Bubble generating device and liquid filtering device

Abstract

The object of the present invention is to provide a bubble generating device (30) capable of causing a plurality of bubbles to hit a filter membrane almost simultaneously. The bubble generating device (30) comprises: a frame (40) having a plurality of side plates and a top plate (32) fixed to the plurality of side plates in a manner that covers a space surrounded by the plurality of side plates from above; a plurality of bubble discharge ports (32a) arranged on the top plate (32) in a manner that is arranged along the long side direction of the top plate (32); and a bubble discharge chamber (35) arranged in the frame (40) and connected to the plurality of bubble discharge ports (32a), wherein the return path (36) has a cross-sectional shape that at least extends downward and then returns upward. The folding path (36) is formed by a folding plate (45) and an inner plate (46) arranged on the inner side of the folding plate (45), one end of each of the folding plate (45) and the inner plate (46) in the long side direction is fixed to one of two side plates that are opposite to each other along the long side direction among the multiple side plates, and the other end of each of the folding plate (45) and the inner plate (46) in the long side direction is fixed to the other side plate of the two side plates, one side of the folding path (36) in the short side direction is connected to the bubble release chamber (35), and the other side of the folding path (36) in the short side direction is connected to the gas storage chamber (35).

Description

Technical Field

[0001] The present invention relates to a bubble generating device and a liquid filtering device using the bubble generating device. Background Art

[0002] Conventionally, in a liquid filtration device that filters liquid through a filter membrane, in order to prevent clogging of the filter membrane, contaminants are generally removed from the surface of the filter membrane by scrubbing. Scrubbing is a method in which bubbles are released from the bottom of the filter membrane toward the filter membrane by a bubble generating device, and the liquid near the surface of the filter membrane is vigorously shaken by the bubbles.

[0003] As a bubble generating device, there is known a bubble generating device including a gas storage chamber and a return path connected to the upper part of the gas storage chamber. The gas storage chamber stores liquid inside and stores gas supplied to the liquid above the liquid. The return path is connected to the upper part of the gas storage chamber and extends downward, then turns back and extends upward.

[0004] As a bubble generating device of this structure, the bubble generating device described in Patent Document 1 is known. The bubble generating device includes a gas storage flow path as a gas storage flow chamber and a gas guide path as a return path. The gas storage flow path and the gas guide path are arranged in a liquid. Gas is supplied from the outside to the liquid in the liquid storage flow path so that it floats in the liquid and is stored in the upper part of the liquid storage flow path. When the storage amount of gas in the liquid storage flow path increases, the gas soon enters the gas guide path from the upper part of the liquid storage flow path. In the gas guide path, the gas moves downward toward the return part of the gas guide path while pressing down the liquid in the gas guide path. The gas that reaches the return part of the gas guide path is connected to the gas in the subsequent gas storage chamber, and floats up all at once while pushing up the liquid that exists on the downstream side of the return part. Then, the gas is released as bubbles from the opening on the outlet side of the gas guide path.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2015 / 146686 Summary of the invention

[0008] Problems to be solved by the invention

[0009] In the bubble generating device described in Patent Document 1, since the opening at the end of the pipe constituting the gas guide path serves as a bubble discharge port for directly discharging bubbles, a spherical bubble is intermittently discharged. In the bubble generating device of this structure, in order to make the bubbles contact with a large area of ​​the filter membrane, it is necessary to arrange a plurality of gas guide paths and discharge the bubbles generated from the respective gas guide paths toward different portions of the filter membrane.

[0010] On the other hand, washing is a cleaning method that removes contaminants from the surface of the filter membrane by vibration of the filter membrane caused by contact with bubbles. Therefore, when multiple bubbles are released toward different parts of the filter membrane, it is preferable to make these bubbles hit the filter membrane almost simultaneously to apply large vibrations.

[0011] However, in the bubble generating device described in Patent Document 1, it is difficult to make the gas supply speed to each gas guide path uniform when a plurality of gas guide paths are arranged and bubbles are released from each gas guide path. Therefore, it is not possible to synchronize the release cycles of bubbles generated from the plurality of gas guide paths, and it is difficult to make the plurality of bubbles hit the filter membrane almost simultaneously.

[0012] The present invention has been made in view of the above background, and an object of the present invention is to provide a bubble generating device capable of causing a plurality of bubbles to collide with a filter membrane substantially simultaneously, and a liquid filtering device using the bubble generating device.

[0013] Means for solving problems

[0014] 14. The air bag of claim 13 wherein the air bag is an air bag and wherein the at least one air bag is in a fluid relationship. The at least one air bag is in a fluid relationship. The at least one air bag is in a fluid relationship. The at least one air bag is in a fluid relationship. The at least one air bag is in a fluid relationship. , the gas storage chamber, the return path and the bubble release chamber are respectively arranged in the frame body in the order of the gas storage chamber, the return path and the bubble release chamber, the return path is formed by at least a return plate with a cross-sectional shape that extends downward and then turns upward and an inner plate arranged on the inner side of the return plate, one end of the return plate and the inner plate in the long side direction is fixed to one of the two side plates opposite to each other along the long side direction among the multiple side plates, and the other end of the return plate and the inner plate in the long side direction is fixed to the other side plate of the two side plates, one side of the return path in the short side direction is connected to the bubble release chamber, and the other side of the return path in the short side direction is connected to the gas storage chamber.

[0015] Effects of the Invention

[0016] According to the present invention, there is an excellent effect that a plurality of bubbles can collide with the filtration membrane almost simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a diagram showing a schematic configuration of a water treatment facility using the liquid filtration device according to the embodiment.

[0018] Figure 2 It is a perspective view showing the membrane module and the bubble generating device of the liquid filtering device.

[0019] Figure 3 It is a perspective view showing the membrane elements and insertion tubes of the membrane module.

[0020] Figure 4 It is a perspective view showing the bubble generating device of the liquid filtering device.

[0021] Figure 5 is a cross-sectional view of the bubble generating device.

[0022] Figure 6 is a top view of the bubble generating device.

[0023] Figure 7 is a cross-sectional view showing the bubble generating device in a non-operating state.

[0024] Figure 8 This is a cross-sectional view of the bubble generating device showing the state of the first stage in the batch process.

[0025] Fig. 9 This is a cross-sectional view of the bubble generating device showing the state of the second stage in the batch process.

[0026] Fig.10 This is a cross-sectional view of the bubble generating device showing the state of the third stage in the batch process.

[0027] Fig.11 This is a cross-sectional view of the bubble generating device showing the state of the fourth stage in the batch process.

[0028] Fig.12 It is a perspective view showing the bubble generating device of the embodiment.

[0029] Fig.13 is a cross-sectional view showing the bubble generating device.

[0030] Fig.14 This is a cross-sectional view showing an example of the state of the bubble generating device in the second phase of the batch process.

[0031] Fig.15 It is a cross-sectional view showing a bubble generating device according to a modified example.

[0032] Fig.16 It is a perspective view showing the turning plate, inner plate and partition plate of the first turning path. DETAILED DESCRIPTION

[0033] Hereinafter, an embodiment of the liquid filter device to which the present invention is applied is described using each figure. In the embodiment, in order to facilitate the understanding of the description, the structure and elements other than the main part of the present invention are simplified or omitted. In addition, in each figure, the same reference numerals are marked on the same elements. It should be noted that the shapes, sizes, etc. of the elements shown in each figure are schematically represented and do not represent the actual shapes, sizes, etc.

[0034] Figure 1This is a diagram showing a schematic structure of a water treatment facility using a liquid filtration device according to an embodiment. The water treatment facility includes a raw water tank 1, a filtered water tank 2, a treated water tank 3, a control device 4, a raw water pump 5, a first water level sensor 6, a raw water transfer pipe 7, a treated water transfer pipe 8, a suction pump 9, a second water level sensor 11, a third water level sensor 12, etc. In addition, the water treatment facility includes a blower 13, an air supply pipe 14, a stand 15, a membrane module 20, a bubble generating device 30, etc.

[0035] Raw water (pre-treatment water) W1 as liquid is stored in the raw water tank 1. A first water level sensor composed of an ultrasonic sensor or the like provided in the raw water tank 1 detects the water level (height of the water surface) of the raw water W1 in the raw water tank 1, and transmits the detection result as a water level signal to the control device 4. The raw water pump 5 provided in the raw water tank 1 sucks and discharges the raw water W1 in the raw water tank 1, and transmits it to the filtration treatment water tank 2 through the raw water transfer pipe 7. As the raw water pump 5, a pump composed of a submersible pump is exemplified, but a pump composed of a surface pump may also be used.

[0036] The filtration treatment water tank 2 is a water tank made of reinforced concrete. A liquid filtration device 50 is provided in the filtration treatment water tank 2. The liquid filtration device 50 includes a stand 15, a membrane assembly 20, and a bubble generating device 30, and the whole is immersed in the raw water W1 in the filtration treatment water tank 2. The blower 13 discharges the air as gas sucked from the suction port to the air supply pipe 14 through the discharge port. The air discharged to the air supply pipe 14 is supplied to the bubble generating device 30 of the liquid filtration device 50. The third water level sensor 12 provided in the filtration treatment water tank 2 detects the water level of the raw water W1 in the filtration treatment water tank 2, and sends the detection result as a water level signal to the control device 4.

[0037] The suction pump 9 suction-filters the raw water W1 in the treated water tank 2 via the treated water transfer pipe 8 and the membrane element to be described later provided in the membrane module 20. The sucked raw water W1 is filtered by the membrane element to become treated water W2, and then is sent to the treated water tank 3 via the treated water transfer pipe 8. The second water level sensor 11 provided in the treated water tank 3 detects the water level of the treated water W2 in the treated water tank 3, and sends the detection result to the control device 4 as a water level signal.

[0038] It should be noted that a pump that generates suction force using water head pressure may be used instead of the suction pump 9. The means of suction is not particularly limited.

[0039] When the water level of the treated water tank 3 has not reached the upper limit and the predetermined operation execution condition is satisfied, the control device 4 operates the suction pump 9 and the blower 13 to perform the filtration process of the raw water W1. However, even if the operation execution condition is satisfied, when the water level of the raw water W1 in the raw water tank 1 is below the lower limit and when the water level of the raw water W1 in the filtration treatment water tank 2 is below the lower limit, the control device 4 stops the execution of the filtration process. It should be noted that the function of the blower 13 will be described later.

[0040] Figure 2 1 is a perspective view showing a membrane assembly 20 and a bubble generating device 30 of a liquid filtering device (50) according to an embodiment. In the figure, Z represents the direction of gravity. In the following, the structure of the liquid filtering device (50) is described using the figures. When the "upper and lower directions" are referred to, the "upper and lower directions" refer to directions in which the membrane assembly 20 and the bubble generating device 30 face each other regardless of the posture of the membrane assembly 20 and the bubble generating device 30 shown in the figures. In addition, when the "upper" is referred to, the "upper" refers to a direction toward the upper side along the "upper and lower directions" regardless of the posture of the membrane assembly 20 and the bubble generating device 30 shown in the figures. In addition, when the "lower" is referred to, the "lower" refers to a direction toward the lower side along the "upper and lower directions" regardless of the posture of the membrane assembly 20 and the bubble generating device 30 shown in the figures. In addition, when the "horizontal direction" is referred to, the "horizontal direction" refers to a direction orthogonal to the "upper and lower directions" regardless of the posture of the membrane assembly 20 and the bubble generating device 30 shown in the figures.

[0041] The membrane module 20 includes a rectangular cylindrical frame 21 and a plurality of membrane elements 22. The plurality of membrane elements 22 are plate-like in shape, arranged in a straight line at intervals in the “horizontal direction” in the frame 21, and held by the inner surface of the frame 21.

[0042] The box-shaped bubble generating device 30 is arranged "below" (directly below) the membrane module 20. The bubble generating device 30 has two pipe connecting parts 31 on the side plate, and the above-mentioned air supply pipes ( Figure 1 14).

[0043] Figure 32 is a three-dimensional diagram showing a membrane element 22 and a cannula 16. The membrane element 22 includes a filter membrane 23 and four retaining components 24. In the liquid filtering device (50) of the embodiment, a filter membrane composed of a plate-shaped flat membrane is used as the filter membrane 23, but the type of the filter membrane 23 is not limited to a flat membrane, and may also be other types such as a hollow fiber membrane. The material of the filter membrane 23 may be an organic material such as PVC (polyvinyl chloride) and PVDF (polyvinylidene fluoride), or may be a ceramic composed of one or more of alumina, cordierite, silicon carbide, and other metal oxides. In addition, the filter membrane 23 may also be a composite membrane formed by combining an organic membrane and a ceramic membrane.

[0044] The filter membrane 23 includes a plurality of hollow spaces 23a extending in the vertical direction. These hollow spaces 23a are arranged at predetermined intervals in the short-side direction of the filter membrane 23, and the upper ends of the hollow spaces 23a are opened toward "upward".

[0045] A cannula 16 is installed at the upper end of the filtration membrane 23. Figure 1 8) is connected to the cannula 16. When the suction pump ( Figure 1 9) When working, an attraction is generated on the surface of the filter membrane 23, and the raw water ( Figure 1 The raw water W1 is sucked into the hollow space 23 a through the countless fine pores of the filtration membrane 23 . At this time, the raw water W1 is filtered, and the pollutants in the raw water W1 remain on the surface of the filtration membrane 23 .

[0046] The four holding members 24 are fixed to the corners of the filter membrane 23 and are respectively connected to the frame ( Figure 2 The engaging portion of the inner surface of 21) is engaged.

[0047] The bubble generating device 30 disposed "below" the membrane module 20 releases bubbles toward the membrane module 20 "above". The released bubbles float in the raw water W1 and enter the frame 21 through the opening at the lower end of the frame 21 of the membrane module 20. After that, the bubbles reach the lower ends of the plurality of filter membranes 23, are divided into a plurality of parts by the filter membranes 23, and then enter the area between the adjacent filter membranes 23 (hereinafter referred to as the "inter-membrane area"). The bubbles floating in the "inter-membrane area" cause the raw water W1 near the surface of the filter membrane 23 to shake violently, thereby peeling off the contaminants attached to the surface of the filter membrane 23.

[0048] Note that, as shown in the figure, the frame 21 is shaped to surround the plurality of membrane elements 22 , but may be shaped such that a portion of the side surface of the frame 21 has an opening as long as bubbles do not leak out of the frame 21 in large quantities.

[0049] Figure 4: is a three-dimensional diagram showing the bubble generating device 30. The bubble generating device 30 includes a frame 40. The frame 40 includes a first side plate 41, a second side plate 42, a third side plate 43, a fourth side plate 44 and a top plate 32. A rectangular long hole extending along the long side direction of the top plate 32 is formed on the top plate 32. A rectangular cover plate 32b is fixed to the top plate 32 to cover the long hole. The cover plate 32b is a part of the top plate 32. On the cover plate 32b, six perfectly circular bubble outlets 32a are formed in a straight line. The bubble generating device 30 does not include a bottom plate, and has a lower end opening 39 at the lower end of the bubble generating device 30 that is relatively large and opens toward "downward".

[0050] Figure 5 is a cross-sectional view of the bubble generating device 30. Figure 6 4 is a top view of the bubble generating device 30. The bubble generating device 30 includes a first gas storage chamber 33, a second gas storage chamber 34, a bubble releasing chamber 35, a first return path 36, a second return path 37, etc. The first gas storage chamber 33, the second gas storage chamber 34, the bubble releasing chamber 35, the first return path 36, and the second return path are respectively arranged in a frame 40.

[0051] Figure 5 The single-dot chain line in is the center line Lc of the top plate 32. The six bubble release ports 32a for releasing bubbles composed of air as gas are arranged so that their centers are located on the center line Lc of the top plate 32 and they are opened toward "upward". The bubble release chamber 35 is arranged "below" (directly below) the six bubble release ports 32a and is connected to the six bubble release ports 32a, respectively.

[0052] like Figure 6 As shown, the shape of the bubble release chamber 35 is an elongated shape extending along the arrangement direction of the six bubble release ports 32a.

[0053] The first gas storage chamber 33 and the second gas storage chamber 34 store raw water (treatment target water) as liquid inside, respectively, and store air as gas supplied to the raw water "above" the raw water. The first return path 36 communicates with the first gas storage chamber 33 and extends "downward", then turns back and extends "upward". The second return path 37 communicates with the second gas storage chamber 34 and extends "downward", then turns back and extends "upward".

[0054] Figure 5 The left-right direction is along the short side direction of the top plate 32. Figure 5The direction perpendicular to the paper plane is along the long side direction of the top plate 32. The first gas storage chamber 33, the first return path 36, the bubble release chamber 35, the second return path 37, and the second gas storage chamber 34 are arranged in the order of the first gas storage chamber 33, the first return path 36, the bubble release chamber 35, the second return path 37, and the second gas storage chamber 34 in the short side direction of the top plate 32.

[0055] The first return path 36 is formed by at least a return plate 45 having a cross-sectional shape (more specifically, a U-shaped cross-sectional shape) that extends toward "downward" and then returns toward "upward" and an inner plate 46 disposed on the inner side of the return plate 45. One end of each of the return plate 45 and the inner plate 46 in the long side direction (the same as the long side direction of the top plate 32) is fixed to the first side plate 41, which is one of the first side plate 41 and the third side plate 43 that are opposite to each other along the long side direction among the four side plates (41 to 44). The other end of each of the return plate 45 and the inner plate 46 in the long side direction is fixed to the third side plate 43 that is the other side plate. One side of the first return path 36 in the short side direction is connected to the bubble release chamber 35. The other side of the first return path 36 in the short side direction is connected to the first gas storage chamber 33.

[0056] The return plate 45 of the first return path 36 is fixed to the first side plate 41 and the third side plate 43 in such a manner that a gap is formed between the upper end of one side in the above-mentioned short-side direction and the top plate 32, and a gap is formed between the upper end of the other side in the above-mentioned short-side direction and the top plate 32. The first return path 36 is connected to the bubble release chamber 35 through the second communication port 36e formed by the gap between the upper end of the return plate 45 of the first return path 36 on one side in the above-mentioned short-side direction and the top plate 32. In addition, the first return path 36 is connected to the first gas storage chamber 33 through the first communication port 36d which is the gap between the upper end of the return plate 45 of the first return path 36 on the other side in the above-mentioned short-side direction and the top plate 32. The inner plate 46 of the first return path 36 is fixed to the first side plate 41, the second side plate 42 and the top plate 32.

[0057] The second return path 37 is formed by at least a return plate 47 having a cross-sectional shape (more specifically, a U-shaped cross-sectional shape) that extends toward "downward" and then returns toward "upward" and an inner plate 48 arranged on the inner side of the return plate 47. The return plate 47 and the inner plate 48 of the second return path 37 each have one end in the above-mentioned long side direction fixed to the first side plate 41. In addition, the return plate 47 and the inner plate 48 of the second return path 37 each have the other end in the above-mentioned long side direction fixed to the third side plate 43. The other side in the above-mentioned short side direction of the second return path 37 is connected to the bubble release chamber 35. In addition, one side in the above-mentioned short side direction of the second return path 37 is connected to the second gas storage chamber 34.

[0058] The return plate 47 of the second return path 37 is fixed to the first side plate 41 and the third side plate 43 in such a manner that a gap is formed between the upper end of one side in the above-mentioned short-side direction and the top plate 32, and a gap is formed between the upper end of the other side in the above-mentioned short-side direction and the top plate 32. The second return path 37 is connected to the bubble release chamber 35 through the first communication port 37e, which is a gap between the upper end of the other side in the above-mentioned short-side direction of the return plate 47 of the second return path 37. In addition, the second return path 37 is connected to the second gas storage chamber 34 through the second communication port 37d, which is a gap between the upper end of one side in the above-mentioned short-side direction of the return plate 47 of the second return path 37 and the top plate 32. The inner plate 48 of the second return path 37 is fixed to the first side plate 41, the third side plate 43, and the top plate 32.

[0059] The second return path 37 is a structure that is line-symmetrical with the first return path 36 based on the center line Lc. The first gas storage chamber 33 is adjacent to the first return path 36 on the other side of the short side direction. In addition, the second gas storage chamber 34 is adjacent to the second return path 37 on one side of the short side direction. The second gas storage chamber 34 is a structure that is line-symmetrical with the first gas storage chamber 33 based on the center line Lc.

[0060] The first return path 36 includes a descending portion 36a extending from the first communication port 36d toward "downward", a return portion 36b returning toward "upward", and an ascending portion 36c extending toward "upward" and communicating with the second communication port 36e. The second return path 37 also includes a descending portion 37a, a return portion 37b, and an ascending portion 37c.

[0061] In the bubble generating device 30 of this structure, as the amount of air stored in the first gas storage chamber 33 increases, the air in the descending portion 36a of the first return path 36 gradually descends in the descending portion 36a. When the amount of air stored in the first gas storage chamber 33 further increases, the air in the descending portion 36a reaches the return portion 36b, rises suddenly in the ascending portion 36c, and enters the bubble release chamber 35. In addition, as the amount of air stored in the second gas storage chamber 34 increases, the air in the descending portion 37a of the second return path 37 gradually descends in the descending portion 37a. When the amount of air stored in the second gas storage chamber 34 further increases, the air in the descending portion 37a reaches the return portion 37b, rises suddenly in the ascending portion 37c, and enters the bubble release chamber 35.

[0062] The air rising in the rising portion 36c of the first return path 36 and the air rising in the rising portion 37c of the second return path 37 merge in the bubble release chamber 35 and are released from the six bubble release ports 32a. Since the raw water existing "below" exerts a substantially uniform pressure in the "horizontal direction" on the air in the bubble release chamber 35, bubbles are released from the six bubble release ports 32a almost simultaneously. Thus, according to the bubble generating device 30, a plurality of bubbles can be made to hit the filter membrane 23 almost simultaneously.

[0063] Figure 7 2 is a cross-sectional view showing the air bubble generating device 30 in a non-operating state. In this figure, hatching on the cross section of the air bubble generating device 30 is omitted for easy viewing. In the air bubble generating device 30 in a non-operating state, as shown in the figure, the internal space of the air bubble generating device 30 is almost filled with the raw water W1.

[0064] The bubble generating device 30 can intermittently form bubbles from the bubble discharge port 32a. Hereinafter, the period from when bubbles are discharged from the bubble discharge port 32a to when bubbles are discharged from the next bubble discharge port 32a is referred to as a batch process.

[0065] Figure 8 1 is a cross-sectional view of the bubble generating device 30 showing the state of the first stage in the batch process. One of the two air supply pipes 14 connected to the bubble generating device 30 opens at the lower part of the first gas storage chamber 33, and supplies air to the raw water W1 in the first gas storage chamber 33. In addition, the other of the two air supply pipes 14 opens at the lower part of the second gas storage chamber 34, and supplies air to the raw water W1 in the second gas storage chamber 34.

[0066] In the first phase of the batch process, the air supplied to the raw water W1 through one of the two air supply pipes 14 floats in the raw water W1 and is stored in the upper part of the first gas storage chamber 33. A part of the air stored in the upper part of the first gas storage chamber 33 thus enters the descending portion 36a of the first return path 36 through the first communication port 36d. In the first gas storage chamber 33 and the descending portion 36a of the first return path 36, the water level of the raw water W1 decreases as the amount of air stored increases. The water level of the raw water W1 in the first gas storage chamber 33 is substantially the same as the water level of the raw water W1 in the first return path 36.

[0067] In the first gas storage chamber 33, the raw water W1 in an amount corresponding to the drop in the water level of the raw water W1 passes through the lower end opening ( Figure 439) flows out of the bubble generating device 30. In addition, in the descending portion 36a of the first return path 36, an amount of raw water W1 corresponding to the drop in the water level of the raw water W1 enters the return portion 36b. With this entry, a substantially equal amount of raw water W1 rises in the ascending portion 36c of the first return path 36 and flows out through the second communication port ( Figure 5 36e) enters the bubble release chamber 35. With this entry, substantially the same amount of raw water W1 flows out of the bubble generating device 30 through the lower end opening of the bubble generating device 30 or the bubble release port 32a.

[0068] The behavior of the air and the raw water W1 in the first gas storage chamber 33 and the first return passage 36 has been described, but the behavior of the air and the raw water W1 in the second gas storage chamber 34 and the second return passage 37 is the same.

[0069] Fig. 9 2 is a cross-sectional view of the bubble generating device 30 showing the state of the second phase in the batch process. In the second phase of the batch process, compared with the first phase, the storage amount of air in the first gas storage chamber 33, the descending portion 36a of the first return path 36, the second gas storage chamber 34, and the descending portion 37a of the second return path 37 increases, and the water level of the raw water W1 decreases.

[0070] When the second phase of the batch process is about to end, in the first return path 36 , the air in the descending portion 36 a enters the return portion 36 b and exceeds the return point of the return portion 36 b .

[0071] Fig.10 3 is a cross-sectional view of the bubble generating device 30 showing the state of the third phase in the batch process. In the third phase, the air exceeding the turning point rises at a high speed in the rising portion 36c of the first turning path 36 and reaches the second communication port 36e, and is then discharged to the outside of the bubble generating device 30 through the bubble discharge chamber 35 and the bubble discharge port 32a. In synchronization with such movement of the air, the air in the first gas storage chamber 33 enters the descending portion 36a of the first turning path 36 through the first communication port 36d, and descends at a high speed in the descending portion 36a.

[0072] The behavior of the air in the first gas storage chamber 33 and the first return path 36 has been described, but the behavior of the air in the second gas storage chamber 34 and the second return path 37 is the same. Above the bubble release port 32a, the air discharged to the outside from the first return path 36 via the bubble release chamber 35 and the air discharged to the outside from the second return path 37 via the bubble release chamber 35 are integrated to form an air aggregate with a circular cross-section.

[0073] The reason why such a large air aggregate is formed above the bubble release port 32a is as follows.

[0074] That is, the flow of the rising air in the bubble release chamber 35 toward the bubble release port 32a is faster than the flow of the air entering the bubble release chamber 35 from the rising portion (36c, 37c) through the second communication port (36e, 37e). In this case, the moving speed of the air in the bubble release chamber 35 is faster than the moving speed of the air flowing into the bubble release chamber 35 from the second communication port (36e, 37e). As a result, a negative pressure is generated in the bubble release chamber 35. Due to this negative pressure, the raw water W1 in the bubble release chamber 35 is introduced into the air, and a gas-liquid mixed flow of the air and the raw water W1 is generated. As a result, the air entering the bubble release chamber 35 from the return path (36, 37) through the second communication port (36e, 37e) is divided by the gas-liquid mixed flow and does not grow into large bubbles.

[0075] One of the reasons why the movement speed of the air in the bubble release chamber 35 is faster than the movement speed of the air flowing into the bubble release chamber 35 from the second communication port ( 36 e , 37 e ) is the flow path resistance of the return portion ( 36 b , 37 b ).

[0076] Therefore, the bubble generating device 30 of the embodiment includes a lower end opening ( ) which is an opening facing “downward” at the lower ends of the two gas storage chambers ( 33 , 34 ) and the bubble release chamber 35 . Figure 4 39). Since the two gas storage chambers (33, 34) and the bubble release chamber 35 are connected to each other at their respective lower parts, the lower end opening ( Figure 4 39) functions as a common opening for the two gas storage chambers (33, 34) and the bubble release chamber 35. If strictly divided, the lower end opening ( Figure 4 In the entire area of ​​39), the area directly below the first gas storage chamber 33 is an opening facing “downward” at the lower end of the first gas storage chamber 33, and the area directly below the second gas storage chamber 34 is an opening facing “downward” at the lower end of the second gas storage chamber 34. In addition, the area directly below the bubble release chamber 35 is an opening facing “downward” at the lower end of the bubble release chamber 35.

[0077] When the air in the bubble release chamber 35 begins to be released to the outside through the bubble release port 32a, the air near the return portion (36b, 37b) begins to move at a slightly slower speed than the previous air due to the flow resistance. As a result, a slight negative pressure is generated in the bubble release chamber 35. Fig.10 As shown by the thick arrow in the middle, the raw water W1 existing "below" the air exerts a force "upward" on the air existing "above". At this time, the raw water W1 existing "below" the bubble generating device 30 directly below the bubble release chamber 35 is about to pass through the lower end opening ( Figure 439) enters the interior of the bubble generating device 30, thereby supporting the above-mentioned force. At the same time, in each of the two gas storage chambers (33, 34), the raw water W1 existing "below" the air exerts a force on the air existing "above" to press into the return path (36, 37) through the first connecting port (36d, 37d). At this time, the raw water W1 existing "below" the bubble generating device 30 directly below each of the two gas storage chambers (33, 34) is about to pass through the lower end opening ( Figure 4 39) enters the interior of the bubble generating device 30, thereby supporting the above-mentioned force.

[0078] As a result of the above, the air inside each of the two return paths (36, 37) smoothly follows the preceding air in the bubble release chamber 35, and quickly flows into the bubble release chamber 35 through the second communication ports (36e, 37e). Therefore, according to the bubble generating device 30 of the embodiment, the following air can smoothly move toward the bubble release port 32a without being separated from the preceding air but connected to the preceding air, and be released from the bubble release port 32a as bubbles with a large diameter.

[0079] As described above, the opening provided at the lower end of the bubble release chamber 35 is the lower end opening ( Figure 4 39), the area directly below the bubble release chamber 35. That is, the opening area of ​​the opening provided at the lower end of the bubble release chamber 35 is the same as the horizontal cross-sectional area of ​​the bubble release chamber 35. In this structure, in the bubble release chamber 35, when bubbles are released, the force that pushes the upper air upward is not concentrated in a part of the cross-sectional direction but is made uniform by the raw water W1 present below the air. As a result, it is possible to more reliably suppress the raw water W1 present near the boundary with the air from being drawn in by the air, and it is possible to more reliably achieve a larger diameter of the bubbles.

[0080] The opening provided at the lower end of the gas storage chamber (33, 34) is a lower end opening ( Figure 4 The area directly below the gas storage chamber (33, 34) is the entire area of ​​the gas storage chamber (39). That is, the opening area of ​​the opening provided at the lower end of the gas storage chamber (33, 34) is the same as the cross-sectional area of ​​the gas storage chamber (33, 34). In this structure, when the bubbles are released from the bubble release port 32a, the force of the air that is intended to push the "upward" air in the gas storage chamber (33, 34) is not concentrated in a part of the cross-sectional direction, but can be uniformed. Thus, by suppressing the raw water W1 that is present near the boundary with the air from being drawn in by the air, it is possible to suppress the raw water W1 from flowing from the gas storage chamber (33, 34) into the return path (36, 37).

[0081] It should be noted that the shape of the bubble outlet 32a is not limited to a circle, and may be other shapes such as a rectangle. In addition, in the illustrated bubble generating device 30, a cover plate 32b having six bubble outlets 32a is fixed to the top plate 32, but a plurality of bubble outlets may be provided on the top plate 32 itself. However, in a structure in which the cover plate 32b is fixed to the top plate 32, the diameter and arrangement interval of the bubble outlet 32a can be easily adjusted by replacing the cover plate 32b.

[0082] The bubble generating device 30 of the embodiment includes two gas storage chambers ( 33 , 34 ), but the number of gas storage chambers is not limited to two, and may be one, or three or more.

[0083] like Figure 4 As shown, the bubble outlet 32a opens toward "upward". In this structure, compared with a structure having a bubble outlet opening in a direction different from "upward", it is difficult to produce a phenomenon in which the peripheral wall of the bubble outlet cuts off the "external preceding air" from the "internal following air", so bubbles with a larger diameter can be formed.

[0084] It should be noted that in the liquid filtering device (50) of the embodiment, bubbles released from the six bubble release ports 32a of equal size are connected to form a longer and larger bubble, which is then divided by the plurality of filter membranes (23) and enters the "inter-membrane region".

[0085] The present inventors have manufactured a test device having the same structure as the liquid filtering device (50) of the embodiment, and have measured the effect of washing the filter membrane ( Figure 3 23) Experiment on the vibration amount. A large value of the vibration amount of the filtration membrane means that the shaking amount of the raw water W1 near the membrane surface is large and the shear force generated by washing is high. Therefore, the shear force on the membrane surface can be indirectly evaluated by measuring the vibration amount.

[0086] Next, an example in which a more characteristic structure is added to the bubble generating device (20) of the embodiment will be described. It should be noted that, unless otherwise specified, the structure of the bubble generating device (20) of the example is the same as that of the embodiment.

[0087] exist Figure 8In the bubble generating device 30 of the embodiment shown, there is a difference in the air supply speed between one side and the other side of the two air supply pipes 14. As a result, the following undesirable situation may occur. That is, in one side of the return portion 36b of the first return path 36 and the return portion 37b of the second return path 37, the internal air reaches the return point earlier than the other side, and only the small-diameter bubbles generated by the supply of this air are released from the bubble discharge port 32a. Afterwards, the internal air of the other side reaches the return point, and only the small-diameter bubbles generated by the supply of this air are released from the bubble discharge port 32a. As a result, small-diameter bubbles are released from the bubble discharge port 32a at a shorter period than the period when large-diameter bubbles are released, which may cause poor cleaning of the surface of the filter membrane (23).

[0088] Fig.12 : is a perspective view showing the bubble generating device 30 of the embodiment. Fig.13 2 is a cross-sectional view showing the bubble generating device 30 of the embodiment. The bubble generating device 30 of the embodiment includes a communication pipe 38 that connects the upper portion (more specifically, the top end) of the first gas storage chamber 33 and the upper portion (more specifically, the top end) of the second gas storage chamber 34 .

[0089] Fig.14 1 is a cross-sectional view showing an example of the state of the bubble generating device 30 in the second phase of the batch process. In the example shown in the figure, the air supply speed to the second gas storage chamber 34 is faster than the air supply speed to the first gas storage chamber 33. Nevertheless, the water level of the raw water W1 is substantially the same in each of the first gas storage chamber 33, the descending portion 36a of the first return path 36, and the descending portion 37a of the second return path 37.

[0090] Due to the difference in the amount of air supplied, the amount of air stored in the second gas storage chamber 34 increases instantaneously compared to the first gas storage chamber 33, but due to this increase, the air pressure in the second gas storage chamber 34 becomes higher than the air pressure in the first gas storage chamber 33. As a result, the air in the second gas storage chamber 34 moves to the first gas storage chamber 33 on the low pressure side to eliminate the pressure difference. As a result, the water level of the raw water W1 is adjusted to the same height in each of the first gas storage chamber 33, the descending portion 36a of the first return path 36, and the descending portion 37a of the second return path 37.

[0091] According to the bubble generating device 30 of this structure, it is possible to avoid poor cleaning of the surface of the filter membrane (23) caused by the difference in air supply speed between the first gas storage chamber 33 and the second gas storage chamber 34.

[0092] It should be noted that, in the bubble generating device 30 of the embodiment, the connecting pipe 38 is configured to be disassembled by four joints, but the connecting pipe 38 may be of any structure as long as the upper portion of the first gas storage chamber 33 is connected to the upper portion of the second gas storage chamber 34. Fig.13 In the figure, for the convenience of explanation, the structure of the connecting pipe 38 is simplified.

[0093] Next, a modification example in which a part of the structure of the bubble generating device 30 of the embodiment is changed to another structure will be described.

[0094] Fig.15 4 is a cross-sectional view showing a modified example of the bubble generating device 30. The modified example of the bubble generating device 30 does not include a second return path. The bubble release chamber and the second gas storage chamber 34 are separated by a partition plate 49 fixed to the first side plate 41, the third side plate 43, and the top plate 32. The first gas storage chamber 33, the first return path 36, the bubble release chamber 35, and the second gas storage chamber 34 are arranged in the order of the first gas storage chamber 33, the first return path 36, the bubble release chamber 35, and the second gas storage chamber 34 in the short side direction of the top plate 32. The bubble release chamber 35 and the second gas storage chamber 34 are connected to each other via a connecting pipe 38.

[0095] Fig.16 3D diagram showing the return plate 45, the inner plate 46 and the partition plate 49 of the first return path 36. A plurality of connecting tubes 38 are arranged in a manner arranged along the long side direction of the top plate (32). The plurality of connecting tubes 38 respectively penetrate the partition plate 49 and the inner plate 46 to connect the first gas storage chamber 33 and the second gas storage chamber 34. In addition, the plurality of connecting tubes 38 are respectively arranged at positions deviated from directly below the bubble discharge port (32a).

[0096] The inventors of the present invention have confirmed through experiments that, in the bubble generating device 30 of the modified example, the range of the appropriate air supply amount can be expanded compared with the embodiment. The air supply amount is the amount of air supplied per unit time to the first gas storage chamber 33 and the second gas storage chamber. In addition, the appropriate air supply amount is the range of the air supply amount that can release bubbles at a stable time interval. In the embodiment, the air entering the bubble release chamber 35 from the first return path 36 and the air entering the bubble release chamber 35 from the second return path 37 are made to collide in the bubble release chamber 35. In contrast, in the bubble generating device 30 of the modified example, since the collision as described above does not occur, it can be considered that the range of the appropriate air supply amount can be expanded compared with the embodiment.

[0097] The present invention is not limited to the above-described embodiments, examples, and modifications, and may adopt structures different from the embodiments and examples within the scope of the structure to which the present invention can be applied. The present invention has unique effects in each of the modes described below.

[0098] [First method]

[0099] The first method is a bubble generating device (for example, the bubble generating device 30), which includes: a gas storage chamber (for example, a first gas storage chamber), the gas storage chamber stores liquid inside and stores gas supplied to the liquid above the liquid; and a return path (for example, a first return path 36), the return path is connected to the gas storage chamber and extends downward, then turns back and extends upward, and the bubble generating device releases the gas passing through the return path as bubbles, characterized in that the bubble generating device includes: a frame (for example, a frame 40), the frame has a plurality of side plates (for example, a first side plate 41 to a fourth side plate 44) and a top plate (for example, the top plate 32) fixed to the plurality of side plates in a manner of covering a space surrounded by the plurality of side plates from above; a plurality of bubble release ports (for example, the bubble release port 32a), the plurality of bubble release ports are arranged on the top plate in a manner arranged along the long side direction of the top plate; and a bubble release chamber (for example, the bubble release chamber 35), the bubble The release chamber is arranged in the frame and is connected to the plurality of bubble release ports. The gas storage chamber, the return path and the bubble release chamber are respectively arranged in the frame in the order of the gas storage chamber, the return path and the bubble release chamber along the short side direction of the top plate. The return path is formed by at least a return plate (such as the return plate 45) having a cross-sectional shape that extends downward and then turns upward and an inner plate (such as the inner plate 46) arranged on the inner side of the return plate. One end of the return plate and the inner plate in the long side direction is fixed to one of the two side plates opposite to each other along the long side direction among the plurality of side plates (such as the first side plate 41), and the other end of the return plate and the inner plate in the long side direction is fixed to the other side plate (such as the third side plate 43) among the two side plates. One side of the return path in the short side direction is connected to the bubble release chamber, and the other side of the return path in the short side direction is connected to the gas storage chamber.

[0100] In this structure, the air entering the bubble release chamber from the return path is pressurized toward the top plate at a uniform pressure, and bubbles are released almost simultaneously from the plurality of bubble release ports connected to the bubble release chamber. Thus, according to the first aspect, the plurality of bubbles can hit the filter membrane almost simultaneously.

[0101] [Second Method]

[0102] The second method is characterized in that it has the structure of the first method, and the return plate is fixed to the two top plates in a manner that a gap is formed between the upper end of one side in the short side direction and the top plate and a gap is formed between the upper end of the other side in the short side direction and the top plate, the return path is connected to the bubble release chamber through the gap between the upper end of one side in the short side direction of the return plate and the top plate, and the return path is connected to the gas storage chamber through the gap between the upper end of the other side in the short side direction of the return plate and the top plate, and the inner plate is fixed to the two side plates and the top plate.

[0103] According to the second aspect, the combination of the turn-back plate and the inner plate forms a turn-back path, and the gas storage chamber communicates with the descending portion of the turn-back path, and the ascending portion of the turn-back path communicates with the bubble release chamber.

[0104] [Third Method]

[0105] The third mode is characterized in that it has the structure of the second mode, and in addition to the first gas storage chamber as the gas storage chamber and the first return path as the return path, it also has a second gas storage chamber (for example, the second gas storage chamber 34) and a second return path (for example, the second return path 37), the first gas storage chamber, the first return path, the bubble release chamber, the second return path, and the second gas storage chamber are arranged in the order of the first gas storage chamber, the first return path, the bubble release chamber, the second return path, and the second gas storage chamber in the short side direction, and the second return path is at least A return plate (for example, the return plate 47) having a cross-sectional shape that extends downward and then turns back upward, and an inner plate (for example, the inner plate 48) arranged on the inner side of the return plate, one end of the return plate and the inner plate in the long side direction are each fixed to one of the two side plates that are opposite to each other along the long side direction among the plurality of side plates, the other end of the return plate and the inner plate in the long side direction are each fixed to the other side plate of the two side plates, the other side of the second return path in the short side direction is connected to the bubble release chamber, and one side of the second return path in the short side direction is connected to the second gas storage chamber.

[0106] According to the third aspect, gas can be supplied to the bubble release chamber from the first return path and the second return path.

[0107] [Fourth Method]

[0108] The fourth method is characterized in that it has the structure of the third method, and the return plate of the second return path is fixed to the two top plates in a manner that a gap is formed between the upper end on one side in the short side direction and the top plate and a gap is formed between the upper end on the other side in the short side direction and the top plate, the second return path is connected to the bubble release chamber through the gap between the upper end on the other side in the short side direction of the return plate of the second return path and the top plate, the second return path is connected to the second gas storage chamber through the gap between the upper end on one side in the short side direction of the return plate of the second return path and the top plate, and the inner plate of the second return path is fixed to the two side plates and the top plate.

[0109] According to the fourth aspect, the second turning path is formed by the combination of the turning plate and the inner plate, and the second gas storage chamber is communicated with the descending portion of the second turning path, and the ascending portion of the second turning path is communicated with the bubble release chamber.

[0110] [Fifth Method]

[0111] The fifth aspect has the structure of the third aspect or the fourth aspect, and the first gas storage chamber and the second gas storage chamber are communicated with each other via a communication pipe (for example, the communication pipe 38 ).

[0112] According to the fifth aspect, it is possible to avoid poor cleaning of the surface of the filter membrane due to the difference in the supply speed of the gas between the first gas storage chamber and the second gas storage chamber.

[0113] [Sixth Method]

[0114] The sixth aspect is characterized in that it has the structure of the second aspect, and in addition to the first gas storage chamber as the gas storage chamber and the first turn-back path as the turn-back path, it also has a second gas storage chamber and a second turn-back path, the first gas storage chamber, the first turn-back path, the bubble release chamber, the second turn-back path, and the second gas storage chamber are arranged in the order of the first gas storage chamber, the first turn-back path, the bubble release chamber, the second turn-back path, and the second gas storage chamber in the short side direction, and the second turn-back path is at least formed by the gas storage chamber being directed downward. A folding plate with a cross-sectional shape that extends in a straight line and then folds back upward, and an inner plate arranged on the inner side of the folding plate, one end of the folding plate and the inner plate in the long side direction is fixed to one of the two side plates that are opposite to each other along the long side direction among the multiple side plates, and the other end of the folding plate and the inner plate in the long side direction is fixed to the other side plate of the two side plates, the other side of the second folding path in the short side direction is connected to the bubble release chamber, and one side of the second folding path in the short side direction is connected to the second gas storage chamber.

[0115] According to the sixth aspect, the range of the appropriate air supply amount can be expanded compared to the fifth aspect.

[0116] [Seventh Method]

[0117] The seventh method is a liquid filtering device (for example, liquid filtering device 50), comprising: a filter membrane (for example, filter membrane 23), wherein the filter membrane has a membrane portion (for example, a portion other than the hollow of the filter membrane 23) and a hollow (for example, hollow 23a) surrounded by the membrane portion, and external liquid is drawn into the hollow through the membrane portion for filtration by being attracted in the hollow when the filter membrane is disposed in liquid; and a bubble generating device, wherein the bubble generating device is disposed below the filter membrane and releases bubbles toward the filter membrane, and is characterized in that the bubble generating device is a bubble generating device of any one of the first to sixth methods.

[0118] According to this configuration, the filter membrane can be well cleaned using the large-diameter bubbles released from the bubble generating device.

[0119] This application claims the priority of Japanese patent application No. 2022-31598 filed on March 2, 2022, and cites all the contents described in the Japanese patent application.

[0120] Description of Reference Numerals

[0121] 20: membrane assembly, 21 frame, 22: membrane element, 23: filter membrane, 23a: hollow, 30: bubble generating device, 32: top plate, 32a: bubble outlet, 33: first gas storage chamber, 34: second gas storage chamber, 35: bubble outlet chamber, 36: first return path, 36a: descending part, 36b: return part, 36c: ascending part, 36d: first communication port, 36e: second communication port, 36f: opening, 37: second return path, 37a: descending part, 37b: return part, 37c: ascending part, 37d: first communication port, 37e: second communication port, 37f: opening, 38: connecting pipe, 39: lower end opening, W1: raw water (liquid)

Claims

1. A bubble generating device, comprising: a gas storage chamber, wherein the gas storage chamber stores liquid inside and stores gas supplied to the liquid above the liquid; and a return path, wherein the return path is connected to the gas storage chamber and extends downward, then returns and extends upward, and the bubble generating device releases the gas passing through the return path as bubbles, characterized in that The bubble generating device comprises: a frame body having a plurality of side panels and a top panel fixed to the plurality of side panels in a manner covering a space surrounded by the plurality of side panels from above; a plurality of bubble release ports, the plurality of bubble release ports being arranged on the top plate in a manner of being arranged along a long side direction of the top plate; as well as a bubble release chamber, the bubble release chamber being arranged in the frame and communicating with the plurality of bubble release ports, The gas storage chamber, the return path, and the bubble release chamber are arranged in the frame in the order of the gas storage chamber, the return path, and the bubble release chamber along the short side direction of the top plate. The return path is formed by at least a return plate having a cross-sectional shape that extends downward and then returns upward, and an inner plate disposed inside the return plate. One end of each of the folding plate and the inner plate in the long side direction is fixed to one of two side plates that are opposite to each other along the long side direction among the plurality of side plates. The other end of each of the folding plate and the inner plate in the long side direction is fixed to the other side plate of the two side plates. One side of the short side direction of the return path is connected to the bubble release chamber, The other side of the short side of the return path is connected to the gas storage chamber. The folding plate is fixed to the two side plates in such a manner that a gap is formed between the upper end on one side in the short side direction and the top plate and a gap is formed between the upper end on the other side in the short side direction and the top plate. The folding path is connected to the bubble release chamber through a gap between an upper end of one side of the folding plate in the short side direction and the top plate. The return path is connected to the gas storage chamber through a gap between the upper end of the other side of the return plate in the short side direction and the top plate. The inner plate is fixed to the two side plates and the top plate, The bubble generating device further includes a second gas storage chamber in addition to the first gas storage chamber as the gas storage chamber. The first gas storage chamber, the return path, the bubble release chamber, and the second gas storage chamber are arranged in the order of the first gas storage chamber, the return path, the bubble release chamber, and the second gas storage chamber in the short side direction. The bubble release chamber and the second gas storage chamber are separated by a partition plate fixed to the two side plates and the top plate. The first gas storage chamber and the second gas storage chamber are communicated with each other via a communication pipe.

2. A liquid filtering device, comprising: A filtration membrane having a membrane portion and a hollow space surrounded by the membrane portion, wherein the filtration membrane is placed in a liquid and receives suction in the hollow space, thereby taking external liquid into the hollow space through the membrane portion for filtration; and a bubble generating device, the bubble generating device being arranged below the filter membrane and releasing bubbles toward the filter membrane, The liquid filtering device is characterized in that: The bubble generating device is the bubble generating device according to claim 1.

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