FI117767B - Plant for drying timber - Google Patents

Description

117767

APPARATUS FOR DRYING WOOD

The invention relates to an apparatus for drying wood, comprising apparatus with an opening lid for sealing a drying chamber for drying wood, an inlet duct, an outlet duct, a heating device, a fan device, and through a heating device to the inlet duct to heat the drying gas and provide a suitable flow into the drying chamber.

Various vacuum vacuum drying systems are known in the art where drying of wood is based on the recirculation of superheated steam in a vacuum drying chamber. Vacuum drying is based on creating a pressure difference between the surface of the wood and the interior, whereupon the moisture in the interior of the wood is transferred to the surface of the wood, where it is evaporated to a drying chamber at a higher temperature. Boiling can also occur inside the wood. The water 15 is then converted to vapor, which causes the wood to become cooler as the evaporation absorbs heat. As a result, new heat is introduced into the wood, for example by means of the Ental pia differential of superheated steam.

Vacuum drying in itself has many advantages over conventional warm air drying under normal pressure. These include process speed, energy efficiency, low wood cracking and less air drying * · · j · *: color changes during drying. Vacuum drying is comparable to: "hot drying at low temperatures. In hot drying, the air is naturally • · removed with steam, but special attention must be paid to vacuum drying * ·» ϊ ,, Α.

However, despite its advantages, vacuum drying with superheated steam has not * become * common. This is due to the poor performance of the equipment on the market. , which, in turn, is mostly due to difficulties with verifiably * * · “* for purifying water vapor from the air because the air has a poor heat transfer property compared to steam or for circulating superheated steam and providing a sufficient flow rate in the drying chamber. The reason for this is that · · the use of vacuum in the drying chamber for vacuum circulation is poor * · ·. *. working propellers. Insufficient propulsion fans • · · | the velocity of the vapor, whereby heat is transferred to the wood to be dried as radiation, when '* the heat should be transferred in the convection caused by the high velocity. In addition: 35 flow will break down otherwise formed '' air pockets '', since under reduced pressure air: 2 117767 will accumulate around cold areas if there is no flow. This will cause the trees in the center of the bundle in the dry chamber to heat less than the surrounding trees, resulting in uneven drying of the timber and the resulting problems. Another disadvantage associated with the use of propeller blowers is the cavitation of the propeller-5 blower at too low flow rates. This can occur in a depressurized state because at a pressure much lower than normal pressure, there is not enough gas to pump the propeller blower (blower underload), because always parallel fans will have difficult to predict flow disturbances with a propeller blower.

It is an object of the invention to provide an apparatus for drying wood which eliminates the above drawbacks associated with existing vacuum drying equipment.

In particular, it is an object of the invention to provide an apparatus for drying wood, whereby the steam recycled in the drying chamber is provided with the required high and uniform flow more reliably and with better efficiency of the pumping device 15. It is a further object of the invention to provide an inexpensive but efficient vacuum drying apparatus which can be applied profitably in the small-scale carpentry industry as well.

The object of the invention is achieved by an apparatus characterized by what is stated in the claims.

The apparatus according to the invention is characterized in that the blower device is a central • · ·: ·· · exhaust fan. In order for the wood surfaces to warm evenly, the wood stack must have a sufficient flow rate (pressure drop) of the heat-producing drying gas.

• · ·. * ·· The centrifugal fan has a significantly higher vacuum boost capacity • * · *. . '1 <than with propellers used in the presently known apparatuses and therefore with a central exhaust exhaust 25, it is easy to achieve a pressure drop which causes gas: ***: flow to transfer heat evenly to various parts of the timber and provide optimal ·· drying conditions. Thus, such an apparatus provides a sufficiently powerful and uniform flow for vacuum drying at significantly greater reliability and better pumping efficiency than before.

• · • · * * · *. *. In a preferred embodiment of the apparatus according to the invention, the apparatus comprises only · · one fan device for providing a gas flow. * * *: *: · The amount of superheated steam that can be recirculated in the drying chamber can be reliably and easily controlled by measuring the power take-off, pressure and speed of the blower and comparing it with the blower characteristic. This makes the entire drying process computationally manageable, making it very easy to adjust the process.

In another preferred embodiment of the apparatus according to the invention, the apparatus comprises a control device for continuously adjusting the blowing power of the blower device. Thanks to this, the flow rate can always be optimized to suit the species of wood to be dried, the size of the batch and the diameter of the pieces of wood to achieve a uniform and rapid drying at low energy costs.

In a third preferred embodiment of the apparatus according to the invention, the apparatus comprises pressure and temperature measuring devices located on the inlet and outlet sides of the fan device for measuring the inlet and outlet pressure and the inlet and outlet temperature. Further, in such an application, the apparatus includes a control system coupled to the pressure and temperature measuring devices for controlling the fan device and the vacuum pump based on the results obtained from the measuring devices. With such measuring devices and control system, the flow rate of the superheated steam, the appropriate superheat degree of steam and the desired pressure and temperature can be accurately and reliably controlled, so that the drying conditions of the timber in the drying chamber can be readily determined.

In a fourth preferred embodiment of the apparatus according to the invention, a vacuum condenser is provided between the vacuum pump and the drying chamber, outside the drying chamber. 20 pounds to condense the suction vapor before the vacuum pump. When there is a condenser between the vacuum pump and the drying chamber, the water vapor entering the suction duct '** is condensed and the condensed water is removed before the vacuum pump. In this way, the air entrained in the chamber steam can be concentrated before the vacuum pump. The water vapor condenses on the way and the air is discharged through the vacuum pump.

25 If the condenser is in the drying chamber, it only condenses the water vapor but does not participate in the removal of air. In addition, air is easily collected around a cold condenser in the drying chamber. This forms a condenser around the #:. *. a thermal insulation that reduces the condensing capacity of the condenser. A condenser located on the ul- '* ·) side of the drying chamber avoids these problems.

In a fifth preferred embodiment of the apparatus of the invention, a vacuum pump • ·

is connected to the outlet duct on the suction side of the fan device. The pressure on the suction side is ma- J

• * *. ·. thinner, which is why it is natural to do the venting at the lowest pressure and • «» j at the coldest point.

* · · «· •«; · Ψ -.- 4.

117767

In a sixth preferred embodiment of the apparatus according to the invention, the heating device is disposed on the outlet side of the blower device in the drying chamber for increasing the heat of the steam to be blown during drying. The centrifugal fan supercharges steam from the boiling moisture of wood. However, in the case of some wood species, the heat of vapor superheat should be further increased to achieve the best possible result. The simplest way to do this is to place the heater in the inlet duct. In this case, a separate additional heater is not required for additional printing, but the same heater used to produce basic system heat can also be used for additional printing. During wood drying, in the final stage of drying, the amount of water vapor circulating in the drying chamber may be reduced to such an extent that the proportion of air in the water vapor / air mixture becomes too high. In this case, water may be injected into the suction side of the fan to provide additional water vapor. This slightly increases energy consumption but improves drying performance.

In a seventh preferred embodiment of the apparatus of the invention, the outlet and / or inlet passageway includes a spray device for injecting water into the passageway to add steam and moisten the surface of the wood. Such an injection device enables the heat exchange of the wood to be improved from the surface of the wood to the inside of the wood. This increases the drying rate achieved by the equipment and improves the drying result achieved by the equipment.

In the following, the invention will be explained in more detail with reference to the accompanying drawings, in which: - a schematic drawing of a vacuum drying apparatus according to the invention;

* i «♦ · · *. * ·: With the vacuum drying apparatus shown in Figure 1, the wood is dried from the wood ***:, .. ί. steam generated from moisture. The apparatus includes a drying chamber 1 with an opening and sealing: 25 closure cover 2 with a drying rack for drying lumber: ***: an outlet duct 5 from the drying chamber to the suction connection of the fan device 7, to the outlet duct: ·. duct-connected vacuum pump 8, condenser 10 connected to suction duct, blower * "·! 8 and heating appliances-

Ifl tea 6 heat generating, operating and controlling devices and fan inlet and outlet:. ·. side-mounted temperature measuring devices 13 and pressure measuring devices 14. Further, the hardware includes a control system (not shown in Figure 1) for controlling and adjusting the operation of the various devices. · · 35 The control system includes software to operate it 4 5 117767 pressure and temperature from the measuring devices automatically.

The drying chamber 1 is in the central part a cylindrical container with curved ends. One of the ends of the container is secured to the end of the cylindrical part by means of hinges and a locking device 5. In addition, the connection between the lid thus formed and the container is provided with seals. Thus, the end forming the closure lid can be easily opened when filling the drying chamber and sealed hermetically during drying. To facilitate the handling of the goods, a lid can be mounted on both ends of the container, allowing the timber to be loaded and unloaded from different ends of the drying chamber. The container walls are formed of a stainless steel inner shell having a wall thickness which is high enough to allow the container to be vacuum-filled inside the container, as well as a coated sheet outer sheath and an insulating layer between the inner and outer sheath, e.g., polyurethane foam. The timber drying rack in the drying chamber is configured to fit the drying chamber 15 so that there is approximately the same distance between it and the walls of the drying chamber. In this way, the superheated steam to be recycled in the drying chamber is made to flow as smoothly as possible at each location. The drying rack includes overlapping shelves at a suitable distance, formed of gratings or the like, into which the pieces of wood can be stacked at appropriate intervals so that there is sufficient space between the pieces of wood for recyclable steam. In addition, if desired, the bundles of wood to be placed in the drying rack can be lined up in a convenient manner to obtain the largest possible amount of lumber in the drying rack at once and to ensure that it dries evenly. The chamber is for timber only and the heaters and condenser are outside the chamber.

The inlet duct 4, the intermediate duct 12, the suction duct 11 and the outlet duct 5 are made of a suitable tubular material which is • insulated from the outside by glass or lining wool, for example. . In this way, the steam circulating in the pipes does not condense on the inner surface of the pipes and the optimum energy efficiency of the ducts is achieved. The basic material of the pipe is the * *; Stainless steel, but can also be used as a duct, for example insulated L,. · * 30 plastic pipes with sufficient heat resistance considering the temperature of the steam.

: V, The ducts are connected to the drying chamber and other equipment in the system • · \ .I by means of rigid and durable flange connections sealed to prevent leakage.

• The fan unit 7 is a centrifugal fan rotated by an AC motor. The shaft seal of the blower unit has a mechanical, double-sided, water-sealed and butter-sealed seal for sufficient sealing. This prevents leaking air from entering the shaft sealing point into the system ductwork. The motor control unit 6 117767 is a frequency converter circuit that allows infinitely variable motor speed control. In the embodiment of Figure 1, the apparatus includes only one outlet device mounted between the exhaust ducts. The amount of water vapor and air flowing in the drying chamber can then be easily controlled by measuring the power take-off, rotational speed and pressure of the blower 5 and comparing them with the blower characteristic.

In this case, the heating device 6 is a pipe coil or a heat exchanger for circulating hot water located in a tubular space of larger diameter and inlet channel. The water is heated outside the heater by a location-10 come with an electric heater. Instead of water, it is also possible to use another liquid, such as oil or, for example, steam instead of the liquid. Further, alternatively, direct electric heating may also be applied to the heating device by placing a heating resistor inside the coil.

The vacuum pump 8 is a vacuum pump 15 of known construction and function, the suction side of which is connected via a condenser 10 to the suction duct 11. The suction duct 11 is connected to the outlet duct 5 on the suction side of the fan device 7. The vacuum pump 8 is connected to a control system which starts the vacuum pump whenever the pressure in the drying chamber rises above the set maximum value. The vacuum pump can also run continuously. In this case, the pressure is adjusted by the amount of water in the condenser or so-called. "Ros-20 with butter air". The condenser 10 is a surface condenser mounted in the condensing chamber, which is y

• in this case, formed of a radiator with a duct system fed at about 8 ° C

• · »* tap water at temperature. In the condenser, a temperature of ~ 45 ° C is reached. now the water can be utilized, for example, in heating a building, etc. The water formed from the condensing steam in the condenser can also be utilized if desired.

The temperature measuring devices 13 are suitable temperature sensors known per se, which are located on the suction and discharge sides of the fan device and in the drying chamber. Similarly, the pressure sensors 14 as pressure measuring devices 14 are also:. on the suction and discharge sides. The measuring devices are connected to a control system which • * ·] generates computers with a control card known per se which reads • «30 measurement results into the computer memory and gives control and adjustment commands to the heating device * · ·: V and the vacuum pump and fan motors.

• · · * ·

Using the apparatus of Figure 1, the lid 2 of the drying chamber 1 is opened and the drying rack is pulled out of the drying chamber. The timber to be dried is placed in a drying rack so that there is adequate space between the individual pieces of wood for superheated steam drying the wood 35. After installation, the drying rack is pushed back into the drying chamber 1 and the lid 2 of the drying chamber is closed. The vacuum pump 8 is then started and the system pressure begins to decrease. Once the target pressure, usually about 150 mbar, is reached, the boiling water vapor is recirculated (the residual air being removed by a condenser and a vacuum-5 pump) with a blower device 7 and the heater 6 between the intermediate channel 12 and the support channel 6 is started. at said pressure of about 54 ° C, the higher the humidity, which evaporates on the surface of the timber, begins to escape from the wood. The steam generated is transported from the suction side of the fan device to the discharge side. As it enters the discharge side of the fan, the pressure of the gas formed by the steam and air 10 increases slightly, thus increasing the temperature. This causes the superheat to occur, which is approximately equal to the axis of the blower device. The blower unit blows the superheated steam back into the drying chamber, where the steam flows through the pieces of wood and transfers heat to the surface of the pieces of wood, whereby more moisture is evaporated. In this way, the apparatus dries the wood in the drying chamber by boiling moisture from the interior of the wood to the surface of the wood. Steam generation tends to increase system pressure. The control system provides the basis of the measurement data from the vacuum pump paineenmittauslaitteilta rosvoilmaventtiilille command, when the suction pressure and the determined received from the outlet side of the measuring instruments, control pressure will increase for a given Ylara-20 the operator. As the vacuum pump operates, water vapor flows into the suction duct 11. This water vapor is condensed in the condenser 10 before the vacuum pump and the water formed. . will be recovered. At this point, the heating device 6 is maintained at a temperature such that the system temperature is maintained at the desired value. If necessary, the temperature of the heater ««: * 'can also be kept slightly higher so that the steam listed by the fan heater is more hot. After a sufficient drying time, when the moisture content of the wood ·· *% has dropped, for example to 15%, the gas circulation is stopped. Then allow the pressure to rise to normal pressure, open the lid (during the final drying phase, air can also be circulated in the chamber to stabilize the heat and residual humidity before the trees are removed) and removed from the drying chamber. 30 buy dried timber by pulling out the drying rack from inside the chamber. Suitable for dry. * ··. The drying time depends on the type and thickness of the timber to be dried. of steam • «superheated heat, selected on the basis of the type of wood to achieve qualitative •« φ i. * optimum result with the shortest drying time and low energy - ···.

• · ♦ · · • *! | The invention is not limited to the preferred embodiments shown, but may vary within the scope of the inventive concept of the claims.

Claims (7)

8 117767 Apparatus for drying wood, comprising: a drying chamber (1) for closing wood (3) with an opening cover (2), an inlet channel (4, 12), an outlet channel (5), a heating device (6), a fan device (7). , a condenser (10) and a vacuum pump (8), and in which apparatus the vacuum pump (8) is connected via a condenser (10) to a drying chamber (1) to create vacuum and to remove air from water vapor and an outlet duct (5) ) to the inlet duct (4) for heating the drying gas and providing a suitable flow to the drying chamber (1), characterized in that the blower device (7) is a centrifugal fan and the condenser (10) is between the vacuum pump (8) and the drying chamber (1) outside the chamber for condensing the vapor absorbed by the vacuum pump (8) prior to the vacuum pump. Apparatus according to claim 1, characterized in that the apparatus comprises only one fan device (7) for providing a gas flow. Apparatus according to claim 1 or 2, characterized in that the apparatus comprises a control device (9) for steplessly adjusting the blowing power of the blower device (7). Apparatus according to one of Claims 1 to 3, characterized in that the apparatus comprises a temperature and [·,;] located on the inlet and outlet side of the fan device (7). pressure measuring devices (13, 14) for measuring inlet and outlet temperature and inlet and outlet pressure • * * l. / 25, and incorporating a control system connected to the temperature and pressure measuring devices (13,. **; 14) and the fan pump (7); (8) to control based on the results of measuring instruments. • * * * * · · Apparatus according to one of Claims 1 to 4, characterized in that the vacuum pump (8) ί.ί, ϊ 30 is connected to the outlet channel (5) on the suction side of the fan device (7). • · · • · • · t Apparatus according to one of Claims 1 to 5, characterized in that the heating device (6) is located on the outlet side of the fan device (7) in the drying chamber **; * (1) for increasing the superheat heat of the blown steam during drying. 35 Apparatus according to one of Claims 1 to 6, characterized in that the outlet and / or inlet channel (4, 5, 12) comprises a spraying device for injecting water into the channel for adding steam and wetting the surface of the wood (3). 117767