Cost comparison and efficiency modeling in the electrodialysis of brine

The separation performance of Na+ ions from NaCl solution has been investigated by electrodialysis at constant voltage mode of operation. TS-1-10 electrodialysis equipment (Tokuyama) modified with rotameters was employed in experimental studies. During an unsteady-state run of the ED system, both inlet and outlet concentrations of both concentrate and dilute streams were measured at time intervals of 5 min until the current drops to less than 0.01 A. The effects of parameters such as electrical potential applied (DC) and flow rate of streams on the performance of separation were observed. The efficiencies of each run were evaluated as specific power consumption with the electrical energy consumed only in stack. Current efficiency was represented as a function of flow rate, which is based upon the mass transfer coefficient. The model proposed was in very good agreement at all flow rates at low potential applied, however, at the highest flow rate at other potentials, small deviations were found.

Within the range of potentials and flow rates applied in the ED system (TS-1-10 Tokuyama), a cost analysis and a model development were carried out for the brine containing 580 mg Na+/L. Although the higher the potential applied, the shorter the operation time of desalination, high values of specific power consumption were obtained at all flow rates. Specific power consumption was not so sensitive to the change in flow rate. A detailed cost analysis covering other cost items is needed to find the optimum process condition in an ED system. The approach to relate the electrical efficiency to the flow rate of dilute stream was based upon the resistance in mass transfer. Model estimates for 5 and 10 V were in very good agreement with the experimental data. However, the parameters determining the electrical resistance of solution for different sets were expected to remain constant irrespective of the potential or flow rate chosen.