Gasification and shell characteristics in slurry droplet burning

The gasification process of the liquid component of freely falling carbon slurry droplets in a hot oxidizing environment is studied both theoretically and experimentally. The theoretical model formulated describes droplet gasification as consisting of two periods: An initial period of regressing droplet size governed by the classical d²-law, and a subsequent d³-law period during which (a) the droplet size remains fixed by a right porous shell, (b) gasification takes place through the shell with a constant rate, (c) the diameter of the inner surface of the shell regresses, with a rate which varies cubically with time, and (d) an internal, expanding vapor cavity is formed whose diameter also varies cubically with time. The situations of both liquid- and vapor-saturated shells are analyzed. The experimental investigation involves quantitative determination of the temporal variations of the droplet diameter and composition, and examination of the characteristics of the shell agglomerate. A comparison between the theoretical and experimental results substantiates the sequential nature of the gasification process, and suggests that the shell is saturated with liquid while gasification progresses, that the shell porosity corresponds to that of the loosely-packed configuration, and that it requires about a three-particle layer thickness for the shell to become rigid.