2. Layers of the Earth
• Heat flows outward from the center
as a result of radioactive decay.
• The crust (about 30 and 60 km
thick), insulates us from the interior
heat
• A solid inner core followed by
liquid outer core, with the mantle
by semi-molten
• Temp at base of crust about
1000o C, increasing slowly into the
core.
• Hot spots located 2 to 3 km form
the surface
3. Tectonic Plates
• Plates are in constant motion
(several centimeters/yr).
• When collision or grinding occurs,
it can create mountains, volcanoes,
geysers and earthquakes.
• Near the junctions of these plates
are where heat travels rapidly from
interior.
4. Types of Geothermal Energy
• Dry Steam Systems
• Wet Steam Systems
• Binary Cycle Systems
5. Dry Steam Systems
• Uses direct steam that shoots up
through a well and rock catcher,
directly into the turbine.
• Dry steam fields are rare.
• Water boils underground and generates
steam at temps of 165oC and pressure
of about 100 psi. Most conventional
fossil-fuel power plants run at 550o C
and 1000 psi.
• Dry steam field of The Geysers were
discovered in 1847 by a hunter looking
for grizzly bear. At first, he thought he
had discovered the gates of hell. Used
for therapeutic hot springs and later for
electric power in 1920.
6. Wet Steam Systems
(AKA Flash Steam)
• Pulls high pressure hot water into
low pressure cool water tanks,
resulting in “flash steam” used to
power turbines.
• Geothermal wells tap wet steam
fields deep in the earth’s surface.
• Taking a look at Yellowstone’s Old
Faithful,” allows us to see the
principles behind periodic geysers.
• Temperatures in a wet steam
system can reach up to 370o C with
boiling.
7. Binary Cycle
• High temperature water brought
from geothermal reservoirs, is
passed through heat exchanger,
containing pipe w/ secondary fluids
(Iso-butane) with a lower boiling
point.
• The resulting flash steam power
turbines, creating an electrical
current.
• The geothermal water is never
exposed to the air and is injected
back into the periphery of the
reservoir.
8. Geothermal Heat Pumps
• A geothermal heat pump system
consists of pipes buried in the
shallow ground near the building, a
heat exchanger, and ductwork into
the building. In winter, heat from
the relatively warmer ground goes
through the heat exchanger into the
house.
• In summer, hot air from the house
is pulled through the heat
exchanger into the relatively cooler
ground. Heat removed during the
summer can be used as no-cost
energy to heat water.
10. Geysers
• Water at bottom of container is
under great pressure and will not
boil until temperature is above
100oC
• When boiling begins, a great
amount of pressure is released,
causing the water to boil rapidly.
• Steam-driven water, under great
pressure, rushes up to the neck, and
sprays steam into the air
11. Direct Use
• Hot water near the earth’s
surface can be pumped
directly to ground-level
facilities.
• This hot water can be used to
heat buildings, grow plants in
a green house, heat water for
fish farms, and pasteurize
milk.
• Much like hot water floor
heating in a house, this mass
amount of hot water can be
pumped under road to keep
them from freezing.
12. Limitations of Geothermal
Energy
• Because the heat of the earth lies at
such great depths it is often
difficult to locate, and accesses
even with today’s drilling
technology
• Lack of substantial funding is
available.
• Lack of proven technology for
extraction and use of geothermal
heat.
13. Environmental Impacts
• Environmental groups protest at many
geothermal plants complaining that the
plants are dangerous, dirty, noisy and
unsightly.
• The emission of hydrogen sulfide,
which smells like rotten eggs.
• The steam used in Dry Steam System
contains minerals that can contaminate
ground water, poisoning fish and other
aquatic life after it condenses
• Geothermal sights can experience
subsidence (setting or sinking of land)
ie: one of Mexico’s steam plant
reported 13 cm of subsidence
