Thermal Analysis Kinetics Of CO₂Capture From Cement Industrial Flue Gases By Calcium-based Sorbents

To develope a technology of CO₂capture from cement industrial flue gases by acombination of oxygen-enriched combustion and calcium based sorbents in a cyclicprocess of calcination and carbonation, investigation were carried out to study thekinetics of limestone thermal decomposition and CaO carbonation in a stacked state anda simulated suspension state respectively under a high CO₂concentration condition（C CO₂≥30%）. The results showed that:Under a stacked state or a simulated suspension state, limestone thermaldecomposition process coud be both modelled as a randomly nucleation, accompaniedby its growth. The reaction order of limestone thermal decomposition varied from2/5to3/4under different CO₂concentrations. The higher the CO₂concentration was, thehigher activation energy E and pre-exponential factor lnA could be. It was measured andcalculated that the activation energy varied from958.28to2556.10kJ/mol and thepre-exponential factor lnA changed from103.67to242.44. In addition, the activationenergy E rised exponentially with an increase of CO₂concentration in a stacked state,fllowed a relationship as E_αâ†'0=655.19e^1.4CCO₂。.Under a stacked state and a simulated suspension state, the mechanism of CaOcarbonation in chemical control phase followed a model of randomly nucleation and itsgrowth. It was calculated that the activation energy varied from86.77to187.46kJ/mol,the pre-exponential factor lnA was from5.9to19.94. In the diffusion controlled phase,however, the reaction mechanism followed a model of spherical interface contractionreaction, where the required reaction activation energy E could be between138.70and 275.44kJ/mol, the pre-exponential factor lnA from10.29to27.56. The higher the CO₂concentration was, the lower activation energy of CaO carbonatation was needed.Containing a certain amount of dolomite in limestone was in favor of limestonedecomposing and CaO carbonating. The smaller the limestone particle size was, thelower activation energy and pre-exponential factor lnA were required for limestonedecomposition and CaO carbonation.Under the same CO₂concentration, both the activation energy E and thepre-exponential factor lnA of limestone thermal decomposition and CaO carbonationin a simulated suspension state were lower than those in a stacked state.