High-efficiency drying technology for low-quality plantation timber

Editor's Note

Recently, the National Forestry and Grassland Administration released 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, improvement of forestry, fruit, flower and grass seed industry, forestry and grassland equipment and informatization, forestry and grassland disaster prevention and control, wildlife protection, and construction of a beautiful living environment. Among them, three achievements from the Research Institute of Wood Industry of the Chinese Academy of Forestry were selected: efficient drying technology for low-quality plantation timber led by Researcher Zhou Yongdong; high-performance wood-bamboo reconstituted timber technology led by Researcher Yu Wenji; and key technologies for the preparation and application of soybean meal adhesive for formaldehyde-free plywood led by Associate Researcher Fan Dongbin.

To further enhance the impact of the findings and fully leverage their demonstrative and guiding role, this platform has selected findings related to the timber industry for promotion, aiming to provide technical support for the timber industry to implement the new development philosophy and build a new development pattern.

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

I. Importance of the Achievements

The state has completely halted commercial logging of natural forests, shifting the domestic timber industry's resource supply from natural forests to plantation forests. However, plantation forest timber is of poor quality and low value, and conventional drying methods are inefficient and costly, posing a technological bottleneck for efficient timber utilization. High-efficiency timber drying technology, based on the characteristics of low-quality plantation forest timber and combining the advantages of superheated steam and high-temperature drying technologies, can improve production efficiency and reduce production costs while ensuring drying quality. This is of great significance for promoting the efficient and high-value-added utilization of low-quality plantation forest timber.

II. Comparison with similar technologies at home and abroad

Superheated steam drying technology for wood is mainly used in countries like Australia and New Zealand, drying wood species such as radiata pine and rubberwood, with maximum drying temperatures reaching 120℃~160℃, significantly improving drying efficiency. High-temperature drying is mainly used in countries like Japan and Australia, drying wood species such as Japanese cedar and radiata pine. However, high-temperature dried wood is usually used for building structures. For example, Japanese cedar square timber, after high-temperature drying, shows improved surface quality and dimensional stability. Although internal cracks sometimes occur, it does not affect its overall performance as structural material. In China, plantation timber is mainly used for furniture, engineered wood flooring, and plywood, where internal cracks are unacceptable. Therefore, this technology uses superheated steam drying at high moisture content to improve wood permeability, and high-temperature drying in the middle and later stages of drying. The dried wood is free of internal cracks, significantly improving drying efficiency, reducing drying costs, and promoting the high-value utilization of plantation timber.

III. Key Technologies and Main Technical and Economic Indicators Achieved in the Results

Key technologies of the achievement: ① When the moisture content is higher than 30%, superheated steam is used for drying, and the wind speed in the material pile is 3-5 m/s; ② When the moisture content is lower than 30%, high-temperature drying process is used, and the wind speed in the material pile is 1.5-3 m/s; ③ At the end of drying, high-humidity air at 90-100℃ is used for humid heat treatment, and the wind speed in the material pile is 3-5 m/s.

Applying this technology to dry 50mm thick fir lumber significantly reduces drying defects such as internal cracking and twisting that easily occur during high-temperature drying. It also rapidly releases residual drying stress, improving dimensional stability compared to conventionally dried lumber and increasing drying efficiency by over 40%. According to GB/T 6491 "Lumber Drying Quality," the pass rate for Grade II dried lumber reaches 95%. The lumber drying quality indicators meet the technical requirements for furniture and plywood products.

IV. Application of Results and Economic and Social Benefits

This technology was demonstrated in a batch drying demonstration at Guangdong Federal Furniture Group Co., Ltd., using 30m³ of 50mm thick fir sawn timber. Results showed that it significantly improved the utilization efficiency of drying equipment by over 40%, reduced drying production costs by over 30%, and ensured the drying quality met the technical requirements of furniture and plywood manufacturing. The application of this technology offers significant economic benefits to enterprises and substantial social benefits for improving the quality and efficiency of plantation timber utilization, saving energy and reducing emissions, and promoting the transformation and upgrading of the timber industry under resource transformation.

V. Prospects for the Promotion of the Results

This technology is applicable to the drying of plantation timber and can be used in any high-temperature heat treatment equipment in enterprises without requiring technical modifications, making it easy to apply. This technology can be applied to plantation timber such as Chinese fir, poplar, Japanese cedar, and Masson pine. Of the approximately 80 million m³ of timber produced annually in China, over 95% is from plantations. If 5% of this timber used this technology, it could generate over 300 million yuan in additional revenue for enterprises. The scale of promotion for this efficient timber drying technology is flexible, and its industrial application prospects are broad.

First affiliated institution of the research: Research Institute of Wood Industry, Chinese Academy of Forestry

Contact Person: Teacher Zhou

Telephone: 010-62889484

Email: zhouyd@caf.ac.cn