Skip to content

U6 #Geothermal #Energy

  • originates from the earth's interior in form of heat
  • E.g. Volcanoes, geysers, hot springs and boiling mud pots
  • Limited to certain sites only as not feasible to access from deep locations

  • Geothermal Fields - Sites where its extraction and use is more feasible due to relative higher concentrations and near surface availability.

    Layers of Earth in Lithosphere: 1. Crust (0-100km) 2. Asthenosphere(100 -) 3. Mantle( - 2900km) 4. Outer Core(2900km - 5100km) 5. Inner Core(5100 - 6378km)

    Advantages: 1. reliable 2. cheap 3. 24 hour availability 4. inherent storage in earth itself 5. little land area for plants 6. weather independent

    Disadvantages: 1. Site specific ( can't build plants on user's whims) 2. low grade heat energy output generally 3. geothermal fluid comes with dissolved gases and solute causing air and land pollution 4. Drilling causes noise pollution 5. The available thermal energy cannot be distributed over long distances 6. corrosive and abrasive geothermal fluid reduces the life of the plant

    Applications 1. Direct Heat Use - Although abundant availability, thermodynamic quality is low! - low and moderate temperature hydrothermal fluids can be used as direct heat source for - Space and water - Drying applications in food - chemical and textile industries - crop drying - washing - warming fish ponds in aquaculture - soil and space heating of glasshouses for agriculture - Extraction gold/silver from ores - Dying Wool - heat sidewalks and roads for winter - 1. Electric Power Generation - High enough temperatures ( > 90 °C), then preference for using in generation of electricity - Normally used for base load power generation - Used to power industrial processes on site or electricity fed into utility grid 2. Examples in India - 7 Geothermal Provinces 1. Himalayas 2. Sohana 3. West Coast 4. Cambay 5. SONATA (Son-Narmada-Tapi) 6. Godavari 7. Mahanadi Components of a geothermal Plant 1. Flash Tank 2. Turbine 3. Generator 4. Cooling Tower 5. Injection Well geothermalPowerPlantComponents.png.png

    Geothermal Electricity Plants 1. Dry Steam - Use steam coming from geysers, etc directly 2. Flashed steam - High temperature water released from pressure of deep reservoir, part of the water flashes(explosively boils) to steam and this force is used to spin turbine 3. Binary Power Plant - working fluid isobutane/isopentane boils and flashes at lower temperature than water, so electricity generated from reservoirs with lower temperatures as well. - Virtually no emissions but are relatively less efficient.

    DRY Steam Type: 1. draw steam directly from under earth's surface 2. First type of geothermal plants built were of this type. drySteamPlantSchematic.png 3. Not common since natural hydrothermal reservoirs of dry steam are very rare! 4. Additional heating boilers and boiler fuel are not required 5. steam or water vapour fill the wells through rock catcher and directly rotates the turbine, which activates a generator to produce electricity Flash Steam Type: 1. Extracts geothermal water exceeding 350°F under extremely high pressure. 2. Upon surfacing, a sudden reduction in pressure causes a portion of the heated water to vaporise, or "flash," into steam. -> turn turbine -> generate electricity 3. As the hot water flows up through wells in the ground, it is collected in a flash tank where drop in pressure causes liquid to boil into steam.flashGeothermalPlant.png.png 4. The steam is separated from the liquid which is then used to run turbines which in turn generate power. The condensed steam is returned to the reservoir. Binary Cycle Type: 1. Binary cycle plants operate in areas with substantially lower- temperature geothermal water (225°F). 2. binary cycle uses the earth's heated water to vaporize a "working fluid," any fluid with a lower boiling point than water (e.g., iso-butane). 3. This type of plant uses high temperature geothermal water to heat another fluid which has a lower boiling point than water. 4. This fluid vaporizes to steam, drives the turbines, then condenses to liquid to begin the cycle again. 5. The water, which never comes into direct contact with the working fluid, is then injected back into the ground to be reheated. 6. Closed Loop System binaryCyclePowerPlant.png

More than 9000 thermal wells and springs are now in use.

previous unit : U5. Tidal Energy