Formation mechanism of the protective layer in a blast furnace hearth

A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, were applied to characterize the adhesion protective layer formed below the blast furnace taphole level when a certain amount of titanium- bearing burden was used. Samples of the protective layer were extracted to identify the chemical composition, phase assemblage, and distribution. Furthermore, the formation mechanism of the protective layer was determined after clarifying the source of each component. Finally, a technical strategy was proposed for achieving a stable protective layer in the hearth. The results show that the protective layer mainly exists in a bilayer form in the sidewall, namely, a titanium-bearing layer and a graphite layer. Both the layers contain the slag phase whose major crystalline phase is magnesium melilite (Ca₂MgSi₂O₇) and the main source of the slag phase is coke ash. It is clearly determined that solid particles such as graphite, Ti(C,N) and MgAl₂O₄ play an important role in the formation of the protective layer, and the key factor for promoting the formation of a stable protective layer is reasonable control of the evolution behavior of coke.