Title

SELECTING LINING MATERIALS TO ACHIEVE LONG AND PRODUCTIVE BLAST FURNACE HEARTH CAMPAIGNS

SELECTING LINING MATERIALS TO ACHIEVE LONG AND PRODUCTIVE BLAST FURNACE HEARTH CAMPAIGNS

Authorship

Sylvén, Peter; Duncanson, Peter L.; Fontes., Luís

Sylvén, Peter

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Duncanson, Peter L.

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Fontes., Luís

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DOI

10.5151/2594-357X-22280

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Abstract

When designing, engineering and constructing the hearth wall of a blast furnace, traditional thinking predicts that the hearth wall will erode to the locations of the 1,150°C isotherm. This philosophy is based on the fact that at elevated carbon content (>2%), iron solidifies at 1,150°C. In strict thermo-chemical theory, it is impossible for a carbon hearth wall refractory to wear beyond that point. Operators even use this theory in their online thermal models to estimate current wear by extrapolating the location of the 1,150°C isotherm from actual temperature measurements. As we will show examples of in this paper, the theory fails to explain why in reality, most large-block hearth walls experience much more severe wear over their lifetimes. It is often reported that block hearth walls have minimal refractory remaining, the carbon blocks are cracked and brittle, and that the wear dictated the end of the furnace campaign, or at least a major repair. Such results are inconsistent with the theory, yet its use continues without regard for its shortcomings. It is also well known that oxidation, thermal stress and chemical attack occur at such elevated temperatures in the blast furnace hearth wall. This paper discuss these root causes of hearth failure in more detail and suggest how these should be taken in consideration when selecting refractory materials and designing hearth walls for best performance in modern high productivity blast furnaces, in line with steel companies’ continuous drive for better results.

When designing, engineering and constructing the hearth wall of a blast furnace, traditional thinking predicts that the hearth wall will erode to the locations of the 1,150°C isotherm. This philosophy is based on the fact that at elevated carbon content (>2%), iron solidifies at 1,150°C. In strict thermo-chemical theory, it is impossible for a carbon hearth wall refractory to wear beyond that point. Operators even use this theory in their online thermal models to estimate current wear by extrapolating the location of the 1,150°C isotherm from actual temperature measurements. As we will show examples of in this paper, the theory fails to explain why in reality, most large-block hearth walls experience much more severe wear over their lifetimes. It is often reported that block hearth walls have minimal refractory remaining, the carbon blocks are cracked and brittle, and that the wear dictated the end of the furnace campaign, or at least a major repair. Such results are inconsistent with the theory, yet its use continues without regard for its shortcomings. It is also well known that oxidation, thermal stress and chemical attack occur at such elevated temperatures in the blast furnace hearth wall. This paper discuss these root causes of hearth failure in more detail and suggest how these should be taken in consideration when selecting refractory materials and designing hearth walls for best performance in modern high productivity blast furnaces, in line with steel companies’ continuous drive for better results.

Keywords

Blast furnace; Refractories; UCAR; Hearth lining; Carbon; Brick; Block.

Blast furnace; Refractories; UCAR; Hearth lining; Carbon; Brick; Block.