WO2013102240A1

WO2013102240A1 - Processing of pre-treated mixed waste

Info

Publication number: WO2013102240A1
Application number: PCT/AU2013/000001
Authority: WO
Inventors: Ewan HARPER; Patrick Cho Chia YUEN; Marc Rene Stammbach; Chris LIVINGSTONE
Original assignee: Sita Australia Pty Ltd
Priority date: 2012-01-03
Filing date: 2013-01-02
Publication date: 2013-07-11
Also published as: AU2013207312B2; AU2013207312A1

Abstract

Disclosed herein is a processing plant (10) and a method for processing residual material from upstream mixed waste treatment processes. The plant (10) a comminutor, preferably in the form of a flail mill (12), for comminuting residual material input into the plant to reduce its average particle size. Downstream of the flail mill (12) is a first screen (14) having openings with a maximum dimension of less than around 30mm. A second vibratory mesh screen (16) may be provided downstream of the first screen (14) to screen material that is caught by the first screen (14). The second screen (16) may have openings with a greater maximum dimension than that of the first screen (14). Conveyors, such as continuous belt conveyors (18) and augers (20), may be provided to move material through the plant (10).

Description

"Processing of pre-treated mixed waste"

The present disclosure relates to processing of residuals from upstream mixed waste treatment processes, such as municipal waste, commercial and industrial waste, and contaminated food and green waste treatment processes, that would otherwise go to landfill. The process disclosed herein has been developed particularly for the production of material that is suitable for use in agriculture and/or in the remediation of mine sites.

Mixed waste is typically processed by a variety of to classify the waste into various fractions, each of which may be subjected to specific treatments. For example, the waste may be sorted^' using a combination of manual sorting, size-based sorting, density-based sorting, and metal-based sorting. Recyclable materials, such as plastics, metals and paper-based products recovered by the sorting are typically recycled. The waste often also includes a relatively large proportion of organic material and other materials not suitable for recycling. The organics are typically treated by digestion, screening and drying.

The non-recyclable "dry" material remaining as a residual after the aforementioned processes is typically sent to landfill, which is undesirable. The residual material typically includes glass residuals and mixed "dry" organic residuals containing glass/metal/plastics (GMP). However, the residual material is typically free from larger particles, which are generally removed by upstream processes including screening with screens having openings of around 50mm. It would be advantageous if the residual material could be further treated to render it suitable for recycling or re-use.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

In a first aspect, the present disclosure provides a method of processing residual material from upstream mixed waste treatment processes, said method comprising: comminuting the residual material to reduce the average size of particles contained in the residual material; and

screening the residual material with a first screen having openings with a maximum dimension of less than around 30mm.

The first screen may have openings with a maximum dimension of less than around 20mm, less than around 12mm, less than around 10mm, or of around 5mm.

The first screen may be a mesh having rectangular or square openings. Alternatively, the first screen may have circular openings. The first screen may be vibratory or rotary.

Residual material that is caught by the first screen may be returned to the comminuting step for reprocessing. Prior to being returned to the comminuting step, the residual material caught by the first screen may be passed through a second screen having openings of greater maximum dimension than the first screen. Material passing the second screen may be returned to the comminuting step and material caught by the second screen may be redirected to another process, such as for use as fuel or for disposal.

Prior to the comminuting step, the residual material may be subjected to a magnetic field to remove ferrous material.

The comminuting step may comprise passing the residual material through a mill. The mill may, for example, be a ripple mill, a hammer mill or a flail mill.

Residual material passing the first screen may comprise less than 2.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm. Such glass, metal and rigid plastics may be of a size, shape (e.g. glass shards), or type that might cause damage or injury to humans, animals, plants or soil. Residual material passing the first screen may comprise less than 1.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm.

Residual material passing the first screen may comprise less than 0.25 dry weight percent of plastic film having a maximum dimension greater than 5mm. Residual material passing the first screen may comprise less than 0.2 dry weight percent of plastic film having a maximum dimension greater than 5mm.

Residual material passing the first screen may have a maximum particle size of

16mm.

Residual material passing the first screen may be stored for use in agriculture and/or in the remediation of mine sites. Residual material passing the first screen may be mixed with other material, such as compost, to produce a product comprising less than 2.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm. The product may comprise less than 1.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm. The product may comprise less than 0.25 dry weight percent of plastic film having a maximum dimension greater than 5mm. The product may comprise less than 0.2 dry weight percent of plastic film having a maximum dimension greater than 5mm. The product may have a maximum particle size of no more than 16mm.

In another aspect, there may be provided a system for performing the method of the first aspect above, said system comprising:

a comminutor for performing said comminuting step; and

a said first screen.

Embodiments of the presently disclosed method and system will now be described by way of example only, with reference to the accompanying representations, in which:

Fig. 1 is a schematic illustration of a processing plant for processing residual material from upstream mixed waste treatment processes;

Fig. 2 is a photograph of residual material for input into the processing plant of

Fig. 1;

Fig. 3 is a photograph of residual material rejected by the second screen of the processing plant of Fig. 1 ; and

Fig. 4 is a photograph of product produced by the processing plant of Fig. 1. Referring to the representations, and initially to Fig. 1, there is shown a system, in the form of a processing plant 10, for performing a method of processing residual material from upstream mixed waste treatment processes. The plant 10 comprises a magnet 11 for creating a magnetic field to remove ferrous material from feed residual material. Downstream of the magnet 11 is a comminutor, in the form of a flail mill 12, for comminuting residual material input into the plant to reduce its average particle size. Downstream of the flail mill 12 is a first vibratory mesh screen 14 having openings of around 5mm x 5mm. A second vibratory mesh screen 16 is provided downstream of the first screen to screen material that is caught by the first screen 14. The second screen has openings of around 12mm x 12mm. Conveyors, such as continuous belt conveyors 18 and augers 20, are provided to move material through the plant 10.

In use, residual material from an upstream waste treatment process is fed into the plant 10. A photograph of typical residual material fed into the plant 10 is shown in Fig. 2. The residual material fed into the plant 10 is moved by a conveyor 18 through a magnetic field generated by the magnet 11 to remove ferrous material from the residual material. The residual material then passes on to the flail mill 12, which comminutes the residual material to reduce its average particle size. After passing through the flail mill 12, the residual material is screened by the first screen 14. Residual material that is caught by the first screen 14 is returned to the flail mill 12 for reprocessing. Prior to being returned to the flail mill 12, however, the residual material caught by the first screen 14 is passed through the second screen 16 to remove larger particles. Any such larger particles which do not pass the second screen 16 are sent to landfill or packaged for use as fuel. A photograph of typical material caught by the second screen 16 is shown in Fig. 3.

Residual material passing the first screen 14 has been found to comprise less than 2.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm, zero dry weight percent of plastic film having a maximum dimension greater than 5mm and a maximum particle size of no more than 16mm.

Residual material passing the first screen 14 may be stored for use in agriculture and/or in the remediation of mine sites. Depending on its intended use, residual material passing the first screen 14 may be mixed with other material, such as refined compost, to produce a product comprising, for example, less than 1.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm, zero dry weight percent of plastic film and a maximum particle size of no more than 16mm.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Examples of possible modifications and/or variations include, but are not limited to:

· replacing the flail mill 12 with another type of comminutor, such as a hammer mill or a ripple mill;

• omitting the second screen and instead sending residual material that does not pass the first screen to another process (eg. land fill or for use as fuel) or returning the material to the mill 12 for reprocessing; optionally in combination with a finer first screen; .

• using a finer or coarser first screen to produce a product with different characteristics;

• using other types of screens for the first and/or second screens, such as trommels or non-vibratory screens; and/or

· omitting the magnet 11.

Claims

CLAIMS:

1. A method of processing residual material from upstream mixed waste treatment processes, said method comprising:

comminuting the residual material to reduce the average size of particles contained in the residual material; and

2. A method according to claim 1, wherein the first screen comprises openings with a maximum dimension of less than around 20mm, less than around 12mm, less than around 10mm, or of around 5mm.

3. A method according to claim 1 or claim 2, wherein residual material that is caught by the first screen is returned to the comminuting step for reprocessing.

4. A method according to claim 3, wherein, prior to being returned to the comminuting step, the residual material caught by the first screen is passed through a second screen having openings of greater maximum dimension than the first screen.

5. A method according to claim 4, wherein material passing the second screen is returned to the comminuting step and material caught by the second screen is redirected to another process.

6. A method according to any one of the preceding claims, wherein, prior to the comminuting step, the residual material is subjected to a magnetic field to remove ferrous material.

7. A method according to any one of the preceding claims, wherein the comminuting step comprises passing the residual material through a mill.

8. A method according to claim 7, wherein the mill is a flail mill.

9. A method according to any one of the preceding claims, wherein residual material passing the first screen comprises less than 2.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm.

10. A method according to any one of the preceding claims, wherein residual material passing the first screen comprises less than 0.25 dry weight percent of plastic film having a maximum dimension greater than 5mm.

11. A method according to any one of the preceding claims, wherein residual material passing the first screen has a maximum particle size of no more than 16mm.

12. A method according to any one of the preceding claims, wherein residual material passing the first screen is mixed with other material to produce a product comprising less than 2.5 dry weight percent of glass, metal and rigid plastics having a maximum dimension greater than 2mm.

13. A method according to claim 12, wherein the product comprises less than 0.25 dry weight percent of plastic film having a maximum dimension greater than 5mm.

14. A method according to claim 12 or claim 13, wherein the product has a maximum particle size of no more than 16mm.

15. A system for performing the method of any one of the preceding claims, said system comprising:

a comminutor for performing said comminuting step; and

a said first screen.