Geothermal waters can be used to generate electricity. The waters used for electricity generation are normally at high temperatures around 300oF. However as technology improves, the temperatures needed are lower. There are four different methods used to generate electricity from geothermal resources – flash power plants, dry steam plants, binary plants, and flash/binary combined plants.
Flash power plants operate by separating the geothermal waters into steam and hot water. As the waters emerge from the ground, they are under pressure. The water “flashes” as it reaches the surface, producing steam along with the hot water. The hot water, or “brine”, is re-injected back into the geothermal reservoir. The steam is utilized to operate a turbine that generates the electricity.
A dry steam plant utilizes steam to run the turbines to produce the power. The wells are dry wells that only produce steam. No hot water or brine is produced by the well so no re-injection is required. Yellowstone National Park is an area where this technology can be used.
A binary power plant is a newer method of electricity generation and uses geothermal water that is lower than 300oF. These power plants use the hot water to heat another liquid. In a heat exchanger, the water transfers its heat to a liquid such as isobutene, pentafluoropropane, or other organic fluid that boils at a lower temperature. The liquids never come in contact with each other. The vapor formed from the other liquid is then used to power the turbine that generates the electricity.
A flash/binary system utilizes both the flash of the water and the steam of the binary system. The initial steam production is used to run turbines. The hot water is then used in a binary system, transferring its heat to the organic fluid. Again, the organic fluid boils at a lower temperature and produces vapors that operate a turbine.