Limestone sorbent regeneration in externally fired rotary kilns

Abstract

Externally fired rotary kilns were evaluated for use as regeneration reactors for the spent limestone sorbent from a fluid-bed combustor. Coke and spent sorbent containing approximately 8 wt % sulfur were reacted at temperatures between 960 and 1060/sup 0/C in two laboratory-scale externally fired rotary kilns to produce lime sorbent suitable for reuse, and concentrated SO/sub 2/. It was possible to achieve a high percent of sorbent regeneration, but the SO/sub 2/ concentration in the off-gas was low. Different operating conditions were required to produce a higher concentration of SO/sub 2/ in the off-gas, and under these conditions, the percent of sorbent regeneration was low. Two empirical equations and the shrinking-core reaction-rate model were examined for application to the experimentally determined kinetic data. The shrinking-core model appeared to fit the data better than the empirical equations, and could be a useful predictor of the conversion of sulfated limestone and of the SO/sub 2/ concentration in the off-gas from a rotary-kiln regenerator. The materials used in the construction of one of the laboratory kilns were typical of commercially available production-size rotary kilns that are externally fired. However, the materials of construction were not sufficiently durable to withstand the high SO/sub 2/ concentrations and high temperatures involved in this reaction.