KINETICS OF SULFATION OF LIMESTONE AND PRECALCINED LIMESTONE

The kinetics of sulphation of large (2-4 mm) limestone and precalcined limestone particles were investigated at temperatures below the decomposition temperature of CaCO3. In both cases it was found that, over a wide range of conditions, the sulphation rate decays with t-1/2, indicating that diffusion of SO2 through the product CaSO4 layer is rate limiting. For the case of limestone sulphation, the effective diffusivity of SO2 in the product CaSO4 layer is two to three orders of magnitude higher than in the case of sulphation of precalcined limestone, leading to Ca utilization up to 50%. A simple parallel pore mathematical model was found to provide a semiquantitative fit to the experimental results.