The Effect of Calcium Carbide Particle Size Distribution on the Kinetics of Hot Metal Desulphurization

The effects of particle size distribution on the kinetics of hot metal desulphurization were investigated by pilot-scale injection. Three different particle size distributions of calcium carbide were injected into 70 kg heats of carbon-saturated iron. The sulphur contents and oxygen activities were measured during the injection. The reaction in the plume during the injection could be described as a first-order, diffusion-controlled reaction, after an incubation period lasting between 20 and 40 sec. This rate constant was found to increase as the particle size decreased. A kinetic analysis based on mass transfer theory was performed considering the total particle size distribution of the calcium carbide. Through this analysis a new average size, directly related to the mass transfer behaviour, was developed. Comparison of the observed and theoretical dependencies of the first-order rate constant on the powder feed rate suggests that the fraction of particles in contact with the melt decreases as the particle size decreases. Finally, issues of scale-up and economic assessment are discussed.