WO2006006837A1

WO2006006837A1 - Method for drying sawn timber and a drier for carrying out said method

Info

Publication number: WO2006006837A1
Application number: PCT/LV2005/000009
Authority: WO
Inventors: Svetlana Andreevna Yagodzinskaya; Sergey Anatolyevich Yagodzinskiy
Original assignee: Gordijs, Jevgenijs
Priority date: 2004-07-15
Filing date: 2005-07-06
Publication date: 2006-01-19
Also published as: RU2277682C2; RU2004121797A

Abstract

The inventive method for drying sawn timber consists in loading sawn timber in a drying chamber, in heating said chamber by means of a heating device, thereby evaporating water and forming steam in the chamber, in condensing said steam by bringing it into contact with condensing means and in transferring the steam condensate to condensate receivers, wherein a vacuum ranging from 90 to 100 mm Hg is produced in the drying chamber which is heated to a temperature of 25-39 °C for forming saturated or near-saturated steam, in measuring the moisture of steam in the chamber by means of a moisture-measuring device, in supplying a flowing coolant to the condensing means at a moisture greater than 98 % for condensing a part of steam from the chamber and in reheating the sawn timber at a moisture less than 70 %. A drier for carrying out said method is also disclosed. The inventive method and drier make it possible to attain the high quality of sawn timber.

Description

METHOD FOR DRYING Lumber and a dryer for its implementation

The invention relates to a method for drying lumber and a dryer for lumber and can be used in the woodworking industry when drying various types of wood.

There is a method of drying wood, which is carried out by blowing it with heated air, venting the released vapors, evacuating and cooling, while before blowing the wood is preliminarily kept under vacuum, and then blowing is carried out at a given temperature while venting the released vapors, and cooling is carried out with air at a constant changing temperature and air speed (SU 1067319 A, 1/15/.84).

The disadvantage of this method is the uneven drying of wood, which leads to a decrease in its quality due to a sharp change in temperature and forced removal of vapors from the chamber.

Known dryer for lumber, comprising a housing, a vacuum pump for creating a vacuum in the drying chamber, means for heating the drying chamber, condensation means for condensing steam and means for draining the condensate into condensate collectors (RU 2115871 C1, 07.20.1998).

A disadvantage of the known dryer is the uneven drying of wood, which leads to a decrease in its quality due to the uneven passage of heated air throughout the stack of lumber and the formation of stagnant zones in the middle of the stack. The objective of the present invention is to improve the quality of lumber, reduce energy consumption and increase the efficiency of the dryer.

The task is achieved by creating a method of drying lumber, which includes loading lumber into the drying chamber, heating it by means of a heating means, ensuring the evaporation of moisture from the lumber and creating steam in the chamber, steam condensation provided by contacting the latter with the condensation means and the removal of steam condensate in condensate collectors, while creating a vacuum in the drying chamber within 90-100 mm Hg and it is heated to a temperature ranging from 25 to 39 ° C to create saturated steam or close to saturated, measure the humidity of the steam in the chamber by means of a humidity meter, and when humidity reaches more than 98%, provide flowing refrigerant to the condensation means to condense part of the steam chambers, and when humidity reaches less than 70%, they resume heating of lumber.

According to a second embodiment of the invention, a method for drying lumber involves loading lumber into a drying chamber, heating it by means of a heating means, evaporating moisture from the lumber and creating steam in the chamber, condensing the steam by contacting the latter with the condensation means, and draining the steam condensate to the condensate collectors while heating the drying chamber and maintaining the temperature in it in the range from 25 to 39 ° C to create saturated steam or close to saturated and when the specified upper temperature value is reached, flow refrigerant is supplied to the condensation means to condense part of the steam from the chamber, and when the specified lower temperature value is reached, heating of the lumber is resumed.

In this case, the temperature inside the chamber is controlled by means of temperature control. The drying agent is steam.

Preferably, the heating means in the form of heating pipes is arranged on the inner surface of the drying chamber.

Upon reaching the specified upper temperature in the chamber, the heating of the drying chamber is stopped and the surface layers of the lumber cool down with an increase in the moisture movement gradient from the middle layers to the colder surface layers.

To ensure the evaporation of bound moisture located in the walls of the lumber cells, a vacuum is additionally created over the entire area of the board in the drying chamber within 90-75 mm Hg. and heat the drying chamber to a temperature in the range of 70-75 ⁰ C.

The lumber loaded into the chamber is stacked, which is divided into two parts, leaving a gap between them and between each board, for the steam to pass up and the cold refrigerant down, at a speed of 0.8-1 m / s to ensure natural convection in the camera.

Mostly, the residual moisture content of the lumber is 4-5%. The task is also achieved by creating a dryer for lumber, which contains a housing forming a drying chamber for loading lumber, a vacuum pump to create a vacuum in the drying chamber, means for heating the drying chamber, condensation means for condensing steam and means for draining condensate into condensate collectors, at the same time, the dryer additionally contains humidity measuring means and temperature control means installed inside it, and the condensation means It is made in the form of condensate pipes placed in the upper part of the drying chamber along its entire length with a means for removing condensate located below them, including a tray and a collector for collecting condensate, and heating means is made in the form of heating pipes, which are placed in the lower part on the inner surface drying chamber. Preferably, the housing of the drying chamber is cylindrical.

Heating pipes located in the lower part on the inner surface of the drying chamber occupy essentially two thirds of this surface. Preferably, the moisture measuring means is in the form of a humidity measuring sensor, the temperature monitoring means is in the form of a temperature control sensor, and the heating means is an electric boiler.

Outside the end wall of the housing of the drying chamber is a working compartment for placing fixed assets and a control panel and monitoring the operation of the dryer. In this case, the heating pipes are combined in the lower part of the drying chamber into one return pipe, which is brought into the working compartment.

Mostly the main facilities include a vacuum pump, an electric boiler with an emergency protection system, a membrane expansion tank, a vacuum gauge for measuring vacuum in the drying chamber, a circulation pump for forced passage of water in the heating pipes, and condensate collectors.

At the same time, the control panel includes a display for determining the readings of the control temperature measurement sensor and the humidity measurement sensor inside the drying chamber and the control temperature measurement sensor inside the electric boiler, and the condensate collectors have inspection windows, valves for condensate drainage and an equalizing valve.

The invention will now be described in more detail with reference to the drawings, in which:

Figure 1 shows a schematic view of a dryer for lumber according to the invention.

Figure 2 shows a cross section A-A in figure 1.

On Fig.z depicts a working compartment with equipment placed in it.

Figure 4 shows a cross section of a dryer with a stack of lumber placed in it.

The lumber dryer includes (Figs. 1-4) a horizontal cylindrical body 1 forming a drying chamber 2 with heating pipes 3 located in the lower part on the inner surface of the chamber and condensate pipes 4 located in the upper part of the drying chamber along its entire length. Heating pipes occupy no more than two-thirds of the inner surface of the chamber so that condensate pipes located in the upper part of the chamber do not heat up. If the heating pipes occupy less than two thirds of the inner surface of the chamber, it will not gain the set temperature at the required time. Condensate pipes run along the entire length of the upper part of the chamber in order to increase the contact area of steam with cold condensate pipes. The heating pipes are combined at the bottom of the drying chamber 2 into one return pipe 5 with a conclusion to the working compartment. Under the condensate pipes 4 is placed a means for draining the condensate, including a tray b and a collector 7 for collecting and draining the condensate. Condensate flows into condensate collectors 8 having inspection windows, condensate drain valves and an equalizing valve. Inside the drying chamber 2, a control temperature measuring sensor 9 and a humidity measuring sensor 10 are installed.

The main means are located in the working compartment: a vacuum pump 11 for creating a vacuum in the drying chamber, an electric boiler 12 with an emergency protection system, an expansion tank 13 of a membrane type, a vacuum gauge 14 for measuring vacuum in the drying chamber, and a circulation pump 15 for forcing water to flow into heating pipes and a control panel 16, including a display for determining the readings of the control sensor 9 for measuring temperature, a sensor for measuring humidity inside the drying chamber, the regulating sensor Single measurement of temperature inside the electric boiler, and sensors measuring wood humidity. The main difference of the proposed invention is the drying of lumber from beginning to end in the presence of saturated steam or close to saturated, which is formed as a result of evaporation of moisture from the lumber. With the constant presence of steam, the lumber dries without internal stresses and deformations. This drying technology is achieved by collecting condensate in the upper part of the drying chamber, the design of the heating pipes, stacking and stacking schedule of drying, which is divided into three stages. At the first stage, the so-called steaming of lumber is provided. In the chamber, a temperature of 25-39 ° C and a vacuum of 90-100 mm Hg are created. in 24 hours. If the temperature in the chamber is below 25 ° C, the sawn timber may become moldy, and at temperatures above 39 ° C, small cracks in the sawn timber and even its deformation may form. Under the above conditions, saturated steam is created, i.e. steam in equilibrium with the liquid that forms it, which evaporates from the lumber. Moisture evaporates from the surface layers of lumber. Steam in rarefied air collects below and gradually rises. When filling the entire volume of the drying chamber, saturated steam is formed. In this case, the evaporation of moisture from lumber is terminated.

In the second stage, after steaming, flowing refrigerant is supplied to the condensate pipes. Steam in contact with condensate pipes begins to condense. Condensate flows down the collector into the condensate collectors. Cold air from condensate pipes rushes down at a speed of 0.8 -1 m / s. by the gap between the two parts of the stack of lumber, which is located in the center of the stack, driving the steam jacket, and the hot air rises from the heating pipes. This is how natural convection occurs. When the upper temperature value is reached, the sensor on the control panel turns off the heating medium (electric boiler). This contributes to the cooling of the surface layers of lumber, which increases the gradient of the movement of moisture from the middle layers to the colder surface layers. Such a pause also provides energy savings, because the boiler is turned off and cooling occurs naturally. When you turn on the flow of flowing refrigerant, the temperature in the drying chamber drops by 5-7 ° C. A temperature measuring sensor located inside the chamber, when the temperature drops, gives the command to turn on the electric boiler, and the temperature rises again to the required value. This heating-cooling process is provided throughout the entire drying process. When condensate leaves the chamber, the degree of steam saturation is violated, this contributes to a slow, soft mode of moisture exit from the lumber, i.e. exactly as much moisture comes out of the lumber as there is condensate, this is approximately 5-10 l / h.

When free moisture leaves the cells of the lumber, when the sensors for measuring the moisture content of the wood show a moisture content of 25-35%, the stresses in the lumber change. Therefore, it is necessary to carry out moisture heat treatment of wood to relieve internal stresses. To do this, the flow of refrigerant to the condensate pipes is stopped, and again the conditions for creating saturated steam or close to saturated within 24 hours.

At the last stage of drying, a vacuum of 90-75 mm Hg is created in the chamber to remove bound moisture from the lumber. and heat the chamber to a temperature of 70-75 ⁰ C. In this case, the refrigerant enters the condensate pipes constantly. Boiling of moisture begins over the entire cross section of the lumber and the bound moisture located in the cell walls evaporates.

The end of drying occurs after there is no condensate leaving the receiving tanks during the last day. Signs of the end of drying are: readings of a moisture meter 5-8%, a significant decrease in the amount of condensate output to 4-5 liters over the past 24 hours. After this, the heating means is turned off, the lumber begins to cool, which contributes to the final equalization of humidity along the thickness of the board and the entire volume of the stack. After 24 hours of cooling, the vacuum in the chamber decreases to 375 mm Hg. The last 24 hours, the pressure in the chamber is equalized with atmospheric, the flow of refrigerant into the condensate pipes is stopped. The camera can be opened. The operation of the dryer is as follows. Lumber is placed on the loading trolley and the trolley is rolled into the drying chamber, the lid is closed with the fastening nuts. Provide access to running water to the vacuum pump and turn on the vacuum pump. Create a vacuum in the chamber up to 100 mm Hg On the control panel, the temperature inside the chamber is set to 39 ° C. Within 24 hours, a lumber is steamed. They include cold water supplied to the condensate pipes. Upon reaching humidity lumber 40-50% set the temperature in the chamber 75 ° C. Upon reaching a moisture content of lumber of 30%, a vacuum is created up to 75 mm Hg. If this vacuum is not provided, then there is a lot of steam in the chamber. Within 1-2 days, re-create a vacuum to the specified value. The moisture content of the lumber is determined using sensors on a scale, taking into account amendments for a specific wood species. At the end of drying, the heating system is turned off and the lumber is held in a closed drying chamber until it is completely cooled. Then equalize the pressure in the chamber with atmospheric. Open the drying chamber, selectively check the moisture content of the wood to make sure that the percentage of moisture corresponds to the desired humidity. Unload lumber in a dry room and store it in a stack.

When the housing cover is closed as a result of the operation of the vacuum pump, a reduced air pressure is created inside the chamber body, which increases the rate of evaporation of moisture from the wood stacked on the trolley.

Evaporation rate increases even more with increasing air temperature from hot heating pipes. The combination of low pressure and high air temperature inside the drying chamber provides high-quality drying of lumber.

The steam formed during drying comes into contact with the cold walls of the condensate pipes, condenses and the condensate flows into the tray, from which it enters the collector. Condensate flows from the collector to the condensate collector.

The liquid heated by the electric boiler is piped to the heating pipes by a water pump. Return liquid from the heating pipes is carried out through the pipeline. When the fluid expands from heating, its excess enters the expansion tank, which together with the valve protects the system from increasing water pressure. The fluid pressure in the system is controlled by a manometer. A valve is used to release air from the system.

The required drying temperature of lumber is set using the temperature gauge on the control panel and is subsequently maintained automatically by means of a thermocouple. To condense steam, process water with a temperature of 10-15 ⁰ C from the enterprise’s circulating water supply system can be used. If a closed water supply system using a pump is used, it is necessary to use a capacity of at least 5 m ^{3 of} water per drying chamber. Condensate collectors are installed below the body of the drying chamber, as a result of which condensate from the chamber flows by gravity through the pipeline into the storage tank.

In the heating system, you can fill in tap water, non-freezing liquid or distilled water (to avoid scale in an electric boiler). In the lower part of the working compartment there is a common cold water inlet, which provides filling of the heating system, fills the condensate pipes inside the chamber and ensures the supply of cold water to the vacuum pump.

For high-quality drying, it is necessary to correctly lay the lumber on the loading trolley. Lumber is manually loaded onto strips throughout the chamber. A gap of 50-100 mm is left in the middle of the chamber so that the cold air from condensate pipes went down, and warm from heating pipes rose up. At the edges of the stack it is imperative to withstand the hemisphere, which allows warm air to penetrate between the boards and to carry out natural convection. Sensors for determining the moisture content of lumber are installed in the inner part of the stack at the top and bottom closer to the middle of the stack. Gaskets are made of any lumber 20x30 mm in size, the step of installing gaskets: for a board with a thickness of 40-60 mm - not more than 70 cm, for a board with a thickness of 25-30 mm - not more than 40 cm. The first and last gaskets are installed from the edge of the stack no more than 10 cm.

The main advantages of the claimed dryer are the following: a universal drying schedule, which ensures drying of any wood species, environmental friendliness, since no emissions are made into the atmosphere, natural convection, since fans are not used, the use of sawn heating-cooling method, which helps save energy, lumber does not change its natural qualities (strength, color, texture), there is no marriage after drying, the moisture drop across the board area and the entire stack does not exceed 1 %

Claims

CLAIM

1. A method of drying lumber, including loading lumber into the drying chamber, heating it by means of a heating means, evaporating moisture from the lumber and creating steam in the chamber, condensing the steam provided by contacting the latter with the condensation means and draining the steam condensate into condensate collectors, characterized the fact that they create a vacuum in the drying chamber within 90-100 mm RT.article and it is heated to a temperature ranging from 25 to 39 ° C to create saturated steam or close to saturated, measure the humidity of the steam in the chamber by means of a humidity meter, and when humidity reaches more than 98%, provide flowing refrigerant to the condensation means to condense part of the steam chambers, and when humidity is less than 70%, they resume heating of lumber.

2. The method according to claim 1, characterized in that they control the temperature inside the chamber by means of temperature control.

3. The method according to claim 1, characterized in that the drying agent is steam.

4. The method according to claim 1, characterized in that the heating means, made in the form of heating pipes, is located on the inner surface of the drying chamber.

5. The method according to claim 1, characterized in that the heating of the drying chamber is stopped when the specified upper temperature value is reached in it and the upper layers are cooled lumber with an increase in the gradient of moisture movement from the middle layers to the colder outer layers.

6. The method according to claim 1, characterized in that it additionally creates a vacuum in the drying chamber within 90-75 mm Hg and heating the drying chamber to a temperature in the range of 70-75 ⁰ C to ensure the evaporation of bound moisture located in the walls of the lumber cells over the entire area of the board.

7. The method according to claim 1, characterized in that the lumber is stacked in a pile that is divided into two parts, leaving a gap between them and between each board, for the steam to pass up and the cold refrigerant down, at a speed of 0.8-1 m / sec to provide natural convection.

8. The method according to claim 1, characterized in that the final moisture content of lumber is in the range of 4-5%.

9. A method of drying lumber, including loading lumber into the drying chamber, heating it by means of a heating means, providing evaporation of moisture from the lumber and creating steam in the chamber, steam condensation provided by contact of the latter with the condensation means and the removal of steam condensate in condensate collectors, characterized the fact that they heat the drying chamber and maintain a temperature in it in the range from 25 to 39 ° C to create saturated steam or close to saturated, and upon reaching the decree Nogo upper temperature values provide a supply of refrigerant flowing in the condensing means for condensing a portion of steam from the enclosure and on reaching said lower temperature values resuming heating lumber.

10. The method according to claim 9, characterized in that they control the temperature inside the chamber by means of temperature control.

11. The method according to claim 9, characterized in that the drying agent is steam.

12. The method according to claim 9, characterized in that the heating means, made in the form of heating pipes, is located on the inner surface of the drying chamber.

13. The method according to claim 9, characterized in that the heating of the drying chamber is stopped when the specified upper temperature is reached and the upper layers of the lumber are cooled with an increase in the moisture movement gradient from the middle layers to the colder outer layers.

14. The method according to p. 9, characterized in that it additionally creates a vacuum in the drying chamber within 90-75 mm RT. Art. and heating the drying chamber to a temperature in the range of 70-75 ⁰ C to ensure the evaporation of bound moisture located in the walls of the lumber cells over the entire area of the board.

15. The method according to claim 9, characterized in that the lumber is stacked, which is divided into two parts, leaving a gap between them and between each board, for the steam to pass up and the cold refrigerant down, at a speed of 0.8-1 m / sec to provide natural convection.

16. The method according to claim 9, characterized in that the final moisture content of lumber is in the range of 4-5%.

17. A dryer for lumber, comprising a housing forming a drying chamber for loading lumber, a vacuum pump for creating a vacuum in the drying chamber, means for heating the drying chamber, condensation means for condensing steam and means for draining the condensate into condensate collectors, characterized in that it contains humidity measuring means and temperature control means installed inside it, and the condensation means in the form of condensate pipes placed in the upper part of the drying chamber along its entire length with a means for condensate drain located below them, including a tray and a collector for collecting and draining condensate, and the heating means is made in the form of heating pipes, which are placed in the lower part on the inner surface of the drying chamber.

18. The dryer according to claim 17, characterized in that the housing of the drying chamber is preferably cylindrical.

19. The dryer according to claim 17, characterized in that the heating pipes located in the lower part on the inner surface of the drying chamber occupy two thirds of this surface.

20. The dryer according to claim 17, characterized in that the moisture measuring means is made in the form of sensors.

21. The dryer according to claim 17, characterized in that the temperature control means is in the form of a temperature measuring sensor.

22. The dryer according to claim 17, characterized in that the heating means is an electric boiler.

23. The dryer according to claim 17, characterized in that is located outside the end wall of the housing of the drying chamber working compartment for the placement of fixed assets and control panel and control the operation of the dryer.

24. The dryer according to claim 17, characterized in that the heating pipes are combined in the lower part of the drying chamber into one return pipe, which is brought into the working compartment.

25. The dryer according to item 23, wherein the main means include a vacuum pump, an electric boiler with a safety system for emergencies, a membrane expansion tank, a vacuum gauge for measuring vacuum in the drying chamber, a circulation pump for forced passage of water in the heating pipes and condensate collectors.

26. The dryer according to item 23, wherein the control panel includes a display for determining the readings of the control temperature measurement sensor and the humidity measurement sensor inside the drying chamber and the control temperature measurement sensor inside the electric boiler.

27. The dryer according to claim 17, characterized in that the condensate collectors have inspection windows, condensate drain valves and an equalizing valve.