GB2457068A

GB2457068A - Aggregate washing apparatus

Info

Publication number: GB2457068A
Application number: GB0801833A
Authority: GB
Inventors: Soren Ingemann Jensen; Philip Mcintyre
Original assignee: WATER MAIDEN HOLDINGS Ltd
Current assignee: WATER MAIDEN HOLDINGS Ltd
Priority date: 2008-01-31
Filing date: 2008-01-31
Publication date: 2009-08-05
Anticipated expiration: 2028-01-31
Also published as: GB0801833D0; GB2457068B

Abstract

An aggregate washing machine 10, such as for reclaiming the constituents of unset concrete, features a screen 30 over which fluid aggregate passes under gravity, from a hopper 20, leaving separated out larger particles 34, on the topmost surface of the screen 30. Finer particles pass into a tank 40, and then into a cyclone or centrifuge device 70, which separates finer aggregate from the remaining fluid. The device may be used for reclaiming or recycling mixed but unset excess concrete from building jobs.

Description

AN AGGREGATE WASHING APPARATUS

The present invention relates to an aggregate washing apparatus for removing unwanted materials from the aggregate. In particular, the invention concerns the reclaiming of constituent materials from unset concrete. The invention also relates to a method of removing unwanted materials from aggregate using an aggregate washing apparatus.

When constructing new buildings or roads or the like, it is often the case that too much concrete is mixed for the job to be undertaken, resulting in an excess of concrete that is surplus to the construction requirement. If this concrete is allowed to set, it must be broken up in order to reclaim the constituent materials of sand and stone, if these materials are to be reusable. To avoid this inconvenience, the concrete industry has preferred to reclaim the constituent materials from the excess concrete before it sets, using a concrete washing apparatus. A known concrete washing apparatus comprises a hopper into which excess concrete is tipped from a concrete lorry. A stream of water is directed into the hopper from a hose pipe in order to wet the concrete before it is fed into an auger screw. As the wet concrete passes through the rotating auger screw, the solid concrete particles, that is stones and sand, become separated from the water and are collected all together at the opposite end of the auger screw for storage andlor re-use in manufacturing fresh concrete.

Whilst the wet concrete passes through the auger screw, the water collects in a tray of the apparatus that is located beneath the screw, for storage or re-use elsewhere. This type of apparatus is in widespread use in the concrete industry.

However, it has the following drawbacks. The concrete can become clogged in the flights of the auger screw and if it is allowed to set, this can significantly reduce the efficiency of the apparatus and perhaps even cause it to become jammed. If the concrete were allowed to set, it would need to be cleaned and scraped off the screw flights. As such, this machine needs constant cleaning to avoid this. The reliance on moving machinery parts also means that the apparatus is relatively expensive to manufacture and service.

The present invention aims to address one or more of the above problems of the

prior art at least to an extent.

According to a first aspect of the invention, there is provided an aggregate washing apparatus for removing unwanted materials from the aggregate, the apparatus comprising a perforated screen having a first end and a second end, a first portion of the perforated screen having at least one perforation of a first size and a second portion of the perforated screen having at least one perforation of a second size, that is smaller than the first size, the first end being arranged to receive an amount of aggregate to be washed, the perforated screen being arranged so as to allow the aggregate to flow over the screen from the first end to the second end under the effect of gravity; a water supply arranged to direct a stream of water onto the perforated screen for washing the concrete as it passes from the first end to the second end; wherein at least a portion of the washed aggregate passes through the at least one perforation in the first portion of the perforated screen; a receptacle arranged to receive the washed aggregate and water that passes through the at least one perforation in the first portion of the perforated screen to form a slurry therein and a centrifugal separator disposed in fluid communication with the receptacle for separating the washed concrete and water slurry into particles sized over or under a pre-determined particle size such that particles sized above the pre-determined size exit the centrifugal separator onto the second portion of the perforated screen such that at least a portion of the washed aggregate slurry particles pass through the at least one perforation in the second portion of the perforated screen and into the receptacle. In an embodiment, the aggregate may be unset concrete.

This apparatus has the advantage that the aggregate is washed in a simple yet effective manner, without complicated moving parts or high power consumption. Furthermore, the washed solid particles that are reclaimed from the aggregate are also size sorted or graded at least to an extent rather than simply being collected together. In the washing process, the larger stones become separated from the sand present in the aggregate slurry, since the stones cannot pass through the perforated screen whilst the smaller particles can. Furthermore, the water that is separated from the sand in the centrifugal separator can be immediately reused in the washing of the next batch of aggregate. The simplicity of the apparatus also makes it cheaper to manufacture than the known apparatus.

In an embodiment, a pump may be employed in the receptacle for agitation of the washed aggregate slurry in the receptacle. Where the aggregate is concrete, the agitation prevents it from becoming set. However, for all aggregates the agitation ensures that any silt or sand does not settle at the bottom of the tank but is processed through the centrifugal separator. Alternatively or in addition to the pump, an agitator may be employed for this purpose.

In an embodiment, the apparatus may comprise a plurality of water supplies, each arranged to direct a stream of water at spaced locations on the perforated screen. This has the advantage of ensuring that plenty of water is directed at the aggregate as it flows over the screen, washing it efficiently and assisting its passage down the screen. However, if the water is directed up the screen, it can also be used to slow down the passage of the washed stones to ensure that they are properly washed. Furthermore, the water supplies may be directed to the back of the screen in order to clean out the perforations and prevent them from becoming clogged. A significant amount of the water passes through the perforations in the screen and thus helps to keep the slurry in the receptacle wet, preventing it from drying out and, in the case of concrete, setting.

In an embodiment, the perforated screen may be gently sloped from the first end to the second end thereof, such that the aggregate does not simply fall off the screen but is able to flow over it, assisted by the water flow. In an embodiment, the perforated screen may be curved from the first end to the second end thereof in a gentle "S" shape. In another embodiment, the screen may have a wave-profile shape.

In an embodiment, at least one of the water supplies may be in fluid communication with the centrifugal separator for reuse of washed aggregate slurry particles that are sized under the pre-determined size, also known as the "cut-off point" of the centrifugal separator. In an embodiment, the cut-off point size may be fifty micrometres. In this case, the material exiting the centrifugal separator containing particle sizes of fifty micrometres or less will comprise of cementatious water in the case of concrete, or simply very small particles held in suspension in the water for other types of aggregate, that can be immediately reused in washing the next batch of aggregate that is flowing down the screen. The perforated screen may comprise a plurality of perforations of the first pre-determined size and a plurality of perforations of the second pre-determined size. The perforated screen may comprise of two separate screens, a first screen having perforations of the first pre-determined size and a second screen disposed adjacent the first screen, having a plurality of perforations of the second pre-determined size. The apparatus may further comprise a hopper disposed at the first end of the perforated screen for receipt of an amount of aggregate to be washed, the hopper comprising an opening for the egress of excess aggregate onto the perforated screen. In this manner, a lorry can simply tip the excess concrete or other aggregate into the hopper from where it can be washed.

According to a second aspect of the invention, a method of removing unwanted materials from aggregate using the apparatus of the first aspect of the invention comprises receiving an amount of aggregate to be washed onto the perforated screen at the first end thereof, directing a stream of water onto the screen in order to wash the aggregate, wherein washed aggregate slurry particles of a size below the first pre-determined size pass through the perforated screen and into the receptacle; pumping the washed aggregate slurry in the receptacle to the centrifugal separator, separating the washed concrete slurry into particles sized above the pre-determined size and particles sized below the pre-determined size, directing the particles sized over the pre-determined size onto the second portion of the perforated screen for re-washing and directing the particles sized under the pre-determined size into at least one of the supplies of water for re-use in washing the aggregate. The aggregate may be unset concrete.

The method further comprises the step of operating a pump and/or an agitator in the receptacle in order to agitate the washed aggregate slurry present in the receptacle to prevent the setting of sand/cement in the slurry. The method may further comprise the step of collecting the washed aggregate particles at the second end of the perforated screen for use in the making of fresh concrete or other appropriate use.

These and other aspects of the invention will become more readily apparent to the skilled person upon reading the following description of preferred embodiments of the aggregate washing apparatus, together with the accompanying drawings, in which: Figure 1 is a schematic side view of an embodiment of an apparatus according to the invention; Figure 2 is a schematic front view of the apparatus of Figure 1; and Figure 3 is a schematic side view of a second embodiment of the invention.

Figure 1 shows an embodiment of an aggregate washing apparatus 10. This embodiment is described in terms of a concrete washing apparatus although other types of aggregate could be used. The apparatus 10 includes a hopper 20 at an upper end thereof, into which excess unset concrete can be tipped. A supply of water 22 is directed at the open end of the hopper, in order to wet and loosen the concrete in the hopper. A front side 25 of the hopper contains an opening 28 from which the wet concrete mixture is egressed from the hopper.

The hopper 20 is disposed over a first or upper end 32 of a perforated screen 30. The perforated screen 30 comprises a steel sheet (e.g. stainless or galvanised steel) that is bent into a curved gentle S-shape (seen in Figure 1) or wave-profile (an example of which is seen in Figure 3) such that concrete particles can travel down the screen at a suitable pace to be washed and to allow material to pass through the perforations in the screen without simply dropping towards the bottom end 34 of the screen. The screen 30 is alternatively made from a polymeric material. The perforated screen 30 is positioned beneath the hopper such that the concrete mixture exiting the hopper is able to flow down the screen towards the bottom end thereof. The screen includes a plurality of perforations 35 that are of a first pre-determined size. In the present embodiment, the perforations are approximately 2.3mm in diameter, meaning that any stones that are larger than this in diameter will not pass through the perforations but will flow down the perforated screen 30 to be collected at the bottom end 34 thereof. Meanwhile, any smaller stones, sand, cement and slurry may pass through the perforations 35. The screen 30 is disposed over a receiving tank or receptacle 40. Any material passing through the perforations 35 of the perforated screen 30 will land in the receiving tank 40. The sides of the tank 40 are steep in order to prevent the concrete material piling up the sides of the tank. Instead, the concrete particles and water slurry settle at the bottom of the tank 40. A pump andlor agitator 60 is operated to agitate the concrete material in the bottom of the tank 40 in order to prevent it from setting. The pump is also used to transfer the slurry material from the bottom of the tank 40 to a hydrocyclone or centrifugal separator 70. A plurality of water jets 50 are directed onto the perforated screen in order to wash the concrete as it flows from the hopper 20 down the screen. Waterjets 50 can also be directed towards the back of the perforated screen 30 to clean out the perforations 35 and prevent them from becoming clogged. The jets of water 50 are also used to encourage the particle matter through the perforations of the screen 30 and to ensure a sufficient amount of water enters the receiving tank 40 so as to prevent the concrete slurry from setting and also to ensure its safe fluid transport from the tank to the hydrocyclone 70.

The hydrocyclone 70 is an off-the-shelf component as is known to the skilled man in the art. The hydrocyclone essentially comprises a centrifugal separator into which the diluted concrete slurry material may be fed in order to separate out particles of below a pre-determined size from those of particles above a pre-determined size. The hydrocyclone comprises an overflow exit 82 and an underfiow exit 84. The diameters of these exits can be chosen to limit the particle sizes that may pass therethrough. In the present embodiment, the overflow exit diameter is chosen such that only particle matter of a size below fifty micrometres may pass through the overflow exit of the hydrocyclone.

This size is chosen to ensure that all the sand particles in the slurry pass to the underfiow 84 and that only cementatious water passes to the overflow 82. All other particles will exit the hydrocyclone through the underfiow exit 84. The hydrocyclone 70 is disposed such that its underfiow exit 84 is positioned above a second portion 80 of the perforated screen that is positioned directly adjacent the first portion of the perforated screen 30. The position of the hydrocyclone is adjustable with respect to the perforated screen 80 so as to be able to adjust the angle at which the underfiow material hits the perforations 85 in the screen. In this way the optimum angle can be achieved for efficient operation of the apparatus. The second portion 80 of the perforated screen 30 includes a plurality of small perforations 85 that are of a smaller size than those of the perforations 35. Any particle matter passing through the perforations 85 lands in the receiving tank 40 as before. The water jets 50 that are directed onto the front screen 30 may also be directed onto the second portion 80 to assist passage of the slurry down the perforated screen. Again, any solid particle matter that is too big to pass through the perforations 85 will be collected at the bottom of the screen 80 for re-use. Meanwhile, cementatious water having a particle size of less than ten micrometres exits the hydrocyclone through the overflow and is directed towards a water jet 50 for direct re-use of the water in washing the next batch of concrete flowing down screen 30.

The receiving tank 40 includes an overflow pipe 42 for water, in the event that the tank becomes too full, the overflow pipe directing the surplus water into a storage tank for use in the making of fresh concrete. In addition, water can be pumped into the tank 40 from another source, such as the storage tank, in order to keep the water levels high enough. The water is piped via conduit 43 into the top of the tank 40. Circulation of the water in and out of the tank helps to agitate the solid matter in the tank to prevent it from setting.

In an alternative embodiment (not shown), the screens 30, 80 may be separate from each other. The water jets 50 may in either embodiment be implemented through the use of pressurised water sprays or they may simply be implemented using pipes whose outflow exits directly onto the screen(s). The hydrocyclone is preferably positioned such that a sufficient gap is left between the underfiow exit 84 thereof and the perforated screen 80 in order that the material exiting the underfiow does not back up and jam the hydrocyclone 70. In a further embodiment, multiple hydrocyclones 70 may be used in order to increase the level of grading of the solid material into finer and finer particle sizes. The hydrocyclones 70 may be of differing sizes so as to have different material grading levels. In such an embodiment, each hydrocyclone preferably has its own screen or portion of perforated screen with suitably sized perforations therein in order for the finer slurry material to pass therethrough and to be recycled through the concrete washing apparatus. The term "perforations" and "perforated screen" will be understood to cover various possibilities of perforated screen, including but not limited to a gridded screen, a wire mesh screen or a drilled sheet.

The term "aggregate" will be understood to include unset concrete as well as other types of "dirty" aggregate that needs to be washed and/or graded so that the virgin materials can be used in e.g. the construction industry. In an embodiment, the aggregate is marine aggregate from which it is desired to remove silt and other unwanted materials and to separate stones from sand. In another embodiment the aggregate is crushed quarry aggregate.

It will be apparent to the skilled person that variations on the above apparatus designs will be possible without departing from the scope of the invention as defined in the accompanying claims.

Claims

I. An aggregate washing apparatus for removing unwanted material from the aggregate, the apparatus comprising a perforated screen having a first end and a second end, a first portion of the perforated screen having at least one perforation of a first size and a second portion of the perforated screen having at least one perforation of a second size, that is smaller than the first size, the first end being arranged to receive an amount of aggregate to be washed, the perforated screen being arranged so as to allow the aggregate to flow over the screen from the first end to the second end under the effect of gravity; a water supply arranged to direct a stream of water onto the perforated screen for washing the aggregate as it passes from the first end to the second end; wherein at least a portion of the washed aggregate passes through the at least one perforation in the first portion of the perforated screen; a receptacle arranged to receive the washed aggregate and water that passes through the at least one perforation in the first portion of the perforated screen to form a slurry therein, and a centrifugal separator disposed in fluid communication with the receptacle for separating the washed aggregate and water slurry into particles sized over and under a pre-determined particle size such that the particles sized above the pre-determined size exit the centrifugal separator onto the second portion of the perforated screen such that at least a portion of the washed aggregate slurry particles pass through the at least one perforation in the second portion of the perforated screen and into the receptacle.
2. The apparatus of claim 1 in which the aggregate is unset concrete.
3. The apparatus of claim 1 or claim 2, further comprising a pump disposed in the receptacle for agitation of the washed aggregate and water slurry in the receptacle.
4. The apparatus of claim 1 or claim 2 comprising a plurality of water supplies, each water supply being arranged to direct a stream of water onto the perforated screen at spaced locations thereon.
5. The apparatus of claim I further comprising a hopper disposed at the first end of the perforated screen for receipt of an amount of aggregate to be washed, the hopper comprising an opening for egress of the aggregate onto the perforated screen.
6. The apparatus of claim I in which the perforated screen is gently sloped from the first end to the second thereof.
7. The apparatus of claim 1 in which the perforated screen is curved from the first end to the second end thereof in a gentle "S" shaped profile.
8. The apparatus of claim 1 in which the perforated screen comprises a wave-shaped profile.
9. The apparatus of claim 4 in which at least one of the water supplies is in fluid communication with the centrifugal separator for reuse of water containing washed aggregate particles sized under the pretetermined size exiting the centrifugal separator.
10. The apparatus of claim 1 in which the first portion of the perforated screen comprises a plurality of perforations of the first pre-determined size and the second portion comprises a plurality of perforations of the second pre-determined size.
11. The apparatus of claim 10 in which the second portion of the perforated screen is provided as a separate perforated screen from the first portion of the perforated screen.
12. The apparatus of claim 1 in which a location of the centrifugal separator is adjustable with respect to the perforated screen.
13. The apparatus of claim I or claim 11, in which the centrifugal separator is a hydrocyclone.
14. The apparatus of any of claims 6-8 in which the perforated screen is adjustable in profile.
15. A method of washing aggregate using the apparatus of claim 1, the method comprising receiving an amount of aggregate to be washed onto the perforated screen at the first end thereof, directing a stream of water onto the screen in order to wash the aggregate, wherein washed aggregate and water slurry particles of a size below the first pre-determined size pass through the perforated screen and into the receptacle; pumping the washed aggregate and water slurry in the receptacle into the centrifugal separator, separating the washed aggregate and water slurry into particles sized above a pre-determined size and particles sized below the pre-determined size, directing the particles sized over the pre-determined size onto the second portion of the perforated screen for re-washing and directing the particles sized under the pre-determined size into at least one of the supplies of water for re-use in washing the aggregate.
16. The method of claim 15 in which the receptacle further comprises a pump, the method comprising the step of operating the pump to agitate the washed aggregate and water slurry present in the receptacle to prevent setting thereof.
17. The method of claim 15, further comprising adjustably controlling a position of the centrifugal separator with respect to the perforated screen.
18. The method of claim 15 comprising the further step of collecting the washed aggregate particles at the second end of the perforated screen for re-use.
19. The method of claim 15, comprising the further step of adjustably controlling the profile of the perforated screen.
20. The method of any of claims 16 to 20 in which the aggregate is unset concrete.
21. A control system for operating an aggregate washing apparatus according to the method of any of claims 15-20.