Perbandingan Termodinamika dan Keekonomian Siklus CO2 Superkritis untuk Memanfaatkan Panas Buang Brine pada PLTP Ulubelu, Lampung
Vincentius Adven Brilian, Dr. Ir. Khasani, S.T., M.Eng., IPM., ASEAN Eng.
2023 | Skripsi | TEKNIK MESIN
Indonesia has a geothermal energy potential of 23.9 GW, which has yet to be utilized optimally. On the other hand, single-flash geothermal power plants (GPP) produce waste heat from the separated brine, which is reinjected into the reservoir without further utilization. If the waste heat of the brine can be utilized, the energy efficiency of GPP and the utilization of geothermal energy potential can be increased to support the energy transition. The Ulubelu GPP in Lampung Province reinjects 2,577 t/h of brine with a temperature of 166 degrees Celsius and a pressure of 7.38 bara. Brine under such conditions still has waste heat energy which can be converted into electrical energy through a thermal power cycle. Thus, there is an opportunity to develop a thermal power cycle for brine waste heat recovery (WHR) at the Ulubelu GPP. The organic Rankine cycle (ORC) and the supercritical CO2 Brayton cycle (SCBC) are thermal power cycles that can be used for WHR. ORC is a mature technology for WHR applications at low to moderate temperatures. Meanwhile, SCBC, which is still under development, has the potential to compete with ORC for WHR applications at low temperatures. SCBC has several advantages, such as using CO2 working fluid, which is inert, non-toxic, non-flammable, non-explosive, and has a GWP of 1. Furthermore, CO2 near its critical point (temperature 31.1 degrees Celsius and pressure 73.9 bar) has very high specific heat and density around its critical point, so compact-sized components can be used. Therefore, this study conducted a thermodynamic and economic comparison of four power cycle configurations: the ORC (simple and recuperative) and the SCBC (simple and recuperative) for WHR brine applications at the Ulubelu GPP. The thermodynamic analysis consists of four main stages: (a) modeling the thermodynamic equation using the Engineering Equation Solver (EES) software; (b) calculation of operating conditions and rating of the cycle’s main components, (c) calculation and optimization of net power output and thermal efficiency; and (d) thermodynamic modeling validation. Furthermore, the economic analysis consists of two main stages: (a) modeling the economic equation; and (b) calculation of capital expenditure (CAPEX), net present value (NPV), internal rate of return (IRR), and payback period. The results of the thermodynamic analysis showed that the recuperative ORC produced the highest net output power and thermal efficiency (27,363 kW and 15.96%, respectively) among the compared power cycles. The validation results show good agreement between the calculated thermal efficiency values and the results of literature studies, so the thermodynamic modeling in this study can be considered valid. Furthermore, the results of the economic analysis show that the recuperative SCBC has the best economic performance with the lowest CAPEX (USD 1,404.42/kW-net), the highest NPV and IRR (USD 414.7 million and 29%, respectively), as well as the shortest payback period (4.83 years).
Kata Kunci : pembangkit listrik tenaga panas bumi, siklus Brayton CO2 superkritis, siklus Rankine organik, waste heat recovery