High Frequency Vacuum Drying Technology of Chinese Fir Plantation Wood

Research and Development of High-frequency Vacuum Drying Technology for Chinese Fir Plantation Wood Gao Ruiqing, Li Xiaoling (Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China) The difference in core moisture content is small. Although the initial moisture content of the test plate is quite different, the initial moisture content of the test plate is from low to high between the negative electrode plate and the positive electrode plate according to the feature that the high frequency vacuum drying of the wood near the positive electrode plate is faster than the drying speed near the negative electrode plate. Placing pallets in order, the moisture content of the dried plates can be even! To.

Dry wood is an important part of wood processing and utilization. Drying methods include natural drying, conventional steam drying, superheated steam drying, high temperature drying, dehumidifying drying, solar drying, microwave drying, high frequency drying, vacuum drying, and the like. Radio frequency vacuum (RF/V) drying of wood was first studied and developed in the former Soviet Union, the United States, Japan, and other countries in the 1970s and applied to production in the early 1980s. High-frequency vacuum drying of wood is a combination of high-frequency drying and vacuum drying. The principle of vacuum drying is that the boiling point of water in the wood is reduced in the vacuum environment, and it can quickly vaporize and migrate outwards at a relatively low temperature to achieve rapid drying of the wood at low temperatures. It is characterized by small drying defects and maintains the natural color of the wood. However, because the drying medium (wet air) inside the vacuum drying tank (kiln body) is significantly reduced under vacuum conditions, thereby affecting the heat transfer, the fund project: special technical cooperation between China and Japan (JICA channel) * Chinese plantation wood One of the subprojects of the research project.

In the air drying, high-frequency heating technology was cited. High-frequency heating does not require humid air as a heating medium, but direct radiation heating with a high-frequency electric field.

When the high-frequency generator starts working, the potentials between the plates frequently alternate, and the water molecules in the wood rapidly polarize. The friction between the molecules can generate a lot of heat, so that the inside and outside of the wood are heated almost at the same time and reach a certain degree. Temperature, thus achieving rapid drying, to solve the shortcomings of low vacuum drying efficiency, especially suitable for drying thick plates and some difficult dry materials. Relevant studies have shown that the color of wood dried with RF/V is the same, the bending amount is reduced by 34%, the yield is increased by 23%; the thick plate (2000~4000mmx 87mm) is dried from the moisture content of 70% to 10%, and the consumption time is only For conventional steam drying 1/6. frequency vacuum drying equipment, artificial forest pine drying test, by changing the drying process parameters and analysis of test results, develop and optimize the artificial forest of high-frequency vacuum drying benchmark.

1 Test materials and methods 1.1 Materials lanceolata), rice from the Dagangshan Experimental Forest Farm of Chinese Academy of Forestry, age 23 years, average diameter 22.7cm, initial moisture content 48%~180%, average basic density 0. Test plate size planing After the test piece (length x width) is 1 120mm, the thickness is divided into two kinds of specifications: thin plate (25mm) and thick plate (50mm).

Frequency generation device, vacuum system and cooling system 3 parts. Maximum load 0.8m3; input voltage of the power supply is 380V, DC output voltage EL minimum 5kV, maximum 6kV, DC maximum output current 0.8A; high frequency oscillation frequency 6.78MHz; equipment minimum vacuum is 2400Pa. In addition, there is Electronic balance, digital display caliper, thickness measuring instrument and oven etc.

1.2 Methods The specimens were planed with a fixed width and thickness and then determined as required. Before the test, the width and thickness of the test plate were measured at the determined position, and visible defects were recorded. After the end of the test, observe and record visible defects again, and measure the width and thickness of the dried test plate at the same position to calculate the shrinkage of the test plate; according to GB 6491-1999, relevant provisions of the quality of sawn timber drying, from On the block test board, the moisture content slice and the stratified moisture content slice were cut, and the final moisture content of the test plate was determined by the drying method.

In this study, six tests were performed on two types of test boards. In addition to changing the high-frequency vacuum parameters, ie, current, voltage, and high-frequency oscillation time, the test board stacking method was also changed based on the test results. According to the experience of drying poplar wood board with the same specifications, see the loading method of high-frequency vacuum drying series test of Chinese fir. Since the wood near the electrode plate is easy to generate condensed water when it is dry, when the stack is stacked, the dried replacement board of the same specification of fir is placed in contact with the electrode plate.

Research | J.. Forestry Science and Technology, 1993 (18): 6. (Responsible Editing by Bao Jiafen) 025 = -2417 2006 Timber Industry Chemicals and Industry "Ordering Notice CN321149/S" Chemicals and Industry of Fujian Province by China Forestry Organized by the Forestry Chemistry and Chemical Industry Branch of the Chinese Academy of Forestry and the Institute of Forestry Chemical Industry of the Chinese Academy of Forestry, it is an academic quarterly newsletter for the forestry chemical industry in China. Coverage: Recyclable wood and non-wood forest resources, chemistry and processing, mainly wood chemistry and Pulp and Paper, Rosin, Turpentine Chemistry and Utilization, Biomass Raw Material Pyrolysis and Activated Carbon, Hydrolysis of Vegetable Fibers and Their Products, Plant Polyphenol Chemistry and Utilization, Forest Spices, Oils, Drugs and Bioactives, Tree Parasites, and Other Forests Chemicals and processing and utilization of natural products; modern biotechnology and its applications in forestry chemistry and industry; forestry chemical industry development strategy, planning and experience summaries for environmental protection, resource protection and sustainable development, economics and business management.

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