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PG6101FA
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GTG Performance ??? Availability
Output
Efficiency
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Why performance
monitoring To maintain high availability Minimize degradation and maintain
operation near design efficiency Diagnose problems and avoid operation in
the region where serious malfunction canoccur
Extend time between inspections and
overhauls Reduce life cycle cost
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Single shaft GT
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GTG PerformanceThe Br ayt on Cycle
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Brayton cycle is characterized by : Pressure ratio
Firing temperature
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The pressure ratio resulting in maximum outputand maximum efficiency change with firingtemperature.
Higher the pressure ratio, the greater thebenefits from increased firing temperature.Increase in firing temperature provide powerincrease at a given pressure ratio, although thereis a sacrifice of efficiency due to the increase incooling air losses required to maintain parts lives.
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In combined-cycle applications pressure ratioincrease have a less pronounced effect onefficiency.
Note : As pressure ratio increases, specific powerdecreases. Increase in firing temperature result
in increased thermal efficiency. The significant differences in the slope of the
two curves indicate that the optimum cycleparameters are not the same for simple andcombined cycles.
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Simple-cycle efficiency is achievedwith high pressure ratios.
Combined-cycle efficiency isobtained with more modest pressureratios and greater firingtemperatures.
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Fact or s A f f ect ing Gas
Tur bine Per f or mance Ai r Temper at ur e
Sit e Elevat ion (Bar omet r ic Pr essur e)
Humidi t y I nlet DP
Exhaust DP
Fuels
Fuel Temper at ur e
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Ai r Temper at ur e and
Sit e Elevat ion GT performance is changed by
anything that affects the density
and/or mass flow of the air intake tothe compressor
ISO conditions
59 F/15 C 14.7 psia/1.013 bar
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Effect of CTIM on output
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Effect of CTIM on heat
rate
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MW 1/CTIM
0.505Average Gain in MW / C
0.4753.5371.057623
0.4833.0621.049424
0.4952.5791.041325
0.5052.0841.033126
0.5161.5791.024927
0.5261.0631.016628
0.5370.5371.008329
0.0001.000030
Gain in MW / CGain in MWCFCTIM
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Effect of Barometric
pressure on output
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Effect of Barometric pressure
on heat Rate
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Humidity Humid air is less dense than dry air
Single-shaft turbines that use
turbine exhaust temperature biasedby the compressor pressure ratio toapproximate firing temperature will
reduce power as a result of increasedambient humidity.
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Effect of RH on output
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Effect of RH on Heat rate
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I nlet and Exhaust
Losses
Inserting air filtration, silencing, evaporative coolers or chillersinto the inlet or heat recovery devices in the exhaust causespressure losses in the system
4 Inches (10 mbar) H2O Inlet Drop Produces: 1.42% Power Output Loss 0.45% Heat Rate Increase 1.9 F (1.1 C) Exhaust Temperature Increase
4 Inches (10 mbar) H2O Exhaust Drop Produces: 0.42% Power Output Loss
0.42% Heat Rate Increase 1.9 F (1.1 C) Exhaust Temperature Increase
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Effect of Inlet DP on
output
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Effect of Inlet DP on heat
rate
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Effect of back pressure on
output
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Effect of back pressure on
heat Rate
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Effect of frequency on
output
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Effect of frequency on
heat rate
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MW Frequency
0.074-3.2380.952548.5
-1.805-3.3120.951549.0
-1.507-1.5070.977349.5
0.0000.0001.000050.0
1.2291.2291.019350.5
1.0272.2561.036051.0
Change in MW / 0.5 HzChange in MWCFFrequency
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Fuel temp Heated fuel results in higher turbine
efficiency due to the reduced fuel
flow required to raise the total gastemperature to firing temperature
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Effect of Fuel temp on
output
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Effect of Fuel temp on heat
rate
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Effect of Fuel LHV on
output
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Effect of Fuel LHV on heat
Rate
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Compressor performance
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Gas t ur bine per f or mance
degr adat ion Recover able loss
Recoverable loss is usually associated with compressor fouling and canbe partially recovered by water washing or, more thoroughly, bymechanically cleaning the compressor blades and vanes after openingthe unit.
N on- r ecover able loss Non-recoverable loss is primarily due to increased turbine and
compressor clearances and changes in surface finish and airfoilcontour.
Since this loss is caused by reduction in component efficiencies, itcannot be recovered by operational procedures, external maintenanceor compressor cleaning, but only through replacement of affected
parts at recommended inspection intervals.
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Design specification for
GTG
11665.56Kcal/SM3Fuel LHV
82.4CFuel Temp
0.85RatioGenerator Power Factor
11.18In H2OExhaust DP
89mm H2OInlet DP
1012.49m BarAtmospheric Pressure
70%Relative Humidity
5231RPMTurbine Speed
30CCompressor Inlet Temperature
50HzFrequency
RatedUnitsParameters
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Performance monitoring Heat rate
Specific fuel consumption
Efficiency Compressor efficiency
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Performance calculationHeat rate =
Fuel consumption (SM3) * Calorific value of fuel (Kcal/SM3)Units produced (KWH)
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Performance calculationSpecific fuel consumption =
Fuel consumed per unit of electricity produced
Natural gas consumed (SM3)
Units generated (KWH)
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Performance calculationTurbine efficiency
MW Output (Kcal) * 100
Fuel Input (Kcal)
860 * 100
Heat rate (Kcal/kwh)
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Performance calculation
Compressor Efficiency
P2
P1
(-1)
-1
T2T1
-1
Cp/Cv
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Inspection Gas turbine must be inspected in
following areas
Inlet air filter & Evaporative coolers Compressor
Combustor
Turbine
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Inlet air filter inspection Time to replace filters
Filter plugging
Inlet duct air leak
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Compressor Consumes around 50-65% of the energy
produced by turbine thus fouling of the
compressor can drastically reduce overallefficiency of the gas turbine.
Fouling of the compressor can cause surgewhich not only creates performance
degradation but also creates bearingproblems and flameouts
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Compressor Parameters to be monitored
Efficiency
Surge map Compressor power consumption
Compressor fouling index
Compressor deterioration index
Humidity effect on fouling Stage deterioration
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Compressor performance
calculations Compressor work or power consumed
Wc = CpavgT1{(P2/P1)((y-1)/y)-1}
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Compressor losses
Losses can be divided in to two categories Controllable losses Loss due to compressor fouling
Loss due to inlet pressure drop
Loss due to inlet temperature increase
Uncontrollable losses Loss due to barometric press drop
Loss due to high ambient temperature
Loss due to high ambient humidity
Loss due to frequency drop
Loss due to ageing
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Compressor fouling graph
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G T C o m p r e s s o r e f f i c i e n c y t re n d
9 0 .0
9 0 .5
9 1 .0
9 1 .5
9 2 .0
9 2 .5
9 3 .0
9 3 .5
1
/0
1
/5
1
/1
0
1
/1
5
1
/2
0
1
/2
5
1
/3
0
2
/4
2
/9
2
/1
4
D a t e
C
o
m
p
resso
rE
fficien
cy
Off line water wash
On line water wash
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Compressor wash Online compressor wash
some plants do it daily and some do it whenpressure ratio drops by 2%
Offline compressor wash Pressure ratio drop by 8% beyond which surge
can occur Once in three months as per GE performance
degradation guarantee contract Not meeting our export targets
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Combustor Following parameters to be
monitored
Combustor efficiency Specific fuel consumption
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Turbine Following parameters to be
monitored
Turbine inlet temperature
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