SIMULATION OF HEAT TRANSFER AND CRYSTALLIZATION OF MOLTEN BLAST FURNACE SLAG DROPLETS DURING CONTINUOUS COOLING

Molten blast furnace slag represents great opportunities for waste heat recovery and natural resource recycling. The use of slag product depends to a great extent on its mineragraphy, which is closely related to heat transfer and crystallization during the continuous cooling process. In this paper, in order to predict the heat transfer and crystallization behaviors of molten blast furnace slag droplets during continuous cooling, the non-Newtonian heat transfer model was coupled with a continuous cooling crystallization kinetics model under conditions of film boiling, natural convection, and forced convection heat transfer. The effects of droplet size, heat transfer condition, and fluid velocity on heat transfer and crystallization of slag droplets were investigated. The results indicate that the droplet size has a significant influence on the cooling rate and degree of crystallization. The effect of heat transfer condition is obvious, and the effect of fluid velocity is negligible. With increasing droplet size, the mean cooling rate of a slag droplet decreases exponentially. The critical crystallization droplet size can be defined under investigated heat transfer conditions. For slag droplets of size less than the critical value, the droplets remain glassy aft er cooling; while for droplets with larger size, the degree of crystallization increases rapidly with increasing droplet size.