GB2339783A

GB2339783A - Recovery and re-use of material from post-consumer waste

Info

Publication number: GB2339783A
Application number: GB9815745A
Authority: GB
Inventors: George Louis Bridge
Original assignee: PLASALLOY Ltd
Current assignee: PLASALLOY Ltd
Priority date: 1998-07-21
Filing date: 1998-07-21
Publication date: 2000-02-09
Also published as: GB9815745D0

Description

2339783 A proicess---and apparatus for recovery and re-use of-mat-erial

from Post- consum This invention relates to a process and apparatus for recovery and re-use of material from post-consumer waste.

An increasing number of products are packaged in containers formed of high grade material, especially when the containers are intended to contain food products, and it is desirable to recover such material from post-consumer waste so that the material may be re-used in industrial processes.

In order that such recovered material is in a condition suitable for reuse, it is necessary to thoroughly clean the material to remove contaminants, such as residual food products.

According to the present invention, there is provided a process for recovery and re-use of material from postconsumer waste including granulating the waste to form granules and subjecting the granules to a washing process.

Following is a description, by way of example only, and with reference of the accompanying drawings, of one method of carrying the invention into effect.

2 In the drawings:- Figure 1 is a schematic diagram of one embodiment of a process for recovery and re-use of material from postconsumer waste in accordance with the present invention, Figure 2 is a diagrammatic representation of apparatus for carrying out high intensity pulse washing in the process illustrated in Figure 1, Figures 3 is a diagrammatic representation of a washing panel of the apparatus shown in Figure 2.

Figure 4 is a view in the direction of arrow A of Figure 3.

Figure 5 is a plan view of a baffle plate of the washing panel shown in Figure 3, and Figure 6 is a plan view of a rotor associated with the panel shown in Figure 3.

Referring now to Figure 1 of the drawings, there is shown one embodiment of a process for recovery and re-use of Polystyrene from post-consumer waste in the form of Polystyrene yogurt containers.

3 Generally, yogurt containers are formed of Polystyrene and provide an open top which is closed by means of Aluminium foil which is united with the Polystyrene at a rim of each container. The waste comprises used containers which are coated with non-consumed yogurt and containers containing yogurt which has passed its sell-by-date. The Polystyrene and Aluminium materials are of high grade in order to satisfy the stringent conditions for packaging of food products and it is desirable to recover the materials for re-use.

The process shown in Figure 1 comprises a reception/ storage stage in which waste in the form of Polystyrene containers contaminated with Aluminium and with residual yogurt are collected and sorted; a wet process stage in which the sorted waste is macerated, washed, shredded, granulated, pulse washed and dried; a dry separation stage in which the Aluminium is separated from the Polystyrene; and a finishing stage in which clean particulate Polystyrene, free of its Aluminium content, is metered into a blender where colour master batches and desiccants are added and the blended particulate Polystyrene is then extruded into sheet form.

The reception/ sorting stage includes a reception trough 10 for receiving contaminated waste material, an elevating conveyor 11 and a sorting platform 12 for receiving the waste material from the conveyor 11 at an elevated location such that an empty container 13 may be located there below.

4 An operator manually removes any obvious unwanted contaminants, these being removed from the sorting platform 12 into the container 11.

The waste material is fed from the reception/ storage stage by means conveyors 14,15 to the wet process stage which comprises a maceration unit 16 in which containers containing yogurt are punctured and drained of their contents and these, together with already empty containers, are fed to a primary wash unit 17 having a drainage feedback 18 whereby slurry collected from the washed containers is drained and fed to a tanker 19, which also receives drained yogurt from the maceration unit 16. The contents of the tanker 19 are deployed for agricultural use. Af ter dewatering, the waste material is fed to a coarse shredder 20 which reduces the waste material to particles of approximately 20 mm. The outfall of the shredder 20 is directed to an input of a granulator 21, rotating cutters of which further reduce the particle size of the waste material to approximately 3 mm. The particles are then delivered by an elevating conveyor 22 to a high density pulse washing unit 23, details of which will be described later with reference to Figures 2,3 and 4. The particles are thoroughly washed in the pulse washing unit 23, any heavy contaminants remaining at this stage being separated and removed and collected in a tank 24. The cleaned particles then pass through a two stage tunnel dryer 25 in which all residual wash fluid is removed.

The dry separation stage includes an air curtain separation unit 26 to which the particles are conveyed pneumatically from the tunnel dryer 25, whereby the Aluminium particles, being lighter than the Polystyrene particles, are drawn off from upper levels of the unit 26 and collected in a silo 27. Further separation is effected by means of a cyclone separator 28, additional Aluminium particles being drawn off by the separator 28 and fed to the silo 27. Batches of Aluminium particles are collected from the silo 27 in a baler 29 which compacts the Aluminium particles into coarse bales 30. The clean Polystyrene particles, free of Aluminium, are fed to a silo 31.

In the finishing stage, batches of the Polystyrene particles are drawn from the silo 31 into a metering screw shredder 32 and then into a blender 33 where colour master batches and desiccants are added and the batch is then metered by a further a metering screw feeder 34 to an extruder feed silo 35 which delivers the Polystyrene material to an extruder 36. The extruder 36 further blends and heat conditions the Polystyrene so that it can be extruded in sheet form. Finishing rollers 37 then serve to reduce the sheet to a final thickness, which will generally be selected in the range 6 to 15 mm, depending on product application. The sheets are parted by a cutter 38 and are trimmed to a final dimension, an industry standard being 8 ft x 4 ft.

6 Referring now to Figures 2 to 4 of the drawings, the high intensity pulse washing unit 23 comprises a tank 39 having a feed chute 40 located below the upper end portion of the elevating conveyor 22. The tank 39 comprises a first weir chamber 41 and a second weir chamber 42 each having corresponding first and second weir plates 43,44. A lower portion of the first weir plate 43 is raised from the bottom of the tank 39 and a lower portion of a conveyor 45 extends below the first weir plate 43 into the first and second weir chambers 41,42. The first weir chamber 41 is provided with a distribution box 46 which controls flow of flotation fluid 47 across the weir chambers 41,42 and progressively over the first and second weir plates 43,44. The flotation fluid 47 is recirculated by means of a pump 48 the fluid being directed through a filter 49. The weir chambers 41,42 may be drained through an outlet 50 containing a valve 51.

The tank 39 also comprises a series of chambers 52 and a helical conveyor 53 extending coaxially within a tube 54, the tube 54 extending through the chambers 52 and being upwardly inclined from a lower end portion which is located adjacent the second weir plate 44 to an upper end portion which extends upwardly and outwardly from the tank 39, there being an upper outlet of the tube 54, as shown at 55.

The tube 54 is provided with a series of radial inlets 56 and radial outlets 57, the pairs of inlets and outlets 56,57 7 each being located in a corresponding one of the chambers 52.

Each inlet 56 comprises a housing 58 having a baffle plate 59 comprising a plurality of apertures 60 and a plurality of spray rubes 61 each in communication with a corresponding one of the apertures 60. Each housing 58 also includes a rotor 62 which is adapted to rotate on a central longitudinal axis of the corresponding housing 58. Each of the inlets 56 has connected thereto a corresponding one of a plurality of inlet tubes 63 and each of the chambers 52 is provided with a corresponding one of a plurality of drain tubes 64 and wash liquid is circulated from each of the chambers 52 through the corresponding inlet and outlet tubes 63,64 by means of a corresponding one of a plurality of pumps 65 and filters 66.

The arrangement is such that contaminated granular material is received from the granulator 21 by means of the conveyor 22, is delivered into the chute 40 and collects on the flotation fluid 47 in the first weir chamber 41. The flotation fluid 47 is fed at a high volume by means of the flow distribution box 46 the function of which is to introduce the flotation fluid 47 in an evenly distributed manner such that it moves forward in an even flow pattern through the weir chambers 41 and 42. The gravity of the flotation fluid 47 is adjusted specifically to ensure that the reclaimed plastic particles float at or near the surface 8 of the fluid 47 and are thus carried forward by the fluid 47 over the first weir plate 43, the height of which is adjustable to facilitate setting up of the correct flow pattern in the weir chambers 41,42.

In the first weir chamber 41, any metals or similar heavy materials present in the waste material sink to the bottom of the chamber 41 and are progressively removed by the extraction conveyor 45 and collect in the tank 24. The flights of the conveyor 45 move rapidly and continuously through the weir chambers 41,42 and propel the flotation fluid 47 towards the first weir plate 43. The fluid 47 thus passes over and below the first weir plate 43, the upper stream carrying the waste materials with it into the second weir chamber 42. The entirety of the granular material is carried over the second weir plate 42 and is received in the washing tube 54.

The granular material is carried by the conveyor 53 upwardly through the tube 54 and rotates within the tube 54. Wash fluid is pumped into the radial inlet 56 in each of the chambers 52 causing the rotors 62 to rotate and impart a swirling motion to the wash fluid which has the effect of violently agitating the particles of the granular material as they are being conveyed along the tube 54 by the helical screw conveyor 53. The particles are very thoroughly washed by this process and contaminants are detached from the surfaces of the particles and carried away in the wash 9 fluid. The fluid drains from the tube 54 into the chambers 52 of the washing tank 39. The fluid is continuously recirculated by means of the high pressure circulation pumps 65 and delivered back to the inlets 56 of the tube 54 at high pressure. The filters 66 eliminate particulate debris arising from the washing process.

The pitch of the flights of the screw conveyor 53 and the spacing of the inlets and outlets 56, 57 of the tube 54 are such that, in passing along the tube 54, the particles are alternately allowed to settle and then subjected to very violent agitation.

The wash tank 39 is provided with an inlet, as shown at 67 at an end portion thereof remote from the weir chambers 41,42. The arrangement is such that dirty wash fluid is withdrawn steadily from the feed end of the wash tank and this is balanced by the introduction of clean fluid at the exit end through the inlet 67. There is thus a progression from feed end to exit end whereby the particles encounter increasingly clean wash fluid.

The provisin of the high intensity pulse washing unit thus ensures that the waste material is subjected to an intense cleaning process such that the material can be re-processed in conventional equipment, such as extruders.

It will be appreciated that products other than containers for food products may be recovered by the process and apparatus in accordance with the present invention. For example, the process and apparatus may be used for recovering material used for packaging pharmaceutical products.

Claims

1. A process for recovery and re-use of material from post-consumer waste including granulating the waste to form granules and subjecting the granules to a washing process.

2. A process as claimed in Claim 1 wherein the washing process includes agitating the granules.

3. A process as claimed in Claim 2 wherein the granules are moved progressively through a series of stations at which they are agitated so that the granules are alternately allowed to settle and then subjected to agitation.

4. A process as claimed in Claim 3 wherein, prior to agitation, the granules are deposited on a liquid.

5. A process as claimed in Claim 4 wherein the liquid is directed over a weir.

6. Apparatus for carrying out the process as claimed in any one of Claims 1 to 5 comprising a plurality of stations for agitating the granules and a conveyor for moving the granules progressively through the stations.

12

7. Apparatus as claimed in Claim 6 wherein each of the stations comprises means for directing a washing fluid into contact with the granules.

8. Apparatus as claimed in Claim 7 wherein the said means comprises a plurality of tubes.

9. Apparatus as claimed in Claim 8 wherein each of the stations includes a rotor for agitating the cleaning fluid.

10. Apparatus as claimed in any one of Claims 6 to 9 wherein there is provided a weir chamber for containing a flotation fluid, a weir and means for effecting flow of the flotation fluid towards the weir whereby when the granules are deposited on the flotation fluid they are carried over the weir to the conveyor.

11. A process and apparatus for recovery and re-use of material from postconsumer waste substantially as hereinbefore described and as illustrated in the accompanying drawings.