RU2780600C1 - Installation and method for drying and heat treatment of wood - Google Patents

Abstract

FIELD: wood treatment.

SUBSTANCE: invention relates to devices for drying and heat treatment of wood, in particular lumber, and can be used for heat treatment of various types of wood in the woodworking industry to improve its physical, chemical and consumer characteristics. The method for drying and heat treatment of wood includes heating the wood stack to a temperature of 50-95°C at a pressure of at least 0.05 MPa with the formation of a vapor-gas mixture as a result of evaporation of excess moisture from the wood, drying until the specified moisture content of the wood stack is reached in a vacuum from -0.008 MPa to -0.005 MPa with its active ventilation in a closed circuit with a vapor-gas mixture at an increased partial pressure and forced circulation of the coolant, vacuum release and cooling of the wood stack by means of increased coolant supply. The installation for drying and heat treatment of wood includes an autoclave chamber connected to a scrubber, heating registers are located in the lower part of the chamber along its walls, a nozzle device connected to a high-pressure fan is introduced in the central lower part of the chamber, a suction device is introduced in the upper central part of the chamber, connected through a bypass external air duct with a high-pressure fan, a condensate collector is installed in the upper part of the chamber, which ensures circulation of the coolant, collection and removal of condensate.

EFFECT: reducing the time of drying and heat treatment of a stack of wood.

12 cl, 4 dwg

Description

Technical field

The claimed invention relates to devices for drying and heat treatment of wood, in particular lumber, and can be used for heat treatment of various types of wood in the woodworking industry to improve its physical, chemical and consumer characteristics. The advantages of wood as a building and construction material are well known. At the same time, wood is an extremely unstable material that is destroyed under the influence of external factors, it is hygroscopic, easily exposed to the destructive effects of the atmosphere, has low biostability and a high fire hazard.

State of the art

To protect wood from the above adverse effects, the use of special means of impregnation and heat treatment is required. The technology of heat treatment and devices for applying impregnation agents can be very different, and, as a rule, depend on the processing conditions, the possibilities for further use of the building material. Known, for example, pressure impregnation in impregnating autoclaves, followed by drying in the same autoclave.

From the prior art, a wood drying plant is known (RU 2 319 086 C1, published on March 10, 2008), in which a drying method is implemented, which consists in heating wood in a drying chamber using convectors, including collecting evaporated moisture inside the chamber on condensers, followed by removal of condensed moisture outside the chamber, while the processes of heating to a temperature of not more than 35-45°C and condensation are carried out without heat exchange with the environment. At the same time, convectors (heaters) are located in the lower part of the chamber, and condensers are pipes (radiators) cooled by water or air of the required temperature.

The disadvantage of this drying method and the installation that implements it are low drying temperatures, which implies a long drying process, resulting in an increased risk of biological wood lesions, such as blue rot, developing on the surface of the lumber.

The design of the drying plant is also known (RU 2 137 995 C1, published on September 20, 1999), containing a sealed cylindrical housing with thermal insulation, a drying agent path with its distribution means and placed in it in a technological order in the direction of flow by a condenser, a fan and a heater , a condensate drain pipeline connected to the bottom of the housing and an outdoor air inlet pipeline, a vacuum pump, where the condenser is made in the form of a non-heat-insulated bottom part of the housing. Thus, when vapors condense in the bottom part of the housing, hot condensate heats the recuperative heat exchanger and the outside air passing through it enters the chamber partially heated.

The disadvantage of this design is the high energy consumption of the drying plant as a result of the technologically determined need to use external air, even partially heated, which contributes to the loss of part of the energy intended for heating the stack due to the removal of heat outside the chamber.

A known method of heat treatment of wood (RU 2 277 045 C2, publ. 05/27/2006), including heating the wood to 140-150°C in an air atmosphere, then heating to 210-230°C in an environment of water vapor created by dosed injection water and displacement of air and gases from the chamber, self-heating of wood up to 240°C and self-heating stop by the same water injection. Heating of wood is carried out through air ducts by a thermal high-temperature fan by means of an air heating control unit, including air heating elements.

This method is not only very energy-consuming, but also unstable and fire hazardous due to the self-heating reaction of wood.

The closest technical solution to the claimed installation is the design of the drying chamber according to the patent RU 2 277 682 C2 (published on 06/10/2006), which contains a vacuum pump for creating a vacuum, a means for heating the drying chamber located in the lower part of the chamber, a means for condensing steam , located in the upper part of the chamber, and a means for removing condensate. To implement the drying method at a temperature of 25-39°C, a vacuum of 90-100 mmHg is created in the chamber, which leads to the formation of saturated steam in the chamber, after which the condensate trap provides natural convection in the chamber by moving cold air from the condensation means down, and when the humidity is less than 70%, heating of the chamber is resumed within 70-75°C at a rarefaction within 90-75 mm Hg. Art. before evaporation of the bound moisture from the wood.

The disadvantages of this method and the design of the drying plant include high energy consumption, increased duration of the drying process, which, depending on the thickness of the lumber and the type of wood, can last from 7 to several tens of days, which is often due to poor convection in the stack and depends on how it ( stack) is stacked.

Known design solutions do not imply that the dryer can operate at elevated pressure and temperature, which does not allow them to carry out processes of deep heat treatment of wood, especially wood pre-impregnated with a modifier.

Thus, there is a need to create a less energy-intensive drying plant, as well as a method for drying wood, which allows to reduce the time of drying and heat treatment relative to known methods.

Brief summary of the invention

The technical result achieved by using the claimed invention is to reduce the time of drying and heat treatment of a stack of wood. The technical advantages of the proposed solution can also include a reduction in the internal stresses of wood, a decrease in the energy intensity of the drying and heat treatment process, as well as an expansion of the technological capabilities of wood processing.

The claimed technical result is achieved in that the method of drying and heat treatment of wood includes

- heating a stack of wood to a temperature of 50-95°C at a pressure of at least 0.05 MPa with the formation of a vapor-gas mixture as a result of the evaporation of excess moisture from the wood,

- drying until the desired moisture content of the wood stack is reached in a vacuum from (-0.008 MPa) to (-0.005 MPa) with its active ventilation in a closed circuit with a vapor-gas mixture at an increased partial pressure and forced circulation of the coolant,

- Vacuum release and cooling of the stack of wood through increased supply of coolant.

Drying of raw wood is carried out until a moisture content of 3-5% is reached. Drying of the wood impregnated with modifying solutions is carried out until a moisture content of 20% is reached, after which the stack is additionally intensively heated to a temperature of 175-200°C and maintained at this temperature for 3-5 hours. Excess gas-vapor mixture at a pressure of more than 0.5 MPa is cleaned of harmful impurities and discharged into the atmosphere. The claimed technical result is also achieved by the solution of the installation for drying and heat treatment of wood, including an autoclave chamber connected through a flange to a scrubber, while heating registers are located in the lower part of the chamber along its walls, a nozzle device connected to a high-pressure fan is introduced in the central lower part of the chamber. , and in the upper central part of the chamber, a suction device is introduced, connected through a bypass external air duct to a high-pressure fan that circulates the vapor-gas mixture in the chamber from the nozzle to the suction device; As a coolant in the heating registers, high-temperature synthetic oil can be used, preheated, for example, in an electric boiler using a block of heating elements, and supplied to the registers using a high-temperature pump. The unit's condensate trap includes condensing pipes for coolant transportation located along the length of the chamber, under which there is a condensate collection tray communicating with a sealed container located outside the autoclave chamber. Heating registers are located in the lower part of the chamber and are equipped with evaporators. The suction device is a vacuum pump. Along the walls of the chamber in the upper part along its entire length, aerodynamic profiles are installed, which are plates of a concave-convex shape, providing redirection of the flow of the vapor-gas mixture. The autoclave chamber may be provided with humidity sensors and/or temperature sensors. The scrubber of the installation includes a tank, with pre-installed cassette filters containing a filter element in the form of zeolite granules.

Brief description of the drawings

The claimed invention is illustrated by the following drawings, where

figure 1 schematically shows a side view of the installation,

figure 2 shows a section of the autoclave installation (section B-B),

figure 3 presents a sketch drawing of the scrubber.

in fig. 4 is a sketch drawing of an airfoil.

Positions in the drawings indicate:

1. High pressure fan;

2. Nozzle device;

3. Evaporator;

4. Heating registers;

5. Aerodynamic profile;

6. Condensate collection tray;

7. Condensing pipes;

8. Suction device;

9. Autoclave flange;

10. Temperature sensor;

11. Humidity sensor;

12. Scrubber tank;

13. Cooler (water);

14. Entrance to the tank with a cooler;

15. Exit from the coolant tank;

16. Inlet for gas-vapor mixture;

17. Cassette filter;

18. Exit to the atmosphere;

19. Bypass duct;

20. Evaporator flange;

21. Flange for condensate outlet into a sealed container,

22. Chamber wall.

Implementation of the invention

From theoretical works (Krechetov I.V. Wood drying., M. Lesn. industry. 1980) it is known that the maximum intensification of the drying process is achieved at temperatures close to 100 ° C, at which the partial vapor pressure is greater than air pressure in the chamber, and this leads to the fact that the steam occupies the entire volume of the chamber, displacing air. When this condition is met, drying, as well as heat treatment, is carried out most efficiently and effectively, by reducing internal stresses in the wood and, as a result, preventing its cracking. The second factor affecting the efficiency of drying is to ensure uniform circulation of the drying agent along the entire length and width of the stack of sawn timber, which is used as water vapor, the constant flow of which from the inner layers of wood to the outer layers can be ensured by the rapid heating of the stack of sawn timber using the appropriate species to be processed. wood processing mode (temperature, pressure, drying agent circulation rate, drying agent volume).

At the same time, the total heat consumption during wood drying (for moisture evaporation, for heating equipment, for radiation, maintaining the required level of humidity in the chamber, etc.) is many (up to 10) times greater than the heat consumption for moisture evaporation from wood. At the same time, accordingly, the use of vacuum even during high-temperature drying helps to reduce the level of both equipment heating and passive radiation, which significantly reduces the cost of drying.

In the claimed method of drying and heat treatment of wood, the drying agent is mainly a gas-vapor mixture released from the outer layers of dried lumber. For its formation, a stack of wood at the beginning of the heat treatment process is subjected to heating at a pressure increased to 0.05 MPa. In this case, wood not impregnated with modifier solutions is heated to a temperature of 50°C, and a stack of pre-impregnated wood, for example, with nitrogen-containing aqueous modifier solutions, is heated to a temperature of 95°C. Upon reaching the specified temperatures, a vacuum is created in the chamber by vacuum from (-0.008) to (-0.005) MPa, respectively, and drying of preheated lumber in the stack is ensured with active ventilation by its vapor-gas medium using forced injection and circulation in the chamber along a closed circuit by means of high-pressure fan, condensate collector, and aerodynamic profile, and in case of insufficient humidity in the chamber - an evaporator.

The condensed moisture released into the condensate collector tray is drained into an external special evacuated container. Upon reaching a moisture content of 3-5% for ordinary wood not impregnated with a modifier, the drying in the stack switches to cooling mode up to 40-50 ° C with the help of an increased supply of coolant to the condensate condensate collector pipes.

During the heat treatment of modified lumber impregnated, for example, with a nitrogen-containing modifier, upon reaching a moisture content of at least 20% in the stack as a result of drying, the stack is further heated, with vacuum release, to a heat treatment temperature of 175-200 ° C, depending on the type of wood being processed and its range.

For example, for modified pine wood at this stage it is necessary to reach a temperature of up to 175°C, and for modified birch - up to 200°C.

In this case, there is an intensive increase in pressure in the chamber, due to chemical reactions occurring in the wood substance, from the effects of temperature and pressure. When the pressure in the chamber reaches no more than 0.5 MPa, the excess pressure of the gas-vapor medium is released through a special filter for cleaning the gas-vapor medium (made, for example, in the form of a scrubber 12, 17), with the discharge of already purified air into the atmosphere. To complete the heat treatment of the stack of modified wood, upon reaching the specified heat treatment temperature of 175°C-200°C, the stack of wood is kept in the unit at this temperature for at least 3-5 hours, depending on the type of treated wood species and its assortment. So, for example, for conifers, a sufficient exposure time is 3 hours, and for hardwoods - up to 5 hours. After that, by analogy with untreated wood, the stack is intensively cooled with the help of the active operation of the high-pressure fan and the greater supply of coolant to the condensate trap condenser pipes.

The above method is implemented by using the inventive drying plant (figure 1), including a sealed autoclave and a scrubber connected to it.

The autoclave is made in the form of an extended horizontally oriented chamber, preferably cylindrical in shape, the central part of which is designed to accommodate a stack of processed wood. Heating registers 4 are located along the inner walls below the central horizontal axis of the autoclave chamber, in which high-temperature synthetic oil circulates as a coolant, heated in an electric boiler using a block of heating elements located on the outside of the autoclave, and supplied to the registers using a high-temperature pump. In the lower central part, along the vertical axis of the autoclave chamber, there is a nozzle device 2 connected to a high-pressure blower fan 1 located on the outer side of the chamber. In the upper part (along the vertical axis) of the autoclave chamber, there is a suction device 8, which is connected to a high-pressure fan 1 by means of an external bypass duct 19. These devices circulate the vapor-gas mixture in the chamber. In this case, the gas-vapor mixture blows over the entire volume of the autoclave and the stack along the spaces and, being heated from the registers, enters the suction device 8 of the bypass air duct. To organize the secondary circulation flow of the coolant, a condensate collector is used, located in the upper part of the chamber and consisting of condensing pipes 7 and a condensate collection tray 6. The collected condensate is discharged through the flange 21 to the outside into a special sealed container. To ensure the optimal quality of the processed wood and create the necessary pressure and humidity in the chamber, the unit is equipped with evaporators 3 located on the lower pressure registers with high-temperature oil through flanges 20. The vacuum in the unit is created by a vacuum pump connected to the chamber. For better circulation in the chamber of the vapor-gas medium, it is equipped in the upper part of the chamber to the left and right of the condensate collection tray with aerodynamic profiles 5, which provide a directed high-speed movement of the vapor-gas mixture from the heating registers 4 to the suction device 8. Aerodynamic profiles can be made, for example, in in the form of concave-convex (with a rounded toe profile) plates along the entire working length of the chamber and are located vertically, near the condensate collection tray 6 and the chamber wall 22 with a gap of 20-30 mm, which ensures an increase in the flow rate of the drying agent and local rarefaction in the high-speed section in the tapering part of the airfoil from the chamber wall.

For the current measurement of the moisture content of sawn timber in the stack, the chamber is equipped with temperature control sensors 10 and wood moisture content 11.

The cleaning filter (scrubber) is connected to the autoclave through the flange 9 of the autoclave and the inlet 16 to the cleaning filter. With an increase in the pressure of the gas-vapor medium during heat treatment, it is discharged into a scrubber consisting of a tank 12 with an inlet 14 and an outlet 15, filled with cooling water 13, and a set of cassette filters 17 containing a filter element made, for example, in the form of zeolite granules. Filter elements provide additional cleaning of the vapor-gas medium. The purified air is discharged into the atmosphere through outlet 18 in the upper part of the scrubber.

The proposed installation works as follows.

A stack of wood (untreated with a modifier or previously impregnated with nitrogen-containing aqueous solutions of the modifier) is placed in the autoclave chamber, which is sealed. The heating of the registers 4 and the high-pressure fan 1 are turned on and the pressure in the chamber is raised to 0.5 MPa. By means of heat exchange from the preheated synthetic oil supplied to the registers 4, the internal volume of the autoclave chamber is heated to 50°C - 95°C, depending on the type of wood being treated (untreated and modified, respectively). Upon reaching the indicated temperatures, a vacuum is created in the chamber by vacuum from (-0.008) to (-0.005) MPa, respectively, using a connected vacuum pump. An active ventilation cycle is started, in which the vapor-gas mixture formed as a result of evaporation during the heating of a stack of wood at the first stage is drawn into the bypass air duct with the help of a suction device and pumped with a high-pressure fan through the nozzle hole into the autoclave chamber. In this case, the flow of the gas-vapor mixture rises from the heating registers and accelerates when passing through the aerodynamic profiles, which also set the direction of the further movement of the flow to the suction device. At the same time, the secondary circulation cycle of the coolant is activated, for which the condensate is collected in a tray under the condensing pipes, where the coolant is preliminarily supplied, and the condensate is discharged through the flange 21 to the outside into a special sealed container.

In this mode, the wood is dried until a predetermined moisture level is reached.

When the moisture content of ordinary wood reaches 3-5%, the vacuum is released by turning off the vacuum pump. The stack is actively cooled using a high pressure fan 1 and an increase in the supply of coolant to the condensing pipes 7.

Upon reaching the moisture content of the impregnated wood at 20%, the vacuum is released by turning off the vacuum pump and an additional heating step is carried out. The stack is actively heated using heating registers 4 at a pressure of 0.5 MPa to a temperature of 175°C (for example, for pine) or up to 200°C (for birch). At the same time, the excess pressure of the gas-vapor medium is released through the inlet 16 of the scrubber, where in the cooler 13 and the cassette filter 17, harmful vapors are separated from clean air, which escapes into the atmosphere through outlet 18. At the reached temperature, the stack is kept for a certain time: for example, for conifers, exposure time 3 hours, and for hardwood - up to 5 hours. At the end of the exposure, the heating is turned off and the stack is actively cooled using a high-pressure fan 1 and an increase in the supply of coolant to the condensing pipes 7.

Example of a specific implementation

As a pilot operation of the proposed installation and the method of wood processing implemented with its help, drying and heat treatment of a stack of pine lumber 40 mm thick, 140 mm wide and 6 meters long, pre-impregnated with an aqueous composition of a nitrogen-containing modifier, was carried out. As a result of the heat treatment from 120% board moisture to 5% moisture after heat treatment, taking into account the time for stack cooling, it took 7 days.

With the combined operation of all units of the installation, the consumed power was 400 kW per cubic meter of wood. Whereas according to A. M. Popov, S. V. Sergeev, V. V. Sergeev and Yu. wood is 450-500 kW. The results obtained confirmed the reduction of drying and heat treatment time and the energy efficiency of the proposed method and installation for drying and heat treatment of wood.

Claims (15)

1. Method for drying and heat treatment of wood, including - heating a stack of wood to a temperature of 50-95°C at a pressure of at least 0.05 MPa with the formation of a vapor-gas mixture as a result of the evaporation of excess moisture from the wood, - drying until the specified moisture content of the wood stack is reached in a vacuum from -0.008 MPa to -0.005 MPa with active ventilation in a closed circuit with a vapor-gas mixture at an increased partial pressure and forced circulation of the coolant, - Vacuum release and cooling of the stack of wood through increased supply of coolant. 2. The method according to claim 1, characterized in that the drying of raw wood is carried out to a moisture content of 3-5%. 3. The method according to claim 1, characterized in that the wood impregnated with modifying solutions is dried to a moisture content of 20%, after which the stack is additionally intensively heated to a temperature of 175-200 ° C and kept at this temperature for 3-5 hours. 4. The method according to claim 3, characterized in that the excess vapor-gas mixture at a pressure of more than 0.5 MPa is cleaned of harmful impurities and discharged into the atmosphere. 5. Installation for drying and heat treatment of wood, including an autoclave chamber connected through a flange with a scrubber, while heating registers are located in the lower part of the chamber along its walls, a nozzle device connected to a high-pressure fan is inserted in the central lower part of the chamber, and in the upper In the central part of the chamber, a suction device is introduced, connected through a bypass external air duct to a high-pressure fan that circulates the vapor-gas mixture in the chamber from the nozzle to the suction device; 6. Installation according to claim 5, characterized in that high-temperature synthetic oil is used as a heat carrier in the heating registers, preheated in an electric boiler using a block of heating elements and supplied to the registers using a high-temperature pump. 7. Installation according to claim 5, characterized in that the condensate collector includes condensing pipes for transporting coolant, located along the length of the chamber, under which there is a condensate collection tray communicating with a sealed container located outside the autoclave chamber. 8. Installation according to claim 5, characterized in that the heating registers located in the lower part of the chamber are equipped with evaporators. 9. Installation according to claim 5, characterized in that the suction device is a vacuum pump. 10. Installation according to claim 5, characterized in that aerodynamic profiles are installed along the walls of the chamber in the upper part along its entire length, which are plates of a concave-convex shape, providing redirection of the flow of the vapor-gas mixture. 11. Installation according to claim 5, characterized in that the chamber is equipped with humidity sensors and/or temperature sensors. 12. Installation according to claim 5, characterized in that the scrubber includes a tank with pre-installed cassette filters containing a filter element in the form of zeolite granules.

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