Geothermal Energy
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.
Bibliography
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Boyle,
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Where are you going with that Energy?. Garden City, Doubleday &
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