•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.
A comparative study on the combined effect of heat treatment and acetylation on jack pine wood properties was undertaken and the results were compared with those of each treatment carried out ...individually. The dimensional stability and mechanical property of wood with different treatments were examined and statistically analyzed. The results demonstrated that combined acetylation of jack pine wood with acetic anhydride and heat treatment at 190 °C has a positive effect on the dimensional stability. Results also suggested that the dimensional stability was affected more than the modulus of rupture (MOR) and modulus of elasticity (MOE) by both heat and acetylation treatments under the experimental conditions used. In addition, the hardness increases after high temperature modification but decreases slightly after acetylation. A comprehensive investigation of the effects of heat treatment and acetylation separately and together (combination treatment) on the fungal durability of jack pine wood against a brown rot fungus,
Poria placenta
(pp), and a white rot fungus,
Trametes versicolor
(tv) has also been performed. The results indicated that the weight loss caused by fungi is reduced by both modifications. It was also found that combination of heat treatment and acetylation offers additional bioprotection. FTIR results indicated that the heat and acetylation treatments have a significant influence on the chemical properties, but less influence on their structures.
Heat-treated wood, a relatively new product treated at high temperatures of 180–260 °C, possesses new versatile and attractive properties, which makes it popular for outdoor applications. It is of ...considerable importance to investigate the influence of sunlight on the weathering degradation processes. In order to understand the degradation processes, kiln-dried (untreated) and heat-treated (210 °C) jack pine woods (Pinus banksiana) were exposed to artificial sunlight irradiation for different periods. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM, FTIR spectroscopy, and XPS. Degradation of middle lamellae, checking of cell wall and destruction of bordered pits were observed on heat-treated wood surfaces due to sunlight irradiation by SEM analyses. FTIR spectroscopy and XPS studies provided information about the behavior of functional groups of lignin during irradiation. The oxygen to carbon ratios revealed that the photo-degradation of lignin and presence of extractives played important roles in discoloration and wetting behavior of heat-treated wood surfaces during irradiation. The structural changes during irradiation also influenced wettabilty of the irradiated samples.
Wood is definitely advantageous for industry because it is a renewable resource environment-friendly produced. However, the biological origin of wood requires some treatments to preserve and ...stabilise it. Heat treatment of wood at high temperature is one of the new techniques that reduce the hygroscopicity, improve dimensional stability, and increase resistance to biological degradation of wood material without the use of chemical products.
In this work, transient heat and mass transfers during heat treatment of wood at high temperature were numerically studied. The averaged energy Reynolds Navier–Stokes equations and concentration equations for the fluid were coupled with the energy and mass conservation equations for the wood. The numerical conjugate problem considered also heat and mass exchange at the fluid-wood interface and was used to study the effects of specie-dependant (specific gravity) and storage-dependant (initial temperature and moisture content) parameters during the heat treatment. Both temperature and moisture content were affected by a low initial temperature during the first hours of the treatment, representing hypothetically a risk for wood quality. A high specific gravity or a high initial moisture content required supplemental heating time to reach the targeted final moisture content that potentially represent a supplemental energy and cost for industry.
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.
•Comparative study on the micro-structures and the chemical compositions of the bio-cokes.•Quantitative study on the spreading and penetration ability (wetting capacity) of the pitch on all bio-coke ...beds.•The relationship between the characteristics of the bio-cokes and its wettability by coal tar pitch was established.
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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.
In recent years, various wood modification technologies have been commercialized as alternatives to the traditional chemical treatments for wood preservation. The high temperature heat treatment of ...wood is one of these commercially viable and environmentally friendly alternative wood modification technologies. During this treatment, wood is heated to temperatures above 200°C by contacting it with hot gas. The chemical structure of wood changes leading to increased dimensional stability and resistance to microorganisms. Wood darkens making it aesthetically more attractive. However, it loses some of its elasticity. Therefore, the high temperature heat treatment has to be optimized for each species and each technology. The mathematical modeling is an important tool for optimization. It can also be used as a powerful tool for furnace modification and design. A reliable and predictive model was developed to simulate numerically the heat treatment process. Heat treatment experiments were carried out in the prototype furnace of the University of Quebec at Chicoutimi. The model was validated by comparing the predictions with the experimental data. In this paper, the results of the model applied to birch heat treatment are presented. The model predictions are in good agreement with the data.
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•Replacement of coke with biocoke in anodes reduces the CO2 emissions (GHG emissions).•Utilization of biocoke deteriorates the anode properties which is not acceptable.•Modification ...of biocoke with additives makes its utilization possible in anodes.•Anodes made with modified biocoke have similar properties to those of standard anodes.•Modification of biocoke changes its surface so that it is better wetted by the pitch.
Calcined petroleum coke, recycled anodes and the coal tar pitch are the raw materials used to manufacture carbon anodes for aluminum production. In order to reduce greenhouse (GHG) emissions from the aluminum industry and to add a value to the residue of wood industry, a small part of the calcined petroleum coke, used for the production of carbon anodes, was replaced with biocoke produced from wood by-products. Since the addition of biocoke deteriorates the properties of carbon anodes, it was modified using an additive in order to assess if the modification can render biocoke more suitable for carbon anode production by modifying the surface chemistry of the biocoke.
Three samples of biocoke, unmodified, modified using 3% additive and modified using 4% additive, were produced and studied before and after modification to identify its effect on biocoke properties. First, the chemical characterization was carried out using X-ray photoelectron spectrometry (XPS) to verify whether the functional groups were added to the biocoke surface during the modification. To study the influence of the biocoke modification on the biocoke/pitch interactions, the wettability of the unmodified and modified biocokes by the coal tar pitch, which is used as a binder in anodes, were measured using sessile-drop test. After, the laboratory scale anodes were produced and their green and baked densities, electrical resistivity, air and CO2 reactivities, and bending strength were measured. The results showed that the biocoke modification was effective. A number of new surface chemical groups were added to the biocoke coke surface. This improved the biocoke/pitch wettability, consequently affected the anode properties.
► Investigate the detailed color variation caused by artificial weathering of three heat-treated regional North American species due to artificial weathering with Kubelka–Munk (K–M) spectra and ...CIE-L*a*b* system. ► Chemical analysis of heat-treated wood main components during weathering. ► Identify the connection between heat-treated wood discolorations and the degradation of wood components.
Effect of artificial weathering on the wood surface color modifications of three North American species (jack pine, aspen, and birch) heat-treated under different temperatures was studied by spectrocolorimetric colormeter (datacolor, CHECK TM). Data was analyzed using the reflectance spectra (400–700nm) as well as the CIE-L*a*b* system and ΔE. Kubelka–Munk (K–M) spectra of samples were recorded as a function of artificial weathering time to obtain the absorption maxima of the chromophore woods formed during artificial weathering. The results were compared with those of the respective untreated (Kiln-dried) species. Analysis of chemical components shows that the lignin percent of jack pine, aspen, and birch increased after heat treatment (28.66–35.9%, 20.27–26.41%, and 19.04–22.71% respectively) which might be due to smaller influence of heat treatment on lignin content than hemicelluloses. This improves the resistance of heat-treated wood to photo-degradation. This is also supported by the smaller change observed in K–M spectra and total color parameters in CIE-L*a*b* system of heat-treated wood samples compared to those of untreated wood when weathered for72h. However, the lignin percent of heat-treated woods reduce to maximum 2.5% after artificial weathering of 1512h. This suggests that the weathering degrades most lignin matrix; consequently, both the colors of heat-treated woods and untreated woods are lighter and very similar after a long period of artificial weathering.
► Investigate detailed structural changes of heat-treated wood due to weathering. ► Identify connection between physical structural changes and chemical degradation. ► Study effect of heat treatment ...conditions on weathering degradation process.
Effect of artificial weathering on the surface structural changes of birch (Betule papyrifera) wood, heat-treated to different temperatures, was studied using the fluorescence microscopy and the scanning electron microscopy (SEM). Changes in the chemical structure of wood components were analyzed by FTIR in order to understand the mechanism of degradation taking place due to heat treatment and artificial weathering. The results are compared with those of the untreated (kiln-dried) birch. The SEM analysis results show that the effect of weathering on the cell wall of the untreated birch surface is more than that of heat-treated samples. The FTIR spectroscopy results indicate that lignin is the most sensitive component of heat-treated birch to the weathering degradation process. Elimination of the amorphous and highly crystallised cellulose is observed for both heat-treated and untreated wood during weathering. It is also observed that heat treatment increases the lignin and crystallised cellulose contents, which to some extent protects heat-treated birch against degradation due to weathering.
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