Sighter

Abstract

Use of a classifier to separate coarse particles from a fiber stream of glued wood fibers during the production of wood fiberboards, with at least one classifier housing (1) which a material inlet (5), at least one air inlet (8) arranged below the material inlet (5), an exhaust outlet (11) and has a coarse material outlet (10), wherein the upper front wall (12) of the classifier housing (1) arranged above the air inlet (8) is oriented at least partially inclined to the vertical, characterized in that the upper edge (13) of the air inlet (8) projects in a side view by a dimension (M) beyond the lower edge (14) of the air inlet (8) and that the upper front wall (12) has a convexly curved guide wall section (12c) adjoining the upper edge (13) of the air inlet (8), that a partition wall (15) is arranged in the classifier housing (1) separating the classifier chamber at least partially into an inlet chamber and an outlet chamber and that the partition (15) is pivotable and additionally height-adjustable along the vertical direction.

Description

[0001] The invention relates to a classifier for separating coarse particles from a particle stream during the production of wood-based panels, in particular wood fiber panels, with at least one classifier housing which has a material inlet, at least one supply air inlet arranged below the material inlet, an exhaust air outlet (arranged above the supply air inlet) and a coarse material outlet (arranged below the supply air inlet), wherein the upper front wall of the classifier housing arranged above the supply air inlet is inclined to the vertical at least in certain areas, i.e., over a certain height section.

[0002] Such a classifier is used to clean particle streams in the wood-based materials industry and, in particular, to remove unwanted components from the particle stream. For example, metal parts, coarse fibers, rust fragments, adhesive particles, or adhesive clumps are removed to protect downstream equipment or components, especially the steel belts of continuously operating wood-based materials presses, from damage. The classifier is particularly advantageous in the production of wood fiberboards for separating coarse particles from the fiber stream and consequently from the (glued) wood fibers (e.g., rubberwood fibers). Fiberboards in this context refer, for example, to MDF (medium-density fiberboard). In the production of fibers for wood fiberboards, the wood is first fiberized (in a refiner) and wet-glued (e.g., in a blow line) and then dried.The classifier is preferably located downstream of these plant components and especially downstream of the dryer of such a plant.

[0003] The classifier operates as an air classifier. The material to be classified is fed into the classifier housing via the material inlet and subjected laterally to an airflow blown into the housing through the supply air inlet. The fibers are captured by the airflow and carried away via the (upper) exhaust outlet and an attached exhaust duct. Larger, heavier particles are not captured by the airflow and fall downwards into the area of ​​the coarse material outlet, which may be equipped with an airlock to remove the (undesired) coarse particles.

[0004] A classifier of the described type is known, for example, from EP 0 795 359 B1. This classifier has a first (upper) material inlet for the supply of top air and a second (lower) material inlet arranged below it for the supply of bottom air. The top air enters the interior of the classifier via an upper duct, and at the outlet of the top air duct, the particles are captured by the airflow and carried upwards. A high material concentration exists at the upper edge of the top air inlet cross-section, which means that the fibers at these points are particularly difficult for the airflow to capture, especially with large quantities of material. While increasing the velocity of the incoming air can allow the airflow to capture larger quantities of material, this has a detrimental effect on the classification process.To avoid these disadvantages, horizontal, parallel components in the form of distribution pipes are arranged at the opening of the upper air duct into the classifier. These are intended to increase the vertical component of the velocity vector of the incoming air, and the distribution pipes are designed to prevent material from entering the upper air duct and accumulating there. Furthermore, the classifying efficiency is to be increased by the additional supply of lower air via the lower air duct. Such a classifier with an upper air duct and a lower air duct has generally proven effective in practice. However, the known design is capable of further development.

[0005] Furthermore, a classifier for separating coarse and fine material in the production of wood fiberboard is known from EP 1 900 445 B1 and DE 20 2006 014 455 U1, which also has several vertically arranged inlet openings for the classifying air. These inlet openings for the classifying air are arranged in stages towards the discharge opening in the conveying direction of the material, i.e., in the direction of the classifying air flow, to improve cross-flow classification. Preferably, three vertically arranged inlet openings for the classifying air are provided.

[0006] Finally, US 5,725,102 A describes an embodiment of a classifier with "zigzag plates" that operates both gravimetrically and centrifugally. A deflection line with a subsequent material diverter follows a zigzag-shaped classifying area, so that centrifugal forces cause a separation into a fiber-air mixture on the one hand and air on the other.

[0007] Based on the prior art and in particular EP 0 795 359 B1, the invention is based on the objective of creating a classifier of the type described above, which is characterized by increased classifying efficiency in the case of a simple structure and economical construction.

[0008] To solve this problem, the invention teaches, according to a first aspect, a classifier with the features of claim 1 and, according to a second aspect, a classifier with the features of claim 2. According to a first aspect of the invention, the upper edge of the supply air inlet projects beyond the lower edge of the supply air inlet by a predetermined amount in a side view. According to a second aspect of the invention, the upper edge of the supply air inlet is arranged flush with the lower edge of the supply air inlet in a side view or projects beyond the lower edge by a predetermined amount, and the upper front wall has a convexly curved guide wall section adjoining the upper edge of the supply air inlet.

[0009] This can be a classifier with only a single air inlet, in which case the embodiment according to the invention relates to this single air inlet. Preferably, however, the classifier has two air inlets, namely a first (upper) air inlet and a second (lower) air inlet, with the described embodiments then relating (at least) to the upper air inlet. It is preferably provided that the air inlet has a free inflow cross-section in the interior of the classifier housing and is therefore designed without any internal components or distribution elements, so that the inflow cross-section is not obstructed by internal components, distribution elements, or the like.

[0010] The invention is based on the understanding that the ingress or falling of (inspectionable) material into the supply air inlet or the connected supply air duct can be reliably prevented by appropriate design of the classifier housing or the front wall of the classifier housing and appropriate arrangement of the air inlet, without the need for protective grilles or similar components in the air ducts. By eliminating such components or protective grilles, pressure losses can be reduced and the flow homogenized, thus increasing the classification efficiency and / or energy efficiency according to the invention. In one embodiment, the upper edge of the supply air inlet projects beyond the lower edge by a dimension M; that is, in a side view, the upper edge of the supply air inlet or of a connected supply air duct projects further into the interior of the classifier housing relative to a vertical line than the lower edge.

[0011] Furthermore, one embodiment provides that the upper front wall has a curved guide wall section adjoining (above) the upper edge of the supply air inlet, and particularly preferably a convexly curved guide wall section. Convexly curved in this case refers to the external dimensions of the housing. Such a curved guide wall section preferably adjoins the upper edge of the supply air inlet directly, so that the upper front wall is connected via this curved guide wall section directly to the upper edge of the supply air inlet and thus to the upper edge of the connected supply air duct. Such a curved guide wall section ensures a more uniform airflow and thus improves operation and inspection efficiency by reducing pressure losses in the classifier. Moreover, such a curved guide wall section also prevents particles from entering the air inlet.the connected supply air duct was avoided.

[0012] In the classifier according to the invention, the upper front wall preferably has a vertically oriented upper wall section, to which (below) a wall section inclined relative to the vertical is attached. Such an embodiment is known, for example, from EP 0 795 359 B1. However, according to the invention, the curved guide wall section already described is preferably attached to the underside of the inclined wall section, so that the front wall then comprises a vertically oriented upper wall section, a middle wall section inclined relative to the vertical, and a curved lower guide wall section. The front wall and preferably the described wall sections extend over the (entire) width of the classifier and consequently from one side wall to the other.

[0013] In a preferred embodiment, the inclined upper front wall or its inclined wall section is arranged at an angle of less than 20°, preferably less than 15°, to the vertical. This front wall or its inclined wall section is therefore oriented at a steeper angle than in the prior art according to EP 0 795 359 B1, thus increasing the overall size of the screening zone within the classifier and thereby improving the separation quality of the classifier. This means that unwanted particles of smaller size and lower weight can be separated. Furthermore, the capacity of the classifier is increased, allowing more material to be processed per meter of classifier width.

[0014] In a preferred further development, the upper front wall, or at least a section of it (e.g., the inclined section), can be adjusted relative to the vertical, thus allowing the angle of inclination to be adjusted. This enables the screening zone to be adapted to the specific application. For example, in applications where screening performance is not particularly demanding, the screening zone can be reduced to improve energy efficiency. Conversely, when screening performance is required (e.g., in the production of thin-walled panels up to 3 mm thick or in the production of rubberwood), the screening zone can be enlarged by steepening the angle of the front wall, as described.

[0015] According to another proposal, the supply air inlet extends continuously across (essentially) the entire width of the classifier housing. While prior art typically involves several adjacent supply air inlets or air ducts connected to the classifier housing, the invention proposes supplying the classifying air via a single, continuous air inlet and corresponding supply air nozzle extending across the entire width. This design can be implemented for both the upper and lower air inlets. The supplied air volume can then be adjusted for each air inlet via a single flap, enabling simple and rapid adjustment of the air volume.Optionally, it is possible to increase the flow velocity in the edge area by means of special air guide plates on the sides of the air ducts.

[0016] As already described, two air inlets arranged one above the other are preferably provided. The invention preferably proposes that a lower front wall be arranged between the first (upper) air inlet and the second (lower) air inlet, which is convexly curved or at least has a convexly curved section. The term "convex" here refers to the outside of the housing. Preferably, the front wall is designed such that a supporting vortex forms in the interior space between the first and second air inlets, which supports the initial airflow entering through the first air inlet. Consequently, a supporting vortex forms between the upper and lower air ducts through the targeted design of the classifier, which ensures that the upper airflow is stabilized even with varying load levels or fluctuating feed rates.

[0017] Furthermore, it is optionally provided that a partition wall is arranged in the classifier housing, separating the viewing chamber (at least partially) into an inlet chamber and an outlet chamber. This partition wall can be designed – as described in EP 0 795 359 B1 – as a pivotable adjustable flap, so that the geometry of the viewing chamber can be changed. According to the invention, however, it is optionally possible for the partition wall to be height-adjustable or height-changeable along the vertical direction of the classifier housing. This partition wall, which is also referred to as a "blade" and is preferably arranged in the center of the classifier, forms a baffle for the fibers, so that the fibers are guided over this baffle to the air outlet. The height adjustment allows the area projecting into the classifier to be adjusted. In this way, the efficiency of the separation can be varied or increased for different tonnages.

[0018] The classifier housing of the classifier according to the invention has the exhaust air outlet already described, through which the air supplied via the supply air inlet is discharged together with the particle stream. An exhaust air duct is typically connected to this air outlet. Preferably, this exhaust air duct has a deflection bend connected to the exhaust air outlet, which extends over a deflection angle of at least 150°, preferably at least 170°, e.g., approximately 180°. A material diverter is then preferably connected to this deflection bend. Due to the centrifugal forces that occur, a separation into a fiber / air mixture on the one hand and air on the other is achieved in this area, so that a specific volume of air can be separated from the fiber volume. The overall system thus operates more energy-efficiently, since a smaller volume of air is transported via a fan with an open impeller. This reduces the power requirement at the shaft.The separated air is fed back to the classifier(s) via a fan with a closed impeller and, if necessary, mixed with fresh air beforehand. The invention is based on the principle of mass flow division known from US 5,725,102, but applies it to a classifier that operates solely gravimetrically.

[0019] The invention will now be explained in more detail with reference to a drawing that illustrates only one embodiment. The drawing shows... Fig. 1 a simplified perspective view of a classifier according to the invention, Fig. 2 a vertical section through a classifier after Fig. 1 and Fig. 3 the object according to Fig. 2 with illustrated particle flows and Fig. 4 the object after Fig. 2 with depicted airflows.

[0020] The figures depict a classifier for separating coarse particles from a particle stream, particularly a fiber stream, during the production of wood-based panels, especially fiberboards. Such a classifier is preferably integrated into a wood-based panel production plant, particularly to separate unwanted components (e.g., metal parts, adhesive lumps, coarse fibers, rust particles, or the like) from a material stream (e.g., glued fibers), primarily to protect downstream equipment or plant components (e.g., steel belts of a continuously operating wood-based panel press) from damage.

[0021] The classifier comprises a classifier housing 1, which in its basic structure has a front wall 2, a rear wall 3, and two side walls 4. The designations front wall 2 and rear wall 3 refer to the main flow direction of the incoming classifying air. The classifier housing 1 has a material inlet 5 at its top, through which, for example, sizing fibers are introduced, which are supplied, for example, from a dryer after sizing. Dissolving elements, such as dissolving rollers 6, can be arranged in the area of ​​the material inlet 5, or also above or below it; these are only indicated in the figures. The fibers F enter the interior 7 of the classifier housing 1 via the material inlet 5. The classifier housing has a first, upper air inlet 8 in the front wall 2 below the material inlet 5.Below the first air inlet 8, a second, lower air inlet 9 is arranged in the illustrated embodiment. In this embodiment, the upper air inlet 8 is formed by an air outlet 8a to which an air duct 8b is connected. The lower air inlet 9 is formed by an air outlet 9a to which a lower air duct 9b is connected. A coarse material outlet 10 is arranged below the air inlets 8 and 9, or at the lower end of the classifier housing 1.

[0022] The upper air inlet 8 supplies the upper air supply L1, and the fibers F entering via the material inlet 5 are captured by the airflow and transported upwards to the exhaust outlet 11, which is formed by an exhaust nozzle 11a to which an exhaust duct 11b is connected. Coarse particles, e.g., metal or rubber particles, are not transported by the airflow to the exhaust outlet 11, but fall downwards to the coarse material outlet 10 and are removed there, e.g., via an airlock (not shown). The additional lower air L2, provided alongside the upper air, optimizes the visualization efficiency in the manner described in EP 0 795 359 B1.

[0023] In the illustrated embodiment, the upper front wall 12, located above the upper air inlet 8 and extending to the area of ​​the material inlet 5, is inclined to the vertical over a certain vertical section. The figures show an embodiment in which the upper front wall 12 has a vertically oriented upper wall section 12a and, below it, a wall section 12b inclined to the vertical. In this embodiment, a (convexly) curved (lower) guide wall section 12c adjoins this (middle) wall section 12b and extends to the upper air inlet 8. In a side view, the upper edge 13 of the air inlet 8 projects a distance M beyond the lower edge 14 of the air inlet 8. In the illustrated side view according to Fig. In Figure 2, the upper edge 13 is therefore positioned a dimension M further to the right and consequently further towards the interior of the classifier. The illustrated design prevents particles, and in particular the material to be classified, from entering the supply air duct 8b or the supply air nozzle 8a through the air inlet 8. This has the advantage that internal components, protective grilles, or the like can be omitted in the area of ​​the air inlet 8, the inlet nozzle 8a, or the air duct 8b, so that the supply air inlet 8 has a free inflow cross-section without internal components.

[0024] The design illustrated with reference to the upper air inlet 8 is implemented in the same way for the lower air inlet 9. There, too, the upper edge of the air inlet 9 projects forward towards the interior by a certain amount compared to the lower edge. No internal components or similar elements are used in the area of ​​the air inlet 9.

[0025] Furthermore, it can be seen in the figures that the upper front wall 12, or rather its inclined wall section 12b, is arranged at a relatively acute angle α of less than 20° to the vertical. This allows the viewing area to be increased compared to the prior art. The length X of the screening zone along the longitudinal direction L of the screener extends (essentially) from the upper edge 13 of the supply air inlet 8 to the area of ​​the lower end of the partition 15 arranged inside the screener housing, which is particularly evident in Fig. Figure 2 shows that this partition 15 is arranged in a substantially vertical orientation approximately in the middle of the classifier housing, starting from the upper end of the classifier, specifically between the two side walls 4. Such a partition 15, which is generally known, causes the fibers to be guided over this baffle to the air outlet 11. This partition 15 can be adjusted along the longitudinal direction of the classifier in a generally known manner, for example, by pivoting it about a horizontal axis 16. Alternatively or additionally, the partition 15 can be height-adjustable or changeable along the vertical direction H. Consequently, the dimension Y by which the partition projects into the classifier housing can be adjusted, and in this way, the separation efficiency can be adapted and increased for different tonnages.

[0026] The lower front wall 17 is arranged between the upper air inlet 8 and the lower air inlet 9. In this embodiment, the front wall is curved, preferably with a convex curve. The design is such that a supporting vortex 18 forms in the interior space between the first air inlet 8 and the second air inlet 9, which supports the first airflow L1 entering through the first air inlet 8. The flow conditions are shown schematically in Fig. 4 indicated, while Fig. Figure 3 simplifies the path of the fibers F on the one hand and the coarse material G on the other. In this context, it is preferably provided that (at least) the second air inlet 9a is inclined upwards towards the horizontal, so that a second air inlet L2 is generated, which enters the interior of the classifier housing in an upwardly inclined orientation towards the horizontal. In the illustrated embodiment, the upper air inlet 8a is also inclined towards the horizontal, so that the first air inlet L1 also enters the interior in an upwardly inclined orientation towards the horizontal.

[0027] In Fig. It is also evident from Figure 1 that both the supply air inlet 8 and the supply air inlet 9, and consequently also the corresponding supply air connections 8a and 9a, extend (essentially) over the entire width B of the classifier housing 1. In contrast to the prior art, therefore, several separate supply air ducts are not used across the width; instead, a single supply air duct 8b or 9b, respectively, is provided, extending over the entire width B of the classifier housing.

[0028] The supply air inlet 8 and the supply air inlet 9 preferably have a rectangular cross-section. The same applies to the supply air nozzles 8a, 9a connected to the classifier housing. The supply air ducts 8b, 9b can have a round cross-section and be connected to the supply air nozzles 8a, 9a via appropriate transition pieces 8c, 9c.

[0029] Furthermore, in Fig.2. It can be seen that the exhaust air duct 11b, which is connected to the exhaust air outlet 11, has a deflection bend U or is designed as a deflection bend with a deflection angle β of approximately 180°. A material diverter 19 is connected to this deflection bend, which splits the fiber / air flow exiting the air outlet 11 into a fiber / air flow on the one hand and an air flow on the other.

[0030] Finally, the figures indicate that additional guide vanes 20 can be arranged inside the classifier housing. Compared to the prior art, however, such internal components in the classifier can be reduced, thus decreasing the tendency to become contaminated and optimizing the overall effectiveness of the classifier (with regard to separation quality and energy efficiency).

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