Geothermal energy represents the inner heat of the earth, produced largely by
the decay of radioactive elements in the mantle and center. The three ways that
the heat is found is both wet and dry steam (wet steam has drops of water in
it), hot water and dry volcanic rocks. We know that the temperature of the earth
at depths of 25 to 50 km range from 200`C to 1000`C. There are areas of the
earth where local concentrations of heat occur, just as mineral concentrations
do. Most of these are located along oceanic ridges and continental rifts, such
as the ‘Ring of Fire’. Geothermal energy is not free from environmental
problems. The steam contains large amounts of hydrogen sulphide with its smell
of rotten eggs, and both steam and hot water contain substantial amounts of
dissolved minerals, many of which are poisonous to the aquatic life in the
streams and rivers into which they are eventually discharged. Also, the removal
of steam or water causes the earth to subside in that region. Geothermal energy
was first used in the era of the ancient Roman bath house, in which they bathed
in hot salt springs. Even though the Romans found an easy way to use geothermal
energy, and we still enjoy natural hot springs, the process of removing
geothermal energy from the earth to use it efficiently is rather difficult. The
only three ways to use geothermal energy is for hot water, space heating and
generating electricity. In order to turn geothermal energy into electricity it
must be brought up from the earth within a metal cased borehole that was driven
deep into the naturally hot ground and put through a geothermal power station,
(see diagram). The high pressure steam for these wells is used to drive turbines
to generate 300 million kilowatts of electricity each year. Which if you compare
all the power that the world produces from all the geothermal power plants, in
1985, to that of one average nuclear power plant the geothermal power will not
yet compare. Due to the acid gases in the steam delicate machinery was getting
damaged. The hot water is corrosive and eating away at the pipes and expensive
equipment making it even harder to removing it from the earth. The problem was
solved by using the acid steam to heat acid-free water. This provided clean
steam that would not damage the machinery. As a bonus, useful by-products were
extracted from the acid steam, including boric acid, ammonia and carbon dioxide.
The possibility of tapping the heat energy stored in subsurface rocks is also
being considered. The plan is to pump water into such regions by means of deep
wells, and then pump the heated water back to the surface. One of the major
problems is the poor thermal conductivity of rocks, and it is thus very
desirable to have hot rocks that lie at relatively shallow depths.BibliographyBooth, Basil. Volcanoes and Earthquakes. East Sussex, Wayland Ltd., 1988
Boyle, Desmond. Energy. Morristown, Macdonald Education Ltd., 1980. Doty, Roy.
Where are you going with that Energy?. Garden City, Doubleday & Company
Inc., 1922. McClory, Paul. Focus on Alternative Energy. East Sussex, Wayland
Ltd., 1985. Siddiqi, Toufiq. World Energy. Artarmon, Holt-Saunders Pty. Ltd.,
1976. Smith, Norman. Energy isn’t easy. Toronto, General Publishing Co. Ltd.,
1984. Thomas, John. The Quest for Fuel. East Sussex, Wayland Ltd., 1978.