High-efficiency drying technology for low-quality plantation wood

Editor's Note

The National Forestry and Grassland Administration recently announced 100 key forestry and grassland scientific and technological achievements for promotion in 2021. These achievements cover eight areas: forestry and grassland ecological protection and restoration, forestry and grassland resource cultivation and management, forestry and grassland resource development and utilization, forestry, fruit, flower and grass seed industry improvement, forestry and grassland equipment and informatization, forestry and grassland disaster prevention and control, wildlife and plant protection, and the construction of a beautiful human settlement environment. Among them, three achievements from the Institute of Wood Industry, Chinese Academy of Forestry were selected: a high-efficiency drying technology for low-quality plantation timber, led by Researcher Zhou Yongdong; a high-performance wood-bamboo recombinant material technology, led by Researcher Yu Wenji; and a key technology for the preparation and application of formaldehyde-free soybean meal adhesives for plywood, led by Associate Researcher Fan Dongbin.

In order to further increase the influence of the results and give full play to the demonstration and leading role of the results, this platform specially selects results related to the wood industry for promotion, in order to provide technical support for the wood industry to implement the new development concept and build a new development pattern.

This issue focuses on "High-efficiency drying technology for low-quality plantation timber."

1. Importance of the Achievements

China has completely stopped commercial logging of natural forests, and the domestic timber industry has shifted its resource supply from natural forests to plantations. However, plantation timber resources are of poor quality and low value. Conventional drying methods are inefficient and costly, creating a technical bottleneck for efficient timber utilization. High-efficiency wood drying technology leverages the characteristics of low-quality plantation timber and combines the advantages of superheated steam and high-temperature drying technologies. While ensuring drying quality, it improves production efficiency and reduces costs, playing a significant role in promoting the efficient and high-value utilization of low-quality plantation timber.

2. Comparison with similar technologies at home and abroad

Superheated steam wood drying technology is primarily used abroad in countries like Australia and New Zealand. It dries wood species such as radiata pine and rubberwood, with maximum drying temperatures reaching 120°C to 160°C, significantly improving drying efficiency. High-temperature drying is primarily used in countries like Japan and Australia, drying wood species such as Japanese cedar and radiata pine. However, high-temperature dried wood is typically used for structural purposes. For example, high-temperature drying improves the surface quality and dimensional stability of Japanese cedar timber. Although internal cracking may occur, it does not affect its overall structural performance. In China, however, plantation wood is primarily used in products such as furniture, engineered wood flooring, and blockboard, where internal cracking is unacceptable. Therefore, this technology utilizes superheated steam drying during the high-moisture content stage to enhance wood permeability. High-temperature drying is then applied in the middle and later stages of drying, eliminating internal cracking defects. This significantly improves drying efficiency, reduces drying costs, and promotes the high-value-added utilization of plantation wood.

3. Key technical achievements and main technical and economic indicators achieved

The key technical achievements are as follows: ① When the moisture content is higher than 30%, superheated steam is used for drying, and the wind speed in the wood pile ranges from 3 to 5 m/s; ② When the moisture content is lower than 30%, high-temperature drying technology is used for drying, and the wind speed in the wood pile ranges from 1.5 to 3 m/s; ③ At the end of drying, high-humidity air at 90 to 100°C is used for wet heat termination treatment, and the wind speed in the wood pile ranges from 3 to 5 m/s.

Applying this technology to drying 50mm thick fir lumber significantly reduces drying defects such as internal cracking and warping that can occur during high-temperature drying. It also rapidly releases residual drying stress, improves dimensional stability compared to conventionally dried lumber, and increases drying efficiency by over 40%. According to GB/T 6491, "Drying Quality of Sawn Timber," the pass rate for second-grade dried lumber reached 95%. This quality meets the technical requirements for dried lumber for products such as furniture and blockboard.

IV. Application of Achievements and Economic and Social Benefits Achieved

This technology has been demonstrated in a 30m³ batch drying of 50mm-thick fir sawn timber at Guangdong Federal Furniture Group Co., Ltd. The results showed that it significantly increased drying equipment utilization by over 40%, reduced drying production costs by over 30%, and achieved drying quality that met the technical requirements of furniture and blockboard manufacturing. The application of this technology has significant economic benefits for the company and significant social benefits, including improving the quality and efficiency of plantation timber utilization, reducing energy consumption and emissions, and promoting the transformation and upgrading of the timber industry under resource transformation.

V. Prospects for the promotion of achievements

This technology can be applied to the drying of plantation timber. It can be used with existing high-temperature heat treatment equipment in any enterprise, requiring no technical modification and making it easy to apply. This process can be applied to plantation timbers such as fir, poplar, cryptomeria, and masson pine. Of the approximately 80 million cubic meters of timber produced annually in China, over 95% comes from plantation timber. If this technology were used on just 5% of this annual timber production, it could generate increased profits of over 300 million yuan for enterprises. High-efficiency wood drying technology offers flexible scale for promotion and broad prospects for industrial application.

First completion unit of the achievement: Research Institute of Wood Industry, Chinese Academy of Forestry

Contact: Mr. Zhou

Tel: 010-62889484

Email: [email protected]