Reinhold Environmental Ltd.2008 NOx-Combustion RoundTable & Expo PresentationFebruary 4-5, 2008 in Richmond, VACeramicsKen JeffersSCR Catalyst Selection & DesignReinhold EnvironmentalNOxRound table & ExpoWPCA SCR TrainingRichmond, VAFebruary 5, 20082Quick Review of SCR BasicszSCR = Selective Catalytic ReductionzPurpose is to reduce NOx(NO & NO2) fromcombustion exhaustzAmmonia (NH3) is injected into flue gas as reducingagent. Flue gas passes through catalyst layersinstalled in a reactorzNH3reacts with NOxon the catalyst surface to formnitrogen and water vaporCatalystCatalyst4NO + 4NH3+ O24N2+ 6H2O2NO2+ 4NH3+ O23N2+ 6H2OFlue Gas: NOx, O2, SO2N2, H2O, O2, SO2(SO3)NH33CatalystCatalystsurfaceGas phase41235761 External diffusion ofNH3to catalyst surfaceInternal diffusion of NH3into the catalyst poreNH3adsorption on theactive centersNO diffusion from gasphase to adsorbed NH3Reaction of NO and NH3to N2and H2ODesorption from N2andH2O to catalyst surfaceDiffusion of N2and H2Ointo gas phase234567How SCR WorksCatalyst has porous structure = lots of surface area4Heavy DutyVehiclesWood-Fired BoilersGas TurbinesMarineEnginesPower PlantsStationaryEnginesGEN SETSWaste IncinerationPlantsGreenhousesSCR ApplicationsNOxControl5SCR Configuration in Power PlantsHigh DustzSCR upstream of air preheater and ESPzCatalyst with higher pitch requiredESPFGDSCR Reactorwith CatalystAirPreheaterBoilerAirPreheaterHot-Side ESPLow DustzSCR between ESP and air preheaterzCatalyst with lower pitch can be suitableTail EndzMostly in Europe, none in US(?)zSCR at the end after air preheaterzFlue gas reheating requiredFlue Gas Reheat6Geometry Selection: Plate-Type CatalystCompositionzStainless steel carrier, ceramic materialrolled onzTiO2, V-oxide/W-oxide/ Mo-oxide asthe active catalytic materialzVariable plate-spacing: 60 to 100 platesper element boxzVariable plate height: 450 to 700 mmAdvantageszMost suitable for high dust configurationszThermal and mechanical resistancezLow pressure losszLow SO2/SO3conversion rate7Geometry Selection: Honeycomb CatalystCompositionzHomogeneously extruded ceramiczTiO2, V-oxide and W-oxide asthe active catalytic materialzVariable monolith height: 250 mm – 1000 mmz10 to 100 cells per square inch (cpsi)AdvantageszMost suitable for low/no dust applicationszOperating temperature range: 340°F - 800°FzHigh active surface area per unit volume8pitchpitchPitch = center to center distancefrom one plate/wall to the nextGeometry: Structure & PitchPlate-Type StructurezFlexible plateszRectangular OpeningszPitch: 5 mm to 7 mmHoneycomb StructurezRigid structurezSquare openingszPitch: 3 mm to 8 mm9Pitch Selection vs Dust Load4 mm – 5 mm8 mmHoneycomb<5 mm5 mm – 7 mmPlateLow DustHigh DustCatalyst Type45670 10 20 30 40 50Dust Load, g/m3

Pitch, mm10Geometry Selection: Module StructurezCatalyst elements arranged in steel-framemoduleszStandardized cross-sectionzModule height can vary as requiredzPossible to interchange catalyst typeswithin reactorzModules can be customized to customerrequirements11Catalyst Design ApproachzStarting PointzNew SCR reactor vs existing SCR reactorzInitial catalyst charge or reloadzSCR reactor layout - # of layers, # of modules per layerzSCR configuration – high dust / low dustzDesired operating period, 16000/24000 hrszUnderstand performance requirementszDeNOx, amount of NOxto reduce, 70 - 90%zSO2oxidation allowed, <0.5% per catalyst layerzNH3slip allowed, 2 ppm standard (5 ppm for low S fuel)zPressure drop limitations, 0.5 - 1.0” WCzDetermine catalyst activity required at end of operating period (EOL)zSpecify appropriate catalyst to do the job: Volume, element height, pitch12Details of the Design ProcesszηNOx=ƒ{kNOx(EOL), area velocity (AV), NH3/NOxratio (α)}zCalculate maximum AV (gas flowper total active surface area)zSelect pitchÎsets the catalyst specific area, Aspec= area/volumezDetermine required volumezAdjust volume as necessary to fit the applicationzDetermine SO2oxidation rate, pressure dropVolcat=VFGAV*AspecHow to get k13kNOxof Fresh Catalyst, k0zk0depends onzTemperaturezComposition of active, catalytic materialÎV2O5zH2O, O2, flue gas flow ratezk0data and correction factors are obtained from controlled experiments14Catalyst Activity vs Temperature450 500 550 600 650 700 750 800 850Temperature, F

kNOx, m/hHigh V2O5Med V2O5Low V2O5kNOx– Influence of Temperature and V2O5NH3+ O2ÎNOx(Side reaction at higher T)15kNOx– Influence of Water and O20 5 10 15 20 25H2O, Vol %

Catalyst Activity0 5 10 15O2, Vol %

Catalyst Activity16T, V2O5, H2O, O2, flow rateÎk0Catalyst deactivates over timeÎkt?17Masking:Macroscopic blockageof catalyst surfaceby cemented fly ashPlugging:Microsopic blockage ofpore systemby small fly ash particlesPoisoning:Deactivation of activesites by chemical attackCatalyst SurfacePoreSystemSmall Fly Ash ParticlesCatalyst SurfacePoreSystemCemented Fly AshCatalyst SurfacePoreSystemActive SitesCatalyst Deactivation Mechanisms18Catalyst PoisonszAlkali metals – Na, KzAlkaline earth metals – CazArsenic – vapor phase As2O3zPhosphorus – P2O519kNOxDeactivation Model – Relative Activity, kt/k0kt/k0decreases exponentially with timeProportionality constant,λzCharacteristic of SCR configuration,fuel, deactivation mechanisms.zObtained from catalyst activity testing1.0Operating Time, hr

Relative Activitykt/k0λincreasingkt/k0= e-λt0.5016000Lignite firing0.6516000PRB firing0.7016000Bituminous firing0.8516000Low dust configkt/k0time, hrApplication20T, V2O5, H2O, O2, flow rateÎk0k0ÎDeactivation ModelÎkt=EOL21SO2to SO3Oxidation, kSOxzUndesired side reaction in SCR catalyst2SO2+ O22SO3zOccurs in the bulk of catalyst material (in the walls)zkSOxdepends on V2O5and Temperaturez“Blue Plume” is a result of SO3/H2SO4zSO3reacts with NH3to form ammonium bisulfate (ABS) and ammonium sulfate (AS)NH3+ SO3+ H2O NH4HSO4(ABS)NH4HSO4+ NH3(NH4)2SO4(AS)2NH3+ SO3+ H2O (NH4)2SO4(AS)zAS is dry, powdery compound that can pass through SCR catalystzABS is sticky, viscous compound thatcan plug catalyst and corrode downstreamequipment – example: air preheater220 0.2 0.4 0.6 0.8 1.0 1.2 1.4RelativeActivityV2O5content [wt-%]012345012345RelativeOxidation RatekSOxkNOxSO2Oxidation – Influence of V2O523SO2Oxidation – Influence of Temperature500 600 700 800Temperature, F

kSO xV2O5 = 1.2%V2O5 = 0.6%24Minimum Operating Temperature, MOT (Tmin)zMinimum temperature for continuousSCR operationzOf particular concern for low loadoperation and firing fuels containingsulfurzOperating above Tmin prevents AS/ABSformationzTmin depends on SO2/SO3, NH3, H2O influe gaszMust stop NH3when operating belowTminTmin vs SO3inletNOx in 250 ppm, 88% DeNOx, NH3Slip 2 ppm5255505756006250 5 10 15 20 25 30SO3inlet (ppm wet)

Tmin (F)12% H2O10% H2O8% H2O25Catalyst Design is an Iterative ProcessDesign Inputs•DeNOx criteria - % of NOx to remove•Operating period – 16,000/24,000 hr•Flue gas flow conditions•Flow rate•Temperature•Pressure•Composition (NOx inlet, O2,H2O, SO2/SO3)•Allowable NH3slip•Catalyst geometry/compositionConsiderations•Reactor configuration/space,flow distribution•Coal type/specs, ash load•Catalyst deactivation•SO2to SO3oxidation•Allowable pressure dropDesign Outputs•Catalyst volume•Catalyst activity•SO2to SO3oxidation rate•Pressure drop•Design margin (safety factor)26204060801001201400 20000 40000 6000080000 100000 120000Operating Time [h]

Activity Potential k t /k 0 [%]024681012 NH 3 Slip [ppmv]Catalyst Management Plan (CMP)Minimum potential to meet DeNOx, NH3slip requirementsAdd L3Replace L1Replace L2Replace L32+1 layer example: initial load 2 layers, L3 emptyCeramicsKen JeffersThank YouReinhold EnvironmentalNOxRound table & ExpoWPCA SCR TrainingRichmond, VAFebruary 5, 2008