Apparatus for treating molten polymer

Abstract

An apparatus (1) for treating molten polymer, comprising a reactor (2) for degassing the molten polymer, characterized in that there is provided at least one level sensor (20) arranged inside the reactor (2), said at least one level sensor (20) being adapted to detect the level of molten polymer in the reactor (2); the apparatus (1) comprising a pump (5) provided with a motor (51), the pump adapted to receive the molten polymer exiting the reactor (2); wherein there is provided at least one pressure sensor (50) adapted to measure the pressure of the molten polymer exiting the pump (5); wherein there is provided a first electronic control unit (42) connected to said at least one pressure sensor (50), the unit adapted to control the motor (51) of the pump (5) according to the values detected by said at least one pressure sensor (50).

Description

[0001] APPARATUS FOR TREATING MOLTEN POLYMER

[0002] Field of the invention

[0003] The present invention relates to the field of apparatuses for treating molten polymer, in particular for degassing molten polymer, in particular for removing contaminants or additives such as acetaldehyde or ethylene glycol.

[0004] Background art

[0005] In order to produce plastic items, for example the preforms of PET bottles, an apparatus comprising an extruder which generates molten polymer starting from granules or flakes is conventionally used. The molten polymer is then sent to a user machine, for example, a forming machine that molds the items.

[0006] PET, in particular when recycled, is to be subjected to degassing, in particular in order to remove contaminants such as acetaldehyde or ethylene glycol.

[0007] Therefore, a reactor for the degassing is provided, arranged fl uidically downstream of the extruder and upstream of the user machine. The user machine is supplied with the molten polymer exiting the reactor by means of a pump.

[0008] The reactor generally is provided with a perforated plate. The molten polymer, crossing the perforated plate, is made in the form of filaments so as to facilitate the degassing thereof. The molten polymer filaments fall by gravity towards the bottom of the reactor and accumulate in the reactor.

[0009] Disadvantageously, to date, the level of molten polymer in the reactor is not controlled in an adequate manner. This has disadvantages.

[0010] The time during which the molten polymer is in the form of filaments is among the factors affecting the degassing. The level of molten polymer in the reactor affects the time during which the polymer is in the form of filaments. Indeed, a higher level decreases said time, while a lower level increases said time.

[0011] Since the level of molten polymer in the reactor is not controlled in an adequate manner, the degassing often occurs in an inadequate and non-uniform manner.

[0012] Moreover, disadvantageously the process reactor in which the molten polymer is degassed is an uncoupling element of the flow of molten polymer between the extruder upstream of the reactor, and the pump and user machine downstream of the reactor. Therefore, the user machine is not supplied in an optimal manner. A further aspect which may result in a non-optimal supply of the user machine is the pressure of the molten polymer exiting the reactor, in particular exiting the pump. Indeed, a constant pressure value of the molten polymer exiting the pump would be needed to stably supply the forming machine downstream of the pump.

[0013] Therefore, the need is felt to improve the supply of a user machine downstream of the degassing reactor and to improve the degassing process of the molten polymer in the reactor.

[0014] Summary of the invention

[0015] It is an object of the present invention to provide an apparatus for treating molten polymer which allows improving the supply of a user machine downstream of the degassing reactor, in particular so as to obtain a particularly stable supply.

[0016] It is another object of the present invention to provide an apparatus which allows improved and more uniform degassing of the molten polymer.

[0017] The present invention achieves at least one of such objects and other objects which will become apparent in light of the present description, by means of an apparatus, according to claim 1 , for treating molten polymer, comprising a reactor for degassing the molten polymer, wherein there is provided at least one level sensor arranged inside the reactor, said at least one level sensor being adapted to detect the level of molten polymer in the reactor; the apparatus comprising a pump provided with a motor, adapted to receive the molten polymer exiting the reactor; wherein there is provided at least one pressure sensor, in particular arranged downstream of the pump, adapted to measure the pressure of the molten polymer exiting the pump; wherein there is provided a first electronic control unit connected to said at least one pressure sensor, adapted to control the motor of the pump according to values detected by said at least one pressure sensor.

[0018] Advantageously, the apparatus allows the pressure of molten polymer exiting the pump to be controlled.

[0019] It is particularly advantageous that the apparatus comprises at least one pressure sensor adapted to measure the pressure of the molten polymer exiting the pump arranged downstream of the reactor. Advantageously, said at least one pressure sensor is connected to the electronic control unit which may control the motor of the pump according to values detected by said at least one pressure sensor, in particular so as to keep substantially constant the pressure of the molten polymer exiting the pump.

[0020] Therefore, advantageously, a user machine downstream of the reactor may be stably and uniformly supplied, in particular so that it is supplied with molten polymer at a substantially constant pressure.

[0021] Advantageously, said at least one level sensor allows monitoring, in continuous or discrete manner, the level of molten polymer in the reactor. Said at least one level sensor may advantageously be connected to an electronic control unit adapted to control the motor of the extruder which generates the molten polymer, in particular so as to adjust the flow rate of molten polymer exiting the extruder according to values detected by said at least one level sensor.

[0022] Advantageously, the flow rate of molten polymer exiting the extruder may be regulated so that the level of molten polymer in the reactor remains substantially constant.

[0023] Therefore, advantageously a user machine downstream of the reactor may be stably and uniformly supplied, and optimal and uniform degassing may be performed. Indeed, since the apparatus according to the invention may allow the level of molten polymer in the reactor to be kept substantially constant, the time during which the molten polymer remains in the form of filaments is constant and substantially is equal to the time defined in the design step.

[0024] Advantageously, in order to stably supply the user machine downstream of the pump, the apparatus according to the invention allows having a pressure value exiting the pump which is substantially constant. The pressure of the molten polymer may advantageously be measured by said at least one pressure sensor, or pressure probe, and the value may be sent to the electronic control unit, or control system, of the motor of the pump so as to stabilize the pressure at the value set (pressure feedback).

[0025] Moreover, advantageously to achieve system stability, with particular reference to the supply of the user machine, and for constant degassing efficiency, the apparatus according to the invention advantageously allows the level of molten polymer to be kept substantially constant inside the reactor. The level of molten polymer in the reactor may be measured, preferably continuously measured, with said at least one level sensor, or level probe, installed in the reactor. The information provided by said at least one level sensor may be processed by the electronic control unit, or control system, of the motor of the extruder so as to keep constant the level set (level feedback).

[0026] The invention also relates to a process, according to claim 9, for treating molten polymer, in particular for degassing the molten polymer, wherein the reactor is supplied with molten polymer coming from an extruder provided with a motor; wherein the motor of the pump is controlled by the first electronic control unit according to values detected by said at least one pressure sensor, in particular so as to keep substantially constant the pressure of the molten polymer exiting the pump, preferably with a tolerance range of ± 5%, preferably of ± 1 %.

[0027] Preferably, in the process, the level of molten polymer in the reactor is detected by means of said at least one level sensor; and the flow rate of molten polymer exiting the extruder is adjusted by means of an electronic control unit adapted to control the motor of the extruder according to values detected by said at least one level sensor; in particular wherein the flow rate of molten polymer exiting the extruder is increased or decreased to keep the level of molten polymer in the reactor substantially constant, preferably with a tolerance range of ± 3%, preferably of ± 1 %.

[0028] Further features and advantages of the invention will become more apparent in the light of the detailed description of exemplary but not exclusive embodiments. The dependent claims describe particular embodiments of the invention.

[0029] Brief description of the figure

[0030] The description of the invention refers to accompanying Fig. 1 , which is provided by way of non-limiting example, which diagrammatically shows an apparatus according to the present invention.

[0031] Description of example embodiments of the invention

[0032] With reference to Fig. 1 , there is described an apparatus 1 for processing plastic, in particular for treating molten plastic, or molten polymer. More particularly, the apparatus 1 is capable of degassing the molten polymer. Degassing is performed in particular to remove contaminants or additives, such as acetaldehyde or ethylene glycol, for example, from the molten polymer. Apparatus 1 is particularly adapted to treat PET, in particular recycled PET, although it may also treat virgin PET or other polymer or plastic material. In other words, said molten polymer preferably is molten PET.

[0033] In all the embodiments, apparatus 1 comprises a reactor 2, or vessel, for degassing the molten polymer. Advantageously, apparatus 1 comprises at least one level sensor 20 (i.e. , one or more) arranged inside reactor 2, said at least one level sensor 20 being adapted to detect the level of molten polymer in reactor 2.

[0034] Reactor 2 is provided with an inlet 21 , or inlet opening, for the molten polymer, and an outlet 29, or outlet opening, for the molten polymer. Preferably, the inlet 21 is in an upper part or area of reactor 2, and the outlet 29 is in a lower part or area of reactor 2. The lower part or area comprises the bottom of reactor 2.

[0035] Reactor 2 preferably is sealingly closed and preferably is provided with one or more openings 28, for example obtained in the side wall, which are adapted to be connected to suction means adapted to decrease the pressure inside reactor 2 so as to be able to degas the molten polymer.

[0036] Preferably, reactor 2 defines a longitudinal axis X. Preferably, said longitudinal axis X is vertical, i.e., it extends substantially perpendicular with respect to the resting plane of apparatus 1 . The side wall of reactor 2 extends around said longitudinal axis X.

[0037] A perforated plate 22 provided with a plurality of holes through which the molten polymer can pass to generate molten polymer filaments, preferably is provided in reactor 2.

[0038] In particular, the perforated plate 22 is arranged in an upper area of reactor 2, proximal to the inlet 21 .

[0039] Reactor 2 preferably is designed so that the molten polymer that has crossed the perforated plate 22 falls by gravity towards the bottom of reactor 2. Since the molten polymer is temporarily made in the form of filaments by means of the perforated plate 22, the degassing thereof is improved.

[0040] An advantage of apparatus 1 is that it may allow, in particular by connecting said at least one level sensor 20 to an electronic control unit 41 , the level of molten polymer in reactor 2 to be kept at a constant and predetermined level so as to allow the degassing, in particular of the molten polymer filaments, for an adequate and substantially constant time so as to obtain optimal and uniform degassing.

[0041] Preferably, said at least one level sensor 20 is arranged below the perforated plate 22, in particular at a height between the perforated plate 22 and the outlet 29 of reactor 2. More particularly, said at least one level sensor 20 is preferably arranged at such a height whereby it is below said one or more openings 28 adapted to be connected to suction means.

[0042] Apparatus 1 preferably further comprises an extruder 3 arranged upstream, in particular fluidically upstream, of reactor 2.

[0043] Extruder 3 in particular is adapted to transform plastic in the solid form, for example in the form of granules or flakes, into molten plastic or molten polymer.

[0044] Extruder 3 is connected to reactor 2, in particular to the inlet 21 of reactor 2, so that the molten polymer generated by extruder 3 can be sent in reactor 2. In other words, reactor 2 is adapted to receive the molten polymer generated by extruder 3.

[0045] Extruder 3 is provided with a motor 31 . Motor 31 , in particular, is connected to the screw 32 of the extruder, and controls the rotation thereof, in particular it controls the rotation speed thereof. The flow rate of the molten polymer supplied by extruder 3 depends on the speed of the screw 32 of extruder 3 set by motor 31 . Motor 31 preferably is an electric motor.

[0046] An electronic control unit 41 adapted to control the motor 31 of extruder 3 is preferably provided. The electronic control unit 41 advantageously can be (electronically) connected to said at least one level sensor 20 and can be configured to adjust the flow rate of molten polymer exiting extruder 3 according to values detected by said at least one level sensor 20.

[0047] In particular, the electronic control unit 41 is configured to adjust the rotation speed of the screw 32 of extruder 3 according to values detected by said at least one level sensor 20.

[0048] More particularly, the electronic control unit 41 is configured to adjust the flow rate of molten polymer exiting extruder 3 according to values detected by said at least one level sensor 20 so as to keep substantially constant the level of molten polymer in reactor 2, preferably with a tolerance range of ± 3%, preferably of ± 1 %, with respect to the predetermined level. For example, the electronic control unit 41 may decrease the flow rate of molten polymer exiting extruder 3, in particular by decreasing the rotation speed of screw 32, if said at least one level sensor 20 detects that the level of molten polymer in reactor 2 is greater than a predetermined level. Moreover, preferably the electronic control unit 41 may increase the flow rate of molten polymer exiting extruder 3, in particular by increasing the rotation speed of screw 32, if said at least one level sensor 20 detects that the level of molten polymer in reactor 2 is less than said predetermined level.

[0049] Preferably, said at least one level sensor 20 is a linear position sensor, preferably capacitive or inductive or radar; and / or said at least one level sensor 20 is adapted to take a continuous measurement, although it may be alternatively provided that the monitoring is performed discretely, in particular with at least two level sensors 20.

[0050] Optionally, a filter 7, or filtering device, adapted to filter the molten polymer generated by extruder 3 before it enters reactor 2, is provided between extruder 3 and reactor 2.

[0051] Apparatus 1 in all the embodiments comprises a pump 5 provided with a motor 51 , the pump being adapted to receive the molten polymer exiting reactor 2. In particular, pump 5 is (fluidically) arranged downstream of reactor 2 and is adapted to receive the molten polymer exiting the outlet 29 of reactor 2. Pump 5 and reactor 2 are preferably mutually distinct components.

[0052] Advantageously, in all the embodiments, apparatus 1 comprises at least one pressure sensor 50 (i.e. , one or more), in particular arranged downstream of pump 5, adapted to measure the pressure of the molten polymer exiting pump 5, in particular the pressure of the molten polymer in a manifold 6 downstream of pump 5. In particular, said at least one pressure sensor 50 preferably is arranged, in particular at least partially arranged, in said manifold 6.

[0053] Pump 5 preferably is a gear pump with gears 59. In particular, motor 51 is adapted to control the movement speed of the gears 59 of pump 5. Said at least one pressure sensor 50 in particular is adapted to measure the pressure of the molten polymer downstream of the gears 59. The aforesaid manifold 6 in particular is arranged downstream of the gears 59 of pump 5. Advantageously, there is provided an electronic control unit 42 (electronically) connected to said at least one pressure sensor 50, adapted to control the motor 51 of pump 5 according to values detected by said at least one pressure sensor 50, preferably so as to keep substantially constant the pressure of the molten polymer exiting pump 5, preferably with a tolerance range of ± 5%, preferably of ± 1 %, with respect to a predetermined pressure value.

[0054] For example, the electronic control unit 42 may decrease the pressure of molten polymer exiting pump 5, in particular by decreasing the rotation speed of the gears 59 of pump 5, if said at least one pressure sensor 50 detects that the pressure of the molten polymer exiting pump 5, in particular in the manifold 6, is greater than a predetermined pressure value. Moreover, preferably, the electronic control unit 42 may increase the pressure of molten polymer exiting pump 5, in particular by increasing the rotation speed of the gears 59 of pump 5, if said at least one pressure sensor 50 detects that the pressure of the molten polymer exiting pump 5, in particular in manifold 6, is less than said predetermined pressure value.

[0055] Although it is preferable to provide two distinct electronic control units 41 , 42, it is possible to provide a single electronic control unit, or control system, which performs the function of the two electronic control units 41 , 42, i.e., capable controlling both the motor 31 of extruder 3 and the motor 51 of pump 5 according to the values detected by said at least one level sensor 20 and by said at least one pressure sensor 50, respectively.

[0056] Optionally, in all the embodiments, apparatus 1 comprises, downstream of pump 5, a forming or transforming machine (not shown), or more in general, a user machine adapted to receive the molten polymer exiting reactor 2, in particular exiting pump 5. The user machine may be adapted to produce bottle preforms, for example. The aforesaid at least one pressure sensor 50 is in particular arranged upstream of the user machine (in particular, forming or transforming machine).

[0057] The invention also relates to a process for treating molten polymer, in particular for degassing the molten polymer, by means of apparatus 1 , wherein reactor 2 is supplied with molten polymer coming from an extruder 3 provided with motor 31 ; and advantageously, the process provides that the motor 51 of pump 5 is controlled according to values detected by said at least one pressure sensor 50, in particular so as to keep substantially constant the pressure of the molten polymer exiting pump 5, preferably with a tolerance range of ± 5%, preferably of ± 1 %.

[0058] In particular, it can be provided that the pressure of molten polymer exiting pump 5 is decreased, in particular by decreasing the rotation speed of the gears 59 of pump 5, if said at least one pressure sensor 50 detects that the pressure of the molten polymer exiting pump 5, in particular in manifold 6, is greater than a predetermined pressure value; and preferably it can be provided that the pressure of molten polymer exiting pump 5 is increased, in particular by increasing the rotation speed of the gears 59 of pump 5, if said at least one pressure sensor 50 detects that the pressure of the molten polymer exiting pump 5, in particular in manifold 6, is less than said predetermined pressure value.

[0059] Preferably, the level of molten polymer in reactor 2 is detected in the process by means of said at least one level sensor 20; and the flow rate of molten polymer exiting extruder 3 is adjusted by means of the electronic control unit 41 adapted to control the motor 31 of extruder 3 according to values detected by said at least one level sensor 20.

[0060] In particular, the flow rate of molten polymer exiting extruder 3 is increased or decreased to keep the level of molten polymer in reactor 2 substantially constant, preferably with a tolerance range of ± 3%, preferably of ± 1 %.

[0061] In greater detail, it may be provided that the flow rate of molten polymer exiting extruder 3 is decreased, in particular by decreasing the rotation speed of screw 32, if said at least one level sensor 20 detects that the level of molten polymer in reactor 2 is greater than a predetermined level; and preferably, that the flow rate of molten polymer exiting extruder 3 is increased, in particular by increasing the rotation speed of screw 32, if said at least one level sensor 20 detects that the level of molten polymer in reactor 2 is less than said predetermined level.

Claims

CLAIMS1. An apparatus (1 ) for treating molten polymer, comprising a reactor (2) for degassing the molten polymer, wherein there is provided at least one level sensor (20) arranged inside the reactor (2), said at least one level sensor (20) being adapted to detect the level of molten polymer in the reactor (2); the apparatus (1 ) comprising a pump (5) provided with a motor (51 ), the pump (5) being adapted to receive the molten polymer exiting the reactor (2); wherein there is provided at least one pressure sensor (50) adapted to measure the pressure of the molten polymer exiting the pump (5); wherein there is provided a first electronic control unit (42) connected to said at least one pressure sensor (50), adapted to control the motor (51 ) of the pump (5) according to values detected by said at least one pressure sensor (50).

2. An apparatus (1 ) according to claim 1 , wherein there is provided a perforated plate (22) arranged in the reactor (2), through which the molten polymer can pass to generate molten polymer filaments.

3. An apparatus (1 ) according to claim 1 or 2, comprising an extruder (3) provided with a motor (31 ) arranged upstream of the reactor (2), wherein the reactor (2) is adapted to receive the molten polymer generated by the extruder (3); wherein there is provided a second electronic control unit (41 ) adapted to control the motor (31 ) of the extruder (3), connected to said at least one level sensor (20), said second electronic control unit (41 ) being configured to adjust the flow rate of molten polymer exiting the extruder (3) according to values detected by said at least one level sensor (20).

4. An apparatus (1 ) according to claim 3, wherein said second electronic control unit (41 ) is configured to adjust the flow rate of molten polymer exiting the extruder (3) according to values detected by said at least one level sensor (20) so as to keep substantially constant the level of molten polymer in the reactor (2), preferably with a tolerance range of ± 3%, preferably of ± 1 %.

5. An apparatus (1 ) according to any one of the preceding claims, wherein said at least one level sensor (20) is a linear position sensor, preferably capacitive orinductive or radar; and / or wherein said at least one level sensor (20) is adapted to take a measurement in continuous manner.

6. An apparatus (1 ) according to any one of the preceding claims, wherein said at least one pressure sensor (50) is arranged in a manifold (6) downstream of the pump (5) and in particular is adapted to measure the pressure of the molten polymer exiting the pump (5) in said manifold (6).

7. An apparatus according to any one of the preceding claims, wherein said first electronic control unit (42) is adapted to control the motor (51 ) of the pump (5) according to values detected by said at least one pressure sensor (50) so as to keep substantially constant the pressure of the molten polymer exiting the pump (5), preferably with a tolerance range of ± 5%, preferably of ± 1 %.

8. An apparatus (1 ) according to claim 6 or 7, wherein the pump (5) is a gear (59) pump; wherein the motor (51 ) is adapted to control the movement speed of the gears (59) of the pump (5) and wherein said at least one pressure sensor (50) is adapted to measure the pressure of the molten polymer downstream of the gears (59), in particular in a manifold (6) downstream of the gears (59).

9. A process for processing molten polymer, in particular for degassing the molten polymer, by means of an apparatus (1 ) according to any one of the preceding claims, wherein the reactor (2) is supplied with molten polymer coming from an extruder (3) provided with a motor (31 ); wherein the motor (51 ) of the pump (5) is controlled by the first electronic control unit (42) according to values detected by said at least one pressure sensor (50), preferably so as to keep substantially constant the pressure of the molten polymer exiting the pump (5), preferably with a tolerance range of ± 5%, preferably of ± 1 %.

10. A process according to claim 9, wherein the level of molten polymer in the reactor (2) is detected by means of said at least one level sensor (20); and wherein the flow rate of molten polymer exiting the extruder (3) is adjusted by means of a second electronic control unit (41 ) adapted to control the motor (31 ) of the extruder (3) according to values detected by said at least one level sensor (20); preferably to keep the level of molten polymer in the reactor (2) substantially constant, preferably with a tolerance range of ± 3%, preferably of ± 1 %.

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