ENGINEERING ASPECTSOF TURBINE.docx
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ENGINEERING ASPECTSOF TURBINE.docx
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ENGINEERINGASPECTSOFTURBINE
ENGINEERINGASPECTSFORSELECTIONOF
MAINSTEAMTURBINEFOR210MWANDABOVE
V.Subramani,ChiefManager/Mech.,PowerStationEngg.,NLCLtd,Neyveli.
1.0TheThermalCycle
BeforegoingintothedetailsoftheengineeringaspectsofmainsteamturbineofaThermalPowerPlant,anunderstandingonthebasicsofthermalcycleisnecessary.ThebasicThermalCycleofaThermalPowerPlantisshowninFig.1.TheThermalCycleofa250MWThermalPowerPlantconsistsofthefollowing:
1.1SteamTurbine-receivessuperheatedsteamat170ata,535deg.Cand764t/hintheHighPressureturbine.AfterworkdoneintheHPTurbine,theexpandedsteamcalledColdReHeat(CRH)steamat45ataand345degCisheatedintheReheatersoftheboiler.AfterreheatingthesteamnamelyHotReHeat(HRH)steamisadmittedat40ata,535deg.Cand667t/hintheIPturbineandthentotheLPturbineat7ata,287degCand583t/h.AfterworkdoneintheIPandLPturbines,theexpandedsteamat0.127ata,49degCand508t/hisadmittedintheneckoftheCondenser.
1.2Condenser–TheexitsteamfromtheLPTurbineiscondensedusingcoolingwaterinthecondenserandcollectedintheHotWelloftheCondenser.Tofacilitatecompletecondensation,constantpressureismaintainedat0.127ata(absolute)(equaltoavacuumofapprox.664mmofHg)byremovingthenoncondensablegasesusingsteamjetairejectors.
1.3CondensateExtractionPumps–Thecondensatefromthehotwellispressurizedto19ataandsenttotheregenerativesystemforheating.
1.4RegenerativeSystem–TheregenerativesystemisacombinationofheaterswhichincludeGlandSteamCondenser,SteamJetAirEjectors,LPHeaters,DeaeratorandHPHeaters.
1.5SteamJetAirEjectors–ThecondensatefromCEPisheatedintheejectorsutilizingtheauxiliarysteamrequiredtocreateandmaintainvacuum.Thetemperatureincreaseofcondensateisapprox.1.2degC.
1.6GlandSteamCondenser–Utilizesoutcomingsteamfromtheturbineglandstoincreasethetemperatureofthecondensateby0.5degC.
1.7LPHeaters–ThecondensateisheatedinLPHeater1to71degC,inLPHeater2to92degCandinLPHeater3to119degCusingtheextractionsteamfromtheintermediatestagesofLPTurbineat0.4ata,0.9ataand2.3atarespectively.
1.8Deaerator–Thedeaeratorisadirectcontacttypeheaterwhichheatthecondensateto157degCusingtheIPexhauststeamandCRHsteamat6ataand270deg.C.
1.9BoilerFeedPumps–Thefeedwaterfromthedeaeratorispressurizedto190ataandsenttotheHPHeatersforheating.
1.10HPHeaters–ThefeedwaterisheatedinHPHeater5to200degC,inHPHeater6to253degCusingtheextractionsteamfromtheintermediatestageofIPTurbineat16ata,407degCandfromCRHsteamat44ata,345degC.Thefeedwateristhenpassedtotheeconomizeroftheboilerthroughfeedcontrolvalves.
1.11SteamGenerator:
ThefeedwaterisheatedintheeconomizerandwaterwallsthroughnaturalcirculationandthesaturatedsteamfromthesteamdrumissuperheatedinthesuperheatersfortheproductionofsuperheatedsteamwhichwillbesenttotheHPTurbineat170ataand535degC.
2.0EfficiencyofaThermalPowerPlant
Theefficiencyofathermalpowerplantrangesfrom35to42%dependingupontheunitsizeasagainst85to90%forhydroelectricand51to58forcombinedcyclepowerplants.ThereasonbeinglowerefficiencyofthecycleastheunutlisedheatisledintothecondenserasshowninFig.2.Thereheatingofthesteamintheboilerandutilizationofaportionofthesteam(approx.200t/h)forheatingthefeedwaterintheregenerativesystemincreasestheefficiencytothetuneofabout4to7%dependingupontheunitsize.Theincreaseinefficiencyincreaseswiththenumberoffeedheatersandthemaximumislimitedto9duetoeconomicconsiderations.
2.1HeatRateofthePowerPlant
Thesteamrate,specificfuelconsumptionandheatratearethecriteriausedfortheperformanceevaluationofthethermalpowerplants.
Steamrate–istherateofgenerationofsteaminKg/sort/hintheboiler
Specificfuelconsumption–istheratioofrateoffuelconsumptioninkg/htonetusefulpoweroutputinkWh
Heatrateofturbine–istheratioofheatutilizedintheturbineinkJ/horKcal/htoelectricalpoweroutputinkWh
Heatrateofthepowerplant–istheratioofrateofheatadditioninthefurnaceoftheboilerkJ/horKcal/h(equaltothemassoffuelinkg/hmultipliedbythecalorificvalueofthefuelinkcal/kg)toelectricalpoweroutputinkWh.
3.0AbbreviationsandTermsassociatedwithSteamTurbine
a)MS–MainSteamalsotermedasLS–LiveSteam–SteamfromsuperheaterofBoilertoHighPressure(HP)Turbine.
b)CRH–ColdReHeat–SteamfromtheexhaustofHighPressureTurbinetotheReheateroftheBoiler.
c)HRH–HotReHeat–SteamfromReheaterofBoilertoIntermediatePressure(IP)Turbine.
d)HPT–HighPressureTurbine.
e)IPT–IntermediatePressureTurbine.
f)LPT–LowPressureTurbine.
g)ESV–EmergencyStopValvealsotermedasHPSV(HighPressureStopValve)–ValveintheMSlinebeforetheHPT.
h)HPCV–HighPressureControlValve–ValveintheMSlinebeforetheHPTbutaftertheESV.
i)RHSV–ReheatStopValvealsotermedasIPSV(IntermediatePressureStopValve)–ValveintheHRHlinebeforetheIPT.
j)IPCV–IntermediatePressureControlValvealsotermedasICV(interceptorvalve)–ValveintheHRHlinebeforetheIPTandaftertheIPStopValve
k)HPBP–HighPressureByPass–SteamlinebypassingtheHPTtakenbeforeESVandconnectedtoCRHline
l)LPBP-LowPressureByPass–SteamlinebypassingtheIPTandLPTtakenbeforeICVandconnectedtoCondenser
m)TGMCR–TurboGeneratorMaximumContinuousRating–RatingoftheTurbineandGeneratorcombinationformaximumcontinuousrunningthroughoutthelifeofthePowerPlant
n)VWO–ValveWideOpen–ThemaximumcontinuousflowpassingcapabilityatHPTControlValve.Itrangesfrom102%to108%
o)HBD–HeatBalanceDiagram–Diagramshowingthepressure,temperature,flowandenthalpybeforeandaftereachequipmentinthethermalcycle,balancingtheheatenergy.AtypicalHBDisshowninFig.3.
p)MOP–MainOilPump–ThepumpconnectedwiththeHPTforsupplyingLub.Oil(controloilalsodependingonthedesign)tothebearingsduringnormaloperation.
q)AOP–AuxiliaryOilPump–ThepumpdrivenbyACmotorsupplyingLub.Oil(controloilalsodependingonthedesign)tothebearingsduringstartupandshutdown.
r)EOP–EmergencyOilPump–ThepumpdrivenbyDCmotorsupplyingLub.Oiltothebearingsduringpowerfailure.
s)JOP–JackingOilPump–ThepumpdrivenbyAC/DCmotorsupplyingOilathighpressuretothebearingsforliftingoftherotorforturning(barring)gearoperation.
t)Turning(barring)Gear–Mechanismtorotatetherotoratslowspeedsforcoolingtheturbine
4.0TheHP/IP/LPTurbineSystemScheme
TheHP/IP/LPTurbineSystemSchemeisshowninFig.4.Superheatedsteamat170ata,535deg.Cand764t/hfromtheBoilerisadmittedtotheHighPressureturbinethroughMSstrainers,ESVandCV.AfterworkdoneintheHPTurbine,theexpandedCRHsteamat45ataand345degCisheatedintheReheatersoftheboiler.AfterreheatingHRHsteamisadmittedat40ata,535deg.Cand667t/hintheIPturbineandthentotheLPturbineat7ata,287degCand583t/hthroughcrossaroundpiping.AfterworkdoneintheIPandLPturbines,theexpandedsteamat0.12ata,49degCand508t/hisadmittedintheneckoftheCondenser.
Steamisextractedforheatingintheregenerativesystemasfollows:
a)FromCRHtoHPheater6
b)FromintermediatestageofIPturbinetoHPheater5
c)FromexhaustofIPturbinetoDeaerator
d)FromintermediatestageofLPturbinetoLPheater3
e)FromintermediatestageofLPturbinetoLPheater2
f)FromintermediatestageofLPturbinetoLPheater1
AlsoauxiliarysteamrequirementfornormalrunningoftheunitshallbetappedofffromtheMSaswellasCRHlines.
5.0OperationalcapabilityRequirements
5.1Theturbine-generatorsetshallbecapableofcontinuousoutputof250MWunderratedsteamconditions,3%make-upand47.5Hzgridfrequency.Thecondenserbackpressurecanalsobespecified.
5.2Theturbineshallalsobecapableofoperatingcontinuouslywithvalveswideopen(VWO)toswallow108%ofTGMCRsteamflowtotheturbineatratedmainsteamandreheatsteamparameters.
5.3.1Thesteamturbinegeneratorunitshallbesuitablefordirectconnectiontosteamgeneratorhavingnointerconnectionwithotherunitseitherontheboilerfeedwatersideormainsteamside.
5.4Thesteamturbineshallhaveuncontrolledextractionsforregenerativefeedheatingbasedonoptimisedcycleandshallbesuitableforsatisfactoryoperationundertropicalconditions.
5.5H.P.heaters(bothstrings)outofservice:
TurbineshallbecapableofcontinuousoperationunderH.Pheaters(bothstrings)outofservicewithmax.outputcommensuratewithboilerheatdutycorrespondingtoturbineVWOconditionoperationwithHPheatersinserviceandthesameshallbedemonstrated.
5.6H.P.heaters(onestring)outofservice:
TurbineshallbecapableofdeliveringtheratedoutputunderH.Pheaters(onestring)outofservice
5,7Overpressureoperation:
TheturbineshallbecapableofwithstandingpossibleoverpressurisationunderVWOandensurecorrespondingcontinuousoutputofTGset.Alsotheturbineshallbecapableofacceptingvariationinsteamtemp.andpressureasperIEC45incasecontinuousoverpressureoperationispossible.
5.8Partload&startupoperation:
Turbineshallbecapableofop
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