Method for 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 performing said method as defined in claim 21. [Background technology]

[0002] Especially in the production of thermoplastics, it is common to filter the polymer melt to remove foreign matter from it. Large area filters are generally used for this purpose, which comprise a filter chamber in which a number of filter cartridges (usually 37 to 169) are arranged. The large number of filter cartridges ensures a large filter surface. In this process, the material to be filtered flows through the filter cartridges from the outside to the inside. The polymer melt to be filtered is filtered through the side walls of the filter cartridges. The side walls usually have a filtering precision of 3 μm to 20 μm.

[0003] For this purpose, it is common to use so-called duplex filter units. These duplex filter units have two identical filter means. Each filter means has a cylindrical filter chamber in which a large-area filter is respectively attached. The filter chambers and the large-area filters attached therein are preferably aligned vertically, through which the material to be filtered flows from bottom to top. The 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 inlet zone and an outlet zone. The polymer melt is fed to the filter cartridges via an inlet to the filter chamber. The feed of the polymer melt is controlled via an inlet valve arranged at the respective inlet to the filter chamber. The side walls of the filter cartridges constitute the filter parts. More specifically, the side walls can be circumferentially corrugated or in any other shape so as to increase the filter surface. The filter surface used is, for example, 45 m2 ~255m 2 where is the sum of the sidewall surfaces of all the filter cartridges. The filtered polymer melt exits through the sidewall downstream of the distributor to the drain zone of the filter chamber and to the drain from the filter chamber. The polymer melt is fed to the filter device via a pump. Instead of filter cartridges, stacked disc filters can also be used.

[0004] Both filter means of the dual filter device are always operated alternately, so that if one filter chamber with a contaminated large-area filter becomes contaminated, it is possible to switch to the other filter chamber with the other clean large-area filter, which ensures continuous operation at all times.

[0005] To switch from one filter means to the other, the valves in the inlet and drain are switched accordingly. The valve in the inlet to the filter chamber containing the contaminated large-area filter is closed, and the drain valve in the drain from the filter chamber containing the contaminated large-area filter is also closed. At the same time, the inlet valve to the other filter chamber containing the clean large-area filter is opened, and the drain valve in 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 via the drain valve in the inlet. Then, the entire filter chamber containing the contaminated large-area filter is removed from the filter device, or the filter chamber is opened and the distributor with the filter cartridge is removed and taken away for cleaning. Depending on the type of polymer, pyrolysis processes, chemical solutions, ultrasonic baths, high-pressure cleaners are used for cleaning, which remove plastic and filtered foreign matter from the side walls of the filter cartridge.

[0006] However, a disadvantage of the prior art method of operating a filter installation is that, due to the unused parallel filter units of the multiple filter installation, the total filter surface is always twice as large as that used in the basic operating mode of the multiple filter installation. This results in very high investment costs and tied up capital. Also, cleaning is very laborious and time-consuming, especially if the filter means have to be transported to a specialist company for cleaning. Also, the cleaning process required so far is disadvantageous from an environmental point of view. Summary of the Invention

[0007] The object of the present invention is therefore to further develop a method for operating a filter device of the type defined in the preamble of claim 1 in such a way that the aforementioned drawbacks are avoided while the efficiency of the filter device is increased and still continuous operation is ensured.

[0008] This object is achieved for a method for operating a filter device by the features of claim 1 in combination with the features of its preamble.

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

[0010] The invention is based on the insight that the parallel operation of both filter chambers reduces the total filter surface and therefore halves the overall size of the dual filter arrangement, resulting in considerable cost advantages, and that in case of contamination of one of the large area filters, this one is cleaned by backwashing with polymer melt already filtered by the other large area filter, while filtration continues using only the other large area filter. Continuous operation is maintained even during backwashing.

[0011] The invention thus provides for the polymer melt to be filtered to be fed simultaneously in the filtering direction to both the first and second large-area filters. In the basic operating mode, parallel and simultaneous filtration through the first and second large-area filters is performed continuously. In the backwash operating mode, filtration of the polymer melt to be filtered is performed using only one of the large-area filters. The backwash operating mode is initiated when both of the large-area filters have reached a predetermined degree of contamination, i.e. when the first large-area filter needs to be cleaned using the backwash operating mode.

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

[0013] Preferably, during a backwash mode of operation, one of the large area filters is cleared of foreign matter by reversing the flow direction of the filtered polymer melt and passing it through the large area filter, a simple method that eliminates the need for complex multi-step cleaning processes, thereby improving the efficiency of the filter apparatus.

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

[0015] After cleaning one of the large area filters, and preferably subsequently cleaning the other, the dual filter apparatus reverts to the basic operating mode with parallel filter operation of both of the large area filters until the backwash parameters are again met to trigger the next backwash cycle. The basic and backwash operating modes can be alternated multiple times, thereby extending the life of the dual filter apparatus.

[0016] In a particular embodiment of the present invention, during the backwash operation mode, the flow into the one large-area filter is interrupted, and at least a part of the filtered polymer melt of the other large-area filter is fed through the drain of the one large-area filter against the filtration direction, passed through the one large-area filter to clean the one large-area filter 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] In order to discharge the contaminated polymer melt from one of the large-area filters, a valve arranged in the area of ​​the inlet can be opened, and the polymer melt that has been filtered by the other large-area filter and then backwashed through the one of the large-area filters can be discharged via the valve.

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

[0019] In order to ensure that the polymer melt is continuously fed even in the backwash operation mode, the drain section of this 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 backwash, so that only a portion of the filtered polymer melt from the other large-area filter is fed to the one of the large-area filters for cleaning.

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

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

[0022] Large area filters with a filtering accuracy of up to 3 μm can be used, which removes particularly small foreign particles from the polymer melt.

[0023] The method according to the invention is preferably carried out 2 More than 255m 2 A large area filter is used with the following filter surface:

[0024] The method according to the invention uses in particular large area filters which are adapted for differential pressures between 1 bar and 100 bar.

[0025] In order to determine the degree of contamination of the large-area filter, the predetermined parameter for the large-area filter for the backwash 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 occurring 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 the large-area filter, since the large-area filter becomes increasingly clogged over time, which directly affects the pressure increase and the differential pressure upstream of the large-area filter. This makes it easier to determine the degree of contamination and to start the backwash operation mode if necessary.

[0026] The predetermined parameter can also be constituted by the operating time of the large-area filter, which reflects the experience, in particular with the polymer melt to be filtered, i.e. how long it takes on average for the large-area filter to become fouled.

[0027] In the method according to the invention, in the basic operating mode there is a laminar flow in the filtration direction through the large-area filter, and in the backwash operating mode there is a pulsating flow against the filtration direction through the large-area filter.

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

[0029] At the drain side of the filter chamber being backwashed, in the backwash mode of operation there is a higher pressure in the polymer melt compared to the pressure differential in the large area filter immediately before the backwash mode of operation was initiated.

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

[0031] And for example, in a backwash operating mode, the throttle located downstream of the large area filter can be completely closed and the entire filtered polymer melt from the first large area filter can be used to backwash the second large area filter.

[0032] In particular, the method of implementing the filter device comprises a first filter chamber in which a first large area filter is arranged, a second filter chamber in which a second large area filter is arranged, a first inlet section including a first inlet valve to the first filter chamber, a second inlet section including a second inlet valve to the second filter chamber, a first drain section from the first filter chamber, a second drain section from the second filter chamber, a first drain valve in the first drain section, and a second drain valve in the second drain section. Preferably, the inlet and drain valves are designed to be hydraulic and / or motorized, and a control device is provided for controlling the inlet and drain valves to set a basic operating mode and to set a backwash operating mode.

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

[0034] More specifically, pressure sensors for measuring the pressure in the polymer melt can be provided upstream and downstream of the large area filter in the melt tube, thus allowing 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 comprised of stacked disc filters or filter cartridges.

[0036] To simplify manufacturing and maintenance, the 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 a common drain line and / or in left and right drain lines and can be used to control both the basic and backwash operating modes.

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

[0039] These terms and associated reference numbers are used throughout the specification, claims and drawings as set forth in the following list of reference numbers. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 is a schematic diagram showing a basic operation mode of a filter device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating the backwash operation mode of the filter device of FIG. [Diagram 3]FIG. 3 is a schematic diagram showing a prior art mode of operation of the filter device of FIG. [Figure 4] FIG. 4 is a schematic diagram showing a basic operation mode of a filter device according to a second embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic diagram illustrating the backwash mode of operation of the filter device of FIG. [Figure 6] FIG. 6 is a schematic diagram showing a basic operation mode of a filter device according to a third embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram illustrating the backwash mode of operation of the filter device of FIG. [Figure 8] FIG. 8 is a schematic diagram showing a basic operation mode of a filter device according to a fourth embodiment of the present invention. [Figure 9] FIG. 9 is a schematic diagram illustrating the backwash operation mode of the filter device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0042] At the sides of the inlet pipes 16, 18 remote from the filter chambers 12, 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 flow direction of the polymer melt 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 respective inlet pipes 16, 18 via the left and right drain valves 26, 28 as required.

[0044] A left large area filter 30 having a number of filter cartridges 30a is arranged in the left filter chamber 12. A right large area filter 32 having a number of filter cartridges 32a is arranged in the right filter chamber 14. The filter cartridges 30a, 32a are aligned vertically parallel to one another and terminate in an upper region in a left distributor 34 or a right distributor 36, respectively. Each large area filter comprises, for example, 169 filter cartridges.

[0045] The filter cartridge 30a terminates in a left distributor 34, whereby the polymer melt passed through the filter cartridge 30a from the outside to the inside joins at the left distributor 34 and is discharged via a left drain pipe 38 connected to the top of the filter chamber 12.

[0046] The filter cartridge 32a terminates in a right distributor 36, whereby the polymer melt passed through the filter cartridge 32a from the outside to the inside joins at the right distributor 36 and is discharged via a right drain pipe 40 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 direction of polymer melt flow in the basic mode of operation. Similarly, the right vent valve 50 is connected upstream of the right stop valve 46 with respect to the direction of polymer melt flow in the basic mode of operation. These vent valves can be used to vent each side of the filter apparatus 10.

[0050] The polymer melt to be filtered is pumped through the large area filters 30, 32 in the filter chambers 12, 14 to the common drain line 42 and thus through the filter device 10 by a melt pump (not shown in detail) or by process induced melt pressure on the common inlet line 20. Different pressures are created in the polymer melt upstream and downstream of the large area filters 30, 32. To measure this pressure difference, a pressure sensor 56 is provided upstream of each of the large area filters 39, 32 and a pressure sensor 58 is provided downstream of each of the large area filters 30, 32.

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

[0052] The large area filters 30, 32 have a maximum filtering accuracy of 3 μm. Preferably, the filter surface of one of the large area filters 30, 32 is 45 m 2 More than 255m 2The differential pressure applied to the large area filters 30, 32 is in the range of 1 bar to 100 bar.

[0053] In the basic operation mode, the polymer melt to be filtered is simultaneously fed to both the left large area filter 30 and the right large area filter 32 in the filtering direction as indicated by the arrow 52 in Fig. 1. Thus, parallel filtering is continuously performed by the left and right large area filters 30, 32. The basic operation mode is shown in Fig. 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 just filtered from the filter cartridge 30a is remixed via the distributor 34 and flows through the left drain pipe 38, through the open left stop valve 44 and into the common drain pipe 42.

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

[0057] 2 shows the backwash mode of operation, i.e., backwashing and cleaning of the right large-area filter 32. The filtered polymer melt is used to remove foreign matter from the filter by reversing the flow direction of the filtered polymer melt and passing it through the right large-area filter 32. In the backwash mode of operation, filtration continues using only the left large-area filter 30. During 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 operating mode is started as soon as the two large-area filters 30 and 32 reach a predefined degree of contamination, i.e. as soon as it becomes necessary to clean the large-area filters 30, 32 using the backwash operating mode.

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

[0060] To initiate the backwash mode of operation on the right side, the right stop valve 24 is first closed, thus blocking the right inlet pipe 18. The right stop valve 46 is then closed and the right drain pipe 40 is blocked. The right drain valve 28 is then opened, allowing the polymer melt to exit the right inlet pipe 18. The right stop valve 46 is then opened again to induce backwashing through the right large area filter 32. The right stop valve 46 can be opened and closed at predetermined time intervals, resulting in a pulsating backwash mode of operation. Alternatively, the stop valve 46 can be open during the entire backwash process, and the backwashed polymer melt flows in a laminar flow through the right large area filter 32.

[0061] Once backwash is complete, the right drain valve 28 is closed and the right stop valve 24 is opened, and the filter apparatus 10 is now back in its basic mode of operation.

[0062] In the backwash operation mode of the right large-area filter 32, the flow direction of the filtered polymer melt is reversed so that the filtered polymer melt passes through the right large-area filter 32, thus removing foreign bodies. The polymer melt is filtered exclusively through the left large-area filter 30. The filtered polymer melt is made to flow against the filtering direction as shown by the arrow 54 until the large-area filter 32 with the filter cartridge 32a is completely cleaned. In this case, as a rule, more than one and less than two times the volume of the right filter chamber 14 is discharged.

[0063] When the backwash operating mode of the right large area filter 32 is completed and the basic operating mode is resumed, the backwash operating mode is automatically initiated for the left large area filter 30 .

[0064] To initiate the backwash mode of operation on the left side, the left stop valve 22 is first closed, thus blocking the left inlet line 16. The left stop valve 44 is then closed, blocking the left drain line 38. The left drain valve 26 is then opened, allowing the polymer melt to exit the left inlet line 16. The left stop valve 44 is then reopened, 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 open during the entire backwash operation, and the backwashed polymer melt flows in a laminar manner through the left large area filter 30.

[0065] During 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 made to flow against the filtration direction as indicated by the arrow 54 until the large-area filter 30 with the filter cartridge 30a is completely cleaned. In the process, as a rule, more than one and less than two times the volume of the left filter chamber 12 is discharged.

[0066] Once the left large area filter 30 has been cleaned, the backwash mode of operation, and thus the backwash cycle in which both large area filters 30 and 32 are cleaned in sequence, is terminated and the basic mode of operation is resumed as previously described.

[0067] A backwash cycle is initiated as soon as predetermined parameters for the backwash operating mode are met. These parameters may be constituted by the pressure occurring in the polymer melt to be filtered upstream of the large-area filters 30, 32, measured by the pressure sensor 56. Additionally or alternatively, these parameters may be constituted by the differential pressure occurring 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 being measured by the pressure sensors 56 and 58, respectively. Additionally or alternatively, the parameters may be constituted by the operating time since commissioning and / or last backwash for this large-area filter 30, 32.

[0068] The stop valves 22, 24 in the inlet pipes 16, 18, the drain valves 26, 28 in the inlet pipes 16, 18, the stop valves 44, 46 in the drain pipes 38, 40 as well as the vent valves 48, 50 in the drain pipes 38, 40 are hydraulic and / or electrically operated and are controlled by a control unit 60. For this purpose, the control unit 60 is connected to the corresponding actuators. For the sake of clarity, the pipe connections and the 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 a fixed setting of the stop valves 44, 46 in the drain lines 38, 40 in the backwash operating mode, for example 1 / 3 closed, the stop valves 44, 46 in the drain lines 38, 40 of the large-area filters 30, 32 to be backwashed can be successively opened and closed for short periods to cause an intermittent flow of filtered polymer melt through this large-area filter 30, 32. Both the basic operating mode and the backwash operating mode are controlled via the control unit.

[0070] In Figures 4 and 5, yet another embodiment of the present invention is shown. It essentially corresponds to the embodiment described with reference to Figures 1 and 2. Therefore, the same reference numbers are used to refer to the same parts. The only difference is that an adjustable throttle 62 is installed in the common drain pipe 42. Figure 4 shows the basic operation mode, and Figure 5 shows the backwash operation mode on the right side. In the backwash operation mode on the right side, the adjustable throttle 62 is used to ensure that the pressure upstream of the throttle 62 increases, and thus the polymer melt is backwashed into the right large area filter 32.

[0071] In Figures 6 and 7, yet another embodiment of the present invention is shown. It essentially corresponds to the embodiment described with reference to Figures 1 and 2. Therefore, the same reference numbers are used to refer to the same parts. The only difference is that an adjustable throttle 64 is installed in the common drain pipe 42. Figure 6 shows the basic operation mode, and Figure 7 shows the backwash operation mode on the right side. In the backwash operation mode on the right side, the adjustable throttle 64 is used to ensure that the pressure upstream of the throttle 64 increases, and thus the polymer melt is backwashed into the right large area filter 32.

[0072] 8 and 9 show yet another embodiment of the present invention, which essentially corresponds to the embodiment described with reference to FIG. 1 and FIG. 2. Therefore, the same reference numbers are used to refer to the same parts. The only difference is that a left control melt pump 66 is attached to the left drain pipe 38 and a right control melt pump 68 is attached to the right drain pipe 40. FIG. 8 shows the basic operation mode, and FIG. 9 shows the backwash operation mode on the right side. In the backwash operation 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 invention, which essentially corresponds to the embodiment described with reference to figures 1 and 2. The same reference numbers are therefore used to refer to the same parts. This figure shows a backwash mode of operation with the throttle 62 closed, which causes the entire washed polymer flow from the left large area filter 30 to flow in and through the right large area filter 32 in the reverse direction for washing.

[0074] The present invention is characterized by providing a simple method of cleaning the large area filters 30, 32 with already filtered polymer melt, which significantly reduces the cost and allows a significant reduction in the size of the filter apparatus 10 by operating both large area filters 30, 32 simultaneously in the basic operating mode. [Explanation of symbols]

[0075] 10 Filter device 12 Left filter chamber 12a Lower region of left filter chamber 12 14 Right Filter Chamber 14a Lower region of 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 Left large area filter 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 showing the direction of polymer melt flow in basic operation 54 Arrows showing 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 Control Melt Pump 66 Left Control Melt Pump 68 Right Control Melt Pump

Claims

1. A method of operating a filter device (10) for filtering a polymer melt, the filter device comprising: at least one first large area filter (30, 32) provided in the first filter chamber (12, 14) and a second large area filter (30, 32) provided in the second filter chamber (12, 14); a first valve (22, 24) at a first inlet (16, 18) to the first filter chamber (12, 14) and a second valve (22, 24) at a second inlet (16, 18) to the second filter chamber (12, 14) for controlling the polymer melt to be filtered; a first drain valve (44, 46) provided at a first drain section (38, 40) for filtered polymer melt from the first filter chamber (12, 14) and a second drain valve (44, 46) provided at a second drain section (38, 40) for filtered polymer melt from the second filter chamber (12, 14); The polymer melt to be filtered is passed under pressure through said filter device (10), the first inlet portion (16, 18) and the second inlet portion (16, 18) are connected to a common inlet portion (20), and the first drain portion (38, 40) and the second drain portion (38, 40) are connected to a common drain portion (42); The polymer melt to be filtered is simultaneously fed in a filtering direction to both the first large-area filter (30, 32) and the second large-area filter (30, 32), and in a basic operating mode, parallel filtering is performed successively through the first and second large-area filters (30, 32), and in a backwash operating mode, filtering is performed only through one of the large-area filters (30, 32); The method is characterized in that the backwash operation mode is initiated when the large area filters (30, 32) reach a predetermined degree of contamination, i.e., when a backwash operation needs to be used to clean the first large area filter (30, 32).

2. 10. The method of claim 1 , The method according to claim 1, further comprising: starting said backwash mode of operation for said second large area filter (30, 32) after cleaning of said first large area filter (30, 32) by said backwash mode of operation.

3. 10. The method of claim 1 , During the backwash operating mode, foreign matter is removed from one of the large-area filters (30, 32) by reversing the flow direction of the filtered polymer melt and passing it through the one of the large-area filters (30, 32).

4. 10. The method of claim 1 , The method of claim 1, wherein the backwash operating mode for one of the large area filters (30, 32) is initiated when a predetermined physical parameter is present in the polymer melt for the large area filter (30, 32).

5. 5. The method of claim 4, In the backwash operation mode, the inflow of polymer melt into the one of the large-area filters (30, 32) is interrupted, and at least a portion of the filtered polymer melt of the other of the large-area filters (30, 32) is supplied in the direction opposite to the filtration direction through the drain portion of the one of the large-area filters (30, 32), passed through the one of the large-area filters (30, 32) to clean the one of the large-area filters (30, 32) by backwashing, and then discharged.

6. 6. The method of claim 5, the valves (22, 24) arranged in the region of the inlets (16, 18) are opened to discharge the filtered polymer melt from one of the large-area filters (30, 32), the valves (22, 24) being used to discharge the polymer melt that has been backwashed through the one of the large-area filters (30, 32) after being filtered by the other large-area filter (30, 32).

7. 10. The method of claim 1 , The method according to claim 1, characterized in that in the backwash operating mode, at least 1, preferably 1.5, preferably 2 times the volume of the filter chamber (12, 14) of one of the large area filters (30, 32) is discharged through the valve (26, 28) at the inlet (16, 18).

8. 10. The method of claim 1 , In the backwash operation mode, the drain section (38, 40) of the one of the large-area filters (30, 32) is partially closed, for example by 2 / 3, 1 / 3 or 1 / 2, via the associated drain valve (44, 46) for backwashing, whereby only a portion of the filtered polymer melt from the other large-area filter (30, 32) is supplied to the one of the large-area filters (30, 32) for cleaning.

9. 10. The method of claim 1 , The method according to claim 1, characterized in that for the backwash operating mode, the filtered polymer melt flows through one of the large-area filters (30, 32), preferably at intervals of several times, in particular intermittently, by briefly opening and closing the drain valve (44, 46) of the one of the large-area filters (30, 32).

10. 10. The method of claim 1 , 10. The method according to claim 9, wherein the polymer melt to be filtered is a low-viscosity polymer melt, in particular comprising plastic raw materials, preferably molten plastics for chemical recycling.

11. 10. The method of claim 1 , 4. A process according to claim 3, characterized in that the viscosity of the polymer melt to be filtered is in the range of 70 to 90 mPas, in particular 80 mPas.

12. 10. The method of claim 1 , A method according to claim 1, characterised in that said large area filters (30, 32) have a filtering accuracy of up to 3 μm.

13. 10. The method of claim 1 , 45m ２ More than 255m ２ 4. A method according to claim 3, wherein said large area filters (30, 32) are used having a filter surface of:

14. 10. The method of claim 1 , The method according to claim 1, wherein the large area filters (30, 32) are used for pressure differences between 1 bar and 100 bar.

15. 3. The method of claim 2, The method, characterized in that the predetermined parameters for the large-area filter (30, 32) for the backwash operation mode are constituted by the pressure exerted on the large-area filter (30, 32) by the polymer melt to be filtered upstream of the large-area filter (30, 32), constituted by the pressure difference occurring between the polymer melt to be filtered upstream of the large-area filter (30, 32) and the filtered polymer melt downstream of the large-area filter (30, 32), and / or constituted by the operating time of the large-area filter (30, 32).

16. 10. The method of claim 1 , The method according to claim 1, wherein in the basic operating mode, a laminar flow in the filtration direction through the large-area filter (30, 32) exists, and in the backwash operating mode, a pulsating flow against the filtration direction through the large-area filter (30, 32) exists.

17. 10. The method of claim 1 , 11. The method of claim 10, wherein 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 a backwash operating mode.

18. 10. The method of claim 1 , 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 in the backwash operating mode is higher compared to the differential pressure across the large area filter (30, 32) immediately before the backwash operating mode is initiated.

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

20. 20. The method of claim 19, The method according to claim 1, wherein the throttle (62) located downstream of the large-area filter (30, 32) is fully closed in a backwash operation mode, and the entire filtered polymer melt from the first large-area filter (30, 32) is used to backwash the second large-area filter (30, 32).

21. A filter device (10) for carrying out the method according to any one of the claims 1 to 20, comprising: a first filter chamber (12, 14) in which a first large area filter (30, 32) is disposed; a second filter chamber (12, 14) in which a second large area filter (30, 32) is disposed; a first inlet (16, 18) having a first inlet valve (22, 24) to the first filter chamber (12, 14); a second inlet (16, 18) having a second inlet valve (22, 24) to the second filter chamber (12, 14); a first drain (36, 38) from said first filter chamber (12, 14); a second drain (36, 38) from said second filter chamber (12, 14); a first drain valve (44, 46) provided in the first drain portion (38, 40); a second drain valve (44, 46) provided in the second drain portion (38, 40); The inlet valves (22, 24) and the drain valves (44, 46) are designed to be hydraulic and / or electrically operated, The filter device is characterized in that a control device (60) is provided that controls the inlet valves (22, 24) and the drain valves (44, 46) to set the basic operation mode and the backwash operation mode, respectively.

22. 22. 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 said filter chambers (12, 14).

23. 22. 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 in the filter chamber (12, 14) upstream of the large-area filter (30, 32) and downstream of the large-area filter (30, 32).

24. 22. The filter device according to claim 21, 1. 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 disc filter or filter cartridge (30a, 32a).

25. 22. The filter device according to claim 21, 10. A filter device, comprising: a filter chamber for filtering a mixture of a first filter chamber and a second filter chamber; a large area filter for filtering a first filter chamber and a large area filter; a drain valve for filtering a first filter chamber and a large area filter;

26. 22. 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 left and right drain pipes (38, 40).

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