GB2128572A - Improvements relating to pneumatic material handling apparatus - Google Patents

Abstract

An apparatus for conveying bulk powders or other granular materials through pipe systems employs a generally cylindrical pressure vessel or blowing tank 44 from which the material is fed as from a hopper via a chute 36 and a valve 32 that can be closed to render the vessel 44 gas tight. Thereafter compressed air is introduced to cause the material to move into the pipeline 43, 47. The vessel 44 is offset from the inlet flange of the apparatus at an angle to the vertical so that the material flows from one side into the top of the vessel and enters via the valve aperture. The inlet valve 32 is not interposed between the hopper 45 and the pressure vessel 44 but is located to one side so that it can be removed easily to permit servicing or to give access to the interior of tie vessel 44. The interior of the vessel is provided with one or more circumferential air distribution rings that give a generally downwards flow of fluidising air that prevents blockages. <IMAGE>

Description

SPECIFICATION Improvements relating to pneumatic material handling apparatus This invention relates to material handling apparatus of the kind in which a powder or granular material is to be conveyed along a pipeline by compressed air.

In particular it relates to a method where the material is fed into a pressure vessel or blow tank through a valve that can be subsequently closed and thereafter compressed air is supplied to the pressure vessel to cause the material to be discharged into the pipeline and to a receiving point such as a distant hopper or processing machine. Blowing vessels of this type invariably stand vertical and are traditionally constructed either wholly conical or partially conical so that, as in hoppers, the material will in theory flow freely from the vessel into the pipeline. There is no consensus on the most suitably included angle of cone. Some makers favour one angle, some another, within the practical range 40 to 90 degrees.

Conical-bottom storage hoppers are functionally viable in that they will normally store only the one material and can, therefore, be designed to suit that material. But commercially viable blowing vessels must be considered as general-purpose material 'pumps' and, as such, capable of handling, if not all, then at least a wide variety of materials. Employment of conical vessels for this purpose can be shown to be far from ideal. There are many hundreds of powder, granular and other particulate materials which can be blown by compressed air through a pipe system, and they all have vastly different flow characteristics. In particular, each has a different 'angle of repose' which dictates the angle of cone from which that material will flow freely and completely.Therefore, it is not reasonable to assume that more than a few of these many materials can be expected to flow consistently from a one rigid design of vessel with a fixed cone angle.

If the chosen cone angle is not steep enough the vessel will not wholly empty and much material will remain on the cone. If the chosen angle is too steep, with many materials, a 'wedging' or 'compacting' action takes place and blockages will occur at the outlet. Furthermore, vessels of the conical type never completely fill since the material will come to rest in an inverted cone approximating its angle of repose, leaving up to a quarter of the capacity of the vessel unfilled.

This empty space absorbs compressed air on each discharge cycle which is a waste of energy, Such vessels are also wasteful of space, having a capacity littie more than half that of a cylinder of the same diameter and height. Larger fabricated cones are also expensive to make.

Some conical vessels have 'bottom discharge' as defined by the open end of the cone terminating in a right-angle bend connecting to an initially horizontal pipeline. Others have 'top discharge' through an internal pipe depending from the top of the vessel to a point adjacent to the bottom of the cone which is closed and which may embody a porous panel through which compressed air is applied to fluidise the material.

The more compact top-discharge mode will only handle lighter materials which can be induced directly into the vertical, or near-vertical pipe.

Heavier materials, granules and those with a considerable moisture content can only be handled by a bottom-discharge vessel.

Historically, manufacturers have tended to advocate and commit themselves to one mode or the other thus limiting the range of materials their equipment can handle.

An object of the present invention is to provide apparatus of simple, low-cost, basic construction that uses standard and readily available materials to produce a range of cylindrical blowing vessels of great flexibility in shape and size, capable of handling virtually any flowable material, and which eliminates the inherent shortcomings of the orthodox conical vessel.

The invention provides apparatus for fitting beneath a bottom discharge outlet of a hopper for particulate material comprising an inlet having a vertical axis adapted for fitting coaxially to the bottom discharge outlet, a chute leading from the inlet obliquely downwards in a first angular direction and a generally cylindrical vessel fluid tightly connected to the chute which opens towards the top thereof so as to receive material therefrom and directed at an opposite oblique angle, an outlet leading from the generally cylindrical vessel, valve means operable to isolate the vessel from the chute and fluid inlet means operable when the vessel is isolated frorn the chute to admit air therein to drive particulate material through the outlet.

It will be understood that the vessel is a pressure vessel ie. it is operated by means of compressed air or other compressed gas and therefore conforms to the relevant safety standards. The working part of the vessel has a cylindrical wall and it differs from the vessels previously known in that although there may be a small frustoconical powder distribution baffle at its lower end, there is no frustoconical surface that has to withstand the fluid pressure.

The above apparatus can provide a material handling unit wherein the material inlet valve is mounted within the general form of the apparatus, and is not concentric with the material inlet but is offset therefrom so that it can be quickly removed from that end (defined as the front end) without disturbing any other connections. The removal of the material inlet valve exposes the whole of the interior of the vessel for servicing and the obligatory regular inspection of pressure vessels without the need to provide an unsightly inspection plate or door.All the operating valves eg. for fluidising air, controls, pipework and tubing are located at the opposite end of the unit (defined as the rear end) and enclosed within the shell so that no access is needed on either side of the assembly thus enabling any number of units to be installed closely together in side-by-side relationship to draw material from a common hopper or bin and deliver to a number of different and widely separated points. The apparatus can be used for both top and bottom discharge pipe arrangements in the same basic design so that all classes of material can be handled.

At the rear end of the shell may be a door, preferably hinged at the bottom. All the accessories, pipework and controls may be located within the space defined by the rear face of the vessel, the side plates, and the door panel so that an entirely smooth and clean exterior is provided.

According to a further feature of the present invention there are provided one or more tubes spaced axially apart along the vessel and leading to respective circumferential air distribution rings on the inner surface of the vessel said ring or rings being of generally angle profile, welded at their top edges to the side wall of the vessel and spaced for at least a major portion of their circumference from the wall of the vessel to pass a downwardly directed flow of air therefrom.

The upper end of the pressure vessel is provided with a relatively thick annular flange, or other termination, drilled and tapped to accept the chosen form of material inlet valve. The lower end of the pressure vessel is provided with a similar relatively thick ring suitably drilled and tapped to accept either: (a) a plain blanking plate or an end closure embodying a fluidising panel of porous material, either of which may be needed for the topdischarge mode, or (b) a material discharge right angle bend as needed for the bottom-discharge mode.

The space behind the conical baffle is similarly connected to the blowing air supply through a boss welded to the vessel but, not being a part of the 'coded' pressure vessel, this baffle may be a relatively thin metal spinning.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic vertical section through a pressure vessel forming part of an apparatus according to the invention; Figure 2 is a diagrammatic partly sectioned view of a second pressure vessel; Figure 3 is a sectional view of a third pressure vessel and associated controls; Figure 4 is a view of a pressure vessel beneath the bottom discharge outlet of a hopper for granular material; and Figure 5 is a view of a hopper for granular materials showing two of the pressure vessels mounted beneath it in side-by-side relationship.

One embodiment of the present invention is shown in Figure 1 which shows a vessel whose height is about 1.5 times its diameter and whose internal layout is such that the vessel is capable of handling a wide middle range of powder and granular materials through a bottom discharge bend 5.

The vessel is constructed from a steel tube 1 provided at its top end with a flange 2. A first annular distribution ring 3 is located closely underneath the top flange so that blowing air emerging therefrom sweeps a major length of the vessel wall, and impinges upon the upward-facing surface of a second ring 4, being deflected therefrom towards the centre of the vessel to loosen the bulk of material and impel it towards the discharge bend 5. The second ring 4 is located low enough down the vessel wall that its air stream impinges strongly upon a conical baffle 7 and is also deflected towards the outlet bend 5.

The vessel is provided with inlet tubes 8 opening beneath the rings 3 and 4 by which air may be admitted thereto. Air can be admitted also between the baffle 7 and the lower end plate 20 of the vessel via an inlet tube 21 but it may be unnecessary to do so under ordinary conditions, in which case the tube 21 is plugged.

The air distribution rings 3, 4 may be rolled from standard angle sections, suitably 2" by 1", with the apex inwards so that the flange ends are adjacent to the inner wall of the steel tube 1. The rings are continuously welded into the vessel at the top edge, or otherwise sealed, but only intermittently so at the lower edge so that there is a substantially continuous narrow gap between the edge of the short flange and the inner wall of the vessel 1. Each ring 3, 4 is connected to the main blowing air supply through an inlet tube 8 in the form of a screwed or flanged boss welded to the outer wall of the vessel 1 so that the compressed air enters the ring 3, 4 and emerges into the vessel through the gap as a thin stream down the inner wall of the vessel.The width of the gap is such that the ring 3 is effectively pressurised, the air thus emerging from the gap at a velocity high enough to ensure that both the inner wall of the vessel 1 and, where necessary, the upward-facing surface of a lower ring 4 are impinged upon and kept clear of material. If the vessel is intended for the handling of a dry freeflowing material the rings 3, 4 can be spaced well apart. If it is intended for the handling of a 'tacky' material likely to adhere to these surfaces the rings 3, 4 are suitably placed closer together.

The lower flange or end plate 20 also includes the frustoconical baffle 7 to provide a smooth transition from the larger diameter of the vessel to the smaller internal diameter of the flange or ring 20. This baffle 7 is welded continuously to the vessel 1 at its top edge but only intermittently to the flange 20 so as to provide a final low gap for air injection into the vessel, either to impinge upon the lowest surface in the top-discharge mode or directly into the bend in the case of a bottomdischarge assembly.

It is an important part of the invention that each inlet 8, 21 for blowing air can be connected separately to the blowing air supply, each line 8 or 21 being provided with its own solenoid-operated on/off valve and an adjustable volume control so that they can be operated automatically in sequence to open simultaneously for a full discharge cycle or in any individual order that is found to be necessary to handle any particular material. In the apparatus of Figure 1 there will be two such controls. Normally, they would be operated simultaneously with the volume of air going to each ring 3, 4 being manually preset.

However, to provide a denser flow of a specific material the top ring 3 could be supplied with the full flow or air for a major portion of the blowing cycle, and then the full flow of air could be transferred to the lower ring 4 for a short burst to clear the remaining material from the cone baffle 7. In the case where the material being handled tends to coagulate in the pipeline, the bottom position 6 could be used to inject air directly into the bend in timed bursts throughout the blowing cycle thus interposing a 'slug' of air between 'slugs' of material to discourage coagulation that would otherwise lead to blockage in the pipeline.

Where granular materials are being conveyed in a dense manner it is essential that the velocity in the pipeline is kept below the point where harmful abrasion or degradation of the material occurs.

There comes a point, however, when the material travelling in the pipeline loosens, the compressed air breaks through to a higher degree and the stream accelerates greatly, resulting in wear at pipe bends and break-up of the material as it is decelerated into the receiving hopper. In the present apparatus the volume-per-minute of compressed air entering the system can be conveniently controlled during the discharge cycle to alleviate this problem. Where the material is sensitive to 'packing', is a delicate food product, or is an 'expanded' granular product, which would collapse if 'thumped' into the discharge bend 5 by pressure from the top of the vessel quite different blowing conditions can be provided.Compressed air in this case can be injected at the low points 4, 7 to ease the product gently down the baffle and into the bend with velocity, pressure, and air/material ratio under control to ensure consistent flow through the pipeline without damage. At the other extreme a vessel of the present kind is equally suitable for the handling of crushed animal product or slurry-like materials such as mixed concrete which will either harden or go foul in a short time, making it necessary to wash or sterilise the whole system after each working period. For this purpose it is merely necessary to connect a source of water, steam, or solvent to all the blowing-air inlets 8, 21 to effectively 'wash' all the interior surfaces of the vessel and the pipe system.

Another embodiment of the present invention is shown in Figure 2 where the vessel 21 is arranged for top discharge through a pipe 9 that passes downwards through the hollow centre of a concentric material valve 10 to a point ciose to a bottom plate 18. The part of the steel tube 11 that acts as a pressure chamber is provided at its top with a flange 1 3 for the concentric valve body.

Such a concentric valve is described for example in Patent Specification No. 1385980 or application No. 8022576. It operates to admit material to the vessel while it is open and then to seal the vessel against material ingress and gas escape so that the filled vessel can be pressurised and may be emptied by the fluidising air. The vessel is provided on its inner surface with three circumferential air distribution rings 14, 1 5 and 1 6 spaced at intervals along its length. A low air injection point 1 7 defined between a base 22 of the vessel and a lower part conical baffle 23 may be brought into the blowing sequence to aerate the material as it approaches the bottom plate 1 8 to ensure smooth flow up the central pipe 9 and into the pipeline.

Referring to Figure 3 the pressure vessel 3 consists of a cylinder extending upwards beyond the actual pressure chamber to provide a flanged mounting for a concentric material inlet valve 32 which in its open position exposes an aperture 33 into the pressure chamber 31 and when it is in the extended position closes the aperture. The concentric valve may be of the type previously mentioned and has a hollow centre so that, in top discharge arrangements, the material can flow upwards through the valve.

The vessel 31 is offset from the inlet 37 by which material enters from the overlying hopper or bin so that the concentric valve 32 can be readily removed without disturbing the connection to the hopper. The vessel 31 has its axis inclined at a small acute angle to the vertical such that a top discharge pipe 34 conveniently clears the larger diameter of the hopper above. An enclosure or shell fabrication 35 supports the vessel 31 and comprises a material inlet chute 36 directed obliquely to the vessel 31 and communicating it with a material inlet 37 having a vertical axis. An enclosure door 38 is provided. All components to be necessarily attached to the pressure vessel such as the blowing air on/off and/or throttle valves are shown at 39 whilst the control components 40 are mounted upon the door 38 which is hinged at the bottom.

Air and electrical connections from the components on the door 38 to the pressure vessel and concentric valve 32 contain flexible sections fitted with quick-connectors or plugs and sockets so that the door 38 can be partially opened for access to settable components located at the top of the door. Alternatively, the complete door 38 can be disconnected, lifted out, and removed to a clean zone for servicing purposes.

When an assembly calling for top discharge is required the depending pipe 41 is fitted through the concentric valve 32 and a plain bottom plate 42 is used, or a similar closure.containing a porous panel may be used. When bottom discharge is required the depending pipe 41 is omitted, the apertured through the valve 32 is plugged and bottom plate 42 is replaced by the bottom bend 43. Thus by a simple change of a small number of components there is provided apparatus that can handle top and bottom discharge with alteration of only a minor proportion of its parts and which is capable of handling a wide range of materials.

Figure 4 shows a vessel 44 of the general kind described above fitted beneath a hopper 45 for granular material, the outflow of which is controlled by means of a control valve 46 connected between the outlet base flange of the vessel 45 and the inlet 37 to the vessel 44. Valve 46 is required to be closed only when it is desired to isolate the hopper 45 eg. so that the vessel 44 can be removed for servicing. Entry of the granular material via the chute 36 is controlled by the valve 32 which, as previously stated, serves to seal the vessel 44 during the blowing part of the inlet/blowing cycle which it performs. The powder flows from the vessel 45 to a pipe 47 which conveys it to where it is required.

Figure 5 shows the use of two of the vessels 44' fitted with respective control valves 46' in side-by-side relationship beneath a hopper 45.

Claims (6)

1. Apparatus for fitting beneath a bottom discharge outlet of a hopper for particulate material comprising an inlet having a vertical axis adapted for fitting coaxially to the bottom discharge outlet, a chute leading from the inlet obliquely downwards in a first angular direction and a generally cylindrical vessel fluid tightly connected to the chute which opens towards the top thereof so as to receive material therefrom and directed at an opposite oblique angle, an outlet leading from the generally cylindrical vessel, valve means operable to isolate the vessel from the chute and fluid inlet means operable when the vessel is isolated from the chute to admit air therein to drive particulate material through the outlet.

2. Apparatus according to claim 1 wherein the valve means includes an annular piston that is movable under fluid pressure towards and away from a seat disposed in the vessel beneath the chute so that when the piston is moved away from the seat particulate material can enter the vessel via the chute and when the piston is engaged with the seat ingress of particulate material is prevented and the vessel is fluid-tightly sealed.

3. Apparatus according to claim 1 or 2, wherein the fluid inlet means comprises one or more tubes spaced axially apart along the vessel and leading to respective circumferential air distribution rings on the inner surface of the vessel said ring or rings being of generally angle profile, welded at their top edges to the side wall of the vessel and spaced for at least a major portion of their circumference from the wall of the vessel to pass a downwardly directed flow of air therefrom.

4. Apparatus according to claim 3, wherein a frustoconical baffle member is at the base of the vessel closely spaced from a bottom plate thereof and fluid inlet means is provided for admitting fluid between the baffle member and the plate.

5. Apparatus according to claim 4, wherein the or each fluid inlet means is connected to a source of high pressure fluid through respective valve means arranged to start and stop the flow of fluid.

6. Apparatus for fitting beneath a bottom discharge outlet of a hopper for particulate material and driving the material through an outlet in a fluidised state substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.