High temperature heat treatment process for wood
The mature heat treatment processes abroad mainly include Thermo Wood from Finland, Plato Wood from the Netherlands, and Correction from France.
Thermo Wood high-temperature heat treatment process involves drying raw or air dried materials first, followed by steam heat treatment. The treatment temperature is generally 180 ℃ to 250 ℃, and the treatment time is 0.5 to 4 hours. The entire treatment process is divided into three stages: heating, treatment, and cooling.
The production process of Plato Wood mainly consists of two different temperature heat treatment stages. In the first stage, the wood is subjected to heat treatment at 160 ℃ to 190 ℃ under gradually increasing pressure, and then the moisture content of the heat-treated wood is reduced through drying; In the second stage, the dried wood is subjected to heat treatment at a temperature of 170 ℃ to 190 ℃, and the treatment time depends on factors such as the tree species, thickness, and shape of the wood.
Correction is the heat treatment of wood with a moisture content of 12% using nitrogen as a medium. The treatment temperature is generally between 200 ℃ and 240 ℃, and the oxygen content does not exceed 2%. Accurate temperature control is required during the heat treatment process, as small changes in temperature can have a significant impact on the final performance of the heat-treated material.
Japan was the first to research and develop the wood fumigation heat treatment process, which uses waste wood as fuel and utilizes the heat energy carried by the incomplete combustion of these fuels to heat treat wood. The processing object can be logs or sawn timber with bark, and heat treated at a temperature of 80-200 ℃. Firstly, raise the temperature to around 80 ℃ and maintain it for a period of time. At this time, lignin softens, water accelerates its movement, and the internal moisture of the wood tends to become uniform, reducing the internal stress of the wood and stabilizing its organizational structure. The wood treated with this process can effectively improve its dimensional stability, durability, and other physical properties, and the color change of the wood is relatively uniform.
The differences in high-temperature heat treatment processes are mainly reflected in conditions such as treatment medium, treatment temperature, and treatment time. If air is used as the thermal medium, wood is prone to combustion when in contact with oxygen at high temperatures, which poses certain safety hazards; If molten metal is used as the thermal conductivity medium, the cost and difficulty of wood heat treatment are relatively high; If inert gas is a thermal conductive medium, a good sealing equipment is required, and collection and production are also more complicated and costly. Therefore, considering economic benefits, safety and other aspects comprehensively, it is better to choose traditional thermal conductivity medium water vapor as the thermal conductivity medium.
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