Method of operating a filter device and filter device

Abstract

The invention relates to a method for operating a filter device for a polymer melt to be filtered, the filter device comprising at least one first and a second large-area filter, a first and a second valve, a first and a second drain valve, the polymer melt to be filtered is passed under pressure through the filter device, the first and the second inlets are connected to a common inlet and the first and the second drains are connected to a common drain. According to the invention, the polymer melt to be filtered is fed simultaneously to both the first and the second large-area filters in the filtering direction, in the basic operation parallel filtration is carried out successively through the first and the second large-area filters. In the backwash operation filtration is carried out only through one of the large-area filters. The backwash operation is started when the large-area filters reach a predetermined degree of contamination, i.e. when it is necessary to clean the first large-area filter using the backwash operation.

Description

Technical Field

[0001] The present invention relates to a method for operating a filter device as defined in the preamble of claim 1, and to a filter device for carrying out said method as defined in claim 21.

Background Art

[0002] Particularly in the production of thermoplastics, it is common to remove foreign substances from a polymer melt by filtering the polymer melt. Large-area filters are generally used for this purpose, and the large-area filter comprises a filter chamber in which a plurality of (usually 37 to 169) filter cartridges are arranged. The large number of filter cartridges ensures a large filter surface. In this process, the substance to be filtered flows from the outside to the inside through the filter cartridges. The polymer melt to be filtered is filtered through the side wall of the filter cartridge. The side wall usually has a filtration accuracy of 3 μm to 20 μm.

[0003] For this purpose, it is common to use so-called double filter units. These double filter units have two identical filter means. Each filter means has a cylindrical filter chamber to which a large-area filter is respectively attached. The filter chamber and the large-area filter installed therein are preferably aligned vertically, and the substance to be filtered flows through them from the lower part to the upper part. A large-area filter is a filter comprising several filter cartridges arranged on a distributor. The filter cartridges and the distributor divide the filter chamber into an inflow zone and an outflow zone. The polymer melt is supplied to the filter cartridges via the inlet to the filter chamber. The supply of the polymer melt is controlled via inlet valves arranged at individual inlets to the filter chamber. The side wall of the filter cartridge constitutes the filter part. More specifically, the side wall can be formed into a corrugated shape in the circumferential direction or any other shape so as to increase the filter surface. The filter surface used is, for example, 45m2 ~255m 2 This is the sum of the sidewall surfaces of all filter cartridges. The filtered polymer melt passes through the sidewalls downstream of the distributor to the drain zone of the filter chamber, and then to the drain section from the filter chamber. The polymer melt is supplied to the filtration device via a pump. A multilayer disk filter can also be used instead of filter cartridges.

[0004] Both filtering means of a dual-filter system are always operated alternately, so that if one filter chamber with a contaminated large-area filter becomes contaminated, it can be switched to the other filter chamber with a clean large-area filter. This ensures continuous operation at all times.

[0005] To switch from one filtering system to the other, valves at the inlet and drain are switched as appropriate. The valve at the inlet to the filter chamber containing the contaminated large-area filter is closed, and the drain valve at the drain from the filter chamber containing the contaminated large-area filter is also closed. Simultaneously, the valve at the inlet to the other filter chamber containing the clean large-area filter is opened, and the drain valve at the drain from the filter chamber containing the clean large-area filter is also opened. The polymer melt in the filter chamber containing the contaminated large-area filter is discharged through the drain valve at the inlet. The entire filter chamber containing the contaminated large-area filter is then removed from the filtering device, or the filter chamber is opened, and the distributor with the filter cartridge is removed and carried out for cleaning. Depending on the type of polymer, a pyrolysis process, chemical solution, ultrasonic bath, or high-pressure washer is used for cleaning, which removes plastic and foreign matter removed by filtration from the side walls of the filter cartridge.

[0006] However, a drawback of conventional filter systems is that, due to the parallel filter units not used in dual-filter systems, the total filter surface is always twice the size of that used in the basic operating mode of a dual-filter system. As a result, investment costs are extremely high, and capital is tied up. Furthermore, cleaning requires a great deal of effort and time, especially if the filter equipment must be transported to a specialized company for cleaning. In addition, the cleaning processes required so far are undesirable from an environmental perspective. [Overview of the project]

[0007] Therefore, an object of the present invention is to further develop the method of operating the type of filter device specified in the preamble of claim 1, so as to avoid the aforementioned drawbacks, improve the efficiency of the filter device, and still ensure continuous operation.

[0008] This objective is achieved by combining the features of claim 1 with the features of its preamble, with respect to the method of operating the filter device.

[0009] The dependent claims relate to advantageous further embodiments of the present invention.

[0010] The present invention is based on the insight that parallel operation of both filter chambers reduces the total filter surface area, thus halving the overall size of the dual-filter system and providing a significant cost advantage. Furthermore, in the event of contamination of one of the large-area filters, filtration continues using only the other large-area filter, while the other large-area filter is cleaned by backwashing with polymer melt already filtered by the other large-area filter. Continuous operation is maintained even during backwashing.

[0011] Therefore, the present invention is for a polymer melt to be filtered that is simultaneously supplied in the filtration direction to both a first large-area filter and a second large-area filter. In the basic operating mode, parallel and simultaneous filtration through the first and second large-area filters is performed continuously. In the backwashing operating mode, filtration of the polymer melt to be filtered is performed using only one of the large-area filters. The backwashing operating mode is started when both large-area filters reach a predetermined level of contamination, that is, when it is necessary to clean the first large-area filter using the backwashing operating mode.

[0012] After cleaning the first large-area filter, the second large-area filter can be cleaned by backwashing. Backwashing one large-area filter always requires backwashing the other large-area filter.

[0013] Preferably, during the backwash operation mode, the flow direction of the filtered polymer melt is reversed and passed through one of the large-area filters, thereby removing impurities from this one large-area filter. This is a simple method that eliminates the need for a complex multi-stage cleaning process, thereby improving the efficiency of the filtering device.

[0014] In particular, when certain parameters for one of the large-area filters are met, a backwash operation is initiated for that filter. These predetermined parameters are related to the degree of contamination of that large-area filter.

[0015] After cleaning one large-area filter, preferably followed by cleaning the other large-area filter, the dual-filter system returns to the basic operating mode with parallel filtering of both large-area filters until the backwash parameters are again met and the next backwash cycle is triggered. The basic operating mode and the backwash operating mode can be alternated many times, thereby extending the lifespan of the dual-filter system.

[0016] In certain embodiments of the present invention, during the backwash operation mode, the inflow to one large-area filter is interrupted, and at least a portion of the filtered polymer melt from the other large-area filter is supplied in the opposite direction to the filtration through the drain of the one large-area filter, passed through the one large-area filter to clean it by backwashing, and then discharged. Thus, the already filtered polymer melt is used to clean the contaminated large-area filter. The filtered polymer melt then absorbs foreign matter from the large-area filter and is discharged and discarded.

[0017] A valve located in the inlet area can be opened to discharge the contaminated polymer melt from one of the large-area filters, and the polymer melt that has been filtered by the other large-area filter and then backwashed through the first large-area filter can be discharged through the valve.

[0018] Preferably, in backwash operation mode, at least 1, preferably 1.5, and preferably 2 times the volume of the filter chamber of the one large-area filter is discharged through a valve at the inlet. A predetermined amount of backwash polymer melt is used to ensure thorough cleaning of the large-area filter.

[0019] To ensure that polymer melt is continuously supplied even in backwash mode, the drain section of one of the large-area filters is partially closed, for example, by 2 / 3, 1 / 3, or 1 / 2 via an associated drain valve for backwashing, so that only a portion of the filtered polymer melt from the other large-area filter is supplied to the first large-area filter for washing.

[0020] The cleaning effect in backwash mode can be improved by briefly opening and closing the inlet valve or drain valve of one of the large-area filters, and thus allowing the filtered polymer melt to flow through the one large-area filter several times, preferably at intervals, especially intermittently.

[0021] Preferably, the polymer melt to be filtered is a low-viscosity polymer melt, for example of 100 mPas, particularly comprising plastic raw materials, preferably molten plastic from chemical recycling.

[0022] A large-area filter having a filtration accuracy of up to 3 µm can be used. This removes particularly small foreign matters from the polymer melt.

[0023] The method according to the present invention preferably uses 45m 2 to 255m 2 large-area filter having the following filter surface.

[0024] The method according to the present invention particularly uses a large-area filter that withstands a differential pressure of 1 bar to 100 bar.

[0025] In order to determine the degree of contamination of the large-area filter, a predetermined parameter for the large-area filter for the backwashing operation mode is constituted by the pressure in the polymer melt to be filtered upstream of the large-area filter. Additionally or alternatively, the predetermined parameter can also be constituted by the differential pressure generated between the polymer melt to be filtered upstream of the large-area filter and the filtered polymer melt downstream of the large-area filter. Pressure measurement is a particularly suitable means for determining the degree of contamination of a large-area filter, because the large-area filter gradually clogs over time, which directly affects the pressure increase upstream of the large-area filter and the differential pressure. This facilitates determining the degree of contamination and initiating the backwashing operation mode when necessary.

[0026] It is also possible to form the predetermined parameter based on the operation time of the large-area filter. The predetermined operation time particularly reflects experience with the polymer melt to be filtered, that is, how long it takes on average for the large-area filter to become contaminated.

[0027] In the method according to the present invention, in the basic operation mode, there is laminar flow in the filtration direction through the large-area filter, and in the backwashing operation mode, there is pulsating flow opposite to the filtration direction through the large-area filter.

[0028] Preferably, in the backwash operation mode, the pressure in the polymer melt on the drain side of the filter chamber to be backwashed is generated by a melt pump arranged downstream of the drain side of the filter chamber.

[0029] On the drain side of the filter chamber to be backwashed, in the backwash operation mode, a higher pressure exists in the polymer melt compared with the differential pressure of the large-area filter immediately before the backwash operation mode is started.

[0030] In the backwash operation mode, the pressure in the polymer melt on the drain side of the filter chamber having the large-area filter to be backwashed can be generated by piping and / or system components such as a throttle or a melt pump arranged downstream thereof.

[0031] And for example, in the backwash operation mode, it is possible to completely close the throttle arranged downstream of the large-area filter and use all of the filtered polymer melt from the first large-area filter to backwash the second large-area filter.

[0032] In particular, a method of implementing a filter device comprises: a first filter chamber having a first large-area filter arranged therein; a second filter chamber having a second large-area filter arranged therein; a first inflow portion including a first inflow valve to the first filter chamber; a second inflow portion including a second inflow valve to the second filter chamber; a first drain portion from the first filter chamber; a second drain portion from the second filter chamber; a first drain valve at the first drain portion; and a second drain valve at the second drain portion. Preferably, the inflow valves and drain valves are designed to be hydraulic and / or electrically driven, and a control device is provided that controls the inflow valves and drain valves to set the basic operation mode and set the backwash operation mode.

[0033] Pressure sensors can be installed upstream and downstream of the filter chamber to measure the pressure in the polymer melt, which may be necessary to determine the degree of contamination of large-area filters in individual filter chambers.

[0034] More specifically, pressure sensors for measuring the pressure in the polymer melt can be installed upstream and downstream of the large-area filter in the melt tube, thus enabling the detection of the differential pressure across the large-area filter.

[0035] In one embodiment of the present invention, the filter surface of the large-area filter in the filter chamber is composed of a stacked disk filter or a filter cartridge.

[0036] To simplify manufacturing and maintenance, individual filter chambers, large-area filters, inlet valves, and / or drain valves are all identical in design.

[0037] For example, melt pumps can be placed in the common drain pipe and / or the left and right drain pipes, and these can be used to control both the basic operation mode and the backwash operation mode.

[0038] Further advantages, features, and possible applications of the present invention will become apparent from the following description with reference to the illustrated embodiments.

[0039] Throughout this specification, the claims, and the drawings, the terms and associated reference numerals are used as set forth in the following list of reference numerals. The drawings are as follows: [Brief explanation of the drawing]

[0040] [Figure 1] Figure 1 is a schematic diagram showing the basic operating mode of a filter device according to the first embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing the backwash operation mode of the filter device shown in Figure 1. [Figure 3]Figure 3 is a schematic diagram showing the conventional operating mode of the filter device shown in Figure 1. [Figure 4] Figure 4 is a schematic diagram showing the basic operating mode of a filter device according to a second embodiment of the present invention. [Figure 5] Figure 5 is a schematic diagram showing the backwash operation mode of the filter device shown in Figure 4. [Figure 6] Figure 6 is a schematic diagram showing the basic operating mode of a filter device according to a third embodiment of the present invention. [Figure 7] Figure 7 is a schematic diagram showing the backwash operation mode of the filter device shown in Figure 6. [Figure 8] Figure 8 is a schematic diagram showing the basic operating mode of a filter device according to the fourth embodiment of the present invention. [Figure 9] Figure 9 is a schematic diagram showing the backwash operation mode of the filter device shown in Figure 8. [Figure 10] Figure 10 is a schematic diagram showing the backwash operation mode of a filter device according to the fifth embodiment of the present invention. [Modes for carrying out the invention]

[0041] Figures 1 and 2 show a filter device 10 for a polymer melt to be filtered, according to a first embodiment of the present invention. The filter device 10 comprises a left filter chamber 12 and a right filter chamber 14. The lower regions 12a of filter chamber 12 and 14a of filter chamber 14 are designed as distributors, respectively. Inlet pipes 16 and 18 are connected to the lower regions 12a and 14a, with the left inlet pipe 16 terminating in the lower region 12a of the left filter chamber 12 and the right inlet pipe 18 terminating in the lower region 14a of the right filter chamber 14.

[0042] On the sides of the inlet pipes 16 and 18 furthest from the filter chambers 12 and 14, these pipes are connected to a common inlet pipe 20. In the region of the common inlet pipe 20, the left inlet pipe 16 has a left stop valve 22, and the right inlet pipe 18 has a right stop valve 24. The left stop valve 22 can be used to control the flow of polymer melt to be filtered into the left filter chamber 12, and the right stop valve 24 can be used to control the flow of polymer melt to be filtered into the right filter chamber 14.

[0043] The left drain valve 26 is connected downstream of the left stop valve 22 in the direction of polymer melt flow in the basic operating mode, and the right drain valve 28 is connected downstream of the right stop valve 24. The polymer melt can be discharged from the individual inlet pipes 16 and 18 via the left and right drain valves 26 and 28 as needed.

[0044] The left filter chamber 12 houses a left large-area filter 30 having multiple filter cartridges 30a. The right filter chamber 14 houses a right large-area filter 32 having multiple filter cartridges 32a. The filter cartridges 30a and 32a are aligned vertically and parallel to each other, and terminate in the upper region at the left distributor 34 or the right distributor 36, respectively. Each large-area filter comprises, for example, 169 filter cartridges.

[0045] The filter cartridge 30a is terminated at the left distributor 34, so that the polymer melt passed through the filter cartridge 30a from the outside to the inside is combined at the left distributor 34 and discharged through the left drain pipe 38 which is connected to the top of the filter chamber 12.

[0046] The filter cartridge 32a is terminated at the right distributor 36, so that the polymer melt passed through the filter cartridge 32a from the outside to the inside is combined at the right distributor 36 and discharged through the right drain pipe 40 which is connected to the top of the filter chamber 14.

[0047] The left drain pipe 38 and the right drain pipe 40 merge into a common drain pipe 42.

[0048] Upstream of the common drain pipe 42, a left stop valve 44 is attached to the left drain pipe 38, and a right stop valve 46 is attached to the right drain pipe 40. The left stop valve 44 and the right stop valve 46 can be used to shut off and open the left drain pipe 38 and the right drain pipe 40, respectively.

[0049] The left vent valve 48 is connected upstream of the left stop valve 44 with respect to the polymer melt flow direction in the basic operating mode. Similarly, the right vent valve 50 is connected upstream of the right stop valve 46 with respect to the polymer melt flow direction in the basic operating mode. These vent valves can be used to vent each side of the filter device 10.

[0050] The polymer melt to be filtered is sent through the large-area filters 30, 32 in the filter chambers 12, 14 to the common drain pipe 42 by a melt pump (not shown in detail) or by the melt pressure applied to the common inlet pipe 20 due to the process, and thus sent through the filter device 10. Different pressures are created in the polymer melt upstream and downstream of the large-area filters 30, 32. To measure this differential pressure, a pressure sensor 56 is used to measure the individual large-area filters 30 The pressure sensor 58 is located upstream of the 32, and downstream of each large-area filter 30,32.

[0051] Both sides of the filter device 10 have the same components; that is, filter chamber 12 corresponds to filter chamber 14, large-area filter 30 corresponds to large-area filter 32, and so on.

[0052] Large-area filters 30 and 32 are used with a maximum filtration accuracy of 3 μm. Preferably, the filter surface of one of the large-area filters 30 or 32 is 45 m 2 More than 255m 2The following range applies: The differential pressure across the large-area filters 30 and 32 is between 1 bar and 100 bar.

[0053] In the basic operating mode, the polymer melt to be filtered is simultaneously supplied to both the left large-area filter 30 and the right large-area filter 32 in the filtration direction, as indicated by the arrow 52 in Figure 1. Therefore, parallel filtration is continuously performed by the left and right large-area filters 30 and 32. The basic operating mode is shown in Figure 1.

[0054] In this case, the left stop valve 22 in the left inlet pipe 16 and the right stop valve 24 in the right inlet pipe 18, as well as the left stop valve 44 in the left drain pipe 38 and the right stop valve 46 in the right drain pipe 40, are all open. Through the common inlet pipe 20, the polymer melt to be filtered flows into the left inlet pipe 16 and the right inlet pipe 18 in equal proportions.

[0055] From the left inlet pipe 16, the polymer melt to be filtered contained in the distributor 12a spreads into the filter chamber 12 and penetrates the filter wall of the filter cartridge 30a. The polymer melt that has just been filtered from the filter cartridge 30a is remixed via the distributor 34 and flows through the left drain pipe 38 and the open left stop valve 44 into the common drain pipe 42.

[0056] Similarly, the polymer melt to be filtered in the distributor 14a, supplied through the right inlet pipe 18, flows into the filter chamber 14 and penetrates the filter wall of the filter cartridge 32a. The polymer melt, just filtered from the filter cartridge 32a, is remixed via the distributor 36 and flows through the right drain pipe 40 and through the open right stop valve 46 into the common drain pipe 42.

[0057] Figure 2 shows the backwash operation mode, i.e., the backwashing and cleaning of the right large-area filter 32. By reversing the flow direction of the filtered polymer melt and passing the polymer melt through the right large-area filter 32, foreign matter is removed from the filter using the filtered polymer melt. In the backwash operation mode, filtration continues using only the left large-area filter 30. During the backwashing and cleaning of the left large-area filter 30, the polymer melt is filtered only by the right large-area filter 32.

[0058] The backwash operation mode is started as soon as the two large-area filters 30 and 32 reach a predetermined level of contamination, that is, as soon as it becomes necessary to clean the large-area filters 30 and 32 using the backwash operation mode.

[0059] In the example shown in Figure 2, a predetermined level of contamination is reached, and the backwash operation mode for the large-area filter 32 on the right is initiated.

[0060] To initiate the backwash operation mode on the right side, first the right stop valve 24 is closed, thus blocking the right inlet pipe 18. Next, the right stop valve 46 is closed, blocking the right drain pipe 40. Subsequently, the right drain valve 28 is opened, allowing the polymer melt to exit the right inlet pipe 18. Then the right stop valve 46 is opened again to cause backwashing through the right large-area filter 32. The opening and closing of the right stop valve 46 can be performed at predetermined time intervals, resulting in a pulsating backwash operation mode. Alternatively, the stop valve 46 can be kept open throughout the entire backwash process, allowing the backwashed polymer melt to flow laminarly through the right large-area filter 32.

[0061] Once backwashing is complete, the right drain valve 28 closes and the right stop valve 24 opens. In this way, the filter device 10 returns to its basic operating mode.

[0062] In the backwash operation mode of the right large-area filter 32, the flow direction of the filtered polymer melt is reversed, and the filtered polymer melt passes through the right large-area filter 32, thus removing foreign matter. The polymer melt is filtered exclusively through the left large-area filter 30. The filtered polymer melt flows against the filtration direction, as indicated by arrow 54, until the large-area filter 32 having the filter cartridge 32a is completely cleaned. In this process, as a rule, an amount between one and two times the volume of the right filter chamber 14 is discharged.

[0063] When the backwash operation mode for the right large-area filter 32 is completed and the basic operation mode is resumed, the backwash operation mode is automatically started for the left large-area filter 30.

[0064] To initiate the backwash operation mode on the left side, the left stop valve 22 is first closed, thus blocking the left inlet pipe 16. Then the left stop valve 44 is closed, blocking the left drain pipe 38. Subsequently, the left drain valve 26 is opened, allowing the polymer melt to exit the left inlet pipe 16. Then the left stop valve 44 is opened again, causing backwashing through the left large-area filter 30. The left stop valve 44 can be opened and closed at predetermined time intervals, resulting in a pulsating backwash mode through the left large-area filter 30. Alternatively, the stop valve 44 can be kept open throughout the entire backwash operation, allowing the backwashed polymer melt to flow laminarly through the left large-area filter 30.

[0065] During the backwashing of the left large-area filter 30, the polymer melt is filtered exclusively through the right large-area filter 32. The filtered polymer melt is then flowed against the filtration direction, as indicated by arrow 54, until the large-area filter 30, which has a filter cartridge 30a, is completely cleaned. In this process, an amount of polymer melt is discharged that is between one and two times the volume of the left filter chamber 12.

[0066] Once the left large-area filter 30 is cleaned, the backwash operation mode, and therefore the backwash cycle in which both the large-area filters 30 and 32 are sequentially cleaned, ends, and the basic operation mode is restarted as described above.

[0067] The backwash cycle is initiated as soon as predetermined parameters for the backwash operation mode are met. These parameters can be comprised of the pressure generated in the polymer melt to be filtered upstream of the large-area filters 30,32, as measured by pressure sensor 56. Additionally or alternatively, these parameters can be comprised of the differential pressure generated between the polymer melt to be filtered upstream of the large-area filters 30,32 and the filtered polymer melt downstream of the large-area filters, the pressures of which are measured by pressure sensors 56 and 58, respectively. Additionally or alternatively, the parameters can also be comprised of the operating time since the commissioning and / or last backwash of the large-area filters 30,32.

[0068] The stop valves 22 and 24 in the inlet pipes 16 and 18, the drain valves 26 and 28 in the inlet pipes 16 and 18, the stop valves 44 and 46 in the drain pipes 38 and 40, and the vent valves 48 and 50 in the drain pipes 38 and 40 are hydraulic and / or electrically operated and controlled by the control unit 60. For this purpose, the control unit 60 is connected to the corresponding actuators. For clarity, the pipe connections and valve actuators are not shown. Furthermore, the control unit 60 is connected to pressure sensors 56 and 58 for measuring the respective pressures in the polymer melt.

[0069] As already explained, instead of setting the stop valves 44 and 46 in the drain pipes 38 and 40 to a constant setting, for example, being closed only one-third of the way, in the backwash operation mode, the stop valves 44 and 46 in the drain pipes 38 and 40 of the large-area filters 30 and 32 to be backwashed can be opened and closed continuously for short periods of time to induce an intermittent flow of filtered polymer melt through these large-area filters 30 and 32. Both the basic operation mode and the backwash operation mode are controlled via the control unit.

[0070] Figures 4 and 5 illustrate yet another embodiment of the present invention, which essentially corresponds to the embodiment described with reference to Figures 1 and 2. Therefore, the same reference numerals are used to refer to the same parts. The only difference is that the adjustable throttle 62 is attached to the common drain pipe 42. Figure 4 shows the basic operating mode, and Figure 5 shows the backwashing operating mode on the right side. In the backwashing operating mode on the right side, the adjustable throttle 62 is used to increase the pressure upstream of the throttle 62, and thus ensure that the polymer melt is backwashed into the right large-area filter 32.

[0071] Figures 6 and 7 illustrate yet another embodiment of the present invention, which essentially corresponds to the embodiment described with reference to Figures 1 and 2. Therefore, the same reference numerals are used to refer to the same parts. The only difference is that the adjustable throttle 64 is mounted on the common drain pipe 42. Figure 6 shows the basic operating mode, and Figure 7 shows the backwashing operating mode on the right side. In the backwashing operating mode on the right side, the adjustable throttle 64 is used to increase the pressure upstream of the throttle 64, and thus ensure that the polymer melt is backwashed into the right large-area filter 32.

[0072] Figures 8 and 9 illustrate yet another embodiment of the present invention, which essentially corresponds to the embodiment described with reference to Figures 1 and 2. Therefore, the same reference numerals are used to refer to the same parts. The only difference is that the left control melt pump 66 is attached to the left drain pipe 38, and the right control melt pump 68 is attached to the right drain pipe 40. Figure 8 shows the basic operating mode, and Figure 9 shows the backwashing operating mode on the right side. In the backwashing operating mode on the right side, the control melt pumps 66 and 68 are used to ensure that the polymer melt is backwashed into the right large-area filter 32.

[0073] Figure 10 shows yet another embodiment of the present invention. This essentially corresponds to the embodiment described with reference to Figures 1 and 2. Thus, the same reference numerals are used to refer to the same parts. This figure shows the backwash operation mode with the throttle 62 closed, so that the entire flow of washed polymer from the left large-area filter 30 flows into the right large-area filter 32 and flows through it in the reverse direction for washing.

[0074] The present invention is characterized by providing a simple method for cleaning large-area filters 30 and 32 using already filtered polymer melt. This significantly reduces costs and allows for a substantial reduction in the size of the filter device 10 by operating both large-area filters 30 and 32 simultaneously in basic operating mode. [Explanation of Symbols]

[0075] 10 Filter device 12 Left filter chamber 12a Lower region of the left filter chamber 12 14 Right filter chamber 14a Lower region of the right filter chamber 14 16 Left inflow pipe 18 Right inflow pipe 20 Common inflow pipe 22 Left stop valve 24 Right stop valve 26 Left drain valve 28 Right drain valve 30 Large-area filter on the left 30a Left Large Area Filter 30 Filter Cartridge 32 Right Large Area Filter 32a Right Large Area Filter 32 Filter Cartridge 34 Left distributor 36 Right distributor 38 Left drain pipe 40 Right drain pipe 42 Common drain pipe 44 Left stop valve 46 Right stop valve 48 Left vent valve 50 Right vent valve 52 Arrows indicating the flow direction of polymer melt during basic operation. 54 Arrows indicating the flow direction of polymer melt during backwash operation. 56. Pressure sensor upstream of large-area filters 30, 32 58 Pressure sensor downstream of large-area filters 30,32 60 Control device 62 Adjustable Throttle 64 Controlled melt pump 66 Left-hand controlled melt pump 68 Right-hand controlled melt pump

Claims

1. A method for operating a filter device (10) for a polymer melt to be filtered, wherein the filter device is At least one first large-area filter (30, 32) is provided in the first filter chamber (12, 14), and a second large-area filter (30, 32) is provided in the second filter chamber (12, 14), To control the polymer melt to be filtered, a first valve (22, 24) is provided at the first inlet (16, 18) to the first filter chamber (12, 14), and a second valve (22, 24) is provided at the second inlet (16, 18) to the second filter chamber (12, 14), A first stop valve (44, 46) is provided in the first drain section (38, 40) for filtered polymer melt from the first filter chamber (12, 14), and a second stop valve (44, 46) is provided in the second drain section (38, 40) for filtered polymer melt from the second filter chamber (12, 14), The system comprises a first drain valve (26, 28) configured to discharge polymer melt from the first inlet (16, 18), and a second drain valve (26, 28) configured to discharge polymer melt from the second inlet (16, 18), The polymer melt to be filtered is sent under pressure through the filter device (10). The first inlet (16, 18) and the second inlet (16, 18) are connected to a common inlet (20), and the first drain section (38, 40) and the second drain section (38, 40) are connected to a common drain section (42). The filter device is configured to perform a basic operation mode and a backwash operation mode. In the aforementioned basic operating mode, With the first and second valves (22, 24) and the first and second stop valves (44, 46) all open, the polymer melt to be filtered is simultaneously supplied from the first and second inlets (16, 18) to the first and second large-area filters (30, 32) in the filtration direction, so that filtration by the first and second large-area filters (30, 32) is performed in parallel. In the aforementioned backwash operation mode, Of the first and second large-area filters (30, 32), one is designated as the filtration-side filter and the other as the backwash-side filter, and of the first and second inlets (16, 18), one corresponding to the filter chamber in which the filtration-side filter is provided is designated as the filtration-side inlet and the other as the backwash-side inlet. With one of the first and second valves (22, 24) located at the filtration-side inlet open and the other closed, the polymer melt to be filtered is supplied from the filtration-side inlet to the filtration-side filter in the filtration direction, so that filtration by the filtration-side filter is performed, With both the first and second stop valves (44, 46) open, and one of the first and second drain valves (26, 28) corresponding to the backwash side inlet open, the filtered polymer melt filtered by the filtration side filter is supplied to the backwash side filter in the direction opposite to the filtration direction, thereby cleaning the backwash side filter. The aforementioned backwash operation mode is, A method characterized in that it is started when either of the first and second large-area filters (30, 32) reaches a predetermined level of contamination, that is, when it is necessary to clean the large-area filters (30, 32) using a backwash operation.

2. In the method according to claim 1, A method characterized in that, after cleaning the first large-area filter (30, 32) by the backwash operation mode, the backwash operation mode for the second large-area filter (30, 32) is started.

3. In the method according to claim 1, A method characterized in that, during the backwash operation mode, the flow direction of the filtered polymer melt is reversed and passed through the backwash side filter, thereby removing foreign matter from the backwash side filter.

4. In the method according to claim 1, The method is characterized in that the backwash operation mode for cleaning the backwash side filter is started when predetermined physical parameters are present in the polymer melt for the backwash side filter.

5. In the method according to claim 4, In the aforementioned backwash operation mode, When one of the first and second valves (22, 24) provided at the backwash side inlet is closed, the inflow of polymer melt into the backwash side filter is interrupted. A method characterized in that both the first and second stop valves (44, 46) are opened, and one of the first and second drain valves (26, 28) corresponding to the backwash side inlet is opened, thereby supplying at least a portion of the filtered polymer melt from the filtration side filter through the drain portion of the backwash side filter in the opposite direction to the filtration direction, passing through the backwash side filter to clean the backwash side filter by backwashing, and being discharged from the drain valve.

6. In the method according to claim 5, A method characterized in that the drain valves (26, 28) located in the region of the inlet (16, 18) are opened to discharge filtered polymer melt from the backwash side filter, and the drain valves (26, 28) are used to discharge polymer melt that has been filtered by the filtration side filter and then backwashed through the backwash side filter.

7. In the method according to claim 1, A method characterized in that, in the backwash operation mode, at least one, preferably 1.5, and preferably 2 times the volume of the filter chamber (12, 14) of the backwash side filter is discharged through the drain valve (26, 28) in the inlet (16, 18).

8. In the method according to claim 1, The method is characterized in that, in the backwash operation mode, the drain portions (38, 40) of the backwash side filter are partially closed, for example, by 2 / 3, 1 / 3, or 1 / 2 via the associated stop valves (44, 46) for backwashing, thereby supplying only a portion of the filtered polymer melt from the filtration side filter to the backwash side filter for washing.

9. In the method according to claim 1, A method characterized in that, for the backwash operation mode, the filtered polymer melt flows through the backwash side filter, preferably several times, at intervals, particularly intermittently, by briefly opening and closing the stop valves (44, 46) of the backwash side filter.

10. In the method according to claim 1, A method characterized in that a low-viscosity polymer melt containing plastic raw materials, particularly molten plastic for chemical recycling, is used as the polymer melt to be filtered.

11. In the method according to claim 1, A method characterized in that the viscosity of the polymer melt to be filtered is in the range of 70 mPas to 90 mPas, and more particularly 80 mPas.

12. In the method according to claim 1, A method characterized by using the large-area filters (30, 32) having a filtration accuracy of up to 3 μm.

13. In the method according to claim 1, 45m ２ More than 255m ２ A method characterized by using the large-area filters (30, 32) having the following filter surfaces.

14. In the method according to claim 1, The method is characterized in that the large-area filters (30, 32) are used for differential pressures of 1 bar or more and 100 bar or less.

15. In the method of claim 2, A method characterized in that predetermined parameters for the large-area filters (30, 32) for the backwash operation mode are configured by the pressure applied to the large-area filters (30, 32) by the polymer melt to be filtered upstream of the large-area filters (30, 32), by the differential pressure generated between the polymer melt to be filtered upstream of the large-area filters (30, 32) and the filtered polymer melt downstream of the large-area filters (30, 32), and / or by the operating time of the large-area filters (30, 32).

16. In the method according to claim 1, The method is characterized in that, in the basic operating mode, there is a laminar flow in the filtration direction passing through the large-area filters (30, 32), and in the backwashing operating mode, there is a pulsating flow opposite to the filtration direction passing through the large-area filters (30, 32).

17. In the method according to claim 1, The method is characterized in that the pressure in the polymer melt on the drain side of the filter chamber (12, 14) to be backwashed is generated by a melt pump located downstream of the drain side of the filter chamber (12, 14) during the backwash operation mode.

18. In the method according to claim 17, The method is characterized in that, on the drain side of the filter chamber (12, 14) to be backwashed, the pressure generated in the polymer melt during the backwash operation mode is higher than the differential pressure applied to the large-area filter (30, 32) immediately before the backwash operation mode is started.

19. In the method according to claim 1, A method characterized in that the pressure in the polymer melt on the drain side of the filter chamber (12, 14) having the large-area filters (30, 32) to be backwashed is generated by pipes and / or system components, such as a throttle (62) located downstream thereof, in the backwash operation mode.

20. In the method according to claim 19, The method is characterized in that the throttle (62) located downstream of the large-area filters (30, 32) is completely closed in the backwash operation mode, and the entire filtered polymer melt from the first large-area filters (30, 32) is used to backwash the second large-area filters (30, 32).

21. A filter device (10) for carrying out the method according to any one of claims 1 to 20, The first filter chamber (12, 14) in which the first large-area filters (30, 32) are arranged, The second filter chamber (12, 14) in which the second large-area filters (30, 32) are arranged, The first inlet (16, 18) having the first valve (22, 24) to the first filter chamber (12, 14), The second inlet (16, 18) having the second valve (22, 24) to the second filter chamber (12, 14), The first drain section (38, 40) from the first filter chamber (12, 14), The second drain section (38, 40) from the second filter chamber (12, 14), The first stop valves (44, 46) provided in the first drain section (38, 40), The system includes the second drain section (38, 40) and the second stop valve (44, 46) provided therein, The valves (22, 24) and the stop valves (44, 46) are designed to be hydraulic and / or electrically operated. A filter device characterized by being provided with a control device (60) that controls the valves (22, 24) and the stop valves (44, 46) in order to set the basic operating mode and the backwashing operating mode, respectively.

22. In the filter device according to claim 21, A filter device characterized in that pressure sensors (56, 58) for measuring the pressure in the polymer melt are provided upstream and downstream of the filter chambers (12, 14).

23. In the filter device according to claim 21, A filter device characterized in that pressure sensors (56, 58) for measuring the pressure in a polymer melt are provided in the filter chambers (12, 14) upstream of the large-area filters (30, 32) and downstream of the large-area filters (30, 32).

24. In the filter device according to claim 21, A filter device characterized in that the filter surface of the large-area filter (30, 32) in the filter chamber is formed by a stacked disk filter or a filter cartridge (30a, 32a).

25. In the filter device according to claim 21, A filter device characterized in that all of the filter chambers (12, 14), all of the large-area filters (30, 32), all of the valves (22, 24), and / or all of the stop valves (44, 46) are of the same design.

26. In the filter device according to claim 21, A filter device characterized in that melt pumps (66, 68) are arranged in a common drain pipe (42) or in the first and second drain sections (38, 40).

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