Introduction Of Geothermal Energy
Historically , the first application of geothermal energy were for space heating , cooking and medical purposes . The earliest record of space heating dates back to 1300 in Iceland .In the early 1800s , geothermal energy was used on what was then a large scale by the conte Franceso de Laderel to recover boric acid . The first mechanical conversion was in 1897 when the steam of the field at Larderallo, Italy , was used to heat a boiler producing steam which drove a small steam engine . The first attempt to produce electricity also took place at Larderello in 1904 with an electricity generator that powered four light bulbs . This was followed in 1912 by a condensating turbine ; and by 1914, 8.5 MW of electricity was being produced . By 1944 larderello was producing 127MW. The Plant was destroyed near end of World war 2, but was fortunately rebuilt and expanded evevtually reached 360 MW in 1981.
In the U.S , the first attempt at developing the geysers field was made in 1922.Steam was successfully , taped , but the pipes and turbines of the time were unable to cope with the corrosive and abrasive steam . The effort was not revived until 1956, till that time stainless steel alloys were developed that could withstand the corrosive steam , and the first electric generating unit of 11MW capacity began operation in 1960.Since then 13 generally progressively larger units have been added to the system . After ward number of units were planned which brought the total capacity to about 1500MW by the late 1980. Other electric- generating fields of note are in New Zealand , japan, mexico, the phillipines, the soviet union and Ice land .
In 1979, the global electricity production from geothermal resources was 1872MW and units under construction were of 1650 MW Capacity . for space and process heat , total power utilization was 1281MW. So that total power production was about 4850MW. This power consumption is likely to grow up to 100000 MW by the turn of next century .
It has been analysed that about 40 to 50 % of total heat required by the society is a heat below 200 degree temperature. 30% heat is required about 150 degrees.. 20% heat is required at about 100 degrees.
Thus there is a vast scope to use geothermal energy for low temperature applications . There is an ample scope to develop geothermal power in India, but still development in geothermal field is in initial stage . There are about 340 known thermal areas in India , each represented by hot/warm spring . About 113 spring area, discovered so far where geothermal power is available . 46 of these systems are of high temperature type , which could be generate 1838 MW for a period of 30 years . 59 of these are intermediate temperature type( 90 to 150 degree of temp), which could be considered for power generation using binary vapour cycle and other are of low temperature type below 90 degree of temp.
Till now only one pilot plant is in operation in puga valley ,in jammu and Kashmir , having 20 MW capacity . Another plant is at parvathi valley , Himachal Pradesh is under construction . A 7.5 tonne capacity capacity cold storage pilot plant based on geothermal energy was installed at Manikaran in Himachal Pradesh . A 5 KW pilot plant is under fabrication at the National Aeronautical Laboratory , Bangalore. This plant will run on geothermal energy which will be recovered from the hot spring s at Manikaran in Himachal Pradesh . Plans are being made to under take further research and development studies in the area of geothermal energy .exploitation of this energy source for non power sectors like poultry farming ,mushroom cultivation ,space eating is possible in this country on fairly large scale
It can been seen that while geothermal energy is not the sought after soul and long range solution to our energy problems, it nevertheless represents a not insignificant factor if its resource are developed ion a careful and efficient manner.
Geothermal energy is also the one of the renewable energy sources, which are defined as those resource that draw on the natural energy floors of the earth (another term THE ALTERNATIVE ENERGY SOURCES is also common in use). Renewable energy sources are so named because they recur , are seemingly inexhaustible, and are free for the taking . geothermal energy as practically no intermittency, has the highest energy density,& is economically not far removed from the conventional technologies .geothermal energy classified as renewable because the earth’s interior is and will continue in the process of cooling for indefinite future .
The word geothermal comes from the Greek words geo (earth) and therme ( heat). So, geothermal energy is heat from within the earth. We can use the steam and hot water produced inside the earth to heat buildings or generate electricity. Geothermal energy is a renewable energy source because the water is replenished by rainfall and the heat is continuously produced in the eath.
ENERGY INSIDE THE EARTH
Geothermal energy is generated in the earth''''s core, about 4,000 miles below the surface. Temperatures hotter than the sun''''s surface are continuously produced inside the earth by the slow decay of radioactive particles, a process that happens in all rocks. The earth has a number of different layers.The core itself has two layers: a solid iron core and an outer core made of very hot melted rock, called magma. The mantle which surrounds the core and is about 1,800 miles thick. It is made up of magma and rock. The crust is the outermost layer of the earth, the land that forms the continents and ocean floors. It can be three to five miles thick under the oceans and 15 to 35 miles thick on the continents. The earth''''s crust is broken into pieces called plates. Magma comes close to the earth''''s surface near the edges of these plates. This is where volcanoes occur. The lava that erupts from volcanoes is partly magma. Deep underground, the rocks and water absorb the heat from this magma. The temperature of the rocks and water get hotter and hotter as you go deeper underground. People around the world use geothermal energy to heat their homes and to produce electricity by digging deep wells and pumping the heated underground water or steam to the surface. Or, we can make use of the stable temperatures near the surface of the earth to heat and cool buildings.
HOW DOES GEOTHERMAL ENERGY WORK
The heat from the earth's core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is lighter (less dense) than the surrounding rock, the magma rises (convects), moving slowly up toward the earth's crust, carrying the heat from below.
Sometimes the hot magma reaches all the way to the surface, where we know it as lava. But most often the magma remains below the earth's crust, heating nearby rock and water (rainwater that has seeped deep into the earth) - sometimes as hot as 370 degrees C. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.
Tapping geothermal resources requires drilling into permeable zones of super-heated water trapped in geothermal reservoirs. Once tapped, these underground reservoirs can provide geothermal plants with water or steam hot enough to generate electricity. .
Nature of Geothermal Field :-
It is convenient to classify earths surface into three broad groups .
1) Non- thermal areas having a temperature gradient of 10-40 temp degree per km depth.
2) Semi-thermal areas having a temperature gradient of 70 degree of temperature per km depth
3) Hyper-thermal areas where the temperature gradients are many times greater than in non- thermal areas.
Geothermal fields may further be classified into three types :-
A) Hyper –thermal Field :-
1)Wet fields. Where the water is pressurized And temperatures are above 100 degree of temperature. When they are led to the surface a fraction will be splashed into steam and a major part remains as the boiling water.
2)Dry fields. They produce dry saturated steam or superheated steam at pressure above atmospheric .
3)Semi-thermal fields:- These are capable of producing hot water at temperature above 100 degree of temperature.