Analysis of blast furnace hearth sidewall erosion and protective layer formation

Abstract

The blast furnace campaign life is largely determined by the damage to the hearth area. Bricks and skulls in the hearth were sampled and investigated after the blowing-out of one commercial blast furnace. A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD), were applied in characterizing the erosion and protection mechanism of the hearth sidewall. The upper area of the hearth was heavily eroded. Large amounts of alkali chlorides were identified in the area, which could be the main contribution to the serious erosion. The taphole area was protected by the formation of the skull, which consisted of slag with CaZnSi3O8, Zn2SiO4 and CaMg2Al2O7 phases. The circulation of the hot metal in the hearth is the major cause of brick erosion in the hearth bottom area, which leads to a ring shaped wear. Controlling peripheral hot metal flow across the hearth wall using long taphole and coke with high degradation resistance may slow the carbon brick erosion. Increasing the carbon content in the hot metal can help reducing the dissolution of the carbon bricks and enhance the formation of a graphite layer to protect the hearth lining.