Analysis and verification of impact of coke structure evolution on blast furnace permeability

As the sole skeletal support in blast furnaces, the degradation behavior of coke exerts a crucial influence on blast furnace permeability. Three types of industrial cokes were selected as research objects. The evolutionary characteristics of coke microporous structure and the degradation distribution characteristics of particle size were analyzed via scanning electron microscopy-energy dispersive spectrometer （SEM-EDS）, mercury intrusion porosimetry, high-temperature carbon loss-drum test and other experimental methods, combined with porous media theory. The heterogeneity of high-temperature coke degradation was quantified, and its potential correlation with blast furnace permeability was further explored. Finally, the relationship between coke degradation heterogeneity and blast furnace permeability was verified through porosity and pressure difference simulation tests.The results show that after the carbon loss reaction, the pore walls of coke are eroded, some originally closed pores are gradually opened, and the interconnection of micropores facilitates the formation of macropores, leading to a significant increase in the number of pores. This structural change reduces the diffusion resistance of reactive gas into coke pores, resulting in a gradual decrease in the gas concentration gradient and a reduction in degradation heterogeneity. Due to differences in initial pore structure characteristics, the relative concentration gradients of the three cokes during the carbon loss process follow the order of Coke C>Coke B>Coke A. A higher concentration gradient leads to a more concentrated carbon loss reaction on the coke surface, i.e., more severe coke degradation heterogeneity. Thus, Coke C exhibits the strongest degradation heterogeneity, while the carbon loss process of Coke A is more uniform, which is beneficial to blast furnace permeability. This finding is fully consistent with the optimal application performance of Coke A in actual blast furnace production. In addition, the results of pressure difference and permeability simulation tests indicate that there are significant statistical correlations between the permeability index and both the post-reaction coke strength and the degradation heterogeneity index, which further verifies the important influence of coke carbon loss heterogeneity on blast furnace permeability.The research results provide an important theoretical basis for the rational regulation of coke pore structure via coking processes, thereby accurately improving coke quality and ensuring the stable operation of blast furnaces.