RU2468319C2 - Method of drying wood and plant for its implementation - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: method of drying wood is implemented as follows: first the wood heating is carried out in a drying chamber 1 at an atmospheric pressure, and in the receiver 5 a vacuum to 0.90 atm. is created with a vacuum pump 6, then the pump is turned off, the receiver is connected via valves 8 with a drying chamber, the time is noted during which the vacuum is equalised in them, then the vacuum pump is switched on, and the vacuum is brought in the drying chamber to 0.90 atm., then the drying chamber is disconnected with the receiver using the valves, the time is noted during which the vacuum in the chamber is reduced to 0.30 atm., and, during this time, it is brought to 0.90 atm. with the vacuum pump in the receiver again, and the receiver is connected again to the drying chamber, the time is noted during which the vacuum is equalised in the chamber and in the receiver, the vacuum pump is switched on and the vacuum is brought in the drying chamber to 0.90 atm., the receiver is disconnected with the drying chamber and repeat the previous steps until the industrial wood achieves the given relative humidity. And each chamber 1 of the plant for drying is made of two horizontally adjacent sections - drying 3 and heat-ventilating 4 that have a common leakproof welded closed housing in the form of two cylindrical surfaces, interconnected by a generator, the inner girders of the chamber 1 are located inside the housing 1, made of profile pipes, and in the heat-ventilating compartment 4 the heat panel and the vent panel parallel to it are mounted along the entire length of the housing that are covered with metal sheets to form with the compartment housing the space which is open from one side to the lateral surface of the industrial wood, and from the other - to the input of stream of vapour-air mixture from the drying compartment to the fans.

EFFECT: reduced costs.

2 cl, 2 dwg

Description

The invention relates to technology and equipment for drying wood in the form of various lumber (boards, beams, blanks from them, etc.) by heating and evacuating them in special chambers.

A known method of drying wood (see RF patent No. 2056602, MKI F26B 5/04, 1994), which includes repeated alternation of purge cycles with a coolant, with the release of vapors and evacuation, while the wood is preheated to a volume average temperature of 80-100 ° C, after which drying is carried out by repeatedly alternating cycles of evacuation and purging with a coolant until 30% humidity is reached, holding is carried out until a pressure equal to atmospheric is reached, and evacuation is carried out at a residual pressure of 10-50 mm Hg. within 30-120 min, and the pressure is released to the residual in 1-30 s, the condensate is drained during evacuation, and the purge is carried out with a coolant with a temperature of 80-150 ° C for a time equal to the evacuation time, the drying process to obtain 30 % humidity is repeated until the total cumulative evacuation time is reached.

This method is carried out by a device that contains a cylindrical drying chamber equipped with a jacket for heating, a vacuum receiver and an air preparation unit.

The disadvantages of this method and device include the high energy intensity and the inability to achieve atmospheric pressure of the vapor of capillary moisture when preheated to a temperature of 80-100 ° C.

The closest technical solution is the method of drying wood (see RF patent No. 2228498, MKI F26B 5/04, 2002), which includes multiple alternating cycles of purging the wood with a coolant, heating the wood to an average volume temperature of 80-100 ° C, evacuating, at in this case, each evacuation cycle is carried out by high-speed evacuation using a receiver of high-speed valves and pipelines with heating of wood and exposure in a drying chamber isolated from the atmosphere, and the exposure of wood in the chamber is carried out to a pressure equal to the equilibrium pressure of the steam in the free volume of the drying chamber at a given temperature.

This method is carried out on a drying unit, which contains drying chambers, each of which is equipped with a device for uniform distribution and fans for supplying coolant throughout the volume of the drying chamber, pipelines with built-in quick valves that connect the drying chambers to the receiver. Each drying chamber has a valve for connecting to the atmosphere and a valve for draining free moisture. Each drying chamber has a hermetic door for loading and unloading wood and air heaters installed in the rear semi-cylindrical walls. A vacuum pump provides the desired vacuum in the receiver and drying chambers. The fluid collector is designed to collect condensate, is connected to the receiver using a valve and is used as a gateway to drain the collected fluid using a valve without depressurizing the entire system.

The disadvantages of this method and the drying unit include a large energy consumption, the duration of the drying process, a decrease in the quality of wood and a small amount of a single load of lumber.

The objective of the present invention is to increase the volume of a single load of lumber and the quality of dried lumber, reducing drying time and capital costs for the manufacture of equipment.

The problem is achieved in that the method of drying wood by repeatedly alternating wood blowing with a heat carrier, heating the wood to a temperature of 80-100 ° C, evacuating with a vacuum pump, receiver and piping with sealed shutters, according to the invention, the wood is first heated in a drying chamber under atmospheric pressure, while in the receiver a vacuum pump creates a vacuum of up to 0.90 atm, after which the pump is turned off, the receiver is connected to the drying chamber using dampers, The time for which the vacuum in them is compared is then determined, then the vacuum pump is turned on and the vacuum in the drying chamber is brought to 0.90 atm, then the drying chamber and the receiver are separated by means of dampers, and the time during which the vacuum in the chamber is reduced to 0.30 atm is maintained. and during this time the vacuum pump in the receiver again brings the vacuum to 0.90 atm and again connects the receiver to the drying chamber, maintains the time during which the vacuum in the chamber and in the receiver is compared, turn on the vacuum pump and bring the vacuum in the drying chamber to 0, 90 atm, disconnect the receiver p with the drying chamber and repeating the previous operations until the sawn predetermined relative humidity.

At the same time, a wood drying installation containing at least two sealed drying chambers, a vacuum pump and a receiver, loading trolleys connected by a pipeline with tight shutters, which is characterized in that each chamber is made of two horizontally adjacent compartments - drying and heat ventilation, which have a common hermetically welded closed case in the form of two cylindrical surfaces interconnected along a generatrix, inside the case there are internal camera trusses made of profile pipes, while in the heat ventilation compartment there is installed a thermal and parallel ventilation panels along the entire length of the casing, which are covered by metal sheets and form a volume with the casing of the compartment, on one side open to the side surface of the lumber, and on the other to the inlet of the steam-air mixture from drying compartment in the fans.

According to the invention, the drying process of lumber impregnated with water-soluble nitrogen-phosphorus compounds and having, as a rule, a relative initial humidity in excess of 100%, accompanied by the release of ammonia at a heating temperature above 70-90 ° C, at which reactions and interaction of the components of the impregnating composition begin with each other and with wood components. Ammonia has a positive effect on the temperature stress-strain state of dried lumber. In the process of drying and heat treatment, it removes residual stresses in the wood, which prevents cracking and warping of dried modified lumber. This allowed us to put into practice a highly efficient method of thermal vacuum ventilation process with periodic discharge of the resulting vapor-air ammonia medium into a cooled vacuum receiver, the volume of which was equal to the volume of the drying chamber, which made it possible to reduce the time of its subsequent evacuation. For accelerated condensation of the vapor-air mixture entering the receiver, a plate condenser is installed in it, cooled by running water, which is supplied through the inlet and outlet pipelines. All this allowed to improve the quality of dried lumber.

Performing a drying chamber in a wood-drying installation from two compartments, which have a common hermetically sealed closed casing in the form of two cylindrical surfaces interconnected along a generatrix, inside the casing there are internal chamber trusses made of profile pipes, while in the heat ventilation compartment they are installed the entire length of the housing is thermal and ventilation panels parallel to it, which are covered by metal sheets and form a volume with the compartment housing, on one side open to the side surface lumber, and the other - to the input stream of vapor from the drying chamber to the fans, thereby increasing the volume of a single load of lumber, reduced drying time and capital cost of the manufacturing equipment.

Figure 1, 2 shows the drying unit for implementing the proposed method.

The wood drying installation, which is claimed, contains sealed drying chambers 1 with sealed lids 2, each of the chambers 1 consists of two horizontally adjacent compartments - drying 3 and heat ventilation 4, receiver 5, vacuum pump 6, which provides a given vacuum in receiver 5 and drying chambers 1, pipeline 7 with integrated airtight shutters 8, connecting the drying chambers 1 with a receiver 5 and a vacuum pump 6, and loading trolleys 9. Compartment 3 is designed to accommodate impregnated wood, and compartment 4 to accommodate warm new panels 10 made of n number of finned tubes and ventilation panels 11, including fans 12 with drives. Drying and heat ventilation compartments 3, 4, having a common hermetically sealed closed casing in the form of two cylindrical surfaces 13, 14, are interconnected along a generatrix, inside the casing there are internal trusses 15 of the chamber 1 made of profile pipes 16 of the inner trusses 15 interconnected by welding. The ventilation panel 11 is covered by insulating metal sheets 17 and creates a volume with the compartment body, open on one side on the side surface of the lumber, and on the other hand, at the inlet of the steam-air mixture from the drying compartment 3 to the fans 12. The hot heat carrier enters the heat panel 10 from the boiler room. The creation of drying chambers, which have a common hermetically sealed closed casing in the form of two cylindrical surfaces 13, 14, provides the largest load volume and the smallest weight in comparison with the known dryers, due to the thickness of the general hermetically sealed closed casing, its dimensions in plan, and radius of curvature ensure the preservation of the form under the action of heat and vacuum.

To implement the convective thermal vacuum ventilation drying process, the drying chambers 1 are connected by a pipe 7 and hermetic shutters 8 to a receiver 5. The receiver 5 consists of two sealed cylindrical containers with a volume of 40 m ³ . Capacities in the receivers are interconnected by sealed pipelines. In each of the cylinders mounted tubular fin condensers, cooled by water, which after passing through them goes to the heating of industrial premises. In the drying chambers 1 and receiver 5, a vacuum is created by means of a vacuum pump 6 of type AVZ-125 (-180) or BBH-12.

The proposed method of drying wood is carried out in this way.

Wet wood is stacked on trolleys in stacks using transverse spacers between the rows. The loaded trolleys 9 are rolled into the drying chamber 1, the lid 2 is tightly closed. The fans 12 of the ventilation panel 11 are turned on. The heat carrier 10 is supplied with hot coolant with a temperature of 120-130 ° C through the sealed pipes from the boiler. The fans 12 of the ventilation panel 11 are turned on. The resulting air flow passes through the thermal panel 10, heats up to 130 ° C and passes into the gaps between the rows of lumber. In the process of repeated blowing of lumber, they are heated to 80-100 ° C. This is judged by the testimony of thermocouples introduced into them. During the heating up of lumber, a vacuum of up to 0.90 atm is created using a vacuum pump 6 in receiver 5. The shutters 8 connect the receiver 5 to the drying chamber 1. Hold the time for which the vacuum in them is compared. The vacuum pump is turned on and the vacuum in the chamber is brought to 0.90 atm, the drying chamber 1 and the receiver 5 are separated by shutters. Under the action of heat and vacuum, moisture is intensively evaporated from the sawn timber, accompanied by the formation of a vapor-air medium, vacuum and temperature drop in the drying chamber. In 60-70 minutes, the vacuum in the drying chamber decreases to 0.30 atm, and the lumber is cooled by 6-8 ° C. At this time, in the receiver 5, using a vacuum pump 6, the vacuum is brought to 0.90 atm. And again, using the dampers, the receiver 5 is connected to the drying chamber 1. They are held until the vacuum is even in them, the vacuum pump 6 is turned on and a vacuum is created in the drying chamber 1 to 0.90 atm. The receiver 5 is disconnected from the drying chamber. According to the readings of the relative humidity sensors embedded in the lumber, the drying process is monitored. The operations are repeated until the lumber reaches a relative humidity of 8-12%.

It was established experimentally that for drying pine and oak lumber 25 mm thick, up to 4.5 m long, impregnated with a fire-bio-protective composition up to 105% relative humidity, it took 32-34 hours to reach the final humidity. The final humidity of the boards varied in length from 8 to 16%. The main reason for the spread of humidity was the longitudinal pumping of the drying air stream with its heating at one end of the chamber. Almost the same drying time for the modified pine and oak boards is explained by the fact that the volume of the protective composition absorbed by the oak wood was less than that of the pine. It is important that neither the pine nor the oak boards had any warping or cracking. The boards got a little darker. But most importantly, drying time was significantly reduced.

A similar result was obtained when drying birch boards with a thickness of 50 mm, a width of up to 450 mm, birch and pine boards with a section of 90 × 90 mm, a length of 2.5 m. From the initial moisture content of 96-110% to the final, average moisture content of 16%, lumber was dried in 2 days. In this case, the drying time increased primarily due to the increase in the time of their heating up to 90 ° C.

The obtained results confirmed the effectiveness of the proposed process for the production of dry environmentally friendly modified lumber.

Claims (2)

1. The method of drying wood by repeatedly alternating blowing wood with a coolant, heating the wood to a temperature of 80-100 ° C, evacuating with a vacuum pump, receiver and piping with tight shutters, characterized in that the wood is first heated in a drying chamber at atmospheric pressure in this case, a vacuum of up to 0.90 atm is created in the receiver with a vacuum pump, after which the pump is turned off, the receiver is connected to the drying chamber with the help of dampers, the time for which the vacuum in them is kept is maintained It is then removed, then the vacuum pump is turned on and the vacuum in the drying chamber is brought to 0.90 atm, then the drying chamber and the receiver are separated by means of dampers, the time during which the vacuum in the chamber is reduced to 0.30 atm, and during this time the vacuum pump is the receiver is again brought the vacuum to 0.90 atm, and again the receiver is connected to the drying chamber, the time during which the vacuum in the chamber and in the receiver is compared is maintained, the vacuum pump is turned on and the vacuum in the drying chamber is adjusted to 0.90 atm, the receiver is disconnected from the drying chamber camera and repeat before previous operations until lumber reaches a predetermined relative humidity. 2. Installation for drying wood, containing at least two sealed drying chambers, a vacuum pump and a receiver, interconnected by a pipeline with tight shutters, loading trolleys, characterized in that each chamber is made of two horizontally adjacent compartments - drying and heat ventilation, which have a common hermetically welded closed case in the form of two cylindrical surfaces interconnected along a generatrix; inside the case there are internal camera trusses made of profile t rub, while in the heat and ventilation compartment there is installed a thermal and parallel ventilation panels along the entire length of the casing, which are covered by metal sheets and form a volume with the casing of the compartment, on one side open to the side surface of the lumber, and on the other to the inlet of the steam-air mixture from the drying compartment into the fans.

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