How to dry wood at high temperature?

Wood drying method with drying medium temperature exceeding 100℃. The method includes normal pressure superheated steam drying and high temperature drying with wet air as medium. The wet bulb temperature of the former medium is kept at the boiling point of water, that is, 100℃, and the medium does not contain air; The wet bulb temperature of the latter is lower than 100℃. In the United States, Canada and other countries, high temperature drying usually only refers to kiln drying with high temperature and humid air as the medium. The scientific research of wood high-temperature drying system was initiated by H.D.Tiemann of the United States during World War I, and his research results soon spread to Europe. F.F.P.Kollmann of the Federal Republic of Germany has done a lot of work in the research and industrial application of high temperature drying. The Institute of Wood Industry of China Academy of Forestry also conducted research on wood drying at high temperature. High temperature drying of wood has been adopted by many countries.

The requirements of high temperature drying for drying kiln are: the thermal power of heater should be large enough; The circulation speed of the medium should be appropriately increased; The kiln shell should have good heat insulation, air tightness and corrosion resistance. The process of high temperature drying is similar to that of conventional kiln drying, but the medium temperature is much higher than that of conventional kiln drying.

In the process of high-temperature drying, the temperature of the medium exceeds the boiling point of water under normal pressure, and the moisture in wood quickly diffuses outward in the form of steam. Coupled with the rapid circulation of airflow in the kiln, the moisture on the wood surface quickly evaporates into the medium. Therefore, the drying speed is several times faster than the traditional kiln drying method. The drying cost is greatly reduced. The energy consumption (electric energy and heat energy) is also lower than that of the traditional kiln drying method. Wood dried at high temperature has good dimensional stability, but the high temperature drying kiln and its equipment are seriously corroded and its service life is shortened. After high temperature drying, the surface color of wood is yellowish brown. The resin overflows and the knot falls off more. The influence of high temperature drying on wood strength, most scholars think: high temperature drying makes wood hardness slightly improved; It has little effect on the transverse compressive strength and static bending strength of wood; The impact strength and parallel shear strength decreased slightly.

Coniferous wood and soft broad-leaved wood should be dried at high temperature. Generally, hard broad-leaved trees should be dried by air drying or conventional drying kiln to reduce the water content to about 25%, and then high temperature drying can be used to obtain good drying quality.