Study on Ore-Coke Coupling Metallurgical Performance and Phase Evolution of Primary Slag Permeation Through Coke Bed Under Different Coke Conditions

During blast furnace ironmaking, the behavior of primary slag in the cohesive zone directly impacts furnace operational stability. This study employed the “Qisunny method” to simulate distinct coke effects on the cohesive zone. Based on experimental results, primary slag permeation through the coke bed was analyzed, specifically investigating how coke types influence primary slag composition and penetration behavior. When high-reactivity coke was used, the reducibility of iron ore was significantly higher compared to using low-reactivity coke. Concurrently, the melting start temperature of the iron ore increased from 1244 °C to 1255 °C, the peak pressure drop temperature rose from 1305 °C to 1329 °C, and melting end temperature of the iron ore increased from 1392 °C to 1400 °C. All three key temperature points showed an upward trend with the application of high-reactivity coke. At peak pressure drop conditions corresponding to different cokes, the primary slag invariably accumulated on top of the coke bed and exhibited identical mineralogical assemblages including Fe, MgO-dissolved wüstite, aluminosilicate phase (CaO–SiO₂–MgO–Al₂O₃–FeO), and silicate phase (CaO–SiO₂–MgO–FeO). As the temperature increased, smelting reduction of FeO by coke and dissolution of coke ash occurred simultaneously. The proportion of SiO₂ and Al₂O₃ in the slag increased, and the MgO liberated from wüstite reduction subsequently contributed to slag formation. The w(CaO)/w(SiO₂) of the aluminosilicate phase in the residual material decreased to approximately 1.10, while the w(MgO)/w(Al₂O₃) increased to around 0.8. However, the w(CaO)/w(SiO₂) of the silicate phase showed no significant changes. When the fluid slag permeated through the coke bed, it further incorporated the coke ash. Therefore, the w(MgO)/w(Al₂O₃) in the aluminosilicate phase of the dripping materials decreased and the calcium silicate phase was precipitated. When high-reactivity coke was employed, silicate phase were detected in the dripping materials. This result was observed likely because the aluminosilicates entrained the silicates and then migrated together through the coke bed when the slag attained sufficient fluidity.