JP5562020B2 - Membrane diffuser - Google Patents

Description

  The present invention relates to a membrane-type air diffuser installed in a tank such as a sewage treatment facility, and relates to a technique for performing air diffusion for biological treatment or stirring.

  Conventionally, there is a diffuser of this type as shown in FIG. 9, for example. In this case, a diffuser film 52 is mounted on the upper surface of the base plate 51, and an air supply port 53 is provided at a predetermined position on the film surface of the air diffuser film 52. The air supply port 53 is connected to the base plate 51 and the air diffuser film 52. It communicates with. The diffuser film 52 is a synthetic resin film or synthetic rubber film provided with a large number of slits 54, and has a structure in which the periphery of the diffuser film 52 is fixed to the base plate 51 by a fixing portion 55.

  The slit 54 is parallel to the longitudinal direction A of the diffuser membrane 52 and has a predetermined length, for example, 0.2 mm. When the diffuser is stopped, the diffuser film 52 receives the water pressure in the tank and is pressed against the upper surface of the base plate 51. The diffuser film 52 does not expand and the slit 54 is closed. At the time of air diffusion, compressed air is supplied from the air supply port 53, the air diffuser film 52 receives the pressure of the compressed air and expands in a mountain shape, and the slit 54 opens in the short direction B of the air diffuser film 52. Bubbles erupt from 54.

  Other examples of the diffuser include those shown in FIGS. 10 to 11. In this case, a diffuser film 62 made of a synthetic resin film or a synthetic rubber film is disposed on the outer peripheral surface of the diffuser pipe 61, and a number of slits 63 are provided in the diffuser film 62. The slit 63 is parallel to the longitudinal direction, which is the axial direction of the diffuser tube 61, and has a predetermined length. At the time of air diffusion, the slit 63 spreads in the short direction which is the pipe circumferential direction, and bubbles are ejected.

  There exists patent document 1 as a prior art document.

JP2007-777

  By the way, in the above configuration, in order to generate fine bubbles with a bubble diameter of 0.5 mm to 1.0 mm, for example, it is necessary to form the slit length as short as about 0.2 mm, for example. However, if the slit length is shortened, the pressure loss at the time of generating bubbles increases and the loss of the air supply energy increases. Conversely, when the slit length is set long, the pressure loss can be suppressed, but there is a trade-off problem that the bubble diameter increases and the oxygen transfer efficiency decreases.

  Further, the slits are arranged in only one direction along the longitudinal direction of the diffuser membrane, and all the slits are similarly opened. However, there are actually factors such as variations in the slit length, and there are slits where bubbles are likely to be generated due to this variation and slits where bubbles are not likely to be generated. Large amount of jetting causes uneven foaming.

  If the slit where bubbles are likely to be generated is biased and close to a part of the diffuser membrane, the generated bubbles are easily bonded and coarsened, and the oxygen transfer efficiency is lowered due to the coarsening of the bubbles, particularly when the air volume is low.

  This invention solves the above-mentioned subject, and it aims at providing the membrane type diffuser which can produce | generate the fine bubble excellent in oxygen transfer efficiency, suppressing a pressure loss.

In order to solve the above-mentioned problems, the membrane-type diffuser of the present invention has a diffuser film that separates the inner supply gas and the outer target liquid, and has a plurality of diffuser holes formed of slits in the diffuser film. The diffuser film expands in a mountain shape when viewed from a predetermined direction , and includes a material having a gas adhesion coefficient γ of 0.2 to 13.7 mN / m and a slit length D of 0.4. -1.0 mm, and each slit has an angle between the predetermined direction of the diffuser membrane within a range of 0-25 °, and a plurality of slits having different angles are arranged in a predetermined arrangement pattern. It is characterized by that.

  In this configuration, the gas adhesive force coefficient γ is a value indicating the affinity of the diffuser membrane for bubbles, and the higher the gas adhesive force coefficient γ, the higher the affinity of the diffuser membrane for bubbles, The air diffuser becomes hydrophobic and the bubble diameter increases. The lower the gas adhesion coefficient γ, the lower the affinity of the diffuser film for the bubbles, and the diffuser film becomes more hydrophilic with respect to the target liquid and the bubble diameter becomes smaller.

  Therefore, micro bubbles having a diameter of 0.5 to 1.5 mm can be generated even when the slit length D is 0.4 to 1.0 mm, and the pressure loss can be reduced by increasing the slit length D. .

The angle formed between the slit and the longitudinal direction of the diffuser membrane is related to the ease of opening the slit. The smaller the angle between the slit and the longitudinal direction of the diffuser membrane, the easier the slit opens during the diffuser, and the greater the angle between the slit and the longitudinal direction of the diffuser membrane, the more the slit opening is suppressed. .

  For this reason, when the air volume is low, bubbles are generated due to air diffusion from the slit having a small angle and easy to open, and bubbles are also generated from the slit having a large angle as the air volume increases. For this reason, since the space | interval of a slit which a bubble produces at the time of low air volume is large, the fall of the oxygen transfer efficiency by bubble coupling | bonding can be prevented by disperse | distributing a bubble, and the raise of a pressure loss can also be suppressed even when an air volume increases.

  As described above, according to the present invention, by appropriately selecting the material of the diffuser membrane and adjusting the wettability of the diffuser membrane, it is possible to promote the separation of bubbles from the diffuser membrane and to improve the oxygen transfer efficiency. Excellent fine bubbles can be generated, and pressure loss can be suppressed under a long slit length.

The perspective view which shows the membrane type diffuser in embodiment of this invention Sectional drawing which shows the principal part of the membrane type diffuser in the same embodiment Schematic diagram showing air diffusion holes in the same embodiment The top view which shows the slit pattern in embodiment of this invention The top view which shows the slit pattern in other embodiment of this invention The top view which shows the slit pattern in other embodiment of this invention The graph which shows the correlation of contact angle (theta) and gas adhesion coefficient (gamma) in other embodiment of this invention Schematic diagram explaining surface tension A perspective view showing a conventional membrane diffuser Perspective view showing another conventional air diffuser The perspective view which shows the aeration state of the aeration apparatus

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 4, a membrane-type air diffuser 1 is installed in an aeration tank of a sewage treatment facility or the like, and has a rectangular base plate 2 made of plastic or metal, and an upper surface of the base plate 2. And a diffused membrane 3 having a rectangular shape (an example of a shape elongated in one direction). The air diffusing membrane 3 has elasticity, and is made of, for example, rubber such as EPDM (ethylene propylene diene), silicon, or resin such as polyurethane.

  The periphery of the diffuser membrane 3 is fixed to the base plate 2 by a fixing portion 6 (for example, a caulking member), and an air supply portion 4 is formed between the base plate 2 and the diffuser membrane 3. Further, a short cylindrical air supply port 5 is provided at one end portion in the longitudinal direction A (an example of a predetermined direction) of the diffuser membrane 3. The air supply port 5 communicates with the air supply unit 4 and is connected to an air supply source (not shown).

  The gas diffusing membrane 3 has a gas adhesive force coefficient γ of 0.2 to 13.7 mN / m in the material, and the gas adhesive force coefficient γ will be described later. For example, a rubber (EPDM) material is used as a hard material. Thickness (A): 50-70, thickness (mm): 1-3, or rubber (silicon) material, hardness (A): 35-55, thickness (mm): 1-3 Alternatively, a resin (polyurethane) material having a hardness (A) of 70 to 98 and a thickness (mm) of 0.3 to 1 can be employed. The properties of the air diffusing membrane 3 are examples, and are not limited to these, and can be appropriately changed and optimized according to the conditions to be used.

  At the time of air diffusion, as shown in FIG. 2B, the air diffusion film 3 expands in a mountain shape when viewed from the longitudinal direction A by the pressure of the air supplied to the air diffusion film 3. At this time, since both ends in the longitudinal direction A of the diffuser membrane 3 are fixed to the base plate 2, the diffuser membrane 3 does not have a mountain shape when viewed from the longitudinal direction A, but most regions excluding both ends of the diffuser membrane 3. Since the diffuser membrane 3 expands in a mountain shape when viewed from the longitudinal direction A, the two ends of the diffuser membrane 3 are excluded here.

  The diffuser film 3 separates the inner supply gas and the outer target liquid, and a plurality of first to third (an example of first to third pore portions) forming the diffuser holes are formed. As shown in FIG. 1, the first slit 8 is a hole (slit) elongated in the longitudinal direction A, and is parallel to the longitudinal direction A. The second slit 9 is an elongated hole (slit) in a direction inclined at a predetermined inclination angle α with respect to the longitudinal direction A (that is, the first slit 8). In the present embodiment, the predetermined inclination angle α is set to 13 ° (acute angle). The third slit 10 is an elongated hole (slit) in a direction inclined at a predetermined inclination angle β with respect to the longitudinal direction A (that is, the first slit 8). In the present embodiment, the predetermined inclination angle β is set to 25 ° or less and close to 25 ° (acute angle).

  A plurality of first to third slits 8 to 10 are arranged in a predetermined arrangement pattern in the longitudinal direction A and the transverse direction B. That is, a plurality of first slits 8 are formed at predetermined intervals in the longitudinal direction A, and the second slits 9 are located between the first slits 8 adjacent in the longitudinal direction A. Further, the third slit 10 is located between the first slit 8 and the second slit 9 adjacent in the longitudinal direction A, and is located between the first slits 8 adjacent in the longitudinal direction A, As a result, the first slit 8 and the second slit 9 are adjacent to each other. The second slit 9 is also located between the first slits 8 adjacent in the short direction B. The slit length D of each slit 8, 9, 10 is 0.4 to 1.0 mm.

Next, the gas adhesive force coefficient γ will be described. As shown in FIG. 3, the buoyancy F <b> 1 of the bubble 20 is balanced with the force F <b> 2 due to the interfacial tension in a state immediately before the separation from the diffuser membrane 3. The bubble buoyancy F1 is πd ³ / 6ρg when the water density ρ, gravitational acceleration g, and bubble diameter d, and the force F2 due to the interfacial tension is the diameter D1 of the air diffuser 21 ≈ slit length D and gas adhesion coefficient γ. πDγ.

  Here, “πD” will be described. As described above, the diffuser membrane 3 expands in a mountain shape when viewed from the longitudinal direction A by the pressure of the air supplied to the diffuser membrane 3 as shown in FIG. At the time of expansion, the diffuser membrane 3 is constrained on the outer peripheral edge thereof, so that the expansion rate decreases in the longitudinal direction A of the long span and increases in the short direction of the short span. For this reason, the slits 8 to 10 are opened in the short direction to form the diffuser holes 21, and the opening circumferential length of the diffuser holes 21 is considered to be approximately regarded as the circumference “πD” as slit length D≈diameter D 1.

The gas adhesion force coefficient γ is related to the force that the diffuser film 3 holds on the film surface the bubbles 20 generated on the film surface of the diffuser film 3 including the diffuser holes 21. It is a value indicating the affinity of the membrane 3. That is, the gas adhesive force coefficient γ includes an interfacial tension γ _S acting between the diffuser membrane 21 and the air 22, an interfacial tension (surface tension) γ _L acting between the target liquid water 23 and the air, It is determined by the interfacial tension γ _{S / L} acting between the gas film 3 and the target liquid water 23.

If the interfacial tension (surface tension) γ _{L of the} water 23 is constant at a water temperature of 4 ° C. and atmospheric pressure, the gas adhesive force coefficient γ is determined by the interfacial tension γ _S and the interfacial tension γ _{S / L} related to the diffuser membrane 3. Change.
The calculation of the gas adhesion force coefficient γ is performed based on the following equation by measuring the generated bubble diameter d.
γ = (πd ³ ρg) / 6πD = (d ³ ρg) / 6D
The higher the gas adhesive force coefficient γ, the higher the affinity of the air diffusing film 3 for the bubbles 20, and the air diffusing film 3 becomes more hydrophobic with respect to the target liquid water 23 and the bubble diameter d becomes larger. The lower the gas adhesive force coefficient γ, the lower the affinity of the air diffusing membrane 3 for the bubbles 20, and the air diffusing membrane 3 becomes more hydrophilic with respect to the target liquid water 23 and the bubble diameter d becomes smaller.

  For example, when the slit length D = 0.4 mm, the gas adhesive force coefficient γ with a bubble diameter of 0.5 to 1.5 mm is 0.2 to 13.7, and when the slit length D = 1.0 mm, the bubbles The gas adhesive force coefficient γ having a diameter of 0.5 to 1.5 mm is 0.2 to 5.5.

When the gas adhesive force coefficient γ is larger than the above range and the slit length is long, the bubbles become large, and when the slit length is 0.4 or less, the pressure loss becomes large.
The above events can also be defined as follows. As shown in FIG. 8, the liquid 101 dropped on the surface of the object 100 is generally rounded by the surface tension, and the following equation is established. That is, the interfacial tension γ _S acting between the object 100 and the air 102, the interfacial tension (surface tension) γ _L acting between the liquid 101 and the air, and the interfacial tension γ acting between the object 100 and the liquid 101. _{S / L,} gamma between the angle θ between the _L and _{gamma S / L} holds true expression of _{γ S = γ L · cosθ +} γ S / L. Here, γ _L is the tangent of the droplet, and the angle θ is the contact angle.

  This contact angle θ is a value indicating the affinity of the diffuser membrane for the bubbles. The larger the contact angle θ, the higher the affinity of the diffuser membrane for the bubbles, and the diffuser membrane is more hydrophobic with respect to the target liquid. As a result, the bubble diameter increases. The smaller the contact angle θ, the lower the affinity of the diffuser film for the bubbles, and the diffuser film becomes more hydrophilic with respect to the target liquid, and the bubble diameter becomes smaller.

  The measurement of the contact angle includes a θ / 2 method, a tangent method, a curve fitting method, and the like. In this embodiment, an example measured by the θ / 2 method is shown below.

散気膜３の３つの材質に対する接触角θを測定した結果を表１に示す。材質（１）、材質（２）、材質（３）は、ＥＰＤＭやシリコンゴム等から選択したものであり、それぞれ接触角θが１１５°、９４°、１０６°となる異なる材質であった。

Table 1 shows the results of measuring the contact angle θ for the three materials of the diffuser membrane 3. Material (1), material (2), and material (3) were selected from EPDM, silicon rubber, and the like, and were different materials having contact angles θ of 115 °, 94 °, and 106 °, respectively.

The contact angle θ was measured with a FACE contact angle meter CA-X150 type (manufactured by Kyowa Interface Science Co., Ltd.).
The measurement conditions are as follows.
1. Liquid used: Distilled water 2. Measurement room conditions: room temperature 25 ° C, humidity 40%
3. Pre-treatment ... Ethanol washing Time until measurement after dropping a drop ... 1 second 5. Droplet drop location ... Site that does not touch the slit Number of measurements ··············································································································

  As shown in Table 1, when the contact angle θ is 94 °, the bubble diameter is as small as 1-2 mm. FIG. 7 shows the correlation between the contact angle θ and the gas adhesion coefficient γ obtained by actual measurement. Here, including the case where the contact angle θ is 94 °, the contact angle θ of the material having a gas adhesion coefficient γ of 0.2 to 13.7 mN / m is 108 ° or less. When the contact angle θ is greater than 108 °, the bubbles become larger.

Hereinafter, the operation of the above configuration will be described.
At the time of the air diffusion operation, air of a predetermined pressure is supplied from the air supply source (not shown) through the air supply port 5 to the membrane-type air diffuser 1, so that the air supply port 5, as shown in FIG. The diffuser membrane 3 expands in a mountain shape when viewed from the longitudinal direction A by the pressure of the air supplied to the air supply unit 4, and a tensile force F in the short direction B is generated in the diffuser membrane 3.

  The tensile force F is a force for opening the slits 8, 9, 10. At this time, the direction in which the first slit 8 opens coincides with the direction of the tensile force F, but the second slit 9 and the third slit 10 are inclined at the inclination angles α and β. The direction in which the three slits 10 open and the direction of the tensile force F do not match. In other words, the first slit 8 is easily opened by the tensile force F, whereas the second slit 9 and the third slit 10 are more difficult to open than the first slit 8 as the inclination angles α and β increase. Become.

  Therefore, when the air is diffused with a low air volume, the first slit 8 is opened before the second slit 9 and the third slit 10, and most of the air supplied to the air supply unit 4 is opened. While passing through the slit 8 and forming bubbles 20 and being ejected from the inside to the outside of the diffuser membrane 3, there are hardly any bubbles ejected to the outside through the second slit 9 and the third slit 10 that are difficult to open.

  Thereby, it is possible to prevent the bubbles ejected from the first slit 8 from being combined with the bubbles from the third slit 10 and the second slit 9 adjacent to the first slit 8, and uniformly disperse the bubbles when the air volume is small. It can be generated, and it is possible to prevent a decrease in oxygen transfer efficiency.

  When air is diffused by increasing the air volume from the small air volume to the large air volume, as the amount of air supplied to the air supply unit 4 increases, the air pressure of the air supply unit 4 increases as shown in FIG. Rises, the second slit 9 and the third slit 10 are easily opened, and the number of the second slit 9 and the third slit 10 that eject the bubbles 20 increases. The air in the air supply unit 4 passes through the slits 8, 9, 10, becomes bubbles 20, and is ejected from the inside of the diffuser membrane 3 to the outside. Thus, at a low air volume, the bubbles 20 are mainly ejected from the first slit 8, but as the air volume increases, the number of the second slits 9 and the third slits 10 that eject the bubbles 20 increases. The pressure loss and the increase in pressure loss can be suppressed.

  When the aeration is stopped, the supply of air to the aeration film 3 is interrupted, and the aeration film 3 is pressed against the upper surface of the base plate 2 by receiving water pressure as shown in FIG. At this time, the diffuser membrane 3 does not expand, and the first to third slits 8 to 10 are closed.

  And when the gas adhesive force coefficient (gamma) which is the value which shows the affinity of the diffuser film 3 with respect to the bubble 20 is 0.2-13.7 mN / m, the diffuser film 3 is with respect to the water 23 of object liquid. It becomes hydrophilic and the bubble diameter d is reduced, and even when the slit length D is 0.4 to 1.0 mm, fine bubbles having a diameter of 0.5 to 1.5 mm can be generated, and the slit length D is increased. Therefore, pressure loss can be reduced.

  Further, when the contact angle θ is 108 ° or less, the diffuser membrane 3 becomes hydrophilic with respect to the target liquid water 23, the bubble diameter d is reduced, and the slit length D is 0.4 to 1.0 mm. Can generate fine bubbles having a diameter of 0.5 to 1.5 mm, and the slit length D can be increased to reduce pressure loss.

  Therefore, by appropriately selecting the material of the air diffusing film 3 and adjusting the wettability of the air diffusing film 3, it promotes the separation of the air bubbles 20 from the air diffusing film 3 and has excellent oxygen transfer efficiency. And pressure loss can be suppressed under a long slit length.

  FIG. 5 shows a slit pattern according to another embodiment of the present invention. Here, a first slit 8 parallel to the longitudinal direction A and a predetermined length with respect to the longitudinal direction A (that is, the first slit 8) are shown. The third slit 10 is inclined at an inclination angle .beta., That is, 25.degree.

  In the membrane-type diffuser of the present invention, the angle between the slit and the longitudinal direction of the diffuser membrane is in the range of 0 to 25 °, but as shown in FIG. The fourth slit 11 can be combined, and a slit pattern in which a plurality of types of slits having different angles are arranged at random is also possible.

  When a polyurethane membrane is used for the air diffuser and the slit length is 0.6 mm, the bubble diameter is 0.5 to 1.5 mm, and the generated bubbles are distributed around the bubble diameter of 1 mm. Most often. In this case, if the bubble diameter is 1 mm, γ = 2.7 mN / m.

When another polyurethane membrane is used for the air diffuser and the slit length is 0.9 mm, the bubble diameter is 0.5 to 1.5 mm, and the generated bubbles are distributed around the bubble diameter of 1.3 mm. The bubble diameter is most often 1.3 mm. In this case, if the bubble diameter is 1.3 mm, γ = 4.0 mN / m.
The present invention is not limited to the configuration of the base plate 2 and the diffuser membrane 3 according to the above-described embodiment, and can be realized by a bag-like diffuser device in which the upper and lower sides are configured by soft sheets.

DESCRIPTION OF SYMBOLS 1 Membrane type diffuser 2 Base plate 3 Air diffuser film 4 Air supply part 5 Air supply port 6 Fixed part 8 1st slit 9 2nd slit 10 3rd slit 11 4th slit 20 Air bubble 21 Air diffuser hole 22 Air 23 Water

Claims (1)

Has Chikimaku separating the feed gas and the outside of the liquid of interest inside, e Bei multiple diffuser pores consisting slit Chikimaku,
The diffuser film expands in a mountain shape when viewed from a predetermined direction, and includes a material having a gas adhesion coefficient γ of 0.2 to 13.7 mN / m and a slit length D of 0.4 to 1. 0.0 mm,
Each slit has an angle between the predetermined direction of the diffuser membrane within a range of 0 to 25 °, and a plurality of slits having different angles are arranged in a predetermined arrangement pattern. Membrane diffuser.

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