Turbine vacuum system.ppt

Turbine vacuum system

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Turbine Vacuum
System

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Presentation outline
Why Vacuum system is required ?
Parts of Vacuum system?
Steam Ejectors
Vacuum Pumps

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Why is it required?
•Thesteamturbineitselfisadevicetoconvertthe
heatinsteamtomechanicalpower.
•Enthalpydropacrosstheturbinedecidesthe
workoutputoftheturbine.Forincreasingthis
enthalpydropacrosstheturbineweneed
effectivecondenservacuumsystem.

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•Bycondensingtheexhauststeamofturbine,the
exhaustpressureisbroughtdownbelow
atmosphericpressure,increasingthesteam
pressuredropbetweeninletandexhaustofsteam
turbine.Thisfurtherreductioninexhaustpressure
givesoutmoreheatperunitweightofsteaminput
tothesteamturbine,forconversiontomechanical
power.

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Parts of Vacuum System
•Condenser
•CW system
•Ejectors/Vacuum pumps
•Gland Sealing System

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Condenser
Steam from last stage
of LPT Exhausts on
condenser tube
condensation of
steam takes place
Water collected in hot
well

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Shell of the Condenser
•Theshellistheoutermostbodyofthecondenser
•shellisfabricatedfromfairlythickcarbonsteelplates.
•Duetoitslargesizetheshellissufficientlystrengthenedor
stiffenedinternallywithcarbonsteelplatestogivesufficient
rigidityfortheshellproper.
•Theshellalsogivessupporttonumberofintermediatesupport
platesforthelongtubes,dependingonthesizeofthecondenser.
•Atthesametimetheintermediatetubesupportplatesallowforthe
freemovementsoftubesinalldirectionsparticularlylengthwise
duetoexpansionandcontractionoccurringduringoperation.

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•The whole condenser is supported on heavy springs, mounted on
steel sole plates at suitable places on the concrete foundation
•At the bottom of the shell where the condensate is allowed to
collect, a sump (often referred to as the hotwell) is provided.
•This sump is common to both the halves but separated by a
partition wall in the middle up to the height of the bottom row of
tubes.
•The inside of shell and outside the tubes as a whole remains
under vacuumunder normal operating conditions. Inside the
tubes the cooling or circulating water passes through.

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Air Zone
•Insidetheshell,acentralorsideportion
longitudinallyisseparatedbyanoutershield
exceptatthebottom.Thispartitioniscalledthe
Airzone.
•Allthegasesreleasedinthecondenserdueto
coolingaretakenoutviatheseairzonetubes.
•Fromasuitableportionofthisairzoneinsidethe
shellanairventpipeistakenoutandbroughtout
oftheshellforconnectiontoanairextraction
device.

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Tube Sheets
•Ateachendoftheshell,tubesheetofsufficient
thicknessisprovided,withholesforthetubestobe
insertedandrolled.
•Totakecareoflengthwiseexpansionoftubessome
designshaveexpansionjointbetweentheshellandthe
tubesheetallowingthelattertomovelongitudinally.

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Water Boxes
•Thetubesheetateachendwithtubeendsrolled,foreachhalf
condenserisenclosedinafabricatedboxknownaswaterbox.
•Thesewaterboxesoninletsidewillalsohavebigsizeflanged
connectionsforcoolingwaterinletatlowerlevelforbutterfly
valves.
•smallventpipewithhandvalveforairventingathigherlevel,and
handoperateddrainvalveatbottomtodrainthewaterboxfor
maintenance.
•Similarlythermometerpocketsarelocatedatinletandoutletpipes
forlocalmeasurementscoolingwatertemperature.

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Tubes
•Generallythetubesaremadeofbrass,aluminumbrass,
cupronickel,stainlesssteelortitaniumdependingon
thecoolingwaterchemistry.
•Thelengthsarefixedatabout20ft(6m)(forthe200
MWdevicementionedabove),dependingonthesizeof
thecondenser.
•Theouterdiameterislimitedtoamaximumofoneinch
foreaseofhandlingandeaseofinsertionthroughthe
shelltubeholesandforrollingatbothends.

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CW system
CW pumps supply cooling
water to condensers
CW maintains vacuum in
condensers
CW flows through
condensers tubes

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STEAM EJECTORS
•Airandwatervaporareremovedfromthemain
steamcondenser,enterthe1ststageejectorandare
compressedtotheinterstagepressurebymeansof
thehighpressuremotivesteam.
•Theloadandmotivesteamaredischargedtothe
intercondenserandaportionofthewatervapor
loadandmotivesteamarecondensedby
condensatefromthemaincondenser.
•Non-condensiblesandassociatedwatervaporare
removedfromtheintercondenserbythe2ndstage
ejector.

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STEAM EJECTORS
Motive
steam
Non condensibile gases and
water vapour from condenser
Convergent
divergent
diffuser
Nozzle
Discharge to condenser

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STEAM EJECTORS
•Multistagecondensingejectorsystemscanbedesignedto
operateatanycondenserpressureanddesignsarenotlimited
bytheavailablecoolingwatertemperaturetothe
intercondenser(condensatecooledsystemsarecommon).
•Thesesystemshavenomovingparts,arethemostreliable,
requiretheleastmaintenanceofallventingsystems,andare
theleastexpensiveininitialcost.
•Onceequipmentisbuiltforagivenmotivesteampressurethat
pressuremustbemaintainedortheejectorwillbecome
unstableandlosevacuum.

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STEAM EJECTORS

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EJECTORS
•MAIN AIR EJECTOR
•STARTING AIR EJECTORS

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Ejectors

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VACUUM PUMPS
•The liquid-ring vacuum pump is a specific form of rotary
positive-displacement pump utilizing liquid as the principal
element in gas compression.
•The working parts of the liquid ring vacuum pump consist
of a multi-bladed impeller mounted eccentrically in a round
casing which is partly filled with liquid. As the impeller
rotates, the liquid is thrown by centrifugal force to form a
liquid ring which is concentric with the periphery of the
casing.

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LRVP
Suction port
Impeller
Gas vapour
mixture Liquid ring
Casing
Discharge port

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LRVP
•In addition to being the compressing medium, the
liquid ring absorbs the heat generated by
compression and friction, absorbs any liquid slugs
or vapor entering with the gas stream, and
condenses water vapor entering with the gas.
•A closed loop (or total recirculation) seal system is
commonly used. The seal water temperature warmer
than the cooling water to the pump heat exchanger,
which is normally taken from the same source as the
condenser cooling water (CW or ARCW).

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LRVP
Separator
vent
Non condensible gases and
water vapour from condenser
Cooling
water
Liquid ring vacuum pump system
Seal water
LRVP
Seal cooler
Makeup

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LRVP
•Thevacuumattainablebyaliquidringvacuumpumpislimitedby
thevaporpressureofthesealfluid.
•Astheoperatingvacuumapproachesthevaporpressureofthe
seal,moreandmoreofthesealfluidwill“flash”intovapor.
•Thecapacityoftheliquidringvacuumpumpisreducedasmoreof
theimpellerspaceisoccupiedbyvaporfromthesealfluid,leaving
lessspaceavailabletoaccepttheincomingload.
•Ifallowedtocontinue,cavitationwilloccurinsidethepump,
resultingindamagetointernalsurfaces,andpreventingthepump
fromachievinggreatervacuumlevels.

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