Exergetic optimization of proposed Takigami binary geothermal power plant, Oita, Japan

The single flash Takigami Geothermal Power Plant is located in the southwestern part of Oita prefecture, Kyushu Island, Japan, with installed capacity of 27.5 MW. Energy and exergy of waste brine from a single flash system were calculated as 45.71%) and 37.64% of the total available energy and exergy of the produced fluid, respectively. The separated brine could be used as a heat source for a combined power production and direct use applications. For a feasibility study of waste heat utilization, a binary plant was selected for power generation in a combined system with the single flash plant. The net power output of the binary plant was calculated to be 8,660 kW. Mathematical models for energy and exergy flows were developed and implemented in Engineering Equation Solver software. The largest exergy destruction for the waste brine occurred at the condenser and evaporator with 16.6% and 30.5%) of total available exergy destroyed, respectively. The overall exergy and energy efficiencies for the binary plant were 31.15%) and 4.67%, respectively. A Grassmann diagram of the overall exergy flow illustrates the overall exergy flow of the process. Exergy analysis is a helpful tool for analyzing geothermal plants from the viewpoint of optimum use of produced energy.