AU2017200716A1 - System and method for processing mixed waste - Google Patents

Abstract

Disclosed is a system 10 for processing municipal solid waste. The system 10 comprises a dry separation station 100, a wet separation station 200 downstream of the dry separation station, and a dewatering station 300 downstream of the wet separation station. The dry separation station 100 comprises a comminutor for comminuting a feedstock of mixed waste, and a separator for separating the comminuted waste into an organic fraction and a non-organic fraction. The wet separation station 200 comprises at least one separation tank for receiving a slurry comprising a mixture of the organic fraction from the separator and water, the at least one separation tank being adapted to separate the organic fraction in the slurry into a more refined organic fraction and a residual non-organic fraction using relative densities of the more refined organic fraction and the residual non-organic fraction. The dewatering station 300 receives and dewaters slurry from the wet separation station 200 containing the more refined organic fraction. r - - -- --- - ------i/-l (31 0 I ~ I ~ """"" I I<Lf) II E (a. > cuU ( to cu 0 u o'ig Icu cu)*~ i r -C-- --N - -- - -- c WI w I -nCD E cu 4-, (Ij coI n U-L 4eI ~II Iu mI I cu CCL_ u cu= CL'4 I,

Description

2017200716 02 Feb 2017 ι “System and method for processing mixed waste”

Cross-reference to Related Applications [0001] This application is related to Australian Patent Application No. 2016900346, filed 3 February 2016 and entitled “System and method for processing mixed waste”, the entire contents of which are incorporated herein by way of reference.

Technical Field [0002] The present disclosure relates generally to processing of mixed waste to reduce the amount of waste sent to landfill. More specifically, the present disclosure proposes a system and method of processing an organic fraction of a stream of mixed waste, such as municipal solid waste (MSW), commercial and industrial waste, street sweepings, food waste and food and green waste, to produce an output suitable for compost or other reuse. Whilst the presently disclosed system and method will be described hereinafter with reference to the production of compost from MSW, it will be appreciated that they are not limited to this application and may be gainfully employed to produce compost from other waste sources or for other purposes.

Background [0003] Municipal solid waste (MSW) includes general waste materials generated by households and business, and contains a vast array of discarded materials, including food wastes, discarded apparel, packaging and paper of various forms, glass and metal objects, plant matter, nappies, household pet wastes, and so on. In some areas, MSW may also include recyclable material, such as plastics, glass and metal containers, paper and cardboard.

[0004] It is desirable to reduce the amount of MSW sent to landfill. One method of reducing MSW sent to landfill is to attempt to classify the MSW into a recyclable fraction (such as certain plastics, glass and metals), an organic fraction (such as food 2017200716 02 Feb 2017 2 waste and plant matter), and a residual fraction. Each of the fractions may then be subjected to a treatment tailored to maximise the value of the respective fraction. For example, the organic fraction may be processed for use as compost.

[0005] In many jurisdictions, there are strict regulations governing the quality of compost. By way of example, the regulations for the state of New South Wales (NSW) in Australia are summarised in the table below: % 'dry weight' Glass/metals/ stones/rigid plastics (> 2mm) Plastic film (> 5mm) The NSW Compost Exemption 2014 MSW compost for Mine application <2.5 <0.25 MSW compost for Agricultural application < 1.5 <0.2 Compost derived from food organics <0.5 <0.05 [0006] Using conventional systems and methods, compliance with these regulations can be difficult and expensive. Accordingly, the production of compost from the organic fraction of a MSW stream can be non-economically viable using conventional systems and methods.

[0007] Accordingly, there is a need to provide a system and method that simplifies and/or reduces the cost of producing compost from the organic fraction of a MSW stream.

[0008] 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 disclosure as it existed before the priority date of each claim of this application.

[0009] Throughout this specification, the term “organic fraction” is to be understood as meaning a fraction of a waste stream containing a relatively high proportion of organic material, the term “recyclable fraction” is to be understood as meaning a 2017200716 02 Feb 2017 3 fraction of a waste stream containing a relatively high proportion of recyclable material, and the term “non-organic fraction” is to be understood as meaning a fraction of a waste stream containing a relatively high proportion of non-organic material.

Summary [0010] In a first aspect, there is provided a system for processing mixed waste, the system comprising: a dry separation station comprising: a comminutor for comminuting a feedstock of mixed waste, and a separator for separating the comminuted waste into an organic fraction and a non-organic fraction; a wet separation station downstream of the dry separation station, the wet separation station comprising: at least one separation tank for receiving a slurry comprising a mixture of the organic fraction from the separator and water, the at least one separation tank being adapted to separate the organic fraction in the slurry into a more refined organic fraction and a residual non-organic fraction using relative densities of the more refined organic fraction and the residual non-organic fraction; and a dewatering station for receiving and dewatering slurry from the wet separation station containing the more refined organic fraction.

[0011] The at least one separation tank may comprise an agitator for suspending relatively light components of the slurry. The at least one separation tank may comprise a lower outlet for removing relatively dense components that settle out of the slurry. The at least one separation tank may comprise an upper outlet, such as a skimmer or overflow weir, for removing relatively light components that are floated out of the slurry. The at least one separation tank may comprise a plurality of tanks in series. A first of the plurality of tanks may be configured for removing relatively dense components of the slurry by settling. A second of the plurality of tanks may be configured to facilitate flotation of relatively light components of the slurry. The first tank may comprise a dissolved air flotation system to facilitate separation of relatively 2017200716 02 Feb 2017 4 light components of the slurry from relatively dense components of the slurry by suspending the relatively light components whilst allowing the relatively dense components to settle. The second tank may comprise an aerator to aerate the slurry output from the first tank to facilitate separation of relatively light components in the slurry from a relatively dense organic fraction in the slurry by flotation. In some embodiments, a third tank may be provided downstream of the second tank and separation of the relatively light components in the slurry from the relatively dense organic fraction in the slurry by flotation may take place in the third tank.

[0012] The dry separation station may comprise packaging removal machine that acts both as the comminutor and the separator. For example, the dry separation station may comprise an “Atritor Turbo Separator”. Alternatively, the comminutor may comprise, for example, a ripple mill, a hammer mill or a flail mill, and the separator may comprise at least one screen.

[0013] The dewatering station may comprise a filter and/or a press for separating water from the slurry output from the wet separation station. A fluid recycling line may extend from the dewatering station to the wet separation station to recycle water removed from the slurry.

[0014] A mixing tank for combining water with the organic fraction from the dry separation station to create the slurry may be provided between the dry separation station and the wet separation station.

[0015] The dry separation station may comprise a sorting sub-station upstream of the comminutor for sorting the mixed waste into a comminutor compatible organic fraction and a non-comminutor compatible fraction. The sorting sub-station may comprise at least one conveyor that is upwardly inclined in the direction of belt travel, such that the waste is separated into a first proportion that rolls backward due to the incline and a second proportion that continues in the direction of belt travel. The second proportion may be fed to the comminutor, optionally via a manual sorting station. A magnetic sorter may be provided to remove recyclable ferrous materials from the first proportion. 2017200716 02 Feb 2017 5

An electromechanical sorter may be provided to remove aluminium cans from the first proportion. A screen may be provided to remove fine materials from the first proportion. A manual sorting station may be provided to classify the first proportion into one or more classes of recyclable and non-recyclable materials.

[0016] The combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the more refined organic fraction output from the wet separation station may be less than 2.5% of the dry weight of the total more refined organic fraction output from the wet separation station. In some embodiments, the combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the more refined organic fraction output from the wet separation station may be less than 1.5% of the dry weight of the total more refined organic fraction output from the wet separation station. In some embodiments, the combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the more refined organic fraction output from the wet separation station may be less than 0.5% of the dry weight of the total more refined organic fraction output from the wet separation station. The combined dry weight of plastic film having a maximum dimension greater than 5mm in the more refined organic fraction output from the wet separation station may be less than 0.25% of the dry weight of the total more refined organic fraction output from the wet separation station. In some embodiments, the combined dry weight of plastic film having a maximum dimension greater than 5mm in the more refined organic fraction output from the wet separation station may be less than 0.2% of the dry weight of the total more refined organic fraction output from the wet separation station. In some embodiments, the combined dry weight of plastic film having a maximum dimension greater than 5mm in the more refined organic fraction output from the wet separation station may be less than 0.05% of the dry weight of the total more refined organic fraction output from the wet separation station.

[0017] The mixed waste may comprise municipal solid waste. 2017200716 02 Feb 2017 6 [0018] In a second aspect, there is provided a method of processing mixed waste, said method comprising: comminuting a feedstock of mixed waste; dry separating the comminuted waste into an organic fraction and a nonorganic fraction; adding water to the organic fraction to create a slurry; wet separating the organic fraction in the slurry into a more refined organic fraction and a residual non-organic fraction using relative densities of the more refined organic fraction and the residual non-organic fraction; and dewatering slurry containing the more refined organic fraction.

[0019] The slurry may be agitated during the wet separating to maintain relatively light components of the slurry in suspension. The agitation may use dissolved air flotation of the relatively light components of the slurry. Relatively dense components of the slurry may be separated from relatively light components of the slurry by settling. Relatively light components of the slurry may be separated from relatively dense components of the slurry by flotation. The flotation may comprise aerating the slurry.

[0020] The comminuting and dry separating may be performed simultaneously. The comminuting and dry separating may be performed by a packaging removal machine, such as an “Atritor Turbo Separator”. Alternatively, the comminuting and dry separating may be performed separately. In such cases, the comminuting may be performed by a ripple mill, a hammer mill or a flail mill, and the separating may be performed using at least one screen.

[0021] The dewatering may comprise filtering and/or pressing the slurry. Water obtained from the dewatering may be recycled and used for creating the slurry.

[0022] The dry separation may comprise sorting the mixed waste, prior to comminution, into a comminutable organic fraction and a non-comminutable fraction. The sorting may comprise gravity-based mechanical sorting, for example using at least 7 2017200716 02 Feb 2017 one conveyor that is upwardly inclined in the direction of belt travel, such that the waste is separated into a first proportion that rolls backward due to the incline and a second proportion that continues in the direction of belt travel. The sorting may also or alternatively comprise manual sorting. The non-comminutable fraction may be magnetically sorted to remove recyclable ferrous materials from the first proportion. The non-comminutable fraction may be electromechanically sorted to remove aluminium cans. Fine materials may be removed from the non-comminutable fraction by a screen. The non-comminutable fraction may manually sorted into one or more classes of recyclable and non-recyclable materials.

[0023] The combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the more refined organic fraction output from the wet separation may be less than 2.5% of the dry weight of the total more refined organic fraction output from the wet separation station. In some embodiments, the combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the more refined organic fraction output from the wet separation may be less than 1.5% of the dry weight of the total more refined organic fraction output from the wet separation. In some embodiments, the combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the more refined organic fraction output from the wet separation may be less than 0.5% of the dry weight of the total more refined organic fraction output from the wet separation. The combined dry weight of plastic film having a maximum dimension greater than 5mm in the more refined organic fraction output from the wet separation may be less than 0.25% of the dry weight of the total more refined organic fraction output from the wet separation. In some embodiments, the combined dry weight of plastic film having a maximum dimension greater than 5mm in the more refined organic fraction output from the wet separation may be less than 0.2% of the dry weight of the total more refined organic fraction output from the wet separation. In some embodiments, the combined dry weight of plastic film having a maximum dimension greater than 5mm in the more refined organic fraction output from the wet separation may be less than 0.05% of the dry weight of the total more refined organic fraction output from the wet separation. 2017200716 02 Feb 2017 8 [0024] The mixed waste may comprise municipal solid waste.

Brief Description of Drawings [0025] An embodiment of the presently disclosed system, and a method of using same, will now be described with reference to accompanying Figure 1, which is a schematic drawing of an embodiment of a system for processing municipal solid waste.

Description of Embodiment [0026] Referring to Figure 1, there is provided a system 10 for processing municipal solid waste. The system 10 comprises a dry separation station 100, a wet separation station 200 downstream of the dry separation station, and a dewatering station 300 downstream of the wet separation station.

[0027] The dry separation station 100 comprises a sorting sub-station 110 for sorting the municipal solid waste into a comminutor-compatible organic fraction suitable for processing by a downstream comminutor, and a non-comminutor compatible fraction. The sorting sub-station 110 comprises a plurality of conveyors 112a-l 12d, wherein conveyors 112a and 112c, respectively, comprise an 80mm ballistic separator and a 25mm ballistic separator having rotating tines for splitting and removing bags from the waste. The conveyors 112a-112d are upwardly inclined in the direction of belt travel, such that the waste is separated into a first proportion (comprising a non-organic fraction of the input waste stream) that rolls backward due to the incline and a second proportion (comprising an organic fraction of the input waste stream) that continues in the direction of belt travel. The second proportion is directed to a manual sorting station 114, in which residual non-comminutor compatible materials, such as metals, large timber, bones and other waste that cannot be comminuted by the comminutor are removed. In the illustrated embodiment, a magnetic sorter, in the form of a belt magnet 116, and an upwardly inclined reject conveyor 118, are provided between the manual sorting station 114 and the comminutor. The sorting sub-station 110 may be configured 2017200716 02 Feb 2017 9 in the manner disclosed in the applicant’s earlier International Patent Publication No. WO 2013/142904, the disclosure of which is incorporated herein by reference.

[0028] The first proportion of the waste, which rolls backward due to the incline of conveyors 112a-112d, along with material rolling backward down the reject conveyor 118, is directed to a sorting station 140 in which it is subjected to the following processes to reclaim recyclable and/or reusable materials: (i) magnetic sorting to reclaim recyclable ferrous materials from the first proportion; (ii) electromechanical sorting using eddy current to reclaim aluminium cans; (iii) screening using a fines trommel to remove small particles unsuited to manual sorting; (iv) manual sorting to classify the first proportion into one or more classes of recyclable and non-recyclable materials, such as batteries, heavy ferrous materials, nappies and organic materials that did not pass over the inclined conveyors 112a-112d, and intact glass.

[0029] Organic materials reclaimed from the first proportion are returned to the upstream end of the sorting sub-station 110 for reprocessing or directly to the manual sorting station 114.

[0030] In the illustrated embodiment, the comminutor for processing the first proportion that passes over the inclined conveyors 112a-112d takes the form of a packaging removal machine 120, such as that known as an “Atritor Turbo Separator”, which simultaneously: (i) comminutes the comminutor compatible organic fraction of the waste received from the manual sorting station 114; and (ii) separates the waste into a more refined organic fraction and a residual non-organic fraction.

[0031] However, in alternative embodiments the comminutor 120 may comprise, for example, a ripple mill, a hammer mill or a flail mill. In such embodiments, a separate 2017200716 02 Feb 2017 ίο dry separator, such as one or more screens, may be provided downstream of the comminutor to separate the comminuted waste into a more refined organic fraction that passes the screen(s) and a residual non-organic fraction that is captured by the screen(s).

[0032] In either case, the residual non-organic fraction typically contains a light fraction comprising a high proportion of high calorific value materials, such as paper and plastic film from packaging. The residual non-organic fraction, along with reclaimable high calorific value materials from the manual sorting station 114 and sorting station 140, is directed to an air classifier 400 to separate it into a light fraction and a heavy fraction. The high calorific value light fraction is collected for use as an input for producing a process engineered fuel and the heavy fraction is sent to landfill.

[0033] The comminuted organic fraction output from the dry separation station 100 is directed into a mixing tank 180, in which it is combined with water to create a slurry for feeding to the wet separation station 200. The mixing tank comprises an agitator to facilitate mixing of the organic fraction and the water.

[0034] The wet separation station 200 comprises a series of tanks 210, 220, 230 in which the organic fraction in the slurry is separated into a yet further refined organic fraction and a residual non-organic fraction using their relative densities.

[0035] Tank 210 comprises a dissolved air flotation system 212 to facilitate separation of relatively light components of the organic fraction and non-organic fraction in the slurry from relatively dense components that typically contain a relatively high proportion of non-organic material, such as glass fragments, stones and rigid plastics. The dissolved air flotation system 212 agitates and suspends the relatively light components, whilst the relatively dense components settle for removal through a lower outlet 214 in the tank. The slurry containing the suspended light components is transferred to downstream tank 220, which comprises an aerator 222 for aerating the slurry to promote flotation of a relatively light non-organic fraction comprising materials such as polystyrene and plastic film. The aerated slurry is 2017200716 02 Feb 2017 11 transferred to tank 230 via a lower pipe 224, whilst any light non-organic fraction that floats to the surface is transferred via an upper overflow pipe or weir 226. In tank 230, a relatively light non-organic fraction remaining in the slurry separates from the organic fraction by flotation and is removed via an upper outlet 232, using a skimmer mechanism or overflow weir. In alternative embodiments, the second 220 and third 230 tanks may be replaced by a single tank in which both aeration and flotation are performed.

[0036] The refined organic fraction remaining in the slurry in tank 230 is transferred to the dewatering station 300, which comprises a filter 310 and screw press 330 for separating water from the organic fraction. A fluid recycling line 320 extends from the dewatering station 300 to an upstream end of the wet separation station 200 to recycle water passing the filter and reduce the amount of external water that would otherwise be required to produce the slurry.

[0037] The combined dry weight of glass, metals, stones and rigid plastics having a maximum dimension greater than 2mm in the organic fraction collected by the filter 310 has been found to be less than 0.5% of the dry weight of the total organic fraction collected by the filter 310. The combined dry weight of plastic film having a maximum dimension greater than 5mm in the organic fraction collected by the filter 310 has been found to be less than 0.05% of the dry weight of the total organic fraction collected by the filter 310. Accordingly, the organic fraction generated using the illustrated system 10 and collected by the filter 310 has been found to meet NSW regulations for compost quality.

[0038] It will be appreciated that the illustrated system 10, and the method of processing MSW enabled by the system 10, facilitate reuse of a significant proportion of MSW that would likely otherwise be sent to landfill. Specifically, the illustrated system 10, and associated method, facilitate processing a feedstock obtained from MSW to reclaim both an organic fraction having a quality suitable for use as compost and high calorific materials for use as an input for producing a process engineered fuel. 2017200716 02 Feb 2017 12

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.

Claims (28)

1. CLAIMS:

   1. A system for processing mixed waste, the system comprising: a dry separation station comprising: a comminutor for comminuting a feedstock of mixed waste, and a separator for separating the comminuted waste into an organic fraction and a non-organic fraction; a wet separation station downstream of the dry separation station, the wet separation station comprising: at least one separation tank for receiving a slurry comprising a mixture of the organic fraction from the separator and water, the at least one separation tank being adapted to separate the organic fraction in the slurry into a more refined organic fraction and a residual non-organic fraction using relative densities of the more refined organic fraction and the residual non-organic fraction; and a dewatering station for receiving and dewatering slurry from the wet separation station containing the more refined organic fraction.
2. 2. A system according to claim 1, wherein the at least one separation tank comprises an agitator for suspending relatively light components of the slurry.
3. 3. A system according to claim 1 or claim 2, wherein the at least one separation tank comprises a lower outlet for removing relatively dense components that settle out of the slurry.
4. 4. A system according to any one of claims 1 to 3, wherein the at least one separation tank comprises an upper outlet for removing relatively light components that are floated out of the slurry.
5. 5. A system according to any one of the preceding claims, wherein the at least one separation tank comprises a plurality of tanks in series.
6. 6. A system according to claim 5, wherein a first one or first group of the plurality of tanks is configured for removing relatively dense components of the slurry by settling, and wherein a second one or second group of the plurality of tanks is configured to facilitate flotation of relatively light components of the slurry.
7. 7. A system according to claim 6, wherein the first tank(s) comprise(s) a dissolved air flotation system to facilitate separation of relatively light components of the slurry from relatively dense components of the slurry by suspending the relatively light components whilst allowing the relatively dense components to settle.
8. 8. A system according to claim 6 or claim 7, wherein the second tank(s) comprise(s) an aerator to aerate the slurry output from the first tank(s) to facilitate separation of relatively light components in the slurry from a relatively dense organic fraction in the slurry by flotation.
9. 9. A system according to claim 6 or claim 7, comprising a third tank downstream of the second tank(s), wherein separation of the relatively light components in the slurry from the relatively dense organic fraction in the slurry by flotation takes place in the third tank.
10. 10. A system according to any one of the preceding claims, wherein the dry separation station comprises a packaging removal machine that acts both as the comminutor and the separator.
11. 11. A system according to any one of claims 1 to 9, wherein: the comminutor is a machine selected from the group comprising: a ripple mill, a hammer mill and a flail mill, and the separator comprises at least one screen.
12. 12. A system according to any one of the preceding claims, wherein the dewatering station comprises a filter and/or a press for separating water from the slurry output from the wet separation station.
13. 13. A system according to any one of the preceding claims, wherein a fluid recycling line extends from the dewatering station to the wet separation station to recycle water removed from the slurry.
14. 14. A system according to any one of the preceding claims, comprising a mixing tank for combining water with the organic fraction from the dry separation station to create the slurry, the mixing tank being between the dry separation station and the wet separation station.
15. 15. A system according to any one of the preceding claims, wherein the dry separation station comprises a sorting sub-station upstream of the comminutor for sorting the mixed waste into a comminutor compatible organic fraction and a non-comminutor compatible fraction.
16. 16. A system according to any one of the preceding claims, wherein the mixed waste comprises municipal solid waste.
17. 17. A method of processing mixed waste, said method comprising: comminuting a feedstock of mixed waste; dry separating the comminuted waste into an organic fraction and a nonorganic fraction; adding water to the organic fraction to create a slurry; wet separating the organic fraction in the slurry into a more refined organic fraction and a residual non-organic fraction using relative densities of the more refined organic fraction and the residual non-organic fraction; and dewatering slurry containing the more refined organic fraction.
18. 18. A method according to claim 17, wherein the slurry is agitated during the wet separating to maintain relatively light components of the slurry in suspension.
19. 19. A method according to claim 18, wherein the agitation involves dissolved air flotation of the relatively light components of the slurry.
20. 20. A method according to any one of claims 17 to 19, wherein relatively dense components of the slurry are separated from relatively light components of the slurry by settling and/or relatively light components of the slurry are separated from relatively dense components of the slurry by flotation.
21. 21. A method according to claim 20, wherein the separation of relatively light components of the slurry from relatively dense components of the slurry by flotation comprises aerating the slurry.
22. 22. A method according to any one of claims 17 to 21, wherein the comminuting and dry separating are performed simultaneously.
23. 23. A method according to claim 22, wherein the comminuting and dry separating are performed by a packaging removal machine.
24. 24. A method according to any one of claims 17 to 21, wherein the comminuting and dry separating are performed separately.
25. 25. A method according to any one of claims 17 to 24, wherein the dewatering comprises filtering and/or pressing the slurry.
26. 26. A method according to claim 25, wherein water obtained from the dewatering is recycled and used for creating the slurry.
27. 27. A method according to any one of claims 17 to 26, wherein the dry separation comprises sorting the mixed waste, prior to comminution, into a comminutable organic fraction and a non-comminutable fraction.
28. 28. A method according to any one of claims 17 to 27, wherein the mixed waste comprises municipal solid waste.