Porosity, surface area, and particle size effects of CaO reacting with SO 2 at 1100° C

Abstract

Calcium oxide (CaO) sorbents derived from calcium hydroxide [Ca(OH) 2] and calcium carbonate (CaCO 3) were tested for their reactivity to gaseous sulfur dioxide (SO 2) in a nitrogen atmosphere with a nominal 1100°C, entrained flow reactor and a solids residence time of 0.74 s. The research allowed for direct examination of the combined effect of porosity, particle size, and surface area upon CaO conversion to calcium sulfate, CaSO 4. Conversion was inversely related to the 0.20 to 0.35 power of particle size for diameters ranging from 0.77 to 12.1 μm. Increased initial surface area from 7 to 62 m 2 g led to higher conversions at all particle sizes, eliminating the possibility of gas film diffusion control. The conversion for both sorbent types is proportional to initial porosity. Substantial expansion of the sorbents during reaction was shown by achieving conversion levels much greater than theoretically possible, given the initial sorbent porosity, the larger-volume product, and an assumed constant particle size. This is contrary to most modelling assumptions, in which the reaction is limited or cut off by pore filling or pore plugging of the sorbent volume.