Gas Turbines
Gas turbines have been used to generate power for about 70 years. The technology revolutionized airplane propulsion industry in 1940s and is currently the economic and environmentally preferred choice for new power generation plants in the United States. Typically, gas turbines are in the 500 kW to 250 MW range. These turbines exhaust high quality heat that can be used in CHP mode to reach overall system efficiency of 70-80%. Gas turbines have been typically used for by the utilities for peaking power capacity, although recent trends show that these turbines are increasingly used for base-load power. Gas turbines have been typically used in combination with steam turbines in a combined cycle plant at central power station with efficiencies approaching as high as 60% LHV. However, simple cycle gas turbines have efficiencies approaching 40% LHV.

Gas turbines operate on the principle of Brayton cycle. In this case, air is compressed in a compressor, heated in a fuel combustion chamber, and then expanded in a turbine (see figure below). The excess power produced by the turbine is used to drive the compressor. The power produced by the turbine and consumed by a compressor is proportional to the absolute temperature of the gas passing through it and is limited by turbine materials. In general, use of high temperature and high pressure ratios results in higher efficiency and specific power.


Three different kinds of gas turbines are common. These include:

• Frame gas turbines: These are the industrial gas turbines for stationary power generation and are available in size range of 1 - 250 MW. These are less expensive, more rugged, and are suited for continuous base-load operation with longer inspection and maintenance intervals.
• Mini and micro turbines: Mini and micro turbines are the newer generation of smaller turbines. The capacities of mini turbines range from 100 kW to 1000 kW and micro turbines range in capacities from 25 kW to 100 kW. It is not uncommon to ignore the differentiation between mini- and micro- turbines. For the purpose of discussion at this website all turbines smaller in capacity than 1 MW will be referred to as microturbines. These turbines can use natural gas, propane, and gases produced from landfills, sewage treatment facilities, and animal waste processing plants as a primary fuel. The fuel source versatility of microturbines allows their application in remote areas.
• Aeroderivative gas turbines: These are typically used for jet and turboshaft aircraft engines, and are lightweight, thermally efficient, but expensive. For the stationary power generation, these turbines are typically operated at compression ratios of 30:1, therefore requiring high-pressure external gas compressor. These turbines are available in sizes typically less than 50 MW.

Links to Manufacturers ALM Turbine Alzeta Corporation Bowman Power Systems Catalytica Energy Systems Capstone Turbine Corporation Elliot Energy Systems General Electric Power Systems Honeywell International Ingersoll Rand Pratt & Whitney Power Systems Siemens Westinghouse Power Generation Solar Turbines Teledyne Technologies Turbec

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