Porous potassium carbonate granules with enhanced diffusion kinetics for thermochemical heat storage

The caking phenomenon poses a significant challenge in thermochemical heat storage systems, which arises from the agglomeration of powdered salt hydrates. This impedes the flow of gas molecules through the reactor bed and negatively impacts the reactions kinetics, leading to decreased overall efficiency of heat storage. To tackle this challenge, an innovative approach is proposed, involving the synthesis of porous potassium carbonate (K₂CO₃) granules using potassium bicarbonate (KHCO₃) as a pore former in varying ratios of 10, 20, 40, and 50 wt%. It is essential to note that the maximum amount of KHCO₃ for effective granulation is around 50 wt% of the total batch, as exceeding this limit prevents granule formation. This method results in the formation of porous K₂CO₃ granules that are 100% pure and free from any additives that could impact the energy density. In terms of diffusion kinetics, the granules with 40 wt% (K40) and 50 wt% (K50) of KHCO₃ demonstrated significant improvements in effective diffusion coefficients in comparison with the K₂CO₃ granule without pore former. Regarding cyclic performance, K₂CO₃ granule without pore former showed slow kinetics and incomplete hydration even after 10 cycles. In contrast, the K40 and K50 granules demonstrated significantly faster hydration kinetics, with K40 achieving complete hydration by the 4th cycle and K50 reaching the highest water loading capacity of 1.5 mol_H2O/mol_K2CO3 from the first cycle. The K50 granule, with a hydrated state density of 1.74 g/cm³, achieved a volumetric energy density of 0.96 GJ/m³. Compared to other developed granules, K50 exhibited superior hydration kinetics, positioning it as a promising candidate for thermochemical heat storage applications. This study highlights the potential of modifying pore structure to improve the efficiency of thermochemical heat storage and demonstrates that the wet granulation technique can be effectively utilized for the mass production of salt hydrate granules.