Effects of porous carbon materials on heat storage performance of CaCl2 hydrate for low-grade thermal energy

Abstract

Thermochemical energy storage (TES) is a promising technology to overcome supply-demand mismatch in the recycling of low-grade industrial waste heat. A novel sorbent is developed for low-grade TES system by employing an ordered mesoporous carbon, CMK-3, as the matrix of CaCl₂ hydrates. Expanded graphite (EG) and activated carbon (AC) as matrixes are also discussed for a comparative study. All the composites show quick kinetic within 120 °C. Salt upload ability and heat storage capacity of the composites follow the order of CMK-3/CaCl₂ (2037.2 kJ kg⁻¹, 50.4 wt%) > EG/CaCl₂ (1637.6 kJ kg⁻¹, 48.1 wt%) > AC/CaCl₂ (1221.8 kJ kg⁻¹, 46.3 wt%). CMK-3/CaCl₂ show the best heat storage performance due to the ordered tubular mesostructure, which limits the deliquescence at a proper level and provided good accommodation for salt solution. The inner solution absorption presents positive thermal effect that add to total heat storage capacity, making actual heat sorption of CMK-3/CaCl₂ much higher than pure chemical reaction heat. A 25-cycle sorption–desorption experiment shows excellent cycling stability of CMK-3/CaCl₂. This study proves CMK-3/CaCl₂ to be a promising composite for low-grade TES system below 120 °C, and provides new insights for improving energy density of the heat storage materials.