Behavior of Sulfur During Direct Reduction of Iron Ores with Carbon.

The removal of sulfur in the rotary kiln is governed by its release during gasification of coal and its pickup by sponge iron and the desulfurizing agent. Literature data indicate that the amount of sulfur released per unit time is proportional to the sulfur content and the gasification rate of coal. The sulfur released is transferred through the gas phase to the sponge iron and the desulfurization agent. Appropriate sulfur-containing gases are H//2O, COS, and S//2. The equilibria during sulfur pickup of the systems Fe-S-O, Ca-S-O, and Mg-S-O are described. Only CaO, but not MgO, can be used as an efficient desulfurizer. The iron carriers are mainly sulfurized in the metal phase. A kinetic model was established for the quantitative description of the reactions. An equation was derived for the partial pressure of COS in the gas phase for use in calculating the parameters which must be adjusted to keep the pressure low enough to avoid sulfurization of sponge iron.