CLEANING APPARATUS FOR CLEANING, IN PARTICULAR DEGASSING, THERMOPLASTIC PLASTICS

Abstract

A cleaning apparatus for cleaning, in particular degassing, thermoplastic plastics, in particular polyolefins, the apparatus including a cleaning container for the thermoplastic plastic to be cleaned and a feed apparatus for feeding the thermoplastic plastic to be cleaned into the cleaning container in pourable form, the cleaning container having a gas feed opening, and a steam generator for generating water vapor being provided and being connected to the gas feed opening in order to feed the water vapor to the cleaning container.

Claims

1. A cleaning apparatus for cleaning thermoplastic plastics, the cleaning apparatus comprising: a cleaning container for the thermoplastic plastic to be cleaned; a feed apparatus for feeding the thermoplastic plastic to be cleaned into the cleaning container in pourable form; the cleaning container having a gas feed opening; and a steam generator for generating water vapor connected to the gas feed opening in order to feed the water vapor to the cleaning container.

2. The cleaning apparatus as claimed in claim 1, further comprising a discharge apparatus for discharging the cleaned thermoplastic plastic from the cleaning container.

3. The cleaning apparatus as claimed in claim 2, wherein at least one of the feed apparatus or the discharge apparatus comprises at least one of a rotary feeder or at least one shut-off valve.

4. The cleaning apparatus as claimed claim 3, wherein the cleaning container has a degassing opening for discharging water vapor together with gases that have escaped from the thermoplastic plastic.

5. The cleaning apparatus as claimed in claim 1, further comprising a drying apparatus for the cleaned thermoplastic plastic connected downstream of the cleaning container.

6. The cleaning apparatus as claimed in claim 4, wherein the cleaning container has a condensate opening for discharging condensed water from the cleaning container.

7. The cleaning apparatus as claimed in claim 6, further comprising an open-loop or closed-loop control device for open-loop or closed-loop control of at least one of: the steam generator, the feed apparatus, the discharge apparatus, at least one valve at the degassing opening, or the condensate opening.

8. A process for cleaning thermoplastic plastics, the process comprising: generating water vapor; and exposing the thermoplastic plastic to be cleaned in pourable form to the water vapor.

9. The process as claimed in claim 8, wherein the thermoplastic plastic to be cleaned is exposed to the water vapor which is present in substantially pure form.

10. The process as claimed in claim 8, wherein the thermoplastic plastic to be cleaned is exposed to the water vapor for between 15 minutes and 240 minutes.

11. The process as claimed in claim 8, further comprising heating the water vapor to a temperature of 90° C. to 150° C. prior to exposure to the thermoplastic plastic to be cleaned.

12. The process as claimed in claim 8, wherein the thermoplastic plastic to be cleaned is provided as at least one of pellets, granules, or flakes when the thermoplastic plastic to be cleaned is exposed to the water vapor.

13. The process as claimed in claim 8, further comprising carrying out the continuously, quasi-continuously or batchwise.

14. The process of claim 8, wherein the thermoplastic plastic comprises polyolefins.

15. A cleaned recycled thermoplastic plastic formed by the process as claimed in claim 8.

16. The process of claim 8, further comprising generating the water vapor using a steam generator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Further advantages and details of the invention will emerge from the figures and from the associated description of the figures. In the figures:

[0054] FIG. 1 shows an exemplary embodiment according to the invention of a cleaning apparatus for cleaning thermoplastic plastics,

[0055] FIG. 2 shows a further exemplary embodiment according to the invention of a cleaning apparatus for cleaning thermoplastic plastics,

[0056] FIG. 3 shows a further exemplary embodiment according to the invention of a cleaning apparatus for cleaning thermoplastic plastics, and

[0057] FIG. 4 shows a graph relating to the effectiveness of the process according to the invention.

DETAILED DESCRIPTION

[0058] FIG. 1 shows an exemplary embodiment of a cleaning apparatus 1 for cleaning, in particular degassing, thermoplastic polymers.

[0059] In this exemplary embodiment, a cleaning container 2 and a steam generator 5 are arranged in a common container.

[0060] Specifically, in this exemplary embodiment, water, which is present in the lower part of the common container, is heated and evaporated as a result. In the present exemplary embodiment, the water is heated by way of a heating coil which has a heating current applied to it.

[0061] The resultant water vapor passes upward into the region of the cleaning container.

[0062] In this exemplary embodiment, the gas feed opening 4 is thus realized through a transverse section of the common container.

[0063] A lining 14 prevents the thermoplastic plastic, which is fed in for example in the form of granules, from passing into the region of the steam generator.

[0064] At the side walls and the upper part of the common container, the lining 14 may function as insulation.

[0065] In order to feed in the thermoplastic plastic, a feed apparatus 3 is provided on the top side of the cleaning container 2.

[0066] In this exemplary embodiment, the feed apparatus 3 comprises two shut-off valves 8 which are connected in series and which prevent advancing thermoplastic plastic from passing into the cleaning container 2.

[0067] Analogously, the discharge apparatus 6 likewise comprises two shut-off valves 8 which prevent cleaned thermoplastic plastic from passing out of the cleaning container 2 in an undesirable manner.

[0068] The cleaning apparatus 1 of this exemplary embodiment may be operated both batchwise and quasi-continuously.

[0069] For batchwise operation, the shut-off valves 8 of the feed apparatus 3 are first opened, such that thermoplastic plastic to be cleaned is filled into the previously empty cleaning container 2. After the cleaning container 2 has been filled in this way, the shut-off valves 8 of the feed apparatus 3 are closed and the cleaning operation begins.

[0070] Once the cleaning operation has concluded, the shut-off valves 8 of the discharge apparatus 6 can be opened, such that the cleaned thermoplastic plastic flows out of the cleaning container.

[0071] For quasi-continuous operation, use may be made of the fact that there is a certain volume present between the shut-off valves 8 of the feed apparatus and of the discharge apparatus, said volume being able to be used for metering.

[0072] If a certain quantity of thermoplastic plastic to be cleaned is to be fed in, the upper shut-off valve 8 of the feed apparatus 3 can first be opened, such that the mentioned volume fills with thermoplastic plastic to be cleaned.

[0073] Then, the upper shut-off valve 8 of the feed apparatus 3 is closed and the lower shut-off valve 8 of the feed apparatus 3 is opened, such that the quantity of thermoplastic plastic to be cleaned present in the mentioned volume passes into the cleaning container 2.

[0074] An analogous procedure can be performed with the discharge apparatus.

[0075] In this way, thermoplastic plastic can be cleaned successively and quasi-continuously in the cleaning container 2.

[0076] According to the invention, the actual cleaning operation is effected in that the thermoplastic plastic in the cleaning container 2 is exposed to the water vapor generated by the steam generator 5.

[0077] The thus improved effectiveness of the cleaning operation is described in more detail in conjunction with FIG. 4.

[0078] In the cleaning container 2, there is a degassing opening 9 via which water vapor together with gas removed from the thermoplastic plastic can exit the cleaning container 2.

[0079] A pressure sensor 12 and a degassing valve 15 are present in a line adjoining the degassing opening 9. The water vapor in the cleaning container 2 can, as a result, be kept at a desired pressure.

[0080] As an alternative or in addition, the pressure sensor 12 could also be provided in the cleaning container 2.

[0081] A condensate opening 11 is also present, by means of which condensed or not yet evaporated water can be discharged, possibly together with substances which have been removed by the cleaning according to the invention from the thermoplastic plastic and which are present in the condensed water.

[0082] A condensate valve 16, which can control the discharging of the condensate or of the not yet evaporated water together with the mentioned substances, is also present in a line adjoining this condensate opening 11.

[0083] Provided adjoining the discharge apparatus 6 is a drying apparatus 10 for drying the cleaned thermoplastic plastic.

[0084] In the present exemplary embodiment, the drying is effected by fed-in hot or cold air.

[0085] A heat exchanger 13 is also provided in the drying apparatus 10.

[0086] In this exemplary embodiment, the heat exchanger 13 is in the form of a meandering tube which leads through the drying apparatus 10 and which is connected to the steam generator 5.

[0087] Water is conducted through the heat exchanger 13 and preheated by the heat present in the drying apparatus 10. Said water then passes, in the preheated state, into the reservoir region of the steam generator 5.

[0088] An open-loop or closed-loop control device 17, which in this exemplary embodiment is signal-connected to the pressure sensor 12, the shut-off valves 8 of the feed apparatus 3 and of the discharge apparatus 6, the steam generator 5, the condensate valve and the degassing valve 15, is illustrated symbolically.

[0089] The open-loop or closed-loop control device 17 can actuate the feed apparatus 3 and the discharge apparatus 6 for batchwise or quasi-continuous operation, as has already been described to some extent further above.

[0090] Furthermore, the open-loop or closed-loop control device 17 can control a degree of opening of the degassing valve 15 and/or a steam generation capacity of the steam generator 5 on the basis of the measurement signals of the pressure sensor 12 in open-loop or closed-loop fashion.

[0091] It is of course also possible for further sensors, such as a temperature sensor and/or a fill level sensor, to be present, the measurement signals of which can be used for such open-loop or closed-loop control or other open-loop or closed-loop controls (for example of the condensate valve 16).

[0092] FIG. 2 shows a further exemplary embodiment of a cleaning apparatus 1.

[0093] A first difference between the cleaning apparatus 1 according to FIG. 1 and that according to FIG. 2 is that the steam generator 5 is embodied separately from the cleaning container 2.

[0094] As a result, the lining 14 may be completely in the form of insulation 14.

[0095] However, the basic functioning is analogous to that in FIG. 1, that is to say that undesired gases are washed out of the thermoplastic plastic by the water vapor.

[0096] A further difference between the cleaning apparatus 1 according to FIG. 1 and that according to FIG. 2 is that the feed apparatus 3 and the discharge apparatus 6 are implemented not by shut-off valves 8 but by rotary feeders 7.

[0097] In principle, this also allows both batchwise and quasi-continuous operation. However, the embodiment from FIG. 2 is preferably operated quasi-continuously.

[0098] That is to say that the rotary feeders 7 are used to refill thermoplastic plastic to be cleaned, and to remove cleaned thermoplastic plastic from the cleaning container 2, quasi-continuously.

[0099] As is indicated symbolically in this regard in FIG. 2, to this end the rotary feeders 7 may be rotated at a defined rotational speed n per hour.

[0100] In the embodiment according to FIG. 2, it would also be possible, in principle, for a preheating means for the steam generator 5 to be provided, said preheating means being fed with heat from the drying apparatus 10. However, this is not provided in the exemplary embodiment depicted in FIG. 2.

[0101] It should also be mentioned that the embodiment according to FIG. 2 also has an open-loop or closed-loop control device 17 which functions analogously, in particular actuates the rotary feeders 7 instead of the shut-off valves 8, but is not illustrated.

[0102] FIG. 3 shows an embodiment which is similar to that from FIG. 2, but with no drying apparatus 10 being provided. This means that the invention can be readily employed even without a drying apparatus 10.

[0103] It should be noted that the different elements of the embodiments described here may by all means be combined with one another in a different manner.

[0104] By way of example, it would also be possible for rotary feeders 7 to be used instead—or partially instead—of the shut-off valves 8 in the embodiment according to FIG. 1.

[0105] FIG. 4 shows a graph of a measurement relating to the effectiveness of the cleaning by means of water vapor according to the invention.

[0106] mg of D-limonene present per kg in the plastic is plotted versus the elapsed time for which the plastic was exposed to the water vapor.

[0107] D-limonene is usually used as measured value for the odor nuisance of plastics, because this compound is the most difficult to remove from the plastic and therefore is washed out of the plastic last.

[0108] As can clearly be seen from the graph from FIG. 4, the concentration of D-limonene in the plastic to be cleaned decreases very sharply at the beginning, that is to say that a large quantity of the gases and other substances to be removed is washed out at the beginning.

[0109] In fact, after approximately 15 minutes a concentration is already achieved that can only be achieved after three or more hours when degassing with hot air.

[0110] In addition, according to the invention, a dwell time of between one or two hours makes it possible to achieve much lower concentrations than with hot air, while a time advantage is still provided.

[0111] As already mentioned, other gases and/or other undesired substances are removed from the thermoplastic plastic more rapidly than the mentioned D-limonene.

[0112] It should also be pointed out that the exemplary embodiments shown may by all means be used in a greatly modified manner. By way of example, it is not necessary for the feed direction for the thermoplastic plastic to be directed vertically downward. If suitable conveying apparatuses are provided, it is for example also possible to implement a horizontal feed.

[0113] Nor is it necessary for the thermoplastic plastic to always be strictly separated from the liquid phase.

[0114] The water vapor to which the thermoplastic plastic to be cleaned is exposed does not have to, as mentioned, be 100% pure. In principle, it would also be conceivable to provide the water vapor with a desired odor component. However, in preferred exemplary embodiments, the water vapor is as pure as possible in order to obtain as odor-neutral a process product as possible.

LEGEND TO THE REFERENCE SIGNS

[0115] 1 Cleaning apparatus

[0116] 2 Cleaning container

[0117] 3 Feed apparatus

[0118] 4 Gas feed opening

[0119] 5 Steam generator

[0120] 6 Discharge apparatus

[0121] 7 Rotary feeder

[0122] 8 Shut-off valve

[0123] 9 Degassing opening

[0124] 10 Drying apparatus

[0125] 11 Condensate opening

[0126] 12 Pressure sensor

[0127] 13 Heat exchanger

[0128] 14 Lining/insulation

[0129] 15 Degassing valve

[0130] 16 Condensate valve

[0131] 17 Open-loop or closed-loop control device.