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Transforming Live, Inventing Future
A
Project Report
On
NTPC POWER STATION, BADARPURBy
SANDEEP JANGIR
(09-ME-1249)
DEPARTMENT OF MECHANICAL ENGINEERING
Echelon Institute of Technology
Kabulpur Faridabad - 121101
Haryana
(JULY 2011)
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ACKN L G N
With profound respect and gratitude, I take the opportunity to convey my thanksto complete the training here.
I do extend my heartfelt thanks to Ms. Rachna singh Bahel for providing me this
opportunity to be a part of this esteemed organization.
I am extremely grateful to all the technical staff ofB
/ N
C for their co -operation and
guidance that has helped me a lot during the course of training. I have learnt a lot working
under them and I will always be indebted of them for this value addition in me.
I would also like to thank the training incharge of Echelon Institute of Technology,
Faridabad and all the faculty members of Mechanical Engineering Department for their
effort of constant co- operation, which have been a significant factor in the
accomplishment of my industrial training.
SANDEEP JANGIR
EIT, FARIDABAD
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CERTIFICATE
This is to certify that student ofBatch Mechanical Branch IIird Year;Echelon Institute of Technology Faridabad has successfully completed his industrial
training at Badarpur Thermal power station New Delhi for 41 days from 18th July to 27th
Augest 2011.
He has completed the whole training as per the training report submitted by him.
Training Incharge
BTPS/NTPC
NEW DELHI
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Trai i gat BTPS
I wasappoi tedtodoeight-weektrai i gatthisesteemedorga izatio from 18th July
to 27thaugust 2011. In theseeight weeks I wasassignedto visit variousdivision oftheplant which were
1. Boiler Maintenance Department(BMD I/II/III)2. Plant Auxiliary Maintenance(PAM)3. Turbine Maintenance Department(TMD)
This 41 daystraining wasa very educational adventure forme. It wasreally amazingto
seetheplantby yourselfand learn how electricity, whichisoneofourdaily
requirementsof life, isproduced.
Thisreporthasbeen madeby self-experienceat BTPS. Thematerial in thisreporthas
been gathered frommy textbooks, seniorstudentreport, andtrainermanual provided
by trainingdepartment. Thespecification & principlesareat learnedby me fromthe
employeeofeachdivision of BTPS.
SANDEEP JANGIR
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INDEX
1. Introduction NTPC Badarpur Thermal Power Station
2. Basic steps of Electricity generation C AL TO STEAM
STEAM TO MECHANICAL POWER
COALCYCLE
ELECTRICITY FROM COAL
3. RANKINE CYCLE PROCESS OF RANKINE CYCLE
RANKINE CYCLE WITH REHEAT
4. Boiler Maintenance Department
BMD I
BMD II
BMD III
5. Plant Auxiliary Maintenance
6. Turbine Maintenance Department
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ABOUT NTPC
NTPCLimited is the largest thermal power generating company of India. A public sector
company, it was incorporated in the year 1975 to accelerate power development in thecountry as a wholly owned company of the Government of India. At present, Government
of India holds 89.5% of the total equity shares of the company and FIIs, Domestic Banks,
Public and others hold the balance 10.5%. Within a span of 31 years, NTPC has emerged as
a truly national power company, with power generating facilities in all the m ajor regions
of the country.
The total installed capacity of the company is 31134 MW (including JVs) with 15 coal
based and 7 gas based stations, located across the country. In addition under JVs, 3
stations are coal based & another station uses naphtha/LNG as fuel. By 2017, the power
generation portfolio is expected to have a diversified fuel mix with coal based capacity of
around 53000 MW, 10000MW through gas, 9000 MW through Hydro generation, about
2000 MW from nuclear sources and around 1000 MW from Renewable Energy Sources
(RES). NTPC has adopted a multi-pronged growth strategy which includes capacity
addition through green field projects, expansion of existing stations, joint ventures,
subsidiaries and takeover of stations.
NTPC has set new benchmarks for the power industry both in the area of power plant
construction and operations. Its providing power at the cheapest average tariff in the
country..
NTPC is committed to the environment, generating power at minimal environmental cost
and preserving the ecology in the vicinity of the plants. NTPC has undertaken massive a
forestation in the vicinity of its plants. Plantations have increased forest area and reduced
barren land. The massive a forestation by NTPC in and around its Ramagundam Power
station (2600 MW) have contributed reducing the temperature in the areas by about 3c .
NTPC has also taken proactive steps for ash utilization. In 1991, it set up Ash Utilization
Division
A "Centre for Power Efficiency and Environment Protection (CENPEEP)" has been
established in NTPC with the assistance of United States Agency for International
Development. (USAID). Cenpeep is efficiency oriented, eco -friendly and eco-nurturing
initiative - a symbol ofNTPC's concern towards environmental protection and continuedcommitment to sustainable power development in India.
As a responsible corporate citizen, NTPC is making constant efforts to improve the socio -
economic status of the people affected by its projects. Through its Rehabilitation and
Resettlement programmes, the company endeavours to improve the overall socio
economic status Project Affected Persons.
NTPC was among the first Public Sector Enterprises to enter into a Memorandum of
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Und
st
ndin
(MOU) withth
Go
n
ntin 1987-88. NTPC h
sb
npl
dund
th
Ex
ll
nt cat
o y (th
b
st cat
o y) every year since the MOU system became
operative.
JOURNEY OF NTPC
NTPC was set up in 1975 with 100% ownership by the Government of India. In the
last 30 years, NTPC has grown into the largest power utility in India
.
In 1997, Government of India granted NTPC status of Navratnabeing one of the
nine
Jewels of India, enhancing the powers to the Board of Directors
NTPC became a listed company with majority government ownership of
89.5%.
NTPC became third largest market capitalization of listed by companies.
1975
1997
2004
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The company rechristened as NTPC Limited in line with its changing
business portfolio
And transforms itself from a thermal power utility to an integrated
power utility.
National Thermal Power Corporation is the largest power generation company
in India.
Forbes Global 2000 for 2008 ranked it 411th in the world.
National Thermal Power Corporation is the largest power generation company
in India.
Forbes Global 2000 for 2008 ranked it317th in the world.
National Thermal Power Corporation has als se up to a plan to achieve a
target of
50,000MW generation capacity
.
National Thermal Power Corporation hase
arke on plans to became
a
75,000MW Company by2017.
ABOUT BTPS
2005
2008
2009
2012
2017
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Badarpur thermal power station started working in 1973 with a single 95 mw unit. There
were 2 more units (95 MW each) installed in next 2 consecutive years. Now it has total
five units with total capacity of720 MW. Ownership ofBTPS was transferred to NTPC with
effect from 01.06.2006 through GOIs Gazette Notification.
Given below are the details of unit with the year they are installed.
Address: Badarpur, New Delhi -110044
Telephone: (STD-011)-26949523
Fax: 26949532
Installed Capacity 720 MW
Derated capacity 705 MW
Location New Delhi
Coal source Jharia coal fields
Water source Agra canal
Beneficary states Delhi
Unit sizes 3x95 MW
2X210 MW
Units Commissioned Unit I-95 MW -July 1973
Unit II-95 MW August 1974
Unit III-95 MW March 1975
Unit IV-210 MW December 1978
Unit V-210 MW - December 1981
Transfer ofBTPS to NTPC Ownership ofBTPS was transferred
to NTPC with effect from01.06.2006 through GOIs
Gazette Notification
BASIC STEPS OF ELECTRICITY GENERATION
Thebasicstepsin thegeneration ofelectricity fromcoal involves followingsteps:
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Coal tosteam
Steamtomechanical powerMechanical powertoelectrical power
COALTO ELECTRICITY: BASICS
\
Coal toSteam
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Coal fromthecoal wagonsis unloadedin thecoal handlingplant. This Coal is
transported uptotheraw coal bunkers withthehelpofbeltconveyors. Coal is
transportedto Bowl millsby Coal Feeders. Thecoal ispulverizedin the Bowl Mill,
whereitisgroundtopowder form. Themill consistsofaroundmetallictableon which
coal particles fall. Thistableisrotated withthehelpofamotor. Therearethree largesteel rollers, whicharespaced 120 apart.
When thereis nocoal, theserollersdo notrotatebut when thecoal is fedtothetableit
packs upbetween rollerandthetableandths forcestherollerstorotate. Coal is
crushedby thecrushingaction between therollersandtherotatingtable. Thiscrushed
coal istaken away tothe furnacethroughcoal pipes withthehelpofhotandcoldair
mixture fromP.A. Fan.P.A. Fan takesatmosphericair, apartof whichissentto Air-
Preheaters forheating whileapartgoesdirectly tothemill fortemperaturecontrol.
Atmosphericair from F.D. Fan isheatedin theairheatersandsenttothe furnaceas
combustion air. Water fromtheboiler feedpumppassesthrougheconomizerandreachestheboilerdrum. Water fromthedrumpassesthroughdown comersandgoesto
thebottomringheader. Water fromthebottomringheaderisdividedtoall the foursidesofthe furnace. Duetoheatanddensity difference, the waterrises upin the water
wall tubes. Waterispartly convertedtosteamasitrises upin the furnace. Thissteamand watermixtureisagain taken totheboilerdrum wherethesteamisseparated from
water.
Water followsthesamepath whilethesteamissenttosuperheaters forsuperheating.
Thesuperheatersare locatedinsidethe furnaceandthesteamissuperheated(540C)
and finally itgoestotheturbine. Fluegases fromthe furnaceareextractedby induced
draft fan, whichmaintainsbalancedraftin the furnace( -5to 10 mmof wcl) with
forceddraft fan. These fluegasesemittheirheatenergy to varioussuperheatersin the
penthouseand finally passthroughair-preheatersandgoestoelectrostatic
precipitators wheretheashparticlesareextracted.
ElectrostaticPrecipitatorconsistsofmetal plates, whichareelectrically charged. Ash
particlesareattractedon totheseplates, sothatthey do notpassthroughthechimney
topollutetheatmosphere. Regularmechanical hammerblowscausetheaccumulation
ofashto fall tothebottomoftheprecipitator wherethey arecollectedin ahopper for
disposal.
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Steamto Mechanical Power
Fromtheboiler, asteampipeconveyssteamtotheturbinethroughastop valve(which
can be usedtoshut-offthesteamin caseofemergency) andthroughcontrol valvesthat
automatically regulatethesupply ofsteamtotheturbine. Stop valveandcontrol valves
are locatedin asteamchestandagovernor, driven fromthemain turbineshaft,
operatesthecontrol valvestoregulatetheamountofsteam used. (Thisdepends upon
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thespeedoftheturbineandtheamountofelectricity required fromthe
generator).Steam fromthecontrol valvesentersthehighpressurecylinderofthe
turbine, whereitpassesthrougharingofstationary blades fixedtothecylinder wall.
Theseactas nozzlesanddirectthesteamintoasecondringofmovingbladesmounted
on adiscsecuredtotheturbineshaft. Thesecondringturnstheshaftsasaresultofthe
forceofsteam. Thestationary andmovingbladestogetherconstitutea stageofturbine
andin practicemany stagesare necessary, sothatthecylindercontainsa numberofringsofstationary blades withringsofmovingbladesarrangedbetween them.
Thesteampassesthrougheachstagein turn until itreachestheendofthehigh-
pressurecylinderandin itspassagesomeofitsheatenergy ischangedintomechanical
energy.
Thesteam leavingthehighpressurecylindergoesbacktotheboiler forreheatingand
returnsby a furtherpipetotheintermediatepressurecylinder. Hereitpassesthrough
anotherseriesofstationary andmovingblades .Finally, thesteamistaken to the low-
pressurecylinders, eachof whichentersatthecentre flowingoutwardsin opposite
directionsthroughtherowsofturbinebladesthroughan arrangementcalledthe
double flow-totheextremitiesofthecylinder. Asthesteamgives upitsheatenergy todrivetheturbine, itstemperatureandpressure fall anditexpands. Becauseofthis
expansion thebladesaremuch largerand longertowardsthe low pressureendsoftheturbine.
Mechanical PowertoElectrical Power
Asthebladesofturbinerotate, theshaftofthegenerator, whichiscoupledtothatofthe
turbine, alsorotates. Itresultsin rotation ofthecoil ofthegenerator, whichcauses
inducedelectricity tobeproduced.
(COAL CYCLE)
From Jharia mines
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Railway wagon
BTPS wagon tripper
Magnetic separator
Crusher house
Coal stock yard
RC bunker
RC feeder
Bowl mill Furna
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ELECTRICITY FROM COAL
Coal fromthecoal wagonsis unloaded withthehelpof wagon tipplersin the C.H.P. this
coal istaken totheraw coal bunkers withthehelpofconveyorbelts. Coal isthen
transportedtobowl millsby coal feeders whereitispulverizedandgroundin the
powered form.
Thiscrushedcoal istaken away tothe furnacethroughcoal pipes withthehelpofhot
andcoldmixtureP.A fan. This fan takesatmosphericair, apartof whichissenttopre
heaters whileapartgoestothemill fortemperaturecontrol. Atmosphericair from F.D
fan in theairheatersandsenttothe furnaceascombustion air.
Water fromboiler feedpumppassesthrougheconomizerandreachestheboilerdrum .Water fromthedrumpassesthroughthedown comersandgoestothebottomring
header. Water fromthebottomringheaderisdividedtoall the foursidesofthefurnace. Duetoheatdensity differencethe waterrises upin the water wall tubes. This
steamand watermixtureisagain taken totheboilerdrum wherethesteamissenttosuperheaters forsuperheating. Thesuperheatersare locatedinsidethe furnaceand
thesteamissuperheated(540 degree Celsius) and finally itgoestotheturbine.
Fuel gases fromthe furnaceareextracted fromtheinduceddraft fan, whichmaintains
balancedraftin the furnace with F.D fan. These fuel gasesheatenergy tothe various
superheatersand finally throughairpreheatersandgoestoelectrostaticprecipitators
wheretheashparticlesareextracted. Thisashismixed withthe waterto fromslurry is
pumpedtoashperiod.
Thesteam fromboilerisconveyedtoturbinethroughthesteampipesandthroughstop
valveandcontrol valvethatautomatically regulatethesupply ofsteamtotheturbine.
Stop valvesandcontrols valvesare locatedin steamchestandgovernordriven from
main turbineshaftoperatesthecontrol valvestheamount used.
Steam fromcontrolled valvesenterhighpressurecylinderofturbines, whereitpasses
throughtheringofblades fixedtothecylinder wall. Theseactas nozzlesanddirectthesteamintoasecondringofmovingbladesmountedon thediscsecuredin theturbine
shaft. Thesecondringturnstheshaftasaresultof forceofsteam. Thestationary and
movingbladestogether.
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MAIN GENERATOR
MAIN TURBINE DATA
Maximum continuous KVA rating 24700KVA
Maximum continuous KW 210000KW
Rated terminal voltage 15750V
Rated Stator current 9050 A
Rated Power Factor 0.85 lagExcitation current at MCR Condition 2600 A
Slip-ring Voltage at MCR Condition 310 VRated Speed 3000 rpm
Rated Frequency 50 HzShort circuit ratio 0.49
Efficiency at MCR Condition 98.4%
Direction of rotation viewed Anti ClockwisePhase Connection Double Star
Number of terminals brought out 9( 6 neutral and 3 phase)
Rated output of Turbine 210 MW
Rated speed of turbine 3000 rpm
Rated pressure of steam before emergency 130 kg/cm^2Stop valve rated live steam temperature 535 degree Celsius
Rated steam temperature after reheat at inlet to receptor valve 535 degree Celsius
Steam flow at valve wide open condition 670 tons/hour
Rated quantity of circulating water through condenser 27000 cm/hour
1. For cooling water temperature (degree Celsius) 24,27,30,33
1.Reheated steam pressure at inlet of interceptor valve in
kg/cm^2 ABS23,99,24,21,24,49,24 .82
2.Steam flow required for 210 MW in ton/hour 68,645,652,662
3.Rated pressure at exhaust of LP turbine in mm of Hg 19.9,55.5,65.4,67.7
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BASIC POWERPLANT CYCLE
Thethermal (steam) powerplant usesadual (vapour+ liquid) phasecycle. Itisaclose
cycletoenablethe working fluid(water) tobe usedagain andagain. Thecycle usedis
Rankine Cyclemodifiedtoincludesuperheatingofsteam, regenerative feed water
heatingandreheatingofsteam.
On largeturbines, itbecomeseconomical toincreasethecycleefficiency by using
reheat, whichisa way ofpartially overcomingtemperature limitations.
By returningpartially expandedsteam, toareheat, theaveragetemperatureat which
theheatisadded, isincreasedand, by expandingthisreheatedsteamtotheremaining
stagesoftheturbine, theexhaust wetnessisconsiderably lessthan it wouldotherwisebe
conversely, ifthemaximumtolerable wetnessisallowed, theinitial pressureofthe
steamcan beappreciably increased. BleedSteamExtraction:
Forregenerativesystem, nos. of non-regulatedextractionsistaken from HP, IPturbine.Regenerativeheatingoftheboiler feed wateris widely usedin modern powerplants;
theeffectbeingtoincreasetheaveragetemperatureat whichheatisaddedtothecycle,thusimprovingthecycleefficiency.
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FACTORS AFFECTING THERMAL CYCLEEFFICIENCY
Thermal cycleefficiency isaffectedby following:
Initial SteamPressure.
Initial SteamTemperature.
Whetherreheatis usedor not, andif usedreheatpressureandtemperature.
Condenserpressure.
Regenerative feed waterheating.
RANKINE CYCLE
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The Rankinecycleisathermodynamiccycle whichconvertsheatinto work. Theheatis
suppliedexternally toaclosed loop, which usually uses waterasthe working fluid. This
cyclegeneratesabout 80% ofall electricpower usedthroughoutthe world, including
virtually all solarthermal, biomass, coal and nuclearpowerplants. Itis named
after William John Macquorn Rankine, aScottishpolymath..
The Rankinecycleissometimesreferredtoasapractical Carnotcyclebecause, when
an efficientturbineis used, theTSdiagrambeginstoresemblethe Carnotcycle. Themain differenceisthatheataddition (in theboiler) andrejection (in thecondens er) are
isobaricin the Rankinecycleand isothermal in thetheoretical Carnotcycle. A pumpis
usedtopressurizethe working fluidreceived fromthecondenserasa liquidinsteadof
asagas. All oftheenergy in pumpingthe working fluidthroughthecompletecycleis
lost, asismostoftheenergy of vaporization ofthe working fluidin th eboiler. This
energy is losttothecyclebecausethecondensation thatcan takeplacein theturbineis
limitedtoabout 10% in ordertominimizebladeerosion;the vaporization energy is
rejected fromthecyclethroughthecondenser.
Butpumpingthe working fluidthroughthecycleasa liquidrequiresa very small
fraction oftheenergy neededtotransportitascomparedtocompressingthe workingfluidasagasin acompressor(asin the Carnotcycle).
Theefficiency ofa Rankinecycleis usually limitedby the working fluid. Withoutthepressurereachingsupercritical levels forthe working fluid, thetemperaturerangethe
cyclecan operateoverisquitesmall:turbineentry temperaturesaretypically 565C(thecreep limitofstainlesssteel) andcondensertemperaturesarearound 30C. This
givesatheoretical Carnotefficiency ofabout63% compared withan actual efficiency of42% foramodern coal-firedpowerstation. This low turbineentry temperature
(compared withagasturbine) is why the Rankinecycleisoften usedasabottoming
cyclein combined-cyclegasturbinepowerstations.
Description
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A R n inecycle escri es odeloftheoperation ofsteamheaten inesmost
commonlyfound inpower eneration plants.Common heatsourcesforpowerplants
usin the Ran inecyclearecoal natural as,oil,and nuclear. The Ran inecycle is
sometimesreferredtoasapracticalCarnotcycleas,when an efficientturbine isused,
the T diagramwillbegin toresembletheCarnotcycle.
Themain difference isthatapump isusedtopressuri eli uid insteadofgas. This
requiresabout 1/100th 1%) asmuchenergyasthatcompressingagas in acompressor
as in theCarnotcycle).Theefficiencyofa Ran inecycle isusuallylimitedbytheworkingfluid. Withoutthepressuregoingsupercriticalthetemperaturerangethecyclecan operateover isquitesmall,turbineentrytemperaturesaretypically C
thecreeplimitofstainlesssteel) andcondensertemperaturesarearound 30C. ThisgivesatheoreticalCarnotefficiencyofaround63% comparedwithan actualefficiency
of42% foramodern coal-firedpowerstation. Thislowturbineentrytemperature
comparedwithagasturbine) iswhythe Rankinecycle isoften usedasabottoming
cycle in combinedcyclegasturbinepowerstations.
Theworkingfluid in a Rankinecyclefollowsaclosedloopand isre-usedconstantly.
Thewatervaporandentraineddropletsoften seen billowingfrompowerstations is
generatedbythecoolingsystems notfromtheclosedloop Rankinepowercycle) and
representsthewasteheatthatcould notbeconvertedtousefulwork.Notethatcooling
towersoperateusingthelatentheatofvapori ationofthecoolingfluid.Thewhitebillowingcloudsthatform in coolingtoweroperation aretheresultof
waterdropletswhichareentrained in thecoolingtowerairflow; it is not,ascommonly
thought,steam. Whilemanysubstancescouldbeused in the Rankinecycle,water is
usuallythefluidofchoicedueto itsfavorableproperties,suchas nontoxicand
unreactivechemistry,abundance,andlowcost,aswellas itsthermodynamicproperties.
Oneoftheprincipaladvantages itholdsoverothercycles isthatduringthe
compressionstagerelativelylittleworkisrequiredtodrivethepump,duetothe
workingfluidbeing in itsliquidphaseatthispoint.Bycondensingthefluidtoliquid,
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theworkrequiredbythepumpwillonlyconsumeapproximately 1% to 3% ofthe
turbinepowerandsogiveamuchhigherefficiencyforarealcycle. Thebenefitofthis is
lostsomewhatduetothelowerheataddition temperature.Gasturbines,for instance,haveturbineentrytemperaturesapproaching 1 00C.Nonetheless,theefficienciesof
steamcyclesandgasturbinesarefairlywellmatched.
Processesofthe Rankinecycle
Tsdiagramofatypical Rankinecycleoperatingbetween pressuresof0.06barand
0bar.Therearefourprocesses in theRankinecycle,eachchangingthestateofthe
workingfluid. Thesestatesare identifiedby number in thediagramtotheright
i.Process 1-2 Theworkingfluid ispumpedfromlowtohighpressure,asthefluid isa
liquidatthisstagethepumprequireslittle inputenergy.
ii.Process 2-3 Thehighpressureliquidentersaboilerwhere it isheatedat
constantpressurebyan externalheatsourcetobecomeadrysaturatedvapour.
iii.Process 3-4 Thedrysaturatedvapourexpandsthroughaturbine,generating
power.Thisdecreasesthetemperatureandpressureofthevapour,andsomecondensation mayoccur.
iv.Process 4-1 Thewetvaporthen entersacondenserwhere it iscondensedata
constantpressureandtemperaturetobecomeasaturatedliquid. Thepressureand
temperatureofthecondenser isfixedbythetemperatureofthecoolingcoilsasthefluid
isundergoingaphase-change.In an ideal Rankinecyclethepumpandturbinewouldbe
isentropic,i.e.,thepumpandturbinewouldgenerate noentropyandhencemaximi e
the networkoutput.Processes 1-2and 3-4 wouldberepresentedbyverticallineson the
TsdiagramandmorecloselyresemblethatoftheCarnotcycle. TheRankinecycle
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shown herepreventsthe vapourending upin thesuperheatregion aftertheexpansion
in theturbine, whichreducestheenergy removedby thecondensers.
Real Rankinecycle(non-ideal) : Rankinecycle withsuperheat
In areal Rankinecycle, thecompression by thepumpandtheexpansion in theturbine
are notisentropic. In other words, theseprocessesare non-reversibleandentropy isincreasedduringthetwoprocesses. Thissomewhatincreasesthepowerrequiredby the
pumpanddecreasesthepowergeneratedby theturbine. In particulartheefficiency ofthesteamturbine will be limitedby waterdroplet formation. Asthe watercondenses,
waterdropletshittheturbinebladesathighspeedcausingpittinganderosion,gradually decreasingthe lifeofturbinebladesandefficiency oftheturbine. Theeasiest
way toovercomethisproblemisby superheatingthesteam. On theTsdiagramabove,state 3 isaboveatwophaseregion ofsteamand watersoafterexpansion thesteam will
be very wet. By superheating, state 3 will movetotherightofthediagramandhence
produceadryersteamafterexpansion.
Rankinecycle withreheat
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In thisvariation,twoturbinesworkin series. Thefirstacceptsvapourfromtheboilerathigh pressure. Afterthevapourhaspassedthroughthefirstturbine, itre-entersthe
boilerand isreheatedbeforepassingthroughasecond,lowerpressureturbine. Amongotheradvantages,thispreventsthevapourfromcondensingduring itsexpansion which
can seriouslydamagetheturbineblades,and improvestheefficiencyofthecycle.
Regenerative Rankinecycle
Theregenerative Rankinecycle isso namedbecauseafteremergingfromthe
condenser possiblyasasubcooledliquid) theworkingfluid isheatedbysteam tapped
fromthehot portion ofthecycle. On thediagramshown,thefluidat 2 ismixedwith
thefluidat 4 bothatthesamepressure) toendupwiththesaturatedliquidat 7. The
Regenerative Rankinecycle(withminorvariants) iscommonlyused in realpower
stations. Anothervariation iswhere 'bleedsteam' frombetween turbinestages issentto
feedwater heaterstopreheatthewateron itswayfromthecondensertotheboiler.
BOILER MAINTENANCE DEPARTMENTBoiler anditsdescription
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A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized
fluid exits the boiler for use in various processes or heating applications Construction of
boilers is mainly of steel, stainless steel, and wrought iron. In live steam models,
copper or brass is often used. Historically copper was often used for fireboxes(particularly
for steam locomotives), because of its better thermal conductivity. The price of copper
now makes this impractical.
Cast iron is used for domestic water heaters. Although these are usually termed "boilers",
their purpose is to produce hot water, not steam, and so they run at low pressure and try
to avoid actual boiling. The brittleness of cast iron makes it impractical for steam pressure
vessels. The boiler is a rectangular furnace about 50 ft (15 m) on a side an d 130 ft (40 m)
tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches (60 mm) in
diameter. Pulverized coal is air -blown into the furnace from fuel nozzles at the four
corners and it rapidly burns, forming a large fireball at the c entre. The thermal radiation of
the fireball heats the water that circulates through the boiler tubes near the boiler
perimeter.
The water circulation rate in the boiler is three to four times the throughput and is
typically driven by pumps. As the water in the boiler circulates it absorbs heat and
changes into steam at 700 F (370 C) and 3,200 psi (22.1MPa). It is separated from the
water inside a drum at the top of the furnace.
The saturated steam is introduced into superheat pendant tubes that hang in the hottest
part of the combustion gases as they exit the furnace. Here the steam is superheated to
1,000 F (540C) to prepare it for the turbine. The steam generating boiler has to produce
steam at the high purity, pressure and temperature required for the steam turbine that
drives the electrical generator. The generator includes the economizer, the steam drum,
the chemical dosing equipment, and the furnace with its steam generating tubes and the
superheated coils. Necessary safety valves are located at suitable points to avoid
excessive boiler pressure. The air and flue gas path equipment include: forced draft (FD)
fan, air preheated (APH), boiler furnace, induced draft (ID) fan, fly ash collectors(electrostatic precipitator or bag house) and the flue ga s stack.
For units over about 210 MW capacity, redundancy of key components is provided by
installing duplicates of the FD fan, APH, fly ash collectors and ID fan with isolating
dampers .On some units of about 60 MW, two boilers per unit may instead be pro vided.
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The steam generating boiler has to produce steam at the high purity, pressure and
temperature required for the steam turbine that drives the electrical generator. The boiler
includes the economizer, the steam drum, the chemical dosing equipment, and
The furnace with its steam generating tubes and the super heater coils. Necessary safety
valves are located at suitable points to avoid excessive boiler pressure. The air and flue
path equipment include: forced draft (FD)fan, air preheater (APH), boiler furnace, induced
draft (ID) fan, fly ash collectors(electrostatic precipitator or baghouse) and the flue gas
stack .
Schematic diagram of typical
coal-fired power plant steam generator highlighting the air preheater (APH) location
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SPECIFICATION:.
MAINBOILER AT 100% LOAD
Evaporation 700t/hr
Feed water temperature 247C
Feed water leaving economizer 276C
STEAM TEMPERATURE::
Drum 341C
Super heater outlet 540C
Reheat inlet 332C
Reheat outlet 540C
STEAM PRESSURE:
Drum design 158.20 kg/cm2 Drum operating 149.70 kg/ cm2
Super heater outlet 137.00 kg/cm2
Reheat inlet 26.35 kg/cm2
Reheat outlet 24.50 kg/cm2
FUEL SPECIFICATION
:COAL DESIGN WORST
Fixed carbon 38% 25%
Volatile matter 26% 25%
Moisture 8% 9%
Grind ability 50% hard grove 45% hard grove
OIL:
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Calorific value of fuel oil 10,000 kcal/kg
Sulphur content 4.5% W/W
Moisture content 1.1% W/W
Flash point 66C
HEAT BALANCE
Dry gas loss 4.63%
Carbon loss 2%
Radiation loss 0.26%
Unaccounted loss 1.5%
Hydrogen in air and water in fuel 4.9%
Total loss 13.3%
Efficiency 86.7%
AUXILIARIES OF BOILER
1.
FURNACE
Furnace is primary part of boiler where the chemical energy of fuel is converted
to thermal energy by combustion. Furnace is designed for efficient and complete
combustion. Major factors that assist for efficient combustion area mount of fuel
inside the furnace and turbulence, which causes rapid mixing between fuel and air.
In modern boilers, water -cooled furnaces are used.
2. BOILER DRUMDrum is of fusion-welded design with welded hemi -spherical dished ends. It is provided
with stubs for welding all the connecting tubes i.e. downcomers, risers, pipes, saturated
steam outlet. The function of steam drum internals is to separate the water from the
steam generated in the furnace walls and to reduce the dissolved solid contents of the
steam below the prescribed limit of1 ppm and also take care of the sudden change of
steam demand for boiler.
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The secondary stage of two opposed banks of closely spaced thin corrugated sheets,
which direct the steam and force the remaining entertained water against the corrugated
plates. Since the velocity is relatively low this water does not get picked up again but runs
down the plates and off the second stage of the two steam outlets. From the secondary
separators the steam flows upwards to the series of screen dryers, extending in layers
across the length of the drum. These screens perform the final stage of separation.
3. Classifier
It is an equipment which serves separation of fine pulverized coal particles medium from
coarse medium. The pulverized coal along with the carrying medium strikes the impact
plate through the lower part. Large particles are then transferred to the ball mill.
4. Worm Conveyor
It is equipment used to distribute the pulverized coal from bunker of one system to
bunker of other system. It can be operated in both directions.
5. WATER WALLS:
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Water flows to the water walls from the boiler drum by natural circulation. The front and
the two side water walls constitute the main evaporation surface absorbing the bulk
of radiant heat of the fuel burnt in the chamber. The front and rear walls are bent at the
lower ends to form a water -cooled slag hopper. The upper part of th e chamber is
narrowed to achieve perfect mixing of combustion gases. The water walls tubes are
connected to headers at the top and bottom. The rear water walls tubes at the top are
grounded in four rows at a wider pitch forming the grid tubes.
6 REHEATER
Reheater is used to raise the temperature of steam from which a part of energy has been
extracted in high- pressure turbine. This is another method of increasing the cycleefficiency. Reheating requires additional equipment I.e. Heating surface co nnecting boiler
and turbine pipe safety equipment like safety valve, non-return valve, isolating valves,
high pressure feed pump, etc. Reheater is composed to two sections namely front and
rear pendant section which is located above the furnace arch between water-cooled
screen wall tubes and rear wall hanger tubes.
7. Super heaters
Whatever type of boiler is used, steam will leave the water at its surface and pass intothe steam space. Steam formed above the water surface in a shell boiler is alway s
saturated and become superheated in the boiler shell, as it is constantly. If superheated
steam is required, the saturated steam must pass through a superheater. This is simply a
heat exchanger where additional heat is added to the steam.
In water-tube boilers, the superheater may be an additional pendant suspended in the
furnace area where the hot gases will provide the degree of superheat required. In other
cases, for example in CHP schemes where the gas turbine exhaust gases are relatively
cool, a separately fired superheater may be needed to provide the additional heat.
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Fi
. A water tube boiler with a super heater
Ifaccurate controlofthe degree ofsuperheatis required, as wouldbe the case ifthe
steam istobe usedtodrive turbines, then an attemperator (desuperheater) isfitted. This
is a device installed after the superheater, whichinjects water intothe superheatedsteam
to reduce itstemperature.
8. ECONOMISER
The functionofan economi
er in a steam-generating unitisto absorbheatfrom the flue
gases and add as a sensible heattothe feed water before the water entersthe
evaporation circuitofthe boiler.
Earlier economi
er were introduced mainly to recover the heat available inthe flue gases
thatleavesthe boiler andprovisionofthis additionheating surface increasesthe
efficiency ofsteam generators. Inthe modernboilersusedfor power generationfeed
water heaters were usedtoincrease the efficiency ofturbine unit andfeed
water temperature.
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Use of economizer or air heater or both is decided by the total economy that will result
in flexibility in operation, maintenance and selec tion of firing system and other related
equipment. Modern medium and high capacity boilers are used both as economizers and
air heaters. In low capacity, air heaters may alone be selected.
. An economizer
Stop valves and non-return valves may be incorporated to keep circulation in economizer
into steam drum when there is fire in the furnace but not feed flow. Tube elements
composing the unit are built up into banks and these are connected to inl et and outlet
headers.
=
9. AIR PREHEATER
Air preheater absorbs waste heat from the flue gases and transfers this heat to incoming
cold air, by means of continuously rotating heat transfer element of specially formed
metal plates. Thousands of these high efficiency elements are spaced and compactly
arranged within 12 sections. Sloped compartments of a radially divided cylindrical shell
called the rotor. The housing surrounding the rotor is provided with duct connecting both
the ends and is adequately scaled by radial and circumferential scaling.
Special sealing arrangements are provided in the provided in the air preheater to prevent
the leakage between the air and gas sides. Adjustable plates are also used to help the
sealing arrangements and prevent the leakage as expansion occurs. The air preheater
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heating surface elements are provided with two types of cleaning devices, soot blowers to
clean normal devices and washing devices to clean the element when soot blowing alone
cannot keep the element clean.
An air preheate
10. PULVERIZER
A pulverizer is a mechanical device for the grinding of many types of materials.
For example, they are used to pulverize coal for combustion in the steam -generating
furnaces of the fossil fuel power plants.
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A Pulverize
Types of Pulverize.
Ball and Tube mills
A ball mill is a pulverizer that consists of a horizontal c ylinder, up to three diameter sin
length, containing a charge of tumbling or cascading steel balls, pebbles or steel rods. A
tube mill is a revolving cylinder of up to five diameters in length used for
finer pulverization of ore, rock and other such mater ials; the materials mixed with water
is fed into the chamber from one end, and passes out the other end as slime.
Bowl mill
It uses tires to crush coal. It is of two types; a deep bowl mill and the shallow bowl mill.
Bowl Mill: - One of the most advanced designs of coal pulverizes presently manufactured.
Motor specification squirrel cage induction motor
Rating-340KW
Voltage-6600KV
Curreen-41.7A
Speed-980 rpm
Frequency-50 Hz
No-load current-15-16 A
An external view of a Coal Pulverizer
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Advantages of Pulverized Coal
Pulverized coal is used for large capacity plants.
It is easier to adapt to fluctuating load as there are no limitations on the combustioncapacity.
Coal with higher ash percentage cannot be used without pulverizing because of
the problem of large amount ash deposition after combustion.
Increased thermal efficiency is obtained through pulverizatio n.
The use of secondary air in the combustion chamber along with the powered coal helps
in creating turbulence and therefore uniform mixing of the coal and the air during
combustion.
Greater surface area of coal per unit mass of coal allows faster combus tion as more coal
is exposed to heat and combustion.
The combustion process is almost free from clinker and slag formation.
The boiler can be easily started from cold condition in case of emergency.Practically no ash handling problem.
The furnace volume required is less as the turbulence caused aids in complete
combustion of the coal with minimum travel of the particles.
CYCLONE SEPARATOR
Cyclonic separation is a method of removing particulates from an air, gas or liquid stream,
without the use of filters, through vortex separation. Rotational effects and gravity are
fine droplets of liquid from a gaseous stream.
A high speed rotating (air)flow is established within a cylindrical or conical container
called a cyclone. Air flows in a spiral pattern, beginning at the top (wide end) of the
cyclone and ending at the bottom (narrow) end before exiting the cyclone in a straight
stream through the center of the cyclone and out the top. Larger (denser) particles in the
rotating stream have too much inertia to follow the tight curve of the stream, and strike
the outside wall, then falling to the bottom of the cyclone where they can be removed. In
a conical system, as the rotating flow moves towards the narrow end of the cyclone, the
rotational radius of the stream is reduced, thus separating smaller and smaller particles.
The cyclone geometry, together with flow rate, defines the cut point of the cyclone. This is
the size of particle that will be removed from the stream with a 50% efficiency. Particleslarger than the cut point will be removed with a greater efficiency, and smaller particles
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with a lower efficiency.
PLANT A XILIAR MAINTENANCE
1. WATE
RCI
RCU
LATION
TE
MTheoryofCirculation
Watermustflowthroughtheheatabsorption surfaceoftheboiler in orderthat itbe
evaporated intosteam.In drumtypeunits(naturalandcontrolledcirculation),the
water iscirculatedfromthedrumthroughthegeneratingcircuitsandthen backtothe
drumwherethesteam isseparatedanddirectedtothesuperheater. Thewaterleaves
thedrumthroughthedown cornersatatemperatureslightlybelowthesaturation
temperature. Theflowthroughthefurnacewall isatsaturation temperature.Heat
absorbed in waterwall islatentheatofvapori ation creatingamixtureofsteamand
water. Theratiooftheweightofthewatertotheweightofthesteam in themixture
leavingtheheatabsorption surface iscalledcirculation ratio.
TypesofBoilerCirculating ystem
i.Naturalcirculation system
ii.Controlledcirculation system
iii.Combinedcirculation system
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Natural circulation System
Waterdeliveredtosteamgenerator from feed waterisatatemperature well below the
saturation valuecorrespondingtothatpressure. Entering firsttheeconomizer, itisheatedtoabout 30-40C below saturation temperature. Fromeconomizerthe water
entersthedrumandthusjoinsthecirculation system. Waterenteringthedrum flows
throughthedown cornerandentersringheateratthebottom. In the water walls, apart
ofthe waterisconvertedtosteamandthemixture flowsbacktothedrum. In thedrum,
thesteamisseparated, andsenttosuperheater forsuperheatingandthen senttothe
high-pressureturbine. Remaining watermixes withtheincoming water fromthe
economizerandthecycleisrepeated. Asthepressureincreases, thedifferencein density
between waterandsteamreduces. Thusthehydrostaticheadavailable will notbeable
toovercomethe frictional resistance fora flow correspondingtotheminimum
requirementofcoolingof water wall tubes. Therefore natural circulation is limitedtotheboiler withdrumoperatingpressurearound 175kg/ cm.
Controlledcirculation System
Beyond 80 kg/ cmofpressure, circulation istobeassisted withmechanical pumpsto
overcomethe frictional losses. Toregulatethe flow through varioustubes, orificesplates
are used. Thissystemisapplicablein thehighsub-critical regions(200 kg/ cm).
ASH HANDLING PLANT
The widely usedashhandlingsystemsare:
i. Mechanical HandlingSystem
ii. HydraulicSystem.
iii. PneumaticSystem.
iv. SteamjetSystem.
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Ash HandlingSystemat BadarpurThermal PowerStation, New Delhi
The Hydraulic Ashhandlingsystemis usedatthe BadarpurThermal PowerStation.
Hydraulic Ash HandlingSystem
Thehydraulicsystemcarriedtheash withthe flow of water withhigh velocity through
achannel and finally dumpsintoasump. Thehydraulicsystemisdividedintoa low
velocity andhigh velocity system. In the low velocity systemtheash fromtheboilers
fallsintoastreamof water flowingintothesump. Theashiscarriedalong withthe
waterandthey areseparatedatthesump. In thehigh velocity systemajetof wateris
sprayedtoquenchthehotash. Twootherjets forcetheashintoatroughin whichtheyare washedaway by the waterintothesump, wherethey areseparated. Themolten slag
formedin thepulverized fuel systemcan alsobequenchedand washedby usingthe
high velocity system. Theadvantagesofthissystemarethatitsclean, largeashhandling
capacity, considerabledistancecan betraversed, absenceof workingpartsin contact
withash.
Fly Ash Collection
Fly ashiscapturedandremoved fromthe fluegasby electrostaticprecipitatorsorfabricbag filters(orsometimesboth) locatedattheoutletofthe furnaceandbeforethe
induceddraft fan. The fly ashisperiodically removed fromthecollection hoppersbelow
theprecipitatorsorbag filters. Generally, the fly ashispneumatically transportedto
storagesilos forsubsequenttransportby trucksorrailroadcars.
Bottom Ash Collection and Disposal
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Atthebottomofevery boiler, ahopperhasbeen provided forcollection ofthebottom
ash fromthebottomofthe furnace. Thishopperisalways filled with watertoquench
theashandclinkers fallingdown fromthe furnace. Somearrangementisincludedto
crushtheclinkersand forconveyingthecrushedclinkersandbottomashtoastorage
site.
WATERTREATMENTPLANT
Asthetypesofboilerare notaliketheir workingpressureandoperatingconditions
vary andsodothetypesandmethodsof watertreatment. Watertreatmentplants used
in thermal powerplants usedin thermal powerplantsaredesignedtoprocesstheraw
waterto water witha very low contentofdissolvedsolidsknown as demineralised
water. Nodoubt, thisplanthastobeengineered very carefully keepingin view thetype
ofraw watertothethermal plant, itstreatmentcostsandoverall economics.
A watertreatmentplant
Thetypeofdemineralization processchosen forapowerstation dependson threemain
factors.i. Thequality ofraw material.ii. Thedegreeofde-ionization i.e. treated waterquality.iii. Selectivity ofresins.
Watertreatmentprocessisgenerally made upoftwosections:
Pre-treatmentsection.
Demineralization sectio
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Pre-treatmentSection
Pre-treatmentplantremovesthesuspendedsolidssuchasclay, silt, organicand
inorganicmatter, plantsandothermicroscopicorganism. Theturbidity may betakenastwotypesofsuspendedsolidin water; firstly, theseparablesolidsandsecondly the
non-separablesolids(colloids). Thecoarsecomponents, suchassand, silt, etc:can be
removed fromthe waterby simplesedimentation. Finerparticles, however, will not
settlein any reasonabletimeandmustbe flocculatedtoproducethe largeparticles,
whicharesettlingable. Longtermability toremain suspendedin waterisbasically a
function ofbothsizeandspecificgravity.
Demineralization
This filter wateris now used fordemineralisingpurposeandis fedtocation exchangerbed, butenroutebeing firstdechlorinated, whichiseitherdoneby passingthrough
activatedcarbon filterorinjectingalongthe flow of water, an equivalentamountof
sodiumsulphitethroughsomestrokepumps. Theresidual chlorine, whichismaintained
in clarification planttoremoveorganicmatter fromraw water, is now detrimental to
action resin andmustbeeliminatedbeforeitsentry tothisbed.
A demineralization tank
A DM plantgenerally consistsofcation, anion andmixedbedexchangers. The final
water fromthisprocessconsistsessentially ofhydrogen ionsandhydroxideions which
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isthechemical composition ofpure water. The DM water, being very pure, becomes
highly corrosiveonceitabsorbsoxygen fromtheatmospherebecauseofits very high
affinity foroxygen absorption. Thecapacity ofthe DM plantisdictatedby thetypeand
quantity ofsaltsin theraw waterinput. However, somestorageisessential asthe DM
plantmay bedown formaintenance. Forthispurpose, astoragetankisinstalled from
which DM wateriscontinuously withdrawn forboilermake-up. Thestoragetankfor
DM waterismade frommaterials notaffectedby corrosive water, suchasPVC. Thepipingand valvesaregenerally ofstainlesssteel. Sometimes, asteamblanketing
arrangementorstainlesssteel doughnut floatisprovidedon topofthe waterin thetank
toavoidcontact withatmosphericair. DM watermake-upisgenerally addedatthe
steamspaceofthesurfacecondenser(i.e., the
Vacuumside). Thisarrangement notonly spraysthe waterbutalso DM watergets
deaerated, withthedissolvedgasesbeingremovedby theejectorofthecondenseritself.
WTP-II Flash mixture (Cl2 +Pac (Poly aluminium chorine) )
Clarifier tank Storage tank Clarifier pump(A or B)
+Cation anion Active carbon filter Pressure filter (A, B, C, D)
Degasser tank (Co2 removed)
Degasser pump -Anion (NaoH used)
Strong base anion Mixed bed(6.57 ph)
DM Storage tank
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Systematicarrangementof watertreatment II
1.DRAUGHTSYSTEM
Thereare fourtypesofdraughtsystem:
i.Natural Draught
ii.Induced Draught
iii.Forced Draught
iv.Balanced Draught
Natural DraughtSystem
In natural draft unitsthepressuredifferentialsareobtainedhaveconstructingtailchimneyssothat vacuumiscreatedin the furnace. Duetosmall pressuredifference, air
isadmittedintothe furnace
A natural draughtsystem
Induced DraftSystem
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In thissystem, theairisadmittedto natural pressuredifferenceandthe fluegasesare
taken outby meansof Induced Draught(I.D.) fansandthe furnaceismaintained under
vacuum.
Forced DraughtSystem
A setof forceddraught(F.D.) fansismade useof forsupplyingairtothe furnaceandsothe furnaceispressurized. The fluegasesaretaken outduetothepressuredifference
between the furnaceandtheatmosphere.
Balanced DraughtSystem
Hereasetof Inducedand Forced Draft Fansare utilizedin maintaininga vacuumin
the furnace. Normally all thepowerstations utilizethisdraftsystem.
1. INDUSTRIAL FANSID Fan
Theinduced Draft Fansaregenerally of Axial-ImpulseType. Impeller nominal
diameterisoftheorderof 2500 mm. The fan consistsofthe followingsub -assemblies:
Suction ChamberInletVane Control
Impeller
Outlet GuideVane Assembly
ID Fans:-Locatedbetween electrostaticprecipitatorandchimney.
Type-radical
Speed-1490 rpm
Rating-300 KW
Voltage-6.6 KV
Lubrication-by oil
An ID fan
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FD Fan
The fan, normally ofthesametypeas ID Fan, consistsofthe followingcomponents:
Silencer
Inlet Bend
Fan Housing
Impeller withbladesandsettingmechanism
FD Fans:- Designedtohandlesecondary air forboiler. 2 in numberandprovide
ignition ofcoal.
Type-axial
Speed-990 rpm
Rating-440 KW
Voltage-6.6 KV
An FD fan
Thecentrifugal andsetting forcesofthebladesaretaken upby thebladebearings. The
bladeshaftsareplacedin combinedradial andaxial anti-friction bearings, whichare
sealedofftotheoutside. Theangleofincidenceofthebladesmay beadjustedduring
operation. Thecharacteristicpressure volumecurvesofthe fan may bechangedin a
largerange withoutessentially modifyingtheefficiency. The fan can then beeasily
adaptedtochangingoperatingconditions.
Therotorisaccommodatedin cylindrical rollerbearingsandan inclinedball bearingat
thedrivesideabsorbstheaxial thrust.
Lubrication andcoolingthesebearingsisassuredby acombinedoil level and
circulating lubrication system.
Primary Air Fan
PA Fan if flange-mounteddesign, singlestagesuction, NDFVtype, backwardcurved
bladedradial fan operatingon theprincipleofenergy transformation duetocentrifugal
forces. Someamountofthe velocity energy isconvertedtopressureenergy in thespiral
casing. The fan isdriven ataconstantspeedand varyingtheangleof theinlet vane
control controlsthe flow. Thespecial featureofthe fan isthatisprovided withinlet
guide vanecontrol withapositiveandprecise linkmechanism.
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Itisrobustin construction forhigherperipheral speedsoastohave unitsizes. Fan c an
develophighpressuresat low andmedium volumesandcan handlehot -air laden with
dustparticles.
Primary Air Fans:- Designed forhandlingtheatmosphericair upto50 degrees Celsius,
2 in number
Andthey transferthepoweredcoal toburnersto firing.
Type-Doublesuction radial
Rating-300 KW
Voltage-6.6 KV
Lubrication-by oil
Typeofoperation-continuous
Primary air fan
1. COMPRESSOR HOUSEInstrumentairisrequired foroperating variousdampers, burnertilting, devices,
diaphragm valves, etc:in the 210 MW units. Station airmeetsthegeneral requirement
ofthepowerstation suchas lightoil atomizingair, forcleaning filtersand for various
maintenance works. Thecontrol aircompressorsandstation aircompressorshavebeen
housedseparately withseparatereceiversandsupply headersandtheirtapping.
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A compressorhouse
Instrument AirSystem
Control aircompressorshavebeen installed forsupplyingmoisture freedry airrequired forinstrument used. Theoutput fromthecompressorsis fedtoairreceivers
viareturn valves. Fromthereceiverairpassedthroughthedryerstothemain
instrumentairline, whichrunsalong withtheboilerhouseandturbinehouseof 210
MW units. Adequate numbersoftappinghavebeen providedall overthearea.
Air-DryingUnit
Aircontainsmoisture whichtendstocondense, andcausestroublein operation of
variousdevicesby compressedair. Thereforedryingofairisaccepted widely in caseof
instrumentair. Airdrying unitconsistsofdual absorption towers withembedded
heaters forreactivation. Theabsorption towersareadequately filled withspecially
selectedsilicagel andactivatedalumina whileonetowerisdryingtheair.
Service Air Compressor
Thestation aircompressorisgenerally aslow speedhorizontal doubleactingdouble
stagetypeandisarranged forbeltdrive. Thecylinderheadsandbarrel areenclosedin
ajacket, whileextendsaroundthe valvealso. Theintercoolerisprovidedbetween the
low andhighpressurecylinder whichcoolstheairbetween tagandcollectsthemoisture
thatcondenses Air fromL.P. cylinderentersatoneendoftheintercoolerandgoes to
theoppositeend where fromitisdischargedtothehigh-pressurecylinder;cooling
water flowsthroughthe nestofthetubesandcoolstheair. A safety valveissetatrated
pressure. Twoselectorsswitchone withpositionsauto load/unloadandanother with
positionsautostart/stop, non-stophavebeen providedon thecontrol panel ofthe
compressor. In autostart-stopposition, thecompressor will start.
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TURBINE MAINTENANCE DEPARTMENT
TURBINE CLASSIFICATION:
1. Impulse turbine:
In impulse turbine steam expands in fixed nozzles. The high velocity steam from nozzles
does work on moving blades, which causes the shaft to rotate. The essential features of
impulse turbine are that all pressure drops occur at nozzles and not on blades.
2. Reaction turbine:
In this type of turbine pressure is reduced at both fixed and moving blades. Both fixed and
moving blades act like nozzles. Work done by the impulse effect of steam due to reverse
the direction of high velocity steam. The exp ansion of steam takes place on moving
blades.
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A95 MW Generator at BTPS, New Delhi
COMPOUNDING:
Several problems occur if energy of steam is converted in single step and so compounding
is done. Following are the type of compounded turbine:
i. Velocity compounded Turbine :Like simple turbine it has only one set of nozzles and entire steam pressure drop takes
place there. The kinetic energy of steam fully on the nozzles i s utilized in moving blades.
The role of fixed blades is to change the direction of steam jet and too guide it.
ii. Pressure Compound Turbine :This is basically a number of single impulse turbines in series or on the same
shaft. The exhaust of first turbine enters the nozzles of next turbine. The total pressure
drop of steam does not take on first nozzle ring but divided equally on all of them.
iii. Pressure Velocity Compounded Turbine:
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It is just the combination of the two c ompounding and has the advantages of allowing
bigger pressure drops in each stage and so fewer stages are necessary. Here for given
pressure drop the turbine will be shorter length but diameter will be increased.
MAIN TURBINEThe 210MW turbine is a cylinder tandem compounded type machine comprising of H.P.
and I.P and L.P cylinders. The H.P. turbine comprises of12 stages the I.P turbine has 11
stages and the L.P has four stages of double flow. The H.P and I.P. turbine rotor are rigidly
compounded and the I.P. and L.P rotor by lens type semi flexible coupling. All the 3 rotor
are aligned on five bearings of which the bearing number is combined with thrust bearing.
The main superheated steam branches off into two streams from the boiler and passe s
through the emergency stop valve and control valve before entering the governing wheel
chamber of the H.P. Turbine.
After expanding in the 12 stages in the H.P. turbine then steam is returned in the boiler
for reheating. The reheated steam from boiler enters I.P. turbine via the interceptorvalves and control valves and after expanding enters the L.P stage via 2 numbers of cross
over pipes. In the L.P. stage the steam expands in axially opposed direction to counteract
the thrust and enters the condenser placed directly below the L.P. turbine. The cooling
water flowing through the condenser tubes condenses the steam and the condensate the
collected in the hot well of the condenser.
The condensate collected the pumped by means of 3x50% duty condensate pumps
through L.P heaters to deaerator from where the boiler feed pump delivers the water to
the boiler through H.P. heaters thus forming a closed cycle.
STEAM TURBINE
A steam turbine is a mechanical device that extracts thermal energy from pressurized
steam and converts it into useful mechanical work. From a mechanical point of view, the
turbine is ideal, because the propelling force is applied directly to the rotating element of
the machine and has not as in the reciprocating engine to be transmitted through a
system of connecting links, which are necessary to transform are reciprocating motion
into rotary motion. Hence since the steam turbine possesses for its moving p arts rotating
elements only if the manufacture is good and the machine is correctly designed, it ought
to be free from out of balance forces. If the load on a turbine is kept constant the torque
developed at the coupling is also constant. A generator at a steady load offers a constant
torque.Therefore, a turbine is suitable for driving a generator, particularly as they are both high -
speed machines. A further advantage of the turbine is the absence of internal lubrication.
This means that the exhaust steam is not contaminated with oil vapour and can be
condensed and fed back to the boilers without passing through the filters. It also means
that turbine is considerable saving in lubricating oil when compared with a reciprocating
steam engine of equal power. A final advantage of the steam turbine and a very important
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one is the fact that a turbine can develop many time the power compared to a
reciprocating engine whether steam or oil.
OPERATING PRINCIPLES
A steam turbines two main parts are the cylinder and the rotor. The cylinder (stator) is a
steel or cast iron housing usually divided at the horizontal centre line. Its halves are bolted
together for easy access. The cylinder contains fixed blades, vanes and nozzles that direct
steam into the moving blades carried by the rotor. Each fixed blade set is mounted in
diaphragms located in front of each disc on the rotor, or directly in the casing. A disc and
diaphragm pair a turbine stage. Steam turbines can have many stages. A rotor is a rotating
shaft that carries the moving blades on the outer edges of either discs or drums. The
blades rotate as the rotor revolves. The rotor of a large steam turbine consists of large,
intermediate and low-pressure sections. In a multiple -stage turbine, steam at a high
pressure and high temperature enters the first row of fixed blades or nozzles through an
inlet valve/valves. As the steam passes through the fixed blades or nozzles, it expands and
its velocity increases. The high velocity jet of stream strikes the firs t set of moving blades.
The kinetic energy of the steam changes into mechanical energy, causing the shaft to
rotate. The steam that enters the next set of fixed blades strikes the next row of moving
blades. As the steam flows through the turbine, its press ure and temperature decreases
while its volume increases. The decrease in pressure and temperature occurs as the steam
transmits energy to the shaft and performs work. After passing through the last turbine
stage, the steam exhausts into the condenser or p rocess steam system.
The kinetic energy of the steam changes into mechanical energy through the impact
(impulse)or reaction of the steam against the blades. An impulse turbine uses the impact
force of the steam jet on the blades to turn the shaft. Steam expands as it passes through
thee nozzles, where its pressure drops and its velocity increases. As the steam flows
through the moving blades, its pressure remains the same, but its velocity decreases. The
steam does not expand as it flows through the movi ng blades.
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STEAM CYCLE
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The thermal (steam) power plant uses a dual (vapor+liquid) phase cycle. It is a closed cycle
to enable the working fluid (water) to be used again and again. The cycle used is Rankine
cycle modified to include superheating of steam, regenerative feed water heating and
reheating of steam.
MAIN TURBINE
The 210 MW turbine is a tandem compounded type machine comprising of H.P. and I.P.
cylinders. The H.P. turbines comprise of12 stages, I.P. turbine has 11 stages and the L.P.
turbine has 4 stages of double flow. The H.P. and I.P. turbine rotors are rigidly
compounded and the L.P. motor by the lens type semi flexible coupling. Al l the three
rotors are aligned on five bearings of which the bearing no. 2 is combined with the thrust
bearing. The main superheated steam branches off into two streams from the boiler and
passes through the emergency stop valve and control valve before entering the governing
wheel chamber of the H.P. turbine.
After expanding in the 12 stages in the H.P. turbine the steam is returned in boiler for
reheating. The reheated steam for the boiler enters the I.P> turbine via the interceptor
valves and control valves and after expanding enters the L.P. turbine stage via 2 nos of
cross-over pipes. In the L.P. stage the steam expands in axially opposite direction to
counteract the trust and enters the condensers placed below the L.P. turbine. The cooling
water flowing throughout the condenser tubes condenses the steam and the condensate
collected in the hot well of the condenser. The condensate collected is pumped by means
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of 3*50% duty condensate pumps through L.P. heaters to deaerator from where the boiler
feed pump delivers the water to boiler through H.P. heaters thus forming a close cycle.
The main Turbine
TURBINE CYCLE
Fresh steam from the boiler is supplied to the turbine through the emergency stop valve.
From the stop valves steam is supplied to control valves situated in H.P. cylinders on the
front bearing end. After expansion through 12 stages at the H.P. cylinder, steam flows
back to the boiler for reheating steam and reheated steam from the boiler cover to the
intermediate pressure turbine through two interceptor valves and four control valves
mounted on I.P. turbine. After flowing through I.P. turbine steam enters the middle partof the L.P. turbine through cross-over pipes. In L.P. turbine the exhaust steam condenses
in the surface condensers welded directly to the exhaust part of L.P. turbine.
The selection of extraction points and cold reheat pressure has been done with a view to
achieve a high efficiency. These are two extractors from H.P. turbine, four from I.P.
turbine and one from L.P. turbine. Steam at 1.10 and 1.03 g/sq. cm. Abs is supplied for the
gland sealing. Steam for this purpose is obtained from deaerator through a collection
where pressure of steam is regulated. From the condenser, condensate is pumped with
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the help of 3*50% capacity condensate pumps to deaerator through the low -pressure
regenerative equipments. Feed water is pumped from deaerator to the boiler through the
H.P. heaters by means of 3*50% capacity feed pumps connected before the H.P. heaters
The turbine cycle
SPECIFICATIONS OF THE TURBINE
Type: Tandem compound 3 cylinder reheated type.
Rated power: 210 MW.
Number of stages: 12 in H.P., 11 in I.P. and 4*2 in L.P. cylinder.
Rated steam pressure: 130 kg /sq. cm before entering the stop valve.
Rated steam temperature: 535C after reheating at inlet.
Steam flow: 670T / hr.
H.P. turbine exhaust pressure: 27 kg /sq. cm., 327C
Condenser back pressure: 0.09 kg /sq. cm.
Type of governing: nozzle governing.Number of bearing; 5 excluding generator and exciter.
Lubrication Oil: turbine oil 14 of IOC.
Gland steam pressure: 1.03 to 1.05 kg /sq. cm (Abs)
Critical speed: 1585, 1881, 2017.
Ejector steam parameter: 4.5 kg /sq. cm.
Condenser cooling water pressure: 1.0 to 1.1 kg /sq. cm.
Condenser cooling water temperature: 27000 cu. M /hr.
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Number of extraction lines for regenerative heating of feed water: seven
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TURBINE COMPONENTS
Casing.
Rotor.
Blades.Sealing system.
Stop & control valves.
Couplings and bearings.
Barring gear.
TURBINE CASINGS
HP Turbine Casings:
Outer casing: a barrel -type without axial or radial flange.
Barrel-type casing suitable for quick start-up and loading.The inner casing - cylindrically, axially split
The inner casing is attached in the horizontal and vertical planes in the barrel casing so
that it can freely expand radially in all the d irections and axially from a fixed point (HP-
inlet side).
IP Turbine Casing:
The casing of the IP turbine is split horizontally and is of double -shell construction.
Both are axially split and a double flow inner casing is supported in the outer casing and
carries the guide blades.
Provides opposed double flow in the two blade sections and compensates axial thrust.Steam after reheating enters the inner casing from Top & Bottom.
LP Turbine Casing:
The LP turbine casing consists of a double flow un it and has a triple shell welded casing.
The shells are axially split and of rigid welded construction.
The inner shell taking the first rows of guide blades is attached kinematically in the
middle shell.
Independent of the outer shell, the middle shell, is supported at four points on
longitudinal beams.Steam admitted to the LP turbine from the IP turbine flows into the inner casing
from both sides.
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ROTORSHP Rotor:
The HP rotor is machined from single Cr -Mo-V steel forging with integral discs.
In all the moving wheels, balancing holes are machined to reduce the pressure difference
across them, which results in reduction of axial thrust.
First stage has integral shrouds while other rows have shrouding, riveted to the bladesare periphery.
IP Rotor:
The IP rotor has seven discs integrally forged with rotor while last four discs are shrunk
fit.
The shaft is made of high creep resisting Cr -Mo-V steel forging while the shrunk fit discs
are machined from high strength nickel steel forgings.
Except the last two wheels, all other wheels have shrouding riveted at the tip of
the blades. To adjust the frequency of thee moving blades, lashing wires have
been provided in some stages.
LP Rotor:
The LP rotor consists of shrunk fit discs in a shaft.
The shaft is a forging ofCr-Mo-V steel while the discs are of high strength nickel steel
forgings.
Blades are secured to the respective discs by riveted fork root fastening.
In all the stages lashing wires are provided to adjust the frequency of blades. In the last
two rows, satellite strips are provided at the leading edges of the blades to protect themagainst wet-steam erosion.
BLADES
Most costly element of the turbine.
Blades fixed in stationary part are called guide blades/ nozzles and those fitted in moving
part are called rotating/working blades.
Blades have three main parts:
Aerofoil: working part.
Root. Shrouds.
Shroud is used to prevent steam leakage and guide steam to next set of moving blades.
VACUUM SYSTEM
This comprises of:
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Condenser: 2 for 200 MW units at the exhaust ofLP turbine.
Ejectors:
One starting and two main ejectors connected to the condenser located near the turbine.
C.W. Pumps: Normally two per unit of 50% capacity.
CONDENSER
There are two condensers entered to the two exhausters of the L.P. turbine. These are
surface-type condensers with two pass arrangement. Cooling water pumped into each
condenser by a vertical C.W. pump through the inlet pipe. Water enters the inle t chamber
of the front water box, passes horizontally through brass tubes to the water tubes to the
water box at the other end, takes a turn, passes through the upper cluster of tubes and
reaches the outlet chamber in the front water box. From these, cooli ng water leaves the
condenser through the outlet pipe and discharge into the discharge duct. Steam
exhausted from the LP turbine washes the outside of the condenser tubes, losing its latent
heat to the cooling water and is connected with water in the steam side of the condenser.This condensate collects in the hot well, welded to the bottom of the condensers.
Typical water cooler condenser
EJECTORS
There are two 100% capacity ejectors of the steam eject type. The purpose of the ejector
is to evacuate air and other non -condensation gases from the condensers and thus
maintain the vacuum in the condensers. The ejector has three compartments. Steam is
supplied generally at a pressure of4.5 to 5kg /cm the three nozzles in the three
compartments. Steam expands in the nozzle thus giving a high -velocity eject which creates
a low-pressure zone in the throat of the eject. Since the nozzle box of the ejector is
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connected to the air pipe from the condenser, the air and pressure zone. The working
steam which has expanded in volume comes into contact with the cluster of tube bundles
through which condensate is flowing and gets condensed thus after aiding the formation
of vacuum. The non-condensing gases of air are further sucked with the next stage of the
ejector by the second nozzle. The process repeats itself in the third stage also and finally
the steam-air mixture is exhausted into the atmosphere through the outlet.
CONDENSATE SYSTEM
This contains the following
i. Condensate Pumps: 3 per unit of 50% capacity each located near condenser hot well.
ii.LP Heater: Normally 4 in number with no.1 located at the upper part of the condenser
and nos. 2,3 & 4 around 4 m level.
iii.Deaerator; one per unit located around 181 M level in CD bay.
Condensate Pumps
The function of these pumps is to pump out the condensate to the desecrator through
ejectors, gland steam cooler and LP heaters. These pumps have four stages and since the
suction is at a negative pressure, special arrangements have been made for providing
sealing. The pump is generally rated for 160 m/ hr at a pressure of13.2 kg/ cm.
L.P. Heaters
Turbine has been provided with no n-controlled extractions, which are utilized for heating
the condensate, from turbine bleed steam. There are 410 W pressure heaters in which thelast four extractions are used. L.P. Heater -1 has two parts LPH-1A and LPH-1B located in
the upper parts of the condenser A and condenser B, respectively. These are of horizontal
type with shell and tube construction. L.P.H. 2, 3 and 4 are of similar construction and
they are mounted in a row of 5m level. They are of vertical construction with brass tubes
the ends of which are expanded into tube plate. The condensate flows in the U tubes in
four passes and extraction steam washes the outside of the tubes. Condensate passes
through these four L.P. heaters in succession. These heaters are equipped with necessary
safety valves in the steam space level indicator for visual level indication of heating steam
condensate pressure vacuum gauges for measurement of steam pressure, etc:
Deaerator
The presence of certain gases, principally oxygen, carbon dioxide and ammonia, dissolved
in water is generally considered harmful because of their corrosive attack on metals,
particularly at elevated temperatures. One of the most important factors in the
prevention of internal corrosion in modern boilers and associated plant therefore, is that
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the boiler feed water should be free as far as possible from all dissolved gases especially
oxygen. This is achieved by embodying into the boiler feed system a deaera ting unit,
whose function is to remove the dissolved gases from the feed water by mechanical
means. Particularly the unit must reduce the oxygen content of the feed water to a lower
value as far as possible, depending upon the individual circumstances. Res idual oxygen
content in condensate at the outlet of deaerating plant usually specified are 0.005/ litre or
less. P
PRINCIPAL OF DEAERATION
It is based on following two laws.
Henrys Law
Solubility
The Deaerator comprises of two chambers:
Deaerating column
Feed storage tank
Deaerating column is a spray cum tray type cylindrical vessel of horizontal construction
with dished ends welded to it. The tray stack is designed to ensure maximum contact time
as well as optimum scrubbing of condensate to achie ve efficient deaeration. The
deaeration
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A Deaerator
Column is mounted on the feed storage tank, which in turn is supported on rollers at the
two ends and a fixed support at the centre. The feed storage tank is fabricated from boiler
quality steel plates. Manholes are provided on deaerating column as well as on feed
storage tank for inspection and maintenance.The condensate are admitted at the top of
the deaerating column flows downwards through the spray valves and trays. The trays are
designed to expose to the maximum water surfaces for efficient scrubbing to affect the
liberation of the associated gases steam enters from the underneath of the trays and
flows in counter direction of condensate. While flowing upwards through the trays,
scrubbing and heating is done. Thus the liberated gases move upwards along with the
steam. Steam gets condensed above the trays and in turn heats the condensate. Liberated
gases escapes to atmosphere from the orifice opening meant for it. This opening
is provided with a number of deflectors to minimize the loss of steam.
FEED WATER SYSTEM
The main equipments coming under this system are:
Boiler feed Pump: Three per unit of 50% capacity each located in the 0 meter level in
the T bay.
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High Pressure Heaters: Normally three in number and are situated in the TG bay.
Drip Pumps: generally two in number of100% capacity each situated beneath the LP
heaters.
Turbine Lubricating Oil System: This consists of the Main Oil Pump (MOP), Starting Oil
Pump (SOP), AC standby oil pumps and emergency DC Oil Pump and Jacking Oil Pump
(JOP). (One each per unit)
Boiler Feed Pump
This pump is horizontal and of barrel design driven by an Electric Motor through a
hydraulic coupling. All the bearings of pump and motor are forced lubricated by a suitable
oil lubricating system with adequate protection to trip the pump if the lubrication oil
pressure falls below a preset value. The high pressure boiler feed pump is a very
expensive machine which calls for a very careful operation and skilled maintenance.
Operating staff must be able to find out the causes of defect at the very beginning, which
can be easily removed without endangering the operator of the power plant and also
without the expensive dismantling of the high pressure feed pump.
Function
The water with the given operating temperature should flow continuously to the pump
under a certain minimum pressure. It passes through the suction branch into the intake
spiral and from there; it is directed to the first impeller. After leaving the impeller it pass es
through the distributing passages of the diffuser and thereby gets a certain pressure rise
and at the same time it flows over to the guide vanes to the inlet of the next impeller. This
will repeat from one stage to the other till it passes through the l ast impeller and the end
diffuser. Thus the feed water reaching into the discharge space develops the necessaryoperating pressure.
Booster Pump
Each boiler feed pump is provided with a booster pump in its suction line which is driven
by the main motor of the boiler feed pump. One of the major damages which may occur
to a boiler feed pump is from cavitations or vapour bounding at the pump suction due to
suction failure. Cavitations will occur when the suction pressure of the pump at the pum p
section is equal or very near to the vapour pressure of the liquid to be pumped at a
particular feed water temperature. By the use of booster pump in the main pump suctionline, always there will be positive suction pressure which will remove the possibility of
cavitations. Therefore all the feed pumps are provided with a main shaft driven booster
pump in its suction line for obtaining a definite positive suction pressure.
Lubricating Pressure
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All the bearings of boiler feed pump, pump moto r and hydraulic coupling are force
lubricated. The feed pump consists of two radial sleeve bearings and one thrust bearing.
The thrust bearing is located at the free end of the pump.
High Pressure Heaters
These are regenerative feed waters heaters operating at high pressure and located by the
side of turbine. These are generally vertical type and turbine based steam pipes are
connected to them. HP heaters are connected in series on feed waterside and by such
arrangement, the feed water, after feed pump enters the HP heaters. The steam is
supplied to these heaters to form the bleed point of the turbine through motor operated
valves. These heaters have a group bypass protection on the feed waterside.
In the event of tube rupture in any of th e HPH and the level of condensate rising to
dangerous level, the group protection devices divert automatically the feed water directlyto boiler, thus bypassing all the 3 H.P. heaters.
An HP heater
Turbine Oil Lubricating System
This consists of main oil pump, starting oil pump, emergency oil pump and each per unit.
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