Design of a Computational Tool for Organic Rankine Cycle Performance Estimation Based on Geothermal Field Data

Abstract

This study evaluates the thermodynamic feasibility of additional power generation from separated brine at a high-temperature geothermal plant in Indonesia, referred to as the “XYZ geothermal plant” to maintain site confidentiality. The plant operates with a single-phase liquid-dominated reservoir, with temperatures ranging from 250 °C to 270 °C and a brine reinjection temperature of approximately 170 °C at a flow rate of 1400 tons per hour.

To ensure safe reinjection conditions, the Silica Scaling Index (SSI) was applied to determine the minimum allowable brine temperature. A finite difference-based Python simulation tool was developed to model heat transfer in the ORC system and assess performance across different working fluids and operating pressures. The results show that n-pentane achieves the best performance, producing a net power output of 5596 kW and a thermal efficiency of 17.21% at an optimal pressure of 1.80 MPa. Isopentane follows closely, while R-1233zd(E) performs less favorably due to pressure constraints.

Model validation against manual calculations resulted in deviations below 0.6%, confirming the simulation’s accuracy. This tool provides a fast and reliable method for evaluating ORC performance and supports practical decision-making for geothermal plant operators. It is intended to assist utilities such as PLN in optimizing geothermal resource utilization.