What is Combined Cycle Power Plant?

COMBINED CYCLE POWER PLANT:

Combined Cycle Generation, system of electricity generation that makes use of both a gas turbine and a steam turbine. Combined cycle power plants are more efficient than conventional power plants, with an energy conversion efficiency of around 40 percent (compared with under 38 percent for conventional plants).

In combined cycle generation, the gas turbine is powered by burning gas fuels and turns as electric generator. The exhaust gases are then used to heat water to produce steam. The steam powers a steam turbine attached to an electric generator, producing additional electricity. Simple cycle operates near max power because they ate not uses in service where efficiency is the prime concern. Regenerative cycles, however, are meaning full only if they are operated near max efficiency. Thus they would have their output reduced from a simple cycle by a much larger percentage, perhaps 10-14 %. In certain applications, an economic compromise b/w capital and operating cost would have to be found.

It can be seen that raising the efficiency of a gas turbine plant by regeneration, while used for stationary applications is costly. A means, therefore, was sought whereby both efficiency and power are increased. The solution was found I using the large quantity of energy leaving with the turbine exhaust to generate steam for a turbine power plant. This is natural solution as the gas turbine is a relatively high temperature machine (1100-1650 C) where as a steam turbine is a relatively low temp machine (540-650 C). This joint operation of a gas turbine at the “hot end” and the steam turbine at the “cold end” is called a combined cycle power plant.

Besides both high efficiency and high power output, combined cycles are characterized by flexibility, quick part-load starting, suitability for both base load and cyclic operation, and a high efficiency over a wide ranged of leads. They have the potential of using coal as well as synthetic and other fuels. Their obvious disadvantage is in their complexity, as they in a sense combine two technologies in one power-plant complex. The idea of combined cycles is cot new, having been proposed as early as the beginning of this century. It was not, however, until 1950 that the first plant was installed. This was followed by a rapid rise in the no of installations, especially in the 1970s.

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