MEMBRANE FILTERS AND METHODS FOR FILTERING

Description

[0001] The invention initially relates to a membrane filter for submerged operation for filtering a liquid with membrane units and a gas distribution system for distributing a gas for flushing purposes to the membrane units, wherein each of the membrane units has a gas inlet opening and at least one membrane element, and wherein each of the membrane elements has the following features: membranes for filtering a liquid permeate from the liquid, a permeate collection space to which the membranes are connected on the permeate side, and a permeate outlet for discharging the permeate from the permeate collection space, and wherein the gas distribution system has exactly one gas outlet for discharging the gas from the gas distribution system into the respective gas inlet opening of the membrane unit for each membrane unit.

[0002] The invention further relates to a method for filtering a liquid in a membrane filter for submerged operation with membrane units and a gas distribution system for distributing a gas for flushing purposes to the membrane units, wherein each of the membrane units has a gas inlet opening and at least one membrane element, and wherein in each of the membrane elements a liquid permeate is filtered from the liquid with the aid of the membranes, the permeate flows from the membranes into a permeate collection space connected to the membranes on the permeate side and is discharged from this through a permeate outlet, and wherein the gas flows from the gas distribution system into the respective gas inlet opening of each of the membrane units from exactly one gas outlet.

[0003] Such a membrane filter and such a process are known from DE 101 61 095 C1. These membrane units are fed with gas through a pipe distributor located below the liquid level. To ensure uniform gas supply to all membrane units in such a pipe distributor, the supply lines to the membrane units must each have a throttling effect. This is often achieved by deliberately incorporating throttle cross-sections. The dimensioning of these throttle cross-sections must always be based on the smallest intended gas flow. The disadvantage is that at higher gas flows, significantly higher pressure losses occur in the throttle cross-sections, which lead to increased energy consumption.

[0004] Since considerable fluctuations in throughput rates often occur, especially in municipal MBR plants, this means that adapting the filtration performance to the fluctuating throughput rates is disadvantageous from an energy point of view.

[0005] From DE 10 2019 129 074 B3, a membrane filter is known in the background of the invention, in which a gas inflow opening into a closed membrane unit is formed by the lower opening of a geyser tube laterally delimiting the gas collection chamber. Inside, this membrane unit has a trough-shaped gas distribution element above the geyser in order to evenly distribute the gas into the membrane element. EP 3 388 138 A1 discloses a geyser element for a membrane unit. DE 10 2013 218 208 A1 discloses a membrane filter with a finger-shaped structured base element, wherein the fingers have a common permeate collection chamber. US 2017 / 087518 A1 and DE 10 2019 115265 A1 disclose further membrane units, but no distribution of gas among several such membrane units.

[0006] In the further background of the invention, JP-H 10-66834 A discloses a membrane filter having plate-shaped membrane units and trough-shaped gas distribution elements which evenly distribute the gas into spaces between the membrane units. Task

[0007] It is the object of the present invention to propose a membrane filter with a gas distribution system that enables uniform gas distribution with low pressure losses over a wide variation range of the gas supply. Solution

[0008] Based on the known membrane filter, the invention proposes that the gas distribution system have the following features: a downwardly open tray, which has a bottom at the top as a boundary for the gas, and a gas inlet for admitting the gas into the tray, wherein the gas outlets are formed in a lateral wall of the tray and are open at the bottom, and the membrane units each have, below the at least one membrane element, a downwardly open gas collection chamber and a geyser element with an outlet device for the pulsed discharge of the gas upwards from the gas collection chamber, wherein the geyser element has the gas inflow opening at the bottom. This eliminates the need for a pipe distributor, which reduces the pressure loss for the introduction of the gas and simultaneously enables operation with only small pressure loss differences, even with a wide variation range of the gas supply.

[0009] The height of the geyser element is utilized to increase the vertical extent of the tank, with the geyser elements positioned laterally next to the tank, beginning just above the gas outlets. In the process according to the invention using this membrane filter, the gas therefore enters completely into one of the gas inlet openings of the geyser elements immediately after flowing out of each of the tank's gas outlets.

[0010] The gas inlet can be slit-shaped with parallel edges or tapered towards the top, for example wedge-shaped, semicircular or curved in a free form.

[0011] The gas is directed into the interior of the membrane unit through the gas inlet opening. Various gas inlet openings and associated means for directing the gas into the interior of the membrane unit are known from the prior art.

[0012] Preferably, such membrane units have their respective gas inlet openings below the bottom. This means that the tray is placed next to the membrane units, not below them. This allows for taller trays to be constructed with the same gas injection depth. This leads to a significant increase in the gas flow cross-section within the tray, ensuring a uniform gas flow distribution even in significantly longer trays. This, in turn, allows for a significant increase in the number of membrane units supplied with gas from one tray.

[0013] The scope of the invention also includes the installation of two or more membrane elements above the geyser element in the membrane units. Such designs, for example, result in so-called double-decker systems when two membrane elements are installed one above the other in the membrane units.

[0014] In the membrane filter according to the invention, the air inlet into the tank can be positioned in various ways. For example, in the simplest case, it can be designed as a pipe socket that allows the gas to flow into the tank from below, separate from the tank. However, it can also be connected laterally, for example, to the front of the tank or to its long side. It can also be connected from above to the bottom of the tank, as in JP-H 10-66834 A, and guide the gas through it.

[0015] It is within the scope of the membrane filter according to the invention that the membrane elements can be equipped with various types of membranes, such as hollow fiber membranes, plate membranes, pillow membranes, or hollow fiber membranes connected to form curtains. The membranes themselves preferably belong to the range of ultrafiltration or microfiltration membranes with pore sizes between 0.02 and 1.0 µm. However, other membranes from the field of nanofiltration or low-pressure reverse osmosis can also be used.

[0016] When operating the membrane filter according to the invention in membrane bioreactors (MBR), the gas used is usually air and the membranes used are from the field of ultra- and microfiltration.

[0017] The design of the membrane elements of the membrane filter according to the invention also encompasses various configurations. For example, the membranes can be surrounded by a tube that is part of the membrane element. This has the advantage that the introduced gas cannot leave the membrane area laterally and can flow upwards alongside the membranes unused.

[0018] When using hollow-fiber membranes, these can be configured in double-header or single-header systems according to the invention. Both configurations are expressly within the scope of the invention for the design of the membrane elements. In double-header systems, the hollow-fiber membranes are secured at the top and bottom in headers. In the single-header design, the membranes float individually sealed at the top in the liquid to be filtered, while they are only secured at the bottom in a foot element.

[0019] In a further advantageous embodiment of the membrane filter according to the invention, a spout is inserted in each of the gas outlets to direct the gas outward into an area spaced apart from the tank. This is particularly useful when there is a gap between the membrane units and the side wall of the tank, through which the gas can flow past the membrane units after exiting the gas outlets. The spouts bridge such a gap, allowing the gas to flow completely into the gas inlet opening.

[0020] To ensure this forwarding of the gas flowing from the gas outlets, it is advantageous if the spout has a downwardly open flow channel for the gas. Alternatively, the flow channel can be covered at the bottom. This flow channel advantageously has its narrowest flow cross-section in the area of ​​the tank wall. This narrowest flow cross-section is advantageously as short as possible and provided with inlet roundings so that, for example, in MBR applications, no sludge particles or impurities can settle on any edges of the spout. In this context, it is also advantageous if the flow channel widens conically again immediately after the smallest flow cross-section in order to offer the gas as little resistance as possible.

[0021] In a further embodiment of the membrane filter according to the invention, the flow channel on the outside of the tank is inclined upwards. This increases the flow velocity in the flow channel and improves the flow. Alternatively, the flow channel can be flat or inclined downwards on the outside. The flow channel is then always filled with gas and is less prone to fouling.

[0022] In the design of the membrane filter according to the invention, the tray can consist of two folded sheets and two end elements. The sheets can be made of stainless steel, for example, and then welded to form the tray or bonded with special adhesives. This manufacturing process allows for the easy production of very tall and narrow trays with low pressure losses.

[0023] In order to avoid swinging of the long side walls of the tub in the case of high tubs, it is part of the scope of the invention that the tub has at least one connecting element between the folded sheets on the inside.

[0024] In addition to the fluidic advantages of tall trays, they also have the added benefit of increasing static strength against deflection. Therefore, in an advantageous design of the membrane filter, the tray is part of a frame in which the membrane units are mounted. In this design, the height of the tray is utilized to increase the strength of the entire membrane filter. The tray can, for example, be bolted to the side panels of the frame.

[0025] In such a configuration of the membrane filter according to the invention, it is further advantageous if a permeate collection channel is attached to the top of the tank, to which the permeate outlets are connected on the sides. The connection between the permeate collection channel and the tank enables the transfer of loads and forces from the membrane units to the tank or to the module frame. Thus, less rigid materials, such as plastics, can also be used in the design of the permeate collection channel.

[0026] Based on the known method, the invention proposes that in the gas distribution system the gas flows through a gas inlet into a downwardly open trough, in which it is delimited at the top by a base, wherein the gas outlets are formed in a lateral wall of the trough and are open at the bottom, and the membrane units each have, below the at least one membrane element, a downwardly open gas collection chamber and a geyser element with an outlet device for the pulsed discharge of the gas upwards from the gas collection chamber, wherein the geyser element has the gas inflow opening at the bottom. The method according to the invention is carried out in particular with a membrane filter according to the invention and is equally characterized by its aforementioned advantages. Examples of implementation

[0027] The invention is explained below using exemplary embodiments. Fig. 1 shows a section through a membrane filter, Fig. 2-5 shows sections and detailed views of a second membrane filter according to the invention, and Fig. 6-9 shows views and detailed sections of a third membrane filter according to the invention

[0028] The drawings shown in the figures are not to scale. All details not shown in the membrane filters or processes described below are identical to the designs of previously described membrane filters or processes.

[0029] The Figure 1shows a section through a first membrane filter 1 not according to the invention with membrane units 2 and a gas distribution system 3. Each of the membrane units 2 has a membrane element 4. In this case, the membrane units 2 each consist of exactly one membrane element 4. Each membrane element 4 has membranes 5 and a permeate collection chamber 6, which is connected to the membranes 5 on the permeate side. The membranes 5 in this case are hollow fiber membranes that are configured according to the single-header principle, i.e. they are individually closed at the top and only fixed at the bottom in a base element 7, which contains the permeate collection chamber 6 and a permeate outlet 8 for discharging the permeate from the permeate collection chamber 6 into a permeate collection channel 9. The membrane element 4 also has a rectangular tube 10, which surrounds the membranes 5 and also the base element 7 and which is penetrated laterally by the permeate outlet 8.

[0030] The gas distribution system 3 has a gas inlet 11 for admitting gas from below into a downwardly open tray 12, which has a bottom 13 at the top to limit the gas. The gas inlet 11 is separated from the tray 12 in the membrane filter 1. The gas distribution system 3 also has downwardly open, wedge-shaped gas outlets 14 in a side wall 15 of the tray 12 for the gas to flow out of the tray 12.

[0031] The membrane units 2 in the membrane filter 1 each have a gas inlet opening 16 below the base 13. During operation, the tray 12 fills with gas until it flows out of the gas distribution system 3 through the gas outlets 14 and then flows into the membrane units 2 through the gas inlet openings 16. The gas inlet opening 16 is the only way for the gas to flow into the respective membrane unit 2.

[0032] The Figure 2shows a view of a second membrane filter 17 according to the invention with four membrane units 18 and a gas distribution system 19. The membrane units 18 each have a geyser element 21 below a membrane element 20. The membrane elements 20 are constructed in the same way as those of the first membrane filter 1.

[0033] The geyser element 21 has a downwardly open gas collection chamber 22 and an outlet device 23 for the pulsed release of a gas from the gas collection chamber 22. The geyser element 21 also has a rectangular geyser tube 24, which is closed at the top and open at the bottom and laterally delimits the gas collection chamber 22. The rectangular geyser tube 24 has the same cross-section as a rectangular tube 25 of the membrane element 20.

[0034] In the gas distribution system 19 of the membrane filter 17 according to the invention, a gas inlet 26 is connected at the front to a downwardly open trough 27 for admitting the gas into the trough 27. The gas distribution system 19 also has four beaks 28 which are inserted into wedge-shaped gas outlets 29 in a lateral wall 30 of the trough 27, which are concealed by these beaks, for passing the gas outwards into an area spaced apart from the trough 27.

[0035] According to the invention, the membrane units 18 have a gas inlet opening 32 below a bottom 31 of the tank 27 (not shown in section). This opening is also the open, lower side of the rectangular geyser tube 24 of the geyser element 21. The gas inlet opening 32 is the only possible inlet for the gas into the respective membrane unit 18.

[0036] Figure 3shows a section through the membrane unit 18 of the second membrane filter 17 according to the invention with the membrane element 20 and the geyser element 21 installed underneath.

[0037] The outlet device 23 of the geyser element 21 has the following features: a gas lift channel 33 for the gas to flow downwards from the gas collection chamber 22, and a deflection region 34 at the bottom of the gas lift channel 33 for deflecting the outflowing gas upwards. An outlet channel 35 adjoins the deflection region 34 at the top for discharging the gas upwards from the geyser element 21. The rectangular geyser tube 24 has a closed upper geyser wall 36 at the top as the upper boundary for the gas collection chamber 22. Since the geyser element 21 in the membrane filter 17 according to the invention is directly connected to the membrane element 20 at the bottom, it also has an inflow tube 37 to enable the liquid to be filtered to flow into the membrane element 20 from below. The inlet pipe 37 and the outlet channel 35 penetrate the upper geyser wall 36. The gas lift channel 33, the deflection area 34 and the outlet channel 35 together form the outlet device 23.

[0038] Figure 4a shows three views of the beak 28 of the membrane filter 17 according to the invention. This has a downwardly open flow channel 38 for forwarding the gas to the outside into an area spaced from the trough 27.

[0039] Figure 4b shows the insertion of the spout 28 into the wall 30 of the trough 27 of the gas distribution system 19. The flow channel 38 is inclined upwards on the outside of the trough 27 to improve the outflow of the gas from the trough 27.

[0040] Figure 5illustrates the inventive operation of the second inventive membrane filter 17 and shows a detailed section through the gas distribution system 19 and the membrane unit 18, or through the geyser element 21 as the lower part of the membrane unit 18. A gas 39 flows through the gas inlet 26 (not shown) into the trough 27, fills it, and then flows continuously out of the trough 27 through the gas outlets 29, or through the flow channels 38 of the spouts 28, and then through the gas inlet opening 32 into the geyser element 21. The gas inlet opening 32 is located below the bottom 31 of the trough 27.

[0041] During the filling process of the gas collection chamber 22 of the geyser element 21 with gas 39, a liquid level 40 in the gas collection chamber 22 drops until it falls below the outflow channel 35. The gas 39 then flows from above through the gas lift channel 33 downward into the deflection area 34, where it is deflected upward and subsequently flows out of the top of the geyser through the outflow channel 35. The gas 39 continues to flow out of the gas collection chamber 22 until it is again flooded with liquid from below. The filling process with gas 39 then begins again. Thus, the continuous gas inflow at the bottom of the geyser element 21 results in a pulsating gas outflow from the top of the geyser element 21 into the membrane element 20 installed above it, in order to effectively flush the membranes (not shown) located therein with the gas 39.

[0042] Figure 6 shows two views of the tub 41 of a third, first in Figure 91 shows a schematic representation of the membrane filter 42 according to the invention as part of its gas distribution system 43. In this embodiment, the trough 41 consists of two folded sheets 44 and two end elements 45 that are welded together. The two sheets 44 form a T-profile 46 at the top of the trough 41 in the longitudinal direction of the trough 41. The lower view shows that the trough 41 has three connecting elements 47 between the folded sheets 44 on the inside, for stiffening the sheets 44 during operation. Each of the sheets has downwardly open, wedge-shaped gas outlets 48 for the gas to flow out of the trough 41.

[0043] Figure 7 shows the lower section of a frame 49 of the first Figure 9 illustrated third membrane filter 42 according to the invention. The trough 41 is part of this frame 49 and is screwed to two side parts 50 of the frame 49.

[0044] Figure 8 shows two views of the tub 41 of the first in Figure 9 1 shows a third membrane filter 42 according to the invention, to which a permeate collection channel 51 is attached at the top. This has a dovetail-shaped groove 52 in the longitudinal direction, with which it is pushed over the T-profile 46. This creates a connection between the permeate collection channel 51 and the tray 41. Nozzles 53 are inserted into the gas outlets 48 to conduct gas into an outer region of the tray 41. The permeate collection channel 51 has eight permeate inlets 54 for the lateral connection of membrane elements 55. In addition, the permeate collection channel 51 has a permeate pipe 56 for discharging the permeate from the membrane filter 42 according to the invention.

[0045] Figure 9shows the third membrane filter 42 according to the invention, only partially equipped with four membrane units 57 to clarify the structure. In operation, the membrane filter 42 accordingly has eight membrane units 57. The membrane units 57 each have a membrane element 55 and a geyser element 58 installed underneath. They are mounted in the frame 49 and connected by their membrane elements 55 to the permeate inlets 54 of the permeate collection channel 51. The membrane units 57 are each positioned above a spout 53, so that the gas flowing out of each spout 53 during operation flows directly from below into a gas inlet opening 59 of the membrane unit 57 positioned above, or of the geyser element 58. According to the invention, the gas inlet openings 59 are located below a base 60 of the tray 41 of the gas distribution system 43.The gas inlet of the third membrane filter according to the invention, not shown, is a separate pipe that lets the gas into the tray 41 from below.

[0046] In the figures are 1 Membrane filter 2 Membrane unit 3 Gas distribution system 4 Membrane element 5 Membranes 6 Permeate collection chamber 7 Base element 8 Permeate outlet 9 Permeate collection channel 10 Rectangular tube 11 Gas inlet 12 Pan 13 Base 14 Gas outlet 15 Wall 16 Gas inlet opening 17 Membrane filter 18 Membrane unit 19 Gas distribution system 20 Membrane element 21 Geyser element 22 Gas collection chamber 23 Outlet device 24 Geyser rectangular tube 25 Rectangular tube 26 Gas inlet 27 Pan 28 Spout 29 Gas outlet 30 Wall 31 Base 32 Gas inlet opening 33 Gas lift channel 34 Deflection area 35 Outflow channel 36 Upper geyser wall 37Inlet pipe 38Flow channel 39Gas 40Liquid level 41Trough 42Membrane filter 43Gas distribution system 44Sheet 45End element 46T-profile 47Connecting element 48Gas outlet 49Frame 50Side part 51Permeate collection channel 52Groove 53Spout 54Permeate inlet 55Membrane element 56Permeate tube 57Membrane unit 58Geyser element 59Gas inlet opening 60Bottom

Claims

1. A membrane filter (1, 17, 42) for submerged operation for filtering a liquid, the membrane filter comprising: membrane units (2, 18, 57) and a gas distribution system (3, 19, 43) for distributing a gas (39) to the membrane units and flushing the membrane units, wherein each of the membrane units (2, 18, 57) includes a respective gas inlet opening (16, 32, 59) and at least one membrane element (4, 20, 55), and wherein each of the membrane elements (4, 20, 55) has the following features: - membranes (5) for filtering a liquid permeate from the liquid, - a permeate collection cavity (6) connected to permeate sides of the membranes (5), and a permeate outlet (8) configured to drain the permeate from the permeate collection cavity (6), and wherein the gas distribution system (3, 19, 43) includes exactly one gas outlet (14, 29, 48) for each membrane unit (2, 18, 57), the exactly one gas outlet (14, 29, 48) configured to exhaust the gas from the gas distribution system (3, 19, 43) into the respective gas inlet opening (16, 32, 59) of the membrane unit (2, 18, 57), characterized in that the gas distribution system (3, 19, 43) includes the following features: - a downward open tub (12, 27, 41) including a base (13, 31, 60) arranged at a top of the tub and forming a boundary for the gas (39), and - a gas inlet (11, 26) configured let the gas (39) into the tub (12, 27, 41), wherein the gas outlets (14, 29, 48) are configured downward open in a lateral wall (15, 30) of the tub (12, 27, 41), and the membrane units (2, 18, 57) respectively include a downward open gas collection cavity (22) below the at least one membrane element (4, 20, 55), and the membrane units (2, 18, 57) respectively include a geyser element (21, 58) below the at least one membrane element (4, 20, 55), the geyser element (21, 58) including an outlet device (23) configured for a pulsating outlet of the gas (39) in an upward direction from the gas collection cavity (22), wherein the geyser element (21, 58) includes the gas inlet opening (16, 32, 59) at a bottom of the geyser element (21, 58).

2. The membrane filter (1, 17, 42) according to claim 1, characterized in that the membrane units (2, 18, 57) include the respective gas inlet opening (16, 32, 59) below the base (13, 31, 60).

3. The membrane filter (1, 17, 42) according to one of the preceding claims, characterized in that a beak shaped spout (28, 53) is inserted into each of the gas outlets (14, 29, 48) and configured to conduct the gas (39) outward into an area offset from the tub (12, 27, 41).

4. The membrane filter (1, 17, 42) according to the preceding claim, characterized in that the beak shaped spout (28, 53) includes a downward open flow through channel (38) for the gas (39).

5. The membrane filter (1, 17, 42) according to the preceding claim, characterized in that the flow through channel (38) is sloped upward on an outside of the tub (12, 27, 41).

6. The membrane filter (1, 17, 42) according to one of the preceding claims, characterized in that the tub (12, 27, 41) is made from two bent sheet metal pieces (44) and two face elements (45).

7. The membrane filter (1, 17, 42) according to the preceding claim, characterized in that the tub (12, 27, 41) internally includes at least one connection element (47) between the bent sheet metal pieces (44).

8. The membrane filter (1, 17, 42) according to one of the preceding claims, characterized in that the tub (12, 27, 41) forms part of a frame (49) that mounts the membrane units (2, 18, 57).

9. The membrane filter (1, 17, 42) according to one of the preceding claims, characterized in that a permeate collection channel (9, 51) is arranged on top of the tub (12, 27 41), wherein the permeate outlets (8) laterally adjoin the permeate collection channel (9, 51).

10. A method for filtering a liquid in a membrane filter (1, 17, 42) configured for submerged operation, the membrane filter including membrane units (2, 18, 57) and a gas distribution system (3, 19, 43) for distributing a gas (39) to the membrane units and flushing the membrane units, wherein each of the membrane units (2, 18, 57) includes a respective gas inlet opening (16, 32, 59) and at least one membrane element (4, 20, 55), and wherein the following steps performed in each of the membrane elements (4, 20, 55) - a liquid permeate is filtered from the liquid by membranes (5), - the permeate flows from the membranes (5) into a permeate collection cavity (6) connected to permeate sides of the membranes (5) and from the permeate collection cavity into a permeate outlet (8) from which the permeate is drained, and wherein the gas flows from the gas distribution system (3, 19, 43) into the respective gas inlet opening (16, 32, 59) of each of the membrane units (2, 18, 57) from exactly one gas outlet (14, 29, 48), characterized in that the gas (39) flows in the gas distribution system (3, 19, 43) through a gas inlet (11, 26) into a downward open tub (12, 27, 41), wherein the gas is delimited at a top of the tub by a base (13, 31, 60) of the tub, wherein the gas outlets (14, 29, 48) are configured downward open in a lateral wall (15, 30) of the tub (12, 27, 41), and the membrane units (2, 18, 57) respectively include a downward open gas collection cavity (22) below the at least one membrane element (4, 20, 55), and the membrane units (2, 18, 57) respectively include a geyser element (21, 58) below the at least one membrane element (4, 20, 55), the geyser element (21, 58) including an outlet device (23) configured for a pulsating outlet of the gas (39) in an upward direction from the gas collection cavity (22), wherein the geyser element (21, 58) includes the gas inlet opening (16, 32, 59) at a bottom of the geyser element (21, 58).