Model for Self-Reactivation of Highly Sintered CaO Particles during CO2 Capture Looping Cycles

Calcium looping is an emerging high-temperature, energy-efficient, CO2, capture technology using CaO as a regenerable sorbent of CO2 through the reversible carbonation/calcination reaction. The stability of the sorbent plays a key role in the design of these systems. This paper revisits the self-reactivation phenomenon that has been reported for some highly deactivated CaO materials when submitted to repeated carbonation/calcination cycles under certain conditions. Self-reactivation is modeled in this paper as the result of a dynamic balance between the loss of activity in one cycle and the accumulated gain of activity by extended carbonation times, because of a product layer of CaCO3 that keeps building up on all surfaces, controlled by the slow diffusion of CO2. Tie model describes reasonably well the trends observed for some limestones and conditions. For other limestones and conditions, the carbonation mechanism is more complex and the model does not fit the evolution of the maximum Ca conversion with the number of cycles as well, although the general patterns of self-reactivation are still well-reproduced.