Steam-Power-Plant-updated.pdf engineering students

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1. Power Plant Engineering
Prepared by-
Nusrat Chowdhury
Assistant Professor, EEE
Daffodil International University (DIU)

2. Steam Power Plant

3. Introduction
Ageneratingstationwhichconvertsheatenergyofcoalcombustion
intoelectricalenergyisknownasasteampowerstation.
•Works on Rankine Cycle
•Steam produced in boiler (usually by burning coal) is expanded in
the prime mover (i.e. steam turbine)
•Condensed steam is fed back to boiler again
•The steam turbine drives the alternator produces electricity

4. Rankine Cycle

5. Rankine Cycle

6. Advantages and Disadvantages
Advantages
(i)Thefuel(i.e.,coal)usedisquitecheap.
(ii)Lessinitialcostascomparedtoothergeneratingstations.
(iii)Itcanbeinstalledatanyplaceirrespectiveoftheexistenceof
coal.Thecoalcanbetransportedtothesiteoftheplantbyrailor
road.
(iv)Itrequireslessspaceascomparedtothehydroelectricpower
station.
(v)Thecostofgenerationislesserthanthatofthedieselpower
station.
Disadvantages
(i)Itpollutestheatmosphereduetotheproductionoflargeamount
ofsmokeandfumes.
(ii)Itiscostlierinrunningcostascomparedtohydroelectricplant.

7. Layout of Steam Power Plant
The schematic arrangement of a modern steam
power station can be divided into the following
stages:
•Coal and ash handling plant
•Steam generating plant
•Steam turbine
•Alternator
•Feed water
•Cooling arrangement

8. Layout of Steam Power Plant

9. Coal and Ash handling plant
•Coalistransportedtopowerstationbyrailor
roadandstoredincoalstorageplantandthen
pulverized
•Pulverizedcoalisfedtotheboilerbybelt
conveyers
•Coalgetsburnedintheboilerandashproducedis
removedtotheashhandlingplantandthen
deliveredtoashstorageplantfordisposal
•A100MWstationoperatingat50%LFmayburn
about20000tonsofcoalpermonthandproduce
3000tonsofash

10. Choice of Site for Steam Power Stations
•Supply of fuel.
•Availability of water.
•Transportation facilities.
•Cost and type of land.
•Nearness to load centers.
•Distance from populated area.

11. Equipment of Steam Power Station
•Steamgeneratingequipment
•Condenser
•Primemover
•Watertreatmentplant
•Electricalequipment.

12. Steam Generating Equipment
•Boiler
•boiler furnace
•Superheater
•Economizer
•air pre-heater

13. Boiler
Aboilerisclosedvesselinwhichwaterisconvertedintosteamby
utilizingtheheatofcoalcombustion.Steamboilersarebroadly
classifiedintothefollowingtwotypes:
(a)Watertubeboilers:waterflowsthroughthetubesandthehot
gasesofcombustionflowoverthesetubes.
(b)Firetubeboilers:inafiretubeboiler,thehotproductsof
combustionpassthroughthetubessurroundedbywater.
Watertubeboilershaveanumberofadvantagesoverfiretubeboilers
•requirelessspace
•smallersizeoftubesanddrum
•highworkingpressureduetosmalldrum,

14. Boiler

15. Different Types of Boiler

16. Fire Tube Boiler

17. Water Tube Boiler

18. Fire Tube Boiler vs Water Tube Boiler

19. Boiler Furnace
Aboilerfurnaceisachamberinwhichfuelisburnttoliberatetheheatenergy.
Inaddition,itprovidessupportandenclosureforthecombustionequipment
i.e.,burners.Theboilerfurnacewallsaremadeofrefractorymaterialssuch
asfireclay,silica,kaolinetc.Thesematerialshavethepropertytoresist
changeofshape,weightorphysicalpropertiesathightemperatures.There
arefollowingthreetypesofconstructionoffurnacewalls:
(a)Plainrefractorywalls:suitableforsmallplantswherethefurnace
temperaturemaynotbehigh.
(b)Hollowrefractorywallswithanarrangementforaircooling:Inlarge
plants,thefurnacetemperatureisquitehighandconsequently,therefractory
materialmaygetdamaged.Insuchcases,refractorywallsaremadehollow
andairiscirculatedthroughhollowspacetokeepthetemperatureofthe
furnacewallslow.
(c)Waterwalls:Theseconsistofplaintubesarrangedsidebysideandonthe
innerfaceoftherefractorywalls.Thetubesareconnectedtotheupperand
lowerheadersoftheboiler.Theboilerwaterismadetocirculatethrough
thesetubes.Thewaterwallsabsorbtheradiantheatinthefurnacewhich
wouldotherwiseheatupthefurnacewalls.

20. Superheater
Asuperheaterisadevicewhichsuperheatsthesteami.e.,itraises
thetemperatureofsteamaboveboilingpointofwater.This
increasestheoverallefficiencyoftheplant.Asuperheaterconsists
ofagroupoftubesmadeofspecialalloysteelssuchaschromium-
molybdenum.Thesetubesareheatedbytheheatoffluegases
duringtheirjourneyfromthefurnacetothechimney.Thesteam
producedintheboilerisledthroughthesuperheaterwhereitis
superheatedbytheheatoffluegases.Superheatersaremainly
classifiedintotwotypesaccordingtothesystemofheattransfer
fromfluegasestosteamviz.
(a)Radiantsuperheater
(b)Convectionsuperheater

21. •Aradiantsuperheaterisplaceddirectlyinthe
combustionchamber.Simplywecansaythatradiant
superheatercanseetheflamesfromburner.
•Aconvectionsuperheaterislocatedinthepathofthe
hotgases.Thatmeansconvectionsuperheatercan’tsee
theflamesfromtheburner.

22. Economizer
•Aneconomiserisessentiallyafeedwaterheaterand
derivesheatfromthefluegasesforthispurpose.
•Thefeedwaterisfedtotheeconomiserbeforesupplying
totheboiler.
•Theeconomiserextractsapartofheatoffluegasesto
increasethefeedwatertemperature.

23. Air Pre-heater
Superheatersandeconomizersgenerallycannotfullyextractthe
heatfromfluegases.Therefore,pre-heatersareemployedwhich
recoversomeoftheheatintheescapinggases.Thefunctionofan
airpre-heateristoextractheatfromthefluegasesandgiveitto
theairbeingsuppliedtofurnaceforcoalcombustion.Thisraises
thefurnacetemperatureandincreasesthethermalefficiencyofthe
plant.Dependinguponthemethodoftransferofheatfromflue
gasestoair,airpre-heatersaredividedintothefollowingtwo
classes:
•Recuperativetype:Therecuperativetypeair-heaterconsistsofa
groupofsteeltubes.Thefluegasesarepassedthroughthetubes
whiletheairflowsexternallytothetubes.Thusheatoffluegases
istransferredtoair.
•Regenerativetype:Theregenerativetypeairpre-heaterconsistsof
slowlymovingdrummadeofcorrugatedmetalplates.Theflue
gasesflowcontinuouslyononesideofthedrumandaironthe
otherside.Thisactionpermitsthetransferenceofheatofflue
gasestotheairbeingsuppliedtothefurnaceforcoalcombustion

25. Condenser
Acondenserisadevicewhichcondensesthesteamatthe
exhaustofturbine.Itservestwoimportantfunctions.
•Firstly,itcreatesaverylowpressureattheexhaustof
turbine,thuspermittingexpansionofthesteaminthe
primemovertoaverylowpressure.Thishelpsin
convertingheatenergyofsteamintomechanicalenergyin
theprimemover.
•Secondly,thecondensedsteamcanbeusedasfeedwater
totheboiler.
Therearetwotypesofcondensers,namely:
(i)Jetcondenser
(ii)Surfacecondenser

26. JetCondenser:Inajetcondenser,coolingwaterand
exhaustedsteamaremixedtogether.Therefore,the
temperatureofcoolingwaterandcondensateisthesame
whenleavingthecondenser.
Advantages:
•lowinitialcost
•lessfloorarearequired
•lesscoolingwaterrequiredand
•lowmaintenancecharges.
Disadvantages:
•condensateiswastedand
•highpowerisrequiredforpumpingwater.
Condenser

27. SurfaceCondenser:Inasurfacecondenser,thereisno
directcontactbetweencoolingwaterandexhausted
steam.Itconsistsofabankofhorizontaltubesenclosedin
acastironshell.Thecoolingwaterflowsthroughthe
tubesandexhaustedsteamoverthesurfaceofthetubes.
Thesteamgivesupitsheattowaterandisitself
condensed.
Advantages:
•condensate can be used as feed water
•less pumping power required and
•creation of better vacuum at the turbine exhaust.
Disadvantages:
•high initial cost
•requires large floor area and
•high maintenance charges.
Condenser

29. Prime Mover
Theprimemoverconvertssteamenergyintomechanicalenergy.
Therearetwotypesofsteamprimemovers:
•steamenginesand
•steamturbines
Asteamturbinehasseveraladvantagesoverasteamengineasa
primemover:
•highefficiency
•simpleconstruction
•Higherspeed
•lessfloorarearequirementand
•lowmaintenancecost.

30. Steamturbinesaregenerallyclassifiedintotwotypesaccordingto
theactionofsteamonmovingbladesviz.
•Impulseturbines:thesteamexpandscompletelyinthestationary
nozzles(orfixedblades),thepressureoverthestationarynozzles,
theremainingexpansiontakesplaceduringitsflowoverthe
movingblades.Theresultisthatthemomentumofthesteam
causesareactionforceonthemovingbladeswhichsetstherotor
inmotion.
•Reactionsturbines:thesteamispartiallyexpandedinthe
stationarynozzles,theremainingexpansiontakesplaceduringits
flowoverthemovingblades.Theresultisthatthemomentumof
thesteamcausesareactionforceonthemovingbladeswhichsets
therotorinmotion.
Steam Turbine

31. Steam Turbine

32. Turbine –Full View

33. Water Treatment Plant
Boilersrequirecleanandsoftwaterforlongerlifeandbetter
efficiency.However,thesourceofboilerfeedwaterisgenerallya
riverorlakewhichmaycontainsuspendedanddissolved
impurities,dissolvedgasesetc.Therefore,itisveryimportantthat
waterisfirstpurifiedandsoftenedbychemicaltreatmentandthen
deliveredtotheboiler.
Thewaterfromthesourceofsupplyisstoredinstoragetanks.The
suspendedimpuritiesareremovedthroughsedimentation,
coagulationandfiltration.Dissolvedgasesareremovedby
aerationanddegasification.Thewateristhen‘softened’by
removingtemporaryandpermanenthardnessthroughdifferent
chemicalprocesses.Thepureandsoftwaterthusavailableisfed
totheboilerforsteamgeneration.

34. Electrical Equipment
(i)Alternators:Eachalternatoriscoupledtoasteamturbineand
convertsmechanicalenergyoftheturbineintoelectricalenergy.
Thealternatormaybehydrogenoraircooled.Thenecessary
excitationisprovidedbymeansofmainandpilotexcitersdirectly
coupledtothealternatorshaft.
(ii)Transformers:Ageneratingstationhasdifferenttypesof
transformers,viz.,
(a)mainstep-uptransformerswhichstep-upthegeneration
voltagefortransmissionofpower.
(b)stationtransformerswhichareusedforgeneralservice(e.g.,
lighting)inthepowerstation.
(c)auxiliarytransformerswhichsupplytoindividualunit-
auxiliaries.
(iii)Switchgear.Ithousessuchequipmentwhichlocatesthefault
onthesystemandisolatethefaultypartfromthehealthysection.
Itcontainscircuitbreakers,relays,switchesandothercontrol
devices

35. Efficiency of Steam Power Station
(i) Thermal efficiency
(ii) Overall efficiency
The thermal efficiency of a modern steam power station is about 30%.
The overall efficiency of a steam power station is about 29%. It may be seen
that overall efficiency is less than the thermal efficiency. This is expected
since some losses (about 1%) occur in the alternator. The following relation
exists among the various efficiencies.
Overall efficiency = Thermal efficiency X Electrical efficiency

36. Example2.1.Asteampowerstationhasanoverall
efficiencyof20%and0·6kgofcoalisburnt
perkWhofelectricalenergygenerated.Calculatethe
calorificvalueoffuel.

37. Example 2.2. A thermal station has the following
data :
Max. demand = 20,000 kW ; Load factor = 40%
Boiler efficiency = 85% ; Turbine efficiency = 90%
Coal consumption = 0·9 kg/kWh ;
Cost of 1 ton of coal = Rs. 300
Determine (i) thermal efficiency and (ii) coal bill per
annum.

38. Example2.3.AsteampowerstationspendsRs.30
lakhsperannumforcoalusedinthestation.
Thecoalhasacalorificvalueof5000kcal/kgand
costsRs.300perton.Ifthestationhasthermal
efficiencyof33%andelectricalefficiencyof90%,
findtheaverageloadonthestation.

39. Example2.5.A100MWsteamstationusescoalof
calorificvalue6400kcal/kg.Thermal
efficiencyofthestationis30%andelectrical
efficiencyis92%.Calculatethecoalconsumptionper
hourwhenthestationisdeliveringitsfullrated
output.