| Abstract |
With geothermal power generation increased year by year, geothermal resources have attracted more and more attention. It has become an important trend to explore new geothermal fields with high-, medium- and low-temperature, and improve geothermal power generation technologies. The screw expander is a kind of full-flow power machine, which can be applied not only to superheated steam and saturated steam, but also to wet steam and even steam-liquid mixtures. The screw expander shows excellent characteristics: anti-contamination, self-cleaning, simple structure, few spare parts, easy maintenance, high equipment reliability and long service life. It has been applied in geothermal power generation in China, such as flash steam system, full-flow two-phase system and binary cycle system (ORC). With its unique technical characteristics, the screw expander will find much wider applications in geothermal power generation, including in high-, medium- and low-temperature geothermal fields and for all kinds of geothermal power generation technologies. In the early 1970s, as the countries in the world paid more attention to the development of new energy sources, China also started booming of geothermal energy development. Tibet is abundant in geothermal resources in China. From 1977 to 1991, nine units of steam turbine generator were installed at YangBaJing in Tibet with total capacity of 25.18MW. Geothermal power generation in YangBaJing is the largest and longest running geothermal power plant and has become the most successful demonstration of geothermal power generation in China. However, since then no new geothermal power generation units were installed until 2008. Under the support of Chinese government, the first screw expander generating unit with the capacity of 1MW, manufactured by Jiangxi HuaDian Electrical Power CO. Ltd., was put into operation in YaBaJing for geothermal power generation in 2008, and another screw expander unit with the same capacity was followed by putting into operation in 2010. This new technology applied in YangBaJing has demonstrated that the screw expander generating unit is more suitable for high temperature geothermal resources. After that, the full-flow screw expander generating unit, which is much more suitable for two phase geothermal sources, was successfully trial produced by Jiangxi HuaDian Electrical Power CO. Ltd. in 2011. Two testing units of full-flow screw expander with capacities of 400kW and 500kW respectively were installed in YangYi, another high temperature geothermal field in Tibet, in 2011 and 2012 respectively. The successful operation of testing units of screw expander proved full-flow technology has higher thermal efficiency than conventional flash steam system for geothermal power generation. The screw expander generating units also found application in medium- and low-temperature geothermal sources by using binary cycle system (ORC). The screw expander generating unit with ORC has been successfully applied in Huabei oilfield in China, which evaporated organic working fluid (R123) by recovering heat of 100Ž liquid from deep oil well and drove the screw expander for electricity generation. Finally, the conclusions are reached: (1) the screw expander generating unit is suitable for geothermal power generation; (2) the full-flow screw expander has proved to be higher thermally efficient than conventional flash steam system; (3) the screw expander also found successful application in medium- and low-temperature geothermal sources by using binary cycle system (ORC). |