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  1. 1. I. Geothermal Energy
  2. 2. Source of Geothermal Energy • Geothermal energy is a renewable and sustainable power source that comes from the heat generated by magma from the earth’s core. "Geo" means earth and "thermal" means heat. • The Earth has four main layers, where each layer has different compositions, functions and temperatures, as is illustrated in the two figures below. Sometimes magma reaches the surface of the crust and is then called lava. The magma reaches the crust and heats nearby rocks and water. The heated water can reach the surface and form hot springs and geysers. • In volcanic areas, magma heats reservoir of water available beneath the surface and forms steam. Large amount of steam with relatively high pressure is formed in the reservoir, and this is the source of geothermal energy.
  3. 3. Geothermal Power Plant • Geothermal power plants are used all over the world, but can not be located just anywhere. They are located in the areas of volcanic activity, where large amount of steam is available from heated ground water reservoir. . • Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring. The steam from the ground flows to the surface by it’s pressure. The steam is the separated from the water and other impurities (sulfur, dirt, etc), before it is used to drive a turbine engine which turns a generator. Usually the water is injected back into the ground to maintain the water availability in the reservoir. The picture below illustrates how the set-up of a geothermal power plant
  4. 4. • Geothermal power plants use thermodynamics Rankine Cycle, to convert thermal energy from the steam into mechanical energy which then converted into electrical energy by the generator. • Typical installation diagram and Rankine Cycle for a geothermal power plant is shown in the figures below. Steam Purification Steam from the Well Water back to the Well Water and Steam Well 0 2 4 6 8 10 1212 0 100 200 300 400 500 s [kJ/kg-K] T[C] 6000 kPa 10 kPa Rankine Vapor Power Cycle 1 2 3 4 23 Steam Purification Plant
  5. 5. Types of Geothermal Power Plant. There are three types of Geothermal Power Plant technology. 1. Dry Steam Power Plants 2. Binary Cycle Power Plants 3. Flash Steam Power Plants Dry Steam Power Plant The characteristics of Dry Steam Power Plant are, • Vapor dominated resources where steam production is not contaminated • Steam is 500°C - 650°C • Steam directly passes through turbine • Need water to inject down into rock • Well is deep
  6. 6. Binary Cycle Power Plants The characteristics of Binary Cycle Power Plant are, • Uses lower-temperatures, usually hot water resources (40° C – 160° C). • Hot water is passed through a heat exchanger in conjunction with a secondary fluid with a lower boiling point (usually a hydrocarbon such as isobutane or isopentane). • Secondary fluid vaporizes, which turns the turbines and drive the generators. • Remaining secondary fluid is simply recycled through the heat exchanger. • Geothermal fluid is condensed and returned to the reservoir. • Lower-temperature reservoirs are far more common, which makes binary plants more prevalent.
  7. 7. Flash Steam Power Plants The characteristics of Dry Steam Power Plant are, • Use very hot (more than 150° C) steam and hot water resources • Steam either comes directly from the resource, or the very hot, high-pressure water is depressurized ("flashed") to produce steam. • Steam then turns turbines, which drive generators that generate electricity.
  8. 8. Source of Geothermal Energy