Theory For Final.docx

Gas turbine engines derive their power from burning fuel in a combustion chamber and using the fast-flowing combustion gases to drive a turbine in much the same way as the high pressure steam drives a steam turbine. A simple gas turbine is comprised of three main sections a compressor, a combustor, and a power turbine. The gas-turbine operates on the principle of the Brayton cycle, where compressed air is mixed with fuel, and burned under constant pressure conditions. The resulting hot gas is allowed to expand through a turbine to perform work.

 Air at room pressure and temperature is compressed to a high pressure in the compressor  Fuel is added in the combustion chamber where combustion takes place resulting in hightemperature combusted gases  The hot gases expand in the turbine back to the atmospheric pressure producing mechanical power. Part of the mechanical power generated by the turbine is used to drive the compressor. THE JOULE CYCLE The Joule (or Brayton-Joule) cycle, [shown in figure from notes], is the ideal cycle for gas-turbine engines. The ideal cycle is made up of the following four reversible processes: 1-2 Isentropic compression 2-3 Constant pressure combustion 3-4 Isentropic expansion 4-1 Constant pressure heat rejection The efficiency of the ideal cycle depends on the type of gas (though the constant 𝑘) and the compression ratio and it increases if 𝑘 and compression ratio increase. Steam Cycle A steam cycle power plant is operated using the Rankine cycle. Water enters a boiler where it is heated to create steam. The steam is then sent through a steam turbine that rotates the shaft of a generator to create electricity. The steam exits the turbine into a condenser, which converts the steam back into saturated water. The saturated water is then pumped back into the boiler to repeat the process. There are many extra components that are added to the basic system which are used to improve the cycle’s efficiency. Some of these components include: reheaters, moisture separators, and feedwater heaters. Components Components on Engaged that are included in Steam Turbine Power Plants: Steam Turbine Boiler Cooling Tower Efficiency

The efficiency of the simple steam cycle is generally lower than for other cycles such as the combined cycle. This is mainly due to the fact that not all the heat can be harnessed or completely used after the steam is sent through the steam turbines. This loss is dictated by the laws of thermodynamics and limits the efficiency of the system. Combined Cycle Power Plant A combined-cycle power plant uses both a gas and a steam turbine together to produce up to 50 percent more electricity from the same fuel than a traditional simple-cycle plant. The waste heat from the gas turbine is routed to the nearby steam turbine, which generates extra power. HOW A COMBINED-CYCLE POWER PLANT PRODUCES ELECTRICITY This is how a combined-cycle plant works to produce electricity and captures waste heat from the gas turbine to increase efficiency and electrical output. 1. Gas turbine burns fuel. 

The gas turbine compresses air and mixes it with fuel that is heated to a very high temperature. The hot air-fuel mixture moves through the gas turbine blades, making them spin.

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The fast-spinning turbine drives a generator that converts a portion of the spinning energy into electricity.

2. Heat recovery system captures exhaust. 

A Heat Recovery Steam Generator (HRSG) captures exhaust heat from the gas turbine that would otherwise escape through the exhaust stack.

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The HRSG creates steam from the gas turbine exhaust heat and delivers it to the steam turbine.

3. Steam turbine delivers additional electricity. 

The steam turbine sends its energy to the generator drive shaft, where it is converted into additional electricity.