The role of hydrogen flow rates in the direct reduction of iron ore pellets: Investigating external mass transfer limitations

Kurzfassung

The successful transition to hydrogen-based direct reduction in ironmaking demands an in-depth comprehension of the complex reaction mechanisms and mass transfer dynamics at play. While high hydrogen flow rates in the reduction of single iron ore pellets are commonly used for mechanism development to neglect external mass transfer effects for simplification, this study critically examines the reduction behavior under low hydrogen flow conditions, where external mass transfer becomes significant, mirroring practical conditions more closely. Thermogravimetric analysis (TGA) experiments were conducted at 1073 K, 1173 K, and 1273 K, with H2 flow-rates of 100 and 300 mL/min, revealing increased external mass transfer resistance at lower flow rates and higher temperatures. To numerically investigate this heterogeneous reacting system, a coupled 1D solid porous and 3D CFD modeling framework is employed, iteratively exchanging data of kinetic rates and gas concentrations at the pellet surface and validating the predictions against experimental data. This work advances reliable kinetic mechanisms for hydrogen-based reduction, addressing model scalability challenges.