Abstract
The urgent need for the reduction of greenhouse gas emission in steel metallurgy in the face of climate change causes a paradigm shift, eventually leading to a transformation of well-established industry processes. Hydrogen-based direct reduction, for example, is a promising pathway but requires knowledge about the interdependencies of all process parameters, something that physically consistent process modeling with high extrapolative power can offer. Existing models, however, remain insufficient: shrinking core models neglect microstructural evolution, other models employ thermodynamically inconsistent formulations, and most pellet models rely on numerous empirical fitting parameters, increasing the risk of overfitting and limiting predictive power [Salucci et al., Am. Chem. Soc. 60 (2024), Büyükuslu et al., steel research int. 2500263 (2025)].
We present our one-dimensional micro-reaction model with explicit time stepping, designed to overcome these limitations. The model explicitly captures nucleation and growth phenomena during the reduction of industrial iron-ore pellets, enabling a mechanistic description of microstructural evolution. By coupling reaction kinetics with mass transport and by resolving local porosity changes and conversion profiles, the model predicts how pellet morphology, gas composition, and pellet size interact to determine reduction behavior. Thermodynamic consistency is ensured through integrated ChemApp calculations, which rigorously predict phase equilibria and driving forces for reduction under varying gas atmospheres. The model accounts for gas-gas reactions as well as diffusion, providing a detailed understanding of the system's dynamic behavior. To further enhance extrapolative robustness, our formulation minimizes the number of empirical parameters, rather than relying on extensive kinetic fitting [Büyükuslu et al., steel research int. 2500263 (2025)].
Our approach enables the integration and optimization of specific input parameters, such as kinetic parameters, properties of the iron oxide pellets, and gas input streams, and hence supports hydrogen’s integration into the industrial landscape for reducing the carbon footprint of the steel industry.