Baking Furnace Research Articles

Quantifying the Carbon Footprint of the Alouette Primary Aluminum Smelter

The Alouette primary aluminum smelter is the largest in the Americas, with an annual production of ~ 630,000 t of aluminum. In this collaborative study, a detailed product carbon footprint analysis was undertaken by Rain Carbon using a large body of primary emissions data to provide a complete cradle-to-gate analysis of the smelter’s emissions. The total carbon footprint of the smelter in 2019 was 3914 kg CO2e/t of aluminum for scope 1, 2, and 3 emissions, and 1835 kg CO2e for scope 1 and 2 emissions. The modeling results were compared to those for global average and Canadian average smelters, using reference datasets developed by the International Aluminium Institute (IAI) and GaBi Professional Database. Alouette’s carbon footprint is ~ 76% lower than a world average smelter and ~ 25% lower than a Canadian average smelter. For the scope 3 emissions, the primary contributors to the lower carbon footprint are lower emissions from the alumina supply and the calcined petroleum coke supply. Today, Alouette produces among the lowest carbon aluminum in the world, and this is set to decrease further following a switch from fuel oil to natural gas in the anode baking furnaces, and a switch to LNG at the alumina supplier refinery.

Modeling Conjugate Heat Transfer in an Anode Baking Furnace Using OpenFoam

The operation of large industrial furnaces will continue to rely on hydrocarbon fuels in the near foreseeable future. Mathematical modeling and numerical simulation is expected to deliver key insights to implement measures to further reduce pollutant emissions. These measures include the design optimization of the burners, the dilution of oxidizer with exhaust gasses, and the mixing of natural gas with hydrogen. In this paper, we target the numerical simulation of non-premixed turbulent combustion of natural gas in a single heating section of a ring pit anode baking furnace. In previous work, we performed combustion simulations using a commercial flow simulator combined with an open-source package for the three-dimensional mesh generation. This motivates switching to a fully open-source software stack. In this paper, we develop a Reynolds-Averaged Navier-Stokes model for the turbulent flow combined with an infinitely fast mixed-is-burnt model for the non-premixed combustion and a participating media model for the radiative heat transfer in OpenFoam. The heat transfer to the refractory brick lining is taken into account by a conjugate heat transfer model. Numerical simulations provide valuable insight into the heat release and chemical species distribution in the staged combustion process using two burners. Results show that at the operating conditions implemented, higher peak temperatures are formed at the burner closest to the air inlet. This results in a larger thermal nitric-oxide concentration. The inclusion of the heat absorption in the refractory bricks results in a more uniform temperature on the symmetry plane at the center of the section. The peak in thermal nitric-oxides is reduced by a factor of four compared to the model with adiabatic walls.

Study on the cracking of carbon anodes used in aluminium industry

AbstractCarbon anodes are used in aluminium electrolysis. Their quality plays a major role in the stability of cell operation and energy consumption. The improvement of the quality of carbon anodes is essential to respond to the many challenges the aluminium industry is facing with respect to issues related to carbon loss, energy use, cell performance, and production cost, especially for high amperage cells. The presence of cracks increases the anode resistivity, and, as a result, power consumption, production cost, and greenhouse gas emissions also increase. Therefore, it is important to know how the cracks form during anode production. An industrial measurement campaign was carried out at the Aluminerie Alouette Inc. (AAI) plant in Sept‐Îles, Québec, Canada. The effect of raw materials (type of coke, pitch, and butts), vibro‐compaction (vibro‐compactor type, balloon pressure, and vibration time), and the position of anodes in the baking furnace on anode cracking was investigated. It was found that the anode centre is the region that contains the most cracks compared to other parts of the anode. The cracks in the horizontal direction are more predominant than those in other directions. The raw materials and the operating parameters of each anode production step affect anode cracking.

Effects of Mesh Generation on Modelling Aluminium Anode Baking Furnaces

Anode baking is critical in carbon anode production for aluminium extraction. Operational and geometrical parameters have a direct impact on the performance of anode baking furnaces (ABF), and hence on the resulting anode quality. Gas flow patterns, velocity field, pressure drop, shear stress and turbulent dissipation rate are the main operational parameters to be optimised, considering a specific geometry that is discretised as a mesh. Therefore, this paper aims to establish the need to generate an appropriate mesh to perform accurate numerical simulations of three-dimensional turbulent flow in a single section of an ABF. Two geometries are considered for generating three meshes, using COMSOL and cfMesh, with different refinement zones. The three meshes are used for creating nine incompressible isothermal turbulent flow models, with varying operational parameters. Velocity field, convergence and turbulent viscosity ratio in the outlet of fuel inlet pipes are the quantification criteria. Quantification criteria have shown that a better physical representation is obtained by refining in the whole combustion zone. COMSOL Multiphysics’ built-in mesh generator allows quadrilateral, tetrahedron and hexahedron shapes. Adaptive cell sizes and shapes have a place within modelling, since refining a mesh in appropriate zones brings the Peclet number down when the incompressible isothermal turbulent flow is simulated.

Analysis of the Aerodynamics in the Heating Section of an Anode Baking Furnace Using Non-Linear Finite Element Simulations

The emissions from the industrial furnaces impact the environment. Among the various factories, those having anode baking furnaces are working on reducing the pollutant emissions. The aerodynamics in the furnace influences the emissions due to the high dependence of combustion and radiation phenomena on the mixing characteristics. Therefore, this paper aims to establish the numerical simulation results for the three-dimensional turbulent flow in a single section of an anode baking furnace with a high rate of fuel injection. The stabilized non-linear finite element approach on the Reynolds-averaged Navier-Stokes (RANS) equation is used with COMSOLMultiphysics. The turbulent viscosity ratio is highly sensitive to the mesh for the standard k-ϵ model. The requirements of the Cartesian and refined mesh near the jet development region is explained. The comparison of meshes generated by two meshing tools namely cfMesh and COMSOL Multiphysics default Mesher is carried out. The high numerical diffusion in the flow models due to the coarser mesh leads to convergence but deficit the precision in the results. This paper shows that the mesh generated by cfMesh with flow aligned refinement combined with the non-linear finite element solver in COMSOL Multiphysics proves to provide accurate results of turbulent quantities.

Numerical Simulation of New Anode Baking Furnace

The quality of baked anode is directly determined by the uniformity of temperature field in the baking furnace flue-wall. The temperature difference between the upstream and downstream of the traditional furnace is large and the temperature distribution in the pit is uneven, and the natural gas energy consumption is high. In this work, the flow field in the flue and the temperature homogeneity in the pit of newly developed anode baking furnace are mainly presented. The industrial test in a carbon plant showed that a uniform temperature distribution is achieved and the quality of the baked anode is improved greatly with the natural gas saving of 10.4 m3 per ton of carbon produced.

Structural and thermal analysis of an innovative baking furnace for carbon anode production

The urgent demands for the high efficiency and low consumption of carbon anode baking process stimulate the structure optimization of the baking furnace. In this paper, a closed-top innovative anode baking furnace (CTABF) with periodically arranged burners and anode crucibles is proposed, and the thermal process in the CTABF is studied via a coupled multi-physics model and the in situ measurement. Results show that the multi-channel design changes the one-way high-temperature flue gas path and increases its residence time in the furnace, while the temperature distributions in the inner and outer crucibles show good uniformity. The average convective heat flux accounts for about 68% of the total heat flux around the crucible surface, and thus the baking rate of anodes can be controlled by adjusting the power of driven fan. Therefore, due to the above structural retrofits, the baking time and energy consumption are reduced and the baking quality is improved, showing the superiority of the proposed CTABF over the traditional ABF.

The Impact of Critical Operational Parameters on the Performance of the Aluminum Anode Baking Furnace

Abstract Minimizing energy consumption and reducing pollutant emissions during the carbon anode baking process are critically important for the aluminum industry. The present study investigates the effects of oxidizer inlet temperature, inlet oxygen concentration, equivalence ratio, refractory wall thermal conductivity, and refractory wall emissivity on the baking process using unsteady Reynolds-averaged Navier–Stokes (URANS)-based simulations in conjunction with the presumed probability density function method. Numerical results are combined with a response surface methodology (RSM) to optimize the anode baking process. The advantage of the coupled method is that it can adequately provide information on interactions of different input parameters. It is remarked that the significance level of the studied parameters varies drastically for different outputs. It is noted that diluting inlet oxygen concentration (from 23% in atmospheric air to 15%) at an elevated oxidizer temperature leads to enhanced furnace fuel efficiency, more uniform temperature distribution, and lower pollutant emissions. A linear model is detected to be adequate for response surface modeling of the anode baking furnace NOx formation. On the other hand, furnace soot formation is modeled with a higher-order model due to the quadratic behavior of the response.

Application of converting HSD to LNG

Anode baking furnace uses oil as fuel. The baking process is decisive for the quality and cost of an anode, and the environmental impact. Using natural gas as fuel can reduce the cost production of the anode by $ 9.45, and reduce emission from combustion in the furnace for CO2 by 28%, NOx by 79 %, and SOx by more than 95 %. Emission reduction correlated to the consumption of NaOH that used for wastewater. NaOH can save by $ 34,000 per year and make more durability of the equipment. The total profit for this improvement is $ 1,245,345 per year.

A system of automated control for the baking process that minimizes the probability of defects

We have designed and investigated a system of automated control for a carbon baking furnace that makes it possible to minimize the probability of defects. Based on the artificial neural networks, it differs from actual systems by the possibility to select the technique to control the process of baking in accordance with the starting conditions and the purpose of the process. Such purposes in the process for baking carbon articles include the obtaining of products with a minimum number of defective structures or a safe reduction in the length of the technological process to save energy. To minimize the number of defective structures in finished products, it is proposed to predict the probability of a defect in a product and, to reduce the duration of the technological process, to apply entropy as an indicator of product readiness. Solving the set tasks is based on the use of artificial neural networks with their capability to generalize data, namely different values of the probability of a defect in the various temperature fields in a baking furnace under operational modes. The issue of the limited amount of data required to train an artificial neural network is resolved by applying a special structure of artificial neural networks, an autoencoder. The designed control system has several advantages over the systems already in use. For example, it makes it possible to select a step of the descent that determines the accuracy of the optimal descent trajectory and, therefore, the accuracy of control in general. Selecting a descent criterion makes the designed system flexible when used under different conditions and for different control tasks. In case of an emergency interruption of the technological process of baking, a given system makes it possible to plan its further progress at any time, thereby providing for an effective continuation of the baking process and thus avoiding unjustified expenditures. The control algorithm used in the system makes it possible to predict the duration of baking and the value of fuel consumption and thus predict the economic efficiency of the technological process. To assess the efficiency of the proposed system of automated control over the baking process, we have performed an experimental study of the designed system operation compared to the actual control system based on a PID-controller. The study results have demonstrated that the use of the new control system makes it possible to reduce fuel consumption by 3‒4 m 3 /h. In addition, there is a decrease in the growth of the temperature of blanks during treatment, which positively affects the quality of the finished products

Multi-objective Optimization of Aluminum Anode Baking Process Employing a Response Surface Methodology

In the aluminum anode baking furnace, the operational parameters have a significant influence on the furnace performance and the resulting anode quality. For this furnace, an important parameter is the fire-cycle, which determines the production rate of the baking kiln and the anodes quality. Shorter fire-cycle results in a higher furnace production rate and a higher fuel consumption (same anode temperature should be obtained in a shorter time). For a particular fire-cycle, flue-gas soaking temperature and soaking time are the other two key parameters that affect anode temperature distribution and furnace energy consumption. Limited studies in the literature focused on employing the traditional one-factor-a-time (OFAT) method to investigate the effect of these factors. Based on a simplified multi-physics model, a high-fidelity computational tool named ABKA (anode baking kiln analysis) software is developed to investigate the effects of these key operational parameters on the anode baking furnace heating performance. ABKA is employed to conduct a three-factors, two-level full factorial design, with a center point, to investigate the effects of varying fire-cycle, soaking temperature, and soaking time on furnace production rate, fuel consumption, and anode maximum, minimum and average temperature. The advantage of the present approach compared to the traditional one-factor-a-time (OFAT) method is that it can provide adequate information on interactions of different input variables, to effectively estimate the significance level of each factor, and to identify clear optimal settings of the three variables. Using ANOVA (analysis of variance), the effect and significance level of each factor and their interactions are effectively estimated. It is observed that soaking temperature has the highest impact on the final anode temperature distribution. Considering the furnace fuel consumption as a response, it is perceived that soaking time and soaking temperature jointly are as significant. Finally, employing RSM (response surface methodology), conducting multi-objective optimization, the optimal settings of the soaking time and soaking temperature for different production rates (fire-cycle values) are also estimated.

In Situ Monitoring of Pit Gas Composition During Baking of Anodes for Aluminum Electrolysis

Carbon anodes, which are consumed in aluminum electrolysis, are fabricated in separate anode plants where coke and pitch are mixed and vibrocompacted to green anode blocks before being baked in anode baking furnaces. The chemical environment inside an anode baking furnace is found to play an important role in the degradation of the furnace refractory lining. In this work, the pit gas composition was recorded during anode baking by a Fourier transformed infrared spectroscopy (FTIR) spectrometer and a gas chromatograph. The temperature dependence of the concentration of gas species during baking was obtained based on three measurement campaigns. The concentrations of CO and CO2 were found to be dependent on temperature, where the concentration of CO peaked around the maximum firing temperature. In addition to varying concentrations of CH4 and HF, water was found in large amounts in the first part of the baking cycle. The water originates to some extent from the cooling of the green anodes after vibrocompaction and is potentially important with respect to the chemical stability of the refractory lining. The variations in pit gas composition are related to operational parameters and are discussed in relation to refractory degradation phenomena.

Research of the influence of fuel flow rate on the temperature fields of a coal product baking furnace

Research of the influence of fuel flow rate on the temperature fields of a coal product baking furnace

Investigating the flue-wall deformation effects on performance characteristics of an open-top aluminum anode baking furnace

The carbon anode baking is typically the bottleneck in the production of anodes for the aluminum industry. The challenge is to produce high quality baked anodes while keeping the energy consumption, environmental emissions, and cost to a minimum. Anode baking homogeneity is an important consideration in the design and operation of the anode baking furnaces. The flue-walls, into which the firing takes place, are the heart of the furnace. The flue-walls must be well designed and well maintained in order to be able to regulate them properly. However, during the service life of a baking furnace, flue-walls deform which affect the baking uniformity and consequently result in over-consumption energy and reduction in carbon anode quality. Studying the effects of flue-wall deformation by plant tests is highly challenging and expensive. Hence, this study aims at investigating this phenomenon by developing a three-dimensional (3D) model which includes many physical phenomena and parameters that play vital roles in the baking process. It was observed that indeed the flue-wall deflection has a significant impact on heat transfer characteristics of the anode baking process and furnace energy consumption. In specific, the flue-wall deformation results in an increase in temperature gradients within the anode pack such that the differences between anode pack minimum, average and maximum temperatures lead to overbaking or underbaking of anodes. In fact, this non-uniform baking gives rise to the evolution of non-homogeneous carbon anodes material properties, which is the main reason for excess energy consumption and various instabilities in the aluminum reduction cell. The insights obtained in the present study can be employed in modifying the furnace geometrical and operational parameters with the deformed flue-walls.

The effects of flue-wall design modifications on combustion and flow characteristics of an aluminum anode baking furnace-CFD modeling

A modern aluminum smelter has a capacity of 1–2 million tons of aluminum per annum which requires more than 0.5–1.0 million tons of heat treated (baked) carbon anodes per year. The anode baking process is very energy intensive, approximately requires 2 GJ of energy per ton of carbon anodes which will be approximately 1–2 million GJ of energy per year. Since the plant testing is very expensive, anode baking furnace modeling is imperative to investigate the effects of different operational and geometrical parameters on the furnace energy consumption.In the numerical modeling of turbulent reactive flows, the accuracy of the model highly depends on the description of turbulence-chemistry interaction, and the robustness of the radiative transfer equation solver. Hence, the present study tested different turbulence-chemistry interaction frameworks and radiative transfer equation solvers for confined turbulent diffusion flames and results are compared with the experimental data. It was observed that the k-ε realizable turbulence model combined with the presumed probability density function method as turbulence-chemistry interaction, and discrete ordinates method as radiative transfer equation solver illustrate excellent agreement with the experimental data.Anode baking homogeneity is an important consideration in the design of the anode baking furnace, which requires appropriate flow distribution in the flue-wall cavity. Hence, the developed numerical framework was employed to investigate the effects of flue-wall design modifications on combustion and heat transfer characteristics of anode baking furnace energy consumption. It was observed that the modified design results in a higher thermal efficiency (lower energy consumption), and more homogenous temperature and flow fields which result in the baking of anodes more uniformly which consequently result in the evolution of more homogenous material properties. Consequently, the energy consumption in the aluminum reduction cell will also be significantly reduced. The present study also investigated the effect of flue-wall flow blockage due to packing coke infiltration on baking energy consumption for the aged anode baking furnaces and introduced three modified flue-wall designs.

Comparison of three combustion models for simulating anode baking furnaces

Carbon anode blocks used in the Hall-Héroult process for primary aluminum production have to be baked up to 1100 °C in dedicated furnaces. These furnaces are equipped with burner ramps to heat the air circulating in the flues at 1200 °C, so that the anodes reach the required temperature. It is therefore mandatory to include the heat provided by the burners in a numerical model of an anode baking furnace. In this work, we modeled the heat input at the burners in three ways: the Eddy-Dissipation model, the Mixture Fraction/PDF approach and a simplified approach consisting in injecting an equivalent calorific value at the burners' inlets. Results obtained with the first two models are very similar in terms of anode baking prediction but slightly different in terms of flame temperature prediction. Results obtained with the simplified approach show that the model can replace combustion model to predict anode baking, but calibration of boundary conditions is necessary in order to match more elaborate combustion models. The importance of other elements of the model in the flue channel of the furnace has been verified: radiation (cannot be ignored, large influence on the spatial temperature distribution), heat transfer due to species diffusion (negligible influence on the baking, but slight effect on flame shape and temperature), and buoyancy (no significant effect on the results in the furnace firing sections).

3D Multiphysics model of the effect of flue-wall deformation on the anode baking homogeneity in horizontal flue carbon furnace

In horizontal flue wall carbon baking furnaces, the flue walls consist of bricks which are usually linked together by mortar. During service, the thermal expansion of flue walls is restrained due the presence of headwalls. This, as well as the load of the packing cokes and the anodes, promotes the deflection of the flue walls limits their life. The development of a 3D computational model able to take into account a large number of phenomena that play a role in the baking process and affect the flue wall aging process is then justified. This model will take into account the Thermo-Hydro-Mechanical coupling due to coupled fluid flow and transient heat transfer, packing coke load and the thermal expansion, and enable us to analyze the influence of these parameters on the resistance to deflection of the flues walls. The mechanical aspect is coupled indirectly by considering a deformed flue wall. The Thermo-Hydro-Mechanical coupling simulations were done by the commercial CFD code for Multiphysics Finite Element Analysis COMSOL. This model can be used as a powerful tool in the development of new furnaces and flue wall design and retrofitting existing ones.

Numerical Investigation of Turbulent Diffusion Flame in the Aluminum Anode Baking Furnace Employing Presumed PDF

A modern aluminum smelter has a capacity of 1-2 million tons of aluminum per annum which requires more than 0.5-1.0 million tons of heat treated (baked) carbon anodes per year. Anode baking homogeneity strongly depends on flow distribution in the flue wall cavity which consists of several baffles with certain geometrical design. Moreover, fuel consumption and pollutants emissions are major concerns in the aluminum anode baking furnace (ABF). In the numerical modeling of the turbulent reactive flows, the accuracy of the model highly depends on the description of turbulence-chemistry interaction (TCI). Hence, the present study tested different TCI frameworks for confined diffusion flames and results are compared the results with the reported numerical and experimental data in the literature. It was observed thatk - ε realizable turbulence model combined with presumed probability density function (PDF) method shows an excellent agreement with the experimental data. The developed numerical framework was employed to investigate the effects of flue wall design modification on combustion and emissions characteristics of ABF. It is observed that by closing the openings at the top of the baffles, the same average flue gas temperature can be obtained by reducing the global equivalence ratio (φglob) from 1.0 to 0.125. Lower φglob value results in a lower fuel consumption which consequently translates into less CO, NOx and soot concentration.

An advanced dynamic process model for industrial horizontal anode baking furnace

• Advanced dynamic process model for industrial horizontal anode baking furnace. • Coupling of fluids, gas and solid parts through an interface at the brick surface on the flue side. • Model prediction of bi-dimensional behaviour of the flue gas. • Pseudo tridimensional prediction of the solids behaviour. • Anode baking performance study to reduce energy consumption. The global aluminum industry is facing new challenges due to new technological developments. Carbon anodes, consisting of mainly petroleum coke and coal tar pitch, are used in the electrolytic production of aluminum. High amperage utilization in the electrolytic cells with the objective of increasing production requires high quality carbon anodes. The anode quality depends both on raw material quality, anode recipe as well as forming and baking conditions of anode manufacturing process. The cost of the baking process constitutes 15 to 25% of the total aluminum production cost [1] . The industrial challenge is to produce better quality anodes consuming less energy, and reducing environmental emissions. A transient two dimensional (2D + ) process model for horizontal anode baking furnace was developed during this study. The main objective was to develop an efficient furnace model with low computation load and time, using the transient Finite Difference Method and simplified furnace geometry. The model represents several phenomena involved during the anode baking process such as heat transfer (convection, radiation and conduction), fuel combustion, volatile matter (tar, methane and hydrogen) generation and combustion, air infiltration and energy loss to the atmosphere from the walls, the top of the furnace and the foundation. The model was developed using two coupled sub-models; the first one describes the thermal conduction through the solid materials (brick refractory wall, packing coke and anode block) as well as the volatile release, and the second one describes the gas flow, heat and mass transfer as well as the combustion of fuel and volatiles in the flue. Compared to the existing process models (where the gas flow in flue is assumed as unidirectional along the horizontal furnace direction), the present model also considers the gas flow in vertical direction and uses four vertical planes per pit section to predict the temperature of the solids. The model predicts 2D temperature distribution within the flue gas (xy plane) and the pit solid materials (yz plane) allowing then the prediction of the pseudo tridimensional distribution of the solid temperature. This model is a useful tool for the continuous monitoring of anode temperature and studying of the horizontal anode baking furnace behaviour. The effect of any change in operational parameters and the energy consumption on the furnace operation can be predicted.

Two Dimensional CFD Simulations of a Flue-wall in the Anode Baking Furnace for Aluminum Production

The quality of carbon anode used in aluminum industry depends strongly on the baking process. Impact of operational parameters and geometry on the performance of baking furnace by using plant tests are generally expensive and may disrupt the baking process. Numerical modelling is an imperative tool to study the effect of different operational parameters on the baked anode quality, and furnace performance. In the present work, a two-dimensional (2-D) computational fluid dynamics (CFD) model is developed that simulates heat transfer and flow characteristics of gas in the baking furnace flue-wall. Effect of several operational parameters on gas temperature distribution is investigated. During anode baking process, the main challenge is to obtain a uniform flow field and consequently a homogenous anode temperature distribution. In the present study, flow and temperature uniformity indices based on mass and area weighted averages are introduced as a quantitative indication of the flow and temperature homogeneity. Effect of variation in flue-wall design for two different geometries on flow field are studied and it is observed that closing the top side of the first baffle results in more uniform flow distribution and less energy consumption.