experience with compressed air cleaning of main st

GER-3636AgpresentedatTheAmericanPowerConferenceApril23—25,1990Chicago,IllinoisGEPowerSystemsExperiencewithCompressedAirCleaningofMainSteamPipingJ.B.PierandG.GoldmanGEPowerSystemsSchenectady,NYP.J.SkrgicAlleghenyPowerNewYork,NewYorkC.BrookinsDetroitEdisonDetroit,MichiganandL.LarsonandD.RotheBasicElectricBismark,NorthDakotaExperiencewithCompressedAirCleaningofMainSteamPipingGEPowerSystemsGER-3636A(08/03)iContentsIntroduction............................................................................1IndustryExperiencewithCompressedAir.................................................1AlleghenyPower.....................................................................1DetroitEdison.......................................................................3BasinElectric........................................................................7GEPowerPlantEngineering............................................................9Conclusion............................................................................15Reference.............................................................................15ListofTables..........................................................................16ListofFigures.........................................................................16ExperiencewithCompressedAirCleaningofMainSteamPipingGEPowerSystemsGER-3636A(08/03)iiExperiencewithCompressedAirCleaningofMainSteamPipingGEPowerSystemsGER-3636A(08/03)1IntroductionThispaperpresentsasummaryoflong-termandshort-termexperiencethatdemonstratescom-pressedair-blowresultsareatleastasgood,andoftenbetterthansteam-blows.Compressedair-blowshavebeenusedeffectivelyonapplicationsforsupercriticalboilers,drum-typeboilers,andheatrecoverysteamgeneratorsforpreopera-tionalcleaningofmainsteamlinesatpowerplantswithratingsfrom35to700MW.Cleaningofthemainsteampipingisrequiredtominimizethepossibilityofdamagetothetur-binebyremovingweldbeaddeposits,pipeslag,andotherforeignmaterialwhichmightother-wisebecarriedoverintotheturbine.Anyparti-clesthatwouldbedislodgedwhileoperatingmustbedislodgedduringthecleaningprocess,andanyparticlesthatareorbecomeloosemustberemovedfromthesystem.Thus,themomen-tumorcleaningforcemustexceedtheforcethatoccursduringthemaximumflowopera-tion.Thisrequirementissatisfiedbyselectingtheinitialpressurelevelsothatthemomentumorcleaningforceratioisgreaterthanone.Theprocedureissimilartoasteamblowdownexceptthatcompressedairisusedastheclean-ingmedium.Thesystemispressurizedusingrentedcompressorsorsiteequipmentanddepressurizedbyrapidlyopeningthetemporaryvalve.Thecycleisrepeateduntilthecleanlinesscriteriahavebeensatisfied.Thenoiselevelissimilartosteam-blows,andmufflersshouldbeusedinpopulatedareas.Acriticalfactorinthesuccessofair-blowsistheuseofafast-actingtemporaryballvalveriggedtoopenveryrapidly,ontheorderof1sec.Typicalopeningtimesforthetemporarygatevalvesusedforsaturatedsteamblowsare15to45sec.Thefast-actingvalveisnecessarytopromptlyestablishthedesiredflowconditionsandmomentumratiosbecausetherechargerateoftheaircompressorsisrelativelylowcomparedtothedischargerate.Thereisaconsistentobjectiontoair-blowsbecausethelargetemperaturechange(thermalcycling)associatedwithsteam-blowsisnotpres-ent.Condensationandfrosthavebeenobservedneartheendofthetemporarypipeduringair-blows,verifyingthecoolingeffectassociatedwiththeexpansionprocess.Thelargestpartofthetemperaturedecreaseoccursinthetempo-rarypipeandthushasaminimalimpactonthepipebeingcleaned.Thefactthatair-blowresultsforbothlargeandsmallsystemshavebeencon-sistentlyratedasgoodorbetterthansteam-blowsbyexperiencedpersonnelindicatesthattheeffectivenessofremovingmaterialthatcoulddamagetheturbinemaybeindependentofthermalcyclingandprimarilyrelatedtoobtainingtherequiredflowormomentumratio.Anothersignificanteffectmaybetheaccelera-tionforcesgeneratedwhenthetemporaryballvalveispoppedopen.Reference1acknowledgesthatcompressedair-blowshavebeenaseffectiveassteam-blowsincleaningsteamlinesandsuggeststhecleaningmethodshouldbeselectedbasedonparticularcircumstances.Themajorbenefitsofcompressedair-blowsareschedulingflexibility,extendedboilerlifebyeliminatingtemperaturecyclesassociatedwithsaturatedsteamblows,andreducedcost.IndustryExperiencewithCompressedAirAlleghenyPowerSince1967,AlleghenyPowerSystemhasplaced10supercriticalonce-thruunitsinservicethatExperiencewithCompressedAirCleaningofMainSteamPipingGEPowerSystemsGER-3636A(08/03)2rangeinsizefrom576to668MWgross.ThefirstofthesewastheFortMartinUnitNo.1,whichwasplacedincommercialoperation37moafterinitialgroundbreaking.Thisveryambi-tiousconstructionandstart-upschedulepromptedtheAlleghenyPowerSystemtoevalu-ateanddecideinfavorofair-blowinginlieuofthecustomarysteam-blowingtoremoverust,debris,pipescale,weldingslag,etc.fromtheboilerandboiler-relatedpipingsystemspriortostart-up.Steamblowingrequiresalongerconstructionandstart-upschedulebecausetheentireboilerandauxiliarysystemsmustbecompletedandcheckedoutbeforesteam-blowingispossible.Air-blowingoftheboilerandboiler-relatedpip-ingsystems,however,m