Geothermal Power Plants
Geothermal Power Plants discussion
Converting the energy from a geothermal resource into electricity is achieved by producing steam from the heat underground to spin a turbine which is connected to a generator to produce electricity. The type of energy conversion technology that is used depends on whether the resource is predominantly water or steam, the temperature of the resource, and the chemical composition of the fluid.
The 3 conventional methods that are used are Dry Steam, Flash Steam, and Binary Cycle power plants.
- Steam from hydrothermal reservoirs is withdrawn from below the Earth's surface via a production well and goes directly to a turbine; the turbine drives a generator that produces electricity. This is the oldest type of geothermal power plant, and in use at the largest single source of geothermal power: The Geysers (in northern California).
- Flash steam power plants are the most common type geothermal power plants. They generally require the use of hydrothermal fluids above in the range of 300 - 700°F. The fluid is vaporized, and the vapor drives the turbine, which then drives the generator."
- Both moderate-temperature (below 400°F) water and a secondary, or "binary", fluid with a much lower boiling point than water are used in binary-cycle power plants. The secondary fluid vaporizes (caused by the heat from the geothermal fluid), which drives the turbine, which drives the generator. Since moderate-temperature water is the more common geothermal resource, and this technology is expected to be used in many geothermal plants in the future.
In closed loop steam systems steam is condensed and cooled prior to re-injection. In the Binary cycle the heat gained in the working fluid must be rejected in order to make continuous power. The 3 typical methods of heat rejection that are used are:
- Water cooling is commonly defined as a method of using water as a heat conduction to remove heat from an object, machine, or other substance by passing cold water over or through it. In energy generation, water cooling is typically used to cool steam back into water so it can be used again in the generation process.
- Air cooling is commonly defined as rejecting heat from an object by flowing air over the surface of the object, through means of convection. Air cooling requires that the air must be cooler than the object or surface from which it is expected to remove heat. This is due to the second law of thermodynamics, which states that heat will only move spontaneously from a hot reservoir (the heat sink) to a cold reservoir (the air).
- An evaporative cooler is a device that cools air through the evaporation of water. Evaporative cooling works by employing water's large enthalpy of vaporization. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation), which can cool air using much less energy than refrigeration. Evaporative cooling requires a water source, and must continually consume water to operate.
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Number of geothermal plants listed: 252
Geothermal Regulations and Permitting for Power Plants
For information about regulations and permitting related to geothermal power plants, see the Regulatory and Permitting Information Desktop Toolkit.