Self-compensation and attenuation mechanisms of carbide slag in multicycle thermochemical heat storage

Utilizing industrial solid waste carbide slag for thermochemical heat storage presents an inexpensive and highenergy-storage-density solution with potential industrial applications. Investigating the performance of carbide slag in thermochemical heat storage cycles can offer insights for efficient resource utilization within the field of heat storage. This study examined the characteristics of cyclic heat storage (dehydration) and heat release (hydration) of carbide slag by establishing a multicycle thermochemical heat storage experimental system combined with advanced characterization techniques. We found that carbide slag underwent complete dehydration and incomplete hydration. The decrease in pore volume within the 3-11 nm pore size range in the dehydrated carbide slag product was the primary cause for the diminishing hydration conversion with increasing cycles. The change in the Ca(OH)2 content, serving as an effective thermochemical heat storage material within the carbide slag, primarily resulted from the gain effect of CaCO3 conversion and the loss effect of incomplete CaO hydration. Based on this phenomenon, we proposed the mechanisms of self-compensation and attenuation of carbide slag during thermochemical heat storage cycles using nitrogen as the direct-contact heat transfer fluid. When air (containing 400 ppm CO2) was used as the direct-contact heat transfer fluid, the thermochemical heat storage capacity of the carbide slag decreased from the initial 805.2 J/g to 205.7 J/g after 20 cycles. Our findings provide valuable guidance for regulating the multicycle heat-storage performance of carbide slag.