Aluminum Electrolysis Cells Research Articles

Undissolved alumina in dynamic chunks piercing through the bath - metal interface in industrial aluminum electrolysis cells

In Hall–Héroult cells the uninvolved alumina precipitates on the top of the cathode to form resistive deposits which could significantly impact the energy consumption. A dynamic energy conservation (DEC) approach has been developed to quantify the flux of undissolved alumina piercing the interface between the electrolyte and the liquid metal inHall–Héroultcells. The proposed DEC model considers both electrochemical and interfacial phenomenon between the electrolyte and the liquid metal. A critical radius at or below which a particle of undissolved alumina is retained at the electrolyte/liquid metal pad interface is defined and quantified considering the heat transfer and electrolysis cell operating parameters: temperature, electrolyte composition, alumina porosity, and current density. The proposed approach appears reliable to quantify the amount of undissolved alumina which pierces the electrolyte/liquid metal pad interface and precipitates to the bottom of the cell to form a deposit on the cathode.

Numerical Simulations and Thermal Diagnostic of Ledge Formation in Hall–Heroult Aluminum Electrolysis Cell with a Solidification Front at the Cryolite-Metal Baths Interface for Reduction of Heat Losses

Numerical Simulations and Thermal Diagnostic of Ledge Formation in Hall–Heroult Aluminum Electrolysis Cell with a Solidification Front at the Cryolite-Metal Baths Interface for Reduction of Heat Losses

A comprehensive review of aluminium electrolysis and the waste generated by it.

Aluminium is produced by electrolysis using alumina (Al2O3) as raw material and cryolite (Na3AlF6) as electrolyte. In this Hall-Héroult process, the energy consumption is relatively large, and solid wastes such as spent anodes and spent pot liner, flue gas and waste heat are generated. Therefore, this article discusses from the perspective of high energy consumption and high pollution and summarizes the methods to reduce energy consumption and solve pollution problems. The functions of carbon anode, carbon cathode, refractory material and sidewall in aluminium electrolysis cells are discussed in detail. The process of aluminium electrolysis and the ways to improve the current efficiency of aluminium electrolysis cells and reduce their energy consumption are outlined. The causes and treatment methods of spent anodes, spent cathodes, spent refractories and spent spot liner are reviewed. The research progress of waste heat recovery and aluminium electrolysis flue gas purification are analysed. And the future research directions of aluminium electrolysis flue gas are provided.

Improved CFD Modeling of the Whole-Cell Side Ledge Behavior in Aluminum Electrolysis Cell

Improved CFD Modeling of the Whole-Cell Side Ledge Behavior in Aluminum Electrolysis Cell

Numerical Simulations of Wettability on Anodic Bubble Expansion in Aluminum Electrolysis Cell Using Lattice Boltzmann Method

Numerical Simulations of Wettability on Anodic Bubble Expansion in Aluminum Electrolysis Cell Using Lattice Boltzmann Method

Analysis of anode current distribution in aluminum electrolysis cell based on equivalent circuit numerical simulation

The development of modern industrial aluminum reduction cell towards the direction of higher line current and more anodes. The distribution of anode current and the stability of the fluid in reduction cell are directly affected by the busbar configuration. In this paper, a simulation model of the multi-loop equivalent circuit of aluminum electrolysis cell was established by using MATLAB/Simulink, and the distribution characteristics of anode current under three different current risers were analyzed. The results show that with the increase of the number of terminals, the cell voltage decreases and anode current distribution is more uniform. The anode current is positively correlated with the distance from the terminal and the current of the nearest column busbar.

Numerical simulation study of the effect of anodic bubble behavior in aluminum electrolysis cell

During the aluminum electrolysis process aluminum is produced at the cathode and CO2 gas bubbles are generated on the anode and released. The bubbles reduce the active surface area of the anode, which increases energy consumption. They also cause the liquid aluminum to fluctuate and oxidize again. The study of anodic bubble behavior is important to reduce power consumption and improve current efficiency. In this paper, the phase field, laminar flow and tertiary current distribution modules in COMSOL Multiphysics are applied to simulate the growth and motion patterns of anodic bubble in the electrolytic cell to visualize and analyze the behavior of anode bubble.

Superheat Degree Recognition of Aluminum Electrolysis Cell Using Unbalance Double Hierarchy Hesitant Linguistic Petri Nets

Superheat degree is a core technical parameter and management index of aluminum electrolysis cell. However, the exiting methods have limited abilities when applied to superheat degree recognition of aluminum electrolysis cell (SDRAEC). In addition, the important hesitant degree is ignored in the unbalance double hierarchy linguistic term set. To address these issues, an unbalance double hierarchy hesitant linguistic Petri net model and extended TOPSIS is proposed for SDRAEC. In this model, the coupling relationships among variables is made to be explicit knowledge, and the unbalance double hierarchy hesitant linguistic term set is proposed to represent the value of knowledge parameter. The relative entropy is introduced to enhance the performance of extended TOPSIS. Moreover, hybrid averaging unbalance double hierarchy hesitant linguistic term set concurrent reasoning algorithm is proposed to improve reasoning efficiency. Finally, thermal analysis experiments conducted in a real-world aluminum electrolysis plant are used to demonstrate the effectiveness of the proposed method. Compared with other methods, the accuracy of SDRAEC has been increased to 89.00%.

Dimensional reduction of a 3D thermoelectric model to create a reliable and time-efficient 2D model representing an aluminum electrolysis cell

In order to optimize the use of their assets, aluminum smelters aim at increasing the line current. In addition, the fluctuations of the energy market push the industry to exploit power modulation strategies. These variable operating conditions directly affect the thickness of the protective layer (ledge) inside the electrolysis cell. Continuous monitoring of the energy balance is therefore of utmost importance, although physical measurements are difficult due to the hostile environment. The 3D thermoelectric slice digital model is the most frequently used to solve the energy balance, but its high computation time prevents it from being used in a control system. For the first time, the creation of a novel 2D model from an existing 3D slice model is proposed for online thermal diagnosis and process control purposes. The creation starts with a detailed dimensional reduction protocol, which is a significant industrial contribution since it can be applied to any industries relying on 3D physical models. The rigorous methodology developed involves the identification of adjustable parameters that are inserted in the 2D model to minimize deviations caused by physical differences between models and ensure its reliability. Once calibrated, the 2D model is tested using a ± 5% input current variation. The results show minor differences (below 1%) between 3D and 2D models for the predicted behavior of the heat losses distribution and generated heat distribution. Side ledge profiles are very close in both models, the largest difference (1.8 cm) being in an acceptable range for this key operational parameter. During all simulations, the 2D model computing time was 40 to 60 times faster than the 3D model. With the 4.0 era, this is a reliable and time-efficient tool for industries wishing to turn to digital twins.

Thermo-mechanical Studies of Thimble Geometry and Stub Materials for Voltage Drop Across the Anode-Rod Connection in Aluminum Electrolysis Cell

Thermo-mechanical Studies of Thimble Geometry and Stub Materials for Voltage Drop Across the Anode-Rod Connection in Aluminum Electrolysis Cell

In-depth purification of spent pot-lining by oxidation-expansion acid leaching – A comparative study

Spent pot lining (SPL) is a hazardous solid waste generated after overhauling the aluminum electrolytic cell. SPL contains carbon resources with high graphitization and toxic impurities, such as NaF, Na3AlF6, and CaF2. These toxic substances are difficult to remove from graphite completely. This study introduces an innovative method of oxidation-expansion acid leaching (OEAL) to eliminate impurities inside the graphitized carbon. For such a purpose, typical purification methods (conventional leaching, flotation-acid leaching) were investigated and compared to OEAL. The experimental outcomes indicated that the process efficiency for removing SPL impurities by various methods had the following sequence from high to low: OEAL > flotation-acid leaching > conventional leaching. The maximum SPL impurities removal rate by conventional leaching and flotation-acid leaching was 89.65 %, while it was 99.36 % with the OEAL method. For understanding fundamental aspects of the SPL impurity removal, their rejection mechanisms in the examined methods were systematically studied by different instrumentals and chemical analysis techniques. As a result of the reaction between H+ and residuals during OEAL process, the distance between graphitized carbon layers expands. This expansion resulted in a qualitative improvement in the SPL impurity removal by OEAL, making SPL one of the graphite or graphene oxide resources.

Primary Production of Aluminium and Its Alloys in Molten Salts with Oxygen Evolving Anodes: Overview

Due to environmental and economic concerns, carbon-free aluminium production has been an ultimate target for aluminium industries. For the last few decades, a considerable amount of research has been conducted to find a suitable inert anode that could replace the consumable carbon anodes for aluminium electrolysis. Material types such as metals, ceramics and cermets have been studied extensively. All the anode materials have their advantages and disadvantages. However, metallic alloys have been considered attractive anode material candidates due to their high electrical conductivity, thermal stability and easy fabrication and machining properties. For a successful adaptation of metallic anodes into the aluminium electrolysis cell, an electrolyte with a low-operating temperature and high alumina solubility is required. Another significant component of the carbon-free aluminium electrolysis cell is a wettable cathode. This overview discusses the research progress on inert anodes, wettable cathodes and electrolytes.

Purification of spent cathode carbon from aluminum electrolysis cells by alkali fusion-acid leaching process

Purification of spent cathode carbon from aluminum electrolysis cells by alkali fusion-acid leaching process

Resource utilization strategies for spent pot lining: A review of the current state

During a long-term operation of the aluminum electrolysis cell, the molten salts continuously infiltrate and corrode the pot lining, resulting in a huge amount of hazardous waste after the overhaul. The first cut of spent pot linings (SPL) contains several carbon-rich materials with potential economic value and hazardous matters such as soluble fluorite and cyanide. The continuous accumulation and disposal of SPL in depots or landfills have created a severe challenge to the aluminum industry. Nowadays, the technologies of harmless disposal and resource utilization of SPL have been paid more attention. This work has explored and presented the properties of SPL (including chemical, physical, and thermodynamic properties, etc.) and methods for its detoxification and purification. In this regard, the resource utilization strategies of SPL are systematically sorted out from three aspects: traditional, co-processing, and high-value technologies. In the end, the current challenges and future perspectives for the environmental recycling of SPL have been analyzed and summarized.

Thermal Behavior of the early Life of an Aluminum Electrolysis Cell

The electrolytic production of aluminium starts after the completion of the cathode lining and the baking process. After that, the cell start-up period is followed by the early operating period. During the early operating period, the following parameters (cell voltage, metal height, electrolyte height, cryolite ratio, electrolyte temperature, and ledge formation) were measured and investigated. The required times for these parameters to reach the steady-state have been investigated. The cell voltage, metal height, electrolyte height, cryolite ratio, and electrolyte temperature were stabilized after 35, 25, 24, 86, and 45 days, respectively from cell start-up. These cells took four months to form a stable ledge at a thickness of 10 cm. Also, the thermal behavior of the sidewall carbon blocks was studied during the early operating period by inserting twenty thermocouples at these locations in three prebaked cells. The cell instability during the early operation period for these cells was illustrated.

Investigation of phase transformation related electrical conductivity of long-term heat treated aluminium electrolysis cathodes

This study presents an investigation on the specific electrical conductivity of the cathode materials used in an aluminium electrolysis cell over a temperature range between room temperature and 950 °C. Those materials are subjected to a diffusion related aging process due to the high operating temperature of the cell, leading to a change in chemical composition and microstructure. The materials were investigated both in the initial state before use in an aluminium electrolysis cell and after an operating period of 5 years. It is shown that the changes in chemical composition and thus also in microstructure over the service life at elevated operating temperature exert an effect on the electrical conductivity. In addition, calculations based on thermodynamic data were used to relate phase transformations to the changes in electrical conductivity. On the one hand, the electrical conductivity of the collector bar at 950 °C is reduced by about 11% after 5 years of service. On the other hand, the ageing process has a positive influence on the cast iron with an increased conductivity by about 41% at 950 °C. The results provide an understanding how diffusion related processes in the cathode materials affect energy efficiency of the aluminium electrolysis cell.

Optimization of aluminum fluoride addition in aluminum electrolysis process based on pruned sparse fuzzy neural network

The aluminum fluoride (AF) addition in aluminum electrolysis process (AEP) can directly influence the current efficiency, energy consumption, and stability of the process. This paper proposes an optimization scheme for AF addition based on pruned sparse fuzzy neural network (PSFNN), aiming at providing an optimal AF addition for aluminum electrolysis cell under normal superheat degree (SD) condition. Firstly, a Gaussian mixture model (GMM) is introduced to identify SD conditions in which the operating modes of AEP are unknown. Then, PSFNN is proposed to establish the AF addition model under normal SD condition identified by GMM. Specifically, a sparse regularization term is designed in loss function of PSFNN to extract the sparse representation from nonlinear process data. A structure optimization strategy based on enhanced optimal brain surgeon (EOBS) algorithm is proposed to prune redundant neurons in the rule layer. Mini-batch gradient descent and AdaBound optimizer are then introduced to optimize the parameters of PSFNN. Finally, the performance is confirmed on the simulated Tennessee Eastman process (TEP) and real-world AEP. Experimental results demonstrate that the proposed scheme provides a satisfactory performance.

Analysis of current distribution of electrode change operation in aluminium electrolysis based on equivalent circuit computer numerical

The development of industrial aluminium electrolytic cells towards higher series currents and a larger number of anodes, coupled with the fact that China has made more restrictions on high energy-consuming industries, has placed higher demands on the management of the aluminium electrolytic industry. In this study, a digital twin model of the electrolytic cell based on the idea of equivalent circuits was constructed using Matlab/Simulink software to simulate the electrode change operation and to study its effect on the change of current field. It is shown that the electrolysis temperature and the change of ACD caused by horizontal current have an effect on the current distribution.

Knowledge Representation and Reasoning with an Extended Dynamic Uncertain Causality Graph under the Pythagorean Uncertain Linguistic Environment

A dynamic uncertain causality graph (DUCG) is a probabilistic graphical model for knowledge representation and reasoning, which has been widely used in many areas, such as probabilistic safety assessment, medical diagnosis, and fault diagnosis. However, the convention DUCG model fails to model experts’ knowledge precisely because knowledge parameters were crisp numbers or fuzzy numbers. In reality, domain experts tend to use linguistic terms to express their judgements due to professional limitations and information deficiency. To overcome the shortcomings of DUCGs, this article proposes a new type of DUCG model by integrating Pythagorean uncertain linguistic sets (PULSs) and the evaluation based on the distance from average solution (EDAS) method. In particular, experts express knowledge parameters in the form of the PULSs, which can depict the uncertainty and vagueness of expert knowledge. Furthermore, this model gathers the evaluations of experts on knowledge parameters and handles conflicting opinions among them. Moreover, a reasoning algorithm based on the EDAS method is proposed to improve the reliability and intelligence of expert systems. Lastly, an industrial example concerning the root cause analysis of abnormal aluminum electrolysis cell condition is provided to demonstrate the proposed DUCG model.

Dynamic Video Image Segmentation Based on Dual Channel Convolutional Kernel and Multi-Frame Feature Fusion.

The color image of the fire hole is key for the working condition identification of the aluminum electrolysis cell (AEC). However, the image of the fire hole is difficult for image segmentation due to the nonuniform distributed illuminated background and oblique beam radiation. Thus, a joint dual channel convolution kernel (DCCK) and multi-frame feature fusion (MFF) method is developed to achieve dynamic fire hole video image segmentation. Considering the invalid or extra texture disturbances in the edge feature images, the DCCK is used to select the effective edge features. Since the obtained edge features of the fire hole are not completely closed, the MFF algorithm is further applied to complement the missing portion of the edge. This method can assist to obtain the complete fire hole image of the AEC. The experiment results demonstrate that the proposed method has higher precision, recall rate, and lower boundary redundancy rate with well segmented image edge for the aid of working condition identification of the AEC.