CALCINATION OF CALCIUM HYDROXIDE SORBENT IN THE PRESENCE OF SO2 AND ITS EFFECT ON REACTIVITY

When calcium hydroxide [Ca(OH)2] is calcined in an isothermal flow reactor with 300 ppm or less sulfur dioxide (SO2) present, the structure of the sorbent is characterized by retention of higher pore volumes and surface areas than when calcined in the absence of SO2. Upon reinjection into the isothermal flow reactor (1,000-degrees-C, 3,000 ppm SO2, 0.8 s) a higher level of reactivity with SO2 is observed for the SO2-modified calcine than for the unmodified sorbent. Structural evidence suggests that a slower initial rate of sintering in the modified calcine accounts for its enhanced reactivity. It is postulated that deposition of small amounts of calcium sulfate (CaSO4) on pore faces and along crystal boundaries retards the solid state diffusion process responsible for sintering. The effects on sintering and reactivity of various combinations of residence time (0.6-2.0 s) and SO2 concentration (10-50 ppm) during precalcination have been tested.