Method and filtering device for filtering liquid

Abstract

The invention relates to a method for filtering a liquid through a membrane (76) in a membrane filter (64) immersed in a liquid. To clean the membrane (76), gas is introduced into the membrane filter (64) from below in the form of continuous pulses using a gas introduction device (63), wherein for each pulse, a gas volume arranged below the liquid surface and defined at the bottom by the liquid level is first filled with gas, the gas (1) simultaneously displacing the liquid from the top to the bottom and exiting from a gas lift channel (70) until the liquid level drops below an inlet cross section (72) of a gas outflow channel (73), the gas then sequentially passes downward through the gas lift channel and from below through a deflection section (71) adjacent to the gas lift channel, upward through the inlet cross section (72) and exits the gas volume from above through a gas outflow channel (73) adjacent to the inlet cross section and then reaches the surface. The invention also relates to a filtering device (84) for carrying out this method, comprising a membrane filter (64) for filtering a liquid through a membrane and a gas introduction device arranged below the membrane. The object of the present invention is to improve the cleaning effect of the air introduced. This is achieved by the housing (80) laterally surrounding the membrane (76) and adjoining the gas introduction device (63) at the top.

Description

Technical Field

[0001] The invention relates to a method for filtering a liquid in a membrane filter immersed in a liquid, wherein the membrane filter comprises a membrane. For cleaning the membrane, a gas is introduced into the membrane filter from below in the form of continuous pulses by filling a gas volume, which is arranged below the liquid surface and is defined at the bottom by the liquid level initially filled with gas, wherein the gas simultaneously displaces the liquid from the top downwards and is discharged from a gas lift channel until the liquid level drops below an inlet cross section of a gas outflow channel, and then the gas passes downwards through the gas lift channel and a deflection section adjoining the gas lift channel at the bottom, upwards through the inlet cross section and flows out of the gas volume from above through a gas outflow channel adjoining the inlet cross section at the top of the gas inlet cross section, and then reaches the liquid surface.

[0002] The present invention also relates to a filtering device, which comprises: a membrane filter for filtering liquid through a membrane, a gas introduction device arranged below the membrane, a downwardly open gas collecting chamber defined by an upper wall and a lower wall, a gas inlet for introducing gas into the gas collecting chamber, a gas lifting channel for lifting gas out of the gas collecting chamber and exhausting the gas collecting chamber (wherein the gas lifting channel comprises a gas lifting inlet at the top of the gas collecting chamber), a deflection portion arranged at the bottom of the gas lifting channel, and an inlet cross section arranged at the top of the deflection portion, wherein a gas outflow channel is adjacent to the top of the gas outflow channel. Background Art

[0003] A generic method and a generic gas introduction device are known from US 2015 / 0265973 A1, CN 104084049 A and CN 105854619 A.

[0004] The known method and the known gas introduction device are configured for introducing gas into a membrane filter, which can be found, for example, in a membrane bioreactor (MBR). The gas introduction device is placed below the membrane filter and is supplied with a substantially constant air volume flow, which then flows out of the gas introduction device in the form of pulses.

[0005] In order to prevent the filter material from clogging the membrane, air is introduced into the membrane filter from below on the way to the liquid surface, and the gas flows through the membrane filter installed on the top of the gas introduction device. The shear force of the two-phase flow formed by the air and the liquid to be filtered washes the membrane.

[0006] The pulsed outflow of liquid creates greater shear forces than continuous gas introduction, while preventing channeling of air, which means that rising bubbles always have to reform and therefore always find a new path through the membrane filter.

[0007] A gas introduction device that supplies air continuously and exhausts it in pulses is also called a geyser.

[0008] When the gas flows out of the gas introduction device through the principle of the connecting pipe, the gas volume accumulated in the gas collection chamber is pulled out through the gas lifting channel connected to the inlet cross section, so that the gas collection chamber is basically emptied.

[0009] During the emptying of the gas collecting chamber, the outflowing gas volume flow draws the liquid through the compensation inlet and conveys the liquid through the outflow channel according to the gas lift pump action. This has the advantage that after the gas collecting chamber is emptied, the gas volume flow rate drops faster, so that the gas introduction device can be operated with more gas flow.

[0010] In the known method and filtering device, air initially flows from the geyser (gas introduction device) into the lateral opening, so that most of the liquid displaced by the air is displaced laterally from the module and is therefore not available for flushing the membrane. In addition, depending on the size of the air pulse, a portion of the air escapes the module in a lateral direction at the bottom of the module and rises to the vicinity of the membrane filter, which means that it is unused and has no flushing effect on the membrane.

[0011] In the context of the inventions WO 2016 / 064466A (Koch Membrane Systems), US 2009 / 0194477A1 (Asahi Kasai), US 10179311B2 (Sumitomo Electric), CN 104519984BB (Samsung Cheil Industries), KR 20190002717A (Mitsubishi Chemical) and WO 2011 / 028341A1 (Zenon Technology Partnership), gas introduction devices are disclosed which do not include a compensating inlet and can therefore only operate in a pulsed manner at a relatively low gas volume supply. Moreover, in these filter devices, the air flows into the lateral open area during the outflow from the geyser. Summary of the invention

[0012] Purpose

[0013] It is therefore an object of the present invention to improve the cleaning effect of the introduced air.

[0014] Workaround

[0015] The known method is improved according to the invention in that the housing laterally surrounds the membrane and directly adjoins the gas introduction device at the top.

[0016] Therefore, this configuration of the membrane filter is advantageous in that, since the housing adjoins the gas introduction device without a gap and laterally encloses the membrane, the gas introduced into the membrane filter cannot flow out of the membrane filter, so that the gas is effectively used to flush the membrane.

[0017] Advantageously, the liquid displaced by the air cannot escape laterally from the membrane filter either, which increases the acceleration of the liquid column. The gas bubbles formed in the housing by the introduced gas and initially rising with cohesive forces accelerate the liquid column arranged above it, so that it also flows through the membrane at high speed and removes deposits from the membrane due to the shear forces generated. The cleaning effect of the introduced air is increased by approximately one order of magnitude by these two effects, and the energy used for cleaning is reduced accordingly.

[0018] Advantageously, a blocked flow of liquid flows through the compensating inlet below the gas lift inlet to the inlet cross section and is then pulled by the gas until the liquid fills the deflection section and thus closes the inlet cross section to the gas.

[0019] According to the method of the invention, the liquid level in the gas introduction device rises again during the emptying of the gas volume, wherein the gas volume is displaced by the liquid flowing in from below. As a result, the suction effect of the gas rising into the outflow channel causes a blocked flow of liquid to be pulled through the compensation inlet and flow to the inlet cross section. This blocked flow of liquid is pulled by the gas, so that the liquid fills the deflection section, thereby filling the inlet cross section, and thus closes like a valve for the gas.

[0020] Therefore, the method according to the invention ensures that the gas outflow is interrupted at a point in time at which the gas volume is substantially emptied and can be filled again even at a large gas volume flow rate supply. Thus, a gas pulse is also ensured when a large gas volume flow rate is supplied.

[0021] Advantageously, in the method according to the invention, the gas flows only through the gas outflow channel after the liquid level has fallen below the inlet cross section until the liquid level rises above the compensation inlet, and only then does the blocking flow flow through the compensation inlet to the inlet cross section. Moreover, even with a greater gas flow, the geyser will be pulled along the liquid shortly before it is emptied, thereby ensuring that the geyser is stopped and refilling begins.

[0022] This means that the compensation inlet is in gas communication at the beginning of the gas flow through the outflow channel, which means that when the method according to the invention is carried out, the compensation inlet is in the gas collecting chamber which is filled with gas. This ensures that even at very low gas volume flows, the evacuation of the gas volume can be started reliably, since there is no liquid flow to hinder the gas suction action, and thus the evacuation of the gas volume is carried out by lifting the gas.

[0023] Then, even with very little airflow, the geyser began to empty.

[0024] The method according to the invention thus has the advantage that the substantially constant gas volume supply can be varied within a very wide range and then introduced into the membrane filter in the form of stable pulses. Thus, the pulsed gas volume flow through the membrane filter can be adapted to the respective filter performance in a wide range of filter performance variations in an energy-saving manner.

[0025] This means that the method according to the invention allows the membrane filter to be operated in a reliable and pulsed manner with a variable filter performance but also with a variable gas volume flow supply in order to achieve effective flushing of the membrane with low energy consumption.

[0026] The housing proposed according to the invention laterally surrounds the membrane and directly adjoins the gas introduction device at the top, thus improving the known filter device. The filter device according to the invention facilitates the implementation of the method according to the invention and is characterized by the advantages mentioned above.

[0027] Advantageously, the filter device according to the present invention comprises a gas introduction device, which comprises a compensating inlet located below the gas lift inlet, wherein the compensating inlet can flow upward along the inlet cross section. Further advantageously, the compensating inlet is arranged at the horizontal height of the inlet cross section or above it. Therefore, the compensating inlet is arranged below the upper wall and above or at the same horizontal height of the inlet cross section. Therefore, when the gas collection chamber is filled, the compensating inlet is gas-connected, and when the gas collection chamber is emptied, the compensating inlet is liquid-connected. This has the above-mentioned advantages for the start and stop process of the geyser process of pulse emptying and filling the gas collection chamber.

[0028] In a simple embodiment of the filter device according to the invention, the compensation inlet opens into the gas lift channel. Since in this embodiment the liquid is introduced directly into the strong downwardly flowing gas volume flow in the gas lift channel, the pulling effect from the gas is relatively strong, which limits the increase in the gas volume flow supply. This effect can be counteracted by enlarging the compensation inlet, since the gas volume above the compensation inlet is not then evacuated, which results in a restriction of the gas volume flow supply in the downward direction.

[0029] In another embodiment of the filter device according to the invention, the compensation channel adjoins the compensation inlet in the direction towards the deflection portion. Through the compensation channel, the position of the compensation inlet and the position of introducing the liquid blocking flow into the outflow gas flow are decoupled, which leads to an increase in the variation of the gas volume flow supply.

[0030] In an advantageous embodiment of the filter device, the compensation channel leads parallel to the gas lift channel to the deflection section. As a result, the point of introduction of the blocking liquid flow is displaced as far downward as possible. This has the advantage that the liquid is separated from the gas volume flow and is supplied precisely to the point where the liquid will have a blocking effect on the gas, which ensures that the outflowing gas flow can also be stopped when a larger gas volume flow is supplied.

[0031] With an alternative embodiment of the filter device according to the invention, when the compensation channel and the gas lift channel are connected parallel to each other to the deflection section, the gas volume flow supply can be further increased while reliably maintaining the pulse by making the cross section of the compensation inlet larger than the smallest cross section of the compensation channel. This increases the choked flow of the liquid and provides a faster and therefore more reliable closing of the gas inlet cross section for a larger gas volume flow supply.

[0032] Thus, the membrane filter can also be equipped with different types of membranes, such as hollow filter membranes, flat membranes, buffer membranes or hollow fiber membranes connected to form a curtain. Advantageously, these membranes are from the field of ultrafiltration membranes or microfiltration membranes with pore sizes between 0.02 μm and 1 μm. However, other membranes from the field of nanofiltration or low-pressure reverse osmosis can also be used.

[0033] Because the liquid volume in the membrane filter must be replaced when flushing the membrane with gas to prevent accumulation of materials previously retained by the membrane in the filter, the gas introduction device includes a liquid flow channel vertically passing through the gas collection chamber to allow liquid to flow into the bottom of the membrane filter.

[0034] In an advantageous embodiment of the filter device according to the invention, the housing of the membrane filter is configured as a tube. The tube can have a circular, rectangular or any other cross section. The advantage of the tube is that it can be manufactured economically, for example by extrusion.

[0035] In order to distribute the air introduced from the gas introduction device into the membrane filter in an optimal manner, one embodiment of the filter device according to the invention comprises a gas distributor below the membrane, wherein the outflow channel opens into the gas distributor.

[0036] In the filter device according to the present invention, the flow channel is partially or completely formed by the wall of the housing of the gas introduction device. The flow channel includes an outflow channel, a compensation channel and a deflection portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention is described in more detail below based on advantageous embodiments with reference to the accompanying drawings, in which

[0038] Figure 1a -i shows the process steps of the method according to the present invention, showing the gas introduction device according to the present invention in a cross-sectional view; and

[0039] Figure 2 A filter device according to the invention is shown.

[0040] The figures are not drawn to scale. All details of the method or gas filter device described subsequently are identical to the above-described embodiments of the filter device according to the invention. DETAILED DESCRIPTION

[0041] Figure 1a The process steps of a first method according to the invention are shown, which process steps introduce a gas 1 into a liquid 2 using a first gas introduction device 3 according to the invention shown in a cross-sectional view.

[0042] The gas introduction device 3 comprises a gas volume 6 which is arranged below the surface 4 of the liquid 2 and is defined in the downward direction by the liquid level 5 of the liquid 2. The gas volume 6 is arranged in a gas collecting chamber 7 defined by an upper wall 8 and a side wall 9. Through a gas inlet 10 which is installed below the gas collecting chamber 7 and separated from the gas collecting chamber 7, the gas 1 is introduced into the gas collecting chamber 7, thereby filling the gas volume 6, so that the liquid level 5 of the liquid 2 drops. Therefore, the liquid 2 in the gas collecting chamber 7 is successively displaced in the downward direction by the inflowing gas 1 at this point in time and replaced by the gas 1.

[0043] The gas introduction device 3 according to the invention comprises a deflection section 11, which comprises an inlet cross section 12 at the top, wherein a gas outflow channel 13 is connected to the inlet cross section at the top. A gas lift channel 14 and a compensation channel 15 lead to the deflection section 11. The gas lift channel 14 comprises an open gas lift inlet 16 at the top of the gas collecting chamber 7, and the compensation channel 15 comprises a compensation inlet 17 below the upper wall 8 of the gas collecting chamber 7, wherein the size of the cross section of the compensation inlet 17 is greater than the smallest cross section of the compensation channel 15. In addition, the gas outflow channel 13 passes through the upper wall 8.

[0044] Figure 1b-1d The additional filling of the gas collecting chamber 7 with gas 1 and thus the additional filling of the gas volume 6 and the additional lowering of the liquid level 5 of the liquid 2 are shown. Figure 1b As shown, when filling the gas volume 6 , the gas 1 moves from above through the gas lift inlet 16 into the gas lift channel 14 , so that the gas lift channel 14 is filled with the gas 1 from top to bottom.

[0045] exist Figure 1c In the example shown in FIG. 1 , the liquid level 5 has dropped below the compensation inlet 17 and the gas 1 moves from above into the compensation channel 15. Figure 1a-1c During the method step shown, the gas outflow channel 13 remains filled with fluid 2 , which means that no gas flows out of the gas introduction device 3 .

[0046] exist Figure 1dIn the embodiment of the present invention, the liquid level 5 of the liquid 2 has dropped below the inlet cross section 12. From this point on, the gas 1 flows out of the gas volume 6 in the downward direction through the gas lifting channel 14 and the compensation channel 15 to the deflection part 11 and then through the inlet cross section 12 and the subsequent gas outflow channel 13 to the surface 4.

[0047] Figure 1e It is shown how the gas volume 6 in the gas collecting chamber 7 is reduced by the outflowing gas 1. As a result, the gas 1 flowing out of the gas collecting chamber 7 is successively replaced by the liquid 2 flowing in from below, so that the liquid level 5 of the liquid 2 rises again.

[0048] The gas 1 flowing out through the gas outflow channel 13 generates a vacuum in the gas outflow channel 13 and the adjacent gas lift channel 14 and the compensation channel 15. Since the gas lift inlet 16 and the compensation inlet 17 are now arranged in the gas volume 6 filled with gas 1 in the gas collecting chamber 7, initially only the gas 1 is guided through the gas outflow channel 13 by the generated suction.

[0049] Figure 1f The moment is shown when the level 5 of the liquid 2 reaches the compensation inlet 17. Up to this point, only the gas 1 flows through the gas outflow channel 13.

[0050] Figure 1g It is shown how the compensation inlet 17 is filled with fluid 2 during a further increase in the liquid level 5 due to the outflow of gas through the gas lift channel 14 .

[0051] Figure 1h It shows how the choked flow 18 of liquid 2 is pulled through the compensation inlet 17 by the suction effect of the gas 1 flowing out of the gas outflow channel 13, so that the choked flow 18 of liquid 2 flows through the compensation channel 15 to the inlet cross section 12 and is pulled by the outflowing gas 1 until the choked flow 18 of liquid 2 fills Figure 1i The deflection section 11 in the embodiment then closes the inlet cross section 12 to the gas 1 like a valve.

[0052] Figure 2A cross-sectional view of a gas introduction device 63 according to the present invention is shown, which is installed below a membrane filter 64. The gas introduction device 63 has a gas collection chamber 65 which is laterally delimited by a side wall 66, which is configured as a rectangular tube with a lateral width of 20 cm. The gas collection chamber 65 is open in a downward direction, and a gas inlet 67 is arranged below the gas collection chamber 65 and is configured to fill the gas collection chamber 65 with gas during operation. A gas lift inlet 69 leads to the gas collection chamber 65 at the top below the upper wall 68, wherein a gas lift channel 70 adjoins the gas lift inlet 69. The gas lift channel 70 leads to a deflection portion 71 at the bottom, which adjoins an inlet cross section 72 at the top. The deflection portion 71 passes through the side wall 66 at the bottom. A gas outflow channel 73 is connected to the inlet cross section 72 at the top. In addition, the gas introduction device 63 includes a compensation channel 74 arranged in the side wall 66. The compensation channel 74 includes a compensation inlet 75 at the top of the gas collection chamber 65 and leads to the deflection portion 71 at the bottom.

[0053] The membrane filter 64 comprises a membrane 76 configured as a hollow fiber membrane 77, which is cast into a base element 78 at the bottom. The base element 78 comprises a permeate collecting chamber 79, to which the hollow fiber membrane 77 is connected with an open cavity side so that filtrate can be extracted from the cavity of the hollow fiber membrane 77. The hollow fiber membrane 77 is individually closed at the top and laterally enclosed by a shell 80, which is configured as a rectangular tube 81, which has the same cross-sectional dimensions as the side wall 66 and adjoins the side wall 66 at the top. Below the base element 78, the membrane filter 64 comprises a gas distributor 82, to which the gas outflow channel 73 opens. The gas introduction device 63 comprises a liquid flow channel 83 vertically passing through the gas collection chamber 65 and the upper wall 68, so that the liquid flows into the bottom of the membrane filter 63. The combination of the gas introduction device 63 and the membrane filter 64 together forms a filtering device 84.

[0054] Reference Symbols and Names

[0055] 1 Gas

[0056] 2 Liquid

[0057] 3 Gas introduction device

[0058] 4 Surface

[0059] 5 Liquid level

[0060] 6 Gas volume

[0061] 7 Gas collection chamber

[0062] 8 upper wall

[0063] 9 Sidewall

[0064] 10 Gas inlet

[0065] 11 Deflection section

[0066] 12 Inlet cross section

[0067] 13 Gas outflow channel

[0068] 14 Gas lifting channel

[0069] 15 compensation channels

[0070] 16 Gas lift inlet

[0071] 17 Compensation entrance

[0072] 18 Blocking Flow

[0073] 63 Gas introduction device

[0074] 64 Membrane Filter

[0075] 65 Gas Collection Chamber

[0076] 66 Sidewall

[0077] 67 Gas Inlet

[0078] 68 upper wall

[0079] 69 Gas lift inlet

[0080] 70 Gas lifting channel

[0081] 71 Deflection section

[0082] 72 Inlet cross section

[0083] 73 Gas outflow channel

[0084] 74 compensation channels

[0085] 75 Compensation entrance

[0086] 76 Membrane

[0087] 77 Hollow filter membrane

[0088] 78 Base element

[0089] 79 Permeate Collection Chamber

[0090] 80 Shell

[0091] 81 tubes

[0092] 82 Gas distributor

[0093] 83 Liquid Flow Channel

[0094] 84 Filter device

Claims

1. A method of filtering a liquid (2) in a membrane filter (64) immersed in the liquid (2) and comprising a membrane (76), the method comprising: Introducing gas (1) in the form of continuous pulses into the base of the membrane filter (64) through a gas introduction device (63) so that the membrane (76) is cleaned, wherein the gas introduction device (3, 63) includes a liquid flow channel (83) that vertically passes through the gas collection chamber (7, 65) and allows the liquid (2) to enter the bottom of the membrane filter (64); and Firstly, a gas volume (6) arranged below the surface (4) of the liquid (2) and defined in the downward direction by the liquid level (5) of the liquid (2) is filled with the gas (1), wherein the gas (1) simultaneously displaces the liquid (2) from the top downwards from a gas lift channel (14, 70) until the liquid level (5) drops below the inlet cross section (12, 72) of a gas outflow channel (13, 73); and The gas (1) then flows downwards through the gas lift channel (14, 70) and the deflection section (11, 71) adjoining at the bottom of the gas lift channel, in an upward direction through the inlet cross section (12, 72) and out of the gas volume (6) through the gas outflow channel (13, 73) adjoining at the top of the inlet cross section (12, 72), whereupon the gas flows to the surface (4), Characterized in that a shell (80) laterally surrounds the membrane (76) and adjoins the gas introduction device (63) at the top thereof, so that bubbles are formed by the gas and the bubbles rise and thereby accelerate a liquid column arranged above the bubbles in the shell, so that the liquid column also flows through the membrane at a high speed.

2. The method according to claim 1, characterized in that The choked flow (18) of the liquid flows through the compensating inlet (17, 75) below the gas lift inlet (16, 69) to the inlet cross section (12, 72) and is pulled by the gas (1) until the liquid (2) fills the deflection section (11, 71), thereby closing the inlet cross section (12, 72) to the gas (1).

3. The method according to claim 2, characterized in that After the liquid level (5) has fallen below the inlet cross section (12, 72), initially the gas (1) flows only through the gas outflow channel (13, 73) until the liquid level (5) rises above the compensation inlet (17, 75), and Only then does the choked flow (18) flow through the compensation inlet (17, 75) to the inlet cross section (12, 72).

4. A filtering device (84), comprising: A membrane filter (64) for filtering a liquid (2), the membrane filter comprising a membrane (76) and a gas introduction device (3, 63) arranged below the membrane (76), the gas introduction device comprising: a liquid flow channel (83) which vertically passes through the gas collection chamber (7, 65) and allows the liquid (2) to enter the bottom of the membrane filter (64); a gas collecting chamber (7, 65) opening at the base and defined by an upper wall (8, 68) and side walls (9, 66), a gas inlet (10, 67) configured to allow gas (1) to flow into the gas collection chamber (7, 65), a gas lift passage (70) configured to siphon gas out of the gas collection chamber (65) and to evacuate the gas collection chamber, the gas lift passage comprising a gas lift inlet (16, 69) at the top of the gas collection chamber (7, 65), a deflection portion (11, 71) arranged at the bottom of the gas lifting channel (14, 70), and an inlet cross section (12, 72) arranged at the top of the deflection section (11, 71), wherein a gas outflow channel (13, 73) is connected to the top of the inlet cross section (12, 72), The invention is characterized in that it comprises a shell (80) which laterally surrounds the membrane (76) and is connected to the gas introduction device (63) at the top of the gas introduction device, so that bubbles are formed by the gas and the bubbles rise and thereby accelerate the liquid column arranged above the bubbles in the shell, so that the liquid column also flows through the membrane at a high speed.

5. The filtering device (84) according to claim 4, characterized in that: A compensating inlet (17, 75) is arranged below the gas lift inlet (16, 69) and can flow toward the inlet cross section (12, 72).

6. The filtering device (84) according to claim 5, characterized in that The compensating inlet (17, 75) is arranged at or above the level of the inlet cross section (12, 72).

7. The filtering device (84) according to claim 5 or 6, characterized in that: The compensating inlet (17, 75) is formed on the gas lifting channel (14, 70).

8. The filtering device (84) according to claim 5, characterized in that A compensation channel (15, 74) is connected to the compensation inlet (17, 75) in the direction towards the deflection section (11, 71).

9. The filtering device (84) according to claim 8, characterized in that The compensating channel (15, 74) opens into the gas lifting channel (14, 70).

10. The filtering device (84) according to claim 8 or 9, characterized in that: The compensation channel (15, 74) opens into the deflection section (11, 71) parallel to the gas lift channel (14, 70).

11. The filtering device (84) according to claim 8, characterized in that The cross section of the compensation inlet (17, 75) is larger than the smallest cross section of the compensation channel (15, 74).

12. The filtering device (84) according to claim 4, characterized in that The housing (80) is a continuous tube (81).

13. The filtering device (84) according to claim 4, characterized in that A gas distributor (82) is located below the membrane (76), wherein the gas outflow channels (13, 73) open into the gas distributor.

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