Effi ciency of GTGEffi ciency of GTG

Presented by:Sanjay Kumar

IIT Kanpur

TATA CHEMICAL LTD., BabralaFertilizer Division

Gas Turbine Generator

The Gas Turbine is a power plant which produces a great amount of energy.

Basic Component of GTG

Compressor CombustorTurbine

Brayton Cycle

INLET AIRFILTER

C T

AIR COMPRESSOR TURBINE

GENERATOR

C.C.

LOAD GEAR

COMBUSTIONCHAMBER

FUEL(NG/HSD/NAP.)

KS STEAM

FEED WATER

STAGE-2

STAGE-1

HEATRECO-VERYUNIT(HRU)

D

G

(AUX.FIRING)

Brayton Cycle P-V Diagram:

P

V

Theoretical Cycle

Real Cycle

Stages in GTG

Compression 1-2 Combustion 2-3Expansion 3-4

Why there is diffrence in real and theoretical cycle???

Compression Stage

Volume decreasesPressure IncreasesTemprature IncreasesAvg. Inlet Temp=27oCInlet Pressure=1 Bar (atm)Outlet Temp= 310oCOutlet press=6.7bar17 stage Compressor

Compression Stage Cont….

Efficiency of the compressor=80% (but we assume it to be 100% while calculation.

Work done on Comp Wc = maCpa(T2-T1)

This is also equal to Wc=-nkRT1((P2/P1)(k-1)/nk-1)/.8(k-1))

n=No. of Stages , R=8.314J/Kmol K

Losses in Compressor

Designing Lossa) Rotar Lossb) Stator Loss

Losses are expressed as “Loss of heat and Enthalpy.” qtot=qth + qdf

qtot=Head Loss From disc Friction

qth=Heat Available from energy equation

Various Loss

qin=Heat loss from shock of the rotor

qsh=incidence loss

qbc=Profile Loss

qc=Clearance Loss (rotor and shroud)

qsf=Secondary Loss encountered in flow purge

qia= qin+ qsh+ qbc+ qc+ qsf

Efficiency Nimp= qia/ qtot

Compressor Stage cont...

qoa= qia- qin- qsh- qbc- qsf

qw=Head loss encountered in the stator from wake caused by impeller. qosf= Frictional Loss qex=Loss of Kinetic Head at the exit of stator.

Nstage= qia/ qtot

Compressor Stage Cont..

Due to all these factor the efficiency of compressor comes down to 80%. And thus the compression's not fully adiabatic.

P

V

Isotherm Line on Actual Curve

P

V

Shaded area= Extra Work that we have to done on Compressor have same pressure level.

Combustion Stage

The Fuel entered at this stageFuel Used:

a) Naphthab) Natural Gas

Reaction Occurred:CH4 + 2O2 ==> CO2 + 2H2O + Heat

Combustor Performance

Combustor performance is measured by:1) Efficiency decrease

encountered in the combustor2) Evenness of the outlet temperature

profile.

Ncomp=(ma+ mf)h3- mah2

(mf * CV)

Combustor Performance Cont.

Heat added to Combustor:

Q=(ma+ mf)h3- mah2

= (ma+ mf)CpgT3- maCpaT2

= (ma+ mf)Cpg(T3-T2)

Loss is Pressure is due to :

Acceleration of the fluid.Pressure drop due to aerodynamic drag:-

a) Friction in the Passage.b) Mixing Losses of the air jets.

As volume increases==>the temperature rises ==> Presure decreases.

Combustor stage cont.

P-V diagram

P

V

Pressure Loss

Expansion Stage

Gas does work in this stage using a turbine.About 25% of the gas is used.Rest is sent to make KS/LS steam in HRU.Average Inlet Temperature=1022oCInlet Pressure= 6.7 bar.Outlet Temp= 520oCOutlet Pressure=1bar (or >1bar)

Expansion Stage Cont.

Work Done by Turbine=Wc

Wc=(ma+mf)(h3-h4) = (ma+mf)Cpg(T3-T4)

Expansion is not ideally adiabatic.

Overall Efficiency of GTG

Three methods to calculate efficiency (as I used):-

a) Theoretical (Temp method)b) Actual (I/O method)c) Graphical (Using graphs)

*Graphical method is not so accurate as it is a averaged graph.

Theoretical Method

Ngtg= Wt - Wc

QNgtg=1- (T4-T1) (T3-T2)

Assumptions: 1) ma>>mf

2) Cair= Cgas

3) P2/P1= P3/P4

GTG Cont.

Known Quantity=T1, T2, T4

Unknown Quantity= T3

T3= T4( P3/ P4)((k-1)/k)

K=1.33 for gas.Approximated efficiency= 28-29 %

Input/Output Method

Efficiency=Ngtg=Power Produced Fuel Energy

GTG

Fuel=Mf*CVCV=Calorific Value

Power

Graphical Method

By graph we generate equations between various parameters.

Efficiency of GTG is Calculated.

Heat Recovery Unit

Input : 1) Feed Water 2) Steam entering inHRU from

GTG Output :1) KS Steam Efficiency of HRU :

Nhru=(mkshks - mfwhfw – mgtghgtg) (mf * CV)

GTG + HRU efficiency

Overall efficiency of GTG + HRU:

Noverall =Power Produced +Steam Generation Fuel Energy (HRU+GTG)

Steam Generation = msteam x hsteam

hsteam =0.7 according to the data in TCL

Efficiency chart

GTG + HRU= 92.7 %

GTG30.2%

62.5%

7.3%

HRU

Power

Losses

Effects of Different Parameters

Parameter which can affect:1) Inlet Temperature of Compressor

2) T3 (Temperature at Combustor outlet) 3) Relative Humidity 4) Compression Ratio

Main Points

Efficiency can be increased if:a) Compression ratio Increasesb) T1 decreases.c) T3 increases.

Presented By:Sanjay Kumar IIT Kanpur