NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 93
flows upward, the pressure decreases and some of the hot water “flashes” into steam. The Geysers in
northern California, which uses steam piped directly from wells, produces the world’s largest single
source of geothermal power.
Flash steam plants are the most common type of geothermal power generation plants in opera-
tion today. They use water at temperatures greater than 182°C that is pumped under high pressure to the
generation equipment at the surface. Upon reaching the generation equipment the pressure is suddenly
reduced, allowing some of the hot water to convert or “flash” into steam. This steam is then used to
power the turbine/generator units to produce electricity. The remaining hot water not flashed into steam,
and the water condensed from the steam is generally pumped back into the reservoir. An example of an
area using the flash steam operation is the Cal Energy Navy I flash geothermal power plant at the Coso
geothermal field.
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.