Hydration-induced reactivation of spent ashes from fluidized bed desulphurization: a comparison between real and simulated bottom ashes

The present study addresses the effectiveness of the reactivation by water hydration of fluidized bed spent ashes. Two materials have been considered in the study, namely bottom ash form the operation of a full-scale utility boiler, and exhausted sorbent particles sulphated in a laboratory-scale reactor (simulated bottom ash). Comparison between the hydration/reactivation behaviour of the two ashes was carried out with the purpose of understanding to what extent simulated lab-scale operation could be representative of the full-scale process. Hydration-induced reactivation was very effective on both samples in promoting further sulphur capture upon re-injection of the hydrated material in the fluidized bed reactor. However, differences in the reactivation behaviour of the two samples were observed. A pronounced redistribution of sulphur in the particles upon hydration was evident for the simulated bottom ash, providing a key pathway to enhanced sulphur uptake. On the other hand, this redistribution mechanism was not detected for the full-scale bottom ash. Possible reasons for this discrepancy may be related to the different residence times and temperatures histories experienced by the two samples during their fluidized bed processing.