By Kevin Widlic, Contributing Editor.
Hydro is moving closer in its work to reduce fossil energy sources at its aluminum casthouses through the use of plasma technology. Positive laboratory scale trials coupled with simulation data have put the company on track to embark on a pilot project at its Casthouse Reference Center in Sunndal, Norway (Figure 1).
The Norwegian aluminum and renewable energy company announced plans to utilize the Casthouse Reference Center as a test bed for plasma technology in January 2024. The aim is to explore the direct electrification of its furnaces using the same renewable energy that powers the company’s primary aluminum plants. If successful, the pilot project has the potential to reduce greenhouse gas emissions within not only the aluminum industry, but also other hard-to-abate industries worldwide.
Sustainability Goals
Hydro believes it is on track to reduce its CO2 emissions by 30% by 2030 compared to a 2018 baseline. Further, the company is aiming to achieve net-zero emissions in its entire aluminum value chain by 2050 or earlier, by stepping up efforts along the three main pathways of its decarbonization roadmap, including phasing out fossil energy sources throughout the value chain, removing direct emissions from production processes, and stepping up recycling of post-consumer aluminum scrap.
As part of its efforts to phase out fossil fuels, Hydro is investigating different technologies with the aim of switching from natural gas to renewable energy sources in its casthouse furnaces. In addition to the testing of emission-free plasma technology, Hydro aims to replace 70% of natural gas consumption at Sunndal with biomethane, while at the Høyanger primary plant further south, Hydro is replacing natural gas with green hydrogen in one of the casting furnaces to unlock the decarbonization potential of hydrogen in aluminum production.
Plasma Technology
Remelting aluminum into new products requires extremely high temperatures, an energy-intensive process which is hard to achieve without fossil energy in the form of natural gas. As part of its casthouse decarbonization efforts, Hydro is evaluating several technologies. One is the plasma torch, which can replace natural gas burners. Plasma torches do not emit carbon dioxide at the point of use, unlike the gas burners currently used in casthouses. They can also potentially offer a clean energy source to melt solid aluminum and hold the liquid aluminum in furnaces.
The steel industry already uses plasma technology to heat up steel and has carried out pilot-scale testing to evaluate the impact of carrier gases during the heating of steel. Historically, the aluminum industry has used plasma torches during the recovery of dross. However, a feasibility study regarding the application of the plasma torch to melt aluminum shows the potential to use these torches in casthouses.
In the plasma torch (Figure 2), an arc is established between the electrodes when power is applied to the torch. A carrier or working gas — in this case nitrogen — is injected and heated to an extremely high temperature (>5,000 K) when it passes through the arc. This results in the formation of a plasma plume, or jet, which can heat up the furnaces and melt aluminum. The high temperature/enthalpy of the plasma gas gives rise to a high theoretical efficiency. In addition, the process does not emit any carbon dioxide and offers a clean source of energy, provided that the electrical power supplied is also generated from renewable sources.
Lab Trials and Simulation Data
As a pre-study in June 2024, laboratory scale trials were conducted at Tetronics Technologies Ltd. in Swindon, U.K. The purpose of the trials was to increase the understanding of the technology, identify potential risks, and develop mitigating solutions. The trials were conducted with a 250 kW non-transferred plasma torch using a lab scale furnace, in which the firing chamber is a vertical chamber. The plasma torch is located at the top. The chamber walls and the roof were water-cooled.
During the lab trials, three aluminum ingots were placed inside the furnace, one close to the torch, one in the mid-section, and one far away at the bottom. These ingots were wrapped by insulating material with only one face exposed. Thermocouples were placed in the ingots and at different locations in the refractory. This provided a framework to understand the temperature evolution and heat transfer and to identify any potential hotspots. Off-gas measurements were also taken.
At the same time, Hydro’s Research & Technology team in Sunndal developed a simulation model that would be used to complement the lab trials. The model provided Hydro with the opportunity to conduct numerical experiments on the furnace at the reference center in Sunndal, which will allow the company to predict the behavior of the plasma torch even before it is installed in the pilot project.
The data from the firing chamber trials was used to compare and evaluate the numerical model. The group observed that the temperature predictions in the simulation were significantly higher, indicating that the firing chamber was cooler than expected during the lab trials. This could suggest the presence of false air — the unintentional admittance of air to the processing chamber.
Visual observations did not show any potential locations of air leaking into the chamber. However, measurements taken at the exhaust showed the presence of leaked air. Consequently, the presence of oxygen, or air, in the firing chamber also led to the generation of thermal NOx. Hydro believes this issue could be resolved or managed by improving the sealing and pressure control of the firing chamber.
The various simulations and measurements did not show any significant hot spots occurring on the refractory lining. This suggests that conventional refractory engineering is compatible with plasma devices.
The results of this research will be presented by Akash Pakanati, senior research scientist at Hydro, on behalf of his colleagues Knut Omdal Tveito, Eirik Manger, and Martin Lorentzon, at the 2025 TMS Annual Meeting & Exhibition Conference. The paper, titled “Development of Numerical Model of Plasma Burner for Primary Aluminium Casthouses,” will summarize the simulation model, comparing the experimental and simulation data and showing how the model predicts the trends from the experiment reasonably well.
Launching the Pilot
The Hydro research group believes that the current process model has provided enough confidence to conduct the simulations for the pilot, supporting the implementation of the technology and ensuring a smooth installation of the plasma torch at the Sunndal Casthouse Reference Center. As part of the pilot, the plasma torch (with 2 MW gross electric power) will be installed in a furnace with a holding capacity of 20 tonnes (Figure 3). The plasma torch is designed to be approximately the same as the natural gas burner that it is replacing.
Hydro aims to complete the pilot set up and start operation of the furnace by mid-2026. The company has received support from Enova, an enterprise established by the Norwegian government, which granted NOK 39.6 million (US$3.5 million) to facilitate the transition to a low-emission society. At Sunndal alone, the pilot would reduce annual CO2 emissions by some 500 tonnes. However, the global potential for reducing emissions from aluminum casthouses and recyclers is 11 million tonnes.
Editor’s Note: This article first appeared in the February 2025 issue of Light Metal Age. To receive the current issue, please subscribe.