Direct-current (DC) electric arc furnaces are used extensively for the recycling of scrap steel as well as primary production of many industrial commodities such as ferro-alloys, titanium dioxide, cobalt, and platinum group metals. The latter processes typically make use of carbothermic smelting, in which raw materials are reacted with a carbon-based reductant such as metallurgical coke to produce the alloy products of value. Although well-proven and economical, such processes are becoming increasingly undesirable due to their significant emissions of carbon dioxide and other harmful materials. Many alternatives to carbothermic smelting are currently being explored, including the replacement of part or all of the furnace reductant feed with hydrogen. A DC smelting furnace using hydrogen reductant has the potential to operate at zero carbon emissions provided renewable resources are used for both electricity and hydrogen production.

The primary heating and stirring element in a DC furnace is the electric arc, a high-velocity, high-temperature jet of gas which has been heated until it splits into a mixture of ions and electrons (a plasma) and becomes electrically conductive. The plasma arc completes the circuit between the tip of one or more graphite electrodes which enter vertically through the roof of the vessel, and the molten bath of process material underneath them. The arc acts as the engine room of the furnace, efficiently transferring thermal and mechanical energy to the process from the electrical power supply as well as facilitating exotic chemistry through the introduction of highly reactive species such as free electrons and monoatomic and ionized species.

Due to the extreme conditions inside operating DC furnace units, studying arcs experimentally is difficult and hazardous. The use of computational models coupling electro- and magneto-dynamics, chemical reactions, thermodynamics, kinetic theory, and fluid flow is therefore of great value in building an understanding of how arcs work under different process conditions. In this work, the authors present a coupled computational multiphysics solver incorporating fluid flow, heat transfer, and electromagnetic fields. Plasma thermodynamic and thermophysical properties – calculated using statistical mechanics principles – are also presented for a range of mixtures of hydrogen and water vapour that might be expected in the gas space of a smelter using pure hydrogen as a reductant. The properties are combined with the multiphysics model and used to generate predictions of the arc dynamics and electrical parameters that can be expected in hydrogen-fed DC smelting furnaces.