Ca3B2O6-modified papermaking white mud for CaCO3/CaO thermochemical energy storage

CaCO 3 /CaO thermochemical energy storage based on concentrated solar power plant is a promising technology because of its high working temperature and energy storage capacity. Papermaking white mud (PWM) from paper mill is a potential CaO-based precursor due to its high content of CaCO 3 . Herein, a novel Ca 3 B 2 O 6 -modified PWM was synthesized to examine its thermochemical energy storage performance. The influences of the types and dopant amounts of B 2 O 3 precursors on the energy storage capacity of Ca 3 B 2 O 6 -modified PWM were discussed. The stable Ca 3 B 2 O 6 -modified PWM with the mass ratio of CaO to Ca 3 B 2 O 6  = 88:12 exhibits superior energy storage performance and heat transfer property during CaCO 3 /CaO cycles. The effective conversion and energy storage capacity of Ca 3 B 2 O 6 -modified PWM are approximately 0.67 and 2129.6 kJ/kg at 31st cycle, respectively, which are 2.48 and 1.76 times as high as those of PWM and pure CaCO 3 , respectively. The introduction of Ca 3 B 2 O 6 improves the sintering resistance and thermal conductivity of PWM, resulting in higher cyclic stability and lower decomposition temperature of CaCO 3 . Ca 3 B 2 O 6 enhances the basicity and improves the strong basic sites of PWM, which is beneficial for the adsorption of CO 2 , leading to greater CO 2 adsorption capacity. Moreover, Ca 3 B 2 O 6 increases the oxygen vacancy concentration of PWM, which is conducive to the diffusion of O 2– and production of CO 3 2– , further improving energy storage capacity. Hence, Ca 3 B 2 O 6 -modified PWM seems to be a suitable energy storage material for the CaCO 3 /CaO process.