,om a .. to its pr,1CljCiJ/ily, especiafly in U,t.'

cement industry. The common perception i<; that oxygen worh but ,t is

expensive. Wllile oxygen represents an added ('Os/. it can be ecollomica l

depending on operating conc1ilioH,~ and specdic c.o~/s .11 the plant. Other

industries. sl.lt.h as steel. glass. and non · ferrous metals. routinely employ

oxygen in lheir high·tcmpcralurc processes.

the volu~ p<' I'",l ty of air (<;ef' panel).

III Jdditlon to Ihe ,mmcd .. !le 1: ... 0 10

inc.emental dinke., oxygen promotes

a mo.1' st;'!bl~ oper;'!!lon by rre.lt lng a hot:<'r, ~hoft~r /la"l(' and imp.uving

burn'ng lone control. Over trme. the

ddd(,(! ~!<lblhly contr btrt\:~ 10 a(k"llonal

p.oduction

~lrKe th iS CMf' ~ pu.ely pfOduchon

c1.jven, the tnO'cmenta l chnker va lue

must b{' grealer Ih,1n Ih .. added CO$ \ of

the m'ygen ,1011 inClenwntll fue l .1nd

In'd costs The ,Idd' \lonal dlnker ,~ be.ng

p.oduced VI,th no change to the plolnf\

I 'l{{'d cO'>ts. Thl'fefo.e. only Ii'll' added

vanable «xts .lre reqLl,red to d{'te'minr

tI'H' net benefl!. The (api t.l l cost 10 Inst.lll

ao OIlygen systrnl ,~ typically very low camp.lIed to othl'r eqUipmenl Of ~y'lem

Llr,~.ade~ .lnd IS not.1 'ignific.lnt l,leto.

Ul considering ol{ygen. In mo~t in~t,lnCeS,

,!In pie payba(k on luta l capital i~ in the

order of two or thr"'f' months_

The variableS that play the grl'a l('l.\ roll'

In the economiC f'volluillion arf' d inkl"

value. unil oxygen cost, and oxygrn

efficiency (\onflf'S of Incremental clinkerl

lonne~ 01 oXYI,Wn) Opcration~ th ~ t hd\!{,

employec1 o.Y!iell for n 5l1st,lined period

enjoy,..! continued m.l, ket demantl for

djn~er with (l,nl(er values .11 or ~hght ly

below the c~1 of oxygen (Oil a U~S/t

ba\is) and oxygen efficlellcies gredle-r

th.Jnthr~

O!<ygen,~ either produc('(l atl-arge cryogen-= IW' 5oep.lrallOl'l plants and

then tr.rnportl'd by tank It\Kk \0 the arn;~r'~ $Ill' (lr In ~ cases It ca~ be !ent'f.a\ed dtfect/y .1 tile eustomer's SIll"

JANUi\l!:\! 10(}') 1(. ~9

COM BUSTiON/F'YROPROC FSSING

Afiemative fuel challenges MQ.(' Jnd 11'10 ' (' (cmcnl plJl1h .lIe " OW

turning to .iltern.1twt' fuels to lowl" theIr

operating (O~t~. Today's alternatlvc f u('~

con~i~t of .1 wid!> raor,e of matenill~ '111111 Sit,:l1 ii ic,\!1 \ variJllons in cnl'mi(al ,10 (1

phyS<Cil l COtl1pO~It ion. Petcoke. Iyrf'~,

waste oi l. Mld chemicals Wf'r r the ongonal

alle.na llY(" fuels but arc now bCln l! IOlflc<l

by ,1 Wide ' ,lOge of material~ mC!uoing

wood wa!;!r. pl.1~tic5. WilsIe paper. JJllnlill

me,ll. etc.

DCPffiding on th~ nature of the fucl

,lnd its dispo5a l CO l t. the ~C()nomi(

bClIehts carl lx- ~ub~tantial. O n the 01111: ' h.md, ,1ItfornatlVf' fupls p'P5ent a majer

challenge 10 the kIt" oper.ltor. Thel'

heilbng valUf'\ r.Jrl,~e between 2000 and 36,OOOld/kt: ,\nd they Un contolln

lip to 50 per cent w.1Ir •. Due to thi!.

widt' ',mge ,n propt. rtie<, . thpre IS often

d p,actical I:mi t to wb~t ltu l lo" levcls In the k~n and p ,ec,lklne •. m,lln taimng

sulf>(K-lIt tcmpe' ,ltu'e I~ pa'dlllount to

thl! efficient prGducticn of clinker. If thl!sl!

tem perature-. tanr1Ct be- mamtalned due

In thl' low heati ng v"lue~ of altematove

lud ~ . prGductlon I cvt'l~ mu ~t be curtailed

A~ a re~u l t, oVl' r.111 fu el ~ub~ti tu ti o n and

tht~ economIC benchts .~ re ~mi:l'd

By U1Uea$Ing the fl,lme If'mperature,

oxygen·enhanced combu~tion enables

Inc(f'a,;cd subsbtutlon of "lll'rn,l tive fuels

"",theut .loy decline il"! prcducbon. The

ccon(>nHCS lot o. ygen ,~ d roVl'" by the

co~ t (MferenD"i belwel'n thl' primary .1nO

a.it ('(fIat,vr tueb. To be tC() rI(>ITlI (,ll. the

OIIer,11! fuel .~avlng~ nll",t oH'of' t the oxygen

cost This I~ .oulillely achoevcd al pl<lnls

tha t are p,l.d to burn wute furk When

th .. c051 d,fferenti,11 betWttn \he pflmary

fucl and " I'I'.n~' ,ve fuel i\ low. Ihe "oded

co, t of oxygen is m DI'e ("h fflwlt to lu~tify

un!..-ss the re a ll' othc ' bc 'I(· llt~

Emission constraints In <;orne Col\l"o J Cl'menl p~lnl ope • .J.boo

I~ CO<1\traJnt'd by t-ml~~lon pem li l Irvd~

Whl'fl thl' emissions ~re directly .elil ted tn

co 'l1 b u ~lion e(('CIency. oxygen ennchmelll

mighl be fea~i b l e. For f' ~" mp l e . cement

planb \hJl alc lImi ted by lo la l ca rbon

monoxide (CO) tml~~'nn~ may benefil

f.om oxygen ennchmcnl. This situatJoo

Iyp,cally occurs w llh prehl'iltc. k'ins

burning tyr!'s 01 precak,nt r ~ ilns th ,l t ale

limi ted by tl lel l terti ary (lir.

To .woid fXpensivp, po~t - I reatm"nl

of CO, ccmcnt planh CoIl1 d ln ,cll), Ifllt'Ct

oxygen 10 re,1(1 '111h thl'; co ,1nd at\.jln

some ex!r.1 bent'!it from thc l C ~l.Ill,n,; heat

tell'<lSe

Thl' key tactol In dctelmlnmg the

benefIt 01 l.I\Inr, o~y.r,cn to combust

e :o:{t'ss CO i~ simil", to Ihe first .'xample

of Increased PtorllJctl(ln. The ~ aJl.I e (>f

the additional p.odl.ldiOIl (o r ,"" , IUl'

of the high ty'C ~ub~ti tu\Jon) n lu~\ be: compared to the r.O.~t of the oxyg!''' . fOl CO (emetJld\lon, thl' volume of oxygen

tends to bl! low!'. Ih,1n for thl! prl!vicu\

l' KJmpll's. The flow rate reqUirement ;\I~ O

t!'nd, to be 5t~'l dy nlllking on-site oxygpn

gC<le ralion morc amenable, which fwl ile r Improves the ov!' ,,)11 pconom>(5..

Summary Th~e siluation~ ,\11 I('Plesenl ope' a t'"g

w<ld itions thai ...... l" ,\nl investiga tiOn 01

o:tygt'n enrichment. Employ,"g mrygl'n

IfIll'c tiOf) 10 100 prove con,busl",n In (ement

kilns I~ technl(ally ilnd I'(onomkaily v~lble

Wllh nlininM! c"plta l investment, wment

plants can implement oxygen rOfi(hn)Cnt

to g'l, n ,1n Incrementa l i ncr ('~s c in

production o~ lower o pWill ing C:O~ t

through glcd!e. substitution o f a lte rna tive

fuels. Each plant mus t wClgh all 0ptions

and dete.mim" the most econom,e,l l

approach 10 IInpmve theIr O~I~tinn~. In

e,lc!' c~~e. the oxygen efficiency VI'II pl" y

a key to le III the bendi ts analy~i~ The

de~ign ,1nli InC,ll ion of the o~yger. Injectm

a'e also cr itiC,'! to Il laXl nll$mg cfh( lency.

Smce each pI,l ot has Uniq Ue oper,ll in);

charade.ist~. it I~ Important to con~tdcf

Ihe expen("lce of the technology p'OIIIffi;f to make ~u".' that o pt.unJ.l ' ewlh a.r "I t,lined. I