JP2023089335A - Membrane type air diffuser - Google Patents

Abstract

To provide a membrane type air diffuser capable of improving air diffusion unevenness.SOLUTION: A membrane type air diffuser 10 includes: a tube-like membrane 17 having a hollow insertion portion; a support 18 inserted into the insertion portion of the membrane 17; and a gas supply portion provided in a central portion of the membrane 17 in a longitudinal direction A, the membrane 17 including a bag-like portion 23 formed in a bag shape by two sheet members 21 and 22 on front and back, and the gas supply portion including a ventilation channel that communicates with an inside of the bag-like portion 23 of the membrane 17 from outside, wherein a plurality of slits 30 are formed in the sheet members 21 forming an outer peripheral surface of the bag-like portion 23 of the membrane 17 to release a gas supplied into the bag-like portion 23 through the ventilation channel of the gas supply portion to outside, and in a state in which the gas is released from the slits 30 to the outside, both ends C in the longitudinal direction A of the membrane 17 are positioned higher than the central portion.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to a membrane-type air diffuser that is installed below the liquid surface and releases air bubbles into the liquid.

Conventionally, as this type of membrane type air diffuser, for example, as shown in FIG. This membrane-type air diffuser 203 has a tube-shaped membrane 204 , a support tube 205 inserted into the membrane 204 , and an air supply section 206 .

The end of the membrane 204 is watertightly fixed to the support tube 205 with a fixture 207 such as a ring-shaped band. Support tube 205 is connected to air supply tube 208 . The air supply part 206 is provided in the central part B in the longitudinal direction A of the support pipe 205, and has a ventilation channel 209 that communicates from the air supply pipe 208 to the inner circumference of the membrane 204 and the outer circumference of the support pipe 205. are doing.

A plurality of slits 211 for releasing air 210 supplied between the inner periphery of the membrane 204 and the outer periphery of the support tube 205 from the air supply pipe 208 through the ventilation channel 209 of the air supply portion 206 to the outside are formed in the membrane. 204.

According to this, air 210 is supplied between the inner periphery of membrane 204 and the outer periphery of support tube 205 from air supply pipe 208 through ventilation channel 209 of air supply portion 206, thereby expanding membrane 204. Air 210 is released into the water 201 to be treated as air bubbles 202 through slits 211 of the membrane 204 .

Incidentally, the membrane-type air diffuser 203 as described above is described in Patent Document 1 below, for example.

JP 2005-81203

However, in the above-described conventional type, the air 210 supplied between the inner periphery of the membrane 204 and the outer periphery of the support tube 205 from the ventilation flow path 209 of the air supply section 206 is distributed from the central portion B in the longitudinal direction A of the support tube 205. The pressure loss at the both ends C becomes larger than the pressure loss at the central portion B because the flow toward the both ends C receives more flow resistance.

As a result, the air 210 is less likely to be released from the slits 211 at both ends C of the membrane air diffuser 203 than at the central portion B, and thus the amount of air bubbles 202 released from the slits 211 is reduced. There is a problem that air diffusion unevenness occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a membrane air diffuser capable of improving air diffusion unevenness.

In order to achieve the above object, the first invention is a membrane air diffuser that is installed below the liquid surface and releases air bubbles into the liquid,
A tube-shaped membrane having a hollow insertion portion, a support inserted into the insertion portion of the membrane, and a gas supply portion provided in the central portion of the membrane in the longitudinal direction,
The membrane has a bag-like portion configured in a bag-like shape with two sheet members on the front and back,
The gas supply unit has a ventilation channel that communicates with the bag-shaped portion of the membrane from the outside,
A plurality of slits are formed in the sheet member constituting the outer peripheral surface of the bag-shaped portion of the membrane for discharging the gas supplied into the bag-shaped portion through the ventilation channel of the gas supply portion to the outside,
Both ends of the membrane in the longitudinal direction are positioned higher than the central portion in a state in which gas is released to the outside through the slits.

According to this, by operating the membrane type air diffuser, gas is supplied into the bag-like portion of the membrane through the ventilation channel of the gas supply portion, the bag-like portion of the membrane expands, and the gas in the bag-like portion expands. is emitted from the slit to the outside. As a result, a large number of air bubbles are released from the membrane air diffuser into the liquid.

At this time, the gas supplied from the ventilation channel of the gas supply unit into the bag-like portion of the membrane receives more flow resistance as it flows from the central portion toward both ends in the longitudinal direction of the membrane, resulting in pressure loss at both ends of the membrane. becomes larger than the pressure drop at the center.

On the other hand, in the state where the gas is discharged to the outside from the slit as described above, both ends in the longitudinal direction of the membrane are positioned higher than the central part, so the depth from the liquid surface to both ends of the membrane The depth becomes shallower than the depth from the liquid surface to the central portion of the membrane, and the hydraulic pressure applied to both ends of the membrane becomes smaller than the hydraulic pressure applied to the central portion of the membrane.

In this way, at both ends of the membrane in the longitudinal direction, the pressure loss that makes it difficult to release bubbles cancels out the action that makes it difficult for bubbles to be released because the liquid pressure is reduced. Since the variation in the amount of released air bubbles between the central portion and both ends in the direction is reduced, the air diffusion unevenness of the membrane type air diffuser can be improved.

In the membrane air diffuser of the second aspect of the present invention, the membrane has more space between the support and the both end portions than the central portion in the longitudinal direction.

According to this, when the gas is released from the slit to the outside, buoyancy acts on the membrane due to the gas supplied into the bag-like portion of the membrane. Since there is a margin between both ends of the membrane in the longitudinal direction and the support, the buoyant force acting on the membrane causes both ends of the membrane to rise above the central portion and to a position higher than the central portion.

In the membrane air diffuser of the third aspect of the present invention, the outer peripheral length of the support is shorter at both ends than at the central portion in the longitudinal direction.

According to this, it is possible to obtain a membrane-type air diffuser configured so that the both end portions of the membrane have more space between them and the support than the central portion in the longitudinal direction.

In the membrane air diffuser of the fourth aspect of the present invention, the inner peripheral length of the membrane is longer at both ends than at the central portion in the longitudinal direction.

According to this, it is possible to obtain a membrane-type air diffuser configured so that the both end portions of the membrane have more space between them and the support than the central portion in the longitudinal direction.

In the membrane air diffuser of the fifth aspect of the present invention, the bottoms of both ends in the longitudinal direction of the support are positioned higher than the bottom of the central portion.

According to this, by inserting the support into the insertion portion of the membrane, both ends in the longitudinal direction of the membrane are positioned higher than the central portion.

As described above, according to the present invention, at both ends in the longitudinal direction of the membrane, the pressure loss increases, making it difficult for bubbles to be released, and the liquid pressure decreases, making it easier for bubbles to be released. As a result, variations in the amount of released air bubbles between the central portion and both ends of the membrane in the longitudinal direction are reduced, so that the air diffusion unevenness of the membrane air diffuser can be improved.

1 is a perspective view of an air diffuser according to a first embodiment of the present invention; FIG. It is a side view of the membrane-type air diffuser provided in the air diffuser. It is a cross-sectional view of an end portion of the membrane type air diffuser. It is a perspective view of the membrane and support pipe of the membrane air diffuser of the same. It is a partially cutaway plan view of the membrane of the membrane type air diffuser. It is a partially notched bottom view of the membrane of a membrane-type air diffuser same. Fig. 3 is a cross-sectional view of a support tube of the membrane air diffuser of the same; Fig. 3 is a cross-sectional view of a connecting portion between a membrane-type air diffuser and an air supply pipe of the air diffuser. FIG. 9 is a view taken along line XX in FIG. 8; 4 is a view taken along line XX in FIG. 3; FIG. It is a perspective view of the gas supply nozzle of a membrane-type air diffuser same. FIG. 12 is a view taken along line XX in FIG. 11; 12 is a view taken along the line YY in FIG. 11; FIG. It is a perspective view of the adapter of aeration equipment same. Fig. 3 is a view of the disassembled adapter, the air supply pipe, and the gas supply nozzle of the aeration equipment; It is a figure which shows the procedure of the manufacturing method of the membrane of a membrane-type air diffuser equally. It is a figure which shows the procedure of the manufacturing method of the membrane of a membrane-type air diffuser equally. FIG. 5 is a cross-sectional view of a support tube of a membrane air diffuser according to a second embodiment of the present invention; It is a cross-sectional view of an end portion of the membrane type air diffuser. FIG. 10 is a partially cutaway side view of a membrane air diffuser according to a third embodiment of the present invention; FIG. 11 is a cross-sectional view of a support tube of a membrane air diffuser according to a fourth embodiment of the present invention; It is a side view of a membrane-type air diffuser of the same. 1 is a diagram of a conventional membrane-type air diffuser. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
In the first embodiment, as shown in FIG. 1, 1 is an air diffuser installed in an aerobic tank (not shown) installed in, for example, a sewage treatment plant. The air diffuser 1 is immersed under the surface of water 3 (an example of a liquid) to be treated made of activated sludge in a tank, and includes a plurality of membrane type air diffusers 10 that release air bubbles 4 into the water 3 to be treated. , an air supply pipe 12 that supplies air 11 (an example of gas for diffusion) to each membrane type air diffuser 10, and an adapter 14 (see FIG. 8) that fixes the membrane type air diffuser 10 to the air supply pipe 12 , and a blower 15 for supplying air 11 to the air supply pipe 12 from outside the tank.

As shown in FIGS. 2 to 6, the membrane diffuser 10 includes a tube-shaped (cylindrical) membrane 17 having a hollow insertion portion 16 in the center, and a horizontal and a gas supply nozzle 19 (an example of a gas supply section) provided in the central portion in the longitudinal direction A of the membrane 17 .

The membrane 17 has a bag-like portion 23 formed by welding front and back sheet members 21 and 22 to form a bag-like shape. The sheet member 21 on the front side and the sheet member 22 on the back side are made of soft elastic synthetic resin. Constructs the inner peripheral surface.

A circular first opening 24 is formed in the upper portion of the membrane 17 at its center in the longitudinal direction A. As shown in FIG. The insertion portion 16 penetrates both end portions of the membrane 17 , and the insertion portion 16 and the upper side of the membrane 17 communicate with each other through the first opening 24 .

8, 9, and 16, circular first and second through holes 26 and 27 are formed in the central portion and lower portion of the membrane 17 in the longitudinal direction A. As shown in FIGS. Among these, the first through holes 26 are formed in the sheet member 21 on the front side. The second through hole 27 has a smaller diameter than the first through hole 26 and is formed in the sheet member 22 on the back side. The center of the first through hole 26 and the center of the second through hole 27 are coaxial.

As shown in FIGS. 4 to 6, both sheet members 21 and 22 are welded together at welded portions 29 . The welded portions 29 are composed of an end welded portion 29a formed along the entire circumference of both ends of the membrane 17, a central welded portion 29b formed around the first opening 24, and a center welded portion 29a and the central welded portion. It has a longitudinal welded portion 29c formed between it and the portion 29b.

The sheet member 21 on the front side is formed with a large number of slits 30 for discharging the air 11 supplied from the gas supply nozzle 19 into the bag-like portion 23 to the outside. As shown by the phantom lines in FIG. 6, a non-formed region 31 in which no slits 30 are formed is provided in the lower portion of the sheet member 21 on the front side. 30 are formed.

Further, for example, in the drawings such as FIG. 2, the slit 30 is drawn in an oval shape to make it easier to see, but in reality, the slit 30 is closed when air diffusion is not performed, and air diffusion is performed. It is a notch that opens slightly when it is running.

As shown in FIGS. 4 and 7, the support tube 18 is a circular straight tube made of resin with both ends opened. A portion 33 is formed. As shown in FIGS. 8 and 9, when the support tube 18 is inserted into the insertion portion 16 of the membrane 17, the position of the first opening 24 of the membrane 17 and the position of the second opening 33 of the support tube 18 are different. match.

Further, as shown in FIG. 7, a bolt insertion hole 34 is formed in the central portion and lower portion of the support tube 18 in the longitudinal direction A. As shown in FIG. As shown in FIGS. 8 and 9, the position of the bolt insertion hole 34 of the support tube 18 and the center position of the second through hole 27 of the sheet member 22 on the back side of the membrane 17 match.

As shown in FIGS. 2, 6, 8, 9, and 11 to 13, the gas supply nozzle 19 has a circular cylindrical portion 37, a collar portion 38, and a top plate portion 39. As shown in FIGS. The cylindrical portion 37 is inserted into the first through hole 26 (see FIG. 16) of the sheet member 21 on the front side of the membrane 17 and protrudes below the membrane 17 . A pair of notch portions 41 and an inlet port 42 opening into the air supply pipe 12 are formed at the lower end portion of the tubular portion 37 .

The collar portion 38 is formed at the upper end portion of the tubular portion 37 and protrudes outward in the radial direction of the tubular portion 37. As shown in FIGS. . A plurality of outflow ports 43 opening into the bag-like portion 23 are formed on the outer peripheral surface of the collar portion 38 . In addition, a gas supply nozzle 19 is attached to the membrane 17 so that the air 11 does not leak from the first through hole 26 (see FIG. 16) of the sheet member 21 on the front side so that the air 11 does not leak from the first through hole 26 during air diffusion. there is

The top plate portion 39 is formed at the upper end portion of the cylindrical portion 37, and a bolt insertion hole 45 is formed through the top plate portion 39 in the vertical direction.

A ventilation channel 46 is formed in the gas supply nozzle 19 to communicate with the inflow port 42 and the outflow port 43 . As a result, the inside of the air supply pipe 12 and the inside of the bag-like portion 23 of the membrane 17 are communicated with each other through the ventilation flow path 46 of the gas supply nozzle 19 . A recessed portion 47 curved in an arc along the outer peripheral surface of the support tube 18 is formed on the upper surface of the gas supply nozzle 19 .

As shown in FIGS. 8 and 9, the membrane diffuser 10 is fixed to the air supply pipe 12 via an adapter 14 . As shown in FIGS. 14 and 15, the adapter 14 includes a rectangular parallelepiped adapter main body 50 sandwiched between the membrane air diffuser 10 and the air supply pipe 12, and the membrane air diffuser 10 via the membrane 17. and a pair of support portions 55 for supporting the support tube 18 from below. The support portions 55 are provided at both ends of the adapter main body 50 in the longitudinal direction A of the membrane diffuser 10 .

The lower surface of the adapter main body 50 is formed with a concave portion 52 curved in an arc shape along the outer peripheral surface of the air supply pipe 12 and an O-ring fitting portion 56 . A circular first fitting hole 53 is formed through the adapter main body 50 in the vertical direction. The O-ring fitting portion 56 is formed to surround the first fitting hole 53 .

As shown in FIG. 1, the air supply pipe 12 is arranged below the membrane air diffuser 10, and is perpendicular to the membrane air diffuser 10 at the central portion in the longitudinal direction A of the membrane air diffuser 10. there is As shown in FIG. 15 , the upper end of the air supply pipe 12 is formed with a plurality of circular second fitting holes 54 penetrating the inside and outside of the air supply pipe 12 .

The position of the first fitting hole 53 of the adapter 14 and the position of the second fitting hole 54 of the air supply pipe 12 match. As shown in FIGS. 8, 9 and 15, the cylindrical portion 37 of the gas supply nozzle 19 is fitted into the first fitting hole 53 of the adapter 14 and the second fitting hole 54 of the air supply pipe 12 from above. The lower end protrudes into the air supply pipe 12 through the second fitting hole 54 .

In addition, O seals simultaneously between the lower surface of the adapter 14 and the outer peripheral surface of the air supply pipe 12 and between the inner peripheral surface of the first fitting hole 53 of the adapter 14 and the outer peripheral surface of the cylindrical portion 37 of the gas supply nozzle 19 . A ring 62 (an example of a sealing member) is fitted into the O-ring fitting portion 56 and held by the adapter 14 .

The air supply pipe 12 , the adapter 14 , the membrane 17 , the support pipe 18 and the gas supply nozzle 19 are connected by a connecting member 51 . The connecting member 51 has a T-head bolt 57 and a nut 58 .

The T-head bolt 57 is inserted into the second fitting hole 54 of the air supply pipe 12, the bolt insertion hole 45 of the gas supply nozzle 19, the second through hole 27 of the sheet member 22 on the back side of the membrane 17, and the bolt of the support pipe 18 from below. It is inserted through the insertion hole 34 and protrudes into the support tube 18 .

The head 57 a of the T-head bolt 57 is fitted from below into both notches 41 of the cylindrical portion 37 of the gas supply nozzle 19 and engaged with the inner peripheral surface of the upper end of the air supply pipe 12 .

A nut 58 is screwed onto the T-head bolt 57 inside the support tube 18 and engages the inner peripheral surface of the support tube 18 .

The peripheral portion of the second through hole 27 of the sheet member 22 on the back side is sandwiched between the outer peripheral surface of the support pipe 18 and the top plate portion 39 of the gas supply nozzle 19 over the entire circumference. A cylindrical packing 60 made of an elastic material such as rubber is fitted in the bolt insertion hole 34 of the support tube 18 . As a result, part of the air 11 supplied from the air supply pipe 12 through the ventilation flow path 46 of the gas supply nozzle 19 and into the bag-like portion 23 of the membrane 17 flows between the bolt insertion hole 34 and the T-head bolt 57 . It is prevented from leaking into the support tube 18 from the.

The peripheral length of the inner peripheral surface of the membrane 17 (hereinafter referred to as the inner peripheral length) is longer than the peripheral length of the outer peripheral surface of the support tube 18 (hereinafter referred to as the outer peripheral length) with a certain margin. As a result, when the air 11 in the air supply pipe 12 is not supplied into the bag-shaped portion 23 of the membrane 17 and the bag-shaped portion 23 is contracted, the inner peripheral surface of the membrane 17 (that is, the inner surface of the sheet member 22 on the back side) The peripheral surface) does not contact the outer peripheral surface of the support tube 18 over the entire circumference without gaps, but a gap with a certain margin is formed between the inner peripheral surface of the membrane 17 and the outer peripheral surface of the support tube 18 .

Here, at both ends C of the membrane 17 in the longitudinal direction A, since there is room for the membrane 17 to float between the inner peripheral surface of the membrane 17 and the outer peripheral surface of the support pipe 18, the air 11 in the air supply pipe 12 is supplied into the bag-like portion 23 of the membrane 17, as shown in FIGS. climb. As a result, as shown in FIGS. 3 and 8 to 10, when the air 11 is discharged to the outside from the slit 30 during air diffusion, the both ends C of the membrane 17 are separated as shown by the phantom lines in FIG. It floats above the central portion B and becomes a higher position.

On the other hand, as shown in FIGS. 8 and 9, a gas supply nozzle 19 is attached to the membrane 17 at the central portion B in the longitudinal direction A of the membrane 17 so that the membrane 17 is downwardly positioned relative to the support tube 18. Due to the deviation, there is little room for the membrane 17 to float between the inner peripheral surface of the membrane 17 and the outer peripheral surface of the support tube 18 , and the air 11 in the air supply tube 12 is forced into the bag-like portion 23 of the membrane 17 . , the upper portion of the membrane 17 hardly floats with respect to the support tube 18 .

The operation of the above configuration will be described below.

As shown in FIGS. 1, 8, and 9, by driving the blower 15, the air 11 is supplied from the blower 15 into the air supply pipe 12, and the air 11 in the air supply pipe 12 flows through the gas supply nozzle 19. From the inlet 42 , it passes through the ventilation channel 46 and flows from the outlet 43 into the bag-like portion 23 of the membrane 17 . As a result, the bag-shaped portion 23 is inflated, and the air 11 in the bag-shaped portion 23 is released to the outside from the slits 30 of the sheet member 21 on the front side, so that a large number of air bubbles 4 are emitted from the membrane type air diffuser 10 to be treated. Released into water 3.

At this time, the air 11 supplied from the outlet port 43 of the gas supply nozzle 19 into the bag-shaped portion 23 of the membrane 17 increases the flow resistance as it flows from the central portion B toward both ends C in the longitudinal direction A of the membrane 17 . Therefore, the pressure loss at both end portions C of the membrane 17 is greater than the pressure loss at the central portion B thereof.

On the other hand, in the state where the air 11 is discharged to the outside from the slit 30 as described above, the air 11 supplied into the bag-like portion 23 of the membrane 17 exerts a buoyant force on the membrane 17, and this buoyant force acts on the membrane 17. 2, both end portions C of the membrane 17 are positioned higher than the central portion B. As shown in FIG. Therefore, the depth D1 from the water surface of the water 3 to be treated in the aerobic tank to both ends C of the membrane 17 becomes shallower than the depth D2 from the water surface to the central portion B of the membrane 17, and both ends of the membrane 17 The water pressure applied to C becomes smaller than the water pressure applied to the central portion B of the membrane 17 .

In this manner, at both ends C of the membrane 17, the pressure loss increases to make it difficult to release the air bubbles 4 and the water pressure decreases to make it easier to release the air bubbles 4, which cancel each other out. Since the variation in the release amount of the air bubbles 4 between the central portion B and the both end portions C is reduced, the air diffusion unevenness of the membrane type air diffuser 10 can be improved.

Furthermore, as shown in FIG. 1, the membrane type air diffuser 10 is perpendicular to the air supply pipe 12 at the central portion in the longitudinal direction A, so that the air 11 passes through the air passage 46 of the gas supply nozzle 19 to the membrane. It is uniformly supplied into the bag-like portion 23 from the central portion B of 17 toward both end portions C. As shown in FIG. For this reason, a large number of bubbles 4 are uniformly released from the membrane 17 without being locally unevenly released from the membrane 17 .

In addition, since the air supply pipe 12 is arranged below the membrane type air diffuser 10 , many bubbles 4 are not blocked by the air supply pipe 12 and pass through the slits 30 of the membrane type air diffuser 10 to the water 3 to be treated. released inside.

A method of manufacturing the membrane 17 of the membrane air diffuser 10 will be described below.

First, as shown in FIG. 16, the tubular portion 37 of the gas supply nozzle 19 is inserted into the first through hole 26 of the sheet member 21 on the front side in which a large number of slits 30 are formed. The gas supply nozzle 19 is attached to the sheet member 21 on the front side by welding to the lower surface of the flange portion 38 of the supply nozzle 19 .

Thereafter, as shown in FIG. 17, the outer peripheral edge 65 (see FIG. 16) of the sheet member 21 on the front side and the outer peripheral edge 66 (see FIG. 16) of the sheet member 22 on the back side are welded to form the bag-like portion 23. A rectangular membrane sheet 67 is formed. The stippled portion in FIG. 17 is the welded portion 29 between the sheet member 21 on the front side and the sheet member 22 on the back side.

After that, as shown in FIG. 17, the opposing long sides 68 of the membrane sheet 67 are joined together to form a tubular shape. A membrane 17 is formed having an insert 16, a first opening 24 at the top and a gas delivery nozzle 19 at the bottom.

In the first embodiment, the front side sheet member 21 and the back side sheet member 22 having substantially the same shape are used to form the tube-shaped membrane 17, but the area required for the back side sheet member 22 is The bag-shaped portion 23 may be formed by welding the sheet member 21 on the front side only to the front side sheet member 21, or the sheet member 22 on the back side may be welded to the sheet member 21 on the front side only in a necessary region to form the bag-shaped portion 23. You may
(Second embodiment)
As shown in FIG. 7 in the first embodiment described above, the support tube 18 is a circular straight tube having a constant outer peripheral length. Thus, the outer peripheral length of the support tube 18 is formed so that the end portions C are shorter than the central portion B. As shown in FIG. That is, the outer diameter E1 of the support tube 18 is smaller at both end portions C than at the central portion B, and gradually decreases from the central portion B toward both end portions C. As shown in FIG.

According to this, as shown by the solid line in FIG. 19, when air diffusion is stopped and the bag-like portion 23 is contracted, the space 64 between the inner peripheral surface of the membrane 17 and the outer peripheral surface of the support tube 18 is is wider at both end portions C than at the central portion B, the membrane 17 has more room between the support tube 18 and the both end portions C than at the central portion B.

As a result, as shown by the phantom lines in FIG. 19, when the bag-like portion 23 expands and the air 11 is released to the outside through the slits 30 during air diffusion, the buoyancy acting on the membrane 17 causes the membrane 17 to move. Both end portions C are raised above the central portion B and are positioned higher.
(Third Embodiment)
In the third embodiment, as shown by the solid line in FIG. 20, the inner peripheral length of the membrane 17 is longer at both end portions C than at the central portion B. As shown in FIG. That is, the inner diameter E2 of the membrane 17 is larger at both end portions C than at the central portion B, and gradually increases from the central portion B toward both end portions C. As shown in FIG. The support tube 18 is a circular straight tube having a constant outer diameter.

According to this, when air diffusion is stopped and the bag-like portion 23 is contracted, the space 64 between the inner peripheral surface of the membrane 17 and the outer peripheral surface of the support tube 18 is wider at both ends C than at the central portion B. Therefore, both ends C of the membrane 17 have more space between them and the support tube 18 than the central portion B of the membrane 17 .

As a result, as shown by the phantom lines in FIG. 20 , when the bag-like portion 23 expands and the air 11 is released to the outside through the slits 30 during air diffusion, the buoyancy acting on the membrane 17 causes the membrane 17 to dissipate. Both end portions C are raised above the central portion B and are positioned higher.
(Fourth embodiment)
In the fourth embodiment, the bottoms of both end portions C of the support tube 18 are positioned higher than the bottom portion of the central portion B, as shown in FIG. That is, both end portions C of the support tube 18 are bent obliquely upward from the central portion B. By inserting the support tube 18 having such a shape into the insertion portion 16 of the membrane 17, as shown in FIG. The bottoms of both ends C of the membrane 17 are positioned higher than the bottom of the central portion B. As shown in FIG.

Although the air 11 is used as the diffusion gas in each of the above embodiments, a gas other than the air 11 may be used.

3 Water to be treated (liquid)
4 Bubbles 10 Membrane air diffuser 11 Air (gas)
16 insertion portion 17 membrane 18 support tube (support)
19 gas supply nozzle (gas supply unit)
21 Sheet member 22 on the front side Sheet member 23 on the back side Bag-shaped part 30 Slit 46 Ventilation flow path A Longitudinal direction B Central part C End part

Claims (5)

A membrane air diffuser that is installed below the liquid surface and releases air bubbles into the liquid,
A tube-shaped membrane having a hollow insertion portion, a support inserted into the insertion portion of the membrane, and a gas supply portion provided in the central portion of the membrane in the longitudinal direction,
The membrane has a bag-like portion configured in a bag-like shape with two sheet members on the front and back,
The gas supply unit has a ventilation channel that communicates with the bag-shaped portion of the membrane from the outside,
A plurality of slits are formed in the sheet member constituting the outer peripheral surface of the bag-shaped portion of the membrane for discharging the gas supplied into the bag-shaped portion through the ventilation channel of the gas supply portion to the outside,
1. A membrane air diffuser, wherein both ends of the membrane in the longitudinal direction are positioned higher than the central part in a state in which gas is discharged to the outside through a slit. 2. The membrane type air diffuser according to claim 1, wherein the membrane has more space between the support and the both end portions than the center portion in the longitudinal direction. 3. The membrane type air diffuser according to claim 1, wherein the peripheral length of the support is shorter at both ends than at the central portion in the longitudinal direction. 4. The membrane diffuser according to any one of claims 1 to 3, wherein the inner peripheral length of the membrane is longer at both ends than at the center in the longitudinal direction. 2. The membrane type air diffuser according to claim 1, wherein the bottoms of both ends in the longitudinal direction of the support are positioned higher than the bottom of the central portion.

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