VOLIIS6FWS.docx
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VOLIIS6FWS.docx
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VOLIIS6FWS
SECTION–6
FEEDWATERsystem
SECTION–6
FEEDWATERSYSTEM
TABLEOFCONTENTS
CLAUSENO.DESCRIPTIONSHEETNO.
1.0.0SCOPEOFSUPPLYANDSERVICES3
2.0.0FEEDWATERHEATERS,BOILERFEEDPUMP
ANDDEAERATOR3
3.0.0PerformanceRequirements10
4.0.0DesignandConstruction10
5.0.0INSPECTION,TESTINGANDREPORTS14
6.0.0PERFORMANCEGUARANTEETESTS15
SECTION–6
FEEDWATERSYSTEM
1.0.0SCOPEOFSUPPLYANDSERVICES
Thebiddersarerequestedtonotethatonlythemajorequipmentarementionedbelow.Anyotherequipment/systemnotspecificallymentionedbelowbutmentionedelsewhereinthespecificationsandanyotherequipment/systemessentialforsmoothandefficientfunctioningofthesystemshallbeconsideredinthescopeofthebidderatnoextracost.
1.1.0Thisspecificationcoversingeneral,theminimumrequirementandguidelinetobeaddressedbythecontractorfordesign,manufacture,testingatmanufacturer’sworks,supply,transportandsupervisionoferection,testingandcommissioningoffeedwatersystem.
1.2.0Themajorcomponentsofthefeedwatersystemforeachturbineunitshallbe:
∙VerticalLowpressure(LP)heater&Horizontaldraincooler
∙SlidingpressureDeaerator(commonfor2x25MWUnit)
∙Three(3)Nos.(3x100%)boilerfeedpump,Commonfor2x25MWunit,eachpumpshallbesuitablefor1x25MWunit.
∙VerticalHighpressure(HP)heater
∙Relatedpipingandvalves
1.3.0Thefollowingsystemshallbecommonforboththeunits
∙SlidingpressureDeaerator
∙Three(3)Nos.(3x100%)boilerfeedpump,Commonfor2x25MWunit,eachpumpshallbesuitableforof1x25MWunit.
1.4.0Noequipmentiscommoninfeedwatersystemsof2x25MWunitsunlessotherwisespecificallymentioned.
2.0.0FEEDWATERHEATERS,BOILERFEEDPUMPANDDEAERATOR
2.1.0LPFeedheatersandDRAINCoolers
LPheatershallbeverticaltype.AdequateprovisionmustbemadetoprotecttheturbineagainstthebackflowofwaterfromtheLPfeedheaters.Thedrainlinesmustbeofadequatesizeand,areequippedwithadraincontrolsystem.Ifthewaterlevelcontinuestorise,alevelmonitormustclosethemotorizedshut-offvalveinthebleedlinetoLPfeedheateratthemaximumpermissiblewaterlevelandcondensatelineacrossLPheaterbypassed.TheLPheaterdrainlevelcontrolvalvescontinuouslydumpscondensatetoexhauststeamductdrainpotviadraincooler.TheLPHeatershallhavebypassstationwhichoperatesintheeventofcondensatereachinghighhighlevelinLPheater.Themaximumwaterlevelisalsotobeappliedfortheturbinetripthroughaseparatelevelmonitor..HeightofL.PheatershallbesuchthatitshallnotprojectaboveSTGBuildingoperatingfloor.
TheLPheatersshallhaveindividualbypassstations.
Theflowresistanceonthedrainsideofthecondensatecoolersmustnotexceedforanassumedflowatbursttubesof50%ofthemaximummaincondensateflow.ThesizingofLPheatercondensatedrainpipingshallbeasperlatestHEIstandards.SteamsidesafetyvalvemustbesuitablefordischargingmaincondensateflowasperHEIstandards.
TheLPfeedheatershallbeofstandardverticaltubeplatetypewithU-tubes.
Thecondensatedraincoolersshallbeofstandardhorizontaltubeplatetype.
Thewaterboxesmustbeprovidedwithflangedcoverstoallowfullaccesstothetubeplate.
Pipeconnectionsshallbeflangedonthemaincondensateside;allotherpipeconnectionsandallconnectionsonthevacuumsideshallbewelded.
Valvesandotherfittingsexceedingnominalsizeof25mm,whicharecontinuouslyorintermittentlyundervacuum,mustbeprovidedwithsealwaterconnections.
Shellandtubebundleshallbeequippedwitheffectivebaffleplatesandprotectionatthesteamanddrainsinlet.Particularcaremustbetakenforproperairextractionsothatnoairpocketscanforminsidetheheatexchangers.
2.2.0HPFeedheaters
Duringlow-loadoperationoftheturbine,whenthepressureinHPfeedheaterisnolongersufficienttodrivethecondensateintothefeedwatertank,thedrainisledtothecondenser(viaanemergencyflashtank)viaalow-loaddraincontrolsystem.TheautomaticswitchoverofthedrainfromthefeedwatertanktothecondenserandviceversashallbedonedependentonthepressuredifferencebetweenHPheaterandfeedwatertankconsideringasuitablehysteresischaracteristic.HeightofH.PheatershallbesuchthatitshallnotprojectaboveSTGBuildingoperatingfloor.
AdequateprovisionmustbemadetoprotecttheturbineagainstthebackflowofwaterfromtheHPfeedheaters.Ifthewaterlevelrisesexcessivelythefeedwaterlinemustbeautomaticallyby-passedandsimultaneouslythemotorizedshut-offvalvesandtheemergencycheckvalvesinthebleedlinesupstreamthefeedheatersaretobeclosed.Atthemaximumpermissiblewaterlevelanothermonitormustinitiateturbinetrip.
ItmustbepossibletooperatethefeedwaterbypassvalvesoftheHPfeedwatersbothmanuallyandautomatically.AutomaticoperationshouldbebymeansofseparatelevelmonitorsintheHPfeedheaters.
ThesafetyvalvetobeprovidedontheshellsideoftheHPfeedheatermustbecapableofdischargingthequantityoffeedwaterwhichwouldtheoreticallybedischargedthroughtwoopen-endedtubesundertheclosedvalveheadofthefeedwaterpumps.
TheHPfeedheatersshallbeofverticaldesign.IfconstructionsotherthanthetypesthisintendedtobeprovidedfortheHPfeedheaters(e.g.tubeplatetypes)thesuppliershallsubmitareferencelisttodemonstratethatheiswellexperiencedinthatfield.TheuseoftheseconstructionsissubjecttotheapprovaloftheOwner.
Thefeedwatertubesmustbebuttweldedtothecylindricalheadersinaccordancewithrecognizedpractice.Easyaccesstotheheadersmustbeassuredforplugginganytubeswhichmaybecomedefective.Theheatersmustbeequippedwithself-sealingcoversforthispurpose.
Allconnectionmustbewelded.Thefeedheatertubesmustbemanufacturedfromhigh-strengthsteel.Adequateprovisionmustbemadeinthedesignforthepossibleexpansionofthetubesandinternalsunderthedifferenttemperatureconditions.Thecompletetubebundlemustbestress-relieved.
Effectivebaffleplatesandprotectionmustbeincorporatedintheshellandtubebundleadjacenttothesteaminlet.
2.3.0FeedwaterTankandDeaeratorforFeedwaterSystem(Commonfor2x25MWUnit)
Thedeaeratorconnectedtothefeedwatertankshouldpreferablybeofthespraycumtraytypeorstroketype.HoweverCascade-typedeaeratorsandsimilartypeswillalsobeaccepted.Inallcasesthefeedwatertanksmusthaveawarming-upsteamline.
Thesizeofthedeaeratormustbesufficientforawaterflowofatleast1.1timesthemaximumboilerfeedwaterflowplusthemaximumfeedwaterinjectionquantityforboththeboilers.
Thefeedwatertankshallbeequippedwithacondensateventsteamcondenser,ifnecessaryaspermanufacturer’sstandards.
Ifthefeedwatertankpressurefalls,asupplementarysteamsupplyistakenfromtheauxiliarymanifold.Thissupplyistakenwhentheturbineisoutofoperationorduringstart-up/shut-downandduringlowloadoperation,inordertomaintaintherequiredminimumfeedwatertemperature.ThedrainfromtheHPfeedheatersandtherecirculationandleak-off-linefromthefeedwaterpumpsarealsoreturnedtothefeedtank.
Thedeaeratorspraynozzlesandthenozzlestrainershallbeofstainlesssteel.
Sufficientdistanceshallbeprovidedbetweenthenormalregulatedwaterlevelofthefeedwatertankandthemaximumpermissiblelevel.ExtractionlineMOVfordeaeratorshallclosewhenlevelinfeedwaterstoragetankreacheshigh-highlevel.Additionallysafetyvalvesmustbeprovidedtobeabletodischargesafelythemaximumpossibleincomingcondensateflow.
Toallowforpossiblesloppingofthecontentsofthefeedtank,ahorizontalimpactforceof10%ofthemaximumverticalloadmustbeassumed.
Inordertoavoidthedangerofcorrosion,diverterplatesshouldbefittedinthedeadcornersofthefeedtanktoimprovecirculation.Thewallthicknessforthefeedtankdeaeratorshallhaveacorrosionallowanceofatleast3mm.Thetankmustbesuitablystiffenedtosafelywithstandfullvacuum.
2.3.1Allinstrumentstapoffpointswithrootvalvesandstubsforthermowells
2.3.2AllnozzlesasperP&IDasminimum.
2.3.3Safetyvalvesandventvalvesasperapplicablestandards.
2.3.4Allfixingmaterialrequiredforthefasteningofthedeaeratorwithitssupportingstructuresincludingmatchingplate,ifany.
2.3.5Cleatsrequiredforfixinginsulationtothedeaeratorandstoragetank.
2.3.6Allcommissioningsparesandspecialtools&tackles.
2.3.7MandatorysparesandO&Msparesfor2yearsoftroublefreeoperation.
2.3.8Completeinstrumentation&controltomakethesystemcomplete.
2.3.9Allelectricalmotorsandpushbuttonstations.
2.3.10SPAREPARTS
EssentialO&Msparepartsfortwoyearsoftroublefreeoperationofthesystemshallbesuppliedandquotedseparatelyalongwithlistofspares.
2.3.11SPECIALMAINTENANCETOOLS&TACKLES
Twosetsofspecialtools&tacklesrequiredforoperation,maintenanceandrepair,neatlypackedinsteelboxes,completewithoperatingdetailsshallbesupplied.Listofmaintenancetools&tacklesbeingsuppliedshallalsobefurnished.
2.3.12DESIGNANDCONSTRUCTION
2.3.12.1Thedeaeratorshallbeeitherpreferablyspraycumtraytypeorstroketype.
2.3.12.2Spraynozzlesandtheirspringsshallbeofprovendesignandmadeofstainlesssteel.Itshallbedesignedtohaveminimumpressureloss.Theinternalsofthedeaeratorshallbearrangedforeasyinspection,andremovalformai
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