Techno-economic comparisons of organic Rankine cycle and supercritical carbon dioxide cycle to utilize brine waste heat in Ulubelu geothermal power plant, Indonesia

Abstract Ulubelu geothermal power plant (GPP) in Indonesia reinjects 2,577 t/h of brine in one of its injection well pads with a temperature of 166°C and a pressure of 7.38 bar. Therefore, the brine still contains considerable waste heat that can be utilized through waste heat recovery (WHR) techniques. Organic Rankine cycle (ORC) and supercritical carbon dioxide (CO 2 ) Brayton cycle (SCBC) are technologies that can be used to convert waste heat into electricity. ORC is already widely used for WHR applications. Meanwhile, SCBC is an emerging technology with the advantage of using CO 2 as the working fluid in a closed-loop system. While CO 2 is inert and non-flammable, supercritical CO 2 has very high specific heat and density, so compact-sized equipment can be used. This study aims to compare the simple ORC, recuperative ORC, simple SCBC, and recuperative SCBC power cycle configurations for brine WHR at the Ulubelu GPP based on the technical and economic aspects. The results show that recuperative ORC produced the highest net output power and thermal efficiency (27,363 kW and 15.96%, respectively). Meanwhile, recuperative SCBC has the best economic performance with the lowest CAPEX (1,404 USD/kW-net), the highest NPV (414.7 million USD) and IRR (29%), and the shortest payback period (4.83 years).