Potential of Return Fines as a Sustainable Feedstock in H2-Based Fluidized Bed Ironmaking Process

Hydrogen-based fluidized bed reactor (FBR) is a promising low-carbon ironmaking technology that allows for the direct utilization of fine iron ores without prior agglomeration. However, the poor melting behavior of the produced fine direct reduced iron (DRI*) remains a challenge in subsequent electric smelting furnace (ESF) operations. This study explored the potential of utilizing return fines as a partial iron ore feedstock in a FBR process to enhance the melting properties of DRI* without significant deterioration of reduction performance. The direct utilization of return fines in a fluidized bed involves complex interactions between the physical and chemical characteristics of the bed. This study decoupled the fluidization behavior, reduction kinetics, and downstream melting behavior to evaluate the precise feasibility of return fines. The minimum fluidization velocity (Umf) of the return fines in the particle size range of 0.5–1.0 mm was determined to be 0.55 m/s, implying that the return fines can be treated in a FBR process. The return fines showed inferior reduction degrees in atmospheres of CO/CO2 and H2/H2O compared to iron ores due to their relatively dense microstructure and higher gangue content. The increased addition of return fines up to 10 wt% to iron ores facilitated enhanced melting behavior while maintaining a comparable reduction degree of approximately 80%. The augmented proportion of return fines to iron ore contributed to improved melting of DRI* due to the presence of low-melting-point calcium ferrite phases. These findings suggest the feasibility of return fines in the H2-based FBR ironmaking process.