(580e) The Influence of Reactivation By Steam Hydration on Attrition of Sorbent Particles in Ca Looping Applications

The present study addresses steam hydration as a reactivation technique of the CO₂ capture ability of spent limestone-based sorbents from fluidized bed calcium looping systems. A reference, high-calcium, reactive limestone was first deactivated by carrying out lab-scale fluidized bed calcium looping tests (calcination at 940°C in a 70% CO₂ atmosphere; carbonation at 650°C in a 15% CO₂ atmosphere), and then it was 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 analysis of particle size distribution were performed during additional calcium looping tests after sorbent reactivation. Thermogravimetric analysis, scanning electron microscopy and porosimetry were directed to characterize the microstructural features of the spent and the 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 following aspects: the changes in the physico–chemical and microstructural properties induced by the hydration treatment; the reactivation of the sorbent CO₂ capture capacity; the attrition/fragmentation tendency of the reactivated materials.

It was observed that steam hydration followed by dehydration of the reactivated sorbent in the hot fluidized bed developed an increased porosity, hence improved the rate and the extent of the CO₂ uptake. At the same time also the attrition and fragmentation propensity of the reactivated sorbent was increased. For the given limestone, the optimal trade off between sorbent reactivity/uptake and mechanical strength was achieved after 60 min hydration of the spent sorbent, but it is expected that this result cannot be generalized, as it is critically dependent on the specific sorbent texture. The comparison between water and steam hydration of the spent sorbent as a reactivation means indicated that steam hydration is more favourable than water hydration. Albeit the latter gave rise to a larger water uptake, the prolonged soaking in liquid water made the reactivated sorbent more susceptible to attrition.