GB2171928A - Debris removal - Google Patents

Abstract

A plant for removing asbestos debris from an air stream which is drawn from a working area includes a collection and discharge hopper 8, comprising upper and lower parts 20 and 21 which are separable for individual transport on skip-loading vehicles. The hopper 8 comprises two identical hopper portions 25, each of which is arranged to be emptied via a chute 30, with which there is associated a fluid-tight cone valve 28 at the bottom of the respective hopper portion 25, and a membrane slide valve 31, disposed in the chute 30. By sequential operation of the valves 28 and 30, each hopper portion 25 may be emptied of debris, whilst the plant continues to function continuously. The debris passes from the chute 30 into a bag 33. Hopper 8 is arranged upstream of a second hopper (9), similarly provided with discharge valves 28, 30 and enclosing a bank of filter bags. Valves 28 are opened and closed by pneumatic bellows and vibrated to induce the flow of debris. <IMAGE>

Description

SPECIFICATION Debris removal This invention relates to debris removal, and is concerned particularly although not exclusively with the collection and discharge of asbestos and asbestos-contaminated material by pneumatic means.

At one time, asbestos was a popular material for thermal insulation. However, over the years, it has progressively become appreciated that asbestos carries numerous health risks. There are many installations throughout the country, where asbestos is still present in large quantities, and removal of this constitutes a hazardous operation.

It is known to collect and dispose of asbestos and asbestos/ contaminated material by means of suction devices which deposit the asbestos in a collection receptacle, from which it is subsequently removed in bags. However, in order to bag the asbestos, the suction device has to be turned off, whilst the receptacle is emptied. This necessary down time of the equipment has a dramatic effect on the cost of operation. Moreover, asbestos removal often has to be carried out in locations where only a limited access time is permissible.

For example, asbestos may require to be removed from a boiler plant of a large installation, under such conditions that, for as long as the boiler plant is out of service, the entire associated operation (e.g. manufacturing, power generation, etc.) is suspended.

There are fairly comprehensive regulations at the present time, dealing with the removal of asbestos.

For example, it is necessary that all working areas should be enclosed. All working areas, where possible, should be kept upder negative pressure. All asbestos contaminated material has to be placed in double polythene bags, for licenced disposal. All of this poses further problems for the designers of equipment for use in removing asbestos.

Preferred embodiments of the present invention aim to provide apparatus for use in removing asbestos and asbestos/ contaminated material, which can enable a pneumatic removal plant to operate continuously, even whilst collected asbestos is being bagged.

More generally, according to a first aspect of the present invention, there is provided a collection and discharge hopper for use in a pneumatic debris removal plant, the hopper comprising; an enclosed body; an inlet for debris-laden air at an upper portion of said body; .an outlet for air at an upper portion of said body; a hopper portion at a lower portion of said body, for collecting debris deposited from air travelling through the body, in use; a discharge chute at the bottom of said hopper portion, for discharging debris from the hopper portion; a first valve adapted to open and close in a substantially fluid-tight manner, thereby to control discharge of debris from the hopper portion into the chute, through the first valve; and a second valve positioned below the first valve and adapted to open and close in a substantially fluid-tight manner, thereby to control discharge of debris from the chute, through the second valve.

Preferably, said first valve is disposed in a bottom portion of said hopper portion, and is adapted to open and close an opening at the bottom of said hopper portion, in a substantially fluid-tight manner.

The second valve is preferably disposed in said chute.

The first valve preferably comprises a bellows operated cone valve. The valve may then comprise double-acting bellows, adapted to urge a cone of the valve positively into either a first, open position or a second, closed position, in dependence upon a selected direction of operation of the bellows.

The first valve may comprise vibrator means for vibrating a cone of the valve.

Preferably, said second valve comprises a membrane slide valve.

The hopper may include venting means for venting the chute to the ambient atmosphere, at a position between the first and second valves. Such venting means may be adapted to operate automatically, in response to the pressure difference between the inside of the chute and the ambient atmosphere.

There may advantageously be provided control means adapted to operate said valves in an automatic predetermined sequence, to effect a discharge cycle. Means may then be provided for adjusting at least one of the timing periods of said predetermined sequence.

The hopper may be provided with valve means for selectively connecting the chute, at a position downstream of the second valve, to the inlet of the hopper.

Means may be provided for securing a collection bag around the chute. Support means may be provided for supporting a receptacle below a discharge orifice of the chute. Such support means may be of adjustable height, and may comprise a dashpot system.

The hopper preferably includes baffle means in an upper portion of said body, for deflecting and/or diffusing air entering the body through said inlet, in use.

Additionally or alternatively, filter means may be provided in an upper portion of said body, for filtering debris from air passing through the body, in use.

In an advantageous arrangement, said body comprises two similar said hopper portions disposed side-by-side, each having a respective discharge chute with first and second valves as aforesaid.

Preferably, said inlet and outlet are so arranged as to cause substantially symmetrical air flows above said two hopper portions.

The hopper may comprise two separable parts which are adapted to stack on one another. Said two parts may be separated at a level which passes between the or each first valve and its respective second valve. The or each chute may be provided with a respective compression seal at said level of separation of said two parts.

In an advantageous arrangement, the hopper is adapted for transport by a skip-loading vehicle.

Where the hopper comprises two separable parts as aforesaid, each of said two parts may be adapted for separate transport by a skip-loading vehicle.

The hopper may include level detection means for detecting the level of debris in the hopper and emitting a control signal when it detects that the debris has risen to a predetermined level.

According to a second aspect of the invention, there is provided a pneumatic debris removal plant, comprising a collection and discharge hopper in accordance with the first aspect of the in#vention, together with a suction unit adapted to draw debris-laden air through the hopper, via said inlet and outlet.

The plant may include a first said hopper adapted to collect debris and, downstream thereof, a second said hopper adapted to collect debris wich has not collected in the first hopper. The second hopper may advantageously be provided with level detection means as forementioned, the suction units being adapted to switch off, in response to said control signal of the level detection means.

The plant may be housed within a portable enclosure, which may comprise a tent. Said suction unit may be provided on its exhaust with an absolute filter which is disposed outside the enclosure.

Pressure means may be provided for maintaining said enclosure under negative pressure. Such pressure means may have an exhaust which is provided with an absolute filter disposed outside the enclosure.

The plant may further comprise a mill for crushing debris, which mill is connected to said inlet of the hopper.

According to a third aspect of the present invention, there is provided a method of collecting debris, comprising the steps of passing debris laden air into a hopper according to the first aspect of the invention, collecting the debris in the or each said hopper portion, and discharging the collected debris into a receptacle, via the discharge chute of the or a respective one of the said hopper portion(s).

The method may be employed with particular advantage where said debris contains asbestos.

Said receptacle may comprise a bag, and the method may include the subsequent step of wrapping said bag within another, outer bag.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a schematic block diagram of an asbestos removal plant; Figure 2 illustrates a first discharge and collection hopper of the plant, in side elevation; Figure 3 is a plan view from above, to show inlet and outlet pipes of the hopper of Figure 2, Figure 4 is a detail view of a lower hopper portion and discharge chute; and Figure 5 illustrates a second hopper of the plant, in section.

The plant 1 that is illustrated in Figure 1 is for removing asbestos debris from a working area 2. For safety reasons, the working area 2 is kept fully enclosed, for example, within a tent 3. To avoid the escape of contaminated air, the tent 3 is kept under a permanent negative pressure, by means of an air displacement unit 4 which is disposed outside the tent 3, and has an exhaust which is provided with an absolute ffiter.

Similarly, the asbestos removal plant 1 is fully enclosed within a tent 5, which is maintained constantly under negative pressure by means of an air displacement unit 6, the exhaust of which is provided with an absolute filter, and which is located outside the tent 5. Within the tent #5, there is provided a suction unit 7, a first collection and discharge hopper 8, and a second collection and discharge hopper 9.

The suction unit 7 provides the negative pneumatic pressure for sucking debris-laden air from the working area 2 to the removal plant 1. The suction unit 7 may be of a conventional type, and be provided at its exhaust with an absolute filter 10, outside the tent 5.

In use, asbestos material to be removed is placed into a crushing mill 11 in the working area 2. From the crushing mill 11, the asbestos-laden air travels via a suction pipe 12 to the first hopper 8, via a two-way valve 13. In the first hopper 8, the majority of asbestos is collected and discharged, as will be described in detail below. The relatively small quantity of asbestos remaining in the air that exhausts from the first hopper 8 is collected in the second hopper 9. The suction unit 7 itself is provided with usual filters, to remove any lastremain- ing particles of material. The two-way valve 13 may be operated to connect the inlet of the first hopper 8 to a filter outlet of the suction unit 7, via a pipe 14, thereby to remove periodically any deposits that build up in the filter unit of the suction unit 7.

The first collection and discharge hopper 8 is shown in more detail in Figure 2. It is constructed as two separable parts 20 and 21, which are separable at a horizontal plane X-X. Each of the parts 20, 21 is adapted to be carried by a skip-loading vehicle. In this way, the hopper 8 may readily be transported from site to site, and readily erected and dismantled.

The hopper 8 comprises an enclosed body 22, in an upper portion of which there are located an inlet pipe 23 and an outlet pipe 24, for asbestosladen air.

The lower portion of the body 22 is divided into two identical hopper portions 25. As shown in chain line in Figure 2, the inlet pipe 23 terminates in a port 26 which is disposed centrally with respectto the two hopper portions 25. Below the port 26, there is disposed a baffle plate, to deflect and/ or diffuse asbestos-laden air discharged from the port 26.

The bottom of each hopper portion 25 is formed with an opening, which is arranged to be closed in a fluid-tight manner by means of a respective cone valve 28, as will be described in further detail be low. Respective compression seals 29 are provided at the bottom of each hopper portion 25, and also at the top of each of two chutes 30, with each of which a respective one of the hopper portions 25 co-operates. Thus, when the two parts 20 and 21 of the hopper 8 are superposed, the opening at the bottom of each hopper portion 25 registers with a respective one of the chutes 30, and the compres sion seals 29 ensure that the hopper portions 25 and chutes 30 engage one another in a fluid-tight manner.

In the lower portion of each chute 30 there is mounted a respective membrane slide valve 31, as will be described in further detail below. Below each slide valve 31, the respective chute 30 termi nates in a mouth 32, around which a collection bag 33 is disposed. Each collection bag 33 is supported on a respective table 34, which is adapted to move up and down, by means of a telescopic support 35.

Each telescopic support 35 may be hydraulically powered. Alternatively, it may comprise a simple viscous damper, to help in supporting the weight of material which is dropped into the bag 33.

Below each slide valve 31, a respective suction pipe 36 leads to a double acting ball valve 37, which in turn leads to a common suction pipe 38 which communicates with the main body 22 of the hopper 8.

The purpose of the various components of Fig ure 2 will be explained in somewhat more detail later, but first, the various components are ex plained in further detail.

Figure 3 illustrates one possible arrangement of the inlet and outlet ports of the first hopper 8. As mentioned above with reference to Figure 2, the inlet pipe 23 terminates in an inlet port 26 which is disposed centrally, with respect to the two upper portions 25.

The outlet pipe 24 extends from a T-piece 41.

Connected to the two branches of the T-piece 41 are two identical pipe sections 42, each of which terminates in a respective outlet port 43. It will be appreciated that the two outlet ports 43 are dis posed symmetrically, with respect to the two hop per portions 25. Because of this, and because of the equality of the two pipe sections 42 which lead to the common T-piece 41, it is ensured that the airflows above the two hopper portions 25, from the common air inlet port 26, are substantially equal. Thus, debris that is deposited in the hopper 8 is likely to be deposited in the two hopper portions 25 in reasonably equal amounts.

The detail view of Figure 4 shows the bottom portion of one of the hopper portions 25, the re spective chute 30, the cone valve 28 and slide valve 31 associated therewith, and other associated parts. This detail view is partly in section.

The cone valve 28 comprises a frusto-conical valve member 50 which is provided around its lower edge with a resilient sealing member 51, which bears against the inner wall of the hopper portion 25. The valve member 50 is held positively in the illustrated position by means of a first pneumatically operated bellows 52, which is secured at one side to a support member 53 which is mounted in the hopper portion 25. The other side of the bellows 52 is connected via securing rods 54 to a support member 55 which is mounted on the valve member 50.

A second bellows 56 is similarly connected between the support members 53 and 55, but acts in an opposite sense to the bellows 52. As illustrated, the bellows 52 is inflated and the bellows 56 is deflated.

Upon deflating the bellows 52 and inflating the bellows 56, the valve member 50 is pushed upwardly to the position illustrated at 57 by chain lines. The maximum lift of the valve member 50 is determined by adjustable tie rods 58, which are secured to the support member 55 and extend through, but are arranged to co-operate with, the support member 53.

A vibrator 59 is secured to the valve member 50.

The membrane slide valve 31 which is disposed in the chute 30 comprises a closure member 60, mounted for sliding movement within a frame 61.

A tough, flexible membrane 62 is secured between the closure member 60 and the frame 61, which in turn is secured in a fluid-tight manner within the chute 30.

The closure member 60 is shown in a partly opened position. When slid fully to the right (as seen in Figure 4), the closure member 60 bears against an opposing wall 63 of the frame 61 and, in this position, it will be appreciated that the membrane 62 completely closes off the chute 30, both above and below the closure member 60, to provide a fluid-tight seal.

Upon withdrawing the closure member fully to the left (as seen), the chute 30 remains fully open, the diaphram 62 continuing to provice a fluid-tight seal to the ambient atmosphere.

In Figure 4, there is additionally shown a pressure release valve 65, which communicates with the inside of the chute 30, between the two valves 28 and 31. The purpose of the pressure release valve 65 will become apparent later.

As may be seen in Figure 5, the second collection and discharge hopper 9 comprises an enclosed body 70, a lower portion 71 of which defines only a single hopper portion.

Above the lower portion 71, an inlet 72 for asbestos-laden air is provided. As will be understood from the above, the quantity of asbestos in the air will be very much lower than that entering the first hopper 8.

An air outlet pipe 73, also disposed above the lower portion 71, communicates with an outlet manifold 74, to which are secured a bank of filter bags 75. As is well known in the art, each filter bag 75 may comprise a bag of filter material supported on a frame. A plurality (e.g. 12) of the filter bags 75 are arranged side-by-side, the interiors of the bags 75 communicating with the outlet manifold 74, and the outer surfaces of the bag 75 communicating with the air in the upper portion of the body 70.

In use, asbestos or asbestos-contaminated particles 76 build/ up in the lower portion 71 of the hopper 9. Means may be provided for vibrating the filter bag 75 at periodic intervals, to shake particles free.

A sensor.77 is disposed in the wall of the lower portion 71, and is arranged to detect whether the level of deposited material in the hopper 9 reaches a predetermined level. When this level of material is detected, the sensor 77 emits an appropriate control signal on a control line 78.

The base of the hopper 9 is provided with a chute 30 and valves 28 and 31, generally as shown in Figures 2 and 4.

Operation of the illustrated plant will now be described, in further detail.

As has been outlined above, the general mode of operation is that air laden with asbestos or asbestos-contaminated material is drawn into the first hopper 8, where it is principally collected. Any remaining material is collected in the second hopper 9, and any further relatively small particles of material are collected in the conventional suction unit 7, for recycling via the pipe 14. Ultimately, any microscopic particles are filtered out by the absolute filter 10.

The asbestos-laden air enters the first hopper 8 through the inlet pipe 23 and, as it is discharged from the inlet port 26, the sudden increase in cross-section of the hopper, relative to that of the pipe, leads to a sudden drop in air velocity, and the particulate material carried in the air stream tends to simply drop down into the hopper portions 25. The baffle 27 also tends to reduce air velocity. As has been described above, the airflow paths from the inlet port 26 to the two outlet ports 43 are substantially identical, so that progressively, asbestos material builds up in the hopper portions 25.

As the plant is operating continuously to deposit asbestos material in the hopper 8, operatives remove the asbestos material from the hopper portions 25 by means of the respective chutes 30. It is envisaged that, in normal operation, material may be removed via the chutes 30, at a rate which is at least as great as that at which material is deposited within the hopper portions 25.

In normal operation, it is expected that each hopper portion 25 would continuously have a quantity of asbestos material therein, although this is not essential for operation of the apparatus.

When an operative wishes to fill one of the bags 33, he initiates a discharge cycle, as follows.

Firstly, it is assumed that the valve 28 is in a closed position, as illustrated in Figure 4, and that the slide valve 31 is also in the closed position, with the closure member 60 urged fully to the right against the wall 63 (as seen in Figure 4). Thus, the bellows 52 is inflated, and a pneumatic cylinder (not shown) controlling operation of the closure member 60 is suitably pressurised.

Operation of the valves 28 and 31 during a discharge cycle is preferably carried out under the automatic control of a control unit (not shown). Upon initiating a discharge cycle, the bellows 56 is caused to inflate and the bellows 52 to deflate, thereby raising the cone 50 of the valve 28 to its maximum position, illustrated at 57, which is defined by the setting of the tie rods 58. The vibrator 59 is activated, to ensure the free flow of asbestos material down towards the bottom opening of the hopper portion 25, and into the chute 30.

After a predetermined time, which may be adjusted, the bellows 52 is inflated and the bellows 56 deflated, to pull the cone 50 down again into its closed position, where the seal 51 bears firmly against the sides of the hopper portion 25, in a fluid/ tight manner. The opening duration of the valve 28 is so adjusted that the chute 30 -only ever becomes part-filled with material.

It will be appreciated that, whilst the cone 50 is in its raised position, the pressure release #valve 65 senses the negative pressure which prevails in the hopper portion 25, and is temporarily present in the chute 30. Upon actuating the valve 65, the chute 30 is temporarily vented to atmosphere. This causes a small inrush of air on a reverse direction, into the hopper 25. Such an inrush may be effective to dislodge any bridging of material which may occur between the cone 50 in its lifted position 57, and the sides of the hopper portion 25.

Such bridging material is indicated by chain lines 66.

Preferably, the pressure release valve 65 is arranged to open by a small amount automatically, upon- sensing a predetermined pressure difference between ambient atmosphere and the inside of the chute 30. In such a way, the valve 65 may "feather" continuously, whilst the cone 50 is in its raised position, thereby to cause vibrations in the air pressure, in the region of the valve 28. We have found that the provision of such an automatically operating valve 65 significantly decreases the discharge time for which the valve 28 must remain open.

After the cone valve 28 has closed, there occurs a predetermined time delay, which may be adjustable (for example, in dependence upon the type of material being dispensed). During this time, the material falls into and settles in the chute, resting on the slide valve 31.

After this time delay, the respective pneum-atic cylinder of the slide valve 31 operates to withdraw the closure member 60 to the left (as seen), to open the slide valve 31 fully. The material in the chute 30 then drops down into the bag 33. After another predetermined but adjustable time delay, the slide valve 31 closes.

The respective ball valve 37, which-is initiallyin a closed position, may then be opened manually to place the lower portion of the chute 30 in communication with the interior of the hopper 8. Thus, the bag 33 is subject to the negative pressue prevailing in the hopper 8, to withdraw excess air from the bag 33. Thus, the bag 33 may be partially "vacuum packed". Moreover, any fine particles of asbestos remaining in the air are evacuated to the inside of the hopper 8, for further cycling.

When the bag 33 has been evacuated, the ball valve 37 is closed, and the neck of the bag is tied, to enclose the contents. The neck of the bag 33 is then removed from around the discharge orifice 32 of the chute 30.

As a modification to these last steps, the ball valve 37 may may remain open, whilst the bag 33 is tied and removed, thereby to suck back into the hopper 8 any asbestos particles which may be dislodged during the bag tying operation.

Once the bag 33 has been tied, it is then placed within another bag and tied again, for extra security against asbestos contamination. A new bag is then fitted to the chute 30, and the discharge cycle may be repeated.

When a new bag 33 is fitted to the discharge chute 30, the support 34 is raised to a high position. As the bag 33 is filled, the support automatically falls, whilst reacting some of the force exerted by the falling material.

Discharge of material 76 from the second hopper 9 is effected in just the same way as has been described above. Preferably, the hopper 9 is emptied regularly, to ensure that it does not overfill. However, should too much material 76 accumulate within the hopper 9, the sensor 77 sends its appropriate control signal on the line 78, to which the suction unit 7 responds, to switch off. The arrangement is preferably such that the suction unit 7 can not be switched on again, until the hopper 9 is emptied. Otherwise, if the hopper 9 were allowed to overfill, then the filter bags 75 may become damaged, as may the filtering units of the suction unit 7, should they become overloaded.

Thus, the illustrated plant provides means for collecting and discharging asbestos and asbestoscontaminated material, the plant being capable of continuous operation, including bagging of the material, in a particularly safe manner.

Although the illustrated plant is described as being for removing asbestos, it will be appreciated that it could also be used for the removal of any other debris. It may be constructed to any size.

However, a particular advantage of the illustrated embodiment is that, although it may provide a large scale unit (for example, the first hopper 8 may have a capacity of between 5 and 10 cubic metres, being adapted to operate with suction pipes of a diameter of the order 10 to 15 centimetres), the unit may nevertheless be portable.

The two/ part construction of the hopper 8 allows it readily to be carried by two skip-loading lorries.

The second hopper 9 and the suction unit 7 may also be carried by respective skip/ loading vehicles, and/or on trailers. Thus, the illustrated plant may be set up and dismantled very quickly, and operated continously to remove- asbestos or other debris from a site, with the minimum amount of downtime of the equipment from which the asbestos or debris is being removed.

A particular advantage of the illustrated plant is that the arrangement for discharging material from the hoppers 8 and 9 comprises very little in the way of wearing parts. In particular, with suitable choice of material for the bellows 52, 56, seal 51 and membrane 62, the bellows 52, 56 and the valves 28 and 31 may have a very long expected service life.

Although the working area 2 is provided with its own air displacement unit 4, this may be unnecessary in certain conditions, where the suction unit 7 itself may provide sufficient negative pressure within the tent 3, via the mill 11.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or to any novel combination, of the features disclosed in this specification and/or drawings, or to any novel one, or any novel combination, of the steps of any method or process disclosed herein.

Just by way of example, one novel combination that is of particular importance is the combination of a pressure release valve (such as 65, for example) between two discharge valves (such as 28 and 31, for example), to improve the rate of discharge of material through the discharge valves.

Claims (41)

1. A collection and discharge hopper for use in a pneumatic debris removal plant, the hopper comprising: an enclosed body; an inlet for debris-laden air at an upper portion of said body; an outlet for air at an upper portion of said body; a hopper portion at a lower portion of said body, for collecting debris deposited from air travelling through the body, in use; a discharge chute at the bottom of said hopper portion, for discharging debris from the hopper portion; a first valve adapted to open and close in a substantially fluid-tight manner, thereby to control discharge of debris from the hopper portion into the chute, through the first valve; and a second valve positioned below the first valve and adapted to open and close in a substantially fluid-tight manner, thereby to control discharge of debris from the chute, through the second valve.

2. A collection and discharge hopper according to Claim 1, wherein said first valve is disposed in a bottom portion of said hopper portion, and is adapted to open and close an opening at the bottom of said hopper portion, in a substantially fluidtight manner.

3. A collection and discharge hopper according to Claim 1 or 2, wherein said second valve is disposed in said chute.

4. A collection and discharge hopper according to Claim 1, 2 or 3, wherein said first valve comprises a bellows-operated cone valve.

5. A collection and discharge hopper as claimed in Claim 4, wherein said first valve comprises double-acting bellows, adapted to urge a cone of the valve positively into either a first, open position or a second, closed position, in dependence upon a selected direction of operation of the bellows.

6. A collection and discharge hopper according to any preceding claim, wherein said first valve comprises vibrator means for vibrating a cone of the valve.

7. A collection and discharge hopper according to any preceding claim, wherein said second valve comprises a membrane slide valve.

8. A collection and discharge hopper according to any preceding claim, including venting means for venting the chute to the ambient atmosphere at a position between the first and second valves.

9. A collection and discharge hopper according to Claim 8, wherein said venting means is adapted to operate automatically, in response to the pressure difference between the inside of the chute and the ambient atmosphere.

10. A collection and discharge hopper according to any preceding claim, comprising control means adapted to operate said valves in an auto matic predetermined sequence, to effect a dis charge cycle.

11. A collection and discharge hopper accord ing to Claim 10, including means for adjusting at least one of the timing periods of said predeter -mined sequence.

12. A collection and discharge hopper accord ing to any preceding claim, including valve means for selectively connecting the chute, at a portion downstream of the- second valve, to the inlet of the hopper.

13. A collection and discharge hopper according to any preceding claim, including means for securing a collection bag around the chute.

14. A collection and discharge hopper accord ing to any preceding claim, including support means for supporting a receptacle below a dis charge orifice of the chute.

15. A collection and discharge hopper accord ing to Claim 14, wherein said support means is of adjustable height.

16. A collection and discharge hopper accord ing to any preceding claim, including baffle means in an upper portion of said body, for deflecting and/or diffusing air entering the body through said inlet, in use.

17. A collection and discharge hopper according to any preceding claim, including filter means in an upper portion of said body, for filtering de bris from air passing through the body, in use.

18. A collection and discharge hopper accord ing to any preceding claim, wherein said body comprises two similar said hopper portions dis posed side-by-side, each having a respective dis charge chute with first and second valves as aforesaid.

19. A collection and discharge hopper accord ing to Claim 18, wherein said inlet and outlet are so arranged as to cause substantially symmetrical air flows above said two hopper portions.

20. A collection and discharge hopper according to any preceding claim, comprising two separable parts which are adapted to stack on one another.

21. A collection and discharge hopper accord ing to Claim 20, wherein said two parts are sepa rated at a level which passes between the or each first valve and its respective second valve.

22. A collection and discharge hopper according to Claim 20 or 21, wherein the or each chute is provided with a respective compression seal at the level of separation of said two parts.

23. A collection and discharge hopper according to any preceding claim, being adapted for transport by a skip-loading vehicle.

24. A collection and discharge hopper according to Claim 23 as appendant to Claim 20, 21 or 22, wherein each of said two parts is adapted for separate transport by a skip-loading vehicle,

25. A collection and discharge hopper according to any preceding claim, including level detection means for detecting the level of debris in the hopper and emitting a control signal when it detects that the debris has risen to a predetermined level.

26. A collection and discharge hopper, substantially as hereinbefore described with reference to Figures 2 to 4, or with reference to Figures 4, and 5, of the accompanying drawings.

27. A pneumatic debris removal plant, comprising a collection and discharge hopper according to any preceding claim, together with a suction unit adapted to draw debris-laden air through the hop- per, via said inlet and outlet.

28. A plant according to Claim 27r including a first said hopper adapted to collect debris and, downstream thereof, a second said hopper adapted to collect debris which has not collected in the first hopper.

29. A plant according to Claim 28, wherein said second hopper is in accordance with Claim 25, and the suction unit is adapted to switch off, in response to said control signal.

30. A plant according to Claim 27, 28 or 29, housed within a portable enclosure.

31. A plant according to Claim 30, wherein said enclosure comprises a tent

32. A plant according to Claim 30 or 31, wherein said suction unit is provided on its exhaust with an absolute filter which is disposed outside the enclosure.

33. A plant according to Claim 30, 31 or 32, including pressure means for maintaining said enclosure under negative pressure.

34. A plant according to Claim 33, wherein said pressure means has an exhaust provided with an absolute filter which is disposed outside the enclosure.

35. A plant according to any one of Claims 27 to 34, including a mill for crushing debris, which mill is connected to said inlet of the hopper.

36. A pneumatic debris removal plant, substantially as hereinbefore described with reference to the accompanying drawings.

37. A method of collecting debris, comprising the steps of passing debris-laden air into a hopper according to one of Claims 1 to 26, collecting the debris in the or each said hopper portion, and discharging the collected debris into a receptacle, via the discharge chute of the or a respective one of the said hopper portion(s).

38. A method according to Claim 37, wherein said debris contains asbestos.

39. A method according to Claim 37 or 38, wherein said receptacle comprises a bag.

40. A method according to Claim 39, including the subsequent step of wrapping said bag within another outer bag.

41. A method of collecting debris, substantially as described herein.