Reducing pumping energy by using different flow rates of high and low concentration solutions in reverse electrodialysis cells

Abstract

a b s t r a c tEnergy use for pumping affects both net energy recovery and operational costs of reverse electrodialysis (RED) systems. In order to reduce the energy needed for pumping, electrical performance and hydrodynamic power losses in a RED stack were investigated by simultaneously (2-140 mL/min) or independently varying the flow rates of the high concentration (HC, 35 g/L NaCl) and low concentration (LC, 0.35 g/L NaCl) solutions. Power was not consistently reduced at lower flow rates due to trade-offs between increases in diffusion boundary layer resistance and decreases in solution resistance of the LC channels. The maximum net power output ( $ 0.04 W) was obtained with both LC and HC flow rates at $ 20 mL/min. Separately varying the flow rates of the HC and LC solutions indicated that the optimum flow rate of the HC solution (10 mL/min) was much lower than that of the LC solution (20 mL/min) due to the more substantial impact of the LC channel on power production. The use of these two optimized flow rates minimized hydrodynamic power losses (pumping energy) while producing comparable power to that achieved with the two higher flow rates (50 mL/min of both HC and LC solutions).

Influence of solution concentration and salt types on the performance of reverse electrodialysis cells

“…The maximum power density of 0.62 W/m 2 -membrane here with HC of 3.6 M and LC of 0.14 M was within the range of previous results of 0.4-1.4 W/m 2 -membrane, although within the lower range of those power densities [14,18,19,36]. Differences in the studied conditions could all be a factor, including the relatively low flow rates (HC of 10 mL/min, linear velocity of 2.5 cm/min, LC of 20 mL/min, linear velocity of 5 cm/min) used here to reduce pumping energy as previously reported [32], the intermembrane distance of 0.5 mm which could be reduced using different spacers [39], and the permselectivity of the ion exchange membranes compared to those used by others [13,40]. Although the optimum HC and LC solution concentrations for other RED cells at different operating conditions might not be the same as those here, the general trends of RED performances with the different HC and LC solution concentrations would be similar to those observed here.…”

“…A fixed concentration of NaCl (35 g/L, 1 L) was recycled through both the anode and the cathode chambers at 100 mL min À 1 to avoid large pH changes in the anolyte or catholyte. The HC and LC solutions separately flowed through the HC and LC channels of the stack in a single pass mode at previously established optimum flow rates of 10 mL/ min for the HC solution, and 20 mL/min for the LC solution [32].…”

Novel bio-electro-Fenton technology for azo dye wastewater treatment using microbial reverse-electrodialysis electrolysis cell

“…On the other hand, the decoloration and the mineralization rate might not always be improved by increasing solution flow rates. It could be due to that the HC and LC flow rate was no longer the predominate limiting factor when it over a certain level (e.g., 1.0 mL min -1 in this study), since the electrical energy output in RED depends on the predominate resistance at a given HC and LC flow rate (Zhu et al, 2015).…”

Osmotically and Thermally Isolated Forward Osmosis–Membrane Distillation (FO–MD) Integrated Module

“…As disccused above, high DS flow rate is desired to enhance both FO and MD performances. However, high DS flow rate requires high energy consumption for the circulation 55. Therefore, the DS flow rate needs to be optimized by considering electric energy consumption and the performance of both FO and MD.…”