Selective Catalytic/NonSelective Catalytic/Non-CatalyticCatalyticReductionReductionConferenceConferenceSCR Operation Optimization:SO3Removal to Optimize Catalyst Life & NH3Distribution in WastewaterSCR Operation Optimization:SCR Operation Optimization:SO3Removal to Optimize Catalyst Life & NHRemoval to Optimize Catalyst Life & NH3Distribution in WastewaterDistribution in WastewaterPresented by:Thomas WrightParsons Energy & ChemicalsChattanooga, TennesseeOctober 30, 20031Agenda!INTRODUCTION!NH3SLIP DISTRIBUTION!SCRíS INCREASED SO3!SO3:NH3MOLAR RATIO!WASTEWATER TREATMENT!ECONOMICS!CONCLUSION2Introduction!Last Yearís PaperñSCR catalyst life"limited NH3slip to ~2 ppm to prevent ammoniumbisulfate (ABS) deposits in air heaterñNH3slip is removed in air heater deposits, on ESP ash & in FGDslurryñNH3issoluble & eventually will end up in a wastewater discharge!Last yearís RecommendationñInstall SO3removal system before air heater, to balance NH3distribution between ESP & FGDñNH3slip sampling for NH3balance, especially air heater wash waterñDetermine critical ABS deposition number (ìRadianî number), byincreasing NH3slip to cause deposits3NH3 SLIP DISTRIBUTION!ABSñABS vapor forms at temperatures >600 FñSO3below 400 F is mostly H2SO4vapor"50% at ~600 F and 90%at 400 FñABS condensate or aerosolforms from 330 F to 360 F F"highertemperatures at higher SO3& NH3concentrationsñABS is aviscous liquid"ìstickyîñTemperature drop required for condensing ABS"such as anairheaterñCondensate or aerosol formation completed at ~320 F"very lowSO3& NH3(< 1 ppm)ñMolar Ratio -SO3:NH3= 4.7 SO3ppmper ppm NH34NH3 SLIP DISTRIBUTION (continued)!Air heaterñRadian developed a thermodynamic & kinetic model forAS & ABSformation in regenerative air heaters (1982)ñRadian Equation for ABS deposition number:!SO3ppmxNH3ppm x[T(IFT)- T(rep)]!Where ìT(rep)î is a combination of air heater gas exit temperature & coldend metal temperatureñPreliminary literature survey showed a ìbreak pointî at 5,000 to7000for the Radian number from minimal ABS deposits to ìincrease inpressure dropî depositsñNH3slip Guidelines"from literature review & typical Molar Ratios!Low sulfur ñ6ppm!Medium sulfur ñ4ppm!High Sulfur ñ2ppm5NH3 SLIP DISTRIBUTION (continued)!Air Heater (continued)ñAcid Dew Point ñhigher ADP from increased SO3may also increaseash deposits in air heaterñLiterature shows that some ABS deposits may decompose incombustion air side of air heaterñWorst case -2ppm slip at end ofcatalyst life & for 12 monthsoperation"up to average ~3,000 ppm NH3in wash water6NH3 SLIP DISTRIBUTION (continued)!ESPñFlue gas conditioning reactionñByproduct Ash ñcan evolve NH3when mixed with cement (high pH)"100ppmNH3in ash is typical limitñWorstcase ñ2ppm NH3slip at end of catalyst life to fly ash!Wet Sluice to Pond"up to ~2 ppm in sluice water!Dry Conveying to LandfillñAsh"up to ~175 ppm(adsorbed on ash)ñLeachate"up to ~150 ppm (fora 1 yearactive cell)!FGDñResidual NH3after air heater & ESP absorbed in FGDñByproduct gypsum (wallboard)"ñWorst Caseñ2ppmNH3slip at end of catalyst life to FGD!Open Loop ñup to ~10 ppm!Closed Loop -up to ~100 ppm7SCRís INCREASED S03!ImpactñSCR ~ doubles boiler SO3"up to 50+ ppm for high sulfur coalñVisible plume"at> 15 to 20 ppm SO3ñAcid Dew point (ADP) corrosion"ADP ~300 F for high sulfur coal!Removal EconomicsñVery few SO3removal systems"limited cost & operationalexperience ñsee Gavin papersñBoiler injection only removes boiler SO3ñnotSCRSO3ñAssume hydrated lime system after SCR!Process Design ñlimestoichiometry~3!Capital -~$10 per KW"~ $0.15 per MWH!O&M ñlime at $100 per ton"~ $0.15 per MWH!Total"~ $0.3 per MWH8SO3:NH3 MOLAR RATIO!SO3ñBoiler + SCR SO3ñHigh (3.0%)"25 + 25 = 50 ppmñMedium (1.7%)"14 +14 = 28 ppmñLow (<1%)"6 + 6= 12 ppm!SO3:NH3 Molar RatiosñFor typical ìend-of-lifeî catalyst"2 ppm NH3ñ1 molar SO3:NH3 = 4.7 NH3 ppmperppmSO3ñABS formation impacted by Molar Ratio"higher driving forceresults in lower temperature drop.For 95% formation completion:!At 1.0 MR"~75 F!At 0.5 & 2.0 MR"~45 F!At 5.0 MR"~40 F9SO3:NH3 MOLAR RATIO (continued)!CasesñWithout SO3removal & 2 ppm NH3ñWith SO3removal & 2 ppm NH3ñEarly catalyst replacement"1 ppm NH3ñLate catalyst replacement"4 ppm NH3!ABS Deposition Number (ìRadianî Number)ñABS deposits (measurable pressure drop) in air heater start around aìRadianî number of ~5,000 to 7,00010SO3:NH3 MOLAR RATIO (continued)W/O SO3RemovalWITH SO3RemovalEARLYCatalystLATECatalystNH3End of CatalystLife2 214SO3High Sulfur505 to 105050MolarRatioSO3: NH3~51 to 2~10~2.5ABSDeposit #(add washes)~6500(1)~1200(0)~3200(0)~13,000(2)Air HeaterNH3Removal~30%~10%~40%~20%Wash WaterNH3ppm~750~500~1100~40011SO3:NH3 MOLAR RATIO (continued)W/ SO3RemovalW/O SO3RemovalEARLYCatalystLATECatalystESPNH3Removal~70%~70%~60%~70%Sluice WaterppmUp to 1.2Up to 1.2Up to 1.0Up to 1.2Dry Ash ppmUp to 120Up to 120Up to 100Up to 120FGDNH3Removal0~20%0~10%Open Loopppm0Up to 20Up to 1Closed Loopppm0Up to 200Up to 1012SO3:NH3 MOLAR RATIO (continued)!Medium Sulfur CoalñLess removal in air heater"lower MRñOnly Early Catalyst has no FGD wastewater treatmentñOnly Late Catalyst hasadditional air heater washes!Low Sulfur CoalñSame removal in air heater & ESP ñ10% & 70%, respectivelyñAll cases need WWT for FGD to maintain byproduct sales13WASTEWATER TREATMENT!Conventional OptionsñMechanical"result in a NH3off-gas or a concentrated-NH3 liquidñBiological"ñABS deposits result in justa different waste for further treatment!Quantity (gpm/MW)ñAir Heater Wash Water<0.5ñAsh LandfillLeachate<0.5ñFGDBlowdown(closed loop)NA (only entrained liquid)ñFGD Blowdown (open loop)~2ñAsh Sluice(~0.5% slurry)~14ñNPDES~2014WASTEWATER TREATMENT (continued)!Comprehensive TreatmentñByproduct recovery from wastewaterñIncrease wastewater pH, strip NH3& absorb NH3in concentratedsulfuric acid"an ABS byproduct fertilizer(liquid)!EconomicsñAir Heater"$2 per KW & $0.04 per MWHñAsh Landfill Leachate"$2 per KW & $0.04 per MWHñFGD Blowdown (open loop)"$5 per KW & $0.08 per MWHñAsh Sluice"$18 per KW & $0.25 per MWHñNPDES"$22 per KW & $0.35 per MWH15ECONOMICS!Catalyst LifeñCatalyst =~10% of SCR cost"~$10 per KWñFor 20,000 hours (2 ppmNH3)"~$0.17 per MWH (base)ñEarly (1 ppmNH3) at 15,000 hours"+$0.05 per MWHñLate (3 to 4 ppm NH3) at25,000 hours"-$0.04 per MWH!Byproduct SalesñFor every $10 per ton for disposal, loss of byproduct sales(from ahigh sulfur coal) due to NH3 contamination"cost is ~$0.35 & $0.65for fly ash & gypsum!Air Heater WashingñWashing Crew (for high pressure washing)"~$0.05 per MWHñ50% Loss ofLoad for 3 days"~$0.05 per MWHñTotal cost per additional washing"~$0.1 per MWH (annualized)16ECONOMICS (continued)W/O SO3REMOVALWITH SO3REMOVALW/O SO3REMOVALW/O SO3REMOVALCATALYSTREPLACEMENTBASEBASEEARLY LATESO3REMOVAL00.300WWT ñASHLEACHATEWWT ñAIRHEATER0.040.040.040.04WWT ñFGD(open loop)00.0800.0817ECONOMICS (continued)W/O SO3REMOVALWITH SO3REMOVALW/O SO3REMOVALWITH SO3REMOVALCATALYSTREPLACEMENT00+0.05(0.04)AIR HEATERWASHING0.1000.2BYPRODUCTSASH0000BYRPODUCTSFGD0000TOTAL0.140.420.090.2818Conclusions!Wastewater TreatmentñAll SCR mayrequire wastewatertreatment for the air heater washwater!SO3RemovalñFor high sulfur coal, the cost ofadditional air heater washings&wastewater treatment is significantly less than the cost of SO3removal!Catalyst LifeñEarly catalyst replacement cost ~ air heater WWT costñEarlier catalyst replacement eliminates the need for SO3removal(high sulfur coal)19Recommendations!SO3measurementsñBefore and during SCR operation ñdetermine where SO3is formedand removedñDuring SCR operation ñdeterminewhether percent removal or ppmremoved is constant with increased SO3!NH3measurementsñWash air heater after first ozone season and collect wash watersamples to estimate NH3in air heater. Monitor NH3slip (at SCRoutlet) andNH3in fly ash"determines NH3slip distributionñAfter first ozone season, increase NOxremoval to increase NH3slip ñto point where deposits are formed in air heater to determineplant specific Radian number