The presence of non-condensable gases (NCG) in a geothermal fluid disrupts the vacuum process in the condenser, reducing turbine efficiency, and decreasing the total power output of the geothermal power plant (GPP). Therefore, to optimize the thermodynamic efficiency of GPP, NCG should be removed with a gas removal system. The main objective of this research is to model and develop a software-based interface to simulate mass and energy balance in a single-flash GPP as well as examine the

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... ynamic performance of the gas removal system, which is the most important step in the planning and designing phase of the GPP. This software was validated using outputs of Kamojang GPP Units 2, 3, and 4 located at Kamojang geothermal field, Garut, West Java, Indonesia. Units 2 and 3 use two ejectors which are installed in series and Unit 4 utilize a hybrid system which is mostly a combination of vacuum pumps and a steam jet ejector. The modeling results yield that Kamojang GPP Units 2 and 3 generate power of 55.295 MW with an absolute error of 0.53%, whereas Unit 4 generates a power of 60.218 MW with a 0.36% absolute error with respect to the field data. These results comply with the expected minimum error, so the model parameters are considered valid and can be used for simulation. It was shown from the simulation that the total saving of steam consumption for the hybrid system at Kamojang GPP Units 2 and 3 is 534 kW. The power requirement of the vacuum pumps is still less than the power generated by the motive steam required by the ejector to dispose the NCG at the same amount. This indicates that Kamojang GPP Units 2 and 3 will be more efficient when using a hybrid system.