Method for cleaning waste plastics

Abstract

The invention relates to a method for cleaning pre-comminuted waste plastic, in particular plastic chips, comprising the following steps: a pretreatment step in which the pre-comminuted waste plastic is pretreated in a pretreatment device, the pretreatment comprises heating the waste plastics to a cleaning temperature by using a heating device of the pretreatment device and / or adding at least one cleaning additive and mixing the waste plastics with the at least one cleaning additive through the pretreatment device; a cleaning step in which the waste plastics pretreated in the pretreatment device are cleaned in a cleaning device comprising two cleaning tools driven to rotate relative to each other, guiding the waste plastic together with a cleaning liquid through a working gap between mutually facing working surfaces of the cleaning tool having cleaning teeth, at which time dirt is removed from the waste plastic by friction; and a drying step in which the waste plastic cleaned in the cleaning device is dried in a drying device.

Description

Technical Field

[0001] The invention relates to a method for cleaning pre-shredded waste plastics, in particular plastic flakes. Background Art

[0002] Conventional washing technology is used for example to utilize cold or hot process water to clean. For example, this method is known from EP 2 832 459 B1, for cleaning by passing the product to be cleaned through a plurality of cleaning tanks when adding a cleaning agent that should especially separate printing ink from waste plastics. But here, for example, hot melt adhesives, printing inks and metal vapor depositions are not completely separated. Complete separation refers to residual contaminants less than 10 ppm, which only slightly cause so-called VOC (volatile organic components) in hot further processing, such as extrusion or melting. In conventional sodium hydroxide solution hot washing, for example, only when using a surfactant specially adapted for sodium hydroxide solution and immersing the fragments in the washing liquid for a long time, printing ink will be separated. The separation of hot melt adhesive is also problematic. The adhesion residues in the range of at least less than 100 ppm that market demand cannot be achieved usually here. This becomes obvious in the application of recycled materials, that is, becomes obvious due to gel or yellowing in the film. Other serious consequences are the gas evolution which occurs during pellet extrusion or during further processing by liquid state polymerization (LSP), in which the PET is condensed in a high vacuum.

[0003] The consequences of purification that is merely "clean" in contrast to "high purity" severely restrict the application of recycled materials and thus their marketability. At the same time, the requirements for polymer quality have also increased, that is, they are similar to those for plastics in primary form. Products made from recycled materials must be essentially free of adhering printing inks, various VOCs that adversely affect degassing and melt filtration in the extruder, and foreign contamination, because such residual impurities can lead to adverse changes in the mechanical and processing properties of the polymer and can also lead to undesirable color and odor changes. If the above-mentioned contaminants are not removed during the cleaning process, the recycled materials cannot be used as packaging for foods as desired.

[0004] EP 2 094 462 B1 discloses a method for separating cellulose and other adhering substances when recycling waste plastics, in particular mixed plastics, wherein thin films and lumps consisting of thick plastic parts in the waste plastics, which may be pre-sorted, are mechanically pre-comminuted into fragments or small particles until a predetermined size is reached, and the comminuted material is fed to a disc mill together with water, without previously producing briquettes or agglomerates from the fragments. The cooperating discs of the disc mill essentially wipe the dirt off the fragments and the dirt is then present as a separate material, which can be separated from the plastic parts by a suitable separation method. A similar method is disclosed in EP 2 094 461 B1.

[0005] Another method for removing dirt from plastic fragments using a disc grinder is known from EP 2 734 302 B1. Here, the disc grinder is not a toothed disc grinder, but a cleaning disc having a plurality of cleaning ribs extending between the inner edge and the outer edge of the cleaning surface, and a plurality of cleaning plates distributed transversely to the extension direction of the cleaning ribs are arranged between at least some adjacent cleaning ribs. At least one side of the cleaning rib is inclined or curved relative to the axial direction of the corresponding cleaning disc, and the cleaning plates are respectively raised in a ramp-like manner and have a height lower than the cleaning ribs. In this way, a smaller mechanical load on the plastic fragments is achieved during cleaning, because the plastic fragments are pulled between the discs, especially between the cleaning ribs, and bending or folding or entanglement of the plastic fragments is avoided, which may lead to insufficient cleaning.

[0006] Furthermore, EP 3 057 751 B1 discloses a device and a method for cleaning plastics, in particular plastic fragments, in a plastic recycling process. A toothed disc refiner is used here, which has a central inlet for feeding the plastics to be cleaned into the working gap and an outlet for the cleaned plastics together with the wiped-off dirt and water, which is arranged at the outer edge of the working gap. The outlet has an outlet pipe, through which water is pumped out during operation, which flows laterally past the working gap and is oriented tangentially relative to the working gap, and which exerts a suction effect on the working gap, thereby conveying the cleaned plastics into the outlet pipe. In this way, in addition to the input and cleaning consistency (Konsistenz), the output consistency can also be flexibly adjusted, in particular independently of the cleaning consistency. Thus, in the sense of maximum energy efficiency and cleaning effect, a high solids consistency can be set in the working gap, and at the same time a well-conveyable or pumpable suspension with a low solids consistency can be set after the working gap. Summary of the invention

[0007] Based on the above-mentioned prior art, the object of the present invention is therefore to provide a method of the aforementioned type with which waste plastics can be cleaned of different impurities to the greatest extent possible.

[0008] The invention achieves this object by means of independent claim 1. Advantageous embodiments are disclosed in the dependent claims, the description and the drawings.

[0009] For the method of the above type, the present invention achieves the object by the following steps:

[0010] • a pretreatment step, in which the pre-shredded waste plastic is pretreated in a pretreatment device, wherein the pretreatment comprises heating the waste plastic to a cleaning temperature using a heating device of the pretreatment device and / or adding at least one cleaning additive and mixing the waste plastic with the at least one cleaning additive through the pretreatment device,

[0011] • a cleaning step, in which the waste plastic pretreated in the pretreatment device is cleaned in a cleaning device, the cleaning device comprising two cleaning tools driven to rotate relative to each other, the waste plastic together with a cleaning liquid is guided through a working gap between mutually facing working surfaces of the cleaning tools having cleaning teeth, whereby dirt is removed from the waste plastic by friction,

[0012] • A drying step in which the waste plastic cleaned in the cleaning device is dried in a drying device.

[0013] The method according to the present invention is used to clean pre-crushed waste plastics, such as plastic fragments or plastic fragments crushed from plastic films. In principle, plastic fragments can be produced by crushing hard plastics or films, etc. The dirt to be removed can be, in particular, surface adhesions, such as cellulose residues of labels, hot melt adhesives, organic pollutants of food residues, printing ink layers that may have printed closures, metallized portions of surfaces, paper adhesive labels, plastic films or metal foils, etc. The method according to the present invention is used to clean pre-crushed waste plastics. The waste plastics can be provided in a state that has been pre-crushed. But the method according to the present invention can also include crushing of the waste plastics before implementing the cleaning method. As mentioned in the present application, the crushing of the waste plastics can be carried out, for example, by a mechanical crushing device, such as a crusher or a cutter.

[0014] In the pretreatment step, in order to achieve optimal subsequent cleaning, the pre-crushed waste plastic is pretreated in a pretreatment device. That is, in the pretreatment step, in particular, the waste plastic has not yet been cleaned. The pretreatment step, in particular, preferably does not substantially include friction and substantially does not include or only includes slight agitation of the waste plastic. The pretreatment includes heating the waste plastic to a cleaning temperature using a heating device of the pretreatment device and / or adding at least one cleaning additive and mixing the waste plastic with the at least one cleaning additive by the pretreatment device. During the pretreatment step, a liquid, such as water, can also be added. This can especially be the cleaning liquid used in the cleaning step. The pretreatment is used, for example, to act on the surface of the waste plastic using a temperature-regulated washing lye with a determined temperature and under a determined action time. As already mentioned, during the pretreatment, there is substantially no friction, such as caused by agitation, applied to the surface of the waste plastic. On the contrary, the task of the pretreatment device is to soften the dirt attached to the surface of the waste plastic, such as the structure of the printing layer or the adhesive layer, and eliminate the van der Waals force. That is, the purpose of the pretreatment is to reduce the physical bonding force that causes dirt to adhere to the plastic surface. The removal of dirt, such as printing ink, is not carried out during the pretreatment step and is not desirable to be carried out during the pretreatment step in order to prevent dirt from migrating to the interface / contact surface of the plastic. The pretreatment device can have a heat-insulating structure in order to keep the waste plastic heated by the heating device at a predetermined cleaning temperature for a predetermined time. After the pretreatment, the waste plastic is optimally prepared for the subsequent cleaning.

[0015] In addition, the method according to the present invention also includes a cleaning step, in which the pre-treated waste plastic is cleaned in a cleaning device. The cleaning device is particularly formed as a toothed disc cleaning machine and includes two cleaning tools facing each other, which can be, for example, cleaning discs. At least one of the cleaning tools is driven to rotate by a rotary drive so that relative rotation occurs between the two cleaning tools. These cleaning tools each have a working surface provided with cleaning teeth. The working surface is configured to be annular, especially annular, and an annular, especially annular working gap is defined between the opposing working surfaces. The cleaning teeth of the opposing working surfaces mesh with each other, so that the cleaning tool forms a positive tool and a negative tool. The teeth on the working surface are particularly individual teeth, that is, these teeth are not connected to each other by ribs or the like. It is possible that each cleaning tool can be adjusted axially relative to each other by a corresponding adjusting device, so that the width of the working gap can be adjusted. In this way, the desired friction can be achieved by the mutually meshing cleaning teeth according to the waste plastic to be cleaned, so that dirt can be optimally removed from the corresponding pre-treated waste plastic. The cleaning of the waste plastic is carried out by friction. In particular, impurities are wiped off the surface of the waste plastic. For this purpose, it is feasible to set a very small spacing between the cleaning teeth of the opposite cleaning tools by means of corresponding axial adjustment until the cleaning tools touch each other. For example, the cleaning teeth can come into contact with the bottom of the opposite cleaning tools. A small spacing can be retained between the tooth sides of the cleaning teeth, so that the waste plastic is forced to pass on the tooth sides to achieve the best cleaning result. The rotation axis of the at least one cleaning tool that can be driven to rotate, in particular the cleaning disk, can simultaneously be the symmetry axis of the cleaning tool, in particular the cleaning disk. For example, an electric drive can be considered as a rotary drive.

[0016] The cleaning device has an inlet, which can be, for example, centrally introduced into the working gap. The waste plastics to be cleaned are guided into the working gap, for example, together with a cleaning liquid, via the inlet. But the cleaning liquid and the waste plastics can also be supplied to the working gap separately. The waste plastics to be cleaned are guided through the working gap together with the cleaning liquid introduced individually or together with the waste plastics. The cleaning liquid can be water in particular. This also applies to the other embodiments mentioned below. The waste plastics are sheared between the cleaning tools and evenly distributed in the working gap in this way. At this time, the waste plastics pass through the tooth row formed by the cleaning teeth. In the process of applying friction to the waste plastics by the cleaning teeth, impurities on the surface are wiped off or detached. Through the outlet, the waste plastics are output from the working gap of the cleaning device together with the detached attachments or impurities and the cleaning liquid for further processing. In combination with the pretreatment completed before, any dirt can actually be reliably and greatly removed from the waste plastics in the cleaning step.

[0017] After the cleaning step, a liquid separation can be carried out, for example mechanically, that is to say the waste plastic is separated from the cleaning liquid. The liquid separation can be carried out in particular immediately after discharge from the outlet of the cleaning device, for example within less than one minute, preferably within less than 30 seconds. This reliably avoids recontamination due to excessive residence time of the cleaned plastic. If a liquid separation is provided in the present application, this can be achieved, for example, by a phase separator and / or a centrifuge.

[0018] Next, a drying step is carried out, in which the waste plastics that have been cleaned in the cleaning device and, if necessary, separated from the cleaning liquid and thus from the separated impurities are dried in a drying device. By means of the drying, the cleaned waste plastics can be brought into a state that can be processed further without any problems. After the drying, the plastics can have, for example, a residual moisture content of less than 5%, preferably less than 3%. After the drying step, a sorting step, for example an air separation step, can also be carried out, in which the three-dimensional plastic fragments are separated from the film fragments. This facilitates further processing.

[0019] With the method according to the invention, a purity of less than 100 ppm, preferably less than 50 ppm and more preferably less than 20 ppm of residual dirt in the cleaned waste plastic can be achieved. This is achieved by combining a pretreatment step including the action of corresponding tempering and / or cleaning additives, but in particular without applying friction to the waste plastics, with subsequent cleaning by friction in corresponding cleaning tools. In this way, in the pretreatment step, an accurate action time can be achieved in combination with a determined temperature and / or a determined cleaning additive, without the separation of dirt from the waste plastics, especially plastic fragments. In contrast, in the method according to the prior art, as described, for example, in EP 2 832 459 Bl, the cleaning of the waste plastics is carried out in a stirred container, and tempering and adding cleaning additives are also carried out in the stirred container. This does not allow a determined cleaning to be achieved, because it cannot be ensured that all plastic particles are subjected to the cleaning action in the same way by a basically random agitation of the waste plastics in the stirred container, for example by stirring. As a result, the cleaning of individual plastic particles is incomplete. This problem is involved in the prior art in the form of working with a higher cleaning temperature and a larger addition amount of cleaning additives and a longer action time. However, this is undesirable from an energy and environmental perspective.

[0020] In contrast, according to the invention, the pretreatment step is not used to clean the waste plastic, but only to carry out a specific pretreatment for the subsequent friction cleaning in the cleaning device. Energy consumption, residence time and the need for cleaning additives can be optimized, while having a correspondingly favorable effect on operating costs and environmental compatibility. The cleaning device ensures that all plastic particles are essentially subjected to the same cleaning friction by means of its cleaning tooth geometry. As a result, the cleaning effect is constantly optimal for all plastic particles. The pretreatment step, which is used only for pretreatment, prevents dirt, such as printing ink or coating, from detaching prematurely and entering the liquid used in the pretreatment step, which could have a negative impact on the cleaning additive's effect and reuse. Intensive pretreatment of the liquid used in the pretreatment step can be avoided.

[0021] In the cleaning step, the solids consistency of the suspension of waste plastic and cleaning liquid is also important. For optimal cleaning, the solids content of the waste plastic to be cleaned in the working gap relative to the cleaning liquid in the working gap should be less than 5 wt.% for waste plastic in the form of film and less than 10 wt.% for waste plastic in the form of PET or hard plastic.

[0022] According to one embodiment, the pretreatment device can have a plurality of pretreatment containers, which contain the waste plastics during the pretreatment process. In this way, the desired temperature control and / or the desired action time of a possible cleaning additive can be set with certainty. Thus, in contrast to the case of a continuously passing product quantity, the batch-wise pretreatment of the waste plastics in a plurality of pretreatment containers ensures in a simple manner the respectively desired minimum residence time for temperature control or for the cleaning additive to take effect. In this case, the waste plastics to be cleaned can be supplied from the pretreatment containers successively and respectively after a predetermined residence time for further processing.

[0023] According to another design solution, the pretreatment device can have at least one pretreatment screw, which conveys the waste plastic during the pretreatment step. The pretreatment screw conveys the waste plastic in particular together with a liquid, for example together with a cleaning liquid used in a subsequent cleaning step. Here, the pretreatment screw can be completely filled with liquid. A certain residence time of the waste plastic can be set by the pretreatment screw. The pretreatment screw can include a heating device and / or a thermal insulation structure. The pretreatment screw can also include at least one supply device for the at least one cleaning additive. However, it is also feasible to supply the at least one cleaning additive to the waste plastic before entering the pretreatment screw and / or to heat the waste plastic before entering the pretreatment screw.

[0024] According to another design solution, the pretreatment device can have at least one pretreatment pipeline system, in particular a tube bundle system, through which the waste plastics are transported during the pretreatment step. The waste plastics are also transported through the pretreatment pipeline system, for example, with the help of a pump together with a liquid, for example, a cleaning liquid used in a subsequent cleaning step. Here, the pretreatment pipeline system can be completely filled with liquid. A certain residence time of the waste plastics can also be set through the pretreatment pipeline system. The pretreatment pipeline system may include a heating device and / or a thermal insulation structure. The pretreatment pipeline system may also include at least one supply device for the at least one cleaning additive. However, it is also feasible to supply the at least one cleaning additive to the waste plastics before entering the pretreatment pipeline system and / or to heat the waste plastics before entering the pretreatment pipeline system.

[0025] Furthermore, the pretreatment device may also include a stirring container in which the waste plastic is stirred into a suspension. As a result, the effect of the cleaning additive is achieved particularly reliably and uniformly and, if necessary, temperature control is also achieved. Furthermore, the stirring container or one of the pretreatment containers or a plurality of the pretreatment containers may have a heating device and / or a heat insulation structure. The stirring container or one of the pretreatment containers or a plurality of the pretreatment containers may also have a supply device, by which the at least one cleaning additive is directly supplied to the one or more pretreatment containers.

[0026] According to another design, the cleaning temperature can be at least 40°C and not more than 90°C, preferably not more than 70°C, and further preferably not more than 60°C. It has been proven that in the method according to the invention, the desired cleaning effect has been achieved at a significantly lower cleaning temperature and, if necessary, a significantly lower cleaning additive dosage and a significantly shortened residence time compared to the prior art. Some plastics, such as amorphous PET, have already crystallized and become brittle at relatively low temperatures in the range of 70°C to 80°C. The use of brittle recycled materials is usually impossible or greatly restricted. Since cleaning can be performed at a relatively low cleaning temperature below 70°C, preferably not more than 60°C, the crystallization of problematic plastics can also be reliably avoided. In addition, from an environmental point of view, it is also desirable to reduce the dosage of cleaning additives.

[0027] The at least one cleaning additive may comprise at least one surfactant and / or at least one sodium hydroxide solution and / or at least one complexing agent. With these cleaning additives, the desired pretreatment can be carried out particularly effectively.

[0028] As already explained, the cleaning tool of the cleaning device can be a cleaning disc. The waste plastic can be introduced into the working gap via an inlet opening into the working gap in the center and can be discharged from the working gap via an outlet arranged at the outer edge of the working gap. In particular, the inlet can open into the working gap in the axial direction of the cleaning disc.

[0029] According to another design, the width of the working gap can be narrowed outwardly in the radial direction in the first section starting from the inlet, and the width of the working gap can be constant in the second section arranged radially outside the first section. The first section and the second section can be, in particular, a first annular section and a second annular section. The inlet area formed by the first section is used to accommodate the amount of material consisting of waste plastics at the inlet. Here, due to the working gap that is first wider in the first section and then narrows outwards, even if the input consistency, i.e., the proportion of waste plastics per unit time and / or unit volume of treatment liquid, fluctuates significantly, homogenization and uniform distribution of the waste plastics are achieved. This homogenization and uniform distribution are decisive for the subsequent cleaning results. Only when the waste plastics are transported outward to the outlet as evenly and dispersedly as possible along the tooth row formed by the opposite cleaning teeth, can the best cleaning be achieved.

[0030] In addition, the second section with a constant working gap width is also of decisive importance here. Only the narrowed first section in combination with the constant second section can achieve an optimal cleaning effect, because the waste plastic is subjected to the necessary homogenization and uniformity in the first section and the physical loading of the waste plastic is achieved in the second section by maintaining a constant working gap width to achieve an optimal cleaning effect. In this way, the waste plastic, in particular plastic fragments, are oriented parallel to the tooth sides of the cleaning teeth in the inlet area formed by the first section, thereby avoiding the accumulation or formation of agglomerates of the waste plastic, which is harmful to cleaning. The waste plastic is processed in the working area formed by the second section as required for cleaning.

[0031] In particular, plastic fragments produced from plastic films are difficult to meter for cleaning, since they have a large dry and wet volume at a low bulk density. By designing the working gap with the first section and the inflow area formed thereby, the cleaning tool can also receive a metering supply that fluctuates, for example, in a sinusoidal manner, without problems, for example, causing clogging. In this case, sandwich or film stacks that are produced, for example, during the comminution of plastic films, can be reliably untied by designing the working gap.

[0032] It is particularly important to achieve optimal cleaning, especially to guide the waste plastic produced by pre-crushing the film to pass through the cleaning teeth with its entire surface, so as to completely clean the surface. Pre-crushing of waste plastic is particularly important, because the extension of pre-crushed waste plastic can be achieved by unfolding the accordion-shaped folded plastic fragments and unraveling the film stack into individual fragments according to the cleaning tool of the present invention. For example, it has been proven in practice that the average particle size of the pre-crushed waste plastic does not exceed 50mm, preferably does not exceed 25mm, for example, about in the range of 20 to 25mm. Thus, when the cleaning teeth have a size that meets the requirements of practice, complete friction of the entire surface of the waste plastic can be achieved in the working area formed by the second section. By the friction applied by the opposite cleaning teeth, the complete separation of dirt, such as printing ink or metallized surfaces that are particularly difficult to clean, is achieved. Thus, a cleaning result of less than 100 ppm, preferably less than 10 ppm of foreign residual contaminants can be achieved. Thus, the recycled materials produced according to the present invention, such as primary form plastics, can be used to manufacture plastic parts.

[0033] Furthermore, the cleaning device can include a mechanism for adjusting the cleaning tools axially relative to one another so that the width of the working gap can be adjusted, in which case the cleaning teeth of the cleaning tools can come into contact with one another in the second section. With this design, even for thin film waste, sufficient friction for cleaning can be achieved by the cleaning tools or the cleaning teeth. In this case, the cleaning teeth of the opposing cleaning tools can engage with one another in a form-fitting manner.

[0034] The second section can be directly connected to the first section. In this way, the transition between the inlet area formed by the first section and the working area formed by the second section is optimized.

[0035] The second section can extend all the way to the outer edge of the working gap. The first section and the second section can together cover the entire working gap. However, it is also conceivable that, for example, an inlet section is provided between the inlet and the first section, on which, for example, no cleaning teeth are provided.

[0036] The working surface of the cleaning tool with the cleaning teeth can be arranged conically in the first section and arranged parallel to each other in the second section. In this way, the first and second sections can be constructed particularly simply.

[0037] Furthermore, the cleaning teeth can be arranged at a greater distance from one another on the surface section of the working surface of the cleaning tool forming the first section than on the surface section of the working surface of the cleaning tool forming the second section. That is to say, the density of the cleaning teeth per unit area is lower in the first section than in the second section. This further simplifies the entry of the waste plastic and further improves the homogenization and homogenization and dispersion of the waste plastic, while in the working area formed by the second section, particularly effective cleaning is achieved by the cleaning teeth arranged more closely to one another.

[0038] The cleaning tool can in principle be designed as described in the parallel, non-prepublished German patent application 10 202 2 117 372.0 of the applicant.

[0039] According to another embodiment, the cleaned waste plastic can be dried in a drying device by pressing and / or air drying, thereby achieving particularly effective drying.

[0040] According to another design scheme, it can be provided that a pre-cleaning step is implemented before the pre-treatment step, in which the shredded waste plastic is cleaned in a pre-cleaning device, which includes two cleaning tools driven to rotate relative to each other, wherein the waste plastic is guided together with the cleaning liquid through a working gap between working surfaces of the cleaning tools with cleaning teeth facing each other, at which time impurities are removed from the waste plastic essentially without friction.

[0041] The cleaning liquid can also be water. In particular, depending on the type of waste plastic to be cleaned, it can be advantageous to pre-clean the waste plastic pre-treated in the pre-treatment device. For waste plastic, in principle, it is distinguished into waste plastic in the consumer field, so-called post-consumer raw materials (PCR) and waste plastic in the industrial field, so-called industrial recycled raw materials (PIR). PCR is distinguished according to its source, that is, its source from home, agriculture or retail. PCR raw materials have very different pollutants with impurities. The pollutants are usually significantly higher than 50,000 ppm. In addition, the pollutants are various, mainly cellulose of adhesive labels, food residues, adhesives, mineral attachments of soil and clay, but can also be printing inks. PIR raw materials usually have an average of 50,000 ppm of pollutants. This pollutant is obviously more limited and almost only includes printing inks, primers, adhesives and sealants. In particular, for PCR waste plastics, the pre-cleaning step is important for achieving the desired cleaning results. For PIR waste plastics, the pre-cleaning step can further improve the cleaning results, but it is not absolutely necessary. The pre-cleaning in the pre-cleaning step is especially carried out without cleaning additives. Pre-cleaning can also be carried out without temperature adjustment, especially with unheated cleaning liquid. At this time, the solid consistency should be set similar to that in the cleaning step. Since the pollutants have been significantly reduced, the pre-cleaning allows for further improved subsequent cleaning in the cleaning step. Pre-cleaning is also used to disperse the debris stack. The pre-cleaning tool can be constructed in principle like a cleaning tool, but basically no friction is applied to the surface of the waste plastic during the pre-cleaning process. In this way, compared with the cleaning tool in the cleaning step, the spacing between the cleaning teeth of the pre-cleaning tool can be selected to be larger. The focus is on the formation of a suspension by waste plastic and detached dirt, such as paper labels, and pulp fibers to be dispersed. Accordingly, there is a certain spacing between the mutually meshing cleaning teeth of the pre-cleaning tool. The pre-cleaning tool can be constructed in particular as described in the parallel, unpublished German patent application 10 2022 117 371.2 of the applicant. After the pre-cleaning step, liquid separation can be performed again, as described above for the cleaning step.

[0042] According to another design, after the pre-cleaning step and before the cleaning step, the pre-cleaned waste plastic can be further pulverized in the pulverizing step. The further pulverization in the pulverizing step can be carried out before the pretreatment step. As described above, the particle size of the plastic fragments used for cleaning in the cleaning step should not exceed 50mm, preferably not more than 25mm. It is possible to achieve complete removal of foreign pollutants. When the plastic fragments are large, for example, when the plastic fragments are folded, there is such a risk that not the entire surface is subjected to cleaning friction. In principle, the desired particle size is determined by the height of the cleaning teeth of the cleaning tool. In order to avoid, for example, the fine portion that may cause yield loss in subsequent steps is too high, the fragment size should not be less than 5 mm. Plastic fragments that fit each other during the pre-cleaning process can also be unfolded, so that there are longer plastic strips after the pre-cleaning, which are difficult to clean in the subsequent cleaning device. For example, in the pulverizing step, this long plastic strip is pulverized into a size suitable for the subsequent main cleaning. As described, pulverization can be carried out, for example, in a mechanical pulverizing device, such as a pulverizer or a cutter.

[0043] According to another design, the waste plastic can be rinsed with a rinsing liquid after the pre-cleaning step and before the cleaning step. The rinsing can also be carried out before the pre-treatment step. The rinsing liquid can especially be water. The rinsing can be carried out at full flow (Vollstrom). The rinsing can be carried out before or after the further comminution. By rinsing with the rinsing liquid, the continued carryover of the already detached impurities into the subsequent steps caused by the pre-cleaned waste plastic is minimized.

[0044] The cleaning liquid used in the pre-cleaning step can be conducted in a pre-cleaning liquid circuit. The cleaning liquid used in the cleaning step can also be conducted in a cleaning liquid circuit. Liquid consumption can be minimized by means of these liquid circuits. In this way, only small portions of liquid need to be supplied to the ongoing process from an external supply source, that is, in order to compensate for small liquid losses that are caused by the cleaning liquid being carried over with the waste plastic to be cleaned. In practice, it is possible to achieve less than 1 m3 of liquid per ton of product to be cleaned. 3 Low liquid consumption reduces operating costs and is desirable from an environmental point of view.

[0045] In addition, the cleaning liquid used in the pre-cleaning step and / or the cleaning liquid used in the cleaning step can also be filtered. Through such a filter device, for example an ultrafiltration device, pollutants can be removed from the liquid guided in the loop, thereby preventing re-contamination due to the liquid circulation and thus continuously ensuring the cleaning effect.

[0046] According to another design, the pre-cleaning liquid circuit can be separated from the cleaning liquid circuit. By separating the "dirty" pre-cleaning liquid circuit from the "clean" cleaning liquid circuit in a "firewall" manner, the contamination between the liquid circuits can be minimized, and thus, for example, the re-contamination of the pre-cleaned waste plastics in the cleaning step can be minimized. Through the reliable separation between the liquid circuits, except for the cleaning liquid that may adhere to the waste plastics, the cleaning liquid and thus, in particular, the dirt contained in the cleaning liquid that has been detached in the pre-cleaning will not be further sent out from the pre-cleaning. If the further comminution is performed when using cleaning liquid, this can also be performed using the pre-cleaning liquid circuit or in a separate comminution liquid circuit. At this time, the comminution liquid circuit is also separated from the cleaning liquid circuit.

[0047] According to another design scheme, it can be provided that a post-cleaning step is carried out after the cleaning step and before the drying step, in which the plastic cleaned in the cleaning device is post-cleaned in the post-cleaning device without adding a cleaning additive, the post-cleaning device comprising two cleaning tools driven to rotate relative to each other, the waste plastic together with the cleaning liquid being guided through a working gap between mutually facing working surfaces of the cleaning tools having cleaning teeth, wherein any cleaning additives remaining after the cleaning step are removed from the waste plastic.

[0048] The cleaning liquid may also be water. The post-cleaning device may be designed like a pre-cleaning device. In the post-cleaning process, friction is basically not applied to the waste plastics that have been cleaned in the cleaning step. The post-cleaning is mainly used to remove possible cleaning additives supplied in the pre-treatment step, especially by fluid dynamic eddies. Of course, impurities can also be further removed to a small extent. The post-cleaning is especially carried out without cleaning additives. The post-cleaning can also be carried out without temperature control, especially using unheated cleaning liquid. After the post-cleaning step, liquid separation can also be carried out, as described in principle above.

[0049] The cleaning liquid used in the re-cleaning step can also be guided in the re-cleaning liquid circuit. The cleaning liquid used in the re-cleaning step can also be filtered. In particular, ultrafiltration can be performed to achieve an optimal re-cleaning result. The re-cleaning liquid circuit can also be separated from the cleaning liquid circuit to avoid corresponding contamination between the individual cleaning steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Figures 1a to 1e The different method steps of the method according to the invention are shown schematically. DETAILED DESCRIPTION

[0051] Unless otherwise indicated, like reference numerals in the drawings denote like objects.

[0052] exist Figure 1a 1 shows the pre-cleaning step of the method according to the present invention. Pre-crushed waste plastics to be cleaned, especially waste plastics in the form of plastic fragments, are supplied to a receiving bin 12 via a plastic inlet 10. The waste plastics to be cleaned enter a heavy material collector 14 from the receiving bin 12, in which, if necessary, coarse heavy materials contained in the waste plastics are separated from the waste plastics to be cleaned and discharged. The waste plastics enter the feeding funnel 16 of the pre-cleaning device from the heavy material collector. In addition, a cleaning liquid, such as water, is also supplied to the feeding funnel 16 via a first liquid inlet 17. The waste plastics enter the working gap formed between two cleaning discs 18 and 20 of the pre-cleaning device from the feeding funnel 16 together with the cleaning liquid. For this purpose, the pre-cleaning device has an inlet that leads to the working gap in the center. For example, one of the cleaning discs 18 and 20 is driven to rotate by a rotary drive 22. The cleaning discs 18 and 20 have cleaning teeth on their surfaces that define the working gap. The waste plastics are conveyed through the cleaning teeth by the relative rotational movement between the cleaning discs 18 and 20 and the waste plastics are pre-cleaned at this time. By means of the rotational movement, the waste plastic reaches an outlet arranged at the outer edge of the working gap, through which the waste plastic is supplied to a mechanical liquid separation device 24. In addition, in the example shown, a liquid pump 26 is provided in the region of the outlet, which conveys a liquid, in particular water, supplied via a second liquid inlet 28 tangentially past the working gap and its outlet. The liquid pump 26 can also be formed by a Venturi nozzle, in which case, due to the Venturi effect, a liquid jet conveyed tangentially past the working gap and its outlet exerts a suction effect on the working gap, thereby conveying the waste plastic away from the working gap and conveying it further, as described in EP 3 057 751 Bl. The liquid jet pumped by the liquid pump 26 or the Venturi nozzle conveys the mixture consisting of pre-cleaned waste plastic and cleaning liquid discharged from the outlet to the liquid separation device 24. In the conveying liquid separation device, a mechanical liquid separation is performed in such a way that the pre-cleaned waste plastic is separated from the liquid. The separated liquid flows out through the liquid outlet 30. The outflowing liquid is preferably filtered and then resupplied in a circuit to the first and second liquid inlets 17, 28. The pre-cleaned waste plastic is discharged via the outlet 32 ​​and reaches the inlet 34 of the comminution device shown in FIG. Figure 1a The pre-cleaning device shown in , does not substantially exert friction on the waste plastic. The pre-cleaning device can be designed as described in the parallel, non-prepublished German patent application 10 2022 117371.2 of the applicant.

[0053] Should refer to Figure 1bA possible comminution step after the pre-cleaning step and before the subsequent cleaning step of the method according to the present invention is described. For this purpose, the pre-cleaned waste plastic supplied through the inlet 34 enters the wet pulverizer 36, and a liquid, such as water, is also supplied to the wet pulverizer through the liquid inlet 38. As described above, in the wet pulverizer 36, the waste plastic is further mechanically pulverized to achieve the optimal size for the subsequent cleaning step. The mixture composed of the further pulverized waste plastic and the liquid reaches the mechanical liquid separation device 40 from the wet pulverizer 36, in which the further pulverized waste plastic is separated from the liquid. The further pulverized waste plastic is discharged through the outlet 42, and the separated liquid is discharged through the liquid outlet 44. The discharged liquid can be guided back to the liquid inlet 38 again in a loop after filtering if necessary.

[0054] Should refer to Figure 1c The subsequent pretreatment and cleaning steps are described. The pre-cleaned and further shredded waste plastic arrives from the outlet 42 at the inlet 46 of the pretreatment device including a plurality of pretreatment containers 48. In addition, a cleaning liquid, such as water, is supplied to the pretreatment container 48 via the liquid inlet 50. The cleaning liquid is supplied from the liquid pretreatment device 52 upstream of the liquid inlet 50 to the mixing and heating container 54 of the pretreatment device. The cleaning liquid in the mixing and heating container 54 can be heated to a predetermined cleaning temperature by a heating device 56, such as a hot steam or gas heating device and a heat exchanger 60. In addition, at least one cleaning additive, such as at least one surfactant and / or at least one sodium hydroxide solution and / or at least one complexing agent, can be added from the cleaning additive container 58 to the cleaning liquid in the mixing and heating container 54. The mixture including the cleaning liquid and the at least one cleaning additive, which is heated to the desired cleaning temperature according to the process, is supplied to each of the pretreatment containers 48 via the liquid inlet 50, where it is mixed with the waste plastic supplied through the inlet 46. Once one pretreatment container 48 is filled, the next pretreatment container 48 is filled. Once the mixture of waste plastic and cleaning fluid and, if necessary, the at least one cleaning additive has reached a certain residence time, the pretreated mixture of waste plastic and cleaning fluid and, if necessary, the at least one cleaning additive is supplied to the inlet 64 of the cleaning device via a pump 62. In this way, the pretreatment containers 48 are filled and emptied one after the other.

[0055] Alternatively or additionally to the pretreatment container 48, the pretreatment device may further include a pretreatment screw for conveying the mixture or a pretreatment pipeline system for conveying the mixture.

[0056] The cleaning device corresponds in its basic structure to the Figure 1aThe pre-cleaning device described. In particular, the cleaning device also includes two cleaning discs 66, 68, which define a working gap, in particular an annular shape, between them, and the waste plastic is supplied to the working gap together with the cleaning liquid and the at least one cleaning additive via a central inlet. The cleaning discs 66, 68 also have cleaning teeth on their surfaces that define the working gap, and at least one of the cleaning discs 66, 68 is driven in rotation by means of a rotary drive 70. As a result, the waste plastic is conveyed through the working gap starting from the central inlet, and is forced to pass over the cleaning teeth of the cleaning discs 66, 68. In this way, the waste plastic is conveyed together with the cleaning liquid and the at least one cleaning additive to an outlet arranged at the outer edge of the working gap, and is conveyed from the outlet to another mechanical liquid separation device 72, such as in Figure 1c As shown by arrow 74 in the figure. The cleaning of the plastic parts that are pre-cleaned, further crushed and pre-treated in a targeted and determined manner in a pre-treatment device is carried out by friction caused by contact with the cleaning teeth of the cleaning discs 66 and 68. As a result, dirt remaining on the surface of the waste plastic is wiped off, especially by friction. Due to the pre-cleaning, further crushing and pre-treatment of the waste plastic, the waste plastic is basically completely cleaned. It has been proven that compared with the prior art, especially due to the use of the pre-cleaning device and the cleaning device configured as a toothed disc cleaner according to the present invention, it is possible to achieve the best cleaning result while working at a significantly lower cleaning temperature of less than 70°C, preferably less than 60°C. Compared with the prior art, the amount of cleaning additives can also be reduced. The cleaning device can be designed as in the unpublished German patent application 10 2022 117 372.0 of the applicant.

[0057] The liquid separation device 72 further separates the cleaning liquid with the at least one cleaning additive and the dirt scraped off from the waste plastic from the cleaned waste plastic, and the waste plastic is discharged through the outlet 76. The separated cleaning liquid with the at least one cleaning additive and the dirt scraped off is discharged through the liquid outlet 78 and supplied from the liquid outlet to the water preparatory treatment device 52, such as in Figure 1c In the water preparation device 52, the cleaning liquid is separated from the dirt and the at least one cleaning additive in a filtering, in particular ultrafiltration process, so that the cleaned cleaning liquid can be supplied to the mixing and heating container 54 in a circuit, such as in Figure 1c As shown by arrow 82 in FIG.

[0058] The cleaned waste plastic discharged from the outlet 76 then arrives at Figure 1d84 of the re-cleaning device shown in FIG. The waste plastics arrive in the charging funnel 86 from the inlet 84, and in addition, the cleaning liquid, especially water, is also supplied to the charging funnel via the liquid inlet 88. The mixture composed of the cleaned waste plastics and the cleaning liquid enters the working gap, especially annular, formed between the two cleaning discs 90 and 92 of the re-cleaning device from the charging funnel 86, especially also via the central inlet. At least one of the cleaning discs 90 and 92 is driven to rotate by a rotary drive 94, and each of the cleaning discs also has cleaning teeth on the surface of the working gap. Through the relative rotational movement between the cleaning discs 90 and 92, the waste plastics supplied with the cleaning liquid are re-cleaned, and the re-cleaning is also basically carried out without friction. Here, in particular, the cleaning additives left on the cleaned waste plastics from the cleaning step are separated from the waste plastics. The re-cleaned waste plastics, together with the cleaning liquid and the possible separated cleaning additives, arrive at the mechanical first liquid separation device 96 through the outlet arranged at the outer edge of the working gap. The post-cleaning device can be constructed like the pre-cleaning device shown in Figure 1. A liquid pump 98 is also provided at the outlet of the post-processing device, which also conveys the cleaning liquid tangentially through the working gap and the outlet of the working gap through the liquid inlet 88, and thereby conveys the re-cleaned waste plastic together with the cleaning liquid containing the cleaning additive from the working gap to the first liquid separation device 96. The liquid pump 98 can also be formed by a Venturi nozzle. In this case, the liquid jet conveyed tangentially through the working gap and the outlet of the working gap exerts a suction effect on the working gap due to the Venturi effect, thereby conveying the waste plastic away from the working gap and conveying it further, as described in EP 3 057 751 Bl. The liquid separated from the re-cleaned waste plastic in the first liquid separation device 96 is discharged via the liquid outlet 100, as described in EP 3 057 751 Bl. Figure 1d The waste plastic dried in the first liquid separation device 96 then passes to a mechanical second mechanical sedimentation device 104, as shown in FIG. 1d by arrow 106. Here, any residual liquid is separated from the waste plastic and is also discharged via a liquid outlet 100, as shown in FIG. Figure 1d As indicated by arrow 107 in FIG.

[0059] The further dried and cleaned waste plastic is discharged through the outlet 108 and arrives at Figure 1e The inlet 110 of the drying device is shown in FIG. The waste plastic is dried in the drying device for subsequent further use. The liquid discharged through the outlet 100 can be guided back to the liquid inlet 88 in a circuit again, if necessary filtered. Figure 1eThe drying step first includes mechanical drying in a mechanical liquid separation device 112. The liquid separated in the liquid separation device is discharged through a liquid outlet 114. Next, the waste plastic passes through a thermal drying device 116, where the waste plastic is dried to a residual moisture content of less than 5%, preferably less than 3%. After the drying step, sorting, especially air separation, can be carried out in a sorting device 118. At this time, three-dimensional plastic fragments can be separated from film fragments. The cleaned and dried waste plastic is discharged through an outlet 120 and can be supplied for further processing.

[0060] Reference numerals list

[0061] 10Plastic inlet

[0062] 12 Receiving warehouse

[0063] 14 Heavy material catcher

[0064] 16 Addition funnel

[0065] 17 First liquid inlet

[0066] 18, 20 cleaning tray

[0067] 22 Rotary drive

[0068] 24Liquid separation device

[0069] 26 Liquid Pump

[0070] 28 Second liquid inlet

[0071] 30Liquid outlet

[0072] 32Exit

[0073] 34 Entrance

[0074] 36 Wet crusher

[0075] 38 Liquid inlet

[0076] 40Liquid separation device

[0077] 42Exit

[0078] 44 Liquid outlet

[0079] 46 Entrance

[0080] 48 pretreatment containers

[0081] 50 Liquid inlet

[0082] 52 Liquid preparation device

[0083] 54Mixing and heating container

[0084] 56 Heating device

[0085] 58 Cleaning Additive Container

[0086] 60 heat exchanger

[0087] 62 Pumps

[0088] 64 entrances

[0089] 66, 68 cleaning plate

[0090] 70 Rotary Drive

[0091] 72Liquid separation device

[0092] 74 Arrows

[0093] Exit 76

[0094] 78 Liquid outlet

[0095] 80 Arrows

[0096] 82 Arrow

[0097] 84 Entrance

[0098] 86 feeding funnel

[0099] 88 Entrance

[0100] 90, 92 cleaning tray

[0101] 94 Rotary drive

[0102] 96 first liquid separation device

[0103] 98 Liquid Pump

[0104] 100 liquid outlets

[0105] 102 Arrow

[0106] 104 second liquid separation device

[0107] 106 Arrows

[0108] Exit 108

[0109] 110 Entrance

[0110] 112Liquid separation device

[0111] 114 Liquid outlet

[0112] 116 Drying device

[0113] 118 sorting device

[0114] Exit 120.

Claims

1. A method for cleaning pre-shredded waste plastics, in particular plastic flakes, characterized in that: • a pretreatment step, in which the pre-shredded waste plastic is pretreated in a pretreatment device, wherein the pretreatment comprises heating the waste plastic to a cleaning temperature using a heating device (56) of the pretreatment device and / or adding at least one cleaning additive and mixing the waste plastic with the at least one cleaning additive through the pretreatment device, • a cleaning step, in which the waste plastic pretreated in the pretreatment device is cleaned in a cleaning device, the cleaning device comprising two cleaning tools (66, 68) driven to rotate relative to each other, the waste plastic together with a cleaning liquid is guided through a working gap between mutually facing working surfaces of the cleaning tools (66, 68) having cleaning teeth, whereby dirt is removed from the waste plastic by friction, • A drying step, in which the waste plastic cleaned in the cleaning device is dried in a drying device (116).

2. The method according to claim 1, characterized in that The pretreatment device comprises a plurality of pretreatment containers (48) which contain waste plastics during the pretreatment process.

3. The method according to any one of the preceding claims, characterized in that The pretreatment device has at least one pretreatment screw which transports the waste plastic during the pretreatment step.

4. The method according to any one of the preceding claims, characterized in that The pretreatment device has at least one pretreatment pipeline system, through which the waste plastics are conveyed during the pretreatment step.

5. The method according to any one of the preceding claims, characterized in that The pretreatment device comprises a stirring container in which the waste plastic is stirred.

6. The method according to any one of the preceding claims, characterized in that The cleaning temperature is at least 40°C and not more than 90°C, preferably not more than 70°C, and further preferably not more than 60°C.

7. The method according to any one of the preceding claims, characterized in that The at least one cleaning additive comprises at least one surfactant and / or at least one sodium hydroxide solution and / or at least one complexing agent.

8. The method according to any one of the preceding claims, characterized in that The cleaning tool (66, 68) of the cleaning device is a cleaning disc (66, 68), and waste plastics are introduced into the working gap through an inlet opening centrally into the working gap and are discharged from the working gap through an outlet arranged at the outer edge of the working gap.

9. The method according to claim 8, characterized in that The width of the working gap narrows outward in a radial direction in a first section starting from the inlet, and the width of the working gap is constant in a second section arranged radially outside the first section.

10. The method according to any one of the preceding claims, characterized in that The cleaned waste plastic is dried in a drying device (116) by pressing and / or air drying.

11. The method according to any one of the preceding claims, characterized in that A pre-cleaning step is performed before the pre-treatment step, in which the shredded waste plastic is cleaned in a pre-cleaning device, the pre-cleaning device comprising two cleaning tools (18, 20) driven to rotate relative to each other, the waste plastic together with the cleaning liquid being guided through a working gap between mutually facing working surfaces of the cleaning tools (18, 20) having cleaning teeth, at which time dirt is removed from the waste plastic in a substantially frictionless manner.

12. The method according to claim 11, characterized in that After the pre-cleaning step and before the cleaning step, in a pulverizing step, the pre-cleaned waste plastic is further pulverized.

13. The method according to any one of claims 11 or 12, characterized in that The cleaning liquid used in the pre-cleaning step is conducted in a pre-cleaning liquid circuit and / or the cleaning liquid used in the cleaning step is conducted in a cleaning liquid circuit.

14. The method according to claim 13, characterized in that The cleaning liquid used in the pre-cleaning step and / or the cleaning liquid used in the cleaning step is filtered.

15. The method according to any one of claims 13 or 14, characterized in that The pre-cleaning fluid circuit is separated from the cleaning fluid circuit.

16. The method according to any one of claims 11 to 15, characterized in that The waste plastic is rinsed with a rinse liquid after the pre-cleaning step and before the cleaning step.

17. A method according to any one of the preceding claims, characterised in that After the cleaning step and before the drying step, a post-cleaning step is performed, in which the plastic cleaned in the cleaning device is post-cleaned in the post-cleaning device without adding a cleaning additive, the post-cleaning device comprising two cleaning tools (90, 92) driven to rotate relative to each other, the waste plastic together with the cleaning liquid is guided through a working gap between mutually facing working surfaces of the cleaning tools (90, 92) having cleaning teeth, at which time any cleaning additive remaining after the cleaning step is removed from the waste plastic.

18. The method according to claim 17, characterized in that The cleaning liquid used in the after-cleaning step is conducted in a after-cleaning liquid circuit.

19. The method according to claim 18, characterized in that The cleaning solution used in the re-cleaning step is filtered.

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