Determination of CaO Carbonation Kinetics under Recarbonation Conditions

This work investigates the kinetics of the reaction of CO2 with CaO particles partially carbonated that are forced to increase their carbonate content at high temperatures in an atmosphere of rich CO2. This additional recarbonation reaction on particles that have already completed their fast carbonation stage is the basis of a novel process that aims to increase the CO2 carrying capacity of sorbents in calcium looping CO2 capture systems. The CaO reaction rates and the maximum carbonation conversions after the recarbonation step were measured on a thermogravimetric analyzer, and the results indicate that they are highly dependent upon the temperature and CO2 partial pressure, with steam also being a contributing factor. The reaction mechanism governing the reaction rates during the carbonation and recarbonation reactions is explained by the combined control of the chemical reaction and CO2 diffusion through the CaCO3 product layer. An extension of the random pore model adapted to multi-cycled CaO particles was successfully applied to calculate the CaO molar conversion as a function of the time and the recarbonation conditions, using kinetic parameters consistent with previously published results on carbonation kinetics under typical flue gas conditions.