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Geothermal energy (GE): An Introduction
Geothermal energy can be termed as a heat found inside the Earth. This type of heat is an uncontaminated, renewable fuel resource that supplies the energy needs of millions of people in the USA as well as all over the world for various utilizations and applications. Though domains like hot springs are more noticeable and are generally the first source of GE resources, the heat underneath the earth is accessible universally, and the scientists are able to utilize in a wide variety of circumstances.
GE is considered a renewable resource since the heat rising from inside the Earth is in fact unlimited. It is constantly emanating from the Earth’s core, which transmits mostly by the conduction process, is projected to be equal to about 40 MW of electrical power, and is anticipated to continue to provide the energy for billions of years to come, implying an unlimited source of energy.
GE reservoir
A geothermal system necessitates heat, permeability, and water. The heat emanating from the Earth's core constantly flows in outward path. When water is heated up by the Earth, the hot water as well as the steam is trapped in porous beneath a layer of water-resistant rock and forms a geothermal reservoir. This boiling geothermal water can be evident on the surface as geysers known as brines; however the majority of it continues to be in the deep underground. This collection of hot water is known as a geothermal reservoir.
Uses of GE
GE can be utilized for the production of electrical power for commercial, industrial, and residential projects heating objectives, and for comprehensive home heating and cooling by means of geothermal heat pumps.
Elements of a GE system
The GE system can be termed as a convective water that lie in the upper crust of the Earth, and which, in a small space, transmit the heat energy from a heat source to a heat basin, generally as a result of free exterior (Hochstein, 31-59).
GE systems can be installed in places with atypical or slightly greater than normal geothermal gradient and particularly in places where the GE tendency may be considerably above the median value. Primarily the systems would be characterized by low temperatures, frequently not greater than 100 degrees Celsius at a profitable depth and instantly the temperatures could reach above 400 °C.
The design fundamental to GE systems is generally followed by fluid convection. Convection takes place due to the heating and ensuing thermal expansion of water in a gravitational field; heat, which is provided at the bases of the circulatory system, is finding the energy that impels the system. Heated water of lower density has a tendency to increase and to be substituted by colder fluid that holds high density, originating from the borders of the system. Convection, intrinsically, has a tendency to raise the temperatures in the upper section of the system which is due to the decline of temperature in the lower part (White, 69-94).
The above-mentioned system may appear quite uncomplicated though the model of the real GE system is in no way simple to realize. It necessitates skill in many fields and a huge skill, particularly when running the high -temperature systems. GE systems also take place physically in various combinations, hence showing in many kinds of the system.
As regards components of a GE system, the heat source are the only one that necessitates being organic. Given that the conditions are positive, the other two features could be simulated. For instance, the geothermal fluids drawn from the reservoir to impel the turbine in a GE power-plant could, following their use, be added back into the reservoir by means of particular injection wells. Accordingly the normal recharge of the reservoir is incorporated by a simulated recharge. For the last few years re-injection was espoused in different regions to sharply decrease the impacts on the surroundings of GE plant operations.
The second important element needed for a GE system is a heat reservoir. This reservoir acts as the boundary between the heat source and the moving fluid. The last important element is the transportation fluid which is usually water. Hence, the heat reservoir must consist of porous rocks, which will facilitate heat flux from the heat source to the moving water.
A GE system can be competently planned. For instance, water can be injected to refill the extracted amount of water by injection wells, hence allowing it compensates the disparity between the exploitation and natural refill occur. Drilling can also be carried out in the regions which lack a pre-existent circulation system to force cold water at great depth. The resultant cooling of the deep rocks will cause cracks, helping in water circulation and raising exchange surface area. The hot water can then be forced back to the surface for energy uses.
GE Resources
A GE resource has been known in different ways (Armstead 1983; Hochstein, 31-59). Moreover, GE resources have been grouped into low, intermediary and strong resources as a result of their reservoir temperatures. Temperature is utilized as the categorization factor since it is believed as one of the simplest factors. Nevertheless, the temperature utilized is the normal reservoir temperature estimated by geo-thermometers (Hochstein, 31-59).
Armstead (1983) categorized the earth's surface into non-thermal and thermal regions. Thermal regions are those with temperature gradients more than 40 degrees Celsius h depth. Armstead made a division between thermal regions and thermal areas. Thermal areas are the regions with sub-surface permeability which helps the control of a fluid that can conduct deep-seated heat to the surface. GE fields are grouped into semi-thermal fields making hot water up to 100 degree Celsius at the surface, hyper-thermal wet fields creating hot water and steam and hyper-thermal dry fields creating dry saturated or superheated steam at the surface. Temperature is applicable as a categorization factor only for its usefulness and being a precise quantity.
Present status of GE Resources
Following the World War II a number of countries were fascinated by GE resources, believing it to be economically viable with other types of energy forms. However, it did not have to be imported into the countries, and, in a number of instances, it was then believed to be the only energy source existed in the domestic market.
All the countries over the world use geothermal energy to provide electricity of the installed GE electrical power in 1995 stood at nearly 6800 MW, in 2000 it reached about 800 MW and the rise in the period 1995-2000 (Huttrer, 7-27). The total capacity at the conclusion of 2003 stood at 8402 MW. The GE power created in the third world countries in 1995 and 2000 represented 38% and 47% respectively of the world’s total.
The use of GE in third world countries has shown a remarkable trend for last several years. In the period 1975-1979 the GE capacity in these countries rose from 75 to 462 MW; by the conclusion of the subsequent 5-year period the number touched 1495 MW, showing a significant rise in its generation (Dickson & Fanelli, 31-57). From 1984-2000, there was an added increase of about 150%. GE contributes a somewhat major part in the energy generation in particular areas; for instance in 2001 the electrical power generated from it stood at about 30% of the total electrical energy created in the Philippines, about 12% in Kenya, nearly 11% in Costa Rica, and just about 4% in El Salvador.
With regards to non-electric use of GE, it was anticipated the energy consumption of 190,699 worldwide for the year 2000. Throughout that year fifty-eight nations reported its direct uses, in contrast to twenty-eight in 1995 and twenty-four in 1985. Many countries with direct utilization have considerably risen ever since, in addition to the total installed power and energy consumption.
The most frequent non-electric utilization of GE globally is heat pumps, followed by bathing, space-heating, greenhouses, aquaculture, and industrial applications (Lund & Freeston, 29- 68).
GE Systems Design
A GE system consisted of three major aspects namely a heating resource, a reservoir as well as a fluid, which is the conductor of the heat. The heating resource can be quite high at about 600 °C that has touched rather shallow depths or, in some low-heated systems, the Earth's average temperature, and raises with the depth. Besides, the reservoir is known as level of hot porous rocks from which the moving fluids draws heat. The reservoir is normally covered by impervious rocks and linked to a special recharge region in which the rapid waters can substitute the liquids that evaporate from the reservoir as a result of boreholes.
Conversion Technologies
Flash Power Plants:
The flash power units consist of a mixture of liquid water and as a consequence steam is generated from the wells. Approximately 40% of GE manufacturing in the USA emanate from flash technology. As a flash unit, hot liquid water from the Earth is maintained under pressure and hence prevents from boiling. As this hot water moves from deeper in the earth to shallower levels, it quickly loses pressure, boils and “flashes” to steam.
Flash power units generally need resource temperatures varying from 177oC-260oC.
Several technological choices can be applied in a flash system environment. Double flashing is considered as the most popular of these, is more costly than a single flash, and could focus on chemical units if they present in the GE water. Despite the fact of the potential limitations, the majority of GE developers think that double flash is more efficient than the single flash since a larger part of the resource is utilized.
Binary Plants:
The plants “binary” GE uses resource temperatures varying from 74-degree Celsius and 177-degree Celsius. Just about 15% of all GE power plants use binary conversion technology. In this process, the GE fluid can be either hot water or a combination of the two heats up another liquid that leads to boiling at a lower temperature than water. The two liquids are separated by the use of a heat exchanger to transmit heat energy from the GE water to the working fluid. When heated up, the working fluid changed into a gaseous state and the expanding gas activates the turbines to produce electrical energy. The analysts’ believe lower temperature resources appropriate for binary cycles would be quite useful for all future energy resources created. Moreover, binary systems can now function at lower temperatures than the analysts earlier thought.
Use of GE Resources
Electrical energy creation is the most notable type of use of high-temperature GE resources. The medium-to-low heat sources are well-matched to various types of uses. The conventional Lindal plan (Lindal, 135-148), illustrates the promising utilization of GE fluids at various temperatures, and it is still valid. Liquids at temperatures less than 20 degrees Celsius are hardly ever used and in very specific circumstances or in heating pump usages. The Lindal diagram stresses in two important fields of the use of GE resources (Gudmundsson, 119-136): (a) with varying and shared usages it is feasible to improve the viability of GE ventures and (b) the resource temperature may restrict the potential uses. The present designs for thermal procedures can, nevertheless, be changed for GE fluid usage in some cases, hence expanding its field of uses.
Electricity generation
Electricity production generally occurs in traditional steam turbines and binary factories, conditional on the aspects of the GE resource.
The traditional steam turbines require liquids at temperatures of not below 150°Celsius and are available with atmospheric and condensing exhausts. Atmospheric exhausts are uncomplicated and inexpensive. The steam moves through a turbine and discharged into the atmosphere.
With this kind of machine, steam consumption per KWH generated is nearly twice that of a condensing component. Nevertheless, the atmospheric exhaust turbines are enormously useful as pilot factories, stand-in factories, for small supplies from remote wells, and for creating electrical energy from test wells throughout field expansion. As well, they are also utilized when the steam has a strong non-condensable gas contents. The atmospheric exhaust machine can be built and installed rapidly and implemented in about a year from the order date. This kind of machine is generally available in small sizes.
The condensing machines, having more supporting units are more complex than the atmospheric exhaust machines and have the larger sizes that can take twice as much time to build and implement. The particular steam use of the condensing components is, nevertheless, nearly half that of the atmospheric exhaust machines. Condensing units of 55-60 MW capacity is quite widespread, however new plants of 110 MW have also been built and put into operation.
The creation of electrical energy ranging low-to-medium heat GE fluids and from the waste hot water emanating from the separators in the GE fields have made significant progress as improvements were made in the fluid technology. The binary factories use a secondary working fluid, generally an organic fluid that holds low boiling-point and high-vapor pressure at low-temperature in contrast to steam. Moreover, the secondary fluid is run as a result of a traditional Rankine cycle: the GE fluid generates heat energy into the secondary fluid by means of various heat exchangers, wherein this fluid is vaporized through heating; the vapor generated impels a typical axial flow turbine, which is afterwards chilled and condensed, and the process of recycling starts.
GE: Its Future Prospects
The GE present in the Earth is enormous. Many analysts have predicted the geothermal prospects all over the world regarding high as well as low temperature sources. If tapped this energy appropriately, GE could definitely play a major part in the energy balance in many countries. In specific situations even small-scale GE resources are able to solve various local problems and for improving the standards of living in remote communities.
Works Cited
Armstead, H.C.H. Geothermal Energy. E. & F. N. Spon, London. 1983.
Dickson, M.H. & Fanelli, M. (Eds.). Small Geothermal Resources: A Guide to Development and Utilization, UNITAR, New York. 1988.
Gudmundsson, J.S. The elements of direct uses. Geothermics, 17. 1988.
Hochstein, M.P. Classification and assessment of geothermal resources. UNITAEWNDP Centre for Small Energy Resources. Rome, Italy.1990.
Huttrer, G.W. The status of world geothermal power generation 1995-2000. Geothermics, 30. 2001.
Lindal, B. Industrial and other applications of geothermal energy. In: Armstead, H.C.H., Ed., Geothermal Energy, UNESCO, Paris. 1973.
Lund, J. W., & Freeston, D. World-wide direct uses of geothermal energy 2000. Geothermics 30. 2001.
White, D. E. Characteristics of geothermal resources. In: Kruger, P. and Otte, C., Eds., Geothermal Energy, Stanford University Press, Stanford. 1973.
