a practile training report

8/4/2019 A Practile Training Report

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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


50/63

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.

a practile training report

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