4 Main Types of Geothermal Power Plants
The following points highlights the four main types of geothermal power plants.
The types are:
1. Flashed Steam Plants
2. Dry Steam Plants
3. Binary Power Plants
4. Hybrid Power Plants.
For conversion of geothermal energy into electrical energy, heat must be extracted first for its conversion into useable form. Mite-or-more-deep wells can be drilled into under-ground reservoirs to tap steam and very hot water that drive turbines coupled to electric generators.
There are basically four types of geothermal power plants which are operating nowadays:
Type 1. Flashed Steam Plants:
The extremely hot water from drill holes when released from deep reservoirs high pressure steam (known as flashed steam) is released. The force of steam is used to rotate turbines. The steam gets condensed and is converted into water again, which is returned to the reservoir. Flushed steam plants are widely distributed throughout the world.
Type 2. Dry Steam Plants:
Usually geysers are the main source of dry steam. The geothermal reservoirs producing mostly steam and little water are employed in electric power generation schemes. As steam from the reservoir shoots out, it is used to drive a turbine, after sending the steam through a rock-catcher. The rock-catcher protects the turbine from rocks which come along with steam.
Type 3. Binary Power Plants:
In this type of power plant, the geothermal water is passed through a heat exchanger where its heat is transferred to a secondary liquid, viz., isobutene, isopentane or ammonia-water mixture present in an adjacent, separate pipe. Because of this double-liquid heat exchanger system, it is called a binary power plant. The secondary liquid, also known as working fluid, should have lower boiling point than water. It turns into vapour on getting required heat from the hot water.
The vapour from the working fluid is employed for rotating the turbines. The binary system is therefore useful in geothermal reservoirs which are relatively low in temperature gradient. Since the system is a completely closed one, there is a minimum chance of heat loss. Hot water is immediately recycled back into the reservoir. The working fluid is also condensed back to the liquid and used over again and again.
Type 4. Hybrid Power Plants:
Some geothermal fields produce boiling water as well as steam, which are also employed in power generation. In this system of power generation, the flashed and binary systems are combined to make use of both steam and hot water. Efficiency of hybrid power plants is, however, less than that of dry steam plants.
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