Influence of technical parameters on reducing efficiency of iron ore fine in continuous fluidized bed

Preheating and reduction of iron ore fine in a multi-stage continuous fluidized bed (FB), which can improve gas utilization, heat efficiency and decrease production cost of hot metal, is a development direction for ore fine reduction with gas as a reductant. Multi-stage FBs coupled with a gasifier for producing hot metal have been successfully industrialized in Southern Korea. However, progress of FBs for iron ore reduction is slow in China. The reduction fraction and utilization ratio of gas are two important parameters for the iron reduction process. The key to feasible estimation of new technologies and design of parameters in the reduction process and reactors is understanding the influence of various parameters. As a result, the coupling kinetic model of iron oxide reduction and reducing gas oxidation in two-stage FB was established to investigate the influence of technical parameters on reducing the efficiency of iron ore fine in a continuous FB. FeO, which comes from a R2 FB, is reduced in a R1 FB using qualified gas as a reducing gas. Fe₂O₃, which comes from R3 preheating of a FB, is reduced to FeO in R2 FB using off-gas from a R1 FB. The results are in a good accordance with literature data. The influence of parameters, such as the size of the ore fine and pressure in the FB, on reducing efficiency was investigated according with this model. For the reduction results to be ≥ 85% metallization ratio, ≥ 38% gas utilization rate and 950~1050 m³·t^-1 ratio of gas flow to ore mass, the technological conditions are an average ore fine size less than 1.5 mm, FB temperature of 780~800℃, gas reduction potential greater than 93%, volume fraction of inert gas less than 5% average pressure of 3.5×10⁵~4.0×10⁵ Pa, the reciprocal of standing time u_g/H of 1.0~1.1 s^-1, average retention time in R1 FB of 30 min and average retention time in R2 FB of 20 min.