Geothermal wells are drilled at suitable locations. Water vaporized into steam comes out of the earth’s surface in a dry condition at around 200°C and 8 bar. The moisture is removed by a centrifugal separator and this steam will run the turbine coupled with a generator. Steam is condensed in a condenser and re injected back into the ground by a rejection well.
Types of Geothermal Sources
Hydrothermal systems
Hydrothermal systems are those in which water is heated by contact with the hot rock. Hydrothermal systems are in turn subdivided into
Vapor-dominated and
Liquid-dominated systems.
Vapor-dominated systems
In these systems the water is vaporized into steam that reaches the surface in relatively dry Condition at about 2050C and rarely above 8 bar.
This steam is the most suitable for use in turboelectric power plants with the least cost.
Liquid-dominated systems
In these systems the hot water circulating and trapped underground is at a temperature range of 174 to 3150C.
When tapped by wells drilled in the right places and to the right depths the water flows either naturally to the surface or is pumped up to it.
Steam well
Pipes are embedded at places of fresh volcanic action called steam wells, where the molten internal mass of earth vents to the atmospheric with very high temperatures.
By sending water through embedded pipes, steam is raised from the underground steam storage wells to the ground level.
Separator
The steam is then passed through the separator where most of the dirt and sand carried by the steam are removed.
Turbine
The steam from the separator is passed through steam drum and is used to run the turbine which in turn drives the generator.
The exhaust steam from the turbine is condensed. The condensate is pumped into the earth to absorb the ground heat again and to get converted into steam.
Location of the plant, installation of equipment like control unit etc., within the source of heat and the cost of drilling deep wells as deep as 15,000 meters are some of the difficulties commonly encountered.
Working
Bore (hole) are drilled into the earth until it reaches wet steam geothermal reservoirs. This wet steam is brought up with very high pressure with the help of pump. So steam remains in liquid state.
When the water comes to the surface of the earth then it is filtered to remove abrasive (solid crushed stone particles. Then it is passed through flash chamber where pressure of high temperature water decreases suddenly.
As pressure drops water is converted into steam in flash tank. This steam is used to run the steam turbine which gives mechanical power. Alternator is coupled with steam turbine which mechanical energy into electrical energy.
ADVANTAGES
Geothermal energy is cheaper.
Used as space heating for buildings.
Used as industrial process heat.
Geothermal energy is inexhaustible.
DISADVANTAGES
Low overall power production efficiency (about 15%).
Large areas are needed foe exploitation of geothermal energy.
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