Desulfurization of liquid steel by passing steel droplets through a slag layer

Abstract

In order to develop a process to effectively desulfurize liquid steel, a desulfurization of liquid steel was performed in a specially designed equipment. Reaction between a layer of liquid slag (CaO-MgO-Al2O3) and multiple steel droplets generated from a liquid steel was attempted in a two-zone heating furnace. The liquid steel containing S was melted in a crucible at an upper zone of the furnace, and droplets were generated by falling the liquid steel through a hole at the bottom of the upper crucible. The droplets were allowed to free-fall and passed through the liquid slag melted in the other crucible at a lower zone of the furnace. The liquid steel accumulated at the lower crucible was sampled and was analyzed for the S content. It was found that desulfurization took place in two distinctive modes: dynamic and static mode. A model equation was formulated in order to interpret the obtained experimental data, and apparent rate constants for the dynamic mode (kd) and the static mode (ks) were obtained. While the ks was in the order of 10-5 m sec-1 which is in agreement with the literature data obtained by usual metal-slag reaction, the kd was much higher than the ks, as high as in the order of 10-3 m sec-1. In order to maximize the desulfurization rate by the droplets/liquid slag, it is required to keep the slag having higher sulfide capacity while the desulfurization takes place. It further requires an even distribution of the droplets in the slag layer.