Conference Agenda

Anode change events introduce significant mass and thermal disturbances to the aluminium reduction process. Smelters aim to mitigate these impacts by setting new anodes at a higher vertical position to accommodate reduced carbon consumption, ensuring that once the new anodes recover their normal current load, their bottom surface aligns with other anodes. However, this increment may not be optimally implemented due to varying local cell conditions and work practice tolerance. Continuous measurements from an Individual Anode Current Monitoring system facilitates the prediction of anode consumption rates and variations in anode-cathode distance following anode changes. This paper proposes re-adjusting the vertical position of new anodes based on the anode current recovery profile, aiming to minimise unnecessary crane usage. Prompt restoration of anode current distribution aids in mitigating process perturbations from subsequent anode change events, thereby enhancing cell stability and energy and operational efficiency.

Decarbonization is a major issue for preserving our planet and the quality of life of its inhabitants. The development of industrial capacities and production methods in line with this challenge is essential. Aluminium Dunkerque is one of the world leaders in the production of low-carbon aluminum. The company has reduced its emissions by 17 % (scope 1 and 2) since 2013 and emits four times less greenhouse gases than the global sector average. Thanks to these assets, Aluminium Dunkerque intends to play a major role in the European production of low-carbon aluminum for the benefit of its customers and its communities. Therefore, in accordance with the objectives of COP21, we are accelerating our energy and environmental transition by giving ourselves an ambitious roadmap to 2050: the LowCAL project.

Although our strategy is geared towards the implementation of a CO2 Capture process, efforts remain sustained to reduce our emissions at their origins as much as possible. In this context, Aluminium Dunkerque was able to test two avenues for reducing net carbon consumption by: increasing the frequency of pot tending to maintain an airtight cover, and by coating the anodes in order to reduce their air burn (oxidation) and CO2 burn (Boudouard reaction). The results are analyzed in a technical-economic context to be validated for generalization or a larger test.

Carbon anodes are an integral component of the molten salt electrolysis for primary aluminium production. Raw materials for anode production are suffering a reduction in quality and the aluminium world faces competition from lithium-ion batteries. The knowledge and improved process control in anode manufacturing has increased, where now anodes are manufactured to a better quality than 40 years ago. Despite the improved quality of the anodes, the problem of carbon particles mixed into the electrolyte (also known as carbon dust) is still prevalent. The usual recommendation in operations in smelters is: "Get better anodes and the problem will take care of itself". This summary of PHD thesis aims to investigate carbon particles and their distribution in industrial electrolyte taken from cells in the TRIMET Hamburg smelter.

An electrolyte sample containing carbon particles was analysed using STEM-EDS. The particles have an increased sodium content on the surface, which indicates sodium intercalation. Analysing the results of the industrial sampling at 600 positions, cells did not reveal fundamental patterns of carbon distribution. Modelling using PCR was able to explain a maximum of 19.1 % variance in the average carbon concentration. No mechanism was found to be acting on the distribution – in contrasts to other components in the electrolyte.

The analysis of frozen electrolyte samples taken under newly changed anodes within eight hours shows layered structures of the frozen bath. Many of the samples contained carbon particles. The size of the particles depended on whether the anode change was carried out using a scoop to clean the surface of the open electrolyte. Fine carbon particles remained in most cases. The formation of spikes, which damage the process, could not be detected in any of the anode changes observed within the first eight hours.

Overall, the methods and analysis conducted in this study did not show common particle patterns. The carbon particle distribution can be random.

This research investigates several characteristics of multi-bubble motion under the bottom surface of a reduced-scale carbon anode sample in a physical air-water model of the Hall-Héroult cell. Applying the principles of similarity to our experimental setup, we used low-temperature water and air to represent the bath and CO2 bubbles in the real cell. Ultra-speed camera imaging and videography technique was implemented to track the bubble evolution under the anode from initial generation to detachment from the anode bottom surface. After post-processing the laboratory data using ImageJ, GIMP, and MATLAB, we determined interesting information on the bubble size, residence time, and velocity under the anode. Considering the effect of anode tilt in the longitudinal direction, we demonstrated that increasing the anode tilt reduced the bubble size and residence time under the anode, while bubble velocity, collision, and coalescence were enhanced. Moreover, the threshold initial volume for bubbles to detach from the anode bottom surface at nucleation sites was decreased by increasing the anode tilt. On top of this, the similarity between the bubble size and velocity data that we have determined in our setup and those reported in existing literature, confirms the success of the current configuration in the prediction of the two-phase bubbly layer features beneath the anode. Consequently, we can provide valuable insights for aluminum smelters by optimizing the resistance of our model cell through modification of the geometrical features.

Rio Tinto Aluminium is known for its high amperage operation and its main primary aluminium production hub is located in the Saguenay Lac Saint-Jean region (Québec, Canada), with five aluminium smelters and a research centre. Over the last decades, cell designs have continuously evolved in a way to allow higher heat dissipation and support amperage increase. Recently, a recurring problem threatening cell life duration expressed by repetitive pot shell temperature peaks was encountered in one of the regional smelters. The situation was addressed by mobilizing R&D teams to understand the provenance of the phenomenon and to propose a solution to mitigate the problem. The results of the investigations pointed out to a solution of lowering the solicitation of the inner sidewalls of the cell by modification of the anode slot design. Industrial tests were carried out using different anode slot designs to better assess the behaviour of the proposed solution. The retained inclined anode slot design has been in operation for more than two years now.

This paper presents the sequence of events that unfolded from the apparition of the problem to its solution. It summarizes the experience gathered through key learnings in both technical and operational fields. It also addresses the thermal impacts that need to be compensated in the operation of the cells with the new anode slot design.