Performance improvement of LiBr-H2O reverse electrodialysis unit for heat to power conversion with finite solution flowrate and large concentration change

Abstract

The reverse electrodialysis heat engine is an emerging technology that converts low-grade heat into electric power. However, the conventional reverse electrodialysis unit, developed based on the “infinite” flowrate assumption, fails to effectively utilize salinity gradient power produced by the regeneration unit that operates under a certain concentration gradient. In this study, a novel LiBr-H2O reverse electrodialysis unit based on the “finite” flowrate assumption is investigated to match the regeneration unit better. The resistance-distributed mathematical model is built and experimentally validated, considering that the resistance along the flow channel shows more significant variation under the condition of finite flowrate and large concentration change. Results show that the finite flowrate assumption is more suitable for the reverse electrodialysis heat engine application, and the utilization rate of Gibbs free energy can reach 99.8 %, indicating that the novel reverse electrodialysis unit is well-matched with the regeneration unit. The valuable salinity gradient power is nearly completely recovered. As a result, the maximum overall efficiency of the novel reverse electrodialysis unit is 28.6 %, which is superior to that of the reverse electrodialysis unit with a recirculating arrangement and comparable with the reverse electrodialysis unit with serious membrane stacks. Moreover, the technical economy and the exergy efficiency of the novel reverse electrodialysis unit are better than the rest. This work proves the capacity of a LiBr-H2O reverse electrodialysis unit based on a “finite” flowrate assumption as a more adaptable arrangement for the REDHE applied for efficient capture of the widespread low-grade energy.