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 coke pitch interaction by XPS, FTIR and sessile-drop techniques.•Interactions of three cokes and two pitches were studied.•Studied calcined coke and coke–pitch by FTIR–DRIFT, not reported ...in published article.•Atomic wt% and functional groups present on coke and pitch surfaces analyzed by XPS.•Wetting was correlated with the functional groups and evidence of reaction found.
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.
The properties of pitch as the binder material for carbon anode manufacturing strongly affect the anode properties. Pitches show significant differences in their chemical composition depending on ...their origin. In this study, five coal tar pitches with different quinoline-insoluble (QI) contents were studied to understand the wettability of one calcined petroleum coke by these pitches using the sessile-drop test. The chemical properties of the coke and pitch were studied using XPS and FT-IR to investigate their wetting mechanism and their interactions. The structures of different pitches and the pitch-coke interface were characterized by optical microscopy and SEM, respectively. The results showed that not only the chemical but also the physical properties of the pitches contribute to the wettability of coke. The wettability increases with increasing heteroatom content in the pitch. The viscosity of pitch is a key parameter controlling the wetting behavior of pitch. The QI content, the solid particle size and their distribution in the pitches play a significant role in the wettability of coke by pitch.
Effect of artificial weathering on the wettability of three heat-treated North American wood species (jack pine, aspen, and birch) is studied from the point of view of the structural and chemical ...changes taking place on the wood surface. Weathering increases wettability of all three heat-treated woods by water. Changes in wettability during artificial weathering differ according to heat treatment procedure and wood species and are likely due to combination of structural and chemical changes of the surfaces. Scanning electron microscopic analysis indicates that cracks form due to degradation taking place during weathering. As a result, water has easier entry into the cell wall, which consequently increases wettability. IR spectra suggest that the OH/CH2 ratio for heat-treated specimens is inversely proportional to the contact angle regardless of the type of wood species. The presence of cellulose-rich layer on wood surface and increasing amount of amorphous cellulose transformed from crystallized cellulose due to weathering result in increase in hydroxyl; consequently, it increases heat-treated wood wettability.
Aluminum is one of the major industries in Canada. The main challenges facing the aluminum industry are carbon loss, energy use, greenhouse gas emissions, cell performance, and production costs, ...especially for high-amperage cells. The quality of carbon anodes plays a major role in the stability of cell operation and energy consumption. Anodes are made from petroleum coke, rejected green and baked anodes and butts, as well as coal tar pitch, which binds all of the particles. Although the industry depends on a steady supply of high-quality anodes, the availability of quality anode raw materialscoke and pitchhas decreased. A means of improving raw material quality is to modify their properties. In this work, using two additives, low- and high-quinoline insoluble (LQI and HQI) pitches were modified. These additives enrich the surface functional groups of the pitch, thereby increasing coke–pitch interactions. Various additive concentrations and pitch percentages were assessed. It is found that the choice of additive type has a marked effect on pitch properties, with different additives improving different pitches. Additive 1 is suitable for the HQI pitch, whereas additive 2 modifies the LQI pitch better. Anode properties are improved by modifying one of the pitches, whereas modifying the other pitch affects the anode quality to a lesser extent. Thus, the results showed that the modification of an already good-quality pitch (LQI pitch) does not significantly affect the anode quality. On the other hand, the modification of the inferior-quality pitch (HQI pitch) improved the anode quality and decreased the optimum pitch percentage necessary to obtain good anodes compared to the percentage of the LQI pitch needed. This would help decrease the anode production cost. The wettability tests give an indication of if the additive has the potential to improve the coke–pitch interactions, but it cannot predict the effect of pitch percent.
•Transient process model of open anode baking furnace.•Coupling of gas and solids parts through an interface at the brick surface on the flue side.•Importance to consider materials variables ...properties on the modelling.•Highlighting of the flue wall deformation (via change on pit width) on the anode baking process.
One important step of the primary aluminum production, is anode manufacturing and its baking is the most expensive step of anode manufacturing process. The challenge for the anode industry is to produce good quality baked anodes while keeping the energy consumption, environmental emissions, and cost to a minimum. A mathematical model can be a useful tool to overcome these challenges and achieve the objectives for the industry.
A transient process model of a horizontal anode baking furnace has been developed. The model represents all the important phenomena such as fuel combustion, generation and combustion of volatiles (tar, methane, and hydrogen), air infiltration, and heat losses to the atmosphere and the foundation. The model consists of two coupled sub-models (flue sub-model and the pit) was validated using the plant data. It simulates the transient behavior of the open ring furnace and predicts furnace operation and performance. In this article, the modelling is described, and the results are presented for an industrial furnace.
•Surface degradation of thermally treated jack pine is delayed by acrylic polyurethane coating.•CeO2 nano particles certainly improved weather ability of acrylic polyurethane coating.•Contact angle ...of water/coated heat-treated wood revealed chain reorientation of PUA coatings during weathering.•Several carbonyl photoproducts were formed during accelerated weathering.•Negligible chain scission of urethane linkages were observed during accelerated weathering.
The thermally treated wood is a new value-added product and is very important for the diversification of forestry products. It drew the attention of consumers due to its attractive dark brown color. However, it loses its color when exposed to outside environment. Therefore, development of a protective coating for this value added product is necessary. In the present study, the efficiency of CeO2 nano particles alone or in combination with lignin stabilizer and/or bark extracts in acrylic polyurethane polymer was investigated by performing an accelerated weathering test. The color measurement results after accelerated weathering demonstrated that the coating containing CeO2 nano particles was the most effective whereas visual assessment suggested the coating containing CeO2 nano particles and lignin stabilizer as the most effective coating. The surface polarity changed for all the coatings during weathering and increase in contact angle after weathering suggested cross linking and reorientation of the polymer chain during weathering. The surface chemistry altered during weathering was evaluated by ATR-FTIR analysis. It suggested formation of different carbonyl byproducts during weathering. The chain scission reactions of the urethane linkages were not found to be significant during weathering.
The thermal treatment of wood is an alternative to the chemical treatment for preservation purposes. The heat treatment process improves wood's resistance to decay and its dimensional stability. ...However, mechanical strength decreases as a result of heat treatment. Therefore, the treatment parameters have to be optimized to keep this loss at a minimum while improving other properties. Thermal treatment is new in North America, and its parameters are not yet adjusted for the Canadian species. Carrying out the parameter adjustment in an industrial furnace requires many trials which are costly in terms of material and man-power. A laboratory study was carried out to determine the effect of different parameters of the heat treatment on the mechanical properties of birch in order to optimize this process. A thermogravimetric analyzer was built to carry out the laboratory tests. The impact of the process parameters-such as maximum treatment temperature, holding time at this temperature, heating rate, and gas humidity-on the mechanical properties of birch was investigated. Temperature distributions in wood and in gas as well as the weight loss of wood were measured during the experiments. Afterwards, hardness, modulus of elasticity, modulus of rupture, and resistance to screw withdrawal of the samples were measured. The relation between the process parameters and the resulting mechanical properties was examined.
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