Kinetics of Calcination of Partially Carbonated Particles in a Ca-Looping System for CO2 Capture

Post-combustion CO 2 capture based on the Ca-looping process (CaL) is a promising technology under development based on the reversible reaction between CaO and CO 2 to form CaCO 3 and the regeneration of CaO by calcination of CaCO 3 in a rich CO 2 atmosphere. This work is focused on the study of the calcination kinetics with typical solid conditions expected in these systems. Calcination rates of carbonated materials derived from two limestones have been measured at different numbers of carbonation–calcination cycles, as a function of the temperature and CO 2 partial pressure. It has been observed that the calcination reaction is chemically controlled for particles below 300 μm of particle size, because internal mass transfer is negligible even under the presence of CO 2 in the reaction atmosphere. The calcination rate (expressed per moles of initial CaO) depends upon the calcination temperature and CO 2 partial pressure, whereas the CaCO 3 content and/or particle lifetime do not affect the reaction rate. The basic kinetic model by Szekely and Evans is shown to be valid to fit the new data. On the basis of these results, it is shown that calcination temperatures between 880 and 920 °C could be sufficient to achieve nearly complete calcination conversion at a typical solid residence time of circulating fluidized-bed calciner reactors (2–3 min) in the CaL system.