METHOD AND DEVICE FOR SEPARATING HEAVY PARTICLES FROM A PARTICULATE MATERIAL

Abstract: In a method for separating heavy particles from a particulate material, the material is introduced in a settling chamber (1) to which a carrier air flow (F2) is supplied for entraining the material while heavy particles contained therein fall to the bottom of the settling chamber (1). The material is introduced in the settling chamber (1) as a downwardly-directed flow of material (F1) through an inlet (2), and is removed from the settling chamber (1) in an upwardly-directed flow of material and air (F3) through an outlet (3) located beside the inlet. Compressed-air jets (S) directed obliquely towards the downwardly-directed flow of material are blown into the settling chamber (1) to decelerate the flow of material and spread it towards the outlet (3). The carrier air flow (F2) is blown into the settling chamber to encounter the decelerated, spread flow of material from below. A device for implementing the method as a settling chamber (1) with a downwardly-directed inlet (2) and an upwardly-directed outlet (3) located beside the inlet. A first means (10, 11) is designed to blow compressed-air jets (S) obliquely towards the inlet (2). A second means (5) is designed to blow an upwardly-directed carrier air flow into the settling chamber (1) on a level below the first means (10, 11).

Description: METHOD AND DEVICE FOR SEPARATING HEAVY PARTICLES FROM A PARTICULATE MATERIAL The present invention relates to a method for sepa¬ rating heavy particles, such as lumps of glue, from a particulate material, such as glue-coated wood fibres, which is pneumatically conveyed from a first station, such as a container, to a second station, such as a plant for making fibreboards, said particulate material being introduced in a settling chamber to which a carrier air flow is supplied for entraining the particulate material while heavy particles contained therein fall to the bottom of the settling chamber, said particulate material being introduced in the settling chamber as a downwardly- directed flow of material through a downwardly-directed chamber inlet and leaving the settling chamber in an upwardly-directed flow of material and air through a cham¬ ber outlet located beside said inlet. The invention also concerns a device for separating heavy particles from a particulate material. In the making of fibreboards, glue-coated wood fibres are pneumatically conveyed, first from a drying plant to a collecting container, and from there to a forming station, where the fibres are spread as a mat on a wire through which the carrier air is drawn off. Then, the fibre mat is compressed into fibreboards under set pressure and tem¬ perature conditions. It is essential, in the making of fibreboards, that impurities in the form of heavy particles are separated from the flow of material. Such separation is conveniently carried out during the transport of the wood fibres from the drying plant to the collecting container. In a prior- art method for separating large-size, and consequently heavy, particles from the wood fibres when transported from the drying plant to the collecting container, the wood fibres are introduced in a settling chamber to which a carrier air flow is supplied for conveying the wood fibres to the collecting container at the same time as heavy particles present therein fall to the bottom of the settling chamber. This prior-art method requires considerable amounts of carrier air to result in effective separation. The separation is performed during the transport of the wood fibres from the drying plant to the collecting container since the carrier air is most advantageously recovered at this container. Only minor carrier air flows can be removed at the forming station. In the making of thin fibreboards with a thickness of down to about 2 mm, how¬ ever, the separation should be performed as close to the forming station as possible, i.e. during the transport of the wood fibres from the container to the forming station, in order to prevent the formation of particle agglomerates. One object of the present invention is, therefore, to provide a method which makes it possible to utilise a relatively small carrier air flow in the separation and, consequently, to perform the separation during the trans¬ port of the wood fibres from the container to the forming station. According to the invention, this object is achieved by a method which is of the type stated by way of intro- duction and which is characterised in that compressed-air jets, which are directed obliquely towards the downwardly- directed flow of material, are blown into the settling chamber to decelerate the flow of material and to spread it in its transverse direction towards the outlet, and that the carrier air flow is blown into the settling cham¬ ber to encounter from below the decelerated, transversely spread flow of material so as to form therewith said flow of material and air. Some of the air in the upwardly-directed flow of material and air is conveniently separated from this flow before the latter reaches the second station, in order to be recycled to the settling chamber. Another object of the invention is to provide a suit¬ able device for implementing the method. According to the invention, this object is achieved by a device which has a settling chamber with a down- wardly-directed inlet for said material and an upwardly- directed outlet located beside said inlet, and which is characterised by a first means for blowing compressed-air jets obliquely towards the downwardly-directed inlet, and a second means for blowing an upwardly-directed carrier air flow into the settling chamber on a level below said first means. The invention will be described in more detail below, reference being had to the accompanying drawing, which schematically illustrates a device for separating heavy particles from a flow of glue-coated wood fibres. The illustrated device is arranged between a con¬ tainer (not shown) holding glue-coated wood fibres, and a forming station (not shown) where thin fibreboards are shaped. Further, the device has a settling chamber 1 with a downwardly-directed inlet 2 for supplying the material and an upwardly-directed outlet 3 for discharging the material, the outlet 3 being located beside the inlet 2. Moreover, the inlet 2 communicates with the container from which glue-coated wood fibres are introduced in the settling chamber 1 in the form of a downwardly-directed flow of material Fl. The container preferably is a meter¬ ing container which is placed directly on the settling chamber 1 and distributes the flow of material Fl over the entire cross-section of the inlet 2. The outlet 3 communicates with the forming station by means of an upwardly-directed trnsport pipe 4 of upwardly decreasing cross-sectional area. In its upper portion, the pipe 4 has a 180° bend 4a and, after the bend, branches into two separate conduits 4b and 4c. The conduit 4b leads to the forming station. The device further has an inlet 5 through which a carrier air flow F2 is blown into the lower portion of the settling chamber 1. Adjustable guide rails 6 are provided in the inlet 5 to distribute the carrier air flow over the entire settling chamber 1. A discharge trough 8 is provided at the bottom of the settling chamber 1, and a conveyor screw 9 is arranged in the trough 8 to discharge heavy particles collected therein. In its lower portion, the inlet 2 has a perforated metal sheet 10 which is inclined about 50° to the hori¬ zontal plane. The sheet 10 is formed with a plurality of perforations which are distributed across the sheet surface and through which the settling chamber 1 communi- cates with a blow box 11. Compressed-air jets S, which owing to the inclination of the sheet 10 are directed obliquely upwards, i.e. obliquely towards to the down¬ wardly-directed flow of material Fl, are blown into the settling chamber 1 to decelerate the flow of material and to spread it horizon¬ tally towards the outlet 3. Glue-coated wood fibres containing impurities in the form of comparatively heavy particles, such as lumps of glue and chips, are, as mentioned earlier, introduced in the settling chamber 1 in the form of a downwardly-direct¬ ed flow of material Fl which preferably is spread over the entire cross-section of the inlet 2. The flow of material encounters the compressed-air jets S, and is thus dece¬ lerated and spread over the entire cross-section of the settling chamber 1. The carrier air flow F2 supplied through the inlet 5 entrains the particulate material in a flow of material and air F3 through the outlet 3 and the transport pipe 4, while heavy particles fall down into the trough 8 to be discharged by the conveyor screw 9. Since the compressed-air jets S are supplied in the manner described above, the carrier air flow can be considerably reduced compared with that required in the prior-art separation method described by way of introduction. This effect is further enhanced when the flow of material Fl is spread, as described above, over the entire cross-section of the inlet 2. The flow of material and air F3 is accele- rated in the transport pipe 4 owing to the decreasing cross-sectional area thereof. The flow then has a high speed in the bend 4a, and the wood fibres therein are thus flung outwards, following the outer wall of the bend 4a and finally being conducted, together with some of the carrier air, into the conduit 4b which leads to the form¬ ing station. The remainder of the carrier air is conducted into the conduit 4c to be recycled into the settling cham¬ ber 1, mainly through the inlet 5. A minor amount is recycled to the settling chamber 1 through the container. It goes without saying that the invention is not restricted to the embodiment described above, and thus can be modified in many different ways within the scope of the appended claims. Thus, perforated metal sheets and blow boxes supplementing the metal sheet 10 and the blow box 11 may, for instance, be arranged adjacent to the walls of the discharge trough 8 to enable the injection of oblique¬ ly and upwardly directed compressed-air jets. This may be necessary if the discharge of material from the container takes place intermittently, so that the compressed-air jets are unable to decelerate and spread all the material. It may then be necessary to further decelerate and spread the material.

Claims: CLAIMS 1. Method for separating heavy particles, such as lumps of glue, from a particulate material, such as glue- coated wood fibres, which is pneumatically conveyed from a first station, such as a container, to a second station, such as a plant for making fibreboards, said particulate material being introduced in a settling chamber (1) to which a carrier air flow (F2) is supplied for entraining the particulate material while heavy particles contained therein fall to the bottom of the settling chamber, said particulate material being introduced in the settling chamber (1) as a downwardly-directed flow of material (Fl) through a downwardly-directed chamber inlet (2) and leav¬ ing the settling chamber (1) in an upwardly-directed flow of material and air (F3) through a chamber outlet (3) located beside said inlet, c h a r a c t e r i s e d in that compressed-air jets (S), which are directed obliquely towards the downwardly-directed flow of material, are blown into the settling chamber (1 ) to decelerate the flow of material and to spread it in its transverse direction towards the outlet (3), and that the carrier air flow (F2) is blown into the settling chamber to encounter from below the decelerated, transversely spread flow of material so as to form therewith said flow of material and air (F3 ) . 2. The method of claim 1, c h a r a c t e r i s e d in that some of the air in the upwardly-directed flow of material and air (F3) is separated from this flow before the latter reaches the second station, in order to be recycled into the settling chamber (1) . 3. Device for separating heavy particles from a par¬ ticulate material, said device having a settling chamber (1 ) with a downwardly-directed inlet (2) for said material and an upwardly-directed outlet (3) located beside said inlet, c h a r a c t e r i s e d by a first means (10, 11) for blowing compressed-air jets (S) obliquely towards the downwardly-directed inlet (2), and a second means (5) for blowing an upwardly-directed carrier air flow into the settling chamber (1) on a level below said first means (10, 11).

Inventors: LARSSON OLA, LENNARTSSON STIG, LARSSON, OLA, LENNARTSSON, STIG
Applicants: FLAEKT AB, ABB FLAEKT AB
Application year: 1991
Main classification: B07B7
IPC codes: B07B4, B27N1