Each wood processing plant that harvests timber and uses it for industrial purposes, seeks to increase the profitability of production, taking into account compliance with the processing technology of lumber. The technology of forced wood drying by various methods was developed more than half a century ago (natural dryers for firewood do not count). Engineers improved equipment for these purposes. What is the advantage of each type of drying system?
Types of equipment
All drying chambers that are used for wood processing are of several types:
- aerodynamic (inductive);
- Microwave;
- convective;
- vacuum (press vacuum);
- dielectric.
The most similar in price and common are convective drying chambers.
The use of other types of equipment is associated with limitations associated with the complexity of technical conditions. The aerodynamic drying chamber requires a large consumption of electricity, which significantly increases the operating costs of the enterprise and leads to a rise in the cost of lumber. The same can be said about the most effective dielectric samples.
A vacuum drying chamber, its equipment and maintenance, is expensive, so not every company can purchase such a line if it is a small sawmill or a DOK. Condensation drying also requires large financial investments. The process of extracting moisture from the board takes twice as long as the popular convection dryer for wood requires.
Drying Methods
Convection method of processing lumber is most widespread. Many forest suppliers opt for it.
Convection drying
Wood can be dried in convection chambers of any breed, and this is one of the main advantages of the equipment. It is characterized by simplicity of design and reliability. The heating process is carried out using a gaseous agent, in the role of which is steam, flue gas or hot air. Conditions are created by moisture released from the wood, and its excess is removed to the outside by ventilation. Significant energy savings due to low air exchange (not more than 2% of the total mass).
Representatives of the woodworking enterprises order from manufacturers the finished design of the drying system, originally equipped with convection equipment, or purchase the equipment separately and install it in the hangar on their own. When installing dryers yourself, you need to follow a number of rules, in violation of which a board dryer will not give a result.
The drying casing is made of hardy carbon steel or aluminum with a corrosion-resistant coating. It is installed on a monolithic columnar foundation.
All equipment: amplifiers, defect detectors and other devices - are made of aluminum. The convection chamber is insulated with mineral wool and assembled in compliance with SNiP with the obligatory consideration of the climatic zone. Below in the photo is a diagram of convective drying.
Vacuum dryer
A vacuum dryer is usually installed for valuable wood, such as wenge, rosewood or teak. It is suitable for any hardwood and coniferous species, but such an expensive purchase for processing budget raw materials will be inappropriate. The principle of operation of units of this type is based on convective heating of wood by analogy with the previous version, however, the removal of moisture provides a vacuum, which contributes to the process at lower temperatures. Vacuum drying system eliminates aggressive thermal effects and protects the natural material from cracking.
When the temperature rises to 65 ˚C, the automatic control of the boiler is triggered, it turns off, the wood surface cools down, and moisture from the deep fibers goes to the drier layers of the material. A vacuum drying chamber in one cycle can repeat this process more than two hundred times, which contributes to an even distribution of moisture throughout the raw material. Its final value as a result is 4–6%. With technical skills, you can create a dryer yourself, so a home-made chamber of this type is not uncommon.
Aerodynamic chamber
Aerodynamic drying chambers are in the form of metal boxes trimmed with sheets of corrugated board. Designs suitable for loading lumber from 3 to 25 m3 and suitable for all types of wood. The advantage of the equipment is maximum automation, and this minimizes the working staff. The frame of the chamber is made of solid sheet metal, which is mounted on a supporting frame. The drying box configuration is suitable if the supply of timber is carried out by rail. Condensate collectors are installed inside the chamber.
The drying process takes place under the influence of aerodynamics: air heated to the desired temperature circulates indoors, for which a fan is installed in it. The way to control the aerodynamic drying system is simple and consists in pressing the "start" button at the start of the process. At its completion, the valve is activated, and the camera opens.
Microwave camera
Microwave cameras are a new generation of equipment and are manufactured in the form of a closed metal container. The drying chamber for lumber functions under the influence of microwave waves in the same way as it does in a microwave oven. Universal dryers of this type allow loading material of any size and grade. Excess moisture is removed from the interior of the room using reversible fans. The main reason for refusing such a purchase is the high price of equipment, although in terms of efficiency it is equivalent to dielectric, which is practically not used in our country due to the huge energy consumption and high price. The approximate cost of installation is more than 1 000 000 rubles.
The main elements of the drying chambers
Regardless of which type of camera will be selected, the main condition for success is that the equipment is high quality and meets all modern requirements. Automation of the process greatly increases its efficiency and minimizes human involvement. What is included in the complete set of chambers for wood drying, and what qualities should each element have?
Ventilation
Fans in the drying chamber are responsible for the even distribution of hot air. According to GOST standards, the air velocity inside the chamber should be within 3 m / s, which only powerful high-performance fans can handle, the connection diagram of which corresponds to the rotor or axial principle.
Thermal units
Devices are selected depending on the model and capacity of the dryer, and the heat generator can be an electric air heater or heat exchanger, which will pump heat and direct it to the boards. Boilers for drying chambers can operate on any type of fuel. It is better if it is wood waste, as their price is the lowest of all energy carriers.
Moisturizing
The humidity level in the chambers where the lumber is dried is regulated using hoods and special humidifiers. When they are launched, a complex system of interaction between the electromagnetic valve, nozzles and communication lines comes into operation. The exhaust is carried out according to the following principle: when the humidity level decreases, the automatics turn off the fan, and the exhaust operation stops, and the air is humidified by evaporation of the liquid entering the nozzle when the valve opens. At the moment of increasing humidity, the process proceeds in the reverse order, that is, the valve closes, and the fan quickly enters the work.
Lumber supply
The board supply paths are planned at the stage of the camera project, and the rail system itself is mounted during the assembly of the structure. First, rails are laid, then trolleys for stacking lumber are installed on them. The raw materials are placed on a movable trolley and moved into the chamber, and upon drying, they are rolled out onto the street, calibrated and sent to production.