Study On The Optimization Design Of Reverse Osmosis Seawater Desalination System

Developing seawater desalination technology is an important approach ofsolving the problem of scarcity of water. Reverse osmosis seawater desalinationtechnology have an instant development in recent 10 years, and it will become theprimary desalination technology in the future because of its many advantage, suchas less equipment investment, lower energy consumption and shorter constructionperiod than other desalination method. In the normal temperature, the energyconsumption of RO desalination on the grounds of the thermodynamics calculationis only 0.7 kwh/m3, therefore it is the most-energy-saving desalination technology intheory. However, at present the technical economical indices of RO don't reach thepublic expected value, and the cost of desalination is on the high side. It shows thatthe current RO system can be improved hi some aspect, such as the RO technology,the engineering design, and the operation etc. The research of RO systemOptimization design started not long ago. In recent years, many scholars devotedthemselves to the research of RO system Optimization design, and presented manyvaluable ideas and methods, such as superstructure methods etc. However becauseof the complexity of the problem itself.the methods proposed have some deficiency,such as they didn't have new mathematic model to describe the new RO technologyafter the appearance of the high-efficient energy exchanger, and they didn't considerthe problem of membrane module cleaning and replacing in all-around. The paperanalyses the process of the RO desalination based on system engineering, taking themathematical programming as a tool, the author makes a systematic and deepresearch on the problem of optimization design of the RO system, and developed aset of sound methods. The main contents are extracted and listed below:1. The optimal technology design of RO desalination process has beeninvestigated. From the beginning, the detailed mathematical models of eachprocess units are given, and the relevant economic models to the ROdesalination process are introduced. Then the interdependence of the abovemathematical models via some corresponding variables constitutes a systemmodel. Single-stage and two-stage processed are considered. The membranemodule can be classed four type, i.e. higher salt-rejection membrane, high-fluxmembrane, normal membrane, lower salt-rejection membrane. Finally, theoptimum design problem can be solved as a mixed-integer non-linear programming (MINLP), which incorporates thermodynamic, technical andflexibility constraints and minimizes the total annualized cost. The differentoptimal design options are obtained for different design specification and feedwater quality and the corresponding design rule are derived. Two examples indifferent cases are solved to illustrate the advantage and effectiveness of thenew method.2. In the reverse osmosis desalination process, the membrane fouling and scaling is a big problem that must be solved. The regular cleaning is one of main measures that prevent and cure the membrane fouling and scaling. Cleaning can eliminate the surfacial contamination of membranes and recover the water flux. On the condition that the water production is ensured, the optimal cleaning frequency and the minimum cleaning cost can be obtained by choosing the appropriate cleaning strategy and time. This paper makes a more deep research on the problem of membrane module cleaning and replacing base on the previous study, and addresses the new fouling model and the criterion of cleaning. The mathematical formulation of the optimum design problem is a mixed-integer non-linear programming (MINLP), which targets the minimum total operation cost during the whole project period. One example was solved and the corresponding optimal time and cleaning strategy was acquired during the five-year project period, which illustrates the effectiveness of the new method for the optimal maintenance cost of the 3-5 year life-span memb...