Thermochemical heat storage performance of CaO particles under fluidization in coupled CaO/Ca(OH)2 cycles and CaO/CaCO3 cycles

Abstract

The sintering of CaO in CaO/CaCO3 heat storage cycles and the agglomeration of CaO in CaO/Ca(OH)2 heat storage cycles are the main reasons for the decay in heat storage performance of CaO-based materials, respectively. In this work, a novel CaO/Ca(OH)2/CaCO3 coupling process using limestone under fluidization was proposed to realize the sequential CaO/Ca(OH)2 heat storage and CaO/CaCO3 heat storage. The exothermic performance of CaO particles under fluidization in the CaO/Ca(OH)2/CaCO3 coupling heat storage process were investigated. Two coupling modes were compared according to the different feeding methods of fresh CaO particles. The maximum exothermic temperature of CaO particles in the optimal coupling mode reaches 456.9 °C in the first CaO/Ca(OH)2 cycle and 783.8 °C in the first CaO/CaCO3 cycle, respectively. The interaction mechanism between CaO/CaCO3 heat storage cycles and CaO/Ca(OH)2 heat storage cycles was determined. The volume shrinkage caused by the sintering of CaO in CaO/CaCO3 cycles improves the volumetric energy density of CaO particles in CaO/Ca(OH)2 cycles. After introducing 10 CaO/CaCO3 cycles in the first coupling step, the energy density of CaO particles in CaO/Ca(OH)2 cycles is improved by 190 %. The CaO/Ca(OH)2 cycles reactivate carbonation activity of CaO particles in CaO/CaCO3 cycles by increasing porosity of CaO. Therefore, after introducing 10 CaO/Ca(OH)2 cycles in the first coupling step, the carbonation conversion of CaO particles increases by 64.7 %. This work provides a novel and promising heat storage process by integrating efficient CaO/Ca(OH)2 and CaO/CaCO3 cycles under the fluidization.