بهينه‌سازي دوهدفه بازيافت حرارت و توليد آب شيرين از سيستم‏ آب خنك كن يكبارگذر

Two-objective Optimization of Heat Recovery and Desalinated Water Production from a Once-Through Cooling System

يكي از مهم ترين منابع اتلاف آب و حرارت در نيروگاه‌هاي حرارتي موجود در حاشيه‌ي درياها، سيستم آب خنك كن يكبارگذر است. در نيروگاه‌هاي حرارتي واقع در نوار ساحلي جنوب ايران نيز سيستم هاي خنك كن يكبارگذر از مهم‌ترين منابع اتلاف انرژي است. لذا بازيافت حرارت از آب خنك كن برگشتي به دريا امري ضروري است. در اين پژوهش، بازيافت حرارت از آب خنك‏كن برگشتي به دريا به‌منظور توليد آب شيرين در نيروگاه‌هاي حرارتي مورد بررسي قرار گرفته است. بدين‌منظور پس از مدل‌سازي سيستم آب شيرين كن‏ چندمرحله‌يي تبخير ناگهاني، با استفاده از تحليل ترمواكونوميك هزينه‌ي محصول توليدي (آب شيرين) مشخص ‌شده است. در ادامه با استفاده از الگوريتم ژنتيك، راندمان اگزرژي و تابع هزينه‌ي آب شيرين توليدي بهينه شده و نتايج حاصل توسط نمودار پرتو نشان داده شده است. ارزيابي ها حاكي از آن است كه به‌واسطه‌ي بازيافت حرارت، هزينه‌ي آب شيرين توليدي در حدود 13‌درصد كاهش يافت.

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 suffer 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 flash desalination system in thermal power plants was also investigated. For this purpose, a multi-stage flash 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 difference of brine heater and condenser). Exergetic efficiency 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 efficiency was maximized. In addition, the effects 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.