Geothermal Energy: Natural heat energy produced by the Earth

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Geothermal EnergyNatural heat energy produced
by the Earth

• Geo (Earth) Thermal (Heat)

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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

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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.

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Types of Geothermal Energy

• Dry Steam Systems
• Wet Steam Systems
• Binary Cycle Systems

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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.

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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
  earths surface.
• Taking a look at Yellowstones 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.

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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.

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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.

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Seasonal GHPs
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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

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Direct Use

• Hot water near the earths 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.

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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 todays drilling technology
• Lack of substantial funding is available.
• Lack of proven technology for extraction and use
  of geothermal heat.

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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 Mexicos
  steam plant reported 13 cm of subsidence