Reactivation by steam hydration of sorbents for fluidized-bed calcium looping

The present study addresses steam hydration as a tool for reactivation of the CO2 capture potential of spent limestone-based sorbents from fluidized-bed calcium looping systems. A reference, high-calcium, reactive limestone was deactivated by carrying out lab-scale fluidized-bed calcium looping process tests (calcination at 940 °C in a 70% CO2 atmosphere and carbonation at 650 °C in a 15% CO2 atmosphere) and then steam-hydrated (at 250 °C in a 50% steam atmosphere) in the same fluidized bed, for times ranging from 10 to 60 min. Online flue gas analysis, continuous capture of the elutriated fines, and evaluation of particle size distribution were performed during additional calcium looping process tests after sorbent reactivation. Thermogravimetric analysis, scanning electron microscopy, and porosimetry were directed to characterize the microstructural features of the spent and steam-hydrated sorbents. Moreover, the different materials were subjected to ex situ impact fragmentation tests. In this way, it was possible to investigate the effect of the hydration time on the changes in the physicochemical and microstructural properties induced by the hydration treatment, the reactivation of the sorbent CO2 capture capacity, and the attrition/fragmentation tendency of the reactivated materials.