Bed and fly ashes originating from industrial-scale fluidized bed combustors (FBCs) were steam hydrated to produce sorbents suitable for further in situ desulphurization. Samples of the hydrated ash were characterized by X-ray diffraction analysis, scanning electron microscopy and porosimetry. Bed ashes were hydrated in a pressure bomb for 30 and 60 min at 200 degrees C and 250 degrees C. Fly ash was hydrated in an electrically heated tubular reactor for 10 and 60 min at 200 degrees C and 300 degrees C. The results were interpreted by considering the hydration process and the related development of accessible porosity suitable for resulphation. The performance of the reactivated bed ash as sulphur sorbent improved with a decrease of both the hydration temperature and time. For reactivated fly ash, more favourable porosimetric features were observed at longer treatment times and lower hydration temperatures. Finally, it was shown that an ashing treatment (at 850 degrees C for 20 min) promoted a speeding up of the hydration process and an increase in the accessible porosity. (C) 2008 Elsevier Ltd. All rights reserved.