A non-destructive technique for the on-line quality control of green and baked anodes

Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant economic and environmental impact. Carbon anodes are made of dry aggregates, composed of petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several factors, defects (cracks/pores) appear in anodes during the fabrication process, affecting their quality. It is thus essential to control the quality of anodes before their use in the electrolysis cell. Current practice for the quality evaluation (visual inspection, core analysis) gives limited information. As an alternative to this practice, electrical resistivity measurements can be used. Electrical resistivity is one of the key indicators for anode quality and its homogeneity. A simple and non-destructive method has been developed for the specific electrical resistivity measurement of anodes (SERMA) for on-line control of anode quality. Various tests have been carried out at both lab scale and industrial scale. In this study, the electrical resistivity distributions in the lab-scale anodes were measured and compared with those of the tomography analysis. The method is able to detect defective anodes even before the baking process

Measurement of anode electrical resistivity for quality control in aluminium industry

The carbon anodes used in the electrolytic production of aluminum are made of petroleum coke, recycled anodes and butts, and coal tar pitch. Due to technological advances in the aluminum production technology, aimed at increasing production and decreasing energy consumption and greenhouse gas emissions, better quality anodes are required. Presently, the anode quality is evaluated by visual inspection and the analysis of a small core taken from 1.5-2% of the anodes produced. The visual inspection is susceptible to human error and limited to surface imperfections. The analysis of cores takes time, and therefore, it is difficult to determine the existence of a problem and intervene at the right time. In addition, the core does not represent the whole anode due to the non-homogeneity of anodes. A validated online anode quality control system can highly improve the situation. In this article, an electrical resistivity measurement method developed for this purpose is presented

An artificial neural network model for predicting the CO2 reactivity of carbon anodes used in the primary aluminum production

Carbon anode is one of the key components for the electrolytic production of aluminum. It is mainly composed of calcined petroleum coke, coal tar pitch, and recycled carbon materials. The impurities in the raw materials, which are mainly by-products of different industries, influence significantly the quality of anodes. Usually, no well-known mathematical relationship exists between the various physical and chemical properties of raw materials and the final anode properties. In such situations, the artificial neural network (ANN) methods can serve as a useful tool to predict anode properties. In this study, published data have been used to show the proficiency of different artificial neural networks using the MATLAB software. The average error between the predicted and experimental values is around 6 %. The artificial neural network was also used to identify the effect of impurities such as, vanadium, iron, sodium, and sulfur on the CO2 reactivity of anodes. ANN also showed the effect of pitch percentage and coke porosity on the CO2 reactivity of anodes. The effect of CO2 and air reactivities of coke on the CO2 reactivity of anode was also studied. The predictions were found to be in good agreement with the results of other studies in the literature

Étude de l’amélioration des propriétés des anodes par le brai modifié

Dans l'industrie de l'aluminium, les anodes sont utilisées afin de fournir le carbone nécessaire à la réduction électrolytique de l'aluminium. Toutefois, la compatibilité des matériaux de base est compromise par la qualité décroissante du coke et du brai nuisant à l'obtention des propriétés finales des anodes. L'objectif de ce travail est de vérifier si l'amélioration de la mouillabilité du coke par un brai modifié chimiquement peut contribuer à améliorer certaines des propriétés d'anodes. La méthodologie prévoit la fabrication d'anodes au laboratoire de carbone de l'UQAC à partir de brais modifiés à l'aide d'un additif chimique et la comparaison avec des anodes standards. Deux additifs chimiques ont été testés. Les anodes sont ensuite carottées et les échantillons sont caractérisés à l'état cru et cuit selon les normes appropriées. Dans cette étude, les deux additifs sélectionnés ont permis de démontrer une amélioration significative de certaines des propriétés des anodes

Interaction of bio-coke with different coal tar pitches

The interactions of pyrolyzed and calcined bio-cokes with three coal tar pitches of different properties were studied using a sessile drop test at 170 °C. A model was employed to characterize and quantify the spreading and penetration of pitch into bio-coke bed. The pyrolyzed bio-cokes were produced from softwood materials by heat treatment at 426 °C. The calcined bio-cokes were produced by calcining the pyrolyzed bio-coke at 1200 °C. Optical microscope, SEM/EDS, XRD, and FTIR techniques were used to analyze the coke–pitch interface and study their interaction mechanisms. The results show that the wettability of bio-coke is related to both pitch and coke properties. It is found that the presence of small amount of uniformly distributed small size quinoline insolubles (QI) in pitch seems to help pitch spread and penetrate into the bio-coke bed. Besides, calcination changes the chemical structure of bio-coke, enriches its carbon (C%) content, increases its crystalline length (Lc), and lowers its wettability by pitch

Wettability of bio-coke by coal tar pitch for its use in carbon anodes

Information on the wettability of a bio-coke substrate is of great value in assessing its possible use as a potential raw material for carbon anode production. In this study, the interaction mechanisms of a coal tar pitch with six bio-coke substrates were studied at a temperature of 170 °C, a typical industrial value for coke-pitch mixing, using a sessile-drop test. Three bio-cokes were produced from different bio-materials by pyrolyzing them to 426 °C, and the other three by further calcining them to 1200 °C. Different techniques were used to analyze the structural and chemical characteristics of the six bio-cokes. The results show that the heat treatment temperature has a significant influence on the chemical properties of bio-cokes and the wettability of pitch/bio-coke systems. The possibility of partial replacement of petroleum coke by bio-coke is discussed from the point view of the suitability of its structure and its wettability

Coke–pitch interactions during anode preparation

The information on the interactions between coke and pitch is of great value for the aluminum industry. This information can help choose the suitable coke and pitch pairs as well as the appropriate mixing parameters to be used during the production of anodes. In this study, the interaction mechanisms of pitch and coke at the mixing stage were studied by a sessile-drop test using two coal-tar pitches as the liquid and three petroleum cokes as the substrate. The results showed that the coke–pitch interactions are related to both pitch and coke chemical compositions. The contact angle of different coke–pitch systems decreased with increasing time and temperature. At high temperatures, decreasing the pitch viscosity facilitated the spreading of pitch and its penetration into the coke bed. The chemical behavior of petroleum cokes and coal tar pitches were studied using the FT-IR spectroscopy and XPS. The results showed that the wettability behavior of cokes by pitches depends on their physical properties as well as the presence of surface functional groups of coke and pitch which can form chemical bonds

Modification of coke by different additives to improve anode properties

Aluminum is produced in electrolytic cells using carbon anodes, which consist of a mixture of coke, pitch, and recycled carbon material. Anodes play an important role in aluminum production. The quality of raw materials can vary based on the source and the process parameters. In spite of the variations in the raw material properties, the industry has to maintain the quality of anodes. In order to manufacture good quality anodes, coke and pitch must interact well with each other. The affinity between these two components depends on good wetting properties, which will lead to good binding of the particles. The main objective of this work is to modify the coke in order to improve its wetting properties using different additives. An FT-IR study was done to identify certain functional groups in non-modified and modified coke as well as in pitch. The wetting tests were carried out using the sessile-drop method to measure the contact angle between cokes and pitch. Based on FT-IR and wettability results, an additive was selected and used for the fabrication of anodes, which were characterized before and after baking. The modification of coke with the selected additive improved the anode properties

The wettability of coke by pitches with different quinoline-insoluble contents

The properties of pitch as the binder material for carbon anode manufacturing strongly affect the anode properties. Pitches show significant differences in their chemical composition depending on their origin. In this study, five coal tar pitches with different quinoline-insoluble (QI) contents were studied to understand the wettability of one calcined petroleum coke by these pitches using the sessile-drop test. The chemical properties of the coke and pitch were studied using XPS and FT-IR to investigate their wetting mechanism and their interactions. The structures of different pitches and the pitch-coke interface were characterized by optical microscopy and SEM, respectively. The results showed that not only the chemical but also the physical properties of the pitches contribute to the wettability of coke. The wettability increases with increasing heteroatom content in the pitch. The viscosity of pitch is a key parameter controlling the wetting behavior of pitch. The QI content, the solid particle size and their distribution in the pitches play a significant role in the wettability of coke by pitch

A non-destructive technique for the on-line quality control of green and baked anodes

Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant impact on economics and environment. Carbon anodes are made of dry aggregates, composed of petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several factors, cracks and defects appear in anodes during the fabrication process, affecting their quality. It is thus essential to control the quality of anodes before their use in the electrolysis cell. Current practice for the quality evaluation (visual inspection, core analysis) gives limited information. As an alternative to this practice, the electrical resistivity measurement, one of the key indicators for anode quality and its homogeneity, can be used. A simple and non-destructive method has been developed for the specific electrical resistivity measurement of anodes (SERMA) for on-line control of anode quality. Various tests have been carried out at both lab scale and industrial scale. In this study, the resistivity distributions in the lab scale anodes were measured and compared with those of the tomography analysis. The method is able to detect defective anodes even before the baking process