Geothermal Power Plant

         

    Geothermal power plant uses its geothermal activity to generate power. This type of natural energy production  is extremely environmentally friendly and used in many geothermal hot spots around the globe.To harness the energy, deep holes are drilled into the earth until a significant geothermal hot spot is found.When the heat source has been discovered, a pipe is attached deep dopower station,wn inside the hole which allows hot steam from deep within the earths crust to rise up to the surface.Geothermal power is considered to be sustainable  because the heat extraction is small compared with the Earth’s heat content. The emission intensity of existing geothermal electric plants is on average 122 kg of CO2 per megawatt-hour (MW·h) of electricity, about one-eighth of a conventional coal-fired plant.In the 20th century, demand for electricity led to the consideration of geothermal power as a generating source. Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904 in LARDERELLO, Italy. It successfully lit four light bulbs.

                                    GEOTHERMAL RESOURCES

Below the Earth’s crust, there is a layer of hot and molten rock called magma. Heat is continually produced there, mostly from the decay of naturally radioactive materials such as uranium and potassium. The amount of heat within 10,000 meters (about 33,000 feet) of Earth’s surface contains 50,000 times more energy than all the oil and natural gas resources in the world. The areas with the highest underground temperatures are in regions with active or geologically young volcanoes. These “hot spots” occur at plate boundaries or at places where the crust is thin enough to let the heat through. The Pacific Rim, often called the Ring of Fire for its many volcanoes, has many hot spots, including some in Alaska, California, and Oregon. Nevada has hundreds of hot spots, covering much of the northern part of the state.These regions are also seismically active. Earthquakes and magma movement break up the rock covering, allowing water to circulate. As the water rises to the surface, natural hot springs and geysers occur, such as Old Faithful at Yellowstone National Park. The water in these systems can be more than 200°C.

Seismically active hotspots are not the only places where geothermal energy can be found.  There is a steady supply of milder heat—useful for direct heating purposes—at depths of anywhere from 10 to a few hundred feet below the surface virtually in any location on Earth.  Even the ground below your own backyard or local school has enough heat to control the climate in your home or other buildings in the community.  In addition, there is a vast amount of heat energy available from dry rock formations very deep below the surface (4–10 km). Using a set of emerging technologies known as Enhanced Geothermal Systems.If these resources can be tapped, they offer enormous potential for electricity production capacity. In its first comprehensive assessment in more than 30 years, the U.S. Geological Survey (USGS) estimated that conventional geothermal sources on private and accessible public lands across 13 western states have the potential capacity to produce 8,000–73,000 MW, with a mean estimate of 33,000 MW.State and federal policies are likely to spur developers to tap some of this potential in the next few years. The Geothermal Energy Association estimates that 132 projects now under development around the country could provide up to 6,400 megawatts of new capacity.As EGS technologies improve and become competitive, even more of the largely untapped geothermal resource could be developed. The USGS study found that hot dry rock resources could provide another 345,100–727,900 MW of capacity, with a mean estimate of 517,800 MW.

                                                      Working principle

Word “geothermal” has its roots in two Greek words, “gheo” which means Earth and “thermal” which means heat. This energy is mainly generated from Earth’s core since temperature of Earth’s center is reaching temperatures above 6000 degrees Celsius which is even hot enough to melt a rock. Lesser part of this energy is gained from the crust, the planet’s outer layer by decay of radioactive elements which are present in all the rocks. In nature this energy is usually shown in the form of the volcanoes, hot water springs and geysers, which are all areas on which heat is concentrated near the earth’s surface.              Geothermal energy from steam, hot water and hot rocks from Earth’s crust. The success of this process depends on how hot the water gets, and water temperature depends on how hot were rocks to start with, and how much water is pumped down to these rocks. The water is pumped down through an „injection well“, it passes through the cracks in these rocks and then comes back up again through a „recovery well“ towards the surface, and because of the great pressure water is transformed into a steam when getting to the surface.This created steam then needs to be separated from brine what is usually done in central separation chamber. After this process of separation is over, complete steam is transferred to heat exchangers which are located inside the power plant. After steam is transferred to heat exchangers it’s possible to transfer it even further to the steam turbines where it can be generated into electricity, and in the same time through the exhaust pipes unused energy is being released.In heat exchangers steam is being cooled under the pressure in condensate and after that heat is transferred into cold water in condensate heat exchangers. This cold water that is gained on this way gets pumped from wells to storage tanks from which is transferred to heat exchangers where water’s temperature gets increased and then passes through deaerators where it boils and where released oxygen and other gases that could cause corrosion  are removed by final water cooling.

Simply term it’s all in the process of water heating and its transfer to steam which can be then used to drive a turbo-generator that generates electricity or this steam passes through heat exchangers and heats water creating necessary heat for central heating of households and industrial facilities.

                                                   Power station types

Geothermal power stations are not dissimilar to other steam turbine thermal power stations – heat from a fuel source (in geothermal’s case, the earth’s core) is used to heat water or another working fluid. The working fluid is then used to turn a turbine of a generator, thereby producing electricity. The fluid is then cooled and returned to the heat source.

                                                  Dry steam power plants

Dry steam plants are the simplest and oldest design. They directly use geothermal steam of 150°C or greater to turn turbines.

                                                Flash steam power plants

Flash steam plants pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines. They require fluid temperatures of at least 180°C, usually more. This is the most common type of plant in operation today

                                              Binary cycle power plants

Binary cycle power plants are the most recent development, and can accept fluid temperatures as low as 57°C.[11] The moderately hot geothermal water is passed by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash vaporize, which then drives the turbines. This is the most common type of geothermal electricity plant being constructed today.[23] Both Organic Rankine and Kalina cycles are used. The thermal efficiency of this type plant is typically about 10-13%.

                          Advantages of Geothermal Energy

  1. Significant Cost Saving : Geothermal energy generally involves low running costs since it saves 80% costs over fossil fuels and no fuel is used to generate the power.

  2. Reduce Reliance on Fossil Fuels : Dependence on fossil fuels decreases with the increase in the use of geothermal energy. With the sky-rocketing prices of oil, many countries are pushing companies to adopt these clean sources of energy.

  3. Environmental Benefits : Being the renewable source of energy, geothermal energy has helped in reducing global warming and pollution. Moreover, Geothermal systems does not create any pollution as it releases some gases from deep within the earth which are not very harmful to the environment.

  4. Direct Use : Since ancient times, people having been using this source of energy for taking bath, heating homes, preparing food and today this is also used for direct heating of homes and offices.

  5. Job Creation and Economic Benefits : Geothermal energy on the other hand has created many jobs for the local people.

                        Disadvantages of Geothermal Energy

  1. Not Widespread Source of Energy : Since, this type of energy is not widely used therefore the unavailability of equipment, staff, infrastructure, training pose hindrance to the installation of geothermal plants across the globe.

  2. High Installation Costs : To get geothermal energy, requires installation of power plants, to get steam from deep within the earth and this require huge one time investment and require to hire a certified installer and skilled staff needs to be recruited and relocated to plant location. Moreover, electricity towers, stations need to set up to move the power from geothermal plant to consumer.

  3. Can Run Out Of Steam : Geothermal sites can run out of steam over a period of time due to drop in temperature or if too much water is injected to cool the rocks and this may result huge loss for the companies which have invested heavily in these plants.

  4. Suited To Particular Region : It is only suitable for regions where temperature below the earth are quite low and can produce steam over a long period of time. For this great research is required which is done by the companies before setting up the plant.

  5. May Release Harmful Gases : Geothermal sites may contain some poisonous gases and they can escape deep within the earth, through the holes drilled by the constructors.