Wet & Dry ScrubbersWet & Dry ScrubbersPaul FarberPaul FarberSargent & Lundy, LLCSargent & Lundy, LLCChicago, ILChicago, ILDry FGD/DSI TopicsDry FGD/DSI TopicsDRY FGDDRY FGDTechnology VariationsTechnology VariationsTechnology DescriptionTechnology DescriptionReagent Handling and PreparationReagent Handling and PreparationAbsorber SystemAbsorber SystemBaghouse SystemBaghouse SystemWaste Recycle SystemWaste Recycle SystemFlue Gas SystemFlue Gas SystemDry FGD Technology SuppliersDry FGD Technology SuppliersDry FGD/DSI TopicsDry FGD/DSI TopicsDRY SORBENT INJECTION (DSI)DRY SORBENT INJECTION (DSI)DSI vs. Other FGD OptionsDSI vs. Other FGD OptionsTypes ofTypes ofSorbentSorbentTrona vs. SBCTrona vs. SBCCurrent Industry TrendsCurrent Industry TrendsDRY FGDDRY FGDTechnology VariationsTechnology VariationsDry ScrubbersDry ScrubbersSpray Dryer Absorber (SDA)Spray Dryer Absorber (SDA)Rotary AtomizerRotary AtomizerDual-Fluid NozzleFluid NozzleCirculating Dry Scrubber (CDS)Circulating Dry Scrubber (CDS)Fluidized Bed FGDFluidized Bed FGDNIDSDrySorbentSorbentInjection (DSI)Injection (DSI)Dry FGDDry FGD–Rotary AtomizerRotary AtomizerDry FGDDry FGD–Dual Fluid NozzleDual Fluid NozzleDry FGDDry FGD–Circulating DryCirculating DryScrubberScrubberDrySorbentSorbentInjection (DSI)Injection (DSI)Dry FGDDry FGDSpray Dry Flue Gas Desulphurization (FGD)Circulating Dry Scrubber (CDS) or CirculatingFluidized Bed (CFB) ScrubberNIDSA subset of CDSDry Alkali Injection for SO2controlCommonality Between Dry SystemsCommonality Between Dry Systems(SDA and CDS)(SDA and CDS)All Systems Require a Particulate Collection DeviceAll Systems Require a Particulate Collection Devicedownstream of the absorberdownstream of the absorber–preferably a baghouse butpreferably a baghouse butcould use an ESPcould use an ESPBoth use a lime derivativeBoth use a lime derivative–Ca(OH)2as the reagentas the reagentSpray Dryer uses it wet in a slurrySpray Dryer uses it wet in a slurryCDS uses semiCDS uses semi-dry hydrate & adds water separatelydry hydrate & adds water separatelyBoth have limited module sizes:Both have limited module sizes:SDA = 450 MWCDS = 400 MW operating, up to 490MWNID = 75 MW/module, multiple modules compose a systemNID = 75 MW/module, multiple modules compose a systemCommonality Between DryCommonality Between DrySystemsSystemsBecause both systems stay at least 30Because both systems stay at least 30°F above the dewF above the dewpoint, both use carbon steel as the primary material ofpoint, both use carbon steel as the primary material ofconstruction.construction.Because both systems stay at least 30Because both systems stay at least 30°F above the dewF above the dewpoint, the existing chimney can be repoint, the existing chimney can be re-used in a retrofit.used in a retrofit.Both systems recycle large amounts of baghouse catch backBoth systems recycle large amounts of baghouse catch backto the absorber to improve lime usage.to the absorber to improve lime usage.Both produce a sulfiteBoth produce a sulfite-sulfate mixed material that must besulfate mixed material that must belandfilledlandfilled.Can be used in low grade concrete aggregate whenCan be used in low grade concrete aggregate whenmixed with fly ash.mixed with fly ash.Dry FGD ChemistryDry FGD ChemistryCoal Sulfur forms gaseous SOCoal Sulfur forms gaseous SO2& SO3Lime is received as CaO (pebble lime)Lime is received as CaO (pebble lime)(3/4”x 0”for Dry FGD or CDS, 1/8for Dry FGD or CDS, 1/8”x 0”for NID)for NID)Lime is slaked/hydrated as follows:Lime is slaked/hydrated as follows:CaO + HCaO + H2O→Ca(OH)2In the absorber, SOIn the absorber, SO2is captured as:is captured as:Ca(OH)22+ SO22→CaSO33•1⁄2H2O + 1/2 HH2O + 1/2 H2O (70-75%)Ca(OH)22+ SO2+ H22O+1/2O22→CaSO44•2H2O (252H2O (25-30%)In a CDS absorber, COIn a CDS absorber, CO2is captured as:is captured as:Ca(OH)2+ CO2→CaCO3+ H2OStoichiometricStoichiometricRatio often referred to as the Ca/SRatio often referred to as the Ca/SratioActual moles of calcium/theoretical amount of calciumActual moles of calcium/theoretical amount of calciumrequired for the moles of SOrequired for the moles of SO22collectedcollectedFor wet FGD it is expressed as a ratio to the SOFor wet FGD it is expressed as a ratio to the SO2collected.collected.Typical values would be 1.03 to 1.05Typical values would be 1.03 to 1.05Dry system suppliers express their usage on theDry system suppliers express their usage on thebasis of the inlet SObasis of the inlet SO2not the SOnot the SO2collected likecollected likethe wet systems.the wet systems.Typical values would be 1.1 to 1.4 for PRB Coal forTypical values would be 1.1 to 1.4 for PRB Coal for95% Efficiency95% EfficiencyStoichiometricStoichiometricratioSpray Droplet ChemistrySpray Droplet ChemistrySlurry droplet drying time is afunction of the flue gas temperaSlurry droplet drying time is afunction of the flue gas temperatureat the SDA inletat the SDA inletHigher the temperature, lower the residence time to dry theHigher the temperature, lower the residence time to dry thedropletdropletTypically 1Typically 1-4 seconds is needed to dry the largest droplet4 seconds is needed to dry the largest dropletDrying time is also a function of chlorides and recycle amountDrying time is also a function of chlorides and recycle amountHigher the CaClHigher the CaCl2, higher the residence time needed to dry the, higher the residence time needed to dry theslurry droplet which can increase the amount of SOslurry droplet which can increase the amount of SO2capturecaptureThe lower the amount of fly ash in the recycle, the higher theThe lower the amount of fly ash in the recycle, the higher theresidence time needed to dry a slurry dropletresidence time needed to dry a slurry dropletSpray Dryer AbsorberSpray Dryer AbsorberDual-Fluid Nozzles Versus RotaryFluid Nozzles Versus RotaryAtomization Spray DryersAtomization Spray DryersFootprint Is Smaller For DualFootprint Is Smaller For Dual-Fluid Spray Dryer Than For Rotary AtomizerFluid Spray Dryer Than For Rotary AtomizerSpray DryerSpray DryerRemoval of One DualRemoval of One Dual-Fluid Nozzle (Out of 40) For Maintenance Has LessFluid Nozzle (Out of 40) For Maintenance Has LessOf An Effect On Emissions ThanOne Rotary Atomizer (Out Of 2Of An Effect On Emissions ThanOne Rotary Atomizer (Out Of 2[B&W] or 6 [[B&W] or 6 [Alstom])Spare Atomizer CostsSpare Atomizer Costs–B&W-$675,000 (1 atomizer per vessel)$675,000 (1 atomizer per vessel)Alstom-$250,000 (3 atomizers per vessel)$250,000 (3 atomizers per vessel)SiemensSiemens-$18,000 (20 nozzles per vessel)$18,000 (20 nozzles per vessel)Maintenance TimesMaintenance Times–Dual-fluid Nozzlesfluid Nozzles-~12–15 man-hours/weekhours/weekRotary AtomizersRotary Atomizers-~20–30 man-hours/weekhours/weekDual-Fluid Nozzles VersusFluid Nozzles VersusRotary Atomization Spray DryersRotary Atomization Spray DryersCosts Between DualCosts Between Dual-Fluid & Rotary AtomizerFluid & Rotary AtomizerFGD Systems About EqualFGD Systems About EqualEnergy Consumption Between The TwoEnergy Consumption Between The TwoTechnologies Is About The SameTechnologies Is About The SameMore Rotary Atomizer FGD Systems In ServiceMore Rotary Atomizer FGD Systems In ServiceThan DualThan Dual-Fluid NozzlesFluid NozzlesRotary AtomizerRotary AtomizerFor utility sized systems many atomizersare mechanical, rotary atomizersSlurry is fed into a disc nozzle rotating at ahigh rate of speedThis spins fine droplets of slurry out into thegas stream –where they dry and arecaptured in the baghouseTypical Rotary AtomizerTypical Rotary Atomizer(1-3 Per Spray Dryer)3 Per Spray Dryer)MotorFlexShaftGearboxAtomizerWheelDual Fluid NozzleDual Fluid NozzleCertain Manufacturers use dual fluidCertain Manufacturers use dual fluidnozzles as an alternative to the Rotarynozzles as an alternative to the RotaryAtomizer in SDAAtomizer in SDAIn the dual fluid nozzle lime slurry isIn the dual fluid nozzle lime slurry isatomized by a high pressure secondatomized by a high pressure secondfluid–predominantly compressed airpredominantly compressed airto produce the fine spray neededto produce the fine spray neededDual fluid nozzles do not have high speedDual fluid nozzles do not have high speedrotating parts like the Rotary atomizerrotating parts like the Rotary atomizer16-20 per absorber20 per absorberTypical Dual Fluid NozzleTypical Dual Fluid Nozzle(16-20 Per Spray Dryer)20 Per Spray Dryer)SLURRY FEEDATOMIZING AIRAIR RESERVOIRINSERTSSDA ROOFSLURRYATOMIZINGAIRSHROUDAIRPENTHOUSE FLOORPERFORATED PLATEGAS DISTRIBUTION316 SSNOZZLE SHROUDEGG CRATEGAS STRAIGHTENERSO2Absorption Continues inAbsorption Continues inBaghouseBaghouseSO3HFHClSO2Baghouse contributes 10 to 20% of the total SO2removal –design SDA and FF as a system“Clean Gas”Bag FabricDust CakeDry FGDDry FGDSubsystemsSubsystemsReagent Handling and PreparationReagent Handling and PreparationAbsorber SystemAbsorber SystemBaghouse SystemBaghouse SystemWaste Recycle and Storage SystemWaste Recycle and Storage SystemFlue Gas SystemFlue Gas SystemReagent Handlingand PreparationReagent Handling and PreparationReagent Handling and PreparationSystemLime Handling and StorageLime Handling and StoragePneumatic Conveying to long term silosPneumatic Conveying to long term silos30 days capacity factor storage30 days capacity factor storagePneumatic conveying to Preparation systemPneumatic conveying to Preparation systemLime Slurry Preparation systemLime Slurry Preparation system24 hours day bin24 hours day bin2 x 100% slakers2 x 100% slakers20% slurry20% slurry8-16 hours slurry storage16 hours slurry storageslurry piping (loop to absorbers)slurry piping (loop to absorbers)Lime Handling and StorageLime Handling and StorageLime Unloading SystemLime Unloading SystemLime Slaking/HydrationLime Slaking/HydrationProcessProcess:Exothermic Hydration ProcessExothermic Hydration ProcessOperating TemperatureOperating TemperatureQuality of LimeQuality of LimeMgO, CaCOMgO, CaCO3,“Grits”Quality of Water (SOQuality of Water (SO44=, SO3=)CaO + HCaO + H2O→Ca(OH)2Ball Mill SlakersBall Mill Slakers•Conventional BallMill Slaker•Rotating cylinder•Steel balls createthe grinding action•Ball mills grind thegritBall Mill SlakerBall Mill SlakerVertiMill SlakersVertiMill Slakers•Steel balls createSteel balls createthe grinding actionthe grinding action•Finer Particle SizeFiner Particle Size•Less Power Than aLess Power Than aBall Mill SlakerBall Mill SlakerVertimillVertimillSlakerDetention SlakersDetention Slakers•Violent AgitationViolent Agitation–No steelNo steelballs•Opposed Pumping TurbinesOpposed Pumping Turbines•Particle to Particle Contact =Particle to Particle Contact =AttritionAttrition•Grit is removed by screensGrit is removed by screensthat follow the slakers. Alsothat follow the slakers. Alsoincluded in recycle trainsincluded in recycle trainsDetention Slakers Require GritDetention Slakers Require GritRemovalRemovalCDS Systems Use HydratorsCDS Systems Use HydratorsInstead of SlakersInstead of Slakers•Same chemical reaction in aSame chemical reaction in ahydrator as a slakerhydrator as a slaker–CaO + HCaO + H22O→Ca(OH)2•500 Btu500 Btu’s of heat released pers of heat released perpound of lime slakedpound of lime slaked(278 kcal/kg)(278 kcal/kg)•Only enough water used toOnly enough water used tohydrate the limehydrate the lime••More difficult to operate than aMore difficult to operate than aslakerAbsorber SystemAbsorber System––Minimum 10 SecondMinimum 10 SecondResidence timeResidence time–Carbon SteelCarbon Steel–AtomizersAtomizers––Slurry mix tankSlurry mix tankSpray DryerSpray Dryer•Spray Dryer introduces a lime slurry into the hot flue gasSpray Dryer introduces a lime slurry into the hot flue gasby means of an atomizerby means of an atomizer–For utility sized systems atomizers are either rotaryFor utility sized systems atomizers are either rotaryatomizers, or dualatomizers, or dual-fluid nozzlesfluid nozzles–With a Rotary Atomizer the slurry is fed into a discWith a Rotary Atomizer the slurry is fed into a discrotating at a high rate of speed (~10,000 RPM).rotating at a high rate of speed (~10,000 RPM).–With a DualWith a Dual-fluid Nozzle compressed air mixes with thefluid Nozzle compressed air mixes with theslurry at the nozzle tipslurry at the nozzle tip•Droplets are dispersed into the flue gas stream, reactsDroplets are dispersed into the flue gas stream, reactswith the SOwith the SO2, and are dried into fine powder, and are dried into fine powderSpray Dry AbsorberSpray Dry AbsorberHot flue gases are often split to aidHot flue gases are often split to aidin drying the slurryin drying the slurrySpray dryers are generally limitedSpray dryers are generally limitedto low to medium sulfur fuels byto low to medium sulfur fuels bythe amount of water in slurrythe amount of water in slurryExit temperatures must stay aboveExit temperatures must stay abovethe adiabatic saturationthe adiabatic saturationtemperature to ensure completetemperature to ensure completedrying of dropletsdrying of dropletsTemperature above saturationTemperature above saturationdefined asdefined as“Approach to SaturationApproach to Saturation”B&WB&WRotary AtomizerRotary Atomizer•Rotary Atomizer showsRotary Atomizer showsdispersion of slurry from diskdispersion of slurry from disk•Atomizers are supplied withAtomizers are supplied withquick disconnectsquick disconnects––as theyas theyare changed while the Unit isare changed while the Unit ison-line–B&W design uses oneB&W design uses oneatomizer in an SDAatomizer in an SDAvessel––Alstomdesign usedesign useseveral atomizers in aseveral atomizers in asingle vesselsingle vesselDual Fluid AtomizerDual Fluid Atomizer•Dual Fluid Atomizer showsDual Fluid Atomizer showsdispersion of slurry from nozzledispersion of slurry from nozzle•Atomizers are supplied withAtomizers are supplied withquick disconnects to permit onquick disconnects to permit on--line maintenanceline maintenance•Siemens design uses 15Siemens design uses 15–20dual fluid nozzles in a singledual fluid nozzles in a singlevesselDual Fluid AtomizerDual Fluid AtomizerSLURRY FEEDATOMIZING AIRAIR RESERVOIRINSERTSSDA ROOFSLURRYATOMIZINGAIRSHROUDAIRPENTHOUSE FLOORPERFORATED PLATEGAS DISTRIBUTION316 SSNOZZLE SHROUDEGG CRATEGAS STRAIGHTENER16-20 per absorberFABRIC FILTERSFABRIC FILTERSPrinciples of OperationPrinciples of OperationParticulate Laden Gas Passes Through A Woven OrParticulate Laden Gas Passes Through A Woven OrFelted FabricFelted FabricForces Of Impaction, Interception, And DiffusionForces Of Impaction, Interception, And DiffusionSeparate The Particles From The Gas StreamSeparate The Particles From The Gas StreamAs The Process Proceeds Particles Will Impinge UponAs The Process Proceeds Particles Will Impinge UponPreviously Collected ParticlesPreviously Collected ParticlesThe Built Up Deposit May Itself Become The CollectionThe Built Up Deposit May Itself Become The CollectionMediumDust Is Removed From The MediaDust Is Removed From The MediaWith an SDA or CDS System the Fabric Filter CanWith an SDA or CDS System the Fabric Filter CanAccount for Up to 20% of the SOAccount for Up to 20% of the SO2removedremovedWaste Recycle SystemWaste Recycle SystemWaste Recycle SystemWaste Recycle SystemWaste Recycle SystemTo increase lime utilizationTo increase lime utilizationRecycle ash day bin (8 hours)Recycle ash day bin (8 hours)Distance between recycle slurrytanks and atomizers should be keDistance between recycle slurrytanks and atomizers should be keptshortCurrent trend is to minimize retention time in recycle tanksCurrent trend is to minimize retention time in recycle tanksWaste Storage SiloWaste Storage SiloSize based on amount of waste to disposalSize based on amount of waste to disposalWaste Storage SiloWaste Storage SiloWaste Recycle SystemWaste Recycle SystemTo increase lime utilizationTo increase lime utilization4-8 hours storage silo8 hours storage siloslurry mix tankslurry mix tank2 x 4 hours slurry storage tank2 x 4 hours slurry storage tankDeposits in the bottom of tankDeposits in the bottom of tank>35% solid>35% solid3-4 day waste storage4 day waste storageFlue Gas SystemFlue Gas SystemInlet/outlet ductworkInlet/outlet ductworkCarbon SteelCarbon SteelKeep Distance short between Absorber Outlet andKeep Distance short between Absorber Outlet andBaghouse InletBaghouse InletMinimize turns and direction changesMinimize turns and direction changesChimneyChimneyTop 20’wall papered with stainless steel (acid resistantwall papered with stainless steel (acid resistantcoating is the lower cost option) requiring morecoating is the lower cost option) requiring moremaintenancemaintenanceTypically low load velocities/possibility of cold air infiltratiTypically low load velocities/possibility of cold air infiltrationCirculating Dry Scrubbers (CDS) orCirculating Fluidized Bed (CFB)Circulating Dry Scrubber SystemCirculating Dry Scrubber SystemThe separate addition of water allows the CDSThe separate addition of water allows the CDSsystem to operate on somewhat higher sulfursystem to operate on somewhat higher sulfurfuels than the spray dryer technologyfuels than the spray dryer technologyCDS system is simpler in components and conceptCDS system is simpler in components and conceptthan the Spray Dryerthan the Spray DryerBoth technologies recycle large amounts of solidsBoth technologies recycle large amounts of solidsto help control lime consumptionto help control lime consumptionHigh efficiencies similar to a wet FGD are possibleHigh efficiencies similar to a wet FGD are possibleLow levels of emissions have been guaranteed inLow levels of emissions have been guaranteed inthe pastthe pastLowest guaranteed emissionLowest guaranteed emission–0.040 lb/mmBtu0.040 lb/mmBtuCirculating Dry ScrubberCirculating Dry ScrubberVery High Recirculation ofBaghouse Solids Results inHigh Utilization of LimeInternal SolidsRecirculationEnhancesReactionsCirculating Dry Scrubber SystemCirculating Dry Scrubber SystemThe absorber is a fluidized bed of solids suspended byThe absorber is a fluidized bed of solids suspended byflue gasflue gasAt low loads clean gas isAt low loads clean gas isrecirculatedrecirculatedto maintainto maintainsolids suspensionsolids suspensionAs opposed to the spray tower design CDS adds dryAs opposed to the spray tower design CDS adds dryhydrate to the absorberhydrate to the absorberWater is sprayed in separately in the fluidized bed toWater is sprayed in separately in the fluidized bed toaid in collectionaid in collectionDry FGD Technology SuppliersDry FGD Technology SuppliersSemi-dry FGDdry FGDAlstomBabcock & WilcoxBabcock & WilcoxSiemens EnvironmentalSiemens EnvironmentalCirculating Dry ScrubberCirculating Dry ScrubberAlstomBabcock & WilcoxBabcock & WilcoxFoster Wheeler (GraffFoster Wheeler (GraffWulff)Allied TechnologyAllied TechnologyBabcock PowerBabcock PowerHitachiHitachiMarsulexMarsulexDSI Technology SuppliersDSI Technology SuppliersADA-ESBabcock & WilcoxBabcock & WilcoxClydeBergemannBergemannF LSmidthFuelTechFuelTechNalco-MobotecMobotecNol-TechSchickUCCWhen Compared to other FGD TechnologiesWhen Compared to other FGD TechnologiesLower Capital CostsLower Capital CostsHigher Operating Costs for ReagentHigher Operating Costs for ReagentSmaller FootprintSmaller FootprintEase of Installation (Installed in Existing Ducts)Ease of Installation (Installed in Existing Ducts)Only Moderate SOOnly Moderate SO2Reduction (50% to 80% SOReduction (50% to 80% SO2Removal)Removal)SO2Control – DSICalcium vs. SodiumCalcium vs. SodiumCalciumCalcium(Limestone or Lime)(Limestone or Lime)Sodium(Trona or Sodium(Trona or SodiumBicarbonate (SBC)Bicarbonate (SBC)1800°F to 2200F to 2200°F OptimumF Optimumfor Furnace Injectionfor Furnace Injection600°F to 800F to 800°F OptimumF Optimumfor Tronafor Trona250°F to 350F to 350°F OptimumF Optimumfor SBCfor SBCLime Could also be InjectedLime Could also be InjectedAfter EconomizerAfter EconomizerDry InjectionDry InjectionSome Reduced ESPSome Reduced ESPPerformancePerformanceImproved ESP PerformanceImproved ESP PerformanceLimited to ~50% SOLimited to ~50% SO2RemovalRemovalUp to ~80% RemovalUp to ~80% RemovalSO2Control – DSISorbentSorbentTronaSBCCapture DeviceESPBGHESPBGHNSR2.61.151.20.75SorbentSorbentIncrease by wt.Increase by wt.3.11.41.61.0Source: Solvay ChemicalsTronaSBCExample NSR at 60% Removal (Refer to Graphs Above)SO2Control – DSIQuestions?Questions?