GB2029258A - Improvements in or relating to bulk material vacuum conveying apparatus - Google Patents

Abstract

The outlet end of a bulk material vacuum conveyor comprises two filters 15 and 16 connected via a switching valve 20 to a suction fan 19, and the valve 20 is operated periodically by a differential pressure switch or timer 27 to direct the air flow through each filter in turn, so that bulk material is continuously drawn into hopper 11 by the air flow created by fan 19. The filter 15, 16 which is not carrying an air flow is cleaned by a respective vibratory shaker 28, 29. The shakers and valve 20 are pneumatically powered. In a preferred example, the two filters and a length of the material feed conduit 21 for material conveyed into the hopper 11 are mounted in a unitary filter housing 10 which can be mounted on the inlet aperture 12 of the hopper. The filter housing 10 may have explosion flaps (41, 42). <IMAGE>

Description

SPECIFICATION Improvements in or relating to bulk material vacuum conveying apparatus The present invention relates to bulk material vacuum conveying apparatus. A well known arrangement for such apparatus comprises a hopper in which the conveyed bulk material is to be collected, a material feed conduit or pipe leading into the hopper from the place where the bulk material is to be picked up or collected and a suction fan drawing air from the hopper so that an air flow is produced into the hopper through the material feed conduit, this air flow being sufficient to convey the bulk material along the conduit into the hopper. With such an arrangement it is important and usual to provide a filter at the air outlet from the hopper so as to filter out any particles of the bulk material from the air withdrawn from the hopper.This is necessary, especially for fine particle bulk material, to prevent dust from being discharged into the atmosphere by the suction fan. However, a problem with this arrangement is that the filter can quite quickly become blocked, thus reducing the air flow out of the hopper and interfering with the vacuum conveying process. It has been the practice, hitherto, to overcome this problem by operating such apparatus in a cyclic manner, periodically halting the suction from the hopper, stopping the conveying process, and cleaning the filter during these periods. It has also been found convenient to discharge the collection hopper during the filter cleaning periods into a bulk hopper or the like.It will be apparent that, although the above prior art arrangement can work quite satisfactorily in some situations, it is rather bulky since it typically employs two hoppers, and also material is being conveyed into the first hopper for only a portion of the total time. This latter point is of especial importance when the vacuum conveying apparatus is used to carry away and collect material being delivered by other apparatus in a continuous stream. During the filter cleaning periods when the vacuum conveying apparatus is not operating, it may become necessary to halt this other apparatus to prevent an excessive buildup of the bulk material before the conveying apparatus starts operating again. In one example, vacuum conveying apparatus is sometimes used for carrying away defines passing through a sieving machine.With the prior art arrangements, it has proved necessary to halt the sieving machine, or at least the delivery to the sieving machine of material of be sieved, during the filter cleaning periods of the vacuum conveying apparatus. This has proved most unsatisfactory since sieving machines are best operating continuously both from the point of view of performance and, of course good economics.

According to the present invention, a bulk material vacuum conveying apparatus comprises a hopper for collection of the material conveyed, a material feed conduit into the hopper, means for producing a material conveying gas flow along said feed conduit into the hopper, and a gas outlet arrangement by which gas can flow out of the hopper, the outlet arrangement including a pair of filters for removing particles of the bulk material from the gas flow from the hopper, switchable means for conducting said gas flow from the hopper through a selected one of the filters cleaning means for clearing particles of the bulk material from the filter which is not selected at any particular time, and actuating means for switching said means for conducting in alternate sequence such that the selected filter at any time does not become sufficiently blocked to inhibit the gas conveying process.

With the arrangement of the invention, the gas, flow, typically air, out of the collection hopper is switched alternately from one of the pair of filters to the other, so that at any time, one of the filters is not operational and is being cleaned. In this way, gas flow from the hopper can be maintained continuously so that the conveying process of material into the hopper can proceed without interruption. It will be apparent that this arrangement has significant advantages over the conveying arrangements employed hitherto. Since the conveying process can proceed continuously, the vacuum conveying apparatus can be used most conveniently with other continuous process machinery, such as sieving machines. A further advantage arises because with the arrangement of the invention, there is no longer any need for a separate bulk hopper.The collection hopper in the arrangement of the invention can itself be filled continuously by continuous operation of the conveying apparatus.

In one embodiment, the actuating means includes a timer for controlling ,said switching to switch from one filter to the other at predetermined regular intervals. It will be appreciated that the timer must be set so that any filter does not remain in operation excessively long so as to become blocked and impede the conveying gas flow. The actual switching period set by the timer will depend on the type of material being conveyed and its tendency to block the filters. It can be appreciated that fine particulate material can be worse in this respect compared with coarse material.

Alternatively, the actuating means may include a pressure sensor operative to effect switching from one filter to the other when the gas pressure differential across the selected filter exceeds a predetermined level. Clearly, the pressure differential across the selected filter is a measure of the blocking of the filter and thus this arrangement can operate to switch from one filter to the other before this blocking becomes excessive. The gas flow producing means may comprise a suction fan for withdrawing gas from the hopper through the outlet arrangement, in which case the pressure sensor is conveniently responsive to the pressure between the suction fan and the selected filter to effect switching when this pressure falls below a predetermined minimum level.

Preferably, part bf the apparatus of the invention is constituted by a unitary filter head mounted on the hopper at an inlet aperture therein, the filter head comprising a gap closing said inlet aperture, said pair of filters mounted in said cap and a length of said material feed conduit extending through said cap into the hopper. Such a unitary filter head has extra advantages in that it can quite conveniently be mounted directly on to a bulk hopper which may be one existing in the factory.

Further, the filter head can be removed again from the hopper when this is full and placed on another hopper.

In a preferred embodiment, the cap defines a chamber in the filter head having an aperture in communication with the inlet aperture of the hopper, and the two filters are mounted inside said chamber to co-operate with respective gas outlet pipes from said chamber. Then, said length of said material feed conduit can extend from outside said chamber through the chamber and the inlet aperture of the hopper so that the outlet of the conduit is inside the hopper. It will be appreciated that in accordance with normal practice for vacuum conveying systems, the conveyed material is introduced into the collection hopper towards the top of the hopper but at a point below the filter through air is withdrawn from the hopper.

The filter head may further comprise at least one explosion flap which can open to relieve gas pressure build-up in the head and the hopper in the event of a powder explosion.

Further, said cleaning means may comprise a respective vibrator unit associated with each filter and operable to shake clear material particles from the filter when the filter is not selected.

An example of the present invention will now be described with reference to the accompanying drawings in which:~ Figure 1 is an elevational view, partly in crosssection, of a vacuum conveying apparatus embodying the present invention and, Figure 2 is a view of the filter head of the apparatus of Figure 1 taken from one side in Figure 1.

In the drawings, there is shown a filter head 10 mounted on a hopper 1 The hopper 11 may be a standard bulk collection hopper having an inlet aperture 1 2 at its top. The filter head 10 is shaped to define a chamber 13 and as an aperture 14 which communicates with the aperture 12 in the hopper so that gas, typically air, from the hopper can flow into the chamber 13 freely. Apart from the aperture 12, the hopper should be substantially gas tight, at least during the vacuum conveying process. Mounted inside the chamber 13 of the filter head 10 there are two filter units 15 and 1 6.The filter units 15 and 16 are associated with respective gas outlet pipes 17 and 18 from the filter head 10 so that the filters separate particles of the bulk rnaterial conveyed by the system from any gas flowing out of the filter head along either one of the pipes 17 and 18.

In operation, air is withdrawn from the chamber 13 of the filter head 10, and thence from the interior of the hopper 11, by means of a suction fan 19. The suction fan 19 is connected to the outlet pipes 1 7 and 18 by means of a switching valve 20 which is operable to connect the fan 19 to a selected one of the filters 1 5 and 16. Thus, at any time, air is being withdrawn from the chamber 1 3 through only the selected one of the filters 1 5 and 16.

The suction fan 19 produces a flow of air into the hopper 11 along a material feed conduit 21.

The air flow is sufficient to vacuum convey the bulk material along the conduit 21 from the inlet of the conduit (not shown) and into the hopper 11. As can be seen in Figure 1, the conduit 21 extends from outside the chamber 13 of the filter head 10 right through the chamber 13 and through the aperture 12 into the interior of the hopper 11, so that the gas and material mixture flowing in the conduit 21 is expelled directly into the hopper 11 from the outlet 22 of the conduit.

The switching valve 20 is actuated to change over the suction from one to the other of the filters 1 5 and 1 6 by means of a double action cylinder 23 operated by compressed air supplied on lines 24 and 25. The compressed air is fed from a supply to a solenoid valve 26 which operates to connect the compressed air alternately to one of the supply lines 24 and 25. The solenoid valve 26 is controlled by a timer 27 which operates the solenoid valve so that compressed air drives the double action cylinder to switch over the valve 20 at regular predetermined intervals.

The filters 15 and 16 have respective vibrator units 28 and 29 operative to-shake their associated filters to clear them of particles of a bulk material which then fall away into the hopper 11. The vibrators 28 and 29 are driven by compressed air supplied along lines 30 and 31 respectively. The supply of compressed air along the lines 30 and 31 is also controlled by the solenoid valve 26 such that, for example, compressed air is supplied only along line 31 to effect cleaning of filter 16 when the double acting cylinder 23 has operated the valve 20 to conduct the suction through the other filter 1 5. Thus, only the vibrator associated with the filter which is not selected by the valve 20 is operating at any time.

It can be seen therefore that the apparatus operates so that air is continually withdrawn from the chamber 13 and the hopper 11 with the two filters 15 and 16 being subject to alternate operational and cleaning cycles. The timer 27 ensures that the period between switching from one filter to the other is not so long that the~ filter in operation at any time becomes so blocked as to impede the air flow in the feed conduit 21.

As can be seen from Figure 2, the illustrated filter head is formed in the shape of a cylinder with its axis horizontal in the drawings, in combination with an extension portion 32 terminating in the aperture 14 connecting with the hopper 11. The filters 1 5 and 1 6 are mounted at the ends of the cylindrical portion of the head 10 to removable circular plates 33 and 34. The plates 33 and 34 effectively close the ends of the cylindrical portion of the head 10 but each can be removed with its associated filter by releasing the screw clamps 35.

A frame 36 is mounted on the inside of each of the plates 33 and 34 on flexible mountings 37 so that the frame can vibrate relative to the plate. The membrane of each of the filters 1 and 16 is in the shape of a bag of flexible filter material lying over the respective frame 36 and being sealed around the edge of its mouth 38 between the circular plate 33,34 and a co-operating circular flange at the respective end of the cylindrical portion of the head 10. The vibrators 28 and 29 are mounted on the frames 36 and are connected to their respective supplies of compressed air on lines 30 and 31 by lengths of flexible tube 39. The air exhausted from the vibrators 28 and 29 is also connected to exhaust outlets in the plates 33 and 34 by means of further lengths 40 of flexible tube.

The filter head 10 is further provided with a pair of explosion flaps 41 and 42. The flaps are shaped and adapted to provide airtight closures for a pair of rectangular openings in the cylindrical wall of the cylindrical portion of the head 10. The flaps 41 and 42 are connected to the wall of the head 10 only by means of respective hinges 43 and 44 which enable the flaps to swing outwards. During normal operation of the conveying apparatus, the pressure within the chamber 13 and the hopper 11 is some what below atmospheric pressure and, therefore, the flaps 41 and 42 are held firmly closed by atmospheric pressure. However, in the event of a powder explosion within the hopper 11 or in the chamber 13, excess pressure within the chamber 13 and the hopper 11 blows the flaps 41 and 42 open, thereby allowing the pressure to be relieved before causing damage.Because of the positioning of the flaps 41 and 42 and the apertures-which they serve to close, material flowing out of the chamber 13 in the event of a powder explosion is directed substantially upwards, which is desirable in a factory environment.

The vibrators 28 and 29 may be of any standard type commonly used hitherto for clearing filters. Further, the suction fan 19, the valve 20, together with the cylinder 23, the solenoid valve 26 and the timer 27 may be of substantially-a standard design and it is not considered necessary to describe these parts further here.

Instead of the arrangement with the timer 27 operating the solenoid valve 26, it may be convenient to provide a pressure sensor for sensing when the pressure drop across the selected filter at any time increases beyond a predetermined level. This would indicate that the filter was becoming blocked at which time the pressure sensor would cause the solenoid valve to operate the cylinder 23 to switch over the switch 20. In the arrangement illustrated in Figure 1, the pressure sensor could be located within the length of pipe between the valve 20 and the fan 19 and be set to operate the solenoid valve 26 when pressure in this length of pipe dropped below a predetermined minimum.

Other arrangements are also possible for the filter head 10. For example, the filter assemblies themselves, including the mounting plates 33 and 34 need not be mutually parallel as in the described example but might be at any angle relative to each other, through it would be preferable for them to be symmetrical relative to the material feed pipe 22. Furthermore, it is not essential for the two filters to be mounted in a filter head. Instead the filters might be mounted directly in the collection hopper itself. However, then the advantage of being able easily to disconnect the system from one hopper, for example when this was full, and reconnecting the system to another hopper, would be lost.

Claims (9)

1. Bulk material vacuum conveying apparatus, comprising a hopper for collection of the material conveyed, a material feed conduit into the hopper, means for producing a material conveying gas flow along said feed conduit into the hopper, and a gas outlet arrangement by which gas can flow out of the hopper, the outlet arrangement including a pair of filters for recovering particles of the bulk material from the gas flow from the hopper, switchable means for conducting said gas flow from the hopper through a selected one of the filters cleaning means for clearing particles of the bulk material from the filter which is not selected at any particular time, and actuating means for switching said means for conducting in alternate sequence such that the selected filter at any time does not become sufficiently blocked to inhibit the gas conveying process.

2. Apparatus as claimed in claim 1, wherein the actuating means includes a timer for controlling said switching to switch from one filter to the other at predetermined regular intervals.

3. Apparatus as claimed in claim 1, wherein the actuating means includes a pressure sensor operative to effect switching from one filter to the other when the gas pressure differential across the selected filter exceeds a predetermined level.

4. Apparatus as claimed in claim 3, wherein said gas flow producing means comprises a suction fan for withdrawing gas from the hopper through the outlet arrangement, and the pressure sensor is responsive to the pressure between the suction fan and the selected filter to effect said switching when this pressure falls below a predetermined minimum level.

5. Apparatus as claimed in any preceding claim wherein part of the apparatus is constituted by a unitary filter head mounted on the hopper at an inlet aperture therein the filter head comprising a cap closing said inlet aperture, said pair of filters mounted in said cap and a length of said material feed conduit extending through said cap into the hopper.

6. Apparatus as claimed in claim 5, wherein the cap defines a chamber in the filter head having an aperture in communication with the inlet aperture of the hopper, adn the two filters are mounted inside said chamber to co-operate with respective gas outlet pipes from said chamber.

7. Apparatus as claimed in claim 6, wherein said length of said material feed conduit extends from outside said chamber through the chamber and the inlet aperture of the hopper so that the outlet of the conduit is inside the hopper.

8. Apparatus as claimed in any of claims 5 to 7 wherein the filter head further comprises at least one explosion flap which can open to relieve gas pressure build-up in the head and the hopper in the event of a powder explosion.

9. Apparatus as claimed in any preceding claim wherein said cleaning means comprise a respective vibrator unit associated with each filter and operable to shake clear material particles from the filter when the filter is not selected.

10 Bulk material vacuum conveying apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.