Exergy Analysis of Reverse Electrodialysis Heat Engine with Multi-Effect Distillation Regeneration Stage

Abstract

The increasing worldwide energy demand is rising the interest on alternative power production technologies based on renewable and emission-free energy sources. In this regard, the closed-loop reverse electrodialysis heat engine (RED-HE) is one of the most promising technologies currently under investigation. This technology produces electric power by harvesting the salinity gradient energy released from the controlled mixing of two artificial salt solutions with different concentrations. Low-grade heat (T < 100 °C), derived from any industrial process is used in a multi-effect distillation (MED) unit to restore the initial salinity gradient of the solutions. In this work, a comprehensive exergy analysis at component level is applied to the RED-MED HE, determining the potential of the waste heat to power conversion. In particular, sensitivity analyses have been performed to assess the influence of the main operating conditions (i.e. solutions concentration and velocity) and design features (stack aspect ratio), identifying the most advantageous scenarios. Also, the effect of new generations of high performing membranes has been considered. Results show that using high-performing membranes, inlet solutions concentration and velocity of 3.87 – 0.01 M and 0.25 – 0.82 cm/s, respectively, and a stack of 0.24  1.03 m (width-to-length), a global exergy efficiency of 26.5% is reached.