Reactivation mode investigation of spent CaO-based sorbent subjected to CO2 looping cycles or sulfation

Abstract

Rapid loss-in-capacity of naturally occurring limestone for CO2 capture is the most prominent issue in the calcium looping process. The synthesis of highly efficient sintering-resisting sorbents is a common solution to mitigate capacity decay. However, the long-term CO2 looping cycles, particularly in the presence of SO2, still cause the generation of large amounts of spent CaO-based sorbents. Comparatively, the reactivation of spent sorbent is more economical than the replenishing of fresh sorbent. In this work, three types of reactivation modes (i.e., hydration, simultaneous hydration/ impregnation and acidification) were applied to recover the CO2 capture capacities of the spent, synthetic CaO-based sorbents (CaO/MgO = 75 wt%/25 wt%). It is found that hydration is effective to recover the cyclic CO2 capture performance of the spent sorbent due to the formation of more cracks and channels that extend to the interior of sorbent particles. Therefore, the sorbent reactivated via sole hydration exhibits a high capacity of 0.390 g/g after 40 cycles. Moreover, NaCl impregnation combined with hydration produce lager amounts of macropores within the reactivated sorbents after initial sever sintering that are responsible for their desirable CO2 capture stability. The introduction of filtration during acidification reactivation process can effectively enhance the initial CO2 capture capacity (an improvement percentage of ~14.7%) owing to the removal of the irreversible CaSO4.