Reactivation by water hydration of spent sorbent for fluidized-bed combustion application: influence of hydration time

A spent limestone sorbent, generated by fluidized-bed desulfurization under simulated combustion conditions, was reactivated by means of hydration with water at 25 °C for times ranging from 10 min to 24 h. A bench-scale fluidized-bed reactor was used to assess sulfur uptake of the original and reactivated sorbent. A combination of XRD, porosimetric, and computer-controlled SEM analyses was used to assess hydration-induced microstructural and chemical modifications of sorbent samples. The ultimate degree of calcium conversion of the exhausted sorbent was 28%. The ultimate degrees of calcium conversion of reactivated/resulfated sorbents ranged from 45% to 53%. A nonmonotonic influence of the hydration time on the ultimate sulfur uptake of reactivated sorbents was observed, which was explained in the light of the competition between the following phenomena: particle swelling, change of pore volume, sulfur redistribution, particle attrition/fragmentation. Two optimal hydration times were found, one on the order of minutes and the other on the order of some hours. Samples hydrated for shorter time showed less propensity to attrition/fragmentation than samples hydrated for long times