Binary power plant system

A binary cycle power plant is a type of geothermal power plant that allows cooler geothermal reservoirs to be used than is necessary for dry steam and flash steam plants. As of 2010, flash steam plants are the most common type of geothermal power generation plants in operation today, which use water at temperatures greater than 182 °C (455 K; 360 °F) that is pumped under high pressure to the generation equipment at the surface. With binary cycle geothermal power plants, pumps are used to pump hot water from a geothermal well, through a heat exchanger, and the cooled water is returned to the underground reservoir. A second "working" or "binary" fluid with a low boiling point, typically a butane or pentane hydrocarbon, is pumped at fairly high pressure (500 psi (3.4 MPa)) through the heat exchanger, where it is vaporized and then directed through a turbine. The vapor exiting the turbine is then condensed by cold air radiators or cold water and cycled back through the heat exchanger.

A binary vapor cycle is defined in thermodynamics as a power cycle that is a combination of two cycles, one in a high temperature region and the other in a lower temperature region.

The use of mercury-water cycles in the United States can be dated back to the late 1920s. A small mercury-water plant which produced about 40 megawatts (MW) was in use in New Hampshire in the 1950s, with a higher thermal efficiency than most of the power plants in use during the 1950s. Unfortunately, binary vapor cycles have a high initial cost and so they are not as economically attractive.

Water is the optimal working fluid to use in vapor cycles because it is the closest to an ideal working fluid that is currently available. The binary cycle is a process designed to overcome the imperfections of water as a working fluid. The cycle uses two fluids in an attempt to approach an ideal working fluid.

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