Technical field

This invention relates to a method for recovery and regeneration of plastics for polyolefin plastic recycling plants and the relative plant for recycling polyolefin plastics.

Background art

Among the polyolefin plastics there is firstly linear low-density polyethylene (LLDPE) coming from the wrapping of pallets and from other industrial uses. They are processed by film production plants, that is to say, plastic films (known in the jargon of the trade as “filming” operations) which work in cast or bubble films and are intended for producers of extendable films and cutting of material. It is also added to low density polyethylene (LDPE) to increase the elasticity.

With regard to this, LDPE plastic originates from consumption items: shopping bags, toys, non-food caps, furnishing items, post-industrial kitchen items, bags, heat-shrink film, wrapping sheets of the bubble type, expanded polyethylene (packaging protections), acoustic packaging... It is also processed by the above-mentioned filming plants, but also by injection moulding. The end market is the following sectors: automotive (bumpers), furnishing items for gardens, home furnishing items, production of industrial films and bottles.

Another type of material which is used for the plant according to the invention is polypropylene (PP), mainly of post-consumption origin, used extensively as “yarn” (transparent bags for sweaters or clothing, pasta bags, disposable packs, non-woven fabric, fabrics, slippers, clothing, home furnishing, various furnishing materials, carpets), but which is also found in rigid products (bottles, caps, home accessories games, chairs, compact disc cases, books, signage, office stationery) or in post-industrial objects (crates, fruit crates, crates, baskets, shells and frames for electronic items, hospital crates), in particular in the automotive sector (dashboards, seat backs, door bumpers), etc... In this case the recycling and regeneration processes are those of filming, thermoforming, injection moulding, blowing or compression moulding. The materials processed in this way find a market in the following sectors: automotive, plastic labels, pallets, textile production, non-woven fabric, TYVEK®, bottles, pipes, hydraulic fittings, chairs, pots, garden furniture, office items, phones, etc.

High-density polyethylene (HDPE) is also a thermoplastic polymer which is recycled by the plant according to the invention, belonging to the family of polyolefins and which originates from post-consumer products such as films (bags, gloves, packaging film, etc.) and rigid material (bottles, caps, toys, gardening articles, clothes hangers, office accessories, office and home furnishing items and components), post-industrial products, also in this case such as films (bags or films) and rigid materials (bumpers, parts of the dashboard, linkages, etc. of cars, pipes, fuel tanks, etc.). The recycling/regeneration process can be carried out by injection moulding, with blow moulding plants (such as bottles) or filming. The outlet market is automotive, bottles, cans, plastic furniture manufacturers, plastic bags, pipes, bottle caps, fly screens, garden items, games, etc.

In recent years, however, it has become necessary to produce in an environmentally sustainable manner, as well as to reuse, repair, recondition and/or recycle waste materials in order to produce a production and consumption model that extends the life cycle of the products, contributing to reducing waste to a minimum, making what is commonly referred to as “circular economy”.

The need is therefore increasingly felt to recycle and regenerate waste materials, especially if deriving from oil.

According to the prior art, the material to be recycled and regenerated is collected by secondary selection centres which take it, directly or indirectly, from the manufacturer or the importer.

The plastics then feed traditional recycling facilities, which include the washing and the subsequent extrusion, and they are then are ready to be marketed - batch by batch - depending on the variability of the selected mixtures, intended for the transformer company.

A problem linked with these recycling and regeneration processes is due to the fact that the recycled materials derived from plastics often have different properties compared with the virgin polymers, losing in mechanical and technical qualities, as well as having unforeseeable variations in technical and mechanical characteristics due to the variability of the regenerated plastic waste material. For this reason, their applications are currently mainly in the low range: street furniture, building works, gardening or crates for fruit and vegetables.

Aims and summary of the invention

The aim of the invention is to overcome the above-mentioned drawbacks of prior art types of method for recovery and regeneration of plastics for plants for recycling polyolefin plastics, which allows the same mechanical and technical properties of virgin polymers to be substantially maintained. In the context of the above-mentioned purpose, an aim of the invention is to provide a method for the recovery and regeneration of plastics for plants for recycling polyolefin plastics, which is able to generate a value from the waste, allowing all the materials and the components to become an input for new products.

Another aim of the plant according to the invention is to enhance goods and products beyond the end of their useful life, by regenerating, by means of processes for regeneration and replacing on the market, by the re-use for purposes other than initial use and recycling raw materials;

Another aim of the invention is the possibility of using renewable energy sources for producing and processing the plastic to be recycled and regenerated, reducing the environmental impact.

Yet another aim of the plant for recycling polyolefin plastics is to make it possible to use secondary raw material of equal quality to the virgin material in the production of semi-finished or consumer products. The secondary raw materials produced are materials derived from the recovery and recycling of waste.

Brief description of the invention

This purpose, as well as these and other aims, which are described in more detail below, are achieved by a method for recovery and regeneration of plastics for polyolefin plastic recycling plants, according to the invention, comprising the technical features described in one or more of the appended claims. The dependent claims correspond to possible different embodiments of the invention.

In particular, according to a first aspect, the invention relates to a method for recovering and regenerating polyolefin plastics which can be actuated in recycling systems, which comprises the following steps, preferably in succession, which consist of:

- accepting the waste transferred to the plant for recycling polyolefin plastics by means of a visual conformity assessment, weighing and registration of the incoming material,

- storing the incoming material in the form of bales of polyolefin plastic and selecting the bales of plastic by type,

- washing the selected plastic distributing it on at least two washing lines, a first washing line for plastic in the form of film and a second washing line for plastic in a rigid form,

- storing the washed plastic in the form of flakes, and

- extruding the flakes, distributing them on at least two extrusion lines, that is, a first and a second extrusion line, respectively, for the flakes coming from the first and second washing lines.

The differentiation between film or rigid plastics is due to the fact that polyolefin can occur in waste as both film and rigid.

Advantageously, the “mixed” flakes, that is to say, both made of plastic in the form of film and plastic in a rigid form, are washed in a third washing line to which a corresponding third extrusion line will be connected.

Advantageously, the step of storing the incoming material comprises at least two pre-selection and refining lines: a first pre-selection and refining line for plastic in the form of film, to which the first washing line is connected, and a second pre-selection and refining line, in sequence relative to the second washing line, for plastic in a rigid form.

Preferably, a third pre-selection and refining line is provided in the case of a third washing line for mixed plastic.

The pre-selection and refining lines comprise a step of picking up the bales of plastic and the subsequent tearing and/or grinding of the plastic picked up from the first or second pre-selection and refining line, depending on the type of material. A selection of the plastics ground will then be performed by optical means, controlled by a sequence defined by algorithms for programming the selection of polyolefin plastics, in such a way as to obtain seven different types of polyolefin plastics. Lastly, there is a temporary storage of said seven different types of polyolefin plastics in such a way as to have a part of the material intended to continuously feed said at least two washing lines and another part of the material which is pressed and set aside in storage for being used during the periods of stoppage of said at least two pre-selection and refining lines.

Advantageously, the washing of the selected plastic comprises:

- dry grinding of the plastic flakes,

- decanting the waste material,

- mechanical drying of the ground plastic for mechanically separating the water from the plastic flakes,

- thermal drying of these plastic flakes in such a way as to bring the moisture content of the flakes to a level useful for them to be stored and mixed, so as to make their homogenisation possible for individual batches and so they can therefore be prepared for the subsequent feeding of the extruders, suitably transported to the first or to the second (or to the third) extrusion line.

In particular, the first extrusion line, dedicated to plastic films, comprises storing and weighing the flakes and therefore compacting them. Their polymer is then sent to be melted, so as to obtain a liquid phase which is filtered a first time to eliminate any impurities. The second filtering occurs after degassing of the liquid phase filtered for the first time. Lastly, they are cut and then filtered to obtain the desired granules.

The second extrusion line, relative to the treatment of rigid plastic, comprises the melting of the polymer of the flakes, stored and weighed beforehand, suitably and, if necessary, with the addition of additives and compacted, in such a way as to obtain a liquid phase before the first filtering to eliminate the potential impurities present. Subsequently, the liquid phase is cut to obtain granules which are centrifuged in order to be drained and cooled. Moreover, any metals, which, purified in this way, are weighed, are moved away from the granules.

Preferably, the third extrusion line, for mixed plastic, is the same as the treatment seen in the first extrusion line and comprises, with the addition of the step of removing dust from the flakes for separating any traces of the plastic in the form of film.

Advantageously, the storage of the plastic washed in the form of plastic flakes comprises firstly dividing the secondary raw material of use from the waste material.

The secondary raw materials consist of materials derived from the recovery and recycling of the waste.

The “light” polymers, that is to say, with a specific weight less than or equal to 1.0, or based on the colour, are then separated from the secondary raw material, to send them to at least said first extrusion line. From the waste material, on the other hand, once dry, the “heavy” polymers, that is to say, which have a specific weight greater than 1 .0, are separated from the rest. This waste material is then stored depending on the type of material processed.

A second aspect of the invention relates to the plant for recycling polyolefin plastics which uses the method described. The plant comprises:

- a zone for the acceptance and storage of the waste which are intended to be assigned to the recycling plant; in that zone there are weighing means and means for recording the incoming material;

- a zone for storing and selecting incoming material shaped in the form of bales made of substantially polyolefin plastic;

- a pre-selection and refining zone for bales of plastic which has at least a first pre-selection and refining line for plastic in the form of film and a second pre-selection and refining line for plastic in a rigid form;

- a washing zone for the production of plastic flakes which has at least one first washing line for plastic in the form of film, that is to say, coming from the first pre-selection and refining line, and a second washing line for plastic in a rigid form, which, on the other hand, comes from the second pre-selection and refining line;

- an area for sorting the material which comes from the first (and third) washing line depending on its type and/or its colour; in the area in question there are means for separating the secondary raw material, which can be used, from the waste material; and

- a zone for extruding the flakes for making plastic granules, which has at least a first extrusion line for these flakes (which come from the first washing line) and a second extrusion line for the flakes (which come from the second washing line).

Preferably, there is a third processing line, for mixed plastic (film and rigid), which goes from the pre-selection and refining zone to the extrusion zone, that is to say, a third pre-selection and refining line upstream of a third washing line and, in succession, a third extrusion line.

Preferably, the pre-selection and refining zone comprises means for personalised selection of the plastic in the form of optically transparent film (neutral film) which comprise reversible conveyor belts.

Advantageously, the plant according to the invention comprises means for automatic control of the production parameters and plant parameters, in such a way as to produce a plastic granulate with predetermined characteristics. These automatic control means consist of a data collection system for monitoring and controlling the performance of the machines and the plant and for its control. This system works by self-learning thanks to the processing of the information received at the entrance, that is, from the production lines.

This information includes, inter alia:

- the qualification of the supplier of raw material of the material to be recycled;

- the production target for the secondary raw material and the granules;

- optimisation of production according to time, methods and costs;

- the development of the industrial costs and its control according to corporate objectives; and

- qualitative, chemical and mechanical specifications of the granule produced.

Brief description of the drawings

Further features and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of the method for recovery and regeneration of plastics for polyolefin plastic recycling plants, illustrated by way of example and without limiting the scope of the invention, with the aid of the accompanying drawings, in which:

Figure 1 illustrates the flow diagram of a plant for recycling polyolefin plastics which uses the method for recovery and regeneration of plastics, according to the invention.

Detailed description of the actuation of invention

The above-mentioned drawings show a preferred embodiment of a method for recovery and regeneration of plastics for plants for recycling polyolefin plastics, according to the invention.

The waste entering the recycling plant is almost entirely made up of polyolefin plastic and, in smaller quantities, other plastics. They come directly from industrial and artisan activities or from the collection of production waste and waste from private surfaces, including packaging industries, plastics industries, ceramics industry and plastic moulding industries, supply chain consortia that deal with recovery through selection and service centres and from post-consumer waste.

The waste is then taken to the acceptance and storage zone and the nonpolyolefin waste is sent to plants specialised in the treatment of other plastics.

The waste assigned to the plant is accepted as follows.

Firstly, there is a visual check of the correspondence of the material transported with what is declared in the waste identification form.

The material coming from the acceptance zone is then shaped into bales of polyolefin plastic in the storage and selection zone and the waste is weighed by means of specific scales and the fields relating to the weight of the plastic bales are completed in the corresponding identification form.

The notes required by applicable legislation are taken in the loading/unloading register.

Further checks are also carried out concerning the homogeneous quality characteristics, the presence or absence of foreign bodies and the nature of the foreign material (visual check, infrared analysis, risk assessment document analysis, etc.).

The bales of plastic, which may appear as film, rigid or mixed (film and rigid), are transported to a pre-selection and refining zone to carry out the regeneration of polyolefins, where they feed, respectively, a first preselection and refining line (for plastic in the form of film), a second preselection and refining line (for rigid plastic) and a third pre-selection and refining line (for mixed plastic).

The capacity of each selection line is approximately 5.00 - 5.5 t/h depending on the material, the size, the consistency of plastic flakes selected.

The operations performed in this zone are described below.

The waste stored in bales in the specific dedicated areas is picked up with lift trucks from the suitable storage hangars and placed under the feed preparation canopy of the pant, for feeding the grinders-tearing devices. Here, the operator loads the tearing-grinding devices at the start of the suitable pre-selection-refining line depending on the nature (film, rigid or mixed) of the plastic bales received.

Once ground into pieces approximately the size of an A4 sheet, the waste is sent by conveyor belts to the selection line, which is controlled by a sequence defined by algorithms for programming the selection of polyolefin which operate to automatically select the plastics ground with optical machines which work close to infrared, that is to say, using “near infrared” technology, of per se known type.

These algorithms select seven different types of polyolefin plastics which are stored in temporary storage bunkers, which are useful, however, to continuously feed the washing lines.

In fact, the material selected is contained in the temporary bunkers, which is not sent to the washing lines, is pressed and stored internally, to be used during stoppages of the pre-selection zone, for example during cleaning or in the case of maintenance of the plant.

According to the preferred embodiment, the pre-selection and refining department has, in addition to grinders, three ballistic separators for separating the plastics by texture, film or rigid, eleven NIR optical selectors for selecting polyolefin and non-polyolefin plastics, and eight bunkers for storage of selected plastics.

From the pre-selection and refining zone, the material to be recovered and regenerated advances towards the washing zone.

It provides in sequence:

- a module for preparing for washing;

- a prewashing module;

- a washing module;

- a mechanical drying module; and

- a thermal drying module.

For the second washing line (rigid material), there is also a hot water washing module which accompanies - or replaces - the washing module. In particular, the double drying, mechanical and hot air, advantageously improves the capacity to remove the moisture content at the end of the line.

The cycles for washing propylene (PP) or polyethylene (PE) are substantially identical, but - as mentioned - only the algorithms for managing the washing cycles for the polyolefins which are presented as film or as a rigid material differ.

In particular, this difference is crucial during the drying step, where the double thermal drying module, which is normally used, cannot be used for rigid flakes.

The materials, selected in the pre-selection and refining department and temporarily stored in the bunkers, are then sent by a conveyor belt (which has the purpose of transporting the material from the bunkers to a dry mill, which grinds and cuts up the flakes of minimum dimensions coming from the pre-selection zone) to suitable washing lines for the washing preparation step, firstly to the washing preparation module where the material is ground, and placed in at least one decanting tank, which has the purpose of processing the plastics soiled by heavy bodies, such as stones, pieces of metal or other voluminous aggregates, obtaining the separation by floatation.

According to the embodiment described here, there is also a dosing buffer which is fed in the next pre-washing module.

At this point, the material, which has been entirely ground and cleaned of any pieces of metal, aluminium, stones or other aggregates, is introduced into the pre-washing module which has the purpose of wetting, washing and rubbing the material and then sending it to the washing module.

According to the preferred embodiment, the prewashing module comprises a machine of the “turbo washer” type which has the purpose of wetting and washing the material, rubbing it vigorously, in such a way as to make it lose the aggregates which are still attached to the flakes, a water mill for grinding and breaking the plastic flakes to a transversal dimension of approximately 30 mm, wetting and further washing the material and a draining screw conveyor which picks up the material from the water mill, decanting the water, and sending it to the washing module.

In this module, the material arrives in dimensions of approximately 30 mm coming from a further grinding. The washing module, which is designed to wash and dry the flakes twice in order to obtain the quality necessary for extrusion, preferably comprises a second stage “turbo washer” type machine which wets and washes the material, rubbing it vigorously, to make it lose the aggregates still attached to the flakes and a floatation tank, equipped with a draining screw conveyor, at ambient temperature. In this tank, the heavy impurities deriving from the washing settle on the bottom, whilst the polyethylene, which has a weight mixed with the water, is sent to the centrifuge for separating the solid part from the liquid.

In the second washing line, the tank bottom preferably contains charged polyolefin and, for this reason, the Applicant has implemented the relative module for management of the tank bottom.

Again with regard to the second line, dedicated to rigid plastics, the bottom of the floatation tank is picked up, dried and centrifuged. Subsequently, it is screened using NIR technology optical selectors to remove the polyvinyl chloride (PVC) present. The polyolefins, as well as the other plastics selected and separated from the PVC, are preferably resent to the recycling or sold, drastically reducing incineration as a system for the distribution of non-recyclable waste.

In the washing module, again for the second washing line, there is a hot water washing module.

The Applicant has, in fact, perceived that it is sometimes necessary to perform the washing autonomously on each line, both cold and hot.

For this reason, if it is necessary and required by the material being processed, the washing is performed with hot recirculation water (at a temperature of approximately 80°C), specifically with additives for removing labels, adhesives and organic residues and having an anti-foam agent to prevent the formation of foam.

This hot washing module preferably has a mixer for the sodium carbonate equipped with a heat exchanger and a disc filter, friction washing means with hot water and a washing system with a high rotation washing machines, again in hot water.

The material then passes to the mechanical drying module, where the water is mechanically separated from the plastic flakes.

According to the proposed embodiment, the mechanical drying module comprises a drainage screw conveyor and a centrifuge for mechanically separating the solid part from the liquid part.

Only for the line dedicated to plastic films (first and third washing lines) there is a press designed to squeeze the flakes of film in order to eliminate the aqueous fraction.

This is followed by a thermal drying module where the scales with residual humidity are dried thermally so as to bring them to a moisture content level useful for being stored and then extruded.

The thermal drying module preferably comprises thermal units in the form of a spiral tube with hot air in counter-current. The hot air is generated by electricity.

At the end of the washing line, the plastic flakes, washed and dried, are sent to silos for storage and mixing, to be homogenized in single batches and prepared for subsequent feeding of the extruders.

The Applicant has designed and integrated in the washing area a closed circuit system for purifying the washing water which allows the high amounts of COD (chemical oxygen demand) and BOD (biochemical oxygen demand) released into water by post-consumption plastic materials to be reduced. The plant, which draws from two authorised artesian wells, has been designed to reduce chemically, physically and biologically the pollutants which have the greatest impact on the environment. This system advantageously offers the possibility of autonomously purifying the process and washing water.

The material, from the storage silos to the end of the washing line, is picked up by means of a dosing screw feeder and feeds the extrusion zone.

As mentioned above, according to the preferred embodiment, there are three extrusion lines: a first extrusion line for plastic in the form of film, a second extrusion line for plastic in a rigid form and a third extrusion line for mixed film and rigid plastic.

The first and third extrusion lines, which are designed to process, at least partly, plastic in the form of film, comprise an extruder of the single-screw - tandem type with double filtration.

The single-screw extruder consists of a single worm screw which rotates inside the cylinder.

The second line, which processes exclusively rigid plastic, has a twin- screw extruder, which is more complex than the single-screw and consists of two screws interpenetrating in the cylinder, with double filtration and a gravimetric additive system.

For this reason, the Applicant has provided for the use of extruders reserved for film (single-screw) and intended for rigid and compound plastic (twin-screw).

Once granulated, the material is stored inside silos or bagged in sacks of about one tonne each.

In particular, with regard to the first and the third extrusion line (film and mixed) from the outlet of the respective (first and third) washing lines, the material is conveyed inside a stainless steel pipe, by means of a pneumatic thrust loading movement, special for lightweight flakes and, thanks to a pneumatic diverting valve, it is directed to corresponding inverted cone storage silos, one for each extrusion line dedicated to the film material.

These silos, made entirely of stainless steel, have a central bridge-breaker reel, and are positioned on load cells for the continuous reading of the weight in such a way as to constantly dose the material on the loading conveyor belt of the first and third extrusion lines. Preferably, the conduit comprises means for detecting metals, for example a metal detector, for excluding metals (ferrous and non-ferrous) which could damage the mechanical parts of the extruders.

Alongside each extruder is mounted a compactor which receives the material from the conveyor belt and, through a centrifugal force applied by a spiral positioned at the base of the belt, it reduces the dimensions of the material rotating at a high speed variable by the inverter. This mechanical action increases the temperature in a constant manner and there are therefore a series of thermal probes, managed by suitable software, which control the temperature of the material with the aim of increasing not only the specific weight of the film but also reducing any residual humidity.

According to the example proposed, each of the extruders of these two lines is equipped with at least one further gravimetric dosing system complete with its own negative pressure loading system, for adding further products such as masters, slippers, peroxides, etc.

By using a worm screw (single-screw), the material slides in a cylinder which is suitably heated and controlled in each single part. The heating is actuated by electrical resistors which melt the polymer so that it can be filtered continuously by means of an automatic mesh filter, so as to separate any residual impurities.

The mesh filter has two filtering surfaces: when the maximum operating pressure set on one of the surfaces is reached, it interrupts the flow of the liquid phase obtained (melt) to allow a drive roller to extract the dirty filter mesh and, at the same time, introduce a clean mesh.

In this way, advantageously, one of the two surfaces of the filter is always available and the flow is not interrupted.

This first filtering has a degree of filtration of between 500 and 100 pm, depending on the material being processed. After the first filtration, the melt is degassed in a special degassing chamber, where any volatile substances/gases developed during the melting evaporate by means of a pump which exerts a vacuum of substantially between -0.8/1 .0 bar. In order to increase the efficiency of the degassing, the polymer passes through a perforated matrix which increases the surface by eleven times.

Subsequently, the liquid phase is restarted by a second single-screw extruder so as to apply a second filtration by means of a mesh filter with a semi-automatic plate. Like the mesh filter of the first filtering, this is also provided with two surfaces. In this case, the removal of the dirty mesh and the introduction of the clean mesh are performed manually by an operator. In this case, the degree of the final filtration ranges from 300 to 60 pm, depending on the material being processed.

During the two filtrations, both the melt temperature and the operating pressure of the polymer is controlled. For controlling the temperature, the cylinders of the single-screws are suitably equipped with ventilation and heat-regulated glycol cooling systems.

At this point, the liquid phase is transformed in the form of a granule by means of a water ring system with the aid of a die, that is to say, a series of rotary blades and water which determine the dimensions of the granule. This all occurs inside a granulation chamber, where the granule is drained and cooled by the excess water, by means of a vertical centrifuge and a screen.

At the outfeed from the centrifuge, the granule passes through a neodymium conduit to expel any presence of metals, after which it is weighed by a continuous weighing system formed using hoppers and scales with load cells.

A pushing loading unit transports the material inside a stainless steel pipe and, by means of a pneumatic diverting valve, arrives in the first vertical mixer silo which is also made entirely of stainless steel and positioned on load cells. After reaching the maximum quantity, verified by the cells, the operators pick up a sample which is promptly examined for a first preliminary and partial laboratory analysis. Only after good conformity is verified are the granules then transferred to a second vertical mixer silo by means of a drain located in the upper part and controlled by a pneumatic shutter. The second silo is identical to the first silo and it is therefore also made entirely of stainless steel and positioned on load cells.

A sample is then picked up from the second silo for a complete laboratory analysis, which will represent the batch with a relative identification code.

After verifying good conformity, the material is transferred into a monolithic stainless steel silo or into an automatic station for filling sacks, through a further pushing loading unit, and then destined to the end customer.

If the granule does not conform, the transfer does not take place, but is emptied and bagged by means of a discharge located in the top part of the second silo by means of a lift truck.

If a change of production is decided or if a poor quality of the granules is visually found, the granules are preferably diverted into suitable containers in order to avoid contamination of the silo.

Advantageously, in the third extrusion line there is a dust separator for separating any traces of film, in such a way as to not only process film but also rigid material and make it more flexible than the first extrusion line.

According to this configuration, the product is transferred into the vertical mixing silo of the third extrusion line or into the vertical mixing silo of the second extrusion line (rigid material), both made entirely of stainless steel, positioned on load cells and equipped with metal detector means.

In this regard, the second extrusion line, dedicated to the rigid plastic, comprises suitable means for moving the material (preferably of the pneumatic type with pushing loading) from the pick-up point of the second washing line to the vertical mixing silo of the first or third extrusion line or destined, after passing through a dust separator, to the storage silo of the respective pre-selection line, passing inside a stainless steel pipe and thanks to a pneumatic diverting valve.

The vertical mixer silo of the second extrusion line, usually made entirely of stainless steel and positioned on load cells for continuously reading the weight, feeds a gravimetric doser through a pneumatic conveyor with pushing loading. The doser is positioned on the supporting structure across the second extrusion line.

On the same supporting structure there are further dosing systems, which are also gravimetric, for adding products such as masters, sliders, peroxide, water (stripping), CaCOa mineral filler and talc.

In this second extrusion line, as mentioned, the material flows inside a cylinder in the form of an eight (°°) and is treated by a co-rotating twin- screw extruder. The cylinder is suitably heated and has three degassing points: one open air and two forced by means of a pump which exerts a vacuum substantially between -0.8 and 1 .0 bar.

Since, due to the way it is formed, the twin-screw extruder does not support operating pressures greater than 70 bar, there is advantageously a gear pump specifically designed for polymers, which conveys the liquid phase of the plastic in the first filtration zone through an automatic continuous mesh filter.

This mesh filter, similarly to those described for the other extrusion lines, has two filtering surfaces. For this reason, when it reaches the maximum operating pressure set on one of the surfaces, the flow of the melt is interrupted to allow the drive roller to extract the dirty mesh and at the same time introduce the clean mesh.

In this case, the primary filtration ranges from 300 to 150 pm, depending the material being processed.

The extruded material is then taken up by a second gear pump and filtered again. The second filtration is performed by a mesh filter with a semiautomatic plate. It is also equipped with two surfaces and in this case the dirty mesh is removed and the clean mesh is introduced manually.

The degree of the final filtration ranges from 200 to 100 pm, depending on the material being processed.

During the first and second filtration, both the melt temperature and the operating pressure of the polymer is controlled. In order to adjust the temperature, the cylinder of the twin-screw extruder is suitably equipped with heat-adjusted glycol cooling systems.

Subsequently, the liquid phase is transformed in the form of a granule by means of an underwater cutting system with the aid of a die, that is to say, with a series of rotary blades and water which determine the dimensions of the granule. All this takes place inside the granulation chamber.

Therefore, by means of a vertical centrifuge and a screen, the granule is drained and cooled by the excess water.

At the outfeed of the centrifuge, the drained and cooled granule passes through a neodymium conduit to expel any presence of metals, after which it is weighed by a continuous weighing system, for example formed using hoppers and scales with load cells.

By means of a pushing loading unit, the material is transported inside a stainless steel pipe and transferred to the first vertical mixer silo, made entirely of stainless steel and positioned on load cells, by means of a pneumatic diverting valve.

After reaching the maximum predetermined quantity of filling the silo, a sample is taken from the granules, which is promptly analysed by the technical staff for a first preliminary and partial laboratory analysis. Only after verification of good conformity, the material is transferred into a second vertical mixer silo, made entirely of stainless steel and positioned on load cells. Also here the material undergoes a second sampling for a complete laboratory analysis which will represent the batch with a relative identification code.

After verifying good conformity, the material is launched, using a further pushing loading unit, into one of the monolithic stainless steel silos or into an automatic station for filling sacks.

In the event that the granule, on the other hand, does not conform, the transfer does not take place, the silos are emptied and the non-conforming material will be bagged by means of a discharge located in the top part of the silo, by means of a lift truck. The material can then be reprocessed in the plant in question or destined for other use.

If it is decided to carry out a production change or if a poor visual quality of the granule is detected, this is diverted into a suitable container in order to avoid contamination of the filter.

Between the washing and the extrusion, the plastic flakes are separated and divided by a specific sorting area on the basis of their type of plastic or according to their colour.

Thanks to a double-sensor system for recycling plastics, plastic fractions are detected based on the colour and, simultaneously, depending on the types of polymer.

This area comprises a decantation tank divided into two parts: the waste material, which lies in the bottom of the tank, coming from the first and third washing line (film and mixed) and the secondary raw material, that is to say, the material for use, of the first and third washing line which is on the surface.

In detail, the waste material at the outlet of the floatation tanks of the first and third washing lines is dried by a vertical drying centrifuge and then transported to the bottom of the tank of the sorting area. The technical and quality characteristics of the polymers are read here and they are separated as a result. The “heavy” ones, that is to say, those with specific weight greater than 1.0 (PET, PS, ABS, PVC, PA, charged PP), are stored in a vertical mixer silo or placed in suitable bags.

Moreover, on the basis of the type of material which is processed in the washing zone, it is established whether to select only the PVC or the charged PP, from the rest of the polymers.

In the first case (PVC only), this is waste material destined for incineration. For this purpose, one of the important requirements to be guaranteed is the presence of polyvinyl chloride less than approximately 1%; the sorting is therefore used to identify and select the PVC separating it from the rest. In the second case (material with a high percentage of charged PP), it is a charged polypropylene with a density greater than 1 .0 which by floatation has been destined as waste; for this reason, in this area the PP is selected and recovered from the rest of the materials and it is destined to storage and then dispatched to the extrusion.

The material of use (secondary raw material) coming from the first and third washing lines is transported into the sorting area for the reading and separation of the polymers with a specific weight of less than 1.0 (HDPE, PP) or for separation by colour. The flakes thus separated are then stored in one of the vertical mixing silos or bagged and then destined for extrusion.

The separation by specific weight is considered when a very high degree of purity of the polymer is to be obtained, equal to approximately 98%, advantageously allowing the extruding of a homogeneous polyolefin material and with a liquid phase index (MFI, “melt flow index”) with a narrow range.

The division by colour, on the other hand, is selected when the presence of a predetermined colour, such as white, blue or red, or optically transparent plastic, are present in a significant percentage, such as to acquire value extracting them from the rest of the colours and therefore being able to select a high quality and optimum colour.

From this zone, the materials, depending on requirements, will enter in the first and third extrusion lines, and continue as described above.

Advantageously, with reference to Figure 1 , the plant comprises automatic management means which operate by self-learning, for example a system for the execution of the Manufacturing Execution System (MES) production, that is to say, a system which acquires and distributes information which allow the optimisation of production activities from the launch of the order to the finished product, by processing the numerous items of information (“big data”) received as input and processed by a SCADA (“Supervisory Control and Data Acquisition”) type monitoring and data acquisition control system, so as to have an entirely automated system, which, after a step of starting the plant and starting production, exploits, crossing it, the following data:

- qualification of the supplier of the waste, used as raw material of the plant;

- production targets for the secondary raw material and the granule, as a function of predetermined parameters (customer specifications);

- optimising production according to time, methods and costs;

- development of the accounting (and hence the industrial costs); and

- qualitative, chemical and mechanical specifications of the granule produced.

This data collection system for monitoring and controlling the performance of the machines and the plant and the relative management, preferably determines in a unique manner, intervening dynamically and in real time, the production and management parameters of the plant to obtain the planned results.

It provides the algorithm for automatic control of the production parameters of the work phases, that is to say, the plant parameters, in such a way as to make the plastic granules with predetermined characteristics, by processing the information received from the production lines.

The Applicant has understood that this is a considerable step forward in the implementation of automatic systems which makes it possible to minimise human error in setting up and control of the plant and allow maximum use of the production, guaranteeing the quality of the granule produced according to customer specifications.

From the above description it may be seen how the invention achieves the preset purpose and aims and in particular it should be noted that a method is implemented for recovery and regeneration of plastics for plants for recycling polyolefin plastics, which - by selecting waste of different origin - always produces a granule of similar quality to the virgin material and, on the other hand, is able to enhance the vale of the waste material.

In particular, the selection of the film in the sorting area, and above all the capacity to select not only the rigid material from the film but also the film from the film separating it in terms of LDPE and LLDPE, allows a purity equal to or greater than 98% for PE-based polyolefin and a purity greater than 90% for LDPE or LLDPE polyolefin.

An advantage of the plant for recycling polyolefin plastics, according to the invention, is due to the verticalization of the entire cycle of recycling and regeneration of the plastic, generically fragmented into different companies, with obvious advantages in terms of management, cost and capacity for controlling the processing steps.

Moreover, with this plant it is possible to treat film, rigid or mixed type (rigid and film) plastics inside the same plant.

Another advantage of the invention is the capacity of the method to enhance the value of goods and products beyond the end of the useful life of plastics, through the regeneration, using renewable energy sources with a view to sustainable production which reduces environmental impact.

Moreover, the method and the system according to the invention make it possible to refine and purify the flake products of the rigid washing line from the PVC, so as to allow a re-use in recovery systems specialised in other non-polyolefin materials and prevent the start of energy recovery.

In addition, thanks to the self-learning of the data collection system for monitoring and controlling the performance of the machines and the plant and for its control, it acts in a forecasting and preventive manner, minimising consumption, costs and impact on the environment. This system will make it possible in practice to use secondary raw material in the production of semi-finished products or consumer products and to have a purity during extrusion with an index of the liquid phase which is almost homogeneous, making the extruders produce batches of granules of secondary raw material with a high degree of uniformity and quality, as required by the manufacturers of heat-shrink, bubble wrap or stretch transparent film.

The invention can be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

Moreover, all the details of the invention may be substituted by other technically equivalent elements.

In practice, the materials used, as well as the dimensions, may be of any type, depending on requirements, provided that they are consistent with their production purposes.