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What Is a Combustion Turbine?

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  • Written By: Andrew Kirmayer
  • Edited By: Shereen Skola
  • Last Modified Date: 23 November 2016
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A combustion turbine is a machine in which air enters, becomes compressed, and is mixed with gas or oil before being ignited. Air is typically drawn in at the front, while compression and combustion generally happen in different sections as well. Heat from the combustion can then move a turbine that converts the force of the fast moving, high-pressure gas into energy. The combustion turbine is often used by power plants to generate electricity, as well as in airplane engines to produce thrust.

Also called a gas turbine, the system is generally an internal combustion engine in which gases are continuously ignited, while in automotive engines this process is typically intermittent. Most of the turbine’s power runs the compressor, while just part of it generates electricity. A common issue with a combustion turbine, therefore, is energy efficiency; the function of the unit is usually defined by the Brayton cycle, in which air is compressed and the pressure increases. The air is heated at a constant pressure until it can expand, during which the pressure and temperature decrease. A decrease in air volume typically occurs as heat escapes the machine into the atmosphere.

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Sometimes a regenerator is added to a combustion turbine to heat the air released by the exhaust, while an intercooler can reduce the temperature of compressed gas. It can minimize the work needed by the compressor, increasing the efficiency of the turbine. In systems where there are two turbines, a reheater is often used on the flow between both of them. Another way to increase the efficiency of a combustion turbine can be to capture the heat from the exhaust, by way of a duct burner, for use in kilns, material drying systems, and other processes that make use of the excess heat.

The efficiency of a combustion turbine can also be affected by climate, as well as altitude. In places that have wide fluctuations in temperature between summer and winter, efficiency and capacity can vary quite a bit. The typical values can help designers decide on what types of components to add to make the turbine run with the most energy efficiency.

Most types of commercial combustion turbine can run anywhere from 500 kilowatts to 25 megawatts, depending on the model. Nitric oxide and carbon monoxide emissions are sometimes a concern, so water injection as well as Selective Catalytic Reduction (SCR) components may be added to reduce the risk of exposure to such gases. A combustion engine is typically reliable and commonly available to power companies and other facilities that can make use of such machinery.

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