Rate Limitations of Lime Dissolution into Coal Ash Slag

Abstract

The rate-limiting mechanisms of lime dissolution from a solid pellet into coal ash slag and synthetic slag was investigated using an experiment involving a rotating cylinder of lime in a liquid slag bath at temperatures of 1450−1650 °C. Scanning electron microscopy (SEM) analysis of the slag composition around the lime cylinder was used to determine the nature of the boundary layer surrounding the pellet and the calcium concentration profile. Predictions using shrinking core models of a cylindrical pellet were compared to experimental results, suggesting that diffusion through the slag boundary layer and the change of the phase of lime from solid to liquid in the boundary layer combine to limit the process. These results indicate that a combination of controlling steps: diffusion through the boundary layer and the phase change of lime from solid to liquid, must be considered when predicting lime dissolution rates.