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| Frances Li | francesl@usc.edu | Undeclared Engineering |
Geothermal: Geographic Characteristics
A good development site for a power plant must have hot geothermal fluid with low mineral and gas content, shallow aquifers for producing and reinjecting the fluid, private land, near existing transmission lines or load, and availability of water to make up for the lost steam. The temperature of the fluid should be at least 300 degrees Fahrenheit, but plants can run on fluid that has temperatures as low as 210 Fahrenheit. An average geothermal plant uses about 400 square meters of land to produce one gig watt of power for over 30 years.
The flow of liquid through a geothermal system depends on the temperature of the fluid, the sink characteristics, and the pumping power need to supply and dispose the fluid. A closed loop binary cycle geothermal plant needs 450 to 600 gallons per minute to generate 1 MW from a 300 F fluid and air temperature of 60 F. A 210 F fluid would need 1,300 to 1,500 gallons per minute to generate the same amount of power. With an evaporative cooling system, it would require 45 to 75 more gpm of clean cooling water is needed to generate 1 MW.
The Geysers power plants have contributed to a clean environment for Lake County, California, where the Geysers are located. It is the only county that is in compliance with all of California’s stringent air quality regulations. It has received numerous recognitions, and its utility company has received awards as well.
In the US, more than 400,000 heat pumps are in operation in homes, schools, and businesses. There is still more to come.
Geothermal reservoirs of 68 F to 302 F can be used for residential, industrial, and commercial uses. A direct use system consists of a production facility, a mechanical system, and a disposal system. The production facility is used to bring the hot water to the surface. A mechanical system consists of piping, heat exchanger, and controls to process and deliver the heat. A disposal system re-injects the cooled geothermal fluid. District heating is a geothermal system that provides heat for the whole district through a stream of pipes.
A heat pump consists of a geothermal earth connection subsystem, a heat pump subsystem, and a heat distribution subsystem. In a earth connection system, a loop, made up of pipes, is installed vertically or horizontally, underground near homes and buildings. Water, or water and antifreeze run through the loop to absorb the heat from the ground. The heat pump takes the heat from the liquid and transfers it to the building or home. The heat is then distributed through ducts in the facility. The excess heat that results from the process can also be used to heat the hot water systems.