Gas Turbine Power Plant.pdf

Elements of Gas turbine power plants, Intercooling, Regeneration & Reheating, Advantages and Disadvantages, Combined Cycle Power Plants, IGCC

1. Gas Turbine
Power Plants
Prepared by
Ankur Sachdeva
Assistant Professor, ME

2. •Invented in 1930 by Frank Whittle
•Patented in 1934
•First used for aircraft propulsion in 1942 on Me262 by Germans during the Second World
War.
•Currently most of the aircrafts and ships use GT engines
•Used for power generation
•Manufacturers: General Electric, Pratt &Whitney, SNECMA, Rolls Royce, Honeywell,
Siemens –Westinghouse, Alstom
•Indian take: Kaveri Engine by GTRE (DRDO)
GAS TURBINES

4. Gas Power Cycle or Brayton Cycle
•TheBraytoncycleisathermodynamic
cyclenamedafterGeorgeBrayton.
•Gasturbinebasepowerplantsrunonthiscycle.
Theefficiencyofthiscycleisexpressedbythe
relation:
Where,

5. LAYOUT OF GAS TURBINE POWER PLANT
Gas Turbine Cycle –Intercooling+ Reheat + Regenerator

6. GAS TURBINE POWER PLANT CYCLE

7. ELEMENTS OF GAS TURBINE POWER PLANT
Startingmotor:
Gasturbinesarenotself-starting.Theyrequireastartingmotortofirstbringtheturbinetothe
minimumspeedcalledcoming–inspeed,forthispurpose,astartingmotorisrequired.
Lowpressurecompressor(LPC):
Thepurposeofthecompressoristocompresstheair.Airfromtheatmosphereisdrawnintothe
LPCandiscompressed.
Intercooler:
TheairaftercompressionintheLPCishot.Itiscooledbytheintercooler.Theintercooleris
circulatedwithcoolingwater.
Highpressurecompressor(HPC):
TheairfromtheintercoolerenterstheHPCwhereitisfurthercompressedtoahighpressure.
Thecompressedairpassesthrougharegenerator.
Regenerator(Heatexchanger):
Theairenteringthecombustionchamber(CC)forcombustionmustbehot.Theheatfromthe
exhaustgasesispickedupbythecompressedairenteringthecombustionchamber.

8. ELEMENTS OF GAS TURBINE POWER PLANT
Combustionchamber:
Thefuel(naturalgas,kerosene,orgasoline)isinjectedintothecombustionchamber.Thefuelgets
ignitedbecauseofthecompressedair.Thefuelalongwiththecompressedairisignitedsometimes
withasparkplug.
High-pressureturbine(HPT):
Inthebeginning,thestartingmotorrunsthecompressorshaft.
Thehotgases(productsofcombustion)expandthroughthehigh-pressureturbine.
ItisimportanttonotethatwhentheHPTshaftrotatesitinfactdrivesthecompressorshaftwhich
iscoupledtoit.NowtheHPTrunsthecompressorandthestartingmotorisstopped.
About66%ofthepowerdevelopedbythegasturbinepowerplantisusedtorunthecompressor.
Only34%ofthepowerdevelopedbytheplantisusedtogenerateelectricpower.

9. Low pressure turbine (LPT):
ThepurposeoftheLPTistoproduceelectricpower.
TheshaftoftheLPTisdirectlycoupledwiththegeneratortoproduceelectricity.
Thehotgases(productsofcombustion)afterleavingtheHPTisagainsenttoacombustion
chamberwhereitfurtherundergoescombustion.
TheexhaustgasesafterleavingtheLPTpassesthroughtheregeneratorbeforebeingexhausted
throughthechimneyintotheatmosphere.
Theheatfromthehotgasesisusedtopreheattheairenteringthecombustionchamber.This
preheatingoftheairimprovestheefficiencyofthecombustionchamber.
ELEMENTS OF GAS TURBINE POWER PLANT

10. OPEN GAS TURBINE CYCLE

11. NET WORK OUTPUT AND EFFICIENCIES

12. WORK RATIO

13. TWO-STAGE COMPRESSION WITH INTERCOOLING
•Whenthecompressorworkinputisreducedthentheworkratioisincreased.
•Theheatsuppliedwhenintercoolingisusedisgreaterthanwithnointercooling.
•Althoughthenetworkoutputisincreasedbyintercoolingitisfoundingeneralthattheincreasein
heattobesuppliedcausesthethermalefficiencytodecrease.
•Whenintercoolingisusedasupplyofcoolingwatermustbereadilyavailable.
•Theadditionalbulkoftheunitmayoffsettheadvantagetobegainedbyincreasingtheworkratio.

14. GAS TURBINE CYCLE WITH REHEATING
•Networkisincreasedbyreheating.
•Theheattobesuppliedisalsoincreased,andtheneteffectcanbetoreducethethermal
efficiency.

15. GAS TURBINE CYCLE WITH REGENERATION

17. Inaclosed-cyclegasturbine,thereisatwo-stagecompressorandatwo-stageturbine.Allthe
componentsaremountedonthesameshaft.Thepressureandtemperatureattheinletof
thefirststagecompressorare1.5barand20°C.Themaximumcycletemperatureand
pressurearelimitedto750°Cand6bar.Aperfectintercoolerisusedbetweenthetwo-stage
compressorsandareheaterisusedbetweenthetwoturbines.Gasesareheatedinthe
reheaterto750°CbeforeenteringintotheL.P.turbine.Assumingthecompressorandturbine
efficienciesas0.82,calculate:
(i)Theefficiencyofthecyclewithoutregenerator.
(ii)Theefficiencyofthecyclewitharegeneratorwhoseeffectivenessis0.70.
(iii)Themassofthefluidcirculatedifthepowerdevelopedbytheplantis350kW.
Theworkingfluidusedinthecycleisair.Forair:
γ=1.4andcp=1.005kJ/kgK
NUMERICAL PROBLEM 1

18. SOLUTION

19. SOLUTION

20. SOLUTION

21. Inanopencycleregenerativegasturbineplant,theairentersthecompressor
at1barabs32°Candleavesat6.9barabs.Thetemperatureattheendof
combustionchamberis816°C.Theisentropicefficienciesofcompressorand
turbinearerespectively0.84and0.85.Combustionefficiencyis90%andthe
regeneratoreffectivenessis 60 percent,determine:
(a)Thermalefficiency,(b)Airrate,(c)Workratio. (AKTU2019-20)

25. Agasturbineunithasapressureratioof6:1andmaximumcycle
temperatureof610°C.Theisentropicefficienciesofthecompressorand
turbineare0.80and0.82respectively.Calculatethepoweroutputin
kilowattsofanelectricgeneratorgearedtotheturbinewhentheairenters
thecompressorat15°Cattherateof16kg/s.
Takecp=1.005kJ/kgKandγ=1.4forthecompressionprocess,andtake
cp=1.11kJ/kgKandγ=1.333fortheexpansionprocess.(AKTU2017-18)

28. COMBINED BRAYTON CYCLE & RANKINE
CYCLE (COGENERATION)
•Powerplantbaseduponthiscombinedcycleisalso
knownascombinedgasandsteam(COGAS)plant.
•Theoverallefficiencyofthesystemcanbeincreasedby
50–60%.
•Forlarge-scalepowergeneration,atypicalsetwouldbe
a270MWprimarygasturbinecoupledtoa130MW
secondarysteamturbine,givingatotaloutputof
400MW.

29. AUXILIARY SYSTEMS
STARTINGSYSTEMS
Twoseparatesystems-startingandignitionarerequiredtoensureagasturbineenginewillstart
satisfactorily.Duringenginestartingthetwosystemsmustoperatesimultaneously.
ElectricalStarter
(i)A.C.and(ii)D.C.
A.C.crankingmotorsareusually3phaseinductiontypesratedtooperateontheavailable
voltageandfrequency.
D.C.startermotortakesthesourceofelectricalenergyfromabankofbatteriesofsufficient
capacitytohandlethestartingload.Engagingordisengagingclutchisused.

30. Auxiliary Systems
LUBRICATION SYSTEM
Elements of Lubrication System
The following are the elements of the lubrication system of a gas turbine
1. Oil tank,
2. Oil pump,
3. Filter and strainer,
4. Relief valve,
5. Oil cooler,
6. Oil and pipe line,
7. Magnetic drain plug,
8. By-pass valve, and
9. Warning devices.

31. Auxiliary Systems
FUEL SYSTEM AND CONTROLS
Fuel System:

32. Auxiliary Systems
FUEL SYSTEM AND CONTROLS
Prime Control System (Hydro -Mechanical):

33. Operations and Maintenance
(a)Starting
Startingthesequenceofanygasturbinefromresttoitsratedspeedrequiresacertainorderofevents
tobeaccomplishedeithermanuallyorautomatically.Themajorstepsinthesequencearecranking,
ignition,acceleration,andgoverning.
Thefollowingisthetypicalstartingsequenceofagasturbine
1.Applicationofcontrolpowerilluminatesallthemalfunctionslights.
2.Operate‘Resetswitch’toresetmalfunctionscircuits:Bydoingso,malfunctionlightsgooffand
allcontroldevicesassumetheconditionforstarting.
3.Operatethe“Start”switchtoinitiatethestartingsequence.Bydoingthis,thelubeoilpumpand
coolingfanstart.Ifthereareseparateswitchesforthese,operatethese.
4.Whenlubeoilreachesapresetpressure,thestarterisenergized,andthecrankingoftheengine
begins.
5.Withthecrankingofstartingofstarter,theengineandexhaustductsarepurgedofany
combustiblegasesthatmightbepresent.
6.Duringthecrankingcycle,thefuelboostpumpisusedandoperatedtoincreasefuelpressure.

34. Operations and Maintenance
7.Assoonasthefuelpressurehasreachedaprescribedminimumvalue,fueland
ignitionswitchesareturnedonprovidedapresetturbinespeedhasbeenreached.
8.Theturbineacceleratesduetocombustionoffuelandassistanceofcrankingmotor.
Atapresetvalue,sayintheorderof70%ofratedspeed,thestarterandignitionare
cut-offautomatically.
9.Theturbinebecomesself-sustainingandacceleratesonitsowntoitsgoverned
speedtillthegoverningsystemtakesoverthecontrol.
(b)Shutdown:
Tostopthegasturbinefuelsupplyshouldbeturnedoff.Thisisaccomplishedby
closingthefuelvalveeithermanuallyorbyde-energizinganelectricallyoperated
valve.Incaseswheresleevebearingsareused,circulationoflubeoiltobearingsafter
shutdownisnecessaryforcooling.

35. Thetypeofmaintenance,whichisdoneonthegasturbine,isthesameasthatofsteamturbines.
Fromtheexperiencesofthemostmanufacturesofgasturbineequipmentforcedoutagesarefrequently
caused-atleastinpartbyinadequatemaintenance.Thebasicpurposesofapreventivemaintenance
programmearetoreduceforcedoutages.
The following are the principal sub-systems of the gas turbine for which manufacturers present maintenance
instructions:
Maintenance Performance
10. Auxillarygear and main gear
11. Gas turbine
12. Lube oil system
13. Overspeed protection
14. Temperature control and monitoring
systems
15. Air conditioning system
16. Emergency power
17. Motors
18. Related station equipment.
1. Turbine gear
2. Starting
3. Clutches and coupling
4. Fuel system
5. Pneumatic system
6. Fire protection system
7. Control equipment
8. Generator-exciter
9. Electrical controls
Maintenance is carried out daily monthly, quarterly, semi-annually and annually.

36. Whileselectingthesiteforagasturbinepowerplant,thefollowingpointsshouldbegivendue
consideration:
1.Theplantshouldbelocatedneartheloadcentretoavoidtransmissioncostsandlosses.
2.ThesiteshouldbeawayfromthePopulatedarea/businesscentreduetonoisyoperations.
3.Cheapandgoodqualityfuelshouldbeeasilyavailable.
4.Availabilityoflabour.
5.Availabilityofmeansoftransportation
6.Availabilityofwater
Site selection of Gas Turbine Power Plant

37. Combined BraytonCycle & RankineCycle
•Powerplantbaseduponthiscombinedcycle
isalsoknownascombinedgasand
steam(COGAS)plant.
•Theoverallefficiencyofthesystemcanbe
increasedby50–60%.
•Forlarge-scalepowergeneration,atypical
setwouldbea270MWprimarygasturbine
coupledtoa130MWsecondarysteam
turbine,givingatotaloutputof400MW.

38. Integrated Gasifierbased Combined Cycle
(IGCC) system
•Anintegratedgasificationcombinedcycle(IGCC)isatechnologythatusesahigh-pressure
gasifiertoturncoalandothercarbon-basedfuelsintopressurizedgas—synthesisgas
(Syngas).
•Itcanthenremoveimpuritiesfromthesyngaspriortothepowergenerationcycle.
•Someofthesepollutants,suchassulfur,canbeturnedintoreusablebyproductsthrough
theClausprocess.Thisresultsinloweremissionsofsulfurdioxide,particulates,mercury,and
insomecasescarbondioxide.
•Withadditionalprocessequipment,awater-gasshiftreactioncanincreasegasification
efficiencyandreducecarbonmonoxideemissionsbyconvertingittocarbondioxide.
•Theresultingcarbondioxidefromtheshiftreactioncanbeseparated,compressed,and
storedthroughsequestration.
•Excessheatfromtheprimarycombustionandsyngas-firedgenerationisthenpassedto
asteamcycle,similartoacombinedcyclegasturbine.
•Thisprocessresultsinimprovedthermodynamicefficiencycomparedtoconventional
pulverizedcoalcombustion.