# Ameren Seminar

August 19–20, 2008

Ef fingham, ILCeramicsKen JeffersSCR Catalyst Management2008 WPCA/AmerenESP and SCR SeminarEffingham, ILAugust 20, 20082AgendazSCR Catalyst BasicszBackground on SCR catalyst and design considerationszProvides basis for relevance of Catalyst ManagementzCatalyst ManagementCeramicsSCR Catalyst Basics4Quick Review of SCR BasicszSCR = Selective Catalytic ReductionzPurpose is to reduce NOx(NO & NO2) fromcombustion exhaustzAmmonia (NH3) is injected into flue gas asreducing agent. Flue gas passes throughcatalyst layers installed in a reactorzNH3reacts with NOxon the catalyst surfaceto form nitrogen and water vaporCatalystCatalyst4NO + 4NH3+ O24N2+ 6H2O2NO2+ 4NH3+ O23N2+ 6H2OFlue Gas: NOx, O2, SO2N2, H2O, O2, SO2(SO3)NH35SCR Configuration in Power PlantsHigh DustzSCR upstream of air preheaterand ESPzHigh concentration of fly ash inexhaustzCatalyst with higher pitchrequiredESPFGDSCR Reactorwith CatalystAirPreheaterBoilerAirPreheaterHot-Side ESPLow DustzSCR between ESP and airpreheaterzLow concentration of fly ashzCatalyst with smaller pitch canbe suitable6Catalyst TypesPlateHoneycombCorrugated7Plate-type CatalystCompositionzStainless steel carrier, ceramicmaterial rolled onzTiO2, V-oxide/W-oxide/Mo-oxide asthe active catalytic materialzNotches (corrugations) formed intoplates to provide separationzInserted in element boxes withvariable spacing: 60 to 90 plateszVariable plate height: 450 to 625 mmAdvantageszIdeal for high dust configurationszPlugging resistancezLow pressure loss8Honeycomb CatalystCompositionzHomogeneously extruded ceramic withsquare-opening cell structurezTiO2, V-oxide and W-oxide asthe active catalytic materialzVariable block height: 1200+ mmz8 to 14 cpsi for coal-fired applicationsAdvantageszIdeal for low/no dust applicationszHigh active surface area per unit volume9pitchpitchPitch = center to center distancefrom one plate/wall to the nextCatalyst PitchPlate-Type StructurezFlexible plateszRectangular OpeningszPitch: 5 mm to 7 mmHoneycomb StructurezRigid structurezSquare openingszPitch: 6.7 mm to 9.2 mm10Pitch Selection vs Dust LoadNA6.5 mm>129.2 mm (16 Cell)6.2 mm10 – 126.7 mm (22 Cell)5.0 mm<28.2 mm (18 Cell)6.0 mm6 – 107.4 mm (20 Cell)5.5 mm2 – 6HoneycombPitchPlatePitchDust Loadgr/dscf11Catalyst ModuleszCatalyst elements arranged in steel frameszPlate – 2 levels of 8 element boxeszHoneycomb – 72 monolithszStandardized cross-sectionzPossible to interchange catalyst types withinreactorzModule height varies with catalyst height12Catalyst Design ConsiderationszSCR ReactorzInitial catalyst charge or reloadzReactor size – layers, modules per layerzPlant configuration – high dust / low dustzFlue Gas Operating ConditionszOperating TemperaturezFuel CharacteristicszFly ash concentrationzPerformance RequirementszAmount of NOxto reduce and operating lifezNH3slip allowed, 2 ppm standardzSO2oxidation allowedzPressure drop limit, < 1.0” wc per layer13Required Reactor PotentialzMinimum catalytic potential required to achieve desired DeNOxandNH3slip rates for given operating periodzCatalyst deactivates with time, k0Îkt(time at end of life)zFresh catalyst activity, k0,depends onCatalyst formulationÎV2O5TemperatureFlue gas composition – H2O, O2, SO2zIterative process to determine required AV and kRP =ktAVAV =VfgVolcat*Aspeckt= activity at time t (EOL)AV = area velocity14Masking: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 Mechanisms15Catalyst PoisonszArsenic – vapor phase As2O3zPhosphorus – P2O5zAlkali metals – Na, K16Relative Activity, kt/k0zInitially (t=0), kt/k0= 1.0zkt/k0decreases with time (exponentially decaying model)zCharacteristic of SCR configuration, fuel, deactivationmechanisms.zObtained from catalyst activity monitoringzHave ktÎk0or have k0Îkt0.50 - 0.5516000Lignite firing0.65 - 0.7016000PRB firing0.70 - 0.7516000Bituminous firing0.80 - 0.8516000Low dust configkt/k0time, hrApplication17Effects of Sulfur in FuelzSO2oxidation, undesired side reaction in SCR catalyst2SO2+ O22SO3zRate depends on T and catalyst formulationzOccurs in the bulk mass of catalyst materialSO3/H2SO4aerosols cause the “Blue Plume”zSO3reacts with NH3to form ammonium bisulfate (ABS) and ammoniumsulfate (AS)NH3+ SO3+ H2O NH4HSO4(ABS)NH4HSO4+ NH3(NH4)2SO4(AS)2NH3+ SO3+ H2O (NH4)2SO4(AS)zAS is dry, powdery compoundzABS is sticky, viscous compound that can plug catalyst and foul otherequipment180 0.2 0.4 0.6 0.8 1.0 1.2 1.4RelativeActivityV2O5content [wt-%]012345012345RelativeOxidation RatekSOxkNOxSO2Oxidation – Influence of V2O519Minimum Operating Temperature, (Tmin)zMinimum temperature for NH3injectionzOf particular concern for low loadoperation and firing fuelscontaining sulfurzOperating above TminpreventsAS/ABS formationzTmin depends on SO3, NH3, H2Oin flue gaszMust stop NH3injection whenoperating below TminTmin vs SO3inletNOx in 250 ppm, 88% DeNOx, NH3Slip 2 ppm5255505756006250 5 10 15 20 25 30SO3inlet (ppm wet)

Tmin (F)12% H2O10% H2O8% H2OCeramicsCatalyst Management21Catalyst Management GoalszMaintain target NOxreduction of the SCR systemzControl NH3slip below required limitzReplace activity potential lost to catalyst deactivationzOptimize use of catalyst activity potentialzConform catalyst replacements to plant outage schedulezConform to plant budgetary constraintszMaximize operating life between catalyst replacementszPrevent excessive pressure loss22Catalyst Management Plan (CMP)zSchedule for maintaining SCR catalytic potential for NOxreductionzProcess of adding, replacing, cleaning catalystzTailored to fit unit performance based on activity monitoring23Relative ReactorPotentialOperating Time (h)0 20,000 40,000 60,000 80,000 100,0000.20.420.81.00.6NH3slip(ppm)1CMP, 2 + 1 ExampleMinimum potential forDeNOx, NH3sliprequirements24Activity MonitoringzRoutine catalyst activity testingzOnce per year (typically)zPull samples from each installed catalyst layerzDetermine relative activity compared to fresh catalystzDetermine rate of catalyst deactivationzPredict when reactor potential reaches minimum levelzVerify or adjust CMP schedule25CMP ActionszInstall new catalystzOnsite (in situ) Cleaning – removing fly ash/LPA buildupzVacuumingzAir blowingzShaking/vibrationzWater washingzRejuvenation – onsite or offsite washing/chemical treatmentzRemove ash/particles from catalyst poreszRemove water soluble poisonszRegeneration – offsite chemical treatmentzRemove chemically bonded poisons – As, PzReplace active catalytic material26Pros/Cons for CMP OptionsDone offsite, may need sparecatalystMay increase SO2conversionPerformance guarantees?Lower cost than new catalystCan restore to “new” activityRegeneration(Service Supplier)Does not restore to “new”activity, limited life extensionPerformance guarantees?Lower cost than new catalystCan be done onsiteRejuvenation(Service Supplier)Lowest activity restorationLimited extension of lifeLow(est) cost optionCan be done in situCleaning(by Owner)Highest Cost OptionLongest operating lifePerformance guaranteesNew Catalyst(Catalyst Supplier)ConsProsCMP Action27Considerations for CMP OptionszCMPs are unit-specificzEconomic Trade-offs: New vs RegenzLower cost for Regen, shorter operating lifezHigher cost for New, longer operating lifezSpare catalyst layer on-hand may be required to replace catalystremoved for regenzCatalyst supplier offers performance guarantees for new catalystzDoes regen supplier offer guarantees for Regen’d catalyst?zConsider which options conform best to plant outage schedulezCleaning/rejuvenation may not extend catalyst life to next outagezConsider operation with lower DeNOx, higher NH3slipzConsider impact to plant emission standards28Catalyst MixingzStandardized module structure – catalyst mixing is possible and commonzMultiple catalyst types in reactorzNew and regen’dzMultiple supplierszConsider tooling requirementszLifting, transport tooling for unloading/loadingzSealing systemszPerformance Guarantees from newsupplier (other than initial)zLayer guarantees – geometry, durability, activity, SO2conversion,pressure drop – based on fuel and flue gas characteristicszSystem guarantees – DeNOx, NH3slip, operating life – based on totalreactor potentialÆrequires info about existing catalyst29Required Info for Existing CatalystzGeometryzCatalyst typezVolumezSpecific area, m2/m3zActivity TrendszFresh catalyst, initial activity – k0zRelative/absolute activity after exposure to flue gaszAge of catalyst at time of testingzAbove info used to . . .zCalculate existing reactor potentialzDetermine rate of deactivationzDevelop CMP30Plant Operation ConsiderationszControl Ash buildupzSootblowers/Sonic hornszCleaning/vacuuming during outageszUniform NH3/NOxdistributionzAIG TuningzMaintain NH3injection nozzleszLimit injecting NH3below TminzShort time operation OK (< 8 hr, 100 hr/yr)zPeriod below Tmin must be followed by higher Temp operation (>350 °C for 8hours)zEffects of Operating changes on SCR performancezFuel changeszEconomizer modification31Thank You!Ken JeffersApplication Engineer, SCR Catalystken.jeffers@argillon.com678 341 7523Argillon LLC5895 Shiloh Road, Suite 101Alpharetta, GA 30005www.argillon.com