Geothermal power plants

Presently, designs for radial inflow turboexpanders in sizes up to 70 MW are available for use in geothermal power plants. Following are some of the most important features that make turboexpanders ideal for the reeovery of power from the vast available resourees of pressurized gas streams. 

Geothermal power plant located in a lava field in Blue Lagoon, Iceland. (Corbis-Bettmann)... 

Some geothermal power plants use a combination of flash and binai y cycles to increase the efficiency of electricity production. An initial flash creates steam that drives a turbine then the binai y cycle is run, using either the hot water remaining after the initial flash or the hot exliaust from the turbine. 

Sato, K. (1988) Mori geothermal power plant. In Geothermal Fields and Geothermal Power Plants in Japan. Int. Syrap. Geothermal Energy, Kumamoto and Beppu, Japan, November 10-14 pp. 21-25. 

Location Mud holes geothermal power plants deep terrestrial oil fields Submarine hot springs vents or black smokers deep submarine oil fields... 

At a geothermal energy source, dry steam at 700 kPa and 170°C is available at a mass flow rate of lOOkg/sec. A barometric condenser at lOkPa is used to decrease the turbine exhaust temperature. Find (a) the power produced by the geothermal power plant as shown in Fig. 2.22a. (b) What is the power produced without the barometric condenser ... 

Figure 2.22b Dry-steam geothermal power plant without condenser.

More commonly than it puts out dry steam, a geothermal well puts out a mixture of steam and water above 130°C, or just hot water. A separator is needed in a hot water steam mixture geothermal power plant to separate the flashing steam from the hot water, as shown in Figure 2.23. An additional throttling valve is required to generate saturated steam in a hot-water geothermal power plant. 

Figure 2.23 Hot water-steam mixture geothermal power plant.

A proposal is made to use a geothermal supply of hot water at 1500 kPa and 180°C to operate a steam turbine. The high-pressure water is throttled into a flash evaporator chamber, which forms liquid and vapor at a lower pressure of 400 kPa. The liquid is discarded while the saturated vapor feeds the turbine and exits at lOkPa. Cooling water is available at 15°C. Find the turbine power per unit geothermal hot-water mass flow rate. The turbine efficiency is 88%. Find the power produced by the geothermal power plant, and find the optimized flash pressure that will give the most turbine power per unit geothermal hot water mass flow rate. 

Build the hot-water geothermal power plant as shown in... 

Fig. 6. Simplified schematic layout of a classic geothermal power plant. The main escape routes for steam are from the cooling tower and gas ejectors, which are located just downstream from the turbine.

Figure 12 shows the quantity of CO2 emitted into the atmosphere from two geothermal power plants in Iceland and how it compares with CO2 emission from fossil fuel plants. At Krafla, the quantity of C02 emitted per MW-year (MWy) is 8401, which is only about 10% of that from a typical coal-fired power plant (8760 t/MWy, Armannsson Kristmannsdottir 1992). The... 

Arnorsson, S., Eli asson, J. Gudmundsson, B. Th. 1999. 40 MW Geothermal Power Plant in Bjamar-flag Evaluation of the Impact on Ground Water and Natural Geothermal Manifestations. Science Institute Report RH-26-99, 36 pp. (In Icelandic.)... 

Axtmann, R. C. 19756. Environmental impact of a geothermal power plant. Science, 187, 795-803. 

Bacci, E., Gaggi, C., Lanzillotti, E., Ferrozzi, S. Valli, L. 2000. Geothermal power plants at Mt. Amiata (Tuscany-Italy) mercury and hydrogen sulphide deposition revealed by vegetation. Chemosphere, 40, 907-911. 

Bargagli, R., Cateni, D., Nelli, L., Olmastroni, S. Zagarese, B. 1997. Environmental impact of trace element emissions from geothermal power plants. Archives of Environmental Contamination and Toxicology, 33, 172-181. 

Bussotti, F., Cenni, E., Cozzi, A. Ferretti, M. 1997. The impact of geothermal power plants on forest vegetation. A case study at Travale (Tuscany, Central Italy). Environmental Monitoring and Assessment, 45, 181-194. 

Kumagai, N. Kitao, K. 2000. Reinjection problems encountered in Sumikawa geothermal power plant, Japan. In Proceedings World Geothermal Congress 2000, Kyushu-Tohoku, Japan, 28 May-10 June 2000, 2683 -2688. 

Fundamental to all heat-power conversion systems is that a significant portion of the heat supplied to the system must be rejected. Depending on their heat-power conversion efficiency, fossil-fueled plants waste 40-60%, nuclear-fueled plants 60-70% of the heat input geothermal power plants make no exception here. 

Fig. 5. Waste heat per unit electric capacity (MWt/MWe) of geothermal power plants, in comparison with other types of power generation. (Modified from DiPippo 1991).

Robertson, R. C. 1980. Waste heat rejection from geothermal power plants. In Kestin, J. (ed) Sourcebook on the Production of Electricity from Geothermal Energy. US Department of Energy, Washington DC, 997 p. 

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