Power Plant Engineering

Fig. 2.36. The Cal Energy Navy I Flash Geothermal Power plant at the Coso Geothermal Field.
Binary Cycle Power Plant (Liquid Dominatd Systems). Binary cycle power plants operate
on water at lower temperatures of about 107°–182°C. These plants use the heat from the hot water to
boil a working fluid, usually an organic compound with a low boiling point. The working fluid is
vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the
ground to be reheated. The water and the working fluid are kept separated during the whole process, so
there are little or no air emissions.
Binary cycle power plant operates on water at lower temperatures of about 107 degrees Celsius
to 182 degrees Celsius. These plants use the heat from the hot water to boil a fluid, usually an organic
compound with a low boiling point.
Binary cycle geothermal power generation plants differ from Dry Steam and Flash Steam sys-
tems in that the water or steam from the geothermal reservoir never comes in contact with the turbine/
generator units. In the Binary system, the water from the geothermal reservoir is used to heat another
“working fluid” which is vaporized and used to turn the turbine/generator units. The geothermal water,
and the “working fluid” are each confined in separate circulating systems or “closed loops” and never
come in contact with each other. The advantage of the binary cycle plant is that they can operate with
lower temperature waters (225°F–360°F), by using working fluids that have an even lower boiling
point than water. They also produce no air.

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POWER PLANT ENGINEERING
Hybrid Geothermal Power Plant-Fossil System. The concept of hybrid geothermal-fossil-
fuel systems utilizes the relatively low-tem-perature heat of geothermal sources in the low-temperature
end of a conventional cycle and the high-temperature heat from fossil-fuel combustion in the high-
temperature end of that cycle. The concept thus combines the high-efficiency of a high-temperature
cycle with a natural source of heat for part of the heat addition, thus reducing the consumption of the
expensive and nonrenewable fossil fuel.
There are two possible arrangements for hybrid plants. These are
(1) Geothermal preheat, suitable for low-temperature liquid-dominated systems, and
(2) Fossil superheat, suitable for vapor-dominated and high-temperature liquid-dominated
systems.