Pore-size and shape effects on the recarbonation performance of calcium oxide submitted to repeated calcination/recarbonation cycles

The use of carbonation/calcination cycles of CaO/CaCO3 is emerging as a viable technique for the capture of Co-2 generated in the combustion of coals for power generation. Specifically, the choice of natural limestones as CO2 carriers is an attractive option because they are cheap and abundant materials, although previous studies indicate that the reactivity of the calcines toward CO2 rapidly drops with cycling. This paper reports on the effects of the internal morphology of CaO particles on their capability of absorbing CO2. Calcines of a natural limestone with different initial textures were repeatedly submitted to carbonation/calcination conditions (up to 100 cycles). The textural evolution, as well as the carbonation conversion, of the calcined and recarbonated samples was followed along the experiments. In addition to the known mechanisms of deactivation due to grain growth and limited diffusion of CO2 through the product layer, we have found that pore closure is also taking place in our samples, together with an overall shrinkage of the particle. All of these factors play a role in limiting the maximum carbonation conversions to around 10% after just 100 cycles.