Evaluation of K2CO3/H2O system for Thermal Storage and Heat Pumps: Insights from Experimental Studies

Abstract

Salt-hydrate-based thermochemical energy storage (TCES) systems are emerging as promising candidates for thermal applications due to their high energy density, cost-effectiveness, safety, and long-term storage possibilities. The hydration and dehydration of salt hydrates, driven by the pressure-temperature relationship, enable thermal storage, cooling, and heat pumping. Among the various salt hydrate systems under investigation, potassium carbonate (K2CO3) has garnered significant interest due to its favourable thermochemical properties and its flexibility to operate in open reactor systems with direct heat transfer. Given the growing demand for efficient and sustainable energy solutions, it is essential to evaluate the performance characteristics of K2CO3 under relevant operating conditions to ensure its successful deployment in practical applications. This study investigates the feasibility of K2CO3/H2O for thermal storage and heat pump applications through experiments conducted at pressures below 1 bar and temperatures ranging from 100 to 150 ℃. Initially, thermogravimetric analysis (TGA) experiments are conducted to identify its operating characteristics. By analyzing the material’s hydration and dehydration behaviour, its energy storage capacity, reachable temperature lift, and cyclic stability are assessed. This research focuses on the feasibility analysis of K2CO3/H2O for heat pump systems at high vapour pressures and temperatures. Preliminary results indicate that K2CO3 exhibits favourable hydration and dehydration characteristics, making it a viable candidate for thermal applications. The TGA results demonstrate that heat discharge is achievable at 130 ℃ with water vapour at 870 mbar, indicating a potential temperature lift of more than 30 ℃. It was observed that hydration requires significantly higher vapour pressures than those reported in the literature, such as approximately 320 mbar at 105 ℃. Four TGA cycles, alternating between hydration at 105 ℃ and dehydration at 150 ℃, demonstrated complete reversibility and thermal stability. Furthermore, understanding the influence of pressure and temperature on K2CO3 performance is crucial for tailoring its integration into heat pump applications, where dynamic operating conditions are common.