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

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

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

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

Measurement of anode electrical resistivity for quality control in aluminium industry

The carbon anodes used in the electrolytic production of aluminum are made of petroleum coke, recycled anodes and butts, and coal tar pitch. Due to technological advances in the aluminum production technology, aimed at increasing production and decreasing energy consumption and greenhouse gas emissions, better quality anodes are required. Presently, the anode quality is evaluated by visual inspection and the analysis of a small core taken from 1.5-2% of the anodes produced. The visual inspection is susceptible to human error and limited to surface imperfections. The analysis of cores takes time, and therefore, it is difficult to determine the existence of a problem and intervene at the right time. In addition, the core does not represent the whole anode due to the non-homogeneity of anodes. A validated online anode quality control system can highly improve the situation. In this article, an electrical resistivity measurement method developed for this purpose is presented

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

An artificial neural network model for predicting the CO2 reactivity of carbon anodes used in the primary aluminum production

Carbon anode is one of the key components for the electrolytic production of aluminum. It is mainly composed of calcined petroleum coke, coal tar pitch, and recycled carbon materials. The impurities in the raw materials, which are mainly by-products of different industries, influence significantly the quality of anodes. Usually, no well-known mathematical relationship exists between the various physical and chemical properties of raw materials and the final anode properties. In such situations, the artificial neural network (ANN) methods can serve as a useful tool to predict anode properties. In this study, published data have been used to show the proficiency of different artificial neural networks using the MATLAB software. The average error between the predicted and experimental values is around 6 %. The artificial neural network was also used to identify the effect of impurities such as, vanadium, iron, sodium, and sulfur on the CO2 reactivity of anodes. ANN also showed the effect of pitch percentage and coke porosity on the CO2 reactivity of anodes. The effect of CO2 and air reactivities of coke on the CO2 reactivity of anode was also studied. The predictions were found to be in good agreement with the results of other studies in the literature