Optimal integration of organic Rankine cycle and desalination systems with industrial processes: Energy-water-environment nexus

Highlights: • Optimization framework for integrated ORC, RO and MD system. • A new index considering brine wastewater disposal mixing potential. • To assess the effect of the MD system in an integrated ORC-RO-MD configuration. -- Abstract: Supplying water for the growing population of the world has become an important issue, therefore, desalination industries are being developed to produce fresh water especially from seawater. Owing to the large energy consumption, the focus is finding alternative solutions to supply energy demand in desalination plants. This work presents a model for the optimal integration of reverse osmosis and membrane distillation systems for seawater desalination through waste heat exploitation from an industrial process plant. In this regard, heat is exploited through organic Rankine cycle (ORC) and the generated power in this cycle is delivered to a reverse osmosis (RO) plant. The brine of the reverse osmosis plant is preheated utilizing the excess heat from the process plant and then is sent to the membrane distillation (MD) plant for further treatment. A multi-objective optimization approach is implemented in this work to take economic and environmental issues into accounts. The first objective function is to maximize the annual profit of the system. Additionally, an environmental measure has been defined in order to ensure that the maximum amount of fresh water production is obtained while the mixing of the brine disposal from this system with seawater is well done. The results show that applying the membrane distillation in ORC-RO-MD integrated system, despite from the working fluid used in the organic Rankine cycle, considerably improves both economic and environmental aspects of the system when compared with ORC-RO system.