Arc physics in hydrogen plasma ironmaking

Iron and steel production is responsible for about 7% of global CO₂ emissions, largely because of the carbon used to reduce iron oxide to iron. Hydrogen is viewed as a possible carbon replacement; however, the reduction of iron oxide by hydrogen gas is endothermic, and the hydrogen reduction process generally requires the use of pellets of high-grade iron ore. Replacing hydrogen gas with a hydrogen plasma can overcome these disadvantages, and efforts to apply hydrogen thermal plasmas to ironmaking are ramping up rapidly.

Hydrogen arc plasmas differ significantly from the argon arcs widely used in thermal plasma applications such as arc welding. The hydrogen arc is hotter, more constricted, less stable, and has a higher voltage. To improve stability and reduce voltage requirements, arcs in mixtures of argon and hydrogen are generally used. Demixing (the separation of gases driven by diffusion) leads to the concentration of hydrogen near the arc axis, increasing the transfer of heat and hydrogen species to the molten pool. On the other hand, the iron vapour emanating from the molten pool of iron oxide tends to cool the arc and decrease the heat flux. Optimizing the hydrogen plasma process will require a thorough understanding of the physics and properties of arcs in argon, hydrogen and iron vapour.

After introducing the possible approaches to decarbonizing iron and steel production, I will present the results of computational modelling of argon-hydrogen arc plasmas, including the influence of iron vapour, together with initial experimental results. The focus will be on providing an understanding of the factors affecting the transport of heat and hydrogen to the molten pool. I will consider the implications of the results for hydrogen plasma ironmaking and outline priorities for further research.