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Twenty..Five Years ofseR Evolution;

Implications For US Application ADd Operation

J. E. Cicb11JlOIDCZ

Consul~

236 N. Santa Cruz Av.enue, Suite #202

Los Gatos, CA 95030

I-J. MudD

Fossil Energy ReS@fCh COJpOnltlon

23342-C South Pointe Drive

Lagtlna Hills, CA. 92653

ABSTRACT

In the 25 yean since the first commercial mstallatiQnS in Japan. seatechnology b.as evol"ett in

response to changing applieatiou conditiOJlS. For example, present..-day catalysts fefl.ture lhmner

wallll, improvedmass tl<QlSfer anil activity, and better poison resistance mlm earlier gener4tion

pm4uots. Additionally, catalystIWluagemenJslrategie& frequently utilize cawyst& from

suppliers and with ~eametty different from the original sp:cificatio~ to :improve opfmtion and

minimize cost. Catalystrc:geoer:aliollJathertbau replacement isplaying a. role. Reactor design

and layout has evolved to adopt where neccsBal)'. static mixersto promOte contacting ofteagem

and flue gas. These features improve perfonnance and offe.rlower cost, butmay increase the

need formonitoringmld diaguostic :measurementS.

INTRODUCTION

By the year 20047 in excess of 100 GW ofcoal~fuedcapacitY in the US nmy be equipped WIth

seRNO;.. control technology, to :mitigate: "seasonal" ozone prodncd-on as mandated by Title 1of

the 1990 CleanAir Act Amendments m. The application oiseRin the US will have evolved

from two prior generations of d~s.ign: the first commercial applications in Japan. in1:be: late 1970s,

and subsequent installationsin Europe (predomimlt.lIJ.y Gcnnany) in tbe mid~ 1980s. SCR

precess design basis and opeming requUernems have significantly evolved from. these prior

generations, both simplifying and, in some: wa.yS, complicating tbe pending operations in the U.s.

This paperreviews the key design and opeta:tional evolutions, and projects bow fumre US

operationmay be affecfCd..

BACKGROUND AND HISTORY

StrictN~ emission limits were implemented Py lhe Japanese ~eral govermnent as early as

1973. Local authorities mandated additioual reductious. lead by Yokohama CitY in 1980 (2).

Regar4ing ~w senemting umts, Japan's Electric PowerPevelopmegt CQm.pauy (EPDC) was

requited to "'cap' the N~ emissions fi'om the two.-U!lit Takehata Station to allow construction of

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a thil"d. coal-fired lUlit. These reqWrement& prompted early R&D and pilot investigations to

evaluate SCR. NO~ contr:ol to achieve at least 50-6<FA! N~ removal Figure 1 presents a timeline

ofsignificant evenlS t"egarding the development and comme:rciaJizatiOJl ofSCR. technology.

Figure 1. Timeline OfKey SCR Events

1stReuofu u.s. Coal

Unil:Merrimaek

t

New Madrid.-

rl J

FiratGl:mlan \ll\U: lSfN~ U.S. Coal

Ne~~ Uoit; CarneysPoint

.Akbacbl.PeiziSBIl

Uuil5 (4:W MW)

I

.fRGpasses

Go\'~l

~far

I..mgeBoiler f;a$li1la~

100 ppm

Holdalido B11:Cttic;

TClmafO-A'lSUlna -

(114 x2S0 MW)

Cbugdr,1J Elec1ric: _

SbimoQl:Ski(17S

MW.50%

I I~

I

l~5ji9~O 1995

2IJ..30 pilotplants on oil.

gus~ and retinety ~iIS

aPOC Takam Unit: 1;

250MW Qexno (800/0,

lowduSl)

.

1985

APienic -

"1!phltmc"

Witn=ssedm

Pilot Plants

I~Or1stU.S. Gas

Unil;LAP~

Haynes

2000

1st Evidence of As

PQisonmg in the

US (OUCJStanwn

Unit2)

Subsequent to the approximalely 20·30 pilot plants oporated in Japan in the late 19705 (mostly

on fuel oil and natutal gas). several demonstrations ofcoaH:ked. units were conduc~ Among

the fi:rsJ SCR. demonsp;ations was the 175 MW Shimonoseki STation ofChugoku Electric,

treatmenf on 25% offlue gas from the Hokbido Eleelrlc Tomato-AtsUma Station~ and.EPPe's

TakeharaStation. where for the latter parallel reactors compared catalyst from two suppliers.

Both the Tomato-Atsuma and Takelmta units employed.l1.ot-side ESPs, providing a low ash

e.nviromneurto the catalyst. NOx removal u-om. tbese unitS ranged from S()..80%. with a 5-10

ppm residual NU3 limit. ThUfi. early coal-fWd experience was divided between high dust and

low dust applications.

Sigpificant expcric:nce with high dusr SCR. continued with se"eral earlyapplicanolls in Germany

in the mid-1980s, inresponse to the Oovernwent Ordinance For Lm-ge Boilers. adopted by themen Fecleral RepUblic ofOenmmy l3}. Neckarwerke's AbbachlDeiszeiu Unit 5 was IePorteclly

the tits! coalftfired commercial unit in Germany on a dry-bottomboiler. and KnepperC the first

-slag·tap.... boilt:.f it-pplication. NO. "!nOva! ped'Ql'DW).ce in the Gezman ana El.P"Qpean

applications increased to generally 80%. with Sl:kcred high NOx.-emitting Wlirs such as

KnepperC achieving 90%. Experience in Gennan.yalso identifiedaTSenic poisoning of catalySIS

through hom pilot: plant and fUll-scale ex.perience, and:Wnher delnoDStrated thal control of

residual N1!3 to 2-3 ppm (~not5 ppm) was in moat casesrequired TO maintain a5.b utiliZation.

In the US. the Haynes Station oflbe Lo¥ Angeles Depanmem afWater And Power was the fIrst:

utility SCRapplication, employing in·duet design. fornatw"al gas firing.. The first coal-fired

applications for new plan:18 (Carney's Point) and fel!ofit (Merrilnaclc Unit 2) followed in the

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early 1990s. Finally, arsenic~isoning was witnessed in the US at the Orlando Otilities

Commission Slanton Uilit 2. f: •

EARLY UNIT DESIGN CHARACTERISTICS

Table 1StJromari2es the key desip variables forseveral early SeR applications in Japan and

Germany. NOli: reduction varied sjgnificamly. with removal efficiencies from 50% to

approaching 90%, the latter applied to high NO... emitting units. The low sulfur level of coals

fued in Japanminimized conCml for SOz conversion, at least forsame units. Also, limited

eJtperic:nce with high dust applica.lions had not identified the trUe impflCt ofresidual ~; thus.

cOl1'trolla 5 ppm (and atlimes 10 ppm) was allowed for coal-filed applications. Figure 2

iUusnatesthe c::a~%geometry elnployed al Tomato-Isaku. and ODe Takehara reacTOr. which

consisted of "pipes" wUh walls of5 nun to avoid erosion. Conversion OfS02 approached 2% for

some ofthese designs. which was 1lOtproblemalic for lbe early low sulfur content coals.

Table 1. Early Commercial SCRJnstaUations; Destgn Fetmu"es

EPPCI Shimonoscki Nc:ckarwl:rkcl Necbrwerke! 'SVSI

'DESIGN T~ (198J) Altbach (l98S) WaIheim Hcilbronn

VAlUABLE (1980) (1986) 11985)

HSm1Pust/4)w Pust LO HD lID IID HD

Inlet NO. (ppm) 300 500 300 7S0 325

NO~ Reduction1%) 80 50 66 88 80

Rel>idual oM'!. (pnm) 5 5 S 3 5

902 Conv. (%) 1 1 ..;2 <2 <2

Space Velocit:Y 2300 3000 3340 1900 2850

(lJh)

Figure 2: Early Pipe--Sbaped Ca-mlyst Geometry

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COMPARISON TODESIGNS FOR US APPUCATION

T!u:re are numerous design featuroS ofSCRprocess equipment which Qistinguish the imminent

US applications from predecessol'S. These include (iI.) ~yst teehnolo8Y~ (b) process condirlOD.S

applied. (e) reactor layout. (d) reagent injection eqQipmenlt (6) coal-fired experience base. (1)

rea-gem fype and handling systemS., awl (g) balance-of-plant activities. Items {a} through (e) will

he addressed in some derail. with. highlights norcd for (t) and. (g). Subsequent lO this t'!isCu:>51on.

data describing long-term operetion and eval.uation ofa caWysl WElImgement strategy employing

regeneration is presented.

Catalyst

Possibly the mostsignificant: 3Clvauc:cs have peen achieve4 incatalyst U:chnology. resulting in

increased performance and lower production COSt. hnprovements r.o both C$llyst geometrY and

composition were realized.

The limited strength ofextnlded material, or ille ability to bond catalytically active ingredients

anto a substrate, dicmtea. ~aJ.y$t geometry for cady desi~. Accordlngly, relatively thick:

exmuled walls or coatmss were necessary to provide erosion resisumce. Figure 2 depicted me

pipe-sJmpe geomeltY employee in sevc:ral early ftPplieations. requiring a 5 mm thick wall Jo

prevent erosion. Table.2 compattsthe geomeuical cba.m~sticsofscveral c:a:rly catalyst

products, showing howme decrease in wall thickness improved a.vailable surface area for

cxl4Ud.ed :ma~l. Mos~ norablc: ill Table 2 is lhe increase in surtace area-to-volume ratio, which

for some specific products is significant Of~tionare the physical chatacrer.istics oEplatetype caTalySIS. which otft:r ~ng the highest open area. {e.g... lowest flue gas pressure drop} and

have fcmuUDed relatively consRnt to exploit that impommt feamce. Also ofnote is the

introduction ofceramic fibers as sullsttate. offering signifioavtsurmcc area. ofreaction pe. unit

weight.

Table 2. Evolution ofQltalyst Physical Properties: 1979 - 2001

PifA:fJ or Cbaracferisrl~ Wall Surface

Ph}'SiCllI ~iOP Thickness ArealVolume Ope4Area

Cbamcterlstic Unit GeometrY lixmn} (mm) mZ/m3 (%)

lllllan 1919 various Dmc 30 5 -200 -60

JapllB 1980 Sbimonoseki ,;uid 9.8 1.8 333 67

JlmlUl19M 18~5 i Yokoouka 2rid 7.4 1.4 438 66

Euto13~ 1985 Alu.d1-Deizsbu. grid 7.2 1.4 448 64

EuroPe 1986 KneuDer md 7.4 I.I 460 73

Euroo~ 1989 Mchrwn Iclaft: 6 <:l 330 82

US.199S oue I'Plate 5.4 <:1 368 84

US.200() NCWtMadrid IfU'lcl 9.2 0.23 383 83

wtious IRnI1 7.4 0.83 480 79

US,2DOI ....arious eorruglJtc4 10.6 1 35)0 78

! lnlatc: (hvddia)

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Forsome scaapplicafions. the higherspecific sw:1ace area.. smaller pitch C1UalysIS are :purposely

not utiliZed., and instead the largerpilch, lowerspecific ~.area. designs are used to avoid ash

plugging and deposition. In f~t. a "casoadinS~' cata1}'st pitch (pitch size decreases with each

catalYSt layerin me diTecnon ofgas flow) is ft~uent1yused in :many STations operating in

EUtope to ~geash dcp<mnon and pluggiu; • Although no SCR. retrofit units in tbe US at

ptesepr: usingme cascacI.iDg approach wiTh iuitial catalyst inventory. some adjusnnent ofpitch

to opemting characteristios i~ anticipated with ex:peri~e.

CtlmpositiDn

Catalyst compoSition changes have increased activity wmle maintaining orteducing convecsion

OfS02 to SOs. and provided resistance to arsenic poisoning. Specmcully, catalyst suppliers have

employed additives as well as improved :manufactUring anel processing techniquesthat in:flucn.ce

the available surface mea. for reaction. The ~mmon Ti~4based catalysts also caD employ

molyPckl1Uln Uioxide (M~) and tungsten trioxide (W0s). in ~tion to the key uctive

ingredient" vanadium. pe1lroJQde (V20S). Perhapslh.e most significau.t oonsequence ofthe

improved l13a.Q..ufac~g process has been the increased ''porQsi~'" ofme catalyst- and WI:

abilitY lO Qffer high mass mmsfer a$"l area. torreacnon- withom: compromise to tmJsion

resistance.

The combination ofbigher S\llface area per ~ohvne ofea.talySt and catalytic activi'Cy, coupled

with ca.Ta!yst managementrecbniquea, has probably rcQuced thewnw volume ofcaJalyst

employed for a given application.. CoPlpmsonsto cady dc:sisns can. be misleading as both NOx

removal targets and the iuitial ea.tal:yst guata:!1tce period have evol'Ved. However. Table 2 data

when compared to presentspace velocilies for 90% NOlt removal and 2 ppm residual NH3

suggest lower voltmle il> currentlyapplied. Thia im.PIOvemcm leaves less margin for design or

operating Im"ors or aoomalies com~ed to themore ~a.live European applica.tions.

Consequently, operatol'S will benefit from detailed process monitoring to diaguose and detect

performance n-c:ndS as early as possible.

Process Conditions

The selection ofSeR "process conditions" - the distn"butiOll oftlue gas veloci'tY. NHVNO ratio,

and the range ofacceptable ternpermure that establish the operating environm.ent for the

catalyst· have evolved to support present perfomnwcc: targetS. There are sev~ml methods of

specifyingme distribution ofvelocity and NHYNO ratio; this:paper will utilize the standard

deviation (SO) of d1e measurements.

Figure 3 iUusrrares the role offlue gas velocitY and NH3INO ratio SD on NO~ renwval

performance fUld :residual NIh. These data represent a perfum:Jance calculation fur an inlet NO~

content of0.30 IbsIMBm. employing a ea.talyst With space velocity of3200 lib, and grid-tY,pe

caralyst of7.4 nun piTCh. The process calculations employ a nmdom distribution ofinitial

velocity and NH~~ ratio across me fiWface ofa. catalyst. chatacterized by varying levels of

non-unifonnity. At each loc:atiQn on t.be catalyst. the local. NO" teducricn and N1!3 slip were

calculated and the results inrcped OVcl" the surface. Unifonn velocUy enhances ped"onnance

by proVlding unifo:an residence time across th.e catalyst., insuringno "'cells" have inadequate

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Figllre 3: Role ofMa1distribu1ionsinVelocityand NHJ!NO on seaPenoI1W\I1ce

10

8

e

0-

Q.. 6

=

4 :r:

z

2

0

80 8S 90 95 100

dNOlc, %

__Vel..$td. Dev. 6%

_ Vol-$tei. Dev. 10%

--6- Vel-5ld Dev. 15%

-&-- VeI-St£L Dev. 22%

_ Vel-Std. De". 34%

(a) VelocityNon-UnifonnilY Effcetl' (NHVN01' Non-UniforndW" 7%)

10

8

§.

c:i. 6

&.

4 r

:2:

2

0

80 85 90 95 100

c1NOJc, %

---NH3JN~. Dev2%

-0-NH3JNQ)(oSn:f. Oev4')b

-a- NHS~~tI:1.Dev5%

.....;r- NH3JNOx-Std. Dew6%

-.-NHSJNQ(-Sttl. Oev 9%

(b) N1I:JI'NO,. Non-UniformityEffect:s (Velocity Non-Uniformity;; 10%)

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reaction time. EquallyUnpo~ iones oferosion-inducing high velocity and deposit-indncing

low velocity are minimized figure 3 shows tlu¢ improved velocity distribm:ian increases

performance. but the payback fot achieving extremely "'fiat" velocifYprofiles dim.inishes.

Figure 3 also show$ Ibe NH3INO~ uniformUyis significantly Ulore bnponam:than. the velocitr

uniformilY in providillg for biSh N~ xcmoval. Ifanyone "cell" oftlue gas ifl deficient in either

reacTant (NH3 orNO). then The teaction will noI proceed to completion - regardless ofthe

\'olume ofcaralyst lha.t is utilized. Pigure 3 also illusttatc=s th~ criticality ofNH3INOl<. U11iformi~

increases as NO~ reductions exceed 90%.

Most elilfly genenmun designs in Japan and Europe are believed to femure distributions of

velocity ofa IS-20% SO, and of'NH:lNO ra.tio of6% or ~rSO. The evohnion to high

performance sys~ms requiring 90% NOx removal at 2 ppm slip has te~ the velocity

distribution modestly to perhaps lO-15% SD, bm signifi~yfor Nfl3/NO ratio. The specified

SO for the latter is :frequently less tlWL So/o, aud for some ~licalions as low as 3%. As a

conaeque.uce ofthesa strict specitlcations~ sea process eqqip:menl: and Cat:a!Yliltsuppliers apQ

ownel"S have conducted. ~essi"'e modeling studies. Regarding physicm "cold-tlow" modehn&

me scale ofnuxtel, (Jetail& ofconstrn~tionmcluded in the sbnula.li.Qt1. and extent of

measurements have significantlyincreasedtIJ support the high performance systems. "!he use of

CFD has been integmYeC1 With ph~l flow models to augment the evaluation, particularly with

the disttibution oftlue gas temperature.

One item that may become ofco:ucem is the abUitY to OCUJStruet and install the ammge~t of

't1lnLing vanes, baftlesl mel tIow l"ectifiers to ate necessmy accuracy as specified by the physical

orCPO model. Consuuctiol1 tolerances ofless'than one mcb. may me problematic in actUally

achieving the flow distribution specifled by me model. The challenge to opmrors ofthese

systems may also be to insure the process conditiollS,. once delivered. bytbe process supplier. are

JIlainta.ined. Finally. as will be disCU5Sed snbsequently, £imply demol:lSUating that th~ stric~

ptocc:ss conditions are actually delivered by the process suppUer lI1fly be a critical issue to SeR

operators.

ReactorLayout

Reactor layout can vmy ~Y. depending upon whelhl!I'sea is irunalled in. a new plant, or

retrofit to an. exi:lting unit.

Comparison ofcontemporwyr~or designs to early applications in Japan and Europe is limited

for severnI reasons. Many eudy SCR tetl:ofilsin1apan wc:rc "low dust" lIJlplieations mal:

inherently required smaller cauuyst awl reactor ~olume. without the complexity ofhandling lllgh

dust lo~ding. Mmt.y boilers in GenmmyentplDY tower designs, allowing a more stnrightforward

~tor (at least in terms ofprocess conditiOIllh ifno~ structuralsteel) thafwas amenable to

improved performance. The flue gas flow path for some tower boilerseamrofilS could

elt1pJoy perhaps twO "'elbow' tUtUs priorto the catalyst,. which a.trords good flue gas handling

practices. CeminlY7!1~ ull European. installations are represented by this concept. Md numerous

challenging retrofits were undenaJcen and SIlCOeSlOfiilly implemented.

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Ofuote with US scaapplicationsis the potential f~r a larger fraction oftlue gas ro be bypassed

around the economizer. to ,provide the open.ling "'floor', dge to higherflue gas s~

content(from higher sulfur coals). The relatively large volume oftlue gas to be bypassed around

the economizer over a Wide J~ nmge can complicate :mixing pauerns. figure 4 depicts a

specifiC' rea.cror awl duclWort layout in which a relatively large volume oftlue gas exiting the eCQno~er bypass was problematic in. p1'\':Ivc:ntblgme disnibutiml. offlue p remperauue and

"'~lQcity to be ~uslyachieved. The di,,~ion offlue gas around the ~onomizer

necessary to meet the t.emperetUre specification. biased the flow field aDd significantly di&to~

me velocilY profile. For ~lc,at mid-load the bypass dampers are only 10-20% open and the

syst~mmust mix the small, low velocity flow diverted around t1le ecoIlP~cr with me larger

bulk tlow. Conversely, at low load the b)l)8SS dampeni are fully opem, and the system must mix

a hu:ge volwne oflarsc, high. v.:loc:ity flow divened ~und me with a. small bulk.

flaw. A combination ofphyaical cold !low and eFD modeling was usecl to specifYthe derails of

ductwork layout and :flue gasrecdfication devices. The s~onwas ultimately attained.

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Reagentlnjecdon Equipment

Historically) the approach to achieving unifann mixWg ()fr~gent with No,. is a higb-densil)'

anangemenr ofindividual uyeetors acros:; a tlue duct. with asmany as 4O~50 injectors per m2.

The injectors can be individually ucljqsted to tl:mc the delivery ofreagen;. In recent European

applications. the use ofa.small number oflarge iqject01'S (4-12) combi!led wiib sonic mix.ers has

emerged as an alternative TO a conventional ammonia iiljecnon grid (AlG). This concept is

receivin~ increased a'f~ntiou due mThe poQmtial for reduced maintenance for individual

itUectors. The necessary hani~ and design expenise botb me otfered ')mckagecr with SOl

e~pmenlor catalysr. andmdiv.i&mly from suppliersofstatic mixers. Specifically. one catalyst

IlUpplier offers two versions ofa matie mixer for use in applicanons that employ their catalyst.

SUniI~lY7 ()~e sea proc~ supplier provides delta-wings as standard equipment in theirsystem

design. Several individua! suppliers ofstatic mixers (Sulze=r. Koch. efC.) wiUprovide smtic

mixer r.ec:hnology as sumd-a.lone offerings to be incorporated into the process design..

Recent US designs have employedup f() five individQal mws ofstalic mixezs to achieve a

reqt.rir~d d~triblf.lion ofvelocitY. rc:mperawre. and NHs/NO raUCi. For exampll!. static m.Di:ers lm"

deployed (1) a.t the :tl.qe gas economizer exit, ~o mcTify imba1ance~ mvelocity. temperaaue. and

composition. (2) downmeam ofthe take-otrduct for the bypitSs2 (3) priorto the

injectors, to :rectify velocitymaldistributions maQce<l by a tight "elbow" tum. required due to

space constraints. (4) following the reag~ injeclOl'S~ to induce mixing,. and (5) prior to the

reactor entry plenum. The nominal gas pte:lSUre lossincuu-ed by each row -less than. 0.3-0.5 in

w.g.- is the tt'3deofffor a COffCCt distribution.

In stmUnary. both the high density AfG and IItatic-mixer CO!1cepJs moe employed in US

appli~a.tions. The need for extremely1Jigh perfommncemay mvor utilizing static mixers and

fewer injectotS etveJ' a. conventional AIG. Experience wiTh STanc mixers suggests that ifinsmlled

cOIteCtlythe uuits will be :alaimenance-free, opetatono are predica.t:ing plans on this

observation.

Coal Experience

Early SCRexperieace inJapan domimlred Py low suln.r coals from Australia and S. Africa,

the primaty coal. .s~es in the llUe 19705. Despite The considemble undersnmding gained with

these coals. generalization l"O EUI"opcan emUs was greeJedwiJh the: observa.T:iOn oflll'Senic

poisoning at pilot Beak. AlJ:bough J10 episode similarto ~opoisoning is anticipa;:ed fOf us

applications. the uncertain't)1 ofbr0a4 deplo~tto a set ofcoals merils lhat operatofS

observe and doeuwent composilion ofcoal tired to relate opera.tio.ns to catalyst activity.

Tabl~ 3 summarizes the key coal c<mstime~ fha.t affect ea:ta1yst deactiyati~ identifYing the

most significant caJalYSJ impact. Most notable is t'he ro~ ofalkali and alkaline earth elementS

that can induce alkali sul1ate poisoning. Calcium sulfate was earlyn:c:ognized as a significant

deactivating agent (Ii) the other more soluble ~1kali cited can penettate eataIys~ :{l(ll'es when

exposed to moisture (ftom n:tbe leaks Of conden~tiondue SUtNp). As described :previously,

arsenic is a well-documentel1 poison that. although most acute far wet-bottom boi1crs"that

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employ iilSh recycle. is still problematic for dry bottom boilers with lower furnace ps exit

temperatures.

Table 3; Key Coal Characteristics That Affect Catalyst Peacnvarion

COllI l'~Or JaplUlese ~OJlcan Atnici~US

Consmuent Calal'iStImT)BCl" ~ah:nce 'Exodicric~ Conditions

Al'GeI'lie :R.~ \Vim V. ncglil1Wg NcsljpJc rdeqtfficd lhtough Varies widt'ly with AS

!tiu: i1etivh;y lllldIor As <:omenl did pilmandmly contem: in coal (2-40

bJockiQgmierOPQrtB nol JdcQl:i~ cammetCiaJ ppm) . DJ1S

Alkaliul;: twlllee$ "!lcidiW- /Slid Taw3IkaU<S% TOllS! alkali S. .)J12% ofash, up to

mUC'\il.\ {IC, ~c:aofQta1~ ofam(obsetve4 lSOA! ofllSh 23%forPlm

Na.Mg) llCmsiIes Wi1b oil bll}

A1IusJinI: canb ReaclS wilh so. fonnecl af O~)-5% 3-5% ofltlW. 2-10% uh, tlfHO 16%

(primarily sil'o': to pt0412Cll CaSo~; ofCOlW fued' SlIllr YaHcy, lIIld forPRB

C:.) pfaggingporcs. abilit;y at (Ausrralia, S. Polillh coaJs

Nro {O &b¢ $iT.e. AiiCll}

Mmim1m1 Ca aee&d lO

nUu2ale llnlc:sm: ZlOisODiu~

Phos.pboTOQS AS pbO$pbQric aPid, elm NOll"~4 lkcopi:.=d in Will dl:pI::llQ on coal P

condl:D8l:, ~, and block so~coaLi ~W14

pores. Dxid~Kc:\.1.lcing

conditioD:lo in fUmac:~

Sultiu' I'ndireotly, ;sulfurprovides 0<0.6% <;1.7% 0.4-3.5%

uource ()fSO•• which COln

teac~ wh:b Ca lO foms

CaSo~

Regarding arsenic) it is known a minimum level ofcalcium i~ We coal is desired to mitigate

afseni.c poisoning. minimum level ofcmciumin ash (-2%) is dcs~eq. PhOSphorous can

also ~activatecatalyst. a.w.! sulfut- although not exerting a direct role - indirectly can

conlribute tlle alPli sulUite fonna-tion by production ofso,.

Figure S compares coals utilized in. the Japanese and European experience wiTh those anticipated

us applicatious. figure 5 CQmpa:r~ the content of(a) SUIM~ (b) ash, (c) calcium. in the fly ash,

and (d) tOW alkalinity of.t1y iISh constituenTS (calcium, po'(&SsiUIQ, magnesium., and sodium).

Figtue 5 shows exp~em:einJapan derived wilh relatively low suttUr (",,(),4%). 2-3%

calcium in ash, and nesligible soluble ~j compounds. The coals Use4 in Burope f;ypically

feamre double the stdfur ~tent. and iDcr~ed caJciuJnand lOtal alkali in fly ash. The rUSt us

SCRimtallalions were on low sulfur coalsthat: (due to compauoility with dxy scmbbing

technology) resembled the: coal used. inEurope. The complete set ofUS coals tha~ willsee SCR

duty in the US may present greater cballen~than the first coals did, due to higher sulftn- and. in

some case Fe ~!1tent, which win incr'ease SOs production by the cam1yst. Forsome coals, low

calcium content in fly ash may be inadequate to negate arsenic poisoning, and adding limestone

or other a.lka!i to the coal will be required. Finally, the case ofPowder ltiveJ"Basin (PRS) coals

may be ofconcern, depending on the application. Short-term exploratory tests suggested the

extreme calcium content ofPRB promotes aUcali sultme poisoning. B.owevet. oOt all catalyst

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supplic::rs shme fhis view~ and themt commel'Ci~ insUlllation with PRE coal has not incurred

any noticeable dc:ac:tivation.

Figure 5: Com.parison OfCoal Characteristics ForJapanese, Buropean, And Anticipated US

Applicmions

J14.1lll

lUln

010.011

!aoo

J&.OP

Z.OlI

0.00

f- .SUJur

I-- .~ 1--""

QCaIcIuM

DTOIaIAIkslIne I-

... ,..

t-- f--

~. I",

.II: • • .. .~ - Awlll'AIIll S. A!l1lllk:l1/1 Ruhlt11 !Illllr{2) POIOIllI llullllr MIlQ SwIlur tflIIIls..nur PRll

~~

In sumtrWY, some US coals are not describc:d bythe existing experience daTabase, and despite

the beSt effons ofca~ysJ:suppliers, some risk to deactivation at balance-of-plant problems

exists.

Reagent Type aud Systems

In comparison to early SCR. applications, which were limit&:d to solely anhydrous ammonilJ. as a

fl:2gentsoutee:, present applications C8I1 employ either atJhydrous, or aqQCOus fomlS ofammonia

(of19.5 or 29% soll.Uionstrength). In addilion, dClJcnding on th~pt'Dgress ofsevera! early

demonstration projects. urea may be applied. From sltict1;y a coststandpoint anhydrous reagenr

is usually preferred. as itrequires the least delivered cos~ and capiral equipment. However.

concerns voiced by local co1tl1U\U1l.lies ba.ve promplOd adoption of aqueous reagentfor many

systems$ and for on a limited basis.

In Europe, the:LUst iustallalinus cmployad rea~ent receivin& srota.get and handling ~sthat

employed consefVmive measures such as UlUlergwund ta.ob" double-wall and numerous

tail-saCsmonitoring concep~. A:ilsea applications migrated from. Iarg~ remotely locatM

ceDtral stationsto uniTS in urban ateas" U1tel'est in aqueDU9-M'Jmonia.roagenl: incTcased with local

concerns for bandling aud sromge. Anhydrous systemS app~ to domina.le planned US

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installations, although numerous aqueous .systenlS will be Ulilized. Urea:-based applications have

received recent intc:rest. In terms. ofimpacti.ngSCR operatio~. the use ofaqueous and m:ea

systems introduces additional complexity. SpecificaUy. both approachl:S require a sepamr.e

vaporization step, which entails additional process reactors. an4 managing and monitoring the

Ieagcnt devolatilizalion.orhydrolysis proces$. The manpower bU1'den for such m.cmitoxmg is not

significant (with much ofthe duty remo~1ymonifored), butlhe addiJi.oual steps for evapotatiQn

oftmUnOAia ~om lbe aqueous foIDl, or devolautization ofHN hgmcms from. utea introduces

time delaysthat must be ~unr.ed for in proceSli control system design or operation. With

target performance of90% standard and:aecess;uy for system compl~e. thest: factors must be

considered in control system design.

Balanc~f...Plal1f

A dewled tr~unentofba_e-of-plant (BOP) factors is outside thl: scope oflhis paper; but

several key items afC ic1enlUled.

Most European uniTS were initiallyeqtli.pped with enam.eled-coated heat exchange baslcet:i in the

cold end ofthe air heiner, and lbus eqjoyed superior PJ'0teCuon from the additioIUll, SCRpromoted S~. The use ofenameled-coa.ted heat excl1~Ge bPSkets is not commonplace in US

applications; howe\'er Cottenis frequently used for higber sulfurcoals. An infonnal SUlVey

suggef3ts that approximateLy 75% ofthe units retrofitting seain the US an: believed to be

upgIaCling air heakl'S to mitigato the impact ofresiduaI NH3 bigber S03. These

modifications i~clude installing enamel~d surftlces~ ulilizing A more "open" geoxm;try to reta.Ul

the moment'UIn ofsootblowin; media. in the axial di:rcctio~ orhorb (1). The evolution ofSCR

process equipmenl has probably eased air heater coucems, as experience in Geonany in the mid1980s suggesled residQal shouldbe lowered from 5 to 2 ppm.. for the putpose ofash

utill2ation. The potential for air heater depDsmOD has been reduced accordingly.

Flue GR$ Handling

The need to retrofit adc:1iumml tlue gas flow capabilit.yto hamUe the tdgber resistance imposed by

the reactOr and process equipmeut varies sigpi:ficamly wiTh sper;jfic mUtS. T}'Pically. the

additional resistance ranges from 3 in. to7 in. w.g'l depending on the application, wilh mo:>!

instalIaticms probably incumng 4-:5 in.. w.g.. It bas been widely ~ned that most European

insmllaTions did not require upgrade to flue gas handling ~ent; however, the nationwide

program. tel relI'Ofit flue gas d~onprocesses completedm1984 {3} requitc:4 fll.le gas

bandling upgrade that in many cases was able to also accommodate sca. Ar:l. informal S\lIVey

suggests that 50% oftbe units re:tmfit with SCR ill the US requite some improvement to flue gas

handling, with upgraded motors Of fans C011U1lQn..

Compared to pieVious ex.perieJ1ce. any reductionsin tlue gas remtaDoc by improved catalyst

desigD have probably been absotbeq bystatic and: AIG components to provide a more

etfcctive NH3/NO distribution - the price for wmch is paid in pr~e drop. Thus. the evolution

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ofSCR. application bas probably notmaterially cluulged Ibe addUional flue gasl1andling

requirements~ or associated O&M.

Since arsenic poiscm:m.g was demansnated a lWlior contributorto catalyst deactivation, the need

for a. minimum. quantity of available calciuminThe fly ashhas been recognized. SeveI8l

European operawlS oonsistel1tly inject or add Uw.esnme ()l'lime to coals med to augment the

namrnllyavailable calcium in.the ash, and claim ft. benefit in mitigating both arsenic poisoning

and S~ outlet com:e:nmmon (3). Generally. anywhere from 0.5-2% ofmes coal mass

eousumplion rate is augmemed widllime. dokJ~lic limcs'Ul~. ()fconventional limestone TO

pro~de alkalinitY. Capital COstS forsuch equipment are l10t excessive, but O&:M procedures

m\1St ~commodale servicing the aUca1i supplyan4 ~pment. The eJttent to which such systems

will be applied. in the US is tmema.iu. One IIllUotseaprQcc:w equipmentsupplierstrongly

adviseS deploymentof:ouch cquiplDCnt:. au4most (butnot all) cafalystsuppliers agree that fpr

certain ~plic$ons the addifional is beneficial. However, Southern Company recently

anno~edthey would forgo albli addiU~and ~t pos:iib1yhigber Cilta1yst deactivation in

excbange for simpli(:ity and teduc:eQ. plant operating4mies. b1 SUlImUliY. the need to inject alkali

to mUigtUe eithermemc poisoning or control SO, emissiousmay slightly increase O&M, but

adoption ofalkali iJUecnonladWtion is!lOtanticipated to be widespread.

LONG-TERM OPERATING CBARACI'ERISTICS

Operating data obtained fur coal-tired SCR-equipped units showstbatperfunnance can vazy over

relatively shan perinds ofti1:ne. Given thai the: N~ lOJl.S cap fat the SIP-Callis e!feetively a

5-mondl average. hourly or daily variances will noT: be ofsisnfficance for many OpeIatotS.

However. in adliition to the S~~ (or annual) tOns cap, some statesrequire some combination

ofa 30 day. 24 nour. or 8 hour rolling a\1e«lgc fO be observed. Specifically, sevend seaequipped qnits planned for operation intlJeHouston are=a.must o"bset\Te 24 hour daily averages of

amagnimde mar are not ~gni1icandyabove the aunum cap. ~. new SCR-e:quippc:d tmilS will

in alllikdihood be requited to abide by a shmHenn average. Data from the Environmental

Proteetion Agency's ElCCQ:onic Data~g(EDR)site is used to explore the vltliabilifY

observed in the US TO dafe.

Figme 6 presents typi~ scauerin sea ouTlet data, obPtined tiom a <lIy bonom. boiler inthe US

with seaoperational far severalyears. The clafa. pteSlm18 N~ emissions within 5% oftblt load.

The di:ta.ils ofopenmOll and the mtel1l oflbeOP"'lS are unlmown; thus it is not possible to

detennine the source ofvariability. However, it is clearthe op'ri:l:wll amount ofreagent required

by a particular Qfprocess condiuons is not consistently delivered to the reactOr.

The variation be quamifiedby a.pplying ma~ pr0ce4W"eS to calculate the 30 day

average, a 24 hour average, and au 8 hourfOiling average. Figare 7 compares this dala fur four

unitS. Two units are 4rybottom boilers retrofit wilh seR far bigb N~ ~ovill trom ~pproximately 0.45 lbsIMStu (UuUs A aud D); g~ cyclone boiler designed for 80-85% N~

removal from 1.2-1.5 IbsIMBtu; (Umt C), and a D~W pl&n~ capable of 5O-600~ sea N~ removal

from 05 lbslMBtu (UxUt E). The dafa iu Fjgut~ 7 show U NO~ tYPifiedby shon-Term

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avetagiug pcrlQas can be significantly than lbe caU:~ 30 day rolling average. These

dara. caJ1 he used to estabJisb an"'opemiD$ marginn NC\. OUtlet thatshould. be latgcted if

short~tem1compliance isrequired.

Figure 6: SCR OutletEmissions Panl Scatter For 90% Removal Systenl

(l.S

Cl

g "

0

6 g

0.5 (I

8

(i Cl 10

•

4 II Q 0° Q

C (l q, <I 0 (l

~M Q {/

Q (I

i 0 0

(l 0

it 0 0 Q 8 Cl 1:1

0.2

0.1

1~O ~~ 2&ID 3~'

PROGIre~liguR5 QF OPImA'trON

Figure 7; Comparison of30 Day, 24 hour: and. 8 ffour N~ Outlet Data for Selected SCREquipped Units

IJNff A uNITe UN!TP

lur ! Z4Kr 'Ile

Z4lfr

3004 IUlr 24-1fr ~l)lI

.wDa - 11K!" r- rZtrlr

~PlI

.. ""'-" n - '-

--

OAO

OJlO

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figme 8 complU'CS this ~matgin" for the foW" units cited, inaddition to a second cyclone unit

(Unit E) and a.second new unitwifu 50% No,. capability. This fipe depicts the wide:

variability in SCR oulletNO:!: from UnitA; howe\fet. ai the subj~ mrll has opetatedwith sea

for less Than one year, the resultsshould be considered prellmiQaty. D~ mnn mos: afthe other

units suggest operatOrS may be required to co:oaider a.ocJitional monitoring activities to align

shorrer and lan~rterm rollinS avemges.

Ofnote: is tha.J the least \'ariabilil)' is exhibited by the unit that (a) t'eafQres the longesT opemling

history, imd (b) rcctuires the least NOx reduction. It is not clearwhicb, ifany, ofthese factors is

responsible for Uris Qbservmion. .

One must be cauti01!S with Figures 6-8. as opetatinstime is limired forsome uniu. anq. the

intention ofthe operatOrsis not cleu'(e.g., minimizing sholt-Tem1 variability maynot be

impottet). Regardless, the data.~1hatprecise ~lionlO o~gdlmes and

development ofa,leaming curve are necessary for successfW. PfOCCSS operation. the results also

SUggesf that" lUly sh()tt-term.monitoring requirements by local ~em:ies consider prncticallimits

to process operations.

Figlll'e 3: EsUmate ofOperadng MatgW. Req'Uire4 For Six SCR-EquippedUnits

!

i

:

I

.

I

:

I

!

._- -- .--

I

I -

I)

II '00

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IMPUCATIONS FOR US O&M ACTIVITIES

Essentiallyall majorutiliw systems are deploying seaas the ccnttal element in their NOx

cootrol strategy, and plan l'Q "overcontrol" N~ on tbe largest plants. al10wiDi smaller, lower

capacitY memr UnilS to adoplless sn.inge:nt oontrols. The success ofeach NQ.. compli<mce

program is heavily dependent on slICCeiSfUl opeJ:auon ofSCRat W'Set levels.

Maximize NO~ Removal

The previous discussion.showsIeprdlesS ofwhetber a. CQuvemional AlG Orsmic mixersystem

is utilized. achieving and maiInaining extremely uniform contacting ofreagent an<!NO is

necessaty. Testini on an annual basis will be necessary to determine the inlet and outlet NO,.

dism"buuon to infer lheNHa/NO Qtio af the cmal}'Sf inlet. Many Eufopean utilities conclm:t lhese

exercises on approximatelY an ammal ba~ which is reconnl1euded for us applieatious. With

conventional hi~ cL=nsity AlG. considerable flexibilil.y is av~1eto hias rea8~t iJlJec~n;0

diff~regions ofthe duonvcrJc. Using s~tic em« alimite4number ofinJecwrs limits

me flexibility, b1lt not: eliminate the ability 10 bias'Che reageut. Process suppliers claim the

mixiDg capabilities ofstatic miX=s elimina~ any need for flexibility, bm: only c=xperience will

prove so. Regatdless. rhe scale ofinfluence ofswic mixers. is limif.l:cl, and compensating for

large-scale variations (e.g., across ihe entire dUC'miQrk) m'*}' not be possible. Th~s. even.litcited

injectors with static mixelSmaytequire attention.

As di:>cUSsed lUlder I&C, m~ lowest SeR outlet NOxlJ:la.y be attained with a boiler NOli: output

optimization for distribution, not uecessal'ily tbe least ma.gniPoJdc:. Consistent testing of

inlet/outlet N~ profiles will identitY optimal opemnngmOdes.

Catillpt Maintenance

The need to achieve high perfonnance requires cm:a1yst to retain activity as projected by the

sllpplier. As both physi~ blPcldng by fly ash aIU! a JCduction in sue acrivi~ (du.e lO arsenic,

aJka.li sulfate tlnli other compounds) contri~ tQ deacti~onliuspection ~d cleaning a1"e

critical. The ofcoupon tests conQuered l1y me catalyst gqpplie:r (and possibly a third PartY) is

essential to provide a snapsho~ ofchange in cmalyst physical features and surface composition.

The inspection and c1eanins ofeata!ysJ: during outages will be ~es5my to assure mar the:

nwcimmn surfilce area. is clean and available to participate in 'N~ reduction..

Data Historian

Operators will need to document me process op~ons and coal COfIlposmon rigorously fa

vaIi.dme thaT the condiMns ofgmuanteea have bee&1 observed. All units to some degree require

this, but particularly those opera~ l!lat have securea a ea.talYBf supply C()~ separale from

the process supply CO!llraCt.

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Manyutilities have e$bli6hed strategio aUi~ with a eautlyst manufacmrerfar caralyst:

supply for an entire system.. The se1~tion ofthe particuliU" supplieris b~ed upcm a firm cost

estimate to provide adequate eatalysl: volume fa achieve a projected pedomumce target,

prestllcing a.fixed. !Set ofprocess conditions. A separate COIltraot is aoanged with a process

supplierto provide the equipment to ~nvcrthose process ccmdidons.

Under this scenario. it may not be snaightforward to attribute responsibilitY for ma1perfonnance.

For exam.pie, ifpedormance tal'gelS ate notsatisfied. it is iilnticipaled the oata1ys~ supplier will

ntst:~~demonsmmoJ.'l.!hal ptocess conditions called for in the specification have been

delivered-pamclllarly iftbe caJalym supplier was IUlt the ~ponsible pany for flow mocl~.

Howcve:r, measuring velocitY disItibutionin high temperature, particulate-laclen .flue gasto

within me a.cCtmlcy required may nOt be viable; thus. itmay not be possible to validate process eollditio~.

Regarding coal composiCW!lt e:atalym:suPPliers wiltlequire asSW'a!lCe that coals as spec:ifie4 are

utilized; for example;. it wJ1l be important to documenl thal a. miuimum level ofcalci1Wl is

available tomiuga:te anienic poisoning. A sys~c a11q cOlllfOUed melho<fowgy to sample and

amUyz~coal. using a.greed uponpn>toCo!s. is necessatY 1'0 eonatt'UCt au adC:'luate ammgemeut:.

System Wide Catalyst Management

The use ofsevernlsea facilities across a ~tmg system aftbl'Qs the oppommity to employ a

systemwide appro~ m catalyst numagemc:n~. Even though a catalyst layer may have suffered

deactivation ~cc:ssUaliug replac:ement, thatspecific la~ can still prQvide adequare NOx

removal- as 100& as the reactor has been designed 10 accommodate the lower initial activity.

Also, catalyst rc,gen~tionteclmiqut\S can increMe aetivi.tyfo! a cost below new catalyst.

Systemwide camlyst mmur-gement hl:JS beell deployed atsevemlstations in Germany, and r~eJ1era.tion lecbniques have evolved in recent: yeaIS. Several providers ofcatalystrecycling

services have refine4 Uleir offotings and m-e plamling to offertiUch services for ~he U.S. market.

Bach regcmcration tc:c1mDlo;y is differe~ but appears to uufizc a combination of(a) physical

cleaning to l"elnove ~h adhered to ca.talys~ ~ingresistance to mass transfer, (b) washing

witb. an aqueous or nOlmtpleous Solventto enhance removal ofash. orremoval ofsoluble alkaJi

suliate compounds. and/or (e) inn"o4J.lotion ofadQitional vanadium on tbe ca.hl1yst service.

The potential benetirs ofa sysremwide ea.tal.ystmanagement strategy can be quautiti~ by a

simple example. CoWiider a. three-unit syatem employiQg a large ~natipn (Unit A) equipped with

a 3+-I reactOr design, Units B muJ C are also equipped with iii- 3+1 reactor desigu, and each offer

50% ofthe genetating capacitY (and catalyst inventorY and tepl#c:emenf ~quUements). AU units

fire a modentte-bigh m=c con«:nJ coal•.install the founb layer at 16,000 operatinghours. ana

(when using m:w eatalys~) n:place existin~ laycn a.t: mletVals ofappmx.i~tely18.000 opernting

hours. ('Spent" catalySt from all units is "pooled" faf resenemi~ elimiuaring the need for new

catalyst after the 16,000 hoursupplemem: and 34,000 bour repbwement. Camlyst: regeneration

tcclmology is assumed to restOre activitr(kIko) to 0.85 fOJ' 65% ofncwcawyst: cost:.

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Table 4 summari2es sysJem catalystJnlmligemem over" 15-yearper.iod. assuming seasonal

operntion forme inilial fouryears and annual op~on lhereafter. The: Baseline Case requires a

total of18 mye;s ofnew ~no be plU'clwsed for aU UUifS. at a. NPV of$11.4 M. The

Regenera.tion Case red.ucestotal new eatal:YStpun:lwsed to Slayers, with a. total of 141~yt!!s

regenetated. The use ofemalY8f l>flower acQvity requires cmc additional layerro be exchanged

for UnitA, over me is-year period. TmaJ incur.red costisreducec1 by almost 20% to $9.5 M.

The scenario descnbed iJl Table: 4 is necessarily simplified; and selecJ:ed to emphasize the

benefi~ QfeatalySt:regClJera1ion. Specifically. the assumption ofmodeiule-mgh arseuie content

coal requitd -rehmvely fi'equenrJeplacement. Also. the scenario assumes success in restoring

activity for- lU'Senic-poisoned ~talyst; that camlyst layeu can be regenerate4 m.ore than OllCe; aDd

that catalyst deat;fivaUQJ1 rate after rc:genem:ion is The same as fur new caf8lyst. An actual

ClUalyst managementstrategy wiD require balancing ofreacfOt po~ ~quired vc:rsus the

generation Qf"spent" camlyst, an4lhe cost and performance oftegenenl1ion tectmologies.

R.egafdless~ the poTeu1ial benefirB are notable. andmerit ao independem an;l1ysis ofthis

alternative to purchase ofnew caMysr.

Table 4: analystManagement StralCgy Iucluding ~8eneration for Hypomenca1 System

Total

Cahilvst Mana2lmlcnt:FaclOr' UllitA UnitB UuiiC Systefl1

Reuetur DesiJm 3"tl 3"1-1 3+1

Initial CataIysrJnventoIv (c..m.) 500 250 250

. CaTalySt Pcr Laver 250 125 125

BalieUae SWate2V

Ca~lysfPurcbase4 (IS years) 61ave:rs 6 layers 6 lavers 18 layers

NPV OfCata!vSJ Mlm~gemmT($M} 5.70 2.85 2.85 11.14

ReeeJlention Case

New CataIvst Purchased Ilaya 2laveJ.,; 2 layers 5 lavers

CamlvstR.e dOSVeafSl 61aYeI$ 41ayers 4la.vers 141ayeIS

NPV OfCa1alvstManaeement ($M) 4.78 2.35 2.35 9.5

Improved I&C/Controls

OJ\e /ilfea.1ha~ has not notably evolved, butwith significant potential. ismat ofprocess cm1'lrols.

Current SCR. processes employa. feedforward.signal for reugent demand (based on boiler NO>..

aT a SUlTOgate such as loild or steam :Bow) with a feedback signal, the Iauer base4 on measured

outlet NO); at the teactOr ex:U orstaclc. Numerous operators have attempted to couple a OOIltWtJO~ on~1ine ammonia monitor as an a4diUonal feedback signal, burundI recently such

insmnnents have notprQVitJed commerciallyacceplable servi~.

In practice, a residual NH3 monitormay no~ proVide significant value over infeniug ammonia

absOfb~ by fly ash. Iftbe deposition ofammonium su.l&les lWet bisulfates (ABS) is a

phenomenon dependemon cumulative. long-term and "low level" cxpoSW'e to residualNH3 and

SOJ. then monit~ring BmIQDma. absoWc:d On fly P3h may be: adequat<:. However. ifprocess

upsets and 'llooaillg" of:re~iQualNH;s is a contribUTOr. then-a teaHime monitor will be

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jun-04-02 02:46~m From-~K\N &GUMP WASH OZ na:;1.::1~ U~ 1.1 ..........,., _._. ---,._•• + T-340 P.Zl!ZZ F-348

useM. As ADS deposition depends on flue gas SO:, conce~ it is likely Ihatlong-term e~sure is dommant

Perhaps more imponamly, the need to maiDtain The UDifQllUity ofNiWNO ratio to St1i11da.nt

deviations of~low 5% may require cannal ofthe boiler NO;.; emission distributioJ1.

Specifically~ opemron> may fuJd to achieve strict SCll ourle~ mrgers the boilershould be operated

'to produce the moSl unifoun, and llOt: necessarily the low~NOx tale. For eJCarop1e. a boiler

NO~ outlet of().35 IbslMBm. cbaucreri2edby a 3% SO may be preferable to 0.32 Ibs/MIhu

characterized by a 6% SO. jfOOOh removal is to be c~tent1yacmeved.

finally, consistently delivering 90% N~ removal may benefitfrom upgrade aime ~ection

system.(either conventional AlG or auu:ic mixer cnnanoed.) from pas~ to active control. NQ..

distribution profiles generated during operation witha penna.nent grid may be coupled to a

series ofcont.rol valves or otherm~to bias reasem ~ss the stitt. Although implementing

this concept is notsimple. the additional COSt aDd O&M COf.l1d significamlylevmge the fixed

invesU'Oe!1t in SCR.

OBSERVATIONS AND CONCLUSIONS

sea tech1'lolagy has evolved. COJ,lSiderably in tbe 3lmast 25 yea1"S since the first commercial

demonstrations in Japan. Equally signi:ficantme ~e oime applications and design

requirem.ent5 oime sea insTallationsfor me SIP-C6U. has increasecJ, with 90% removw and the

need for N;fuINO mtio as low as 3% SD. AB a ccmsequence, enti'fe geneta"dng system. NO;r<

compliance suaregies dependan suecessfiJI ~loymcnt oftbe SCR. And lackint a.tobust NOx

allowancem.arket (at least b:t me earlyyears), seas)'Stempetfo:muwcewin directly impact the

geuoIa'tian available :from anyone unit in a season. 'The fonowing observations offered

regtU'ding O&M activities preserve the OPCl"8tiOJl oftbese sysu:ms:

L Design Margin. Both competitivemadcet forces and the use ofcatalyst management

strategies that mi:o.i:mi2e least fum cost probably leave less design margln in catalYIU sizing

(compared to the Japanese audEuropean experience), to "insmc'" against vnforeseen events.

MoniTOring process panunetelll is essential to understand sea operation., and detect: any

problems early.

2. PrcuI&:ti"e DiagnosticMeuuremeDts. Effotts to detennine the disuitnuion ofNlliNO Iatio

and othel' key pfOceS$ <lpetaUng~csare essential to mamWning nigh perl"()tIlWlce.

Although Time-eonsuming and cumbefSOme, ~blishing 1be grid ofmlet and/or outlet N01o.

from which one can inferthe NH:JNO distriburion will be useful. Also important will be

inspeetiQa and ev~onofcam.lyst deactivation (possibly including a third pany) during the:

annual outage.

3. Sllort-Term sea OlnteJ NOx YariabiUty. Actual NOli. outlet data can vaty widely over

~or; periods oftitne. so that an 8-holltrolling average may be as much as 200% above the

3<klayavezage. For units thar: must obsuve So strict: sbort-terIn avezage in addition to a 5-

month or annual NO. "cap11, a "target'" should be determined to assure compliance.

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Jun-04-02 02:46pm From-AKIN &GUMP WASH 02

Ma=:l 31 (J~ U~: .I. up -,,-••-----. + T-S40 P,22/22 F-S48

4. DataBbforian. A"d= bisrorian" activitywillbebeneficial to the owner/opentor 1:0 uack

and document key opetating ~tBrs, iDcludiug coal supply. aJJd evtUuation oftrends

betWeeij proceslS operation and coal cbaraeteristics.

5. CaJalyst ManagcmJcut Opdou. Catalystm~toptions are numerous, panieularly

across a llMty operating system.wbcmeata1ysr canbe intcrclumgt:ld be&wemunits. The

abiliTY ~o regenetam cawystshould. be evaluated by degr~ ofactivity restoration versus

C~ ami the Det sa.vings ava.ilable within an entire: system. Openltol'S should consider an

i;Qdependent assessment ofsystemwide ~atalYSt m=gement, inclUding competing

regatetation options, in. addition to new eatalysfpUtCbase.

6. l&C Improvements. VarioliS improvements to I&C systems shoUld be considered, that are

logical exte:usions to lever4ge the inv~ in Sell TO extract addiliomU N0l> tons. Such

sysl'eU1.~ may not be optional bu~ necessi1ies. ifadditiotml compl=dtY introduced by

aqueous/mea. rea.genl systems tndlK-"\: LiuJg l~Ci into j&C G~.

TheSe actions may not necessarily be ap~v~Pu.t comprise a4ditional duties 'in a ccmpl:titive

matlretplace that are essential to presexve plantreliability.

REFERENCES

l. H. Zinder & Associates,.Evaluarton DfThe CosrOfSale COllrrol Strategies In The SIP-Call.

fmal reportpreplU'Cd forfbe MidweitOzone Group, October 16,2000.

2. NWibayashi. Y. Research andDqyelopmen'f on NO" .Removal in Japan andRaul1s oj

ERIX:s.Research andDevelop11lf4nt ~fdw J)eNO~ PrOCf!SS; ~edings ofthe Second NO"

Control Technolagy Seminar. EPRl Sp~ia1 RepOll, EPRIFP-II09-SR, July 1979.

3. 0.>Applicarion OJDeNO~ Tec1mol()g;esIn The FederalRepublic ()fG~a"J'.AmI

Europe. Proceedings OrThe 1$ISS SymposiumOn Sumomuy Combustion NO);. Control.

Volume 1. Utility Boiler Applications. EPlU CSa4360, Volume l~ JamlatY 1986.

4. Engelmeyer, T., Orlando fJlili'lies'Experience with SCR AtSramon Unir 2, EPRl seR

Workshop. March 22-24. 1999, Or1ando~ FL

5. Cichanowicz. J.E., An Asse.rsmem ofEuropean Experience With Selective C{ltalytic

Reducfion.In Gtrrmany andDenmqrk. Proccedinp ofthe BPRJ..OOE-EPAAir Pollution

Control Symposium- The Mega. Sy.m:po~ Vohmle 2. A1Jgust. 1999, Atlanta, GA.

6. Uitalysl TecJ:nolagy in MHJ; Pt~ DftheMiw1:Jishi SCR. Symposim '87, October 22.

1987. Weisbadeu. FRG.

7. aondutan~ Louis P. :ur. SCR CompQrtbililyfor lireLjungsrrom AtrPremu:m:r; p!'Qcccd.ings of

the EPRl-DOE-EPA Air PollutionControl Sympoliium-The Mega Symposium, Volume 2,

August, 1999, Atlanm, GA.

8. Gutberlet, H., S02 Convc:rston R418 ofDeNO~ Caralysrs- EffeclS OnDownstream P1Qm

Components AndRemedial Measures, Praceedmss ofthe EPlU-DOB-EPA Alr Pollution

Control Symposium - Tbe Mep Symposium;, Volume 2, Au$USt. 1999, Atlan~ GA.

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