Particle agglomeration behavior in fluidized bed during direct reduction of iron oxide by CO/H₂ mixtures

The agglomeration behavior of particles significantly impacts on the defluidization occurring in a fluidized bed during the direct reduction process. The influence of CO/H₂ ratio on surface diffusion of iron atoms was proposed, and the solid bridge force between iron oxide particles was quantificationally analyzed. Moreover, the solid bridge force was successfully added into a CFD–DEM (computational fluid dynamics–discrete element method) model combined with heat transfer and mass transport to investigate the detailed information of agglomeration in a fluidized bed, including the spatial distribution of temperature, velocity and metallization of iron oxide particles. The region of defluidization is sensitive to the reduction temperature. At the same reduction temperature, the iron oxide powder will perform higher metallization and stable fluidization properties with molar fraction of H₂ in the range of 0.6–0.8, when iron oxide is reduced by CO/H₂ mixture.