Continuous power production using flowable electrodes based on waste-heat assisted capacitive mixing

Abstract

• A thermally assisted capacitive mixing system is proposed for harvesting low-grade heat. • The system can produce power continuously via adopting multiple electrode flow capacitors. • Various parameters are adjusted to optimize the performance of the system. • The thermal efficiency of the system is calculated based on the exergy analysis. • The temperature effect contributes to an increase in the power density of the system by a factor 1.5. The capacitive mixing method generates energy through spontaneous ionic mixing caused by the salinity gradient between sea and river waters. We introduce a continuous thermal regenerative system to combine an intermittent cycle with electrode flow capacitors using flowable slurries as electrodes to improve the efficiency of the existing capacitive mixing method by adding low-grade heat as another energy source. A continuous harvesting system was constructed to utilize the capacitive Donnan potential effect by switching the temperature and salt concentration with four separate reactors and two flow-electrode slurries. Experiments were conducted for continuous cycle operations by varying the active carbon and salt concentrations of the slurry as well as a single electrode flow capacitor test to evaluate the contributions of two different energy sources, i.e. , concentration and temperature differences. The continuous cycle operation was further optimized, resulting in a maximum power density of 3.84 mW/m 2 . Based on the exergy analysis, the theoretical thermal efficiency of the thermally–assisted continuous system was calculated at 10.8%. Waste-heat energy was successfully used for continuous power production using an electrode flow capacitor, and a continuous power generation cycle was implemented by combining the concentration and temperature differences without supplying external power.