Enhancement of sulfur uptake by hydration of spent limestone for fluidized-bed combustion application

The reactivation of spent limestone generated by-fluidized-bed desulfurizat ion of simulated flue combustion gases was studied. The regeneration techni que consisted of spent sorbent hydration by immersion in water under contro lled conditions. The effectiveness of the reactivation process was assessed by re-injection of the hydrated material in a fluidized-bed reactor under simulated desulfurization conditions. At the same time, the influence of hy dration on the propensity of limestone to undergo attrition was evaluated b y following the changes of particle size-distribution and by collection of elutriated fines during sorbent utilization in the fluidized-bed reactor. T he total calcium sulfation degree of hydrated samples was nearly twice that of the: original spent sorbent. Apparently, reactivation did not bring abo ut any significant enhancement of limestone attrition upon re-injection int o the fluidized:bed. Mechanistic aspects of sorbent reactivation were inves tigated with the aid of computer-aided scanning electron microscope-energy- dispersive X-ray analysis mapping of polished cross sections of sulfated, h ydrated, and resulfated limestone particles. This analysis highlighted a pr onounced redistribution of sulfur in the particles upon hydration that appa rently provides the key pathway to enhanced sulfur uptake.