Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/02—Separating plastics from other materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/30—Destroying solid waste or transforming solid waste into something useful or harmless involving mechanical treatment
  • B09B3/35—Shredding, crushing or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/04—Disintegrating plastics, e.g. by milling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B2017/001—Pretreating the materials before recovery
  • B29B2017/0015—Washing, rinsing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B2017/0094—Mobile recycling devices, e.g. devices installed in truck trailers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/02—Separating plastics from other materials
  • B29B2017/0213—Specific separating techniques
  • B29B2017/0286—Cleaning means used for separation
  • B29B2017/0289—Washing the materials in liquids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/04—Disintegrating plastics, e.g. by milling
  • B29B2017/0424—Specific disintegrating techniques; devices therefor
  • B29B2017/044—Knives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
  • B29B17/04—Disintegrating plastics, e.g. by milling
  • B29B2017/0424—Specific disintegrating techniques; devices therefor
  • B29B2017/0476—Cutting or tearing members, e.g. spiked or toothed cylinders or intermeshing rollers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/52—Mechanical processing of waste for the recovery of materials, e.g. crushing, shredding, separation or disassembly
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• the present invention relates to an apparatus for processing waste plastic.
• the present invention further relates to a method for processing waste plastic.
• the invention finds use in processing a wide range of waste plastic materials and has particular advantages in the processing of waste fishing nets.
• waste plastic material is a significant and growing worldwide problem. Historically, waste materials, including waste plastic, were disposed of by dumping, for example in landfill sites. More recently, significant efforts have been made to develop technology to process waste plastic material into a useable raw material. In an attempt to control the disposal of waste plastic, the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal was adopted on 22 March 1989. A key aspect of the Basel Convention is the control of the shipping of plastic waste from one country to another.
• waste plastic materials There is a wide range of plastic waste materials.
• different waste plastic materials can be processed to produce a useable plastic raw material by comminuting the waste material to produce chips, strips or strands.
• the waste material is required to be cleaned to remove contaminants, which may be carried out before and/or after the comminuting step.
• Nets are used to catch fish in the seas and oceans in large quantities.
• the nets may be static nets or trawl nets. Static comprise from 20 to 30% of the nets employed by commercial fisheries. Over 100,000 tons of static nets are produced and sold each year.
• a commercial static fishing net for use in marine and freshwater fishing will last for from 3 to 6 months, after which it is generally replaced.
• the reasons to replace commercial fishing nets include the formation of excessive build up of algal biofilm and physical wear.
• significant quantities of waste fishing nets are being produced by commercial fishing operations. For example, the fishing fleet based in Newlyn, United Kingdom produces from 40 to 60 tonnes of waste static fishing nets each year.
• waste fishing nets represent a significant source of waste plastic material. It is estimated that waste fishing gear, including fishing nets, represents 10 percent of ocean plastic, making up a large proportion of large plastic pollution in seas and oceans. In some areas, waste fishing gear contributes the vast majority of plastic rubbish. For example, it is estimated that discarded fishing equipment makes up more than 85 percent of the plastic pollution on sea mounts, ocean ridges and the sea floor (‘Ghost Gear: The Abandoned Fishing Nets Haunting Our Oceans’, Greenpeace Germany, November 2019).
• Commercial fishing nets are generally made of synthetic polymeric fibres such as polyolefins, in particular high density polyethylene (HDPE), polyester, polyethylene terephthalate (PET) or polyamides (PA), such as nylon.
• HDPE high density polyethylene
• PET polyethylene terephthalate
• PA polyamides
• these materials are not biodegradable and are very persistent in the environment, including in marine environments.
• WO 2016/203041 discloses a method for comminuting a range of plastic materials.
• the method comprises the steps of provision of plastic material in the form of blocks, granules or foils; introducing the plastic material to be shredded into at least one comminution device; and crushing the plastic material in the at least one comminution device below a temperature of 40 °C.
• WO 2017/012623 concerns a method and apparatus for the comminution of fishing nets.
• the apparatus comprises a comprising at least one comminutor having a first shaft and a second shaft, each shaft having at least four knife blades, each of which comprises a number of teeth with a convex portion and a concave portion, the knife blades being configured with similar teeth, but each arranged on the shaft such that the knife blades are successively, mutually rotated along the shaft.
• the teeth of the knife blades on each shaft comprise cutting edges on both the convex portion and the concave portion of the teeth.
• WO 2017/012623 is particularly concerned with comminuting waste fishing nets in order to allow the different plastics materials in the nets to be separated.
• CN 112265188 discloses an apparatus and a process for recycling polystyrene waste.
• the apparatus comprises a comminuting assembly for forming polystyrene fragments and a washing assembly.
• KR 101565540 discloses a waste fishing net recycling apparatus, in which the waste nets are first cut and then washed to remove salt and foreign substances.
• KR 102298441 discloses a waste fishing net recycling apparatus, in which the waste nets are first cut and then crushed, after which the resulting particles are washed to remove salt and foreign substances.
• a process for processing waste plastic is disclosed in CN 212860069, in which the waste material is first pulverised and then cleaned.
• CN 111958879 discloses a method and apparatus for processing waste nylon tubes.
• the waste nylon tubes are first pulverised and then cleaned.
• CN108890922 discloses a method and apparatus for processing waste plastic beverage bottles. The waste bottles are pulverised and then cleaned.
• JP 2014223778 discloses a method and apparatus for cutting and cleaning waste plastic materials.
• an apparatus for processing waste plastic material comprising: a comminution assembly comprising: a comminutor comprising: an inlet for plastic material to be comminuted; an outlet for comminuted plastic material; and a blade assembly comprising a plurality of blades; and a washing assembly comprising: a washing vessel having an inlet for comminuted material and an outlet for washed material; and an agitator for agitating the contents of the washing vessel.
• the present invention provides a method for processing waste plastic material, the method comprising:
• the apparatus and method of the present invention offers a number of technical advantages.
• the process scheme employed is relatively simple, yet effective in treating a range of waste plastic material into a high quality raw material for forming new plastic items and components.
• the process scheme allows the apparatus to be arranged in a compact manner, in particular having a small footprint and occupying a relatively low volume.
• this allows the apparatus to be readily transportable, which is advantageous when the present invention is to be employed in remote locations, and further allows the apparatus to be arranged in a mobile form. This is particularly advantageous by avoiding the need to transport waste plastic materials to a site for recycling and the increasing problems with such transportation, as discussed above.
• the apparatus is advantageously arranged to fit within a standard shipping container, within which the apparatus can be operated without significant modification.
• This embodiment represents a particularly mobile arrangement, which is easily shipped and transported to one or a series of locations for use in the recycling of waste plastic materials.
• references to a ‘standard shipping container’ are references to an intermodal or shipping container that meets the requirements of the relevant international standards.
• ISO 830.(1999) Freight Containers which sets out the terminology to be used in relation to standardised freight containers
• the apparatus and method of the present invention can be used to process a wide range of waste plastic materials and to produce high quality recycled plastic raw materials, which then find use in the manufacture of a wide range of components and items.
• the present invention finds particular use in the processing of waste polyamide materials, including nylon, such as nylon 6.
• Other plastic materials that may be processed using the present invention include polyolefins, such as polyethylene and polypropylene, polyester, polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC).
• one preferred embodiment is the processing of waste plastic materials that are ductile, that is exhibit a low brittleness at ambient temperatures, that is the failure mechanism of the polymer at ambient conditions is not brittle failure.
• Polyamides such as nylon are a range of polymers that are generally ductile at ambient conditions. As a result, it is generally not effective to process polymers of this kind, such as waste polyamides, by breaking the raw waste material. Rather, it is preferred that the waste raw material is cut, as described in more detail below.
• the waste plastic material processed in the present invention may take a range of different forms.
• the waste plastic material to be processed may be in the form of sheets, blocks, rods or filaments, or components, in whole or parts thereof.
• the apparatus and method of the present invention are particularly suitable for processing waste plastic materials in the form of filaments.
• a filamentous waste plastic material that is very suitable for processing using the present invention is waste netting material, in particular waste or used fishing nets.
• the present invention finds use in the processing of waste nylon materials, more preferably waste nylon filaments, such as waste fishing nets, especially static fishing nets.
• the product of the present invention is a high quality raw plastic material, that finds a range of uses in forming new plastic components and items, as noted above.
• the product may be provided in a wide range of different forms, for example pellets, granules, films, sheets, rods and the like.
• the particular form of the end product will be determined, in part or wholly, by the use to be made of the product. End uses of the product of the present invention include many applications for processing plastic.
• the product of the present invention has been found to be particularly suitable for and useful as a starting material for injection moulding and 3D printing.
• the product is provided in the form of filaments for use in 3D printing.
• the requirements and specification of filaments for use in 3D printing are known in the art.
• Suitable techniques for providing the washed comminuted plastic product in a form suitable for use in 3D printing are known in the art and include extruding the washed comminuted plastic particles into a filament.
• the present invention is applied to the processing of waste fishing nets to produce nylon filaments for use in 3D printing processes.
• the apparatus of the present invention comprises a comminution assembly comprising a comminutor.
• the action of comminutor is to reduce the particle size and/or shape of the waste plastic starting material.
• the change in particle size and/or shape has a number of technical aspects.
• comminution assembly is arranged to provide a comminuted plastic material having a particle size and shape that is suitable for further processing into a plastic component or article. Further, the comminution assembly is arranged to provide a comminuted plastic material that has a particle shape that optimises the cleaning of the waste plastic material during washing, as described in more detail below.
• the comminution assembly comprises a comminutor, as noted hereinbefore.
• a comminutor comprises a blade assembly to cut the waste plastic starting material.
• cutting the waste plastic material allows the cut particles to be shaped.
• the action of the comminutor on the waste plastic material is to cut the material to form particles.
• references to ‘cutting’ are to the predominant action of the comminutor to cut the waste plastic material rather than to break or tear it.
• the form and shape of the particles is one that is formed by cutting the waste material, rather than tearing the waste material. It has been found that cutting the waste material to form the particles allows the form and shape of the particles to be controlled, in particular to provide a form and shape of particles that results in an efficient cleaning of the particles in the subsequent washing procedure.
• the design and arrangement of the blades of the blade assembly can be selected to provided particles that are sharper, that is have surface features, such as ends, which have sharp edges, or blunter, that is have surface features, such as ends, which are more rounded. It has been found that the use of a blade assembly having blades with sharp cutting edges causes the waste plastic material to be cut and produces sharp particles. In contrast, blades with rounded cutting edges act to both cut and stretch the waste plastic material, resulting in particles that are blunter and have more rounded features. By employing blade assemblies in the present invention to cut the waste plastic starting materials allows the shape of the particles of the comminuted plastic material to be controlled, as required for the washing process, discussed in more detail below.
• the blade assembly of the comminutor comprises a plurality of blades arranged on a blade support, such as a shaft, cylinder or drum.
• a blade support such as a shaft, cylinder or drum.
• the blades are rotated, preferably by rotation of the blade support.
• the blades are brought into a cutting region of the comminutor, in which the blades contact and cut the waste plastic material introduced into the comminutor.
• the cylinder is rotated about its longitudinal axis, thereby moving the blades in a circular pattern.
• the blades may be arranged on the blade support in a number of different patterns.
• the blades may be arranged on the blade support in a helical pattern, as is known in the art.
• each blade extends in a helical pattern on the blade support.
• Rotation of the blade support brings adjacent portions of each blade in position in the cutting region of the comminutor in turn to cut the waste plastic material.
• arranging the blades in a helical pattern on the blade support produces a comminuted product having a finer, that is smaller, particle size, but at a relatively lower cutting efficiency.
• One problem with using a helical arrangement of the blades on the blade support is that the arrangement is not self-feeding in operation.
• the arrangement is selffeeding, that is once a first portion of the waste plastic material is introduced into the comminutor the action of the blade assembly is to draw the material into the comminutor. In this way, an apparatus for actively feeding the waste material into the comminutor is not required.
• the blade assembly of the comminutor has the blades arranged on the blade support in a step-wise pattern, that is all or substantially all of each blade enters the cutting region of the comminutor at the same time. Adjacent blades are spaced apart on the blade support in the direction of rotation, with adjacent blades entering the cutting region at successive times. It has been found that a step-wise arrangement of the blades on the blade support provides a higher cutting efficiency, albeit producing a relatively coarser comminuted material, having a larger particle size.
• a particular advantage of the step-wise arrangement of the blades of the comminutor is that the arrangement is self-feeding, in particular for waste plastic materials comprising filaments, especially for waste fishing nets.
• the shape and size of the comminuted plastic particles leaving the comminutor assembly affects the cleaning of the comminuted material in the washing stage.
• the comminution assembly may be arranged and operated to produce comminuted plastic particles having different sizes, as required.
• the comminuted particles have a major dimension, that is the largest dimension of the particles, of up to 8 mm, more preferably up to 7 mm, still more preferably up to 6 mm, more preferably still up to 5 mm, especially up to 4 mm.
• the comminuted particles may have a major dimension of from 0.5 mm, preferably from 1 mm, more preferably from 1.5 mm, still more preferably from 2 mm, more preferably still from 2.5 mm, especially from 3 mm.
• comminuted particles having a major dimension of from 1 to 8 mm are particularly suitable, preferably from 1.5 to 7 mm, more preferably from 2 to 6 mm, still more preferably from 2.5 to 5 mm, especially from 3 to 4 mm.
• the major dimension of the comminuted particles is the length of the particles.
• the filaments typically have a diameter of from 0.3 to 1 mm, more typically from 0.55 to 0.7 mm, for example about 0.65 mm.
• the comminuted particles produced from waste fishing nets are generally cylindrical.
• the comminuted cylindrical particles have a length of from 0.5 to 8 mm, more preferably from 1 to 7 mm, still more preferably from 1 .5 to 6 mm, more preferably still from 2 to 5 mm, especially from 3 to 4 mm in length.
• the method of the present invention further comprises the steps of: (ii)(a) screening the comminuted plastic material to produce an oversized comminuted plastic material and a sized comminuted plastic material; and
• the comminution assembly may comprise a single comminutor with a recirculation assembly.
• the comminution assembly comprises a plurality of comminutor stages with a recirculation assembly.
• the comminution assembly comprises from 2 to 4 comminutors in combination with a recirculation assembly, with 3 comminutors being a particularly preferred arrangement.
• the comminution assembly comprises a recirculation assembly.
• the recirculation assembly acts to separate the comminuted plastic particles that are at or below the size required for the comminuted plastic product and those particles that are oversized, that is size the comminuted plastic product.
• the oversized particles are recycled for further comminution.
• the recirculation assembly recycles the oversize particles to the inlet of the comminution assembly, such that the oversize particles pass through all the comminutor stages.
• the oversize particles can be recycled to pass through some but not all of the comminutor stages, for example be introduced into the second or subsequent comminutor stage.
• the recirculation assembly comprises a recirculation screen with apertures and having an inlet for receiving comminuted plastic material, a first outlet for comminuted plastic material passing through the recirculation screen and a second outlet for comminuted plastic material retained by the recirculation screen.
• comminuted plastic material leaving through the first outlet is passed to the subsequent processing stage, while material leaving through the second outlet is recycled to the comminutor, as discussed above.
• the final particle size of the comminuted plastic material can be controlled by the appropriate selection of the apertures in the recirculation screen.
• reducing the diameter of the apertures in the screen reduces the particle size of the comminuted plastic material product, while increasing the diameter of the apertures in the screen increases the size of the comminuted plastic product.
• the particle size of the comminuted plastic material can be controlled by appropriate selection of the recirculation screen. This avoids the need to change the blades or the blade assembly of comminutor.
• the size of the apertures in the recirculation screen may be selected to provide finished particles of the desired size.
• the recirculation screen may have apertures having a diameter of at least 1 mm, preferably at least 1 .2 mm, more preferably at least 1 .3 mm, still more preferably at least 1 .4 mm, more preferably still at least 1 .5 mm.
• the recirculation screen may have apertures having a diameter of up to 5 mm, preferably up to 4 mm, more preferably up to 3.5 mm, still more preferably up to 3.25 mm, more preferably still up to 3 mm.
• the apertures have a diameter of from 1 to 5 mm, more preferably from 1 .2 to 4 mm, still more preferably from 1 .4 to 3.5 mm, more preferably still from 1 .5 mm, to 3.25 mm, especially from 1 .5 to 3 mm.
• knots in the waste fishing nets are processed by being cut in the comminution assembly.
• the knots are recirculated to pass through part or all of the comminution assembly a plurality of times.
• the recirculation of knots can be controlled by the selection of the size of the apertures in the recirculation screen.
• the apertures in the recirculation screen have a diameter that is no greater than the diameter of the knots.
• the diameter of the apertures in the recirculation screen is from 1.1 to 5 times the diameter of the filaments of the fishing net being processed, more preferably from 1.5 to 4.5, still more preferably from 2 to 4, still more preferably from 2.5 to 3.5 times the diameter of the filaments of the net.
• the diameter of the apertures in the recirculation screen is from 1 .6 to 3.4 times the diameter of the filaments of the net, more preferably from 1.7 to 3.3, still more preferably from 1.8 to 3.2, more preferably still from 1.9 to 3.1.
• Apertures have a diameter about 3 times the diameter of the filaments of the fishing net is particularly suitable for many embodiments.
• a recirculation screen having apertures of from 1 .8 to 2.2 mm in diameter is preferred, with a screen having apertures of about 2 mm (Mesh #10) being particularly suitable.
• a recirculation screen having apertures of from 2.3 to 3.5 mm in diameter is preferred, with a screen having apertures of about 2.4 mm (Mesh #8) being particularly suitable.
• the recirculation screen may have apertures of any particular shape or configuration and arranged in any suitable pattern.
• the apertures in the recirculation screen are circular.
• other suitable shapes include rectangular and triangular.
• References herein to the ‘diameter’ of the apertures of the recirculation screen are references to the diameter of the apertures, if circular, or to the major dimension across the aperture.
• the recirculation assembly further comprises a transport assembly for transporting oversize comminuted plastic material from the second outlet of the recirculation screen to an inlet of the comminutor.
• Suitable techniques and apparatus for moving the oversize comminuted plastic material to a comminutor inlet include use of gravity, for example allowing the comminuted plastic material to drop under gravity down a chute or through a hopper, mechanical conveyors, such as belt conveyors and bucket conveyors, and air conveyors, where the comminuted plastic material is conveyed by entrainment in a stream of gas, especially air.
• the energy requirement of the comminution operation per kg of comminuted plastic material will vary according to the operating parameters of the comminution assembly.
• the energy requirement for comminution per 30 kg of comminuted plastic particles may be up to 6 kWh, more preferably up to 5 kWh, with 4.5 kWh being applicable for many preferred embodiments.
• the energy requirement for comminution per 30 kg of comminuted plastic particles may be from 2 kWh, more preferably from 3 kWh.
• the comminuted plastic material is subjected to further processing, in particular cleaning by an agitated cleaning process.
• the comminuted plastic product leaving the comminution assembly may be passed directly to the washing assembly.
• Suitable techniques and apparatus for separating fines from the comminuted plastic material are known in the art.
• the separation of fines is performed dry, that is without the addition of a liquid, such as water.
• Suitable dry separation techniques include blown air sizing, for example separation using one or more cyclones.
• Suitable cyclones and their use for removing the fines are known in the art and available commercially.
• the comminuted plastic material may be fed directly to the washing stage of the present invention.
• the comminuted plastic material may be stored temporarily in a suitable storage vessel, such as a hopper, or other storage facility.
• a suitable storage vessel such as a hopper, or other storage facility.
• the comminuted plastic material is subjected to a washing stage.
• the function of the washing stage is to remove contaminants present in and/or on the waste plastic material.
• biofouling In the case of waste fishing nets, the major contaminants are as a result of biofouling and include algal and bacterial contamination, also known as ‘biofilms’. It has been found that salt from the marine environment does not enter the plastic material of the fishing nets in a significant amount. However, salt from the marine environment is retained in the biofilms. The object of the washing stage is to remove the biofouling and the accompanying salt, to a level acceptable for use of the comminuted plastic material as a raw plastic material in the forming of new plastic components and items.
• the comminuted plastic particles are mixed with water to form a suspension of the particles in water.
• the suspension is then agitated to perform an agitated cleaning of the plastic particles.
• the washing stage does not employ any form of detergent or other chemical cleaning agent. Rather, the cleaning action is as a result of collisions between the particles in the suspension occurring as a result of the agitation of the suspension.
• cleaning of the comminuted plastic particles is achieved substantially solely due to inter-particle collisions.
• water is present during the washing stage, it is being used as a carrier for the comminuted particles, as a medium in which inter-particle collisions can occur and as a vehicle for removing the contaminants. Some contaminants will be soluble in water and will leave the comminuted plastic particles by dissolving in the water. However, the removal of contaminants in this way will be minor.
• the water used during the washing stage may be heated. However, as the water is being employed as a carrier and not as a washing agent, it is preferable that the water is not heated and is used at ambient temperatures.
• the comminuted plastic material may be sufficiently cleaned without heating the water, in turn avoiding the energy requirements that a heated washing procedure would require.
• the action of comminution assembly on the waste plastic material is to produce comminuted particles by cutting, that is cutting is the dominant mechanism by which particles are formed.
• the cutting action produces particles having features with sharp edges. It has been found that comminuted particles having sharp edges produced as a result of cutting are effective in self-cleaning when agitated in water and caused to collide.
• the efficiency of the particles in self-cleaning as a result of collisions between the particles can be accurately controlled using the cutting procedure to provide the particles with an appropriate form and shape.
• appropriate selection of the parameters of the comminution stage such as the geometry of the cutting blades and particle size, can be used to optimise the washing stage and improve the cleaning of the particles in the washing stage.
• the efficiency of the cleaning process can be determined by such factors as the length of time the comminuted particle/water mixture is required to be agitated under a given set of agitation conditions to reduce the contaminants in the comminuted material to a specified level, or by the energy input required to agitate the comminuted particle/water mixture to achieve a specified level of contaminants in a specified time. It has been found that the selection of the operating parameters of the comminution assembly can be used to control, especially to improve, in particular optimise, the efficiency of the washing stage.
• the present invention provides a method of removing contaminants from a waste plastic material, the method comprising:
• step (ii) mixing the comminuted plastic material with water to form a suspension; and (iii) agitating the suspension to induce collisions between the particles of the comminuted plastic material to remove contaminants from the comminuted plastic material; the method comprising adjusting the operating parameters of the comminutor to control the removal of the contaminants from the comminuted plastic material in step (iii).
• the present invention provides the use of comminution of waste plastic material to control the removal of contaminants from the comminuted plastic material in a process comprising agitating the comminuted plastic material in suspension in water.
• Operating parameters of the comminutor which may be adjusted to control the removal of contaminants from the comminuted plastics material are as discussed above and include, for example, blade geometry, blade configuration, comminuted particle size, ratio of cutting:tearing of waste plastic material, number of comminutor stages, and aperture size of the recirculation screen (if present).
• the shape of the comminuted particles also affects the efficiency of the washing process.
• the aspect ratio of the comminuted particles affects the efficiency of the washing process, in particular with higher aspect ratios reducing the efficiency of the cleaning of the comminuted particles in the washing process.
• references to the ‘aspect ratio’ of the comminuted particles refers to the ratio of the major dimension to the minor dimension of the particle.
• the aspect ratio is the ratio of the length of the comminuted filament particle to the diameter of the filament.
• the comminuted particles preferably have an aspect ratio of from 1 to 10, more preferably from 2 to 8, still more preferably from 3 to 7.5, more preferably still from 3.5 to 7, still more preferably from 4 to 6.5.
• An aspect ratio of from 4.5 to 6.5 has been found to be suitable for many embodiments, especially for the processing of waste fishing nets.
• a preferred length for the comminuted particles is from 3 to 4 mm, giving an aspect ratio of from about 4.6 to about 6.15.
• the first step in the washing stage is to combine the comminuted plastic material with water.
• Any suitable technique may be employed to combine the comminuted plastic material with water.
• One preferred technique is to feed the comminuted plastic material and water to a vessel and agitate the components, for example with a suitable impellor.
• water is employed as a carrier for the comminuted plastic material, to provide a medium in which interparticle collisions can be induced and a vehicle for transporting the contaminants removed from the comminuted particles.
• the ratio of water to comminuted plastic material may be up to 6:1 by weight, preferably up to 5:1 , more preferably up to 4:1 , still more preferably up to 3.5:1 , more preferably still up to 3:1 by weight.
• the ratio of water to comminuted plastic material may be from 0.5:1 by weight, preferably from 1 :1 , more preferably from 1.5:1 , still more preferably from 2:1 , more preferably still from 2.5:1 by weight.
• Preferred ratios of water to comminuted plastic material are in the range of from 0.5 to 6 by weight, more preferably from 1 to 5, still more preferably from 1 .5 to 4, more preferably still from 2 to 3.5, especially from 2.5 to 3 by weight.
• Agitation of the mixture of comminuted plastic material and water may be conducted at an elevated temperature, for example by heating the mixture or employing hot water.
• the washing stage is conducted at ambient temperature. It is an advantage that cleaning of the comminuted plastic material can be carried out using water without the addition of any cleaning agents, such as detergents, and without the need to heat the water.
• Water can act to soften certain contaminants, in turn facilitating their removal from the particles by interparticle collisions.
• the water provides a vehicle for separating the removed contaminants from the plastic particles. Further, the clarity of the water can be used to provide a visual indication of the progress of the cleaning.
• the particles are separated from the water.
• the water may be allowed to drain from the vessel.
• the particles and water may be separated by other techniques, such as filtration, centrifugation and/or settling.
• Washing of the comminuted plastic material may be carried out in a continuous mode or batchwise. Batchwise operation is preferred for many embodiments.
• Cleaning of the comminuted plastic material may be carried out in the wash stage in a single cycle of combining with water, agitating and removing water. More preferably, cleaning of the comminuted plastic material is carried out in the wash stage in a plurality of cycles, each cycle comprising combining the comminuted plastic material with water, agitating the mixture, and removing water.
• the number of cycles required will be determined by the number required to clean the comminuted plastic material to the required level.
• the number of cycles employed may be up to 10, preferably up to 8, more preferably up to 6, still more preferably up to 5, more preferably still up to 4, especially up to 3. In many preferred embodiments, it has been found that performing from 2 to 5 washing cycles is effective in cleaning the comminuted plastic material to the required level, more preferably from 2 to 4 washing cycles, for example 3 washing cycles.
• the completion of the washing stage may be determined by analysis, for example analysis of the water leaving the washing stage to determine its salinity and/or clarity.
• the action of the first cycle of cleaning is to remove water soluble contaminants from the comminuted plastic material, which dissolve in the water.
• the action of the first cycle of cleaning is to remove a significant amount of salt from the comminuted net material, which dissolves in the water.
• the water separated from the comminuted plastic material is preferably disposed of, for example being passed to a drain.
• the water may be processed to remove the contaminants, for example in a desalination plant to remove salt. Water cleaned in this way may be recycled and reused in the process.
• the present invention employs a desalination assembly operable to remove salt from water.
• the desalination assembly may be operated to remove salt from the water recovered from the washing cycles.
• the desalination assembly is operated to purify water being fed to the process.
• the present invention may be practised at locations where a supply of brackish water is available. This in turn reduces the demand made by the present invention on supplies of clean water, which is advantageous.
• the water may be recycled for use again, for example in further washing operations.
• the cleaned comminuted plastic particles are then rinsed with clean water.
• Rinsing may be carried in the same vessel or a different vessel to the agitated cleaning operation.
• Rinsing of the comminuted plastic material may be carried out in a continuous mode or batchwise. Batchwise operation is preferred for many embodiments.
• Rinsing of the cleaned comminuted plastic material may be carried out in a single cycle of combining with water, agitating and removing water. More preferably, rinsing of the comminuted plastic material is carried out in a plurality of cycles, each cycle comprising combining the comminuted plastic material with water, agitating the mixture, and removing water.
• the number of cycles required will be determined by the number required to rinse the comminuted plastic material to the required level.
• the number of cycles employed may be up to 10, preferably up to 8, more preferably up to 6, still more preferably up to 5, more preferably still up to 4, especially up to 3.
• performing from 1 to 5 rinsing cycles is effective in cleaning the comminuted plastic material to the required level, more preferably from 1 to 4 rinsing cycles, for example from 1 to 3 rinsing cycles.
• the washed comminuted plastic material is dried, to remove any remaining water from the material. Any suitable technique may be used to dry the washed comminuted plastic material.
• the action of the drying operation is to physically separate free water from the washed comminuted plastic material.
• the water removed in this way may contain contaminants, it may be necessary to treat the water recovered in this way before being re-used in the process or sent for disposal, as discussed hereinbefore.
• Drying the washed comminuted plastic material may be carried out using any suitable drying technique, such as mechanical dewatering, heating or a combination of such techniques. Drying the washed comminuted plastic material is preferably carried out by a mechanical dewatering operation. Suitable mechanical dewatering assemblies are known in the art and are commercially available, including centrifugal dryers.
• the washed comminuted plastic material may be dried by heating the material. If heating is employed, preferably, the material is heated in the drying stage to a temperature below 120°C sufficient to evaporate water bound to the surface of the washed comminuted plastic particles.
• Suitable techniques for drying the washed comminuted plastic material by heating the material include, for example using heated air and/or radiant heat, such as infra-red (IR) heating.
• Apparatus for removing water using heat include a heated conveyor, for example an IR-heated conveyor, blown air systems, such as a blown air cascade or screen, or a fluidised bed dryer.
• the washed comminuted plastic material is subjected to a first drying stage employing a mechanical drying technique, such as centrifugation and, thereafter, in a second drying stage to heating.
• a mechanical drying technique such as centrifugation
• Drying in this way creates a physical distinction between the polymer material and any biological contaminants that may remain after the washing stage, which may be used to cleanse the final product before use, if required.
• the biological contaminants present in the washed comminuted plastic material are preferably present in an amount of less than 0.05% by weight, more preferably less than 0.04%, still more preferably less than 0.03%, more preferably still less than 0.02%, especially less than 0.01 % by weight of the final product. It is preferred that any remaining biological contaminants, such as algae, are present only as particles less than 500 microns in diameter, more preferably less than 400 microns, still more preferably less than 300 microns, more preferably still less than 200 microns, especially less than 100 microns in diameter. These levels of biological contaminants may be achieved by washing, by a combination of washing and rinsing, or by a combination of washing, rinsing and drying the comminuted plastic material.
• the washed comminuted plastic material may be dried to remove water to any desirable level in the final bulk product.
• the water-content of the final product is less than 5% by weight, more preferably less than 4%, still more preferably less than 3%. It is especially preferred to reduce the water-content of the final material to less than 2% by weight. Below a water-content of 2% by weight, biological material, such as algae, will not grow. This in turn produces a product that is stable in dry storage and readily transported using conventional techniques.
• the washed comminuted plastic material is not dried to a water-content below its dry air equilibrium water-content. In this way, having the material draw moisture from the ambient air is avoided. This renders the material more stable for storage and transport.
• the drying operation may be carried out batch-wise or continuously. It is preferred that the drying operation is continuous for many embodiments, in particular where space is not constrained and energy consumption of the process is not a significant factor. However, a batch-wise operation may be preferred for other embodiments, for example in more remote locations with little or no utilities or where space is constrained, for example when the entire apparatus is required to be housed within a standard shipping container, as discussed hereinbefore. In many embodiments, equipment for batch-wise drying of the washed comminuted plastic material takes up less space, can be arranged to have a smaller footprint and may require less energy than an equivalent continuous process regime.
• blown air systems such as blown air cascades, blown air screens or fluidised beds, provide the advantage of entraining the fines in the air stream, which can then be removed from the bulk material.
• the fines may be separated from the air stream using known techniques, such as filtration, for example using candle filters, and/or by cyclone separation. Again, such techniques are known in the art and apparatus for separating the fines from the air stream are commercially available.
• the fines are removed using cyclone separation, more preferably multi-stage cyclone separation in which the air stream containing the fines is passed sequentially through a plurality of cyclone separators. It has been found that a cyclone separator assembly having two cyclone separators arranged in series is very suitable for many embodiments. Apparatus for drawing air through the cyclone separator assembly are known in the art and include industrial vacuum units. A filter, such as a bag filter, is preferably employed to capture any super fine particles.
• the air may simply be exhausted to the atmosphere.
• drying systems relying on radiant heat, such as IR, are suitable for use.
• Figure 1 is a diagrammatic representation of an apparatus according to one embodiment of the present invention.
• Figure 2 is a diagrammatic representation of a first portion of the apparatus of Figure 1 comprising the comminution assembly of the apparatus;
• Figure 3 is a diagrammatic representation of a second portion of the apparatus of Figure 1 comprising the washing assembly of the apparatus;
• Figure 4 is a diagrammatic representation of the water supply assembly of the apparatus of Figure 1 ;
• Figure 5 is a diagrammatic representation of a process scheme of one embodiment of the method of the present invention.
• the apparatus comprises a comminution assembly, generally indicated as 102, and a washing assembly, generally indicated as 202.
• the components of the comminution assembly 102 and the washing assembly 202 are configured to fit within a 40 foot intermodal (shipping) container 4 (ISO 668:2020; ISO designation 1 A).
• the intermodal container 4 is indicated by a dotted rectangular line in Figure 1 .
• the apparatus 2 further comprises a water supply system, generally indicated as 302. In use, the water supply system 302 is connected at its inlet to a supply of water.
• the water supply system 302 lies outside the intermodal container 4 of the embodiment of Figure 1 .
• the apparatus may be configured to house the water supply system 302 inside the intermodal container 4.
• the apparatus 2 of the embodiment of Figure 1 is readily transportable from location to location and, once connected to utilities, in particular electrical power and water, can be ready to operate with minimal further work.
• the comminution assembly comprises a comminutor 104.
• the comminutor 104 comprises three comminutor stages, 104a, 104b, 104c, each stage comprising a blade assembly 106a, 106b, 106c having a plurality of blades 108a, 108b, 108c arranged in a step wise manner on a drum 110a, 110b, 110c providing a blade support.
• Each comminutor stage 1041 , 104b, 104c is driven by an electric motor 112a, 112b, 112c.
• the comminutor assembly 104 has an inlet 114 to receive waste plastic material and recycled oversize comminuted plastic particles.
• a hopper 116 collects comminuted plastic particles from an outlet 118 of the comminutor assembly 104.
• the hopper 116 delivers comminuted plastic particles from the outlet 118 of the comminutor assembly 104 onto an inclined screw conveyor 120 driven by an electric motor 122.
• the screw conveyor 120 delivers comminuted plastic particles received from the hopper 116 to a screening assembly, generally indicated as 130.
• the screening assembly 130 comprises an inlet 132 and a sizing screen 134 having apertures therein.
• a first outlet 136 is provided to remove oversize comminuted particles retained by the sizing screen, which are fed to the inlet 114 of the comminution assembly 104.
• a second outlet 138 is provided to remove sized comminuted plastic particles for further processing.
• An electric motor 140 drives the screening assembly, in particular vibrating the sizing screen 134 to facilitate separation of the sized and oversize comminuted particles.
• a blower 142 driven by an electric motor 144 is provided to remove hot air from the comminutor assembly 104.
• raw waste plastic material to be processed and recycled is fed into the assembly at A and into the inlet 114 of the comminutor assembly 104.
• the waste plastic material is comminuted in three stages, in comminutor stages 104a, 104b, 104c successively and leaves the comminutor assembly 104 through the outlet 118 to be collected in the hopper 116.
• the comminuted plastic material is conveyed by the screw conveyor 120 to the inlet 132 of the screening assembly 130. Oversize comminuted particles are retained on the sizing screen 134 and leave the screening assembly 130 through the first outlet 136, from where they are fed to the inlet 114 of the comminutor assembly 104.
• Sized comminuted particles passing through the sizing screen 134 leave the screening assembly 130 through the second outlet 138 and leave the comminution assembly at B for further processing.
• Hot air generated by the comminution operation is removed from the comminutor assembly 104 by the blower 142 and is removed at C.
• FIG. 3 the details of the washing assembly 202 are shown.
• Comminuted plastic material from the comminution assembly 104 is held in a feed hopper 204.
• a surge hopper 206 is provided upstream of the feed hopper 204, to accommodate surges in the production of comminuted plastic material from the comminution assembly, with feed of comminuted material from the surge hopper 206 to the feed hopper 204 being controlled by a valve 208.
• An inclined screw conveyor 210 driven by an electric motor 212 receives comminuted plastic material from the feed hopper 204 for delivery to a wash tank 214.
• a line 216 is provided to deliver water to the wash tank 214, with the flow of water being controlled by a valve 218.
• the wash tank 214 is provided with an impellor 220 driven by an electric motor 222.
• the wash tank 214 is provided with a water outlet 224, allowing water to be drained from the wash tank 214. Water leaving the wash tank 214 passes through a filter 226. The flow of water from the outlet 224 is controlled by a valve 228.
• An inclined screw conveyor 230 driven by an electric motor 232 is arranged to receive cleaned comminuted plastic material from the wash tank 214 and deliver it to a rinse tank 234.
• a line 236 is provided to deliver water to the rinse tank 234, with the flow of water being controlled by a valve 238.
• the rinse tank 234 is provided with an impellor 240 driven by an electric motor 242.
• the rinse tank 234 is provided with a water outlet 244, allowing water to be drained from the rinse tank 234. Water leaving the rinse tank 234 passes through a filter 246. The flow of water from the outlet 244 is controlled by a valve 248.
• Water from the outlets 224 and 244 of the wash tank 214 and rinse tank 234 respectively is combined and fed to the inlet of a water recycle pump 250 driven by an electric motor 252.
• Water from the wash tank 214 and the rinse tank 234 is processed in a filtration plant 254 to remove particulates.
• An inclined screw conveyor 260 driven by an electric motor 262 conveys the cleaned and rinsed comminuted plastic material away from the washing assembly 202.
• the wash tank 214 is provided with a water drain outlet 270, through which water may also leave the wash tank 214, depending upon the cleaning cycle. Water leaving the wash tank 214 through the water drain outlet 270 passes through a filter 272 and flows to a drain 274. The flow of water is controlled by a valve 276.
• comminuted plastic material from the comminution assembly 104 is fed to the surge hopper 206 at B and passes to the wash feed hopper 204.
• the surge hopper 206 is provided to accommodate surges in the production of comminuted plastic material by the comminution assembly 104, which would exceed the capacity of the wash feed hopper 204.
• Comminuted plastic material from the wash feed hopper 204 is conveyed to the wash tank 214 by the screw conveyor 210. Cleaning of the comminuted plastic material is conducted in a plurality of cycles.
• water is provided at D and fed to the wash tank 214.
• the comminuted plastic material and water mixture is agitated in the wash tank 214 by the action of the impellor 220, causing the comminuted plastic particles to collide. The collisions between the particles removes contaminants from the plastic material, which is entrained in the water.
• water is removed from the wash tank 214.
• the water produced in the first cleaning cycle has a significant concentration of water- soluble contaminants, such as salt, dissolved therein.
• the water is removed from the wash tank 214 through the water drain outlet 270 and passed to the drain 276 for disposal.
• the water may be fed to a desalination plant (not shown for clarity) for processing before disposal or recycling.
• water is provided at D and again fed to the wash tank 214.
• the comminuted plastic material and water mixture is agitated in the wash tank 214 by the action of the impellor 220, causing the comminuted plastic particles to collide.
• water is removed from the wash tank 214, through the outlet 224. As the concentration of water-soluble contaminants, such as salt, in the water after the first cleaning cycle is low, the water can be recycled for use again.
• Cleaned comminuted plastic material is conveyed from the wash tank 214 to the rinse tank 234 by the belt conveyor 230.
• Water provided at D is fed to the rinse tank 234.
• the comminuted plastic material and water mixture is agitated in the rinse tank 234 by the action of the impellor 240 and the comminuted plastic material rinsed.
• water is removed from the rinse tank 234 through the outlet 244.
• the rinsing operation is repeated for the required number of rinsing cycles, each cycle comprising feeding water to the rinse tank 234, agitating the mixture of water and comminuted plastic material, and removing water from the rinse tank 234 through the outlet 244.
• the cleaned and rinsed comminuted plastic material produced at E may be further processed, most preferably by drying.
• the apparatus shown in Figures 1 and 3 comprises separate wash and rinse tanks 214 and 234. It is to be understood that the wash operation and the rinse operation may be carried out in a single vessel having the general configuration of the wash tank 214.
• Water from the outlets 224 and 244 of the wash tank 214 and the rinse tank 234 is fed via the pump 250 to the filtration plant 254, where solid material in the water is removed. Solid waste is produced at F for disposal. Cleaned water is produced at G for recycling.
• the water supply assembly 302 comprises a water tank 304 having a first inlet 306 for fresh water, a second inlet 308 for recycled water and an outlet 310 connected to a pump 312 driven by an electric motor 314.
• water is stored in the water tank 304, which receives fresh water provided at G and water recycled from the washing assembly 202 at F.
• the pump 31 delivers water from the water tank 304 to the washing assembly 202 at D.

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• Chemical & Material Sciences (AREA)
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• Materials Engineering (AREA)
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• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)

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• 2021
  • 2021-11-02 GB GB2115711.0A patent/GB2612371B/en active Active
• 2022
  • 2022-04-21 WO PCT/GB2022/051007 patent/WO2023079255A1/en not_active Ceased
  • 2022-04-21 EP EP22720484.9A patent/EP4426531A1/de active Pending

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