GEOTHERMAL POWER PLANTS
Geothermal Is clean Energy
Geothermal power plants are used to Generate Electricity Using Geothermal
Energy (the Earth’s internal thermal energy).
The Concept Behind Geothermal Power Plants
Geothermal power plants essentially work the same as a coal or nuclear power plant, the main difference being the heat source. With geothermal, the Earth’s heat replaces the boiler of a coal plant or the reactor of a nuclear plant.
Hot water or steam is extracted from the Earth through a series of wells and feeds the power plant. In most geothermal plants the water pulled up from the ground is returned to the subsurface. The rate of water used is often larger than the rate of water returned, so make-up water supplies are generally needed.
There are 3 main types of geothermal power plants (Dry Steam, Flash Cycle Steam, Binary Cycle) with the flash cycle being the most common. The choice of plant depends on how much geothermal energy is available, and how hot the resource is. The hotter the resource, the less fluid needs to flow from the ground to take advantage of it, the more useful it is.
GEOTHERMAL IS CLEAN ENERGY
Types of geothermal power plants:
THEY'RE NOT VERY COMMON SINCE DRY STEAM RESOURCES ARE RARE.
Geothermal Dry Steam Power Plants
These plants use dry steam that is naturally produced in the ground. This steam travels from the production well to the surface and through a turbine, and after transferring its energy to the turbine it condenses and is injected back into the Earth. These types are the oldest types of geothermal power plants, the first one was built back in 1904 in Italy. Because this type of power plant requires the highest temperatures they can only be used where the temperature underground is quite high, but this type requires the least fluid flow.
The dry steam plants at the Geysers in northern California, first drilled in 1924, are the largest geothermal source of electricity. At their peak production in the late 1980s they produced a whopping 2 GW of electricity - the equivalent of two large coal or nuclear power plants. However due to high rates of extraction, power has since declined to 1.5 GW of capacity, with an average output of less than 1 GW.
MOST COMMON DUE TO THE LACK OF NATURALLY OCCURRING HIGH-QUALITY STEAM
Geothermal Flash Cycle Steam Plants
These types are the most common due to the lack of naturally occurring high-quality steam. In this method, water must be over 180°C, and under its own pressure, it flows upwards through the well.
This has a lower temperature than dry steam plants. As its pressure decreases, some of the water "flashes" to steam, which is passed through the turbine section. The remaining water that did not become steam is cycled back down into the well and can also be used for heating purposes.
THE GEOTHERMAL POWER PLANTS OF THE FUTURE
Geothermal Binary Cycle Power Plants
A Binary cycle power plant is one of three types of geothermal power plants used to generate electricity. The other two are Dry steam power plant and Flash steam power plant.
How it Works
The geothermal fluid is extracted from an underground reservoir and flows up the production well through pipelines to the heat exchanger. A heat exchanger is simply a device that transfers heat from one medium to another. Inside the heat exchanger, the geothermal fluid heats and vaporizes a secondary working fluid which is organic, with a low boiling point. The organic vapours rotate the turbine which rotates a shaft connected to the generator to produce electricity. The vapour is then condensed into a liquid, cooled by either air or water, and recycled back into the heat exchangers by a pump, completing the cycle in a closed system.
The cooled geothermal fluid is re-injected into the reservoir where it is reheated. The reheated fluid once again flows up the production well and the process is repeated. Therefore, geothermal energy is renewable energy.
DGDC has decided to install a Binary Cycle plant in Laudat because it is the most environmentally friendly option. In this case all the fluids removed from the reservoir via the production well are returned to the reservoir through the injection well. Nothing remains on the surface to create a risk to the environment. Only the heat is extracted from the geothermal fluids for use in producing electricity. DGDC has also selected the air-cooled option, thus limiting water usage by the power plant. Even though the Binary Cycle plant is more costly than the others of the same size, the long-term benefits accrued by not causing pollution, far outweigh the additional cost.