Change in Slag Composition and Sulfur Content of Hot Metal in the Process Chain of Blast Furnace — Hot Metal Desul furization Complex — Converter (BOF)

Abstract

Introduction. Modern conditions of iron and steel making industry require production of high-quality competitive metal products. Thus, the removal of sulfur at the lowest cost has been becoming increasingly important.
Problem Statement. The major amount of sulfur in iron and steel making comes with charge materials in sintering blast furnace production. When using out-of-furnace processing of hot metal in hot metal desulfurization
and slag removal facilities, the degree of hot metal desulfurization can be 75—99%. This ensures the production of hot metal with a sulfur content in the range of 0.002—0.015%.
Purpose. The analysis of changes in the sulfur content of hot metal and in the slag composition in the process
chain of steel production, followed by the development of technical solutions and process methods to eliminate the
resulfurization of hot metal.
Materials and Methods. Our calculations, based on the actual data of Ukrainian and Chinese iron and steel
making facilities. The selected samples of slag and hot metal have been analyzed with the use of raster spectral
microscopy methods. In the studies of sulfur content at various stages of smelting, the method of material balance
calculation has been employed.
Results. In the slag phase, along with systems of CaO ∙ SiO₂ ∙ Al₂O₃ type with diff erent ratios of components
containing 0.2—3.5% sulfur, Ca_xSi_yAl_z type systems containing up to 1% sulfur have been detected. In the beads, the sulfur content varies within 0.1—0.85%. Sulfur is present in the form of sulfi des of (Fe, Mn)S type, mainly
MnS, while in non-metallic inclusions of the beads, the sulfur content ranges within 15—30%. The residing ladle
slag after desulfurization should not exceed 0.5—0.7 kg/t of hot metal.
Conclusions. To prevent the resulfurization of hot metal during its discharge from a blast furnace, it is advisable to rationalize ladle slag modes, by adjusting ladle slag composition, increasing the degree of ladle cleaning from the slag residing from previous loads and inducing a slag cover in the absence of ladle slag. The conducted studies have shown that sulfur from the slag does not return to the hot metal and resulfurization does not occur, which is explained by the protective eff ect of residual magnesium.