Smelting Vanadium–Titanium Magnetite by OY Furnace: Effect of Prereduction Degree on the Softening, Melting, and Dropping Behavior of Direct Reduction Iron in Melter Gasifier

OY furnace, an improvement of COREX, is the vigorously developed environmentally friendly iron-making process. However, it has a higher fuel ratio than blast furnace. The high prereduction degree (PRD) of direct reduction iron (DRI) is beneficial to decrease the fuel consumption of OY furnace but also affect the softening, melting, and dropping properties of DRI in the final reduction process. In the study, the qualitative and quantitative relationships between the PRD (60 to 90 pct) and the softening, melting, and dropping behavior of the V–Ti-bearing DRI under the simulated OY furnace conditions were investigated. Results indicated that the increase in PRD of DRI improved its creep resistance, increasing its end temperature of softening (T₄₀). However, it also accelerated the reduction of TiO₂ to TiC and the slag foaming, which leaded to an increase in the melting temperature (T_S) and the dropping temperature (T_d). The slag foaming temperature (T_f) was declined from 1504 °C to 1441 °C as the PRD of DRI increasing from 60 to 90 pct, which inhibited the liquid permeability of the V–Ti-bearing bed, resulting in the deterioration of the dropping rates of molten iron and slag from 96.7 and 86.9 to 25.2 and 12.8 pct, respectively. In addition, the gas permeability of the V–Ti-bearing bed was also decreased due to the generated TiC and slag foaming. The maximum pressure drop (P_Peak) and gas permeability index (S_D) of the pressure drop curve after temperature T_f were multiplied from 8.06 kPa and 218.41 kPa °C to 20.14 kPa and 1324.17 kPa °C, respectively. Therefore, the V–Ti-bearing DRI with higher PRD is more likely to foam in the semi-coke bed, which is not recommended for the smelting of OY furnace.