EP0728562B1 - Apparatus and method for wetting particles with a fluid - Google Patents

Description

The invention relates to a method for wetting Particles with a fluid according to the preamble of Claim 1 and a device for wetting Particles with a fluid according to the preamble of Claim 10. Such methods and devices are used, for example, for gluing fibers in the course of Manufacture of plate-shaped materials from chips and fibers, especially fiberboard (wood-based panels and building boards from mineral and / or textile and / or synthetic Fibers used.

Document DE-A-3 143 895 discloses a method and such an apparatus with a gluing zone for Glueing of chips, which has a constant Has cross section, being within that of the particles cross-section through which a gluing nozzle is arranged is. It has been shown that with such an arrangement Problem of glue spots when gluing chip and fibrous particles cannot be controlled since it not succeed with the known arrangement, which for Particles tend to form fibers before gluing to loosen or separate sufficiently.

DE-A 16 32 450 describes a method and an apparatus for continuous mixing of small quantities of a fine particle Component with an air flow Carrier, especially for wetting chip and fibrous substances with binders according to the preambles of claims 1 and 10 known. In this An embodiment is disclosed in which the mixing tubes are narrowed in the area of the nozzles. This results in a longer dwell time Carrier, especially the heavier Mixture components.

The invention is therefore based on the object of creating a method or a device according to the type mentioned above, which makes it possible to achieve economical wetting with a fluid, which is distinguished by a particularly uniform and fine distribution, with little mechanical outlay. This object is achieved in the inventive method according to the characterizing part of patent claim 1 in that the particles pass through a drying device before reaching the wetting zone. The object is further achieved by a device according to the characterizing part of claim 10 in that
is upstream of the wetting zone of a dryer.

By the solution according to the invention by generating a turbulent Flow during wetting becomes such a high resolution of the particle flow reaches that individual particles are wetted can. Ball formation is surely avoided. Because of the sudden A reduction in flow velocity creates a particular high turbulence in the wetting zone, so that any existing Particle clumps are torn apart.

The particle resolution can still be increased if the wetting zone an accelerated section with a reduced diameter is connected upstream, as this results in the effect of the sudden conversion a fast laminar flow into a slow turbulent Flow is amplified.

A particularly suitable field of application of the invention is Gluing of fibers, especially wood fibers. Because through that extremely high resolution of the particle stream, in this case one Fiber flow, it is even possible to have already dried fibers, which tend to form lumps or balls, to glue economically and evenly in the air flow. So far because of the problematic ball formation, the glue was added damp fibers performed, which then dried were. The fiber drying after gluing has the big disadvantage that 5 to 15% of the amount of glue used by pre-curing and volatilization are lost, in addition to note that the proportion of formaldehyde proportional to the amount of glue the dryer exhaust air polluted and caused complex environmental protection measures. The glueing of already dried fibers also has the advantage that the lower humidity (5 to 12%) Influence of the pH value on the resin is greatly reduced.

To regulate the moisture of the material flow after gluing can, it is provided in one embodiment of the invention that steam can be injected into the material flow.

Furthermore, it is advantageous if in the process or in the Device a weighing station for determining the actual existing throughput is provided, which as an input variable to control the amount of fluid to be sprayed and / or Fluid composition is used.

In order to tackle the wetting fluid on the delivery line in the Avoid area of the wetting zone, it is advantageous if the walls of the wetting zone can be tempered. So can, for example, when using the invention as a gluing station a drop below the dew point on the inner surface can be achieved by cooling, thereby baking the Glue is prevented safely.

A particularly fine wettability is also favored by that a station to influence the state of charge of the flowing particles is provided, which in combination with the connection a certain charge state of the wetting fluid between fluid and particles improved and thus a Stains prevented.

To be independent of the load, that is, with a changing flow rate Fluid to always create a uniformly fine spray it is advantageous if the spraying of the fluid by known return nozzle lances.

If the delivery line is fed with a preheated air flow, the air temperature below 100 ° C, preferably is between 50 and 70 ° C, so is a more uniform Particle moisture, especially with wood fibers, achievable; further it is possible to glue in a second dryer stage and it can also be done without adding steam when producing Wood fiber boards shorten the pressing times.

In an advantageous embodiment of the invention, that use with a preheated binder he follows. The binder temperature should be below 80 ° C, especially around 40-60 ° C. This measure enables it works with a lower proportion of dilution water, which in turn can save dryer performance. Also can binders with a higher proportion of solid resin be used. This binder becomes less strong from sucked up by the particles, causing the so-called "sagging" is avoided. The binder viscosity remains through that Warming even without thinning in an area where there is a optimal atomization can take place through the nozzles.

Further advantageous features as well as the structure and the functional sequences the invention will become apparent from the following Description of an embodiment with reference to the drawing.

For this purpose, FIG. 1 shows a schematic overview the use of the invention for fiber gluing in the course of Production of fiberboard, Figure 2 shows one of the invention Device containing section of the delivery line.

FIG. 1 shows a section of a block diagram Plant for the production of wood-based panels from wood fibers or, for example, MDF boards made from wood fibers. Here are the previously processed fibers are first fed to a dryer 1, from where they are transported to a fiber bunker by air transport 2 3 arrive. Now there is a moisture measurement 4, whose Output signal controls dryer 1. Before the fibers are pneumatic the wetting zone is transported by a conveyor line 6, they pass through a mass determination station 5, which is designed as a belt scale or as a mass flow measuring device can be.

In the wetting zone 6 there is at least one described later Gluing nozzle arranged, which spray into the delivery line can. For this purpose, the glue nozzle with a high pressure pump 6a connected, which is fed from a storage container 6b becomes. After gluing, which will be described later with reference to Figure 2 the glued fibers pass through the classifier 7 and are then pneumatic (air transport 8) Scatter bunker 9, which is assigned to the molding station 10. There the glued fibers are scattered to a mat and then pressed into plates.

FIG. 2 shows a section of the delivery line between the mass determination station 5 and the classifier 7, which contains the wetting zone 6. For this purpose, a reducer 21, an intermediate tube 22 and a diffuser section 23 are integrated in the delivery line 20, which has a diameter d ₁ . The reducing piece 21 tapers in the conveying direction, corresponding to a Venturi nozzle, to the diameter d _{2 of} the intermediate tube 22. The diameter d _{2 of} the reducing piece 22 is approximately 25 to 35% smaller than the diameter d _{1 of} the conveying line 20. The diffuser section 23 widens in the direction of flow first seen as a bulbous diameter d ₃ , which is about 10 to 70% larger than the diameter d _{1 of} the delivery line 20. This expansion takes place over a length l ₃ ; This extension is followed by a taper over a length l ₄ to a smaller diameter, which in turn corresponds to the diameter d _{1 of} the delivery line 20 to which the diffuser section 23 is flanged.

Still in an area of the diffuser section 23 in which if the cross section increases, there are several, evenly Scope distributed glue nozzles 24 arranged so that all fibers flowing past with equal probability of that sprayed glue mist can be wetted evenly. To do this The spray cone of each glue nozzle can be reached safely and their orientation α in relation to the horizontal The central axis of the delivery line is provided to be adjustable.

The gluing nozzles 24 are known as return nozzle lances trained to ensure that regardless of the changing flow rate over time, automatically, a uniformly fine spray is always generated.

The diffuser section consists of high-quality, pore-tight and polished material to prevent glue deposits. Around a drop below the dew point on the inner surface of the diffuser section to get that also baked on the glue is prevented, the diffuser section is of several Cooling tube windings 25 with a coolant inlet 26 and a Coolant drain 27 surrounded. To avoid caking it is also beneficial to have a lining of the wetting zone a smooth release film. It could also Lining with a double film, through which then one Bath liquid can be passed.

The fibers pneumatically conveyed in the horizontally running conveyor line 20 are accelerated when the reducer 21 is reached and reach their maximum speed v ₂ in the intermediate tube 22. This creates a laminar flow. When flowing into the diffuser section 23, the fibers are abruptly braked to the speed v ₃ , so that a turbulent flow occurs. As a result, the fiber flow is loosened up very strongly, so that the conveyed material is present as a single fiber. Any balls of fiber previously formed are dissolved. This finely resolved fiber stream passes through the wetting zone (this corresponds approximately to the section l _3), the sprayed from the Beleimungsdüsen 24 binder mist. There the individual fibers are evenly wetted with the fine glue mist.

Because the fibers of the wetting zone have already dried glueing can take place at room temperature, whereby the amount of glue to be used per fiber amount an economically favorable low value can be set can. It goes without saying that the glueing in a preheated air flow with temperatures below 100 ° C preferably 50 to 75 ° C can be carried out, if possible to bring a lot of thermal energy into the fiber mat to be spread. In addition, binders based on Isocyanate base are built up and that in conventional Glueing due to its sensitivity to moisture and temperature are not suitable.

In an area of the conveyor line in front of the gluing zone 20 are not shown protruding into the delivery line Ionizing bars arranged with which the electrical charge state the fibers can be influenced. In connection with an opposite charge state of the glue this is the gluing quality and the efficiency. At more appropriate There are also steam injectors, not shown, in the Delivery line provided to regulate the fiber moisture exactly to be able to.

It goes without saying that the delivery line 20, the Reducer 21, the intermediate tube 22 and the diffuser section 23 instead of the described rotationally symmetrical cross sections can also have a polygonal cross-sectional shape. Also the diffuser section 23 and / or the reducer 21 not necessarily the streamlined course described have, but it can also cross-sectional jumps or ramps are used.

Claims (21)

1. A method of wetting particles with a fluid comprising the following method steps:

   a) feeding the particles from a bunker into a feed line (20),

   b) pneumatically conveying within this feed line to a further processing location and

   c) spraying the particles flowing through the feed line (20) in a wetting zone,

   d) increasing the flow velocity of the particles in a section of the line (21, 22) which precedes the wetting zone (23),

   e) thereafter, dispersing the stream of particles by reducing the flow velocity within the wetting zone (23),

   characterised in that the particles are passed through a drying device (1) before reaching the wetting zone.
2. A method in accordance with any of the preceding Claims, characterised in that the moisture of the particles is precisely controlled by injecting steam in the region of the feed line by means of steam injectors.
3. A method in accordance with any of the preceding Claims, characterised in that, in a further method step, the throughput of particles is determined, the magnitude of the throughput then serving as an input variable for controlling the quantity of fluid that is to be sprayed and/or the composition of the fluid.
4. A method in accordance with any of the preceding Claims, characterised in that a method step for controlling the state of charge of the particles is provided prior to the wetting of the particles.
5. A method in accordance with any of the preceding Claims, characterised in that a binding agent is used as the wetting fluid.
6. A method in accordance with any of the preceding Claims, characterised in that the wetting process is effected with a preheated binding agent.
7. A method in accordance with any of the preceding Claims, characterised in that the wetting process is effected during a horizontal, pneumatic advancement of the particles.
8. A method in accordance with any of the preceding Claims, characterised in that the temperature of the enclosing surface of the wetting zone is controlled in such a manner that the internal surface temperature of the wetting zone lies below the dew point.
9. A method in accordance with any of the preceding Claims, characterised in that the wetting process occurs at temperatures below 100 °C and preferably at 50 to 75 °C.
10. A device for wetting pneumatically advanced particles with a fluid, wherein the fluid is sprayed into a feed line through which the particles are flowing by means of at least one jet, wherein the at least one jet (24) is arranged in a diffuser section (23) of the feed line having an enlarged cross sectional area (23), and wherein the feed line comprises a section of reduced cross-section (22) prior to the diffuser section (23) as seen in the direction of flow, characterised in that the wetting zone (23) is preceded by a drying device (1).
11. A device in accordance with any of the preceding Claims, characterised in that the feed line incorporates injectors for feeding-in steam.
12. A device in accordance with any of the preceding Claims, characterised in that a device for determining the throughput of particles is provided.
13. A device in accordance with any of the preceding Claims, characterised in that the quantity of fluid and or the composition thereof is controllable.
14. A device in accordance with any of the preceding Claims, characterised in that the temperature of the enclosing surface of the wetting zone (23) is controllable.
15. A device in accordance with any of the preceding Claims, characterised in that an ionising device is arranged prior to the wetting zone.
16. A device in accordance with any of the preceding Claims, characterised in that the maximum cross-sectional area in the wetting zone (23) is greater than the cross-section of the feed line (20).
17. A device in accordance with any of the preceding Claims, characterised by self-regulating jet lances for spraying the fluid.
18. A device in accordance with any of the preceding Claims, characterised in that the spray pattern of the jets is adjustable.
19. A device in accordance with any of the preceding Claims, characterised in that the alignment of the jets (24) relative to the feed stream is adjustable.
20. A device in accordance with any of the preceding Claims, characterised in that a plurality of jets (24) distributed around the periphery of the wetting zone (23) is provided for the spraying process.
21. A device in accordance with any of the preceding Claims, characterised in that the feed line (20) is fed with pre-heated air and is insulated against the radiation of heat.

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