RU2386912C1 - Method of drying and impregnation of wood - Google Patents

Abstract

FIELD: woodworking industry. ^ SUBSTANCE: according to method of drying and impregnation of wood performed with free moisture removal by alternating stage of heating wood at temperature 80-90C at simultaneous moistening and impregnation and stage of vacuumising wood is heated completely immersed into circulating heated hydrophilic liquid; upon completion of vacuumising stage wood is subject to effect of air pressure of 2.5 atm during 10-15 min. Alternation of stages of wood heating in hydrophilic liquid, holding under air pressure and vacuumising is carried out till achieving average volume humidity 28-35% depending on wood breed. A radiation-contact method is used at wood heating for removal of bound moisture. Notably, such heating is applied for wood of moderately and hard-impregnated breeds of circular section with diametre over 180 mm. ^ EFFECT: reduced terms of drying wood of big cross section without formation of cracks. ^ 2 dwg

Description

The present invention relates to a method for drying and impregnating lumber and may find application in forestry, woodworking and other industries.

A known method of combined drying of wood, including immersing it in a hydrophobic liquid in a sealed drying chamber, liquid heating the wood in a hydrophobic liquid to achieve a predetermined moisture content of the wood, stabilization of the final moisture of the wood and its cooling. The heating process is carried out with high-frequency currents (see RF patent application No. 2005135886 IPC F26B 7/00, 2006).

The main disadvantage of this method is the large energy consumption for the process of heating wood with high frequency currents.

There is also a known method of drying lumber, which includes successively alternating stages of heating and evacuation, the heating of wood is carried out by circulating superheated steam in a sealed chamber (see patent No. 2186305 IPC ⁷ F26B 5/04, 7/00, 2005).

The main disadvantage of the above method is the long duration of the process of drying wood of large cross section and the lack of simultaneous impregnation.

The closest set of essential features to the proposed method is a method of impregnating and drying wood, including the removal of free and bound moisture and impregnation, carried out by alternating heating cycles of wood at a temperature of 80-100 ° C and creating a vacuum in the cavity of the drying chamber. In this case, moistening and impregnation of wood with an impregnating liquid (water and / or steam and / or impregnation with an antiseptic and / or flame retardant, dye) is carried out while heating the wood to a predetermined temperature (see RF patent No. 2238491 IPC F26B 9/06, 2003 )

The main disadvantage of this method should include the complexity of the technological process of drying and the high duration of drying of wood of large cross section from the associated moisture.

The aim of the present invention is to reduce the drying time of large cross-section wood without cracking.

This goal is achieved by the fact that in the method of drying and impregnating wood, carried out by removing free moisture by alternating the stage of heating wood at a temperature of 80-90 ° C, proceeding with simultaneous moistening and impregnation, and the stage of evacuation, the wood is heated by complete immersion in a circulating heated hydrophilic liquid, after the end of the evacuation stage, the wood is exposed to air pressure of 2.5 atm for 10-15 minutes, the alternation of the stages of wood heating in hydrophilic liquid, exposure to air pressure and evacuation is carried out until the volumetric average humidity of 28-35% is reached, depending on the type of wood, and when the associated moisture is removed, the stage of wood heating is carried out by the radiation-contact method, while drying in this way is carried out for wood in a moderate and difficult impregnated rocks of circular cross section with a diameter of more than 180 mm.

A distinctive feature of the claimed invention is that when drying wood of moderately and difficultly impregnated round cross-sectional rocks with a diameter of more than 180 mm, the material is heated by its complete immersion in a circulating heated hydrophilic liquid, after the vacuum stage is completed, the wood is exposed to air pressure of 2.5 atm for 10-15 minutes, the alternation of the stages of wood heating in a hydrophilic liquid, exposure to air pressure and evacuation are carried out until medium removable humidity of 28-35%, depending on the type of wood, and when removing associated moisture, the stage of heating of the wood is carried out by the radiation-contact method.

An example of the method is illustrated by drawings: figure 1 - installation diagram for drying of logs; figure 2 is a section of a drying chamber.

The installation consists of drying chambers 1, formed by pipes and combined with each other in one common heat-insulated jacket 2. Inside the chambers 1 are placed the logs 3 that are to be dried. The ends of the chambers 1, in turn, are tightly closed by covers 4. The installation also includes working tanks 5 and 6 for storing a hydrophilic drying agent and coolant, liquid pumps 7 and 8, a condenser 9 for removing steam, and a water ring vacuum pump 10 for pumping air from the chamber during the creation of the vacuum, compressor 11, heaters 12 and 13.

Drying of logs is as follows. Initially, a cylindrical log 3 is placed inside each chamber 1. Moreover, the design of the chambers 1 is arranged so that they are connected by pipes to each other and to the circulation system of the drying agent. After this, the chambers are hermetically closed by covers 4, and from the working vessel 5, inside the chambers 1, with the help of the pump 8, with the open valves 14 and 15, the hydrophilic liquid preheated with the help of the air heater 13 is pumped. Moreover, the air inside the entire system is vented while filling it with liquid through the open valve 16. Then, with the heater 13 and pump 8 turned on, the valves 14 and 17 open and the valves 18 and 15 closed, the drying agent circulates, which can act as concentrated aqueous solution of table salt - the process of heating wood occurs. Exposure of logs under given conditions is carried out until the temperature in the center of the material reaches 80-90 ° C, then the hydrophilic liquid from the chambers 1 is drained into the tank 5 and the evacuation stage begins. To do this, the vacuum pump 10 and the condenser 9 are turned on, which pump the steam-air mixture from the working cavity of the chambers 1 to a residual pressure of 0.15-0.2 atm through the liquid trap 19. For this, valves 17 and 20 open; gates 14, 15, 16 and 18 are closed. After the temperature in the center of the material drops to 30-35 ° C, the evacuation stage ends. After the evacuation process is completed, the wood is exposed to air pressure of 2.5 atm for 10-15 minutes. To do this, the compressor 11 is turned on with the previously closed valves 14, 16, 17 and the open valve 18. Next, the heating stage in the hydrophilic liquid begins again. Thus, the cycle "heating in a hydrophilic liquid - evacuation" is repeated several times.

With a decrease in the moisture content of the dried wood to 28-35% depending on the species, i.e. when removing bound moisture, the wood heating stage is carried out by the radiation-contact method. To do this, turn on the pump 7 and the air heater 12 and the coolant is supplied to the jacket 2 from the working tank 6. Air bleeding in the system occurs through valve 21. Heating of the coolant is carried out by circulation in a closed circuit with open valves 22 and 23 and closed valve 24. In this case, the lower part the logs in contact with the wall of the chamber 1 will receive thermal energy by the contact method, the rest of the log will be heated by thermal radiation from the heated walls of the chambers and, in part, by natural convection of the vapor medium, located in the chamber 1. After reaching a temperature in the center of the material of 80 ° C, the coolant is drained from the jacket 2 into the working tank 6 and the evacuation stage begins, after which the “radiation-contact heating - evacuation” cycle is repeated.

After the wood drying process is completed, the chamber is depressurized with valve 16 and dried wood is recovered.

Experiments were conducted under various technological conditions and a comparative analysis with the prototype, the optimal parameters were selected.

The lower limit of the temperature range in the center of the wood during the heating process of 80 ° C is due to the increase in the duration of the drying process, due to the insignificant amount of energy stored. The upper limit of the temperature range of 90 ° C is determined by the color change of the wood.

Exposure at an air pressure of 2-2.5 atm is due to the need to inject air into the pores of the wood, which will prevent the wood from soaking with hydrophilic liquid at the heating stage.

The lower limit of the 2 atm range is due to an increase in the duration of the process, the upper limit of the range is due to increased energy consumption.

The lower limit of the duration of the air pressure stage for 10 minutes is due to the large cross-sectional size of the wood, which requires a long time for air to enter the wood. The upper limit of the 15 min range is determined by the increase in the duration of the drying process.

The lower limit of the transitional humidity range of 28% is typical for dense hard-to-impregnated wood species (oak), the upper limit of 35% is for moderately-impregnated species with an average density (pine).

The lower limit of the pressure range at the evacuation stage of 0.15 atm is determined by the technical characteristics of the vacuum equipment, the upper limit of 0.2 atm is an increase in the drying time.

The lower limit of the temperature range of the wood during the evacuation process of 30 ° C is due to an increase in the duration of the drying process, due to the insignificant residual amount of accumulated energy. The upper limit of the temperature range of 35 ° C is also determined by the increase in the duration of the drying process, due to a decrease in the amount of moisture removal per one heating-evacuation cycle.

Claims (1)

The method of drying and impregnation of wood, carried out by removing free moisture by alternating the stage of heating wood at a temperature of 80-90 ° C with simultaneous moistening and impregnation and the stage of evacuation, in which the moistening and impregnation of wood with an impregnating liquid is carried out while heating the wood to a predetermined temperature, characterized the fact that in the process of heating wood of moderately and difficultly impregnated round cross-sectional wood with a diameter of more than 180 mm is completely immersed in a circulating heated hydrophilic liquid bone, after the end of the evacuation stage, the wood is exposed to an air pressure of 2-2.5 atm for 10-15 minutes, the stages of heating the wood in a hydrophilic liquid, exposure to air pressure and vacuum are alternated until a volume average humidity of 28-35% is reached, depending from the wood species, and when the associated moisture is removed, the wood heating stage is carried out by the radiation-contact method.

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