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Another factor is the power consumed by the CTs compressor. The
work required to compress
air is directly proportional to the temperature of the air, so
reducing the inlet air temperature
reduces the work of compression and there is more work available
at the turbine output shaft.
Gas turbines typically operate at as little as 80% of their
rated capacity on hot days due to the
lower air density and higher temperatures. Inlet air cooling
helps to make up the difference by
increasing the air mass flow through the turbine and by cooling
the air, which reduces the work
of compression.
Cooling of Compressor Air Inlet of a Gas Turbine Power Plant
Using Ammonia-Water Vapor
Absorption System
the generated power and efficiency of gas turbine plants depend
largely on the temperature ofthe inlet air, so that they both
increase as the inlet air temperature decreases. Decreasing the
temperature of air inlet to the compressor could be achieved by
installing an absorption
refrigeration cycle (ARC) at gas turbine inlet
Specificaio Value Unit
Rated
Power
24.6 MW
Air Flow
Rate
118 kg/s
Exhaust
Temperatu
re
484 C
Efficiency 32.98 %
Pressure Ratio 10.5
The outlet, which goes to the combustion chamber, is determined
by assuming zero pressure
drops at the compressor inlet, a compressor ratio of 10.5, and
an isentropic efficiency of 83%[3].
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The combustion chamber has two inlets, the compressor outlet and
the fuel, the fuel was
assumed to be pure methane at 15C and 1300 kPa. At full load its
mass flow rate is set to match
the manufacturer-specified firing temperature. Once the full
load fuel rate is set in this case 6230
kg/hr, part loading is simulated by adjusting the fuel mass flow
rate. The chamber is assumed to
have zero pressure drops. The reactor products exit the
combustion chamber and enter the
turbine. The turbines isentropic efficiency is assumed to be
85%, the pressure ratio is taken to be
10.5 and the pressure drop at the gas turbine exit is assumed to
be zero. The turbine exhaust is
synonymous with the exhaust of the gas turbine. The gas turbine
exhaust goes to a heat
exchanger block, which simulates the removal of waste heat. Zero
pressure drops was assumed,
and the exit temperature of the block was selected to be 200C.
This is because condensation
issues might arise at temperatures lower than 200C, thus, 200C
is a conservative
approximation
Table 2. State points and assumptions Assumptions
1. The pressure losses and heat transfer losses to the
surroundings in the absorption cycle are igno
2. The condensing pressure of the refrigerant of the absorption
system is equal to the pressure o
ambient temperature amounts 1555 kPa.
3. The evaporator pressure of the absorption system is constant
and amounts to 288 kPa. The
corresponding evaporator temperature is -10C. The evaporator
pressure is chosen so that the
inlet air can be cooled to a temperature that is close to the
required temperature for optimum
operation of.
4. The outlet temperature of gas in the desorber of the
absorption system at 14 is 20 higher than
the temperature of the strong solution at the outlet of the
desorber at 10.
5. The concentrations of the strong and weak solutions of the
absorption system are 0.4 and 0.3
respectively. The assumed values are chosen within the operating
range of the Ammonia/Water
absorption systems and are commonly used.
6. The effectiveness of the absorption system heat exchanger is
80 percent.
7. Polytropic efficiency of compressor and turbine are 0.9 and
0.85 respectively.
8. Minimum inlet temperature to prevent icing at the compressor
inlet is 12C.
9. Methane (CH4) with low heat value of 50010 kJ/kg is used as
fuel and its pressure and
temperature are the same as that of combustion chamber
inlet.
