FI110029B - Procedure for a three-phase drying of wood and equipment needed for this - Google Patents

Description

110029

Three-step wood drying process and equipment

The invention encompasses a novel method of drying wood and apparatus for carrying it out.

Current methods of drying wood and related problems are well known in the art. The biggest difficulties for the industry have been: - slowness of wood drying - high energy consumption - drying errors (loss of FIM 2-3 billion a year) - hard-to-dry trees such as solid wood, whole logs, birch, several 10 hardwoods such as oak, beech and the like dense trees.

The most commonly used drying methods today are: - chamber drying: The lumber is heated with hot air blowers. The steam is led out. In order to prevent cracking, water vapor is used according to the drying formula.

: · *: 15 - Vacuum drying: The timber is loaded into a vacuum chamber, which is depressurized to • I · 0.2-0.6 bar, whereby the water evaporation point decreases accordingly. Heating • M * comes inside the chamber with water heaters and powerful fans. Free from wood • *. · · ·. the steam is led out to the condensers.

f "*; - quick drying: The wood is heated to above 100 ° C with steam blown through the wood at high speed • * ... 20. Steam is discharged from the drying space in a controlled manner according to the drying formula. The air pressure is normal.

- RF drying: The timber is placed between two metal sheets. The high frequency energy • · · * '· is conducted to the metal plates. High frequency causes the water molecules in the wood to circulate, causing friction and heating and evaporation of the water.

:. '. 25 - Combined RF Heating and Vacuum: On a small scale, this has been experimented with Ka • «· ·. ···. in Nassau, Japan and also in Finland. The results have been very promising in the elimination of drying errors. The drying time has also been very short compared to '.:. 'Other methods. The disadvantage is expensive electricity. The RF generator has a low efficiency, only 50%.

30 - There are other methods, but they are of no practical importance to industry.

There are many problems when drying wood: - Drying errors. If water is allowed to evaporate from the surface of the wood too quickly and there is no pressure inside the wood to drive water to the surface, a gradient phenomenon occurs and the wood splits from the surface. It can also be warped. The inner cracks are created for the opposite reason, ie the interior of the wood is overheated, the water penetrates into the outer layers and the interior of the wood 110029 2 dries too quickly. Boiling of the resins and detachment of the branches are due to too high temperatures.

- Color errors. Some types of wood, such as birch, will easily darken. The reason may be too high temperature, long drying time, oxidation, etc.

5 - Long drying time. Fresh wood conducts heat well. It can be introduced into the wood from the outside. When the wood dries, it becomes a highly heat-insulating material, so that the heat needed to enter the wood can no longer be introduced. There is no force that drives water out of a tree. Therefore, the drying time will be long.

- Waste energy. Thermal energy is easily escaped from the drying plant. In practice, only a fraction of the energy can be used to drive water out of the wood.

- Hard-to-dry trees. In practice, it has been virtually impossible to dry whole tree trunks used by the log and column industries by known methods. The same applies to certain types of wood.

The method according to the invention and the equipment necessary for it can eliminate the disadvantages of the prior art.

Advantages of the Invention: · · · · # *. : - Minimizing drying errors. · · ·. 20 - Necessary speed for industrial scale. Large enough drying capacity.

- Low energy consumption. Access to a cheap energy source. More expensive ... t energy relatively low. Efficient energy recovery: low waste energy.

- Process control can be performed by a computer program.

- Structure package solutions. The package is delivered in its entirety to the subscriber by truck. Installation at the customer's end remains minimal.

: The basic idea of the invention is to perform wood drying in three successive stages. ···. you.

:.:.: 30 Step 1: • “· The wood pulp is heated with boiling water in a vacuum chamber to the desired degree, for example 80-90 ° C. The viscosity of the water in the wood changes so that it easily comes out of the wood under pressure. Boiling water effectively releases the heat it binds to its wood pulp. The circulating water is continuously heated to the boiling point. Icy or completely fresh solid wood will warm up to this temperature in a matter of two to three hours.

110029 3

Step 2:

Water is pumped from the vacuum chamber into the surrounding container and a strong vacuum, for example 0.05 bar, is drawn into the vacuum chamber. Compared to this, strong pressure is exerted on the wood, which drives the free water out of the wood. The water evaporates in the sub-5 pressure chamber and exits through the condenser. The walls of the vacuum chamber at a temperature of +100 ° C release the heat lost to the chamber and the timber surface by evaporation. The moisture content of the wood in this 2-stage drops sharply, from completely fresh to less than 20%.

10 Step 3:

Now wood has become a good thermal insulation. It is no longer able to effectively run into the heat energy, which would cause internal pressure difference between the timber and the exterior driving water out of the wood. Now turn on the RF heating. It can stabilize the internal temperature of the wood to the desired level. In this way, the differential pressure that expels the water bound to the 15 cells of the wood can be maintained, and less than 8% humidity can be achieved without drying defects.

• »· · •: · Criteria under which the idea of the invention works: /·.· Water in the wood will not move unless it is driven by the trigger can -. * ·. 20 countries. Centrifugal force and force due to differential pressure are available. For the rest ....: the forces probably have little significance. Water absorbs a lot of thermal energy in the evaporation .... so this energy needs to be arranged. But the thermal energy alone inside the wood without pressure differences is quite inefficient. The wood is warm, but it does not dry out except by the effect of the water evaporating from the surface, which creates a suction power or pressure difference.

"; ': 25 In this method, the pressure difference inside and outside the tree is kept as high as possible, whereas there is no pressure difference within the tree and thus no internal tensions or gradients. is prevented by a water bath and at the same time the necessary heat energy is injected into the wood to create a differential pressure when step 2 begins. "The pressure pushes the water out of the wood very quickly. Once the free water has left the wood quite easily, to continue the process, you have to go to step 3, which is to do the same thing, which is to keep the pressure Therefore, it is driven directly into the wood by RF energy and penetrates where the moisture This is and causes the necessary pressure to drive the moisture trapped in the wood cells to the wood surface for evaporation. With this method, completely fresh, even icy logs, not to mention other lumber, can be dried in a few hours to a tree-dry with relatively flawlessness.

The invention will now be described in more detail with reference to the accompanying figures.

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Figure 1 is a block diagram of the apparatus used in the method of the invention.

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Claims (11)

A method of drying wood, wherein the process is dried at elevated temperature by means of vacuum and RF energy in a closed drying chamber (2), characterized in that prior to the drying process, the temperature of the wood is raised in the drying chamber (2). to a desired level using a medium which is hot, preferably boiling water. Process according to claim 1, characterized in that the drying of the wood takes place in the same drying chamber (2) in three successive steps, in which the first stage of the wood temperature is raised by hot water to the desired temperature and in the second stage the water is removed from the drying chamber (2). ), in the chamber an underpressure is arranged and the wood is heated by heating the chamber and in the third step, an underpressure is maintained in the chamber (2) and the wood is heated by RF energy. 3. A process according to claim 1, characterized in that the wood yarns which are dried are heated with hot water to a temperature of the order of 80-90 ° C. 15 4. A process according to claim 1, characterized in that '. arranged in the drying chamber (2) is of the order of 0.05-0.1 bar. • · · Process according to claim 1, characterized in that the water used at *: ··: the heating of the wood varnishes is used during the vacuum drying for heating the drying chamber (2). .20 6. Process according to claim 1, characterized in that when the drying starts with * · RF energy, the moisture content of the wood products is of the order of 20%. . 7. Wood drying plant (1), which has a vacuum chamber (2) for drying the woodwork with vacuum and means for directing (3) RF energy to the woodworking, characterized in that the plant also has means: :: 25 for heating (6) the water and for conveying (7, 8) the heated water to the: · · · in the pressure chamber (2) and away from it. Wood drying system (1) according to claim 7, characterized in that said means comprises a water container (8) which has been placed to enclose the drying chamber (2) to raise the temperature of the chamber by means of the heated water. Wood drying plant (1) according to claim 7, characterized in that the plant has a control system (10) for controlling the drying process. 110029 t Control system (10) according to claim 9, characterized in that the control system (10) has a computer and a computer program or software for controlling the wood drying system (1). Wood drying plant (1) according to claim 7, characterized in that the plant can be placed in an easily movable package which can easily be put into functional condition. • · * *