Performance Evaluation of Geothermal Power Production Using EES (Case Study Ulumbu Geothermal Power Production Unit 4 East Nusa Tenggara, Indonesia)

Abstract

Ulumbu geothermal working area (GWA) is in Ruteng district, East Nusa Tenggara province, Indonesia. Ulumbu GWA is owned by PLN. There are four geothermal power plants (GPP) in Ulumbu, which capacity 4 x 2.5 MW. It has operated since 2013. Steam used to generate electricity comes from ULB-2 production well. Wellhead temperature and pressure were 180-200°C and 11 bar. Ulumbu GPP Unit 4 uses a condensing type turbine. It has specific steam consumption (SSC) during commissioning around 9.8 T/MW. After 6 (six) years of operation, SSC becomes 10.04 T/MW on average. It gives a chance to perform optimization in the GPP’s equipment. Before performing optimization, evaluation for every equipment based on as-built data is done by modeling using EES software. The method of evaluation is performed by thermodynamics analysis in each GPP’s equipment. EES is chosen due to its simplicity to arrange many equations in a single window. EES could communicatively display calculation results through a parametric table, solution window, and diagram window. Operation data give information that turbine inlet pressure is operated under its specification. Turbine inlet pressure is operated under its specification because of the change of operating wellhead pressure. Non-Condensable Gas (NCG) content also decreases based on the last ULB-2 well fluid sampling. Using EES, parameter changes in turbine inlet pressure and NCG content are simulated to get optimum power generation value. The simulation results indicate that optimum turbine inlet pressure is obtained at 9.3 bar with SSC 9.17 T/MW. Ulumbu GPP Unit 4 that operated in that condition could reach cycle efficiency of about 10.39%.