Aluminum Reduction Technology: Reduction Cell Operation and Process Control
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Jayson Tessier, Alcoa Corporation
Tuesday 8:30 AM
February 25, 2020
Room: 6D
Location: San Diego Convention Ctr
Session Chair: Daniel Whitfield, Boyne Smelters Limited
8:30 AM Introductory Comments
8:35 AM
Study of Heat Distribution due to Acd Variations For Anode Setting: Choon-Jie Wong1; Yuchen Yao1; Jie Bao1; Maria Skyllas-Kazacos1; Barry Welch1; Ali Jassim2; Jing Shi1; 1University of New South Wales; 2Emirates Global Aluminum
The carbon anodes in a Hall-Héroult cell undergo continuous electrochemical oxidation and thus require periodic replacement. During setting of a cold new anode, bath freezes around it, causing the current flow to be impeded and redistributed to the other anodes. As the freeze slowly melts, anode current gradually increases, which causes further anode current redistribution. This event introduces significant disturbances which affect cell stability and thermal balance. Consequently, it is important to improve energy management and cell control during this event, which can be achieved through model-based approaches. Therefore, this work aims to develop a model that describes the effect of bath freezes on the dynamics of anode current pick up and redistribution, which will be useful for optimizing and further developing control strategies for anode setting. The anode current profiles during an anode setting event are simulated and compared to industrial cell measurements.
8:55 AM
Anodic Incident Detection Through Multivariate Monitoring of Individual Anode Current Signals: David LaJambe1; Éric Poulin1; Carl Duchesne1; Jayson Tessier2; 1Laval University; 2Alcoa Primary Metals Smelting Center of Excellence
Anodic incidents occur when an aluminum electrolysis cell short circuits at a specific anode position as a result of a spike or other deformation forming on the bottom surface of the anode. These undesirable process events reduce the current efficiency of the affected cell, which makes early detection critical for minimizing losses. This paper describes the development of an anodic incident detection system based on monitoring individual anode current signals with a multivariate Principal Component Analysis (PCA) model. The model and monitoring system were developed and tested using individual anode current signals collected from an aluminum smelter. The results indicate that anode current signals may be useful for detecting anodic incidents in advance relative to regular detection methods based on typical process signals. Anodic incidents appear to alter the correlation structure of individual anode current signals, which could make detection possible by monitoring the Squared Prediction Error (SPE) statistic.
9:15 AM
Fault Detection and Diagnosis of Alumina Feeding System using Individual Anode Current Measurement: Yuchen Yao1; Jie Bao1; Maria Skyllas-Kazacos1; Barry Welch1; Ali Jassim2; Choon Jie Wong1; Jing Shi1; 1University of New South Wales; 2Emirates Global Aluminum
With the growth in sizes of the Hall-Héroult cells, the detection and diagnosis of faults in the Hall-Héroult process has becoming more difficult, as the information from the cell resistance, which is obtained from the line current and cell voltage, only indicates overall cell conditions. In order to achieve improved process efficiency, the measurement of individual anode current has been studied extensively. Unlike conventionally measured line current and cell voltage, individual anode currents provide the information about the localized cell conditions. This paper presents a method to detect faults in the alumina feeding system in the Hall-Héroult cells from individual anode current measurement. It involves the dynamic estimation of the feeding system status by incorporating a mass balance model, without using physical sensors attached to the feeders. This method is shown to be effective in observing feeder failure, identifying failed feeder location and reporting calibration error in feeder dump weight.
9:35 AM
Change of Anode Operation Pattern from Single to Double Staircase at Albras: Camila Silva1; Vanderlei Fernandes1; Nilton Nagem1; Ivar Sousa1; 1Albras - Alumínio Brasileiro S/A
Most essential operational procedures in prebaked cells are performed with cranes in Albras, which leads to high usage and dependence of these equipment, making it difficult to handle possible failures. The old anode change pattern was single staircase, where anodes were replaced one at a time. Aiming to improve logistics and reduce crane time usage, Albras has tested a new anode operation strategy, where two anodes are changed per cell, keeping a pattern sequence during the transition period. Due to expected pot instability increase, several parameters as bath generation, temperature, noise and anode effect were tracked to evaluate process impacts. Anode current pick up and current distribution measurement were also analyzed together with time of activity, comparing cells in single and in double anode change strategy. This paper also discusses further strategies to keep cells in double anode pattern more stable after anode change operation
9:55 AM
An Advanced Nonlinear Control Approach for Aluminum Reduction Process: Jing Shi1; Yuchen Yao1; Jie Bao1; Maria Skyllas-Kazacos1; Barry Welch1; Ali Jassim2; 1University of New South Wales; 2Emirates Global Aluminum
With the increase in amperage and associated reduction of electrolyte to anode mass, the existing cell control method is facing more challenges due to greater variability in process conditions spatially and temporally. Therefore, it is beneficial to develop advanced control strategies that can achieve a more balanced cell with even distribution of, e.g., alumina concentration and individual anode current, and hence improve energy efficiency and reduce greenhouse gas emission. In this paper, an advanced nonlinear control approach is developed, which determines the optimal local control actions based on the measurements including the individual anode current and cell voltage. This new approach is flexible as it can optimize the control action to achieve different cell performance targets. This work illustrates the effectiveness of the proposed control with examples of different performance targets. The optimal control targets for best cell efficiency is also discussed.
10:15 AM Break
10:30 AM
Model Based Approach for Online Monitoring of Aluminium Production Process: Lucas Jose Da Silva Moreir1; Gildas Besancon1; Francesco Ferrante1; Mirko Fiacchini1; Hervé Roustan2; 1University Grenoble Alpes, CNRS, Grenoble INP*, GIPSA-lab; 2Rio Tinto
In Hall-Heroult process for aluminium production, estimating the alumina concentration and the anode-cathode distance (ACD) remains a challenge. One of the difficulties arise from the fact that it is not possible to measure those quantities continuously during the pot operation. This article presents a novel approach for estimating on line alumina concentration and ACD in a regular aluminum-reduction pot cell using a Linear Kalman Filter. This is done by using an appropriate dynamical model for the pot, which is obtained by combining the first principle modeling and experimental identification of alumina concentration behavior from irregular sampled data. Moreover, a dynamical model for the pot resistance is identified as a function of the alumina concentration and ACD data. The proposed approach is validated on an industrial platform.
10:50 AM
Predictive Analytics for Enhancing Productivity of Reduction Cells: Shanmukh Rajgire1; Abhijeet Vichare2; Amit Gupta1; Devendra Pathe3; 1Abstcpl; 2Presently affiliated with Meritus Interlytics Private limited; 3Hindalco Industries Limited
With increasing energy prices and lower LME, aluminum smelters across the globe are focusing on reducing specific energy consumption. Increasing current efficiency (CE) not only reduces energy but also increases productivity. Since, early 90s, fundamental studies and lab-scale experiments have provided insights on CE and its dependence on process parameters, however these were based on ideal conditions and actual plant data should also be considered. This article presents a predictive model for CE utilizing machine learning algorithm (random forest regressor) on 360kA pot-line data. The model helps in identifying the optimal parameter range to maximize CE of individual pot. Results are compared with fundamental and lab-scale experiments published in literature, showing good agreement in most cases along with few insights. Impact of parameters such as cathode drop, bath height, composition, etc. has been discussed.
11:10 AM
Restart of Shutdown Pots - Troubles, Solutions and Comparison with Normal Pots to Improve Results: Ved Rai1; Vibhav Upadhyay2; 1Hindalco Industries Limited; 2HIindalco Industries Limited
We recognized the premature failure of the pots as a big challenge and worked on the projects to do sidelining and repairing of the shutdown pots to restart. This “Pioneering Work” was carried out at Hindalco Industries Limited, Renukoot, which is recognized as a worldwide leader in this field of Aluminium Production. This paper provides failure analysis of low amperage Hall-Heroult cell and an overview of the sidelined pot. Its method of sidelining, cathode change, baking, and working. This paper also makes comparisons of new pots of same life with the sidelined pots, benefits and way forwards. One of the main objectives of this project is the comparison of the sidelined pot with normal pots. The present work is a part of the project “Side-Lining of low amperage Hall-Héroult cell”. The experiments were performed in some selected pots to observe and analyze the parameters like baking conditions, noise, used voltage, lining drop.