Carbon structure of coke at high temperatures and its influence on coke fines in blast furnace dust

Abstract

A thermal annealing study of three industrial cokes was carried out in a horizontal tube furnace at a range of temperatures up to 1600 °C under N2. Evolution of the carbon structure of cokes was established by determining the stack height (L002) of aromatic carbon layers on the basis of the 002 carbon peak in their X-ray diffraction (XRD) spectra by using the classical Scherrer’s approach. The heat-treatment temperature is shown to have a strong impact on the growth of crystalline order of coke carbon by demonstrating a linear correlation between the carbon crystallite height (L002) and the annealing temperature. The intensity of the thermal effects on the growth of the crystalline order of coke carbon is influenced by the coke ash chemistry, particularly with the iron content of the coke. The carbon structure of blast furnace (BF) dust samples was also analyzed by using XRD and scanning electron microscopy (SEM). Under a similar range of heat-treatment temperatures, growth of the carbon crystallite (L002) of coke, in both the laboratory and the industrial BF, was found to be of the same order of magnitude. The correlation between the carbon structure (L002) of coke and the annealing temperature is used to ascertain the temperature of the origin of coke fines in a BF. The carbon structure of coke is shown to have a significant influence on the coke behavior in a BF such that highly ordered coke displayed lower reactivity as well as higher proportion of coke fines in the dust. The carbon structure of coke fines in BF dust has been shown as an indicator of the crystallite dimension (L002) of the coke in a BF, and has a potential to assess coke performance, particularly of the coke fine generations from different thermal regimes of a BF and also their subsequent consumption.