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

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

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

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

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

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

Comparison of the protection effectiveness of acrylic polyurethane coatings containing bark extracts on three heat-treated North American wood species: Surface degradation

High temperature heat-treatment of wood is a very valuable technique which improves many properties (biological durability, dimensional stability, thermal insulating characteristics) of natural wood. Also it changes the natural color of wood to a very attractive dark brown color. Unfortunately, this color is not stable if left unprotected in external environment and turns to gray or white depending on the wood species. To overcome this problem, acrylic polyurethane coatings are applied on heat-treated wood to delay surface degradations (color change, loss of gloss, and chemical modifications) during aging. The acrylic polyurethane coatings which have high resistance against aging are further modified by adding bark extracts and/or lignin stabilizer to enhance their effectiveness in preventing the wood aging behavior. The aging characteristic of this coating is compared with acrylic polyurethane combined with commercially available organic UV stabilizers. In this study, their performance on three heat-treated North American wood species (jack pine, quaking aspen and white birch) are compared under accelerated aging conditions. Both the color change data and visual assessment indicate improvement in protective characteristic of acrylic polyurethane when bark extracts and lignin stabilizer are used in place of commercially available UV stabilizer. The results showed that although acrylic polyurethane with bark extracts and lignin stabilizer was more efficient compared to acrylic polyurethane with organic UV stabilizers in protecting heat-treated jack pine, it failed to protect heat-treated aspen and birch effectively after 672 h of accelerated aging. This degradation was not due to the coating adhesion loss or coating degradation during accelerated aging; rather, it was due to the significant degradation of heat-treated aspen and birch surface beneath this coating. The XPS results revealed formation of carbonyl photoproducts after aging on the coated surfaces and chain scission of C-N of urethane linkages

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

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

Impact of the form of a trailer on its aerodynamic performance

Today, energy efficiency is a topic of great importance not only due to limited energy resources, but also their impact on environment. In the case of vehicles, great effort is being spent on reducing weight and making the form more and more aerodynamic to reduce fuel consumption and increase energy efficiency. However, there is a limit to this form because a vehicle should never lose traction. A highly aerodynamic form reduces the downward force which provides the vehicle its traction. A trailer with a highly aerodynamic form was investigated to determine if it would lose traction at different speeds and under different wind conditions. Simulations were carried out using the CFD commercial code ANSYS CFX to determine the flow field and the forces (lift, drag, downward force, etc.) around the trailer. The calculation domain was taken large enough not to affect the flow field. The partial differential turbulent flow equations (continuity, momentum, and turbulence equations) were solved in three dimensions to find the velocity and pressure distributions. Different trailer forms were also investigated. The type of vehicle towing the trailer also has an impact on the flow field around it. Thus, different types of vehicles were considered in the simulations. The results demonstrated that certain forms could cause the loss of traction at high enough speeds. In this article, the model is explained, and the results of a number of cases are presented and discussed