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Clean Energy Systems and Experiences Part 5

Tham khảo tài liệu 'clean energy systems and experiences part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Development of sustainable energy research and applications 53 USA EU 25 Fig. 9. Distribution of industrial CHP capacity in the EU and USA 3 2 2 USA UK Ukraine South Africa Russia Poland Nigeria Mexico Japan Italy Others Colombia China Canada Brazil Australia Fig. 10. World landfill methane emissions MMTCO2e 54 Clean Energy Systems and Experiences Geothermal energy Geothermal steam has been used in volcanic regions in many countries to generate electricity. The use of geothermal energy involves the extraction of heat from rocks in the outer part of the earth. It is relatively unusual for the rocks to be sufficiently hot at shallow depth for this to be economically attractive. Virtually all the areas of present geothermal interest are concentrated along the margins of the major tectonic plates which form the surface of the earth. Heat is conventionally extracted by the forced or natural circulation of water through permeable hot rock. There are various practical difficulties and disadvantages associated with the use of geothermal power Transmission geothermal power has to be used where it is found. In Iceland it has proved feasible to pipe hot water 20 km in insulated pipes but much shorter distances are preferred. Environmental problems these are somewhat variable and are usually not great. Perhaps the most serious is the disposal of warm high salinity water where it cannot be reinjected or purified. Dry steam plants tend to be very noisy and there is releases of small amounts of methane hydrogen nitrogen amonia and hydrogen sulphide and of these the latter presents the main problem. The geothermal fluid is often highly chemically corrosive or physically abrassive as the result of the entrained solid matter it carries. This may entail special plant design problems and unusually short operational lives for both the holes and the installations they serve. Because the useful rate of heat extraction from a geothermal field is in nearly all cases much higher than the .