Cohesive behavior of CaO-based particles in fluidization during CaO/CaCO3 heat storage process: Experiments and molecular dynamics simulations

Abstract

CaO/CaCO3 heat storage is considered a promising technology to solve the intermittency of solar energy. Fluidized-bed reactor is commonly used as calciner/carbonator to efficiently achieve heat storage. In the fluidized-bed reactor, the particle cohesion impedes fluidization of CaO/CaCO3 particles, adversely impacting heat storage. However, the current research rarely focuses on the cohesive behavior of CaO-based particles in fluidization during CaO/CaCO3 heat storage process. Furthermore, current research on cohesive behavior primarily focuses on experimental studies, lacking an explanation of the underlying mechanisms at the molecular level. In this work, the cohesive behavior of CaO-based particles in CaO/CaCO3 heat storage process was studied on a fluidized-bed reactor. The particle cohesion is reflected by the tensile yield strength during the transition from static state to fluidization state. The results indicate that the cohesive behavior of CaCO3 particles gradually is strengthened with increasing temperature. The tensile yield strength of CaCO3 particles at 800 °C is 1770 Pa, which is 200 % higher than that at 500 °C. Additionally, the carbonation enhances the cohesive behavior of CaO particles. The tensile yield strength of CaO particles after the carbonation is 55 % higher than that of before the carbonation. The enhanced cohesive behavior of CaO particles during the carbonation results in the defluidization. Molecular dynamics simulation shows that the formation of sintering necks at above 650 °C in the carbonation stage results in cohesive behavior of CaO particles. The introduction of 5 % Al2O3 fines (50–75 μm) as lubricant effectively improves the fluidization quality of CaO particles in the carbonation stage, thereby enhancing the exothermic performance of CaO particles. These findings provide valuable insights for the industrial application of CaO/CaCO3 heat storage in fluidization.