Industrial & Engineering Chemistry Research, Vol.43, No.18, 5715-5720, 2004
Cyclic steam reactivation of spent limestone
Steam reactivation experiments were conducted in a specially designed dual-environment fixed-bed reactor to determine the reactivation effect of multiple cycles of sulfation and steam hydration at conditions simulating those experienced by sorbent particles in circulating fluidized-bed combustors (CFBCs) with steam reactivation in the return loop. Three spent sorbents from industrial CFBCs utilizing three different limestones for emission control were tested. Only two showed improved sulfur capture capacity after steam reactivation at 250 degreesC for a total of 180 min distributed over 1-18 cycles. These two spent sorbents responded very differently to cyclic sulfation and hydration; one showed significantly higher reactivation after the second cycle than after the first, whereas the other showed better performance after the first cycle. The increase in the reactivation effect after the second cycle in the one case is likely due to calcination of calcium carbonate formed in the outer reaches of the calcium core during storage of the sorbent. The cyclic experiments showed that, for the conditions investigated, one long-term hydration can be more effective than hydration over multiple short-term hydration cycles of the same overall duration.