An update of second law analysis and optimization of a single-flash geothermal power plant in Dieng, Indonesia

Dieng geothermal power plant is one of the Geothermal plants located in Indonesia with a total estimated potential of 400 MWe. The reservoir is characterized by water-dominated with 240 to 333 degrees C temperature. Recently, the company operated one unit of single-flash system with a capacity of 60 MW. To improve its capacity, unit expansion of unit 2 and 3 are designed with each capacity of 60 MW. Apart from this expansion, another effort is optimizing the existing plant. It can be conducted with a thermodynamic approach using energy and exergy analysis. Therefore, this study aims to evaluate and optimize the existing geothermal power plant using energy and exergy analysis. With the latest data obtained, the results show that the exergy value of production wells is around 106,515 kW. The electricity production with the system is around 40,680 kW, resulting in an exergy efficiency of about 38.19%. Furthermore, the optimization is carried out on the turbine because it shows the greatest irreversibility of 11,217 kW. Optimization is done by varying the incoming turbine pressure. These results indicate that higher inlet pressure increases irreversibility and lowers energy efficiency. Furthermore, the optimum inlet turbine pressure is achieved at 5.5 bar with the maximum change depending on the ambient temperature.