Improvement of Desulfurization by Aluminum Addition into Hot Metal in Powdered Lime Injection Process

Abstract

Improvement was obtained for the reaction efficiency of hot metal desulfurization by lime powder injection with N₂ gas by prior addition of aluminum. That is, the desulfurization rate was markedly faster for Fe-C_sat-Si-Al-S melt than for Fe-C_sat-Si-S melt. Reaction layers on a lime lump immersed in the melts were examined by use of electron probe microanalysis and X-ray diffraction. The improvement of reaction efficiency of lime by aluminum addition was interpreted by the following results of the investigation.
In Fe-C_sat-Si-S melt, solid 2CaO·SiO₂ and 3CaO·SiO₂ layer were formed on the lime surface, which retarded sulfur transfer to its interior. On the contrary, for Fe-C_sat-Si-Al-S melt, molten CaO-Al₂O₃-FeO layer was formed on the lime surface, which enhanced sulfur transfer, and moreover the layer disolved sulfur up to appoximately 50%.
Aluminum concentration to get the improvement of reaction efficiency of lime for plant scale operation in 250^t torpedo ladle was determined to be 0.005+ΔAl%, where ΔAl is the amount of aluminum loss during the desulfurization.