Characterization of optical texture of high-temperature processing coke and feed/tuyere coke for investigating the deterioration of coke in blast furnace

Abstract

This study systematically investigates the optical texture evolution of laboratory heat-treated coke under varying temperatures (1100–1500°C) and atmospheres (N₂/CO₂), with findings validated through comparative analysis of coke specimens (including feed coke and tuyere coke) from industrial blast furnaces (BFs). The effects of heat-treatment temperature, gasification reaction, radial position of lump coke, alkali loads, particle size degradation, and effective volumes of BFs on optical texture were quantitatively analyzed. The results demonstrated that under the N₂ atmosphere, the proportion of isotropic textures increased from 32.5% to 41.2% with increasing temperature, while anisotropic textures decreased. Under the CO₂ atmosphere, the Optical Texture Index (OTI) also decreased from 144.0% to 124.8%. This indicates a tendency of coke optical texture to transform from anisotropy to isotropy at high temperatures. Notable differences exist in the radial distribution of the optical texture of tuyere coke. Specifically, the optical texture in the outer edge regions of the lump coke is more significantly influenced by the conditions inside the blast furnaces BFs. Smaller particle sizes in tuyere coke correlated with higher alkali metal content and lower anisotropy. Furthermore, a declining trend in the OTI of tuyere coke was observed with an increasing effective volume of BFs, decreasing from 146% to 109%, suggesting a potential correlation between effective volume of BFs and the OTI of coke. These findings provide critical insights into the evolution of coke optical texture and the degradation mechanisms of coke in high-temperature zones of BFs.