Abstract

This thesis explores the fundamental mechanisms and practical feasibility of hydrogen-based plasma smelting reduction (HPSR) of iron oxide particles using non-equilibrium elongated arc discharges at atmospheric pressure. The research addresses critical aspects of plasma-particle interactions, examining how variations in gas composition, particularly through argon dilution and the introduction of CO2, affect plasma stability, particle heating, and reduction performance. Optical emission spectroscopy and electrical diagnostics were extensively employed for plasma characterization, alongside comprehensive particle characterization methods such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). Experimental findings indicate significant plasma stability improvements due to iron vapor dissociation when hematite particles are introduced, alongside pronounced non-equilibrium among gas, electron, and particle temperatures. The metallization degree reached approximately 50% at optimized hydrogen-rich conditions, despite short particle residence times (18-30 ms), with a notable role played by excited hydrogen species in enhancing reaction kinetics. Moreover, investigations using hydrogen-CO2 mixtures demonstrated that CO2 addition beneficially stabilizes the plasma, enhances particle and gas heating via exothermic reactions, and optimizes reductant availability, achieving a metallization degree of approximately 37% at 30% CO2 dilution, in approximately 10-20 ms. Additionally, further in-flight reduction experiments with pure hydrogen plasma, confirmed the technical feasibility of the process across different feedstocks, achieving metallization levels above 70% for hematite and combusted iron, and 62% for an industrial ore, at similar short residence times (18-30 ms) and with an efficiency of 26.8 g/kWh. These results demonstrated the potential of in-flight melting to correct morphology defects, while also revealing challenges posed by gangue phases such as Al-bearing species forming spinels that hinder further reduction. Overall, this work underscores the viability of HPSR as a sustainable alternative for iron production and combusted iron recycling, emphasizing the importance of hydrogen-rich plasmas and highlighting the potential for net-zero carbon emission processes through CO2 recycling. Future research direction recommendations are provided at the end of this work.

Biography

Jordan Figueiredo received the B.S. degree in renewable energy engineering in 2019 from the Federal University of Paraiba. He joined the Mechanical engineering program in the PSE division at King Abdullah University of Science and Technology and received the  M.S. degree in 2021. Since 2022, he has been a Ph.D. candidate at the King Abdullah University of Science and Technology in Saudi Arabia. His research mainly focuses on gas discharge plasma at atmospheric pressure and its application.