Improvement of Desulfurization by Addition of Aluminum to Hot Metal in the Lime Injection Process

抄録

The reaction efficiency of hot metal desulfurization by lime powder injection with nitrogen gas is improved by prior addition of aluminum. That is, the rate of desulfurization is higher in a Fe–C_sat.–Si–Al–S melt than in a Fe–C_sat.–Si–S melt. The reaction layers of lime lumps immersed in the melts were examined by electron probe microanalysis and X-ray diffraction. The investigation revealed the mechanism by which the addition of aluminum improves the reaction efficiency of the subsequent lime injection.
In the Fe–C_sat.–Si–S melt, solid 2CaO·SiO₂ and 3CaO·SiO₂ layers are formed on the lime surface, and thereby retards the transfer of sulfur to its internal part. On the other hand, a fusible CaO–Al₂O₃–FeO layer is formed on the lime surface in the Fe–C_sat.–Si–Al–S melt, promoting the inward transfer of sulfur. Furthermore, the layer dissolves as much sulfur as up to approximately 50%.
The aluminum concentration needed to obtain this improvement of desulfurization in a 250 ton torpedo ladle was the aluminum content of (0.005+ΔAl)%, where ΔAl is the aluminum lost during the desulfurization process.