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Geothermal power plant, Overview:
Geothermal Power Plant– Geo means earth and thermal means heat; geothermal is energy of earth so it is the mechanism of extracting of heat from the earth. Heat from the earth crust warm water has seeped into underground reservoirs. When water becomes hot enough it can break through the earth surface as steam, this occurs when the plates meet in the earth crust. Engineers have developed few different ways to produce power from geothermal wells drills into the ground.
Geothermal energy is heat energy acquired by the earth. Heat inside the earth is available at a depth of more than 80KM. In some location it is available at a depth from 300 to 3000 meters. Such location is referred to as geothermal fields. Geothermal energy is used for heating water, air conditioning, electricity generation, green house heating etc. Geothermal power plant may be attractive for developing countries since these require less investment in infrastructure and investment.
Layers of earth:
We will discuss the layers of the earth for producing energy or heat energy. The earth temperature increases with increase in depth at a rate of about 30° C per kilometer. At a depth of 3 to 4 kilometer water bubbles up while at a depth of 19-15 kilometer the earth interior is as hot as 1000° to 1200° C.
Core is the center of the earth whose temperature is approximately about 4200° C. the heat in the core is produce due to the decay of the radioactive element and molten rock present in the core.
The core of the earth consists of a liquid rock known as magma having a temperature of about 4000° C and we know that water start boiling at 100° C, so this is hot water and is a major source of geothermal energy. Magma layer is very hot and in liquid form. It is found in hot geysers and springs earth reservoir or surface deep in the ground. From this magma layer a solid rock is connected by the conduction. This solid rock will be heated by the heat of the magma and above the solid rock there is porous rock in which there are many holes traveling water in between this rock and above the porous rock is the surface. So this is the method which is used to extract energy from the layers of the earth. The heat from this hot inner core flows to the cooler outer crust to the earth. Approximately 42 × 1012 W can be captured from this vast amount of heat. This energy from these heat sources is called the geothermal energy source.
Firstly a hole or well is drilled in the surface of the earth to the porous rock. Another well is also drilled on the other side to the porous rock. From these wells steam will be liberated or hot water will be liberated. From this hot water or steam we can extract energy which will further produce electrical energy
The outer layer of the magma is mantle which is approximately 2897 thick. The mantle layer is between the crust and the outermost layer of the core. The mantle consist of hot, dense, semi-solid rock. Heat transfer from the semi fluid mantle maintains a temperature difference across a relatively thin crust of 1000° C and a mean temperature gradient of 30°C/km.
The outermost layer of earth is called crust. It is 3 to 5 miles thick under the oceans and 15 to 30 miles thick on the continents. The earth crust is made up of pieces of land and oceans called plates. Magma is extended near to the earth surface, near the edges of these plates where volcanic activities occur. Volcano is a vent in the earth crust through which lava, steam, ashes etc are expelled, either continuously or at a regular intervals.
Core of the earth:
It consists of a mixture of iron and nickel and has a radius of approximately 3500 Km. The inner core has estimated temperature of 7200° C and is therefore hotter than the surface of the sun. While the inner core with a radius of 1200 km in solid, the outside core is liquid with a thickness of approximately 2300 Km.
Geothermal energy can be utilized for a variety of application including electric generation, heat pumps and heating building. Geothermal energy used is high in such place where the weather is cold such as America, Canada. As these countries are very cold due to which there sewerage system freeze. In order to reduce this freezing the steam is injected in it so this is the major application of the geothermal energy to prevent the blockage of the sewerage system and work as heat pump. The geothermal energy is reliable, clean and cost effective. Geothermal resources are abundant and may be considered as a secure source of energy. Geothermal refer to producing energy from the internal heat of earth is generated from radioactive decay of minerals and continual heat loss from the earth original formation. Geothermal power plants are very reliable when compared to conventional power plants. Geothermal wells are drilled in to the earth crust at approximately a depth of 3 to 10 kilometers. The heat is extracted with a variety of methods but in most cases drawn from the earth using water and steam. Hot water from the earth may be directly extracted to heat homes and building. This is done either by directly circulating the hot water through buildings or by pumping it through a heat exchanger that transfer the heat to the building. Geothermal heat can also be used to produce electricity in a geothermal power plant. Electricity is generated when geothermal heat produces steam that turns turbine on a generator. The major regions of geothermal development are in the most volcanically and tectonically regions of the world. One of its key advantages is its reliability and consistent power generation which means it can provide base load electricity. In the past taking advantage of geothermal energy was limited to areas where hot water flows near the surface
When the temperature of the geothermal energy is 60 to 70 degree then this heat is not used for the generation of the electricity and is used for heating the building. When the geothermal energy exceeds up to 400 to 500 degree then it becomes dry steam through which we can rotate the turbine. It can provide an abundant source of energy source with minimal environmental impact. A geothermal power plant emits no nitrogen oxides, very few sulphur dioxides and between 1000 and 2000 times less carbon dioxide then a fossil fuels and can be operated 24 hr a day. It can reduce dependence on imported fuel. The average geothermal heat flow at the earth surface only 0.06 w/m2.
The quantification and identification of geothermal resource require geophysical, geological, geochemical, and hydrological techniques that allow gathering of information regarding the potential use of specific sites. The information is necessary to determine if the site is suitable for development as a geothermal energy source.
To utilize the geothermal energy a steady rise of the earth temperature with increasing depth is necessary. It is called geothermal gradient. Where the geothermal gradient can be represented as:
Where T represents temperature, D represent the depth and G represent the geothermal gradient. The normal gradient of the earth is 30°C/KM .
History of Geothermal power plant:
The world first geothermal power plant was built in 1911 Larderallo Italy. The ideal location for the geothermal power plant is in USA, Russia, Japan, Italy, New Zealand and Mexico. These countries are producing electrical energy from the geothermal energy. The first use of geothermal energy occurred more than 10000 years ago in North America by American Palelo Indians. People used water from hot spring for cooking, bathing and cleaning. The first industrial use of geothermal energy began near Pisa Italy in late 18th century. Steam coming from natural vents (and from drilled holes) was used to extract boric acid from the hot pools that are known as the Larderello fields.
Top 10 geothermal countries installed capacity in Mega watt:
This survey was conducted according to which the USA produce maximum energy through geothermal power plant.
|Country Name||Installed Capacity (Mega watt)|
Working principal of Geothermal Power plant:
There are three type of geothermal power plant which are:
- Dry steam power plant
- Flash steam power plant
- Binary cycle power plant
Dry steam power plant:
In 1904 in Italy dry steam power plant was invented to produce electricity. The core of the earth is estimated to be around five to seven thousand degrees Celsius and this heat is radiated outward through the earth. In this power plant steam is generated directly from the geothermal reservoir. The operation and construction of the dry steam power plant is very simple. Water is injected into the injection well and this water goes to the underground level. Water is converted into hot steam when the water came in contact with magma. This hot steam is tapped in production well and forced in the upward direction by the pump. The dry steam will enter through the holes in the pipes and will go up as it rises to the surface. It might have to might have to travel 1 to 3 KM to get back up to the surface. Underground steam flows directly to turbine to drive a generator that produces electricity. This steam is directly supplied to the turbine which is coupled with generator. The flow of the steam causes the turbine to rotate and it also rotates the generator because of this generator electric energy after rotating the turbine steam goes to the condenser where it is converted in to water. This water is called condensate and it is injected back to the earth through the injection well. Natural dry hydrothermal power reservoirs are very rare. When the steam has done its work we need to condensate it and to return it back to the earth. Dry steam turbine is available only in Italy and California.
Flash steam power plant:
This type of power plant is used where there is an availability of geothermal heated water at a high temperature of over 350 Fahrenheit. This water is called bine and it is transferred to a vessel where steam is generated. A pump pushes hot fluid into tank at the surface where it cools. As it cools the fluid quickly turns into a vapour or flash vaporises. The vapour then drives a turbine and power a generator. This steam drives the turbine coupled with a generator to produce electricity. The waste brine is injected back in to the earth.
Binary cycle Power plant:
Binary cycle power plant is used when the geothermal resource is at lower temperature of up to 100 Fahrenheit. It uses two types of fluid hot fluid from underground heats a second fluid called a heat transfer fluid in a giant heat exchanger. The hot water is passed to a heat exchanger which is combined with the secondary liquid with a lower boiling point such as butane and pentane hydrocarbon. The second fluid has a much lower boiling point than the first fluid and so it flashes in to vapour at a lower temperature. When the second fluid flashes it spins a turbine that drives a generator. A mixture vapour is generated and it runs the turbine. The mixture vapour is cooled by condenser and the liquid is recycled. Waste water is injected back to the earth as this power plant requires two liquids water and secondary liquid so due to which it is called binary power plant.
Advantages of geothermal power plant:
- Thermal and nuclear power plant need fuels to produce electricity whereas geothermal power plant does not any fuel for production of electricity ultimately this saves expanses on fuel
- Geothermal power plant does not pollute the environment
- It requires minimum land space as compare to other power plants
- Geothermal energy can also help recycle waste water
- In California waste water from the city of Santa Rosa is injected into the ground to generate more geothermal energy
Disadvantages of geothermal power plant:
- As geothermal fields are not available universally these power plant are found rarely
- The cost of infrastructure and drilling is very high
- Heating water
- Air conditioning
- Electricity generation
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