GB2465839A

GB2465839A - A processing line for recycling plastics

Info

Publication number: GB2465839A
Application number: GB0822234A
Authority: GB
Inventors: Michael Buckley; Brian Buckley
Original assignee: GREYHOUND POLYOLEFINS RES Ltd
Current assignee: GREYHOUND POLYOLEFINS RES Ltd
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-09
Also published as: GB0822234D0

Abstract

The present invention is directed to an improved processing line and process for the segregation and recycling of many different types of plastics on an industrial scale. The plastics recycling line comprises a conveyor for delivery of waste plastics material through a number of sequentially arranged stations/stages including a primary shredding station to a particle size of 100-500mm, a primary contaminant removal station, a secondary shredding station (32) to a particle size of 50-150mm, a secondary contaminant removal station, a primary granulating station (49), a primary flotation station, a drying station (64, 66), a primary optical separation station (e.g. infra red) and a storage station (82) wherein the processed plastic is stored in an end product silo (82) prior to further processing, such as moulding. A rotary screen 22, ferrous metal separator 24 and/or a manual contaminant removal using a picking line 26 may be used at the primary contaminant removal stage. A non-ferrous metal separator 40, air separation and/or a plastic film separator 38 may be employed as a secondary contaminant removal stage. At station (49), the plastic material is granulated to a particle size of 10-50mm.

Description

"A Processing Line"

Introduction

The present invention is directed to an improved processing line and process for the segregation and recycling of many different types of plastics on an industrial scale.

Waste recycling and in particular the recycling of plastic waste is becoming a difficult problem. The problem is caused by the fact that the plastic waste is generally not homogenous and comprises non-plastic material and many different types of plastics. In fact, the sorting and classification of plastic waste is now a major part of any recycling activity. Generally speaking, in the case of plastics, sorting and classification is done according to resin category because in order for plastic to be recycled into reusable resins, a pure stream of resin must be obtained.

Plastic materials generally consist of the following types PET (polyethylene terephthalate), HDPE (high density polyethylene), LDPE (low density polyethylene), PVC (poly vinyl chloride), PP (polypropylene) and PS (polystyrene). Other materials to be sorted include other plastic types such as ABS (Acrylonitrile butadiene styrene) and also various rubber types, including natural and synthetic rubbers (e.g. latex) and EPDM rubber (ethylene propylene diene M-class rubber).

Current commercially available systems and processes for recycling plastics can generally only separate a narrow range of plastic types. Thus, the plastics must be sorted according to plastic type prior to further processing. Generally, plastic sorting in this manner is carried out by hand, which is expensive and time consuming.

Furthermore, conventional systems can generally only process one specific type plastic at a time.

Additionally, in such conventional systems contaminant tolerance level is low.

The present invention aims to overcome these problems and provide a more robust plastics recycling processing line and process suitable for use on an industrial scale.

Statements of the Invention

According to a general aspect of the invention there is provided, a plastics recycling processing line for mixed waste plastics material including a conveyor for delivery of waste plastics material through a number of sequentially arranged stations comprising a primary shredding station for shredding the waste plastics material to an average size from approximately 100 to 500mm; a primary contaminant removal station including a rotary screen (22), ferrous metal separator (24) and/or a manual contaminant removal station (26); a secondary shredding station (32) for shredding the waste plastics material to an average size from approximately 50 to 150mm; a secondary contaminant removal station including a non-ferrous metal separator (40), and/or a plastic film separator (38); a primary granulating station (49) for granulating the plastics material to an average size from approximately 10 to 50mm; a primary floatation station wherein the granulated plastics material is passed through a flotation tank (60); a drying station (64, 66) wherein the plastics material from the sink and/or float stream of the floatation tank is dried; a primary optical separation station, preferably utilising near infra-red (NIR) technology; and a storage station (82) wherein the processed plastic is stored in an end product silo (82) prior to further processing.

According to a more specific aspect, the processing line further comprises the following sequentially arranged stations located downstream from the optical separation station a secondary granulation station (72) for granulating the plastics material to an average size from approximately 2 to 10mm; a secondary flotation separation station wherein the granulated plastics material is passed through a further floatation tank (76); and a secondary drying station (78, 80) wherein the plastics material is dried prior further processing.

Currently no there are no commercially available systems which can process highly mixed and size-varied plastic material streams. The improved process of the invention allows the segregation of the order of ten to twenty different plastic types on a single plastics recycling line. This has not been possible previously and is a major advantage of the improved process It will be understood that the plastics to be recycled may be derived from both post-consumer or pre-consumer waste. That is plastics of any size and of any origin both after consumer use and pre-consumer use, such as plastic waste from industrial processes.

The plastics material processed in the present invention may be either rigid plastic or plastic film, covering every major type of plastic (PVC, PE, PP, PET etc). It will also be understood to include various different rubber types, such as natural and synthetic rubber and/or EPDM. As the source s generally post-consumer waste, the plastic materials being processed are generally a mixture of many of the afore-mentioned plastic/rubber types.

Bulk sources for plastics to be recycled include waste management companies, automotive recovery facilities, waste electrical reprocessing companies and plastics and components manufacturers. For example, durable goods plastics sources include household plastics (such as toys, garden furniture, house furnishings, drink and food containers, chemical packaging etc), commercial plastics (such as drums, barrels, component parts, packaging, pallets etc.), agriculture plastics (such as chemical containers, etc), construction and demolition plastics (such as piping, guttering, drums, buckets, etc), automotive plastics (such as car parts, bumpers, etc), and manufacturing plastics (such as off-spec components, sprue and purge, packaging, traffic cones, barriers, traffic lights, etc).

Thus, unlike current commercially available systems the improved process can accept and accurately and efficiently separate plastic materials of all components shapes, sizes, wall thickness and colour in a single processing line.

In addition, the present invention is more tolerant of high in-feed impurities due to the set-up of the processing line. Thus, in addition to circumventing the need for the plastics to be separated according to plastic type, the processing line can tolerate a high level of impurities which would be expected from processing many different plastics of different origin.

A yet further advantage of the improved process is that it provides a very high throughput. This means that the system is optimised for use on an industrial scale. It is estimated that the throughput for the improved process and plastics recycling line is approximately 5 tonnes per hour. This is a significant increase compared to conventional process lines, which typically only process about 1 to 1.5 tonnes per hour which in addition to providing a much lower throughput It will be understood that the processing line of the invention may be used as a continuous processing line or as a batch processing line.

Thus, even though the stations are located sequentially, the process may be stopped at any stage and the resultant plastics material may be stored and reintroduced to the processing line for further processing at a later time. This is a significant advantage of the processing line of the invention.

For example, polyolefins may be recycled on one complete run of the processing line and the plastics obtained which are not polyolefins can then be collected and separated at a future time, for example once processing of the polyolefins has been completed. In addition, processed plastic may be collected at various stages during the process, for example, after shredding and contaminant removal or after granulation and/or passing through the sink/float tank and retained for further processing at a later time.

It will be understood that conveyors, such as screw conveyors, are used to transport the plastic through the processing line. At various stages the plastic may be stored in storage bins or silos. Hoppers may then be used to reintroduce the stored plastics to the processing line.

According to one embodiment of the invention, the processing line may comprise one or more floatation tanks are used in series.

According to another embodiment of the invention, the flotation tank may comprise baffles, ideally located approximately mid-tank, to physically separate the different fractions of separated plastics, i.e. the sink fraction from the float fraction, and to prevent turbulence within the tank when the sink fraction or float fraction is removed for further processing.

It will be understood that the floatation media used in the sink/float tank may be water or metal salt solutions, such as sodium chloride (NaCl) or calcium chloride (CaCI2).

Ideally, the primary or secondary floatation steps utilise one or more flotation media types, preferably selected from water or salt solutions, such as sodium chloride or calcium chloride, with different salt concentrations.

According to one embodiment of this aspect of the invention, an initial low concentration of salt is used in the floatation tank and the salt concentration is increased incrementally by the addition of further salt to enable the use of a single floatation tank to separate different plastic fractions.

For example, if the plastic material to be separated and removed are polyolefin resins, including polypropylene (PP) and polyethylene (PE), a first floatation media comprising water is used and the polyolefins float to the top of the flotation tank and are removed as the float fraction, subsequently salt is added to the water to form a second floatation media to separate out the different higher density fractions of plastics material present in the sink fraction.

According to one embodiment of the invention the shredding station comprises a shredder such as, for example, a shredder described in our co-pending Patent Application No. 0219813.3 comprising a plurality of hammer-like projecting flails which beat and abrade the material.

According to an alternative embodiment of the invention, the shredder may comprise a single shaft shredder with screen basket discharge. This type of shredder is ideally used in secondary shredding to achieve a smaller particle size then the primary shredding step.

In one embodiment, the shredder has a cutting face and an angled pusher system to press materials to the shredder cutting face, so that shredding is more effective.

According to one embodiment of the invention, the plastics material is subjected to an optical separation step.

Such an optical separation step, ideally takes place using near infrared (NIR) technology although other optical separation techniques may be used.

It will be understood that the processing line may comprise one or more optical separation stations which are ideally located downstream of the drying station.

The optical separation station comprises a light source for emitting light onto the plastics material and a sensor for detecting light reflected from the plastics material.

In use, the optical separation step comprises the steps of emitting light onto the plastics material and detecting the light reflected from the plastics material, such that detected plastics material are selected for further processing and the non-detected plastics material are separated and removed.

Ideally, the light source emits light in the near infrared (NIR) spectrum and a NIR spectrum of the plastics material is obtained. Preferably, light is emitted at a wavelength range from 800 to 2500nm.

Essentially, the plastics materials are transported by a conveyor through the optical separation station. The plastics material first pass through a near infra red (NIR) sensor. The NIR sensor recognizes the specific type of plastic based on the spectrum of light reflect as it passes through the sensor. The NIR sensor, is programmed to detect a particular plastic type of interest and once detected the information obtained is electronically processed, so that the desired materials are separated from the undesired material. Generally, the materials are separated by high-precision jets of air located at the end of the conveyor belt after the optical sensor.

This type of NIR separation is not conventionally used in the separation of mixed plastics.

An optional electrostatic separation step may also take place to separate plastic of the same colour and density, preferably after the optical separation step.

Detailed Description of the Invention

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a process outline of the plastics recycling process; Fig. 2 is a process outline of part of the plastics recycling process; Figa. 3a to c are a schematic illustration of the plastics recycling processing line; Fig. 4 is a schematic illustration of the shredder/plunger of step 4; Fig. 5 is a schematic illustration of the floatation tank of step 7.

Referring to the drawings and initially to Figs. 1 in particular, there is illustrated a plastic recycling processing plant, indicated generally by the reference numeral 1.

The plastic recycling processing plant 1 comprises various stages, all indicated generally by reference numerals, namely, a primary shredding station 2, primary contaminant removal station 3, a secondary shredding station 4, a secondary contaminant removal station 5, a primary and secondary granulation station 6/10, a primary and secondary flotation separation station 7/11, drying stations 8/12, optical and/or electrostatic station 9 and a further processing station 14.

The various stages of the improved plastics recycling process line are outlined as follows: Referring to the drawings, Figs. 1 and 2 show the general steps involved in the plastics recycling process of the invention generally indicated by the reference numeral 1.

In step 2 (Primary Shredding) the waste plastics material undergoes an initial shredding step to form a first shredded plastics material. This shredding step may take place as the first step of the processing line or may be a separate station to the processing line.

As the waste plastics material is of many difference types and from many different sources, such as but not limited to office waste (e.g. chairs, computer cases), packaging, industrial waste (e.g. pipes) etc, it is important that this initial shredding step can reduce the side of the source plastic material to a relatively uniform size which may be easily processed in the rest of the plastics recycling line.

Ideally, the waste plastic material is reduced to a size range of approximately 100mm to 500mm.

Ideally, a primary crusher is used to reduce the size of the source plastic material although other shredder types may be used. For example, a typical shredder used in this operation is a conventional shear shredder. The shaft speed and teeth configuration will be such that the plastic material is drawn into the shredder without bridging, bouncing or blocking.

According to one embodiment of the invention, the shredder has a typical shaft speed of approximately 5 to 15 rpm.

According to a further embodiment of the invention the shredder has tiered off-set teeth.

In step 3 (Primary Contaminant Removal) the first shredded plastics material is subjected to an initial contaminant removal step. This step aims to remove contaminants from the shredded plastic by removing, for example, dirt, debris and metals. This step prevents damage and maximises the life of the shredding installations and maintains the purity of the shredded plastic.

Step 3 may involve many different stages as follows: Rotary screen/Trommel screen The shredded plastic is passed through a conventional rotary or trommel screen to remove contaminants. This is an important step as many different plastics are processed at the same time, thus, many different types of waste will be present.

Some of the shredded plastic will have contaminants, for example plastics pipes could potentially have contaminants, in the form of stone and mud, attached. Such contaminants must be removed before the shredded plastic undergoes further processing. The trommel screen works in the conventional manner and removes the majority of external contaminants.

Ideally, the trommel screen is run at a slower speed, from approximately 5rpm to 10rpm, than used for standard waste screening operations. This is to allow dry cleaning of dirt and mud deposits from the shredded plastic through the friction process.

In addition, ideally the trommel drum incline is preferably maintained at a minimum incline to maximise retention time and increase contaminant removal.

Thus, according to one embodiment, the rotary or trommel screen may be a conventional rotary screen.

According to another embodiment, the rotary screen or trommel screen comprising a substantially cylindrical drum mounting a perforated screen cloth; and a plurality of inwardly directed elongate teeth projecting beyond the screen cloth mounted spaced-apart circumferentially and axially within the screen, wherein each tooth comprises a substantially triangular flat spear head-like blade having a relatively thick inner portion of at least 5mm converging into a blunt rounded leading edge, the converging sides of the blade subtending an angle greater than 6O and terminating in a rounded free distal end.

The advantage of the present invention is that because the blades are relatively blunt, they will not carry around with them harder materials such as pieces of wood and the like while, at the same time, they are sufficiently sharp to abrade and cut the material being processed.

In a still further embodiment, the leading edge of the tooth subtends an angle greater than 90 and indeed may subtend an angle of the order of 120g.

In another embodiment of the invention, the teeth extend from adjacent a proximal entrance end of the screen for of the order of two thirds of the length of the screen and in another embodiment of the order of one quarter of the length of the screen.

In another embodiment of the invention, the teeth project at an angle inclined to the radius of the screen. -11 -

In the rotary screen according to the present invention, a cover plate is mounted above the screen and spaced-apart a relatively small distance therefrom to prevent delivery of material out of the screen.

In a still further embodiment of the invention, brushes are mounted on the exterior of the screen in contact with the screen cloth to clean the screen.

In a still further embodiment of the invention, the screen is inclined downwardly from entrance to exit and ideally between 2 and 5 to the horizontal.

Manual contaminant removal This involves the manual removal of contaminants at a picking station to remove any contaminants which the trommel screen did not. This is important in order to ensure the plastics stream is a pure as possible prior to undergoing further processing.

Typically, non-plastic material contaminants such as wood, insulation, foams, etc are removed in this step.

Metal removal The step involves the use of a magnetic separator to remove and contaminant ferrous metals from the plastics material.

SteD 4 (Secondary Shredding) involves a further shredding step to achieve a second shredded plastics material with a typical average particle size of approximately 50 to 150mm.

Ideally, a single shaft shredder with screen basket discharge is used. In a preferred embodiment, the shredder comprises a cutting face and an angled plunger system to press materials to the shredder cutting face.

Stei 5 (Secondary contaminant removal) involves the removal of non-ferrous metals, such as aluminium, and again aims to prevent damage, to maxim ise the life of the shredding installations and to maintain purity of the shredded plastic.

Non-ferrous metal removal occurs by passing the secondary shredded plastics -12-material through an Eddy current to remove non-ferrous materials, such as aluminium. It is important that this step is separated from the magnetic separator step as both steps would potentially interfere with each other if there were located in close proximity.

Air separation This comprises the removal of light contaminants such as film, paper, foams, and other wastes using density separation. Ideally, air shifter units or aspirators are used.

It is possible to set the air volumes/velocity to obtain different removal rates etc. A fan system and/or plastics film removal system may be used.

Step 6 (Primary Granulation) is an essential step when rigid plastics are being processed.

When materials such as plastics film are being processed, this step is not required and the light contaminants isolated in the air separation step bypass this granulation step.

Granulation may be wet or dry. Surprisingly, this step can incorporate a wet granulation procedure which would not be expected in situations like this. Wet granulation allows further washing and cleaning of the shredded plastic through introduction of water and/or water based detergents and chemicals into the abrasive cutting zone.

The aim of this granulation step is to process the plastics material to a primary granulated plastics material with an average size from approximately 10 to 50mm, preferably from approximately 8 to 15 mm. Granulation prior to floatation separation is critical as introduces a small uniform particle into the process. This ensures surface area and shape do not influence separation leading to unhindered and rapid separation of the plastic in the media.

Step 7 (Primary floatation separation) separates granulated plastics material from contaminants and into desirable/undesirable plastic types using conventional differential density based floatation separation technology.

In order to maximise throughput and optimise the system, the granulated plastic is ideally processed through various floatation or sink/float tanks. Such a floatation tank comprises a plastics material inlet and a sink fraction outlet and a float fraction outlet.

It will also be understood that a single floatation tank may be used, wherein the density of the floatation media is sequentially increased or decreased to allow the separation of different plastic types and/or contaminants.

Alternatively, one or more floatation tanks may be used in series.

Excessive Turbulence within the tanks is a problem and can affect the accurate segregation and recovery of the targeting plastic resins. In order to overcome this problem, the flotation tank used has baffles located mid-tank to separate the different fractions of separated plastics (i.e. the float and sink fractions) and to ensure that when the top layer of plastics (the float fraction) is removed, the turbulence created does not disturb the bottom layer (the sink fraction).

The floatation system can use a wide range of floatation media depending on the plastic which are being separated. Water and metal salt solutions (NaCI and CaCl) are preferred. However, the actual media used is dictated by the plastics being processed and what is needed to be separated.

Typical densities for different plastic types are outlined below: Polymer type Density [kg/dm3] 0.8 0.9 1.0 1.1 1.2 1.3 1.4

BS

oft natural rubber II _______________ Hard rubber _______ [iLl JTT1 __

PA

PC I

PE

PET _____J[_

PMMA -

PaM IIIIIIIIII(

PS

Pvc..u ______ IlilIli EPDM, rubber, HDPE, PE and PT have densities less than 1 kg/dm3 and form a sink fraction in water. The remaining have densities greater than 1 kg/dm3 and form a float fraction in water.

According to one specific embodiment, for separation of polyolefin resins (PP/PE) the flotation tanks use water to ensure that the polyolef ins will float to the top of the tank and the heavier plastics will remain at the bottom of the tank. The top layer of polyolef in is then removed and salt can be added to the water in the tank to separate out the different high density fractions of plastics remaining. An initial low concentration of salt is used, which can be increased incrementally by the addition of further salt. This ensures that a single tank may be used for separating out different fractions of the heavier density plastics.

This sequential use of different water and salt concentrations will separate different fractions and will ensure that only one flotation tank is used thereby reducing waste and providing a more efficient system.

In stei 8 (Drying), the plastics material from the sink stream is dried. Drying may occur using a standard column dryer and/or a centrifugal dewaterer. Alternatively, drying can take place wherein air is heated through an element and blown through metal coils allowing the material passing through to dry.

In step 9 (Optical Separation), the dried plastic from either the float or sink fraction is subjected to an optical separation step, utilising X-ray or near infrared technology.

Such an optical separation station comprises a light source for emitting light onto the plastics material and a sensor for detecting light reflected from the plastics material to allow a target plastics material to be selected and separated from non-targeted plastics material.

Targeted segregation of plastic resin types ideally uses a combination of optical separation devices utilising near infra-red (NIR) technology. This can split the multi-resin plastics material into fractionated streams. This has an advantage that when further floatation tanks are located downstream of the optical separation station, the floatation media can be adapted to suit the composition of the infeed plastics material.

Essentially, in this step the dried plastic material is transported by conveyor through the NIR sensor area. The plastic is analysed and depending on the programmed sorting criterion setting, the detected materials are separated from the dried plastic material being transferred along the conveyor by high precision jets of pressurized air.

One of the downsides to optical separation is that opaque and black plastics cannot be separated. Thus, in order to overcome this, other techniques, such as electrostatic separation may also be used. Electrostatic separation is the selective sorting of solid species by means of utilizing forces acting on charged or polarized bodies in an electric field. Separation is effected by adjusting the electric and coacting forces, such as gravity or centrifugal force, and the different trajectories at some predetermined time. Separations made in air are called Electrostatic Separation Optional electrostatic separation (not shown) may be used in addition to or in place of the optical separation station. Such electrostatic separations stations separate plastics of the same colour and density, such as polystyrene (PS) and acrylonitrile butadiene styrene (ABS) or flexible and rigid polyvinyl chloride (PVC). Such electrostatic separation would generally take place after the plastics material is dried to separate the polyolef ins The processed plastics material may then be subjected to a further round of granulation, floatation separation and drying prior to final processing or may go directly to final processing.

In step 10 (Secondary granulation), the plastics material may then be subjected to another round of granulation 10. This secondary granulation step is desirable because step 9, optical separation requires plastics material of a larger size than acceptable for end use. Ideally, this secondary granulation achieves a secondary granulated plastics material with a typical average size of approximately 2 to 10mm.

In step 11, (Secondary flotation separation) the secondary granulated plastics material is subjected to another floatation separation step. This secondary granulation step loosens up dirt and gum layers from the granulated plastics material.

Thus, this secondary floatation separation step is required to further clean the plastics material after secondary granulation In step 12 (Drying), the plastics material is dried prior to washing and further processing. Drying may occur using a standard column dryer and/or a centrifugal dewaterer.

Figure 1 also shows an optional optical separation and/or electrostatic separation step which may take place between step 12 and step 13.

In step 13, the recycled plastic is then stored in an end product silo. Jt will be understood that one or more recycled plastics types are selected as outputs of the process.

In the final step 14 (Futher Processing), which is an optional step, the processed plastic from step 9 or step 12 is subjected to a washing and further dewatering step.

This post separation washing step further facilitates the water and/or chemical washing of plastic streams to remove any final residual dirt, resins, glues or other coatings. Secondary washing polishes the segregated stream and ideally incorporates solvent recovery system to minimise chemical usage and process emissions Ideally, this step involves a high speed centrifugal washing step to remove any residual moisture followed by a hot air drying step to produce a dry product for packaging and sale.

At this stage, the processed plastics are highly varied and the process is designed to facilitate all plastic types (soft/film, semi-rigid and rigid).

The cleaned and dried recycled plastics may then be collected and subjected to further processing. For example, the recycled plastics may be compounded and pelleted.

It will be understood that the dried recycled plastics may be subjected to extrusion moulding. Essentially, extrusion moulding forces a plastic or molten material through a shaping die on a continuous basis. The feedstock may enter the extruder device in a molten state, but generally consists of solid material that is subject to extruder melting, mixing and pressurisation. Most plastic extruders incorporate a single screw rotating in a horizontal cylindrical barrel with an empty port mounted over one end and a shaping die located at the discharge end. A simple screw design for a solid fed single screw extruder must convey the plastic entering the screw into a heated compacted environment where the shear force developed by the rotating screw melts the plastic and mixes it to a reasonably uniform temperature while pressurising the melt and pumping it uniformly through the die.

It will also be understood that the processing line may be worked as a continuous processing line or may be used for batch processing. When used for batch processing, the plastics material may be stored for further processing after the various steps of the process. For example, the process may be stopped after secondary contaminant removal and the plastics material may be stored in a silo for further processing at a later date. Storage bins or silos may also be present after primary or secondary granulation or after primary or secondary floatation separation.

This has the added advantage that the mixed plastics materials may be sorted in the processing line into the constituent single plastic types. One plastic type will be selected to be processed through the entire processing line and the other plastic type can be stored as a single plastic type after for example, granulation and/or optical or electrostatic separation.

Figs. 3a to c shows a schematic illustration of one embodiment of the invention. The plastics recycling processing line comprises a conveyor belt (20) which delivers plastics material which have undergone a primary shredding step (not shown) to the drum screen (22). The primary shredded plastics material is then passed through a ferrous metal separator (24) and subjected to manual contaminant removal using a manual picking line (26). This is primary contaminant removal (step 3) The plastics material is then passed on a further conveyor belt (28) to undergo a secondary shredding step (step 4) in shredder (32). Ideally, this shredder is a single shaft shredder with a shredder cuffing face and an angled plunger system to press the plastics material to the shredder cutting face.

The secondary shredded plastics material then undergoes a secondary contaminant removal step (step 5). This step involves the removal of non-ferrous metals using a non-ferrous metal separator (40) and/or a plastic film separator (38). The fan system (34, 42) is used to transport the material to a silo/storage bin as needed.

After secondary contaminant removal, the plastics material undergoes a primary granulation step 6 in a granulator (49). The aim of this granulation step is to process the recycled plastics to an average size from approximately 10 to 50mm, preferably from approximately 8 to 15 mm.

Screw conveyors (36, 44, 48, 52, 56, 68, 74) are used in part of the processing line.

The plastics material may be stored in various silos (54, 46, 62, 82) either at the end of the process or after secondary contaminant removal or even when separated into different plastic types after granulation and floatation separation.

The primary granulated plastics material is then passed to silo (54) and then to a floatation tank (60) a screw conveyor. This is the primary floatation separation step 7 which separates granulated plastic from contaminants and into desirable/undesirable plastic types using conventional differential density based floatation separation technology. It will be understood that one or more sink/float tanks may be used in series (not shown). Cyclone (58) is present to aid the passage of LDPE through the processing line.

As mentioned previously, excessive turbulence within the tank can be a problem and ideally the flotation tank used has battles mid-tank to separate the different fractions of separated plastics and to ensure that when the top layer of plastics is removed, the turbulence created does not disturb the bottom layer.

Ideally, the floatation media is water or metal salt solutions, such as NaCI and CaCI In step 8, the plastics from the sink stream are dried. Drying may occur using a standard column dryer (64) and/or a centrifugal dewaterer (66). At this stage the dried plastics material may be stored for further processing at a later time in end product silo (62).

In step 9, the dried plastic is subjected to an optical separation step (not shown), utilising near infra-red (NIR) technology, and/or electrostatic separation. It will be understood that optical or electrostatic separation may take place after any drying step in the process.

The processed plastics material may then be subjected to a further round of granulation, floatation separation and drying prior to final processing or may go directly to further processing.

In step 10 (Secondary granulation), the recycled plastics (after drying or optical separation) may then be subjected to another round of granulation in granulator (72) to achieve a typical average size of approximately 2 to 10mm.

In step 11 (Secondary flotation separation) the dried plastic is subjected to another -20 -floatation separation step in floatation tank (76).

In step 12 (Drying) the processed plastics material are dried prior to washing and final processing using dessicator (78) and a centrifugal dryer (80).

In step 13, the recycled plastic is then stored in an end product silo (82) before further processing (not shown).

Fig. 3 also shows various electric panels (30, 50, 70).

Fig. 4 is a schematic illustration of the shredder/plunger of step 4. In use, the plastic material enters the shredder (32) via a hopper (86). The plastic material then passes through the shredder cuffing blades (92). Ideally the cutting blades (92) are offset cutting teeth. A pusher (88) forces the plastics material onto the cutting blades (92) via a pusher arm (90) using a hydraulic based system.

In one embodiment, the pusher is an angled pusher system designed to press materials to the shredder cutting face. Ideally, the shredder is a single shaft shredder.

The shredded plastic then passes through a screen basket (94) to a screw conveyor (96) where is then passes to the next stage in the process secondary contaminant removal (5). Ideally, the screen is held by the hydraulic arm (102). The screen may be of any suitable shape and the mesh size of the screen can be altered to any desired size as necessary. The flange (100) and handwheel (98) provide access to the cuffing blade and screen as necessary.

Fig. 5 is a schematic illustration of the floatation tank of steps 7 and 11.

The floatation tank separates the high and low density plastic material and generally comprises an elongate tank with an inlet for receiving an inlet mixture of high and low density plastic materials, and outlets spaced away from the inlet for the separated high and low density plastic materials respectively, and at least one baffle in the tank located between the inlet and outlets. Ideally, the first outlet is for removing high density plastic materials and a second outlet is for removing low density plastic materials.

The floatation media can be water or a salt solution. The type of floatation media used depends on the plastics materials being separated.

According to one specific embodiment of this aspect of the invention, the flotation tank (60, 76) comprises one or more baffles located mid-tank to separate the different fractions of separated plastics and to ensure that when the top layer (float fraction) of plastics material is removed, the resultant turbulence created does not disturb the bottom layer (sink fraction).

We have found that a configuration of approximately 4 to 10 baffles is ideal for the present purposes. The first baffle located in proximity to the inlet ensure the plastics material is fully wetted, an essential feature if density separation is to work to the full potential. The second and third baffles assist the downward flow of the fully wetted plastics material and also reduce the turbulence in the tank.

As shown in Figure 5, the baffles (106) are evenly spaced within the floatation tank.

Ideally, the baffles are made of elongate metal sheeting and are fixed to both side-walls of the floatation tank. The baffles are located between the paddles (106) and screw conveyor (108). Ideally, the baffles are set at an approximately 45 degree angle from the vertical. As shown in Figure 5, eight baffles are used. It will be understood that the baffles are spaced apart from the inlet and outlets.

We have found that a tank wherein the outlet for the sink fraction is located at an approximate mid-point between the front and back sides of the tank advantageously minimizes the turbulence within the tank.

Thus, the baffles have a three main functions, namely to assist in the wetting of the plastics material, to prevent turbulence re-mixing the separated sink and float fractions and also to assist the sink fraction in moving to the base of the floatation tank.

-22 -There are several paddles (106) located above the baffles in the tank to assist in the mixing of the plastics material and the floatation media. Ideally, the paddles comprise a series of elongate fingers affixed to a rotable device, wherein the fingers mix the plastics material and the floatation media as needed, whilst minimizing the turbulence caused if the paddles were continuous elongate members.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is in no way limited to the embodiment hereinbefore described but may be varied in both construction and detail. -23-

Claims

CLAIMS: 1. A plastics recycling processing line for mixed waste plastics material including a conveyor for delivery of waste plastics material through a number of sequentially arranged stations comprising a primary shredding station for shredding the waste plastics material to an average size from approximately 100 to 500mm; a primary contaminant removal station including a rotary screen (22), ferrous metal separator (24) and/or a manual contaminant removal station (26); a secondary shredding station (32) for shredding the waste plastics material to an average size from approximately 50 to 150mm; a secondary contaminant removal station including a non-ferrous metal separator (40), and/or a plastic film separator (38); a primary granulating station (49) for granulating the plastics material to an average size from approximately 10 to 50mm; a primary floatation station wherein the granulated plastics material is passed through a flotation tank (60) to form a sink stream and float stream of plastics material; a drying station (64, 66) wherein the plastics material from the sink stream and/or float stream of the floatation tank is dried; a primary optical separation station, preferably utilising near infra-red (NIR) technology; and a storage station (82) wherein the processed plastic is stored in an end product silo (82) prior to further processing. -24-
2. The processing line according to claim 1 further comprising the following sequentially arranged stations located downstream from the optical separation station a secondary granulation station (72) for granulating the plastics material to an average size from approximately 2 to 10mm; a secondary flotation separation station wherein the granulated plastics material is passed through a further floatation tank (76); and a secondary drying station (78, 80) wherein the plastics material is dried prior further processing.
3. The processing line according to claim 2 comprising a secondary optical separation station downstream of the drying station.
4. The processing line according to any of the preceding claims wherein the primary and secondary optical separation stations comprise a light source for emitting light onto the plastics material, a sensor for detecting light reflected from the plastics material and an air-jet source.
5. The processing line according to claim 4 wherein the light source emits light in the near infrared (NIR) spectrum and a NIR spectrum of the plastics material is obtained.
6. The processing line according to claim 5 wherein light is emitted at a wavelength range from 800 to 2500nm.
7. The processing line according to any of the preceding claims further comprising an electrostatic separation station, preferably directly downstream of the optical separation station.

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8. The processing line according to any of the preceding claims wherein the primary or secondary floatation separation stations comprise one or more floatation tanks in series.
9. The processing line according to any of the preceding claims wherein the flotation tank comprises a series of baffles which physically separate the sink fraction and float fractions of plastics material and prevent the generation of turbulence within the tank when the sink fraction and/or float fraction is removed.
10. The processing line according to any of the preceding claims wherein the floatation tank includes water or metal salt solutions, such as sodium chloride or calcium chloride, as the floatation media.
11. The processing line according to any of the preceding claims wherein the drying station comprises a column dryer (64), dessicator (78, 80) and/or a centrifugal dewaterer (66).
12. A process for recycling mixed plastics comprising passing waste plastics material on a conveyor belt through a number of sequentially arranged stations wherein the process comprises a primary shredding step for shredding the waste plastics material to obtain a first shredded plastics material with an average size from approximately 100 to 500mm; a primary contaminant removal step wherein the first shredded plastics material is passed through a rotary screen, a ferrous metal separator (24) and/or subjected to manual contaminant removal using a picking line (26); a secondary shredding step for shredding the waste plastics material to a second shredded plastics material with an average size from approximately 50 to 150mm; -26-a secondary contaminant removal step wherein non-ferrous metals are removed from the second shredded plastics material using a non-ferrous metal separator (40) and other contaminants are removed from the second shredded plastics material using air separation and/or a plastic film separator (38); a primary granulation step wherein the resultant plastics material is placed in a granulator (49) to achieve a primary granulated plastics material with an average size from approximately 10 to 50mm, preferably from approximately 8 to 15 mm; a primary floatation separation step wherein the primary granulated plastics material is passed to a floatation tank (60) and the sink stream and/or float stream plastics material is recovered; a primary drying step wherein the plastics material from the sink and/or float stream is dried; a primary optical separation step wherein the dried plastics material is separated according to plastic type utilising an optical separation step, preferably utilising near infra-red (NIR), technology; and the resultant plastics material is stored in an end product silo (82) before further processing.
13. The process according to claim 12 further comprising the following processing steps prior to storing the plastics material in the end product silo (82) a secondary granulation step wherein the plastics material is subjected to further granulation in granulator (72) to achieve a secondary granulated plastics material with an average size of approximately 2 to 10mm; -27 -a secondary flotation separation step wherein the secondary granulated plastics material is subjected to a further floatation separation step in floatation tank (76) and the sink and/or float stream plastics material is recovered; and a secondary drying step wherein the plastics material is dried.
14. The process according to claims 12 or 13 further comprising a secondary optical separation step downstream of the drying station.
15. The process according to any of claims 12 to 14 wherein the optical separation step comprises emitting light onto the plastics material and detecting the light reflected from the plastics material, such that detected plastics material are selected for further processing and the non-detected plastics material are separated and removed from the processing line.
16. The process according to claim 15 wherein the light source emits light in the near infrared (NIR) spectrum and a NIR spectrum of the plastics material is obtained.
17. The process according to claim 16 wherein light is emitted at a wavelength range from 800 to 2500nm.
18. The process according to any of claims 12 to 17 further comprising an electrostatic separation step.
19. The process according to any claims 12 to 18 wherein the primary or secondary floatation separation stations comprise one or more floatation tanks in series.
20. The process according to any of claims 12 to 19 wherein the flotation tank comprises baffles which physically separate the sink fraction and float fraction of plastics material and prevent the generation of turbulence within the tank when the sink fraction or float fraction is removed.

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21. The process according to any of claims 12 to 20 wherein the primary or secondary floatation steps utilise one or more flotation media types, preferably selected from water or salt solutions, such as sodium chloride or calcium chloride, with different salt concentrations.
22. The process according to claim 21 wherein an initial low concentration of salt is used in the floatation tank and the salt concentration is increased incrementally by the addition of further salt to enable the use of a single floatation tank to separate different plastic fractions.
23. The process according to claim 21 wherein the plastic material to be separated and removed are polyolef in resins, including polypropylene (PP) and polyethylene (PE), wherein a first floatation media comprising water is used and the polyolefins float to the top of the flotation tank and are removed as the float fraction, subsequently salt is added to the water to form a second floatation media to separate out the different higher density fractions of plastics material present in the sink fraction.
24. A processing line and/or process for recycling mixed plastics as described herein with reference to and as illustrated in the accompanying drawings.