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a seminar report on geothermal energy

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1. Chapter 1 INTRODUCTION 1.1 ABSTRACT Electricity is produced by geothermal in 24 countries, five of which obtain 15-22% of their national electricity production from…
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  • 1. Chapter 1 INTRODUCTION 1.1 ABSTRACT Electricity is produced by geothermal in 24 countries, five of which obtain 15-22% of their national electricity production from geothermal energy. Direct application of geo- thermal energy (for heating, bathing etc.) has been reported by 72 countries. By the end of 2004, the worldwide use of geothermal energy was 57 TWh/yr of electricity and 76 TWh/yr for direct use. Ten developing countries are among the top fifteen countries in geothermal electricity production. Six developing countries are among the top fifteen countries reporting direct use. China is at the top of the latter list. It is considered possible to increase the ins-talled world geothermal electricity capacity from the current 10 GW to 70 GW with present technology, and to 140 GW with enhanced technology. Enhanced Geothermal Systems, which are still at the experimental level, have enormous potential for primary energy recovery using new heat-exploitation technology to extract and utilise the Earth's stored thermal energy. Present investment cost in geothermal power stations is 2-4.5 million euro/MWe, and the generation cost 40-100 euro/MWh.2 Direct use of geothermal energy for heating is also commercially competitive with con- ventional energy sources. Scenarios for future development show only a moderate increase in traditional direct use applications of geothermal resources, but an exponential increase is foreseen in the heat pump sector, as geothermal heat pumps can be used for heating and/or cooling in most parts of the world. CO2 emission from geothermal power plants in high-temperature fields is about 120 g/kWh (weighted average of 85% of the world power plant capacity). Geothermal heat pumps driven by fossil fuelled electricity reduce the CO2 emis-sion by at least 50% compared with fossil fuel fired boilers. If the electricity that drives the geothermal heat pump is produced from a renewable energy source like hydropower or geothermal energy the emission savings are up to 100%.3 Geothermal energy is available day and night every day of the year and can thus serve as a supplement to energy sources which are only available intermittently. Renewable energy sources can contribute significantly more to the mitigation of climate change by cooperating than by competing. 1.2 INTRODUCTION Electricity is produced by geothermal in 24 countries, five of which obtain 15- 22% of their national electricity production from geothermal energy. Direct applicati- on of geothermal energy (for heating, bath ing etc.) has been reported by 72 countries. By the end of 2004, the worldwide use of geothermal energy was 57 TWh/yr of electricity and 76 TWh/yr for direct use. Ten developing countries are among the top fifteen countries in geothermal electri-city production. Six developing countries are among the top fifteen countries report-ing direct use. China is at the top of the latter list. It is considered possible to in-crease the installed world geothermal elec-tricity capacity from the current 10 GW to 70 GW with present technology, and to 140 GW with enhanced technology. Enhanced Geothermal Systems, which are still at the experimental level, have enormous potential for primary energy recovery using new heat-exploitation tech- nology to extract and utilise the Earth’s stored thermal energy. Present investment cost in geothermal power stations is 2-4.5 million euro/MWe, and the generation cost 40-100 euro/MWh. 1
  • 2. Direct use of geothermal energy for heating is also commercially competitive with conventional energy sources. Scenarios for future development show only a moderate increase in traditional direct use applications of geothermal resources, but an exponential increase is foreseen in the heat pump sector, as geo-thermal heat pumps can be used for heating and/or cooling in most parts of the world. CO2 emission from geothermal power plants in high-temperature fields is about 120 g/kWh (weighted average of 85% of the world power plant capacity). Geothermal heat pumps driven by fossil fuelled electricity reduce the CO2 emission by at least 50% compared with fossil fuel fired boilers. If the electricity that drives the geothermal heat pump is produced from a renewable energy source like hydropower or geothermal energy the emission savings are up to 100%. Geothermal energy is available day and night every day of the year and can thus serve as a supplement to energy sources which are only available intermit-tently. Renewable energy sources can con- tribute significantly more to the mitigation of climate change by cooperating than by competing. The most important source of informa-tion for this contribution is a position pa-per of the International Geothermal Asso-ciation (IGA) presented at the IPPC Meet-ing on Renewable Energy Sources (Frid-leifsson et al., 2008). The cost analysis is based on a very detailed Geothermal Energy Association paper (GEA, 2005). 1.3 PRESENT STATUS Although geothermal energy is catego-rised in international energy tables am-ongst the “new renewables”, it is not a new energy source at all. People have used hot springs for bathing and washing clothes since the dawn of civilisation in many parts of the world. An excellent book has been published with historical records and stories of geothermal utilisation from all over the world (Cataldi et al., 1999). Electricity has been generated com-mercially by geothermal steam since 1913, and geothermal energy has been used on the scale of hundreds of MW for five decades both for electricity generation and direct use. The utilisation has increased rapidly during the last three decades. Geothermal resources have been identified in some 90 countries and there are quan-tified records of geothermal utilisation in 72 countries. Summarised information on geothermal use in the individual countries for electricity production and direct use (heating) is available in Bertani (2005) and Lund et al. (2005), respectively. Electricity is produced by geothermal energy in 24 countries. Five of these countries obtain 15-22% of their national electricity pro-duction from geothermal (Costa Rica, El Salvador, Iceland, Kenya and the Philip-pines). In 2004, the worldwide use of geothermal energy was about 57 TWh/yr of electricity, and 76 TWh/yr for direct use. The installed electric capacity in 2004 was 8,933 MWe. The world geothermal electricity pro-duction increased by 16% from 1999 to 2004 (annual growth rate of 3%). Direct use in-creased by 43% from 1999 to 2004 (annual growth rate of 7.5%). Only a small fraction of the geothermal potential has been developed so far, and there is ample opportunity for an increased use of geo-thermal energy both for direct applications and electricity production (Gawell et al. 1999). The installed electrical capacity achi-eved an increase of about 800 MWe in the three year term 2005-2007, following the rough standard linear trend of approxi-mately 200/250 MWe . 2
  • 3. Geothermal energy has until recently had a considerable economic potential only in areas where thermal water or steam is found concentrated at depths less than 3 km in restricted volumes, analogous to oil in commercial oil reservoirs (Cataldi, 1999, Fridleifsson, 1999). This has changed in the last two decades with the development of power plants that can economically uti-lise lower temperature resources (around 100°C) and the emergence of ground source heat pumps using the earth as a heat source for heating or as a heat sink for cooling, depending on the season. This has made it possible for all countries to use the heat of the earth for heating and/or cooling, as appropriate. It should be stressed that heat pumps can be used basically everywhere. CHAPTER 2 GEOTHERMAL RESERVOIRS 2.1 WHAT IS RESERVOIR 3
  • 4. A geothermal reservoir is a volume of rocks in the subsurface which exploitaton in terms of heat can be economically profitable. It should be noted that for producing the heat from the subsurface is necessary the presence of a transport fluid (usually water), and that drilling to an enough depth to reach the optimum operation temperatures is also necessary. These factors and the technical and other concerns entail costs which increase with depth. The temperature of the fluid and the possible applications are important to sort reservoirs. Thus, four types of geothermal reservoirs can be defined: 2.1.1 High temperature: These reservoirs provide enough heat to make electricity from steam profitably. High temperature reservoirs are generally more than 150° C, and are located in areas of thin lithospheric thinness or active volcanism. Within the group of high-temperature geothermal reservoirs there are "Hot Dry Rock" (HDR) geothermal reservoirs, which are exploited by the techniques called "stimulation of geothermal reservoirs" (EGS: Enhanced Geothermal System). They consist of fracturing a mass of deep rock to create a geothermal reservoir allowing the circulation of fluids inside it. These reservoirs not require high thermal gradients, but a very specific geological context. Although the implementation of such reservoir is still experimental (i.e. Soultz-sous-Fôrets, in France) in Catalonia have been granted some exploration permits. 2.1.2 Middle temperature: Despite these reservoirs have a lower temperature compared to the high temperature ones, they allow extracting sufficient heat to produce electricity (but with lower performances) using a volatile fluid. The reservoirs usually reach temperatures between 100 and 150 ºC, and are located in areas with favourable structural and geological contexts and geothermal gradients higher than the average. Their direct use may be in heating mode and their main applications are in district heating systems and industrial processes. 2.1.3 Low temperature: The temperature of these reservoirs is between 100 and 30 °C. They are located in areas with a favourable geological context including deep aquifers; the geothermal gradient is like the average in the region. Their exploitation involves pumping hot groundwater from the aquifer and re-injecting it after it has delivered the heat and is cold again. These are used in direct applications and for district heating systems and industrial processes. 2.1.4 Very low temperature: The temperature of these reservoirs is below 30 °C. In these, the underground is used as a heat exchanger, by means of a heat pump in a closed circuit. Their applications are in domestic and agricultural air conditioning systems. These kinds of reservoirs may be anywhere, because their efficiency is just determined by the underground thermal inertia in normal (average) geothermal gradient conditions. 4
  • 5. Geothermal heat pumps (GHPs) are one of the fastest growing applications of renewable energy in the world today (Ry-bach, 2005). They represent a rather new but already well-established technology, utilising the immense amounts of energy stored in the earth´s interior. This form for direct use of geothermal energy is based on the relatively constant ground or gro-undwater temperature in the range of 4°C to 30°C available anywhere in the world, to provide space heating, cooling and domestic hot water for homes, schools. CHAPTER 3 USES OF GEOTHERMAL ENERGY 3.1 OVERVIEW Geothermal reservoirs of low-to moderate-temperature water — 68°F to 302°F (20°C to 150°C) — provide direct heat for residential, industrial, and commercial uses. This resource is widespread in the United States, and is used to heat homes and offices, 5
  • 6. commercial greenhouses, fish farms, food processing facilities, gold mining operations, and a variety of other applications. In addition, spent fluids from geothermal electric plants can be subsequently used for direct use applications in so-called "cascaded" operation. Direct use of geothermal energy in homes and commercial operations is much less expensive than using traditional fuels. Savings can be as much as 80% over fossil fuels. Direct use is also very clean, producing only a small percentage (and in many cases none) of the air pollutants emitted by burning fossil fuels. 3.2 THE DIRECT-USE RESOURCE Low-temperature geothermal resources exist throughout the western U.S., and there is tremendous potential for new direct-use applications. A survey of 10 western states identified more than 9,000 thermal wells and springs, more than 900 low- to moderate- temperature geothermal resource areas, and hundreds of direct-use sites. The survey also identified 271 collocated sites — cities within 5 miles (8 kilometers) of a resource hotter than 122 degrees F (50 degrees C) — that have excellent potential for near-term direct use. If these collocated resources were used only to heat buildings, the cities have the potential to displace 18 million barrels of oil per year! 3.3 ACCESSING THE RESOURCE Direct-use systems typically include three components: • Production facility — usually a well — to bring the hot water to the surface; • Mechanical system — piping, heat exchanger, controls — to deliver the heat to the space or process; and • Disposal system — injection well or storage pond — to receive the cooled geothermal fluid. 3.4INDUSTRIAL AND COMMERCIAL USES Industrial applications include food dehydration, laundries, gold mining, milk pasteurizing, spas, and others. Dehydration, or the drying of vegetable and fruit products, is the most common industrial use of geothermal energy. The earliest commercial use of geothermal energy was for swimming pools and spas. In 1990, 218 resorts were using geothermal hot water. 6
  • 7. 3.6GEOTHERMAL ELECTRICITY PRODUCTION Most power plants need steam to generate electricity. The steam rotates a turbine that activates a generator, which produces electricity. Many power plants still use fossil fuels to boil water for steam. Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth's surface. There are three types of geothermal power plants:dry steam, flash steam, and binary cycle. Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States: The Geysers in northern California and Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers. Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource. Binary cycle power plants operate on water at lower temperatures of about 225°-360°F (107°-182°C). These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected 7
  • 8. back into the ground to be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions. 3.7GEOTHERMAL HEAT PUMPS (GHPS) Geothermal heat pumps take advantage of the Earth’s relatively constant temperature at depths of about 10 ft to 300 ft. GHPs can be used almost everywhere in the world, as they do not share the requirements of fractured rock and water as are needed for a conventional geothermal reservoir. GHPs circulate water or other liquids through pipes buried in a continuous loop, either horizontally or vertically, under a landscaped area, parking lot, or any number of areas around the building. The Environmental Protection Agency considers them to be one of the most efficient heating and cooling systems available. Animals burrow underground for warmth in the winter and to escape the heat of the summer. The same idea is applied to GHPs, which provide both heating and cooling solutions. To supply heat, the system pulls heat from the Earth through the loop and distributes it through a conventional duct system. For cooling, the process is reversed; the system extracts heat from the building and moves it back into the earth loop. It can also direct the heat to a hot water tank, providing another advantage — free hot water. GHPs reduce electricity use 30–60% compared with traditional heating and cooling systems, because the electricity which powers them is used only to collect, concentrate, and deliver heat, not to produce it. 3.8 HEATING USES Geothermal heat is used directly, without involving a power plant or a heat pump, for a variety of applications such as space heating and cooling, food preparation, hot spring 8
  • 9. bathing and spas (balneology), agriculture, aquaculture, greenhouses, and industrial processes. Uses for heating and bathing are traced back to ancient Roman times. (2) Currently, geothermal is used for direct heating purposes at sites across the United States. U.S. installed capacity of direct use systems totals 470 MW or enough to heat 40,000 average-sized houses. The Romans used geothermal water to treat eye and skin disease and, at Pompeii, to heat buildings. Medieval wars were even fought over lands with hot springs. The first known "health spa" was established in 1326 in Belgium at natural hot springs. And for hundreds of years, Tuscany in Central Italy has produced vegetables in the winter from fields heated by natural steam. CHAPTER 4 TYPES OF GEOTHERMAL PLANT 4.1 GEOTHERMAL POWER PLANT Geothermal power comes from the slow decay of radioactive minerals such as uranium, which causes the rocks to become magma. Tectonic plate movement causes the movement of magma up from the edges, forming a reservoir in which geothermal steam and hot water can be recovered through wells. 9
  • 10. Geothermal energy uses heat to produce steam, which in turn powers a generator to produce electricity. Geothermal energy is generated deep in the ground, in the form of hot molten rock, or a Magma formed from the collapse of radioactive materials like uranium. This energy becomes available to us at the borders of tectonic plates, when rubbing together and sliding under the another, causing the magma to break from the edges and pushed to the Earth’s surface forming a geothermal reservoir. 4.2 DRY STEAM POWER PLANT The first is the dry steam power plant which is used to generate power directly from the steam generated inside the earth.In this case, we do not need additional heating boilers and boiler fuel, as steam or water vapour fill the wells through rock catcher and directly rotates the turbine, which activates a generator to produce electricity. This type of power plant is not common since natural hydrothermal reservoirs dry steam are very rare. There are four commercial types of geothermal power plants: a. flash power plants, b. dry steam power plants, c. binary power plants, and d. flash/binary combined power plants. 10
  • 11. 4.3 FLASH STEAM POWER PLANT The most common type of geothermal power plant, flash steam plants use waters at temperatures greater than 360F. As this hot water flows up through wells in the ground, it is collected in a flash tank where drop in pressure causes the liquid to boil into steam.The steam is separated from the liquid which is then used to run turbines which in turn generate power. The condensed steam is returned to the reservoir Flash Steam Power Plants are the most common f
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