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Gas Turbine WHRU
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GAS TURBINE WASTE HEAT
RECOVERY UNITS (WHRU)
Aug 2012
AcknowledgmentGPSA Section 15
Pictures from many sources, suppliers, internet
Gas Turbine
Prime mover to drive compressors and generators
2 Types: Aero-derivatives and industrial Aero-derivatives are light weight; preferred offshore and are
used to 25 MW
Heavier industrial units are used for higher duties and on onshore
Ambient air (gas) is compressed in an axial air compressor to 10 to 20 bar similar to BFW pump in a steam system
Fuel is fired in a combustion chamber into hot compressed air. Hot and pressurized flue gas is let down in pressure first thru a "gas producer" turbine -similar to steam turbine, to provide energy for inlet compression
Balance energy in the hot gas is used for jet-action in an aircraft. In industrial unit, it is recovered thru a "power turbine" to run a compressor or generator
Inlet compression takes 2/3 energy developed in turbines. Recycled energy!
GT fuel efficiency: 30-40% based on Xs air and Exhaust Temp
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ExhaustAir
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GT Single Vs Split Shaft
Industrial GTs are made of single shaft - that is air compressor, power turbine and driven equipment (compressor or generator) all share the same common shaft Single shaft is more stable, lesser bearings but requires
higher starting power. Narrow speed range to avoid surging in inlet air compressor
Aero-derivatives have dual shafts, the air compressor components in one shaft and power turbine and driven unit in another shaft Air compressor is run at its best speed and power
turbine runs at speeds to suit the driven equipment
Single shaft: Power generation with a gearbox; Variable speed 2 shaft for compressor/ pumps
Driven unit can be near the air-end ("cold end drive) or exhaust end ("hot end" drive)
Driven Compressor/
Generator
ExhaustAir 100 u
Fuel35 u
65 u
GTs efficiency: 35%
GT exhaust heat can be used to generate steam or heat oil in a WHRUGT + exhaust steam turbine provide a combined cycle power plant with 45% efficiency
Gas Turbine Performance
Rated by Power Delivered, kW and Heat Rate, kJ/kWh energy supplied to get a kWh at ISO conditions: 15C; 0 m elevation, atmospheric pressure of 101.325 kPa a and 0%
Relative Humidity - dry air, without any inlet loss (due to air filter) and outlet loss (due to silencers/WHRU)
Ambient Temp & Altitude Correction: Inlet air compressor is a constant volume machine. Altitude and air temperature impact air density and mass flow and power delivered
Inlet air filter and outlet WHRU/ silencer impact air flow and head developed hence power delivered The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Suitable corrections are then applied for site
conditions of these variables to derive site
delivered power, heat rate
Gas Turbine Typical Data
Higher the compression ratio, hotter the gas,
less fuel required to reach a given combustion
zone T1 temperature
Make Power, kW Effcy, % Comp
Ratio
Xs Air, % Exhaust
T, C
Solar Taurus 70 8,140 35.3 15 240 510
Solar Mars 100 11,860 34.4 17.5 260 485
GE LM 2500 25,060 37.1 18 200 566
Nuovo Pignone MS5002 28,340 29.2 8.4 280 516
Rolls Royce RB 211 30,910 38.6 20.8 250 490
Gas Turbine WHRU
WHRU
GTs employ 250 - 350% excess air to limit combustion
chamber metal temperature
Exhaust at 500C with 15% O2: Source of waste heat - either
as hot combustion air or in a waste heat recovery exchanger
Combustion Air: Extensive ducting and load co-ordination
GT Vs heater load. Post firing 2-3 times of GT based on Xs air
Waste Heat: Because of high Xs air, heat recovery is limited.
Usually WHRU duty GT load. As air flow remains same, GT
part load exhaust temperature is low
Xs air reduction: Large machines use Inlet Guide Vanes.
IGV reduce air to 80% during part load. Below 80%
inlet Axial Flow Compressor will surge
Driven Compressor/
Generator
ExhaustAir 100 u
Fuel
35 u
30 u
GTs efficiency: 35%
35 u
Exhaust
65 u
With WHRU
70 %
As combustion air
Low NOX burners operate with lean fuel: air mix. They
employ recycle loop across air compressor to limit Xs air
in combustion chamber during part load
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GT WHRU
Heat hot oil, hot water, crude, amine, regen gas
generate and superheat steam
Finned tubes, similar to heater convection section
CIBAS: (concentric integral bypass and silencer). Finned helical coils in annulus between outer casing and internal bypass
WHRU
Bypass
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WHRU
Bypass Bypass
Common WHRU
for 2 Turbines
Parts
soot-blowers, by-pass stack, auxiliary firing (oil or
gas firing)
Diverter dampers control outlet temperature
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GT WHRU Supplementary Firing
Lower the ambient temperature, lower is exhaust temperature; Exhaust temperature is also low at GT part load
Additional firing in WHRU inlet duct boosts GT exhaust temp or waste heat recovery, specially during GT part load
As exhaust has 15-18% O2, fuel (oil or gas or both ) can be directly fired in the duct
Duct Burners
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GT WHRU Supplementary Firing
Duct burners: Many small burners across duct
cross section
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GT WHRU Ducting
A fired heater convection is usually castable
cement or ceramic fiber lined internally on
carbon steel casing. In GT WHRU gases travel at
high velocity (Heater P = 0.5 WC (o.125 kPa);
WHRU P = 6 WC (1.5 kPa)) that will erode
insulation
GT /WHRU ducts are usually made of SS sheets
with external mineral wool type of insulation
THANK YOU