1. Combined_Cycle_Power_Plant Prepared by: Nimesh Gajjar

2. Introduction Combined cycle power generation combines 2 cycles for operation, namely the gas turbine cycle and the vapour power (or steam turbine) cycle. In a gas turbine power plant, natural gas and compressed air undergo combustion. The resultant high pressure gas drives the gas turbine which in turn produces electricity. Although it is clean and fast in starting up, the gas turbine power plant suffers from low thermo efficiency of about 25 to 30%. Much of the energy is wasted in the form of gas turbine exhaust. The combined cycle power generation makes use of the merits of the high temperature (1100 to 1650°C) gas turbine cycle and the lower temperature (540 to 650°C) steam turbine cycle. The hot exhaust gas from the gas turbine, instead of being released as waste, is captured and channelled to the steam turbine where steam is heated by the exhaust to drive the turbine.

3. Arrangements of CPP

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6. Intro… The combined cycle has a better thermal efficiency compared to either of gas turbine cycle and steam turbine cycle individually. The thermal efficiency of a combined cycle is given by where gas Wgas is the net power produced by the gas turbine, steam Wsteam is the net power produced by the steam turbine, and in Qin is the rate of heat transfer to the gas turbine

7. Advantages  The efficiency of combined cycle power plant is higher than simple gas based or steam based power plant.  The capital cost of combined cycle power plant is slightly higher than a gas turbine power plant and much below the steam power plant at the same power capacity.  The cooling water requirement of combined cycle power plant is much lower than a pure steam power plant having the same output.  It gives high ratio of power output to occupied ground space.  combined power plant exhaust emission can be reduced and thermal efficiency &generating capacity can be increased.

8. Disadvantages  The combined cycle power generation system is not without its disadvantages.  As natural gas is the fuel used, its higher cost compared to coal and oil will result in higher operating cost. The system is also less flexible with regards to the types of fuel to be used, thus this limit in resources means the supply of fuel is critical to the  plant’s operation.  Also, the combined cycle power generation system is a combination of two technologies, the complexity will result in higher maintenance cost and also it will require highly skilled and better trained operating staffs.  The capital cost of a combined cycle power generation plant is higher than that of gas turbine plant.

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11. Parameters Affecting Thermodynamic Efficiency of Simple GT Cycle and Combined Cycle Compressor inlet temperature Gas turbine inlet temperature Pressure ratio Gas turbine exit temperature