Integrated Approaches to Optimal Multi-Period Desalination Synthesis Involving Water-Energy Nexus

This work develops novel tools for the multi-period and multiscale synthesis of water desalination systems for systematically optimizing the benefits of the integration of emerging desalination technologies and the water-energy nexus. The research develops the optimization frameworks for the following problems: (1) optimization of multi-effect distillation (MED) design via MD brine treatment and process heat integration, (2) synthesis of desalination systems for multi-period capacity planning, and (3) synthesis and scheduling of solar-assisted membrane distillation (MD) for domestic water desalination. To solve the three problems, the water-energy nexus must be addressed in the planning, design, and operation of the water desalination system. In the first problem, an optimization approach to the design of MED-MD in the context of water-energy nexus with an industrial process is developed. The hybrid MED-MD desalination system is thermally integrated with industrial facility while any additional required thermal energy is supplied from external sources. The optimization framework targets optimizing the operating and design variables of the MED and MD units as well as the excess heat extracted from the industrial facility. In the second problem, an optimization approach was used to identify the optimal capacity planning of distressed water desalination systems considering the integration of emerging desalination technologies. Despite the economic challenges many emerging technologies face, some new desalination technologies such as MD demonstrate promising candidacy in the optimal expansion of desalination systems due to their modularity and other advantages. The developed framework also addresses the multiscale nature of the problem. Unit-specific decision variables such as the top brine temperature (TBT) and MD recycle ratio are simultaneously optimized with the synthesis of the multi-period flowsheet. In the third problem, a systematic approach for the design and scheduling of a skid-mounted solar-assisted membrane distillation system is developed. The problem targets domestic water demand in remote areas that are not supported by fresh water infrastructure. The proposed system consists of both thermal and photovoltaic (PV) solar systems to provide the energy required for desalination and system’s equipment. Storage tanks are used to collect thermal energy and to supply the feed to the MD system while PV cells are connected to electric-energy storage batteries to drive the pumping. Conventional fossil fuel is used to supplement the solar thermal energy as needed. The aim of the optimization framework is to determine the number and size of the storage tanks, the operating variables, the collection and dispatch times, the extent of solar and fossil-energy uses, and the operating schedule for the integrated system. The merits of the developed frameworks are illustrated in three distinct case studies with clear focus on MD as an example of emerging technologies integrated with conventional technologies. In all the three case studies, MD desalination as a standalone solution was suboptimal when compared to conventional desalination technologies. However, with the introduction of water-energy nexus with adjacent processing facilities and solar thermal heating, interesting results evolved with MD as a constituent of the global optimum. In addition, emerging technologies have shown economic merits when utilized at the end of the planning horizon in expanding systems, due to its modularity