Experimental Study Of Low-temperature Organic Rankine Cycle

Electricity generation from low-temperature waste heat is a technology that transform low grade thermal energy into electric energy, the principle is the Organic Rankine Cycle in which organic compounds are chosen instead of water as the working fluid of Rankine Cycle. Organic Ranking Cycle(ORC) is not only an effective method of recovery and utilization of low grade waste heat resources, but also a method in the utilization of solar energy and geothermal energy. ORC has received extensive attention recently because of massive fossil energy consumption and increasing serious environmental pollution. This dissertation comes from the project of “the ration principle of waste heat’s energy level and cascade utilization, and its application in the thermodynamics system”. A self-designed low-temperature waste heat utilization ORC experimental facility was constructed and R245 fa was chosen as the working fluid of this experimental system based on theoretical calculation. Fortunately, Output power of the expander achieves the design aim 2kW.This paper summaries the research progress of ORC from classification of waste heat resources, selection of organic working medium and experimental study and optimization of ORC. Meanwhile, a detailed introduction of the basic principle, thermodynamics process and influencing factors of ORC are presented for organic working medium selection and design of experimental system.Different kinds of organic compounds results in big differences of the output performance of the ORC system. This article calculates the thermal efficiency of ORC power generation system. From this point, the most suitable organic working medium is chosen from 19 pure potential organic compounds for low-temperature industrial waste heat in the temperature range of 85~200℃. At last, R245 fa with the optimized comprehensive properties as working medium of experimental system is selected for experiments in this paper.A mini-ORC experimental system for heat recovery from low-temperature waste heat resources is designed on the basis of the completed thermodynamic analysis of electricity generation, and a self-designed rod baffle heat exchanger is implemented as condenser in this system. Three series experiments were conducted successfully while different asynchronous motor was chosen as electric generator under different environmental conditions to explore the output performance of this ORC power generation system after equipment selection and system test. The results show that higher heat source temperature lead to greater output power. The ORC system has better output performance under lower ambient temperature. In addition, synchronous speed of asynchronous motor has great influence on the output performance of ORC system so that it is important to match a suitable motor for this system. Comparing the results of these three experiments, the ORC system yields the best output performance while quadrupole motor as the electric generator and running in winter. Under this working condition the heat source temperature is 92℃, net output power of expander, generated power and net generated power are 2.0kW, 1.4kW and 1.2kW respectively. The corresponding thermal efficiency and power generating efficiency are 7.8% and 4.5%.