Guru Hargobind Thermal Power Plant, Lehra Mahobbat

8/1/2015 GuruHargobindThermalPowerPlant,LehraMahobbat

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Home AcademicProjects GuruHargobindThermalPowerPlant,LehraMahobbat

GuruHargobindThermalPowerPlant,LehraMahobbat

StudentTeam/Author:AjaypalBansal

GuideBy:Er.D.S.Bhullar

Degree:MechanicalEngg

College:GuruGobindSinghCollegeofEngineering&Technology,TalwandiSaboo

MySelfAjaypalBansal

1PROJECTREPORTONSIXMONTHSINDUSTRIALTRAININGATG.H.T.P.LEHRAMOHABBATBATHINDASubmittedtoPUNJABTECHNICALUNIVERSITY,JALANDHARInpartialfulfillmentoftherequirementsfortheawardoftheDegreeofBachelorofTechnologyinMechanicalEngineeringByAJAYPALBANSALUniv.RollNo.100361130198Semester:7thUndertheguidanceofAcademicTutorIndustrialTutorEr.YadwinderpalSharmaEr.D.S.Bhullar(TRAININGCOORDINATOR)(A.S.E./TRAINING)DepartmentofMechanicalEngineeringGURUGOBINDSINGHCOLLEGEOFENGINEERING&TECHNOLOGYTALWANDISABO,BATHINDA(PUNJAB)2GURUGOBINDSINGHCOLLEGEOFENGINEERING&TECHNOLOGY,TALWANDISABO(BATHINDA)CERTIFICATEOFORIGINALITYOFWORKIamAjaypalBansalUniv.RollNo.100361130198studentofBachelorinTechnologyBranchMechanical4thYear,haveundergonethesixmonthindustrialtrainingatG.H.T.P.LEHRAMOHABBATBATHINDA.Ihavedonethefollowingprojectduringmytrainingperiod:1.MethodstoremovefailureinBoilerTubes.Iherebydeclarethattheworkisanoriginaloneandhasnotbeensubmittedearliertothisuniversityoranyotherinstitutionforfulfillmentoftherequirementofacourseofstudy.AjaypalBansalUniv.RollNo.:100361130198Branch:MechanicalEngg.Semester:7thG.G.S.C.E.T.TalwandiSabo(Bathinda)Er.YadwinderpalSharma(AcademicTutor)3ThesixmonthindustrialtrainingatGURUHARGOBINDTHERMALPOWERPLANT,LEHRAMOHABBAT(BATHINDA)commencedfrom04June,2013to30Nov,2013.ItwasaveryknowledgeableexperienceformeundertheableguidanceoftheemployeesofvariousdepartmentsatGHTP,LehraMohabbat.IamthankfultotheinchargeofthetrainingcellEr.D.S.BHULLAR(A.S.E./TRAINING)Whomadegreateffortstomakemytraininginformative.Iamalsothankfulfortheverykindcooperationoftheemployeesofthevariouscellswhoforwardedtheirbesthandtomakemytraininginterestingandknowledgeable.MyheartiestthanksgotoEr.BEANTSINGHEr.PARAMJITSINGHEr.BALJEETSINGHBEDIEr.INDERJITSINGHEr.JASKARANSINGHAjaypalBansalACKNOWLEDGEMENT4ABOUTTHETRAININGPunjabTechnicalUniversity,Jalandhar,PTUscurriculumforB.Tech.specifiesthecompletionofthesixmonthsprojectworkinsomeindustry,inpartialfulfillmentoftherequirementsfortheawardofthedegreeofBachelorinTechnologyinMechanicalEngineering.Towardsthefulfillmentoftherequirementofthesixmonthindustrialtraining,afirstinanyoftheIndianUniversities,mourinstitutionGuruGobindSinghCollegeofEngg.&Tech.,TalwandiSabo,(Bathinda)Pb.deputedmeformyindustrialtrainingduringtheseventhsemestertoGURUHARGOBINDTHERMALPOWERPLANT,LEHRAMOHABBAT,BATHINDA.IjoinedG.H.T.P.Asatraineeon04062013andIamworkinghereformyindustrialprojectsundertheguidanceofEr.JaskaranSingh(AE/BMC).Mymajorprojecthereis,MethodstoremovefailureinBoilerTubes.WiththeactivehelpofTrainingDepartmentandeventhepeopleattheseniormostleveloftheplant.Icouldachievethesetasksquitesatisfactorilyandfinishedwithalltheseprojectsby(30112013).5TECHNICALDETAILSANDFEATURESOFSYSTEMPLANTOVERVIEWINTRODUCTIONTOTHERMALPOWERPLANTBYPASSSYSTEMTURBINELUBOILSUPPLYSYSTEMGOVERNINGSYSTEMGENERALASPECTSOFBOILERCOALPULVERISINGSYSTEMPLANTOVERVIEWDESCRIPTIONVARIOUSCYCLESINVOLVEDINPOWERGENERATIONWORKINGOFTHERMALPOWERPLANTATG.H.T.P.DEMINERALISEDWATERPLANTCOOLINGTOWERSINSTRUMENT/SERVICEAIRCOMPRESSORSCOALHANDLINGPLANTASHHANDLINGSYSTEMELECTROSTATICPRECIPITATOR(ESP)HYDROGENGASPLANTDETAILOFPROJECTCONTENTS6TECHNICALDETAILSANDFEATURESOFSYSTEMPart1:SiteDetails1.0SiteFeaturesNameofVillageV.P.O.LehraMohabbatNameofDistrictBathindaNearestTownandDistanceRampuraPhul8KmsNearestRailwayStationandDistanceLehraMohabbat1.5KmsNearestAirportandDistanceAmritsar190KmsUltimatePotentialofTheSite(MW)920MW2.0LandTotalareaoflandavailableatsiteforPowerPlant774AcresAshPond160AcresTownship91Acres3.0FuelTypeBituminouscoalandoilSourceCoalIndiaLtd.AndIndianOilCorporationDistanceAppx.1500Kmsforcoaland350KmsforoilFuelAvailabilityThroughRail74.0AshDisposalProposedMethodofDisposalDryandWetProposalforUtilisation(1)Useincementplant(2)Useinbrickplant5.0PowerEvacuationProposalTomaingridofPSEBthrough8nos.220KVLines.8PLANTOVERVIEWConveyerbeltFDFanHeatreleasedContinueOnNextPageCOALPLANTBOILERBUNKERSPULVERISINGMILLSBOILERBURNERCOMBUSTIONCLEAREDFUELGASPASSTOCHIMNEYVIAINDUCEDDRAUGHTFANCOALBURNBOILSWATERWHICHGIVESSTEAMSTEAMISSUPERHEATEDPASSESTOH.PTURBINEDustAsh9CONTINUEDFROMTHELASTPAGE:SteamPowerLinesTURBINEBLADESCAUSESTURBINETOROTATESTEAMISRETURNEDTOBOILERFORREHEATINGTIRBINESHAFTISCOMPLEDTOROTOROFGENERATORGENERATORROTORISENCLOSEDINSTATORELECTRICITYISPRODUCEDATSTATORWINDINGFROMWHICHITGOESTOTRANSFORMEREXHAUSTEDSTEAMENERGYCONDENSERUSEDAGAININBOILERWATERISPUMPEDHEATEDINLPHEATERSDEAERATEDINDEAERATORPRESSUREINCREASESBYBOILERFEEDPUMPSHEATEDINHPHEATERSECONOMIZERSTEAMDRUMSTEAMISHEATEDINSUPERHEATERHPTURBINEPOWERISSTEPEDUPBYTRANSFORMERGRIDSYSTEMS10INTRODUCTIONTOTHERMALPOWERPLANTFig1.1showsbasicblockdiagramofthethermalpowerplant.Itbasicallyconsistsofthreepartsviz.,Turbine,GeneratorandBoiler,whicharefurtherdividedasshowninthefigure.Fig1.1BlockDiagramofThermalPowerPlantSteamTurbineSpecificationsMW:250MWSpeed:3000rpmSteaminletPressure:147atmSteamoutletpressure:0.1033atmSteam

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Temperature:535CCoolingwatertemperature:33CThermalPowerPlantTurbineGeneratorBoilerSteamTurbineStatorRotorDVARHPTLPTIPT11DescriptionItisasingleshaftmachinewithseparateHP(HighPressure),IP(IntermediatePressure)andLP(LowPressure)module.HPandIPsectionsaresingleflowcylinderswithHP&LPflowsinoppositedirectionsandLPsectionisadoubleflowcylinder.Therotorsofturbineandgeneratorarecoupledwithrigidcoupling.HPandIPcylindersarecontrolledbythrottlecontrolgoverning.Theturbineissupportedby3bearingsoneeachforLP,HPandIPsections.Allvalvesareactuatedbyindividualhighpressureelectrohydraulicactuatorsatanoilpressureof160bar.Turbinehasahighpressureelectrohydraulicgoverningsystem,whichcontrolsspeedandoutputbyanelectricsystem.Aclosedcircuitoilsystemisprovidedforlubricatingandcoolingthebearings.Forcontroloilpurpose,separatehighpressureoilsystemisprovided.Thehighpressuresuppliedbyliftingoilpumppreventsmetaltometalcontactofbearingsduringstartupandshutdown.GeneratorSpecificationsKVA:147060StatorCurrent:8086AKW:250000RotorVolts:364VPowerfactor:0.98lagRotorCurrent:819.5ASpeed:3000rpmInsulation:FclassNo.ofphases:3Cooling:CACWConnection:YOverspeed:10%maxFrequency:50HzStatorVolts:10500VDescriptionThetwopolegeneratorusesdirectaircoolingfortherotorwindingandindirectcoolingforthestatorwinding.Thelossesintheremaininggeneratorcomponents,suchasironlosses,windagelossesandstraylossesarealsodissipatedthroughair.ThemaincomponentsofGeneratorareasfollows:1.Stator:Statorframe,Statorcore,Statorwinding,Statorendcovers2.Rotor:Rotorshaft,Rotorwindings,Rotorretainingrings,Fieldconnections3.Bearings124.AirfiltersThefollowingadditionalauxiliariesarerequiredforgeneratoroperation:1.Oilsupplysystem2.ExcitationsystemExcitationSystemThebrushlessDCexcitationsystemusedinthisplantconsistsofthefollowingmaincomponents:1.Rectifierwheel2.Threephasemainexciter3.Threephasepilotexcitercooler4.MeteringandsupervisoryequipmentSteamCycleTheoryThepowerstationoperatesusingaclosedsteampowercycle,wherewaterundergoesvariousthermodynamicprocessesinacycle.Fig.1.2showsthesimplifieddiagramofthesteamplant,showingtheessentialelementsoftheplant.Onehalfofthecycleconsistsoftheboileri.e.steamgeneratoranditsauxiliaries.Theotherhalfi.e.theturbinecycleconsistsofturbine,generator,condenser,feedpumpandfeedwaterheaters.13Fig1.2SimplifiedPowerplantcycleFirstweconsidertheboilerplantinvolvedinthecycle.Feedwaterissuppliedtotheboilerdrumthrougheconomizer,wherewaterisboiledandconvertedintodrysaturatedsteam.ThisdrysteamisfurthersuperheatedinthesuperheaterandthenfedtotheHPcylinderthroughmainsteamlinesviaEmergencyStopValvesandControlValves.Thesteamexpandsintheturbinegivingupheatenergy,ahighproportionofwhichisconvertedintoworkenergyontheturbineshaft.Theshaftturnsanelectricalgeneratorwhichproduceselectricpower.SteamleavingtheHPcylindersreturnstotheboiler,whereitisreheated.ThereheatedsteamisDCONDENSERHOTWELLLPHDeaeratorBFPHPHHPTLPTIPTGBoilerSuperheaterReheaterEconomiser14suppliedtotheIPcylinderthroughhotreheatlinesviainterceptorvalvesandcontrolvalves.AfterdoingworkonIProtor,thesteamexhaustedfromIPcylinderisdirectlyfedthroughcrossaroundandcrossoverpipestoLPcylinder.FinallythesteamexhaustedbyLPcylindergoestocondenser.TheshaftsofHPIPLPandgeneratorareconnectedinseries,sogeneratorreceivesthemechanicalpoweraddedbyallthethreecylinders.Inthecondenser,whichisalargesurfacetypeheatexchanger,thesteamiscondensedbytransferringitslatentheatofevaporationtothecoolingwater(KW).Thesteamhavingbeencondensedinthecondenserisnowintheformofcondensateatverylowpressureandsaturationtemperature.Thiscondensateispumpedbycondenserextractionpumpfromcondenserhotwellandpassedthroughthelowpressureregenerativefeedheatingsystemanddeaerator(directcontactheatexchanger)toincreasethetemperatureofwaterandremovedissolvedgasessuchasO2andCO2toformfeedwatersuitableforboiler.Boilerfeedpumpsucksfeedwaterfromdeaeratorandpumpstoboilerdrumviahighpressureregenerativefeedheatingsystem(HPheater).Inmodernregenerativecycle,usedinthisplant,someofthesteampassingthroughtheturbinecylinderisbledfromaseriesofextractionbeltslocatedafterselectedmovingbladestagesandfedtothecondensateheater(LP)andfeedwaterheaters(HP),whichareofsurfacetypeheatexchangers.TheBFPincreasesthefeedwaterpressuretoalevelinexcessofthedrumpressure,toprovideforthepressurelossintheboilercircuitandHPheatingtrain.Thecycleisnowcompleted.TurbineEfficiencyTheefficiencyofturbineisgivenbythefollowingformula:or,AcomparisonofactualandisentropicexpansionsisillustratedinFig.1.3(Mollierdiagram).Thedeviationofactualexpansionlinefromisentropicexpansionisduetolossesor15irreversibilitycorrespondingtoanincreaseinentropy.FromFig.1.3wecanseethatforanexpansionbetweentwopressures,thegreatertheentropyrise(morelosses),thelessenergythereisavailableforwork.Toreducethelossesandtoincreasetheavailableenergy,turbinesareconstructedwithspecialdesignfeatures.P1AHAActualP2IsentropicExpansionExpansionHBHCEntropySFig.1.3ComparisonofActualExpansionwithIsentropicExpansioninTurbineMainComponentsofTurbineTheturbineisatandemcompoundmachinewithHP,IPandLPparts.TheHPandIPpartsaresingleflowcylindersandtheLPpartisadoubleflowcylinder.Theindividualturbinerotorsandthegeneratorrotorareconnectedbyrigidcouplings.TheHPcylinderhasathrottlecontrol.Theinitialsteamisadmittedbeforethebladingbytwocombinedmainsteamstopandcontrolvalves.ThelinesleadingfromtheHPexhaustbranchestothereheaterareprovidedwithswingcheckvalveswhichpreventhotsteamfromthereheaterflowingbackintotheHPturbine.EnthalpyH16ThesteamcomingfromthereheaterispassedtotheIPpartviatwocombinedreheatstopandcontrolvalves.CrossaroundpipesconnecttheIPandLPcylinders.Bladesarearrangedatseveralpointsoftheturbine.Themaincomponentsoftheturbineare:1)Innerandoutercasing2)Fixedbladesordiaphragms3)Rotorwithmovingblades,shaftandcoupling4)ShaftGlandsandBladeSealingStrips5)Bearings6)Valves7)Mainoilpumpetc.HPCasingsTheoutercasingoftheHPturbineisofthebarreltypeandhasneitheranaxialnoraradialflange.Thispreventsmassaccumulationswithhighthermalstresses.Thealmostperfectrotationalsymmetrypermitsmoderatewallthicknessesofnearlyequalstrengthatallsections.Theinnercasingisaxiallysplitandkinematicallysupported.Asthepressuredifferenceacrossthewallofinnercasingislow,thehorizontalflangeandconnectionboltscanbekeptsmall.Thebarreltypecasingpermitsflexibilityofoperationintheformofshortstartuptimesandahighrateofchangeofloadevenathighinitialsteamconditions.IPCasingsTheIPpartisalsoofsingleflowconstruction.Attachedintheaxiallysplitoutercasingisaninnercasingsupportedkinematicallyandtakingtheguideblades.Thereheatedsteamisadmittedtotheinnercasingthroughthetopandbottomcenterofthecasing.Thearrangementofaninnercasingconfinesthehighsteaminletconditionstotheadmissionbranchofthecasing,whilethejointoftheoutercasingisonlysubjectedtothelowerpressureandlowertemperatureattheexhaustoftheinnercasing.17LPCasingsThecasingofthedoubleflowLPcylinderisofthreeshelldesign.Theshellsareaxiallysplitandofrigidweldedconstruction.Theinnershelltakingthefirstrowsofguidebladesisattachedkinematicallyinthemiddleshell.Independentoftheoutershell,themiddleshellissupportedatfourpointsonlongitudinalbeams.Tworingscarryingthelastguidebladerowsarealsoattachedtothemiddleshell.BladingTheentireturbineisprovidedwithreactionblading.ThemovingbladesoftheHPandIPpartsandthefrontrowsoftheLPpartwithinvertedTrootsandshroudingaremilledfromthesolid.ThelaststagesoftheLPpartconsistoftwisted,dropforgedmovingbladeswithfirtreerootsinsertedincorrespondinggroovesoftherotor.HighlystressedguidebladesoftheHPandIPpartswithinvertedTrootsandshroudingaremachinedfromonepiecelikethemovingblades.TheotherguidebladeshaveinvertedLrootswithrivetedshrouding.ThelastthreestagesoftheLPturbineareguidebladerowsoffabricatedconstruction.BearingsTheHProtorissupportedbytwobearings,adoublewedgejournalbearingatthefrontendoftheturbineandacombinedjournalandthrustbearingdirectlyadjacenttothecouplingwiththeIProtor.TheIPandLProtorshaveajournalbearing



eachattheendoftheshaft.Thecombinedjournalandthrustbearingincorporatesaselfadjustingdoublewedgejournalbearingandathrustbearingwhichtakesupresidualthrustfrombothdirections.Thebearingtemperaturesaremeasuredbythermocouplesinthelowershelldirectlyunderthewhitemetallining.ShaftGlandsandBladeSealingStripsAllshaftglands,sealingthesteaminthecylindersagainstatmosphereareaxialflowlabyrinths.TheyconsistofalargenumberofthinsealingstripswhichintheHPandIPpartsarealternatelycaulkedintogroovesintheshaftsandsurroundingsealingrings.ThesealingstripsintheLPpartareonlycaulkedintothesealingrings.Theseringsaresplitintosegmentswhichare18forcedradiallyagainstprojectionbyhelicalspringsandareabletoyieldintheeventofrubbing.Sealingstripsofsimilardesignarealsousedtosealtheradialbladetipclearances.ValvesTheHPturbineisfittedwithtwoinitialsteamstopandcontrolvalves.Astopandacontrolvalvewithstemsarrangedatrightanglestoeachotherarecombinedinacommonbody.TheIPturbinehastwocombinedreheatstopandcontrolvalves.Thereheatstopvalvesarespringloadedsingleseatvalves.Thecontrolvalves,alsospringloaded,havediffusers.Thecontrolvalvesoperateinparallelandarefullyopenintheupperloadrange.Inthelowerloadrange,theycontrolthesteamflowtotheIPturbineandensurestableoperationevenwhentheturbosetissupplyingonlythestationload.Allvalvesareactuatedbyindividualoilhydraulicservomotors.TurbineMaterialsDesignRequirementsThesteamturbineischaracterizedasahighspeedrotatingmachine.Therotatingpartsaresubjectedtohighstressescausedbycentrifugalforcesaswellashightemperaturecyclicload.Thestaticpartsarealsohighlystressedduetosteampressuredropaswellashightemperature.cyclicload.Hencetocounteractthesestressesunderchangingoperatingconditions,theselectionofsuitablematerialisvitalinturbinedesign,particularlycomponentsintemperaturerange4500Candabove.ThemajorcomponentsworkingincreeprangeareHPandIPsteamchests,valves,casings,rotors,diaphragms,bladenozzles,boltsandsteamadmissionpiping.Also,thecomponentsworkingunderlowtemperaturezone(LPturbine)arehighlystressedduetoitslargesizeandfacedwithproblemslikecorrosionanderosionduetowetsteam.Metallurgicalconsiderationsarealsoofutmostimportanceintheselectionofmaterialsinordertohavegreaterreliabilityandgoodserviceduringoperation19CriteriaforSelectionofMaterialsTurbinematerialsareselectedonthebasisoffollowingconsiderations:Physicalpropertiesa.Thermalcoefficientofexpansionb.Thermalconductivityc.Modulusofelasticityd.Poisonsratioe.DensityMechanicalpropertiesa.Hotyieldb.Creepandrupturec.Relaxationpropertiesd.Cyclicloadingbehaviore.Fatiguebehaviorf.Fracturetoughnessg.Rateofcrackgrowthh.ResistancetoscalingThephysicalpropertiesareimportantforselectionofmaterialforthecomponentsworkingatelevatedtemperature.Thethermalconductivityismoreimportantforquickdissipationofheatincomponentsinordertominimizethermalstresses.Thermalcoefficientofexpansionandthemodulusofelasticityplayanimportantroleininducingthermalstressesandensuringthedesignclearanceandtheminimumvaluesarefavourable.Themechanicalpropertiesarenowdiscussedwithsomedetail.HotyieldThehotyieldistakenintoconsiderationfordesignforthosecomponentsthatworkatelevatedtemperaturebutnotinthecreeprange.Thehotyieldisdeterminedfromthestressstrainsrelationshipat6500C.Thecomponentsaredesignedforstressoccurringat0.2%strain.Thehotyieldofsteeldecreaseswithanincreaseoftemperature.20CreepandRupturePropertiesThegradualdeformationundertheactionofconstantloadtestiscalledcreepandsoaconstantloadtestiscalledCreepTest.Theconventionalstressi.e.,loaddividedbyinitialcrosssectioniscalledasCreepStresswhereasthegradualstrainiscalledasCreepStrain.Therupturetestisbasicallysimilartocreeptestwiththeexceptionthatitisalwayscarriedoutuptothefailureofthematerial.Thestressrupturetestmeasurestheeffectoftemperatureonthelongtimeloadsustainingcharacteristics,i.e.thetimetocausefailureatagivennominalstressforaconstanttemperature.Thestressrequiredforcausing1%creepis100,000hoursandcorrespondingrupturestressareconsideredtoevaluatematerialbehaviorofthesteamturbinecomponents.StressRelaxationInsomehightemperaturecomponentsthestressdoesnotremainconstantbutdecreaseswithtimeatelevatedtemperatureduetocreep.Therelaxationofstressinboltedjointsmayleadtoloosejointsandsubsequentleakagewhichrequiresretighteningofbolts.Similarly,duetostressrelaxation,theshrunkfittedassemblies(e.g.discrotoronshaft)willbecomeloose.So,thematerialselectedfortheseapplicationsmusthavehighstressrelaxationresistance.Itisthedatarequiredfordesigningofboltsandflanges,whichisgeneratedupto30,000hoursatdifferenttemperatures.ResistancetoScalingThecomponentsworkingatelevatedtemperaturemaybesubjecttoscaleformation.Excessivescalingofcomponentscarryinghighpressuresteamcansignificantlyreducetheeffectivethickness,sothattheremainingmetalisoverstressedandmayburst.Whenoxidestightlyadheretothesurfacetheysometimesactasinsulatingfilm,therebyreducingheatturbinerates.ResistancetoCorrosionandErosionThechancesofcorrosionanderosionofcomponentinlowtemperaturezonearemuchmorepredominantthanthecomponentsinelevatedtemperaturezone.Thisisbecausethewetconditionofsteamformswaterdropletsandstrikethecomponentsatveryhighspeed.Thiscauseserosion,mostly,oftheLPturbinelaststagebladeswhicharefurthersubjectedtocorrosionduetowetatmosphere.21MaterialsusedforTurbineComponentsAlargevarietyofheatresistantsteelsareusedformeetingdiversetechnicalrequirementsofvariouscomponents.Thecompositionofalloysteelscontainingcarbon,chromium,molybdenumandvanadiumareusedaccordingtoweldabilityorhardenabilityofthecomponentsdescribedasfollows:BladingMaterial12%Cr.StainlesssteelsareusedforLPturbinebladingbecauseofsuperiormaterialdamping.SomeconsiderationsforLPTbladingare:CorrosionandscalingresistanceAdequatetensilestrengthtowithstandcentrifugalandbendingstressesImpactstrengthtoresisterosionandimpactloadingMaterialdampingtocopeupwithvibratorystressdevelopedinturbineblades.The12%Cr.Stainlesssteelsretainallthesepropertiesaslongastemperaturedoesnotexceedabout4800C.ForshorterbladesworkingathightemperatureforHPturbine,12%CrMoVisusedwithsuitableheattreatmentstogiveadequatecreepresistance.Additionofniobiumto12%CrMoVsteelsfurtherincreasesthestressrupturestrengthandcreepstrengthintheshortterm.Theintermediateblades,whichareneitherhighlystressednorveryhot,aremadefrom12%Crsteelswithlinearalloyingcontentandheattreatedtoappropriatehardness.Thetypicalsteelhasacompositionof11%Cr,0.6%Mo,0.25%V,0.3%Nb.Thisalloysteelhasgoodcreepresistanceupto5500C.HPandIPRotorMaterialsAstheserotorsworkinhightemperaturezone,sotheyrequireacombinationofcreepstrength,rupturestrengthandductility.Thisisconferredbyrotorsmanufacturedfromforgedchromiummolybdenumvanadiumalloysteel.Thisisaferritematerial,whichprovidesthebestpossiblecreepproperties.22ThereducedtemperaturesencounteredatthelasttwostagesoftheIPturbineareoffsetbyincreasedborestressduetolongerbladelength,whichdemandsanadequatelyhighproofstrength.Thisisachievedbytheuseof1Cr1Mo0.25Valloysteel.LPRotorMaterialLProtorsworkinlowtemperaturezoneandhavelongerbladesanddiameterduetowhichtheyencountertheimpactofmoistureinthelaststages.Hencethemainrequirementsoftheserotorsarehightensilestrengthcombinedwithhightoughness.The3.5NiCrMoVmonoblocrotorforgingiscurrentlyusedasitavoidsthecomplicationofshrinkfitsinthecaseofbuiltuprotors.Vacuumdegassinghaseradicatedtheformerproblemsofhydrogenembrittlementcrackingandgivesgoodfracturetoughness.TurbineCasingMaterialsHPandIPcasingswheretemperatureover3500Cisencounteredaremadefromcreepresistantsteels.Twodifferentalloysteelsareusedforthemviz.2.25Cr1Mofortemperatureupto5380Cand0.5Cr0.5Mo0.25Vfortemperaturesupto5650C.Casingsinthesematerialsiscastratherthanfabricatedbecauseofthedifficultyofqualitycontrolandlikelihoodofthermaldistortioninthethicksectionsinvolved.LPcylindercasingsaregenerallyfabricatedfromcarbonsteel,althoughinnercasingmaybecastfromspheroidalgraphiteiron.Hightemperatureboltsaremadefromlowalloysteelsdesignedespeciallyforcreepresistantbolting.Thenickelalloysareusedmainlyoninnercylinderswherethecompact



flangeismostadvantageous.LowtemperatureboltsonLPcasingsaremadefromnormalhightensileboltingsteels.TurbineAnchoringandExpansionFixedPointsofTurbineIndesigningthesupportsfortheturbineonthefoundation,attentionisgiventotheexpansionandcontractionofthemachineduringthermalcycling.Themethodofattachmentofthemachinecomponentandtheircouplingtogether,arealsodecisivefactorsindeterminingthemagnitudeoftherelativeaxialexpansion(differentialexpansion)betweentherotorandturbinecasing.Thefixedpointsoftheturbineareasfollows:23ThebearingpedestalbetweentheIPandLPturbines.FromthispointtheIPandHPcasingsexpandtowardsthefrontbearingpedestaloftheHPturbine.TherearbearinghousingoftheLPturbine(LP/Generatorbearingpedestal).ThemiddleportionofeachlongitudinalgirderofLPturbine.Fromthesepointsthelongitudinalgirdersexpandinbothdirections(TurbinesideandGeneratorside).ThethrustbearinginrearbearingcasingofHPturbine.CasingExpansionThefrontbearingpedestalsoftheHPandIPturbinecanslideontheirbaseplatesinanaxialdirection.Anylateralmovementperpendiculartothemachineaxisispreventedbyfittedkeys.TheHPandIPcasingsaresupportedbylugsonbearingpedestals.Theguidesareprovidedinturbinestomaintaintheircentralpositionaswellasaxialmovement.ThustheoriginofthecumulativeexpansionofthecasingsisatthefrontbearinghousingoftheI.Pturbine.TheoutercasingoftheIPturbineislocatedaxiallyinthecenterareaofthelongitudinalbeambyfittedkeyscastinthefoundation.Freelateralexpansionisallowed.Thecenterguidesforthiscasingarerecessedinthefoundationcrossbeams.Thereisnorestrictiononaxialmovementofthecasings.Hence,whenthereisatemperaturerise,theoutercasingoftheLPturbineexpandsfromitsfixedpoint.Differencesinexpansionbetweentheoutercasingandthefixedbearinghousingstowhichthehousingsfortheshaftglandsareattachedaretakenupbybellowsexpansionjoints.RotorExpansionThethrustbearingisincorporatedintherearbearinghousingoftheH.P.turbine.Sincethisbearinghousingisfreetoslideonthebaseplate,theshaftingsystemmoveswithit.Seenfromthispoint,boththerotorandcasingoftheH.P.turbineexpandtowardsthefrontbearinghousingoftheH.P.turbine.TherotorandcasingoftheI.P.turbineexpandtowardsthegeneratorinasimilarmanner.TheL.P.turbinerotorisdisplacedtowardsthegeneratorbytheexpansionoftheshaftingsystemfromthethrustbearing.Themagnitudeofthisdisplacement,however,isreducedbythe24amountbywhichthethrustbearingismovedintheoppositedirectionbythecasingexpansionoftheI.P.turbine.DifferentialExpansionDifferentialexpansionbetweentherotorsandcasingsresultsfromthedifferencebetweenthecasingexpansionoriginatingfromthebearinghousingbehindtheI.P.turbineandthatofrotorfromthethrustbearing.ThismeansthatthemaximumdifferentialexpansionoftheHPandIPturbinesoccursattheendfurthestfromthethrustbearing.DifferentialexpansionbetweentherotorandcasingoftheL.P.turbineresultsfromthedifferencebetweentheexpansionoftheshaftingsystem,originatingfromthethrustbearing,andthecasingexpansionoriginatingfromthefixedpointoftheL.P.casingonthelongitudinalgirder.25BYPASSSYSTEMDuringtripoutoftheunitthesteamfromboilertotheturbineiscutoffandaftertrippingisovertheturbineisrequiredtoberolledagainstforsynchronizing,thisrequirepropersteamathighertemperature.HPBypassisusedforattainingthesteamparametersatafasterrate.AlsoHPbypasssystemprovidesanalternatepathfrommainsteamlinetocoldreheatlinebypassingtheHPturbine.Similarly,LPbypasssystemenablesanalternativepathfordumpingthesteamfromreheateroutlet(HRHline)directlyintocondenseratsuitableparametersbypassingtheIPandLPturbines.TheHP/LPstationisinoperatedduringfollowingconditions:Coldstartup,warmstartup&hotstartup.Loadrejection.Trippingoftheturbine.ThemainadvantagesofHP/LPbypasssystemareasbelow:Toestablishrequiredsteamparametersatsuperheaterandreheateroutletsinshorttimeforbestmatchingofsteamandturbinemetaltemperatures.Toachievequickstartupsfasterloadingandreducelossesduringstartupandshutdown.TosaveconsiderableamountofDMwater,whichotherwisewouldhavebeenwastedduringstartup.Toenablequickerwarmingupofsteamlines.Tominimizeoperationofsafetyvalves.HPBypassStationTheHPbypassvalveisacombinedtypeofpressurereducinganddesuperheatingstationwithspraywaterbeingtappedofffromBFPdischargeandissuppliedtoHPbypassdownstreamchamberviaspraycontrolvalve.WhileoperatingwithaLPbypassstation,theHPbypassstationenablesboileroperationbyestablishingsteamflowfrommainsteamlinetoCRHlineandfromHRHlinetocondenser26withoutcoordinationwithturbine.Thisallowsquickraisingofsteamparameterstoalevelacceptabletoturbineforrolloffduringstartup.MainPartsofHPBypassHPbypassstationconsistsofthefollowingmainequipments:HPBPValves:Itconsistsof2nos.mainvalvewithhydraulicactuators.InboththetwounitsthesteamsidevalvesaresameandoftypeARS100offollowingtechnicaldata:Maxvalvestroke43mmPressure170/50KgcmTemp540485CFlow216T/HrSincethevalvehastothrottlethesteamfromaveryhightolowPr.Level,thisisassociatedwithsonicvelocities,noiseandvibration.Tokeepdownthenoiselevelslottedstemconstructionhasbeenused.SprayValves:TheHPBPsteamvalvesareprovidedwith2sprayvalvetypeBPEandanisolatingvalvetypeBD.Thevalvebodyisofcylindricalshape&madeofcarbonsteel.Astheflowmediumiserosiveinnaturethetotalpr.Dropinthevalvehasbeendividedinthreestages.Thevalvestemismadeof11%Cr&1%Mo.Oilsupplyunit:Oilsupplyunitconsistsofatankinwhichthehydraulicmediumiskept.Auxiliarypistonpumpsuppliesenergyintheformofoilunderpressureformovingthehydraulicactuator.Theabnormalpressureriseislimitedbyasafetyreliefvalve.Oilunderpressureflowsthroughtheoilfilterintotheaccumulatorwhichstoresenergytocoverpeakdemands.Pressureswitcheslocatedontheoilsupplyunit,controlthepumpmotoroperationaccordingtothepressureintheaccumulator.Thepressurereducingvalvelocatedintheconnectionblockkeepsthesystempressuretotheservovalvewithinnarrowlimits.27Servovalves:Itismadeupofelectricalandhydraulicparts.Ittransformstheelectricalsignalsintocorrectquantityofoilatcorrectlocation.Theblockingunitallowstheoiltoflowfreelytothehydraulicactuator.Ifthesupplyfailsoroilpressurefallsbelowacertainlimit,theblockingunitblockstheoilflowtoandfromtheactuator.Blockingunit:Theelectrohydraulicallypilotoperatedblockingunitismountedbetweentheservovalveandtheactuator.Itclosesoffbothportstotheactuator.Ifelectricallydeenergizedorwithinsufficientoilpressure,andholesthepistonoftheactuator(disregardingsomeleakagedrift)initslastposition.Amechanicaloverrideontheblockingunitpermitsalsolocalmanualdeblocking.OperationofHPBPValvesTheoilfromtheoilunitispassedthroughindividualservovalvesandblockingunitsbeforeentryintothecylinderofactuatorsandtheyactascontrollersoftheactuators.Theservovalvesandtheblockingelementsareoperateddependingupontheimpulsefromthecontrolsystem.TheoilunithasanaccumulatorwhichensuresregularavailabilityofPr.Oil.NormallywiththeuseofservovalveandblockingwiththemainHPBPValvecanbeopenedfullyin1015s.However,aquickopeningdeviceconsistingofseparatesolenoidvalveandaccumulatorhasbeenprovidedtoopenthevalvesquickly(3s)wheneverrequired.TheaccumulatorhasapressureofNitrogenat55Kg/cm.ProtectionsinHPBPSystemTheHPBPsystemhasthefollowinginterlocks/protection:Condenserpressureverylow:BPvalveswillcloseonpriorityat0.7Kg/cm.28DownStreamtemperatureveryhigh:BPvalveswillcloseonprioritywiththedownsteamtemperature>380C.BD/BPEvalveopensifHPBPvalveopening>2%.BD/BPEvalvecloseswhenBPvalvesopening



ensurethatblockingunitleverisinlowerpositioni.e.normalposition.Inordertoclosethevalve,theleverattheotherendwhereC&Isocketisprovidedistobeoperated.Inthiscasealsofirstofallblocktheblockingunitandthenlifttheleverofservovalveupwardtillthedesiredclosingisachieved.Afterthevalvehasclosedtodesiredpositionlowertheblockingunitlever.ConditionsforautoopeningofByPassvalve:WhenGTBreakeropenstheByPasswillshiftfrommanualtoautomode&opensfullthereafter.Whenthemainsteampressureexceeds12Kg/cm2thanthepressuresetpointatHPBPconsole.LPBypassStationLPbypassvalvesmaintaintherequiredpressureinthereheatsystembybypassingthesurplussteamthroughsteamdumpingdevice.ThedesuperheatingandpressurereductiontakesplaceinthedumpingdeviceforwhichspraywateristakenfromCEPdischarge.ThisensuresthatonlytherequisiteflowismaintainedthroughtheIPandLPturbines.ThecontrolofLP29bypasssystemishookedupbysamecontroloilwhichisenvisagedfortheturbinegoverningsystem.ThecontrolsofLPbypasssystemareessentiallyacombinationofelectricalandwellprovenhydraulicsystem.Electrohydraulicconverterprovidesthenecessarylinkbetweenelectricalsystemandhydraulicactuationsystem.Theelectroniccontrolleractsasapressurecontrollerandregulatesthereheaterpressuretodesiredsetvalue.Ifreheaterpressureexceedsthissetvalue,thecontrollercausestheelectrohydraulicconvertertooperateandinitiatebypassoperations.EmergencystopandcontrolvalvesoftheLPbypassarecombinedinacommonbody.Thereisadoubleshutoffarrangementwhichseparatesthecondenserfromthereheaterduringnormaloperations.ThesafetydevicesincludedintheelectrohydraulicLPbypasscontrolsystempreventthedumpingofsteamintocondenserifthewaterinjectionpressureistooloworifpressureinsidecondenseristoohigh.Asameasureofadditionalprotections,LPbypassstationclosesinfollowingcases:CondenservacuumlowSpraywaterpressurelowTemperatureofcondenserwallhigh.30TURBINELUBOILSUPPLYSYSTEMTheturbineoilsystemfulfillsfollowingfunctions:LubricationandcoolingofbearingsJackinguptheshaftanprovidehydrostaticlubricationduringlowspeedoperationSupplyofcontroloiltogoverningandprotectionsystemSupplyofcontroloiltoLPbypassgoverningThemainoiltankisdesignedtobeairtight.Theextractorsproduceaslightvacuum(25100mimic)inthemainoiltankandthebearingpedestalstodrawoffanyoilvapour.MainOilTankThemainoiltankcontainstheoilrequiredforlubricatingandcontrolsystemsoftheturbine.Itnotonlyservesasastoragetankbutalsofordeaeratingtheoil.Thecapacityofthetankissuchthatthefullquantityofoiliscirculatednotmorethan8timesperhour.Thisresultsinaretentiontimeofapprox.7to8minutesfromentryintothetanktosuctionbythepumps.Thistimeallowssedimentationanddeaerationoftheoil.OilFlowinTankOilreturningtothetankfromtheoilsupplysystemfirstflowsthroughasubmergedinletintotherisersectionofthetankwherethefirststageofdeaerationtakesplaceastheoilrisestothetopofthetank.Oiloverflowsfromtherisersectionthroughtheoilstrainerintotheadjacentsectionofthetankwhereitisthendrawnoffontheoppositesidebythesuctionpipeoftheoilpumps.OilStrainerThebaskettypeoilstrainerismountedinthetank.Itisofstainlesssteelwiremeshof0.25mmfiltrationparticlesizeandcanbechangedbyopeningthetankcover.31OilVapourExhausterThewholetankismadeasairtightaspossible.Oilvapourexhausterproducesaslightnegativepressure(25100mmwc)inthetank,inthereturndrainlinesandinthespacesinthebearingpedestalssothatoilvapoursaredrawnout.OilLevelIndicatorThemainoiltankhasamagneticfluidlevelindicator.Extratankvolumeisprovidedbetweenthenormaloperatinglevelandthetankcovertoacceptoilfromtheentireoilsupplysystemwhentheturbineisshutdown.Thetankisconstructedwithastoppingbottomwithdrainconnectionsofthelowestpoint.Capacitancetypelevelswitchesareinstalledforindicatingnormal,lowandverylowlevel.DuplexoilfilterTheduplexfilterconsistsoffourfilterbodiesandisfittedwithachangeoverdevice,whichenablesthefilterstobeisolatedasdesired.Thefilterbodiesaredesignedaccordingtothepressurestageandtherelevantcodesandthefilteritselfisdesignedtoprovidesafety,takingintoaccountthedifferentialpressure.DifferentialpressureGaugeThefunctionofthedeviceistomeasureandgiveavisualindicationofthedifferentialpressure,whichoccursforexamplewhenfiltercontaminationincreases.OilPumpsandtheirFunctionsThemainoilpumpdrawstheoilthroughasuctionpipesituatedattheflowendofthetank.Thissuctionpipeactsasaninjectiontoaidthesuctionofthemainoilpump,whichhastoovercomeacertainsuctionheadpressureoilisconductedtotheinjectorviaaninjectionpipe.Thisinjectionpipealsofillsthesuctionpipeofthemainoilpumpwithoilwhentheplantisbeingstartedup.Theauxiliaryoilpumpsandemergencyoilpumparrangedonthetankareelectricallydrivenrotaryoilpumps.Thejackingoilpumpsalsosituatedonthetankareelectricallydriven32jackscrewimmersionpumps.Allpumpsimmersedintheoilcontainedinthetank,drawoilfromthedeepestpointinordertoobtainoilasfreeofairaspossibletodrivingelements.Thepumpsarefixedtothebaseplatesofthetankcover.MainOilPumpThemainoilpumpissituatedinthefrontbearingpedestalandsuppliestheentireturbinewithoilthatisusedforbearinglubrication,coolingtheshaftjournalsandascontroloilforthehydraulicgoverningsystem.Themainoilpumpisdrivendirectfromtheturbineshaftviathecoupling.Iftheturbosetisoutofoperationorthemainoilpumpfails,theauxiliaryoilpumpstakeoverthenecessaryoilsupply.Thesepumpsalsosupplyoilinthesuctionbranchesofthemainoilpumpuntilthemainoilpumptakesover.AuxiliaryoilpumpsTheauxiliaryoilpumpisaverticalonestagerotarypumpwitharadialimpellerandspiralcasing.Itisfixedtothecoveroftheoiltankandsubmergesintotheoilwiththebody.Itisdrivenbyanelectricmotorthatisboltedtothecoverplate.Theoilentersthesuctionconnectionfromtheunderneathandissuppliedtotheoilsystemviathepressurepipe.Thepumpshafthassleeveboringinthepumpcasingandgroovedballbearinginthebearingyoke.Thebearingsarelubricatedfromthepressurechamberofthepump,thesleevebearingviaaboreinthecasing,thegroovedballbearingviaalubeline.D.CEmergencyoilpumpTheemergencyoilpumpisofthevertical,centrifugalsubmergedtypeandserviceforlubricationandcoolingofthebearingsduringemergencyconditions.TheunitislocatedontopofthemainoiltankanddrivenbyaD.Cmotor.Thecompletepumpmotorassemblyisattachedtomountingplate,whichisboltedtothetopofthemainoiltank.JackingoilpumpThejackingoilpumpisaselfprimingscrewspindlepumpwiththreespindlesandinternalbearings.Thepumpsuppliesthejackingoilthatisneededforliftingtheshaftingatlowspeed.33TurbineOilCoolerTwooilcooler(2x100%)havebeenprovidedinthelubeoilsystemforcoolingtheoilusedforlubricationandcoolingofturbinebearings.Essentiallytheoilcoolerconsistsofatubenest,innerandoutershellslowerwaterboxandupperwaterbox.Thetubenest,throughwhichCoolingwaterflows,issurroundedbytheoilspaceformedbytheoutershell.Theoiltobecooledenterstheoutershellatinletnozzleandflowsintotheinnershell.Theshellsupportsthelargebaffleswhichareprovidedwithanopeninginthecenter.Betweeneverytwolargebaffles,thereisasmallbaffleplateheldandsupportedbyshorttubesplacedinsteelrods.Theintermediateplatesaresmallerindiameterthantheinnershellandthusleaveanannulargap.Thisarrangementservestoachieveacrossflowpatternforcingtheoilflowingtowardsoutlettoflowthroughthemiddleoflargebafflesandovertheedgeofthesmallerbafflesandincreasestheheattransferrate.Theinnershellandthelargebafflesaresupportedonthelowertubeplate,intowhichadmiralbrasstubesareexpanded.ThecoolingwaterentersandleavesthroughthelowerwaterboxwhichisdividedbyapartitionplatesoastoforcewaterthroughonehalfofthetubesystemtotheupperwaterboxIandfromtherethroughotherhalfbacktolowerwaterbox.Closedendtubesarearrangedintubesysteminlinewiththepartitionplatetoavoidoilbypassing.Inletandoutletbranchesofwaterboxareprovidedwiththermometers.Whenfillinginoil,opentheventvalve2.Fordrainingtheshell,drainvalve19isprovided.Thecoolingwaterflowisadjustedthroughouttogetthedesiredoiloutlettemperature,iftheoiloutlettemperatureishighevenwithmaximumCWflow,theoilcoolershouldbecleared.OilCoolerChangeoverDevice(SegmentPlateValve)Theoilofaturbosetiscooledinoilcoolers.Asegmentplatevalveisusedfordirectingtheoiltothecoolerinquestion,whileatthesametimeshuttingoffthereserveoilcooler.The



arrangementofthevalveissuchthatthehandleautomaticallyoperatesthesegmentplatesinboththeinflowoutflowlinesofonecooler.34ThreewayControlValveThethreewaycontrolvalveiselectricallydrivenandhasthefunctionofregulatingthelubricatingoiltemperature45oC.Possibleoilflowpathsforregulatingtheoiltemperature:Alllubricatingoilflowsthroughoilcooler.Lubricatingoilflowsthroughoilcoolerandbypasspiping.Alllubricatingoilflowsthroughthebypasspiping.35GOVERNINGSYSTEMGoverningschemecompriseofmainElectrohydraulicgoverningsystemandbackuphydraulicgoverningsystem.Thereferenceelectricalsignalsforturbinespeed,generatorload(MW)andM.SpressurearepickedupbyfieldmountedsensorsandprovidedtoElectricalgoverningcabinetforprocessing.AfterprocessingbyElectronicControllersandselectioncircuit,thesignalintheelectricalformistransmittedtoelectrohydraulicconverterforamplificationandconversionintohydraulicsignalforpositioningofcontrolvalves.ElectrohydraulicconverteralongwithhydraulicgovernorandotherhydraulicprotectionequipmentarelocatedinthegoverningsystemracksituatedbesidesturbineandthelayoutofhydraulicequipmentrackisillustratedinFig5.1.Allhydrauliccomponentsareopenandcanbeoperatedlocally.Thespeedsignalintheformofhydraulicpressureisprovidedtohydraulicgovernorfromhydraulictransmitter.ThehydraulicandelectricalspeedsensorsaremountedonMainOilpumpshaft,whichisenclosedinthefrontpedestalofturbine.Theoilpipelines,namelyControloil,tripoilandsecondaryoil,areextendedtoHP&IPstopandcontrolvalveservomotorsforoperation.TheprotectionschemecomprisesofelectricalprotectionandhydraulicprotectiondevicessuchasRemotetripsolenoidvalve,maintripvalveandlowvacuumtripforshuttingdowntheturbineduringemergencycondition.Thisgoverningandprotectionschemefacilitatesthetotaloperationofturbinefromremote,i.e.fromplantcontrolroom.36Fig5.1HydraulicEquipmentRackofGoverningsystem37Stop&ControlValveSchemeValveArrangementAsshowninFig5.2,mainsteamfromsuperheaterisadmittedtoHPTurbinethroughtwosetsofcombinedHPstopvalveandcontrolvalve(ESV&HPCV).SimilarlyhotreheatsteamisadmittedtoIPTurbinethroughtwosetsofcombinedIPstopvalvecontrolvalve(IV&IPCV).TheexhaustofIPturbineisdirectlyadmittedtoLPTurbinethroughtwocrossaroundpipes.TheturbineloadIscontrolledbythrottlegoverningmethod.TheturbinestartupisperformedbyadmittingsteamintoHPturbinefirst.Duringloadingofthemachine,IPcontrolvalvesarethrottledupto20%loadandthenkeptfullopenforminimizingthethrottlinglossesatnormaloperationofturbine.Soafter20%loadtheturbineiscontrolledthroughHPcontrolvalves.Fig5.2SteamAdmissionSystemforTurbine38HPStop&Controlvalve(ESV&HPCV)Themainstopandcontrolvalvearecombinedinacommonbody.Thestopvalve(ESV)isarrangedverticallywhilstcontrolvalvehorizontally.ThemainstopvalveprovidedbetweenmainsteamcircuitandHPturbinecaninterruptthesteamsupplytoturbineextremelyquicklyduringtripping.ThefunctionofthecontrolvalveistocontrolthemasssteamflowratebyvaryingthefirststagepressureofHPturbineinaccordancewiththeloadrequirementoftheunit.H.PStopvalve(ESV)ThearrangementofstopandcontrolvalveisexplainedinFig5.3steamentersthevalvecasing(14)viatheinletconnectionsabovethemainstopvalvedisc(2).Apilotvalveintegralwiththevalvesteam(10),operatesinsidethemainstopvalvedisc.Packingrings(6)sealthevalvestemwhereitpassesthroughthevalvebody.Thevalvedischasabackseatingarrangement,whichisforcedagainstthebasebushing(3)andwhenthevalveisfullyopenedformtheseatatthispoint.Thisalsoprovidesadditionalsealingforthepassageofthesteam.Thevalvebody(4)issecuredinthevalvecasing(14)bymeansofthethreadedring(8).ThesealinggasketisUsectionring(5)thelegsofwhichareflexiblyexpandedbythesteampressureandforcedagainsttheassociatedsealingfacesoftheeasing.Themainstopvalveisopenedhydraulically(TripOil)byservomotor(13)andclosedbyspringforcewhentripoilisdrained.H.PControlvalve(HPCV)Thecontrolvalvediscisintegralwiththestem(17).Theeffortrequiredtoopenthevalveisreducedbyreliefpoleinthevalvedisc.Valvediscandstem(17)areguidedbybushingsinthevalvebody(18)thestembeingsealedbypackingrings.(21).Additionalsealingisprovidedbythebackseatingarrangementofthevalvediscwhichliesagainstthebasebushing(20)whenthevalveiswideopen.Aswiththestopvalve,thevalvebody(18)issecuredinthevalvecasing(14)byathreadedring(23)andsealedbytheUshapedsealring(2)Thecontrolvalveisoperatedbythepistonoftheactuator(29)whichisopenedhydraulically(secondaryoilsignalandcontroloil)andclosedbyspringforceservomotor.39Fig5.3HPStopandControlValve(ESVandHPCV)1.Drainconnections2.Valvediscofstopvalve3.Basebushingwithscrewjoint4.ValveBody5.Sealring6.Packingring7.Glandbushing8.Threadedring9.Bushing10.Valvediscwithpilotvalve11.Pistonrod12.Column13.Servomotorforstopvalve14.Valvecasing15.Valveseat16.Valveseat17.Valvediscwithvalvestem1.18.Valvebody2.19.Drainconnection20.Basebushingwithscrewjoint21.Packingring22.Sealring23.Threadedring24.Glandbushing25.Sealring26.Flangewithbushing27.Column28.Pistonrod29.ActuatorforcontrolvalveL1,L2Leakagesteam40CombinedIPStop&Controlvalve(IV&IPCV)functionsStopvalveandcontrolvalvearecombinedinacommonbodywiththeirstemsarrangedatrightanglestoeachother.ThestopvalvecaninterruptthesupplyofsteamfromthereheatedtotheIPandLPturbinesextremelyquickly.ThecontrolvalvecontrolsthesteamflowratetotheIPandLPturbinesduringstartup(upto20%load)orduringbulkloadrejection.Thecontrolvalvesremainsfullopenabove20%to100%loadrangetoeliminateanythrottlinglosses.IPStopvalveTheassemblyofvalveisshowninFig.5.4.Thestopvalveisasingleseatvalvewithintegratedpilotvalve.Steamentersviatheinletofthevalvebody(1)andremainsabovethevalvedisc(4)whenthestopvalveisclosed.Apilotvalve,integralwiththevalvestem(6)isprovidedforrelieving,therebyreducingtheforcenecessaryforopening.Thevalvedisc(4)slidesinthebushingofthevalvecover(5)andhasbeadonthebackwhichliesagainstthebasebushing(7)andprovidesadditionalsealingatthispoint.Metalpackingrings(8)sealthevalvestem.Bothstemandvalvediscarepreventedfromrotating.Thestopvalveisopenedhydraulically(TripOilPressure)andclosedbyspringforce.IPControlvalveThecontrolvalveassemblyisshownisFig.5.4.Thecontrolvalvehasapipeshapedvalvedisc(14)thatisboltedtothevalvestem(16)andslidesinthebushinginthevalvecover(18).Thevalvediscisprovidedwithrelievingholestoreducethenecessaryactuatingforces.Aringfixedinthebushingofthevalvecoverpreventsthevalvediscfromrotating.ThisvalvediscalsohasabacksealingthatoperateswhenthevalveisfullyopenPackingrings(17)sealtheValvestem(16)inthevalvecover(18)Thecontrolvalveisoperatedbythepistonoftheservomotor(20)i.e.itisopenedhydraulically(withsecondaryoilpressuresignalandcontroloilpressureforce.Valveisclosedbyspringforce.Intheeventofdisturbanceinthesystemorontripout,bothstopandcontrolvalvecloserapidly.41Fig5.4IPStopandControlValve(IVandIPCV)1.Valvecasing2.Valveseat3.Drainconnection4.Valvedisc5.Valvecover6.Valvestemwithpilotvalve7.Basebushing8.Packingring9.Glandbushing10.Pistonrod11.Column12.Stopvalveoperator13.Valveseat14.Valvedisc15.Drainconnection16.Valvestem17.Packingring18.Valvecover19.Pistonrod20.ControlvalveoperatorL1Leakagesteam42GenerationandFunctionofGoverningOilsThevariousgoverningoilswiththeirsourceofgenerationarediscussedinthefollowingsubsections:ControlOil:Controloilissuppliedbymainoilpumporauxiliaryoilpump.Twocontroloilsareinitiatedinthegoverningrack.Oilisfilteredandthensuppliedtovariousgoverningequipmentsatnormalpressureof6.58.5Kg/cm2.Controloilservesfollowingfunctions:Sourceoilforgenerationofallotheroilssuchastripoil,AuxTripoil,secondaryoil,Auxiliarysecondaryoil,StartupandTestoil.SuppliedtoHP&IPcontrolvalve(HPCV&IPCV)servomotorpistonsforactuatingcontrolvalves.StartupOilThisoilisgeneratedbystartingandloadlimitingdevicewhenitspositionisbroughttozero.Thesourceoilbeingcontroloilandnormalpressurewouldbe4.5kg/cm2.Thefunctionofoilistolatch(readyforopening)theservomotorsplitpistonsofHP&IPstopvalves(ESV&IV).ThisissuppliedtothetestvalveofESV&IV.Whenstartingdevicepositionisraised,theoilpressureapproachedtozero.TripOilThisoilisgeneratedatremotetripsolenoidvalvewhenitisheldopen.Thesource



oilisfilteredcontroloilsuppliedfromcontroloilfiltersofnormalstream.Thenormaltripoilpressureisintherangeof57.5kg/cm2itservesfollowingfunctions:ToopenHP&IPstopvalves(ESV&IV)SourceoilforgenerationofAuxiliarysecondaryoilandsecondaryoilforoperationofcontrolvalves.43Whenturbinetripisinitiatedremotetripsolenoidoperatesandconnectsthetripoiltodrainwhichreducesthetripoilpressureinstantly.ThisinturnoperatemaintripvalvestodrainthetripoilcircuitresultinginclosureofHP&IPstop&controlvalves.PrimaryoilThisoilisgeneratedathydraulicTransmitterfittedonshaft.Thesamesourceoil,i.e.filteredcontroloilisfedtohydraulictransmitter.Inturnprimaryoilpressure,whichisproportionaltoturbinespeed,issuppliedtohydraulicspeedgovernorasaspeedsignal.Thenormalvalueofprimaryoilpressureis1.32.4kg/cm2forgovernorcontrol.SecondaryOilThisoilisgeneratedathydraulicconverterandelectrohydraulicconverterfollowuppistonswhichareconnectedinparallel.Thesourceoilforgenerationofsecondaryoilistripoilfedtohydraulicandelectrohydraulicconverterfromtripoilcircuit.Secondaryoilpressureprovidestheproportionalcontrolvalveopeningsignaltothecontrolvalveservomotors.Infacttheservomotorpilotvalveisoperatedbysecondaryoilpressurewhichinturnfeedscontroloiltoservomotorpistonsforproportionateopeningofcontrolvalve.Thesecondaryoilpressureremainsintherange2.55kg/cm2.TestOilTestoilisdrawnfromcontroloilfiltersforATTscheme.Thisoilisusedtofeedtripoilcircuitduringprotectivedevicetesting.Testoilisalsousedtoactuateoverspeedtripstrikersandthrustbearingdevice,duringtestwhenturbineisrunningnormal.44GENERALASPECTSOFBOILERThesteamgeneratorisofradiant,reheat,naturalcirculation,singledrumdrybottomsemioutdoortypeunit,designingforfiringcoalastheprincipalfuelandtheHFOoilfiringcapacityisequivalentto22.5%boilerMCR.4LDOburnersarecapablefor7.5%boilerMCRheatinput.AsperlayoutarrangementthemillsarelocatedbetweenboilerandESPs.Thecompletefurnacesectionisoffusionweldedwalltype.45LOWTEMPERATURESUPERHEATERTheLTSHsectionisofthecontinuousloops,plain,tubular,nondrainable,verticalinthelinetangenttubetype,arrangementandlocatedabovetheeconomizersection,inthebacksection,passoftheboiler.Theconsecutivespacedheatingsurfacehas120assemblies,4elementperassembly.TheoutletsectionofLTSHaloneisarrangedvertically.RADIALPLATENSUPERHEATERTheradialplatensuperheatersectionisofthecontinuousloops,plain,tubular,nondrainable,verticalinthelinetangenttubetype,arrangedforparallelflow.Theplatensuperheatersectionassembliesarewidelyspacedandlocatedintheradiantzoneatthefurnaceoutletsection.Theradialplatenheatingsurfacehas29assemblies,7elementperassembly.FINAL(FINISHPENDANT)SUPERHEATER(FSH)Finishpendantsuperheater(FSH)sectionisofspacedtypecontinuousloops,plain,tubular,nondrainable,andverticalinthespacedtypearrangedforparallelflow.ThisFSHislocatedinthehorizontalpassafterthereheatersection.Theconvectivefinalsuperheaterhas119assemblies,2elementsperassembly.REHEATERSYSTEMThereheatersystemisasinglestage,spacedtype,continuousloops,plain,tubular,nondrainable,andverticalinthelinespacedtype,arrangedforparallelflow.Thereheaterfrontpendantandrearpendantsectionislocatedinthehorizontalpassinbetweentheradiantplatensuperheaterandfinalsuperheatersection.Theconvectivesuperheatersectionhas59assemblies,6elementperassembly.Theapprox.totalconvectiveheatingsurfaceis2910msq.Theentirereheatersectionissuspendedfromtheroofstructuralsteelsections.SUPERHEATERDESUPERHEATERForcontrollingthefinalsuperheatsteamtemperatureattheratedvalue,twonumberofspraytypedesuperheatersarelocatedinthestemconnectinglinksbetweentheLTSHoutletheaderandplatenSHinletheader.Theseinterstagedesuperheatersareofweldedtype.Spraytubeandlinersareprovided.Foremergencycontrolofthereheateroutlettemperaturetwonumbersspraytypesuperheatersareprovided.Thesearelocatedinthecoldreheatpipingandusedduringanyemergencyconditionsforthesteamtemperaturecontrol.Thedesuperheatersareofweldedtype,spraynozzlesandlinesareprovided.46ECONOMIZERSYSTEMTheeconomizer,intwobanks,isofthecontinuousloop,plaintubular,drainableandhorizontal,inlinearrangementwithwaterflowupwardandgasflowdownwards.Theeconomizertubesaresuspendedfromeconomizerintermediateheaders,usingladdertypesupports.Theheatingsurfaceis5450msq.Aneconomizerrecirculationsystemisprovided,connectingthedowncomer(nearwaterwalllowerringheader)andeconomizerinletpipetoensurerequiredflowthrougheconomizertubesduringstartingconditionsoftheboiler.STEAMDRUMThesteamdrumisofthefusionweldedconstruction,fabricatedfromcarbonsteelplates.Ateachendofthedrum,amanholeof406mmdiameterisprovided,arrangedtoopeninwards.Thedrumislocatedintheupperfrontoftheunit.Thedrumisequippedwithprimaryturboseparators,secondarycorrugatedscrubbersandscreendryer,tolimitthesolidcarryoverinthesteamleavingthedrum.Alldruminternalareofcarbonsteelconstruction.Theturboseparatorsandthescreendryersareoftheremovabletype.Thedrumissuspendedfromtheboilerroofstructures.BOILERPARAMETERS1.Steampressureatsuperheateroutlet155kg/cm22.Steamtemp.atsuperheateroutlet540DegreeC3.Steampressureatreheaterinlet37.6kg/cm24.Steampressureatreheateroutlet36.1kg/cm25.Steamtemp.atreheaterinlet342DegreeC6.Steamtemp.atreheateroutlet540DegreeC7.Feedwatertemp.enteringeconomizer243DegreeC8.Ambientairtemp.40DegreeCFILLINGOFBOILERThefollowingportionoftheboilerhastobefilledwithwaterbeforethefurnaceislightedup:1.Waterwallportionofboiler2.Economizer3.Boilerdrumupto60mmlevelTheinitialfillingoftheboilerisdonebyboilerfillpump.Normalfillingisdonebyboilerfeedpump.47FEEDREGULATINGSTATIONThelocationofthisstationisatfiringfloorandfeedwatersupplytotheboilerisregulatedthroughthisstation.Duringtheinitialperiodofstartingtheunit,feedisregulatedthrough30%linebecausetherequirementofwaterissmallduringthisperiod.Lateronduringnormaloperation,eitherofthe100%lineontheleftorrightischarged,otherisstandby.AllthevalvesareoperatablefromUCB.BeforetakingtheabovelinesintoservicethewholepipinghastobethoroughlyventedtoavoidpossibilityofairlockinthesystemSOOTBLOWERSootblowershavebeenprovidedforcleaningandsootblowingthewaterwalls,superheaterandreheatertubesforefficientheattransfer.FILLINGCAPACITYOFBOILER1.Boilerdrum35Ton2.Economizer25Ton3.Waterwall130Ton4.Superheaters95Ton5.Reheaters50Ton6.Waterrequiredfornormallightup190Ton48COALPULVERISINGSYSTEMAtGHTP,bowlmillshavebeeninstalledforpulverizingtherawcoal.Coalofmaximumsizeof25mmisreceivedinRawCoalBunkersfr

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Guru Hargobind Thermal Power Plant, Lehra Mahobbat