Assessing Energy and Exergy Recovery from Separated Brine via Second Flash at the Ulubelu Geothermal Power Plant Using EES

Geothermal power plants operating with single-flash systems typically reinject separated brine despite its remaining potential for energy and exergy recovery. This study evaluates the effects of second-flash pressure on the thermodynamic recovery potential of separated brine at the Ulubelu Geothermal Power Plant using Engineering Equation Solver (EES). Secondary geofluid data from previous research were used as simulation inputs, comprising an initial pressure of 980 kPa, temperature of 179°C, and mass flow rate of 271.94 kg/s. The first-flash process was modeled at 800 kPa, followed by an isenthalpic second-flash process at 300, 400, 500, 600, and 700 kPa. Energy recovery, exergy recovery, Energy Recovery Ratio (ERR), and Exergy Recovery Ratio (ExRR) were calculated for each scenario. First-flash simulation produced 266.9 kg/s of separated brine for subsequent processing. Increasing second-flash pressure consistently reduced steam production and all four recovery indicators. At 300 kPa, the highest recovery values were obtained, with an energy recovery rate of 51,537 kW, exergy recovery rate of 12,686 kW, ERR of 31.35%, and ExRR of 41.15%. At 700 kPa, these values declined to 8,195 kW, 2,367 kW, 4.98%, and 7.68%, respectively. Thus, 300 kPa provided the greatest thermodynamic recovery potential among the investigated pressures, but it cannot be considered the optimal operating pressure for the complete power plant. The calculated recovery rates describe energy and exergy carried by generated steam, not additional net electrical output. Because the simulations remain unvalidated against actual plant operating data, further evaluation of turbine performance, reinjection constraints, and practical operational feasibility is necessary.