Electrode Technology for Aluminum Production: Anode Production
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Duygu Kocaefe, University of Quebec at Chicoutimi

Tuesday 8:30 AM
February 25, 2020
Room: 3
Location: San Diego Convention Ctr

Session Chair: Claude Lavoie, RTA


8:30 AM Introductory Comments

8:35 AM  
Development of a Soft Sensor for Detecting Overpitched Green Anodes: Adéline Paris1; Carl Duchesne1; Éric Poulin1; Julien Lauzon-Gauthier2; 1Laval University; 2Alcoa Primary Metals Smelting Center of Excellence
     Increase in coke variability over the past few years has led to frequent changes in the optimum pitch demand (OPD) defined as the amount of pitch that yields the best anode properties for a given dry aggregate mix.Exceeding the OPD may cause post-baking anode sticking problems, thereby requiring additional operator interventions when unloading the baking furnaces and increasing losses due to scrapped anodes. This paper describes a new soft sensor developed for early detection of anodes with the potential to have sticking problem based on electrical resistivity measurements. Five resistivities measured at different points on approximately 120 000 individual anodes were used to build a Principal Component Analysis (PCA) model. A correlation was found between the anode sticking potential and the electrical resistivity data. It was shown that a breakdown in this correlation, as measured by the statistics of the Squared Prediction Error (SPE), may be used to detect post-baking sticking problems.

9:00 AM  
Diffusion Measurements of CO2 within Carbon Anodes for Aluminium Smelting: Epma Putri1; Geoffrey Brooks2; Graeme Snook3; Lorentz Lossius4; Ingo Eick4; 1CSIRO, Swinburne University of Technology; 2Swinburne University of Technology; 3CSIRO; 4Hydro Aluminium
    Study of CO/CO2 gas transport mechanism between the active electrolysis sites and the anode pores will be addressed in this paper to further understand bubble nucleation for energy saving possibilities in the aluminium production. The gas diffusion experiment was conducted to predict and measure the diffusion coefficient of CO2 in conjunction with characterization of anode carbons in terms of its impurities, porosity and permeability. The diffusion coefficient value obtained varied from 1.38 x10-6 m2/s to 7.89 x10-6 m2/s in the range of temperature 25 to 960°C. The relationship between permeability and properties of porous anode has also been determined numerically with the help of COMSOL Multiphysics software. The results showed there are a few factors that effecting the diffusion coefficient of carbon dioxide such as anode pore characteristics, pressure differences related to material permeability and the chemical reaction between carbon dioxide and anode carbon due to Boudouard reaction above 600°C.

9:25 AM  
Testing of SERMA Technology on Industrial Anodes for Quality Control in Aluminum Production: Yasar Kocaefe1; Duygu Kocaefe1; Dipankar Bhattacharyay1; Abderrahmane Benzaoui1; Jean-François Desmeules1; 1University of Quebec at Chicoutimi
     Carbon anode quality has a strong influence on the electrolytic process, cost, energy use and environmental emissions. The current practice by visual inspection and the testing of cores taken from 1.5 to 2 % of the anodes produced is prone to errors. A more reliable quality control is desirable.The SERMA technology gives the electrical resistivity distribution in industrial anodes (green or baked) based on a simple and non-intrusive measurement technique. Since the electrical resistivity is a good indicator of anode quality, SERMA can be used for on-line quality control. Its use in the paste plant would help eliminate defective green anodes and avoid their further processing. Testing of baked anodes would help save energy by eliminating the use of high-resistivity anodes during the electrolysis. The SERMA technology has been tested on a number of industrial anodes. This article presents the results for both green and baked anodes tested.

9:50 AM  
Modelling of Gas Injection on Anode Baking Furnace and Application to Operations: Sandra Besson1; Solène Bache1; Arnaud Bourgier1; Jean-Philippe Schneider1; Thierry Conte1; 1Rio Tinto
    In the aluminium industry, the carbon anodes are baked in the anode baking furnace by means of the combustion of both the volatile matters emitted by the green anodes and the fuel injected. The essential objectives for baking furnaces are to achieve a uniform baking level while optimizing the fuel consumption, maintaining the refractory condition, and limiting the emissions. Those requirements are strongly influenced by the fuel injection in the heating sections, and the precise study of this phenomenon is essential to better grasp the impact of the process parameters. In this paper, a 3D model for the combustion of pulses of gas in the heating sections will be presented. This model focuses on the flame behavior in order to precisely represent the gas pulses, the quality of the combustion, the heat transfer and the emissions. The effect of the parameter variations on operation will also be presented.

10:15 AM Break

10:30 AM  
Higher Baking and Production Levels in Anode Baking Furnaces and Associated Challenges: SyedArif Ali1; Charles Lebel-Tremblay1; Pierre-Yves Brisson1; Alexandre Gagnon1; 1Rio Tinto Aluminium
     Anode baking in the aluminium industry is very often one of the most critical step in achieving the right anode quality in a safe and cost effective way. Moreover, in many situations plants will want to increase the baking level and / or their production output. This requires the baking furnaces to be driven at higher temperatures and shorter anode cycles, all while keeping the process safe. To achieve this, the process must therefore be optimized to avoid the risks associated with unburnt volatiles and uncontrolled pitch front and temperature increases. This paper describes two projects that were run simultaneously in two of Rio Tinto’s North American plants and deals with the approaches that were taken to achieve both higher baking level and production outputs. The baking curves optimization is discussed, along with the issues that arise during the project and the solution that were put in place.

10:55 AM  
Major Reconstruction of Central Casing of Open Top Baking Furnace with a View to Increase Its Lifespan and Reduce the Total Costs Comparing to Full Reconstruction: Christos Zarganis1; Arnaud Bourgier2; 1Mytilineos Metallurgy Business Unit, Agios Nikolaos Viotia; 2Rio Tinto Aluminium
    Aluminium Company of Greece operates with success its anode baking furnace since its start-up more than five decades ago. Thermal and mechanical stresses created by the baking process however affected the integrity of the concrete casing in the central part. Distortions, deformations and cracks were indeed visible in comparison to the outside part of the casing. This paper goes through the different phases undertaken by Aluminium Company of Greece in order to successfully develop and safely realize the replacement of the casing walls in the central passage as well as the anode conveyor supporting structure while limiting costs and impacts on production and anode inventory. The article details the technical challenges and innovative solutions as well as the project and operation organization put in place in order to realize the work without any safety incident and in a strict schedule of ninety days.