Modeling And Optimization Of Capacitive Deionization Process For Seawater Desalination

Lack of fresh water makes the development of novel desalination technologies more and more urgent. Compared with the traditional technologies for desalination such as reverse osmosis, low temperature multi-effect distillation, the capacitive deionization (CDI), as a new technology and widely used in water treatment, demonstrates a promising prospect in desalination due to its remarkable features of energy saving and free of pollution.Two models based on different theories were compared in this dissertation. One is based on pseudo first-order reaction kinetics and another one is based on molar purification rate. The results indicated that the model based on pseudo first-order reaction kinetics was only suitable for a narrow range. And the physical meaning of the parameters in the model was not clear. Therefore, this model was not practically useful. However, the physical meaning of the parameters in the model based on molar purification rate was clear thus it could be applied to discuss the influence of parameters on the process. Therefore, the model was suitable for modeling and analyzing the CDI process. In order to make the simulation and analysis results to be in good agreement with practical circumstantial conditions, the electrical resistance in the model of the regeneration process was modified.The influences of the parameters on the lowest concentration and the lowest concentration time were investigated according to the selected model based on molar purification rate. The results showed that the lowest concentration increased with the increase of flow rate, spacer volume and dead volume while decreased with the increase of voltage and capacitance. The lowest concentration time increased with the increase of capacitance and dead volume while decreased with the increase of flow rate. The stepwise voltage model was proposed to analyze and design the procedure in order to decrease the energy cost. Different voltage was adopted at different stage. The energy cost and the water yield were calculated by one module, two modules and three modules, respectively. The calculation results showed that compared with one module, the energy cost decreased by26.80%and12.22%for the three modules and two modules, respectively.In order to reduce dead volume, the analysis on the velocity field in the spacer was conducted numerically. Three corrugated models were established and analyzed to optimize the surface structure of the plates and the influence of the flow rate on the velocity field in the spacer was also analyzed. The results showed that simple structure on the surface and small velocity were preferred to decrease the effect of dead volume.The capacitive deionization for sea water desalination procedure was designed based on the molar purification rate model. The treatment capacity of the device was5Ot/d. The results indicated that the detailed information of the sea water desalination procedure was:20modules were arranged in parallel and every module consisted of10channels arranged in series. All the modules operated at the same time and the proper pumps, flow meters and valves were selected to fulfill the requirement of treatment capacity and desalination rate. The whole process contained4stages:charging for2.5min, working for10min, regeneration for3min under inverse voltage and discharging for2.5min.