Five different fly ashes and their carbon-free derivatives from commercial-scale circulating fluidized-bed combustion (CFBC) boilers were hydrated with liquid water or steam, to determine whether hydration would improve sorbent utilization in the samples under fluidized-bed combustion conditions. After hydration by water, for one fly ash (FA1) and two carbon-free fly ashes (FA2-A and FA3-A), the capacity of the ashes for taking up SO2 showed limited improvement; however, hydration was not effective in reactivating the remaining samples. Generally, for these fly ashes, reactivation by hydration with either liquid water or steam seemed to be less promising than that for bed ashes, which have been shown to exhibit significant improvement in sulfur capture during resulfation. Hydration, whether by steam or liquid water, is not recommended for fly ash, which has a very limited residence time in the boiler, because of its small particle size. This paper recommends alternative strategies.