Optimization Research Of Large-Scale Reverse Osmosis Seawater Desalination System

With the rapid development of society and economy,the fresh water crisis is becoming more and more severe worldwide.As one of the most efficient desalination technology,film Reverse Osmosis Seawater Desalination now has been the most promising one for its low cost and simple process.However,the operation cost of film desalination during its producing process is still too high.Therefore,reducing the operation cost of the SWRO system with system engineering method is the present research focus.After consulting various literatures,this subject carried out the operation optimizing research,based on the SWRO system analysis and modeling,and tried to reduce the operation cost of the SWRO system from the operation aspect.1.The flow sheet and the parameter variation of the whole SWRO system is analyzed here,and the mechanical model of the RO module is established with distributed equations,according to the Mass Conservation law,Energy Conservation law,and Diffusion-Film Theory.To overcome the accurate and quick problem solving difficulty resulting from the Nonlinear algebraic-Differential equations,a simultaneous method combining with finite element configuration is proposed to discrete the status variables and control variables in the differential equations,meanwhile,the interior point and the sparse technology are adopted to realize the fast solving goal.Then,the salt rejection rate and producing rate calculated by this model are compared to the Dow's RONA 9.0 software and the site data,verifying the satisfying accuracy of this model and laying a foundation of the next operation optimizing.2.The dynamic process model,the variable parameter model are established according to the characters of the full-scale SWRO system,while the energy consumption and operation cost model of each process is built up based on the flow sheet characters.Then the optimization problem is formulated with the objective function and the equations and various bound constraints to minimize total operational cost.And the previously proposed simultaneous solving strategy,combined with a practical SWRO system is adopted to carry out the case study,which helps to obtain the optimal operation curve and the variation curves of the system key indexes under different parameters.The calculation results show that the resolving strategy adopted here is of relatively high solving efficiency,and the operation optimizing method here can reduce the operation cost by a large margin.3.Considering the features of the large scale SWRO system,the network structured SWRO system operation optimization is studied which contains several RO units and storage tanks.A network structured large-scale SWRO system optimization problem is established to reduce the daily operation cost at most.And finally,the optimal operation trajectories of the control variables and status variables are obtained by case study.4.Considering that membrane fouling has an influential effect on the energy consumption of RO process and other performances,an optimal membrane cleaning and replacing strategy is discussed under the condition of system long time operation.Firstly,membrane fouling influence on RO performance indexed is analyzed;an influence model the membrane fouling has on membrane permeation and the relation model between membrane cleaning and membrane performance recovery are established,combining with mechanism equations and semi-experience equations.Then,integrating the membrane cleaning cost and replacing cost with the operation cost of the SWRO system to build up the optimization problem and its corresponding resolving strategy which contains the objective of minimum operation cost,the optimization variables of membrane cleaning frequency,cleaning timing and replacing timing,and the constraints of open equations.Finally,the optimal membrane cleaning and replacing periods of the SWRO system in long time operation can be calculated quickly with the optimization strategy.