Overview of Wood Drying Process Control
The control of the wood drying process is a very important part of the drying process. It is directly related to the quality of the wood drying. Good control is the organic combination of the operator and the control equipment. Otherwise, no matter how advanced the control system is without the correct operation of the operator, it will be No practical effect. Therefore, the premise of controlling the drying process is to have well-trained operators who have a good understanding of the knowledge of wood drying. my country's wood drying industry currently does not have a certificate-holding system. In some developed countries, it is mandatory. Drying operators must pass the assessment and have a comprehensive understanding of the principles, equipment and control systems of wood drying. Only after obtaining a qualification certificate Allow the post to perform wood drying operations.
Wood drying control is to control the temperature and humidity state of the humid air in the drying room through the actuator that controls the temperature and humidity according to the moisture content and stress state of the wood at that time, such as opening the heating solenoid valve or electric valve when heating, Open the steam spray solenoid valve or electric valve when steaming, and open the intake and exhaust valves when dehumidifying. The design of the control scheme will directly affect the benchmark hardness (caused by the temperature deviation range) performed in the actual wood drying process, thereby affecting the quality and cost of wood drying. First, the impact on the quality of wood drying, such as drying defects such as cracking, deformation and other quality problems; second, the impact on the energy consumed in the wood drying process, wood drying consumes the most energy in the process of wood product processing, accounting for 40%-70% of the total energy consumption of production, so it directly affects the cost of wood products. The higher the cost, the smaller the profit, and even lose the competitiveness with other similar products; third, during the drying process, common accessories such as heating The number of actions of valves, steam injection valves, intake and exhaust valves, etc. affect the cost of wood drying. Frequent actions of accessories will shorten the life of parts and indirectly increase the cost of products.
The control of the wood drying process is relatively late compared with other research aspects, and it is often taken for granted that it is relatively simple, and the control process is nothing more than the control of temperature and humidity. This is mainly due to the lack of understanding of the important role of the drying control system in exerting the maximum efficiency of wood drying equipment and improving product quality; in addition, the online measurement technology is not perfect, such as measuring the moisture content of wood and the stress change in the wood drying process. The results are not very satisfactory; moreover, the understanding of the complexity of the wood drying process is not enough. The typical large inertial and highly nonlinear systems of wood drying, especially conventional steam drying, are difficult to effectively deal with with classical control theory. This kind of problem. However, due to the progress of computer technology and modern control theory and practice in the past 20 years, this kind of problem has been solved to some extent. With the continuous development of sensor technology and control concept, it is believed that wood drying control will have better development.
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