GB2054345A - Fluidised bed - Google Patents

Abstract

A fluidised bed has a first zone A separated from a second zone B by a barrier in the form of a weir 40, and a rotatable hopper valve 25 for transferring treated particulate material from zone A to zone B while avoiding leakage of air between the zones. The bed is particularly useful where the material is to be treated at different temperatures in the two zones, though zone B may be outside the bed, the hopper valve merely removing material from the bed. The hopper valve 25 may itself act as the barrier, and the weir 40 is then dispensed with. <IMAGE>

Description

SPECIFICATION Fluidised bed The invention relates to fluidised beds used for treating particulate or powdered material.

Multi-zone fluidised beds are commonly used for treating powdered or particulate material such as food products. The products can be subjected to preliminary treatment in a first zone, for example they may be roasted by supplying the bed with high temperature air, and subjected to further treatment in a second or subsequent zone, for example they may be cooled by supplying air to the bed at a low temperature.

Transferring the material from one zone in the bed to another presents problems of contamination or leakage of air from one zone to another. For example, where roasting of a food product is carried out in one zone and cooling in an adjacent zone, substantial energy loss can occur due to leakage of hot air into the cooling zone, and this can adversely affect the efficiency of the process.

The present invention provides an apparatus which is adapted to transfer particulate material from one zone to another whilst minimising leakage of air between the two zones. The apparatus may also be utilised for removing particulate material from one end of a fluidised bed.

According to the present invention there is provided a fluidised bed for the treatment of a particulate or powdered material comprising a first zone bounded at one end by barrier means preventing or restricting the passage of material therethrough, and a hopper valve for transferring material from the first zone beyond said barrier means, said hopper valve comprising rotatable hopper means mounted for rotation about an axis extending adjacent and substantially parallel to said barrier means, and means for continuously or intermittently rotating the hopper means whereby material in the fluidised bed is picked up by the hopper means from the first zone and transferred to a point beyond said barrier means.

Preferably, the first zone is a first fluidised bed treatment zone and a second fluidised bed treatment zone is located beyond said barrier means, whereby the hopper valve is operable to transfer material from the first zone over said barrier means to the second zone.

Advantageously, means are provided for maintaining said first and second zones at different temperatures. In an example, the bed is intended for the heat treatment of a food product such as nuts or chopped coconut product, whereby the product is roasted in the fluidised bed in the first zone and is then transferred by the hopper valve into a second zone where it is cooled.

Alternatively, the first zone is the treatment zone of the fluidised bed, and the hopper valve is operable to remove material therefrom, i.e. the hopper means may be adapted to continuously discharge treated material from one end of the bed.

Suitably, said rotatable hopper means comprises a plurality of scoops disposed radially about a central boss mounted for rotation about a substantially horizontal axis extending transversely across the fluidised bed.

The barrier means may comprise a wall member extending transversely across the fluidised bed, and this wall member may extend upwardly from a point spaced above the base of the fluidised bed.

Preferably, the fluidised bed comprises an enclosed chamber defined by a deck, walls and a roof member, and said barrier means includes a shield member extending downwardly from the roof member substantially parallel to said wall member, said hopper valve being located between said wall member and said shield member. The shield member reduces air leakage from one zone to another.

In an alternative embodiment, the barrier means comprises the hopper valve itself.

In order that the invention may be more fully understood, embodiments in accordance therewith will now be described by way of example with reference to the accompanying drawings, in which Fig. 1 shows a longitudinal section of a fluidised bed enclosure fitted with a rotary hopper valve according to the invention; and Fig. 2 shows a horizontal sectional view of the fluidised bed enclosure shown in Fig. 1,taken along the line l-l, with parts removed for clarity.

Referring to the drawings, these show a fluidised bed enclosure 10 which is defined by a perforated base or deck 11, a roof 12, and side walls 13 and 14.

In known manner air is supplied under pressure through the perforated deck 11 in the direction of the arrows 16 in Fig. 1. The enclosure is mounted on resilient supports such as pneumatic cushions, and is vibrated at high frequency by out-of-balance motors.

The fluidised bed is divided into two zones, a first zone A which is intended to operate at high temperature, and a second zone B which is intended to operate at low temperature. The air supply to the bed is separated by wall member 17. In this embodiment, the fluidised bed is intended for roasting a food product such as peanuts 18 and these are subjected in zone A two high temperature air at around 200"C supplied through the plenum chamber 20 at approximately 8-9 ins. water gauge. The second zone B is a cooling zone which is supplied via the plenum chamber 21 with air at a reduced (e.g. ambient) temperature. Air is exhausted from the enclosure 10 via exhaust ducts 22.

In order to achieve transfer of the treated peanuts 18 from zone A to zone B during operation of the bed, whilst at the same time minimising leakage of hot air from zone A into zone B (and cold air from zone B into zone A), the fluidised bed is fitted at the end of zone A with a hopper valve generally indicated at 25. The hopper valve 25 comprises a series of blades 26 (in this case four) which are mounted on a boss 27 rotatably journaled between the side walls 13 and 14 in bearings 29. The boss 27 and the blades 26 extend transversely across the full width of the fluidised bed enclosure 10, as shown in Fig. 2.

Plates 30 are secured (e.g. by welding) between adjacent blades 26, and the tips 31 of the blades are angled as shown in Fig. 1 to form, with the plates 30, scoops which are capable of picking up the product from zone A when the hoppervalve is rotated.

One end ofthe boss 27 is fitted with a pulley 37 over which a drive belt 38 runs and which is con nected to drive motor 39. The drive motor 39 is suit ably an infinitely variable electric motor and is adapted to rotate the hopper valve 25 continuously during operation of the fluidised bed at a speed of e.g. 10 r.p.m. This speed can be varied at will depending on the nature of the process being carried out in the fluidised bed enclosure 10, and the speed with which it is desired to remove product from zone A.

The fluidised bed is started up with the hopper valve stationary and the blades in the position shown in Fig. 1. This seals off zone A from zone B whilst the product is treated during its movement from the delivery end to the valve. So that the exact positioning of the valve is known from the outside of the enclosure, the end of the boss opposite the drive motor end incorporates indicator means such as pointers or dots which show the position of the blades.

When the product is ready to be discharged into zone B, the valve 25 is rotated and the product is picked up by the scoops formed at the ends of the blades 26, (as shown at 34 in Fig. 1) and after rotation through approximately 180 , is dumped over a weir 40 into zone B, where it is cooled. The weir 40 is made for example from sheet metal and extends transversely across the enclosure 10 over the full width thereof. As shown in Fig. 1, the weir terminates at a point just above the level of the deck 11 and this enables product 42 missed by the blades 26 during rotation to pass under the weir through gap 43 and travel into zone B. This prevents build up of product at the base of the weir 40. The weir also enables the depth of product in the two zones to be maintained at different levels.

The design of the hopper valve 26 and weir 40 assist in preventing leakage of air between the two zones A and B, and this leakage is further restricted by means of a shield member 44 (omitted from Fig. 2 for clarity) which extends downwardly from the roof 12 of the enclosure 10. Air leakage can be further reduced by forming the tips of the blades 31 from a resilient material such as rubber, and maintaining these in contact with the shield member and the deck during rotation.

The slow but continuous removal of the product from the end of the zone A during operation ofthe fluidised bed ensures that the bed can continually be filled at the same rate from the opposite end with untreated product, and assists in controlling of the treatment operation. The design of the hopper valve 25, and the weir 40 and shield 44 ensure that heat loss from zone A is kept to a minimum. In addition, the valve enables small pressure differences to be maintained between zones A and B, which may be desirable in some circumstances.

It will be appreciated that instead of transferring product into a cooling zone of the bed, the hopper valve may be utilised to remove the product from the fluidised bed after treatment. This may be applied to the example illustrated by fitting a second hopper valve at the end of zone B; this may if desired be driven by the same drive motor 39, or by a second motor synchronised with drive motor 39.

In an alternatve embodiment, the barrier means may comprise the hopper valve 25 itself. There is then no need for the weir 40, which may be dispensed with.

Claims (10)

1. A fluidised bed for the treatment of a particulate or powdered material comprising a first zone bounded at one end by barrier means preventing or restricting the passage of material tharethrough, and a hopper valve for transferring material from the first zone beyond said barrier means, said hopper valve comprising rotatable hopper means mounted for rotation about an axis extending adjacent and substantially parallel to said barrier means, and means for continuously or intermittently rotating the hopper means whereby material in the fluidised bed is picked up by the hopper means from the first zone and transferred to a point beyond said barrier means.

2. Afluidised bed as claimed in Claim 1, wherein the first zone is a first fluidised bed treatment zone and a second fluidised bed treatment zone is located beyond said barrier means, whereby the hopper valve is operable to transfer material from the first zone over said barrier means to the second zone.

3. A fluidised bed as claimed in Claim 2, wherein means are provided for maintaining said first and second zones at different temperatures.

4. Afluidised bed as claimed in Claim 1, wherein the first zone is the treatment zone of the fluidised bed, and the hopper valve is operable to remove material therefrom.

5. A fluidised bed as claimed in any of Claims 1 to 4, wherein said rotatable hopper means comprises a plurality of scoops disposed radially about a central boss mounted for rotation about a substantially horizontal axis extending transversely across the fluidised bed.

6. A fluidised bed as claimed in any of Claims 1 to 5, wherein the barrier means comprises a wall member extending transversely across the fluidised bed.

7. A fluidised bed as claimed in Claim 6, wherein said wall member extends upwardly from a point spaced above the base of the fluidised bed.

8. A fluidised bed as claimed in Claim 6 or Claim 7, wherein said fluidised bed comprises an enclosed chamber defined by a deck, walls and a roof member, and said barrier means includes a shield member extending downwardly from the roof member substantially parallel to said wall member, said hopper valve being located between said wall member and said shield member.

9. A fluidised bed as claimed in Claim 1, wherein the hopper valve itself forms said barrier means.

10. Afluidised bed and a hoppervalvetherefor, substantially as herein before described with reference to Figs. 1 and 2 of the accompanying drawing.