Reactivation by water hydration of the CO_2 capture capacity of a calcium looping sorbent

摘要

The potential of water hydration as a mean to reactivate a spent reactive limestone-based sorbent used in a fluidized bed calcium looping process for CO_2 capture is demonstrated. The study has been specifically targeted at investigating the changes of sorbent properties induced by hydration, and the influence that this treatment had on the CO_2 capture capacity and on the attrition tendency of the reactivated material. To this end, the spent sorbent obtained from calcium looping tests in a lab-scale fluidized bed reactor (calcination at 940 ℃ in 70% CO_2, carbonation at 650 ℃ in 15% CO_2) was hydrated at 25 ℃ for times ranging from 10 to 60 min, and characterized by TG, SEM and porosimetric analyses. The hydrated materials were further subjected to calcium looping cycles under the same operating conditions, and the CO_2 capture capacities, the elutriation rates and the particle size distributions after each stage were measured and compared with those obtained in the tests before reactivation. It is demonstrated that hydration is effective in reactivating the spent sorbent: the CO_2 capture capacity increased from 0.04 g g~(-1) (last carbonation before hydration) to 0.32-0.37 gg~(-1) (first carbonation after hydration). The capacity, however, rapidly decayed along with the cycles. Results suggested that the CO_2 capture capacity, the sorbent properties and the attrition tendency are linked one to the other. The sorbent hydrated for the longest time (60 min) not only developed an enhanced active porosity, but was also characterized by a limited attrition tendency (with respect to the material hydrated for 10 min). Notably, results obtained in the present study differed from those obtained in a previous study on a different limestone, highlighting the importance of sorbent reactivity for an optimally tailored sorbent regeneration process.