IMPROVEMENTS RELATING TO CONVEYING AND SEPARATION APPARATUS

IMPROVEMENTS RELATING TO CONVEYING AND SEPARATION APPARATUS.

The present invention relates to a distribution plate for use in conveying and separation apparatus.

There are a number of known forms of apparatus which are used for the conveying and/or separation of material such for example as tobacco leaf and stem, tea, cerial and other bulk material, using an air stream.

W089/04802 describes both a conveying apparatus and also an apparatus for separating different grades of a material. Both forms of apparatus use a distribution plate which has a plurality of apertures through which a fluid such as air can flow. The distribution plate is adapted to direct the fluid therethrough in a direction which has a component extending along a surface of the plate as a result of which material disposed above the plate is fluidised and conveyed along the surface of the plate.

Accordingly the present invention provides a distribution plate for a conveying or separating apparatus of the type in which material is conveyed by or separated by an air stream, the distribution plate having a plurality of apertures for directing fluid flow therethrough in a direction which has a component extending along a surface of the plate and wherein the apertures extend through the plate at respective angles to the surface of the plate in the range substantially 40° to 90°.

Advantageously, selected apertures extend at different angles to the surface of the plate to selected other apertures. Preferably the angle is in the range of substantially 65° to 85°.

Advantageously at least some of said apertures are at an angle of 70° to the surface of the plate.

In the accompanying drawings:-

Figure 1 shown in diagrammatic form a side view of one example of a conveying apparatus incorporating a distribution plate in accordance with the invention;

Figure 2 shows a section through the apparatus of Figure 1;

Figure 3 is a plan view of part of the apparatus of Figure 1;

Figure 4 shows to an enlarged scale the detail of the part seen in Figure 3;

Figure 5 shows a modified form of the part shown in Figure 3;

Figure 6 is a diagrammatic side elevation of a separating apparatus incorporating a distribution plate in accordance with the invention, and

Figure 7 is a sectional view of part of the apparatus seen in Figure 6.

With reference to Figures 1 and 2 the conveying apparatus comprises a conveying trough 10 having a base wall defined by a distribution plate 11 and side walls 12. The trough is closed by a loose fitting cover 13. The base wall of the trough may comprise in section, a central flat portion and side portions which incline upwardly and outwardly to the lower edges of the side walls 12 and furthermore, the side walls may incline inwardly by a small amount. A feed hopper 14 is located at the inlet end of the apparatus and material fed to the hopper falls down an inclined member and is deposited onto the distribution plate. Beneath the conveying trough 10 there is formed a first plenum chamber 15 to which air is supplied by means of a fan 16, the air passing through apertures to be described, in the distribution plate 11 into the conveying trough. The air leaves the trough through apertures in the side walls 12 thereof and flows into a pair of second plenum chambers 17 and is conveyed back towards the fan for recirculation. In use, materials such as tobacco is loaded into the hopper and is conveyed as will be explained, along the trough to the outlet end of the apparatus.

The distribution plate 11 will now be described with reference to Figures 3 and 4. The arrow A indicates the direction of flow of the material along the trough and it will be seen that the plate is formed so as to define two series of zones 18, 19 of apertures or holes. The zones are alternately arranged with spaces 19A between adjacent zones, in which there are no holes. The zones 18, 19 of holes may be formed in individual plates which are assembled to form the base wall of the trough however, it is preferred that the distribution plate is a one piece item extending if possible, the length of the apparatus.

In the zones 18 which are of a length considered in the direction of the arrow A, longer than the zones 19, the holes are angled in the direction A but in the zones 19 they are angled in the opposite direction. The material forming the distribution plate is conveniently stainless steel sheet and the holes are chemically etched. The holes are angled in the range 65° - 85° preferably 70°, to the surface of the plate so that the air leaving the holes has a similar angle to the surface of the plate.

The air flow through each hole has a component normal to the surface of the plate and a further component parallel to the surface of the plate and extending in the direction A or in the opposite direction depending upon the zone in which the particular hole is situated. The components of the air flow which are normal to the plate lift the material clear of the surface of the plate by an amount which depends upon a number of factors such for example as the air pressure in the first plenum chamber 15 and the size of the holes. The component of the air flow which extends parallel to the surface of the plate and which issues from the holes in the zones 18, moves the material along the trough. If the holes in the plate were all angled in the same direction A, the material supplied to the trough from the hopper would tend to accelerate as it moved along the trough since the force acting on the material in the trough due to the components of air flow parallel to the surface of the plate, is cumulative. It is possible to provide a zone of appreciable length at the end of the trough, in which the air flow through the holes in that zone is such as to decelerate the material flowing along the trough however, by providing the intervening zones 19 the rate of flow of the material is controlled throughout the length of the trough. Since the zones 19 are shorter in length than the zones 18 the material does move along the trough in the direction A as the resultant force factor extends in the direction of the arrow A.

In a specific example the holes are angled at substantially 70° however, holes lying in the range 65° - 85° can be used. The stainless steel sheet forming the plate has a nominal thickness of 0.71 mm, the hole size is approximately 1.0 mm and there are approximately 1.8 holes per square centimetre.

The side walls 12 of the trough 10 are also provided with holes indicated at 20 to permit air to pass into the second plenum chambers 17. The holes 20 are arranged normal to the surfaces of the side walls and conveniently the holes are shaped to provide a small entry aperture for the air and a larger exit aperture into the respective second plenum chamber 17.

In a first modification to the arrangement of the zones, the zones 19A in which there are no holes are omitted.

A second modification to the arrangement of the holes in the distribution plate is shown in Figure 5 in which the zones 18 and 19 of the previously described arrangement are replaced by diagonal zones 21, 22. In the zones 21 the holes are angled in the direction of the arrow A to achieve motion of the material supplied to the trough, in the desired direction. In the zones 22 the holes are angled in the opposite direction and the practical effect of this arrangement is to achieve an even more uniform flow of the material along the trough.

With reference now to Figures 6 and 7 there is shown a separating apparatus having a separation chamber 23 to which material such for example as tobacco leaf and stem can be supplied by means of a belt conveyor 24. Instead of a belt conveyor a conveyor of the type described above can be used. The upper portion of the chamber communicates with an outlet duct 25 and the lower wall of the chamber is defined by a pair of inclined distribution plates 26 which are spaced at their lower ends to define an outlet 27 beneath which is arranged a conveyor 28. The side walls of the outlet are formed by plates 33 respectively in which are formed holes which incline upwardly at substantially 45°. Air under pressure is supplied through the holes in the plates 33 from plenum chambers 34. The distribution plates 26 are provided with holes through which air can flow into the separation chamber from plenum chambers 29 respectively. The air is supplied to the plenum chambers 29 through a conduit 30 by means of a fan 31 which draws air from the outlet duct 25. The conduit 30 leads into a diffuser section 35 which incorporates baffles to provide the desired air flow to the plenum chambers 29 and 34.

The distribution plates 26 are provided with holes in the same manner as the plates 11 described with reference to the conveyor. The air flowing through the holes in the plates 26 forms two upwardly flowing outer air streams the velocity of which can be controlled for example by controlling the speed of the fan 31 and the air flowing through the holes in the plates 33 forms a central air stream and the air flowing through the holes in the plates 33 forms a central upwardly flowing air stream. The velocity of the air streams is adjusted, in such a manner that the components of the material which have a so called lower terminal velocity than the velocity of the air stream, are discharged through the outlet duct 25. The components of the material having a higher terminal velocity fall through the outlet 27 onto the conveyor 28. In some cases, it is desired to modify the upward flow of air in the separation chamber and this can be achieved by providing valve controlled by pass ducts 29A which connect the plenum chambers 29 respectively to the outlet duct 25. By adjusting the valves the vertical air flow in the separation chamber can be modified. The air in the apparatus is recirculated by the fan 31 and a separation unit 32 of known form is provided in the outlet duct 25 and this collects those components of the material fed into the separation zone which have the lower terminal velocity. The collected material is led away from the separation unit 32 by means of a conveyor 32A which can be a belt conveyor or a conveyor of the type described with reference to Figures 1 and 2. The separation unit 32 will not retain dust and this will be recirculated by the fan 31. In order to prevent build up of the dust a proportion of the air delivered by the fan 31 is removed by the extractor unit which filters the air. The air which is withdrawn has to be replaced and this is conveniently effected by a pair of booster fans 37 which deliver air more or less directly into the plenum chambers 29 respectively. By careful control of the fans 37 the air pressure in the separation chamber 23 can be arranged so that it is substantially atmospheric and as a result there is no need to provide an air lock at the entrance of the conveyor 24 into the separation chamber.

The holes in the plates 26 are arranged in the same way as are the holes in the distribution plates of the conveyor. In a typical example the plate 26 is 0.71 mm thick, the hole size 1.0 mm and there are 18.8 holes per square centimetre. The plates 26 are positioned at substantially 45° and by using holes at 70° in the configurations described, the air flow in the outer zones in the separation chamber is substantially vertical. This is because the air flow in the separation chamber produced by the holes which extend upwardly would without the provision of the holes extending in the opposite direction, progressively incline towards the plate in other words towards the sides of the separation chamber. The ratio of the holes in the zones 18 and 21 to the holes in the zones 19 and 22 is substantially 3:1. In the case of the separating apparatus where the conveyors 24 and 32A are of the type described with reference to Figures 1 and 2 the supply of air thereto may be delivered from the conduit 30 in the case of the conveyor 32A and from one of the plenum chambers 29 in the case of the conveyor 24.