Influence of Steam Injection during Calcination on the Reactivity of CaO-Based Sorbent for Carbon Capture

Calcium looping is an emerging CO2 capture technology based on cyclic calcination/carbonation reactions using calcium-based sorbents. Steam is typically present in flue/fuel gas streams from combustion or gasification and in the calciner used for sorbent regeneration. The effect of steam in the calciner on sorbent performance has received little attention in the literature. Here, experiments were conducted using a thermogravimetric analyzer (TGA) to determine the effect of steam injection during calcination on sorbent reactivity during carbonation. Two Canadian limestones, Cadomin and Havelock, were tested, and various levels of steam (up to 40%) were injected in the sorbent regeneration process for 15 calcination/carbonation cycles. All concentrations of steam examined were found to increase sorbent reactivity for carbonation for both sorbents. In these experiments, 15% steam concentration with calcination had the largest impact on carrying capacity for both sorbents. Steam changes the morphology of the sorbent while calcination is occurring, probably causing a shift from smaller to larger pores, resulting in a structure which increases carrying capacity. It was also demonstrated that steam addition produced a larger impact on sorbent reactivity for carbonation than for calcination.