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

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

Study on the surface changes of heat-treated aspen wood due to aging by different techniques

Heat-treated wood undergoes degradation induced by weathering factors such as solar radiation, temperature variations, rain, and snow. The aging of heat-treated wood affects significantly its surface properties. In this study, the artificial aging test of heat-treated wood using a UV chamber was carried to see the effect of aging on the wood surface. The net radiative heat transfer to the wood sample surfaces in this chamber was estimated in order to determine the corresponding natural weathering times. A complete understanding of the surface changes during the weathering process would allow the development of new treatments and finishes that would greatly enhance the durability of heat-treated wood against degradation due to weathering. Study of the heat-treated wood surface before and after weathering by different techniques helps provide an insight into the degradation process. The techniques and tools for studying heat-treated wood surfaces include color measurement, contact angle test for wettability analysis, light microscopy, FTIR, XPS, and SEM. Each technique gives information on different aspects such as chemistry, structure, and appearance. In this article, the utilization of these techniques is discussed. A number of results for different cases are presented. The aging affects the color of the tangential and radial surfaces differently. During aging, lignin decreases and OH increases; and this increases the wettability of wood.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

A novel high temperature heat treatment process for wood

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.Wood is heated to temperatures in the range of 180–240°C in heat-treatment furnaces. At these temperatures, the wood structure undergoes changes leading to better dimensional stability, better resistance to biological attacks, and a darker attractive color. The high-temperature heat treatment of wood is an alternate and ecologically-sound wood preservation process to chemically treated wood. During heat treatment, wood goes through simultaneous heat and mass transfer. The heat is transferred from the hot gases to the wood boards in the furnace. As the temperature of wood increases, water content of wood vaporizes and diffuses out of the boards. At higher temperatures, a number of irreversible structural changes take place in wood cells. The furnace design is important to carry out the heat treatment process uniformly and effectively. A new heat treatment furnace design has been proposed at UQAC and a prototype furnace has been built and tested. Also, a 3D model of the furnace was developed to complement the experimental work and to gain insight into the heat treatment process taking place in the furnace. In this article, the new furnace design and its advantages are discussed. Results of the measurements and predictions of the mathematical model are presented to show the effectiveness of the new furnace design for heat treating standard wood boards as well as pieces of wood with different geometries.The authors would like to thank the administration of the University of Quebec at Chicoutimi (UQAC), the Foundation of the University (FUQAC), The Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Economic Development for Quebec Regions (CED), Ministère de l’Économie, de l’Innovation et des Exportations (MEIE, previously MDEIE) and SOVAR.am201

Comparison of the 1D and 3D models for the simulation of wood heat treatment process

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Wood heat treatment at high temperatures (in the range of 180–240°C) is an ecological alternative to the chemical treatment of wood for its preservation. Thermal treatment provides dimensional stability and biological durability to wood due its structural changes. The dark color attained also gives the wood an aesthetic appearance. Various mathematical models have been developed for wood heat-treatment furnaces. In this article, two models, 1D and 3D, will be described. They have been used to simulate the furnace behaviour for a number of wood species, and parametric studies have been carried out to determine the impact of various factors. Some of the results of the calculations with the two models will be presented. They will be compared and the applicability and limitations of the 1D approach will be discussed.dc201

Investigation of the refractory bricks used for the flue wall of the horizontal anode baking ring furnace

Anode manufacturing, particularly the baking process, is an important part of the primary aluminium production process. Anode baking is carried out in closed or open top ring furnaces. The anodes are placed in pits and surrounded by packing coke to prevent oxidation by infiltrated air and mechanical support. The anodes are baked through indirect contact with the hot gas flowing in the flues on both sides of the pit. The flue walls are made of commercial refractory bricks, which are subjected to chemical (high temperature corrosion), mechanical (creep, walls, anode loading and unloading) and thermal (high temperature, thermal shock) conditions during the baking process. The resulting stress causes chemical and physical alterations across the width of the wall. This stress generally manifests in the collapsing, cracking and bending of flue walls. The chemical composition and physical properties of refractory bricks taken from degraded flue walls in an industrial plant were investigated, and it was shown that regular redressing and maintenance of flue walls can prevent or reduce additional energy consumption due to pit deformation, consequently reducing the cost of anode production

Study of the degradation of heat-treated jack pine under different artificial weathering conditions

Heat-treated wood is a natural product heat-treated at high temperatures in the range of 180 to 240°C. Heat treatment modifies wood both chemically and physically. However, heat-treated wood is susceptible to weathering degradation. It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood under different conditions. Jack pine (Pinus banksiana) heat-treated at different temperature were exposed to artificial weathering with and without water spray for different periods in order to understand the effect of weathering factors on degradation processes. Before and after weathering, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using florescent microscopy imaging, SEM, FTIR spectroscopy, and XPS. The results revealed that heat-treated wood was degraded more during weathering with water spray than without water spray

Comparison of weathering behavior of heat-treated jack pine during different artificial weathering conditions

Heat treatment improves the dimensional stability (reduced hygroscopicity and wettabilty) of wood and its resistance to fungi, and results in darker color. However, wood loses its color when exposed to weathering (sunlight, rain etc.). In this study, the surface degradation and color loss of het-treated wood taking place during weathering were investigated under different conditions. Jack pine (Pinus banksiana) samples, heat-treated at 210°C, were exposed to artificial weathering with and without water spray for different times. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using florescent microscopy, SEM, FTIR spectroscopy, and XPS. The results revealed that the photo-degradation of lignin play important roles in color change and wetting behavior of heat-treated wood surfaces during weathering. Heat-treated wood was degraded more during weathering if exposed to water spray

Study on weathering behavior of jack pine heat-treated under different conditions

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood. Kiln-dried (untreated) jack pine (Pinus banksiana) and jack pine heat-treated at three different temperatures (190°C, 200°C, and 210°C) were exposed to artificial weathering for different periods in order to understand the degradation processes due to weathering. 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. The results revealed that the photo-degradation of lignin and the presence of extractives play important roles in color change and wetting behavior of heat-treated wood surfaces during weathering. The structural changes also influence the wettability. The effects of weathering for woods heat-treated under different conditions were similar, but different from those for untreated wood.dc201

3D-modelling of conjugate heat and mass transfers: effects of storage conditions and species on wood high temperature treatment

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