RU2255276C2 - Method of drying wood - Google Patents

Abstract

FIELD: wood treatment.

SUBSTANCE: method comprises supplying live steam to the drying chamber, leveling humidity over the cross-section of timbers, and heating timbers. The operations are performed with the use of sectional looped air ducts, fans, distributors, air heaters, and deflectors which provide uniform distribution of the flow over the height and length of the timber pile. The flow of the live steam and saturated air-steam mixture is distributed in two stages: in diffusers mounted between the fans and air heaters and through deflectors at least at two levels over the height of the pile.

EFFECT: improved method of drying.

3 cl, 3 dwg

Description

The invention relates to wood processing, in particular to the construction of vacuum plants and wood drying technology, for example, furniture, and can be used in enterprises processing soft and hard wood.

Wood drying plants are widely known, containing directly a chamber with a hermetically sealed door and a heater with a fan supplying heated air to the chamber cavity.

The disadvantages of such plants are the lengthy process of drying wood from 8 to 20 days, depending on the species of wood, the low quality of drying, moisture associated with the capillaries from wood in such plants is removed for a long time, as well as high specific energy costs.

A more advanced installation is known, with the help of which a method of drying building materials using vacuum and repeated alternation of heating cycles with simultaneous purging of the material with a coolant and evacuation is carried out. A known installation contains a drying chamber, a vacuum pump, which are connected to the receiver using pipelines and valves. See A.S. USSR No. 1000701, class F 26 V 5/04, publ. 1981 year. In the known apparatus for drying wood in each cycle between heating and evacuation, adiabatic aging is carried out, the duration of which is equal to the duration of the purge. The purge is carried out with a gas-air mixture with a temperature of 160 degrees C and a humidity of 15 g / kg for 6 minutes at atmospheric pressure. Evacuation is carried out for two minutes at a residual pressure of 300 mm RT. Art.

The disadvantages of the known method and device include its high energy intensity, the duration of the process and the low quality of wood drying along the cross section and along the edges of the stack.

A better technical solution is known - the prototype, which is the installation used to implement the method of drying wood according to the patent of Russia No. 2056602, M. cl. F 26 V 5/04, F 26 V 3/04.

The installation comprises a heating vacuum drying chamber connected through a quick-acting valve through a system of vacuum pipelines with a receiver and a vacuum pump. The ratio of the volume of the drying chamber to the volume of the receiver to create a vacuum of the required depth should be at least 1:10.

The wood is loaded into the drying chamber, tightly closed and heated. At the same time, a vacuum is created in the receiver with a vacuum pump, after which a sharp discharge - impulse - of pressure is carried out in the drying chamber by quickly opening the high-speed valve and connecting the receiver to the drying chamber. After that, the wood in the drying chamber is subjected to evacuation - exposure to the created vacuum for a certain time. Then the drying chamber volume is isolated from vacuum and connected to the atmosphere and the atmosphere is heated to atmospheric pressure to a predetermined temperature. These operations are repeated many times until the specified moisture content of the wood is reached. The depth of a given vacuum in the process of pulsed evacuation is created by the receiver, which has an excess of volume compared to the full volume of the drying chamber by 10 times. The installation allows you to implement a method of drying wood, which significantly increases the productivity of drying wood compared to existing analogues.

However, the known installation - the prototype has some unsatisfactory performance. So, when heating and drying wood, timber or logs due to different moisture levels in the surface layers of the wood and in its core, which occurs both during natural drying and traditional drying, tense sections are created in the wood that lead to its deformation and cracks. .

The objective of the present invention is to eliminate the disadvantages of the prototype, in particular the creation of conditions under which the quality of drying of wood, timber and round logs is improved, moisture differences outside and inside the wood are eliminated and thermal surface stresses resulting in cracks in the wood are not generated and her deformation.

The task is achieved by the fact that the wood is heated evenly along the length and height of the stack initially in a hermetically sealed drying chamber with steam to a temperature of 30-35 degrees C and moistened to 100% abs, then the wood is heated with a steam-air mixture formed during heating using sectioned rings with a chamber drying fans, diffusers, air heaters and air ducts, followed by high-speed evacuation.

The heated steam and the air-vapor mixture are initially uniformly distributed across the width of each section using at least two distributors mounted in the diffuser, then distributed along the height of the stack using at least two rails mounted along each side wall of the drying chamber under each with a heater and repeatedly pump them perpendicular to the stack with the help of air ducts, fans, diffusers and air heaters looped in each section until the wood reaches the specified parameters temperature and humidity.

The wood is heated with steam and saturated steam-air mixture without fumes from the hermetically sealed drying chamber.

High-speed evacuation is carried out using a receiver, the volume of which is such that when it is connected to the drying chamber, the latter creates a pressure less than the equilibrium vapor pressure at a given temperature, high-speed valves that connect the drying chamber to the receiver in 0.1-0.5 sec .

Signs that the wood is heated evenly along the length and height of the stack in the hermetically sealed drying chamber with steam to a temperature of 30-35 degrees C and moistened to 100% abs, then the wood is heated with the steam-air mixture formed during the heating process by means of fans sectionally looped with the drying chamber , diffusers, heaters and air ducts, followed by high-speed evacuation, are significant, non-obvious, feasible and aimed at achieving the set image The current task is to improve the quality, efficiency and productivity of drying lumber, thick-walled and round wood.

The signs of the heated steam and air-vapor mixture are initially uniformly distributed over the width of each section with at least two distributors mounted in the diffuser, then distributed over the height of the stack using at least two rails mounted along each side wall of the drying chamber under each heater and repeatedly pump them perpendicular to the stack with the help of air ducts, fans, diffusers and air heaters looped in each section until the wood reaches the specified pairs Meters of temperature and humidity are new, significant, non-obvious signs and are aimed at achieving the feasibility of the drying method and the task set by the invention. Thus, the uniform distribution of sharp steam over the entire height and length of the stack allows you to evenly heat and moisten the wood stack and avoid undesirable thermal stresses and the formation of “dead” - unheated and un-moistened zones.

The signs of wood heating using steam and saturated steam-air mixture are carried out without venting vapors from a hermetically sealed drying chamber - they are signs that complement and explain the correctness and order of operations of the proposed method of wood drying and are aimed at achieving the objectives of the invention.

Signs that high-speed evacuation is carried out using a receiver, the volume of which is such that when it is connected to the drying chamber, the latter creates a pressure less than the equilibrium vapor pressure at a given temperature, high-speed valves that connect the drying chamber to the receiver for 0.1- 0.5 sec, are signs that clarify the features of the proposed method, which are aimed at achieving the objectives of the invention, creating the necessary conditions to ensure high-quality wood drying.

Figure 1 schematically shows the installation for implementing the proposed method of drying wood.

Figure 2 presents the drying chamber in cross section.

Figure 3 is a fragment of a camera in longitudinal section, explaining the distribution of flows.

The wood drying installation, by which the proposed method is carried out, consists of two drying chambers 1 and 2, connected by pipelines 3 and 4 to the receiver 5. Pneumatic quick valves 6 and 7 are installed on pipelines 3 and 4 of the drying chambers 1 and 2. Vacuum pump 8 is connected via a pipe 9 with a ball valve 10 to a receiver 5. The lock chamber 11 is connected to a receiver 5 by a pipe and a pneumatic valve 12. The lock chamber 11 has a pneumatic valve 13 for connecting to the atmosphere and a pneumatic valve pan 14 to drain the fluid. The compressor 15 through the remote control 16 provides control of the valves with compressed air. Each drying chamber 1 and 2 has a valve 17 for connecting the inner volume of the chambers with the atmosphere and supplying steam to the chamber and a valve 18 for draining the liquid from the drying chambers 1 and 2. On the outer surface of the drying chambers, quick-acting pneumatic valves 6 and 7, fans 19 s are mounted heaters 20 and air ducts 21, 22 for supplying and pumping out the resulting vapor-air mixture. The air distribution system inside the chambers, consisting of two at least distributors 23 (see Fig. 3) and guides 24, 25, 26 installed along the longitudinal side walls of the drying chamber, provides an optimal zone for blowing and heating wood 27 along the length and the height of the stacked layers. Between the fans 19 and the heaters 20, diffusers 28 are mounted in which the distributors 23 are placed. A stack of wood intended for drying is laid on a cart 29.

The method of drying wood is as follows.

Preparing the installation for work. The wood intended for drying is stacked in stacks on carts 29 which are pulled out of the drying chambers, which, together with the wood, are rolled after loading into each chamber 1 and 2. Chambers 1 and 2 are cold when loaded, doors, valves 6, 7 and cranes 17 and 18 tightly closed.

By turning on the vacuum pump 8 with the valve 10 open, a vacuum of up to 1-10 mmHg begins to be created in the receiver 5. Art. Sharp steam is supplied to the drying chamber to heat the wood to a temperature of 30-35 degrees C and equalize surface and internal humidity. Simultaneously with the vacuum pump 8, the compressor 15 and each of the fans 19 and air heaters 20 of one of the drying chambers, for example, chamber 1 are turned on. The pressure in the compressor receiver is set to 5-6 atm and the wood is uniformly heated along the entire length of the stack to a temperature of 40-95 degrees C depending on the type of wood and its thickness. Each fan-heater coil produces sectional heating of the wood using a supply duct, first heated air, and then a steam-air mixture and selection of a steam-air mixture formed during wood heating using a duct 22. Heating lumber in a second drying chamber and performing subsequent drying operations carried out at intervals of 30 minutes.

After reaching the set temperature of the wood in the first drying chamber 1, through a control panel 16, quick-acting pneumatic valves 6 are opened in 0.1-0.5 sec, connecting the receiver 5 to the drying chamber 1. When the wood is exposed to vacuum, the temperature of the latter decreases by 15-30 degrees C depending on the initial temperature of the wood. In this case, free moisture, under the influence of the pressure difference in the inner and outer layers of the wood, begins to be displaced in the form of liquid from the wood capillaries and accumulates at the bottom of the drying chamber and collector 11. The wood is exposed to the vacuum under the created vacuum for 30 minutes, after which the pneumatic valve 6 is closed thereby disconnecting the camera from the receiver.

After closing the pneumatic valves 6 in the receiver again begin to create the same vacuum level of 1-40 mm RT. century, and in the drying chamber, the wood is kept at a residual vacuum for 15-60 minutes, constantly heating the wood with saturated juice steam to a temperature of 80-98 degrees C. Then, the above operations with wood in the drying chamber 1 are repeated several times to a residual moisture content of 18 -32% depending on the structure of the wood.

After removal of free moisture proceed to the removal of bound.

To do this, the wood is again heated with the closed valve 17 and high-speed valves 6 to a temperature of 80-110 degrees C. During the heating time, a vacuum of 1-40 mmHg is again created in the receiver 5. Art. After reaching the indicated temperature and vacuum parameters, they begin to vacuum the wood. For this, in a time of 0.1-0.5 sec using high-speed valves 6, the drying chamber 1 is connected to the receiver 5, after which, in a time of 0.5-5 sec, the pressure in the drying chamber 1 and in the receiver 5 is released to a pressure lower equilibrium pressure of saturated steam for a given temperature with open valves 6 and make exposure in the created vacuum for 30 minutes. The exposure time under vacuum is determined by the rate of decrease in wood temperature, and this time is different for different types of wood. The indicated time of 30 minutes is determined for pine wood, in particular for a board with dimensions of 50 × 200 × 6000 mm. Upon reaching a moisture content of 12%, the heating is completely switched off and residual moisture (2%) up to 10% is removed by using the internal heat of the wood. When drying solid wood species - oak, beech, the exposure time in vacuum and at a residual pressure increases from 30 to 60 minutes, and the total drying time - from 10 hours to 136 hours from an initial humidity of 55% to a final of 10%.

After evacuation, the drying chamber is disconnected from the receiver and the wood is heated under residual vacuum with saturated juice steam of wood to a temperature of 80-98 degrees C.

When drying ordinary wood, thick timber or round logs, when as a result of the natural drying process, the moisture in the upper layers becomes less than the moisture content of a freshly sawn wood, i.e. less than in the core, through the valve 17, the distributors 23 and the guides 24, 25, 26 supply steam to the drying chamber and heat the wood by condensation of steam by 15-20 degrees C, while the moisture content of the wood on the surface becomes equal to the humidity in the core . After leveling the moisture, drying of the wood is started by exposing it to a vacuum with exposure to wood after each exposure to a residual vacuum while heating it. In the future, the indicated exposure to vacuum, exposure, heating is repeated until the required final moisture content of the wood is reached.

The diameters of connecting pipelines and the flow area of high-speed valves, as well as the receiver volume, chosen equal to the free volume of the drying chamber, calculated on the basis of the developed mathematical dependence (formula), can effectively influence the wood by vacuum.

After every two or three drying cycles, liquid is removed from the lock chamber 11, for which the pneumatic valve 12 is first closed and valves 13 and 14 are opened. After draining the liquid, valves 13 and 14 are closed and valve 12 is opened.

After completion of the drying process with closed pneumatic valves 6 open the ball valve 17, connecting the drying chamber with the atmosphere in which create atmospheric pressure. Fans shut off. The drying chamber is opened and dry wood is rolled out of the chamber and sent to the warehouse.

The operations described for drying chamber 1 are repeated for drying chamber 2 with a shift of 30 minutes.

A specific example of the method.

The drying of a thick pine bar with dimensions of 150 x 150 mm was started by stacking the cart on a cart and rolling the cart into the drying and humidification chamber by supplying steam overheated to a temperature of 150 degrees C, since some time has passed since the sawing of the tree and a difference in moisture in the surface layers and in the core.

Under the influence of steam, wood was heated for 30 minutes due to steam condensation by 15-20 degrees C, while the initial wood moisture on the surface of 64% gradually leveled off and approached the humidity in the core of 85%, thereby relieving internal stresses in the wood.

Upon reaching a wood temperature of 30 degrees C and a humidity of 85-100%, the wood in the drying chamber was exposed to vacuum, alternating it with exposures in the residual vacuum and heating of the wood, first removing free and then bound moisture. In this case, the steam, and then the steam-air mixture heated by the juices of the wood heated by the heaters, was repeatedly pumped by fans through the diffusers and guides near the walls inside the chamber and passed through a stack of wood perpendicular to the cart.

The distribution of the air flow, and subsequently the vapor-air mixture, with the help of distributors and guides passed evenly over the entire height and length of the stack. The moisture content of dried wood along the length and cross section of the stack and beams was within the limits established by the standards. Subsequently, these operations of exposure to wood were repeated until 10% moisture content of the wood was reached.

The indicated modes were tested on an industrial installation with loading of 8 cubic meters into each chamber. wood.

A pilot industrial plant for drying wood was manufactured with two drying chambers with a loading volume of 8 cubic meters each. each wood. The drying time of a pine timber 150 × 150 mm was 60 hours, oak timber 150 × 150 mm - 196 hours, with an initial moisture content of 60%. The final moisture content of pine and oak timber was 10%.

In another pilot industrial installation with a camera 12 m long and a loading volume of 12 m3. pine and spruce logs with a diameter of 400-450 mm and a length of 4 meters were dried. The total length of the stack, made up of three stacks of 4 meters in succession, was 12 meters. To equalize the internal and surface humidity, the logs were heated with steam to a temperature of 35 degrees C, while the humidity was raised to 100%. Subsequently, the logs were dried to a moisture content of 10%, the drying time was 120 hours. The formation of cracks as a result of drying inside and on the surface of the logs did not occur.

The proposed method does not cause difficulties in its implementation and is suitable for industrial use. All the components and assemblies included in the installation are mass-produced and can be manufactured in industry, and the sequence of operations is easily feasible and automated with the help of industrial instruments.

The quality of wood drying is high, meets the requirements defined for building structures, furniture, parquet, musical instruments.

Claims (4)

1. The method of drying wood, which consists in repeatedly alternating cycles of purging the wood with a coolant for heating wood, evacuating, characterized in that the wood is uniformly along the length and height of the stack, initially in a hermetically sealed chamber, is heated with steam to a temperature of 30-35 ° C and moistened to 100% abs, then the wood is heated by the steam-air mixture formed during the heating process using fans, diffusers, air heaters and air ducts, sectioned with a drying chamber, and then vacuum umirovanie. 2. The method of drying wood according to claim 1, characterized in that the heated steam and steam-air mixture are uniformly distributed initially over the width of each section using at least two distributors mounted in a diffuser, then distributed over the height of the stack using at least at least two rails mounted along each side wall of the drying chamber under each heater, and repeatedly pump them perpendicular to the stack using air ducts, fans, diffusers and air heaters looped in each section up to m ment timber achieve predetermined temperature and humidity. 3. The method of drying wood according to claim 1, characterized in that the heating of wood using steam and saturated steam-air mixture is carried out without venting vapors from a hermetically sealed drying chamber. 4. The method of drying wood according to claim 1, characterized in that the evacuation is carried out using the receiver, high-speed valves, providing a connection between the drying chamber and the receiver for 0.1-0.5 s.

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