Exergoeconomic analysis and optimization of single and double flash cycles for Sabalan geothermal power plant

In this study single and double flash systems were designed to utilize the Sabalan geothermal fluid as a heat source. An Exergoeconomic model was applied on plant' equipment in order to calculate the thermodynamic and economic performances of the cycles. Parametric analysis was done to examine the effect of important key parameters including flash pressures and steam quality at turbine outlet on plant performance. Optimization process for maximum net power output was carried out on the plant using direct searching method in EES (Engineering Equation Solver). This process aimed to find the optimum flashing pressures corresponding to the maximum potential power output as an objective function. Additionally, the major exergy destruction locations were shown graphically and side by side for both systems to observe the effect of secondary flash process on exergy destruction at each component. Afterward, an environmental study was done in order to calculate the amount of fossil fuel saving and pollutants emission reduction compared to conventional fossil fuel power plants. The result showed that in double flash energy and exergy efficiency were increased from 16.26% and 40.06% to 17.73% and 50.89%, respectively. Moreover, double flash resulted in higher net power output compared to that of single flash (28,838 kW vs. 36,055 kW) while both cycles were using the same geofluid. Optimization results revealed that thermodynamically optimum cycle could not result the best and lower energy production cost and vice versa. Therefore, the single flash generates electricity within lower price compared to double flash system. Moreover, double flash considerably reduces the required fossil fuel and various pollutants emission more than single flash if they were replaced by fossil fuel power plants with same amount of production.