Analysis of existence state and deterioration mechanism of coke in a blast furnace hearth

Pursuing green, low-carbon ironmaking technology primarily aims to reduce fuel ratios, especially coke ratios. Simultaneously, the reduction in coke ratios causes the coke layer in the blast furnace (BF) to become thinner, deteriorating the gas and liquid permeability of the burden column. This exacerbates coke degradation, significantly impacting the smelting process and increasing the demand for high-quality coke. To investigate the existence state of coke in the hearth, a 2500 m³ BF in China was taken as the research object, and three sets of samples at different heights of the hearth were obtained during planned outage. The results indicate that coke undergoes a significant degradation upon reaching the hearth. The proportion of coke particles smaller than 50 mm ranges from 81.22% to 89.50%. The proportion of coke particles larger than 20 mm decreases as the distance from the centerline of the tuyere increases, while the proportion of particles smaller than 10 mm increases with this distance. Additionally, the closer the bottom of the furnace is, the smaller the coke particle size becomes. The composition of slag filling the coke pores is similar to that of the final slag in the blast furnace, and the graphitization of coke is comparable to that of the final slag. The graphitization of coke starts from the surface of coke and leads to the formation of coke fines, and the graphitization degree of − 74 μm coke fines is the highest. The temperature has an effect on the reaction rate of coke solution loss, and the higher the temperature is, the faster the reaction rate is.