EP1934030A1

EP1934030A1 - Process and apparatus for handling plastics material and device for conveying and simultaneously heating material, in particular plastics parts

Info

Publication number: EP1934030A1
Application number: EP06791980A
Authority: EP
Inventors: Fredl RÜDIGER; Martin Schoeller
Original assignee: Schoeller Pet Recycling GmbH
Current assignee: Schoeller Pet Recycling GmbH
Priority date: 2005-09-13
Filing date: 2006-09-11
Publication date: 2008-06-25
Also published as: DE102005043526A1; WO2007031255A1

Abstract

The present invention provides a process and an apparatus for handling plastics, such as polyesters, in particular for recycling polyethylene terephthalate (PET), for example from beverage bottles, preferably for the production of PET suitable for food contact applications, and in particular for the conversion of amorphous plastics material that is present for example in the form of granules or flakes into crystalline plastics material. Furthermore, a device (1) for conveying and simultaneously heating material, in particular plastics parts, such as plastics flakes and particles, comprising a conveying zone, means for conveying, means for producing (2, 5) a mixture of a material-conveying atmosphere and a source (3) for irradiating with electromagnetic radiation, in particular infrared radiation, is presented, which device can be used inter alia as a means for predrying, for crystallizing and, before the post-condensation of solids, for preheating. With the aid of the present invention, PET granules suitable for food contact applications can be produced while at the same time maintaining the same high level of quality, it being possible for the previous process to be simplified and, in particular, the apparatus involved to be reduced in its complexity, the capacity of existing installations to be increased and energy to be saved.

Description

Method and device for treating plastic material and device for conveying and simultaneously heating material, in particular plastic parts

The present invention relates to a method for treating plastic material according to the preamble of claim 1, a device for conveying and simultaneous heating of plastic parts according to the preamble of claim 7 and an apparatus for treating plastic material according to the preamble of claim 18.

Plastic materials, such as polyesters, in particular polyethylene terephthalate (PET), are widely used today, for example for the production of beverage bottles, qualified films and fibers, medical devices, in particular medical syringes and medical containers. Due to a growing ecological awareness and increasing economic interests is increasingly sought after methods to further utilize these plastic materials after their intended use, so as completely as possible in the recycling cycle. This is currently only possible with extensive precautions, in particular in the abovementioned fields of application of food packaging and medical technology, which prevent volatile contaminants from remaining in the plastic.

An effective process for producing recycled PET material which meets the requirements for food-safe PET, ie substantially free from contamination, is described in WO 2004/106025 A1. This process comprises the process steps of extrusion and / or granulation under essentially vacuum and the carrying out of a solid secondary condensation under substantially vacuum, these steps, with or without stripping, being used to further develop away from residual contamination. Before the extrusion / granulation, an additional predrying step and / or an additional crystallization step is carried out between the extrusion / granulation and the solid postcondensation. The predrying step leads to a lower water or water vapor content in the extruder, as a result of which the viscosity of the PET material does not drop so much during the extrusion or the recycled material has a higher viscosity, which in turn favors further processing, for example to beverage bottles. In addition, the reduced water vapor content in the extrusion process promotes the degassing of acetaldehyde. The additional crystallization step results in that the extruded / granulated PET increases the subcrystallinity by about 50%, which prevents sticking of the PET granulate. As a result, the solid post-condensation process can be carried out better and faster. These two measures, which can be carried out alternatively or together, result in efficient process management combined with a very uniform product quality.

In the method of WO 2004/106025 A1, the disclosure of which is hereby incorporated in full, the present invention is based on a further simplification, in particular in terms of equipment complexity, with a further increase in economic efficiency and consistent product quality this generic method.

This object is achieved by a method for treating plastic material with the features of claim 1, a device for conveying and simultaneous heating of material with the features of claim 7 and a device for treating plastic material with the features of claim 18. Advantageous embodiments each subject of the dependent claims.

The present invention is based on the finding that the generic method can then be simplified, in particular with less equipment complexity, if individual steps of conveying to one Treatment device, for example, to a crystallizer, and the treatment process itself, for example, so the crystallization, are suitably interconnected.

So far, for example, after the extrusion / granulation, the granules were conveyed to a heated Rüttelbett to crystallize there for preferably 15 minutes at 140 ° C. Such a crystallization could also take place in a screw conveyor described in EP 0 891 526 B1, which has an infrared radiation source. Although a treatment process with a material transport is purely factually associated with these two devices, the connection of these two steps is not yet suitable. On the one hand, the material still has to be conveyed away to such a device and away from it to the next treatment station, since these devices operate adequately only in horizontal operation, but individual treatment stations usually lie on different vertical levels. On the other hand, the material flow with these devices is not continuous but in relation to the material flow, which is necessary, for example, for filling a solids reactor, in particular a tumble dryer.

Now it has surprisingly been found that by the subject matter of the present invention, the three steps of transport, treatment (in the case just described a crystallization) and further transport can be combined into a single conveying and treatment step in a single device and so the equipment cost considerably can be reduced. As a result, a cost savings and a reduction in the required footprints are achieved.

The present invention thus provides, on the one hand, a device which simultaneously conveys and heats any material, in particular plastic material, in the form of individual parts of material, namely by irradiating same during the delivery of the plastic parts with radiation in the infrared range. While in the previous technique (Rüttelbett) heating by means of Air took place and the heat so slowly penetrated into the material or heating by means of infrared radiation was carried out (screw conveyor EP 0 891 526 Bl) and the material had to be circulated tedious, so that all material parts were irradiated and therefore long residence times of the plastic material with these previous techniques were necessary in a heating apparatus, residence times in the range of seconds are sufficient with the device according to the invention, in which the application of electromagnetic radiation is provided. This is because this electromagnetic radiation, in particular infrared radiation and preferably radiation in the near infrared, penetrates directly into the plastic material, thereby achieving a depth effect and thus enables the complete heating of the material substantially at once.

There are different frequency ranges of electromagnetic radiation used. Which type is used depends on the given material and its geometry, that is, on which type of radiation is most effective at the same time to effectively and fully heat a material part.

However, it is important for the use of the electromagnetic radiation for heating with simultaneous promotion of the plastic material that every plastic part, for example, a Kunsstoffflake or a particle, the radiation is directly exposed. The device is according to the invention in addition to a conveyor line, means for conveying and a source of electromagnetic radiation further provided with means for producing a plastic part Förderatmosphären- mixture (as conveying atmosphere is understood the atmosphere within the conveyor line), so that the plastic parts are separated and Thus, essentially all transported plastic parts are irradiated.

Advantageously, in the conveyor device according to the invention, the conveying path and the means for producing the material-conveying-atmosphere mixture are realized in a combined manner. On the one hand, this can happen because the material falls down gravitationally in a vertical conveying tube (gravity) and, depending on the amount of material falling down, a mixing ratio between So plastic parts and conveying tube atmosphere, ie a certain plastic part density forms, which allows to irradiate at a certain pipe section all transported over plastic parts simultaneously with infrared radiation. On the other hand, a common realization of the conveying path and the means for producing the material-conveying atmosphere mixture can be realized by conveying the plastic parts in a conveying pipe, for example vertically from a lower to an upper level, by means of an airflow conveying. This air flow promotion is preferably achieved via a blower device, however, the use of a suction device is conceivable. Again, a plastic part-Förderrohratmosphären mixture forms with a certain plastic part density. This density can then be specifically influenced, for example, by adjusting the delivery rate or the metered addition, which is regulated by a metering device.

In an advantageous embodiment, the means for producing a plastic part conveying atmosphere mixture are adapted to homogenize its density. This homogenization ensures that all parts of the material are exposed to substantially the same intensity of radiation over substantially the same time, which results in a particularly uniform material quality.

The plastic density of the part can be specifically influenced by additional means. Thus, for example, suitable screens, swirlers, deflecting plates, displacement bodies or blowers for adjusting the density, in particular by inhibiting the flow of material, can be provided, which as a side effect can also bring about an advantageous homogenization of the material density over the conveyor cross section. In order that the additional means does not result in a jam in the conveyor tube, suitable means for shaking may further be provided which, for example, vibrate a sieve in such a way that always a contingently equal amount of plastic parts passes through the sieve.

In addition, the conveying path and / or means for producing the Matrial conveying tube atmosphere mixture can be compared with the conveying path in the transverse direction. cut enlarged container, in particular a cyclone, which also serves to separate the material-conveying atmosphere mixture include. In such a container, the electromagnetic radiation source may advantageously be integrated in the lid and / or in the side walls. In order to increase the efficiency of the irradiation, reflectors for the electromagnetic radiation can be provided in the conveyor line, so that, for example, even in the case that only over a certain Umfangsb area of the conveyor line emitters are attached, the vorbeabeförderte material part-conveying atmosphere mixture on all sides Radiation is applied.

Furthermore, the heating effect and thus the set temperature in the plastic parts can be set in addition to a suitable setting of the radiation intensity on the conveying speed. The conveying speed can in turn be set via the blower power, screens, swirlers or the like introduced into the conveyor line or, in the case of gravity conveying, by an air flow acting against the direction of fall, for example generated by a blower.

In a preferred embodiment of the device according to the invention, the device comprises means for stripping the plastic parts, for example in air, steam, inert gases, such as nitrogen, or hot air, and it is preferred that means for aspirating evolved volatile products, such as water vapor, contaminants or the like .. as they are released inter alia stripping, are provided.

The inventive device for conveying and simultaneous heating is now in the context of the plastic treatment method according to the invention and the plastic treatment device according to the invention but also in other methods and devices universally applicable, as with the help of the application of electromagnetic radiation arbitrary material temperatures in the second range directly during the delivery are adjustable. For example, the pre-drying conveying and simultaneous heating means may be used prior to extrusion / granulation of the prepurified PET material coming from a washer, for example, when material temperatures of about 150 ° C are set. For PET material, the use of infrared radiation, in particular of near infrared radiation, is recommended. By heating z. B. plastic flakes is still adhering to the washer or located in the interior of the flakes of water, with residual moisture of up to 2 wt .-% are common, evaporated and discharged either by the air flow in a flow of airflow or by suitable means in a gravity feed aspirated. The residual moisture of the conveyed with the inventive device for conveying and simultaneous heating for extrusion / granulation material is lowered to values up to <0.2 wt .-% in spite of taking place in seconds range infrared radiation. By using the device according to the invention as a pre-dryer, the expenditure on equipment is thus again reduced while the drying capacity remains constant.

Furthermore, the inventive device for conveying and simultaneous heating can be used directly for the crystallization of coming from the extrusion / granulation PET granules. For this purpose, the conveyed material is heated in the device by infrared irradiation to 140 ° C, so that the granules also forms a partial crystallinity within the short irradiation time in the second range. This leads to the fact that the PET granules do not stick together and thus the solids after-condensation in the solids reactor, for example a tumble dryer, can be carried out better and faster. As a result, compared with the previous process step, for example, crystallization on a heated vibrating bed, the expenditure on equipment can be substantially reduced.

A further field of application is the device according to the invention for conveying and simultaneous heating as a preheating device for preheating the semi-crystalline material in a substantially direct filling from an intermediate storage in the solid reactor, for example a tumble dryer. at In this process, the semicrystalline PET granules are conveyed via the device according to the invention into the tumble dryer and heated during conveying to about 200 ° C. to 250 ° C., so that the postcondensation process in the tumble dryer can begin directly after it has been filled up.

In particular, when the inventive means for conveying and simultaneous heating is used simultaneously as a crystallizer and preheating, results in a significant reduction of the aparativen expense and at the same time an energy saving.

In addition, the present invention provides an apparatus for recycling plastics. This has at least one extruder, granulator or solid secondary condenser and at least one pre-dryer or a crystallizer. In this case, the device according to the invention for conveying and simultaneous heating forms at least either the pre-dryer, the crystallizer or before the solid secondary condenser preheating.

In an advantageous embodiment, the device according to the invention additionally comprises means for filtering the molten PET material, in particular exchangeable filters and / or sieve combinations in candle and disc form, whose pore size is advantageously less than 100 microns.

In a further embodiment, the device according to the invention comprises at least one stripper, which contributes to an additional removal of volatile contaminants, in particular of acetaldehyde and oligomers.

In a further advantageous embodiment, the device according to the invention further comprises means for comminuting the plastic material, which are adapted to comminute the plastic material so that plastic flakes arise which have a wall thickness less than 2 mm in at least one dimension, but the wall thickness in the other dimensions can be much larger. Preferably, the means for crushing are adapted so that the Plastic flakes have a length and / or width in the range 1 to 20 mm, in particular 5 to 12 mm. By this crushing the removal of residual contaminants from the plastic material is significantly promoted, since the diffusion length of these contaminants in the material is usually greater than 1 mm, so that the contaminants from the maximum 2 mm thick plastic flakes easily escape in the direction of the dimension with the small wall thickness can.

Furthermore, it may also be expedient to use, instead of the means for comminution, means for finely grinding the plastic material into plastic particles, wherein the means for fine grinding are adapted to produce plastic particles with an average mean particle size of 0.12 to about 2.6 mm in diameter. Even from these plastic particles, contaminations can be removed more easily than with uncomminuted material.

Other characteristics, features and advantages of the present invention will become apparent from the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. It is purely schematic in

Fig. 1 shows a preferred embodiment of the device according to the invention for conveying and simultaneous heating.

In Fig. 1, a preferred embodiment of the inventive device for conveying and simultaneous heating 1 is shown. This device 1, which is designed as a gravity conveyor for plastic parts, comprises a substantially vertical downpipe 2, which is only partially shown here. Along the circumference is an annular radiator 3 for irradiation with near infrared radiation, which has a certain width B. Depending on the speed of the plastic parts falling by, in particular plastic flakes and particles, and the intensity of the radiator 3, this width B is designed such that a single plastic part is subjected to the desired temperature during a sufficient residence time in the region B, ie about 150 ° C for the Pre-drying, 140 ° C for crystallization and 200 ⁰ C to 250 ° C for preheating. In the area of the radiator 3, the downpipe 2 has an opening 4, so that the radiation can act unimpeded on the conveyed plastic material. To protect the radiator 3, the opening 4 can be closed by a windowpane of suitable material, for example quartz glass, which allows the radiation to pass through substantially without absorption.

Instead of an annular opening 4 in the downpipe 2, a circular segment-shaped opening can also be provided and a reflector which subsequently covers the inside of the downpipe 2 at the opening in the circumferential direction and ensures optimum radiation distribution in the downpipe 2.

By additionally in the downpipe 2 above the radiator 3 attached means such. B. a sieve 5 with adapted to the size of the plastic parts mesh size, a homogenization of the flow of plastic material is achieved in the conveyor section and adjusted together with the delivery pipe (2) the density of the plastic part conveying atmosphere mixture. On the other hand, by a targeted adjustment of the distance of the screen 5 of the radiator 3, the conveying speed of the plastic material can be adjusted and so the duration of exposure to the radiation are set. The sieve 5 can additionally be shaken by suitable means so that it does not clog but the plastic parts continuously fall through. This also improves the separation of the plastic parts and the homogenization of the plastic part conveying tube atmosphere mixture. Furthermore, the plastic part density can also be adjusted directly by a rotary feeder (not shown).

For adjusting the conveying speed, a blower (not shown) may additionally be used, which generates an air flow up the downpipe and thus slows down the plastic parts. This air flow also advantageously absorbs and transports volatile products, such as moisture, from the plastic material so that, for example, the predrying is done even more effective. But even volatile contaminants are eliminated faster.

The method according to the invention will now be described with reference to a preferred embodiment.

In a first step, for example, PET flakes are removed from a car wash. These flakes are usually formed by crushing PET bottles that have been prewashed in rinse water mixed with caustic soda solution to remove beverage residues and other adhering soils and adhesives from pasted labels, and those of dissimilar materials such as caps or other foreign matter such as other plastics , Metal parts and the like were separated.

In a second step, the predrying of coming from the car wash PET flakes, which are therefore still affected by moisture. This pre-drying takes place directly in a conveying line with the aid of the application of near-infrared radiation of suitable intensity, so that a material temperature of about 150 ° C is established in the transported flakes, wherein the PET flakes are conveyed either by conveying airflow or by gravity conveying and the air Particle density is adjusted. The heat spreads in each flake immediately within a short time due to the irradiation. As a result, the passage of the flakes, which takes a period of time in the range of seconds, passes along an irradiation window in order to achieve a significant reduction in the residual moisture in and at the flakes.

In a third step, the flakes are fed to a 1-wave, 2-shaft or multi-screw extruder (ring extruder) with a diameter of about 50 mm and a screw speed of about 350 rev / min, which has several, in particular three degassing zones with vacuum pump stands and in which the material is extruded under near vacuum (<100 mbar) at a temperature of 280 ° C. Due to the friction and the high temperatures, a melt of the PET flakes. This melt is filtered by means of filters with a pore size smaller than 100 microns, thereby freed of dirt particles and then fed to a granulator. As a result, granules are produced with a granule size of less than 3 mm.

After the third step of extrusion and granulation is completed, the granules are transported directly into a silo. With the storage of the granulate in the silo, the continuous process management ends. After the silo has a sufficient level to fill the tumble dryer, it is filled directly during the fourth step. Again, the necessary transport of the granules by means of a flow of air or gravity with simultaneous separation of the individual granules, which are applied during separation with radiation of the near infrared of appropriate intensity, so that sets a temperature of about 140 ° C in the granules , Although the irradiation of the individual granules takes place only in seconds, this time is sufficient to bring about a partial crystallinity of about 40% in the granules. By laying the beginning of the discontinuous process management also takes place energy savings.

This semicrystalline granules is postcondensed in a fifth step in a solid reactor and that a tumble dryer at temperatures of 200 ° C to 250 ° C and a pressure less than 1 mbar for 4 to 18 hours, wherein the tumble dryer performs up to 2 revolutions per minute. The PET recyclate produced in this way has only traces of contamination in the ppm range so that it can be used in the food industry.

Advantageously, the preheating of the semi-crystalline granules in the tumble dryer from 140 ° C to temperatures of about 200 ° C to 250 ° C, which are necessary for post-condensation, also carried out using the erfϊndungsgemäßen means for conveying and simultaneous heating. And especially advantageous if both the crystallization and the preheating happen simultaneously with the inventive device when filling the tumble dryer. This is the previously necessary preheating dispensed with, since this intermediate step is coupled directly to the infestation of the tumble dryer. Instead of six process steps so far: removal of the flakes from the scrubbing unit, predrying, extrusion / granulation, crystallization, preheating, solid state postcondensation, the process is thus shortened to five process steps: removal of the flakes from the scrubbing plant, predrying, extrusion / granulation, crystallization / preheating, solid postcondensation , It is not only a heating step, it also saves a step, since previously had to be transported before and after the crystallization, but now the promotion takes place directly during the crystallization / preheating. Because the beginning of the batch process was relocated before crystallization and the conveying paths are reduced, cooling of the crystalline material is prevented. This can save energy and increase the capacity of existing plants.

Of course, the inventive means for conveying and simultaneously heating material may be used in partially crystalline or crystalline plastic material not only in recycling plastic material but also in converting amorphous plastic material purchased, for example, in the form of recycled or fresh PET granules or flakes , In this case, the process consists only of the steps of crystallization / preheating and Feststoffnachkondensation.

From the above description it has become clear that the advantages of the generic method of WO 2004/106025 are maintained with the aid of the present invention, with additional simplifications, in particular in terms of equipment, a more efficient use of energy and an increase in the capacity of existing facilities are possible.

Claims

claims

1. A method for treating plastic material, such as polyester, in particular for recycling polyethylene terephthalate (PET), e.g. from beverage bottles, preferably for the production of food-grade PET, and in particular for the conversion of amorphous plastic material, for example in the form of granules or flakes, into crystalline plastic material, with at least one of the process steps extrusion, granulation or solid postcondensation, wherein before the extrusion / granulation a predrying step and / or before crystallization after solidification a crystallization step is carried out, characterized in that

Plastic parts from the plastic material, in particular plastic flakes or granules, at least during the pre-drying step, conveyed and heated simultaneously during the crystallization step or during preheating of the plastic material during or before the Feststoffnachkondensationsschritt, wherein the heating by irradiation with electromagnetic radiation, in particular infrared radiation, preferred Radiation in the near infrared, takes place and the plastic parts are separated during conveying to the effect by producing a plastic part Förderatmosphären- mixture so that substantially each plastic part is irradiated and thus heated.

2. The method according to claim 1, characterized in that the crystallization step and the preheating step occur simultaneously.

3. The method according to claim 1 or 2, characterized in that the promotion and production of the plastic part Förderatmosphären- mixture by gravity caused falling down of the plastic parts are performed in a downpipe.

4. The method according to claim 1 or 2, characterized in that the promotion and production of the plastic part Förderatmosphären- mixture is carried out by an air flow promotion.

5. The method according to any one of claims 1 to 4, characterized in that the plastic parts are braked during conveying.

6. The method according to any one of claims 1 to 5, characterized in that the density of the plastic part conveying atmosphere mixture is adjusted during the conveying and homogenized.

7. Device (1) for conveying and simultaneous heating of material, in particular plastic parts, such as plastic flakes, plastic granules, plastic particles or the like., Preferably made of polyester, in particular polyethylene terephthalate (PET), with a conveyor line (2) and means for promotion characterized by a radiation source (3) which irradiates and heats the material at least along a part of the conveying path with electromagnetic radiation, in particular infrared radiation, preferably near infrared radiation, and means for producing (2, 5) a material Förderatmosphären- mixture, so that essentially each material part is irradiated with infrared radiation and thus heated.

8. Device according to claim 7, characterized in that the conveying path comprises a conveying pipe (2).

9. Device according to claim 7 or 8, characterized in that the means for conveying a blower device or a suction device, which conveys the material parts in the air flow.

10. Device according to one of claims 7 to 9, characterized in that the conveying tube is designed as a substantially vertical downpipe (2), so that the carriage is effected by the action of gravity on the material parts.

11. Device according to one of claims 7 to 10, characterized in that the means for producing (2, 5) of the material conveying atmosphere mixture are adapted to adjust the density and homogenize, so that all material parts substantially over the same time are subjected to the substantially same radiation intensity.

12. Device according to one of claims 7 to 11, characterized in that the means for producing the material-conveying atmosphere mixture comprise at least one of the elements sieve (5), swirler, deflector plate, displacement body or blower.

13. Device according to claim 12, characterized in that the means for producing the material-conveying atmosphere mixture furthermore comprise means for shaking, in particular of the sieve (5).

14. Device according to one of claims 7 to 13, characterized in that the conveying path and / or the means for producing the Matrial- Förderrohratmosphären mixture comprise a container, in particular a cyclone.

15. Device according to one of claims 7 to 14, characterized in that reflectors are provided for the electromagnetic radiation in the conveying path.

16. Device according to one of claims 7 to 15, characterized in that further means for stripping the material parts in air, steam, inert gases or hot air are provided.

17. Device according to one of claims 7 to 16, characterized in that means are further provided for aspirating evolved volatile products, such as water vapor, contaminants or the like ..

18. An apparatus for treating plastic material, such as polyester, in particular for recycling polyethylene terephthalate (PET), eg from beverage bottles, preferably for the production of food-safe PET, and in particular for the conversion of amorphous plastic material, for example in the form of granules or flakes, in crystalline plastic material , with at least one extruder, a granulator or a solid-state reactor, for example a tumble dryer, and at least one pre-dryer, a crystallizer or a heating apparatus, which preheats the plastic material before or in the solid reactor, characterized in that at least the pre-dryer, the crystallizer or the heating apparatus as a means (1) for conveying and simultaneous heating according to one of claims 6 to 15 is executed.

19. The apparatus according to claim 18, characterized in that the crystallizer and the preheater are designed together as a means (1) for conveying and simultaneous heating according to one of claims 6 to 15.