Experimental study of single screw expander used in low-medium temperature geothermal power system

摘要

Research and development of renewable energy is one solution to energy crisis and its related environmental problem. Among all kinds of renewable energy, geothermal energy has good development feasibility due to its low investment and operation costs, independence to weather and climate change, and stable power generation. In China, high-temperature geothermal resource is rare; however, low-medium temperature geothermal resource is widely distributed. Therefore, small and medium sized geothermal power system based on low-medium temperature organic Rankine cycle(ORC) is a good choice for geothermal exploitation. Expander is the key device in such system. Single screw expander has proper size and good output performance. Therefore, in order to test the application of single screw expander in geothermal exploitation, compressed air was used as working fluid to conduct experimental study at different temperature. The results show that at the same rotational speed, the single screw expander at a higher air temperature has a bigger output power, a smaller gas consumption rate, a bigger expansion ratio, a bigger temperature drop, a higher thermal efficiency, and a smaller irreversible loss. Moreover, if a lubricant circle is added in the experimental system, the single screw expander with lubricant at a lower air temperature will have the same performance as the expander without lubricant at a higher air temperature. Therefore, the performance of single screw expander can be improved by adding a lubricant circle and raising compressed air temperature.