The effect of flow modes on the capture of the energy between concentrated brine and seawater by reverse electrodialysis

The discharge of concentrated brine from the desalination unit waste amounts of salinity gradient energy, which could be harvested and converted to electric energy by reverse electrodialysis (RED). However, the poor power and restricted conversion efficiency obstacle its development. A suitable flow mode of feed solutions in a RED stack can improve energy conversion efficiency. Here, the influences of co- and counter-current flow modes on the performances of a single-stage RED stack and multi-stage stacks harvesting the energy are studied in the work. Based on this, the models of flow mode affecting the RED performances are built and experimentally verified. Results show that the counter-current in a single-stage stack is better than the co-current, and the advantage is more obvious with the concentration increase of the concentrated solution, the concentration decrease of the diluted solution, and the decrease of flow rate. Besides feed parameters, the stack sizes also influence the performances of the single-stage stack in both modes. The counter-current in the multi-stage stacks is also more excellent than the co-current. However, the difference decreases with the increase of stage number. This work provides some support for utilizing the salinity gradient energy between concentrated brine and seawater.

Automated summary

This study investigates the effect of ideal flow modes on the conversion efficiency of reverse electrodialysis (RED) for harnessing salinity gradient energy. Models of flow mode influencing RED performances are built and experimentally verified. Results show that counter-current flow mode is superior to co-current flow mode in a single-stage RED stack, especially with increasing concentration of the concentrated solution, decreasing concentration of the diluted solution, and decreasing flow rate. In multi-stage stacks, counter-current flow mode remains better than co-current flow mode, but the difference decreases with increasing stage number. This study provides support for utilizing the salinity gradient energy between concentrated brine and seawater.