RU2424857C2 - Method and complex of equipment for production of dry modified sawn timber - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to impregnation and drying of sawn timber. Every mixer or protective composition components consists of electrically driven cylindrical container with two-line blade mixer and autoclave. Autoclave is connected to high-frequency proportioning pump. Drying chamber is made up of two housings communicated horizontally. Every housing consists of box carcass rectangular tubes carcass and rectangular cylindrical plates welded together. One housing accommodates pile of sawn timber. Second housing accommodates ventilation and heat panels communicated via tubes and gates with vacuum pump and heat source. Sawn timber is impregnated by protective composition at excess pressure increased step-by-step. Drying is carried out in vacuum chamber by thermal vacuum vent flow of hot steam-air mix precipitated out from sawn timber. Sawn timber is preheated at atmospheric pressure and subjected to evaporation and curing in communicating periodically drying chamber with receiver periodically evacuated.

EFFECT: pollution-free dry, resistant to fire, bio and ambient effects.

3 cl, 3 dwg

Description

It is proposed to consider a set of equipment and a method for the production of environmentally friendly dry fire-bio-atmospheric-resistant lumber.

To obtain such lumber, a complex of equipment is proposed that provides preparation of a protective composition, impregnation and drying of wood lumber. These are three separate pieces of equipment. Each of them provides its own technological process. After their implementation, we obtain dry lumber with the above properties.

The first is the preparation of the protective composition. It consists of a number of mixers of the individual components of the composition with water, which in appropriate quantities are fed into the total mixing tank.

The second is the impregnation section, which includes an autoclave and a shunting tank with a protective composition, transferring, vacuum and power pumps.

The third is the lumber drying section, which includes a sealed drying chamber, consisting of two horizontally communicating bodies connected by a piping system to a vacuum cylinder, in which a cooling device for condensing the air-vapor mixture coming from the drying chamber, a vacuum pump, ventilation and heating panels are installed environment formed during the evaporation of moisture from lumber.

A known set of equipment for the impregnation of sleepers, transverse beams and building lumber at the Borisov sleeper impregnation plant, Belarus [1]. The impregnation complex was made according to project 1376 / 2K-1-Tx2-5. The main impregnating equipment is autoclaves [2] for impregnating lumber with oil and water-soluble protective compounds of type [3] under pressure. But this complex does not provide drying of impregnated lumber.

A known method of impregnation of lumber under cyclic pressure [4]. The disadvantage of this method is the reusable rise and pressure relief of the impregnation, as a result of which there is a decrease in the efficiency of autoclaves. It is difficult to achieve a rapid discharge of the working pressure in the autoclave for (0.1-0.5) s due to the formation of a liquid-air mixture in it during impregnation. There is no simplification of the impregnation installation, as Applied equipment for high-temperature processing of wood.

A known method of impregnation according to the patent [5], where in order to increase the depth of penetration of the protective composition into the wood and to intensify the impregnation process, it is proposed to alternate the actions of static and variable pressures of certain values. The static pressure is 0.8 MPa, and a variable pressure is created with an amplitude of (0.05-0.5) MPa. The disadvantage of this method is the need to include in the complex equipment of pumps of two types of pressure generation - static and variable. It has been established that the effect of variable pressure increases the mass of the protective composition introduced into the wood.

Industrial technology and equipment for fire-retardant impregnation of wood lumber are given in [6, 7].

Unlike those mentioned in this application, the impregnation of natural moisture with a protective composition of sawn timber is carried out in autoclaves in steps of 6 atm and increasing to 30 atm by high-frequency pressure created by a metering pump with an exposure at each stage for a given time. These pumps create a pulsating pressure with a pulsation amplitude ΔР 3 ati and a frequency of up to 100 pulsations per minute. The introduction of a stepwise increase in pulsating pressure allows you to increase the depth of impregnation of hardwood lumber along the length, up to through. The proposed impregnation process allows to ensure the environmental friendliness of all operations of the process of introducing the protective composition into the wood. It has been established experimentally that to ensure the required degree of fire protection and weather resistance, it is necessary to introduce in 1 m ³ lumber of various species and the initial relative humidity of 130 to 250 kg of a protective composition, which contains up to 50% of water. This circumstance required the development of effective methods and equipment for drying lumber.

In the known drying methods [8], [9], a convective method is used. According to them, a package of lumber in a sealed chamber is subjected to blowing with a hot stream of air or steam. Under their influence, lumber is heated and moisture is evaporated. The process is accelerated by the effect of ventilation. The resulting vapor-air mixture enters the condensers and is removed from the chamber as a liquid.

The drying process lasts depending on the initial and required final moisture content of the lumber, their thickness and wood species from five days to several tens of days.

Reducing the drying time while ensuring the required quality of dried lumber (without cracking, without warping) was achieved by conducting thermal-vacuum convective ventilation drying in a sealed chamber [10]. Optimal, from the point of view of the creators, the diameter of the dryer body made it possible to abandon the fans and thermal gaskets. Heat and energy costs per unit of dried lumber decreased, and drying time was also reduced. But it is still quite large and the volumes of lumber loaded are small. The increase in the volume of lumber loaded into thermal vacuum ventilation dryers [10] is limited by the size of the pipes from which they are made.

The way out of this situation is the creation of dryers in the form of two interconnected bodies, consisting of a three-dimensional frame of rectangular pipes, welded to them rectangular in plan cylindrical plates, which are obtained by rolling sheets of structural steel. Cylindrical plates are welded with longitudinal edges to the tubes of the frame of the dryer body, and are welded together in a curved fashion. One case is designed to accommodate lumber. In another, a panel with reversible fans is installed and, at a given distance, parallel to it, thermal panels of finned bimetallic pipes into which a heated coolant is supplied from a heat source. The dryer body is exposed to temperature and vacuum pressure, which are the main type of load. Along the length of the dryer, the casing is divided into separate communicating compartments formed by frame tubes, flat segment and rectangular cylindrical plates, which in the design scheme can be considered as a typical rectangular cylindrical plate with embedded edges, loaded with external pressure (vacuum) in the direction normal to its surface. The bearing capacity of a cylindrical plate with pinched edges is determined from the dependence:

where E is the modulus of elasticity,

δ is the plate thickness,

in - the width of the plate,

a is the length of the plate,

R is the radius of curvature of the plate,

µ is the Poisson's ratio,

n is the number of dents formed around the circumference of the plate with loss of stability.

For n≤1

δ / R√12 (1-µ ² ) << (πR / a ) ² >> R√12 (1-µ ² ) / δ

The loss of stability by cotton occurs only when the dimensions of the plates satisfy the conditions:

K = in ² / Rδ≥40 and a / in = 2.

In all other cases, there is a monotonous bending of the plate.

From the fact that the vacuum cannot be greater than 1 atm and a ≤ b , from dependences (1) or (2) we obtain the radius of curvature of a typical rectangular cylindrical plate at a given thickness, or, conversely, from a given radius of curvature of the plate we find its thickness , which ensures the preservation of the form of the dryer during operation.

The basics of designing drying shops, the design of various dryers are given in the book [11]. All of them are convective with advantages and disadvantages inherent in this process. The main disadvantage is the high energy consumption and drying time.

Of the known methods and drying devices closest to the claimed is the method described in the patent [12]. According to [12], wood is dried in airtight cylinders connected to the receiver by repeatedly alternating vacuum cycles and blowing lumber with a hot coolant. In the initial period, lumber is heated to (85-95) ° C at atmospheric pressure. The disadvantages of this method include energy intensity, the duration of the drying process, a decrease in the quality of wood.

A better method of drying in a sealed chamber according to the patent [13] is known - a prototype. In this complex, reusable cycles of purging the sawn timber with a coolant, with the removal of vapors, and evacuating the sawn timber, preheated at atmospheric pressure to a temperature of (85-95) ° С, are carried out.

The disadvantages include the inability to achieve atmospheric vapor pressure of capillary moisture during preheating.

The objectives of the present invention are: the creation of a set of equipment that reduces energy costs, drying time and capital costs for the manufacture of drying equipment, increasing the load of lumber in the dryer.

For this, in the proposed complex of equipment, panel two-case dryers with a thermal vacuum ventilation process of dehydration are used.

The drying process of lumber modified with the composition [3] is significantly different from the drying of non-impregnated ones. Firstly, the relative initial humidity of the impregnated lumber, as a rule, exceeds 100%. Secondly, upon heating lumber impregnated with aqueous nitrogen-phosphorus compounds [3], at a heating temperature above (80-90) ° С, chemical reactions and the interaction of the components of the impregnating composition with each other and with the components of the wood begin, accompanied by the release of ammonia. Ammonia reduces the temperature stress-strain state of the dried lumber. In the process of drying and heat treatment, it removes residual stresses in the wood, which prevents cracking and warping of the dried modified lumber. This allowed us to put into practice a method of thermal vacuum ventilation process with periodic discharge of the resulting vapor-air ammonia medium into a cooled vacuum cylinder. For accelerated condensation of the vapor-air mixture entering the cylinder, a plate condenser is installed in it, cooled by running water.

Figure 1 shows a General view of a complex of equipment for the production of dry fire-atmosphere-resistant environmentally friendly building lumber.

The complex includes a mixer 1 for the preparation of modifying compositions, into which aqueous solutions of urea 2, borax 3, sodium phosphate 4 and, in addition, technical water are supplied through pipelines. Each of the mixers consists of a cylindrical tank and an electric mixer, on the shaft of which there are two belts of horizontal blades spaced in height and inclined along the belts towards each other. As a result, with stirring, the fluid flow trapped by the blades of each belt is discarded in the radial-axial direction towards each other, which ensures effective mixing of component solutions.

The resulting aqueous modifying composition is supplied by a pump 5 through a pipeline to a shunting tank 6.

From the shunting tank 6, the aqueous modifying solution is supplied by gravity and using a sectional pump 7 to the autoclave 8. Before filling with the solution, it is loaded with lumber and vacuumized using a vacuum pump 9. Excessive impregnation pressure and acceleration of filling with a protective compound in the autoclave are created using the pump- 10. At the first stage - up to a pressure of 6 atm, pump 7 operates as a more productive one, at the second stage - up to 30 atm - a metering pump 10.

After impregnation, the lumber enters the drying chamber 11, shown in figure 1. The camera 11 consists of two horizontally interconnected buildings 12 and 13 of FIG. 2. Figure 3 shows a typical cross-section of a drying chamber. Case 12 is designed to accommodate impregnated lumber. Case 13 is designed to accommodate thermal 14 and fan 15 panels. The cylindrical plates of the drying chamber are interconnected by means of rectangular pipes 16, which form a three-dimensional frame. The fan panel 14 is covered from above by an insulating metal sheet 17, forming a fan compartment with the section 13 case, open at the front on the side surface of the sawn timber, and at the rear at the inlet of the steam-air mixture from the case 12 to the fans 15. The hot heat carrier enters the heat panel 14 through pipes from the heat boiler eighteen.

The creation of drying chambers from rectangular cylindrical plates ensures the smallest weight of dryers with the same loading volume as other chambers, and due to the thickness of the plates, their dimensions in plan, and radius of curvature, ensure the shape preservation under the action of the generated heat and vacuum.

Figure 2 and figure 3 shows the geometric dimensions of the drying chamber, where R and R ₁ are the radii of curvature of the panels, N is the total height, S is the total width, L is the total length of the dryer, B is the height of the compartment and the lumber loading farm, h and h ₁ are the arrows of the deflection of the panels; in and in ₁ is the width of the trusses of the lumber loading compartment and the fan heater compartment, l is the length of one cylindrical panel along the chamber.

To implement the convective thermal vacuum ventilation drying process, the drying chamber 11 is connected by pipelines and airtight shutters with a receiver. The receiver consists of two vertically sealed cylindrical containers 19, 20. The tanks in the receiver are interconnected by an airtight pipe. 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 chamber and the receiver, a vacuum is created using the pump 21. The pump 22 carry out the transfer of condensate from the tank 20 to the mixer 1.

The equipment set shown in figure 1, operates as follows.

Lumber is delivered to the autoclave 8 on trolleys, pressurized, and a pre-impregnation vacuum of up to 0.90 ati is created with pump 9. After exposure for (20-30) minutes, the autoclave 8 is reported with a protective solution capacity 6.

Initially, the autoclave is filled due to the vacuum in it, and after reducing the suction effect, the drain valve is opened in the autoclave and refilled with a protective compound using pump 7 until the composition appears at the outlet of the upper drain valve. Close the valve, turn off pump 7 and turn on pump 10. Create in the autoclave stepwise in stages of 6 ati, with a soak at each stage (5-10) minutes, a pulsating impregnating pressure of up to 30 ati. Withstand lumber under this pressure for 30 minutes, relieve excess pressure to atmospheric pressure, withstand (3-5) minutes. In this sequence, another 4-5 cycles of impregnation are realized. Upon completion of the impregnation, as judged by the amount of protective compound introduced into the lumber, pump it with pump 7 into the shunting tank 6. After the impregnation, create a post-impregnation vacuum of up to 0.90 ati, hold it under it for 30 minutes, report the autoclave with the atmosphere, open the autoclave stand and roll out trolleys with impregnated lumber.

The impregnated lumber is loaded onto the bogies of the drying chamber 11. Laying is carried out using transverse gaskets between the rows and vertical couplers after laying the last row of lumber in height.

Roll carts into the camera. Close the lid tightly. The fans of the ventilation panel 15 are turned on, and hot heat carrier is supplied from the boiler 18 to the heating panel 14. The lumber is heated in the chamber to (85-95) ° C, which is judged by the readings of thermocouples embedded in the lumber. Next, a drying chamber with a receiver 19-20 is reported, where a vacuum of up to 0.90 ati has already been created by pump 21. After equalizing the vacuum, the receiver is turned off in them, the vacuum pump is turned on and the vacuum in the drying chamber is raised to 0.90 ati with the fans working and the heated thermal panel. Turn off the vacuum pump, give exposure. Under the influence of vacuum, heat of the heated lumber and the flow of the resulting vapor-air mixture, intensive evaporation of the liquid from the lumber occurs. The drying process is accompanied by a drop in vacuum and lumber temperature. During the drying of lumber in the chamber 11 in the receiver 19-20 create a vacuum of up to 0.90 ati. The dryer is informed with the receiver, kept until the vacuum in them is equalized. Disconnect. Raise the temperature of lumber in the dryer to a value of (85-95) ° C, and then once again increase the vacuum in the drying chamber to 0.90 ati. Turn off the vacuum pump 21 and again maintain the drying chamber to the previous level of vacuum drop. It was found that the process of vacuum drop in the dryer lasts more than 1 hour. Repeat the cycle until the lumber reaches the required relative humidity, after which the heat supply is turned off, the lumber is cooled and removed from the dryer.

It was experimentally established that for drying pine and birch lumber 25 mm thick, up to 4.5 meters long, impregnated with 105% relative humidity with a fire-retardant composition [3], it took (32-34) hours to a final relative humidity (8-16)% .

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 modified pine and oak boards is explained by the fact that the amount of protective composition absorbed by oak wood was less than that of pine. It is important that neither buckling, nor cracking, neither pine nor oak. The boards got a little darker. But most importantly, the 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, boards of birch and pine with a section of 90 × 90 mm, 2.5 m long.

From the initial initial moisture content (96-110)% to the final average moisture content of 16%, the lumber was dried in less than 2 days.

The obtained results confirmed the effectiveness of the proposed complex of equipment, including the preparation of the protective composition, impregnation of lumber and drying.

Thus, we propose a complex of equipment for the production of dry modified wood lumber, consisting of mixers of components of protective composition, shunting capacity, autoclave, vacuum, transfer and power pumps, a sealed drying chamber connected to a vacuum receiver, with a vacuum pump, heat source, pipelines, valves , instrumentation, characterized in that each of the mixers consists of a cylindrical tank with an electric double-row paddle mixer , an autoclave attached to a high-frequency metering pump, and the drying chamber is made in the form of two buildings communicating horizontally, each of which consists of a three-dimensional frame of rectangular pipes and rectangular cylindrical plates welded together, a stack of lumber is placed in one case, and in the second - ventilation and thermal panels are placed, connected by means of pipes and dampers to a vacuum pump and a heat source. Dimensions in plan, thickness and curvature of the cylindrical plate provide the required volume and preservation of the original shape of the drying chamber under the influence of vacuum.

A method for the production of dry modified lumber, including through-impregnation in an autoclave and thermal vacuum drying in a sealed drying chamber, is also proposed. Protective impregnation of lumber is carried out by a cyclic stepwise increasing high-frequency overpressure of the protective composition, and drying is carried out in a sealed chamber with a thermal vacuum ventilation stream of hot steam-air mixture released from lumber, which is preheated at atmospheric pressure with a stream of hot air, subjected to vacuum and exposure, followed by periodic chamber communication drying with a receiver, in which periodically create a vacuum.

Information sources

1. Sleeping impregnation plant, Borisov, Belarus, those. project 1376 / 2K-1-TX2-5.

2. Autoclave impregnation with water-soluble protective equipment under pressure. GOST 20022.7-82.

3. Protective compound. Patent No. 213191 MKI B27K 3/52, EB 31/20, 1997.

4. The method of cyclic impregnation of wood. A.S. 1186475, B27K 3/10, 1985.

5. The method of impregnation of wood. A.S. No. 1242364, 1985.

6. Arinkin S.M. Industrial technology and equipment for fire-retardant treatment of wood lumber. Fire safety. Materials of the II International Conference. Information collection of the Republican Scientific and Practical Center PB, 1997.

7. Tychino N.A. The process of obtaining weather-resistant fire and bio-protected lumber. Problems of fire safety, Kiev, Ministry of Internal Affairs of Ukraine, 1995.

8. High-tech technical materials with the technology of chamber drying saw-timber. Sushinnya villages. Lviv, 2007.

9. Krechetov I.V. Wood drying. Fourth edition, M .: "Breeze", 1997.

10. Pilipovich A. Vacuum drying oven. Sushinnya villages. Lviv, 2007.

11. Gorbey V.M., Ozarkov I.M. Basics of the design of the drying kiln. Lviv: Olis Plus, 1996.

12. The method of drying wood. RF patent No. 2228498, F26B 5/04.

13. The method of drying wood. RF patent No. 2056602, F26B5 / 04.

Claims (3)

1. A set of equipment for the production of dry modified wood lumber, consisting of mixers of components of protective composition, shunting capacity, autoclave, vacuum, transfer and power pumps, air-tight drying chamber connected to a vacuum receiver, with a vacuum pump, heat source, pipelines, valves, control -measurement devices, characterized in that each of the mixers consists of a cylindrical tank with an electric double row paddle mixer, an autoclave, attached about to a high-frequency metering pump, and the drying chamber is made in the form of two buildings communicating horizontally, each of which consists of a three-dimensional frame of rectangular pipes and rectangular cylindrical plates welded together, a stack of lumber is placed in one case, and in the second there is a ventilation and heat panels connected by pipes and dampers to a vacuum pump and a heat source. 2. The equipment complex according to claim 1, characterized in that the plan dimensions, thickness and curvature of the cylindrical plate provide the required volume and preservation of the initial shape of the drying chamber under the influence of vacuum. 3. A method for the production of dry modified lumber, including through-through impregnation in an autoclave and thermal vacuum drying in a sealed drying chamber, characterized in that the protective impregnation of the lumber is carried out by a cyclic stepwise increasing high-frequency overpressure of the protective composition, and drying is carried out in a sealed chamber with a thermal vacuum ventilation flow of hot air-vapor mixture released from lumber, which is preheated at atmospheric pressure by a stream of mountains which air is evacuated followed by aging and periodic communication drying chamber with a receiver, which periodically evacuated.

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