A Kinetic Model Demonstrating the Effect of FeO in the Slag and Silicon in the Metal on Hot Metal Desulfurization

摘要

The kinetic model developed previously was expanded to predict the desulfurization behavior in the proposed AISI Direct Steelmaking external desulfurization process. The model was also extended to describe hot metal desulfurization in conventional practices where reagent is injected. In the AISI process, FeO is present in the smelter slag. This FeO must be reduced before desulfurization can commence. Silicon is added to the metal to reduce the FeO in the slag and start desulfurization. The model results show that the effect of FeO in the slag on desulfurization is sensitive to the amount of silicon in the metal. High silicon contents in the metal enhance desulfurization.In conventional practice, FeO is contained in slag carried over from the blast furnace. Desulfurizer (in this case CaO and Mg) is injected into the molten metal and desulfurization occurs at two sites. Sulfur is removed by the transitory (rising particles) and permanent contact (top slag) reactions. The model predicts that about 60% of the sulfur removal takes place via the transitory reaction. For CaO at high sulfur contents, mass transfer of sulfur through the solid product layer surrounding the particle controls the transitory rate. At low sulfur levels, mass transfer of sulfur in the metal to the injected CaO particles controls the rate. For Mg, mass transfer of sulfur in the metal to the Mg bubble always controls the rate. The model shows that desulfurization improves when less blast furnace slag is present. This effect is magnified when the silicon content in the metal is decreased.