Reactivation of fluidized bed calcium looping sorbents by steam hydration

This paper deals with steam hydration as a reactivation technique of the CO2 capture potential of spent limestone-based sorbents from fluidized bed (FB) calcium looping (CaL) systems. A reference, high-calcium, reactive limestone was deactivated by carrying out lab-scale FB-CaL tests (calcination at 940°C in a 70% CO2 atmosphere; 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. On-line flue gas analysis, continuous capture of the elutriated fines and particle size distribution analysis were performed during calcination/carbonation stages, while thermogravimetry, scanning electron microscopy and porosimetry were employed as experimental techniques to characterize the spent and the steam hydrated sorbents. In this way, it was possible to focus the attention, taking into account the effect of the hydration time, on the changes in the physico–chemical and microstructural properties induced by the hydration treatment, on the reactivation of the sorbent CO2 capture capacity, and on the effect that this reactivation technique has on the attrition/fragmentation tendency of the reactivated materials.