GB2227482A - Fluidising bulk particulate material - Google Patents

Abstract

A device of the kind used for fluidising particulate matter in a container by introducing under pressure into the container a gas or other suitable fluidising medium, comprises a partition 2 positioned in, or forming part of, the container and having a number of cavities 7, each cavity being connected to a source 9 of fluidising medium; a plurality of holes formed in the partition, each hole providing a conduit between a cavity and the container; and means selecting the cavity or cavities to which fluidising medium is, in use, to be supplied. <IMAGE>

Description

FLUIDISING DEVICE Background to the Invention The invention relates to a device for fluidising particulate matter, and is more specifically concerned with a device which achieves such an effect by introducing under pressure to the particulate matter a suitable fluidising medium.

The process of fluidisation is generally used to facilitate the handling of particulate matter, and in many situations forms a necessary part of the handling of that matter.

The fluidisation of particulate matter can be achieved by agitating the individual particles of that matter, and can be used for a number of purposes.

For example, where the handling of the matter involves transferring it from one point to another, the process of fluidisation may be used to give the matter the required properties of bulk mobility, and to prevent the formation of accretions of the matter. Additionally or alternatively, particulate matter which is being stored may be fluidised so as to prevent the particles sticking together and hence coagulating, and to disintegrate any coagulations which may have already formed.

In one application, the process of fluidising may be used in relation to packaging equipment in which a succession of containers are filled, via suitable filling means with particulate matter from an overhead hopper. In this case, the fluidisation of the matter serves to both enable the matter to be more readily transferred from the hopper and to inhibit or prevent the formation of coagulations of matter as well as to disintegrate any existing coagulations or accretions on the side of the hopper.

The fluidisation of the matter is conveniently achieved using sintered metal (or porous plastic) caps which are mounted in the side or base of the hopper, and through which air or a suitable gas is introduced into the particulate material to appropriately agitate the individual particles. One problem with this apparatus is that, in some instances a phenomenon which is well known in the handling of particulate matter and known as "rat-holing" can occur.

"Rat-holing" occurs in this case when the air blown through the sintered metal caps forms channels in the particulate matter instead of fluidising it. Furthermore, the sintered metal caps are prone to clogging which also impairs the effectiveness of the apparatus.

In an attempt to tackle this problem it is known to use vibrating or undulating walls either alone. or in conjunction with the caps. However, such walls are mechanically complex, and tend to be expensive, and do little to prevent the problem of clogging.

According to the invention in its broadest aspect, there is provided a device of the kind used for fluidising particulate material in a container by introducing under pressure into the container a gas or another suitable fluidising medium, the device - comprising a partition positioned in, or forming part of, the container and having a number of cavities, each cavity being connected to a source of fluidising medium, a plurality of holes formed in the partition, each hole providing a conduit between a cavity and the container, and means selecting the cavity or cavities to which fluidising medium is to be supplied.

The cavities preferably form a closed cellular structure within the partition, and each cavity may with advantage be sealed from the other cavities.

The fluidising medium may be air, a gas or a fluidising fluid.

It has been found that, by supplying the fluidising medium to the cavities in a predetermined sequence, the particulate matter may more effectively be fluidised. It is believed that this occurs because the rat holes produced by the fluidising medium expelled from one cavity tend to be collapsed by the fluidising medium subsequently expelled from adjacent cavities.

In another broad aspect, the invention provides a method of fluidising particulate matter in a hopper having a wall or part of a wall formed as a device previously described, the device having a lower cavity and a succession of other cavities arranged at successively increasing heights from the lower cavity, the method comprising the step of supplying fluidising medium to each of the successive cavities in a predetermined sequence, or in a sequence determined by control means operating in response to signals generated by one or more sensors.

In yet another aspect, different predetermined sequences of fluidisation may be used, each sequence being appropriate to a particular state of the hopper and particulate matter.

For example, one sequence may operate as the hopper is being filled initially, a different sequence for "steady state" fluidisation and yet another sequence to restart fluidisation from a collapsed mass of particulate matter.

Rather than predetermined sequences appropriate to the state of the particulate matter being handled, sequence control may be effected by the use of appropriate sensors which, in use, indicate the localised need for fluidisation of the particulate matter.

Brief Description of the Drawings The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cut away side view of part of a hopper having a device according to the invention Figure 2 shows the device when viewed from the front; and Figure 3 schematically shows the system for selectively supplying fluidising medium to the device.

Description of an Embodiment The hopper shown in figure 1 supplies particulate matter, in this case milk powder, to a filling station (not shown), at which the powder is transferred to a succession of containers. The powder is introduced into the top of the hopper, and subsequently travels to the filling station via a conduit (not shown) opening onto the bottom of the hopper. The hopper is defined by a pair of parallel vertical walls (not shown) a vertical side wall 1 disposed between, and running perpendicular to, the parallel walls and an inclined wall 2.

The inclined wall 2 is formed as a partition having a front face 3 and a rear face 4 which is parallel to, and spaced from, the front face 3. The front face 3 is separate from the rear face 4 by a peripheral wall 5 which also seals the space between the two faces. A parallel array of dividing stips, one of which is referenced 6, perpendicularly rise from the rear face 4, each stip sealing against the front face 3, the rear face 4 and the peripheral wall 5 in such a way that there are defined between the faces 3 and 4 of the partition 2 an array of parallel parallelepipedal cavities, for example the cavity 7.

A plurality of holes, for example the hole 8, are formed in the front face 3, each hole providing a conduit between a cavity between the faces 3 and 4 and the space outside the face 3. The holes a typically of t millimetre in diameter, and the spacing between adjacent holes is 2-3 millimetres.

The holes are formed over the whole of the surface of the face 3 so that each cavity (for example cavity 7) communicates with the rest of the hopper via a group of holes in the face 3.

Each cavity also communicates with one of a number of supply lines 9, each of which is connected at one end to an aperture (not shown) in the face 4 and hence to its respective cavity. The other end of each supply line 9 is, in turn, connected via a control valve 10 to a source of fluidising medium 11 (figure 3). In this case, the fluidising medium is compressed air.

The valves 10 are controlled by a sequencing controller 12 which is operable to selectively open the valves 10.

The arrangement is such that, if only one of the valves 10 is open, compressed air will be transmitted along the supply line 9 to its respective cavity in the partition 2. The material forming the partition 2 is impermeable to the compressed air, which is consequently expelled only from the group of holes which communicate with that cavity. Thus, by selecting which of the valves 10 is to be opened, it is possible to select the cavity to which air is to be supplied, and hence the group of holes through which air is to be expelled.

Referring to figure 1, the hopper includes particulate matter which has been left in the hopper for a period of time sufficient for the particles to settle and for the matter to coagulate. This may happen if the filling process is interrupted by, for example, equipment failure.

In such an event, the sequencing control 12 may be used to break up the matter 13 in the following way. Firstly, by opening the appropriate valve 10, air is supplied to the lower most cavity 7 in the partition 2 for a predeter mined period of time. Air is then supplied to the cavity 7a adjacent to the cavity 7 for the same period of time, and then to the cavity 7b which is adjacent the cavity 7a. Once the cavity 7b has been supplied with air, the cavities 7, 7a and 7b are again successively supplied with air, but this time the next cavity 7c, is incl8ez in the sequence.

The process repeats itself until eventually all of the cavit ies are supplied in succession, starting with the lower cavity 7 and finishing with the top cavity in the partition 2.

In this way, the device first breaks up the lower layers of particulate matter 13 so that these first fall through the hopper, and thus undermine the support of the upper layers. The resulting stress exerted on the upper lays by weight of the matter 13 will aid in the process of breaking up, and hence fluidising, the matter 13.

The partition 2 may be formed by the "tWin-walled" polycar bonate currently on sale in this country under the trading

style THERMOCLEARZ This material is commonly used as a substitute for double glazing, and is consequently both cheap and readily available. To adapt this material for use as the partition 2, it is only necessary to provide fittings for the supply lines 9, and to puncture the material to form the holes in the front face 3.

In alternative embodiments, instead of having a single column of cavity, each cavity spanning the width of the partition 2, the partition 2 may include two or more columns of cavities. In such a case, each cavity would still be supplied by its own supply line, but would not span the width of the partition 2 (the structure would thus be that of a "multi-walled" polycarbonate).

Claims (6)

CLAIMS:

1. A device of the kind used for fluidising particulate matter in a container by introducing under pressure into the container a gas or other suitable fluidising medium, the device comprising a partition positioned in, or forming part of, the container and having a number of cavities, each cavity being connected to a source of fluidising medium; a plurality of holes formed in the partition, each hole providing a conduit between a cavity and the container; and means selecting the cavity or cavities to which fluidising medium is, in use, to be supplied.

2. A device according to claim 1 in which each cavity is sealed from the other cavities in the partition.

3. A- device according to claim 2 in which the cavities form a closed cellular structure within the partition.

4. A device substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

5. A method of fluidising particulate matter in a hopper having a wall, or part of a wall, formed as a device according to any of the preceding claims, the method comprising the step of supplying the fluidising medium to the cavities in a predetermined sequence, or in a sequence determined by control means operating in response to signals generated by one or more sensors.

6. A method substantially as described herein with reference to the accompanying drawings.