WO2023115106A1

WO2023115106A1 - A process for recycling used absorbent hygiene products, and a process for manufacturing products from the recycled material

Info

Publication number: WO2023115106A1
Application number: PCT/AU2022/051518
Authority: WO
Inventors: Clarke Duncan Kelland; Oliver Clarke Alexander Kelland
Original assignee: Kelland Environmental Technology Pty Ltd
Priority date: 2021-12-21
Filing date: 2022-12-16
Publication date: 2023-06-29

Abstract

A process for recycling used absorbent hygiene products (AHP) and shredding and washing the AHP before separating by screening into two streams by the size of the suspended matter. A first recovery stream (not shown) in which the sheet plastics material is recovered, and a second recovery stream (Fig 4) in which the fibre and the SAP pass 5 through a screw press (82), delumper (83), screw press (85) am extruder (86) and drier (87) to produce fibre pellets having an average diameter in the range of four to eight millimetres. The dried absorbent pellets produced in accordance with this process are suitable for use as spill kit material, cat litter, or animal bedding. (Figure 4) 10

Description

A Process for Recycling used Absorbent Hygiene Products, and a Process for Manufacturing Products from the Recycled Material.

FIELD OF THE INVENTION

This invention relates to the recycling of waste absorbent hygiene products such as used disposable baby diapers, and to the production of animal litter or other consumer products from some of the materials recovered from the recycling process.

BACKGROUND

Absorbent hygiene products (AHP's) are an effective method of managing urinary incontinence and leakage of other body fluids and are increasingly used in the form of disposable baby diapers. Disposable AHP's are popular due to their convenience, low cost and increased level of hygiene, when compared to a reusable product. AHP's typically consist of an inside layer comprising a cellulose fibre and a super-absorbent polymer (SAP), an outer layer on a first side that forms a porous liner, and which is made of a sheet of polypropylene (PP) plastics material, and an outer layer on a second side that forms a waterproof layer, and which is made of a sheet of polyethylene (PE) plastics material.

Disposable diapers are the most widely used AHP with products available to suit children and adults of all ages. It is estimated that more than 27.4 billion disposable diapers are used in the US each year, with a mass of 3.4 million tonnes. Disposable AHP's are discarded after one use and will typically end up in landfill, with few alternative disposal methods available. In landfill the cellulose fibre will decompose into carbon dioxide (CO?) and methane (CH4) gas. Methane gas is one of the leading causes of global warming. The Intergovernmental Panel on Climate Change considers one unit of methane to be equivalent to 84 units of CO2, over a 20-year period. The amount of AHP waste created each year continues to increase as populations grow and developing countries adopt the use of disposable AHP's.

AHP waste poses a problem to countries trying to reduce waste to landfill and meet net zero carbon emissions. Current alternative methods of AHP disposal include incineration or use as waste to energy fuel, which releases a significant amount of CO2 in the combustion process due to the low calorific value of the AHP waste. As such there is a need for a recycling solution where the materials of used AHP can be recovered and reused or re-purposed in other products.

There is strong unsatisfied demand by consumers, product manufacturers and local governments to recycle post-consumer AHP waste but the problem is that AHP waste recycling is currently uneconomic. This has been due to the recycled plastic and fibre materials from the AHP having no market value due to poor quality, high recycling and logistic costs relative to the alternative of landfill disposal and waste to energy incineration. Significant research has been undertaken by others to find sustainable economic solutions as evidenced by the number of patents registered. There appear to be no successful commercial examples of these patents being implemented apart from preparing AHP waste for incineration.

The problem for major nappy, incontinence and other absorbent hygiene product manufacturers, is that they are suffering a reputational issue due to the lack of a sustainable end-of-life solution for their products within a world that is increasingly concerned about climate change and is focusing on how to reduce the use of unsustainable products.

A number of organisations have attempted to mitigate the environmental impact of AH P's by developing processes for recycling at least a part of the material used to make the products.

Previous recycling attempts have been made to recover the component materials of waste AHP with limited success. This can be attributed to the difficulty of separating the materials once the product has been used. Moisture present in a used AHP hydrates the cellulose fibre and SAP, where it acts like a glue and impedes separation from the PP (polypropylene porous inner)/PE (polyethylene waterproof outer) lining. The SAP is also seen to embed itself into the cellulose fibre adding complications to the removal of contaminants. Recovering cellulose fibre, SAP and PP/PE as separate streams is therefore very difficult, requiring intensive processing. It is believed that no previous attempt has been able to economically separate and recover individual materials to a marketable quality.

Patent AU2010249864 describes a process for recycling used diapers, and various plants have been constructed which use the process described. However, it is understood that these plants have experienced difficulties resulting from excessive odour emissions, and a relatively low quality of the recovered plastic and fibre.

US8979005 describes a process in which a rotary autoclave is used to tear apart and sterilise, used diapers at a high temperature. However, the costs associated with providing steam for the elevated temperatures, and condensing equipment to control odorous steam, contribute to the costs of this process.

AU2015272850 describes a process to recycle fibre from AHP waste to produce new AHP products. The process is capital intensive involving an ionization process to destroy the SAP thereby producing an uncontaminated fibre for recycling into new AHP products. Alternate processes use energy intensive paper processing equipment to remove SAP from the fibre.

WO2017/039615 describes a process that separates used AHP into its three constituent materials; plastic, SAP and fibre. The process initially shreds and pulps the used AHP, and then uses sodium chloride and seawater to initially dewater the SAP. Enzymes are used to help remove fibre from any recovered plastic. However, the use of enzymes increases the cost of production, requires holding times to break down the cellulose and special conditions to store the enzyme.

The production of marketable recycled materials has and continues to be the biggest problem, due to the price of virgin materials being relatively cheap. On top of this are the issues of collecting and separating waste as well as environmental factors such as odour and dust control, noise and waste water treatment. In this specification unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.

DEFINITIONS

AHP is the standard abbreviation for an "Absorbent Hygiene Product".

Throughout this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers, or steps.

SAP refers to a super-absorbent polymer. A superabsorbent polymer is a waterabsorbing polymer that can absorb and retain extremely large amounts of a liquid relative to its own mass. Water-absorbing polymers absorb aqueous solutions through hydrogen bonding with water molecules. The most commonly used SAP in AHPs is Sodium polyacrylate (ACR), also known as "waterlock"

A trommel screen, is a type of rotary screen separator. It has a perforated cylindrical drum that is normally elevated at an angle at the feed end. Physical size separation is achieved as the feed material spirals down the rotating drum, where the undersized material smaller than the screen apertures passes through the screen, while the oversized material exits at the other end of the drum.

The term "wt.%" used herein is intended to mean a ratio of the weight of solids or solutes, compared to the total weight of a wet slurry or solution, expressed as a percentage.

OBJECT

It is therefore an object of the present invention to provide a process for recycling used absorbent hygiene products, and/or a process for producing a useful product from the resultant recycled material, which will at least go some way towards overcoming one or more of the above-mentioned problems, or at least provide the public with a useful choice.

STATEMENTS OF THE INVENTION

There are many processes for shredding and washing AHP and where the dewatering salt is added to the process, and whether any water released is recycled or not. The focus of this invention is the separation of the shredded and washed AHP into two or more streams.

In one aspect the invention provides a process for recycling used absorbent hygiene products (AHP) that have an inside layer comprising a fibre and a super-absorbent polymer (SAP) and an outer layer on at least one side of the inside layer that is made of sheet plastics material; the process comprising at least the following steps;

• an initial shredding and water washing step that is configured to remove a majority of any contaminants present in the used AHP, and

• then further shredding or pulping of the used AHP, and separation of the used AHP into two main recovery streams, a first recovery stream in which the sheet plastics material is recovered, and a second recovery stream in which the fibre and the SAP are recovered.

Preferably the process is configured to recycle AHPs in which the fibre is a cellulose fibre, and which have an outer layer on a first side that forms a porous liner, and which is made of a sheet of polypropylene (PP) plastics material, and an outer layer on a second side that forms a waterproof layer, and which is made of a sheet of polyethylene (PE) plastics material.

Preferably the initial shredding and water washing step includes the use of de-watering salts mixed with the water used for washing. Preferably the water used to wash the used AHP in the initial shredding and water washing step includes recycled water that is removed from the recovered fibre and SAP during a later step in the process.

Preferably the water used to wash the used AHP in the initial shredding and water washing step is removed from the shredded AHP using a mechanical pressing action, for example using a screw compactor.

Preferably the air that surrounds the used AHP during the initial shredding and water washing step is extracted and is passed through an odour scrubbing or other air purification system.

Preferably the step of separating of the used AHP into two main recovery streams is primarily carried out using a rotating drum or trommel screen.

Preferably the material that is recovered in the first recovery stream by the rotating drum or trommel screen, is passed through a friction washer to assist in further separating any remaining fibre from the recovered sheet plastics material.

Preferably the material that is recovered in the first recovery stream by the rotating drum or trommel screen, is passed through a first sink/f loat tank in which any remaining fibre is removed from the first recovery stream and is re-directed to join the second recovery stream.

Preferably any intertwined sheet plastics material and fibre that is present in the first recovery stream is removed at the first sink/f loat tank.

Preferably the sheet plastics material that is recovered in the first recovery stream is mechanically dried, for example in a spin drier, after passing through the first sink/float tank.

Preferably the sheet plastics material that is recovered in the first recovery stream and which has been mechanically dried, is further dried using a thermal drying method, for example using a tubular thermal drier. Preferably the thermally dried sheet plastics material is passed through a cyclone separator, to separate the sheet plastics material from an airflow that is used to pass the sheet plastics material through the thermal drying step.

Preferably the material that is recovered in the second recovery stream by the rotating drum or trommel screen, is passed through a second sink/f loat tank in which small pieces of sheet plastics material that passed through the screen can be removed from the second recovery stream and be redirected to the first recovery stream.

Preferably the material that is recovered in the second recovery stream, and which has passed through the second sink/f loat tank, is passed through a screen, for example a static screen or a wedge wire screen, to initially dewater the fibre and SAP.

Preferably de-watering salts and peracetic acid are added to the material in the second recovery stream.

Preferably the fibre and SAP of the second recovery stream is further dewatered in a press

Optionally the fibre and SAP of the second recovery stream is sent to an industrial composting facility.

In a second aspect, the invention may broadly be said to consist in a process for producing a consumer product from fibre and super-absorbent polymer (SAP) material that is recovered from used absorbent hygiene products (AHP), the process comprising at least the following steps;

• cleaning the recovered fibre and SAP material in clean water and a sterilising agent,

• dewatering the cleaned fibre and SAP material, and

• forming the dewatered fibre and SAP material into a specified form.

Preferably the fibre and SAP material that is recovered from used AHP is material that is recovered in a second recovery stream using the process for recycling used AHP substantially as specified herein. Preferably the initially dewatered fibre and SAP of the second recovery stream is further dewatered in a screw press and is then passed into an agitated reaction tank.

Preferably clean water, de-watering salts and a sterilising agent, for example peracetic acid, are added to the fibre and SAP of the second recovery stream while the fibre and SAP are in the agitated reaction tank.

Preferably the fibre and SAP remains in the agitated reaction tank, and exposed to the clean water, the de-watering salts and the sterilising agent, for at least fifteen minutes.

Preferably the fibre and SAP is dewatered, for example using a screw press, when it is removed from the agitated reaction tank.

Preferably the recovered fibre and SAP material is cleaned in an agitated reaction tank.

Preferably the sterilising agent includes peracetic acid.

Preferably dewatering salts are added to the clean water before or during the cleaning step.

Preferably the recovered fibre and SAP material is substantially de-watered before the cleaning step, for example using a screw press.

Preferably the recovered fibre and SAP material is substantially de-watered after the cleaning step using a screw press.

Preferably the recovered fibre and SAP remains in the agitated reaction tank and exposed to the clean water and the sterilising agent, for at least fifteen minutes.

Preferably the cleaned and dewatered fibre and SAP material is formed into pellets.

Preferably the cleaned and dewatered fibre and SAP material is formed into pellets using a wet extrusion process.

Preferably the pellets have an average diameter in the range of four to eight millimetres, and ideally approximately six millimetres. Preferably the fibre and SAP material is dried after it is formed into pellet form.

Preferably the fibre and SAP material is dried using a mesh belt or tray pellet drier.

Preferably the dried fibre and SAP pellets are classified into size ranges using a multi-tiered vibrating screen.

In a third aspect, the invention may broadly be said to consist in a processing plant configured to carry out the process for recycling used absorbent hygiene products substantially as specified herein.

In a fourth aspect, the invention may broadly be said to consist in a processing plant configured to carry out the process for producing a consumer product from fibre and super-absorbent polymer (SAP) material that is recovered from used absorbent hygiene products (AHP) substantially as specified herein.

In a fifth aspect, the invention may broadly be said to consist in a product produced by the process for recycling used absorbent hygiene products substantially as specified herein

In a sixth aspect, the invention may broadly be said to consist in a product produced by the process for producing a consumer product from fibre and super-absorbent polymer (SAP) material that is recovered from used absorbent hygiene products (AHP) substantially as specified herein.

Preferably this comprises dried absorbent pellets produced in accordance with the process of this invention and suitable for use as spill kit material, cat litter, or animal bedding.

The invention may also broadly be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of the parts, elements or features, and where specific integers are mentioned herein which have known equivalents, such equivalents are incorporated herein as if they were individually set forth.

DESCRIPTION

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

FIGURE 1 is a flow diagram of a process for recycling used absorbent hygiene products (AHP), and

FIGURE 2 is a flow diagram of a process for producing a consumer product from material recovered from used absorbent hygiene products.

FIGURE 3 is the first part of a flow diagram of an improved process for recycling used absorbent hygiene products (AHP), showing the first stream leading to plastic pellets. The second stream is shown in the next figure.

FIGURE 4 shows the second part of the flow diagram of figures 3 showing the second stream leading to absorbent pellets.

EXAMPLE 1

With reference to Figure 1, a process for recycling used absorbent hygiene products (AHP) according to the present invention will now be described. The process for recycling used AHP has been primarily designed for use in the recycling used diapers.

The process for recycling used AHP can be used on any AHP that has an inside layer comprising a fibre and a super-absorbent polymer (SAP) and an outer layer on each side of the inside layer that are made of sheet plastics material. The process is configured primarily to recycle AHPs in which the fibre is a cellulose fibre, and which have an outer layer on a first side that forms a porous liner, and which is made of a sheet of polypropylene (PP) plastics material, and an outer layer on a second side that forms a waterproof layer, and which is made of a sheet of polyethylene (PE) plastics material.

The super-absorbent polymer, or SAP, that is most often used in diapers is poly-acrylic acid sodium salt, or sodium polyacrylate, and is usually in a fine granular format.

In broad terms, the process comprises the following main steps;

• then further shredding or pulping of the used AHP, and separation of the used AHP into two main recovery streams, a first recovery stream in which the sheet plastics material is recovered, and a second recovery stream in which the fibre and the SAP are recovered together.

In the example shown in Figure 1, the process begins when bags containing used AHP (11) are put into a five cubic metre hopper (13) having an apron feeder discharge. The apron feeder discharge meters a controlled number of used AHP (11) bags into the recycling process through a gate at the end of the hopper. The hopper gate has blades that tear the bags, releasing the contents of the bag onto a belt conveyor below.

The released contents are visually inspected or screened by an operator who is located at the belt conveyor. Any tramp material such as glass is removed by the operator. The screened contents are then conveyed into a first two-shaft shredder (15).

The first two-shaft shredder (15) has 12mm blades that are configured to tear open the used AHP (11), and spray bars positioned inside the shredder mouth deliver wash water. The wash water is sourced from a downstream part of the process as will be explained below. A dewatering salt such as magnesium chloride or calcium chloride is added to the wash water. This wash water is used to carry out the initial water washing step and is intended to remove the majority of the contaminants, such as urine and faecal matter, present in the used AHP.

Gasses released in this initial shredding stage are removed by an extraction fan installed in a hood of the first two-shaft shredder (15). These gasses are then passed through an odour scrubber or other air purification system (17) before being released to the surrounding atmosphere.

The shredded and initially washed AHP is then compressed in a screw compactor (19). High concentration contaminants removed from AHP in liquid form can be further treated by an appropriate water treatment system, for example a struvite precipitation and separation system (21), or a Lamella clarifier (23), before being discharged into a local sewer, to meet local wastewater discharge requirements.

The compacted AHP is then shredded in a second two shaft shredder (25) which is also equipped with 12mm blades and spray bars. Wash water is sprayed onto the shredded material to assist with removal of fibre from the plastic.

The shredded and sprayed AHP is then sluiced into a wet rotating drum screen, or trommel screen (27), using additional wash water recycled from downstream processes. The dilute slurry ideally enters the trommel screen (27) at a concentration in the range of 0.1- 0.3wt%. The trommel screen (27) has 5mm diameter hole screen plates with an open area of 60% or greater and rotates at up to 3 rpm.

Spray bars that are installed on the outside of the drum of the trommel screen (27) deliver a high-pressure wash water, to prevent the screen plates from blinding as fibre and SAP are separated from the plastic as the drum rotates. In this way, the drum screen (27) separates the plastic, which by now is primarily in 12mm wide x 10-20mm long plastic shreds, from the fibre and SAP. The plastic continues along the first recovery stream, and the fibre and SAP continue together along the second recovery stream.

In the first recovery stream, the plastic material that is discharged from the end of the drum screen (27) is passed into a third two-shaft shredder (29), which also has 12mm blades. The third shredder (29) provides mechanical rubbing and further plastic size reduction to help loosen any remaining fibres.

The shredded plastic and recycled wash water then enter a friction washer (31) that is fitted with a 3mm perforated screen basket. At this stage, the majority of any remaining fibre is washed from the plastic by a rubbing action and is separated from the plastic by the 3mm perforated screen basket and is redirected into the second recovery system. The washed plastic is then discharged into a first sink/float tank (33).

The first sink/float tank (33) removes any remaining loose fibre from the plastic, and also separates any intertwined plastic/fibre strings that have a specific gravity >1 and which cannot be used for plastic reprocessing. The intertwined plastic/fibre strings that are separated out of the first recovery stream at this point are redirected to a standard waste management facility, and likely end up in landfill. This waste is only a very small percentage of the total mass of AHP that is processed.

Clean plastic is then floated off the top of the first sink/float tank (33). The collected clean plastic is dewatered in a spin dryer (35) followed by drying in a thermal tubular dryer (37). The dried plastic is collected in a cyclone and then bagged as an end-product for plastics re-processors. This is the end of the first recovery stream.

In the second recovery stream, the mixed fibre and SAP slurry that passes through the screens of the trommel (27) is collected and is directed into a second pyramidal bottom sink/float tank (39).

Water from the first sink/float tank (33) spills out and is directed into the second sink/float tank (39) having a pyramidal bottom. This flow of water from the first sink/float tank (33) contains any fibres that were attached to the plastic in the first recovery stream, and which were subsequently detached by the friction washer (31). The purpose of the second pyramidal bottom sink/float tank (39) is to "float off" any plastic particles, typically those with a width or length smaller than 5mm, that may have passed through the drum screen plate holes of the trommel (27). The fibre and SAP slurry in the second pyramidal bottom sink/float tank (39) is pumped to, and recovered, on a static screen (41). The static screen (41) is a wedge wire screen with 0.7mm slots. The fibre and SAP slurry is partially dewatered on the static screen (41) and is thickened to approximately 5 wt.%.

The used water or filtrate from the static screen (41) is recycled as a counter-current wash solution for the initial washing steps that are carried out in the first and second two-shaft shredders (15) and (25) as noted above.

Consumer Product Processing

With reference to Figure 2, it can be seen that the thickened fibre and SAP slurry is further dewatered in a first screw press (43), to approximately 25-30 wt.% before entering an agitated reaction tank (45).

With reference to Figure 2, a process for manufacturing a consumer product from the thickened fibre and SAP slurry that is recovered in the second recovery stream will now be described. This process has been designed for use in manufacturing consumer products such as cat litter, absorbent material for spill kits, and pet bedding.

Fresh water, dewatering salt (magnesium chloride or calcium chloride) and peracetic acid (PAA) (5% peracetic acid, 6-10% glacial acetic acid, 20-30% hydrogen peroxide) are metered into the agitated reaction tank (45). The fibre and SAP slurry is diluted from 25- 30 wt.% to approximately 8-10 wt.% and held for about fifteen minutes to allow a sterilization reaction and bleaching action to occur. The contents of the reaction tank (45) are continuously agitated mechanically via a paddle on a rotating shaft.

The wash solution added is fresh water with an electrical conductivity of approximately 2.7 mS/cm and a pH of 2.9-3.3 and is created by the dissolution of MgCb or CaCh into the fresh water and the addition of peracetic acid. The continued agitation, and the dwell time of about fifteen minutes, washes out any soluble contaminants that may have been carried over from the initial washing described above. The resultant spent wash solution has a pH of approximately 5.6-5.9. The net result of this process step is a sterilized and washed fibre and SAP slurry, with the SAP optimally swollen.

After treatment in the reaction tank the fibre and SAP slurry is pumped by a screw pump (47) into a second screw press (49). The second screw press (49) dewaters the slurry to approximately 25-27 wt.%. The used water or filtrate from the first and second screw presses (43 & 49) is recycled back to the second pyramidal bottom sink/float tank (39).

At this point in the process, deodorants or fragrances can optionally be added into the dewatered fibre and SAP within a mixer (51), prior to further processing.

The dewatered fibre and SAP mixture is then extruded into pellets in a wet extruder (53). The wet extruder (53) can be a meat mincer/mixer, meat grinder or other extruder that uses a 6-8mm die plate.

The extruded pellets are transferred to the infeed of a mesh-belt or tray pellet dryer (55) where the pellets are dried to approximately 80 wt.%. A drying time of approximately forty to fifty minutes at approximately 80 degrees Celsius is generally required.

The dried pellets are discharged onto a conveyor that feeds a multi-tiered vibrating screen (57) that size classifies the pellets. By using a three-tiered vibrating screen (57) the dried pellets can be classified into cat litter (59), animal bedding (61) and a fines reject fraction. The cat litter pellets are then transferred to a hopper to feed a pellet product packaging line. The dried pelletized material can also be used as a spill kit material (60).

EXAMPLE 2

In this process the major separation into two streams is by the use of one or more screens (size separation). The density separation described with reference to the sink/float tanks is primarily to remove heavy tramp components such as glass. It is also possible to remove heavy plastics such as PVC using the sink/float tanks. The sink/float tank does not recover much fibre as that will have already been recovered via the screen(s) - preferably a trommel. There are several steps that aim to recover fibre that has been carried forward stuck on the plastics. This happens in the friction washers and in the plastics press, where the fibre is detached and carried away in a flood of water

Figure 3 shows the first part of the process resulting in the first stream leading to the recovery of the plastic fraction. Preferably as either fine worm shaped plastic agglomerate or plastic pellets.

The second stream diverges from the first part of the process at static screen 81 and this second stream is shown in Figure 4 leading to the production of absorbent pellets.

As shown in Figure 3, feedstock material - absorbent hygiene products (AHPs) - (101) are fed into the shredder (71) together with one or more dissolved salts (102) and water reclaimed from downstream in the process (121). The dissolved salts are dewatering salts as discussed in Example 1 - typically magnesium chloride or calcium chloride. Alternatively, the de-watering salts (102) may be added to the screw compactor (72).

In the shredder (71) the feedstock material is reduced in size by a cutting or tearing action and the dewatering salt reacts with the super absorbent polymers (SAP) in the feedstock causing them to release their retained water and other liquids.

The shredded material (103) is then fed into a screw compactor (72) which squeezes out much of the liquid (105) which is forwarded to the second sink/f loat tank (80).

The partially dried solids (104) pass to a second shredder (73) with additional reclaimed water (122) which further reduces the size of its components. This twice shredded material (106) is transferred to a trommel screen (74) and is flushed with large volumes of reclaimed water (119). Inside the trommel the fine fibre and SAPs (108) are flushed through the holes in the trommel and drain into the second sink/float tank (80), in dilute form.

The larger components which are mostly plastics (107) pass through the trommel and are forwarded to another shredder (75) to cut up the agglomerations that formed in the trommel (74). This shredded material (109) is washed in friction washers (76) to remove additional amounts of fibre and SAP (111) which are sent to the second sink/float tank (80) in dilute form.

The washed material (110) passes into the first sink/float tank (77), where materials with a density greater than water sink and are removed as waste. Materials with a density less than water float (112), are extracted and forwarded to a dryer (78). Overflow water and any entrained fibre and SAPs (113) are returned to the friction washers (76).

In the first stream, the drier (78) extracts water in liquid form (115) which is sent to the second sink/float tank (80). Additional moisture is driven off as water vapour. The dried materials (114) from the squeezer dryer (78) (Koeen ™ plastics squeezer dryer or similar machine with extrusion die-plate with 6-10mm holes) results in a fine worm like plastic agglomerate that can either be blended directly for plastics products re-manufacture or further processed in a granulator (79) prior to melting the plastics to form particles approx. 6mm in diameter (116).

The fibre and SAPs (117) that accumulate in the second sink/float tank (80) are pumped to the static screen (81), where much of the water is extracted. (See below for the fibre component shown in Figure 4). The majority of this water (119) is fed to the trommel screen (74), with the remainder (120) forwarded to the water tank (80A). A portion of the water arriving in the water tank (80A) is sent to sewer (125), possibly after on-site treatment, carrying away the excess water in the system and dissolved materials washed out of the feedstock. From the water tank (80A) flows water (121) to the first shredder (71); water (122) to the second shredder (73); water (123) to the friction washers (76) and water (124) to the first sink/float tank (77).

As shown in Figure 4, the concentrated fibre and SAPs (126) from the static screen (81) are squeezed in the press (82) to further remove water (128) which is returned to the second sink/float tank (80). The pressed fibre and SAPs (127) are processed in a delumper (83) to make the material loose and free flowing. Steriliser (129) is also added to the delumper (83) to kill bacteria and other potentially infectious components. The delumped and sterilised material (130) is forwarded to the reaction tank (84) where it is mixed with dissolved salts (131) and held to release additional water from the SAPs and permit additional anti-bacterial action. The fresh water (132) required to balance the sewage discharge (125) and vapour losses is also introduced at the reaction tank (84).

The treated fibre and SAPs (133) are then discharged to a press (85) to remove the excess water (135) which is return to the second sink/f loat tank (80). The pressed fibre and SAPs (134) are processed in the wet extruder (86) to form it into absorbent pellets of a size suitable for their intended use (136). These pellets are then dried in a drier (87) to the target moisture content, creating the final product (137).

The dried absorbent pellets can be used for spill kit material, cat litter, animal bedding, or any use where liquids need to be absorbed.

Industrial Composting

As an alternative to the production of a pelletized consumer product, the fibre and SAP slurry from the second pyramidal bottom sink/float tank (39) can be processed and sent for industrial composting.

In this alternative process, the fibre and SAP slurry from the second pyramidal bottom sink/float tank (39) is partially dewatered on the static screen (41) and then dewatering salt, and peracetic acid or another sterilising agent is added. The fibre and SAP slurry is then passed through a screw press (63) before being transported away for industrial composting.

The used water or filtrate from the static screen (41) and from the third screw press (63) is recycled as a counter-current wash solution for the initial washing steps that are carried out in the first and second two-shaft shredders (15) and (25) as noted above.

Processing Plants

Processing plants incorporating some or all of the equipment mentioned above, and the processes described herein, could be set up wherever there is a large population, and where a large volume of used AHP could be collected efficiently. The result of such plants would be a significant reduction in AHP that ends up in landfill, a reduction in harmful greenhouse gas emission from the decomposing AHP in landfills, and the production of useful consumer products such as cat litter, animal bedding and absorbent material for spill kits.

VARIATIONS

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

ADVANTAGES

The invention enables the fibre and SAP mixture recovered from waste AHP to be manufactured into a relatively high value absorbent products such as cat litter, animal bedding and spill absorbent products. The cat litter market is a large market with a relatively high retail value in many western countries. The cat litter from the AHP waste has a bulk density approximately half that of competitor recycled cat litter products (mainly newsprint cat litter pellets).

The lower bulk density allows half the weight of spent cat litter to be disposed to landfill resulting in half the emissions when in landfill which is advantageous in a climate constrained environment. Further advantages are lower transport costs for delivery due to the lower product weight.

The value-added fibre/SAP marketed into consumer products enables the overall AHP recycling process to become economically viable. As a result, the invention becomes the "economic key" to unlocking waste AHP recycling in regions where there are supportive landfill waste fees and cat litter markets. Examples of jurisdictions where there are moderate to high landfill fees and markets for cat litter include the major cities of the western world. This allows significant scope for the use of the inventions described herein.

Claims

1. A process for recycling used absorbent hygiene products (AHP) that have an inside layer comprising a fibre and a super-absorbent polymer (SAP) and an outer layer on at least one side of the inside layer that is made of sheet plastics material; the process comprising at least the following steps; an initial shredding and water washing step that is configured to remove a majority of any contaminants present in the used AHP, and then further shredding or pulping of the used AHP, and separation of the used AHP into two main recovery streams, a first recovery stream in which the sheet plastics material is recovered, and a second recovery stream in which the fibre and the SAP are recovered.

2. A process for recycling used absorbent hygiene products as claimed in claim 1, wherein the initial shredding and water washing step also includes the addition of a de-watering salt.

3. A process for recycling used absorbent hygiene products as claimed in claim 1 or claim 2, wherein the two streams are separated by size of the suspended matter.

4. A process for recycling used absorbent hygiene products as claimed in any one of claims 1 to 3, wherein the separation into two streams is achieved by using a trommel.

5. A process for recycling used absorbent hygiene products as claimed in any one of claims 1 to 4, wherein the first recovery stream is further processed by an additional shredding step or steps, drying and heating to form plastic flakes or pellets. A process for recycling used absorbent hygiene products as claimed in any one of claims 1 to 5, wherein the second recovery stream passes through at least one sink/float tank to remove any floating plastics residue. A process for recycling used absorbent hygiene products as claimed in any one of claims 1 to 6, wherein the second recovery stream is separated into water and fibre and the fibre component is pelletised to form pellets. A process for recycling used absorbent hygiene products as claimed in claim 6, wherein the pellets have an average diameter in the range of four to eight millimetres. A process for recycling used absorbent hygiene products as claimed in any one of claims 6 to 8, wherein the pellets have an average diameter of about six millimetres. A process for recycling used absorbent hygiene products as claimed in any one of claims 6 to 8, wherein the fibre and SAP material is dried after it is formed into pellets. A process for recycling used absorbent hygiene products as claimed in any one of claims 6 to 10, wherein the fibre and SAP material is dried using a mesh belt or tray pellet drier. A process for recycling used absorbent hygiene products as claimed in any one of claims 6 to 11, wherein the dried fibre and SAP pellets are classified into size ranges using a multi-tiered vibrating screen. Dried absorbent pellets produced in accordance with the process of any one of claims 6 to 12, suitable for use as spill kit material, cat litter, or animal bedding.