RU66492U1 - DRYING AND IMPREGNATING PLANT FOR WOOD - Google Patents

Abstract

The unit is designed for drying and impregnation of wood with either flame-retardant, antiseptic, or coloring compositions based on convective-vacuum-pulse technology of cold pressing of moisture from porous materials. Time and energy consumption for drying and impregnation of wood are reduced due to the organization of an automated depressurization system of the drying chamber at the stage of wood heating and impregnation. 3 s.p. f-ly, 2 ill.

Description

The invention relates to techniques for drying wood and can find application in forestry, woodworking and other industries.

Currently, a significant number of installations for drying wood are known, containing directly a chamber with a hermetically sealed door and a heater with a fan supplying heated air to the chamber cavity.

The disadvantages of such plants are the lengthy process of drying wood from 5 to 45 days depending on the species and type of wood, which entails high energy consumption, the relatively low quality of the final product due to the presence of microcracks due to the use of a heat carrier with a high temperature.

Installations are also known in which wood is dried by repeatedly alternating a heating cycle with simultaneous purging of the material with a coolant and an evacuation cycle with adiabatic exposure, the duration of which is equal to the duration of the purge.

The disadvantages of the known installations are significant energy consumption, low quality of wood in the cross section and significant unevenness of the final moisture content along the length of the stack.

Also known installations that use technology using pulsed modes - alternating heating and moisture removal during intensive circulation of the drying agent and air exchange with the environment. With this technology, energy savings of up to 30% are achieved, but the issue of uniformity of the final moisture in the stack is not resolved.

The disadvantages of the known installations are significant capital costs for the manufacture of special equipment to ensure discharge

pressure in the drying chamber, duration and high energy intensity of the drying process.

A known installation containing a heating drying vacuum chamber connected through a quick valve through a system of vacuum pipelines with a receiver and a vacuum pump. The ratio of the volume of the drying chamber to the volume of the receiver to create a vacuum of the required depth should be at least 1:10 (patent No. 2056602, Russia, IPC F26В 5 \ 04, priority 01.09.94, publ. 20.03.96). In the known device, the wood is loaded into the drying chamber, tightly closed and heated. At the same time, a vacuum is created in the receiver with a vacuum pump, after which a sharp discharge - impulse - of pressure is carried out in the drying chamber by quickly opening the high-speed valve and connecting the receiver to the drying chamber. After that, the wood in the drying chamber is subjected to evacuation - holding under the created vacuum for a certain time, after which the pressure in the volume of the drying chamber is equalized with atmospheric purging with a heat carrier with a temperature of 80-150 ° C, these operations are repeated many times until the desired moisture content of the wood is reached. The depth of a given vacuum in the process of pulsed evacuation is created by a receiver having a tenfold excess in volume compared with the volume of the drying chamber.

The disadvantages of the known installation is that for the manufacture of a receiver with a volume exceeding the volume of the drying chamber by at least ten times, significant capital costs are required. The presence of condensate - liquid removed from the wood, and its discharge require depressurization of the entire system, which also leads to an increase in energy costs when the drying process is resumed. The process of repeated repetition of pulses of evacuation of wood in a drying chamber, followed by exposure to residual vacuum, depressurization of the system

leads to inefficient use of individual installation nodes and poor performance.

Close to the claimed technical solution is the installation for drying wood, which is selected as an analogue (patent No. 2213309, Russia, IPC F26В 9 \ 06, 5 \ 04, priority 02/26/02, publ. 09/27/03). The installation contains two drying chambers connected through quick valves via pipelines to the receiver, airlock and a vacuum pump. Moreover, the receiver volume is equal to the free volume of one drying chamber after filling it with wood. The pipelines connecting the drying chambers to the receiver are tangentially installed in relation to the receiver.

The disadvantages of the known installation are unsatisfactory performance, since with the simultaneous operation of two drying chambers, it is necessary to organize a sequential pressure release of a high-temperature vapor-droplet medium into the receiver. This leads to an increase in the temperature of the medium in the receiver, which is in the form of vapor droplets (smog), which, when the receiver is evacuated, leads to an increase in the temperature of the working medium (water) in the liquid ring vacuum pump, and, as a result, to a decrease in the level of rarefaction in receiver. The use of other types of pumping means, in particular, oil vacuum pumps, does not eliminate these drawbacks. Moreover, in this case, the evacuation of the vapor-droplet medium from the receiver leads to its “breakdown”, rapid wear and breakdown of the pump. In addition, with the simultaneous operation of two wood drying chambers, it is not possible to achieve their optimal, asynchronous operation, in which lumber is heated in one chamber and vacuum is produced in the other.

Even when loading one type of lumber of the same grade and one initial moisture into both chambers, the heating and evacuation times, subject to the optimal drying conditions, vary significantly, which ultimately leads to the drying mode

lumber in one chamber becomes pre-privating with respect to the drying regime in another chamber, i.e. one camera becomes “slave” and the other “master”.

This circumstance leads to an increase in drying time and unjustified energy costs for drying lumber.

Closest to the claimed technical solution that eliminates the disadvantages of the analogue is a wood drying plant, which is selected as a prototype (patent No. 48218, Russia, IPC F26B 9 \ 08, F26В 5 \ 04, priority 05/19/2005).

The installation contains two drying chambers, connected by pipelines to valves with a receiver unit, located on the pressure relief line from the drying chambers in series with respect to each other, a fluid collector; the drying chambers are equipped with a water or steam supply system and an impregnation system, and the vacuum pump is connected to the upper point of the receiver, which closes the receiver chain.

The main disadvantage of this prototype wood drying plant is, in the first place, the same drawback as in the wood drying analogue plant, namely, as a result of the practical operation of the complexes, it was revealed that the asynchronous operation of two wood drying chambers is practically impossible. As a result, the authors came to the conclusion that the most optimal, from the point of view of increasing the convective-vacuum-pulsed method of drying wood production facilities, is the construction of a modular system of drying complexes, each of which consists of one drying chamber, a receiver unit connected to the drying chamber with the help of high-speed valves, and each complex is involved in a single system of evacuation, water treatment and automated control of the complexes.

The authors were tasked to develop a modular system for drying wood, based on the technology of convective-vacuum-pulse drying of porous materials, with high performance properties in part

reduce capital costs, lower energy costs and increase wood drying productivity.

The problem is solved in that the installation for drying wood, including a drying chamber, connected via pipelines to valves with a receiver unit located on the pressure relief line from the drying chamber in series with respect to each other, a liquid collector; the drying chamber is equipped with a water or steam supply system and an impregnation system, a fluid drainage unit, louvres, heaters and reversible fans to ensure uniform blowing of wood with a vapor-gas medium, and the vacuum system is connected to the upper point of the receiver closing the receiver chain, and is additionally equipped with a droplet separator on the vacuum line receivers, as well as an automated system for depressurization of the drying chamber, periodically depressurizing the drying chamber for this not heating wood after holding a vacuum pulse and installed in the zone of maximum temperatures in the drying chamber directly in the area of the block of heaters.

The technical effect of the claimed utility model consists in high productivity, low energy consumption of the installation, reduced drying time and improved quality of wood drying.

The utility model is illustrated by drawings, which shows a block diagram of a wood drying installation module of FIG. 1 and a block diagram of a multi-module wood drying complex of FIG. 2 with a closed water treatment system at a drying complex.

The block diagram of the wood drying installation module of FIG. 1 includes a drying chamber 1, valves 2, pipelines 3 connecting the drying chamber 1 to the receivers 4 and 5 connected in series, the vacuum pipe of the receivers 6 with a drop separator 7 located on it, a check valve 8, a vacuum shutter 9 and a vacuum pump 10, valves 15 and 16 for supplying water to the vacuum pump 10, containers for draining water from the vacuum pump 14, the drying chamber 1 with dried lumber 20 is equipped with fan blocks 17, blocks of heaters 19, louvres the distribution of flows 21, a steaming and impregnation system, including an injection manifold 18 and 22, a water or steam preparation unit with a boiler 23, supply valves 24, 25, 26, a preparation unit, either a flame retardant, or an antiseptic, or a coloring substance 30 with supply valves 29, a depressurization system of the drying chamber with an air preparation (heating) assembly 28 and a depressurization valve 27, a fluid collector 37 with shut-off valves 11, 12, 13.

The block diagram of the multi-module wood drying complex of Fig. 2 in addition to the above elements further includes an integrated collector for evacuation of the receivers 34 and corresponding shutoff valves 31, 32, 33, 35, 36.

Installation for drying wood works as follows.

Wood 20, intended for drying and stacked in piles on mobile carts, is located inside the drying chamber 1.

We consider the operation of a multi-module installation using the example of a single module.

The doors of the chamber 1, valves 2, 16, 24, 25, 26, 27, 29, 12, 13 are closed, valve 11 and valve 9 are open.

By sequentially turning on the vacuum pump 10 and opening the valve 16 for supplying water to the vacuum pump, the receivers 4 and 5 and the liquid collector 37 are evacuated to a predetermined pressure, for example, 0.004 MPa. Simultaneously with the vacuum pump 10, the fan blocks 17 and the blocks of heaters 19 are switched on in series, the wood is heated to a temperature of 40 ÷ 50 ° C. When this temperature is reached, the valves 2 are opened, connecting the drying chamber 1 with the receiver 4, the pressure is equalized in the receivers 4 and 5 and the drying chamber 1, then the valve 2 closes, the valves 24, 25, 26 open, steam or water with a temperature of 90- 100 ° C into the drying chamber 1 until equilibrium saturated vapor pressure is reached for a given temperature, then valves 24, 25, 26 are closed. This thereby replaces the air coolant with a heat capacity of Ср = 1 kJ / kg hail with a more energy-intensive heat carrier - water vapor with a heat capacity of Ср = 2.09 kJ / kg hail, which allows to accelerate the heating of wood, thereby significantly reducing the drying time of wood. By supplying water with a temperature of 90-100 ° C or steam to the drying chamber, another effect is achieved. With such a difference in temperatures between the heat carrier (heated water or steam) and wood, water vapor condenses on the wood surface with the release of latent heat of vaporization r = 2262.6 kJ / kg, which qualitatively changes the pattern of wood heating. Along with accelerating the heating of wood, due to the condensation of water vapor on the wood, water diffuses (penetrates) into the thickness of the wood, thereby equalizing the moisture content of the wood in thickness and relieving surface stresses in the wood, the presence of which in other types of drying leads to surface cracking of wood on stage of free moisture removal.

After the heated water or steam is supplied, the wood is heated by means of blocks of heaters 19 and fans 17 to continue to a predetermined temperature for each type of wood. When the set temperature of the wood is reached, the valves 2 are opened, connecting the drying chamber 1 with the receivers 4 and 5, and a sharp pressure relief occurs in the drying chamber.

The so-called vacuum-pulp extraction of wood occurs.

After equalizing the pressure in the drying chamber 1 and the receivers 4 and 5, the drying chamber is held at a residual pressure. Time

Exposure is determined by the type of wood, the rate of temperature drop in the wood. After holding the wood under residual pressure, the valves 2 are closed, and again the wood is heated to a predetermined temperature. In the first heating period, steam or water is supplied with a temperature of 90-100 ° C to a saturated steam pressure for a given residual temperature in the drying chamber 1.

At the end of the steam or water supply with a temperature of 90-100 ° C, the valve 24 closes, the valve 27 opens and the drying chamber 1 is depressurized, combined with the wood heating step. After closing valve 2, successively closing valve 11 and opening valves 12 and 13, condensate is drained from the liquid collector 37. After condensate is drained, valves 12 and 13 are closed, valve 11 is opened, and the free volume of the liquid collector is combined with the volume of receivers 4 and 5. When the wood at a predetermined set temperature is again subjected to vacuum-pulp pressing of the wood, which is repeated until the process of removing free moisture.

With a sharp pressure drop in the drying chamber, the following physical phenomena are realized: a low level of residual pressure in the drying chambers and a high rate of reaching this pressure provide the conditions under which the moisture in the capillaries and intercapillary space under the action of a pressure drop (the pressure in the chamber is much lower than the pressure in capillaries) is displaced to the surface without a phase transition. This is facilitated by the gases dissolved in the water, which perform the expansion work. Being more mobile, the gases are the first to move, contributing to the establishment of an ordered stream in the capillaries. As water is displaced, the pressure inside the capillaries is maintained by the process of vaporization inside the capillaries.

As free moisture is removed from the wood, the temperature drop in the wood decreases, the vacuum depth increases when the drying chamber 1 and receivers 4 and 5 communicate with each other. A sharp increase in the vacuum depth characterizes the end of the free moisture removal process. After that, the removal of bound moisture begins. The removal of bound moisture is carried out similarly to the removal of free moisture. Valves 24, 25, 26 reopen, water or steam is supplied until the saturated vapor pressure reaches equilibrium for a given temperature, but now with a time delay depending on the wood to relieve surface stresses and equalize moisture in thickness. Bound moisture is removed with increasing temperature in the drying chambers and in the wood, while the maximum temperature is determined by the type of wood. Upon reaching the set temperature, pulsed-vacuum wood pressing is carried out, the wood is kept under residual vacuum, but the wood is held in time under

vacuum is much longer than when removing free moisture. The exposure time depends on the type of wood.

At the end of the drying process of wood, it is conditioned, equalized by moisture, both by thickness and by length of lumber. Air conditioning is carried out by the method of "steaming", by injection of water with a temperature of 90-100 ° C or steam into a previously evacuated volume of the drying chamber with subsequent exposure to time. The amount of water or steam and the exposure time depends on the type and variety of wood. The conditioning phase ends with the opening of valves 2, the release of excess pressure into the receiver 4 and 5.

At the end of the conditioning process, the step is to impregnate the wood with antiseptic, or flame retardant, or coloring compounds, opening the valves 25, 26, 29 and feeding the pre-prepared compounds in the cooking unit and supplying 30 to the drying chamber 1. The process of impregnating the wood with antiseptic, or flame retardant, or coloring the composition consists in the alternation of cycles: evacuation of the drying chamber 1 by depressurizing the previously evacuated receivers 4 and 5, injection of the impregnating compositions into the chamber drying 1 with the fans 17 turned on, depressurizing the drying chamber of the aging time of wood at atmospheric pressure. The number of cycles of vacuum-injection-depressurization - exposure of wood at atmospheric pressure depends on the type and assortment of wood, the requirements for the depth of impregnation. Upon completion of the entire drying and impregnation process with closed valves 24, 29, the drying chamber 1 is depressurized, by opening the valves 25, 26, 27, the pressure in the chamber is equalized to atmospheric pressure, and the process of wood cooling in the drying chamber begins. When the wood reaches a temperature of about 40 ° C, the doors of the drying chamber open, the loading trolley with wood rolls out of the chamber and goes for further processing. The presence in the inventive installation of a separator on the vacuum line sharply reduces the mass-average temperature of the pumped medium from the receivers due to separation, separation of droplets, thereby reducing the load on the vacuum pump, and as a result, the vacuum time of the receivers decreases, the vacuum depth in them increases, which allows you to create a deeper pulse in the drying chamber, on which the quality and the whole process of drying wood depends.

The presence of an automated control system for wood drying, including control of a depressurization system, allows optimizing the drying and impregnation of wood.

Depressurization of the drying chamber sequentially carried out after cycles of a vacuum pulse, supplying steam, or water, or impregnating compositions to the drying chamber leads to an acceleration of the heating and impregnation of wood due to an increase in the heat transfer coefficient from

coolants to the dried lumber associated with an increase in the density of the coolant. In addition, the difference between the pressure of the gas-vapor and impregnation medium in the drying chamber and the vacuum pressure in the capillaries accelerates the diffusion of the gas-vapor medium and the impregnating composition into the wood.

Periodic drainage of condensate from the receiver unit 4 and 5 into the liquid collector 37 with its subsequent removal to the sewer after each pulse sharply reduces the load on the vacuum pump due to the exclusion of gas entry into the free volumes of the receivers from the evaporation of condensate accumulating in the liquid collector.

Periodic depressurization of the fluid collector, made as an individual receiver in volume much smaller than the free volume of the receivers, has an additional physical meaning. When the liquid collector is connected after the condensate is drained to the receiver unit, a portion of cold air with an ambient temperature accelerates the condensation of the gas-vapor medium contained in the receivers, which also reduces the load on the vacuum pump due to a decrease in the temperature of the pumped medium and vapor condensation.

The inventive installation was manufactured, underwent pilot-industrial testing and showed high technical and economic indicators when drying and impregnating wood of various species, it received a certificate of conformity No. ROSS RU. AY79.O2604. The inventive installation is a closed, environmentally friendly system and meets international standards for environmental safety ISO 9001. It provides periodic, multiple conditioning of wood during heating due to the process in an isolated chamber with multiple steaming, which makes it possible to dry and impregnate the wood without any defects. Installation is highly efficient, easy to install and operate. Allows you to get wood with additional properties, such as fire resistance, due to the impregnation of wood with flame retardants, biostability, due to the impregnation of wood with antiseptic compounds. And also allows you to get wood in various shades and colors.

Claims (4)

1. Installation for drying wood, including a drying chamber connected via pipelines to valves with a receiver unit located on the pressure relief line from the drying chamber in series relative to each other, the liquid collector, the drying chamber is equipped with a water or steam supply system and an impregnation system, and the vacuum pump is connected to the upper point of the receiver closing the receiver chain, characterized in that it is additionally equipped with a droplet separator on the receiver vacuum line, as well as an automatic The drying chamber depressurization system performs periodic depressurization of the drying chamber at the stage of wood heating after holding a vacuum pulse and installed in the maximum temperature zone in the drying chamber directly in the area of the heater block, and an individual receiver is periodically disconnected from the receiver block as a condensate collecting tank to drain condensate. 2. Installation according to claim 1, characterized in that the wood drying installation is equipped with a heating system for air or gas-vapor medium entering the drying chamber for depressurization. 3. The installation according to claim 1, characterized in that it is made in the form of a modular system of drying complexes containing one drying chamber and a block of receivers involved in a single system of water treatment, vacuumization and automated control of the drying process. 4. Installation according to claim 1, characterized in that the liquid collector is equipped with an automated condensate drain system after each vacuum pulse.