Modeling And Optimization Of Dynamic Process For Reverse Osmosis Seawater Desalination System

As an open-source technology for fresh water,Reverse Osmosis Seawater Desalination now is becoming the most promising one for its lower cost and simple process in the 21 st century.However,compared to the municipal ordinary water cost,the operational cost of film desalination is still too high.In the meantime,as the basic of optimization,the SWRO system model has already attracted a wide range of national and international experts.Various literatures were consulted,this paper carried out a dynamic SWRO system model on the background of operation optimizing research.While conducting the discrete problem with finite element method,some optimization was completed.The contributions of the thesis include the following four aspects.1.Considering the simple RO system,analysis of the characteristics of the overall flow sheet and the main associated variables were focused on.According to the Diffusion-Film Theory and Mass Conservation law,a rigid mechanical model of the RO module include water storage units were established with process parameters equations.To overcome the solving difficulty resulting from the model contained large numbers of Nonlinear Differential-algebraic equations,we proposed a simultaneous method combining with finite elements configuration to discrete the status variables and control variables in the differential equations,and then using the IPOPT solver to realize the solution.Eventually,the results of simulation were compared to the DOW's ROSA 9.0 software,verifying the accuracy of the local RO process steady state model.2.After analysis the partial steady state simulation of SWRO process,we proposed a dynamic process model based on the fluid mechanic and RO mechanism known in advance.Because the model contains partial differential algebraic equations varied in time and space,twice discretized were taken with finite element method to calculate the solution on GAMS.The model was then used for further simulation to study the impact of various process under dynamic conditions by step response.All of these contribute to the basis of SWRO optimization control system.3.Considering the accuracy problem after discretizing the SWRO model in simultaneous approach.A moving mesh refinement strategy based on the error of discretization was developed.In order to reduce the number of elements with the guarantee precision,the method also took in the idea of cycle detection during discrete process.At last,the advantages of moving finite elements method were elaborated in SWRO's solution.4.The influence of RO membrane fouling to the system's performance were discussed,Considering the change of cake layer,concentration polarization factors and the degradation ofmembrane itself,a developed SWRO system model with membrane fouling dynamic process equations was established,and then was simulated.A new strategy was proposed for optimal membrane module cleaning and replacement.The results of dynamic simulation and optimization can provide the effective criterion for membrane cleaning and membrane replacement.