Gas turbine functions in the same way as the Internal Combustion engine. It sucks in air from the atmosphere, compresses it. The fuel is injected and ignited. The gases expand doing work and finally exhausts outside. The only difference is instead of the reciprocating motion, gas turbine uses a rotary motion throughout.
This article details the three main sections of the Gas Turbine.
The compressor sucks in air form the atmosphere and compresses it to pressures in the range of 15 to 20 bar. The compressor consists of a number of rows of blades mounted on a shaft. This is something like a series of fans placed one after the other. The pressurized air from the first row is further pressurised in the second row and so on. Stationary vanes between each of the blade rows guide the air flow from one section to the next section. The shaft is connected and rotates along with the main gas turbine.
This is an annular chamber where the fuel burns and is similar to the furnace in a boiler. The air from the compressor is the Combustion air. Burners arranged circumferentially on the annular chamber control the fuel entry to the chamber. The hot gases in the range of 1400 to 1500 °C leave the chamber with high energy levels. The chamber and the subsequent sections are made of special alloys and designs that can withstand this high temperature.
The turbine does the main work of energy conversion. The turbine portion also consists of rows of blades fixed to the shaft. Stationary guide vanes direct the gases to the next set of blades. The kinetic energy of the hot gases impacting on the blades rotates the blades and the shaft. The blades and vanes are made of special alloys and designs that can withstand the very high temperature gas. The exhaust gases then exit to exhaust system through the diffuser. The gas temperature leaving the Turbine is in the range of 500 to 550 °C.
The gas turbine shaft connects to the generator to produce electric power. This is similar to generators used in conventional thermal power plants.
More than Fifty percent of the energy converted is used by the compressor. Only around 35 % of the energy input is available for electric power generation in the generator. The rest of the energy is lost as heat of the exhaust gases to the atmosphere.
Three parameters that affect the performance of a of gas turbine are
- The pressure of the air leaving the compressor.
- The hot gas temperature leaving the Combustion chamber.
- The gas temperature of the exhaust gases leaving the turbine.
The above is a simple description of the Gas Turbine. Actually it is a very sophisticated and complex equipment which over the years have become one of the most reliable mechanical equipment. Used in Combined Cycle mode gives us the most efficient power plant.