When selecting the type of drying kiln, we should consider the advanced technology, the reliability of the process and the rationality of the economy, and according to the types, specifications and quantity of the wood to be dried, the requirements of the wood use for drying quality and the specific situation of the production unit.
Steam heating wood drying method is the most traditional and commonly used drying method widely used at home and abroad. Its main advantages are stable technical performance, mature technology and easy adjustment and control of temperature and humidity; It can provide central heating and dry all kinds of materials, and has a wide application range; If the drying process is reasonable and the operation is correct, the drying quality is guaranteed and the drying room has a large capacity. The disadvantage is that a steam boiler is needed. The equipment investment is high, and the drying cost is moderate or high.
Hot water heating wood drying method has some advantages of steam drying. Wood processing residues can be used as fuel, which greatly reduces the drying cost. Because of the large heat capacity of hot water, the air condition in the drying room is stable and easy to control. Its main disadvantages are that the outlet temperature of atmospheric hot water is not high (about 95℃) and the drying cycle is slightly longer.
The main advantages of wood drying method by indirect heating of furnace gas are that it does not need a boiler, uses the processing residue of the factory as energy, and the drying cost is low. The disadvantage is that the temperature and humidity of the drying medium are not easy to adjust and control, which requires high operating technology and responsibility, and the labor intensity is relatively high. The reliability of this kind of equipment is closely related to the rationality of design. Without reasonable design and construction, the "earth chamber" is not only uneven in drying, long in drying time and uncertain in drying quality, but also prone to fire.
The advantage of dehumidification and drying method is that it can recover the latent heat of vaporization released by condensation of wet air, that is, there is little or no exhaust heat loss; The process is simple, easy to operate, dry and safe, and generally does not cause wood damage. Disadvantages are low drying temperature, long drying cycle, difficulty in thoroughly drying thick plates or materials difficult to dry, and high drying cost.
Vacuum drying method is to put wood in a closed drying container, on the one hand, to increase the temperature of wood, on the other hand, to reduce the pressure in the container, so that the moisture in wood begins to evaporate at a relatively low temperature, thus achieving the purpose of drying wood. This drying method is characterized by short drying cycle and good drying quality, but it has high energy consumption, small container volume and complicated control of drying equipment and drying process. Suitable for hard broad-leaved thick plates with good air permeability or easy-shrinking wood.
Microwave and high-frequency drying method has a series of advantages, such as simultaneous heating inside and outside, uniform heating, fast drying speed, short cycle, good drying quality, natural wood color, continuous automatic production and so on. The disadvantage is that electricity is used as energy source, the cost is high and the equipment performance is not perfect. Preliminary practice has proved that it is suitable for precious tree species (redwood, etc. ), high-grade wood and hard-to-dry wood.
Solar drying is also an energy-saving wood drying method. It uses solar collectors to convert solar energy into heat energy to heat wood. The biggest feature of this drying method is energy saving, but the drying cycle is long, which is affected by regional, seasonal and climatic conditions. Therefore, the use of this drying method has certain limitations.