Original Article

Multi-scale relationship between coke gasification kinetics and its microstructure evolution in the blast furnace

¹ School of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, Shaanxi, China
² Metallurgical Engineering Technology Research Center of Shaanxi Province, Xi’an 710055, Shaanxi, China
³ School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China

^* e-mail: liuqihang2@126.com

Received: 11 November 2022
Accepted: 6 March 2023

Abstract

There is a precise theoretical correspondence between the microscopic chemistry and physical structure of coke and its apparent rate constant k_rea and pore diffusion coefficient D_eff of carbon loss process, and a certain precise mathematical relationship between k_rea/D_eff and the degradation gradient or degradation behavior of coke in blast furnace should exist. This is the key basis for predicting and evaluating coke degradation behavior in blast furnace through coke microstructure. In this work, the evolution relationship between the chemical and physical structure of coke and the macroscopic kinetic parameters k_rea, D_eff was studied by gasification experiment of coke with different particle sizes. The results show that with the deepening of coke solution loss, minerals gradually precipitate on the surface of coke, and play a catalytic role in the process of solution loss, resulting in a decrease in activation energy and an increase in k_rea. 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 decreases, and D_eff increases gradually. In the middle and late period of solution loss, the active components in coke are consumed and the ash in coke is precipitated, which increases the activation energy and decreases the k_rea. 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 and the increase of D_eff. k_rea/D_eff represents the gradient reaction ability of coke on the macro level. The higher the k_rea/D_eff value, the greater the reaction gradient of coke under the same conditions, which further affects the degradation gradient and degradation behavior of coke in the blast furnace.