Indonesia is the second largest country that has geothermal energy resources after USA. Unfortunately, utilization of this energy source in this country is still limited. One of the challenges is that many of these energy sources are classified as low and medium enthalpy energy sources. In geothermal power plant in Indonesia, still many brines are still hot before reinjected to the reservoir. They are potential to utilize to increase energy efficiency using a binary power plant. So far, its utilization using conventional steam power plants is less than satisfactory.

To increase the utilization of the geothermal energy sources, the ORC system has been used in Lahendong geothermal field at North Sulawesi as a secondary power plant. The ORC is supported by German Research Center of Geoscience (GFZ Potsdam), in collaboration with Pertamina Geothermal Energy (PGE) and Agency for the Assessment and Application of Technology (BPPT). The Lahendong ORC adds intermediate cycle in front, where the intermediate cycle is aimed to prevent scaling problems occurred in the ORC modular.

In this paper, a comparison review between the existing ORC system and the simple cycle ORC system (without intermediate cycle) was carried out. The simulation work is also done to get the best type of the ORC system that is applied in Lahendong. The simulation was done by using a software "Engineering Equation Solver (EES)". Based on the simulation, the using of the intermediate cycle can decrease net efficiency 1.23% if compared with the simple cycle ORC design. Furthermore, the results of this study can be used to improve the performance of the existing ORC system and can also be used to exploit the potential of other geothermal resources that are very abundant in Indonesia.

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