TWO-OBJECTIVE OPTIMIZATION OF HEAT RECOVERY AND DESALINATED WATER PRODUCTION FROM A ONCE-THROUGH COOLING SYSTEM

A once-through cooling water system is a major source of water and energy loss in power plants located in coastal areas of the Persian Gulf; the relatively high temperature discharged water causes some operational problems in these power plants. In addition, the once-through cooling system is a major source of environmental pollution in power plants located along the south coastline of Iran. On the other hand, Persian Gulf coastal areas suer from a shortage of natural fresh water; therefore, water treatment (natural fresh water production), and heat recovery from the discharged cooling water to the Persian Gulf is essential. In this research, heat recovery from the discharged cooling water to the Persian Gulf was studied, and application of the recovered energy for water treatment (fresh water production) using a multi-stage ash desalination system in thermal power plants was also investigated. For this purpose, a multistage ash desalination system was thermodynamically modeled, and then, a thermoeconomic model )based on exergy and economic analysis( was studied to determine the water cost. In the next step, a two-objective genetic algorithm was applied as a suitable optimization approach to obtain the optimal values of the decision variables (number of stages, top brine temperature, last stage temperature, terminal temperature dierence of brine heater and condenser). Exergetic eciency and the cost of water were considered the objective functions of the optimization procedure. By applying the optimization technique, the cost of water was minimized, while exergetic eciency was maximized. In addition, the eects of heat recovery on the cost of the water desalination process were studied, and results demonstrated that the cost of water desalination was reduced by 13% using heat recovery from the discharged cooling water. Also, a sensitivity analysis was performed in order to show the relationship between the cost of water and some important parameters of desalination systems.