Abstract：Coke is an important raw material for blast furnace smelting, and the multi-scale characterization of its microstructural evolution plays a crucial role in the rational evaluation of coke quality and blast furnace operation. During carbon loss reaction, different degrees of degradation gradients generate inside the porous structure of coke, which have a very important impact on coke behavior, but the current coke evaluation system fail to take this factor into account. The ratio of the reaction rate constant krea to the diffusion coefficient Deff (krea/Deff) was proposed to characterize the effect of the carbon loss reaction on the deterioration of the coke's spatial structure, it could provide a basis for further accurate characterization and prediction of the degradation gradient inside the coke, thus optimizing the coke quality. The matrix reaction characteristics and pore structure evolution characteristics of coke with different particle size were studied. The composition and pore structure parameters of different carbon loss cokes were analyzed by Fourier transform infrared spectroscopy, optical microscope, SEM-EDS and BET specific surface area pore size distribution analyzer. The results show that with the deepening of coke's carbon loss, minerals gradually precipitate on the surface of coke, and play a catalytic role in the process of carbon loss, resulting in a decrease in activation energy Ea and an increase in krea. At this point, the micropores in coke expand and merge into mesopores and macropores, the diffusion path of CO2 molecule decreases, the diffusion activation energy ED decreases, and Deff increases gradually. In the middle and late period of carbon loss reaction, the active components in coke are consumed and a large amount of ash in coke is precipitated, which increases the activation energy Ea and decreases the krea. Moreover, the number of macropores in coke is further increased, and the tortuous degree of porous structure is greatly reduced, which leads to the decrease of diffusion activation energy ED and the increase of Deff. Sudying the ratio of coke krea and Deff shows that krea/Deff decreases rapidly with the increase of carbon loss reaction. And the larger the krea/Deff is, the larger the deterioration gradient inside the coke is, and the coke powder is easily generated from the coke surface, which is not conducive to the actual production of the blast furnace. Therefore, on the basis of reducing the coke dissolution loss rate or CSR, controlling krea/Deff within a reasonable range is an effective measure to further improve the coke quality.
刘起航, 王帝, 赵晓微, 杨双平, 胡蕖. 高炉焦炭微观结构演变的多尺度表征及应用[J]. 钢铁, 2022, 57(10): 43-54.
LIU Qi-hang, WANG Di, ZHAO Xiao-wei, YANG Shuang-ping, HU Qu. Multiscale characterization and application of microstructural evolution of blast furnace coke[J]. Iron and Steel, 2022, 57(10): 43-54.
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