CLEANING GASES FROM THE DEGASSING OF POLYMER MELTS

Abstract

A method and a device for the purification of gases from the degassing of polymer melts—in particular, for the continuous further processing to form stretched polymer films. In this case, the gas to be purified is fed from a vacuum zone of a plasticizing unit, via at least one vacuum or degassing line, to a vacuum separator with a gas inlet and a gas outlet in which condensible, separable by freezing, and/or re-sublimable substances are separated from the supplied and purified gas by means of a cooling arrangement, and the separated substances are removed from the vacuum separator. By means of a heating arrangement, the substances separated by means of the cooling arrangement are at least partially liquefied or softened in the vacuum separator and removed from the vacuum separator in particular by suction.

Claims

1. Method for purifying gases from the degassing of polymer melts—in particular, for continuous further processing to form stretched polymer films—having the following features: from a vacuum zone of a plasticizing unit, the gas to be purified is fed, via at least one vacuum or degassing line, to a vacuum separator with a gas inlet and a gas outlet, in which condensible, separable by freezing, and/or re-sublimable substances from the fed and purified gas are separated by means of a cooling arrangement, and the separated substances are removed from the vacuum separator, wherein the separation of the substances from the gas to be purified in the vacuum separator takes place by means of freezing-out by cooling the substances to be separated by means of the cooling arrangement, the substances separated by means of the cooling arrangement are at least partially liquefied or softened by means of a heating arrangement and are removed from the vacuum separator, and in that, by means of a mechanical purifying device—in particular, with at least one scraper—the substances separated on the cooling arrangement are superficially scraped off at least partially.

2. Method for the purification of gases from the degassing of polymer melts according to claim 1, wherein the separation of the substances from the gas to be purified in the vacuum separator occurs by means of freezing-out by cooling to a temperature below the triple point of the substances to be separated—in particular, in the range of minus 18° C. or below.

3. Method for the purification of gases from the degassing of polymer melts according to claim 1, wherein the freezing-out of the substances from the gas to be purified in the vacuum separator takes place at a negative pressure of below 100 mbar or below 10 mbar.

4. Method for the purification of gases from the degassing of polymer melts according to claim 1, wherein the substances separated by means of the cooling arrangement are heated to a temperature in the range of the liquefaction or softening temperature of at least part of the separated substances, wherein the heating takes place in particular to a temperature in the range of 100° C. or above.

5. Device for the purification of gases from the degassing of polymer melts, wherein the gas to be purified is fed from a vacuum zone of a plasticizing unit to the device by means of at least one vacuum or degassing line, with a vacuum separator, which has a housing having a gas inlet for the gas to be purified and a gas outlet, having a cooling arrangement, by means of which condensible, separable by freezing, and/or re-sublimable substances can be separated from the supplied gas to be purified, and from which the separated substances can be removed from the housing of the vacuum separator, wherein, the cooling arrangement is designed so that the separation of the substances from the gas to be purified in the vacuum separator occurs by freezing-out the substances to be separated, the vacuum separator is provided with a heating arrangement which is suitable for at least partially liquefying or softening substances separated by means of the cooling arrangement, it further has a mechanical purifying device—in particular, with at least one scraper—for at least partial surface scraping of the cooling arrangement, and in that a removal opening is provided in the lower region of the housing of the vacuum separator, via which removal opening the substances to be at least partially liquefied or softened can be removed.

6. Device for the purification of gases according to claim 5, wherein the cooling arrangement is designed to cool the gas to be purified in such a way that the freezing-out is effected by cooling to a temperature below the triple point of the substances to be separated—in particular, at a temperature in the range of minus 18° C. or below.

7. Device for the purification of gases according to claim 5, wherein the freezing-out takes place at a negative pressure of below 100 mbar, and in particular below 10 mbar.

8. Device for the purification of gases according to claim 5, wherein the heating arrangement is designed to heat the substances separated by means of the cooling arrangement to a temperature in the range of the liquefaction or softening temperature of at least part of the separated substances, wherein the heating occurs in particular to a temperature in the range of 100° C. or above.

9. Device for the purification of gases according to claim 5, wherein the heating arrangement has at least one heating pipe extending into the interior of the housing of the vacuum separator, which heating pipe is designed in particular as a double-walled heating pipe for receiving a heating medium, wherein in particular several heating pipes and/or inner and outer pipes of one or more double-walled heating pipes are interconnected in a meandering manner.

10. Device for the purification of gases according to claim 9, wherein the housing of the vacuum separator has a cover which forms a feed and/or discharge line for heating medium to several heating pipes extending in particular in parallel and/or formed as a double pipe.

11. Device for the purification of gases according to claim 5, wherein the heating arrangement is arranged at least partially in the wall of the housing and has at least one heating pipe extending in the wall of the housing and/or at least one or more heating pipes connected to one another in a meandering manner and/or one or more interstices extending in a planar way over the wall of the housing for receiving a heating medium.

12. Device for the purification of gases according to claim 5, wherein the cooling arrangement and the heating arrangement of the vacuum separator have at least one common pipe and/or at least one interstice for receiving a heating medium and a coolant, wherein in particular at least one switching valve is connected upstream and downstream of the at least one common pipe and/or interstice, so that a selective application of heating medium or coolant to the common pipes and/or interstices is possible.

13. Device (1) for the purification of gases according to claim 5, wherein the vacuum separator has a solvent feed by means of which a solvent for the separated substances can be fed to the housing in such a way that the supplied solvent impinges on the cooling arrangement and is suitable for at least partially dissolving substances separated thereon, so that the at least partially dissolved substances can be removed from the housing of the vacuum separator via the removal opening.

14. Device for the purification of gases according to claim 5, wherein the mechanical purifying device—in particular, the at least one scraper—is designed as part of the heating arrangement.

15. Device for the purification of gases according to claim 5, wherein the mechanical purifying device is provided with at least one scraper which is oriented obliquely to a vertical of the vacuum separator and is suitable for purifying the surface of the cooling arrangement with the substances separated thereon and scraping off said substances.

16. Device for the purification of gases according to claim 5, further having at least one auxiliary filter arranged downstream in the gas flow and suitable for filtering out non-separated substances in the gas to be purified.

17. Device for the purification of gases according to claim 5, wherein several vacuum separators are provided, which are arranged upstream and downstream of at least one switching valve and which in particular are associated with further auxiliary filters, so that an alternative operation of individual vacuum separators and/or auxiliary filters is made possible.

18. Device for the purification of gases according to claim 5, having a controller which is connected to several sensors for detecting operating parameters of the device—in particular, the temperature, pressure, time, volume, or mass—and to several actuators for controlling the device—in particular, for controlling the gas flow, the heating arrangement, the cooling arrangement, the vacuum arrangement, and/or the purifying arrangement.

Description

[0060] The invention is explained by way of example below on the basis of a preferred exemplary embodiment with reference to the figures. The invention is not limited to this preferred exemplary embodiment.

[0061] FIG. 1 shows a schematic representation of an R+I diagram of an exemplary device for the purification of gases, and

[0062] FIG. 2 shows a schematic representation of the structure of a preferred vacuum separator.

[0063] FIG. 1 schematically shows an R+I diagram of an exemplary device 1 for the purification of gases.

[0064] The device 1 for the purification of gases from the degassing of polymer melts has a schematically illustrated vacuum zone 2, which is assigned to a plasticizing unit, by means of which a plastic granulate is softened, so that it can be fed to further processing in the context of a production process, and in particular a plastic stretching process. The heating results in the generation of substances which are discharged from the plastic granulate into the surrounding gaseous atmosphere and which are disruptive to the further plastics processing process. The gaseous atmosphere thus presents a gas which is mixed with disruptive substances.

[0065] The vacuum zone 2 is connected to the device 1 by means of at least one vacuum or degassing line 3 and thus enables the gas to be purified to be supplied from the vacuum zone 2 to the device 1 for the purification of gases.

[0066] The vacuum or degassing line 3 divides into two partial lines 3, which open into two vacuum separators 40 via gas inlets 42. Furthermore, these are provided with gas outlets 43, via which the gas exits from the vacuum separators 40 and is guided to downstream auxiliary filters 8, in which the gas is purified once again after a first purification in the vacuum separators 40, which form a first purifying stage. The auxiliary filters 8 form a purifying stage.

[0067] The gas to be purified is drawn in through the device 1 by means of a vacuum arrangement, not shown, from the vacuum zone 2 via the vacuum and degassing line 3, via the first purification stage, which is formed by the vacuum separator 40, via the second purification stage, which is formed by the auxiliary filter 8.

[0068] In the region of the gas inlets 42, a valve 9 is arranged in each case, which is connected upstream of the vacuum separators 40 which are downstream in the gas flow, and which valve can block or release the gas flow of the gas to be purified into the subsequent vacuum separator 40. The two valves 9 enable the function of a switching valve 9. The two valves 9 thus enable an alternating application of the two vacuum separators 40.

[0069] A valve 9 is arranged downstream of the two auxiliary filters 8 in each case in the gas flow, which valve is thus also connected downstream of the vacuum separators 40, which are upstream in the gas flow, and which valve can block or release the gas flow of the purified gas from the upstream auxiliary filter 8. The two valves 9 enable the function of a switching valve 9. The two valves 9 thus enable an alternative discharge of the purified gas from the auxiliary filters 8 arranged in parallel.

[0070] The gas flow downstream of the two valves 9 positioned downstream of the auxiliary filters 8 is brought together via a common central discharge line 11 of purified gas and is conveyed in the direction of the vacuum arrangement.

[0071] In this case, the vacuum separators 40 are designed such that each has a cooling arrangement 50, by means of which disruptive, condensible, separable by freezing, and/or re-sublimable substances can be separated from the supplied gas to be purified.

[0072] The disruptive substances from the gas to be purified are preferably separated in such a way that the disruptive substances are frozen out into ice in the form of an ice layer on the cooling arrangement 50. For this purpose, the cooling arrangement 50 is in particular cooled to a temperature in the range of minus 18° C. or below.

[0073] In addition, each vacuum separator 40 is provided with a heating arrangement 60 which is suitable for at least partially liquefying or softening substances separated by means of the cooling arrangement 50. The at least partially softened or liquefied substances can subsequently be removed from the vacuum separator 40 via a removal opening 44 in a particularly simple manner.

[0074] The liquefying of the frozen-out disruptive substances from the gas to be purified preferably takes place in such a way that the disruptive substances frozen out to form an ice layer are liquefied by means of the heating arrangement 60. For this purpose, the heating arrangement 60 is subjected to a heating medium, which in particular is heated to a temperature in the range of 160° C.

[0075] By providing the heating of the separated substances, which in particular contain hydrocarbons of different chain length and structure, in the vacuum separator 40, by means of the heating arrangement 60, it is possible to enable an efficient separation process in the vacuum separator 40. By heating, which normally leads to an at least partial liquefying or softening of the separated substances, it is, advantageously, possible to remove the separated substances from the cooling arrangement 50 in a simple and efficient manner, which normally takes place by draining or dripping from the cooling arrangement 50. As a result, the cooling effect of the cooling arrangement 50 is improved, and thus an efficient cooling of the gas to be purified and thus a particularly effective separation of the disruptive substances in the gas to be purified is achieved.

[0076] In this case, a removal opening 44 is provided in the lower region of the housing 41 of the vacuum separator 40, by means of which removal opening the separated and at least partially to be liquefied or softened substances can be removed.

[0077] As a result of the liquefying or softening, the separated substances can be removed from the cooling arrangement 50 in a simple manner, which is brought about by mechanical, chemical, or physical aids—in particular, by the action of the weight of the substances—and causes the substances to collect in the region of the lowest point of the interior 45 of the vacuum separator 40, where a removal opening 44 is arranged. This makes it possible to suction the at least partially liquefied or softened substances, which have originally been separated on the cooling arrangement 50 and have been liquefied or softened by heating by means of the heating arrangement 60, and thus have detached from the cooling arrangement 50.

[0078] It is particularly advantageous to provide a suction opening as a removal opening 44, which is of significantly smaller diameter than a conventional removal opening of a vacuum separator in the prior art, which is intended to enable the introduction of tools and, if appropriate, the intervention of the operator of the device for collecting and removing the collected solid materials. An inner diameter of a few cm, and in particular in the range of 5 cm, is sufficient.

[0079] Each vacuum separator 40 has a cooling arrangement 50 which is connected to a common cooling unit 53. The coolant is conducted from the cooling unit 53 via coolant lines to the cooling arrangements 50 and is thereby fed via the feed 54 for coolant to the vacuum separator 40 with the cooling arrangement 50. A valve 10 is connected upstream of the feed 54 for coolant and can block or release the coolant flow into the subsequent vacuum separator 40. In a corresponding manner, after leaving the cooling arrangement 50, the coolant is discharged from the vacuum separator 40 via a discharge line 55 for coolant and is returned via a valve 10 in a coolant line to the cooling unit 53. In this case, the coolant flow from the upstream vacuum separator 40 to the cooling unit 53 can be blocked or released by the valve 10. The two valves 10 enable the function of a switching valve 10 for the coolant.

[0080] Each vacuum separator 40 additionally has a heating arrangement 60, which is connected to a common heating unit 63. The heating medium is guided from the heating unit 63 via heating medium lines to the heating arrangements 60 and is thereby fed via the feed 64 for heating medium to the vacuum separator 40 with the heating arrangement 60. The feed 64 for heating medium is preceded by a valve 10, which can block or release the heating medium flow into the subsequent vacuum separator 40. In a corresponding manner, after leaving the heating arrangement 60, the heating medium is discharged from the vacuum separator 40 via a discharge line 65 for heating medium and returned to the heating unit 63 via a valve 10 in a heating medium line. In this case, the heating medium flow from the upstream vacuum separator 40 to the heating unit 63 can be blocked or released by the valve 10. The two valves 10 enable the function of a switching valve 10 for the heating medium.

[0081] In this case, the valves 10 are designed and arranged such that, in alternation, either heating medium or coolant can be supplied to the cooling arrangements 50 or heating arrangements 60 arranged in the vacuum separators 40, which cooling arrangements are designed as common arrangements 50, 60.

[0082] The device 1 for the purification of gases is provided with a central controller, which is provided with several sensors 12 for detecting operating parameters of the device 1—in particular, the temperature, the pressure, the time, the volume, or the mass—and with several actuators 9, 10, 53, 63 for controlling the device 1—in particular, for controlling the gas flow, the heating arrangement 60, the cooling arrangement 50, the vacuum arrangement, and/or the purifying arrangement 70.

[0083] In FIG. 1, various sensors are symbolically shown as a circle with an inscription. For example, in the region of the vacuum zone 2, a pressure sensor 12 is shown, with which the pressure of the gas to be purified upstream of the vacuum and degassing line 3 is measured. A further pressure sensor 12 is arranged in the region of the gas outlet 43, and thus in the gas flow downstream of the vacuum separator 40, and can thus measure the pressure of the gas purified by the vacuum separator 40 as the first purification stage. It is thus also possible, in conjunction with the information of the pressure sensor 12 arranged in the region of the vacuum zone 2, to determine the pressure drop between the sensors 12 and to deduce therefrom the degree of separation of the disruptive substances in the vacuum separator 40 through which the flow passes and, depending upon this degree, to stop the cooling process in this vacuum separator 40, to start the heating process with the mechanical scraping of the separated substances on the cooling arrangement 50, and to enable removal via the removal opening 44 or to switch removal to the corresponding vacuum separator 40 with the aid of the switching valves 9 on the parallel branch. A further pressure sensor 12 is thus arranged in the region of the auxiliary filter 8 and thus in the gas flow downstream of the vacuum separator 40, such that it can measure the pressure at the output of the auxiliary filter 8. It is thus also possible, in conjunction with the information of the pressure sensor 12 arranged in the region of the gas outlet 43, to determine the pressure drop between these sensors 12 and to deduce therefrom the degree of separation of the disruptive substances in the auxiliary filter 8 through which the flow passes and, if necessary, to switch, with the aid of the switching valves 9, to the parallel branch with the corresponding vacuum separator 40 with auxiliary filter 8. It is thus possible to clean the auxiliary filter 8 with the extensively separated substances without having to interrupt the method of purifying gases from the degassing of polymer melts.

[0084] With the aid of the single central controller, various states of the device 1 can be controlled, and the sequence—in particular, the start-up or the shutdown of the entire device 1 or also individual parts of the device 1—can be influenced. This makes it possible to enable an efficient operation of the device 1 for the purification of gases and an effective execution of the method for the purification of gases from the degassing of polymer melts, and in particular for the continuous further processing to form stretched polymer films.

[0085] FIG. 2 shows a schematic representation of a preferred vacuum separator 40. The two parts of the vacuum separator 40 shown are a housing 41 of the vacuum separator 40 and an insert 49 in the housing 41 of the vacuum separator 40.

[0086] The housing 41 has a gas outlet 43 in the upper region and a gas inlet 42, not shown, via which the gas to be purified is fed to the vacuum separator 40 and discharged therefrom in the lower region. The gas inlet 42 and the gas outlet 43 have a large diameter, so that the gas to be purified experiences only a low flow resistance.

[0087] The wall 48 of the housing 41 is of double-walled design and forms an interstice 52, 62, which can be used both for cooling and for heating by means of supplied and removed coolant or heating medium. In this case, the interstice 52, 62 extends substantially over the entire circumference of the cylindrical housing 41 and over almost the entire height of the wall 48 of the housing 41. Via a feed 54, 64 for coolant or heating medium in the lower region of the housing 41 in the wall 48, the coolant is fed to the interstice 52, 62 and discharged via the discharge line 55, 65 for coolant or heating medium in the upper region of the housing 41 in the wall 48.

[0088] The housing 41 of the vacuum separator 40 is held by a stand 47 in an upright, and in particular vertical, orientation.

[0089] The insert 49 in the housing 41 of the vacuum separator 40 has a cover 46, from which a plurality of cooling pipes 51 project downwards. These cooling pipes 51 are designed as double-walled cooling pipes 51, such that the inner pipe ends in the outer pipe in front of the lower end of the outer pipe, and the lower end of the outer pipe is designed so as to be closed such that a connection space is formed between the interior of the inner pipe and the interstice between the inner and outer pipes. As a result, a coolant fed to the inner pipe can be guided downwards via the inner pipe, deflected in the connection space, and guided upwards again via the interstice between the inner and outer pipes. It is also possible to guide the coolant in the opposite direction through the double-walled cooling pipes 51.

[0090] The cooling pipes 51 are arranged in parallel to one another. The cover 46 is connected to a feed 54 for coolant and enables the coolant to be supplied to the inner pipes of the double-walled cooling pipes 51 via channels arranged in the interior of the cover 46.

[0091] The double-walled cooling pipes 51 and the feed 54 for coolant and the discharge line 55 for coolant are part of the cooling arrangement 50 and can alternatively be used as part of the heating arrangement 60, and thus form double-walled heating pipes 61 and the feed 64 for heating medium and the discharge line 65 for heating medium. They thus represent common double-walled pipes 51, 61 and common feeds 54, 64, as well as common discharge lines 55, 65.

[0092] The cover 46 is connected to a discharge line 55 for coolant and enables a discharge of the coolant from the interstices between the inner and outer pipes of the double-walled cooling pipes 51 via channels arranged in the interior of the cover 46.

[0093] The double-walled pipes 51, 61 belong, with the interstice 52, 62, to the cooling arrangement 50 or to the heating arrangement 60, and thus enable a very efficient cooling effect or heating effect in the vacuum separator 40.

[0094] Furthermore, the insert 49 has nine scrapers 71, which are part of the mechanical purifying device 70 and can be displaced along the double-walled cooling pipes by means of a drive rod 73, which extends downwards in parallel with the double-walled cooling pipes 51 through the cover 46. The drive rod 73 is driven by means of a drive 72 of the mechanical purifying device 70 above the cover 46, and is thereby moved displaceably. The drive 72 is designed as an electric drive.

[0095] The scrapers 71 have substantially the shape of a semi-oval plate and are fixedly connected to the drive rod 73. In this case, the scrapers 71 are oriented obliquely to the drive rod 73 or to the double-walled pipes 51, 61, so that they are arranged in a V-shaped manner, offset to one another, over the length of the drive rod 73.

[0096] The scrapers 71 have at least as many recesses as double-walled pipes 51, 61, and are designed and arranged such that their edge is suitable for scraping deposits on the surface of the double-walled pipes 51, 61. In addition, the outer contour of the scrapers 71 is designed such that it is suitable for scraping off the inner wall of the wall 48 of the housing 41 of the vacuum separator 40 according to the surface of the double-walled pipes 51, 61 when the insert 49 is inserted into the housing 41 and is fixedly connected thereto. The double-walled pipes 51, 61 and the purifying device 70 project with the scrapers 71 and the drive rod 73 into the interior 45 of the housing 41. The double-walled pipes 51, 61 in the interior 45 extend almost to the lower end, and thus to the bottom of the housing 41. The removal opening 44 designed as a suction opening is arranged in the base.

[0097] The gas inlet 42 in the wall 48 is arranged below the gas outlet 43 in the housing 41, as a result of which an upward gas flow of the gas to be purified is produced in the interior 45 of the housing 41 and thereby moves along the cooling arrangement 50. In this case, the gas inlet 42 is arranged in such a way that the gas which is flowing into the interior 45 of the housing 41 and is to be purified impinges in a targeted manner on the cooling arrangement 50 in the region of the lower end of the double-walled cooling pipes 51 and is subsequently guided upwards in the direction of the gas outlet 43 along the cooling pipes 51 and the interstice 52 for coolant. This design makes it possible to achieve an efficient cooling of the gas to be purified with the aid of the cooling arrangement 50.

[0098] In this case, silicone oil or a brine solution based upon water has proven particularly useful as a heating medium or as a coolant, since they allow, on the one hand, low temperatures of the coolant in the range of minus 20° C. and, on the other, high temperatures of the heating medium in the range of 100° C. to 160° C.

LIST OF REFERENCE SIGNS

[0099] 1 device for the purification of gases [0100] 2 vacuum zone [0101] 3 vacuum or degassing line [0102] 40 vacuum separator [0103] 41 vacuum separator housing [0104] 42 gas inlet [0105] 43 gas outlet [0106] 44 removal opening [0107] 45 interior of the housing [0108] 46 cover [0109] 47 vacuum separator stand [0110] 48 wall of the housing [0111] 49 insert [0112] 50 cooling arrangement [0113] 51 cooling pipe [0114] 52 interstice for cooling [0115] 53 cooling unit [0116] 54 feed for coolant [0117] 55 discharge line for coolant [0118] 60 heating arrangement [0119] 61 heating pipe [0120] 62 interstice for heating [0121] 63 heating unit [0122] 64 feed for heating medium [0123] 65 discharge line for heating medium [0124] 70 mechanical purifying device [0125] 71 scraper [0126] 72 drive of the mechanical purifying device [0127] 73 drive rod [0128] 8 auxiliary filter [0129] 9 switching valve for gas to be purified [0130] 10 switching valve for heating medium or coolant [0131] 11 central discharge of the purified gas [0132] 12 sensors