23-07-2014, 02:58 PM
GEOTHERMAL ENETRGY
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INTRODUCTION
Geothermal energy is the earth’s natural heat available inside the earth. This thermal energy contained in the rock and fluid that filled up fractures and pores in the earth’s crust can profitably be used for various purposes. Heat from the Earth, or geothermal — Geo (Earth) + thermal (heat) — energy can be and is accessed by drilling water or steam wells in a process similar to drilling for oil. Geothermal energy is an enormous, underused heat and power resource that is clean (emits little or no greenhouse gases), reliable (average system availability of 95%), and homegrown (making us less dependent on foreign oil).
Geothermal resources range from shallow ground to hot water and rock several miles below the Earth's surface, and even farther down to the extremely hot molten rock called magma. Mile-or-more-deep wells can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications.
Hydrothermal resources
Hydrothermal resources are those that are associated with natural convection systems. Their thermal reservoirs consist of porous or fractured rocks, containing hot water or steam, which in the natural state, transported towards the surface by density-driven thermo-artesian flow. All the currently identified geothermal resources are hydrothermal in origin. Hydrothermal system may be further divided into liquid-dominated or vapour-dominated, depending on the ratio of water to steam in the reservoir. Liquid dominated hydrothermal systems may be of low, moderate or high-temperature type and are the most common kind of geothermal system being exploited commercially today. Vapour dominated reservoir is much less common but includes Larderello in Italy and Geyser in USA.
Binary power plant
In this type of power plant, the geothermal water is passed through a heat exchanger where its heat is transferred to a secondary liquid, namely isobutene, isopentane or ammonia–water mixture6 present in an adjacent, separate pipe. Due to this double-liquid heat exchanger system, it is called a binary power plant. The secondary liquid which is also called as working fluid should have lower boiling point than water. It turns into vapour on getting required heat from the hot water. The vapour from the working fluid is used to rotate turbines. The binary system is therefore useful in geothermal reservoirs which are relatively low in temperature gradient. Since the system is a completely closed one, there is minimum chance of heat loss. Hot water is immediately recycled back into the reservoir. The working fluid is also condensed back to the liquid and used over and over again
Geothermal Resources of India
There are some 340 hot springs spread all over India. Of this, 62 are distributed along the northwest Himalaya, in the States of Jammu and Kashmir, Himachal Pradesh and Uttarakhand. They are found concentrated along a 30-50-km wide thermal band mostly along the river valleys. Naga-Lusai and West Coast Provinces manifest a series of thermal springs. Andaman and Nicobar arc is the only place in India where volcanic activity has been reported. Some of the islands like Barren are still active. The area is in the continuation of the Indonesian geothermal fields and can be good potential sites for geothermal energy.
Cambay graben geothermal belt is 200 km long and 50 km wide with Tertiary sediments. Thermal springs have been reported from the belt although they are not of very high temperature and discharge. The area contains oil and gas at considerable depths. High subsurface temperature and thermal fluid have been reported in deep drill wells in depth ranges of 1.7 to 1.9 km. Steam blowout have also been reported in the drill holes in depth range of 1.5 to 3.4 km. The thermal springs in the peninsular region are more related to the faults, which allow down circulation of meteoric water to considerable depths. The circulating water acquires heat from the normal thermal gradient in the area, and depending upon local condition, emerges out at suitable localities. The area includes Aravalli range, Son-Narmada-Tapti lineament, Godavari and Mahanadi valleys and South Cratonic Belts. Some of the important geothermal fields of India are described as follows
Geothermal Fields of Beas and Pārbati Valleys, Himachal Pradesh
Beas and Pārbati valleys are well known for their hot springs in Kulu district, Himachal Pradesh. The springs lie between altitude of 1300 m and 3000 m. The famous thermal springs in the Beas valley are Bashist, Kalath, Rampur and Kulu, whereas in the Pārbati valley, the springs are at Jan, Kasol, Manikaran, Pulga and Khirganga. The rocks in the area belong to Proterozoic age and are classified in Vaikrita, Kulu and Rampur Groups. The temperature of springs ranges from 22°C to 59°C in Beas and 21°C to 96°C (96°C being the boiling point at the altitude) in Pārbati valley, respectively.
In the Pārbati valley, the thermal springs and drill holes contain low TDS water, which rarely exceeds 1000 mg/l in the Beas valley, except at Kulu where it goes up to 4094 mg/l. The pH varies from neutral to slightly alkaline. Classification of thermal water has been made on Shoeller and Giggenbach diagrams, which
Geothermal Field of Tattapani, Chattisgarh
The incoming of primates including hominids and their evolution giving rise to modern man was the most interesting biotic event during the Cenozoic Era. Early ancestors of man were ape-like non-human primates. Among the earliest primates akin to hominids, was Ramapithecus, whose fossils have been found in 12 million year old rocks of Siwalik Hills in India. These probably walked on their two feet for a while. However, the first definite member of human lineage known as Australopithecus appeared about 4 million years ago; these were ape-faced pre-humans who could stand erect, walk on two hind limbs and were probably the first stone tool users. Earliest human (Homo habilis) appeared about 2 million (20 lakh) years ago in Africa. In the initial stages probably, he did not look like a human. Gradually, he used tools, started living in caves, hunted animals, lived in settlements and finally became the man of the modern age.
CONCLUSION
Although India has made considerable progress in other renewable energy sectors like solar wind biodiesel etc not much progress has made to develop geothermal energy. The world over about 3000 MW equivalent of energy being generated using their geothermal resources by my many countries like US Japan Italy New Zeeland Iceland Phillipines etc. India is lagging behind as compared to other countries. This is mainly due to lack of high temperature hot springs. Although we have as many as 400 hot springs distributed at many locations in our country except in Himalayan terrain the other locations were considered to be not much useful. The recent progress with new technology has proved now to use low temperature hot water springs also in an effective way. In order to develop all the geothermal locations for electric power and other uses NTPC has taken up a major initiative to develop the geothermal fields in India. As a part of this MOU Tatapani hot spring region located in Surguja district in Chattisgarh has been identified as its first site location for development with an initial capacity of 5 to 10 MW of electric power generation.