Kinetics of CaCO3 decomposition at low CO2 partial pressure in a vacuum fixed bed

Abstract

Calcium looping often suffers from sintering during CaCO₃ decomposition process, and CaCO₃ decomposition in vacuum is a potential solution. Kinetic analysis of CaCO₃ decomposition in vacuum is seldom, and most of the kinetics in the literature is obtained from thermogravimetric analyzer in atmospheric pressure. In addition, the reported kinetic data seems scattered, and varies depending on the analyzer employed. This study is focused on the intrinsic kinetics of isothermal CaCO₃ decomposition in a vacuum fixed bed from 700 °C to 850 °C. Besides conventional internal/external mass transfer elimination via reducing size/increasing gas velocity, the effect of CO₂ partial pressure is specially discussed under vacuum condition. It is found that, this influence could be eliminated only when the relative difference between equilibrium pressure and maximum CO₂ partial pressure (P_eq -P*_CO2)/P_eq was higher than 0.98. Tests at atmospheric pressure were also conducted with the same particle size and gas volumetric feeding rate for comparison. The intrinsic reaction rate constants of CaCO₃ decomposition in vacuum are 1.05 × 10^-3 s⁻¹– 4.76 × 10^-3 s⁻¹ between 700 °C and 850 °C, and the activation energy of this reaction is 92.58 kJ/mol.