Numerical simulation of the hydrogen direct reduction of hematite pellets based on three-step random pore model

The current study focuses on developing a novel 3D mathematical model to simulate the hematite pellet reduction process by integrating a three-step random pore model with a computational fluid dynamic framework, taking into account the mass and heat transfer in a hydrogen (H₂) atmosphere. The model incorporates critical factors such as porosity variation and gas evolution to capture their interactions and influence on reduction behaviour across different temperatures. Reduction experiments use a spherical pellet that is reconstructed from CT images based on X-ray microcomputed tomography to represent the real internal pellet structure. The results show that the model can predict the porosity variation and gas diffusion during the reduction process precisely. The complete conversion time decreases from 3300 s at 973 K to 800 s at 1273 K. The water vapour and hydrogen gas species are more uniformly distributed throughout the pellet and more advanced at 1273 K than at 973 K. Additionally, the accumulation of water vapour within the pores forms a diffusion barrier, restricting hydrogen from reaching the reaction sites. The accuracy and reliability of the developed model were validated through comparison with our previously conducted experimental data. This model provides a robust framework for the realistic, dynamic modelling of industrial reduction processes.