Mirko Skiborowski, Korbinian Krämer, Adel Mhamdi, Wolfgang Marquardt:
Structural optimization of hybrid RO-MED desalination plants
13th Aachener Membran Kolloquium Proceedings, 263-270
Today there are already about three billion people having no access to potable water while over 97% of the worlds water resources are reposing in the oceans. Thus, membrane based processes and thermal desalination plants are two alternatives to overcome the problem of fresh water supply by means of seawater desalination. Reverse Osmosis is the major membrane based seawater desalination technology and accounts for approximately 56:5% of the worlds seawater desalination capacities. As a thermal desalination technology, multi effect distillation is stated to be more flexible and less energy consuming then the common multi-stage flash process. The performance and cost of a desalination plant depend on the the type of plant, the interconnection of the different unit operations and their parametrization and site specific characteristics. While membrane manufacturers provide engineering tools to support the engineer in the design of stand-alone RO plants utilizing their membrane modules and software like WTCost of the Bureau of Reclamation can be applied for the cost estimation only structural optimization allows to consider all impacts at once and find an economical optimal desalination plant. For the optimization of a hybrid desalination plant the combination of a reverse osmosis network (RON) with a forward feed multi-effect distillation (FF-MED) plant is considered in this work. An extendable superstructure is combined with rigorous process models and a detailed techno-economial model of the whole plant. For the RON pressure vessels containing a series of membrane modules, a pressure exchange system as well as pumps and turbines are considered as possible unit operations. By the application of heuristics a reduction of the of the superstructure is accomplished and an initialization scheme is proposed creating a robust optimization model. The resulting mixed integer non linear programming problem (MINLP) is then solved using the general algebraic modeling system (GAMS).
Desalination, Reverse Osmosis, Multiple-Effect Distillation, Hybrid Plant, Structural Optimization, MINLP