A Cost Approach for Optimization of a Combined Power and Thermal Desalination System through Exergy and Environmental Analysis

In this Article, a systematic approach of cost analysis and optimization for combining the multieffect thermal vapor compression (METVC) desalination system with the gas turbine power plant (GT) was proposed on the basis of thermodynamic, economic, and environmental attributes. The total annual cost (TAC) of the combined system, including annual capital and operating costs, was modified to define an efficient cost objective function by adding the exergy destruction cost as a lost opportunity cost, and environmental emissions cost as a damage cost of the system to the operating cost. A parametric analysis was conducted to evaluate the effects of the key thermodynamic parameters for combining the GT and METVC systems, including the gas turbine inlet temperature (TIT), the HRSG outlet temperature (HOT), and the temperature difference between the effects of the METVC system (Delta T-METVC) on the modified total annual cost (MTAC). The parameter optimization was achieved using a genetic algorithm (GA) to find the optimal key thermodynamic parameters with minimization of the MTAC of the combined system. In addition, the methodology was applied to optimize the combining of a METVC desalination system with a GT power plant located in Mahshar, Iran. The optimization results indicated that the METVC systems with less than five effects cannot be combined with the current GT power plant because the combined systems cannot produce the power and fresh water requirements. Among the combined systems with more than four effects in the METVC system, the combined system with five effects in the METVC system was selected as the best system, which can produce 28 543 m(3)/day fresh water and 127 MW power, respectively, and reduce the NOx emission by 3.6% as compared to the current power plant.