Wet FGD System Overview and Operation

1 Wet FGD SystemOverview and OperationRay GansleyWPCA Wet FGD SeminarPower Gen InternationalDecember 1, 2008 Agenda Introduction Major Process Equipment Balance of Plant Equipment Controls SummaryWPCA Wet FGD Seminar - December 1, 2008 MAKE-UP WATER TANKCHLORIDE PURGEHYDROCLONEBELT FILTERSPRAY TOWER ABSORBERELECTROSTATIC PRECIPITATORSTACKWATERAIRLIMESTONEBALL MILLTO BALL MILLFROM MW TANKGYPSUMREAGENT PREPARATIONABSORBERDEWATERINGP rocess Flow DiagramWPCA Wet FGD Seminar - December 1, 2008 Agenda Introduction Major Process Equipment Balance of Plant Equipment Controls SummaryWPCA Wet FGD Seminar - December 1, 2008 Absorber IslandAbsorberOxidation CompressorsSpray PumpsSwitchgearWPCA Wet FGD Seminar - December 1, 2008 Jet Bubbling ReactorTray TowerFountain TowerOpen Spray TowerAbsorber DesignsWPCA Wet FGD Seminar - December 1, 2008 Absorber Unit OperationsUnit operations Inlet gas distribution, humidification Spray zone gas/liquid contact Mist eliminator zone liquid/gas separation Reaction tank oxidation, dissolution, crystallizationDesign Goals Lowest lifecycle cost Capital O&M High reliabilityWPCA Wet FGD Seminar - December 1.

2 2008 Absorber Inlet Highly corrosive environment SO3condensation Deposits/splash-back Design/construction Solid 3/16 thick C-276 10 slope toward absorber Extends 10-15 ft. from shell Internal overhead deflector and side shields Test ports and emergency quench nozzles Gas velocity 3,000-3,600 ft/minWPCA Wet FGD Seminar - December 1, 2008 Absorber ShellStraight-SideFlared-SideWPCA Wet FGD Seminar - December 1, 2008 Multiple spray levels with dedicated pumps allows efficient turndown Gas velocity 13-14 ft/secContact Zone Spray flow Typical afternoon thunderstorm 1-2 in/hr Spray tower 10 ft/minWPCA Wet FGD Seminar - December 1, 2008 Design Approach Intimate gas/liquid contact No gas sneakage Multiple spray stages depending on SO2inlet and removal efficiency Overall spray coverage (>200% at 3-feet)

3 And nozzle distribution to provide even distribution and prevent gas sneakage. Wall rings to prevent gas sneakage near side walls. Pressure drop vs. pumping power trade-offContact ZoneWPCA Wet FGD Seminar - December 1, 2008 Spray Nozzles Multiple counter-current spray stages Nozzle type Top stage single orifice hollow cone Lower stages dual orifice hollow cone Sauter mean droplet diameter of ~2,000 micron at 8 psig Silicon carbide constructionWPCA Wet FGD Seminar - December 1, 2008 Spray ZoneMist EliminatorMist EliminatorzTwo stages of vertical-flow chevron vaneszConstruction Polypropylene Polysulfone FRP Alloy/stainless steelWPCA Wet FGD Seminar - December 1, 2008 Gas Flow510152025 CarryoverGas Velocity (ft/sec)

4 Mist Eliminator OperationWPCA Wet FGD Seminar - December 1, 2008 Mist Eliminator Wash System Fresh water wash on intermittent basis First stage washed from below ( gpm/ft2) and above ( gpm/ft2) Second stage washed from below ( gpm/ft2) Construction Piping FRP, polypropylene, alloy/SS Nozzles polypropylene, alloy/SS WPCA Wet FGD Seminar - December 1, 2008yTypical size: 50,000-75,000 gpm at 55-85 TDHyPump Efficiency: 87-90+%y1,000-2,500 hpyHorizontal, centrifugalyRubber lined casingyImpeller Hard metal Rubber-coveredAbsorber Recycle PumpsWPCA Wet FGD Seminar - December 1, 2008 Spray Pump Capacity10,00020,00030,00040,00050,00060 ,00070,0001970198019902000 Flow (gpm)WPCA Wet FGD Seminar - December 1, 2008 Recycle Pump CurveWPCA Wet FGD Seminar - December 1, 2008 Integral to absorber Functions Limestone dissolution Oxidation Gypsum crystallization Design considerations Solids and liquid residence time Foaming/freeboard Side entry agitators with air lancesReaction TankWPCA Wet FGD Seminar - December 1, 2008 Materials of ConstructionShellzRubber-lined carbon steelzFlakeglass-lined carbon steelzStainless steel (317 LMN)zDuplex stainless steel (2205, 255)zNickel-based alloyzRoll-clad alloyzLined concrete (tile, polypropylene)

5 External Spray PipingzFRPzRubber-lined carbon steelzSS/alloyMist EliminatorszFRPzPolypropylenezPolysulfon ezSS/alloyHeaderszRubber-lined carbon steelzFRPzStainless steel (317 LMN)zDuplex stainless steel (2205, 255)zNickel-based alloyInletzC-276 WPCA Wet FGD Seminar - December 1, 2008 Reagent Preparation IslandDay BinBall MillFeed TankClassifierWPCA Wet FGD Seminar - December 1, 2008 BALL MILLFROM MW TANKL imestone Grinding SystemWPCA Wet FGD Seminar - December 1, 2008 BALL MILLRECYCLETANKREAGENTFEEDTANKCLASSIFIER REAGENT SILOTOABSORBER Limestone grinding Horizontal/verticalwet ball mills On-site vs. off-sitepreparation Product ground to 90-95% < 44 ; 30% solids Rubber-lined with hardened steel ballsLimestone PreparationWPCA Wet FGD Seminar - December 1, 2008 Pre-Ground Limestone Injection Dry, pre-ground limestone feed options Pneumatic injection into reaction tank below slurry level Pre-slurry in small tank Advantages Low capital cost ( no ball mills, auxiliary equipment, buildings, etc.)

6 Less equipment to maintain Disadvantages Higher delivered cost Lifecycle cost evaluation on case-by-case basisWPCA Wet FGD Seminar - December 1, 2008 Dewatering IslandHydrocloneBelt FilterVacuum PumpWPCA Wet FGD Seminar - December 1, 2008 Primary Dewatering Initial solid/liquid separation step Feed: 15-20% TSS Underflow: 50-55% TSS Overflow: 3-5% TSS Overflow enriched with CaCO3due to particle size difference; improved reagent utilization Steel casing with rubber, urethane, and ceramic internalsWPCA Wet FGD Seminar - December 1, 2008 Secondary Dewatering Horizontal belt filter 8-10% moisture in gypsum Optimal for cake washing Rotary drum filter 10-15% moisture Smaller footprint Other options Gypsum stacking Centrifuge ThickenerWPCA Wet FGD Seminar - December 1, 2008 Typical specification: >95% CaSO4 2H2O < CaSO3 H2O <100 ppm Cl <10% moisture pH 6 8 30 40 MMD Requires.

7 High purity limestone (95 96%) High efficiency ESP/FF 99+% oxidation Belt filter Cake washingWallboard GypsumWPCA Wet FGD Seminar - December 1, 2008 Agenda Introduction Major Process Equipment Balance of Plant Equipment Controls SummaryWPCA Wet FGD Seminar - December 1, 2008 Truck, rail, or barge delivery x 0 (20 x 0 mm) crushed limestone Outdoor long-term storage feasible in most areas Indoor/covered storage in harsh/wet climatesLimestone Delivery/StorageWPCA Wet FGD Seminar - December 1, 2008 Limestone Silo Provide buffer between limestone pile and ball mill Operation 16-24 hr capacity Carbon steel construction with polymer or stainless steel hopper lining Vibrating bottom/mechanicalactivation Vent filter for fugitive dust controlWPCA Wet FGD Seminar - December 1, 2008 Covered storage options Direct discharge to bunker/ manual reclaim Convey to dome/manual reclaim Convey to building or silo/ automated reclaim Open pile Feasible Possible issues.

8 Moisture, fugitive dust, leaching Selection depends on: On-site storage requirement Gypsum contractGypsum Storage/HandlingWPCA Wet FGD Seminar - December 1, 2008 Fan Arrangement Retrofit ELECTROSTATIC PRECIPITATORSTACKID FANWPCA Wet FGD Seminar - December 1, 2008 Fan Arrangement Retrofit ABSORBERELECTROSTATIC PRECIPITATORSTACKID FANWPCA Wet FGD Seminar - December 1, 2008 Fan Arrangement Retrofit ABSORBERELECTROSTATIC PRECIPITATORSTACKID FANBOOSTER FANWPCA Wet FGD Seminar - December 1, 2008 Fan Arrangement Retrofit ABSORBERELECTROSTATIC PRECIPITATORSTACKID FANBOOSTER FANWPCA Wet FGD Seminar - December 1, 2008 Purge stream required to control chlorides/inert solid for wallboard gypsum Purge stream treatment strategy is site-specific; depends on: Discharge limits Receiving body FGD process design Fuel, limestone, make-up water Treatment options: Direct discharge Volume reduction (evaporation.)

9 Physical/chemical treatment Suspended solids pH adjustment Heavy metals removal COD removalWastewater TreatmentWPCA Wet FGD Seminar - December 1, 2008 Agenda Introduction Major Process Equipment Balance of Plant Equipment Controls SummaryWPCA Wet FGD Seminar - December 1, 2008 WFGD Controls Distributed Control Systems Overview Redundancy Primary WFGD Control Loops & Instrumentation Absorber Area Flue Gas SystemWPCA Wet FGD Seminar - December 1, 2008zDistributed Control Systems (DCS) Control and automation of WFGD processes and components Interface with remaining power plant controls Monitor key process parameters Process trends, reports, historical data loggingzLocal Control Panels (LCP)zProgrammable Logic Controllers (PLC)

10 ZMain FGD Control Area Dedicated WFGD Control Station Centralized WFGD Control with Boiler/Power PlantWFGD Control SystemsWPCA Wet FGD Seminar - December 1, 2008 Redundant Data HighwayOperatorStationLaser PrinterLocalI/OOperatorStationRedundantP rocessControllerEngineeringStationLine PrinterLine PrinterRemoteI/OSerialDeviceSerialDevice LocalI/ORedundantProcessControllerRemote I/OSerialDeviceSerialDeviceLocalI/ORedun dantProcessControllerDCS CONFIGURATION DIAGRAMD istributed Control SystemWPCA Wet FGD Seminar - December 1, 2008 Major Control Loops - AbsorberMake-Up WaterLSolids / Gypsum BleedDpHReagent FeedWPCA Wet FGD Seminar - December 1, 2008zScrubbing Liquor pH Most important process variable to be controlled in WFGD continuous, in-line monitoring, daily lab verification Indication of the amount of CaCO3in scrubbing solution Scrubbing liquor below desired range lower SO2removal efficiency Scrubber liquor above desired range higher SO2removal efficiency, excess CaCO3and reduced gypsum byproduct Scrubbing Liquor pHNeutral H2 OacidbasepH / Reagent Feed ControlWPCA Wet FGD Seminar - December 1, 2008 Limestone slurrypHpHReaction TankAbsorberFEpH ControllerLS Flow ControllerSO2 Boiler Load (MW)