Electrical Conditions and their Process Interactions in High Temperature Metallurgical Reactors (ElMet)

The design and operation of smelting furnaces have been gradually improved through industrial experience, research, modern process control, new and/or improved measurements, and so on. Nevertheless, due to the complexities of the processes, several process variations are not properly understood. Smelting processes are energy intensive. The power is normally supplied by high electric currents, often more than 100 000 amps. The current paths depend on electrical resistivity of the raw materials, intermediate reaction products, and the metal that is produced. As a result, there is a strong interaction between electrical current paths, temperature distribution, and chemical reactions. The knowledge-building project "Electrical Conditions and Their Process Interactions in High-Temperature Metallurgical Reactors (ElMet)" applies mathematical modelling to shed light on this challenging problem. The internal conditions of the furnace are described using mathematical equations. Subsequent mathematical analysis of these equations provides insight into the physical processes that take place in the furnace. The equations have also been adapted to computer simulations using advanced software. The ElMet project is built on previous knowledge established by the project team, as well as other researchers and industry partners. The project has been carried out in close collaboration among NORCE Norwegian Research Centre, the companies Elkem and Eramet, and researchers at the Norwegian University of Science and Technology (NTNU), the University of Oxford, and the University of Santiago de Compostela. The aluminium producer Alcoa participated in the project in its early phases, but withdrew after they stopped their research on carbothermic aluminium production. The ElMet project has been ambitious, interdisciplinary, and challenging. The project has included * a PhD project at Oxford focusing on adequate theoretical descriptions of electrical and thermal conductivities of granular materials * a PhD project in Santiago de Compostela by a researcher at NORCE focusing on effects of alternating currents in the furnace hearth and lining * CT scans of granular carbon materials (cokes) that has provided information about the number of contact points each particle makes with its neighbors - this is essential to understand electrical conduction * contribution to development of a method for measuring the electric conductivity of granular materials at high temperatures at NTNU * studies of flow of granular materials using advanced methods from discrete element modelling (DEM); these models have also been implemented in simulations of carbon calciners * development of a fully coupled model for a pilot smelting furnace, including granular flow, electric currents, heat transport, and chemical reactions; this work is now carried forward by NORCE in SFI Metal Production * development of three-dimensional simulation models for electrical conditions in industrial (ferro)silicon and ferromanganese furnaces * case studies that have demonstrated formation of strong currents in the furnace steel shell by induction; these currents carry information about the internal conditions of the smelting furnace * studies of induction in carbon electrodes demonstrating skin and proximity effects * development of metamodels in cooperation with NTNU, engineering cybernetics; efficient metamodels are suitable for real-time process control, and inverse metamodels can be used to infer the internal conditions of the furnace from external measurements * production of education materials for students and process operators The project results have been communicated to the project partners, partners in SFI Metal Production, and to the international research community though participation at conferences and publications in scientific journals. Results will continue to be published after the project has ended, particularly at INFACON XVI in Trondheim in September 2021.

Not Applicable

Mathematical modelling has successfully been applied for various aspects of metallurgical processes. Nevertheless, due to all complexities in the processes, the design and operation of smelting furnaces are still to a large degree empirically based, and several process variations are not properly understood. Representatives from Eramet and Elkem have identified a knowledge gap concerning the effects of 3-phase alternating current, including how the associated power distribution governs the chemical reactions and temperature distribution. Strong interdisciplinary research is required to deal with this challenge. Best available model competence must be combined with world-class metallurgical competence, including extensive industrial experience. In the project, Teknova will work in close cooperation with these companies together with NTNU, University of Oxford, and University of Santiago the Compostela. The project will develop suitable mathematical models based on in-depth understanding of the industrial challenges. Appropriate mathematical equations will be developed and analysed, followed by numerical simulations. Our experience has shown that comparatively simple models will improve the understanding and reveal what needs to be further examined, by more detailed simulations and/or experiments. The project will also propose and follow up experiments for model validation. The project will be linked to accompanying R&D activities in the companies with potentially large, step changing, metallurgical innovations. The project is anticipated to build up new, relevant, competence for studying existing, modified, and new high temperature processes. The results will be generalized for generic/similar problems and then published. The project will thus contribute significantly to the open, national competency within metallurgy. Impact on the Norwegian metallurgical industry will be secured through close cooperation with SFI Metal Production.