Technical Performance of Organic Rankine Cycle (ORC) for Low-Enthalpy Geothermal Power Generation

The present study evaluates the performance of low-enthalpy geothermal brine as a heat source for power generation using Organic Rankine Cycle (ORC) technology at the Kiejo-Mbaka hot springs. The Kiejo-Mbaka pilot well brine temperature, pressure, and mass flow rate were measured as 348 K, 1.3 bar, and 1 kg/s, respectively. Besides, five environmentally friendly working fluids with low boiling points and low global warming potential (R600, R123, R245ca, R245fa, and R141b) were selected for this analysis. A thermodynamic investigation of the ORC system was conducted considering the effects of expander inlet temperature, expander inlet pressure, mass flow rate, and condensation temperature. The system performance was assessed using net power output (Pnet) and thermal efficiency (ηth) as key indicators. The results show that the dry fluids R141b and R600 achieved the highest performance, with thermal efficiency reaching approximately 39.0% and net power output of 177.48 kW. Among the tested fluids, R245ca and R141b demonstrated strong performance in terms of thermal efficiency, while R600 and R141b excelled in net power output under the given operating conditions. Overall, R141b emerged as the most promising working fluid for the Kiejo-Mbaka geothermal source, by achieving a thermal efficiency of 42.20% along with consistently high-power output across different conditions.