There are three principle ways of converting geothermal energy into electricity. Each is designed to exploit a specific type of geothermal resource. The simplest situation occurs where a geothermal reservoir produces high-temperature dry steam alone. Under these circumstances it is possible to use a direct-steam power plant which is analogous to the power train of a steam turbine power station but with the boiler replaced by the geother-mal steam source.
Most high-temperature geothermal fields produce not dry steam but a mixture of steam and hot water. This is most effectively exploited using a flash-steam geothermal plant. The flash process converts part of the hot, high-pressure liquid to steam and this steam, together with any extracted fluid directly from the borehole, is used to drive a steam turbine.
Where the geothermal resource is of a relatively low temperature a third system called a binary plant is more appropriate. This uses the lower-temperature geothermal fluid to vaporise a second low boiling point fluid contained in a separate, closed system. The vapour then drives a turbine which turns a generator to produce electricity.
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