Development of Micro Scale PRC Using Low Grade Geothermal Thermal Energy

In order to enhance the versatility, we proposed a design method in which a micro ORC of 10 kW class. The micro ORC is small scale power generation system for using renewable thermal energy such as hot springs. However, such thermal energy is of very low grade and involves temperature variations, so it is necessary to develop a versatile small power generation cycle. In this study, the design conditions of heat exchanger, expander, and pump were fixed for the micro ORC, and the power generation performance was investigated using six different working fluids for multiple heat source conditions. The heat source flow rate set to be 3,000 kg/h and the heat source temperature was 393 K. The heat sink flow rate set to be 18,000 kg/h and the temperature was 293 K. The pump discharge pressure was 1,500 kPa. As a result, Among the selected working fluids, butane showed the highest power generation performance of 12.9 kW. To predict the power generation performance of the micro ORC, we correlated the power generation of each working fluid with the thermophysical properties of the working fluid, but low correlation was obtained. Therefore, we introduced new parameter, Exergy Parameter Index (EPI), for predicting the power generation of a micro ORC. It was found to be a very reliable parameter for forecasting the power generation of a micro ORC.