Flash cycle optimization of Sabalan geothermal power plant employing exergy concept

The Sabalan geothermal field in northwest Iran is currently under development. A single flash cycle has been selected for power generation. The analysis of the proposed design shows the maximum net power output of the plant can reach 31 MW if the pressures of the separator and condenser are 5.5 and 0.3 bar, respectively. To achieve optimum energy utilization, a double flash cycle was also evaluated for power generation. The results indicate the maximum net power output of the plant reaches 49.7 MW if the pressures for the high- and low-pressure steps and condenser are 7.5, 1.1, and 0.1 bar, respectively. Mathematical models for energy and exergy flows were developed and implemented in Engineering Equation Solver (EES) software. In the single flash cycle, the energy and exergy of the waste water were calculated as 54.8% and 41.4% of the total available energy and exergy, respectively. The energy and exergy of waste water were respectively calculated as 19.88% and 15.3% of the total available energy and exergy, in the double flash cycle. The parts of the system with largest exergy destruction in both cycles were compared and the overall exergy and energy efficiencies for the power plant were calculated. The total exergy available from production wells at Sabalan was calculated to be 111 MW for the single flash system, and 114 MW for the double flash system. The results of the analysis suggest a double flash cycle system for the Sabalan power plant.

► Geothermal single (S) and double (D) flash (F) cycles were compared employing exergy concept.
► The DF cycle extracts more exergy compared to the SF cycle.
► In the SF cycle, the overall exergy and energy efficiencies are 32.7% and 7.3% respectively.
► In the DF cycle, the overall exergy and energy efficiencies are 43.4% and 10% respectively.