A Primer On Geothermal Energy & Power Plants
- Date: 2010-07-07 - Word Count: 706
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The following is short primer on geothermal energy and the various types of power plants used to produce electricity.
Before we get into geothermal, I would like to provide a little background information on electricity for context. Almost all electricity (excluding solar panels) is produced by basically the same mechanism, an electrical generator. The generator - which works by the movement of a loop of wire, or disc of copper between the poles of a magnet - needs another form of energy. It needs a mechanical energy or kinetic energy. Common sources of this energy are steam, water, wind, internal combustion engines, compressed air and even via a hand crank.
One of the most common is steam. We burn coal to heat water which is run through a turbine which turns an electrical generator. Nuclear energy produces steam via nuclear fission. Natural gas is burned to produce steam (and also for gas turbines), geothermal energy taps steam and or heat directly from the earth. Though this is a simplified breakdown of electricity production, in the end some mechanical or kinetic energy is necessary.
Geothermal energy works by tapping into the Earth's heat which is created far below the surface, in the form of hot molten rock or magna, generated from the action of decaying radioactive materials such as uranium. This energy becomes accessible to us at the boundaries of tectonic plates, which by rubbing together and one sliding under the other, columns of magma break up from the edges pushing them nearer to the surface of the earth forming a geothermal reservoir.
Not every geothermal reservoir is the same. They are classified as either low temperature (150°C). When it comes to generating electricity from geothermal energy, different power plants are designed to match the reservoir. There are three main types of geothermal power plants: flash, dry steam and binary.
The following definitions are taken from U.S Department of Energy:
Flash Steam
Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 360°F (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.
Dry Steam
Power plants using dry steam systems were the first type of geothermal power generation plants built. They use steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity. An example of a dry steam generation operation is at the Geysers Region in northern California.
Binary Cycle
Binary cycle geothermal power generation plants differ from dry steam and flash steam systems because 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 to 360°F) by using working fluids that have an even lower boiling point than water. They also produce no air emissions.
Here in the U.S., geothermal energy is a very important source of clean, renewable power. A fact that many people are unaware of. Actually the U.S. is the largest producer in the world of electricity from geothermal power with 3.15 gigawatts (GW) of installed capacity. Geothermal power plants do emit pollutants into the atmosphere (mostly trace amounts of nitrogen oxides, sulfur dioxide and particulate matter), these emissions are much less than those from conventional power stations. There are already technologies being developed to mitigate or even eliminate even these minor emissions. I think it's time people got to know geothermal as a vital source of green energy for the U.S. and the world and push for additional exploration and development.
Before we get into geothermal, I would like to provide a little background information on electricity for context. Almost all electricity (excluding solar panels) is produced by basically the same mechanism, an electrical generator. The generator - which works by the movement of a loop of wire, or disc of copper between the poles of a magnet - needs another form of energy. It needs a mechanical energy or kinetic energy. Common sources of this energy are steam, water, wind, internal combustion engines, compressed air and even via a hand crank.
One of the most common is steam. We burn coal to heat water which is run through a turbine which turns an electrical generator. Nuclear energy produces steam via nuclear fission. Natural gas is burned to produce steam (and also for gas turbines), geothermal energy taps steam and or heat directly from the earth. Though this is a simplified breakdown of electricity production, in the end some mechanical or kinetic energy is necessary.
Geothermal energy works by tapping into the Earth's heat which is created far below the surface, in the form of hot molten rock or magna, generated from the action of decaying radioactive materials such as uranium. This energy becomes accessible to us at the boundaries of tectonic plates, which by rubbing together and one sliding under the other, columns of magma break up from the edges pushing them nearer to the surface of the earth forming a geothermal reservoir.
Not every geothermal reservoir is the same. They are classified as either low temperature (150°C). When it comes to generating electricity from geothermal energy, different power plants are designed to match the reservoir. There are three main types of geothermal power plants: flash, dry steam and binary.
The following definitions are taken from U.S Department of Energy:
Flash Steam
Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 360°F (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.
Dry Steam
Power plants using dry steam systems were the first type of geothermal power generation plants built. They use steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity. An example of a dry steam generation operation is at the Geysers Region in northern California.
Binary Cycle
Binary cycle geothermal power generation plants differ from dry steam and flash steam systems because 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 to 360°F) by using working fluids that have an even lower boiling point than water. They also produce no air emissions.
Here in the U.S., geothermal energy is a very important source of clean, renewable power. A fact that many people are unaware of. Actually the U.S. is the largest producer in the world of electricity from geothermal power with 3.15 gigawatts (GW) of installed capacity. Geothermal power plants do emit pollutants into the atmosphere (mostly trace amounts of nitrogen oxides, sulfur dioxide and particulate matter), these emissions are much less than those from conventional power stations. There are already technologies being developed to mitigate or even eliminate even these minor emissions. I think it's time people got to know geothermal as a vital source of green energy for the U.S. and the world and push for additional exploration and development.
Related Tags: geothermal energy, geothermal power plants, flash steam, dry steam, binary cycle
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