The kinetics of calcium-ion exchange of coal and the combustion of calcium-exchanged coals in a laminar flow furnace were investigated. Particle diffusion was found to be the rate-determining step for the process of ion exchange. A diffusion model gave good agreement with observed rates of ion exchange. Diffusion of ions in PSOC 680, a bituminous coal, was observed to be much slower than in PSOC 623, a lignite.
Retention of sulfur during combustion of calcium-exchanged coals was observed to increase with increasing particle residence and oxygen concentration in the combustion gas. Chemical reaction was found to be the rate-determining step in the capture of SO2 by CaO in coal ash. The results of this study were interpreted in a proposed mechanism for the release and capture of SO2.
