Geothermal Energy:Natural heat energy produced

by the EarthGeo (Earth) Thermal (Heat)

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

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.

Types of Geothermal Energy

• Dry Steam Systems

• Wet Steam Systems

• Binary Cycle Systems

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.

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.

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.

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.

Seasonal GHP’s

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

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.

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.

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