Modelling of high temperature heat treatment of wood using thermowood technology

Heat treatment of wood at relatively high temperatures (in the range of 180–240°C) is an effective method to improve the dimensional stability and to increase the biological durability of wood. During the heat treatment process, the heat and mass transfer takes place between the solid and the drying medium, and the moisture evaporation occurs within the solid due to the capillarity action and diffusion. In this article, a coupling method is presented for high temperature heat treatment of wood based on ThermoWood technology. A three-dimensional mathematical model considering the simultaneous unsteady heat and moisture transfer between a gas phase and a solid phase during heat treatment has been developed. The conservation equations for the wood part are obtained using the diffusion equation with variable diffusion coefficients, and the 3-dimensional incompressible Reynolds-averaged NavierStokes equations have been solved for the flow field. The coupling between the two parts is achieved by expressing the continuity of the state variables and their respective fluxes through the interface. A detailed discussion of the computational model and the solution algorithm is given

Recipe adaptation and new recipe development for high temperature heat treatment of North American wood species

The thermal treatment of wood at high temperatures is an environment friendly and commercially viable alternative wood modification technology. In this process, wood is heated to temperatures above 200ºC. This modifies the structure of wood and improves its hardness, dimensional stability, and resistance to biological attacks compared to those of the untreated wood. Its color also becomes darker and more attractive. However, this treatment may cause a decrease in wood elasticity. Therefore, optimization of the treatment parameters is necessary for a quality product. In addition, the high temperature heat-treatment processes for wood were first developed in Europe, and the recipes used for the European species were not necessarily applicable to the North American species. Thus, adaptation of the technologies to the latter species was necessary. The industrialists in the Saguenay-Lac-St-Jean region of Quebec brought two heat treatment technologies (Bois Perdure from France and Thermowood from Finland) to Canada. The adaptation of the technology is a very costly procedure at industrial scale. The Research Group on the Thermotransformation of Wood (GRTB – Groupe de recherche sur la thermotransformation du bois) at the University of Quebec at Chicoutimi (UQAC) which works closely with these industries developed a method for adapting the existing recipes to the North American species as well as for developing new ones for other species. UQAC is the first North American university which has such a unique research structure to carry out this type of research. The recipe development starts in a laboratory scale furnace. The high temperature heat-treatment experiments are carried out in a thermogravimetric system under different conditions until a promising set of conditions is identified for the properties sought by the industry. Consequently, the trends are identified for a given species. To determine the properties, various characterization tests (bending, dimensional stability, screw withdrawal, etc.) are done. Then, the heat treatment trials in a prototype furnace are carried out to finalize the recipe. This is followed by trials in an industrial-scale furnace for validation of the results

Effect of thermal modification on mechanical properties of Canadian White Birch (Betula papyrifera)

Wood is a renewable material widely used in the construction industry. However, it is susceptible to fungal degradation. Several chemical products have been developed to improve its durability, but the toxicity of some of these products limits their use. One alternative to chemical treatment is thermal modification of wood. This method improves the dimensional stability of wood and reduces its susceptibility to decay. The impact of different parameters (maximum temperature, heating rate, holding time and gas moisture content) of thermal modification on the mechanical properties of Betula papyrifera was studied in a prototype furnace. The results show a marked decrease in the modulus of rupture with increasing temperature while the modulus of elasticity does not seem to be affected. The hardness increases with maximum modification temperature, and in the absence of moisture in gas, and there is an improvement in the dimensional stability after thermal modification

Simulator of Non-homogenous Alumina and Current Distribution in an Aluminum Electrolysis Cell to Predict Low-Voltage Anode Effects

Perfluorocarbons are important contributors to aluminum production greenhouse gas inventories. Tetrafluoromethane and hexafluoroethane are produced in the electrolysis process when a harmful event called anode effect occurs in the cell. This incident is strongly related to the lack of alumina and the current distribution in the cell and can be classified into two categories: high-voltage and low-voltage anode effects. The latter is hard to detect during the normal electrolysis process and, therefore, new tools are necessary to predict this event and minimize its occurrence. This paper discusses a new approach to model the alumina distribution behavior in an electrolysis cell by dividing the electrolytic bath into non-homogenous concentration zones using discrete elements. The different mechanisms related to the alumina distribution are discussed in detail. Moreover, with a detailed electrical model, it is possible to calculate the current distribution among the different anodic assemblies. With this information, the model can evaluate if low-voltage emissions are likely to be present under the simulated conditions. Using the simulator will help the understanding of the role of the alumina distribution which, in turn, will improve the cell energy consumption and stability while reducing the occurrence of high- and low-voltage anode effects