MP244rev6Impacts of Texas Lignite on SCR Catalyst Life andPerformance2007 EPRI SCR WorkshopPensacola, FLNovember 12 to 14, 2007Dave BroskeEPRICharlotte, NCBennett JonesLuminant PowerDallas, TXRandy SmithFERCoLaguna Hills, CAMP244rev62Project ParticipantsyJEC, Inc. – Ed CichanowiczySargent & Lundy – Raj GaikwadyHitachi – Bill GrettayLuminant Power – Bob WiemuthySandow SES – Brad Masek, Luis Cordova, David SvrcekMP244rev63Test Program DriversProgram Objective: Develop knowledge of SCR catalystperformance and longevity to apply to full-size SCR designson Texas lignite-fired units.Regulatory Drivers: 2009 NOx CAIR; 2015 NOx CAIR; Sandow 5approval specifies SCR on Sandow 4; approved Oak GroveUnits 1 & 2 PSD permits requires SCRs (BACT)With the exception of a limitednumber of units operating inEastern Europe, essentiallyno experience with coalsclassified as lignite. EasternEurope units firing ligniteutilize a lignite-like coal primarily from Czechoslovakia, butthe ash, sulfur & silica contents do not reflect U.S. lignites.For both northern and Texas lignites, effectively no experienceto draw upon in the design ofan SCR NOx control process.MP244rev64Earlier TestingMartin Lake “in-situ” test program – Report 1004732 Dec 2003yMini-reactor testing performed in May 2002 through June2003yShowed no significant issues with maintaining activityover ~ 14 months for bothhoneycomb and plate catalystsamplesyOnly 4” x 4” catalyst cross sectionyLignite/PRB blendIn-situ results validated moving to pilot-scale SCR systemslipstream reactorMP244rev65Test Program Overview and Design ParametersyOne-year test period on 100% Texas Lignite firingyOne catalyst layer; focus on simulating catalyst erosion andpoisoning with catalyst activity measured intermittentlyyReactor sized to minimize the deposition and accumulationof ash adjacent to the reactor wallyDownward flow direction; controlled flue gas extraction flowrate (through the use of bothbypass and isolation valves);capability of reducing flue gastemperature at the extractionpoint and a venturi to monitor flow rateyMonthly in-situ activity measurementsyPhysical samples collected at6 and 12 months for vendoranalysisyHg and SO3oxidation measurements at 1, 6 and 12 monthsMP244rev66Host SiteSandow Steam Electric Station Unit 4yTwin-furnace, tangentially-fired, CE unityOriginally 575MW, later upgraded to 640 MWyStarted operation 1980yESP and limestone scrubberySpring 2010 full-scale SCRyYear-round operationyTwo reactorsy3 + 1 configurationMP244rev67Slipstream OverviewySargent & Lundy designyCatalyst section 2 ft x 2 ftySingle catalyst layer (approx.1 meter in length)yFlue gas flow ~1360 scfm(velocity ~13 ft/sec, actual)yDriving force provided by airheater pressure dropyActive control of flue gasflow rateyLPA screen on inlet scoopMP244rev68Inlet Scoop and LPA ScreenMP244rev69Reactor Inlet DuctworkyHorizontal duct from inletscoop 7 in x 24 inyInlet gas sample locationand ammonia injectionyExpansion to 24 in x 24 inMP244rev610Reactor HousingySootblowersyLarge catalyst loading doorySmall inspection door (12” x 12”)yInlet & outlet sampling ports forHg and SO3oxidation testsMP244rev611Slipstream Reactor Control SystemyAutomatic control of gas flowrate and temperatureyAutomatic shutdown and restarttriggers based on Sandow Unit 4loadyAutomatic catalyst sootblow andbackpurge cyclesyMass flow controller for NH3injectiony2-stream (inlet/outlet) gasanalysis system (NO/O2) formonitoring catalyst activityyFull access for control andremote activity testing viainternet/VPN connectionMP244rev612Control System User InterfaceMP244rev613Fly Ash Deposition IssuesCatalyst condition uponinstallationTypical condition found aftershutting reactor down forinspectionMP244rev614Splitter Vanes and Sootblowers Above CatalystCondition upon installationTypical condition found aftershutting reactor down forinspectionyNote deposits accumulated onsurfaces above catalystySootblowers found to beineffective in clearing depositsafter a host unit outageMP244rev615SootblowersyOriginal design had the sootblowers positioned 48 inches abovethe catalyst surface, with 1/8” diameter jetsyPilot-scale performance showed this design to be ineffectiveyNumerical (EPRI) and cold-flow (FERCo) modeling studies wereperformed to redesign the sootblowersyDistance above the catalyst was reduced to 18 inchesyJet diameter was increased to 3/8”yMarked increased effectiveness in clearing surface deposits afterhost unit outageMP244rev616Catalyst Cleaning and Sampling: 10/4/07yAll eight modules removed andcleaned with compressed airySample plates removed from 2modules, for analysis by vendoryAfter cleaning andreassembly, catalystpressure drop was reducedfrom ~1.25” H2O to ~0.48”H2O (close to that whennew)MP244rev617Catalyst Pressure Drop TrendsCatalyst cleaningSootblowers installedCatalyst plugging eventMP244rev618Activity Test ProtocolReactor Potential = -ln(1-∆NO)Sandow Unit 4 Pilot SCR 3/2/0701020304050607080901000.0 0.5 1.0 1.5 2.0NH3/NO

NO Removal (%)yMeasure NO removal as afunction of NH3injectionrateyCalculate RP from point ofmaximum NO removalyRP calculation accounts forboth K/K0and blockageyK = -AV·ln(1-∆NO) = AV·RPyNeed geometric surface areaof catalyst to calculate Kfrom NO removalMP244rev619Reactor Potential ResultsRP/RP0Versus Catalyst dP Over Eight Months of OperationyAfter 5 months (~2900 hrs)RP/RP0down to ~0.8, and dPhas doubled to 0.9” H2OyAt 3500 hours (after thecatalyst plugging event) dPclimbs to 1.1” H2O and RP/RP0drops to 0.5yAfter catalyst cleaning (4300hrs) dP was reduced to ~0.5”H2O and RP/RP0recovered to0.88yMajority of initial RP decreasewas due to plugging ratherthan catalyst deactivationyCurrently at 5100 hours,RP/RP0= 0.77 and dP = 0.49”Sandow Unit 4 Pilot SCR0.00.20.40.60.81.01.20 1000 2000 3000 4000 5000 6000Operating Hours

RP/RPo, Catalyst dP ("H2O)RP/RPoCatalyst dPMP244rev620SummaryyDeposition of fly ash accumulated on surfaces above thecatalyst has been an issue after host unit outagesyInitial sootblower design provedto be ineffective in clearingsurface deposits from catalystyRedesigned sootblower system showed marked increase ineffectivenessyHowever, significant catalyst plugging had already occurredand physical cleaning of the modules was necessaryyAfter cleaning:yCatalyst pressure drop was reduced to the level wheninstalled in March (~0.48” H2O)yRP/RP0increased dramatically from 0.50 to 0.88yTesting is continuing