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(#(# '* 0  b.0(#(#Temperature: TheNOxreductionreactioniseffectiveonlywithinagiventemperaturerange.The  optimumtemperaturerangedependsonthetypeofcatalystusedandthefluegascomposition.Optimumtemperaturesvaryfrom480 Fto800 F(250 Cto427 C)(_ICAC_,1997).TypicalSCRsystemstoleratetemperaturefluctuationsof200F(90C)(EPA,2002). (#(# b s(88b 0  c. 0(#(#PollutantLoading: SCRcanachievehighreductionefficiencies(>70%)onNOxconcentrations " aslowas20partspermillion(_ppm_).HigherNOxlevelsresultinincreasedperformance;however,above150_ppm_,thereactionratedoesnotincreasesignificantly(_Environex_,2000).Highlevelsofsulfurandparticulatematter(PM)inthewastegasstreamwillincreasethecostofSCR. (#(#  0  d.0(#(#OtherConsiderations: Ammoniaslipreferstoemissionsof_unreacted_Ԁammoniathatresultfrom '$ incompletereactionoftheNOxandthereagent.Ammoniaslipmaycause:1)formationofammoniumsulfates,whichcanplugorcorrodedownstreamcomponents,and2)ammoniaabsorptionintoflyash,whichmayaffectdisposalorreuseoftheash.IntheU.S.,permittedammoniasliplevelsaretypically2to10_ppm_.Ammoniaslipatthislevelsdonotresultinplumeformationorhumanhealthhazards.Processoptimizationafterinstallationcanlowersliplevels. (#(#         (  0  0(#(#WastegasstreamswithhighlevelsofPMmayrequireasootblower.SootblowersareinstalledintheSCRreactortoreducedepositionofparticulateontothecatalyst.Italsoreducesfoulingofdownstreamequipmentbyammoniumsulfates. (#(#  D/6%. 0 0X X 0  0  0(#(#Thepressureofthewastegasdecreasessignificantlyasitflowsacrossthecatalyst.ApplicationofSCRgenerallyrequiresinstallationaneworupgradedinduceddraftfantorecoverpressure. (#(#  EmissionStreamPretreatmentRequirements: Thefluegasmayrequireheatingtoraisethetemperature )y totheoptimumrangeforthereductionreaction.SulfurandPMmayberemovedfromthewastegasstreamtoreducecatalystdeactivationandfoulingofdownstreamequipment. CostInformation:  y  3@`@`CapitalcostsaresignificantlyhigherthanothertypesofNOxcontrolsduetothelargevolumeofcatalystthat # s  isrequired.Thecostofcatalystisapproximately10,000$/_m3_(283$/ft3).A350MMBtu/hrnaturalgasfired  F  boileroperatingat85%capacityrequiresapproximately#@`3@`c#3@`@`17_m3_#@`,3@`#3@`,@`(#@`3@`#3@`@`Ԁ600ft3#@`,3@`#3@`,@`Ԛ).Forthesamesizedcoalfiredboiler,    therequiredcatalystisontheorderof#@`3@`#3@`@`42_m3_#@`,3@`#3@`,@`(#@`3@`,#3@`@`1,500ft3#@`,3@`s#3@`,@`).(_NESCAUM_Ԁ2000).#@`3@`#Ԛ   SCRisaproprietarytechnologyanddesignsonlargecombustionunitsaresitespecific.RetrofitofSCR B  onanexistingunitcanincreasecostsbyover30%(EPA,2002).Theincreaseincostisprimarilydueto_ductwork_Ԁmodification,thecostofstructuralsteel,andreactorconstruction.Significantdemolitionandrelocationofequipmentmayberequiredtoprovidespaceforthereactor.TheO&McostsofusingSCRaredrivenbythereagentusage,catalystreplacement,andincreasedelectrical a powerusage.SCRapplicationsonlargeunits(>100MMBtu/hr)generallyrequire20,000to100,000gallons 4 ofreagentperweek(EPA,2002).Thecatalystoperatinglifeisontheorderof25,000hoursforcoalfiredunitsand40,000hoursforoilandgasfiredunits(EPA,2002).Acatalystmanagementplancanbedevelopedsothatonlyafractionofthetotalcatalystinventory,ratherthantheentirevolume,isreplacedatanyonetime.Thisdistributesthecatalystreplacementanddisposalcostsmoreevenlyoverthelifetimeofthesystem.O&McostsaregreatlyimpactedbythecapacityfactoroftheunitandannualversusseasonalcontrolofNOX. &v   O&McostandthecostpertonofpollutantremovedisgreatlyimpactedbythecapacityfactorandwhetherSCRisutilizedseasonallyoryearround.s  Table1a:SummaryofCostInformationin$/MMBtu/hr(1999Dollars)a,b s  s  s  s  s  s  s  s  s  s  s  h  +{z        (   2    <    F    P   z{*ddd Xdd Xdd X(#(#,,,,,r+  :YY)  "  :  UnitType MY@2!$YY M"  CapitalCost <Y/! %"Y <,#  O&MCostd <Y/! &"Y <#  AnnualCostd <Y/! '"Y <#  CostperTonofPollutantRemoved \YK,!)"  Y  \ :Y)i")Y :c$  ($/MMBtu) @Y/!u"*"Y @7%($/MMBtu) @Y/!u"+2Y @($/MMBtu) @Y/!u","Y @($/ton) QG,u"-"  Y  QIndustrialCoalBoiler 9/!M#. 910,00015,000 ZP!M#/" r@300r@Z300 |rBM#0" r@300 r@ @1600@|1,600 [QCM#1" @1600 @ [2,0005,000 QG,M#2"    QIndustrialOil,Gas,Woodc 9/!%$u3 94,0006,000 ZP!%$u4"  |@450 |@Z450 {qB%$u5"  |@450  |@ @700@{700 ZPB%$u6" @700 @ Z1,0003,000 QG,%$u7"    QLargeGasTurbine 9/!$M 8 95,0007,500 [Q!$M 9" X@3500X@[3,500 }sC$M :" X@3500 X@ @8500@}8,500 [QC$M ;" @8500 @ [3,0006,000 XYG,$M <"    XSmallGasTurbine @Y/!%%!=Y @17,00035,000 bYQ!%%!>"Y p@1500p@b1,500 YsC%%!?" p@1500 p@Y p@3000p@3,000 bYQC%%!@" p@3000 p@Y b2,00010,000<20%%!A"   Y <  &!A 6    & N     Table1b:SummaryofCostInformation @h in$/MW(1999Dollars)a,b~  ~  *ddrr(#(#,,F,,e,+  2Y% V  2 <Y/!b3Y <CapitalCost <Y/!b"Y <O&MCostd <Y/!b"Y <AnnualCostd <Y/!b"Y <ЀCostperTonofPollutantRemoved XYG,5"  Y  XUnitType @Y/! ] Y @($/MW) @Y/! ] "Y @($/MW) @Y/! ] "Y @($/MW) @Y/! ] "Y @($/ton) QG, ] "  Y  QIndustrialCoalBoiler 9/!5 91,0001,500 YO!5"  >@30>@Y30 zpA5"  >@30 >@ d@160d@z160 ZPB5" d@160 d@ Z2,0005,000 QG,5"    QIndustrialOil,Gas,Woodc 9/!  9400600 YO! "  F@45F@Y45 yoA "  F@45 F@  Q@70Q@y70 YOA "  Q@70 Q@ Y1,0003,000 QG, "    QLargeGasTurbine 9/!  9500750 ZP! " u@350u@Z350 {qB " u@350 u@ @850@{850 ZPB " @850 @ Z3,0006,000 XYG, "    XSmallGasTurbine @Y/!m Y @1,7003,500 aYP!m "Y b@150b@a150 YqBm " b@150 b@Y r@300r@300 aYPBm  " r@300 r@Y a2,00010,000<20m !"   Y <    a(_ICAC_,1997;_NESCAUM_,2000;EPA,2002)  \"   bAssumes85%capacityfactorandannualcontrolofNOx  / #   cSCRinstalledonwoodfiredboilerassumesahotsideelectrostaticprecipitatorforPMremoval  $   dCoalandoilO&Mandannualcostsarebasedon350MMBtuboiler,and  %   gasturbineO&Mandannualcostsarebasedon75MWand5MWturbine'N . TheoryofOperation:  !)   TheSCRprocesschemicallyreducestheNOxmoleculeintomolecularnitrogenandwatervapor.Anitrogenbasedreagentsuchasammoniaorureaisinjectedintothe_ductwork_,downstreamofthecombustionunit.Thewastegasmixeswiththereagentandentersareactormodulecontainingcatalyst.Thehotfluegasandreagentdiffusethroughthecatalyst.ThereagentreactsselectivelywiththeNOxwithinaspecifictemperaturerangeandinthepresenceofthecatalystandoxygen.Temperature,theamountofreducingagent,injectiongriddesignandcatalystactivityarethemainfactorsthatdeterminetheactualremovalefficiency.TheuseofacatalystresultsintwoprimaryadvantagesoftheSCRprocessoverthe_SNCR_:higherNOxcontrolefficiencyandreactionswithinalowerandbroadertemperaturerange.Thebenefitsareaccompaniedbyasignificantincreaseincapitalandoperatingcosts.Thecatalystiscomposedofactivemetalsorceramicswithahighlyporousstructure.Catalystsconfigurationsaregenerallyceramichoneycombandpleatedmetalplate(monolith)designs.Thecatalystcomposition,type,andphysicalpropertiesaffectperformance,reliability,catalystquantityrequired,andcost.TheSCRsystemsupplierandcatalystsuppliergenerallyguaranteethecatalystlifeandperformance.Newercatalystdesignsincreasecatalystactivity,surfaceareaperunitvolume,andthetemperaturerangeforthereductionreaction.b (5h08sbCatalystactivityisameasureoftheNOxreductionreactionrate.Catalystactivityisafunctionofmanyvariablesincludingcatalystcompositionandstructure,diffusionrates,masstransferrates,gastemperature,andgascomposition.Catalystdeactivationiscausedby:^>b b')DTU_`a(\x0b33 '3     '3ZF2\3  0    poisoningofactivesitesbyfluegasconstituents,'3ZFF݌$F ?(#(# Ќ   '3     '3OG2\3  0    thermalsinteringofactivesitesduetohightemperatureswithinreactor,'3OGG݌%,!@(#(# Ќ   '3     '3ZH2\3  0    blinding/plugging/foulingofactivesitesbyammoniasulfursaltsandparticulatematter,and'3ZHH݌&"A(#(# Ќ   '3     '3xI2\3  0    erosionduetohighgasvelocities.'3xII݌'"B(#(# Ќ  33HF  Asthecatalystactivitydecreases,NOxremovaldecreasesandammoniaslipincreases.Whentheammoniaslipreachesthemaximumdesignorpermittedlevel,newcatalystmustbeinstalled.ThereareseveraldifferentlocationsdownstreamofthecombustionunitwhereSCRsystemscanbeinstalled.Mostcoalfiredapplicationslocatethereactordownstreamoftheeconomizerandupstreamoftheairheaterandparticulatecontroldevices(hotside).Thefluegasinthislocationisusuallywithintheoptimumtemperaturewindowfor NOxreductionreactionsusingmetaloxidecatalysts.SCRmaybeappliedafterPMandsulfurremoval -(I 80 8 8  equipment(coldside),however,reheatingofthefluegasmayberequired,whichsignificantlyincreasestheoperationalcosts. SCRisverycosteffectivefornaturalgasfiredunits.LesscatalystisrequiredsincethewastegasstreamhaslowerlevelsofNOx,sulfur,andPM.CombinedcyclenaturalgasturbinesfrequentlyuseSCRtechnologyforNOxreduction.AtypicalcombinedcycleSCRdesignplacesthereactorchamberafterthe_superheater_Ԁwithinacavityoftheheatrecoverysteamgeneratorsystem(_HRSG_).Thefluegastemperatureinthisareaiswithintheoperatingrangeforbasemetaltypecatalysts.SCRcanbeusedseparatelyorincombinationwithotherNOxcombustioncontroltechnologiessuchaslowNOxburners(_LNB_)andnaturalgas_reburn_Ԁ(NGR).SCRcanbedesignedtoprovideNOxreductionsyearroundoronlyduringozoneseason.J Advantages:  g  33 '3     '3Q2\3  0    HigherNOxreductionsthanlowNOxburnersandSelectiveNonCatalyticReduction(_SNCR_)'3QQ݌` (#(# Ќ   '3     '3R2\3  0    ApplicabletosourceswithlowNOxconcentrations'3RS݌F (#(# Ќ   '3     '3S2\3  0    Reactionsoccurwithinalowerandbroadertemperaturerangethan_SNCR_.'3S T݌,(#(# Ќ   '3     '3T2\3  0    Doesnotrequiremodificationstothecombustionunit'3T4U݌(#(# Ќ  33Q Disadvantages:  { 33 '3     '3EV2\3  0    SignificantlyhighercapitalandoperatingcoststhanlowNOxburnersand_SNCR_'3EV|V݌$t(#(# Ќ   '3     '3sW2\3  0    RetrofitofSCRonindustrialboilersisdifficultandcostly'3sWW݌ Z(#(# Ќ   '3   0  '3pX2\3  0(#(#  Largevolumeofreagentandcatalystrequired.'3pXX݌@(#(# Ќ   '3   0  '3fY2\3  0(#(#  Mayrequiredownstreamequipmentcleaning.'3fYY݌&(#(# Ќ   '3   0  '3XZ2\3  0(#(#  Resultsinammoniainthewastegasstreamwhichmayimpactplumevisibility,andresaleor   disposalofash.'3XZZ݌ (#(# Ќ  333V References:  [ EPA,1998.U.S.EnvironmentalProtectionAgency,InnovativeStrategiesandEconomicsGroup, OzoneTransportRulemakingNonElectricityGeneratingUnitCostAnalysis,PreparedbyPechan_Avanti_ԀGroup,ResearchTrianglePark,NC.1998.EPA,1999.USEnvironmentalProtectionAgency,CleanAirTechnologyCenter. TechnicalBulletin:NitrogenOxides(NOx),WhyandHowTheyAreControlled.ResearchTrianglePark,NC.1998.EPA,2002.U.S.EnvironmentalProtectionAgency,OfficeofAirQualityPlanningandStandards.EPAAir $ & PollutionControlCostManualSection4Chapter2.EPA452/B02001.2002. % ' 44O  5  http://www.epa.gov/ttn/catc/dir1/cs4-2ch2.pdf6^O^em.  74p^ o&!( _Gaikwad_,2000._Gaikwad_,_Kurtides_,and_DePriest_. OptimizingSCRReactorDesignforFutureOperatingFlexibility.PresentedattheInstituteofCleanAirCompaniesForum2000.WashingtonD.C._ICAC_,1997.InstituteofCleanAirCompanies,Inc. WhitePaper:SelectiveCatalyticReduction(SCR)ControlofNOxEmissions.Washington,D.C.1997._ICAC_,2000.InstituteofCleanAirCompanies. OptimizingSCRReactorDesignforFutureOperatingFlexibility.Washington,D.C.2000. .)2 _NESCAUM_,2002.NortheastStatesforCoordinatedAirUseManagement. StatusReportsonNOxControlsforGasTurbines,CementKilns,IndustrialBoilers,andInternalCombustionEngines:Technologies&CostEffectiveness.Boston,MA.2002._OTAG_Ԁ1998._OTAG_ԀEmissionsInventoryWorkgroup. _OTAG_ԀTechnicalSupportingDocument:Chapter5.Raleigh,NorthCarolina,USEnvironmentalProtectionAgency.1998.