Jayson Tessier

Towards On-line Monitoring of Alumina Properties at a Pot Level

Aluminum reduction cells typically use about 1.9 kg of alumina in order to produce 1 kg of aluminum. Hence, for modern reduction cells operating in the 350 to 400 kA range, 5000 to 6000 kg of alumina is fed to reduction cells on a daily basis. However, no information is available in an on-line fashion about the alumina properties fed to the pot. Alumina feeding control systems assume that alumina properties are constant for all pots within a potroom and also over time. Therefore, these control systems aim at controlling alumina concentration dissolved in the bath without accounting for the time varying effects of alumina properties and/or pot condition on alumina dissolution. Based on sampling campaigns, this paper presents evidences of time varying alumina properties impacting its dissolution rate and also proposes a novel approach in order to measure on-line, at the pot, parameters that are related to alumina dissolution.

Multivariate Monitoring of the Prebaked Anode Manufacturing Process and Anode Quality

Prebaked anode quality is available through a weekly average of core sample laboratory measurements. Unfortunately, long delays between production and results (approximately 4-6 weeks) can lead to poor abnormal operation and faulty anode detection, and difficult process control. Extensive raw material and process data are available at Alcoa Deschambault smelter’s carbon plant. Using projection to latent structures, a multivariate statistical method, it was possible to correlate raw material and process conditions to weekly lab results. The effect of different petroleum coke and coal tar pitch was analyzed and instant weekly prediction of anode properties was achieved.

Real-Time Measurement of Coke Aggregate Size and Vibrated Bulk Density Using Image Texture Analysis

The objective of this work is to develop a rapid and nondestructive machine vision sensor to predict Vibrated Bulk Density (VBD) of coke aggregate samples based on their surface textural characteristics obtained by imaging. This information could be useful for ultimately making real-time process adjustments to reduce green anode variability. Coke samples from different sources and sieved in a number of size classes were investigated individually and in blends. Wavelet Texture Analysis (WTA) was used to extract textural features of coke samples, and these were related to their VBD using Partial Least Squares (PLS) regression. It is shown that WTA captures variations in coke size and source and leads to good VBD predictions.

Multiblock Monitoring of Aluminum Reduction Cells Performance

Aluminum reduction cells performance are affected by many factors. In order to efficiently understand possible causes of performance upsets, all major sources of variations have to be monitored. This implies monitoring all anode and alumina properties, as well as pot state and manipulated variables, while also taking into account pot design or integrity after start-up. Considering the high number of variables involved in such a task, this is practically impossible using typical statistical process control tools. The problem is even worst when applied on a pot basis. This paper proposes the use of multiblock PLS (MBPLS) to build a monitoring scheme on a pot basis, simultaneously taking into account the influence of alumina and anode properties, of pot state and manipulated variables, as well as the pot state following its start-up. Derived from a regression model, the monitoring policy ensures that only variations relevant to pot performance variations are highlighted.

Inspection of baked carbon anodes using a combination of multi-spectral acousto-ultrasonic techniques and principal component analysis

HIGHLIGHTSAcousto‐ultrasonic inspection is proposed for industrial‐size carbon anode blocks.Most exhaustive NDT study on this material and at this size.A frequency‐modulated wave is used to excite the anode blocks at multiple points.Detection and localization of cracks were achieved, and crack severity assessed.Inspection scheme will be applied for process monitoring and anode quality control. ABSTRACT This paper reports on the application of an acousto‐ultrasonic (AU) scheme for the inspection of industrial‐size carbon anode blocks used in the production of primary aluminium by the Hall‐Héroult process. A frequency‐modulated wave is used to excite the anode blocks at multiple points. The collected attenuated AU signals are decomposed using the Discrete Wavelet Transform (DTW) after which vectors of features are calculated. Principal Component Analysis (PCA) is utilized to cluster the AU responses of the anodes. The approach allows locating cracks in the blocks and the AU features were found sensitive to crack severity. The results are validated using images collected after cutting some anodes.

On the Use of Multivariate Statistical Methods to Detect, Diagnose and Mitigate Abnormal Events in Aluminium Smelters

This work aims to demonstrate how the use of latent variable methods can detect and diagnose the onset of an abnormal situation in aluminium reduction cells. Using recent data from Alcoa Fjardaal, Principal Component Analysis (PCA) was used to model typical variations occurring in 336 different pots. A drift in process operation was correctly identified sooner than with traditional statistical control technique. Additionally, concentration in low trace elements in the metal also corresponded to a drift in process operation. Such an early warning could help mitigate the impact of abnormal events.

Investigation of Alumina Concentration Gradients Within Hall-Héroult Electrolytic Bath

Aluminium reduction cells consume about 1.9 kg of alumina for each kilogram of aluminum they produce. Control of the alumina concentration within the electrolyte is of prime importance to achieve high metallurgical and energy efficiency and to reduce environmental footprint related to PFC and CO2 emissions. However, modern high amperage reduction cells, oftentimes operated at much higher amperage than their nominal design, are facing challenging conditions to ensure a homogeneous alumina concentration over time and across the pot at a given time. This has negative impact on the cell efficiency. This paper presents findings from different sampling campaigns performed at different amperage and pot condition for a given cell technology. It is shown that large gradients of alumina concentration are present over time and spatially.

Airflow and heat stress in a metallurgical industrial building under different working conditions

ABSTRACT Potrooms are elongated buildings in which hundreds of aluminum smelting pots are housed, and have the particularity, among others, to be naturally ventilated. A CFD model simulating a potroom is developed to study its thermal comfort when the aluminum smelting pots take in less volume of air so as to facilitate waste heat recovery from the pot draft. The influences of wind and buoyancy on the ventilation performance of the potroom are simultaneously considered. The heat stress during hot weather is estimated for different cases. A 50% reduction in the pot draft rate is assessed in terms of its influence on the heat stress in the potroom. It is found the 50% reduction of pot draft will not cause a significant change in the ventilation pattern of potroom and the draft reduction can be realised without significantly increasing the potrooms heat stress.

Empirical Modeling of The Baking Furnace To Predict Baked Anode Properties

A soft-sensor model developed from historical carbon plant data and multivariate statistical methods was proposed in past work to obtain quick predictions of individual anode properties right after baking for quality control purposes. It could only be used for anodes baked at the coldest and hottest positions within the furnace due to the core sampling method used at the partner plant and the way the data is collected. To complement the soft-sensor, this work proposes a strategy to account for the thermal history of anodes baked at any position. It is shown that combining categorical variables for pit and baking positions and routinely available firing equipment data is sufficient to predict the temperature history of anodes baked in different positions, which is typically not measured during normal operation. The model will be integrated to the soft-sensor in the future to account for the impact of baking position on anode properties.

Improvement of Alumina Dissolution Rate through Alumina Feeder Pipe Modification

Aluminum reduction cells use about 1.9 kg of alumina in order to produce 1 kg of aluminum. That is, for modern reduction cells operating in the 350 to 400 kA range, 5000 to 6000 kg of alumina is fed daily. Considering that 5000 to 10000 kg of molten bath is available to dissolve the alumina, the dissolution rate is an important factor in order to avoid muck and enable alumina feed control system to operate within the 2 to 5% alumina concentration. However, on top of cell status, alumina properties have an impact on alumina dissolution rate. Hence, supplier changes and/or segregation of alumina within the delivery system may have negative impact on alumina dissolution rate leading to muck and/or anode effects. This paper discusses modification to an alumina feeder pipe promoting the dissolution rate. Promising results obtained during trial in a pilot plant section are presented and discussed.