Modeling reduction kinetics of iron ore/biochar composite pellets during inert heating and gas-based reduction

Kurzfassung

The steel industry is a major source of greenhouse gas emissions, motivating low-carbon ironmaking routes such as hydrogen direct reduction of iron ore. While this route avoids fossil carbon input, carbon is still required for downstream steelmaking. Iron ore composite pellets containing biochar can supply this in-situ carbon, offering higher fixed-carbon yield and greater thermal stability than raw biomass. In addition, part of the biochar contained in cold-bonded composite pellets can advantageously participate in the pre-reduction of the pellets through devolatilization and gasification prior to external gas reduction. Available modeling studies of direct reduction for composite pellets are scarce and typically restricted to isothermal conditions. In this work, a transient model is developed for single porous composite pellets subjected to experimental temperature profiles. Heating under inert gas followed by isothermal reduction under H2, H2/CO, and a biomass derived biogenic gas is simulated to predict pellet composition and mass loss evolution. The modeling framework accounts for moisture evaporation, devolatilization of biochar volatiles, gasification of biochar fixed carbon, and subsequent reduction of iron oxides by coupling intra-pellet transport with heterogeneous reaction kinetics. Model predictions show agreement with thermogravimetric measurements, demonstrating that the framework captures the reduction behavior of composite pellets under relevant experimental conditions.