The hot solution [water - steam] leaving the production well, is inserted into an expansion tank [flash], where the reduced pressure causes the water to flash into vapor. The generated steam is fed into a steam turbine, which turns the shaft of an electric generator. Water that remains liquid in the flash tank and the condensed vapor, which exits the steam generator, are forced by an underground pump back down into the earth. The enrichment well must drive the solution deep enough to reach the underground rock at a higher temperature than the boiling point of water, with the aim of re-volatilisation. The water is filtered by the rocks, becomes warmer and rises up through the production well.The installation may be used for the electricity production and district heat. Therefore, the use of the geothermal field is referred to combined heat and power (CHP) systems. |
Several geothermal power plants are based on high-temperature steam, so as to directly provide the energy required for the operation of generators. This type of installation is called "dry steam power plant" because the steam is released from the pressure of a deep reservoir, through a rock catcher and then past the power generator turbines. Dry steam reservoirs use the water in the earth's crust, which is heated by mantle and released from vents in the form of steam. This plant is suitable where the geothermal steam is not mixed with water. The superheated steam is led through steam turbines and produces electricity. In simple installations, the low pressure steam output from the turbine is vented to the atmosphere, but more commonly the steam passes through a condenser to convert it to water. This improves the efficiency of the turbine and avoids the environmental problems caused from the direct release of steam into the atmosphere. This water is reinjected into the ground with reinjection wells.The underground water reservoirs that feed such a system are refilled when rain falls on the land. Because this occurs on o continuous basis, geothermal energy is considered as a renewable resource. This is the oldest type of geothermal power plant. At peak production the plant can provide up to 2.000 MW of electricity per hour. This is about twice the amount of electricity a large nuclear power plant can produce. The unit emits only excess amounts of steam and very minor amounts of gases. |
These installations are applied if the geothermal fluid is at a low temperature, which is not enough to produce steam that would spin a turbine by itself. The water from the geothermal reservoir never comes into direct contact with the blades of the turbine generator and uses geothermal resources between 80ο and 180ο C. In the binary cycle system, warm geothermal water is pumped to the surface and passes through a heat exchanger which contains a fluid such as butane or pentane hydrocarbon with a much lower boiling point than water.The heat from the geothermal water causes this secondary or “binary” fluid to flash into vapor. The vapor created by heating pentane is what spins the turbine powering the generator, while the hot geothermal fluid is rejected into the geological formation, where it heats up again and is available to eventually re-circulate through the heat exchanger. That is why geothermal energy is a renewable source of energy, as an appropriately shaped rock formation can produce energy indefinitely. The moderate-temperature geothermal fluids are much more common than high-temperature geothermal fluids. |
These systems work along the same principle as natural geothermal energy. Geothermal power originated when hot rocks with cracks convert water into steam. With natural geothermal energy, the earth provides the cracked rock and steam to power a generator. With artificial or enhanced geothermal energy, we have to coax the rock to crack by injecting water down a well, passing it through the resulting crevices in hot rock, and then extracting steam through another well. The advantages of these systems is that they prevent the risk of dry hole associated with conventional hydrothermal geothermal energy, which require finding existing fractures that contain high flows of hot water. In the case of hot rocks, the productive well has to be drilled first, and then the enrichment well is created. The water goes from the surface to the hot rocks so as to be heated and to receive the same solution in the form of steam through the production drilling. An artificial geothermal plant can recover approximately 40% of underground heat and convert 15% into electricity, through low temperature turbines on the surface. |