Electrodialysis Process For Saline Water Concentration

Water comprehensive utilization process could successfully solve the concentrated brine discharge troubles, which will be of great importance in utilization efficiency improvement and environmentally friendly achievement. The utilization process indicates zero liquid discharge after chemical resources extraction, saline water concentration and crystallization. The dissertation directed at saline water concentration in water comprehensive utilization process, and contained the following studies:The electrodialyzer (ED) design model for saline water concentration was established. The design parameters were optimized under the target function of minimum overall cost. VC++language program was exploited for the model and visual interface. The design parameters considered in the model include the solution properties and flow state, membrane characteristics, spacer structure and spacer-shadow effect, limited current density and so on, then the ED structure, the current and voltage drops through the stack, energy consumption and costs were determined under the premise of minimum overall cost. The model validation was verified through the comparison between the model output and data from open literature, the result showed higher reliability of the model. The ED was designed and optimized for the primary concentration based on the concentrated brine discharged from the LT-MED of1ton/day desalted water pilot test apparatus.The effect of spacer thickness, membrane resistance, length-width ratios, and feed concentrations on the economy of the electrodialysis system was analyzed with the aid of the previously established model. Orthogonal test was applied to assess the influence of the design parameters on the financial performance of the system. The simulation results indicated that with the increase of velocity, the overall cost presented upward trend; the thin spacer was favorable for decreasing produce cost; different length-width ratios had little influence on system cost; it was favorable to reduce the concentrated cost if membrane resistance was reduced; to achieve the same concentration level, feeding salt water with higher concentrations could reduce concentrated and membrane cost, but cause pumping cost to rise up. Orthogonal tests indicated that the influence degree on system financial performance showed a ascending sequence that spacer thickness, spacer thickness and membrane resistance.Experimental electrodialysis system for brine concentration was built up, and then the effects of feed ratio and flow rate of concentrated and desalted cell, as well as control voltage on the relative concentrating rate and system energy cost were invested. Experimental data showed that the influencing degree on relative concentrating rate in ascending order was:feed ratio of concentrated and desalted cell, flow rate of concentrated and desalted cell and control voltage, besides, effect of flow rate in desalted cell was close to that in concentrated cell; The influencing degree on system costs in order greatest on top was:feed ratio, control voltage, flow rate of desalted cell, where, effects of control voltage and flowrate of desalted cell was comparable.Finally, saline water with initial concentration of25.4g/L was concentrated step by step; The final concentration of NaC1reached at81.0g/L as the result of three-step’s concentration; The experimental results indicated that the higher concentration of feed saline water was, the lower concentrating velocity of NaCl proceeded; and because of the serious water osmosis, the membranes reached the limitation when the concentration of salty water was81.0g/L and the concentrating process was hindered.