Experimental Study of Small Scale Hybrid Hot Spring Thermal Energy Conversion

Abstract

Japan has a huge geothermal resource with geothermal power generation capacity of about 550 MWe. The hot water geothermal resources in Japan are mostly in the range of 53-120 °C. Hot spring thermal energy conversion (STEC) can provide a stable power output so introduction of small-scale STEC based on organic Rankine cycle (ORC) is expected. Hybrid hot spring thermal energy conversion (H-STEC) is a combination of distillation and ORC; thus, it is able to produce electric power and water to supply the cooling tower simultaneously. H-STEC has a flash chamber to prevent scaling in heat exchangers due to the supersaturated Ca, Si, and so on. The system characteristics of H-STEC are such that power output and supplied water ratio can be clarified by using parametric analysis, however, there has been no significant research proving such in actual experiments. In this study, the system characteristics of H-STEC were clarified by using a small-scale demonstration equipment. Pumped hot spring water was used as the heat source of H-STEC where the hot spring water was delivered after heat utilization. To evaluate the available power for a power generation system using a finite heat source, the maximum power output and the maximum power efficiency were defined. The maximum power efficiency is the ratio of the gross power to the maximum power. The maximum gross power was 15.9 kW, and the maximum power efficiency was 22.1%. The condensed water from evaporator could supply 100% of the water consumption in the cooling tower.