Numerical simulation and experimental investigation of anisotropic reduction in iron ore pellets using X-ray micro-computed tomography

Direct reduced iron (DRI) provides a promising pathway for the iron and steel industry to achieve carbon neutrality in response to global decarbonization goals. Iron ore pellets are critical feedstocks for the DRI process; however, existing studies typically adopt overly simplified models, failing to accurately represent the complex reduction behaviors occurring in actual pellets. This study investigates the anisotropic reduction behaviors of pellets at various stages under a hydrogen (H₂) atmosphere by employing interrupted reduction experiments, X-ray micro-computed tomography (micro-CT), and computational fluid dynamics (CFD). The results show that pellet morphology and porosity significantly influence the heterogeneous distribution of H₂, resulting in pronounced anisotropic reduction behaviors. At 973 K, the outer region of the pellet achieved homogeneous H₂ concentration and metallization within 50 and 35 s, respectively, whereas the core required 210 s. At 1273 K, the outer region homogenized within 10 s, with the core achieving similar conditions after 100 s. Gas flow distribution and internal pore structures notably affected this anisotropic behavior. Micro-CT analyses revealed new pore formation during pellet reduction, especially prominent in the α₂ and α₃ stages, facilitating H₂ diffusion and promoting faster and more uniform reduction at higher temperatures. The porosity increased by up to 38 % at 1273 K, compared to an 8.45 % increase at 973 K. This research provides insights that could enhance efficiency in industrial-scale iron ore pellet reduction processes.