Method for recycling plastic packaging
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- ALPLA WERKE ALWIN LEHNER
- Filing Date
- 2024-07-12
- Publication Date
- 2026-05-20
AI Technical Summary
Existing plastic recycling processes face issues with flakes agglomerating and sticking together during drying, leading to uneven drying, contamination retention, and difficulties in sorting and separation, which results in energy inefficiency and environmental impact.
A process using a silo with a removal cone and spatially and temporally inconsistent air blasts from nozzles to break up agglomerates, combined with a controlled base flow, effectively preventing flakes from sticking and ensuring uniform drying, while minimizing dust formation and energy loss.
The solution allows for efficient and uniform drying of plastic flakes, preventing agglomeration and contamination retention, enhancing separation capabilities and reducing energy consumption and environmental impact.
Smart Images
Figure EP2024069904_23012025_PF_FP_ABST
Abstract
Description
[0001] Process for recycling plastic packaging
[0002] Field of the invention
[0003] The invention relates to a method for recycling plastic packaging according to the preamble of claim 1 and a silo for implementing the drying step of the method according to the preamble of claim 14.
[0004] State of the art
[0005] In the course of a plastics recycling process, used plastic packaging is kept in circulation. The packaging is rarely washed in its original form. It is common practice to deliver the packaging in compressed bales, which are usually pressed and perforated.
[0006] After breaking the bales, the packaging undergoes a visual inspection, metal removal, and optional label removal. Typically, the bottles are ground into flakes (chips), and the flakes are washed.
[0007] After washing, the flakes are dried. Common methods for this include presses, centrifuges, and dry-air dryers, or combinations thereof. Air dryers have the advantage of discoloring some of the contaminants. These discolored contaminants are easily detectable with optical sensors and can therefore be easily separated. In addition, volatile, low-molecular-weight contaminants adhering to the material—particularly odorous aldehydes, carboxylic acids, lactones, as well as allergenic substances and substances that pose a risk for future food or skin contact—are much more easily removed than if these low-molecular-weight contaminants were incorporated into the recycled material during melting.
[0008] However, drying with dry hot air has some serious disadvantages:
[0009] - The flakes change their shape during hot drying, hook together and form agglomerates.
[0010] - The flakes stick together, especially as they become softer and stickier with temperature. - Due to static effects, the flakes also form clumps and agglomerates that are impervious to air.
[0011] - The washing water remaining on the flakes can act like an adhesive, so that the flakes do not behave like a free-flowing bulk material and the air cannot flow through them evenly.
[0012] So-called bridges and agglomerations form, which hold the flakes in bulk form, so that the material flow in a silo comes to a standstill or cannot be discharged from the silo opening. The formation of bridges and agglomerations also leads to uneven airflow, which does not completely permeate the material and therefore does not dry, discolor, or decontaminate it evenly.
[0013] To prevent agglomeration, agitators are used that constantly stir the flakes with great force and high energy consumption. These agitators crush and break up the flakes, creating dust. Sorting after the dryer is only possible with large flakes and particles; small particles and adherent particles cannot be sorted out at all or only to a small extent. In the presence of dust, the sensors are further interfered with and contaminated by the dust.
[0014] Other known options include rotary silos that constantly move the material and push it through the silo with welded webs, or silos with integrated screw, shaft, and discharge devices that force the material through. Another alternative is systems that use excess air and energy and a very high Reynolds number to prevent agglomeration or even attempt to convert the flakes into a fluid bed.
[0015] Simply releasing large amounts of hot air into the environment is critical because a lot of energy is lost and the contaminants in it disturb the environment.
[0016] Object of the invention
[0017] The disadvantages of the described prior art give rise to the task of preventing agglomeration of the flakes while simultaneously drying them using a gentle and inexpensive process, or of breaking up agglomerations that have already formed. Description
[0018] The stated problem is solved in a process for recycling plastic packaging by the features stated in the characterizing portion of patent claim 1. Further developments and / or advantageous embodiments are the subject of the dependent patent claims.
[0019] The invention is preferably characterized in that the drying of the flakes is carried out in a silo having a discharge cone, and in that a drying fluid, in particular drying air, is blown into the silo via a base flow and a nozzle flow, wherein the nozzle flow is blown into the silo via a plurality of air nozzles at inconstant locations and times. A separate logic is provided which controls how and where the air pulses are introduced through the air nozzles in order to loosen the flake material. A logic in the pressure pulses has proven particularly helpful, which either specifically controls nozzles at locations in the silo that have repeatedly led to problems. The release of the bridges is detectable. Likewise, those material areas that have not yet received a pressure pulse while passing through the silo are specifically blown.
[0020] The air nozzles mobilize the flakes by specifically introducing air or air blasts through the air nozzles, which break up flake agglomerates, adhesions and bridges and allow the flake bed in the silo to flow through completely again.
[0021] The base flow is conveniently introduced into the silo near the discharge cone and flows from bottom to top. This utilizes the natural rise of the warm drying air. However, to ensure uniform drying of all flakes and ensure that as many flakes as possible are reached, a nozzle flow is used.
[0022] In a particularly preferred embodiment of the invention, a portion of the jet stream is blown into the silo via a plurality of air nozzles arranged on an injection device for injecting the base stream. This not only delivers targeted air to the flakes via air nozzles arranged on the outside of the silo, but also via air nozzles arranged on the injection device inside the silo. Consequently, virtually any agglomeration can be reached by the air blasts and broken up in a targeted manner. In the context of this application, agglomerates are understood to mean flake clusters or stuck-together flakes. The air nozzles described in the last paragraph can also be supplied by branching off drying air from the base stream, for example, via a double jacket, from whose annular space air is blown through the nozzles into the interior of the silo.
[0023] It is preferred if the drying step is carried out with a total flow volume measured at the outlet of 1.5 to 5 Nm 3 Air / kg plastic and preferably between 3 to 4 Nm 3 Air per kg of plastic. This provides sufficient air volume to reliably dry and decontaminate the flakes.
[0024] It has proven effective to feed up to 80% of the drying air into the silo via the nozzle stream and at least 20% of the drying air via the base stream. This ensures, on the one hand, sufficient air is available to feed it into the silo through all air nozzles and thus break up agglomerations. On the other hand, the base stream contains sufficient drying air to dry the entire flake volume, if possible.
[0025] In a preferred variant of the invention, the drying air is purified via a condensate separator, and the thermal energy is recovered via a heat exchanger. This allows the hot, contaminated air to be converted into clean air through purification and a heat exchanger. The purified air can be recirculated to the silo after preheating as a base and nozzle stream.
[0026] The invention is also preferably characterized in that pressure pulses at a pressure of 1.2 to 12 bar are delivered into the silo through the air nozzles, breaking up flake agglomerates, adhesions, and bridges formed in the silo. This allows the drying air to be blown into the silo at a higher temperature. The increased temperature causes contaminants to be entrained and removed from the flake surface, preventing them from entering the melt or granulate. Laminar, adherent and stagnant air masses are unsuitable for removing contaminants. Only local pressure pulses dissolve the contaminants.
[0027] To ensure that the pressure pulses are not counterproductive, they are applied carefully so that dust formation from the flakes is as low as possible and the flakes remain detectable by an optical sensor. Compared to conventional agitators, which break up agglomerations but cause severe comminution and the corresponding undesirable dust formation, dust formation due to the pressure pulses is negligible. In another particularly preferred embodiment of the invention, the drying air has a maximum temperature of 20°C and preferably 0°C below the softening temperature of the flakes to be dried. As already explained above, the drying air can have an elevated temperature, since any agglomerates that form can be broken up again by the provision of the air nozzles.
[0028] In a further preferred embodiment of the invention, the arrangement of the air nozzles through which the compressed air blasts are delivered and the intensity of the compressed air blasts are determined by locations of increased agglomeration affinity in the silo. A control logic is preferably used for implementation. A logic in the pressure blasts has proven particularly helpful, which either specifically controls nozzles at locations in the silo that have repeatedly caused problems first. The release of the bridges is detectable, thus identifying the neuralgic locations of bridge formation. In addition, those flake areas that have not yet received a pressure blast and the associated agitation during their passage through the silo are blown into the air.
[0029] To break up flake agglomerates, the extraction cone is oscillated with an amplitude of over 0.5 mm and a frequency of 2 to 200 Hz. This loosens the flakes, allowing them to flow through the narrow outlet area.
[0030] In a particularly preferred embodiment of the invention, the drying air transports away substances adhering to the surface of the flakes, such as allergens, in addition to the wash water to be evaporated. Due to the drying at higher temperatures and the evaporation of the water from the surface, even surface-adhering contaminants are entrained during the active evaporation. These contaminants would otherwise only detach much later, given their boiling point.
[0031] In particular, allergens dissolve and thus largely no longer enter the melt and subsequently the granules. For the purposes of this application, an allergen is defined as a substance that can trigger hypersensitivity reactions (allergic reactions) via the immune system. The various hypersensitivity reactions include allergies, pseudoallergies, and intolerances. For example, the process according to the invention reduces hexyl cinnamaldehyde, a known allergen with a boiling point of 170 to 180°C, from 30 mg hexyl cinnamaldehyde / kg HDPE flake to less than 0.2 mg hexyl cinnamaldehyde / kg HDPE flake at temperatures around 120°C on and in HDPE flakes.
[0032] Because substances adhering to the surface of the flakes heat up and discolor due to the drying air, the flakes on which the discolored contaminants adhere are easily recognizable by the sensory system and can be easily separated.
[0033] A further aspect of the invention relates to a silo for implementing the drying process described above. The silo is characterized by a plurality of air nozzles arranged on the surface of the silo that comes into contact with the flakes, through which drying air can be blown into the silo. This allows agglomerations and bridges of the flakes, which also arise due to the deliberately selected higher temperature of the drying air, to be broken down. The increased temperature of the drying air allows for contaminants to be removed much more effectively than with prior art drying processes, which aim for lower drying temperatures to avoid agglomeration or clumping of the flakes.
[0034] According to a particularly preferred embodiment of the invention, the air nozzles are arranged on the cylinder shell, the discharge cone, and the injection device. This allows any agglomeration or clumping of air blasts forming in the silo to be reached and broken up.
[0035] The discharge cone preferably has an opening angle between 50 and 70 degrees, and preferably between 55 and 65 degrees. This dimensioning of the discharge cone slope has proven effective for the reliable discharge of plastic flakes from the silo.
[0036] The discharge opening of the discharge cone should ideally have a diameter between 10 and 25 cm, and preferably between 15 and 20 cm. This dimension of the discharge opening ensures that the formation of flake bridges is impeded and that the flakes can be removed from the silo in a free-flowing manner.
[0037] Due to the local pressure surges, much less hot air is required than if the entire silo were flowed at the same intensity. The energy loss and the purification of the large volumes of air resulting from a uniform air flow would be far too high and far too costly. Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to the schematic representations. These are not to scale:
[0038] Figure 1: Longitudinal section through a silo according to the invention for drying and decontamination of flakes;
[0039] Recycling processes for plastic packaging, particularly plastic containers, are known from the prior art. These processes involve the production of plastic granules from discarded packaging through the following process steps. Discarded packaging can be all types of containers, particularly plastic bottles. The granules can be used to manufacture new packaging.
[0040] After the packaging is delivered, preferably perforated and pressed into cubic bales, it is sorted. The bales are opened and subjected to visual inspection, magnetic separation, and optional label removal. The packaging can also be pre-washed. The packaging is then shredded or ground into flakes (also called chips), and the flakes are washed.
[0041] The wash water must be removed from the flakes 12. Therefore, they are dried in a silo, designated overall by reference numeral 11. The interior of the silo is typically defined by a cylindrical shell 13, a discharge cone 15, and a top cover 17.
[0042] The drying air 19 is blown into the silo via an injection device 21 in the area of the extraction cone 15. This allows the drying air 19 to flow from bottom to top and exits the silo 11 at the cover 17, laden with wash water and entrained substances previously adhering to the flakes 12, through an outlet or exit opening 22. The basic flow 23 of the drying air is formed in the injection device 21. A nozzle flow 25 is branched off from the basic flow 23 outside the silo 11. The nozzle flow 25 could also be generated separately, without being branched off from the basic flow 23. The nozzle flow 25 is blown into the silo 11 via a plurality of air nozzles 27 positioned on the casing 13 and on the extraction cone 15. In addition, the nozzle stream 25 is split so that it can also be introduced into the silo 11 via air nozzles 27 arranged along the injection device 21.
[0043] Conveniently, the extraction cone 15 has an opening angle α of 55 to 65 degrees. The extraction opening 31 of the extraction cone preferably has a diameter of between 15 and 20 cm. A vibration device 33 is arranged on the outside of the extraction cone 15, which can cause the cone to vibrate. An amplitude of more than 0.5 mm and a frequency of 2 to 200 Hz is preferred. These three precautions ensure that the dried and decontaminated flakes 12 flow reliably out of the silo 11 as bulk material and do not clog the extraction opening 31.
[0044] The drying step is carried out with a flow volume of drying air of preferably between 3 and 4 Nm 3 Air per kg of plastic. Up to 80% of the drying air is fed into the silo via nozzle stream 25 and at least 20% of the drying air via base stream 23.
[0045] The drying air introduced via the air nozzles 27 enables the agglomerations 35 of flakes 12 to be broken up. For this purpose, the air nozzles 27 are arranged at locations where agglomerations 35 preferentially form and are therefore accessible via the pressure pulses emitted from the air nozzles 27. Pressure pulses at a pressure of 1.2 to 12 bar can be delivered into the silo through the nozzles, breaking up the flake agglomerations, adhesions, and bridges that have formed. Furthermore, the pressure pulses are applied so gently that dust formation from the flakes is minimized and the flakes remain detectable by an optical sensor after drying. Dye, yellowing, and polymer sorters thus achieve a high degree of detection. A further advantage of local pressure surges is that much less hot air is required than if the same intensity were to flow through the entire silo.The energy loss and the cleaning of the large volume of air resulting from a uniform air flow would be far too high and far too costly.
[0046] The provision of air nozzles 27 enables the drying air to have a maximum temperature of 20°C and preferably 0°C below the softening temperature of the flakes to be dried. This allows for extremely efficient drying and decontaminating. Large molecules of contaminants adhering to the flakes are removed before extrusion, while these contaminants are still on the flakes or have only penetrated the surface of the material. Especially during the washing step, a container containing residues (e.g., mineral oil, peanut butter, lactose) can contaminate many containers during the washing process. According to the invention, these contaminants, which first reach the flake surface during the washing step, can be removed before the extruder, since the contaminants are very difficult to remove once they have penetrated the melt or the granules.
[0047] Tests on granules have shown that allergens, in particular, can only be removed after 10 hours of deodorization. It is much more efficient to remove these surface contaminants directly after washing. This is made possible by the drying step according to the invention.
[0048] Due to drying at higher temperatures and the evaporation of the wash water from the surface, even surface-adhering contaminants are entrained during active evaporation, even though the drying temperature is still far from the boiling point, and one would expect the contaminants to only dissolve at much higher temperatures. Allergens, in particular, dissolve and thus largely no longer reach the melt and later the granules.
[0049] Due to flake drying at elevated drying temperatures, which, surprisingly, is only made possible by the targeted air blasts through nozzles 27, substances adhering to the surface of the flakes heat up and discolor more intensely. These discolored substances are particularly easily detectable and separable.
[0050] Legend:
[0051] 11 Silo
[0052] 12 flakes
[0053] 13 Cylinder barrel
[0054] 15 extraction cones
[0055] 17 Cover
[0056] 19 Drying air
[0057] 21 Blowing device
[0058] 22 Outlet
[0059] 23 Basic current
[0060] 25 nozzle flow
[0061] 27 air nozzles
[0062] 31 Removal opening
[0063] 33 Vibration device
[0064] 35 agglomerations a opening angle
Claims
1 . Process for recycling plastic packaging comprising the following process steps (a) Delivery of the packaging, preferably in bale form, (b) packaging sorting, (c) shredding the packaging into flakes (12), (d) washing step, (e) drying the flakes (12) with a dry hot fluid, in particular hot drying air, (f) flake sorting and (g) granulating the flakes (12) in an extruder, characterized in that - that the drying of the flakes (e) takes place in a silo (11), a discharge cone (15) and - that the drying air (19) is blown into the silo (11) via a base flow (23) and a nozzle flow (25) and the nozzle flow (25) is blown into the silo (11) via a plurality of air nozzles (27) in a spatially and temporally inconstant manner.
2. Method according to claim 1, characterized in that the base stream (23) is fed into the interior of the silo (11) in the region of the extraction cone (15) and flows from bottom to top.
3. Method according to one of the preceding claims, characterized in that a part of the nozzle stream (25) is blown into the silo (11) via a plurality of air nozzles (27), which air nozzles (27) are arranged on an injection device (21) for blowing in the base stream (23).
4. A method according to any one of the preceding claims, characterized in that the drying step (e) is carried out with a total flow volume measured at the outlet of 1.5 to 5 Nm 3 Air / kg plastic and preferably between 3 to 4 Nm 3 Air / kg plastic.
5. Method according to one of the preceding claims, characterized in that the drying air (19) is cleaned via a condensate separator and the thermal energy is recovered via a heat exchanger.
6. Method according to one of the preceding claims, characterized in that up to 80% of the drying air (19) is fed into the silo (11) via the nozzle stream (25) and at least 20% of the drying air (19) is fed into the silo (11) via the base stream (23).
7. Method according to one of the preceding claims, characterized in that pressure pulses with a pressure of 1.2 to 12 bar are delivered into the silo (11) through the air nozzles (27), whereby flake agglomerates (35), adhesions and bridges formed in the silo (11) are dissolved.
8. Method according to one of the preceding claims, characterized in that the pressure pulses are applied carefully so that the dust formation of the flakes (12) is as low as possible and the flakes (12) remain detectable for an optical sensor.
9. Method according to one of the preceding claims, characterized in that the drying air (19) has a maximum temperature of 20°C and preferably 0°C below the softening temperature of the flakes (12) to be dried.
10. Method according to one of the preceding claims, characterized in that the arrangement of the air nozzles (27) through which the compressed air pulses are emitted and the intensity of the compressed air pulses are determined by locations of increased agglomeration affinity in the silo (11).
11. Method according to one of the preceding claims, characterized in that the extraction cone (15) is set into vibration with an amplitude of more than 0.5 mm and a frequency of 2 to 200 Hz in order to dissolve flake agglomerates (35).
12. Method according to one of the preceding claims, characterized in that the drying air (19) transports away substances adhering to the surface of the flakes (12), for example allergens, in addition to the washing water to be evaporated.
13. Method according to one of the preceding claims, characterized in that substances adhering to the surface of the flakes (12) are heated and discolored by the drying air (19).
14. Silo (11) for implementing the drying step (e) and the decontamination of substances adhering to the flakes (12) according to one of the preceding claims, comprising - a cylinder jacket (13), - a removal cone (15) connected to the casing (13), - a vibration device (33) which can cause the extraction cone (15) to vibrate, an injection device (21) with which drying air (19) can be injected into the silo (11), and - an outlet opening (22) for the drying air loaded with washing water and substances, characterized in that a plurality of air nozzles (27) are arranged on the surface of the silo (11) which comes into contact with the flakes (12), through which drying air (19) can be blown into the silo (11).
15. Silo according to claim 14, characterized in that the air nozzles (27) are arranged on the cylinder jacket (13), the extraction cone (15) and the injection device (21).
16. Silo according to claim 14 or 15, characterized in that the extraction cone (15) has an opening angle (a) between 50 and 70 degrees and preferably between 55 and 65 degrees 17. Silo according to one of claims 14 to 16, characterized in that the removal opening (31) of the removal cone (15) has a diameter between 10 and 25 cm and preferably between 15 and 20 cm.