Performance enhancement of composite salt hydrate-based thermochemical energy storage unit

The structural optimization of a reactor in an open thermochemical energy storage (TCES) system utilizing composite salt hydrates is missing. This study concentrates on the structural optimization of a honeycomb reactor utilizing Wakkanai siliceous shale (WSS) combined with 9.6 wt.% LiCl by developing a three-dimensional numerical model considering coupled heat and mass transfer. Experimental validation of the model was performed for both thermal energy storage/release (TES/TER) processes. The length of the WSS + 9.6 wt.% LiCl unit inversely affects TES density. A thicker salt hydrate layer extends the duration of high outlet air temperature release but reduces the volumetric TES density due to elevated transfer resistances. A cross-sectional area ratio of the air channel at 0.45 demonstrates superiority in achieving high TES density. Furthermore, a hexagonal-shaped channel exhibits the highest TES density. From a fabrication perspective, adopting a TCES unit with a hexagonal shape, a 0.15 mm layer, and a cross-sectional area ratio of the air channel of 0.45 proves optimal for cyclic storage/release processes. The structured optimized WSS + 9.6 wt.% LiCl unit has shown a comparative TES density of 890 MJ·m−3, higher heat recovery efficiency of 92.6%, and lower regeneration temperature of 60°C compared to other TCES systems. Factors like cost, scalability, and integration with existing energy systems would be considered in future applications.