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Study On Power Plant Configurations To Optimize Mass Flow Consumption With Respect To Silica Scaling For Dieng Unit 2, Indonesia
Dieng geothermal field located at Central Java, Indonesia, operated by PT Geo Dipa Energi (Persero) with existing power plant Unit 1 commissioned since 2002 of 60 MW and a complementary small-scale plant commissioned since 2021 of 10 MW. As a continuation, project Dieng unit 2 has started to develop another 55 MW net. To develop this new unit, one of the main challenges in Dieng, silica scaling shall be considered due to the high concentration of silica in Dieng. Studies and testing to find the recommended power plant design parameter for Unit 2 have been done several times by the consulting company and internally. The testing itself is known as the pilot plant which was conducted for 21.2 bara high pressure separation pressure and 3 bara low pressure and also for Organic Rankine Cycle (ORC) binary plant. Findings from the pilot plant testing to date indicate that significant potential difficulties in operating a binary combined cycle plant at Dieng due to heat exchanger scaling from high concentrations of heavy metal sulphides in the fluid. After the testing, with Silica Scaling Index (SSI) >1.2 as the manageable limit, the calculation was conducted using Python and Ms. Excel and verified with EES, the correlation between mass flow from wells and separator pressure including the Specific Steam Consumption (SSC) are found. The power plant configuration used is single flash condensing type and double flash condensing type with enthalpy assumption 1300 kJ/kg and 1600 kJ/kg. Based on this study, the required mass flow for single flash separator pressure ranging from 12.5 bara to 25.7 bara will be 260 kg/s to 405 kg/s with pressure directly proportional to the mass flow required from the wells. While for double flash calculation, the overall required mass flow is ranging from 235 to 360 kg/s and the separator pressure correlation with mass flow is directly proportional. For Specific Steam Consumption (SSC), the pressure inversely proportional with the SSC which means the higher the pressure, the lower SSC. Recommendation on the power plant use is double flash using high pressure separator 25 bara and low pressure 12.5 bara. Second recommendation is single flash using 25 bara. This recommendation, especially the double flash need to be check in the pilot plant to gather more comprehensive information about silica scaling index and silica scaling rates.