What is Gas Turbine Power Plant?

GAS TURBINE POWER PLANT:

Gas Turbine, also combustion turbine, engine that employ gas flow as the working medium which heat transforms energy into mechanical energy. Gas is produce in the engine by the combustion of certain fuels. Stationary nozzle discharge jets of this gas against the blades of a turbine wheel. The impulse force of the jets causes the shaft to turn. A simple-cycle gas turbine includes a compressor that pumps compressed the air into a combustion chamber. Fuel in gaseous or liquid-spray from is also injected into this chamber, and combustion take place there. The combustion products pass from the chamber through the nozzle to the turbine wheel.

In a compressor or turbine, a row of fixed blades and a corresponding row of fixed blades attached to a rotor is called a stage. Large machines employ multi-stage axial-flow compressor and turbines.

In shaft arrangements, in initial turbine stage (or stages) powers the compressor on one shaft while the later turbine stage (or stages) powers the external load on a separate shaft.

The efficiency of the gas-turbine cycle is limited by the need for continuous operation at high temperatures in the combustion chamber and early turbine stages. A small, simple-cycle gas turbine may have a relatively low thermodynamic efficiency, comparable to a conventional gasoline engine. Advances in heat-resistant materials, protecting coatings, cooling arrangements have made possible large units with simple-cycle efficiencies of 34 percent or higher.

The efficiency of gas-turbine cycle can be enhanced by the use of auxiliary equipment such as intercoolers, regenerators, and reheaters. These devices are expensive, however, and economic considerations usually preclude their use.

In a combined-cycle power plant, the considerable heat remaining in the gas turbine exhaust is directed t the boiler called a heat-recovery steam generator. The heat so recovered is used to raise steam for an associated steam turbine. The combined output is approximately 50 percent greater than that of the gas turbine alone. Combined cycle with thermal efficiency of 52 percent and higher are being put into service. Gas turbines have been applied to the propulsion of ships and railroad locomotives. A modified form of gas turbine, the turbojet, is used for airplane propulsion. Heavy-duty gas turbines in both simple and combined cycles have become important for large scale generation of electricity. Unit rating is exceeds of 200 megawatts (MW) are available. The combined cycle output can exceed 300 MW.

The usual fuels used in gas turbine are natural gas and liquids such as kerosene and diesel oil. Coal can be used after conversion to gas in a separate Gasifier.

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