Coke graphitization and degradation across the tuyere regions in a blast furnace

Changes in particle size distribution and in the degree of graphitization of coke samples from various locations across the tuyere entrance of a blast furnace were examined. X-ray diffraction and a fixed bed reactor were used to measure carbon structure and reaction rate of the coke. The feed coke size was observed to decrease by more than 50% in the descent to the tuyere in the majority of the tuyere-level locations. About 60 wt.% of the core matter from the "bosh" and "raceway" locations consisted of less than half-size feed coke particles. The percentage of -3 mm and -0.45 mm size fractions observed in the recovered drill core material were less than 10 wt.% and 3 wt.% respectively particularly around the raceway locations. The graphitization degree of half-size coke particles is shown to be a suitable indicator of the temperature profile of tuyere-level regions of a blast furnace. The degree of graphitization of tuyere-level coke samples showed an inverse relationship with amount of potassium adsorbed as well as with the apparent reaction rate. The carbon structure as well as anisotropic texture of coke fines indicated higher ordering of carbon compared to the half-size cokes from the similar locations. The -0.45 mm size fraction of fines displayed a large proportion of graphite crystals. The study has confirmed the contribution of surface graphitization of cokes on the fines generation particularly in the "raceway" and "birds nest" regions. The study has implications for using the bench-scale assessment of coke performance and modeling of coke behavior to provide an understanding as to what is likely to occur in an industrial blast furnace. (C) 2013 Elsevier Ltd. All rights reserved.