Aluminerie Alouette (Canada)

Recent investigations on aluminum electrolysis cell demonstrated limitations to the commonly used tier-3 slope methodology to estimate perfluorocarbon (PFC) emissions from high-voltage anode effects (HVAEs). These limitations are greater for smelters with a reduced HVAE frequency. A novel approach is proposed to estimate the specific emissions using a tier 2 model resulting from individual HVAE instead of estimating monthly emissions for pot lines with the slope methodology. This approach considers the nonlinear behavior of PFC emissions as a function of the polarized anode effect duration but also integrates the change in behavior attributed to cell productivity. Validation was performed by comparing the new approach and the slope methodology with measurement campaigns from different smelters. The results demonstrate a good agreement between measured and estimated emissions as well as more accurately reflect individual HVAE dynamics occurring over time. Finally, the possible impact of this approach for the aluminum industry is discussed.

In aluminium production, the performance of the anode assembly is a great concern which is mainly associated with its energy consumption, aging, fabrication and cleaning process. There fore, a better understandi ng of its in situ behavior is required to efficiently optimize the process using an improved design. In this work, electrical and the rmal data have been me asured on anode assemblies using a specific in situ instrumentation during a complete anode cycle at Aluminerie Alouette Inc. With the help of a numerical model developed on the ANSYS Workbench platform, the evolution of the electrical resistance and current distribution along the anode assembly components has been determined over a complete anode cycle. Considering these information, an innovative prototype has been designed and gave promising results at the laboratory scale. The next step is to confi rm the performance of thi s new design in a real cell.

Electrical resistivity is one of the key performance parameters of prebaked anodes. Nowadays, the desire to lower anodic incidents and energy consumption can be attained with a state-of-the-art equipment, which is able to accurately measure the electrical resistance of baked anodes on a production line. Anode/carbon plant improvements will be achieved by a better understanding of the impact of the physical properties of the anode in the cell and the fundamental causes of anode defects. This paper presents an overview of the milestones and challenges of implementing such a device into a mature carbon plant and ensuring acceptance from the production (or operation) team. This innovative device will provide opportunities for smelters to improve their cost-effectiveness by reducing process variation and maximi zing anode performance in the cell.

Primary aluminum production is generating a significant amount of greenhouse gases. CO2 is the dominant compound but during anode effects, perfluorocarbons (PFCs) are released as well. Even when no generalized anode effects are present, intermittent emissions of PFC have been reported in small concentrations but the root causes of these emissions are hardly understood.

The quality of carbon anodes, consumed in electrolysis during the primary aluminum production, has an important impact on the electrolytic cell performance. Coke and pitch are the raw materials used in anode manufacturing. The raw material properties and the process parameters during production determine the anode quality. A plant receives these materials from different sources, and the variability in their properties is usually a major concern during anode production. The interaction between coke and pitch influences strongly the anode properties. Study of coke and pitch individually as well as the interactions between them using different techniques (spectroscopic, optical, etc.) such as XRD, FTIR, XPS, and SEM help identify their compatibility. Each technique gives information on different aspects of the raw materials. In this article, the use of a number of these techniques for studying coke, pitch, and their interactions will be discussed. Results will be presented for a number of cases.

In aluminum industry, it is important to determine the concentration of contaminants present in anode raw materials as rapidly as possible in order to adjust the anode recipe. Sodium, which is an impurity coming largely from anode butts, significantly influences the anode reactivity, and an increase in its concentration increases the anode consumption. A simple and inexpensive method was developed to quantify the sodium content in dry aggregates and anodes without grinding the samples. The method is based on potentiometric principles using a sodium-ion specific electrode. A sample can be analyzed easily within thirty minutes. In order to prevent the rapid degradation of the specific electrode due to experimental conditions, sodium is extracted from samples by electrophoresis prior to the test. The comparison shows that the measured sodium concentrations obtained are similar to the results determined by other test methods.