The Evolution of Structural Order as a Measure of Thermal History of Coke in the Blast Furnace

Investigations were carried out on cokes heat treated in the laboratory and on cokes extracted from the experimental blast furnace (EBF) raceway and hearth. X-ray diffraction (XRD) measurements were performed to investigate changes in structural order (L _c), chemical transformations in coke ash along with comparative thermodynamic equilibrium studies and the influence of melt. Three data processing approaches were used to compute L _c values as a function of temperature and time and linear correlations were established between L _c and heat treatment temperatures during laboratory investigations. These were used to estimate temperatures experienced by coke in various regions of EBF and estimated raceway temperatures were seen to follow the profile of combustion peak. The MgAl₂O₄ spinel was observed in coke submerged in slag during laboratory studies and in cokes found further into the raceway. Coke in contact with hot metal showed XRD peaks corresponding to presence of Fe₃Si. The intensity of SiO₂ peak in coke ash was seen to decrease with increasing temperature and disappeared at around 1770 K (1500 °C) due to the formation of SiC. This study has shown that the evolution of structural order and chemical transformations in coke could be used to estimate its thermal history in blast furnaces.